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1
Milewski, Thomas. "Stratospheric chemical-dynamical ensemble data assimilation". Thesis, McGill University, 2012. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=110352.
Testo completoAbstract (sommario):
Ensemble data assimilation uses Monte-Carlo methods to estimate flow-dependent error covariances which allow the transfer of information from observed variables to correlated ones. As the winds are largely unobserved in the stratosphere and models have biases there, the possibility to constrain the dynamical analysis from temperature or ozone observations is attempted using ensemble data assimilation.The applicability of coupled chemical/dynamical ensemble data assimilation in the stratosphere is tested in idealized perfect model observation system simulation experiments with the IGCM-FASTOC chemistry-climate model. Covariance localization is found to be necessary for stability of the Ensemble Kalman Filter (EnKF) data assimilation system and optimal localization parameters yield a strong constraint on the global dynamical state of the model when assimilating synthetic limb-sounding stratospheric temperature or ozone observations only. The multivariate coupling between ozone, temperature and winds is investigated in the optimized EnKF system. Stratospheric temperature and ozone observations induce valuable dynamical analysis increments during the analysis step. There is additional feedback during the forecast steps in the ensemble data assimilation system, further constraining the global dynamical and ozone states. The potential impact of assimilating observations posterior to analysis time in multivariate mode was estimated with an Ensemble Kalman Smoother (EnKS). Assimilation of additional asynchronous observations up to 48 hours posterior toanalysis time provided improvements on the EnKF analysis nearly similar to the ones obtained from the assimilation of a same amount of additional synchronous observations. The EnKS assimilation showed beneficial impacts on the unobserved variables analysis state but mixed impacts on the observed variable analysis state.The capacity to constrain the unobserved stratospheric winds by assimilating ozone observations is demonstrated in the ensemble data assimilation system with the EnKF and EnKS. The chemical-dynamical error covariances are critical to reduce the wind error in the model analysis state particularly through the ozone-wind covariances effective in the upper-troposphere lower-stratosphere region. Additional tests with strongly-biased initial forecasts, within a stratospheric sudden warming experiment, confirm the ability of the EnKF to efficiently propagate information from ozone observations to the dynamical model state.L'assimilation d'ensemble utilise une méthode de Monte-Carlo pour estimer les covariances d'erreur du moment qui permettent le transfert d'information des variables observées aux variables corrélées à celles-ci. Puisque les vents sont très peu observés dans la stratosphère et que les modèles y présentent des biais, la possibilité de contraindre l'état dynamique du modèle par l'assimilation d'observations de température et d'ozone par la technique d'ensemble est tentée. L'applicabilité de l'assimilation d'ensemble dans un système chimique/dynamique couplé est testé lors d'une expérience idéalisé (modèle parfait) de simulation de système d'observation avec le modèle de chimie-climat IGCM-FASTOC. La localisation des covariances est indispensable à la stabilité du système d'assimilation avec filtre de Kalman d'ensemble (EnKF) et les paramètres optimaux offrent une forte contrainte sur l'état dynamique global du modèle lorsque l'on assimile des observations satellites synthétiques de température et d'ozone stratosphériques uniquement. Le couplage entre l'ozone, la température et les vents est étudié dans le système EnKF optimisé. Les observations de température et d'ozone stratosphériques créent des incréments dynamiques bénéfiques lors des phases d'analyses. Il y a également une rétroaction lors de la phase de prédiction du système d'assimilation de données, qui aide à contraindre davantage les états chimiques et dynamiques globaux. L'impact potentiel de l'assimilation de données postérieures au temps d'analyse en mode multivarié est estimé avec un lisseur d'ensemble de Kalman (EnKS). L'assimilation d'observations additionnelles asynchrones, ayant jusqu'à 48 heures d'écart avec le temps d'analyse, offre des améliorations aux analyses de l'EnKF presque équivalentes à celles obtenues par assimilation d'une quantité égale d'observations additionnelles synchrones. L'EnKS présente des impacts bénéfiques sur l'état d'analyse des variables non observées mais des impacts mitigés sur l'état analysé des variables observées. La capacité de contraindre les vents stratosphériques non-observés grâce à l'assimilation d'observations d'ozone est démontrée dans le système d'assimilation d'ensemble avec l'EnKF et l'EnKS. Les covariances d'erreurs chimiques- dynamiques sont essentielles à la réduction de l'erreur de vents dans l'état analysé du modèle, en particulier les covariances ozone-vent qui font effet dans la haute troposphère et basse stratosphère. Des expériences additionelles avec un état initial fortement biaisé, en l'occurence un réchauffement stratosphérique soudain, confirment l'abilité de l'EnKF à transférer de façon efficace l'information depuis les observations d'ozone vers l'état dynamique du modèle.
2
Gerothanassis, I. P. "Application of a DSc in the School of Chemical Sciences". Thesis, University of East Anglia, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.539366.
Testo completo
3
Gunasekaran, Subbiah, M. Sadikbatcha e P. Sivaraman. "Mapping chemical science research in India: A bibliometric study". NISCAIR, New Delhi, India, 2006. http://hdl.handle.net/10150/299580.
Testo completoAbstract (sommario):
Chemical sciences research in India has been mapped with data collected from the CD-ROM version of Chemistry Citation Index [publication year : 2002]. Roughly, 4.5% of the global R&D output in chemical sciences was contributed by Indian in 2002. Indian researchers published 6186 papers from 569 journals and 12 non-journal sources. More than 45% of these papers appeared in journals with an impact factor less than 1.000. Around 2% of the papers were either published in journals with no impact factor or not indexed in JCR 2003. The average impact factor for journal articles during this period is 1.359. While 26% of papers published by Indians were in US journals, the percentages for Indian and UK journals were 21 and 20%, respectively. Among Indian journals, the Asian Journal of Chemistry (IF 0.211) took the major chunk of 269 papers, while the Journal of Indian Chemical Society (IF 0.275) and the Indian Journal of Chemistry B (IF 0.492) carried 224 and 209 papers, respectively. In all, 563 institutions contributed 6199 papers in 2002. Of these papers, 68% were contributed by 10% of Indian institutions. The Indian Institute of Science, Bangalore ranks first with 345 papers. This is followed by the Indian Institute of Chemical Technology, Hyderabad with 263 papers. Bhabha Atomic Research Centre, Mumbai with 259 papers and the National Chemical Laboratory, Pune with 246 papers come in the third and fourth places, respectively. The largest contributions came from Mumbai, Bangalore, Hyderabad and Kolkata. In terms of states, Maharashtra, Tamil Nadu, Karnataka, Andhra Pradesh and West Bengal are major contributors. About 16% of the papers had international collaboration (with as many as 53 county ies). Major collaborating countries in chemical sciences were the US, Germany, Japan and Great Britain.
4
Lohse, Peter A. (Peter Andreas). "Distribution of knowledge production in the chemical sciences in the US". Thesis, Massachusetts Institute of Technology, 2011. http://hdl.handle.net/1721.1/65786.
Testo completoAbstract (sommario):
Thesis (M.B.A.)--Massachusetts Institute of Technology, Sloan School of Management, 2011.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 43-44).
A citation analysis was carried out to gain an understanding of the geographical and institutional distribution of highly cited articles in the chemical sciences in the US over the last thirty years. The contribution of US chemistry departments was determined by quantifying the number of highly cited articles published by individual authors or groups of authors from the same department. Articles stemming from collaborative research across schools were not considered. The results show that a dilution in intradepartmental knowledge production has occurred both on a geographical and institutional level. Three chemistry departments have emerged as strong producers of high impact articles over the last thirty years: the University of North Carolina, Texas A&M University and the University of Utah. In terms of aggregate numbers of highly cited articles these three schools are in the top ten of over seventy schools which were evaluated; their chemistry departments are en par in terms of scientific impact with those from Ivy League schools like Stanford University, Harvard University and the California Institute of Technology. While the literature reports increasing concentration for the US research base, the present analysis shows a dilution in chemical knowledge production when collaborative efforts across departments and schools are excluded. This finding suggests that the increase in concentration in the US science base is not a uniform trend when studied on a more granular level.
by Peter A. Lohse.
M.B.A.
5
Degrand, Elisabeth. "Evolving Chemical Reaction Networks". Thesis, KTH, Skolan för elektroteknik och datavetenskap (EECS), 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-257491.
Testo completoAbstract (sommario):
One goal of synthetic biology is to implement useful functions with biochemical reactions, either by reprogramming living cells or programming artificial vesicles. In this perspective, we consider Chemical Reaction Networks (CRNs) as a programming language. Recent work has shown that continuous CRNs with their dynamics described by ordinary differential equations are Turing complete. That means that any function over the reals that is computable by a Turing machine in arbitrary precision, can be computed by a CRN over a finite set of molecular species. The proof uses an algorithm which, given a computable function presented as the solution of a PIVP (PolynomialInitial Values Problem), generates a finite CRN to implement it. In the generated CRNs, the molecular concentrations play the role of information carriers, similarly to proteins in cells. In this Master’s Thesis, we investigate an approach based on an evolutionary algorithm to build a continuous CRN that approximates a real function given a finite set of the values of the function. The idea is to use a two-level parallel genetic algorithm. A first algorithm is used to evolve the structure of the network, while the other one enables us to optimize the parameters of the CRNs at each step. We compare the CRNs generated by our method on different functions. The CRNs found by evolution often give good results with quite unexpected solutions.Ett mål med syntetisk biologi är att genomföra användbara funktioner med biokemiska reaktioner, antingen genom omprogrammering av levande celler eller programmering av artificiella vesiklar. I detta perspektiv anser vi Chemical Reaction Networks (CRNs) som ett programmeringsspråk. Det senaste arbetet har visat att kontinuerliga CRNs med dynamik som beskrivs av vanliga differentialekvationer är Turingkompletta. Det betyder att en funktion över de realla talen som kan beräknas av en Turing-maskin i godtycklig precision, kan beräknas av en CRN över en ändlig uppsättning molekylära arter. Beviset använder en algoritm som, givet en beräkningsbar funktion som presenteras som lösningen av ett PIVP (Polynomial Initial Values Problem), genererar en ändlig CRN för att implementera den. I de genererade CRN:erna spelar molekylkoncentrationerna rollen som informationsbärare, på samma sätt som proteiner i celler. I detta examensarbete undersöker vi ett tillvägagångssätt baserat på en evolutionär algoritm för att bygga en kontinuerlig CRN som approximerar en verklig funktion med en ändlig uppsättning av värden för funktionen. Tanken är att använda parallell genetisk algoritm i två nivåer. En första algoritm används för att utveckla nätets struktur, medan den andra möjliggör att optimera parametrarna för CRN:erna vid varje steg. Vi jämför de CRN som genereras av vår metod på olika funktioner. De CRN som hittas av evolutionen ger ofta bra resultat med ganska oväntade lösningar.
6
Attwell, Jane Louise. "Heterogeneous chemical processing by stratospheric aerosol". Thesis, University of Oxford, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.390491.
Testo completo
7
Webb, Penelope Eugenia. "Chemical inflation for assisted assembly". Thesis, Massachusetts Institute of Technology, 2017. http://hdl.handle.net/1721.1/114060.
Testo completoAbstract (sommario):
Thesis: S.M., Massachusetts Institute of Technology, School of Architecture and Planning, Program in Media Arts and Sciences, 2017.Page 85 blank. Cataloged from PDF version of thesis.
Includes bibliographical references (pages 81-84).
This thesis aims to utilize an output method for popup fabrication, using chemical inflation as a technique for instant, hardware-free shape change. By applying state-changing techniques as a medium for material activation, we provide a framework for a two-part assembly process, starting from the manufacturing side, whereby a structural body is given its form, through to the user side, where the form potential of a soft structure is activated and a form becomes complete. The process discussed in this thesis is similar in nature to existing chemical reaction home-activation kits, such as hand warmers or cold packs, however, with the inclusion of volume-change and automatic assembly, this method gives way to alternative application possibilities and component-free construction. Along with structural configuration, this thesis provides material development for the application of volume changing membranes for the purpose of material surprise and transformation.`
by Penelope Eugenia Webb.
S.M.
8
Puhl, Jacqueline L. "Chemical instabilities in isotropic turbulent flows". Doctoral thesis, Universite Libre de Bruxelles, 1988. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/213327.
Testo completo
9
Khannoon, Eraqi Radwan R. "Comparative chemical ecology, behaviour, and evolutionary genetics of acanthodactlylus boskianus (Squamata: Lacertidae) : comparative chemical ecology, behaviour and evolution". Thesis, University of Hull, 2009. http://hydra.hull.ac.uk/resources/hull:2415.
Testo completoAbstract (sommario):
Acanthodactylus boskianus is a common lizard species frequently occurring in different habitats throughout Egypt. Both males and females have well developed epidermal femoral glands. This species is territorial and males acquire dominance hierarchies in captivity. The current work included three different techniques to study the importance of femoral gland secretions in communication and signal evolution of A. boskianus. These are behaviour, chemical and DNA analyses techniques. Behavioural bioassays in different experiments showed that the femoral gland secretions are used in communication between the lizards. Communication includes possible roles in mate choice, agonistic behaviour between potential competitor males, and chemical trailing of scent pheromones. These behavioural results reflect the chemical results which showed the chemical variability between male ages, sexes, and allopatric populations. Chemical analysis of the secretions resulted in the identification of natural compounds not previously reported in reptiles, glycerolmonoethers and monoglycerides. The secretions seem to be used as scent pheromones, which are involved in signal evolution processes resulting in divergence of the chemical fingerprints of the gland secretion between allopatric populations.
10
Ballhaus, Florentine. "Investigating plant autophagy with new chemical modulators". Thesis, Uppsala universitet, Institutionen för biologisk grundutbildning, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-428075.
Testo completoAbstract (sommario):
Autophagy is a major catabolic pathway in which cell components get sequestered in a double membrane vesicle, transported to the vacuole, degraded by vacuolar hydrolases and recycled. Through this process, cells ensure cell homeostasis and remobilise nutrients. The autophagic flux can be enhanced as an adaptive stress response, improving plants resistance against stress, reducing aging and ultimately increasing yield. However, autophagy regulation in plants remains poorly understood. Novel plant-specific modulators can be used in a chemical genetic approach for identification of proteins involved in the autophagy pathway. Furthermore, autophagy enhancers can find their application in agriculture for improved plant fitness. Known autophagy modulators have severe off-target effects, affecting plant growth and development. A recent screening identified two potential autophagy modulators. We developed a novel method for photoaffinity labelling and pulldown assay in Arabidopsis thaliana to identify potential interactors of the modulators. The identification of autophagy-related proteins will help to further elucidate the autophagic pathway in plants. The effect of the new autophagy enhancers on plant growth and development was analysed by automated growth assays. In comparison with a currently available autophagy enhancer, treated plants showed higher viability, indicating possible further applications for the new autophagy modulators in planta.
11
Rozenbeek, Erik. "Surface reactivity of ultrathin atomic layer deposited Al2O3 on Li[Ni0.8Mn0.1Co0.1]O2". Thesis, Uppsala universitet, Institutionen för kemi - Ångström, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-416702.
Testo completoAbstract (sommario):
The nickel-rich cathode material Li[Ni0.8Mn0.1Co0.1]O2 is a much sought after material in Li-ion batteries for the future of electric vehicles due to its high specific capacity. However, it exhibits fast degradation during its use due to the interaction between the electrolyte and the cathode surface leading to capacity loss. In this thesis, the surface interaction of pristine and alumina coated NMC811, and NiO powder with electrolyte was investigated to observe difference in surface reactivity and if hydroxide groups on the surface could be a potential culprit in degradation. Thermogravimetric analysis (TGA) and Brunauer–Emmett–Teller (BET) analysis were used to measure thermal properties, surface area and adsorptive properties respectively between pristine and coated powders but no distinct difference was found. A soaking experiment was performed to induce electrolyte degradation on the powders by soaking them in the electrolyte LP40 for a duration of two weeks at 50°C. The electrolyte and the soaked powders were thereafter investigated through various spectroscopy methods like Attenuated Total Reflection – Fourier Transform Infrared (ATR-FTIR) and Raman spectroscopy to find potential degradation products but were found insignificant or inconclusive difference. The electrochemical testing was performed on NMC811 half-cells at 3-4.2V and 3-4.4V with a 0.5C – rate. The coated heat-treated NMC811 was found to have the best cyclability at both potential ranges. In conclusion, the difference in surface reactivity of the pristine, coated, and coated heat-treated powders were found to be insignificant. However, the coated heat-treated NMC811 was found to have improved electrochemical performance at both potential ranges but it remains uncertain if hydroxide groups could be a culprit in the degradation.
12
Ait, Chaalal Farid. "Bimolecular chemical reaction in a two-dimensional Navier-Stokes flow". Thesis, McGill University, 2012. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=110480.
Testo completoAbstract (sommario):
This thesis studies an infinitely fast bimolecular chemical reaction in a two-dimensional Navier-Stokes flow using a local Lagrangian stretching theory approach. Our flow, large scale and characterized by chaotic Lagrangian trajectories, is an idealized framework for stirring and mixing in the wintertime midlatitude deep stratosphere (WMDS). The dynamics of the WMDS are indeed non-local with chaotic advection thought to occur. The reactants are initially segregated and separated by a one-dimensional contact line. Because the chemical reaction is instantaneous, this problem simplifies to the study of a passive tracer defined as the difference between the reactants. We investigate the effect of the reactants diffusion on the their concentration in order to understand the effect of spatial resolution on similar stratospheric reactions in Climate-Chemistry models. In chapter 1 we review (a) chaotic advection for mixing of chemicals in the WMDS, (b) previous numerical and theoretical works dealing with the issue of horizontal resolution in Climate-Chemistry models in the WMDS, (c) local Lagrangian straining theories applied to the passive tracer problem in large scale flows, like chaotic advection or the Batchelor regime of turbulence. Chapter 2 and chapter 3 focus on the initial regime of the reaction where the contact line between the reactants, independent of the diffusion, is a material line only function of the dynamical properties of the flow. In Chapter 2, we theoretically show that, over an ensemble of realizations of a statistically stationary flow with chaotic trajectories, the ensemble averages of the contact line length, of the reactants gradients along it and of the time derivative of the domain average reactants concentration can be predicted knowing the diffusion and the statistics of the Lagrangian stretching properties (LSP) of the flow. In chapter 3, we adopt the same approach to express the probability density function of the tracer gradients along the contact line and of the tracers as a function of the LSP and of diffusion. In both chapters, the theoretical results are tested with an ensemble of direct numerical simulations (DNS) of the two-dimensional Navier-Stokes flow using a pseudospectral model. Chapter 4 discusses the long-term decay of a passive tracer fluctuation in our dynamically consistent flow, emphasizing on the differences with kinematics flow that are generally used in the literature.L'objet de cette thèse est l'étude d'une reaction chimique bimoléculaire infiniment rapide dans un fluide doublement périodique et solution des équations de Navier-Stokes en deux dimensions. Ce fluide définit un cadre idéalisé pour le touillage et le mélange dans la stratosphère l'hiver et aux latitudes tempérées. La dynamique y est en effet non locale et l'état actuel des connaissances suggère que l'advection chaotique y prend place. Ce travail utilise une approche locale et lagrangienne de la dilatation des particules de fluides. Les réactifs sont initialisés dans deux parties différentes du domaine et sont séparés par une ligne de contact de dimension un. Nous examinons l'éffet de la diffusion des réactifs sur l'avancement de la réaction, afin de comprendre la dépendence de réactions chimiques similaires dans la stratosphère à la résolution horizontale des modèles numériques du climat couplant dynamique et chimie. Le premier chapitre constitue une revue de littérature (a) de l'advection chaotique d'éspèces chimiques dans la stratosphère (b) de précédents travaux concernantléffet de la resolution horizontale des modelèles couplant chimie et climat sur la chimie de la stratosphère l'hiver aux latitudes moyennes (c) des théories locales et Lagrangiennes de la dilatation des particules de fluides pour expliquer la phénoménologie d'un traceur passif dans un fluide grande échelle, par exemple charactérisé par une advection chaotique ou dans le régime turbulent de Batchelor. Les deux chapitres suivant concernent le régime initial de la réaction, où la ligne de contact entre les réactifs, ne dépendant pas de la diffusion, est une ligne materielle fonction uniquement des propriétés dynamiques du fluide. Nous montrons, de manière théorique, que sur un ensemble de réalisations du fluide statistiquement stationnaires avec trajectoires chaotiques, la moyenne de la longueur de la ligne de contact, des gradients des réactifs le long de cette ligne et de la dérivée temporelle des concentrations moyennes des réactifs sur le domaine peuvent être prédites à partir de la diffusion et des propriétés lagrangiennes de dilatation des particules de fluides (PLD). Les PLD sont constituées des exposants de Lyapunov à temps fini et de deux temps équivalents pouvant être calculés sur une trajectoire à partir de l'évolution de l'éxposant de Lyapunov. L'inverse de l'éxposant de Lyapunov définit sur une trajectoire le temps caractéristique de dilatation d'une particule de fluide au temps t, alors que les temps équivalents le mesurent respectivement dans le passé récent avant t et aux moments initiaux de la trajectoire. Les résultas théoriques sont éprouvés à l'aide de simulations numériques avec un modèle pseudo-spectral du fluide solution des équations de Navier-Stokes en dimension deux. Le quatriéme chapitre s'intéresse au déclin d'un traceur passif dans ce même fluide. Nous mettons l'accent sur les différences avec le déclin dans des fluides cinématiques largement décrits dans la littérature. Comprendre la dépendence dece déclin avec la diffusion s'applique directement à une réaction infiniement rapide.
13
Richmond, Mitchell D. "CHEMICAL TOPPING BURLEY TOBACCO". UKnowledge, 2018. https://uknowledge.uky.edu/pss_etds/103.
Testo completoAbstract (sommario):
The act of topping tobacco (Nicotiana tabacum L.) involves the removal of the terminal bud or inflorescence of the tobacco plant. This practice ordinarily is accomplished by manually removing the top of each tobacco plant in an entire field which is labor intensive and costly. Chemical topping utilizes sucker control products to inhibit the terminal bud and axillary bud growth without manually removing the top of the tobacco plant. There were several research objectives in order to determine the utility of a chemical topping system: 1) determine if burley tobacco could be chemically topped with currently registered suckercide products while maintaining control of subsequent sucker growth; 2) compare chemical topping to manual topping for yield and leaf quality; 3) identify burley tobacco varieties that are better suited for chemical topping systems; 4) determine the optimum plant growth stage at which chemical topping treatments should be applied; and 5) identify genes that are differentially expressed following suckercide applications. To pursue our objectives, studies were initiated investigating the optimum timing of application, ideal variety maturity, and efficacy of suckercide applications using combinations of maleic hydrazide (MH), butralin, and fatty alcohols (FA). The terminal bud was not well controlled with FA or butralin alone nor was acceptable sucker control or total yield achieved. Our data suggest that chemically topping burley tobacco with a tank mixture of MH and a local systemic may be a suitable alternative to manual topping, as total yield and leaf quality grade index were not significantly different and total TSNA and MH residues were not significantly higher compared to manual topping. The 10% button and 50% button application timings were best suited for chemical topping practices. Treatments that targeted the 10% bloom stage did not completely halt flower development, but all application timings resulted in excellent sucker control. Medium and late maturity burley varieties were found to be suitable for chemical topping methods; however, timing the suckercide application may be less difficult in later maturing varieties. Chemically topping burley tobacco at 10 to 50% button stages with a tank mixture of MH and a local systemic suckercide was found to be a suitable alternative to manual topping, and would potentially result in labor savings for burley tobacco growers. Expression of genes related to phytohormones, meristem development, cell division, DNA repair and recombination were affected following MH treatment, which likely leads to the inhibition of apical and axillary meristem development.
14
Ingle, Stéphanie. "Chemical geodynamics of the early kerguelen plume". Doctoral thesis, Universite Libre de Bruxelles, 2003. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/211324.
Testo completo
15
Guillemard, Véronique. "Design and chemical synthesis of selective cancer therapeutics". Thesis, McGill University, 2004. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=85073.
Testo completoAbstract (sommario):
The clinical use of chemotherapeutic agents against malignant tumors is successful in many cases but suffers from major drawbacks. One drawback is the lack of selectivity which leads to severe side effects and limited efficacy, and another is the emergence/selection of drug-resistance. To limit non-specific toxicity and to improve the efficiency of cancer therapy, "tumor markers", which are proteins generally overexpressed on the surface of tumor cells, can be selectively targeted.Growth factor receptors are one of the most extensively studied groups of tumor markers. The implication of growth factor receptors in the pathogenesis of cancer has clearly been established and therefore, provides a rationale for therapeutic intervention. The targeting of cytotoxic substances to defined cell populations with "magic bullets" is an old idea that raised high expectations but also disappointment. Over the past decade, newly gained understanding of mechanisms for targeted therapy have brought new hopes. Pharmacological agents that selectively target and block the action of growth factors and their receptors have been attempted, such as monoclonal antibodies (mAbs) (whole molecule or fragments), bispecific antibodies, mAbs conjugated to drugs, toxins or radioisotopes, small peptidic and peptidomimetic molecules in free form or conjugated to drugs, anti-sense oligonucleotides, immunoliposomes-encapsulated drugs, and small molecule inhibitors. We designed, synthesized and characterized new chemotherapeutic agents consisting of Paclitaxel or Doxorubicin as anti-cancer drugs chemically coupled to growth factor receptor-selective monoclonal antibodies or small peptides as targeting agents. We show that the conjugates were selective and specific towards the targeted receptors, and had significant increased efficiency compared to parent drugs. More importantly, the conjugates were able to bypass p-glycoprotein-mediated resistance both in vitro and in vivo. These findings have considerable importance since drug resistance is a major cause of cancer treatment failure.
16
Ezzat, Kariem. "CELL PENETRATING PEPTIDES : CHEMICAL MODIFICATION AND FORMULATION DEVELOPMENT". Licentiate thesis, Stockholms universitet, Institutionen för neurokemi, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-56364.
Testo completoAbstract (sommario):
Cell penetrating peptides (CPPs) have been extensively studied and exploited as drug delivery vectors for a wide variety of therapeu-tic cargos. However, several issues remain to be addressed regarding the enhancement of their efficiency and stability. In addition, to be available for patients, CPP-based therapeutics have to be formulated into suitable pharmaceutical forms that can be readily manufactured, transported, stored and conveniently used.In this thesis, three chemically modified CPPs are developed having superior delivery properties for several nucleic acid-based the-rapeutic cargoes including: plasmids, small interfering RNA (siRNA) and splice switching oligonucleutides (SSOs), in different in-vitro and in-vivo models. In Paper I, we show that an N-terminally stearic acid-modified version of transportan-10 (TP10) can form stable nanopar-ticles with plasmids that efficiently transfect different cell types and can mediate efficient gene delivery in-vivo when administrated intra muscularly (i.m.) or intradermaly (i.d.). In paper II, stearyl-TP10 is further modified with pH titratable trifluoromethylquinoline moieties to facilitate endosomal release. The new peptide, denoted PepFect 6 (PF6), elicited robust RNAi responses when complexed with siRNA in several cell models and promoted strong RNAi responses in differ-ent organs following systemic delivery in mice without any associated toxicity. In paper III , a new peptide with ornithine modification, PF14, is shown to efficiently deliver SSOs in different cell models including HeLa pLuc705 and mdx mouse myotubes; a cell culture model of Duchenne‟s muscular dystrophy (DMD). Additionally, we have developed a method for incorporating this delivery system into solid formulation that could be suitable for several therapeutic appli-cations. Solid dispersion technique is utilized and the formed solid formulations are as active as the freshly prepared nanocparticles in solution even when stored at elevated temperatures for several weeks.Taken together, these results demonstrate that certain chemical modifications could drastically enhance the activity and stability of CPPs in-vitro and in-vivo. Moreover, we show that CPP-based thera-peutics could be formulated into convenient and manufacturable do-sage forms.
17
Davies, Matthew John. "Chemical communication in the European otter, Lutra lutra". Thesis, University of Hull, 2008. http://hydra.hull.ac.uk/resources/hull:2574.
Testo completoAbstract (sommario):
European otter (Lutra lutra) scent marks (spraint and anal sac secretion material) from captive and wild animals were analysed using solvent extraction and solid phase micro extraction (SPME). An ageing study (using SPME) mapped spraint chemical composition changes following deposition and how low temperature storage and exposure to the environment affected these changes. Chemicals with opposite time dependence were found; providing a possible spraint ageing mechanism. Temperature and environmental conditions affected the rates of production and deterioration of these chemicals and therefore the accuracy of spraint age estimations. Identification of the fatty acid content of otter scent marking material from 4 otter species led to both intra-specific (L.lutra) and inter-specific (Canadian river, Lontra canadensis; Asian short claw, Aonyx cinerea; and Giant, Pteronura brasiliensis) comparisons. Low volatility fatty acids (C10-C24.1) were found in all scent mark types. Intra-specifically, differentiation was seen in spraint fatty acid profiles based on sexual identity. Differentiation was observed between L. lutra scent marking material types (Captive spraint; Wild spraint; Wild anal sac secretion). Inter-specific differences relied on a mixture of ‘digital’ and ‘analogue’ coding. SPME and gas chromatography – mass spectrometry (GCMS) were used to investigate intra- (L.lutra) and inter- specific (L. lutra, A. cinerea, L. canadensis, and badger, Meles meles) differences in the headspace chemicals of otter scent marks. Inter-sanctuary (possibly diet related) differences in spraint odour of L. lutra were seen. No overall male - female differences were found, although possible intra-sanctuary sexual differences were seen. Inter-specific differentiation in scent mark odour profiles due to a combination of both analogue and digital coding elements was observed.
18
Fisher, Duncan Southam. "Chemical weathering of sulfide mineralization on Mars". Thesis, Massachusetts Institute of Technology, 1990. http://hdl.handle.net/1721.1/52911.
Testo completoAbstract (sommario):
Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1990.Includes bibliographical references (leaves 68-76).
by Duncan Southam Fisher.
M.S.
19
Gonneea, Meagan Joan Eagle. "Temporal variability in chemical cycling of the subterranean estuary and associated chemical loading to the coastal ocean". Thesis, Massachusetts Institute of Technology, 2014. http://hdl.handle.net/1721.1/87514.
Testo completoAbstract (sommario):
Thesis: Ph. D., Joint Program in Oceanography/Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2014.Cataloged from PDF version of thesis.
Includes bibliographical references.
At the land-ocean interface, terrestrial groundwater interacts with seawater to form a subterranean estuary, which can play host to dynamic biogeochemical cycling of nutrients, trace metals and radionuclides. This chemically altered groundwater enters the ocean through submarine groundwater discharge (SGD), a process that is driven by a number of physical processes acting on aquifers and the coastal ocean. In this thesis, seasonal variability in chemical cycling and associated loading to the coastal ocean was observed in a monthly time series within the Waquoit Bay (MA, USA) subterranean estuary. The position of the aquifer mixing zone moved seaward with an increase in hydraulic gradient, resulting in low salinity conditions and reduced mixing, while a decrease in gradient led to landward movement, high salinity groundwater and enhanced mixing. At this location, seasonal variability in sea level, not groundwater level, was the dominant variable driving the hydraulic gradient and therefore SGD. Fluxes of sediment bound cations to the ocean increased coincidently with sea level rise due to desorption. There was enhanced nitrogen attenuation during winter, potentially due to longer groundwater residence times, with greater nutrient delivery to coastal waters during the spring and summer bloom. Interannual climate fluctuations that control sea level and precipitation may ultimately control the timing and magnitude of chemical and water flux via SGD. In addition to temporal variability, aquifer lithology influences chemical export. This thesis also demonstrates that SGD from karst subterranean estuaries may play a role in local and global element budgets. The potential for the chemical signature of SGD to be recorded in the coral record was tested through a combination of coral culture experiments and field and modeling studies in the Yucatan Peninsula. Coral barium was well correlated with precipitation for a twelve-year record, with coral geochemistry reflecting the passage of a hurricane in 2002. While additional complexities in deciphering coral records remain, this proxy offers the potential to extend SGD records into the past.
by Meagan Joan Eagle Gonneea.
Ph. D.
20
Fox, Susan. "A Comparison of Chemical Composition & Fermentation Patterns of Alternative Silages to Whole Plant Corn Silage". TopSCHOLAR®, 1989. https://digitalcommons.wku.edu/theses/2346.
Testo completoAbstract (sommario):
A comparison of the relationship of fermentation to chemical composition was made for forages which were wilted and ensiled at 35 to 45 percent dry matter. Trial I consisted of three forages ensiled in October, 1981: interseeded soybeans and grain sorghum. whole plant corn with added anhydrous ammonia, and whole plant corn with shelled corn added at a rate of 150 kg/t of fresh forage. Trial II consisted of two forages ensiled in 1982: interseeded soybeans and pearlmillet, and wheat. Temperatures of fermentation were collected, and chemical composition during the first 25 days of fermentation analyzed.
Production data were also collected in Trial I. The cash expenses and yields do not indicate a significant advantage to either crop in this study in terms of yields and return over variables. In terms of plant nutrient content there was an advantage for soybean/grain sorgum silage in protein yield of 854 kilograms per hectare as compared to whole plant corn silage.
Temperature data collected on the forages in Trial I covered 57 days from October 8 through December 4. The maximum recorded temperatures for soybean/grain sorghum, corn silage with added anhydrous ammonia and the corn silage control were 37, 37, and 24 degrees Celcius. achieved by day 11, 4, and 11 of ensilement respectively. The rapid temperature increase for material treated with anhydrous ammonia confirmed previous reports. Small fluctuations occurred in silage temperatures but these were not correlated to ambient temperature. Temperatures declined very slowly in all forages, with the lowest reading for silages by day 57 recorded at 19 C for soybean/grain sorghum silage. Ambient temperature was not reached in the ensiled mass during the 57 day period in which data were recorded.
The soybean/pearlmillet ensiled in Trial II quickly reached a high peak temperature of 44 C at 4 days of ensilement, gradually decreasing over a 57 day period to 35 degrees on October 19. The silage did not reach a desireable pH. Initial forage pH was high, 7.4, dropped rapidly to 5.1 on day 5, but did not decline further in succeeding samples. Samples were low in lactic acid and high in acetic acid content.
Initial buffering capacities for both of the soybean mixture forages were considerably higher than the other forage materials. Buffering capacities at day 0 for whole plant corn, whole plant corn treated with anhydrous ammonia, soybean/grain sorghum, soybean/pearlmillet and wheat forages IA ere 19.4, 20.0, 35.3, 35.3. 38.6 and 22.2 milliequivalents/100 g of dry matter respectively. Increases in buffering capacities during fermentation were smaller for soybean/grain sorgum and soybean/pearlmillet . Buffering capacity increases for the forages were 133.5, 290.5, 69.1, 64.2 and 87.4%.
High ammonia nitrogen levels were found in samples of whole plant corn silage with added anhydrous ammonia obtained on days 10 and 20 of ensilement. These contained .282 and .351% ammonia-nitrogen and tested 18.0 and 20.1% crude protein. The increase in buffering capacity which occurrs with addition of anhydrous ammonia was confirmed by the higher acetic acid and pH levels, with corresponding decreases in lactic acid from samples taken days 10 and 25. Crude protein levels were 17.9 and 17.4 percent while the other samples contained only 10-12% crude protein. It appeared that application of anhydrous ammonia was not uniform throughout the silage. Where high concentrations of ammonia occurred fermentation was prolonged as indicated by excessive amounts of lactic and acetic acids and a high pH in these samples. Values for L(+) lactic acid ranged from .2 to .523 in fresh forage to 5.66% of dry matter on day 25. Concentrations of ammonia-nitrogen in the other silages ranged from .061 to .131%.
The low buffering capacity of whole plant corn silage was reflected by normal concentrations of lactate and acetate but a more acidic pH when compared to the other forages. Lactic and acetic acid production for soybean/grain sorghum silage was similar to that of the corn silage control. Corn silage pH was lower, however, throughout fermentation and reached a stable pH by day 5 of fermentation. The wheat silage went through a gradual fermentation with low lactic acid production, and an intermediary ending pH of 4.0.
Fermentation was essentially complete by day 10 in all silages as indicated by pH, buffering capacity, and lactic acid production: however, there was a tendency for buffering capacity and acetic acid content to increase in all of the ensiled materials throughout the 25 day collection period.
21
Cooper, Roland Arthur 1963. "Pyrrolizidine alkaloids: Chemical basis of toxicity". Diss., The University of Arizona, 1996. http://hdl.handle.net/10150/290581.
Testo completoAbstract (sommario):
In humans, livestock and experimental animals, pyrrolizidine alkaloids (PAs) are toxic as a consequence of their hepatic metabolism to reactive pyrrolic esters, or dehydroalkaloids (DHAs). Despite their similarity in structures, PAs often vary markedly in their lethality (LD₅₀s) and in the organs in which toxicity is expressed. We have examined whether there are differences in the physicochemical properties of certain DHAs which are associated with differences in patterns of metabolism and toxicity produced by the parent PA. Using a potentiometric method to measure hydrolysis, it was determined that the half-lives of the corresponding DHAs of retrorsine, seneciphylline, monocrotaline and trichodesmine were 1.06, 1.60, 3.39 and 5.36 sec, respectively. These values were supported by similar results from experiments measuring reactivity of DHAs toward 4-(p-nitrobenzyl)pyridine. Studies from the isolated rat liver perfused with PAs show that DHA stability is related to patterns of metabolism and toxicity. Perfusion of the primarily hepatotoxic retrorsine and seneciphylline is associated with a greater proportion of metabolite released as non-toxic 7-glutathionyl-6,7-dihydro-1-hydroxymethyl-5H-pyrrolizine (7-GSDHP), a greater proportion alkylating liver macromolecules, and a lower proportion released as DHA into the circulation. Perfusion with monocrotaline and trichodesmine, PAs producing extrahepatic toxicity, produced lower proportions of 7-GSDHP release and liver alkylation, and higher proportions of DHA released into the circulation. Other studies characterizing DHAs included the use of an in vitro enzyme assay in which DHAs were shown to inhibit the phosphotransferase activity of yeast and rat brain hexokinase. Parent PAs, and the hydrolysis product of DHAs, (±)-6,7dihydro-1-hydroxymethyl-5H-pyrrolizine (DHP) did not affect enzyme activity. In vivo studies in rats have established that glutathione and cysteine-conjugated pyrrolic metabolites of PAs likely represent detoxication pathways, providing further support for DHAs as the primary toxic metabolite. We have examined the chemical form of sulfur-bound pyrroles to establish the importance of the 7-ester position in PA toxicity. Additionally, we have developed an efficient technique for the rapid separation and purification of large quantities of PAs using high-speed counter-current chromatography.
22
Marc, Katya. "Thermo-chemical recovery of styrene from polystyrene waste". Thesis, McGill University, 1992. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=61312.
Testo completoAbstract (sommario):
Styrene was recovered from polystyrene by thermo-chemical treatment in a nitrogen atmosphere carried out at 330$ sp circ$C to 410$ sp circ$C, for 30 to 60 minutes. Up to 70% of the polystyrene was converted to styrene at a reaction temperature of 406$ sp circ$C and reaction time of 45 minutes. The styrene yield increased with temperature. At the lower temperatures, the molecular weight of the polystyrene was reduced from 138 000 to 8 900. At the higher temperatures, the polystyrene residue obtained consisted mainly of styrene dimer and trimer. The use of catalysts was evaluated. The catalysts were mixed with the polystyrene in 10% by weight mixtures. They were: silica-alumina, poly($ alpha$-methylstyrene), an antioxidant (2,2$ sp prime$-Methylenebis(4-methyl-6-tert-butyl phenol)), and zeolite. The above catalysts were found to have no effect on the thermal degradation of polystyrene under the conditions of the present study. The initial rate of thermal degradation of polystyrene was found to fit a first order model. The activation energy obtained was 181 kJ/mol, which is in accordance with literature values.
23
Grewal, Burrinder S. "Mechanisms of chemical and physical transdermal penetration enhancement". Thesis, Aston University, 1999. http://publications.aston.ac.uk/10978/.
Testo completoAbstract (sommario):
The underlying theme of this thesis is one of exploring the processes involved in the enhancement of percutaneous absorption. The development of an attenuated total reflectance Fourier-Transform infrared (ATR-FTIR) spectroscopic method to analyse diffusion of suitable topically applied compounds in membrane is described. Diffusion coefficients (D/h2) and membrane solubility (AO) for topically applied compounds were determined using a solution to Fick's second law of diffusion. This method was employed to determine the diffusional characteristics of a model permeant, 4-cyanophenol (CP), across silicone membrane as a function of formulation applied and permeant physicochemical properties. The formulations applied were able to either affect CP diffusivity and/or its membrane solubility in the membrane; such parameters partially correlated with permeant physicochemical properties in each formulation. The interplay during the diffusion process between drug, enhancer and vehicle in stratum corneum (SC) was examined. When enhancers were added to the applied formulations, CP diffusivity and solubility were significantly enhanced when compared to the neat propylene glycol (PG) application. Enhancers did not affect PG diffusivity in SC but enhancers did affect PG solubility in SC. PG diffusion closely resembled that of CP, implying that the respective transport processes were inter-related. Additionally, a synergistic effect, which increases CP diffusivity and membrane solubility in SC, was found to occur between PG and water. Using 12-azidooleic acid (AOA) as an IR active probe for oleic acid, the simultaneous penetration of CP, AOA and PG into human stratum corneum was determined. It was found that the diffusion profiles for all three permeants were similar. This indicated that the diffusion of each species through SC was closely related and most likely occurred via the same route or SC microenvironment.
24
Nemer, Randa J. "Anaerobic-aerobic treatment of chemical industrial effluents". Thesis, McGill University, 1994. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=26410.
Testo completoAbstract (sommario):
Several chemical industries in Canada discharge untreated effluents containing substantial amounts of organic pollutants. Environmental concern regarding the pollution of water bodies has led the authorities to issue stringent regulations with respect to the quality and quantity of wastewater that can be discharged. Chemical characterization and biotreatability of some waste streams generated by a chemical industry in Quebec was therefore undertaken. The study showed that two highly concentrated effluents were amenable to biological treatment. The first effluent, "plastifiant", was generated from the production of plastics, while the second, "colonne", was the product of a resin distillation column. Batch assay tests, including biochemical methane potential (BMP) and anaerobic toxicity assay (ATA), showed a moderate degree of anaerobic treatability with soluble COD removals of 45 to 61% and 11 to 67% for the colonne and plastifiant, respectively. Percentage COD removal was found to vary depending on the source of seed sludge. A mixture of biomasses from different sources was shown to be preferable for the anaerobic degradation of both effluents. The colonne effluent did not exhibit any toxicity to methanogenic bacteria. Inhibition of anaerobic microorganisms from the plastifiant effluent was found to be directly proportional to the increase in concentration, indicating that this effluent should be diluted. Continuous flow studies revealed that the selected effluents could be treated by anaerobic, aerobic or sequential anaerobic-aerobic techniques with soluble COD removals of 58, 80 and 89%, respectively. A significant impact of the type of anaerobic sludge and operating parameters with respect to the extent of biological treatment was noted, suggesting that the treatment efficiencies can be further improved. The one-step anaerobic or aerobic process was found to be applicable as a pre-treatment, while for a full treatment and direct discharge into receiving water
25
Shen, Li 1968. "Nutritional and chemical properties of sorghum, rapeseed, and sunflower pollens". Thesis, The University of Arizona, 1992. http://hdl.handle.net/10150/278204.
Testo completoAbstract (sommario):
The nutritional and chemical properties of three Chinese pollens, sorghum (Sorghum sp.), rapeseed (Brassica napus) and sunflower (Helianthus annuus), were studied. All three pollens were highly preferred, with sunflower pollen the highest, by young honey bees (Apis mellifera). Rapeseed pollen increased honey bee's longevity the greatest; however, sorghum and sunflower pollens also increased the longevity relative to the no-pollen group. All three pollens had high energy (about 5 kcal/g) and carbohydrate quantities (58%). The protein, fat, and fiber levels were 27%, 7%, and 9% in rapeseed pollen, 26%, 5%, and 13% in sorghum pollen, and 15%, 5%, and 10% in sunflower pollen. alpha-Tocopherol was high in sunflower pollen (61 μg/g), lower in rapeseed (33 μg/g) and sorghum pollen (15 μg/g). K, Ca, Mg, Fe, Cu, and Mn were high in all three pollens. These data suggest that a pollen which is highly preferred by honey bees is not necessarily the most nutritious.
26
Huang, Wei Hua. "Chemical investigation on root barks of Oplopanax horridus". Thesis, University of Macau, 2012. http://umaclib3.umac.mo/record=b2590373.
Testo completo
27
Brooker, Michael R. "Physical and Chemical Characterization of Self-Developing Agricultural Floodplains". The Ohio State University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=osu1513778530623727.
Testo completo
28
Hamid, A. "Artificial immune systems for optimization, clustering and classification applications in chemical sciences and engineering". Thesis(M.Sc.), CSIR-National Chemical Laboratory, Pune, 2012. http://dspace.ncl.res.in:8080/xmlui/handle/20.500.12252/2110.
Testo completo
29
Dix, Garry R. "Chemical exposure and lung function in fragrance industry employees". Thesis, University of Portsmouth, 2012. https://researchportal.port.ac.uk/portal/en/theses/chemical-exposure-and-lung-function-in-fragrance-industry-employees(91a9ece1-2e21-4715-bdf6-837ec228893f).html.
Testo completoAbstract (sommario):
Introduction Production employees within the UK fragrance industry are exposed to large quantities of chemical substances and mixtures over working shifts. Occupational respiratory exposure within this industry is managed in line with relevant legislation and guidelines. There is a lack, however, of published literature studying the effects of respiratory exposure to chemicals on fragrance production employees. A multi-site cross-sectional study was conducted using employees from the UK fragrance industry. The primary aim was to answer the research question: In fragrance industry employees, is occupational respiratory exposure to chemicals linked to a statistically significant change in lung function as measured using spirometry? The secondary aim was to use the data acquired to develop a weighted questionnaire that is predictive for potential lung function problems, for use as a preplacement occupational health tool within the fragrance industry. Methods A cross-sectional study was designed, using an exposed group (fragrance production and associated functions, n = 60) and a control group (non-exposed fragrance industry employees, e.g. office staff, n = 52). 5 UK companies took part, giving a total of 112 participants. This was calculated as sufficient to achieve 80% power and 5% significance. Spirometric measurements (FEV1, FVC and PEF*) were taken pre-shift and postshift.Information was provided by participants for information on potential confounding factors (smoking, personal or family history of respiratory problems, body mass index). Post-shift measurements were compared between groups, using analysis of covariance (ANCOVA) to adjust for the baseline pre-shift measurements. A pilot questionnaire was developed. The weightings for each of the questions contained within the questionnaire were found by performing simple and multiple linear regression on the spirometric and demographic data. The unstandardised coefficient (B) was used as a measure of effect size in order to calculate a weighted score for each question response. * FEV1 = forced expiratory volume in 1 second; FVC = forced vital capacity; PEF = peak expiratory flow Results Adjusted mean difference in post-shift measurements between groups (exposed vs. control) for each outcome measure was NOT observed to be statistically significant. Adjusted p-values for FEV1, FVC and PEF were 0.722, 0.883, and 0.676, respectively. Internal validation checks showed that the weighted questionnaire scores correlated with FEV1 measurements, with a high score correlating with a reduced FEV1 performance. Further validation is necessary to determine a threshold score corresponding to FEV1 of <80 predicted, the lower limit of normal for FEV1 performance. Conclusions The present study showed no significant effects of occupational respiratory exposure on the spirometric performance of the study population. On first inspection the present findings support the suggestion that protective measures in place in the fragrance industry are sufficient in minimising occupational risk to respiratory health. Further validation of airway hypersensitivity measurement methods used in spirometry and the questions asked in the questionnaire is vital in order to determine a threshold score corresponding to FEV1 of <80%predicted, the lower limit of normal for FEV1 performance. The pre-placement occupational health questionnaire has potential to be employed as a predictive tool for potential lung functionality in fragrance industry employees, subject to further development. Subsequent external validation in future studies will be required before the questionnaire can be released for widespread use. In conclusion, this work is the first step in a novel area of research, and the industry would benefit from the follow-up or expansion of this research.
30
Rojas, Rosario. "Secondary metabolites of Vernonia gigantea roots : isolation, antimicrobial, chemical and biotransformation studies". Connect to resource, 2000. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1228166792.
Testo completo
31
Yimamu, (Imam) Maiwulidan (Mewlude). "Chemical vapour deposition of boron-carbon thin films from organoboron precursors". Licentiate thesis, Linköpings universitet, Tunnfilmsfysik, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-123909.
Testo completoAbstract (sommario):
Boron-carbon (BxC) thin films enriched in 10B are potential neutron converting layers for 10Bbased solid-state neutron detectors given the good neutron absorption cross-section of 10B atoms in the thin film. Chemical Vapour Deposition (CVD) of such films faces the challenge that the maximum temperature tolerated by the aluminium substrate is 660 °C and low temperature CVD routes for BxC films are thus needed. This thesis presents the use of two different organoboron precursors, triethylboron –B(C2H5)3 (TEB) and trimethylboron – B(CH3)3 (TMB) as single-source precursors for CVD of BxC thin films. The CVD behaviour of TEB in thermal CVD has been studied by both BxC thin film deposition and quantum chemical calculations of the gas phase chemistry at the corresponding CVD conditions. The calculations predict that the gas phase reactions are dominated by β-hydride eliminations of C2H4 to yield BH3. In addition, a complementary bimolecular reaction path based on H2-assisted C2H6 elimination to BH3 is also present at lower temperatures in the presence of hydrogen molecules. A temperature window of 600 – 1000 °C for deposition of X-ray amorphous BxC films with 2.5 ≤ x ≤ 4.5 is identified showing good film density (2.40 – 2.65 g/cm3) which is close to the bulk density of crystalline B4C, 2.52 g/cm3 and high hardness (29 – 39 GPa). The impurity level of H is lowered to < 1 at. % within the temperature window. Plasma chemical vapour deposition has been studied using TMB as single-source precursor in Ar plasma for investigating BxC thin film deposition at lower temperature than allowed by thermal CVD and further understanding of thin film deposition process. The effect of plasma power, total pressure, TMB and Ar gas flow on film composition and morphology are investigated. The highest B/C ratio of 1.9 is obtained at highest plasma power of 2400 W and TMB flow of 7 sccm. The H content in the films seems constant at 15±5 at. %. The B-C bond is dominant in the films with small amount of C-C and B-O bonds, which are likely due to the formation of amorphous carbon and surface oxidation, respectively. The film density is determined as 2.16±0.01 g/cm3 and the internal compressive stresses are measured to be <400 MPa.
32
Aratikatla, Eswarakumar. "Design and synthesis of artemisinin-dipeptidyl vinyl phosphonate hybrid molecules as novel antimalarial agents; synthesis of biologically active molecules and studies directed towards bioactives from vernonia arborea". Thesis(Ph.D.), CSIR-National Chemical Laboratory, Pune, 2019. http://dspace.ncl.res.in:8080/xmlui/handle/20.500.12252/4591.
Testo completoAbstract (sommario):
Design and Synthesis of Artemisinin-Dipeptidyl Vinyl Phosphonate Hybrid Molecules as Novel Antimalarial Agents; Synthesis of Biologically Active Molecules and Studies Directed Towards Bioactives from Vernonia arboreaAcSIR
33
Rivera, Michael Kirn. "Protection, exposure, and recovery for chemical field engineering". Thesis, California State University, Long Beach, 2015. http://pqdtopen.proquest.com/#viewpdf?dispub=1604869.
Testo completoAbstract (sommario):
This project is a compilation of information from public sources as well as from private unclassified military sources combined with first hand field engineering knowledge. This report should be read prior to any and all who will be entering any Superfund site and/or Formally Used Defense Site (FUDS). Reading of this report should be done in order to make the individual aware of the risk they are under taking by entering a Superfund and FUD site. Primarily the health risks that include but are not limited the development of cancer and death. It should be noted that this report does not cover all contaminates, but focuses on the most detrimental to human health and widely found hazards. Primarily the effects Radiation, Lead, Cyanobacteria Blooms, and MTBE have on the human body and how these chemicals came to be in the environment. Ways to prevent exposure and treatment for when exposure occurs.
34
Perricane, Lisa Helen. "County Demographic Influence on Toxic Chemical Activities of Chemical-Related Industry in Michigan". ScholarWorks, 2015. https://scholarworks.waldenu.edu/dissertations/1420.
Testo completoAbstract (sommario):
There are a large number of chemical facilities that emit toxic chemicals in Michigan, and there is a concern regarding toxic chemical exposure to the residents of Michigan counties. However, it is uncertain whether chemical companies that emit toxic chemicals in Michigan are influenced by county demographic factors in deciding whether to engage in voluntary pollution prevention (P2) activities and whether this decision influences U.S. Environmental Protection Agency's (U.S. EPA) Risk-Screening Environmental Indicators (RSEI) scores. Using Bullard's theory of environmental justice, the purpose of this quantitative study was to determine if there was a correlation between chemical-related industry's voluntary P2 participation, U.S. EPA's RSEI scores for chemical-related facilities, and demographic factors in Michigan counties between 2007 through 2011. A cross-sectional design using hierarchical multiple regression analysis was used to study potential environmental inequality in 20 Michigan counties. Publically available data from the U.S. Census Bureau and the U.S. EPA included demographic data, voluntary P2 participation data, and RSEI scores for 20 counties in Michigan. A statistically insignificant correlation was found between voluntary P2 participation and median annual RSEI scores of Michigan industry; while a statistically significant, inverse correlation was found between median annual RSEI scores and educational attainment. The results from this study can be used by policy makers to promote more effective voluntary P2 policy and to create county-specific public education programs promoting toxic chemical awareness that will lead to positive social change in Michigan.
35
Zhang, Dong. "Chemical communication and its ecological consequence in the Lysmata shrimp". Thesis, University of Hull, 2009. http://hydra.hull.ac.uk/resources/hull:2422.
Testo completoAbstract (sommario):
Male crustaceans must find and identify receptive females to mate successfully. Mate recognition depends mainly on sex pheromones, which are detected by antennae and antennules. Distance (soluble)pheromone mediates mating behaviour of some decapod crustaceans. Contact pheromone (an insoluble coating on the body surface) has been proposed but not confirmed to be used by male decapod crustaceans to detect females. Here we report for the first time the involvement of both distance and contact pheromones in the mating processes of Lysmata shrimp (a group of protandric simultaneous hermaphrodites), and we have partially identified the soluble and contact pheromones. Additionally, evolution of the sex pheromone system of Lysmata shrimp, and role of the sex pheromones in reproductive isolation of Lysmata shrimp were investigated.
36
Ochoa, Loza Francisco Javier 1956. "Physico-chemical factors affecting rhamnolipid (biosurfactant) application for removal of metal contaminants from soil". Diss., The University of Arizona, 1998. http://hdl.handle.net/10150/282826.
Testo completoAbstract (sommario):
Contamination of soil and groundwater environments by toxic metals and organic compounds is of major concern because of the potential health hazard posed for humans. Remediation of such sites may require the addition of chemical agents that help in the mobilization of contaminants which are likely to be bound to solid surfaces. Surfactants are one of the agents proposed for addition to enhance the removal of soil-bound contaminants. In this dissertation, a series of laboratory experiments were conducted to investigate constraints to the potential application of a microbially produced surfactant (biosurfactant) for removal of metal contaminants from soil. The first part of the dissertation describes the measurement of stability constants and 13 metals including ten of the metals most frequently found in contaminated sites as well as three of the most common metal cations found in soil, Ca²⁺, Mg ²⁺, and K⁺. The second part of the dissertation describes a series of experiments designed to determine the interaction of the biosurfactant with soil matrix components including clays, metal oxides, and organic matter. The biosurfactant used in this research was monorhamnolipid produced by Pseudomonas aeruginosa ATCC 9027. A mixture of mono- and dirhamnolipid produced by P. aeruginosa UG2 was also used in some cases. Results showed that selectivity of the monorhamnolipid followed the order: Al³⁺ > Cu²⁺ > Pb²⁺ > Cd²⁺ > Zn²⁺ > Fe³⁺ > Hg ²⁺ > Ca²⁺ > Co²⁺ > Ni²⁺ > Mn²⁺ > Mg²⁺ > K⁺. These results suggest that monorhamnolipid binds common metal contaminants in preference over common soil cations such as Ca²⁺, Mg²⁺, and K⁺. Rhamnolipid was shown to bind to some soil constituents very strongly including hematite, illite, kaolinite, and montmorillonite. These results indicate that the effectiveness of rhamnolipid in soils with high amounts of iron oxide or clay may be limited due to extensive sorption. Finally, it was found that monorhamnolipid sorbed more strongly than a rhamnolipid mixture containing both monorhamnolipid and dirhamnolipid. This suggests that the use of a biosurfactant mixture may improve the effectiveness of rhamnolipid in the removal of organic and metal contaminants from soil.
37
Toerien, René. "Mapping the learning trajectories of physical sciences teachers' topic specific knowledge for teaching chemical bonding". Doctoral thesis, University of Cape Town, 2017. http://hdl.handle.net/11427/25508.
Testo completoAbstract (sommario):
Education in South Africa is a national concern and the training and professional development of teachers, especially in science and mathematics, has consequently been prioritised by the National Government. More than 60 percent of the teachers in South Africa are older than 40 years of age, which means that within the next 10-15 years many experienced teachers will exit the system, leaving a younger and less experienced cohort of teachers behind. This study aims to make explicit the learning trajectories of physical sciences teachers, specifically with respect to their knowledge for teaching chemical bonding, in order to support other teachers and thereby accelerating the route to expertise. Learning can be viewed as change, and change has a trajectory. Mapping the learning trajectories, and the significant events that influenced teachers' learning over time, can give insight into how the change had taken place. This study used a mixed methods approach within the pragmatic research paradigm to map learning trajectories for a group of 60 South African physical sciences teachers. Pedagogical content knowledge (PCK), the unique knowledge held by teachers, was used for the theoretical framing of the study. An adapted version of the Model of Teacher Professional Knowledge and Skill, including PCK, was used as an analytical framework. A measuring instrument for topic specific knowledge for teaching chemical bonding was designed and validated using the Rasch measurement model. Quantitative and qualitative analysis of the teachers' responses to the instrument and a grounded analysis of story-line interview data from ten purposively selected teachers were used to identify the factors that played a role in the development of the teachers' knowledge. A further qualitative analysis of PCK episodes from the interview data revealed how the above factors influenced the teachers' knowledge. Findings revealed that teaching the same content multiple times and at multiple grade levels, embracing changes in the curriculum as opportunities for learning, and further studies at tertiary level, especially completing post-graduate studies in education, all played a role in the teachers' perceived shifts in their topic specific knowledge for teaching (TSKFT). Three learning trajectories were identified for the teachers in this study: teachers shifted towards deeper conceptual understanding of the content and used more sophisticated explanatory frameworks; teachers shifted towards more integrated topic specific knowledge for teaching; and teachers shifted from being text book bound and teacher-focussed towards becoming more student-focussed in their approach to teaching. The findings from this study provide guidelines for professional development programmes in terms of differentiated support to teachers according to their career stages and the inclusion of content specific training programmes which makes teaching for conceptual progression explicit. A further recommendation includes encouraging teachers to embark on post-graduate studies in education as this played a pivotal role in shifting teachers' topic specific knowledge for teaching chemical bonding.
38
Van, Orman James Ashton 1969. "Kinetics of chemical exchange during melting of planetary interiors". Thesis, Massachusetts Institute of Technology, 2000. http://hdl.handle.net/1721.1/57964.
Testo completoAbstract (sommario):
Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, September 2000.Includes bibliographical references.
Experimental and numerical modeling studies are used to place constraints on the kinetics of chemical exchange during partial melting within the mantles of the terrestrial planets. Chapter 1 presents experiments on the diffusion rates of La, Ce, Nd, Dy and Yb in diopside at pressures of 0 to 2.5 GPa and temperatures of 1050 to 1450 'C. The results demonstrate a large variation in diffusivity among the rare earth elements, with the diffusion coefficient for La a factor of -35 smaller than for Yb at a given temperature and pressure. Chapter 2 presents experiments on the diffusion of Sm, Dy and Yb in pyrope at 2.8 GPa and 1200-1450 "C. No significant difference in diffusivity is found among these elements, and their absolute diffusion rates are similar to those of the heavy rare earth elements in diopside at the same pressure and temperature. Chapter 3 presents a numerical model for diffusion-controlled fractionation of trace elements during adiabatic decompression melting of a polyphase solid. The model is used to simulate the fractionation of rare earth elements between solid and melt during partial melting of Earth's upper mantle. Diffusion is found to exert a strong control on the evolution of the system at conditions typical of melting beneath ocean spreading centers, leading to less efficient fractionation of the rare earth elements than under conditions of local chemical equilibrium. Chapter 4 presents experiments on the diffusion of U and Th in diopside at I atm pressure. Uranium and thorium are found to diffuse at similar rates, and diffusive fractionation between these elements is therefore unlikely to be significant during partial melting in Earth's upper mantle. Thorium and radium may be diffusively fractionated, however, enhancing the production of 22 Ra/230Th radioactive disequilibrium during partial melting while inhibiting chromatographic fractionation during melt transport. Chapter 5 presents phase equilibrium and dissolution kinetics experiments that constrain hypotheses for the origin of lunar high-Ti ultramafic glasses. The experimental results demonstrate that assimilation of ilmenite-bearing cumulates is not a viable mechanism for production of the high-Ti glasses. It is proposed that the source of the high-Ti ultramafic glasses formed by shallow level mixing and reaction of late-stage magma ocean liquids with underlying olivine-orthopyroxene cumulates, followed by sinking of these dense hybrid materials into the lunar mantle.
by James Ashton Van Orman.
Ph.D.
39
Parrill, Abby Louise 1970. "Supplementing traditional chemical education on the World Wide Web". Thesis, The University of Arizona, 1996. http://hdl.handle.net/10150/278553.
Testo completoAbstract (sommario):
Emerging technologies provide impetus for supplements to the way chemistry is taught. Students of the current generation are conditioned to expect high-quality visual images to reinforce other informational media. Multimedia teaching tools can take advantage of this pre-conditioning. The World Wide Web (WWW) provides new opportunities for multimedia distribution. Supplemental materials for chemical education have been developed to take advantage of these emerging technologies. Molecular animations have been developed for use in lecture and for distribution via the WWW. These animations were designed to demonstrate chemistry from a "Big Picture" view. Interactive, exploratory tutorials have also been developed as student study aids. These tutorials promote concept understanding within a hands-on, trial-and-error atmosphere. The WWW has also been utilized as a low-cost avenue for implementation of a laboratory exercise emphasizing the importance of chemical structure and its impact upon chemical reactivity through computational chemistry.
40
Flagg, Melissa L. "Bioprospecting, chemical investigations and drug discovery from Chilean plants". Diss., The University of Arizona, 2000. http://hdl.handle.net/10150/284167.
Testo completoAbstract (sommario):
This dissertation, completed as part of an International Cooperative Biodiversity Group (ICBG) Program, encompasses the field collection, taxonomic determination, bioassay-guided isolation, and chemical characterization of three plants native to Chile, each of which was collected using a distinct collection approach. Chuquiraga ulicina ssp. ulicina , collected by the ecological or environmental strategy, yielded ten compounds including four novel taraxastane-type triterpenoids, 3β-acetoxy-6β-hydroxytaraxasta-20-ene (1), 6β-hydroxytaraxast-20-en-3-one (2), 6β-hydroxytaraxasta-20-ene 3β-palmitate (3), and 3β, 6β-dihydroxytaraxasta-20-ene (4), together with the known triterpenoids lupeol (5), lupenyl acetate (6), lupenone (7), friedelinol ( 8), 3β-acetoxy-30-nor-lupan-20-one (9), and 30-norlupan-3β-ol-20-one (10). Lupeol (5) was the only compound to show antitubercular activity. Sphacele salviae, collected by the ethnobotanical or ethnomedical approach, allowed the isolation of three known compounds, including the two abietane diterpenoids carnosol ( 11) and rosmadial (12), as well as one pentacyclic triterpenoid, ursolic acid (13). Greigia sphacelata, collected according to the random approach, afforded nine compounds. These include the two novel flavanones 5,7,3'-trihydroxy-6,4' ,5'-trimethoxy flavanone (14) and 5,3'-dihydroxy-6,7,4',5 '-tetramethoxy flavanone (15), as well as four known phenylpropanoids, 1,3-O-di-trans-p-coumaroylglycerol (16), 1-O-trans-cournaroylglycerol (17 ), 1-(ω-feruloyldocosanoyl)glycerol and 1-(ω-feruloyltetracosanoyl)glycerol (18), and trans-ferulic acid 22-hydroxy docosanoic acid ester (19), and three known pentacyclic triterpenoids, arborinone (20), arborinol (21), and isoarborinol (22).
41
Jepson, Donald Paul. "Development of new electro-chemical methods for determination of tinplate quality". Scholarly Commons, 1992. https://scholarlycommons.pacific.edu/uop_etds/2819.
Testo completoAbstract (sommario):
Five electrochemical test methods were evaluated for prediction of tinplate performance during this study. In addition, test packs were performed which provided some tinplate performance data. Three of the electrochemical methods gave inconclusive results in predicting tinplate performance. Two of these were anodic polarization in citric acid solutions involving different cell configurations. Another was anodic polarization of stress fractured samples in citric acid solution. One method, measuring the tin/steel alloy couple potential and current, gave results which appeared to predict tinplate performance, but the procedure was time consuming and the results were not easily reproducible. One method gave results which predicted tinplate performance and is recommended for use by the industry. This method measured tin dissolution rate and peak current as a function of time. The best performing tinplates gave lower peak currents and longer dissolution times. New electrochemical test cells were designed for four of the test electrochemical methods. One cell was designed to do five tinplate samples at once. A computerized test apparatus was developed for two of the test methods. This test apparatus greatly improved data handling and storage. A software program was configured to collect and evaluate data for the two computerized electrochemical methods.
42
Stievano, Lorenzo. "Petit Voyage vers la surface : Structure et réactivité de solides inorganiques". Habilitation à diriger des recherches, Université Pierre et Marie Curie - Paris VI, 2005. http://tel.archives-ouvertes.fr/tel-00092493.
Testo completoAbstract (sommario):
Dans ma carrière, j'ai eu la chance et le privilège de m'attaquer à des problématiques scientifiques très variées, qui peuvent être ressemblées par le concept fédérateur de l'application de méthodes d'analyses physico-chimiques pour la compréhension de la structure et de la réactivité d'un matériau inorganique. Parmi les techniques d'analyse que j'ai utilisées, une place d'honneur doit sûrement être attribuée à la spectroscopie Mössbauer, qui a été la technique principale d'analyse de ma thèse et qui a continué jusqu'aujourd'hui, à travers différentes collaborations, à faire partie de mes intérêts. Les types principaux de matériaux étudiés sont les suivants :1. Matériaux d'intérêt historique
En parallèle avec mes études de thèse, je me suis intéressé à la caractérisation de trois classes de matériaux inorganiques d'intérêt historique : des céramiques archéologiques, des faïences et des verres rouge rubis à l'or.
Dans le cas des céramiques archéologiques, ce travail à permis de mieux comprendre les propriétés de certaines céramiques anciennes et de reconstruire leur méthode de fabrication. Ces informations sont fondamentales pour les archéologues pour étudier le degré d'avancement et les connaissances de civilisations anciennes.
Dans le cas des verres rouge rubis à l'or, notre travail a permis de clarifier quel est l'état chimique de l'or dans le verre avant l'apparition de la coloration rouge, et de mieux comprendre le rôle chimique d'adjuvants tels que l'oxyde d'étain ou d'antimoine, connus pour influencer la vitesse d'apparition de la couleur et la teinte finale du verre.
Enfin, dans l'étude des faïences, nous avons pu, par le biais de répliques obtenues en suivant des recettes anciennes, clarifier les évènements chimiques lors de l'obtention d'un émail blanc à base d'oxyde d'étain. Ces connaissances nous ont permis par la suite d'étudier convenablement des faïences anciennes.
2. Matériaux d'intérêt catalytique
A partir de mes études de thèse, en participant à des collaborations scientifiques avec différents groupes de recherche, j'ai pu contribuer au développement de plusieurs types de catalyseurs : la majorité de ces matériaux consistait en des catalyseurs à base de métaux supportés, et ma contribution était surtout liée à leur caractérisation structurale, souvent réalisée in situ. Dans certains cas, toutefois, j'ai participé aussi au développement de nouvelles méthodes de synthèse (entre autres, la mise au point d'un système de préparation de catalyseurs bimétalliques modèles par vaporisation laser et la préparation de catalyseurs bimétalliques par dépôt de clusters bimétalliques préformés) et, dans un cas, à l'étude d'activité catalytique des matériaux synthétisés (étude cinétique en hydrogénation du toluène et en hydrogénation de la tétraline en présence du soufre des catalyseurs Pd-Pt/Al2O3 préparés par vaporisation laser.)
3. Surfaces et interfaces
Mon initiation aux surfaces et aux interfaces a débuté déjà pendant ma thèse, avec deux études : la première portait sur l'étude de nanoparticules d'or englobées dans une matrice de mylar, n'interagissant pas avec cette dernière ; la deuxième concernait l'adsorption d'un complexe d'or monovalent avec la thio-urée dans la porosité de solides différents. Dans le premier cas, nous avons pu détailler les propriétés électroniques de la surface nue des nanoparticules d'or, alors que dans la deuxième étude nous avons montré que ce complexe peut être utilisé, en combinaison avec la spectroscopie Mössbauer de 197Au, comme sonde pour étudier la force des liaisons hydrogène avec des surfaces de nature différente.
Ensuite, en intégrant le groupe du Prof. J.-F. Lambert au Laboratoire de Réactivité de Surface, j'ai pu affiner mes connaissances sur la chimie aux interfaces, en suivant trois axes thématiques de recherche : la première thématique est le dépôt en phase vapeur de complexes de métaux de transition comme méthode alternative dans la préparation d'un catalyseur. Dans ce cadre, nous avons pu mettre en évidence, au niveau moléculaire, le mécanisme d'interaction entre un complexe de nickel et une surface d'oxyde, sans la médiation d'un solvant.
La deuxième thématique concernait la préparation d'argiles à pilier ferriques en utilisant une approche originale, le pontage par l'intercalation de polycations de structure précisément définie stabilisés par un agent complexant organique. Dans ce cadre, nous avons pu détailler au niveau moléculaire l'adsorption d'un polycation ferrique (Fe8-tacn) entre les feuillets d'une saponite naturelle.
La dernière parmi ces trois thématiques, résumée dans le paragraphe suivant, est devenue maintenant le sujet porteur de ma recherche actuelle et qui sera développé dans le futur.
4. L'interface entre matériau inorganique et petites molécules biologiques
L'étude systématique de l'adsorption d'acides aminés et d'oligopeptides sur des surfaces peut avoir une grande importance fondamentale et pratique dans plusieurs domaines, tels que la chimie prébiotique, la synthèse de polypeptides à l'état solide, en chromatographie et dans la fabrication de matériaux hybrides organiques/inorganiques. De plus, l'étude de l'adsorption de polypeptides peut fournir des modèles pour l'étude de l'adsorption de protéines (polypeptides de masse moléculaire élevée), ce qui est en effet un problème de grande importance appliquée.
Dans ce cadre, nous avons entrepris une étude systématique de l'adsorption d'acides aminés et oligopeptides sur des surfaces d'oxyde, mettant l'accent sur la compréhension moléculaire des phénomènes impliqués. Du point de vue méthodologique, nous avons décidé de coupler deux approches complémentaires : une approche expérimentale, en utilisant toute une batterie de techniques physico-chimiques disponibles au LRS, et une approche théorique, qui nous a permis de modéliser les sites d'adsorption, et de les valider en comparant les paramètres spectroscopiques calculés avec les résultats expérimentaux.
Cette stratégie, novatrice par rapport aux études précédentes sur ce sujet, nous a fourni un modèle moléculaire précis de la glycine adsorbée et de son interaction avec un site d'adsorption spécifique en surface de la silice.
Nous comptons maintenant faire évoluer ce sujet en envisageant une étude intégrée et systématique de l'adsorption de molécules biologiques selon trois axes de complexité indépendants (complexité des surfaces, complexité du milieu et complexité des adsorbats), tout en mettant l'accent sur la compréhension moléculaire des phénomènes impliqués.
43
Bassolino, Giovanni. "Tuning ultrafast chemical reaction dynamics in photoactive proteins". Thesis, University of Oxford, 2015. http://ora.ox.ac.uk/objects/uuid:42c19c5c-c6df-48e9-bb1c-8a7098eca8b4.
Testo completoAbstract (sommario):
This dissertation investigates the origins of tunable and efficient photochemistry in three different photoactive proteins, bacteriorhodopsin (BR), rhodopsin (RHO) and green fluorescent protein (GFP). In all cases, significant differences exist between the photoreactivity of model chromophores in solution and in the protein environment, in terms of excited state lifetime and efficiency of the primary photochemical process (opsin proteins) or the type of reaction (excited state proton transfer versus C=C double bond photoisomerisation for GFP). The work presented here investigates for each case to what extent the protein environment is necessary to alter the photochemistry of model chromophores in solution. For GFP and BR steric and electrostatic interactions between the protein pocket and the chromophore are shown to be likely responsible for shaping the excited state surface along which the photoreactions take place. For RHO it is suggested, contrary to current belief, that selection of a reactive ground state conformer might be the main effect generating the observed differences between solution and protein environment. The solution photochemistry of structurally modified retinal protonated Schiff bases, taken as model chromophores for the opsin proteins, is studied with continuous wave irradiation experiments and ultrafast transient spectroscopies. Surprisingly large differences are observed for the isomerisation reaction depending on the starting configuration (trans or cis) of the photoactive double bond. The current model for BR based on the tuning of the excited state barrier encountered along the isomerisation coordinate is expanded to include the changes in selectivity, speed and efficiency observed for a series of all-trans derivatives. For 11-cis, the photoisomerisation in solution is proposed to take place along a barrierless isomerisation coordinate, in contrast with the models currently available in literature. It is suggested that the protein might be discriminating between ground state conformers rather than significantly changing the topography of the reaction coordinate. For GFP, excited state Raman spectra are recorded for the wild-type protein, two mutants and a model chromophore in solution. It is suggested that the high frequency vibrational modes observed in the excited state spectra of the proteins but not of the model chromophore in DMSO are a sign of a tighter chromophore environment that inhibits the photoisomerisation reaction occurring in solution.
44
Kavvada, Klairi M. "Modelling the gastric epithelium for testing of new chemical entities". Thesis, Aston University, 2004. http://publications.aston.ac.uk/11029/.
Testo completoAbstract (sommario):
A cell culture model of the gastric epithelial cell surface would prove useful for biopharmaceutical screening of new chemical entities and dosage forms. A successful model should exhibit tight junction formation, maintenance of differentiation and polarity. Conditions for primary culture of guinea-pig gastric mucous epithelial cell monolayers on Tissue Culture Plastic (TCP) and membrane insects (Transwells) were established. Tight junction formation for cells grown on Transwells for three days was assessed by measurement of transepithelial resistance (TEER) and permeability of mannitol and fluorescein. Coating the polycarbonate filter with collagen IV, rather with collagen I, enhanced tight junction formation. TEER for cells grown on Transwells coated with collagen IV was close to that obtained with intact guinea-pig gastric epithelium in vitro. Differentiation was assessed by incorporation of [3H] glucosamine into glycoprotein and by activity of NADPH oxidase, which produces superoxide. Both of these measures were greater for cells grown on filters coated with collagen I than for cells grown on TCP, but no major difference was found between cells grown on collagens I and IV. However, monolayers grown on membranes coated with collagen IV exhibited apically polarized secretion of mucin and superoxide. The proportion of cells, which stained positively for mucin with periodic Schiff reagent, was greater than 95% for all culture conditions. Gastric epithelial monolayers grown on Transwells coated with collagen IV were able to withstand transient (30 min) apical acidification to pH 3, which was associated with a decrease in [3H] mannitol flux and an increase in TEER relative to pH 7.4. The model was used to provide the first direct demonstration that an NSAID (indomethacin) accumulated in gastric epithelial cells exposed to low apical pH. In conclusion, guinea-pig epithelial cells cultured on collagen IV represent a promising model of the gastric surface epithelium suitable for screening procedures.
45
Xu, Sheng. "Oxide nanowire arrays for energy sciences". Diss., Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/42876.
Testo completoAbstract (sommario):
Oxide nanowire arrays are playing an important role in energy sciences nowadays, including energy harvesting, energy storage, and power management. By utilizing a wet chemical growth method, we demonstrated the capabilities of synthesizing density controlled vertical ZnO nanowire arrays on a general substrate, optimizing the aspect ratio of the vertical ZnO nanowire arrays guided by a statistical method, epitaxially growing patterned vertical ZnO nanowire arrays on inorganic substrates, epitaxially growing patterned horizontal ZnO nanowire arrays on non-polar ZnO substrates, and the lift-off of the horizontal ZnO nanowire arrays onto general flexible substrates. In addition, single crystalline PbZrxTi1-xO3 (PZT) nanowire arrays were epitaxially grown on conductive and nonconductive substrates by hydrothermal decomposition. Beyond that, based on the as-synthesized ZnO nanowire arrays, we demonstrated multilayered three dimensionally integrated direct current and alternating current nanogenerators. By integrating a ZnO nanowire based nanogenerator with a ZnO nanowire based nanosensor, we demonstrated solely ZnO nanowire based self-powered nanosystems. Also, utilizing a commercial full-wave bridge rectifier, we rectified the alternating output charges of the nanogenerator based on PZT nanowire arrays, and the rectified charges were stored into capacitors, which were later discharged to light up a laser diode (LD). In addition, blue/near-ultraviolet (UV) light emitting diodes (LED) composed of ordered ZnO nanowire arrays on p-GaN wafers were presented.
46
Sandoval, Kathia a. "Physical and Chemical Characterization of Crude Oil-Water Mixtures: Understanding the Effects of Interfacial Process to Chemical Bioavailability". FIU Digital Commons, 2016. http://digitalcommons.fiu.edu/etd/2464.
Testo completoAbstract (sommario):
This work detailed the physical and chemical characterization of oil water mixtures prepared using fresh and weathered Macondo related oils under different conditions of mixing energy/time and in the presence/absence of chemical dispersants. The results indicated that WAFs produced consistent, droplet free solutions for both source and weathered oils with concentration ranges that represented the soluble components of the oil used. Chemically enhanced WAFs prepared with the source oil generated a large amount of micron-size droplets; however the viscosity of the weathered oils were a limiting factor for the preparation of CEWAFs with weathered oils. Droplet size distributions were influenced by the amount of energy in the system and the oil weathering stage, when high energy WAFs were made the increase in weathering of the oil resulted in the formation of smaller droplets that were more stable over time.
47
Thinnes, Cyrille Christophe. "Chemical and biological studies on human oxygenases". Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:455f2e65-f294-461b-b44f-cd53796b14a0.
Testo completoAbstract (sommario):
As depicted in Chapter I, 2-oxoglutarate- (2OG) dependent oxygenases are ubiquitous in living systems and display a wide range of cellular functions, spanning metabolism, transcription, and translation. Although functionally diverse, the 2OG oxygenases share a high degree of structural similarities between their catalytic sites. From a medicinal chemistry point of view, the combination of biological diversity and structural similarity presents a rather challenging task for the development of selective small molecules for functional studies in vivo. The non-selective metal chelator 8-hydroxyquinoline (8HQ) was used as a template for the generation of tool compound I for the KDM4 subfamily of histone demethylases via application of the Betti reaction. Structural analogue II was used as the corresponding negative control (Figure A). These compounds were characterised in vitro against a range of 2OG oxygenases and subsequently used for studies in cells. I displays selectivity for KDM4 and increases the level of the H3K9me3 histone mark in cells. It has an effect on the post-translational modification pattern of histone H3, but not other histones, and reduces the viability of lung cancer cells, but not normal lung cells, derived from the same patient. I also stabilises hypoxia-inducable factor HIF in cells via a mechanism which seems to be independent from prolyl hydroxylase inhibition. This work is described in Chapters II and III. The chemical biology research in epigenetics is complemented by qualitative analysis conducted in the social sciences at Said Business School. With a global view on how innovation occurs and may actively be fostered, Chapter IV focuses on the potential of epigenetics in drug discovery and how this process may actively be promoted within the framework of open innovation. Areas of focus include considerations of incremental and disruptive technology; how to claim, demarcate, and control the market; how knowledge brokering occurs; and insights about process, management, organisation, and culture of open innovation. In contrast to the open-skies approach adopted for the development of a tool compound in Chapters II and III, a focused-library approach was taken for the generation of a tool compound for the OGFOD1 ribosomal prolyl hydroxylase. The development of a suitable in vitro activity assay for OGFOD1 in Chapter V enabled the development of lead compound III in Chapter VI. III is selective for OGFOD1 against the structurally closely related prolyl hydroxylase PHD2.
48
Pereira, José Augusto Caldeira. "Aplicação de técnicas de ressonância magnética nuclear ao estudo de processos dinâmicos em solução". Doctoral thesis, Universidade do Porto. Reitoria, 1994. http://hdl.handle.net/10216/10215.
Testo completo
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Crowley, Michael J. A., Lijun Shang e Malcolm R. Dando. "Preventing chemical weapons as sciences converge". 2018. http://hdl.handle.net/10454/16678.
Testo completoAbstract (sommario):
YesStark illustrations of the dangers from chemical weapons can be seen in attacks using toxic industrial chemicals and sarin against civilians and combatants in Syria and toxic industrial chemicals in Iraq, as well as more targeted assassination operations in Malaysia and the United Kingdom, employing VX and novichok nerve agents, respectively. Concerns about such malign applications of chemical technology are exacerbated by the unstable international security environment and the changing nature of armed conflict, “where borderlines between war, civil war, large-scale violations of human rights, revolutions and uprisings, insurgencies and terrorism as well as organized crime are blurred” (1). It is thus essential that the global community regularly review the nature and implications of developments in chemistry, and its convergence with the life and associated sciences, and establish appropriate measures to prevent their misuse. With the parties to the Chemical Weapons Convention (CWC) convening a Review Conference to address such issues beginning 21 November 2018, we highlight important scientific aspects (2)
50
Fradet, João Filipe Pinto Queirós. "Magnetic Nanowires with Chemical Constraints". Dissertação, 2019. https://hdl.handle.net/10216/125049.
Testo completo