Dissertations / Theses on the topic 'Thermal Hysteresi'

Una proteina in grado di legare i cristalli di ghiaccio è definita proteina legante il ghiaccio o IBP acronimo dall’inglese ice-binding protein. Le IBP grazie alla loro capacità di abbassare il punto di congelamento dell’acqua, aumentando il gap di isteresi termica (TH). Questo intervallo è definito come la differenza tra il punto di fusione e di congelamento dell’acqua. La seconda attività delle IBP è l’inibizione della ricristallizzazione del ghiaccio (ice recrystallization inhibition, IRI). Infatti, queste proteine stabilizzano i piccoli cristalli di ghiaccio impedendo la formazione di cristalli di ghiaccio di grosse dimensioni che sono dannosi per le cellule. Le IBP sono state identificate in numerosi organismi tra cui pesci, insetti, batteri, alghe e lieviti. Queste proteine rappresentano un esempio di evoluzione convergente, infatti tutte le IBP condividono lo stesso meccanismo di legame con il ghiaccio nonostante una sorprendente diversità strutturale e funzionale. Questo lavoro di tesi è focalizzato sulla caratterizzazione funzionale e strutturale di EfcIBP, una IBP batterica identificata da analisi di metagenomica effettuate sul ciliato Antartico Euplotes focardii e sul consorzio batterico ad esso associato. La struttura 3D di EfcIBP è stata risolta mediante cristallografia ai raggi X e consiste in un β-solenoide con un α-elica parallela all’asse principale della proteina. L’analisi strutturale ha permesso di identificare tre diverse facce del solenoide denominate A, B e C. Simulazioni di docking suggeriscono che EfcIBP è in grado di legare i cristalli di ghiaccio tramite le facce B e C del solenoide. Questa ipotesi è stata verificata attraverso la progettazione razionale di 6 varianti che sono state prodotte e saggiate per la loro attività. In generale, questi risultati indicano che EfcIBP è in grado di legare i cristalli di ghiaccio attraverso le facce B e C del solenoide. Questa peculiarità strutturale si riflette in un’insolita combinazione di attività di IRI e TH. Infatti, EfcIBP presenta una notevole attività di IRI in un intervallo di concentrazione nanomolare e una attività di isteresi termica di 0.53°C alla concentrazione di 50 μM che la rende una IBP moderata. All’interno del gap di TH, i cristalli di ghiaccio presentano una forma esagonale, mentre a temperature al di sotto della temperatura di congelamento presentano una forma a “Saturno". La proteina chimerica formata dalla “green fluorescent protein” e da EfcIBP è stata utilizzata per determinare a quali piani del cristallo di ghiaccio la proteina è in grado di legarsi e con quale cinetica. I dati sperimentali suggeriscono che le peculiarità funzionali di EfcIBP sono dovute alla sua capacità di legare velocemente i piani basali e piramidali del cristallo di ghiaccio. Questi dati, insieme alla presenza di una sequenza segnale per la secrezione, suggeriscono che EfcIBP è secreta e svolge la funzione di mantenere liquido l’ambiente circostante aumentando lo spazio vitale. In conclusione, EfcIBP è un nuovo tipo di IBP con proprietà insolite di legame al ghiaccio e di attività di IRI. Questo studio ha contribuito ad identificare una nuova classe di IBP moderate che potrebbero essere sfruttate come crioprotettori in diversi settori come la criobiologia e quello alimentare.
Ice-binding proteins (IBPs) are characterized by the ability to control the growth of ice crystals. IBPs are active in increasing thermal hysteresis (TH) gap as they decrease the freezing point of water. On the other hand, IBPs can inhibit ice recrystallization (IRI) and stabilize small ice crystals at the expense of the harmful, large ones. IBPs have been identified in several organisms including higher Eukaryotes and microorganisms such as bacteria, yeasts and algae. Although IBPs share the ability to bind ice crystals, proteins from different sources present different 3D structures, from α-helix to β-solenoid proteins. This thesis is focused on the structural and functional characterization of EfcIBP, a bacterial IBP identified by metagenomic analysis of the Antarctic ciliate Euplotes focardii and the associated consortium of non-cultivable bacteria. The 3D structure of EfcIBP, solved by X-ray crystallography, consists in a β-solenoid with an α-helix aligned along the axis of the β-helix. It is possible to distinguish three different faces: A, B and C. Docking simulations suggest that B and C faces are involved in ice binding. This hypothesis was tested by the rational design of six variants that were produced and assayed for their activity. Overall, these experiments indicate that both solenoid faces contribute to the activity of EfcIBP. EfcIBP displays remarkable IRI activity at nanomolar concentration and a TH activity of 0.53°C at the concentration of 50 μM. The atypical combination between these two activities could stem from the ability of this protein to bind ice crystals through two faces of the solenoid. In the presence of EfcIBP, ice crystals show a hexagonal trapezohedron shape within the TH gap, and a unique “Saturn-shape” below the freezing point. A chimeric protein consisting of the fusion between EfcIBP and the green fluorescent protein was used to deeper investigate on this aspects by analyses of fluorescence ice plane affinity and binding kinetics. Overall, experimental data suggest that the EfcIBP unique pattern of ice growth and burst are due to its high rate of binding at the basal and the pyramidal near-basal planes of ice crystals. These data, together with the signal sequence for the secretion, suggest that EfcIBP is secreted in local environment where it becomes active in increasing the habitable space. In conclusion, EfcIBP is a new type of IBP with unusual properties of ice shaping and IRI activity. This study opens new scenarios in the field of IBPs by contributing to identify a new class of moderate IBPs potentially exploitable as cryoprotectants in several fields, such as cryobiology and food science.

L'échelle moléculaire est de plus en plus considérée comme une solution alternative pour la miniaturisation des composants électroniques en vue de la construction de dispositifs fonctionnels. L'approche actuelle "top-down" basée sur la technologie du silicium force les chimistes du solide, les physiciens et les électroniciens à manipuler progressivement des quantités de matière de plus en plus faibles. Dans ce domaine, les dispositifs moléculaires offrent des perspectives remarquables avec des niveaux de sensibilité et de sélectivité qui ne peuvent pas être atteints avec les matériaux à semi-conducteurs conventionnels. Dans ce contexte, les complexes ou polymères de coordination représentent une classe importante de composés possédant des propriétés de commutation magnétiques, optiques et électrochimiques intéressantes. En particulier, les composés à transition de spin (transition intra-métallique de l'état haut spin vers l'état bas spin) des métaux de transition sont bien adaptés à cette stratégie car ils peuvent être le siège d'une transition réversible du premier ordre avec hystérésis sous l'effet d'une perturbation extérieure (température, pression ou éclairement) impliquant des modifications magnétique, optique et structurale. Dans ces travaux de thèse, des matériaux susceptibles de présenter des propriétés de bistabilité avec hystérésis autour de la température ambiante sont présentés et discutés. Un des objectifs est d'étudier l'évolution de leurs propriétés en fonction de la taille et de valoriser ces matériaux. Pour cela, ces composés ont été nano-structurés. Ainsi nous avons élaboré des nanoparticules à base de composé à transition de spin par différentes voies de synthèse et réalisé des films minces et des nanostructures de ces matériaux par des méthodes de lithographie douce et de lithographie électronique. Pour caractériser les propriétés de ces nouveaux objets, nous nous sommes orienté vers l'utilisation de nouvelles techniques de détection optiques et en particulier vers des techniques qui permettent la mesure de la variation du changement d'indice optique de ces matériaux, à savoir, des mesures de la variation des plasmons de surface lorsque des couches minces bistables de ces composés sont mises au contact de surface d'or et des mesures de variation de l'efficacité de diffraction à partir de réseaux de motifs de tailles micro- et nanométriques. Par ailleurs, une méthode basée sur la variation de l'intensité de fluorescence d'un fluorophore sélectionné et intégré au sein de composé mixte (composé à transition de spin - fluorophore) a également été développée. L'ensemble de ces méthodes concourt à pouvoir détecter un objet unique de taille nanométrique
The thesis is devoted to the preparation of new nanoobjects and nanocomposites of spin crossover complexes [Fe(Htrz)2(trz)](BF4) and [Fe(NH2-trz)3](NO3)2 (where Htrz - 1,2,4-triazole, trz - 1,2,4-trazolato, NH2-trz - 4-amino-1,2,4-triazole) and investigation their properties. Nanoobjects of mixed-ligand complexes with different ratio of 4-amino-1,2,4-triazole to 1,2,4-triazole were synthesized in reverse emulsions. It was shown that the increasing of the of 4-amino-1,2,4-triazole quantity leads to the increasing of nanoparticles anisotropy while spin crossover temperatures decrease. Double-step spin transition was observed at 20% mol of 4-amino-1,2,4-triazole, while at concentrations over 50% mol. spin crossover properties of [Fe(Htrz)2(trz)](BF4) completely disappear. Investigations of their morpholgy, size and spin transition characteristics as well as investigations of mechanisms of the fluorescent properties change under the spin switching process are shown. We consider obtaining nanoobjects of mixed-ligand complexes of iron (II) based on 1,2,4-triazole and 4-amino-1,2,4-triazole. The ligands ratio influences the morphology, size and characteristics of the spin transition of nanoobjects obtained. New modification of the complex [Fe(NH2-trz)3](NO3)2 in the form of nanoobjects was obtained using ligand excess. High transition temperature of this form was evidenced by various methods of analysis. This form was found to be isostructural with a resolved structure of [Fe(NH2-trz)3](NO3)2 · 2H2O. Series of nanocomposites with plasmonic and luminescent properties were prepares. For the core-shell composite with gold nanoparticles higher efficiency of the spin state switching due to the photothermal effect was demonstrated in comparison to the control sample. Fluorescent spin crossover composites with quantum dots, organic luminophors and terbium complexes were described. For all these composites the luminescence intensity variation as a function of temperature have been found. The mechanisms responsable of the luminescence intensity variation at two spin state are discussed. These mechanisms include resonant energy transfer, mechanical strain and photon reabsorption. High photostability fort he terbium - spin crossover composite is demonstrated comparing to previously obtained similar spin crossover luminescetnt composites. An example of a practical application of obtained composites for manufacturing fluorescent thermosensitive paper is shown

This thesis deals with computer modeling of temperature hysteresis during phase change, namely complete and partial phase change. There is performed a review of methods for modeling temperature hysteresis based on the enthalpy method and the effective heat capacity method. In the case of complete phase change, there are several methods that use the effective heat capacity method, as well as the heat source method, which, on the contrary, is a certain analogy of the enthalpy method. The following are works dealing with modelling of partial phase change, the most interesting of which is due to the validation method of static hysteresis and the method designed by Bony and Citherlet. The second part of this thesis deals with the hysteresis behavior of the material with phase change, which is organic paraffin RT 27. The input data obtained by differential scanning calorimetry was converted to the dependence of the enthalpy on temperature. These curves was represented by piecewise linear function. In the case of partial phase transformations, a modeling method based on the methods proposed by Bonym and Citherlet was designed. An one-dimensional model enabling thermal simulation of the material was implemented in the MATLAB software environment. The results obtained with this simulation are finally compared with a model that does not consider thermal hysteresis.

Blazars are variable emitters across all wavelengths over a wide range of timescales, from months down to minutes. It is therefore essential to observe blazars simultaneously at different wavelengths, especially in the X-ray and gamma-ray bands, where the broadband spectral energy distributions usually peak. In this work, we report on three " target-of-opportunity" observations of Mrk 421, one of the brightest TeV blazars, triggered by a strong flaring event at TeV energies in 2014. These observations feature long, continuous, and simultaneous exposures with XMM-Newton (covering the X-ray and optical/ultraviolet bands) and VERITAS (covering the TeV gamma-ray band), along with contemporaneous observations from other gamma-ray facilities (MAGIC and Fermi-Large Area Telescope) and a number of radio and optical facilities. Although neither rapid flares nor significant X-ray/TeV correlation are detected, these observations reveal subtle changes in the X-ray spectrum of the source over the course of a few days. We search the simultaneous X-ray and TeV data for spectral hysteresis patterns and time delays, which could provide insight into the emission mechanisms and the source properties (e. g., the radius of the emitting region, the strength of the magnetic field, and related timescales). The observed broadband spectra are consistent with a one-zone synchrotron self-Compton model. We find that the power spectral density distribution at greater than or similar to 4 x 10(-4) Hz from the X-ray data can be described by a power-law model with an index value between 1.2 and 1.8, and do not find evidence for a steepening of the power spectral index (often associated with a characteristic length scale) compared to the previously reported values at lower frequencies.

Thesis (Ph.D.); Submitted to Iowa State Univ., Ames, IA (US); 19 Dec 2004.
Published through the Information Bridge: DOE Scientific and Technical Information. "IS-T 2309" Mangui Han. US Department of Energy 12/19/2004. Report is also available in paper and microfiche from NTIS.

Durant cette thèse, nous avons d'abord développé un dispositif expérimental permettant de mesurer la dynamique de l'angle de contact avec une précision record de 0,01° sur 7 décades de vitesses de la ligne triple, gamme jamais atteinte auparavant. Pour la première fois, la résolution numérique des équations de lubrification a permis de déduire l'angle de contact à l'échelle microscopique de ces mesures macroscopiques, découplant donc le problème hydrodynamique multi-échelles de la physique de la ligne de contact à petite échelle. Avec ces outils, nous avons montré qu'une pseudo-brosse - une couche nanométrique de polymères - peut complètement piloter la dynamique, en produisant des hystérésis les plus faibles jamais mesurées (<0,07° !) et des surdissipations massives provenant de la nature visco-élastique de la couche. Cette étude ouvre la voie à la nano-rhéologie, permettant de sonder la dynamique extrêmement rapide (~100 ns) de polymères confinés à l'échelle nanométrique. Grâce à un travail collaboratif fructueux, nous avons ensuite développé un modèle permettant de décrire quantitativement et de façon unifiée la dissipation hydrodynamique, l'hystérésis et l'activation thermique. Enfin, beaucoup d'efforts ont été fournis pour la fabrication de surfaces aux défauts nanométriques contrôlés en taille, forme et concentration. La dynamique s'est révélée insensible à cette échelle de désordre, la présence des défauts n'affectant que l'hystérésis. Ces résultats ont été interprétés semi-quantitativement avec des lois d'échelle, et la caractérisation complète des défauts devrait permettre à terme de développer des modèles plus quantitatifs
During this thesis, we first developed an experimental set-up to measure contact angle dynamics with a record precision of 0.01° over 7 decades of velocity of the triple line, a range never before attained. For the first time, numerically solving the lubrication equations has allowed us to deduce the contact angle at the microscopic scale from these macroscopic measurements, and thus enabled the multi-scale hydrodynamic problem to be disentangled from the physics of the contact line at small scales. With these tools we have shown that the dynamics can be completely piloted by a pseudo-brush -a nanometric layer of polymers-, producing the lowest ever reported hysteresis (<0.07°!) and giving rise to a huge source of dissipation originating from the viscoelasticity of the coating. This study points the way towards nano-rheology, to probe extremely fast dynamics (~100 ns) of polymers confined at the nano-scale. Thanks to a fruitful collaborative work, we then developed a model that provides a single quantitative framework to account for hydrodynamic dissipation, hysteresis and thermal activation. Finally, a great deal of effort has been made to produce nano-defects whose size, shape and density are controlled. The dynamics appears to be insensitive to this scale of disorder, and the presence of defects is observed to only modify the hysteresis. These results have been interpreted semi-quantitatively with scaling laws, and we expect that the complete characterization of the defects should eventually allow the development of more quantitative models

Depuis longtemps, les dispositifs ou systèmes électromagnétiques sont omniprésents dans les milieux industriel et domestique. Le circuit magnétique de ces systèmes est un des éléments clefs d'une conversion énergétique efficace. Outre l'optimisation de la géométrie du circuit magnétique, la maîtrise de l'efficacité énergétique passe par l'utilisation de matériaux magnétiques performants et par une connaissance approfondie de leur comportement, notamment sous contraintes élevées comme les températures et fréquences élevées que l'on rencontre de plus en plus aujourd'hui. Notre travail s'intègre dans le cadre des recherches menées par l'équipe matériaux du laboratoire AMPERE, notamment sur les modèles comportementaux de matériaux magnétiques. Partant de nombreuses caractérisations expérimentales en fonction de la température, nous avons développé un modèle " dynamique " adapté à différents types de matériaux ferromagnétiques, et permettant de simuler rapidement l'influence de la température sur le fonctionnement permanent et transitoire de systèmes électromagnétiques simples. Il s'appuie sur l'association des modèles d'hystérésis de Jiles-Atherton et dit " tubes de flux ". Ce modèle, et la démarche associée de couplage entre phénomènes magnétique, thermique et électrique, sont validés sur un capteur de courant et une inductance. Les résultats confirment l'importance de l'effet de la température sur les performances des systèmes, et la pertinence de disposer d'un tel modèle pour optimiser ces systèmes

Šio darbo tyrimo tikslas – ištirti elektros energijos apskaitos prietaisų, indukcinių ir elektroninių, charakteristikas. Buvo atlikta informacijos šaltinių analizė apie indukcinių ir elektroninių elektros energijos skaitiklių ir srovės matavimo transformatorių parametrus, apsprendžiančius jų charakteristikas. Remiantis informacijos šaltinių apibendrinimu suformuota hipotezė: ne visos elektroninių elektros energijos prietaisų charakteristikos geresnės už indukcinių elektros energijos apskaitos prietaisų charakteristikas. Suformuoti tyrimo uždaviniai: ištirti elektroninių ir indukcinių elektros energijos prietaisų paklaidų priklausomybes nuo apkrovos srovės, galios koeficiento, eksploatacijos laiko, pasvyros kampo ir srovės matavimo transformatorių srovinės paklaidas. Padarytos išvados, nurodomas naudotos literatūros sąrašas.
The aim of this paper is to investigate the electricity metering devices, i.e. inductive and electronic, characteristics. It was made the analysis of the sources about the inductive and electricity meters and current transformers for measuring the parameters that define their characteristics. According to sources of information was formed the hypothesis: not all electronic power devices characteristics are better than inductive energy metering devices characteristics. The study objectives are to investigate experimentally the electronic and inductive power devices values of the load current, power factor, operating time, against an adverse list angle and current measuring transformer errors stream. Findings are discussed; the list of references is presented.

Shape memory alloys (SMAs) can recover large strains (e.g., up to 8%) by undergoing a temperature-induced phase transformation. This strain recovery can occur against large forces, resulting in their use as actuators. The SMA elements in such actuators integrate both sensory and actuation functions. This is possible because SMAs can inherently sense a change in temperature and actuate by undergoing a shape change, associated with the temperature-induced phase transformation. The objective of this work is to develop an SMA based cryogenic thermal conduction switch for operation between dewars of liquid methane and liquid oxygen in a common bulk head arrangement for NASA. The design of the thermal conduction switch is based on a biased, two-way SMA actuator and utilizes a commercially available NiTi alloy as the SMA element to demonstrate the feasibility of this concept. This work describes the design from concept to implementation, addressing methodologies and issues encountered, including: a finite element based thermal analysis, various thermo-mechanical processes carried out on the NiTi SMA elements, and fabrication and testing of a prototype switch. Furthermore, recommendations for improvements and extension to NASA's requirements are presented. Such a switch has potential application in variable thermal sinks to other cryogenic tanks for liquefaction, densification, and zero boil-off systems for advanced spaceport applications. The SMA thermal conduction switch offers the following advantages over the currently used gas gap and liquid gap thermal switches in the cryogenic range: (i) integrates both sensor and actuator elements thereby reducing the overall complexity, (ii) exhibits superior thermal isolation in the open state, and (iii) possesses high heat transfer ratios between the open and closed states. This work was supported by a grant from NASA Kennedy Space Center (NAG10-323) with William U. Notardonato as Technical Officer.
M.S.
Department of Mechanical, Materials and Aerospace Engineering
Engineering and Computer Science
Mechanical, Materials and Aerospace Engineering

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Conselho Nacional de Desenvolvimento Cient?fico e Tecnol?gico
We report a theoretical investigation of thermal hysteresis in magnetic nanoelements. Thermal hysteresis originates in the existence of meta-stable states in temperature intervals which may be tuned by small values of the external magnetic field, and are controlled by the systems geometric dimensions as well as the composition. Two systems have been investigated. The first system is a trilayer consisting of one antiferromagnetic MnF2 film, exchange coupled with two Fe lms. At low temperatures the ferromagnetic layers are oriented in opposite directions. By heating in the presence of an external magnetic field, the Zeeman energy induces a gradual orientation of the ferromagnets with the external field and the nucleation of spin- op-like states in the antiferromagnetic layer, leading eventually, in temperatures close to the Neel temperature, to full alignment of the ferromagnetic films and the formation of frustrated exchange bonds in the center of the antiferromagnetic layer. By cooling down to low temperatures, the system follows a different sequence of states, due to the anisotropy barriers of both materials. The width of the thermal hysteresis loop depends on the thicknesses of the FM and AFM layers as well as on the strength of the external field. The second system consists in Fe and Permalloy ferromagnetic nanoelements exchange coupled to a NiO uncompensated substrate. In this case the thermal hysteresis originates in the modifications of the intrinsic magnetic
Relatamos um estudo de histerese t?rmica em sistemas magn?ticos nanoestruturados. A histerese t?rmica se origina da exist?ncia de estados meta-est?veis em intervalos de temperatura que s?o control?veis pelas dimens?es f?sicas e composi??o do sistema magn?tico e pelo valor do campo magn?tico externo. Dois sistemas s?o investigados. O primeiro sistema consiste de uma tricamada contendo um filme antiferromagn?tico de MnF2 com intera??o de troca de interface com dois filmes ferromagn?ticos de Fe. Em baixa temperatura os dois filmes ferromagn?ticos t?m magnetiza??o em dire??es opostas. Ao aquecer o sistema em presen?a de campo magn?tico externo a energia Zeeman se sobrep?e a ordem magn?tica do filme de MnF2 induzindo uma orienta??o progressiva dos filmes ferromagn?ticos com o campo externo, e a forma??o de estados com spins fora da dire??o f?cil (spin flop) no material antiferromagn?tico, evoluindo para alinhamento dos filmes ferromagn?ticos em temperaturas ao redor da temperatura de N?el, com a forma??o de liga??es com frustra??o da energia de troca no centro do filme antiferromagn?tico. Ao resfriar o sistema segue uma sequ?ncia diferente de estados devido a barreira de anisotropia dos materiais. A largura da histerese t?rmica depende da espessura dos filmes e da intensidade do campo magn?tico externo. O segundo sistema estudado consiste de nanoelementos de Fe e Permalloy em substratos n?o-compensados de NiO. Nesse caso a histerese t?rmica se origina nas modifica??es, impostas pelo acoplamento de troca na interface, na ordem magn?tica intr?nseca do nanolemento ferromagn?tico. Ao aquecer al?m da temperatura de N?el, o nanoelemento se ajusta gradualmente ao padr?o magn?tico imposto pelo seu pr?prio campo dipolar e, no processo de resfriamento pode seguir uma sequ?ncia diferente de fases magn?ticas devido a barreira imposta por sua alta anisotropia de forma. Mostramos que histerese t?rmica ? mais prov?vel em nanoelementos de Fe, devido ao valor elevado da magnetiza??o de satura??o, e para nanoelementos de base quadrada, com dimens?es laterais ao redor de 100nm, devido a possibilidade de nuclea??o de v?rtices. Comentamos no poss?vel impacto de histerese t?rmica no funcionamento de c?lulas de tunelamento, usadas em mem?rias magn?ticas de acesso aleat?rio

Depuis quelques années, les matériaux à transition de spin présentant une bistabilité thermique ou photoinduite sont très étudiés en raison des applications futures potentielles pour le stockage de l'information. Dans ce contexte, ce travail a pour objectif la synthèse de nouveaux systèmes bistables du fer (ll). Pour ce faire, deux stratégies ont été utilisées : l'une consiste à augmenter les interactions intramoléculaires en substituant le contre-ion d'un système à transition de spin, l'autre consiste à associer un ligand neutre polydentate à un co-ligand anionique pontant.Dans une première partie, Ia modification du contre-ion a permis l'obtention d'un système discret mononucléaire à base d'un ligand macrocyclique présentant de la bistabilité thermique. Le second système discret est un complexe dinucléaire à base du ligand tmpa (triméthylpyridyl amine] qui a permis de mettre en avant les effets de la substitution du Iigand sur les caractéristiques de la transition de spin.Dans un deuxième temps, nous nous sommes orientés vers la synthèse de systèmes à structures étendues en utilisant des ligands anioniques rigides pontants de type tétracyanométallate [M(CN)4 ]²zassociés au ligand organique 8-aminoquinoléine (aqin). Cette association a conduit à l'obtention de chaînes monodimensionnelles présentant une transition abrupte avec hystérésis.Enfin, pour obtenir des systèmes bi- et tri-dimensionnels, nous avons associé le ligand 4-(2pyridyl)-1,2,4, 4H-triazole (trz-pyJ, potentiellement pontant, aux ligands anioniques [tcpd]L et [Pt(CN]al].Le système [Fe[trz-pyJz[Pt[CNJ4)].3H20 obtenu est un réseau 2D de type Hofmann avec des propriétés magnétiques et photo-magnétiques originales se distinguant par la présence d'une hystérésis cachée révélée par pho to-irradiation
In recent years, Spin Crossover materials [SCO) with thermal or Iight induced bistability are extensively studied because of their futur potential applications in memory display devices. In this context, the aim of this work is the synthesis of bistable new spin crossover systems based on Fe(ll). Two strategies were used: the first one is to increase the intramolecular interactions by substituting the counter-ion nature in a spin crossover system, the second one is to associate a neutral ligand to a bridging polydentate co-ligand.In rhe ffrst part, the modification of the counter-ion enabled us to obtain a discrete mononuclear system based on macrocycle ligand with thermal bistability. The second discrete system is a dinuclear complex based on tmpa (triimethylpyridyl amine) which led us to study ligand substitution effects of the Spin Cross-Over behaviour.In rhe second part, the aim is the synthesis of extended structures systems by using rigid anionic bridging ligands like tetracyanometallate anions [M[CN)4]2-and the organic ligand quinolin-8-amine. This association allowed to obtain 1D chains with abrupt spin crossover presenting hysteresis.Finally, to synthesise SCO 2D and 3D systems, we have associated the potentially bridging 4-[2pyridyl)-t,2,4,4H-triazole (trz-pyJ ligand to inorganic bridging anions tcpd²- and [Pt[CN)4]²-. The [Fe[trzpy)2(Pt[CN)4]].3H20 system obtained is as Hofmann-like 2D network with novel magnetic and photomagnetic properties with hidden hysteresis revealed by photo-switching

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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior
In this work was evaluated the influence of multiple quenching in the peak temperatures of phase transformation (PTPT) in the alloy Cu-11.8Al-0.6Be-0.5Nb-0.27Ni (%wt), as well as the influence that deformation applied in temperatures above Ms, at nominal composition Cu-11.8Al-0.6Be-0.5Nb-0.27Ni, Cu-11.8Al-0.55Be-0.5Nb-0.27Ni and Cu-11.8Al-4Nb-2.16Ni-0.5Be, would have on the residual deformation. The alloys were melted, homogenized during 12h by 850ºC and machined using wire electroerosion. Then, the samples were quenched in water at room temperature and subsequently analyzed by optical microscopy, scanning electron microscopy, using energy dispersive x-ray, differential scanning calorimetric analysis and x-ray diffractometry. For samples quenched successively, it was found a large change in PTPT after 22 quenching, there is no reverse transformation in this range. From the 34th quenching, the PTPT remained constant around 420ºC and severe changes in your micrographs were detected. Nevertheless, there was no change in Cu/Al able to change the PTPT. Alloys with containing nominal composition 0.4% and 0.2%Be indicated strong influence of the Be in the PTPT. When analyzed by x-ray diffractometry, the sample with 0.2Be indicated the presence of β' and γ' phases, when aged by 530ºC. For quantifying the residual deformations, the samples were subjected to static tensile and loading/unloading tests. When subjected large deformation and temperature near Ms, the results showed a great residual deformation, whereas small deformations with temperatures above Af showed not to be viable. The alloy Cu-11.8Al-4Nb-2.16Ni-0.5Be when tractioned, showed excessive weakness even after treatment of solubilization.
Neste trabalho avaliou-se a influência de têmperas múltiplas, nas temperaturas de pico da transformação de fase (TPTF) e na microestrutura da liga Cu-11,8Al-0,6Be-0,5Nb-0,27Ni (% em peso), bem como a influência que deformações aplicadas, em temperaturas a partir de Ms, às ligas de composição nominal Cu-11,8Al-0,6Be-0,5Nb-0,27Ni, Cu-11,8Al-0,55Be-0,5Nb-0,27Ni e Cu-11,8Al-4Nb-2,16Ni-0,5Be, teriam nas deformações residuais. As ligas foram fundidas, homogeneizadas durante 12h a 850ºC e usinadas via eletroerosão à fio. Em seguida, os corpos de prova foram temperados em água a temperatura ambiente sendo posteriormente analisadas via microscopia óptica, microscopia eletrônica de varredura, utilizando-se energia dispersiva de raios-x (EDS), análise calorimétrica diferencial de varredura (DSC) e difratometria de raios-X. Para as amostras cicladas termicamente, verificou-se que após 22 têmperas uma mudança significativa nas TPTF ocorre, não havendo a partir deste intervalo transformação reversa. A partir da 34ª têmpera, as TPTF permaneceram constantes em torno de 420ºC e as micrografias indicaram mudanças severas em suas microestruturas. Não obstante, não se verificou alteração na relação Cu/Al capaz de alterar as TPTF. As amostras contendo composição nominal de 0,4% e 0,2% de Be indicaram que as ligas estudadas são fortemente influenciadas pela presença do Be. Quando analisada por difratometria de raios-x, a amostra com 0,2Be indicou a presença das fases β e γ , quando submetida a tratamento de envelhecimento a 530ºC. Para a quantificação das deformações residuais, os corpos de prova foram submetidos aos ensaios de tração estática e de carregamento/descarregamento. As amostras submetidas a deformações próximas as de ruptura e com temperatura de ensaio próximo a Ms mostraram resultar em deformações residuais de maiores intensidades, enquanto quedeformações de pequena magnitude, com temperaturas acima de Af, mostraram não serem viáveis. A liga de composição nominal Cu-11,8Al-4Nb-2,16Ni-0,5Be, quando ensaiada sob tração, mostrou fragilidade excessiva mesmo após tratamento térmico de solubilização.

Dans un contexte de réchauffement climatique et de fin programmée des énergies fossiles, le secteur du bâtiment vise à réduire de 38% sa consommation d’énergie et à atteindre 10% de matériaux bio-sourcés utilisés dans la construction à l’horizon 2020. Ainsi, le béton de chanvre peut jouer un rôle majeur grâce à son bilan environnemental et à ses propriétés hygrothermiques qui lui permettent d’assurer un rôle d’amortisseur thermique et de stabilisateur de confort. Or le comportement hygrothermique du béton de chanvre à l’échelle du bâtiment est peu abordé dans la littérature et jamais pour les bâtiments tertiaires. L’objectif principal de ce projet est de combler ce vide en étudiant et en optimisant les performances énergétiques d’un bâtiment en béton de chanvre destiné à usage de bureaux et/ou de salles d’enseignement. Afin d’assurer le confort thermique intérieur différentes solutions techniques seront couplées au bâtiment et comparées entre elles : - une ventilation double flux thermodynamique associant une pompe à chaleur à une centrale double flux. - Une ventilation simple flux associé à un puits canadien qui récupère la chaleur du sous-sol pour préchauffer l’air de ventilation en hiver ou le rafraîchir en été. - Une ventilation double flux associé à un puits canadien. Par le biais de la simulation numérique et de mesures faites d’abord à l’échelle des composants, il sera ainsi possible d’évaluer le potentiel de chaque composant sur l’énergétique et le confort hygrothermique de bâtiments tertiaires intégrant principalement le périmètre du projet Grand Campus de Reims mais également pouvant être élargi à la spécificité d’autres climats français
In a context of global warming and planned end of fossil fuels, the construction industry aims to reduce by 38% its energy consumption and to achieve 10% of bio-based materials used in construction in 2020. Thus, the hemp concrete can play a major role thanks to its positive environmental impact and its hygrothermal properties that allow it to ensure a role of heat damper and comfort stabilizer. Or hygrothermal behavior of hemp concrete throughout the building is little discussed in the literature and never for commercial buildings. The main objective of this project is to fill this gap by studying and optimizing the energy performance of a hemp concrete building designed for offices and / or classrooms. To ensure inside thermal comfort, different technical solutions will be coupled to the building and compared with each other: - A double flow thermodynamical ventilation combining a heat pump with a double flow central. - A simple flow ventilation associated to a pipe system which recovers heat from the basement to preheat ventilation air in winter and cool in the summer. - A double flow ventilation associated to a Canadian well. Through computer simulation and measurements made initially at the level of components, it will be possible to evaluate the potential of each component on the energy and hygrothermal comfort of commercial buildings mainly integrating the project boundary Grand Campus Reims but also can be extended to other French specificity climates

Ce travail de thèse met en évidence deux phénomènes microscopiques dissipatifs au voisinage de la ligne de contact dans les phénomènes de capillarité et d'adhésion. L'étude s'appuie sur des expériences dynamiques et des modélisations théoriques. La mesure expérimentale de quantités macroscopiques et la théorie hydrodynamique permettent d'extraire les informations dynamiques localisées au voisinage la ligne de contact. Les différents phénomènes dissipatifs localisés au voisinage de la ligne de contact ont pour origines les propriétés des substrats sur lesquels se déplace la ligne de contact. Pour une surface rigide hétérogène, nous avons développé un modèle rhéologique de la ligne de contact fondé sur l'hydrodynamique, permettant d'établir théoriquement l'évolution temporelle de la ligne de contact et de ses déformations. Une décomposition modale fondée sur la réduction de l'énergie par la théorie du chemin de réaction fournit une prédiction quantitative de la dynamique thermiquement activée de la ligne de contact, en accord avec l'expérience réalisée. Pour un substrat déformable, à partir de l'analyse de deux expériences différentes de mouillage dynamique et de l'estimation de la dissipation dans le substrat, fondée sur sa viscoélasticité, nous avons développé une compréhension générale du comportement dynamique d'une ligne de contact sur un substrat viscoélastique. Pour finir, ce modèle de dissipation viscoélastique est appliqué au cas de l'adhésion réversible, où expérimentalement nous mesurons la dynamique de pelage et de recollement sur un substrat viscoélastique. Cette extension à l'adhésion permet de relier les phénomènes interfaciaux en une compréhension générale
This thesis reveals two dissipative microscopic phenomena close to the contact line in the fields of capillarity and adhesion. The study is based on dynamic experiments and theoretical predictions. Experimental measurement of macroscopic quantities and the hydrodynamic theory give access to dynamic information located close to the contact line. The different dissipative phenomena, located close to the contact line, originate from the properties of the substrates on which the contact line moves. For a heterogeneous rigid surface, we have developed a rheological model of the contact line based on hydrodynamics, in order to theoretically establish the temporal evolution of the contact line and its deformations. A modal decomposition based on the reduction of the energy by the reaction path theory allows a quantitative prediction of the thermally activated dynamics of the contact line, in agreements with the experiment carried out. For a deformable substrate, based on the analysis of two different experiments of wetting dynamics and on the estimation of the dissipation in the substrate founded on its viscoelasticity, a general understanding of the dynamical behavior of contact lines on viscoelastic substrates is achieve. Finally, this viscoelastic model is applied to the case of weak adhesion, where experimentally we measured the peeling dynamics from a viscoelastic substrate. This extension to adhesion bridge the gap between different interfacial phenomena into a general understanding

Les solutions solides (1-x)Na0,5Bi0,5TiO3 (NBT) – xCaTiO3 (CT) ont été étudiées par diffraction des rayons X, spectroscopie Raman, microscopie électronique à balayage, spectroscopie d’impédance et DSC. Ce sont des matériaux présentant la structure cristalline pérovskite. L’étude révèle la complexité mais aussi la richesse des phénomènes physiques dans cette famille de composés : les séquences des transitions de phases, l’influence du dopant Ca2+ sur les propriétés physico-chimiques du matériau, la relation étroite entre propriétés diélectriques et caractéristiques structurales. Des solutions solides (1-x)NBT – xCT, avec 0 ≤ x ≤ 1,00, ont été synthétisées par voie solide classique puis frittées selon une procédure spécifique dans un milieu confiné pour éviter toute perte de sodium et de bismuth. Les caractéristiques cristallines des solides obtenus imposent clairement de distinguer trois domaines suivant les valeurs de x. En effet, pour les valeurs croissantes de x et à la température ambiante, on observe un premier domaine (Région I, pour x ≤ 0,07) dans lequel le solide obtenu est une solution solide de structure cristalline, de groupe d’espace R3c, identique à celle de NBT pur. Pour les valeurs les plus élevées de x (Région II, pour x ≥ 0,15), le solide obtenu est une solution solide de structure cristalline, de groupe d’espace Pnma, identique à celle de CT pur. Enfin, entre ces deux domaines (Région III, 0,09 ≤ x ≤ 0,13), les solides obtenus sont biphasés, R3c + Pnma, en se limitant aux appellations des groupes d’espacé des phases formées. Dans la région I, lors du chauffage, la séquence des transitions de phases R3c → P4bm → Pm3m est mise en évidence; les températures des transitions se déplacent vers les plus basses températures quand la concentration en Ca2+ augmente. Les solides sont ferroélectriques à l’ambiante puis développent un caractère relaxeur, par coexistence de deux phases, avec l’augmentation de la température. Dans la région II, les solides révèlent un comportement relaxeur dès l’ambiante. Une transition de phase diffuse au sein de la phase orthorhombique Pnma est toutefois mise en évidence ; le solide passe d’un état relaxeur à un état paraélectrique tout en conservant, a priori, la même structure cristalline. Le phénomène de relaxation dans ces composés est expliqué par la formation de micros ou nanorégions polaires. La région III, quant à elle, est caractérisée par l’apparition d’une hystérésis thermique mise en évidence pour la première fois ; elle est expliquée par la relation entre la microstructure cristalline et les propriétés diélectriques. Enfin, l’ensemble de nos résultats a été regroupé dans un diagramme de phase original en composition et en température
The solid solutions (1-x)Na0,5Bi0,5TiO3 (NBT) – xCaTiO3 (CT) were studied by X-ray diffraction, Raman spectroscopy, scanning electron microscopy, impedance spectroscopy and DSC. These materials have a perovskite crystalline structure. This study reveals not only the complexity but also the richness of physical phenomena in these compounds: phases transitions sequences, the Ca2+ effect on the physical-chemistry properties and the relation between dielectric properties and crystalline structure. Thereby, (1-x)NBT – xCT solid solutions (0 ≤ x ≤ 1.00) were synthesized by chemical solid route, then they were sintered by a particular procedure in order to avoid sodium and bismuth volatilization. The solid crystalline characteristics obtained prove clearly the necessity to distinguish three fields as a function of x values. First of all, for increasing x at room temperature, there is a first region so called region I (x ≤ 0.07), wherein the crystalline structure of solid solutions obtained has a space group R3c identical to that of pure NBT. For the highest values of x, (Region II, x ≥ 0.15), the solid obtained has a space group Pnma, identical to that of pure CT. Finally, between these two regions, (0.09 ≤ x ≤ 0.13), the solid solutions obtained are biphasic, R3c + Pnma, limited to appellations of the space groups formed phases. In region I, upon heating, phase transition sequence R3c → R3c + Pnma → Pnma was determined; the corresponding transition temperatures move to low values with increasing Ca2+ concentration. These solids are ferroelectric at room temperature and then develop a relaxor character, by coexistence of two phases, with increasing temperature. In region II, these solids reveal a relaxor behavior at room temperature. However, a diffuse phase transition within the orthorhombic phase Pnma has been identified; the solid changes from relaxor to paraelectric while maintaining the same crystal structure. This phenomenon was explained by the formation of micro or nano-polar regions. Region III, demonstrated for the first time, is characterized by thermal hysteresis, and explained by the relation between crystalline microstructure and dielectric properties. Finally, all our results were assembled in an original phase diagram as a function of concentration of Ca2+ dopant and temperature

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Conselho Nacional de Desenvolvimento Cient?fico e Tecnol?gico
The effect of confinement on the magnetic structure of vortices of dipolar coupled ferromagnetic nanoelements is an issue of current interest, not only for academic reasons, but also for the potential impact in a number of promising applications. Most applications, such as nano-oscillators for wireless data transmission, benefit from the possibility of tailoring the vortex core magnetic pattern. We report a theoretical study of vortex nucleation in pairs of coaxial iron and Permalloy cylinders, with diameters ranging from 21nm to 150nm, and 12nm and 21nm thicknesses, separated by a non-magnetic layer. 12nm thick iron and Permalloy isolated (single) cylinders do not hold a vortex, and 21nm isolated cylinders hold a vortex. Our results indicate that one may tailor the magnetic structure of the vortices, and the relative chirality, by selecting the thickness of the non-magnetic spacer and the values of the cylinders diameters and thicknesses. Also, the dipolar interaction may induce vortex formation in pairs of 12nm thick nanocylinders and inhibit the formation of vortices in pairs of 21nm thick nanocylinders. These new phases are formed according to the value of the distance between the cylinderes. Furthermore, we show that the preparation route may control relative chirality and polarity of the vortex pair. For instance: by saturating a pair of Fe 81nm diameter, 21nm thickness cylinders, along the crystalline anisotropy direction, a pair of 36nm core diameter vortices, with same chirality and polarity is prepared. By saturating along the perpendicular direction, one prepares a 30nm diameter core vortex pair, with opposite chirality and opposite polarity. We also present a theoretical discussion of the impact of vortices on the thermal hysteresis of a pair of interface biased elliptical iron nanoelements, separated by an ultrathin nonmagnetic insulating layer. We have found that iron nanoelements exchange coupled to a noncompensated NiO substrate, display thermal hysteresis at room temperature, well below the iron Curie temperature. The thermal hysteresis consists in different sequences of magnetic states in the heating and cooling branches of a thermal loop, and originates in the thermal reduction of the interface field, and on the rearrangements of the magnetic structure at high temperatures, 5 produce by the strong dipolar coupling. The width of the thermal hysteresis varies from 500 K to 100 K for lateral dimensions of 125 nm x 65 nm and 145 nm x 65 nm. We focus on the thermal effects on two particular states: the antiparallel state, which has, at low temperatures, the interface biased nanoelement with the magnetization aligned with the interface field and the second nanoelement aligned opposite to the interface field; and in the parallel state, which has both nanoelements with the magnetization aligned with the interface field at low temperatures. We show that the dipolar interaction leads to enhanced thermal stability of the antiparallel state, and reduces the thermal stability of the parallel state. These states are the key phases in the application of pairs of ferromagnetic nanoelements, separated by a thin insulating layer, for tunneling magnetic memory cells. We have found that for a pair of 125nm x 65nm nanoelements, separated by 1.1nm, and low temperature interface field strength of 5.88kOe, the low temperature state (T = 100K) consists of a pair of nearly parallel buckle-states. This low temperature phase is kept with minor changes up to T= 249 K when the magnetization is reduced to 50% of the low temperature value due to nucleation of a vortex centered around the middle of the free surface nanoelement. By further increasing the temperature, there is another small change in the magnetization due to vortex motion. Apart from minor changes in the vortex position, the high temperature vortex state remains stable, in the cooling branch, down to low temperatures. We note that wide loop thermal hysteresis may pose limits on the design of tunneling magnetic memory cells
Os efeitos de confinamento e o forte acoplamento dipolar na estrutura de v?rtices de nano-elementos ferromagn?ticos ? um tema de interesse atual, n?o apenas pelo valor puramente acad?mico, mas tamb?m pelo impacto em grande n?mero de dispositivos da ?rea de spintr?nica. Muitos dispositivos, como nano-osciladores para transmiss?o de dados sem fio, podem tirar grande proveito da possibilidade de controlar o padr?o magn?tico do n?cleo do v?rtice magn?tico. Relatamos um estudo te?rico da nuclea??o de v?rtices em um par de cilindros coaxiais de ferro e de Permalloy, com di?metros desde 21nm at? 150nm e espessuras de 12nm e de 21nm, separados por uma fina camada n?o-magn?tica. Cilindros isolados de ferro e Permalloy com espessura de 12nm n?o permitem a forma??o de v?rtices, enquanto que cilindros de espessura de 21nm possuem v?rtices quando isolados em reman?ncia. Nossos resultados indicam que ? poss?vel controlar a estrutura magn?tica dos v?rtices, bem como a chiralidade e polaridade relativa dos dois v?rtices, pela escolha apropriada dos valores dos di?metros e da separa??o dos dois cilindros ferromagn?ticos. Dependendo do valor da separa??o entre os cilindros, a intera??o dipolar pode induzir a forma??o de v?rtices em pares de cilindros de espessura de 12nm e inibir a forma??o de v?rtices em pares de cilindros de 21nm de espessura. Al?m disso, mostramos que a rota de prepara??o do estado magn?tico em campo nulo, pode ser usada para determinar a chiralidade e polaridade relativa dos dois v?rtices. Por exemplo: partindo da satura??o da magnetiza??o de um par de cilindros de ferro com di?metro de 81nm e espessura de 21nm, na dire??o do eixo f?cil da anisotropia uniaxial do ferro, resulta um par de v?rtices com n?cleo de 36nm, mesma chiralidade e mesma polaridade. Partindo do estado saturado em uma dire??o no plano e perpendicular ao eixo de anisotropia uniaxial, resulta um par de v?rtices com n?cleo de 30nm de di?metro, com chiralidade e polaridade opostas. Relatamos tamb?m um estudo te?rico do impacto de v?rtices magn?ticos na histerese t?rmica de um par de nanoelementos el?pticos de ferro, de 10nm de espessura, separados por um espa?ador n?o-magn?tico e acoplados com um substrato antiferromagn?tico por energia de 3 troca. Nossos resultados indicam que h? histerese t?rmica em temperatura ambiente (muito menor do que a temperatura de Curie do ferro), se o substrato for uma superf?cie n?o compensada de NiO. A histerese t?rmica consiste na diferen?a da sequ?ncia de estados magn?ticos nos ramos de aquecimento e resfriamento de um ciclo t?rmico, e se origina na redu??o do valor do campo de interface em altas temperaturas, e na reestrutura??o das fases magn?ticas impostas pela intera??o dipolar forte entre os dois nanoelementos de ferro. A largura da histerese t?rmica varia entre 500K ? 100K para dimens?es laterais de 125nm x 65nm e 145nm x 65nm. Focamos nos ciclos t?rmicos de dois estados especiais: o estado antiparalelo, com o nanoelmento em contato com o substrato alinhado na dire??o do campo de interface e o outro nanoelemento alinhado em dire??o oposta; e o estado paralelo em que os dois nanoelementos est?o alinhados com o campo de interface em temperaturas baixas. Esses s?o os dois estados magn?ticos b?sicos de c?lulas de mem?rias magn?ticas de tunelamento. Mostramos que a intera??o dipolar confere estabilidade t?rmica ao estado antiparalelo e reduz a estabilidade t?rmica do estado paralelo. Al?m disso, nossos resultados indicam que um par de cilindros com dimens?es de 125nm x 65nm, separados por 1.1nm, com campo de interface de 5.88kOe em temperatura de 100K, est? no estado paralelo. Essa fase se mant?m at? 249K, quando h? uma redu??o de 50% da magnetiza??o devido ? nuclea??o de um v?rtice no nanoelemento com superf?cie livre. Pequenas varia??es da magnetiza??o, devidas ao movimento do v?rtice, s?o encontradas no ramo de aquecimento, at? 600K. O estado encontrado em 600K se mant?m ao longo do ramo de resfriamento, com pequenas mudan?as na posi??o do v?rtice. A exist?ncia de histerese t?rmica pode ser um s?rio limite de viabilidade de mem?rias magn?ticas de tunelamento

As the major electricity consumer, electrical machines play a key role for global energy savings. Machine manufacturers put considerable efforts into the development of more efficient electrical machines for loss reduction and higher power density achievements. A consolidated knowledge of the occurring losses in electrical machines is a basic requirement for efficiency improvements. This thesis deals with iron losses in electrical machines. The major focus is on the influences of the stator core magnetic material due to the machine manufacturing process, temperature influences, and the impact of inverter operation. The first part of the thesis gives an overview of typical losses in electrical machines, with focus put on iron losses. Typical models for predicting iron losses in magnetic materials are presented in a comprehensive literature study. A broad comparison of magnetic materials and the introduction of a new material selection tool conclude this part. Next to the typically used silicon-iron lamination alloys for electrical machines, this thesis investigates also cobalt-iron and nickel-iron lamination sheets. These materials have superior magnetic properties in terms of saturation magnetization and hysteresis losses compared to silicon-iron alloys. The second and major part of the thesis introduces the developed measurement system of this project and presents experimental iron loss investigations. Influences due to machine manufacturing changes are studied, including punching, stacking and welding effects. Furthermore, the effect of pulse-width modulation schemes on the iron losses and machine performance is examined experimentally and with finite-element method simulations. For nickel-iron lamination sheets, a special focus is put on the temperature dependency, since the magnetic characteristics and iron losses change considerably with increasing temperature. Furthermore, thermal stress-relief processes (annealing) are examined for cobalt-iron and nickel-iron alloys by magnetic measurements and microscopic analysis. A thermal method for local iron loss measurements is presented in the last part of the thesis, together with experimental validation on an outer-rotor permanent magnet synchronous machine.

QC 20140516

Les systèmes de récupération d'énergie sont prometteurs pour l'auto-alimentation des dispositifs intégrés. Les matériaux pyroélectriques couplant un changement de température à un changement de polarisation électrique peuvent être utilisés pour la conversion de l'énergie thermique en énergie électrique sans nécessité de maintien de gradients thermiques qui constitue un inconvénient majeur dans les modules thermoélectriques compacts. Dans cette thèse, le PbZro.52Tio.48O3 (PZT) et le BaxSr1-xTiUO3 (x = l et x = 0.7) à fort coefficients pyroélectriques, sont choisis, élaborés en couches minces épitaxiées, caractérisés pour étudier leur potentiel de récupération d'énergie thermique. Ce travail comporte deux aspects : le premier consiste au développement et l'optimisation des conditions de croissance des hétérostructures intégrées et épitaxiées sur silicium. Le deuxième est focalisé sur l'étude des propriétés fonctionnelles (ferroélectriques, diélectriques et pyroélectriques) et à l' estimation du pouvoir de récupération d'énergie principalement des couches de PZT. Une corrélation entre ces deux aspects est ainsi présente. Un changement de la structure cristalline est montré sur les empilements intégrés sur Si, en comparaison avec des structures équivalentes réalisées sur substrat de STO. L'impact de ceci a été directement constaté sur les propriétés fonctionnelles des couches hétéroépitaxiées de PZT. Ainsi une anisotropie importante de ces propriétés a pu être mise en évidence, en complétant cette étude par des mesures dans le plan a l'aide de peignes interdigités. Ces observations ont été cohérentes avec les mesures de la diffraction des rayons X en fonction de la température. Par ailleurs, les différentes méthodes et configurations de mesures du coefficient pyroélectrique sur PZT ont permis une meilleure compréhension du phénomène et la distinction des diverses contributions existantes. La mesure statique indirecte issue de la variation de la polarisation rémanente en fonction de la température renseigne sur l'effet pyroélectrique intrinsèque (et secondaire). Cependant les mesures dynamiques du courant pyroélectrique pendant un changement de la température contiennent toutes les contributions pyroélectriques et non pyroélectriques, comme les effets extrinsèques et le courant de relaxation. Des mesures pyroélectriques dynamiques sous champ électrique, se rapprochant des conditions de cycles de récupération d'énergie thermique, ont permis de montrer que des courants de conduction apparaissaient même pour des bonnes couches de PZT diélectriques épaisses. Ces courants masquent les courants pyroélectriques et rendent l'application de générateur électrique par cycles thermodynamiques sous champ électrique rédhibitoire. Des composants passifs n'utilisant pas ou peu de champs électriques tels que des capteurs devront plutôt être envisagées
Due to the wasted heat in ever more compact microelectronic devices, the harvesting of thermal energy has become interesting for self-powering small devices. Consequently, pyroelectric materials witch couple a change in temperature to a change in electrical polarization may be used for the conversion of the thermal energy to an electric energy without necessity of maintaining thermal gradients that is a main drawback in compact devices with thermoelectric materials. In this thesis, PbZro.52Tio.48O3 (PZT) and BaxSr1-xTiUO3 (x = l and x = 0.7), with high pyroelectric coefficients are chosen, elaborated in thin epitaxial layers, characterized structurally and electrically to study their potential for thermal energy harvesting. This work has two aspects: the first consists in the development and optimization of the growth conditions of epitaxial heterostructures integrated on Si. The second one focuses on the study of the functional properties ( ferroelectric, dielectric and pyroelectric) and the estimation of the energy harvesting efficiency mainly of PZT layers. A correlation between these two aspects is then done. A change in the crystal structure is shown on the Si-integrated stacks in comparison with equivalent structures grown on STO substrate. This structural behavior impacts directly the functional properties of the heteroepitaxial layers of PZT. Th us, an important anisotropy of these properties was demonstrated and completed by a study of the in plane properties using measurements by interdigital capacitors. These observations were consistent with measurements of X - ray diffraction as a function of temperature. Otherwise, different methods and configurations of pyroelectric coefficient measurements on PZT have allowed a better understanding of the phenomenon and the distinction of the various existing contributions. The indirect static measurement resulting from the variation of the remnant polarization as a function of the temperature gives the intrinsic (and secondary) pyroelectric contributions. However, the dynamic measurements of the pyroelectric current during a change of the temperature contain all the pyroelectric and non-pyroelectric contributions, such as the extrinsic effects and the relaxation current . Dynamic pyroelectric measurements under an electric field are near to the conditions of thermal energy harvesting cycles. Conduction currents appeared, even for good layers of thick dielectric PZT, and mask the pyroelectric currents. This makes the application of electric generator by thermodynamic cycles under electric field prohibitive. Passive components using low or no electrical field such as sensors should be considered

[EN] The test for determining the resonance frequencies has traditionally been used to investigate the mechanical integrity of concrete cores, to assess the conformity of concrete constituents in different accelerated durability tests, and to ascertain constitutive properties such as the elastic modulus and the damping factor. This nondestructive technique has been quite appealed for evaluation of mechanical properties in all kinds of durability tests. The damage evolution is commonly assessed from the reduction of dynamic modulus which is produced as a result of any cracking process. However, the mechanical behavior of concrete is intrinsically nonlinear and hysteretic. As a result of a hysteretic stress-strain behavior, the elastic modulus is a function of the strain. In dynamic tests, the nonlinearity of the material is manifested by a decrease of the resonance frequencies, which is inversely proportional to the excitation amplitude. This phenomenon is commonly referred as fast dynamic effect. Once the dynamic excitation ceases, the material undergoes a relaxation process whereby the elastic modulus is restored to that at rest. This phenomenon is termed as slow dynamics. These phenomena (fast and slow dynamics) find their origin in the internal friction of the material. Therefore, in cement-based materials, the presence of microcracks and interfaces between its constituents plays an important role in the material nonlinearity. In the context of the assessment of concrete durability, the damage evolution is based on the increase of hysteresis, as a result of any cracking process. In this thesis three different nondestructive techniques are investigated, which use impacts for exciting the resonant frequencies. The first technique consists in determining the resonance frequencies over a range of impact forces. The technique is termed Nonlinear Impact Resonant Acoustic Spectroscopy (NIRAS). It consists in ascertaining the downward resonant frequency shift that the material undergoes upon increasing excitation amplitude. The second technique consists in investigating the nonlinear behavior by analyzing the signal corresponding to a single impact. This is, to determine the instantaneous frequency, amplitude and attenuation variations corresponding to a single impact event. This technique is termed as Nonlinear Resonant Acoustic Single Impact Spectroscopy (NSIRAS). Two techniques are proposed to extract the nonlinear behavior by analyzing the instantaneous frequency variations and attenuation over the signal ring down. The first technique consists in discretizing the frequency variation with time through a Short-Time Fourier Transform (STFT) based analysis. The second technique consists of a least-squares fit of the vibration signals to a model that considers the frequency and attenuation variations over time. The third technique used in this thesis can be used for on-site evaluation of structures. The technique is based on the Dynamic Acousto- Elastic Test (DAET). The variations of elastic modulus as derived through NIRAS and NSIRAS techniques provide an average behavior and do not allow derivation of the elastic modulus variations over one vibration cycle. Currently, DAET technique is the only one capable to investigate the entire range of nonlinear phenomena in the material. Moreover, unlike other DAET approaches, this study uses a continuous wave source as probe. The use of a continuous wave allows investigation of the relative variations of the elastic modulus, as produced by an impact. Moreover, the experimental configuration allows one-sided inspection.
[ES] El ensayo de determinación de las frecuencias de resonancia ha sido tradicionalmente empleado para determinar la integridad mecánica de testigos de hormigón, en la evaluación de la conformidad de mezclas de hormigón en diversos ensayos de durabilidad, y en la terminación de propiedades constitutivas como son el módulo elástico y el factor de amortiguamiento. Esta técnica no destructiva ha sido ampliamente apelada para la evaluación de las propiedades mecánicas en todo tipo de ensayos de durabilidad. La evolución del daño es comúnmente evaluada a partir de la reducción del módulo dinámico, producido como resultado de cualquier proceso de fisuración. Sin embargo, el comportamiento mecánico del hormigón es intrínsecamente no lineal y presenta histéresis. Como resultado de un comportamiento tensión-deformación con histéresis, el módulo elástico depende de la deformación. En ensayos dinámicos, la no linealidad del material se manifiesta por una disminución de las frecuencias de resonancia, la cual es inversamente proporcional a la amplitud de excitación. Este fenómeno es normalmente denominado como dinámica rápida. Una vez la excitación cesa, el material experimenta un proceso de relajación por el cual, el módulo elástico es restaurado a aquel en situación de reposo. Este fenómeno es denominado como dinámica lenta. Estos fenómenos ¿dinámicas rápida y lenta¿ encuentran su origen en la fricción interna del material. Por tanto, en materiales basados en cemento, la presencia de microfisuras y las interfaces entre sus constituyentes juegan un rol importante en la no linealidad mecánica del material. En el contexto de evaluación de la durabilidad del hormigón, la evolución del daño está basada en el incremento de histéresis, como resultado de cualquier proceso de fisuración. En esta tesis se investigan tres técnicas diferentes las cuales utilizan el impacto como medio de excitación de las frecuencias de resonancia. La primera técnica consiste en determinar las frecuencias de resonancia a diferentes energías de impacto. La técnica es denominada en inglés: Nonlinear Impact Resonant Acoustic Spectroscopy (NIRAS). Ésta consiste en relacionar el detrimento que el material experimenta en sus frecuencias de resonancia, con el aumento de la amplitud de la excitación. La segunda técnica consiste en investigar el comportamiento no lineal mediante el análisis de la señal correspondiente a un solo impacto. Ésta consiste en determinar las propiedades instantáneas de frecuencia, atenuación y amplitud. Esta técnica se denomina, en inglés, Nonlinear Single Impact Resonant Acoustic Spectroscopy (NSIRAS). Se proponen dos técnicas de extracción del comportamiento no lineal mediante el análisis de las variaciones instantáneas de frecuencia y atenuación. La primera técnica consiste en la discretización de la variación de la frecuencia con el tiempo, mediante un análisis basado en Short-Time Fourier Transform (STFT). La segunda técnica consiste en un ajuste por mínimos cuadrados de las señales de vibración a un modelo que considera las variaciones de frecuencia y atenuación con el tiempo. La tercera técnica empleada en esta tesis puede ser empleada para la evaluación de estructuras in situ. La técnica se trata de un ensayo acusto-elástico en régimen dinámico. En inglés Dynamic Acousto-Elastic Test (DAET). Las variaciones del módulo elástico obtenidas mediante los métodos NIRAS y NSIRAS proporcionan un comportamiento promedio y no permiten derivar las variaciones del módulo elástico en un solo ciclo de vibración. Actualmente, la técnica DAET es la única que permite investigar todo el rango de fenómenos no lineales en el material. Por otra parte, a diferencia de otras técnicas DAET, en este estudio se emplea como contraste una onda continua. El uso de una onda continua permite investigar las variaciones relativas del módulo elástico, para una señal transito
[CAT] L'assaig de determinació de les freqüències de ressonància ha sigut tradicionalment empleat per a determinar la integritat mecànica de testimonis de formigó, en l'avaluació de la conformitat de mescles de formigó en diversos assajos de durabilitat, i en la terminació de propietats constitutives com són el mòdul elàstic i el factor d'amortiment. Esta tècnica no destructiva ha sigut àmpliament apel·lada per a l'avaluació de les propietats mecàniques en tot tipus d'assajos de durabilitat. L'evolució del dany és comunament avaluada a partir de la reducció del mòdul dinàmic, produït com resultat de qualsevol procés de fisuración. No obstant això, el comportament mecànic del formigó és intrínsecament no lineal i presenta histèresi. Com resultat d'un comportament tensió-deformació amb histèresi, el mòdul elàstic depén de la deformació. En assajos dinàmics, la no linealitat del material es manifesta per una disminució de les freqüències de ressonància, la qual és inversament proporcional a l'amplitud d'excitació. Este fenomen és normalment denominat com a dinàmica ràpida. Una vegada l'excitació cessa, el material experimenta un procés de relaxació pel qual, el mòdul elàstic és restaurat a aquell en situació de repòs. Este fenomen és denominat com a dinàmica lenta. Estos fenòmens --dinámicas ràpida i lenta troben el seu origen en la fricció interna del material. Per tant, en materials basats en ciment, la presència de microfissures i les interfícies entre els seus constituents juguen un rol important en la no linealitat mecànica del material. En el context d'avaluació de la durabilitat del formigó, l'evolució del dany està basada en l'increment d'histèresi, com resultat de qualsevol procés de fisuración. En esta tesi s'investiguen tres tècniques diferents les quals utilitzen l'impacte com a mitjà d'excitació de les freqüències de ressonància. La primera tècnica consistix a determinar les freqüències de ressonància a diferents energies d'impacte. La tècnica és denominada en anglés: Nonlinear Impact Resonant Acoustic Spectroscopy (NIRAS). Esta consistix a relacionar el detriment que el material experimenta en les seues freqüències de ressonància, amb l'augment de l'amplitud de l'excitació. La segona tècnica consistix a investigar el comportament no lineal per mitjà de l'anàlisi del senyal corresponent a un sol impacte. Esta consistix a determinar les propietats instantànies de freqüència, atenuació i amplitud. Esta tècnica es denomina, en anglés, Nonlinear Single Impact Resonant Acoustic Spectroscopy (NSIRAS). Es proposen dos tècniques d'extracció del comportament no lineal per mitjà de l'anàlisi de les variacions instantànies de freqüència i atenuació. La primera tècnica consistix en la discretización de la variació de la freqüència amb el temps, per mitjà d'una anàlisi basat en Short-Time Fourier Transform (STFT). La segona tècnica consistix en un ajust per mínims quadrats dels senyals de vibració a un model que considera les variacions de freqüència i atenuació amb el temps. La tercera tècnica empleada en esta tesi pot ser empleada per a l'avaluació d'estructures in situ. La tècnica es tracta d'un assaig acusto-elástico en règim dinàmic. En anglés Dynamic Acousto-Elastic Test (DAET). Les variacions del mòdul elàstic obtingudes per mitjà dels mètodes NIRAS i NSIRAS proporcionen un comportament mitjà i no permeten derivar les variacions del mòdul elàstic en un sol cicle de vibració. Actualment, la tècnica DAET és l'única que permet investigar tot el rang de fenòmens no lineals en el material. D'altra banda, a diferència d'altres tècniques DAET, en este estudi s'empra com contrast una ona contínua. L'ús d'una ona contínua permet investigar les variacions relatives del mòdul elàstic, per a un senyal transitori. A més, permet la inspecció d'elements per mitjà de l'accés per una sola cara.
Eiras Fernández, JN. (2016). Studies on nonlinear mechanical wave behavior to characterize cement based materials and its durability [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/71439
TESIS
Premiado

碩士
國立清華大學
動力機械工程學系
95
Silicon piezoresistive pressure sensor technology has recently been gaining ground in its use in many advanced applications. In order to meet the needs of mechanical signal sensing in the industry, the different characteristics of pressure sensors need to be crucially taken into account. Therefore, our research employs simulations and experiments to determine the factors which produce the thermal hysteresis voltage in thermal cycle loadings. The purpose of this is to achieve measurement accuracy and avoid the thermal hysteresis phenomenon. The silicon piezoresistive pressure sensor is fabricated by the MEMS process, and utilizes the ion implant technique to form the piezoresistors on the silicon substrate. The main principle for operation is that the external pressure loading causes the deflection on the silicon membrane. Then a piezoresistive effect results in a resistance change in the piezoresistor on the silicon membrane. Using the Wheatstone Bridge transforms the mechanical signal to an output voltage in order to obtain the unknown pressure loading. However, the sensitivity of the piezoresistive pressure sensor is relatively high for the environmental temperature, thereby reducing accuracy. Therefore, the drifts of the output voltage in the same temperature result in a residual stress on the aluminum trace under thermal cycle loading. This situation is called the thermal hysteretic phenomenon, and the variation in output voltage is called the thermal hysteresis voltage. Given these, one goal of the current research is to analyze the relation between the residue stress of the trace and the thermal hysteresis voltage in order to reduce the measurement error in the thermal hysteresis phenomenon. The thermal hysteresis phenomenon is produced by the thermal expansion coefficients’ mismatch with the nonlinear properties of the aluminum trace in the thermal cycle loadings. Furthermore, this research will input the nonlinear properties of aluminum trace in ANSYS® and will base on the process of the pressure sensor to obtain the thermal hysteresis voltage. After several numerical analyses of the thermal hysteresis voltage, experiments will be performed to validate the simulation results. We will revise the process simulation for the etching effect in order to analyze the thermal hysteresis voltage’s differences. The research will also do a series of simulations and experiments on the creep effect that usually affects the thermal hysteresis voltage in the pressure sensor. To sum up, both the simulations and experiments systematically discuss the hysteresis phenomenon of the pressure sensor. The study’s conclusions will hopefully provide designers with relevant guidelines in the relative field.

This work presents a novel and elaborate framework to evaluate promising materials for magnetocaloric application. In the first step, the molecular meanfield theory (Bean-Rodbell model) is applied to simulate various magnetic systems covering the first and second order transition. The magnetic systems of second order transition are analyzed to find the appropriate composition for a magnetic field change comparable to practical values (up to 2 Tesla). Moreover, the intrinsic hysteresis occurring in first order materials is estimated, under certain magnetic field change, and its impact on the materials’ cooling capacity is calculated. The most efficient candidate in terms of cooling capacity is detected via the comparison between materials of various transition behavior. A set of samples of La2/3(Ca1-xSrx)1/3MnO3 magnetocaloric family with transitions ranging from second to first order is produced and the data is fitted with the simulation tool to parameters such as spin value and the magnetovolume coupling parameter. Magnetic systems similar to experimental samples are simulated and the cooling capacity of the simulated system and experimental samples are compared to verify the theoretical model. The temperature dependence of the thermal conductivity of the La-Ca-Sr-Mn-O and Mn-Fe-P-Si systems are measured and show up to 50% change within the operating temperature ranges along with fully contrasting behaviour for the two families of magnetocaloric materials. It is also shown that the temperature dependence of thermal conductivity is coordinated with the order of the magnetic transition. By synthesizing La1-x(Ce, Pr, Nd)xFe11.6Si1.4 samples via a combination of induction melting and suction casting techniques, the substitution range is expanded up to x=0.4. The impact of La substitution on the magnetocaloric characteristics including magnetic entropy change, adiabatic temperature change, Tc and hysteresis is investigated. Finally, the phase transition order is studied using methods based on field dependence of magnetocaloric effect (including the Bean-Rodbell model).
Este trabalho apresenta uma abordagem inovadora para a avaliação de materiais promissores para aplicações magnetocalóricas. Inicialmente, a teoria do campo médio molecular (modelo Bean-Rodbell) é aplicada para simular vários sistemas magnéticos que descrevem transições de primeira e de segunda ordem. Os sistemas magnéticos de transição de segunda ordem são analisados para encontrar a composição com performance otimizada para uma mudança de campo magnético comparável aos valores práticos (até 2 Tesla). Além disso, a histerese intrínseca que ocorre em materiais de primeira ordem é estimada, sob certas alterações de campo magnético, e o seu impacto na capacidade de arrefecimento dos materiais é calculado. O candidato mais eficiente em termos de capacidade de refrigeração é detectado através da comparação entre materiais com vários comportamentos diferentes na transição. Um conjunto de amostras da família magnetocalórica La2/3(Ca1-xSrx)1/3MnO3 com transições variando de segunda e primeira ordem foi produzido e os dados foram ajustados com a ferramenta de simulação e parâmetros como valor de spin e o parâmetro de acoplamento magneto-volume. Sistemas magnéticos semelhantes às amostras experimentais foram simulados e a capacidade de arrefecimento do sistema simulado e amostras experimentais foram comparadas para verificar o modelo teórico. A dependência da temperatura da condutividade térmica dos sistemas La-Ca-Sr-Mn-O e Mn-Fe- P-Si foi medida e mostra alterações de até 50% dentro das faixas de temperatura de operação, além de um comportamento totalmente contrastante para as duas famílias de materiais magnetocalóricos. Também é mostrado que a dependência na temperatura da condutividade térmica é coordenada com a ordem da transição magnética. Sintetizando a família de amostras de La1-x(Ce, Pr, Nd)xFe11.6Si1.4 por meio de uma combinação de técnicas de fusão por indução e fundição por sucção, a faixa de substituição é expandida até x = 0.4. O impacto da substituição de La nas características magnetocalóricas, incluindo alteração da entropia magnética, mudança de temperatura adiabática, Tc e histerese, é investigada. Finalmente, a ordem de transição de fase é estudada usando métodos baseados na dependência de campo do efeito magnetocalórico (incluindo o modelo Bean-Rodbell).
Programa Doutoral em Ciência e Engenharia de Materiais

Matric suction has proven to be a key parameter in the study and application of soil mechanics for unsaturated soils. Field measurements of suction are necessary in many engineering analyses, such as the prediction of total heave, the analysis of the slope stability due to changes in soil suction, and the monitoring of moisture flux through a soil cover or barrier structure used to impede contaminant transport. There are a number of methods to measure soil suction in the field. The thermal conductivity sensor proves to be one of the most promising means of in situ suction measurement. The thermal conductivity sensor measures matric suction by measuring the rate of dissipation of thermal energy in the ceramic sensor tip. The thermal diffusivity. of the ceramic is dependent upon the water content of the ceramic. The water content is a function of the matric suction in the surrounding soils. This function is referred to as capillary function or soil-water characteristic curve and exhibits hysteresis. In other words, the same value of matric suction may correspond to different ceramic water contents, thus different sensor outputs, depending upon the drying and wetting history. The objective of this study is to investigate the properties of capillary hysteresis of the sensor ceramic and its effects on the measurement of matric suction. Two groups of laboratory tests involving drying and wetting processes were carried out; one group measured the relationship between water content and matric suction of the sensor ceramics, the other group measured the relationship between sensor output and matric suction for a newly developed sensor. The result shows that, although the hysteresis loop is relatively narrow compared with those of coarse­-grained materials found in the literature, the effects of capillary hysteresis on suction measurement using the thermal conductivity sensor are not negligible. If the capillary hysteresis is not taken into account, the maximum possible relative error of suction measurement caused by the capillary hysteresis is from 24% to 50% for the sensors used in the tests. The problems associated with the conventional method of calibration are also discussed in the thesis. To make the suction measurement more accurate, the sensor output versus suction relationship of each of the possible wetting and drying processes should be measured in calibrating the sensor. However this calibration is impractical. Therefore, it is desirable to predict the hysteresis curves from limited measured data using a mathematical procedure. There are a number of models found in the literature to simulate the capillary hysteresis of a porous material. Some of these models were examined using the experimental data of the sensor ceramic. It was found that the models in the literature either require a large amount of measured data to make the prediction, or fail to reproduce the measured curves of hysteresis. Therefore, an analytical approximation was developed which used a curve fitting method to fit the measured main drying curve and to predict the main wetting curve and the primary scanning curves. Based on the above experimental and modeling studies, suggestions were made on the calibration of the sensor.

Antifreeze proteins (AFPs) help cold-adapted organisms survive below 0 ◦C by binding to and inhibiting the growth of ice crystals. In this way, AFPs depress the freezing point of aqueous fluids below the melting point of ice (thermal hysteresis; TH). They also have the ability to inhibit ice recrystallization in the frozen state (ice recrystallization inhibition; IRI). Some AFPs show an order of magnitude higher TH activity than others, and are termed ‘hyperactive’. One of the objectives of this thesis was to see if IRI activities of the hyperactive AFPs are also an order of magnitude higher than the moderately active AFPs. Using a capillary-based assay for IRI, the activities of three hyperactive and three moderately active AFPs were determined. There was no apparent correlation between hyperactivity in TH and high IRI activity. However, mutations of residues on the ice-binding face (IBF) of both types of AFP reduced IRI and TH activities to a similar extent. In this way, the use of IBF mutant AFPs showed that the IBF responsible for an AFP’s TH activity is also responsible for its IRI activity. Analysis of the diverse AFP structures solved to date indicate that their IBFs are relatively flat, occupy a significant proportion of the protein’s surface area and are more hydrophobic than other surfaces of the protein. The IBFs also often have repeating sequence motifs and tend to be rich in alanine and/or, threonine. The de novo design of an ice-binding protein was undertaken using these features to verify the underlying physicochemical requirements necessary for a protein’s interaction with ice. Using site-directed mutagenesis, a total of sixteen threonine substitutions were made on one of the four faces of a cyanobacterial protein with no endogenous TH activity. The inclusion of eight paired threonines on one face of this quadrilateral helix gave the engineered protein low levels of TH activity, but at the cost of destabilizing the structure to some extent. The results of this study have validated some of the properties needed for the ice-binding activity of AFPs.
Thesis (Master, Biochemistry) -- Queen's University, 2010-01-29 17:37:24.322

碩士
國立交通大學
機械工程系所
106
Around 81% of electricity is provided by fossil fuel. Fossil fuel could cause severe environmental pollution and deteriorate the greenhouse effect. Therefore, developing renewable energy becomes an urgent issue. Most of the renewable energy comes from solar energy. Photovoltaics would be limited by the diurnal limit of solar energy. On the contrary, concentric solar power plants would not be restricted by the diurnal limit because it can store solar energy as heat. However, concentric solar power plants occupy a large size of land and can only store a limited amount of heat. Therefore, adding phase change materials would be a solution to enhance the heat storage. During the applications of the phase change materials, a phenomenon called hysteresis temperature is widely observed. Hysteresis temperature is defined as the temperature difference between the melting point and crystallization point of a phase change material. Hysteresis temperature would lower the efficiency of the system, cause extra heat loss, and diminish the advantage of the phase change material. In this work, core-shell particles with two different shell materials (Zn microparticles coated with TiO2 and Al2O3) have been synthesized and investigated. The synthesized particles showed good thermal stability. Moreover, Zn microparticles coated with Al2O3 perform could lower the hysteresis temperature. Besides, the mechanism causing the hysteresis was investigated and it was found that the hysteresis resulted from heating rate effect and heterogeneous nucleation. Moreover, a thermal conductivity measurement system has been built. After the ultrasonication procedure, 1.2 vol.% Hitec doped with Al2O3 nanoparticle showed the highest thermal conductivity in this work. The thermal conductivity was 0.908 ± 0.005 W/m-K and was 21% enhancement compared with that of pure Hitec. The reason for the enhancement of thermal conductivity is that the nanoparticles in the fluid disperse very well after ultrasonication procedure. In addition, the measurements of the specific heat capacity of Hitec nanofluid have also been done. Based on the results, the specific heat capacity of Hitec nanofluid decreased with the increasing concentration. Compared to Hitec, Al2O3 nanoparticles have lower specific heat capacity, the addition of the Al2O3 nanoparticles will lower the specific heat capacity. The result in this work would be able to apply on the concentric power plants to enhance the heat storage and the heat transfer.

The central concern of this thesis is the study of non-equilibrium behaviour in magnetic materials and its interpretation within the framework of the Preisach model of hysteresis. Comprehensive experimental characterizations of the field and temperature and time dependence of a suite of standard magnetic response functions have been performed on a variety of magnetic materials, including a naturally occurring mineral of nanodimensional titanomagnetite particles embedded in volcanic glass, a compressed powder of nanodimensional magnetite particles immobilized in an organic binder, a thin film of nanodimensional Fe particles embedded in alumina, and a series of sintered, bond-disordered CaxSr1-xRuO3 ferromagnets. The measurements were compared with numerical simulations based on a model Preisach ensemble of thermally activated two-level subsystems, characterized individually by a double well free energy profile in a two-dimensional configuration space, an elementary moment reversal, a dissipation field and a bias field, and characterized collectively by a distribution of these characteristic fields. Our efforts were concentrated on two principal spheres of investigation. (1) By performing detailed numerical simulations of the relaxation response of model Preisach collections of two-level subsystems under the same field and temperature protocols used to probe experimentally the relaxation dynamics of spin glasses, we have been able to show that aging, memory and rejuvenation effects are ubiquitous features of all materials which possess a broad distribution of free energy barriers which block the approach to thermal equilibrium. (2) We propose a general strategy for isolating and quantifying the two principal mechanisms, thermal fluctuations and barrier growth, which are jointly responsible for shaping the measured temperature dependence of the magnetic properties of all magnetic materials which exhibit a history dependent response to an external field excitation, and is based on the analysis of viscosity isotherms and, in particular, on a plot of T ln(tr/0) versus Ha , where tr is the time at which a viscosity isotherm measured in a field Ha at temperature T reverses sign. When thermal activation dominates barrier growth, this plot will yield a universal curve while, in the opposite limit the plot fractures into a family of isothermal curves. The strategy is applied to the analysis of each magnetic material listed above.
February 2009