Mecanismos de difusão de energia vibracional em biomoléculas têm sido relacionadas a função, alosterismo e sinalização intramolecular. Neste trabalho nós utilizamos uma metodologia computacional para analisar o fluxo de energia em proteínas. Simulações de Dinâmica Molecular são utilizadas para o estudo de difusão térmica, provendo artifícios que não são possíveis experimentalmente: a proteína é esfriada a baixas temperaturas e apenas um resíduo é aquecido através do acoplamento de um banho térmico. Consequentemente, o calor flui do aminoácido aquecido para a proteína, revelando os caminhos da difusão da energia vibracional. Pelo fato de que proteínas termoestáveis possam ter particulares mecanismos de relaxação, distribuição e dissipação da energia vibracional, elas são sistemas interessantes para serem utilizadas por este método. Um padrão de difusão de calor de uma proteína termofílica pode ser identificado e comparado com outro de uma proteína homóloga mesofílica. Aqui estudamos um conjunto de proteínas em particular, as pertencentes à família 11 de Xilanases. O mapa de difusão térmica obtido da proteína no vácuo mostrou diferenças entre xilanases mesofílica e termofílica, e termofílica e hipertermofílica: qualquer que seja o resíduo aquecido, aminoácidos específicos respondem com alta temperatura. Esta resposta em alta energia de certas regiões é decorrente de processos de relaxação. Simulações adicionais e outras análises, como da mobilidade de cada resíduo, levam à hipótese que estas regiões de superfície possuem grande flexibilidade e uma importante interação estrutural com a água. Mapas de difusão térmica para duas proteínas homólogas, diferindo em apenas 7 mutações, sendo 6 delas no N-terminal, apresentam-se diferentes nesta região. Em especial, a mutação Ser35Glu se destaca tanto no mapa quanto em outras medidas realizadas, apresentando-se na proteína mais estável com um maior nível de mobilidade, solvatação e energia de interação. Simulações em água não resultaram em padrões de difusão diferentes, por não apresentarem processos de relaxação. Entretanto, elas evidenciaram as mesmas regiões frias para cinco xilanases da família 11, especialmente o núcleo e a região de ligação do substrato, sugerindo uma possível característica funcional de difusão de calor. Por fim, evidenciado pelos mapas, observou-se que a região do cordão de xilanases termoestáveis, em especial a hipertermoestável, é maior se comparado à proteína mesofílica. Desta forma, através de comparações entre mapas de difusão e estruturas de proteínas similares, esta metodologia pode sugerir novas abordagens em engenharia racional de proteínas com estabilidade modulada. / Vibrational energy dissipation in biomolecules have been related to function, in particular alosterism and intramolecular signaling. In this work, we use a computational method to analyze the energy flux through proteins. Molecular Dynamics simulations are used to study thermal diffusion in protein structure, in an artificial way which is not accessible experimentally: the protein is cooled down to very low temperatures and a single residue is heated by coupling a thermal bath to it. Heat flows from the heated residue to the rest of the protein, revealing the paths of vibrational energy dissipation. Since thermostable proteins may have specific mechanisms for vibrational energy relaxation, dissipation and distribution, they are interesting subjects for the application of the present methodologies. The heat dissipation patterns of thermophilic proteins can be compared to the ones of less stable structures. Here, we focus in a specif set of proteins known as Xylanases of Family 11. The thermal diffusion maps obtained for hiperthermostable, thermostable and mesphilic xylanases in vacuum were different, some of them displaying apparent thermal responses whatever the heated residue. These high temperature regions appeared because of differential structural relaxation processes in each structure. The analysis of the mobility of the structures in equilibrium simulations revealed that these regions are mobile and belong to the surface of the proteins, thus interacting significantly with water molecules. Thermal diffusion maps for homologous proteins differing in only 7 residues, being 6 of them at the N-terminal region of the proteins, were different in this region. One particular mutation was determined to be more mobile in the less thermostable protein, as well as displaying a higher solvation and stronger interaction energies with remaining protein structure. Thermal diffusion simulations in water were not able to discern any difference between the structures, particularly because the relaxation processes observed in vacuum were suppressed. Nevertheless, these maps reveal that every Xylanase display the same cold regions, which were observed to belong the protein core and the catalytic site, suggesting that thermal diffusion may have some functional role. Finally,we observed that a loop which relaxed systematically in thermostable protein resulting in high temperatures is larger than in non-thermostable structures. The addition of the loop to nonthermostable proteins make the maps equivalent. Therefore, the comparison of the thermal diffusion maps of similar structures highlight important structural differences which may be useful for providing insights into the design of proteins with modulated thermal stability.

<p>The formation of surface films on electrodes in contact with non-aqueous electrolytes in lithium-ion batteries has a vital impact on battery performance. A basic understanding of such films is essential to the development of next-generation power sources. The surface chemistry, morphology and thermal stability of two typical anode and cathode materials, graphite and LiNi_0.8Co_0.2O₂, have here been evaluated by X-ray photoelectron spectroscopy (XPS), X-ray diffraction, scanning electron microscopy and differential scanning calorimetry, and placed in relation to the electrochemical performance of the electrodes. </p><p>Chemical and morphological information on electrochemically formed graphite surface films has been obtained accurately by combining XPS measurements with Ar⁺ ion etching. An improved picture of the spatial organisation, including thickness determination of the surface film and characterisation of individual component species, has been established by a novel sputtering calibration procedure. The stability of the surface films has been shown to depend strongly on temperature and choice of lithium salt. Decomposition products from elevated-temperature storage in different electrolyte systems were identified and coupled to effects such as capacity loss and increase in electrode resistance. Different decomposition mechanisms are proposed for surface films formed in electrolytes containing LiBF₄, LiPF₆, LiN(SO₂CF₃)₂ and LiCF₃SO₃ salts.</p><p>Surface film formation due to electrolyte decomposition has been confirmed on LiNi_0.8Co_0.2O₂ positive electrodes. An overall surface-layer increase with temperature has been identified and provides an explanation for the impedance increase the material experiences on elevated-temperature storage. </p><p>Surface phenomena are clearly major factors to consider in selecting materials for practical Li-ion batteries.</p>

<p><font face="Times-Roman"> <p align="left">The growth of the Internet has led to many interesting developments for both educational and commercial purposes. In this project an attempt was made to use the Internet for a research purpose to facilitate the determination of the thermal stability of diffusion barriers. Another purpose of this thesis is to investigate the teaching and training use of the Internet through the development of online interactive tools and activities as well as materials. The training aspects are mentioned as it is hoped that this thesis can serve as a form of documentation of the use of the Internet, while the central part was the determination of thermal stability of TiN, TaN and TiW diffusion <font face="Times-Roman">barriers on Ag.</font></p> </font></p>

The formation of surface films on electrodes in contact with non-aqueous electrolytes in lithium-ion batteries has a vital impact on battery performance. A basic understanding of such films is essential to the development of next-generation power sources. The surface chemistry, morphology and thermal stability of two typical anode and cathode materials, graphite and LiNi0.8Co0.2O2, have here been evaluated by X-ray photoelectron spectroscopy (XPS), X-ray diffraction, scanning electron microscopy and differential scanning calorimetry, and placed in relation to the electrochemical performance of the electrodes. Chemical and morphological information on electrochemically formed graphite surface films has been obtained accurately by combining XPS measurements with Ar+ ion etching. An improved picture of the spatial organisation, including thickness determination of the surface film and characterisation of individual component species, has been established by a novel sputtering calibration procedure. The stability of the surface films has been shown to depend strongly on temperature and choice of lithium salt. Decomposition products from elevated-temperature storage in different electrolyte systems were identified and coupled to effects such as capacity loss and increase in electrode resistance. Different decomposition mechanisms are proposed for surface films formed in electrolytes containing LiBF4, LiPF6, LiN(SO2CF3)2 and LiCF3SO3 salts. Surface film formation due to electrolyte decomposition has been confirmed on LiNi0.8Co0.2O2 positive electrodes. An overall surface-layer increase with temperature has been identified and provides an explanation for the impedance increase the material experiences on elevated-temperature storage. Surface phenomena are clearly major factors to consider in selecting materials for practical Li-ion batteries.

The different topics of this thesis include high-temperaturestable fiber Bragg gratings, photosensitivity and fiber basedcomponents. Fiber Bragg gratings (FBG) are wavelength dispersiverefractive index structures manufactured through UV exposure ofoptical fibers. Their applications range from WDM filters,dispersion compensators and fiber laser resonators fortelecommunication applications to different types of point ordistributed sensors for a variety of applications. One aim of this thesis has been to study a new type of FBGreferred to as chemical composition grating. These gratingsdiffer from other types of FBG in that their refractive indexstructure is attributed to a change in the chemicalcomposition. Chemical composition gratings have shown to beextremely temperature stable surviving temperatures in excessof 1000 oC. Photosensitivity of pure silica and germanium-dopedcore fibers in the presence of hydroxyl groups has also beenstudied and different types of fiber based components have beendeveloped. The main result of the thesis is a better understanding ofthe underlying mechanism of the formation of chemicalcomposition gratings and their decay behavior at elevatedtemperatures. The refractive index modulation is caused by aperiodic change in the fluorine concentration, which has beenverified through time-of-flight secondary-ion-mass spectrometryand through studies of the decay behavior of chemicalcomposition gratings. A model based on diffusion of dopants hasbeen developed, which successfully predicts the thermal decayat elevated temperatures. Studies of the dynamics of chemicalcomposition grating formation have resulted in a manufacturingtechnique that allows for reproducible gratingfabrication. The main results regarding photosensitivity is a method tosignificantly increase the effect of UV radiation on standardtelecommunications fiber. The method, referred to asOH-flooding, has also been applied to pure-silica core fibersresulting in the first report of strong grating formation insuch fibers. Finally, research into different schemes for developingfiber-based components has resulted in two types of singlefiber integrated Mach-Zehnder interferometers; one passiveinterferometer that can be used as an optical filter and oneactive interferometer controlled with internal metalelectrodes. Keywords:optical fibers, fiber Bragg gratings,photosensitivity, thermal stability, fiber sensors, chemicalcomposition gratings, fiber components, Mach-Zehnderinterferometer, optical switch, optical modulator. / QC 20100607

No description available.

This research explores the thermal stability of ZrCrAlN material system. For this purpose fourteen different compositions of ZrCrAlN coatings were deposited onto tungsten carbide substrates by using reactive cathodic arc evaporation. These compositions were further annealed at 800oC, 900oC, 1000oC and 1100oC temperatures. EDS was employed to specify the compositions. The crystal structure of the coatings were analysed by XRD, and the hardness of these coatings was determined by Nanoindentation. The experimental findings reported a significant age hardening of Zr0.16Cr0.12Al0.72N and a delayed h-AlN formation in Zr0.07Cr0.40Al0.52N. ZrCrAlN was thus proved to be thermally stable. / Multifilms,A4:2 Growth and characterization of Multicomponent Nitrides by Magnetron Sputtering and Arc evaporation

Grouper nervous necrosis viruses belong to the Betanodavirus genus in the Nodaviridae family that is a group of small, non-enveloped icosahedron viruses. More than 30 species of fish are infected by the betanodaviruses, which cause massive mortality in hatchery-reared larvae and juveniles. The infection causes great economic losses to aquaculture and sea-ranching. To study the effects of N-terminus and disulfide bonds of capsid protein on particle formation and thermal stability of grouper nervous necrosis virus, virus-like particles (VLPs) of dragon grouper nervous necrosis virus (DGNNV) were used. Deletion of 35 residues at the N-terminus completely ruined the VLP assembly. When deletions were restricted to 4, 16, or 25 N-terminal residues, the assembly of VLPs remained. Site-directed mutagenesis was used to investigate the effects of N-terminus of capsid protein on particle formation and thermal stability of grouper nervous necrosis virus. Althought all arginine mutants could produce VLPs, the relative amounts and thermal stabilities of arginine-mutated VLPs were decrease. The VLPs from £GN25-R29A and £GN25 mutants have similar structural properties on particle formation and thermal stability. Therefore, the effects of Arg29 mutations are negligible. The relative amounts and thermal stabilities of VLPs from £GN25-R30A and £GN25-R31A mutants are lower than £GN25-R29A VLP. When 25 amino acids at N-terminus of DGNNV capsid protein were removed, Arg30 and Arg31 are important for particle formation and particel stability. Although particle could form as 12 positively charged amino acids were lost (¡µN25-R293031A), the efficiency of particles assembly were decrease to 1.2 ¡Ó 0.9% as compare to wild-type VLPs (WT-VLPs). Site-directed mutagenesis and chemical reducing reagents were used to investigate the roles of disulfide bonds in particle formation and thermal stability of grouper nervous necrosis virus. The homogeneous particles from C187A, C331A and C187A/C331A mutants are indistinguishable from the native virus and WT-VLPs in their sizes and shapes. C115A and C201A mutants could not produce VLPs. The dissociated capsomers from arginine- or cysteine-mutant VLPs all can be reassembled to icosahedrons with efficiencies as high as 100%. When VLP particles are pre-fabricated, the reducing agent cannot disrupt the VLP icosahedron structure. The thiol reduction only caused effects on the disulfide linkages inside the icosahedrons. £]-mercaptoethanol-treated WT-VLPs could not tolerate the thermal effects at a temperature higher than 70¢XC. Once the disulfide linkages in dissociated capsomers were entirely disrupted by £]-mercaptoethanol treatment, the resulting capsomers could not reassemble back to icosahedron particles.These results indicated that Cys115 and Cys201 were essential for capsid formation of DGNNV icosahedron structure in de novo assembly and reassembly pathways, as well as for the thermal stability of pre-fabricated particles. In the observation of Cryo-EM, the shapes and sizes of the N-terminus truncated particle (£GN25-VLP) are indistinct from the full-length particle (WT-VLP). The maximum diameter of DGNNV is approximately 380 Å. Like that of the insect nodaviruses, the surface morphologies of £GN25-VLP and WT-VLP are consistent with a T = 3 quasi-equivalent lattice. The protrusions (~154 to 192 Å), the inner shell of the capsid (~112 to 154 Å), and the RNA (¡Õ112 Å) were observed in the DGNNV structure. The protrusion domain is consisting of three capsid subunits, and the interactions between these subunits are different. Deletion of 25 residues at the N-terminus did not affect VLPs formation and the structure of £GN25-VLP is similar to WT-VLPs. Resolutions was calculated by Fourier shell correlation, and the resolution of WT-VLPs and £GN25-VLPs is 6.5Å and 11.8Å, respectively.

In this study, shelf life of three different crosslinked double base (XLDB) propellants stabilized with 2-nitrodiphenylamine (2-NDPA) and n-methyl-4-nitroaniline (MNA) were determined by using the stabilizer depletion method. Depletions of the stabilizers were monitored at different aging temperatures using High Performance Liquid Chromatography (HPLC). Kinetic models of pseudo zero, pseudo first, pseudo second and shifting order were used to find the best model equation that fits the experimental data. The rates of depletion of stabilizers were calculated at 45, 55 and 65&deg / C based on the best fit kinetic models. Using the rate constants at different temperatures, rate constants at room temperature were calculated by Arrhenius equation. The activation energies and frequency factors for the depletion of 2-NDPA and MNA were obtained for all XLDB propellants. Moreover, the results were evaluated based on the NATO standard / STANAG 4117 and the propellants were found stable according to the standard. Vacuum thermal stability (VTS) tests were also conducted to evaluate the stability of XLDB propellants. The propellant that includes the stabilizer mixture of MNA and 2-NDPA was found to have less stability than the propellants that include 2-NDPA only. However, there were rejection (puking) and migration of stabilizer derivatives for the aged samples of propellants that were stabilized with only 2-NDPA. Moreover, formation of voids and cracks were observed in block propellant samples due to excess gas generation.

Inspired by Poirier¡¦s mechanism of self-assembled monolayers (SAMs) formation, we realized that observation of the change of molecular orientation relative to the surface using a suitable spectroscopic method might be able to reveal the self ¡V assemblied processes. We mimicked the SAMs formation under UHV conditions, the Reflection Absorption Infrared Spectroscopy (RAIRS) and Temperature-Programmed Desorption / Reaction Spectrometry (TPD/R) were utilized to understand the adsorption, self-assembling and thermal stability after vapor desorption of 1H, 1H, 2H, 2H-perfluorodecanethiol on Cu(111). At 100K, the adsorption of 1H, 1H, 2H, 2H-perfluorodecanethiol was entirely molecular. As the surface was annealed above 220K, the cleavage of the S ¡V H bonds occurred to afford chemisorbed thiolates. By comparisons of spectra to the SAMs / Au(111) and the bulk compound, forming of an orderly and densely packed monolayer on Cu(111) was inferred. Focusing on room temperature deposition experiments, We found that the increase in ratios of I£h(CF2 ¡ü chain) (bands in 1300cm-1 ~ 1400 cm-1) to I£h(CF2 ¡æ chain) (bands in 1100cm-1 ~ 1300 cm-1) as a function of exposure implicates a transition from that the lying ¡V down geometry to the more upright orientation relative to the surface as we anticipated, the phase transformation concomitant with the SAMs formation could be identified by RAIRS. By TPD/R measurements, the molecular desorption occurred at 220K and 290K, corresponding to the condensed multilayer and a physisorbed layer on top of the chemisorbed monolayer, respectively. Furthermore, the monolayer would undergo the S ¡V C bond dissociation to sender surface ¡V bound semifluorinated alkyl groups and sulfur atoms. The semifluorinated decene and decane were evolved above 360K as results of £] ¡V hydride elimination and hydrogen addition.