Rozprawy doktorskie: „Nitrite Stress”

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Okeremi, Akinyemi. "The effect of nitrite on pitting and stress corrosion cracking of corrosion resistant alloys (CRA) under oil field conditions". Thesis, University of Manchester, 2011. https://www.research.manchester.ac.uk/portal/en/theses/the-effect-of-nitrite-on-pitting-and-stress-corrosion-cracking-of-corrosion-resistant-alloys-cra-under-oil-field-conditions(aced05b8-f8b0-40de-bbc5-990474d87794).html.

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The need to inject treated seawater to enhance reservoir pressure and secondary oil recovery is increasing in the oil field, so also is the reservoir souring potential caused by the activities of Sulphate Reducing Bacteria (SRB) generating H2S in the reservoir. The total cost of SRB mediated corrosion in the United States alone is estimated to be 1-2 billion US dollars per year. In the last few years, a number of potential souring mitigation and prevention tools have been studied. These include: sulphate-reduction using membranes, biocide injection and nitrate injection. Out of all the various methods used for the mitigation and prevention of reservoir souring, the use of nitrate injection in conjunction with waterflood projects is becoming more popular because of its economic benefits and least environmental impact. However, nitrate injection is still widely considered as an emergent technology because there are still many unknowns. One of the major unknowns, of great concern is the susceptibility of subsea hardware components to nitrite, which is a by-product of nitrate anti-souring treatment. Any detrimental effect can compromise the technical integrity of subsea installations. The objective of this research is to study the corrosion susceptibility of CRA (13Cr- Martensitic, 22Cr, and 25Cr super duplex stainless steel) to pitting and stress corrosion cracking in the presence of nitrite. Research hitherto, has investigated corrosion susceptibility of carbon steel to nitrite and found out that nitrite causes pitting in carbon steel. This research work built on previous studies and extensively investigated the effect of nitrite on CRA materials in terms of pitting and stress corrosion cracking. Using electrochemistry techniques in conjunction with C-ring test and slow strain rate test, with variables such as temperature, and nitrite concentration all under anaerobic conditions. Metallographic examination and further evaluation using scanning electron microscopy confirmed pitting and intergranular stress corrosion cracking of 13Cr-L80 and 25Cr due to presence of nitrite.Test data confirmed that sodium nitrite is an anodic inhibitor; it shifts the corrosion potentials to more noble potential and also shifts the anodic curve to lower current, given a net reduction in corrosion rate. A critical concentration of 400ppm is required for inhibition to be effective on 13Cr-L80 and 25Cr. However, below the critical concentration, nitrite significantly increases the corrosion rate. The experimental data generated from this research work provides very valuable information that will tremendously assist the materials selection process for subsea and subsurface hardware components and also serve as a guide in the corrosion management process in existing systems.

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SCULCO, FRANCESCA. "Effetti dello stress ossidativo sulla tolleranza ai nitroderivati". Doctoral thesis, Università degli Studi di Roma "Tor Vergata", 2009. http://hdl.handle.net/2108/784.

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Nel secolo scorso, la nitroglicerina è stato il farmaco più comunemente usato come agente antiischemico ed antianginoso. La sua continua somministrazione, però, ne fa svanire piuttosto rapidamente l’efficacia terapeutica. L’attivazione neuroormonale dei segnali vasocostrittori e l’espansione del volume intravascolare costituiscono le iniziali risposte contro-regolatorie (pseudotelleranza), mentre il trattamento a lungo termine induce cambiamenti vascolari intrinseci, come per esempio la perdita delle risposte nitrovasodilatatorie (tolleranza vascolare). Tutto ciò è causato da un’incrementata produzione di anione superossido e da una ipersensibilità verso vasocostrittori secondari per una tonica attivazione della PKC. Come fonti di anione superossido sono state proposte la NADPH ossidasi e la eNOS disaccoppiata. Il superossido ed il nitrossido vascolare formano rapidamente perossinitrito, che aumenta la tolleranza promuovendo il disaccoppiamento della eNOS e l’inibizione della guanilato ciclasi solubile e della prostaciclina. Questo concetto di stress ossidtivo può spiegare perché gli scavangers dei radicali e le sostanze che riducono indirettamente lo stress ossidativo, sono capaci di attenuare la tolleranza e la disfunzione endoteliale. Un lavoro recente ha definito un nuovo meccanismo di tolleranza basato sull’inibizione dell’ALDH-2, l’enzima deputato alla bioconversione enzimatica del GTN in NO, ed ha identificato i mitocondri come una fonte addizionale di specie reattive dell’ossigeno (ROS). Le specie reattive indotte dal GTN inibiscono la 6 bioattivazione della nitroglicerina medinte l’ossidazione tiolica dell’ALDH-2. Sia l’increnmento dello stress ossidativo che l’alterazione della bioconversione del GTN in NO, possono fornire un nuovo concetto di tolleranza ai nitrati nonché di cross-tolerance. Nel presente lavoro abbiamo documentato che la somministrazione a lungo termine di IS-5-MN in vitro ed in vivo induce tolleranza al GTN (definita cross-tolerance). Si sono altresì studiati gli effetti di CPT, ENA e NAC sulle risposte in vivo al GTN dopo trattamento cronico dei ratti con IS-5-MN e sono stati paragonati gli effetti di CPT, ENA o glutatione con quelli della NAC sugli effetti antipiastrinici del GTN in assenza o in presenza di TSMCs e TECs e sulla produzione di perossinitrito da GTN in un Krebs buffer. Per finire, sono stati valutate le risposte emodinamiche al GTN in ratti tolleranti e non, in presenza ed in assenza di co-trattamento con MnTBAP (1, 20 mg/kg/die, i.p.). Il presente studio, nel tentativo di chiarire i meccanismi molecolari che sottendono alla tolleranza ai nitrati, ha incentrato l’attenzione sul ruolo, che in tale fenomeno hanno, enzimi essenziali, quali la SOD e l’ALDH-2, i quali risultano, rispettivamente, down-regulated ed inattivata dal fenomeno della tolleranza. Il MnTBAP, un SOD-mimic di ultima generazione, si è rivelato in grado di inibire lo sviluppo di tolleranza ai nitrati organici in maniera dose-dipendente, ripristinando l’effetto del GTN sulla pressione sanguigna e sull’ggregazione piastrinica, riducendo la formazione di perossinitrito, come dimostrato dallo staining della nitrotirosina ed antagonizzando l’inibizione dell’ALDH-2 indotta dallo stress ossidativo. La formazione di perossinitrito gioca un ruolo 7 cruciale durante lo sviluppo di tolleranza ai nitroderivati in quanto riduce la biodisponibilità di NO. Quindi, quanto riportato nel nostro studio potrebbe aprire una nuova frontiera nel management delle malattie cardiovascolari, consentendo l’uso a lungo termine dei nitrati organici, senza che si sviluppi tolleranza.
During the last century, nitroglycerin has been the most commonly used antiischemic and antianginal agent. Unfortunately, after continuous application, its therapeutic efficacy rapidly vanishes. Neurohormonal activation of vasoconstrictor signals and intravascular volume expansion constitute early counter-regulatory responses (pseudotolerance), whereas long-term treatment induces intrinsic vascular changes, eg, a loss of nitrovasodilatorresponsiveness (vascular tolerance). This is caused by increased vascular superoxide production and a supersensitivity to vasoconstrictors secondary to a tonic activation of protein kinase C. NADPH oxidase(s) and uncoupled endothelial nitric oxide synthase have been proposed as superoxide sources. Superoxide and vascular NO rapidly form peroxynitrite, which aggravates tolerance by promoting NO synthase uncoupling and inhibition of soluble guanylyl cyclase and prostacyclin synthase. This oxidative stress concept may explain why radical scavengers and substances, which reduce oxidative stress indirectly, are able to relieve tolerance and endothelial dysfunction. Recent work has defined a new tolerance mechanism, ie, an inhibition of mitochondrial aldehyde dehydrogenase, the enzyme that accomplishes bioactivation of nitroglycerin, and has identified mitochondria as an additional source of reactive oxygen species. Nitroglycerin-induced reactive oxygen species inhibit the bioactivation of nitroglycerin by thiol oxidation of aldehyde dehydrogenase. Both mechanisms, increased oxidative 3 stress and impaired bioactivation of nitroglycerin, can be joined to provide a new concept for nitroglycerin tolerance and crosstolerance. In this work we have demonstrate that long-term administration of isosorbide-5-mononitrate in vitro ed in vivo induces tolerance to GTN (this is the so-called cross-tolerance). Here we have studied the effects of CPT, NAC or ENA on the in vivo responses to GTN after long-term treatment of rats with IS-5-MN. In addition, we have compared the effects of CPT, ENA or glutathione to those of NAC on the anti-platelet effects of GTN in the absence or presence of tolerant cultured SMCs or ECs and on production from GTN in Krebs buffer. Finally, we have valuated the haemodynamic responses to glyceryl trinitrate in non-tolerant rats and in tolerant rats with or without pharmacological co- treatment with MnTBAP (1-20 mg/kg, i.p.). The present study was designed to elucidate the mechanisms of nitrate tolerance by assessing the function of essential enzymes implicated in this phenomenon. We demonstrated that SOD and ALDH-2 are downregulated and inactivated, respectly, during nitrate-tolerance. MnTBAP, a new generation antioxidant, is able to inhibit the development of tolerance to organic nitrates in a dose dependent fashion restoring the GTN effect on blood pressure and on platelets aggregation and reducing the peroxynitrite formation as evaluated by the inhibition of the nitrotyrosine staining and antagonizing the ALDH-2 inhibition oxidative stress-induced. Peroxynitrite formation play a crucial role during the development of tolerance to organic nitrates most likely via reduction of nitric oxide bioavalaibility. The broader implications 4 of these findings may open a new frontier in the clinical management of cardiovascular disease, in particular allowing the use of long-term organic nitrates treatment without development of tolerance.

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Choi, Sukwon. "Stress metrology and thermometry of AlGaN/GaN HEMTs using optical methods". Diss., Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/49108.

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The development of state-of-the-art AlGaN/GaN high electron mobility transistors (HEMTs) has shown much promise for advancing future RF and microwave communication systems. These revolutionary devices demonstrate great potential and superior performance and many commercial companies have demonstrated excellent reliability results based on multiple temperature accelerated stress testing. However, a physical understanding of the various reliability limiting mechanisms is lacking and the role and relative contribution of the various intrinsic material factors, such as physical stress and strain has not been clearly explained in the literature. Part of issues that impact device reliability are the mechanical stresses induced in the devices as well as the self-heating that also limit device performance. Thus, quantification of stress and temperature in AlGaN/GaN HEMTs is of great importance. To address some of the needs for metrology to quantify stress in AlGaN/GaN HEMTs, micro-Raman spectroscopy and micro-photoluminescence (micro-PL) were utilized to quantify the residual stress in these devices. Through the use of micro-Raman and micro-PL optical characterization methods, mapping of the vertical and lateral stress distributions in the device channels was performed. Results show that stress can be influenced by the substrate material as well as patterned structures including metal electrodes and passivation layers. Previously developed and reported micro-Raman thermometry methods require an extensive calibration process for each device investigated. To improve the implementation of micro-Raman thermometry, a method was developed which offers both experimental simplicity and high accuracy in temperature results utilizing a universal calibration method that can be applied to a broad range of GaN based devices. This eliminates the need for performing calibration on different devices. By utilizing this technique, it was revealed that under identical power dissipation levels, the bias conditions (combination of Vgs and Vds) alter the heat generation profile across the conductive channel and thus influence the degree of device peak temperature. The role of stress in the degradation of AlGaN/GaN HEMTs was also explored. A combined analysis using micro-Raman spectroscopy, coupled electro-thermo-mechanical simulation, and electrical step stress tests was conducted to investigate the link between performance degradation and the evolution of total stress in devices. It was found that in addition to stresses arising from the inverse piezoelectric effect, the substrate induced residual stress and the operational themo-elastic stress in the AlGaN layer play a major role in determining the onset of mechanically driven device degradation. Overall, these experiments were the first to suggest that a critical level of stress may exist at which point device degradation will start to occur. The optical characterization methods developed in this study show the ability to reveal unprecedented relationships between temperature/stress and device performance/reliability. They can be used as effective tools for facilitating improvement of the reliability of future AlGaN/GaN HEMTs.

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Herrman, Kyle S. "Mechanisms controlling nitrogen removal in agricultural headwater streams". Columbus, Ohio : Ohio State University, 2007. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1181667344.

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Lízalová, Martina. "Aplikace vybraných metod k analýze oxidačního stresu". Doctoral thesis, Vysoké učení technické v Brně. Fakulta chemická, 2010. http://www.nusl.cz/ntk/nusl-233302.

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Chronic pancreatitis (CP) is a heterogeneous disease defined as chronic inflammatory changes of the pancreatic tissue caused by variety of aetiologies. Oxidative stress accompanying the inflammatory processes has been suggested as an important factor contributing to CP development. The aim of this study was to determine levels of lipid peroxidation products malondialdehyde (MDA) and 4-hydroxynonenal (4-HNE), together with nitrites, the total antioxidant capacity, cytokines, biochemical and haematological parameters in the plasma of patients with CP and control subjects. Levels of MDA and 4-HNE were analyzed using high-performance liquid chromatography. The total antioxidant capacity of plasma against peroxyl radicals was evaluated using chemiluminescence determination. Nitrites were determined using Griess reaction. Cytokines - TNF-alfa; TNF RI; PDGF-AB; TGF-beta, together with myeloperoxidase and hyaluronan were determined using ELISA Kits. Biochemical and haematological parameters were measured by standard methods.

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Silva, Petterson Costa Conceição. "Papel da glutamina na regulação do influxo de nitrato em raízes de feijão-caupí expostas à salinidade". reponame:Repositório Institucional da UFC, 2015. http://www.repositorio.ufc.br/handle/riufc/19323.

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SILVA, Petterson Costa Conceição. Papel da glutamina na regulação do influxo de nitrato em raízes de feijão-caupí expostas à salinidade. 2015. 91 f. Dissertação (Mestrado em solos e nutrição de plantas)-Universidade Federal do Ceará, Fortaleza, 2015.
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There are many studies showing that the salinity may directly affect the nitrate uptake, from their osmotic effect, nature of the salt and its ionic composition. However, little is known about the mechanisms related to the salt ability to inhibit the nitrate acquisition indirectly. This study was carried with aim to induce inhibition of NO3- influx in cowpea roots of indirect form triggered by a negative feedback mechanism, caused by the increase in the pool of free amino acids in the tissue, induced by salt stress.For this, were done three isolated studies and continuous.The exogenous glutamine application promoted an increase in the free amino acids content.The presence of glutamine decreased significantly the nitrate acquisition.The free ammonium can also be listed as a key-compound in the role of nitrate influx regulation, since use of the MSX (Methionine sulfoximine) promoted the increase of NH4+ content and also reduced nitrate influx, but, in a lesser degree when compared to treatment with AZA (Azaserine). Salt stress caused a reduction in NO3- influx by decrease in the growth of plants induced by salt. The data indicated which this reduction in the influx is triggered by increase of amino acids content, mainly the glutamine, that is main likely compound to act as signal in the N-feedback regulation.
Existem muitos estudos mostrando que a salinidade pode afetar a absorção de nitrato de forma direta, a partir do seu efeito osmótico, da natureza do sal e de sua composição iônica. Entretanto, pouco se sabe sobre os mecanismos relacionados com a capacidade do sal em inibir a aquisição de nitrato de forma indireta. O presente estudo teve como objetivo induzir a inibição do influxo de NO3- em raízes de feijão-caupí de forma indireta desencadeada por um mecanismo de feedback negativo, provocado pelo aumento no pool de aminoácidos livres no tecido, induzido por estresse salino. Para isso, foram realizados três estudos isolados e contínuos. A aplicação de glutamina exógena promoveu um aumento no conteúdo de aminoácidos livres. A presença de glutamina reduziu significativamente a aquisição de nitrato. O amônio livre também pode ser listado como um composto-chave no papel da regulação do influxo de nitrato, pois a utilização do MSO (Metionina sulfoximina) promoveu o aumento do conteúdo de NH4+ e também reduziu o influxo de nitrato, porém em menor grau quando comparado ao o tratamento com AZA (Azaserina). O estresse salino causou uma redução no influxo de NO3-, pela diminuição no crescimento das plantas induzida pelo sal. Adicionalmente, estes dados indicaram que esta redução no influxo está ligada ao aumento do teor de aminoácidos, principalmente a glutamina, que é o principal componente para atuar como sinal na regulação por N-feedback.

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Masson, Isabelle. "Détermination des propriétés mécaniques en fluage a haute température et étude des microstructures de déformation de céramiques a base de nitrure d'aluminium". Vandoeuvre-les-Nancy, INPL, 1993. http://www.theses.fr/1993INPL136N.

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En vue d'applications en sidérurgie dans les nouveaux procédés de coulée continue de bandes minces, plusieurs céramiques à base de nitrure d'aluminium (AlN fritte (SAlN), AlN presse a chaud (HPAlN) et composites al#2o#3-AlN) ont été déformées en compression uniaxiale soit sous contrainte constante (150-250 MPa) soit à vitesse de déformation imposée (5. 10##6s##1) à des températures variant de 1200 à 1650c puis caractérisées en microscopie électronique à balayage, en microscopie électronique à transmission et par analyse EDX. En fluage a charge constante, la vitesse de déformation est proportionnelle à la contrainte appliquée à la puissance 1,5 et varie exponentiellement avec la temperature, l'énergie d'activation apparente ayant une valeur moyenne de 650 kj. Mol##1 (la valeur maximale de la vitesse de déformation atteinte pour HPAlN déformé à 1650c sous 250 MPa étant de 4. 10##6s##1). A vitesse imposée, les courbes contrainte-déformation passent par une contrainte maximale qui croit quand la température diminue (la valeur maximale obtenue pour HPAlN déformé à 1550c étant de 670 MPa) puis décroissent. Après essai, la présence de nombreuses cavités aux joints de grains et aux points triples montre que la déformation est surtout intergranulaire. Les grains se déforment aussi plastiquement par mouvement de dislocations situées majoritairement dans le plan de base et de vecteur de burgers 1/3<1120>. Nous avons également observé plusieurs preuves de la montée de ces dislocations et de glissement dévié dans des plans prismatiques ou pyramidaux favorisée par l'absence de dissociation

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Nguyen, Chi Tam. "Identification et caractérisation d'un canal chlorure, AtCLCg, impliqué dans la réponse au stress salin chez Arabidopsis thaliana". Phd thesis, Université Paris Sud - Paris XI, 2012. http://tel.archives-ouvertes.fr/tel-00856592.

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Dans les cellules végétales, les canaux et les transporteurs anioniques sont essentiels pour les fonctions clés telles que la nutrition, l'homéostasie ionique et la tolérance aux stress biotiques ou abiotiques. Chez Arabidopsis thaliana, les membres de la famille CLC (pour ChLoride Channel), situés sur le tonoplaste, sont requis pour l'homéostasie du nitrate (AtCLCa et AtCLCb) ou impliqués dans la tolérance au sel (AtCLCc).Dans mon travail de thèse, j'ai identifié et caractérisé un canal chlorure, AtCLCg, chez A. thaliana. L'étude de la protéine fusion AtCLCg::GFP a révélé que cette protéine est localisée sur le tonoplaste. Deux lignés mutants indépendants d'insertion ADN-T, atclcg ont été sélectionnés. Les études physiologiques sur ces deux lignés ont démontré qu'AtCLCg joue un rôle dans le passage de chlorure mais pas dans l'homéostasie du nitrate au travers du tonoplaste. En effet, aucune différence de contenu en nitrate (NO3-) racinaire et foliaire n'a été observée entre le sauvage et les mutants dans nos conditions. Par contre, les plantes mutantes présentent un phénotype par rapport au sauvage lorsqu'elles se développent sur milieu de croissance contenant 75 mM NaCl: (i) une diminution de 20% de la masse fraîche ; (ii) une diminution de 16% de la longueur de racines primaires et une réduction de 19% du nombre de racines secondaires ; (iii) une sur-accumulation de 21% et 26% de chlorure et sulfate foliaire, respectivement. Ces phénotypes sont abolis chez les lignés complétées avec 35S::AtCLCg. De plus, les mutants atclcg présentent un phénotype similaire à la présence de 75 mM KCl, mais aucune différence n'est détectée en réponse à 140 mM mannitol. Ce résultat suggère que le phénotype d'hypersensibilité des mutants atclcg dépend du chlorure et non du l'effet osmotique du stress salin.Sachant qu'AtCLCg et AtCLCc partagent un haut degré d'homologie, environ 75% d'identité au niveau des protéines, et que les deux sont impliquées dans la réponse au stress salin de la plante, nous avons généré le double mutant atclcc/atclcg. L'analyse phénotypique a montré que le double mutant ne présente pas un phénotype additif sur milieu de stress 75 mM NaCl. En parallèle, l'analyse de l'expression des gènes a montré qu'AtCLCg est réprimé dans le fond mutant atclcc, et inversement. Par ailleurs, l'analyse de l'expression de gène rapporteur démontre que PAtCLCg::GUS est fortement exprimé dans les cellules du mésophylle alors qu'une forte expression de PAtCLCc::GUS dans les cellules de garde et le pollen est observé. Ainsi, l'ensemble de ces résultats montrent que ces deux protéines AtCLCc et AtCLCg sont impliquées dans la réponse au stress salin de la plante, mais elles n'ont pas de fonction redondante.

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Ke, Jiaxin. "Stress engineering with silicon nitride stressors for Ge-on-Si lasers". Thesis, University of British Columbia, 2017. http://hdl.handle.net/2429/62116.

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Silicon compatible lasers are in great need for applications such as on-chip and short-reach optical interconnects. Although InAs/GaAs quantum dot lasers monolithically grown on Si have been realized and are well-performed, due to material contamination issues, it is time and cost intensive for those III-V materials to enter mainstream Si processing facilities. Germanium(Ge)-on-Silicon(Si) laser is promising as a solution to solve the Si-compatible laser problem as it is compatible with Si processing. So far, the main problems in Ge lasers are that they have a high threshold current density and low efficiency. Laser structure designs with top and side silicon nitride stressors were proposed in this work and shown to be effective in reducing the threshold current (Ith) and improving the wall-plug efficiency (ηwp) of Ge-on-Si lasers. Side stressors turned out to be a more efficient way to increase ηwp than using the top and side stressors together. With the side stressors and geometry optimizations, a maximum ηwp of 34.8% and an Ith of 36 mA (Jth of 27 kA/cm²) were achieved with a defect limited carrier lifetime (𝜏𝑝,𝑛) of 1 ns. With 𝜏𝑝,𝑛 being 10 𝑛𝑠 , an Ith of 4 mA (Jth of 3 kA/cm²) and a ηwp of 43.8% were achieved. These are tremendous improvements from cases without any stressors. Compared to other stress introduction methods, such design is much more suitable for Ge laser structure implementation. These results provide a strong support to the Ge-on-Si laser technology and create an effective way to improve the Ge laser performance.
Applied Science, Faculty of
Materials Engineering, Department of
Graduate

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Paterson, Stuart. "Studies of dietary nitrate induced nitrosative stress in the upper gastrointestinal tract". Thesis, University of Glasgow, 2008. http://theses.gla.ac.uk/394/.

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The incidence of neoplasia at the gastroesophageal junction has increased markedly over the past 20 years, but the mutagen responsible for this remains unknown. Human saliva contains substantial quantities of nitrite and is the main source of nitrite entering the stomach. It is derived from the enterosalivary recirculation of dietary nitrate and its reduction by buccal bacteria. Carcinogenic N-nitrosocompounds may be formed from the nitrite in swallowed saliva by bacterially-catalysed nitrosation in the achlorhydric stomach or acid-catalysed nitrosation in the healthy acid secreting stomach. Protection against luminal acid-catalysed nitrosation is provided by the ascorbic acid content of human gastric juice which reduces nitrite to nitric oxide (NO). A high luminal concentration of NO generated from salivary nitrite has been shown at the gastroesophageal junction. A bench top model has been developed to explore the chemistry occurring in an aqueous phase, representing the lumen at the gastroesophageal junction, after the addition of nitrite. Within this model an adjacent lipid phase has been created. The lipid phase represents the adjacent mucosa to the lumen or the dietary fat shown to sit within the fundus of the stomach. In this two-phase model, addition of physiological concentrations of nitrite to an acidic aqueous phase in the absence of ascorbic acid generated nitrosative stress within the aqueous phase. The addition of physiological concentrations of ascorbic acid to the aqueous phase prevents nitrosative stress within the aqueous phase but in so doing generates nitrosative stress within the lipid phase. This can be explained by the ascorbic acid converting the salivary nitrite to NO which diffuses into the lipid phase and there reacts with O2 to form the nitrosating species N2O3. The bench top model has been developed further to include the lipid antioxidants, α-tocopherol, β-carotene and BHT. All three of these antioxidants are effective in inhibiting nitrosative stress within the lipid phase. The concentration of α-tocopherol required to inhibit nitrosation is less than would be expected from the reaction equation. A possible explanation for this is that ascorbic acid recycles the active antioxidant α-tocopherol from its reduced form. Further studies to support recycling of α-tocopherol by ascorbic acid are presented within this thesis. The design of a model used in vivo to assess for nitrosative stress is discussed. The model consisted of a hydrophobic silastic tubing containing a secondary amine at a neutral pH. The hydrophobic membrane that the tubing is composed of allowed the passage of gaseous NO. Human studies in healthy volunteers were performed using the silastic tubing. The data presented shows that after a nitrate rich drink there is significantly more nitrosative stress within the upper gastrointestinal tract and this is particularly the case in the first part of the stomach where salivary nitrite meets acidic gastric juice containing ascorbic acid. Finally, the studies explore directly measuring nitrosative stress in biopsy samples from humans and rats. As nitrite has been shown previously to be a marker of nitrosative stress in bench top models biopsy samples were assessed for nitrite and nitrate concentrations. Methods for assessing nitrite and nitrate concentrations within biopsy samples from the upper gastrointestinal tract are discussed, as nitrite and nitrate have not been analysed from this region previously. Thereafter, upper gastrointestinal biopsy samples from healthy human subjects were analysed after a control drink and a drink rich in nitrate. The studies presented show that biopsy nitrate and nitrite was higher in samples taken from the proximal stomach as compared to the oesophagus and distal stomach. This suggests that there is more nitrosative stress in the biopsies from the same area as where NO is generated after a nitrate meal. Together the data presented supports a novel mechanism for N-nitrosation in the upper gastrointestinal tract of a healthy subject. The N-nitrosation is maximal where swallowed salivary nitrite from dietary nitrate meets acidic gastric juice containing the aqueous antioxidant ascorbic acid.

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Ahluwalia, H. S. "Stress corrosion cracking of 70/30 brass in nitrate solutions and waters". Thesis, University of Newcastle Upon Tyne, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.377847.

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Chen, Ying. "RESIDUAL STRESS IN GALLIUM NITRIDE FILMS GROWN BY METALORGANIC CHEMICAL VAPOR DEPOSITION". Ohio University / OhioLINK, 2000. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1171567935.

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Ng, S. G. "The influence of processing on the fracture characteristics of reaction-bonded silicon nitride". Thesis, University of Sunderland, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.380993.

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Saugnon, Damien. "Contribution aux analyses de fiabilité des transistors HEMTs GaN : exploitation conjointe du modèle physique TCAD et des stress dynamiques HF pour l'analyse des mécanismes de dégradation". Thesis, Toulouse 3, 2018. http://www.theses.fr/2018TOU30164/document.

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Dans la course aux développements des technologies, une révolution a été induite par l'apparition des technologies Nitrures depuis deux décennies. Ces technologies à grande bande interdite proposent en effet une combinaison unique tendant à améliorer les performances en puissance, en intégration et en bilan énergétique pour des applications hautes fréquences (bande L à bande Ka en production industrielle). Ces technologies mobilisent fortement les milieux académiques et industriels afin de proposer des améliorations notamment sur les aspects de fiabilité. Les larges efforts consentis par des consortiums industriels et académiques ont permis de mieux identifier, comprendre et maîtriser certains aspects majeurs limitant la fiabilité des composants, et ainsi favoriser la qualification de certaines filières. Cependant, la corrélation et l'analyse physique fine des mécanismes de dégradation suscite encore de nombreux questionnements, et il est indispensable de renforcer ces études par une approche d'analyse multi-outils. Nous proposons dans ce travail de thèse une stratégie d'analyse selon deux aspects majeurs. Le premier concerne la mise en œuvre d'un banc de stress qui autorise le suivi de nombreux marqueurs électriques statiques et dynamiques, sans modifier les conditions de connectiques des dispositifs sous test. Le second consiste à mettre en œuvre un modèle physique TCAD le plus représentatif de la technologie étudiée afin de calibrer le composant à différentes périodes du stress.Le premier chapitre est consacré à la présentation des principaux tests de fiabilité des HEMTs GaN, et des défauts électriques et/ou structuraux recensés dans la littérature ; il y est ainsi fait état de techniques dites non-invasives (c.-à-d. respectant l'intégrité fonctionnelle du composant sous test), et de techniques destructives (c.-à-d. n'autorisant pas de reprise de mesure). Le second chapitre présente le banc de stress à haute fréquence et thermique développé pour les besoins de cette étude ; l'adjonction d'un analyseur de réseau vectoriel commutant sur les quatre voies de tests permet de disposer de données dynamiques fréquentielles, afin d'interpréter les variations du modèle électrique petit-signal des modules sous test à différentes périodes du stress. [...]
In the race to technologies development, disruptive wide bandgap GaN devices propose challenging performances for high power and high frequency applications. These technologies strongly mobilize academic and industrial partners in order to improve both the performances and the reliability aspects. Extensive efforts have made it possible to better identify, understand and control first order degradation mechanisms limiting the lifetime of the devices; however, the correlation (and fine physical analysis) of different degradation mechanisms still raises many questions, and it is essential to strengthen these studies by mean of multi-tool analysis approach. In this thesis, we propose a twofold analysis strategy. The first aspect concerns the implementation of a stress bench that allows the monitoring of numerous static and dynamic electrical markers, without removing the devices under test from their environment (in order to have a consistent data set during the period of the strain application). The second aspect consists in implementing a physical TCAD model of the technology under study, in order to calibrate the component before stress, and to tune the model at different periods of stress (still considering stress-dependent parameters potentially affecting the device). The first chapter is devoted to the presentation of the main reliability tests of GaN HEMTs, and of the electrical and/or structural defects identified in the literature; it thus refers to so-called non-invasive techniques (i.e. respecting the functional integrity of the component under test), and destructive techniques (i.e. not allowing additive electrical measurement). The second chapter presents the high frequency and thermal stress bench dedicated to this study; the addition of a vector network analyzer switching between the four test channels provides dynamic frequency data, in order to interpret the variations of the small signal electrical model of the devices under test at different stress periods.[...]

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Santos, Jaqueline Rocha Borges dos. "Inibição da sintese do oxido nitrico em ratos adultos submetidos a modelos comportamentais". [s.n.], 2002. http://repositorio.unicamp.br/jspui/handle/REPOSIP/311364.

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Orientador : Nancy Airoldi Teixeira
Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Ciências Médicas
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Resumo: Neste estudo, investigamos as alterações comportarnentais produzidas pela inibição aguda da síntese do óxido nítrico em ratas fêmeas adultas no labirinto em cruz elevado, campo aberto, teste de retração da cauda, esquiva ativa sinalizada, esquiva passiva e desamparo aprendido. Os animais receberam L-NAME por via i.p. na dosagem 100mg/kg (grupo tratado, N=10) e solução salina 0,9% (grupo controle, N=10) 30 minutos antes do teste no labirinto em cruz elevado, campo aberto e teste de retração da cauda. No desamparo aprendido, os animais receberam solução salina 0,9%, ou L-NAME 10 e 100mg/kg, 30 minutos antes do confinamento ou choques inescapáveis; 24 horas após, foram submetidos a choques escapáveis. No labirinto em cruz elevado, diferenças estatisticamente significantes foram observadas no tempo e na freqüência de entradas nos braços abertos do grupo tratado em relação ao controle. No campo aberto, diferenças estatísticas foram observadas no tempo de centro e levantar-se (rearing), no grupo tratado em relação ao controle. No teste de retração da cauda, houve diferença estatisticamente significativa no tempo de latência de retração da cauda do grupo tratado em relação ao controle. Na esquiva passiva, os animais receberam por via i.p. solução salina 0,90.10ou L-NAME 100mg/kg30 minutos antes do treino e teste, consistindo os seguintes grupos: grupo C-C (os animais receberam solução salina 0,9% no dia do treino e teste); C-D (os animais receberam solução salina 0,90.10 no dia do treino e LNAME 100mg/kg no dia do teste); D-C (os animais receberam L-NAME 100mg/kg no dia do treino e solução salina 0,9% no dia do teste); D-D (os animais receberam L-NAME l00mg/kg no dia do treino e teste). Não foram observadas diferenças estatísticas na porcentagem de aprendizagem nos grupos. Na esquiva ativa sinalizada, diferenças estatístcas foram observadas entre os grupos satina e tratado, no dia do treino, causando um déficit no escape, mas não os impediu de aprender a tarefa. Desta forma, a inibição da síntese do óxido nítrico alterou parcialmente o comportamento exploratório e emocional, reduziu a ansiedade, produziu analgesia, não prejudicou a aprendizagem e memória, apresentou efeito antidepressivo na dosagem 100m/kg de L-NAME
Abstract: In this work we investigated behaviour altered produced foracute inhibition of nitric oxide synthesis in adults female rats in plus maze test, open field, tail flick test, ative avoidance signalling, passive avoidance and learned helplessness. The animaIs received L-NAME i.p. 100mg/kg(treated group, N=lO) and saline solution 0,9% (contro1group, N=10) 30 minutes before of plus maze test open field and tail flick test. In leamed helplessness, the animals received saline solution 0,9%, or LNAME 10 and l00mg/kg, 30 minutes before confinament or inescapable shocks; 24 hours before, were submetted at escapable shocks. In the plus maze test, significant statistical differences were observed in time and frequency of entries into open arms of treated and control groups. In the open field, statistical differences were observed in center time and rearing, in treated group reIative to control group. Statistical differences were seen at tail flick test in latency time of tail flick of treated group relative to control group. In passive avoidance, the animais received i.p. saline solution 0,9% or L-NAME 100mg/kg 30 minutes before training and test, divided in four groups: group C-C (the animaIs received saline solution 0,9% in the training and test days); C-D (the animais received saline solution 0,90.10 in the day of training and L-NAME 100mg/kg in the test); D-C (the animais received L-NAME 100mg/kg in the day of training and saline solution 0,90.10 in the test); D-D (the animaIs received L-NAME 100mg/kg in the training and test days). No statistical differences were seen in percentage of learning tn the groups. In ative avoidance signaling, statistical differences were observed between controI group and treated group, in the training day caused an escape deticit, but did not avoided them to learn task. Thus, the acute inhibition of nitric oxide synthesis altered partialy exploratory and emotional behaviour, reduced anxiety, produced analgesy, did not injured learned and memory, presented antidepressive effect at dose of 100mg.kg-1
Mestrado
Mestre em Farmacologia

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Taochy, Christelle. "Transport membranaire de NO3 sous contrainte saline : rôle de NAXT2 dans la translocation du NO3 vers les feuilles et le contrôle du fonctionement stomatique chez A. thaliana". Thesis, Montpellier, SupAgro, 2012. http://www.theses.fr/2012NSAM0024/document.

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Les systèmes de sécrétion de NO3– de la membrane plasmique des cellules végétales jouent un rôle important dans l'activité stomatique et la réponse des plantes à des stress biotiques et abiotiques. Malgré quelques avancées récentes, ces systèmes restent mal connus sur le plan moléculaire. Mon travail de thèse a consisté à caractériser le rôle physiologique de NAXT2, un membre du sous-groupe NAXT (NitrAte eXcretion Transporter) de la famille des transporteurs NRT1/PTR chez Arabidopsis thaliana. Mes résultats montrent que NAXT2 est un transporteur de NO3– et qu'il est principalement exprimé dans les cellules du péricycle de la racine, au voisinage des vaisseaux xylémiens. Sous contrainte saline et comparativement aux plantes sauvages (WT), un mutant knock-out pour NAXT2 (naxt2-1) présente un défaut de distribution du NO3– vers les feuilles et de sécrétion du NO3– dans la sève xylémienne, qui se traduisent par une diminution des teneurs en NO3– foliaires. NAXT2 est donc impliqué dans la charge du xylème en NO3– sous contrainte saline. Aucune des différences phénotypiques mises en évidence entre le mutant et WT sous contrainte saline n'a été observée sous stress osmotique ou en condition standard, suggérant que NAXT2 est essentiellement impliqué dans la réponse à la composante ionique du stress salin. Enfin, après un traitement salin prolongé, la biomasse foliaire de naxt2-1 est inférieure à celle de WT, ce qui indique que NAXT2 joue un rôle important dans l'adaptation des plantes aux contraintes salines modérées. Dans l'ensemble, ce travail suggère que NAXT2 est impliqué dans une fonction physiologique majeure, la translocation du NO3–, point de contrôle de la distribution du nitrate, et dans l'adaptation de la plante aux contraintes salines
NO3– secretion systems at the plasma membrane of plant cells play an important role in stomata activity and plant response to biotic and abiotic stresses. Despite of few recent advances, these systems are still poorly known at the molecular level. During my thesis, I worked on the characterization of the physiological role of NAXT2, a member of the NAXT (NitrAte eXcretion Transporter) sub-group from the large NRT1/PTR transporters family in Arabidopsis thaliana. The results presented here show that NAXT2 is a NO3– transporter and that it is mainly expressed in root pericycle cells, close to the xylem vessels. Under salinity constraint and relatively to wild type plants (WT), a NAXT2 knock-out mutant (naxt2-1) displayed a defect in NO3– distribution towards the shoots and in NO3– secretion into the xylem sap, which lead to a decrease in shoot NO3– content. Thus, NAXT2 is involved in NO3– xylem loading under salinity constraint. None of the phenotypic differences described in this work between WT and mutant was observed under osmotic stress or standard culture conditions, suggesting that NAXT2 is specifically involved in response to the ionic component of salt stress. Finally, after a prolonged salt treatment, naxt2-1 shoot biomass was lower than that of WT, indicating that NAXT2 plays an important role in plant adaptation to mild salinity constraint. Altogether, this work suggests that NAXT2 is involved in a major physiological function, the NO3– translocation, control point of nitrate distribution and in plant adaptation to salinity constraint

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Martins, MÃrcio de Oliveira. "RegulaÃÃo da fotossÃntese por deficiÃncia hÃdrica, nitrogÃnio e CO2 elevado em cana-de-aÃÃcar". Universidade Federal do CearÃ, 2012. http://www.teses.ufc.br/tde_busca/arquivo.php?codArquivo=8515.

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FundaÃÃo Cearense de Apoio ao Desenvolvimento Cientifico e TecnolÃgico
CoordenaÃÃo de AperfeiÃoamento de Pessoal de NÃvel Superior
A cana-de-aÃÃcar Ã uma planta de grande potencial econÃmico, sendo utilizada principalmente para produÃÃo de aÃÃcar e biocombustÃveis. O Brasil tem destaque internacional na produÃÃo de cana-de-aÃÃcar, sendo o maior produtor mundial dessa cultura. Apesar dessa lideranÃa, o Brasil estÃ localizado em uma regiÃo tropical e apresenta vÃrias adversidades climÃticas. O estudo da fisiologia da cana-de-aÃÃcar em situaÃÃes de estresse, como deficiÃncia hÃdrica, torna-se fundamental para manutenÃÃo e melhoria da produÃÃo dessa cultura. A cana-de-aÃÃcar Ã uma espÃcie de fotossÃntese C4, com um mecanismo de concentraÃÃo de CO2. Dessa maneira, espera-se que a crescente elevaÃÃo de CO2 na atmosfera nÃo afete a produtividade da cana-de-aÃÃcar de maneira relevante, mas os estudos acerca do assunto sÃo ainda bem escassos. Diante desse quadro, objetivou-se avaliar a regulaÃÃo da fotossÃntese por deficiÃncia hÃdrica, suprimento de nitrogÃnio e CO2 elevado em plantas de cana-de-aÃÃcar. O CapÃtulo 1 comtempla o estado da arte a respeito do tema em estudo. No capÃtulo 2, foi realizado um trabalho com o objetivo de avaliar as respostas de duas cultivares de cana-de-aÃÃcar consideradas contrastantes em relaÃÃo Ãs respostas Ã deficiÃncia hÃdrica, IAC SP 94-2094 e IAC SP 95-5000. Estas cultivares foram expostas a dÃficit hÃdrico severo, com suspensÃo da irrigaÃÃo por cinco dias, e recuperaÃÃo, reirrigadas por dois dias apÃs o estresse. O tratamento aplicado foi capaz de afetar fortemente as trocas gasosas, com fechamento estomÃtico nas duas cultivares, levando a fortes reduÃÃes de transpiraÃÃo e assimilaÃÃo de CO2. Os parÃmetros da fluorescÃncia da clorofila a foram afetados, mas nÃo o suficiente para apresentar fotoinibiÃÃo. A cultivar tolerante apresentou maior atividade de PEPcase no estresse, mas a atividade de Rubisco nÃo foi alterada. Na cultivar sensÃvel, nÃo houve alteraÃÃo na atividade de PEPcase enquanto que a atividade de Rubisco foi reduzida em 40% no estresse mas com total recuperaÃÃo. A expressÃo de PEPcase foi aumentada no estresse mas com maior incremento na cultivar tolerante, com padrÃo semelhante na quantidade de rubisco. No capÃtulo 3, foi realizado um trabalho com o objetivo de avaliar o sistema de defesa anti-oxidativo em plantas de cana-de-aÃÃcar expostas ao estresse hÃdrico moderado. Neste capÃtulo, apenas a cultivar IAC SP 94-2094 foi utilizada e a deficiÃncia hÃdrica foi aplicada atravÃs de ciclos de irrigaÃÃo, com plantas irrigadas a cada cinco dias por um perÃodo de 15 dias e recuperaÃÃo de trÃs dias. O estresse hÃdrico aplicado causou reduÃÃes marcantes na condutÃncia estomÃtica, na transpiraÃÃo foliar e na fotossÃntese lÃquida, com recuperaÃÃo parcial, refletindo em uma menor eficiÃncia do uso da Ãgua e eficiÃncia de carboxilaÃÃo. Os parÃmetros fotoquÃmicos apresentaram modificaÃÃes transitÃrias, completamente revertidas pela recuperaÃÃo. As atividades da Rubisco e PEPcase nÃo mostraram modificaÃÃes, mas houve aumento na quantidade relativa de PEPcase e estado de ativaÃÃo da Rubisco. O estresse hÃdrico aplicado aumentou a peroxidaÃÃo lipÃdica e o conteÃdo de H2O2, induzindo aumentos de atividades de SOD e APX, principalmente APX tilacoidal e Fe-SOD. O perfil de aÃÃcares foi alterado nas plantas estressadas, com aumento de hexoses e diminuiÃÃo do teor de amido nas folhas. O objetivo do capÃtulo 4 foi avaliar as modificaÃÃes fisiolÃgicas e bioquÃmicas em relaÃÃo aos processos fotossintÃticos em cana-de-aÃÃcar submetida a um ambiente de elevado CO2 e baixo suprimento de nitrogÃnio (-N). A fotossÃntese lÃquida foi reduzida nas plantas com CO2 elevado e -N. Os parÃmetros fotoquÃmicos foram reduzidos apenas no tratamento -N, mas sem sinal de fotoinibiÃÃo. As enzimas da carboxilaÃÃo, PEPcase e Rubisco, sofreram regulaÃÃes diferenciadas, tanto pelo alto CO2 como pelo baixo suprimento de nitrogÃnio. A determinaÃÃo de nitrato mostrou acÃmulo nas raÃzes, indicando deficiÃncia no transporte para parte aÃrea. O tratamento âN diminuiu o conteÃdo de aminoÃcidos, proteÃnas solÃveis e nitrogÃnio total. O teor de sacarose foi reduzido em todos os tratamentos. Por fim, verificamos que a cultivar IAC SP 94-2094 possui maior fotoproteÃÃo indicada pelo maior NPQ e possui ainda maior atividade e expressÃo de PEPcase, permitindo melhor performance em perÃodos de dÃficit hÃdrico severo. Quando estudada com dÃficit hÃdrico moderado, as plantas desta cultivar apresentaram uma organizada defesa anti-oxidativa para proteÃÃo contra as espÃcies reativas de oxigÃnio. Quando sob elevada concentraÃÃo de CO2, as plantas de cana-de-aÃÃcar exibem modificaÃÃes estomÃticas e bioquÃmicas, reduzindo a atividade fotossintÃtica pela reduÃÃo da assimilaÃÃo de nitrato e atividade de redutase do nitrato, mostrando uma forte relaÃÃo entre a assimilaÃÃo de carbono e nitrogÃnio.
Sugarcane is plant of great economic potential, mainly utilized to sugar and biofuel production. Brazil has an international importance, leading the world production of this culture. In despite of this high production, Brazil is located in a tropical region and presents several climatic adversities. The study of sugarcane physiology in stress situations, like water deficit, becomes essential to maintenance and improvement of the production. Sugarcane is a C4 species, with a CO2 concentration mechanism. It is expected that the growing elevation of CO2 in the atmosphere does not the sugarcane productivity in a relevant way but the studies about this subject are very scarce. Thus, it was aimed to evaluate the photosynthesis regulation by water deficit, nitrogen supply and high CO2 in sugarcane plants. Chapter 1 contains the state of the art concerning the study theme. In the chapter 2, it was performed an work in order to evaluate the responses to water deficit of two sugarcane cultivars considered contrasting about water deficit, IAC SP 94-2094 and IAC SP 95-5000. These cultivars were exposed to severe water deficit, with withholding water for five days, and recovery, irrigated after for two days after stress. The applied treatment strongly affected the gas exchanges, with stomatal closure in both cultivars, leading to great reductions in transpiration and CO2 assimilation. The chlorophyll a fluorescence parameters were affected, but without photoinhibition. Tolerant cultivar showed higher PEPcase activity in stress, but Rubisco activity was not altered. In the sensitive cultivar there was not alteration in the PEPcase activity whereas Rubisco activity was reduced 40% in stress but totally recovered. PEPcase expression was increased in stress but with a higher increment in sensitive cultivar, with a similar pattern in the Rubisco amount. In the chapter 3, it was performed an work in order to evaluate the antioxidative system in sugarcane plants exposed to mild water stress. In this chapter, IAC SP 94-2094 was utilized and the water deficit was applied with irrigation cycles, with plants irrigated each five days for fifteen days and recovery for three days. Water stress applied caused remarkable decreases in the stomatal conductance, leaf transpiration and net photosynthesis, with partial recovery, causing lower water use and carboxylation efficiencies. Photochemical parameters showed transient changes completely reversible by recovery. PEPcase and Rubisco activities did not show modifications but it was increase in the relative amount of PEPcase and Rubisco activation state. Water stress increased the lipid peroxidation and H2O2 content, inducing increases in SOD and APX activities, mainly thylakoidal APX and Fe-SOD. Sugars profile was altered in stressed plants, with increase in hexoses and decrease in starch content in leaves. The aim of the chapter 4 was evaluate the physiological and biochemical changes in concern to photosynthetic processes in sugarcane exposed to high CO2 and low supply of nitrogen (-N). Net photosynthesis was reduced in plants subjected to high CO2 and -N. Photochemical parameters were decreased only in -N treatment, but with no photoinhibition. Carboxylation enzymes, PEPcase and Rubisco, did suffer differential regulations either by high CO2 or by low nitrogen. Nitrate determination showed accumulation in roots, indicating deficiency in transport to shoot. -N treatment decreased the amino acids content, soluble proteins and total nitrogen. Sucrose content was reduced in all treatments. At last, it was verified that IAC SP 94-2094 cultivar has more photoprotection indicated by higher NPQ and more PEPcase activity and expression, conferring a better performance in severe water deficit periods. When studied under mild water stress, the plants showed an organized anti-oxidative defense for protection against reactive oxygen species. When under high CO2, sugarcane plants exhibit stomatal and biochemical changes, reducing the photosynthetic activity by reduction in nitrate assimilation and nitrate reductase activity, showing a strong relation between carbon and nitrogen assimilation.

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Abendroth, Barbara. "Ion induced stress relaxation during the growth of cubic boron nitride thin films". Doctoral thesis, [S.l.] : [s.n.], 2004. http://deposit.ddb.de/cgi-bin/dokserv?idn=972228373.

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Abendroth, B. "Ion-induced stress relaxation during the growth of cubic boron nitride thin films". Forschungszentrum Dresden, 2010. http://nbn-resolving.de/urn:nbn:de:bsz:d120-qucosa-28863.

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Abendroth, B. "Ion-induced stress relaxation during the growth of cubic boron nitride thin films". Forschungszentrum Rossendorf, 2004. https://hzdr.qucosa.de/id/qucosa%3A21713.

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Abadias, G., L. E. Koutsokeras, P. A. Patsalas, W. Leroy, D. Depla, S. V. Zlotsi i V. V. Uglov. "In situ stress evolution during growth of transition metal nitride films and nanocomposites". Thesis, Видавництво СумДУ, 2011. http://essuir.sumdu.edu.ua/handle/123456789/20742.

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The issue of stress evolution during growth of hard transition metal nitride (TMN) based coatings is of vital importance to understand origin of intrinsic stress development and to control stress level in order to avoid mechanical failure of coated components and devices. By using in situ and real-time wafer curvature measurements based on a multiple- beam optical stress sensor (MOSS), basic insights on the atomistic mechanisms at the origin of stress development and stress relaxation can be obtained. In the present paper, a review of recent advances on stress development during reactive magnetron sputter-deposition of binary TMN films (TiN, ZrN, TaN) as wells as ternary systems (TiZrN, TiTaN) will be presented. The influence of growth energetics on the build-up of compressive stress will be addressed. A correlation between stress, texture and film morphology is demonstrated. Finally, illustration will be given for quaternary TiZrAlN nanocomposites. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/20742

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Segonzac, Cécile. "Caractérisation moléculaire et physiologique d'un transporteur d'efflux de nitrate de la membrane plasmique chez Arabidopsis thaliana". Montpellier, ENSA, 2006. http://www.theses.fr/2006ENSA0026.

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L’absorption racinaire de nitrate (NO3-) résulte du bilan entre son influx actif et son efflux passif. En réponse à divers stress biotiques ou abiotiques, l’intensité de l’efflux peut dépasser celle de l’influx et mener à une excrétion de NO3-, dont les bases moléculaires et la signification biologique sont encore inconnues. L’objectif de ce travail a été de valider et de caractériser un transporteur candidat pour l’efflux de NO3-, antérieurement identifié chez Arabidopsis thaliana au cours d’une approche de biochimie fonctionnelle. La protéine NAXT1 (pour NITRATE EXCRETION TRANSPORTER 1) appartient à la grande famille PTR et à une sous-famille de 7 protéines similaires, nommée famille NAXT. Un test d’inhibition fonctionnelle a validé la fonction d’efflux de NO3- des NAXT au niveau de la membrane plasmique (MP) isolée à partir de racines. NAXT1 est exprimé dans le cortex mature de la racine, mais aussi dans les feuilles. Dans les racines soumises à une charge acide, les mesures d’efflux de NO3- réalisées in planta et in vitro sur les mutants naxt1 ont montré que NAXT1 est responsable d’une excrétion soutenue de NO3- vers le milieu extérieur, liée à une accumulation de la protéine sur la MP, mais dé-corrélée de l’accumulation du transcrit. Une première exploration du rôle de NAXT1 dans les feuilles a montré que les mutants naxt1 présentent un phénotype de tolérance accrue au dessèchement progressif du sol et une sensibilité accrue à un stress salin par rapport aux plantes sauvages. Enfin, des données d’expression sur les différentes isoformes NAXT ont été recueillies afin d’envisager leur(s) rôle(s) dans l’excrétion de NO3- déclenchée par les stress ou dans la composante d’efflux de l’absorption racinaire de NO3-.

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Carlin, Samira Domingues [UNESP]. "Mecanismos fisiológicos de cana-de-açúcar sob efeito da interação dos estresses hídrico e ácido no solo". Universidade Estadual Paulista (UNESP), 2009. http://hdl.handle.net/11449/105234.

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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)
No presente trabalho foi verificado o ajuste osmótico no crescimento inicial de cana-de-açúcar, cv. IAC91-5155, sob efeito da interação dos estresses hídrico e ácido no solo. Para tanto, foram quantificados os teores de três solutos compatíveis, prolina, glicina betaína e trealose. Também foi estudada a atividade da nitrato redutase e os teores de clorofilas. O estudo de todas estas variáveis teve por objetivo propor a utilização destes compostos como indicadores fisiológicos de aclimatação da cana-deaçúcar sob efeito da interação de ambos os estresses. O experimento foi realizado em casa de vegetação com 29,7±4,3oC e 75±10 UR%. Foram utilizados três tratamentos de disponibilidade hídrica (capacidade de campo, CC): controle (70%), estresse moderado (55%) e estresse severo (40%) e três tratamentos de acidez no solo (saturação por bases, V%): controle (55%), média acidez (33%) e alta acidez (23%). O delineamento experimental utilizado foi o de blocos casualizados em esquema fatorial 3x3, com quatro repetições. Após 60 dias sob estresses foram determinados os teores dos solutos compatíveis, a atividade da nitrato redutase e os teores das clorofilas. Os resultados mostram que houve acúmulo dos três solutos compatíveis evidenciando que ocorreu ajuste osmótico. Prolina e glicina betaína são indicadores fisiológicos do efeito da interação de ambos os estresses enquanto trealose é indicadora apenas para o estresse hídrico. Também, a atividade da nitrato redutase pode ser utilizada como indicador do estresse hídrico e os teores das clorofilas a, b e total para os estresses hídrico ou ácido. A massa de matéria seca da parte aérea, o número de folhas e a área foliar das plantas jovens de cana-de-açúcar, ajustadas osmoticamente, são reduzidos pelos estresses. Os efeitos interativos de ambos...
In this present work was verified the osmotic adjustment in the initial plant growth sugarcane cv. IAC91-5155 under interaction effect of water and acid stress in the soil. For this, were quantified three compatible solutes content, as follows: proline, glycine betaine and trehalose. It was verified also the nitrate reductase activity as well the chlorophyll content. The study of all parameters aimed to propose the use components as physiological indicators to acclimation of sugarcane plants under interaction the both stress. The experiment was carried out in a greenhouse under 29.7±4.3oC and 75±10%. Three water availability treatments (Field Capacity – FC%): control (70%), moderate stress (55%), and extreme stress (40%) and three soil acidification treatment (Base Saturation – BS%): control (55%), average acidity (33%), and high acidity (23%) were used. The experimental design used was the randomized blocks in a 3x3 factorial scheme and four replicates. After sixty days under stress were determined compatible solutes, nitrate reductase and chlorophyll content. Our results showed that there was the accumulation of three compatible solutes exhibiting osmotic adjustment. Glycine betaine and proline are both physiologic indicators of stresses interaction effect whereas trehalose indicates only water stress. The nitrate reductase activity can be used as water stress indicator and chlorophylls a, b and total are indicators to water or acid stress. The dry mass of shoot part, leaves number and leaf area are significantly reduced by stress in young sugarcane plants adjusted osmotically. The interaction of stresses cause decrease of dry mass while water stress reduces leaves number and leaf area.

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Porpino, Suênia Karla Pacheco. "Nitrato orgânico 2-nitrato-1,3-dibutoxipropano (NDBP) atenua o estresse oxidativo e a hipertensão arterial mediada por angiotensina II via produção de óxido nítrico em animais experimentais". Universidade Federal da Paraíba, 2016. http://tede.biblioteca.ufpb.br:8080/handle/tede/9694.

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Background: Nitric oxide (NO) donors can act in the control and treatment of various cardiovascular complications, such as hypertension. In particular, an organic nitrate, 2-nitrate-1,3-dibutoxipropane (NDBP) developed in recent years by UFPB has shown great therapeutic potential. However, its mechanisms are not fully clarified. Aim: To investigate the effects and mechanisms of NDBP, elucidating their therapeutic potential in angiotensin II-mediated hypertension. Methods: In the first stage of the study, were performed in vitro experiments in normotensives Wistar rats (n=11) tissues for characterization of compound about ability to release NO by direct measurement of NO; and modulation of NADPH oxidase activity, by chemiluminescence technique. In the second stage of the study, in vivo experiments in C57BL / 6J mice (n=24), divided in four groups (control, NDBP, Ang II and Ang II + NDBP) were performed to investigate the therapeutic potential of NDBP in angiotensin II-mediated hypertension. The animals had implantation of osmotic minipumps containing Ang II (400 mg / kg / 24h) and after 9 days were treated with NDBP (40 mg / kg / day; ip). Blood pressure (BP) was measured by tail-cuff. At the end of the experiments, the animals were euthanized and blood and tissues were collected for analysis. Histopathological analyzes were performed using staining picrosirius. Superoxide levels were measured by NADPH oxidase activity via chemiluminescence and DHE fluorescence (5 mmol • L-1). Levels of serum nitrate/nitrite and cGMP were performed using specific kits. NADPH oxidase subunit expression were analyzed by real time qPCR. Putative antioxidant activity was determined by autoxidation with pyrogallol. Results: In vitro experiments revealed a dose-dependent increase in NO production mediated by NDBP in liver and kidney tissues, which was attenuated by the xanthine oxidase inhibitor febuxostat. In addition, the NDBP reduced NADPH oxidase activity and prevented its activation induced by ANG II. In vivo experiments showed that NDBP prevents the increase in hypertension in mice with chronic infusion of ANG II. This results were associated to the attenuation of cardiac hypertrophy, renal fibrosis, and reduced NADPH oxidase-derived oxidative stress in the kidneys, the heart, and liver. Furthermore, NDBP also increased plasma levels of nitrite and nitrate. On the other hand, the autoxidation with pyrogallol revealed that NDBP does not act as a direct antioxidant, justifying its involvement in the modulation of NADPH oxidase. Conclusions: The organic nitrate NDBP prevents the progression of angiotensin II-mediated hypertension. Regarding the mechanisms, our findings suggest that NDBP treatment is associated with sustained NO release and attenuated activity of NADPH oxidase, which requires functional xanthine oxidase.
Introdução: Doadores de óxido nítrico (NO) podem atuar no controle e tratamento de diversas complicações cardiovasculares, como por exemplo, a hipertensão arterial. Em particular, um nitrato orgânico, 2-nitrato-1,3-dibutoxipropano (NDBP) desenvolvido nos últimos anos pela UFPB vem apresentando grande potencial terapêutico. No entanto, seus mecanismos não estão totalmente esclarecidos. Objetivo: Investigar os efeitos e os mecanismos de ação do NDBP, elucidando seu potencial terapêutico na hipertensão arterial induzida por Angiotensina II (ANG II). Métodos: Na primeira etapa do estudo foram realizados experimentos in vitro em tecidos de ratos Wistar normotensos (n=11) para caracterização do composto, sobre sua capacidade de liberação de NO, por meio da medida direta de NO; e modulação da atividade da enzima NADPH oxidase, pela técnica de quimioluminescência. Na segunda etapa do estudo, experimentos in vivo em camundongos C57BL/6J (n=24), classificados em quatro grupos (Controle, NDBP, ANG II e ANG II + NDBP), foram realizados para investigar o potencial terapêutico do NDBP na hipertensão induzida por ANG II. Os animais tiveram implante de minibombas osmóticas contendo ANG II (400 μg/kg/24h) e após 9 dias receberam tratamento com NDBP (40 mg/kg/dia; i.p.). A pressão arterial (PA) foi verificada via pletismografia de cauda. Ao término dos experimentos, os animais foram eutanasiados e tecidos e sangue foram coletadas para análise posterior. Análises histopatológicas foram realizadas utilizando a coloração com Picro-sirius. Os níveis de superóxido foram mensurados por meio da atividade da enzima NADPH oxidase, via quimioluminescência e fluorescência com DHE (5 mmol·L−1). Além disso, os níveis séricos de nitrato/nitrito e cGMP foram realizados, utilizando kits específicos. Foi investigada também a expressão de subunidades da enzima NADPH oxidase pela técnica de qPCR em tempo real e a possível atividade antioxidante por meio da autoxidação com pyrogallol. Resultados: os experimentos in vitro utilizando tecidos de fígado e rim revelaram um aumento dose-dependente na produção de NO, mediado pelo NDBP, que foi atenuado pelo inibidor da enxima xantina oxidase, o febuxostato. Além disso, o NDBP reduziu a atividade da NADPH oxidase e preveniu sua ativação induzida pela ANG II. Os experimentos in vivo mostraram que o NDBP previne o aumento da hipertensão arterial em camundongos com infusão crônica de ANG II. Esses resultados foram associados à atenuação da hipertrofia cardíaca, fibrose renal, e redução do estresse oxidativo mediado pela redução da atividade da enzima NADPH oxidase nos rins, coração e fígado. Além disso, o NDBP aumentou os níveis plasmáticos de nitrito e nitrato. Por outro lado, a autooxidação com pyrogalol revelou que o NDBP não atua como um antioxidante direto, justificando então sua participação na modulação da NADPH oxidase. Conclusão: o nitrato orgânico NDBP impede a progressão da hipertensão arterial mediada pela angiotensina II. Em relação aos seus mecanismos, os achados sugerem que o tratamento com NDBP está associado a uma contínua liberação de NO e redução da atividade da enzima NADPH oxidase, que parece ser dependente da xantina oxidase funcional.

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25

Anutgan, Mustafa. "Investigation Of Plasma Deposited Boron Nitride Thin Films". Master's thesis, METU, 2007. http://etd.lib.metu.edu.tr/upload/12608611/index.pdf.

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Hexagonal boron nitride (h-BN) thin films are deposited by plasma enhanced chemical vapor deposition (PECVD). Effects of heat treatment and source gases on the structure and physical properties are investigated. Chemical bonding is analyzed in comparison with the better understood isoelectronic carbon compound, graphite. It seems that the basic difference between h-BN and graphite arises from the different electronegativities of boron and nitrogen atoms. Optical absorptions in UV-visible range for crystalline and amorphous structures are outlined. The expressions used for the evaluation of mechanical stress induced in thin films are derived. The deposited films are considered to be turbostratic as they do not exhibit the characteristic optical absorption spectra of a crystal. A new system, stylus profilometer, is implemented and installed for thin film thickness and mechanical stress measurements. Hydrogen atom density within the films, estimated from FTIR spectroscopy, is found to be a major factor affecting the order and mechanical stress of the films. Heat treatment of the films reduces the hydrogen content, does not affect the optical gap and slightly increases the Urbach energy probably due to an increased disorder. Increasing the nitrogen gas flow rate in the source gas results in more ordered films. The virtual crystal of these films is detected to be unique. Relative bond concentrations of the constituent elements indicate a ternary boron-oxygen-nitrogen structure. The physical properties of h-BN such as high resistivity and wide band gap seem suitable for optoelectronic applications such as gate dielectrics in thin film transistors and light emitting devices in the blue region.

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26

Lupica, Samuel J. "Nitrate Toxicity to Common Carp Measured Noninvasively by Novel Enzyme-linked Immunosorbent Assay for Cortisol". University of Toledo Health Science Campus / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=mco1226956326.

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Silva, Petterson Costa ConceiÃÃo. "Role of glutamine in the regulation of nitrate influx in cowpea roots exposed to salinity". Universidade Federal do CearÃ, 2015. http://www.teses.ufc.br/tde_busca/arquivo.php?codArquivo=16067.

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Conselho Nacional de Desenvolvimento CientÃfico e TecnolÃgico
There are many studies showing that the salinity may directly affect the nitrate uptake, from their osmotic effect, nature of the salt and its ionic composition. However, little is known about the mechanisms related to the salt ability to inhibit the nitrate acquisition indirectly. This study was carried with aim to induce inhibition of NO3- influx in cowpea roots of indirect form triggered by a negative feedback mechanism, caused by the increase in the pool of free amino acids in the tissue, induced by salt stress.For this, were done three isolated studies and continuous.The exogenous glutamine application promoted an increase in the free amino acids content.The presence of glutamine decreased significantly the nitrate acquisition.The free ammonium can also be listed as a key-compound in the role of nitrate influx regulation, since use of the MSX (Methionine sulfoximine) promoted the increase of NH4+ content and also reduced nitrate influx, but, in a lesser degree when compared to treatment with AZA (Azaserine). Salt stress caused a reduction in NO3- influx by decrease in the growth of plants induced by salt. The data indicated which this reduction in the influx is triggered by increase of amino acids content, mainly the glutamine, that is main likely compound to act as signal in the N-feedback regulation.
Existem muitos estudos mostrando que a salinidade pode afetar a absorÃÃo de nitrato de forma direta, a partir do seu efeito osmÃtico, da natureza do sal e de sua composiÃÃo iÃnica. Entretanto, pouco se sabe sobre os mecanismos relacionados com a capacidade do sal em inibir a aquisiÃÃo de nitrato de forma indireta. O presente estudo teve como objetivo induzir a inibiÃÃo do influxo de NO3- em raÃzes de feijÃo-caupÃ de forma indireta desencadeada por um mecanismo de feedback negativo, provocado pelo aumento no pool de aminoÃcidos livres no tecido, induzido por estresse salino. Para isso, foram realizados trÃs estudos isolados e contÃnuos. A aplicaÃÃo de glutamina exÃgena promoveu um aumento no conteÃdo de aminoÃcidos livres. A presenÃa de glutamina reduziu significativamente a aquisiÃÃo de nitrato. O amÃnio livre tambÃm pode ser listado como um composto-chave no papel da regulaÃÃo do influxo de nitrato, pois a utilizaÃÃo do MSO (Metionina sulfoximina) promoveu o aumento do conteÃdo de NH4+ e tambÃm reduziu o influxo de nitrato, porÃm em menor grau quando comparado ao o tratamento com AZA (Azaserina). O estresse salino causou uma reduÃÃo no influxo de NO3-, pela diminuiÃÃo no crescimento das plantas induzida pelo sal. Adicionalmente, estes dados indicaram que esta reduÃÃo no influxo estÃ ligada ao aumento do teor de aminoÃcidos, principalmente a glutamina, que Ã o principal componente para atuar como sinal na regulaÃÃo por N-feedback.

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Fu, Yankun. "Residual stress in gallium nitride films grown on silicon substrates by metalorganic chemical vapor deposition". Ohio : Ohio University, 2000. http://www.ohiolink.edu/etd/view.cgi?ohiou1171653515.

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Winter, Jack. "Studies of in situ nitrosative stress following nitrate ingestion in the human upper gastrointestinal tract". Connect to e-thesis, 2008. http://theses.gla.ac.uk/207/.

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Thesis (M.D.) - University of Glasgow, 2008.
M.D. thesis submitted to the Faculty of Medicine, Division of Cardiovascular and Medical Sciences, University of Glasgow, 2008. Includes bibliographical references. Print version also available.

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30

Winter, Jack Westwood. "Studies of in situ nitrosative stress following nitrate ingestion in the human upper gastrointestinal tract". Thesis, University of Glasgow, 2008. http://theses.gla.ac.uk/207/.

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Nitrate ingestion leads to high luminal concentrations of nitric oxide being generated where saliva meets gastric acid. Nitric oxide generates N-nitrosative stress on reacting with oxygen at neutral pH. We aimed to ascertain if luminal nitric oxide exerts nitrosative stress in the upper GI tract, and to assess the influence of acid reflux. We utilised a specialised silicone tube as an epithelial model, inserting it into the upper gastro-intestinal tract of humans. Healthy volunteers were studied with and without ingestion of 15N enriched nitrate and Barrett’s oesophagus patients with and without stimulation of reflux. In volunteers, nitrate ingestion resulted in significantly higher concentrations of N-nitrosomorpholine in the tube sections exposed to acid. In Barrett’s patients, generation of N-nitrosomorpholine shifted proximally, with most nitrosative stress occurring within the oesophagus during reflux episodes. This chemistry may be harmful to patients with erosive esophagitis whose epithelium will be more sensitive to chemical mutagenesis.

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Wang, Kehua. "Effects of Nitrate and Cytokinin on Nitrogen Metabolism and Heat Stress Tolerance of Creeping Bentgrass". Diss., Virginia Tech, 2010. http://hdl.handle.net/10919/39049.

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Creeping bentgrass (Agrostis stolonifera L.) is a major low-cut cool-season turfgrass used worldwide. The objectives of this research were to: 1) to gain insight into the diurnal fluctuation of N metabolism and effects of cytokinin (CK) and nitrate; 2) to characterize the impacts of N and CK on creeping bentgrass under heat stress; 3) to investigate the simultaneous effects of CK and N on the antioxidant responses of heat stressed creeping bentgrass; and 4) to examine the expression pattern of the major heat shock proteins (HSPs) in creeping bentgrass during different heat stress periods, and then to study the influence of N on the expression pattern of HSPs. The transcript abundance of nitrate reductase (NR), nitrite reductase (NIR), plastidic glutamine synthetase (GS2), ferredoxin-dependent glutamate synthase (Fd-GOGAT), and glutamate dehydrogenase (GDH) and N metabolites in shoots were monitored during the day/night cycle (14/8 h). All the measured parameters exhibited clear diurnal changes, except GS2 expression and total protein. Both NR expression and nitrate content in shoots showed a peak after 8.5 h in dark, indicating a coordinated oscillation. Nitrate nutrition increased diurnal variation of nitrate content compared to control and CKHowever, CK shifted the diurnal in vivo NR activity pattern during this period. Grass grown at high N had better turf quality (TQ), higher Fv/Fm, normalized difference vegetation index (NDVI), and chlorophyll concentration at both 15 d and 28 d of heat stress than at low N, except for TQ at 15 d. Shoot NO3-, NH4+, and amino acids increased due to the high N treatment, but not water soluble proteins. High N also induced maximum shoot nitrate reductase activity (NRmax) at 1 d. CK increased NDVI at 15 d and Fv/Fm at 28 d. In addition, grass under 100 ÂµM CK had greatest NRmax at both 1 d and 28 d. Under high N with 100 ÂµM CK, root tZR and iPA were 160% and 97% higher than under low N without CK, respectively. Higher O2- production, H2O2 concentration, and higher malonydialdehyde (MDA) content in roots were observed in grass grown at high N. The activities of superoxide dismutase (SOD), ascorbate peroxidase (APX), and guaiacol peroxidase (POD) in roots were enhanced by high N at 19, 22, and 24% levels, respectively, relative to low N. Twenty-eight days of heat stress resulted in either the development of new isoforms or enhanced isoform intensities of SOD, APX, and POD in roots compared to the grass responses prior to heat stress. However, no apparent differences were observed among treatments. No CK effects on these antioxidant parameters were found in this experiment. At week seven, grass at medium N had better TQ, NDVI, and Fv/Fm accompanied by lower shoot electrolyte leakage (ShEL) and higher root viability (RV), suggesting better heat resistance. All the investigated HSPs (HSP101, HSP90, HSP70, and sHSPs) were up-regulated by heat stress. Their expression patterns indicated cooperation between different HSPs and that their roles in creeping bentgrass thermotolerance were affected by N level.
Ph. D.

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32

Brough, David B. "Investigation of Low-Stress Silicon Nitride as a Replacement Material for Beryllium X-Ray Windows". BYU ScholarsArchive, 2012. https://scholarsarchive.byu.edu/etd/3402.

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The material properties of low stress silicon nitride make it a possible replacement material for beryllium in X-ray windows. In this study, X-ray windows made of LPCVD deposited low stress silicon nitride are fabricated and characterized. The Young's modulus of the LPCVD low stress silicon nitride are characterized and found to be 226±23 GPa. The residual stress is characterized using two different methods and is found to be 127±25 MPa and 141±0.28 MPa. Two support structure geometries for the low stress silicon nitride X-ray windows are used. X-ray windows with thicknesses of 100 nm and 200 nm are suspended on a silicon rib support structure. A freestanding circular geometry is used for a 600 nm thick X-ray window. The 100 nm and 200 nm thick low stress silicon nitride X-ray windows with a silicon support structure are burst tested, cycling tested and leak rate tested. The average burst pressure for the 100 and 200 nm films on a silicon support structure are 1.4 atm and 2.2 atm respectively. Both 100 nm and 200 nm windows are able to withstand a difference in pressure of 1 atm for over 100 cycles with a leak rate of less than 10-10 mbar-L/s.The low stress silicon nitride with 100 nm and 200 nm thicknesses, the 600 nm freestanding low stress silicon nitride windows and freestanding 8 micron thick beryllium windows are mechanical shock resistance tested. The support structure low stress silicon nitride and beryllium windows are tested with an applied vacuum. The freestanding 600 nm thick low stress silicon nitride windows burst at 0.4 atm and are therefore mechanical shock wave tested without an applied vacuum. The support structure low stress silicon nitride windows fractured when subjected to an acceleration of roughly 5,000 g. The 8 micron thick beryllium windows are subjected to accelerations of over 30,000 g without fracturing. A quasistatic model is used to show that for low stress silicon nitride with a freestanding circular geometry, an acceleration of 106 g is required to have the same order of magnitude of stress caused by a pressure differential of 1 atm. Low stress silicon nitride can act as a replacement for beryllium in X-ray windows, but the support geometry, residual stress, and strength of the material need to be optimized.

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Renso, Nicola. "Analysis of degradation mechanisms induced by electrical over-stress on high efficiency gallium nitride LEDs". Doctoral thesis, Università degli studi di Padova, 2019. http://hdl.handle.net/11577/3422340.

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This thesis investigates the reliability of state-of-the-art InGaN LEDs for lighting applications and the impact of the diffusion-related mechanisms on optoelectronic GaN-based wafers, with the aim to identify the physical mechanisms responsible for the premature degradation of those devices. By means of custom experimental setups, developed during the triennial research activity, it is possible to identify the dominant failure modes and degradation mechanisms of GaN LEDs subjected to electrical over-stress (EOS), both in forward and reverse bias, and to correlate specific failures with the epitaxy related weaknesses of state-of-the-art LEDs. In particular, to understand the role of defects in the device degradation, advanced techniques such as Deep-Level Transient Spectroscopy (DLTS) and Deep-Level Optical Spectroscopy (DLOS) are employed. An extensive analysis aimed to correlate the epitaxial growth parameters (indicated with letters from A to E due to confidentiality agreements) and LEDs electro-static discharge (ESD) robustness in reverse bias is presented. The analysis investigates separately the roles of the epitaxial features on the n- and p-side by means of DC and pulsed characterizations. The results suggest: i) on the n-side, the value of the parameter A is critical in the robustness to ESD events; ii) on the p-side, C is the critical parameter; iii) leakage paths in the structure can act as radiative recombination centers in reverse bias conditions and can be responsible for the failure via junction shorting; iv) nitrogen vacancies may be the physical origin of those defects. The information about the physical mechanisms responsible for degradation are used as a feedback for devices manufacturers, for the improvement of the technological processes. The analysis of the failure modes trigged by EOS events in forward bias describes the power dissipation as the main cause of damage: according to the amount of power delivered to the chip, due to the strong self-heating, the failure can interest the chip (leading to a short-like failure) or the whole package (inducing an open-like failure). Further experiments allow to identify four different regions before the failure of the device: i) radiative recombination is the dominant recombination process and non-uniform band-filling can be detected, ii) by increasing the current density, strong self-heating can be noticed, and then iii) the saturation of the quantum wells (QWs) induces a strong overflow and may lead to additional power dissipation. Finally, (iv) the extreme high current density induces the current crowding effect, leading to a progressive decay of the optical properties of the device and to the device failure. Avalanche generation in state-of-the-art high power InGaN LEDs is detected: the extremely high electric field generated by strong reverse biases triggers band-to-band tunneling, leading to impact ionization. Current-voltage characterizations at cryogenic temperatures detect the shift of IV curves with increasing temperatures, confirming the role of avalanche generation. Further analysis of the electro-luminescence spectral distribution, in this extreme bias conditions, shows that (i) hole and electron pairs generated by the avalanche process recombine radiatively, generating photons, (ii) which are partially re-absorbed in the In-containing layers and n-GaN side and then (iii) re-emitted as internal photoluminescence of the yellow-emitting defects in the n-GaN layer. Experiments on color coded structures with different QW order and electron blocking layer (EBL) Al content show that i) leakage current increase in reverse and low forward bias conditions is related to diffusion, ii) the optical degradation is not dominated by diffusion but is related to the defects propagation triggered by the energy released by SRH recombination, iii) the optical degradation starts from the p-side and iv) the physical origin of those defects are impurities on the AlGaN/GaN interface or nitrogen vacancies.
Questo lavoro di tesi è focalizzato sullo studio dell’affidabilità di dispositivi LED allo stato dell’arte per applicazioni di illuminotecnica e sull’impatto dei meccanismi di diffusione in wafer optoelettronici in nitruro di gallio, con l’obiettivo di identificare i meccanismi fisici responsabili per il degrado prematuro di tali dispositivi. Mediante l’utilizzo di setup sperimentali, sviluppati durante i tre anni di attività di ricerca, è stato possibile identificare i meccanismi di failure e di degrado dominanti in dispositivi LED basati su GaN sottoposti a condizioni di over-stress elettrico (EOS), sia in polarizzazione diretta che inversa, e correlare le specifiche modalità di fallimento con le difettosità epitassiali di LED allo stato dell’arte. In particolare, al fine di appurare il ruolo dei difetti cristallini nel degrado del dispositivo, sono state utilizzate tecniche di caratterizzazione avanzate: il Deep-Level Transient Spectroscopy (DLTS) e il Deep-Level Optical Spectroscopy. In questa tesi è presentata un’analisi approfondita finalizzata alla correlazione dei parametri di crescita epitassiale (nominati con lettere dalla A alla E poichè coperti da un accordo di non divulgazione) con la robustezza dei dispositivi LED alle scariche elettrostatiche. La trattazione analizza separatamente i ruoli dei parametri epitassiali di lato p ed n, attraverso caratterizzazioni DC e impulsate. I risultati suggeriscono che: i) sul lato n, A è il parametro critico per la robustezza alle scariche elettrostatiche; ii) mentre sul lato p, il parametro critico è C; iii) i percorsi di leakage nella struttura possono fungere da centri di ricombinazione radiativa quando il dispositivo è polarizzato inversamente e possono favorire il fallimento previa corto-circuitazione della giunzione; iv) le vacanze di azoto possono essere la causa fisica delle difettosità epitassiali. Le informazioni relative ai meccanismi fisici di degrado sono state condivise con il produttore dei dispositivi, al fine di promuovere il miglioramento della tecnologia di processo. L’analisi dei meccanismi di fallimento indotti da EOS in condizioni di polarizzazione diretta indica la dissipazione di potenza come la principale causa di degrado: in base al livello di potenza dissipata nel dispositivo e al conseguente auto-riscaldamento, il fallimento può interessare il chip (portando ad un fallimento come corto-circuito) o l’intero package (portando ad un fallimento di tipo circuito-aperto). Ulteriori esperimenti hanno permesso di identificare quattro regioni di funzionamento, prima del fallimento del dispositivo: i) la ricombinazione di tipo radiativo è dominante ed il riempimento delle buche quantiche non è uniforme, ii) l’incremento della densità di corrente induce un forte auto-riscaldamento, iii) e porta alla saturazione delle buche quantiche e all’overflow dei portatori. Infine, iv) l’estrema densità di corrente induce l’effetto di current crowding, portando ad un progressivo decadimento delle proprietà ottiche del dispositivo e al successivo fallimento. La generazione del processo avalanche è identificata in dispositivi LED di potenza: a causa del forte campo elettrico indotto nel dispositivo, sottoposto a polarizzazione inversa, si instaura il processo di tunneling banda a banda dei portatori e la conseguente ionizzazione da impatto. La caratterizzazione elettrica effettuata a temperature criogeniche evidenzia lo spostamento delle curve IV all’incremento della temperatura, confermando la presenza della generazione avalanche. Ulteriori analisi dell’elettroluminescenza e dei suoi diversi contributi spettrali mostrano che: i) le coppie elettrone-lacuna generate dal processo di avalanche ricombinano radiativamente, generando fotoni, ii) i quali sono parzialmente riassorbiti nel lato n della struttura e successivamente iii) riemessi come fotoluminescenza nelle lunghezze d’onda del giallo dai difetti presenti nel cristallo. Esperimenti su strutture color coded con buche quantiche disposte con diverso ordine nello stack epitassiale e diversa concentrazione di Al all’interno dell’electron blocking layer (EBL) mostrano che i) l’incremento della corrente di leakage in condizioni di polarizzazione inversa e debolmente diretta sono correlate alla diffusione, ii) il degrado ottico non è dominato da tale processo di diffusione, ma è collegato alla propagazione di difetti indotta dall’energia termica rilasciata da ricombinazione di tipo SRH, iii) il degrado ottico ha inizio dal lato p della giunzione e iv) l’origine fisica di tali difetti è rappresentata da impurezze all’interfaccia AlGaN/GaN o vacanze di azoto.

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Lautz, Laura K. "Hyporheic interaction and nitrate uptake in a semi-arid stream". Related electronic resource: Current Research at SU : database of SU dissertations, recent titles available full text, 2005. http://wwwlib.umi.com/cr/syr/main.

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Newham, Michael John. "Nitrate Retention and Removal in Sub-Tropical Riparian Zones". Thesis, Griffith University, 2011. http://hdl.handle.net/10072/366141.

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Worldwide, contamination of streams and groundwater with excess nitrate has been linked to agricultural land use and particularly to the application of nitrogen fertilisers to increase agricultural production. Nitrate is an effective contaminant in agricultural areas; it is highly mobile, having a low affinity for soil sorption, and so moves with runoff and sub-surface flows. Excess nitrate can cause ecological impacts on waterways and coastal receiving water through eutrophication and, in some cases, contributes to coastal ‘dead zones’. Nitrate also has toxicological effects on aquatic organisms and those using contaminated water as a drinking source. Riparian zones, those zones where interaction of aquatic and terrestrial environments occurs, are identified as areas of intense biogeochemical cycling and can act as buffers against excess nitrate by reducing the amount of nitrate reaching stream channels. Nitrate retention processes of biotic uptake and transformation to less mobile forms can increase the residence time of nitrate within the riparian zone, while removal processes of denitrification can permanently remove nitrate-nitrogen in gaseous forms.
Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
Griffith School of Environment
Science, Environment, Engineering and Technology
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田中, 啓介, Keisuke TANAKA, 義明秋庭, Yoshiaki AKINIWA, 裕介森下 i Yusuke MORISHITA. "ショットピーニングしたセラミックスの表面下の残留応力分布". 日本機械学会, 2005. http://hdl.handle.net/2237/9134.

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Ronchi, Nicolò. "An investigation of defects and reliability issues on Gallium Nitride devices". Doctoral thesis, Università degli studi di Padova, 2012. http://hdl.handle.net/11577/3421973.

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In this thesis a extensive study of devices based on AlGaN/GaN heterostructure is reported. The work is fundamentally divided in two main topic: the first part is related to the investigation of traps and defects and their effects on the device performances; the second part is instead related to the reliability studies of this type of devices. The investigation of trapping effects is based on pulsed measurements of output characteristic and transcharacteristic of the device under test. The measurements carried out on High Electron Mobility Transistors (HEMT) with different gate materials (Ni/Au/Ni or ITO) and absence or presence of the surface passivation layer have shown how this technique can be used as a rapid and effective method to distinguish between the trapping phenomena occurring in the region under the gate and those occurring in the gate - drain access region. In particular we have seen that unpassivated devices have a transconductance peak dispersion, which can be ascribed to the presence of surface traps (absent in passivated devices). On the other hand the presence of a threshold voltage shift (found in the ITO samples) is related to traps below the gate electrode. The presence of traps under the ITO contact has been confirmed by low frequency capacitance - voltage measurements. Also the pulsed measurements have been correlated to electroluminescence characterization of the transistor showing the role of traps in limiting the maximum gate-drain electric field and, consequently, the intensity of the emitted light, related to the equivalent electron temperature. The combined dynamic IV - electroluminescence measurement technique has been also used in the analysis of state of the art GaN-HEMTs on Silicon substrate. The measurements carried on samples with different gate recess width and same gate length show better performances (in terms of frequency dispersion and gate - drain electric field) for transistors with shorter recess width. The analysis of defects in GaN-based devices has been carried out also by means of low frequency noise measurements. The purpose of the work on noise was to find a correlation between the intensity of the measured noise and the performances of the device (in particular the breakdown). Several devices have been tested (transistors and transmission line model - TLM) with different realization technology (aluminum content, ohmic contact annealing temperature, composition of ohmic contact electrode). A real correlation between noise in the conductive channel and breakdown has not been found; while measurements on the TLM show a possible relation between ohmic contact specific resistance and noise. The reliability of several samples has been investigated by means of both long-term stress (1000 h DC life-test) and short-term stress (2 min step-stress). The long - term stress has been carried out on AlGaN/GaN HEMTs processed on composite SopSiC substrate developed within the European HYPHEN project. These substrates have been realized through the transfer of a thin single crystal silicon layer on the top of a thick polycrystalline silicon carbide wafer. The aim of this project is to provide a valid and less expensive substrate for GaN - based devices in respect to the traditional bulk-SiC substrates. Three stress conditions (different DC biases and different ambient temperatures) have been selected for the test. The results at the end of the stress present good device stability and promising performance; reliability issues found in few samples are linked to the high levels of gate leakage current reached during the stress. This proves that devices failure can be ascribed to the technology used for the realization of transistors and does not appear correlated to the nature of the composite substrate. With concern the short-term stress, we have studied the influence of gate reverse bias test on the overall behavior of the transistor. This type of accelerated test usually brings to the definition of a critical voltage beyond that the gate leakage current increases drastically up to the failure of the device. In literature the phenomenon is called inverse piezoelectric effect and it is considered related to the lattice strain occurring during the stress. Our study was based on a split wafer experiment adopting passivated AlGaN/GaN HEMTs with different gate metallizations: Ni/Au/Ni, ITO, Ni/ITO. The results obtained suggest that the critical voltage is not related only to the piezoelectric strain, but also the initial gate leakage current of the fresh device plays a role in the degradation process. Moreover the dynamic of the degradation during the test seems to indicate that the ageing process can be ascribe to a defect percolation process in the AlGaN barrier layer
L'argomento esposto in questa tesi riguarda uno studio approfondito di dispositivi su eterostruttura AlGaN/GaN. Questo lavoro puo’ essere suddiviso in due argomenti principali: la prima parte riguarda lo studio di trappole e difetti e il loro effetto sulle prestazioni del dispositivo; la seconda parte e’ invece dedicata allo studio dell'affidabilita’ di questo tipo di dispositivi. L'analisi degli effetti trappola e’ basata sulla misurazione impulsata della caratteristica di uscita e della transconduttanza del dispositivo in esame. Le misure eseguite su transistor con diversa composizione dell'elettrodo di gate (Ni/Au/Ni o ITO) e presenza o assenza dello strato di passivazione hanno mostrato come questa tecnica puo’ essere utilizzata come rapido e valido sistema per distinguere tra gli effetti di trappole presenti nella regione sottostante il gate e quelli di trappole nella regione di accesso gate - drain. In dettaglio si e’ visto che dispositivi non passivati presentano una diminuzione del picco della transconduttanza, fenomeno riconducibile alla presenza di trappole superficiali; mentre nel caso di variazione della tensione di soglia (dispositivi con elettrodo di gate in ITO) le trappole sono localizzate nella regione al di sotto del contatto di gate. La presenza di trappole sotto il contatto in ITO e’ stata inoltre confermata da misure di capacita’ vs. tensione a bassa frequenza. Le misure impulsate sono state poi messe in relazione con le misure di elettroluminescenza effettuate sui transistor: questo confronto ha mostrato come le trappole presenti nel dispositivo limitino il massimo campo elettrico tra gate e drain e quindi l'intensita’ della radiazione emessa. Questa metodologia e’ stata poi applicata per l'analisi di dispositivi GaN su silicio caratterizzati da identica lunghezza del contatto di gate ma diversa ampiezza del recesso di gate. Dai risultati ottenuti si puo’ vedere che le prestazioni migliori, in termini di dispersione in frequenza e massimo campo elettrico, si hanno nei dispositivi con recesso piu’ piccolo. L'analisi dei difetti presenti nei dispositivi su GaN e’ stata effettuata anche per mezzo di misure di rumore a bassa frequenza. Lo scopo di questa parte di attivita’ era di trovare una correlazione tra il livello di rumore misurato e le caratteristiche elettriche del dispositivo (in particolare il breakdown). Diversi dispositivi sono stati testati (transistor e transmission line model - TLM) con differenti tecnologie di realizzazione (percentuale di alluminio, temperatura di processo, composizione dell'elettrodo dei contatti ohmici). Una correlazione rumore del canale conduttivo e breakdown non e’ stata trovata; mentre le misure sulle TLM hanno mostrato un possibile legame tra rumore e resistenza specifica del contatto ohmico. L'affidabilita’ dei dispositivi è stata studiata per mezzo di prove di stress a breve (2 min step - stress) e lungo termine (1000 hour). Lo stress a lungo termine e’ stato eseguito su dispositivi AlGaN/GaN processati su substrato composito di tipo SopSiC sviluppato nell'ambito del progetto europeo HYPHEN. Questi substrati sono realizzati tramite il trasferimento di un sottile strato di Silicio monocristallino su uno strato piu’ spesso di Carburo di Silicio policristallino, il loro scopo e’ di rappresentare una valida ed economica alternativa ai substrati in Carburo di Silicio monocristallino. Per questo esperimento sono state individuate tre condizioni a differente polarizzazione e temperatura; i risultati finali presentano una buona stabilita’ dei dispositivi ed inoltre mostrano come i problemi riscontrati durante il test siano riconducibili agli elevati livelli di corrente di perdita del gate. Il degrado dei dispositivi e’ quindi strettamente legato alla tecnologia del processo utilizzato per la realizzazione del transistor e non e’ legata alla natura del substrato. Per quanto riguarda la prova di stress accelerato, si e’ studiato l'effetto sulle prestazioni del dispositivo di elevate tensioni negative applicate al contatto di gate. Questo tipo di test solitamente porta all'individuazione di una tensione critica oltre la quale si verifica un brusco aumento della corrente di gate. Nella letteratura scientifica questo fenomeno e’ indicato come effetto piezoelettrico inverso (inverse piezoelectric effect) ed e’ associato alla creazione di difetti nel reticolo cristallino sottoposto a sollecitazione durante lo stress. Lo studio si e’ basato su un wafer con differenti metallizzazioni di gate (Ni/Au/Ni, ITO, Ni/ITO) e con passivazione dei dispositivi. I risultati ottenuti suggeriscono che la tensione critica non sia legata solo alla tensione che si induce nel reticolo; infatti anche il livello iniziale della corrente di perdita del gate sembra giocare un ruolo nel processo di degradazione. Inoltre l'evoluzione del degrado durante il test sembra indicare che il processo di invecchiamento avvenga per filtrazione dei difetti all'interno della barriera di AlGaN (percolation process)

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Rosselin, Marie. "Design of amphiphilic nitrones with improved spin-trapping and antioxidant properties". Thesis, Avignon, 2014. http://www.theses.fr/2014AVIG0258/document.

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Le stress oxydant se définit comme un déséquilibre entre la production d’espèces oxygénées et azotés réactives et les défenses antioxydants. Ce phénomène est associé à de nombreuses pathologies telles que des maladies neurodégénératives et cardiovasculaires ou des cancers. Pour contrecarrer les dégâts causés par le stress oxydant, l’utilisation d’antioxydants synthétiques s’est avérée intéressante car il devient alors possible de modifier les propriétés physico-chimiques des antioxydants et de leur assurer un meilleur ciblage cellulaire et tissulaire. Nos travaux de recherche se positionnent dans la recherche de nouveaux agents antioxydants synthétiques. Au cours de cette thèse nous nous sommes focalisés sur l’utilisation de l’alpha-phényl-N-tert-butylnitrone (PBN), qui présente une bonne activité pharmacologique contre les dégâts liés aux radicaux libres, et qui est également largement utilisée en tant que sonde analytique pour l’identification d’espèces radicalaires par la technique de piégeage de spin couplée à la résonance paramagnétique électronique (RPE). Dans la première partie de ces travaux de thèse, nous avons tenté d’améliorer les propriétés intrinsèques de la PBN en greffant divers substituants soit sur le cycle aromatique, soit sur le groupement N-tert-butyl de la fonction nitrone. L’analyse des propriétés physico-chimiques et biologiques de ces composés nous a permis de mesurer l’impact de la nature et de la position des substituants sur les propriétés antioxydantes de la PBN. La seconde partie de ces travaux a consisté à greffer le motif PBN sur des structures moléculaires amphiphiles dérivées d’un acide-aminé. Cette deuxième partie a pour but d’améliorer l’activité biologique et la biodisponibilité des dérivés PBN
Oxidative stress is defined as an unbalance between the production of free radicals and the antioxidant defenses. The oxidative stress state has been associated with several pathologies such as neurodegenerative and cardiovascular diseases or cancers. To prevent oxidative stress-mediated damage, the use of synthetic antioxidants is attractive as it allows to tune their physico-chemical properties as well as their cellular targeting specificity. Of particular interest is the linear alpha-phenyl-N-tert-butylnitrone (PBN) which exhibits pharmacological activity against radical-mediated pathophysiological conditions and has been widely used as analytical reagent for the identification of radical species by the spin-trapping method coupled to electron paramagnetic resonance (EPR) spectroscopy. In this thesis report, we first tried to improve the intrinsic antioxidant properties of PBN by grafting various substituents either onto the aromatic ring or the N-tert-butyl-group of the nitronyl function. The physico-chemical and biological properties of the compounds were then determined. With optimized nitrone derivatives in hand, the second part of this project consisted in improving the bioactivity and bioavailability of our nitrone agents using amphiphilic carriers or specific targeting ligands

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Betton, Catherine. "Nitrate-N levels in British streams and rivers : a countrywide perspective". Thesis, University of Exeter, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.277094.

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Tyra, Heather Marie. "The exaptation of nitrate/carbon stress-induced smRNAs and their targets from transposable elements in the unicellular green alga Chlamydomonas reinhardtii". Thesis, University of Iowa, 2009. https://ir.uiowa.edu/etd/269.

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Transposable elements (TEs) are acknowledged sources of genetic change within organisms. The effects of transposition can range from the disruption or creation of a single gene to large-scale genome rearrangements. Transposition events can result in beneficial mutations which allow an organism to adapt to a new environment. In the last three years, several studies have reported that some miRNAs, small RNAs involved in post-transcriptional gene regulation, have evolved from TEs. miRNAs play an important role in the stress responses of many organisms. Interestingly, TEs are derepressed under the same stress conditions that miRNAs are known to ameliorate. The observation that miRNAs are known to evolve from TEs and that TEs are derepressed under stress conditions lead me to question whether TEs play a role in environmental adaptation through the creation of small RNA networks. To test this idea, Chlamydomonas reinhardtii cultures were grown under low carbon, nitrate enriched conditions and the small RNA pool was analyzed. I found that these conditions do stimulate the expression of novel small RNAs and that some of these RNAs and their targets are derived from transposition events.

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Kropp, Joel Miron [Verfasser]. "Low-Stress LPCVD Silicon Nitride Membranes and Applications for Physical and Biological Sensor Systems / Joel Miron Kropp". München : Verlag Dr. Hut, 2015. http://d-nb.info/1076437435/34.

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Moore, Tom. "Nitrate-nitrogen effects on benthic invertebrate communities in streams of the Canterbury Plains". Thesis, University of Canterbury. Biological Sciences, 2014. http://hdl.handle.net/10092/9936.

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Aquatic ecosystems are especially vulnerable to human impacts associated with agricultural land-use, which provide multiple stressors altering community composition, important ecosystem functions and human valued properties of freshwaters. However, the increased occurrence of excessive levels of nitrate-nitrogen has raised major concerns about toxicity and stress on aquatic life, especially in regions such as the Canterbury Plains, New Zealand. The aims of this thesis were to identify nitrate-nitrogen effects on stream communities, and additionally provide field data to inform proposed national bottom lines for nutrients in New Zealand streams. A field survey was conducted on 41 small streams on the Canterbury Plains spanning a nitrate-nitrogen gradient (mean 0.4 – 11.3 mg/L). Spot nitrate-nitrogen was collected during and after the field survey to measure temporal variation in stream nitrate-nitrogen concentration for six months. This showed nitrate-nitrogen concentration varied between season and sub-region, where concentrations increased in winter and Ashburton had higher nitrate-nitrogen than Rangiora and Lincoln, respectively. These regimes of nitrate-nitrogen showed similar patterns in mean, median and maximum concentrations. To be confident my spot nitrate-nitrogen provided a true representation of long-term water chemistry, I compared Environment Canterbury 12 monthly data with my six monthly data in a sub-set of 15 sites. This comparison showed similar nitrate-nitrogen patterns and range of values between the two datasets. I then compared 12 common benthic invertebrate biotic metrics with my nitrate-nitrogen data and found none were correlated with this contaminant. For example, the Macroinvertebrate Community Index and quantitative variant (QMCI) derived to measure the response to organic pollution provided inconsistent results when applied to my streams. Nevertheless, gut content stoichiometry of the common mayfly grazer Deleatidium spp. indicated improvement in food quality (lower C:N ratio) with higher nitrate-nitrogen concentrations. These results indicated either nitrate-nitrogen does not alter invertebrate structural metrics across this nitrate-nitrogen gradient, or that these biotic metrics measure community structure aspects not affected by nitrate-nitrogen. I then investigated possible community composition patterns across the nitrate-nitrogen gradient. Unconstrained ordination (on presence/absence data) showed invertebrate communities at my sites were influenced primarily by discharge and shade, with the next most important driver being nitrate-nitrogen. A constrained ordination (on the same data) testing the singular effect of nitrate-nitrogen showed a marginally non-significant change in composition, with higher variability in community composition at higher nitrate-nitrogen concentrations. A further aim of my study was to test the draft nitrate-nitrogen bands proposed by Hickey (2013). These nitrate-nitrogen bands may advise guidelines to protect aquatic organisms as required by the National Policy Statement on Freshwater. Analysis of my invertebrate communities showed differences in composition, particularly at < 1 and > 6.9 mg/L bands. Several predatory caddisfly taxa: Triplectides, Neurochorema and Oeconesus were identified as potential indicator species of communities associated with low nitrate-nitrogen. These findings show that nitrate-nitrogen effects are difficult to detect, and that it is not the main driver of community composition in Canterbury streams. However, nitrate-nitrogen may be an important stressor for sensitive benthic invertebrate communities, as effects were observed on pollution tolerant organisms in this study. Therefore, this research has implications for freshwater ecologists and environmental managers striving to improve the health of streams on the Canterbury Plains.

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Hossain, Tasnia. "GaN based structures on patterned silicon substrate : stress and strain analysis". Nice, 2012. http://www.theses.fr/2012NICE4096.

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This work deals with the stress and strain analysis of GaN grown on patterned Si substrate in order to avoid crack generation and to obtain the suitable size of the pattern for device (LED, LD, transistor etc. ) applications. Using patterned substrate we have grown thick crack free continuous GaN layers by MBE and by MOCVD. In this work, we have used different sizes of patterns, different trench widths, trench heights, different shapes and in-plane orientations of the patterns and two crystal orientations of Si substrate. We have found that beyond a critical film thickness, the number of cracked mesa increases with the increase in mesa size for a particular shape of mesa. In the case of square and lozenge shape mesas of 200 μm length, 96 and 88% mesas respectively are found crack free for 12 μm thick GaN film. To analyze the stress and strain, micro-Raman spectroscopy and micro-photoluminescence measurements are carried out on GaN mesa. A U-shape stress distribution is observed on different sizes of mesa where the maximum tensile stress is found at the center of the mesa while towards the free edges or corners of the mesa the stress gradually relaxes. It is also revealed that the in-plane stress increases with the increase in mesa size. In contrast, the in-plane stress decreases with the increase in trench height of Si substrate. However, the trench width shows no significant effect on the in-plane stress. An analytical model has been used to account for the stress distribution in the patterns. This study of thick GaN on patterned Si substrate seems to be promising for the fabrication of optoelectronic and electronic devices which were limited by the planar substrate
Le présent travail concerne l’étude des contraintes et des déformations dans le matériau GaN épitaxié par EJM et par EPVOM sur substrat silicium texturé en vue d’éviter la fissuration du matériau et ainsi obtenir des motifs compatibles avec la réalisation de composants (DELs, Lasers, transistors etc. ). Nous avons étudié des motifs différents en tailles, séparations, hauteurs de tranchées, formes, orientations dans le plan ainsi que deux orientations cristallines du substrat silicium. Au-delà d’une épaisseur critique du film déposé, pour une forme de motif donnée, la fraction de motifs fissurés augmente avec la taille des motifs. 88% des motifs en losange et 96% des motifs carrés sont exempts de fissures pour des films GaN épais de 12 μm pour une largeur égale à 200 μm. Une distribution en U de la contrainte en tension est mise en évidence par spectroscopie micro-Raman et par micro-photoluminescence pour les différentes tailles de motifs étudiés, le maximum de contrainte se situant en leur centre et la contrainte se relaxant graduellement vers les bords libres. La contrainte augmente avec la taille des motifs, mais diminue avec la hauteur des tranchées réalisées dans le substrat. Un modèle analytique a été adapté pour rendre compte de la répartition des contraintes. La distance séparant les motifs influe peu. Quoi que la répartition des contraintes puisse être différente durant la croissance, nous avons montré la possibilité d’obtenir des films de GaN avec une bonne qualité cristalline sur ces motifs, ce qui montre que cette voie est prometteuse pour la fabrication de composants optoélectronique et électroniques jusqu’ici limités par la croissance sur substrat planaire

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Pfrang, Christian. "Nitrate radicals in the atmosphere : reactions with man-made and stress-induced plant emissions, and with peroxy radicals". Thesis, University of Oxford, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.427757.

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O'Brien, Katie Alice. "Investigation into metabolic profile changes in environmental hypoxia and the potential for dietary nitrate to alleviate hypoxic stress". Thesis, King's College London (University of London), 2017. https://kclpure.kcl.ac.uk/portal/en/theses/investigation-into-metabolic-profile-changes-in-environmental-hypoxia-and-the-potential-for-dietary-nitrate-to-alleviate-hypoxic-stress(26f38d92-b9b2-45f4-8231-b3c68da0575f).html.

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Oxygen (O2) insufficiency (hypoxia), either in response to environmental exposure or pathological states is a driver of metabolic remodelling, the details of which are ill- defined. This work aimed to further understanding of metabolic responses to environmental hypoxia. In the first study, plasma metabolite changes were measured in 198 human subjects upon ascent to Everest Base Camp (5300m) using metabolomic and lipidomic techniques. Results were indicative of a shift towards anaerobic glycolysis, a mobilisation of fat stores and alterations to fat lipoprotein transport with ascent. In the second study, a pilot study, subjects (n=5) were examined pre and post an attempted winter crossing of Antarctica, including a 24 week stay above 2,500m. Metabolomics analysis of serum samples alongside whole body physiological and exercise measurements were indicative of a shift in metabolic signature, including an increased reliance upon carbohydrate metabolism during exercise. Developing a means of attenuating the metabolic stress of hypoxia would be highly beneficial for aiding human adaptation and ameliorating the effects of disease states where hypoxia is a comorbidity. An additional aim was to explore the potential of dietary nitrate for this purpose. In the third study, the potential for nitrate supplementation to aid hypoxic acclimatisation of skeletal muscle mitochondria and the role of PPARα (a master regulator of fat oxidation) were assessed using a mouse model of wild type (n=42) and PPARα-/- strains (n=42). Nitrate supplementation (0.7mM) recovered hypoxic induced decreases in fatty acid and carbohydrate oxidation in response to prolonged, severe hypoxic exposure (10% O2, 28 days) and did so independently of PPARα. In the fourth study, the effects of acute dietary nitrate supplementation (12mM nitrate vs. placebo ingested 3 hours pre-exercise) upon exercise endurance and related metabolite changes were investigated in chronic obstructive pulmonary disease (COPD) patients (n=21, age 68+7 years). Whilst neither median endurance time nor targeted plasma metabolites differed between treatments, O2 consumption was significantly lower following nitrate treatment vs. placebo. The absence of plasma lactate changes between treatments indicates this effect was not mediated through increased reliance upon anaerobic metabolism. In conclusion, this work highlighted several potential biomarkers of interest in healthy humans exposed to environmental hypoxia, including alterations to carbohydrate and lipid metabolism. Dietary nitrate demonstrated potential for recovering metabolic function in vitro, yet failed to illicit beneficial effects in a clinical population in vivo.

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Awwad, Monzer. "Synthèse de nouveaux outils moléculaires pour l’imagerie in vivo d’oligo- et polysaccharides à la surface cellulaire". Thesis, Paris 11, 2013. http://www.theses.fr/2013PA112174/document.

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La première partie de ce travail est réalisé dans le but de préparer des produits pouvant jouer un rôle très important de l’imagerie cellulaire des lipopolysaccharides sur la surface des cellules bactériennes, tout en utilisant des méthodes fiables telle que la ‘’chimie click’’. Dans un premier temps, nous avons synthétisé une première génération d’outils fluorescents à base de rhodamine B et fluorescéine modifiée par une fonction oxyde de nitrile. Dans un deuxième temps nous avons cherché les meilleures conditions d’applications de la chimie click 3+2 sans cuivre, entre la fonction oxyde de nitrile et le motif saccharidique complémentaire portant une fonction vinylique. Finalement, nous avons appliquée, avec succès, la méthode click avec cuivre sur plusieurs types de bactéries portant sur leur membrane cellulaire des lipopolysaccharides ayant un motif ‘’Kdo’’ fonctionnalisé par un groupement azoture déjà synthétiser au sein de notre équipe, et une sonde fluorescente porteuse d’une fonction alcyne. Une nouvelle génération d’outils de marquage saccharidique est en cours de finalisation dans le but d’optimiser les conditions finales, tel que le dérivé de ‘’Kdo’’ fonctionnalisé cette fois-ci par des dérivées cycliques, bicycliques et aromatiques porteurs d’une fonction alcyne ou alcène, pour réaliser les derniers essais de marquage in vitro. Le stress oxydant est lié au vieillissement des cellules et à de nombreuses maladies: cardiovasculaire, cancer, diabète, Alzheimer… Il est dû à un déséquilibre entre le système oxydant / antioxydant au niveau des cellules, et se caractérise par la présence principalement de substance radicalaires réactives oxygénées. Dans le but d'identifier le taux de substances réactives oxygénées dans les cellules, le travail dans la deuxième partie de la thèse reposait sur la synthèse multi étape d'une molécule fluorescente dérivée de la coumarine. Le composé ciblé est le peroxyde d'oxygène, connu sous le nom d'eau oxygénée. Possédant un ester vinyl-boronique, notre molécule sera oxydée et réarrangée en aldéhyde conduisant à la condensation intramoléculaire avec le groupement aminé adjacent pour former un cycle indolique, libérant ainsi de la fluorescence. La recherche des conditions optimales de la dernière étape de la voie synthétique sont toujours en cours d’optimisation. Dans le futur, on cherchera les conditions optimales de la dernière étape de la synthèse de la sonde spécifique au peroxyde d’oxygène. Cette molécule est d'une importance remarquable comme sonde du stress oxydant. En réussissant cette étape, on pourra avoir en main une bibliothèque de ‘’KDO’’ fonctionnalisé afin d’avoir des résultats satisfaisants in vivo
The first part of this work is done in order to prepare products that play a very important role in cellular imaging lipopolisaccharides on the surface of bacterial cells, while using reliable methods such as '' click chemistry ''. Initially, we synthesized the first generation of tools based fluorescent rhodamine B and fluorescein -modified nitrile oxide function. In a second step we sought the best possible applications of click chemistry 3+2 copper free, between the nitrile oxide function and the additional saccharide unit with a vinyl function. Finally, we applied successfully, the click method with copper on several types of bacteria on their cell membrane lipopolysaccharides having a pattern Kdo functionalized azide group already synthesized within our team, and a probe carrying a fluorescent alkyne. A new generation of tools saccharide marking is being finalized in order to optimize the final terms, such as derivative functionalized Kdo this time by cyclic, bicyclic and aromatic derivatives holders of an alkene or alkyne function to perform final testing of in vitro labeling. Oxidative stress is linked to cell aging and many diseases: cardiovascular disease, cancer, diabetes, Alzheimer's ... It is due to an imbalance between oxidant system/antioxidant in cells, and is characterized mainly by the presence of radical substance reactive oxygen. In order to identify the rate of reactive oxygen substances in cells, work in the second part of the thesis based on multi- step synthesis of a fluorescent molecule derived from coumarin. The target compound is oxygen peroxide, known as the name of hydrogen peroxide. Having a vinyl boronic ester, this molecule will be oxidized and rearranged aldehyde leading to intramolecular condensation with the adjacent amino group to form an indolique ring , thereby releasing fluorescence. The search for optimal conditions for the last step of the synthetic pathway is still being optimized. In the future, the optimal conditions for the last step of the synthesis of specific probe oxygen peroxide are sought. This molecule is remarkable importance as a probe of oxidative stress. By passing this step, we will have on hand a library of KDO functionalized to have satisfactory results in vivo

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Wanschel, Amarylis Claudine Bonito Azeredo. "Biodisponibilidade cardiovascular do oxdo nitrico em camundongos LDLr-/-". [s.n.], 2010. http://repositorio.unicamp.br/jspui/handle/REPOSIP/314780.

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Orientador: Marta Helena Krieger
Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Biologia
Made available in DSpace on 2018-08-15T17:17:07Z (GMT). No. of bitstreams: 1 Wanschel_AmarylisClaudineBonitoAzeredo_D.pdf: 3059995 bytes, checksum: afbb018ffe3bb06b61c7420a0fa4664f (MD5) Previous issue date: 2010
Resumo: O objetivo deste trabalho foi avaliar a biodisponibilidade do óxido nítrico (NOo) nas disfunções cardiovasculares, especificamente na hipertrofia ventricular esquerda e na aterosclerose. Para tanto, realizamos dois estudos em camundongos deficientes do receptor de LDL (LDLr-/-): o primeiro realizado em continuidade aos estudos desenvolvidos anteriormente em nosso grupo de pesquisa, os quais demonstraram a ação do doador de NOo na prevenção da hipertrofia ventricular esquerda e na proteção contra arritmia via indução do acoplamento adrenoceptor-beta2 (ß2AR) à proteína G inibitória (Gi); e no segundo estudo, foi avaliada a biodisponibilidade de NOo na fase inicial da aterogênese, com objetivo de caracterizar as alterações sistêmicas e locais. No primeiro estudo mostramos que o doador de NOo, S-Nitroso-N-acetilcisteína (SNAC) administrado, promoveu ação cardioprotetora contra o remodelamento cardíaco via redução do estresse oxidativo e apoptose celular, os quais foram determinados pelas medidas ventriculares da produção de superóxido (O-o2) e peróxido de hidrogênio (H2O2) e pelo índice de morte celular por apoptose. Esta ação cardioprotetora foi vista no aumento da expressão e no conteúdo de S-nitrosação do ß2AR. Estes efeitos foram associados à cardioproteção contra a arritmia via indução do acoplamento ß2AR à Gi. O objetivo do segundo estudo foi avaliar a biodisponibilidade de NOo na fase inicial da aterogênese em camundongos LDLr-/- no curso temporal de 15 a 60 dias de dieta, com a quantificação de parâmetros sistêmicos representados pela pressão arterial, perfil lipidêmico e ateroma, bem como de parâmetros locais representados pela atividade e expressão da via NO/NOS e suas modificações póstraducionais no processo inflamatório via CD40-CD40L. Camundongos LDLr-/-submetidos à dieta rica em gordura apresentaram progressão do tamanho do ateroma no curso temporal analisado, contudo não foi associado a similares incrementos nos níveis de dislipidemia. Não foram detectadas alterações na pressão arterial do fenótipo hipertenso deste animal. Contudo, localmente foi verificado incremento na atividade da eNOS via fosforilação de resíduos de serina 1179 (S1179) em 30 dias de dieta rica em gordura, que pode ser considerado um mecanismo emergencial à aterosclerose . Posteriormente, com a evolução do ateroma (60 dias) houve redução desta ativação, bem como do conteúdo de proteínas S-nitrosadas. O desenvolvimento de ateroma em 30 e 60 dias induzido pela dieta mostrou aumento da atividade inflamatória por meio da denitrosação de tióis críticos da via CD40. Portanto, a análise das alterações no curso temporal apresentou somente mudanças locais como alteração na biodisponibilidade de NOo, ativação inflamatória via denitrosação do receptor CD40 e redução do conteúdo de S-nitrosação total, enquanto as alterações sistêmicas neste período de tempo ainda não são evidentes
Abstract: The objective of this study was to evaluate the bioavailability of nitric oxide (NOo) in cardiovascular disorders, specifically on the left ventricular hypertrophy and atherosclerosis. Therefore, we performed two studies with LDL receptor-deficient mice (LDLr-/-): the first one was performed in sequence to the studies previously developed in our research group, which showed the NOo donor action on the prevention of left ventricular hypertrophy and protection against arrhythmia via induction of the coupling from beta adrenoceptor-2 (ß2AR) to the inhibitory G protein (Gi); and the second study,it was evaluated the bioavailability of NOo to characterize the systemic and local alterations in the early stages of atherogenesis. The first study showed that the administration of NOo donor S-Nitroso-N-Acetylcysteine (SNAC) promoted cardioprotective action by blocked the cardiac remodeling through reduction of oxidative stress and of apoptosis, which were determined by measures of ventricular superoxide (O-o2) and hydrogen peroxide (H2O2) production and the cell death index, respectively. This cardiprotective action was charactherized by the increase of expression and content of S-nitrosation of ß2AR. These effects were associated with cardioprotection against arrhythimia via induction of ß2AR coupling Gi. The objective of the second study was to evaluate the bioavailability of NOo in the LDLr-/- mice early atherogenesis in LDLr-/ - mice from 15 to 60 days, with the quantification of systemic parameters represented by the blood pressure, lipidemic profile and atheroma as well as local ones represented by the activity and expression of NO/NOS pathway and its post-translational modifications on the inflammatory process via CD40- CD40L. Mice LDLr-/ - maintained on high-fat diet showed progression of atheroma size, although it was not associated with similar increase in dyslipidemic profile. No changes in blood pressure were detected in the hypertensive phenotype of this animal. However, increased activity of eNOS via phosphorylation of Ser1179 (S1179) at 30 days of high-fat diet was detected and it can be considered an emergential mechanism to early atherosclerosis. The development of atheroma (60 days) blocked that activation as well as the protein content of S-nitrosated. The atheroma induced at 30 and 60 days by high-fat diet revealed increase inflammatory activity through denitrosation of critical thiols via CD40. Therefore, the analysis of changes in this time course showed only local changes as changes on NOo bioavailability alteration inflammatory activation via denitrosation of CD40 receptor and the content of total S-nitrosation reduction. However, systemic changes in this period of time have not been evident yet
Doutorado
Fisiologia
Doutor em Biologia Funcional e Molecular

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Stewart, Rebecca M. "Land Cover Influences on Stream Nitrogen Dynamics During Storms". Thesis, Virginia Tech, 2012. http://hdl.handle.net/10919/76799.

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Previous studies on the effects of land cover influence on stream nitrogen have focused on base flow conditions or were conducted specifically within urbanized or primarily agricultural watersheds. While these studies have shown relationships between land cover and nitrogen, this relationship and the scale of influence could change during storms. The purpose of my study was to understand how land cover influences nitrogen in streams during storms. This was address using nine watersheds within the Little Tennessee Basin in North Carolina. While this basin is primarily forested, the nine watersheds have mixed agricultural, built, and forest land cover. Land cover influences were addressed through nitrogen concentration/discharge patterns, nitrogen concentration relationship to land cover, and comparison of storm and base flow nitrogen concentrations over time. Weekly base flow samples and samples from six storm were collected in 2010-2011. Total dissolved nitrogen (TDN), nitrate (NO??), dissolved organic nitrogen (DON), and ammonium (NH?⁺) concentrations were compared among sites. During most storms, DON peaked before the peak of the discharge while NO?? peaked after the peak of the storm. This suggest that DON could be coming from a near stream source or surface runoff while NO?? could be from longer pathways such as subsurface flow or from sources further away on the watershed. NO?? concentration varied among sites, while DON concentration varied more between base flow and storm samples. Examining the different landscape scales from 200-m local corridor, 200-m stream corridor, and entire watershed, watershed land cover was the best predictor for all the nitrogen concentrations. Agricultural and built combined best predicted TDN and NO??, while agricultural land cover was a better predictor of DON. For storms, nitrogen concentrations did not show seasonal patterns but was more related to discharge. Nitrogen concentration increased with discharge during storms and the more intense and longer storms had higher TDN and NO?? concentrations. However, conflicting seasonal trends were seen in monthly base flow. The more forested watersheds had high NO?? during the summer and low NO?? in the winter. For sites with higher NO??, the seasonality was reversed, with higher winter NO?? concentration. The least forested site had relatively constant nitrogen through the year at base flow and concentration decreased for most storms. Further studies on storms and nitrogen transport are needed to understand better the seasonal patterns of nitrogen input during storms.
Master of Science

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Jones, Jason Patrick. "Electro-thermo-mechanical characterization of stress development in AlGaN/GaN HEMTs under RF operating conditions". Thesis, Georgia Institute of Technology, 2015. http://hdl.handle.net/1853/53528.

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Gallium nitride (GaN) based high electron mobility transistors (HEMTs) offer numerous benefits for both direct current (DC) and radio frequency (RF) power technology due to their combination of large band gap, high electrical breakdown field, high peak and saturation carrier velocity, and good stability at high temperatures. In particular, AlGaN/GaN heterostructures are of great interest because of the unique conduction channel that develops as a result of the spontaneous and piezoelectric polarization that occurs in these layers. This channel is a vertically confined plane of free carriers that is often called a 2 dimensional electron gas (or 2DEG). Although these devices have shown an improvement in performance over previous heterostructures, reliability issues are a concern because of the high temperatures and electric fields that develop during operation. Therefore, characterizing electrical and thermal profiles within AlGaN/GaN HEMTs is critical for understanding the various factors that contribute to device failures. Little research has been performed to model and characterize these devices under RF bias conditions, and is therefore of great interest. Under pulsed conditions, a single cycle consists of an “on-state” period where power is supplied to the device and self-heating occurs, followed by an “off-state” period where no power is supplied to the device and the device cools. The percentage of a single cycle in which the device is powered is called the duty cycle. In this work, we present a coupled electro-thermo-mechanical finite-element model for describing the development of temperature, stress, and strain profiles within AlGaN/GaN HEMTs under DC and AC power conditions for various duty cycles. It is found that bias conditions including source-to-drain voltage, source-to-gate voltage, and pulsing frequency directly contribute to the electro-thermo-mechanical response of the device, which is known to effect device performance and reliability. The model is validated by comparing numerical simulations to experimental electrical curves (Ids-Vds) and experimental strain measurements performed using scanning joule expansion microscopy (SJEM). In addition, we show how the operating conditions (bias applied and AC duty cycle) impact the thermal profiles of the device and outline how the stress in the device changes through a pulsed cycle due to the changing thermal and electrical profiles. Qualitatively, the numerical model has good agreement across a broad range of bias conditions, further validating the model as a tool to better understand device performance and reliability.

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Faës, Camille. "Effets d'un exercice ou d'un stress d'hypoxie / réoxygénation sur le stress oxydant, l'adhésion vasculaire et la biodisponibilité de l'oxyde nitrique dans la drépanocytose". Thesis, Lyon 1, 2014. http://www.theses.fr/2014LYO10248.

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Rozprawy doktorskie na temat „Nitrite Stress”

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