Dissertations / Theses: 'Solid-state mechanisms'

1

Schmitz, Guido [Verfasser]. "Microstructural mechanisms of solid state interreactions / Guido Schmitz." Münster : Universitäts- und Landesbibliothek der Westfälischen Wilhelms-Universität, 2004. http://d-nb.info/1042742332/34.

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2

Purser-Hallard, Beatrice. "Kinetics and mechanisms of solid-state phase transitions and reactions." Thesis, Open University, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.422026.

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3

Meere, Gerard Martin. "Non-linear diffusion mechanisms in compound semiconductors." Thesis, University of Nottingham, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.335789.

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4

Fitzgerald, Emma T. "Studies of surface reaction mechanisms for chemical beam epitaxial growth." Thesis, University of Oxford, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.317723.

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5

Chen, Giin-Shan. "Mechanisms of direct electron beam nanolithography and nanostructure fabrication methods." Thesis, University of Cambridge, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.321028.

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6

French, Catherine Louise. "Surface science investigations of reaction mechanisms in semiconductor growth and etching." Thesis, University of Oxford, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.305988.

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7

Kirk, Andrew Graham. "An investigation of electrical dissipation mechanisms in high-Tâ†c superconductors." Thesis, University of Nottingham, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.240191.

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8

Brown, Simon D. "Magnetization reversal mechanisms and remanent states in magneto-optic thin films." Thesis, Keele University, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.259551.

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9

Murrell, M. P. "A study of the oxidation mechanisms of silicon, using nuclear reaction analysis." Thesis, University of Oxford, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.293545.

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10

Spruce, G. "A study of parameters affecting switching mechanisms in chiral smectic liquid crystals." Thesis, Glasgow Caledonian University, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.376568.

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11

Zong, Zhixin. "Studies on the mechanisms of solid state and solution instability of drugs." Diss., University of Iowa, 2011. https://ir.uiowa.edu/etd/2795.

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The overarching objective of this thesis is to demonstrate a systematic approach for addressing the instability issues associated with low limit degradants by developing quantitative degradation models that incorporate key instability determinants into predictive equations. Chlorhexidine was used as model compound in aqueous solution to demonstrate the application of the predictive models to issues of formulation design and manufacturing. Chorhexidine degrades to p-chloroaniline, a well-established toxicant, by various pH-dependent pathways. In acidic conditions, the direct formation of p-chloroaniline from chlorhexidine is the major pathway whereas the indirect formation of p-chloroaniline via p-chlorophenylurea is the main alkaline pathway. Rate laws and mechanisms for each pathway were presented. Shelf life predictions equations for chlorhexidine formulations were derived based on the kinetics of p-chloroaniline appearance as a function of formulation strength, solution pH, bulk chlorhexidine purity and storage temperature. The pH range for optimal shelf-life was 5.0 to 5.5. Simple extraction procedures used during formulation preparation were identified to improve bulk chlorhexidine purity and thereby extend product shelf-life. Gabapentin degrades directly to gabapentin-lactam in the solid-state. The established limit on gabapentin-lactam in gabapentin pharmaceutical formulations is <0.5% w/w thus gabapentin instability was studied as a model compound for solid state formulation applications. Mechanical stress associated with drug product manufacturing in unit operations such as milling increased the subsequent lactamization rate upon storage due to increased gabapentin crystal disorder. The effect of environment moisture was to decrease the rate of gabapentin-lactam formation due to competitive recovery of gabapentin crystallinity which was accelerated by humidity. A degradation model that combined both physical and chemical instability pathways including autocatalytic branching, spontaneous intra-molecular cyclization and moisture-induced physical transformation steps was shown to be consistent with lactamization kinetics as a function of both environmental (temperature and humidity) and manufacturing-related effects. This kinetic model was used to predict the shelf-life of gabapentin tablets prepared under various exemplary manufacturing conditions thereby demonstrating the ability of the model to link manufacturing variation and shelf-life stability in for solid-state drug formulations.

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12

Khan, Mohammad Younis. "The mechanisms of plastic flow in semi-plastic crystals under the hardness indentation." Thesis, University of Cambridge, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.279911.

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13

Levoguer, Carl Louis. "An investigation of surface reaction mechanisms during thin film growth of compound semiconductors." Thesis, University of Oxford, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.260715.

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14

Earl, Joseph Stewart. "A model of time dependence and mechanisms of magnetisation reversal in magneto-optic media." Thesis, Keele University, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.245878.

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Rahman, M. Habibur. "Optical properties and electrical conduction mechanisms of electron beam evaporated Cu-GeO2 thin cermet films." Thesis, Brunel University, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.241553.

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Optical, DC, and Hall effect measurements were performed on a number of Cu-GeO2 thin cermet films with the aim of obtaining information about DC conduction mechanism. Optical absorption studies showed that incorporation of Cu in the matrix of GeO2 introduces defect states leading to a reduction in the optical energy gap. The DC conductivity results revealed that above a certain temperature Tc, conductivity increases sharply with activation energy lying in the range 0.66 to 0.77 eV. Below Tc, the conductivity is weakly activated with activation energy lying in the range 0.10 to 0.25 eV. A sign reversal in Hall mobility was observed for all the samples. Furthermore, the Hall mobility showed a maximum at a critical temperature (Tc) identical to that of the DC conductivity. This suggests that the DC conductivity is dominated by a mixed conduction process and the small polaron model best describes the conduction mechanism. From the combined knowledge of optical absorption, DC conductivity and Hall effect results a room-temperature band diagram (for 30 at.wt% Cu films) is proposed in which the mobility gap is calculated to be 3.78 eV. Above Tc, the mobility gap reduces to 2.62 eV. The frequency response of dielectric loss and the AC conductivity showed striking minima around a cut-off frequency (fm≈10⁵ Hz) indicating that a single universal power-law cannot describe the conduction mechanism for the entire frequency range. Instead, a two power-law hypothesis is advanced. Below 10⁵ Hz, the small polaron tunnelling model best describes the conduction mechanism, while above 10⁵ Hz, the conductivity is identified with photon-activated resonant processes.

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16

Grenier, Antonin. "Development of solid-state Fluoride-ion Batteries : cell design, electrolyte characterization and electrochemical mechanisms." Thesis, Paris 6, 2016. http://www.theses.fr/2016PA066128/document.

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Les batteries tout-solides à ions fluorures reposent sur l'échange réversible d'ions F- entre un métal et un fluorure métallique au travers d'un électrolyte solide. Ces dispositifs électrochimiques peuvent théoriquement permettre l'obtention de fortes densités énergétiques, bien supérieures à celles des batteries conventionnelles Li-ion commerciales. En conséquence, les batteries à ions F- suscitent un fort engouement. Dans ce contexte, une partie de nos travaux ont portés sur le développement d'une cellule permettant d'évaluer leurs performances. De plus, les propriétés électrochimiques de l'électrolyte solide LaF3 dopé BaF2, La1-xBaxF3-x, ont fait l'objet d'une attention particulière. Finalement, les changements structuraux s'effectuant au sein des électrodes lors des cycles de charge/décharge ont été étudiés afin de mieux comprendre les mécanismes électrochimiques mis en jeu
Solid-state fluoride-ion batteries rely on the reversible exchange of the F- ion between a metal and a metal fluoride through a solid electrolyte. These electrochemical devices can theoretically reach energy densities superior to conventional Li-ion commercial batteries. Consequently, fluoride-ion batteries can be seen as a new promising chemistry generating a growing interest. In this context, a part of our work has been dedicated to the development of a cell allowing the evaluation of their electrochemical performance. Moreover, particular attention was given to the electrochemical properties of the solid electrolyte, BaF2-doped LaF3, La1-xBaxF3-x. Finally, the structural changes taking place at the electrodes upon charge/discharge were studied in order to gain insight into the electrochemical mechanisms involved in these devices

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17

de, Vries Edgar. "Mechanics and mechanisms of ultrasonic metal welding." The Ohio State University, 2004. http://rave.ohiolink.edu/etdc/view?acc_num=osu1078415529.

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18

Chen, Chao-Hsu. "Atomistic Computer Simulations of Diffusion Mechanisms in Lithium Lanthanum Titanate Solid State Electrolytes for Lithium Ion Batteries." Thesis, University of North Texas, 2014. https://digital.library.unt.edu/ark:/67531/metadc700110/.

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Solid state lithium ion electrolytes are important to the development of next generation safer and high power density lithium ion batteries. Perovskite-structured LLT is a promising solid electrolyte with high lithium ion conductivity. LLT also serves as a good model system to understand lithium ion diffusion behaviors in solids. In this thesis, molecular dynamics and related atomistic computer simulations were used to study the diffusion behavior and diffusion mechanism in bulk crystal and grain boundary in lithium lanthanum titanate (LLT) solid state electrolytes. The effects of defect concentration on the structure and lithium ion diffusion behaviors in LLT were systematically studied and the lithium ion self-diffusion and diffusion energy barrier were investigated by both dynamic simulations and static calculations using the nudged elastic band (NEB) method. The simulation results show that there exist an optimal vacancy concentration at around x=0.067 at which lithium ions have the highest diffusion coefficient and the lowest diffusion energy barrier. The lowest energy barrier from dynamics simulations was found to be around 0.22 eV, which compared favorably with 0.19 eV from static NEB calculations. It was also found that lithium ions diffuse through bottleneck structures made of oxygen ions, which expand in dimension by 8-10% when lithium ions pass through. By designing perovskite structures with large bottleneck sizes can lead to materials with higher lithium ion conductivities. The structure and diffusion behavior of lithium silicate glasses and their interfaces, due to their importance as a grain boundary phase, with LLT crystals were also investigated by using molecular dynamics simulations. The short and medium range structures of the lithium silicate glasses were characterized and the ceramic/glass interface models were obtained using MD simulations. Lithium ion diffusion behaviors in the glass and across the glass/ceramic interfaces were investigated. It was found that there existed a minor segregation of lithium ions at the glass/crystal interface. Lithium ion diffusion energy barrier at the interface was found to be dominated by the glass phase.

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Raghunathan, Vinodhkumar. "Elucidation of molecular recognition mechanisms of a peptide involved in biomineralization using solid state nuclear magnetic resonance spectroscopy /." Thesis, Connect to this title online; UW restricted, 2006. http://hdl.handle.net/1773/8644.

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20

Leoni, Stefano. "Theoretical and Experimental Investigations on Solid State Reactions: Phase Transition Mechanisms, Ionic Conduction, Domain Formation and Interface Reactivity." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2012. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-79219.

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In the practice of solid state chemistry, structural phase transitions are fairly common events. Nonetheless, their understanding, in terms of both: A rationalization of the observed changes in symmetry pattern and; An understanding of the mechanisms allowing for a particular transformation, are outstanding problems. The thermodynamic classification of phase transitions distinguishes between first and second order transitions, on the basis of the discontinuous behavior of quantities related to first or second derivatives of the free energy, respectively. Small atomic displacements are typically associated with second order phase transitions, and latent heat changes amount to a few calories per gram only. Additionally, the symmetries of the phases surrounding the transition are typically in the relation of a group and a subgroup. Reconstructive phase transitions, on the contrary, involve breaking of (large) parts of the bond scaffolding of the initial structure, and exhibit drastic changes at the transition point, with large latent heat and hysteresis effects. The corresponding atomic displacements can be in the order of the lattice parameters, and no group-subgroup is found, between the symmetry of the phases. These type of transitions have generally a strong first-order character. Landau theory accounts for continuous, second-order phase transitions. As a phenomenological theory, it does not establish the existence of a phase transition, which remains an experimental fact. It only bridges microscopic characteristics, like space-group symmetries and structural changes, or phonon softening effects, with measurable macroscopic quantities. Therein, distortions are carried by an order parameter, which fully specifies the form of the analytical variational free energy. The latter is continuous and derivable with respect to temperature, pressure and atomic displacement, at the transition point. First order, non-continuous phase transitions are still within the scope of Landau theory in the mentioned special case of the existence of a group-to-(isotropic) subgroup relationship. In the majority of cases, however, and for the most interesting phase transitions (for basic and applied research), such a relationship is missing, making the choice of an order parameter less straightforward. Most of the allotropic transformations of the elements, many intermetallic systems, and numerous insulating systems belongs to this class. This class also includes most interesting and fundamental electronic effects, like metallization in perovskites or spinel oxides for example. This very simple fact of a missing symmetry condition has helped reinforcing the opinion of first-order phase transitions being a world apart, and possibly contributed to discouraging a firm theory to develop, able to account for their transformation mechanisms and the change of physical properties across phase transition. The thermodynamic distinction between first and second order phase transitions is too narrow, as, in case of first order phase transitions, it embraces both weakly discontinuous transition and reconstructive ones, where bonds are being strongly modified. Especially, a mean to qualify the distance between two structures (geometric, with respect to symmetry, a.s.o.), is missing. Clearly, a group-subgroup relationship may, and typically does imply shortest shifting distances, as a tiny atomic displacement can already do for a symmetry lowering. Naively, missing such a relation means no constraints, and apparently no means to conclude at a connection of two structures in general, let alone a full mechanistic analysis. First order phase transitions proceed by nucleation and subsequent growth of the new phase from the initial one. Different from (second-order) continuous phase transitions, they do imply coexistence of the transforming motifs. The discontinuity in some order parameter between the two phases is driven by lowering of the free energy as the new phase forms. However, close to the transition, the original phase remains metastable, and a fluctuation is needed to cause the formation of the new phase to set in. Such a process responds to thermal changes, and depending on the height of the nucleation barrier, its rate may be slower or faster. In the former case, large deviations from equilibrium may be required to achieve transformation to the stable phase, which means that large hysteresis effects will be observed in the course of transformation. The intent of this work consists in giving a face to the intermediate configurations appearing in first order phase transitions, in solid-solid reconstructive processes. Apart of a mechanistic elucidation, consisting in answering the question “Which atomic displacements bring structural motif A into structural motif B ?”, another purpose of this work is a rather pedagogical one, that is, showing that first-order phase transitions can be understood in detail, not only in principle but in fact. The core of the examples illustrated in this work is concerned with phase transformations where pressure represents the thermodynamic controlling parameter. Pressure is extensively used in chemical synthesis, as a mean to achieve novel properties, optical or mechanical just to mention a few. Additionally, reports on novel high-pressure polymorphs are regularly appearing. In this sense, pressure is a relevant parameter for approaching fundamental questions in solid state chemistry.

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21

Hsia, Chungwei. "Mechanisms and rate of solid state diffusion in iridium-hafnium intermetallic compound (iridium(3) hafnium) and calcium sulfate /." The Ohio State University, 1993. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487848078448938.

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22

Todd, Devin Marlin James. "The Mechanisms of Luminescence from ZnO Under Electron Irradiation." Wright State University / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=wright1341465661.

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23

Williams, Robert Earl Jr. "Simulation and Characterization of Cathode Reactions in Solid Oxide Fuel Cells." Diss., Georgia Institute of Technology, 2007. http://hdl.handle.net/1853/16309.

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In this study, we have developed a dense La0.85Sr0.15MnO3-δ (LSM) Ce0.9Gd0.1O1.95 (GDC) composite electrode system for studying the surface modification of cathodes. The LSM and GDC grains in the composite were well defined and distinguished using energy dispersive x-ray (EDX) analysis. The specific three-phase boundary (TPB) length per unit electrode surface area was systematically controlled by adjusting the LSM to GDC volume ratio of the composite from 40% up to 70%. The TPB length for each tested sample was determined through stereological techniques and used to correlate the cell performance and degradation with the specific TPB length per unit surface area. An overlapping spheres percolation model was developed to estimate the activity of the TPB lines on the surface of the dense composite electrodes developed. The model suggested that the majority of the TPB lines would be active and the length of those lines maximized if the volume percent of the electrolyte material was kept in the range of 47 57%. Additionally, other insights into the processing conditions to maximize the amount of active TPB length were garnered from both the stereology calculations and the percolation simulations. Steady-state current voltage measurements as well as electrochemical impedance measurements on numerous samples under various environmental conditions were completed. The apparent activation energy for the reduction reaction was found to lie somewhere between 31 kJ/mol and 41 kJ/mol depending upon the experimental conditions. The exchange current density was found to vary with the partial pressure of oxygen differently over two separate regions. At relatively low partial pressures, i0 had an approximately dependence and at relatively high partial pressures, i0 had an approximately dependence. This led to the conclusion that a change in the rate limiting step occurs over this range. A method for deriving the electrochemical properties from proposed reaction mechanisms was also presented. State-space modeling was used as it is a robust approach to addressing these particular types of problems due to its relative ease of implementation and ability to efficiently handle large systems of differential algebraic equations. This method combined theoretical development with experimental results obtained previously to predict the electrochemical performance data. The simulations agreed well the experimental data and allowed for testing of operating conditions not easily reproducible in the lab (e.g. precise control and differentiation of low oxygen partial pressures).

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Ding, Weixuan. "Syntheses of ternary oxyhydrates and oxides in the calcium-uranium system : stoichiometric influences on their structural affinity, precipitation mechanisms, and solid-state transformations." Thesis, University of Leeds, 2017. http://etheses.whiterose.ac.uk/19431/.

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Calcium uranyl(VI) oxyhydrates and uranates are structurally related U(VI)-phases featuring uranium oxo-polyhedral sheets, with calcium ions occupying the interlayer. Both coordination environments appear throughout the nuclear fuel-cycle as alteration products, colloids, and sorption complexes. However, concerted studies spanning the aqueous precipitation mechanisms of uranyl(VI) oxyhydrates, their solid-state transformations, and structural relationships with uranates, have hitherto remained largely unexplored. A series of calcium-based uranyl(VI) oxyhydrates were precipitated via alkalisation of aqueous precursor solutions in titration and batch reactions. The bulk stoichiometric ratio of calcium to uranium (Ca/U) of precipitates was varied by modifying precursor stoichiometry, reaction temperature, or extraction pH. The rate of precipitation and its dependency on temperature was quantified in-situ using a quartz crystal microbalance. Novel insight was revealed on the mechanisms influencing nucleation and growth, by determining associated kinetic barriers as a function of precursor-Ca/U. Remarkably, as the bulk precipitate Ca/U increased from ~⅛ to unity, there was a transition from crystalline Becquerelite to primary or secondary amorphous phases, with uranate-like coordination environments. Formation of the latter was driven by solution alkalinity, and comprises a poorly-ordered matrix with occlusions of Ca2+-rich nano-clusters. A congruency limit lies Ca/U of ~1.5 Ca/U, whereupon discrete Portlandite crystallises. Solid-state transformation of all Ca2+-U(VI)-phases studied involved dehydration, dehydroxylation-decarbonation, and desorption processes. Associated kinetic barriers were catalysed by higher Ca2+-contents, and was reflected by reaction enthalpies for dehydration and desorption. Crystalline Becquerelite (~⅛ Ca/U) underwent amorphisation-crystallisation via partial egress of interlayer calcium, followed by reduction of β-UO3 to form a novel intercalation compound Ca0.18.α-U3O8. The endmember uranates Ca3U11O36, CaU2O7, Ca2U3O11, and CaUO4 crystallised from amorphous precursors with higher bulk Ca/U (~⅓, ~½, ~⅔, ~1), where Ca3U11O36 is a novel compound that is isostructural to (Pb/Sr)3U11O36. Nucleation and growth became predominant in the presence of Ca2+-rich occlusions. A higher Ca2+-loading facilitated the progressive ingress of interlayer-Ca2+, inducing a concerted axial compression in uranyl(VI) oxo-polyhedra towards the uranate-like coordination environment.

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25

Muralidharan, Priyadarshini, and Priyadarshini Muralidharan. "Advanced Design and Development of Novel Microparticulate/Nanoparticulate Dry Powder Inhalers Targeting Underlying Mechanisms in Respiratory Diseases." Diss., The University of Arizona, 2017. http://hdl.handle.net/10150/626331.

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Chronic respiratory diseases such as asthma, COPD, pulmonary fibrosis are more prevalent throughout the world. For some of these diseases there is no cure, the current treatment options manages the symptoms and acute exacerbation. The new approach to find a curative therapy for respiratory diseases is by targeting the cellular / molecular pathways that either cause the disease or has the potential cure the disease. It becomes important to target the respiratory system in treating these diseases to increase the delivered dose and reduce the unwarranted adverse effects. Dry powder inhaler (DPI) is a targeted drug delivery dosage form commonly used to target the airways to treat respiratory diseases. There are two components to dry powder inhaler product – powdered drug formulation and inhaler device; a unified performance of the two is essential for a successful product. In this study, dry powder aerosol of novel drug compounds that targets the underlying cellular and molecular mechanism are developed for the first time. Advanced organic closed mode spray drying technique was used to the produce microparticulate/ nanoparticulate formulations. The formulation of the novel compounds involved utilizing sugar based excipients. Each formulation that was produced was comprehensively characterized in the solid state. The safety of these formulations were tested in in vitro human pulmonary cell lines. The in vitro aerosol dispersion of the spray dried drugs were tested using three FDA approved human inhaler devices. The influence of the inhaler device resistance and spray drying process conditions on the aerosol dispersion was evaluated. Preliminary testing of the formulations in in vivo animal models shows promising results in treating chronic respiratory diseases with these superior aerosol formulations.

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26

Leoni, Stefano [Verfasser], Gotthard [Akademischer Betreuer] Seifert, Michael [Akademischer Betreuer] O'Keeffe, and Yuri [Akademischer Betreuer] Grin. "Theoretical and Experimental Investigations on Solid State Reactions: Phase Transition Mechanisms, Ionic Conduction, Domain Formation and Interface Reactivity / Stefano Leoni. Gutachter: Gotthard Seifert ; Michael O'Keeffe ; Yuri Grin." Dresden : Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2012. http://d-nb.info/1067729623/34.

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27

Elbagerma, Mohamed A. "Analytical method development for structural studies of pharmaceutical and related materials in solution and solid state : an investigation of the solid forms and mechanisms of formation of cocrystal systems using vibrational spectroscopic and X-ray diffraction techniques." Thesis, University of Bradford, 2010. http://hdl.handle.net/10454/4467.

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Analysis of the molecular speciation of organic compounds in solution is essential for the understanding of ionic complexation. The Raman spectroscopic technique was chosen for this purpose because it allows the identification of compounds in different states and it can give information about the molecular geometry from the analysis of the vibrational spectra. In this research the ionisation steps of relevant pharmaceutical material have been studied by means of potentiometry coupled with Raman spectroscopy; the protonation and deprotonation behaviour of the molecules were studied in different pH regions. The abundance of the different species in the Raman spectra of aqueous salicylic acid, paracetamol, citric acid and salicylaldoxime have been identified, characterised and confirmed by numerical treatment of the observed spectral data using a multiwavelength curve-fitting program. The non-destructive nature of the Raman spectroscopic technique and the success of the application of the multiwavelength curve-fitting program demonstrated in this work have offered a new dimension for the rapid identification and characterisation of pharmaceuticals in solution and have indicated the direction of further research. The work also covers the formation of novel cocrystal systems with pharmaceutically relevant materials. The existence of new cocrystals of salicylic acid-nicotinic acid, DLphenylalanine , 6-hydroxynicotinic acid, and 3,4-dihydroxybenzoic acid with oxalic acid have been identified from stoichiometric mixtures using combined techniques of Raman spectroscopy (dispersive and transmission TRS), X-ray powder diffraction and thermal analysis. Raman spectroscopy has been used to demonstrate a number of important aspects regarding the nature of the molecular interactions in the cocrystal. Cocrystals of salicylic acid - benzamide, citric acid-paracetamol and citric acid -benzamide have been identified with similar analytical approaches and structurally characterised in detail with single crystal X-ray diffraction. From these studies the high selectivity and direct micro sampling of Raman spectroscopy make it possible to identify spectral contributions from each chemical constituent by a peak wavenumber comparison of single-component spectra (API and guest individually) and the two- component sample material (API/guest), thus allowing a direct assessment of cocrystal formation to be made. Correlation of information from Raman spectra have been made to the X-ray diffraction and thermal analysis results. Transmission Raman Spectroscopy has been applied to the study cocrystals for the first time. Identification of new phases of analysis of the low wavenumber Raman bands is demonstrated to be a key advantage of the TRS technique.

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Lafuente, Hernández Mª Pilar. "Computational Study of the Mechanisms that Stabilize Organic Molecule‐Based Magnets." Doctoral thesis, Universitat de Barcelona, 2016. http://hdl.handle.net/10803/400864.

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The objective of this PhD thesis has been the study of the mechanisms that stabilize high-spin states in organic molecule-based magnetic materials. These materials require organic radicals with permanent magnetic moment as building units. Additionally, these molecules need to interact ferromagnetically, and expand that interaction along all three directions of the space. We have carried out our studies using computational chemistry techniques, mostly ab- initio methods (MP2, CASSCF and CASMP2), and DFT-based methods (B3LYP or M06L). Besides, we have also used the hybrid Molecular Mechanics Valence Bond method (MMVB) for alternant hydrocarbons with high number of active electrons. We have demonstrated that in organic radicals the energy gap between two spin states is usually higher when the stabilization of the spin centers occurs by means of through- bond (TB) instead of through-space (TS) interactions. As a result, alternant hydrocarbons (π-delocalized, with TB interactions) are more stable than non-alternant hydrocarbons (π-localized, with TS interactions). Therefore, alternant hydrocarbons would be preferable in the design of permanent molecular magnets. Polymerization of high-spin radicals leads to high-spin systems. However, our research showed that the gap of energy between the first and second spin states decreases with the number of units bonded when these are alternant hydrocarbons. On the other hand, it has been proved that, when the synthesis of macro-radicals follows the SU-CU- SU methodology (SU=spin-containing unit; CU=coupling unit), the SU and CU units keep their multiplicity once coupled. In that case, the energy gap between the spin states of the system can be described considering the energy gap of the spin states of the constitutive units. McConnell-I theory is widely applied to describe ferromagnetic intermolecular interactions. Our research has revised systematically this approach. We have explored the existence of a magneto-structural relationship using pairs of well-known radicals (H2NO·, ·CH3 and ·C3H5) at different geometrical orientations. We demonstrated that McConnell-I model predicts correctly the spin preference of the ground state when the interacting spin-containing radical centers are placed in parallel planes and there are mainly TS interactions between them. However, in other cases, the prediction of the spin preference becomes very complex, and more detailed quantum calculations are required. Overall, we have demonstrated that this model must be used carefully when predicting the multiplicity of the through-space interaction between two radicals. Further, we evaluated whether McConnell-I theory could be applied to assess the magnetic character of real crystals on the subset of experimentally FM crystals of the α- nitronyl nitroxide (α-NN) family. We analyzed the closest contacts between two intermolecular ONCNO groups (atoms where the spin densities are mainly located) for each chosen crystal. We concluded that the ONCNO interactions do not describe entirely the observed macroscopic magnetic property for all the systems. Consequently, TS interactions not considered in the simplistic ONCNO model must play an important role defining the magnetic character. Secondly, we proved there is not a simple magneto-structural relationship, such as the one suggested in McConnell-I model, that can be applied to all through-space interactions in the crystals. This conclusion was reached after a twofold statistical analysis (namely, factor and cluster analyses) of the geometrical parameters as a function of the calculated energy gap ΔES-T. Charge-transfer salts are successful examples of molecular magnets. However, the formation of diamagnetic dimers of the donor species, [D]22+, or the acceptor species, [A]22-, causes the loss of the magnetic properties. We studied the causes of this dimerization studying the formation of TCNE dimers, [TCNE]22-], as a prototypical example of an organic acceptor. The Eint of two charged molecules has two components: the Coulomb contribution (Ecoul > 0, for molecules with the same charge) and the bonding energy (Ebond < 0). If the repulsion energy is higher than the bonding energy in absolute value (|Ecoul|>|Ebond|) the two molecules will repel and the formation of the dimer will not be stable (Eint > 0). However, if there is any force that counterbalances the repulsion between the two charged molecules, the bonding energy could overcome the repulsion energy in absolute value (|Ecoul|<|Ebond|), and the metastable minima would become stable (Eint < 0). The calculations performed described three metastable minima that agree with those observed experimentally. Besides, the spectroscopic features of each class of these three dimers have been calculated and are in agreement with the available experimental data. Extended calculations performed in the presence of cations or polar solvents resulted in the stabilization of the dimers, which demonstrates that counterbalance of the repulsive energy is needed for the formation of these long multicenter bonds. The two electrons - four centers (2e-/4c) bond described is unique since it involves 2e- and takes place among four carbon atoms chemically equivalent.
El objetivo de esta tesis ha sido estudiar computacionalmente las bases teóricas del magnetismo molecular para poder utilizar el conocimiento adquirido en el diseño de materiales magnéticos moleculares. Hemos analizado los mecanismos a través del enlace (TB: through-bond) y a través del espacio (TS: through-space) que estabilizan moléculas de alto spin (radicales) y sus interaccionan intermoleculares ferromagnéticas. Para llevar a cabo dichos estudios se han utilizado métodos híbridos como el Molecular Mechanics Valence Bond (MMVB), métodos DFT como el B3LYP y métodos ab-initio como MP2, CASSCF, y CASMP2. Así pues, por un lado, se ha estudiado la estabilidad de moléculas orgánicas de alto spin y su posible polimerización manteniendo su alta multiplicidad de spin. Se ha llegado a la conclusión que el mecanismo TS es de menor coste energético que el TB. Por lo tanto, los radicales cuyos centros de spin se estabilizan a través del enlace TB son más estables. Asimismo, compuestos que presentan ambos mecanismos, los estados de spin de los estados fundamental y primer excitado vendrán determinados por el mecanismo TS. Por otro lado, se estudiaron las interacciones intermoleculares entre radicales, con el objetivo de establecer las condiciones que favorecen las que son ferromagnéticas. En este contexto, se evaluó la teoría denominada McConnell-I. Tras metódicos estudios de la interacción entre dos radicales (H2NO·, ·CH3 y ·C2H6) en diferentes orientaciones en el espacio, se concluyó que el ámbito de aplicación de esta teoría está limitado a cuando los centros de spin interaccionan en planos paralelos y existe una interacción TS predominante. Estudios adicionales en cristales de la familia α-nitronil nitróxido demostraron que la teoría de McConnell-I no se puede aplicar de forma general a cualquier interacción intermolecular entre radicales. Se observó que esta teoría no predice correctamente el comportamiento magnético de cristales cuando se analiza sólo la interacción entre los átomos que contienen mayoritariamente la densidad de spin (ONCNO). Así pues, el estudio se debe ampliar a otros contactos entre las moléculas para poder describir correctamente el comportamiento magnético observado. Finalmente hemos establecido que, en sales de transferencia de carga, se dan casos de dimerización de las especies constituyentes, por ejemplo tetracianoetileno (TCNE), cuando la repulsión entre especies de la misma carga se minimiza por la presencia de contra-iones o disolventes polares. De esta manera, se favorece la formación del enlace en el dímero al permitir la interacción de los electrones desapareados.

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Rodriguez, Alonso Elvira. "Contribution to the study of formation mechanisms of condensable by-products from torrefaction of various biomasses." Phd thesis, Toulouse, INPT, 2015. http://oatao.univ-toulouse.fr/15784/1/Rodriguez_Alonzo_Elvira.pdf.

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The objective of the present work is to better understand chemical evolution of both solid and gaseous phases during torrefaction of various biomasses. Torrefaction experiments were carried out with a dynamic profile of temperatures between 200 and 300°C, under inert atmosphere, for pine, ash-wood, miscanthus and wheat straw. Mass loss and formation of condensable species were analyzed by TGA-GC-MS, and chemical evolution of solid phase was characterized by 13C CP/MAS solid-state NMR. Thirty condensable species could be detected; a half of these species were formed during the whole temperature range, and a third were formed by all biomass types. The main phenomena that occurred in solid phase were found to be decrystallization of cellulose, severe degradation of hemicellulose, devolatilization of acetyl groups, conservation of methoxyl groups and charring. It was also found that mass loss and chemical evolution of solid were not directly correlated for different biomasses. Based on the experimental results, a conceptual model was developed to describe biomass degradation duringtorrefaction. Thirty reactions were determined for the three major macromolecular constituents, namely cellulose, hemicellulose – represented by C5 and C6 sugars – and lignin – represented by H, G and S units. The main innovations of this model are in thedetailed approach of hemicellulose and lignin compositions, as well as in the prediction of sixteen condensable and five permanent species, and six forms of solid char, through chemically meaningful and stoichiometrically valid reactions.

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Lechner, Ruep Ekkehard, Goetz Schuck, and Klaus Langer. "Mechanism of proton conduction in solid-state protonic conductors." Universitätsbibliothek Leipzig, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-186538.

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Gottardo, Laura. "Élaboration, traitement et propriétés des fibres SiBCN obtenues par voie PDC." Thesis, Lyon 1, 2009. http://www.theses.fr/2009LYO10200.

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Les matériaux céramiques à base de bore dans le système quaternaire Si-B-C-N présentent des propriétés de grand intérêt grâce aux liaisons covalentes et à la faible mobilité des éléments bore et silicium dans leurs phases nitrure et carbure, ce qui amène une grande fiabilité mécanique et une bonne stabilité thermique. Ces dernières années, la voie « polymères précéramiques » est devenue la plus intéressante pour la préparation des ce type de céramiques avancées. En utilisant la thermolyse de polymères, une large variété de céramiques dérivées de polymères précéramiques peut être produite à partir de précurseurs moléculaires, en contrôlant la structure de l'unité monomérique, la polymérisation et la procédure de thermolyse. Notamment la thermolyse directe des polymères est une voie compatible avec plusieurs types de techniques de mise en forme, entre autres l'infiltration ou le filage, qui offrent la possibilité de réaliser structures et objets avec des formes complexes avec une approche simple et à faible coût. La première génération de fibres SiBCN a été obtenue à partir du polymère de type [B(C2H4SiCH3NCH3)3]n. Celle-ci présentait de bonnes propriétés mécaniques et une bonne stabilité thermique. Ce manuscrit présente une étude sur le développement de ce type de polymères, en particulier l'optimisation du filage et de la qualité de fibres à travers la modification des voies de synthèse et des traitements de thermolyse. De plus, une élaboration de nouveaux précurseurs moléculaires est développée afin de produire une nouvelle génération de fibres SiBCN
Boron-based ceramic materials in the quaternary Si-B-C-N system are of great interest because of their covalent bonding and the poor mobility of boron and silicon elements in their respective nitride and carbide which both provide mechanical reliability and high temperature stability. In recent years, the PDCs route became of increasing interest for the preparation of such advanced ceramics. Using the general polymer thermolysis route, a large variety of net-shaped polymerderived ceramics can be built up from molecular units and shaped by controlling the structure of the molecular units as well as the polymerization and thermolysis procedures. Interestingly, the direct polymer thermolysis route makes polymers compatible with many shaping techniques such as infiltration or melt-spinning offering the opportunity to realize complex shapes/structures in a simple and cost-efficient way.The first generation of such fibers obtained from a polymer type [B(C2H4SiCH3NCH3)3]n showed good mechanical properties and thermal stability. This document is about the development of such a polymer in order to optimize spinnability and fibers quality throught synthesis modification and thermolysis treatments. Moreover, design of new preceramic polymers is investigate to produce a new generation of SiBCN fibers

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Boudghene, Stambouli Amine. "Degradation mechanism in zinc sulphide/manganese electroluminescent displays." Thesis, University of Nottingham, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.328389.

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Ina, Toshiaki. "Study on Cathodic Reaction Mechanism of All Solid State Electrochemical Devices." Kyoto University, 2012. http://hdl.handle.net/2433/157658.

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Kyoto University (京都大学)
0048
新制・課程博士
博士(人間・環境学)
甲第16947号
人博第590号
新制||人||141(附属図書館)
23||人博||590(吉田南総合図書館)
29622
京都大学大学院人間・環境学研究科相関環境学専攻
(主査)教授内本喜晴, 教授杉山雅人, 教授田部勢津久, 准教授藤原直樹, 准教授雨澤浩史
学位規則第4条第1項該当

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Pandey, Devashish. "Quantum transport in Solid state devices for Terahertz frequency applications." Doctoral thesis, Universitat Autònoma de Barcelona, 2020. http://hdl.handle.net/10803/671285.

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El treball presentat en aquesta tesi es dedica a la comprensió de desafiaments pràctics i conceptuals en la simulació de propietats dinàmiques més enllà de l’aproximació quasi-estàtica en dispositius quàntics d’estat sòlid en escenaris on és necessari un tractament mecànic quàntic complet. Els resultats d’aquesta tesi són particularment rellevants per al càlcul de les fluctuacions del corrent elèctric en el règim de THz, per a l’avaluació dels temps de túnel que defineixen la freqüència de tall dels dispositius operats a alta freqüència, o per a l’avaluació del treball termodinàmic per a la realització de motors tèrmics quàntics. Les propietats dinàmiques esmentades impliquen mesures en diversos temps i, per tant, són sensibles a la “”retracció”” quàntica de la mesura. En el context de la mecànica quàntica ortodoxa, la definició d’aquestes propietats dinàmiques no es pot desvincular de l’especificació de l’aparell de mesura. És a dir, definir propietats dinàmiques intrínseques o independents dels aparells de mesura és incompatible amb els postulats de la mecànica quàntica ortodoxa. Per tot plegat, un enginyer de dispositius com jo, que treballa en problemes pràctics relacionats amb els dispositius d’estat sòlid actuals i futurs, es veu obligat a aprofundir en els fonaments de la mecànica quàntica. En aquest sentit, mostraré que les dificultats associades a la comprensió de propietats dinàmiques de sistemes quàntics es poden resoldre mirant més enllà de la mecànica quàntica ortodoxa. En particular, he explorat la interpretació modal de la mecànica quàntica, que és una teoria quàntica matemàticament precisa que reprodueix tots els fenòmens de la mecànica quàntica. Mostraré que les propietats intrínseques es poden definir fàcilment en aquest nou context (no ortodox). Demostraré també que les propietats intrínseques es poden identificar amb la mesura de “weak values” i, per tant, que es poden mesurar. Centrat en una teoria modal particular, viz., la mecànica de Bohm, es discutirà i s’aplicarà un simulador de transport d’electrons per abordar qüestions tant metodològiques com pràctiques relacionades amb la simulació del transport quàntic d’electrons. L’ontologia de la mecànica de Bohmian permet descriure de manera natural sistemes quàntics oberts monitoritzats contínuament amb una descripció precisa dels estats condicionals per als règims markovians i no markovians. Això ajuda a proporcionar un enfocament alternatiu a la matriu densitat en la descripció de sistemes quàntics oberts, que escala exponencialment amb el nombre de graus de llibertat. Tantmateix, l’estratègia d’estats condicionals Bohmians, que ha conduït al desenvolupament del simulador de transport d’electrons BITLLES, es demostrarà en el càlcul dels temps de permanència dels electrons en una barrera de grafè de dos terminals. Es demostrarà que les trajectòries de Bohmian són molt adequades per proporcionar una descripció inequívoca dels temps de trànsit (túnel) i la seva relació amb les freqüències de tall en dispositius electrònics pràctics. Finalment, es discutirà un protocol que incorpora mesures similars als “collective measurements” per eludir la incertesa de mesura en dispositius electrònics de computació clàssica i quàntica.
El trabajo presentado en esta tesis está dedicado a la comprensión de desafíos prácticos y conceptuales en la simulación de propiedades dinámicas más allá de la aproximación cuasiestática en dispositivos cuánticos de estado sólido en escenarios donde es necesario un tratamiento mecánico cuántico completo. Los resultados de esta tesis son particularmente relevantes para el cálculo de las fluctuaciones de la corriente eléctrica en el régimen THz, la evaluación de los tiempos de tunelización que definen la frecuencia de corte de los dispositivos operados por alta frecuencia, o la evaluación del trabajo termodinámico para realizar motores térmicos cuánticos. Las propiedades dinámicas mencionadas anteriormente implican medidas en múltiples tiempos y, por lo tanto, son sensibles a la ""retroacción "" cuántica de la medida. En el contexto de la mecánica cuántica ortodoxa, la definición de estas propiedades dinámicas no puede separarse de la especificación del aparato de medida. Es decir, definir propiedades dinámicas intrínsecas o independientes del aparato de medida es incompatible con los postulados de la mecánica cuántica ortodoxa. Con todo, un ingeniero de dispositivos como yo, que trabaja en problemas prácticos relacionados con los dispositivos de estado sólido presentes y futuros, se ve obligado a profundizar en los fundamentos de la mecánica cuántica. En este sentido, mostraré que las dificultades asociadas a la comprensión de las propiedades dinámicas se pueden resolver mirando más allá de la mecánica cuántica ortodoxa. En particular, he explorado la interpretación modal de la mecánica cuántica, que es una teoría cuántica matemáticamente precisa que reproduce todos los fenómenos de la mecánica cuántica. Mostraré que las propiedades intrínsecas pueden definirse fácilmente en este nuevo contexto (no ortodoxo). Es importante destacar que demostraré también que las propiedades intrínsecas pueden identificarse con la medida de ""weak values"" y que, por lo tanto, ¡pueden medirse! Enfocado en una teoría modal particular, a saber la mecánica de Bohm, se discutirá y aplicará un simulador de transporte de electrones para abordar cuestiones metodológicas y prácticas relacionadas con la simulación del transporte cuántico de electrones. La ontología de la mecánica bohmiana permite describir de manera natural sistemas cuánticos abiertos monitoreados continuamente con una descripción precisa de los estados condicionales para los regímenes Markoviano y no-Markoviano. Esto ayuda a proporcionar un enfoque alternativo al de la matriz de densidad en la descripción de sistemas cuánticos abiertos, que escala exponencialmente con el número de grados de libertad. Por lo tanto, se mostrará que la estrategia de estado condicionales de Bohm, que ha llevado al desarrollo de un simulador de transporte de electrones BITLLES, permite, por ejemplo, calcular los tiempos de permanencia de los electrones en una barrera de grafeno de dos terminales. Se demostrará también que las trayectorias bohmianas son muy apropiadas para proporcionar una descripción inequívoca de los tiempos de tránsito (de tunel) y su relación con las frecuencias de corte en dispositivos electrónicos. Finalmente, se discutirá un protocolo que incorpora mediciones de tipo colectivo para evadir la incertidumbre de medición actual en los dispositivos electrónicos de computación clásica y cuántica.
The work presented in this thesis is dedicated to the understanding of practical and conceptual challenges in simulating dynamical properties beyond the quasi-static approximation, in solid-state quantum devices in scenarios where a full quantum mechanical treatment is necessary. The results of this thesis are particularly relevant for the computation of the fluctuations of the electric current in the THz regime which aids in determining the correlations, the evaluation of tunnelling times that define the cut-off frequency of high-frequency operated devices, or the assessment of thermodynamic work to realize quantum thermal engines.The above mentioned dynamical properties involve multi-time measurements and hence are sensitive to quantum backaction. In the context of Orthodox quantum mechanics, the definition of these dynamical properties cannot be detached from the specification of the measurement apparatus. That is, defining apparatus-independent or intrinsic dynamical properties of quantum systems is incompatible with the postulates of Orthodox quantum mechanics. All in all, a device engineer like me, working on practical problems related with the present and future solid-state devices, is forced to delve into the foundations of quantum mechanics if I really want to properly understand the high-frequency performance of solid-state devices. In this regard, I will show that the difficulties associated to the understanding of dynamical properties can be solved by looking beyond Orthodox quantum mechanics. In particular, I have explored the modal interpretation of quantum mechanics, which is a mathematically precise quantum theory that reproduces all quantum mechanical phenomena. I will show that intrinsic properties can be easily defined in this new (non-orthodox) context. Importantly, I will prove that intrinsic properties can be identified with weak values and hence that they can be measured! Focused on a particular modal theory, viz., Bohmian mechanics, an electron transport simulator will be discussed and applied to address both methodological and practical issues related to the simulation of quantum electron transport. The ontology of Bohmian mechanics naturally enables describing continuously monitored open quantum systems with a precise description of the conditional states for Markovian and non-Markovian regimes. This helps to provide an alternate to density matrix approach in the description of open quantum systems, which scales poorly computationally with the number of degrees of freedom. Thus the Bohmian conditional state strategy, which has led to the development of an electron transport simulator, BITLLES will be shown to compute the dwell times for electrons in a two-terminal graphene barrier. It will be demonstrated that Bohmian trajectories are very appropriate to provide an unambiguous description of transit (tunnelling) times and its relation to the cut-off frequencies in practical electron devices. Finally, a protocol incorporating collective-like measurements to evade the current measurement uncertainty in the classical and quantum computing electron devices will be discussed.

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35

Vargas-Gonzalez, Lionel Ruben. "Microstructural optimization of solid-state sintered silicon carbide." Diss., Georgia Institute of Technology, 2009. http://hdl.handle.net/1853/34691.

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In this work, the development of theoretically-dense, clean grain boundary, high hardness solid-state sintered silicon carbide (SiC) armor was pursued. Boron carbide and graphite (added as phenolic resin to ensure the carbon is finely dispersed throughout the microstructure) were used as sintering aids. SiC batches between 0.25-4.00 wt.% carbon were mixed and spray dried. Cylindrical pellets were pressed at 13.7 MPa, cold-isostatically pressed (CIP) at 344 MPa, sintered under varying sintering soaking temperatures and heating rates, and varying post hot-isostatic pressing (HIP) parameters. Carbon additive amounts between 2.0-2.5 wt.% (based on the resin source), a 0.36 wt.% B4C addition, and a 2050°C sintering soak yielded parts with high sintering densities (~95.5-96.5%) and a fine, equiaxed microstructure (d50 = 2.525 µm). A slow ramp rate (10°C/min) prevented any occurrence of abnormal grain growth. Post-HIPing at 1900°C removed the remaining closed porosity to yield a theoretically-dense part (3.175 g/cm3, according to rule of mixtures). These parts exhibited higher density and finer microstructure than a commercially-available sintered SiC from Saint-Gobain (Hexoloy Enhanced, 3.153 g/cm3 and d50 = 4.837 µm). Due to the optimized microstructure, Verco SiC parts exhibited the highest Vickers (2628.30 ± 44.13 kg/mm2) and Knoop (2098.50 ± 24.8 kg/mm2) hardness values of any SiC ceramic, and values equal to those of the "gold standard" hot-pressed boron carbide (PAD-B4C). While the fracture toughness of hot-pressed SiC materials (~4.5 MPa m1/2) are almost double that of Verco SiC (2.4 MPa m1/2), Verco SiC is a better performing ballistic product, implying that the higher hardness of the theoretically-dense, clean-grain boundary, fine-grained SiC is the defining mechanical property for optimization of ballistic behavior.

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Takasu, Ichiro. "The study of the coercivity mechanism of gas atomized P/M MnAlC permanent magnet." Thesis, University of Salford, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.360473.

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Miller, Christopher W. "Set-up and evaluation of laser-driven miniflyer system." Thesis, Atlanta, Ga. : Georgia Institute of Technology, 2009. http://hdl.handle.net/1853/28184.

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Thesis (M. S.)--Mechanical Engineering, Georgia Institute of Technology, 2009.
Committee Chair: Thadhani, Naresh; Committee Member: Das, Suman; Committee Member: Fajardo, Mario; Committee Member: Zhou, Min.

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Wang, Tsueh-Hua. "A study of the electroluminescence properties of a-SiC:H thin-film light emitting diodes and the recombination mechanism of a-Si:H and its alloys." Thesis, University of Sheffield, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.242308.

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39

Hong, Youlee. "Elucidation of Chain-Folding Structure and Crystallization Mechanism of Semicrystalline Polymer by Solid-State NMR." University of Akron / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=akron1430246993.

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WANG, SHIJUN. "CHAIN FOLDING AND CRYSTALLIZATION MECHANISM OF POLY(L-LACTIDE) AS INVESTIGATED BY SOLID STATE NMR." University of Akron / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=akron1541091884494995.

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Asmadi, Aldi. "Crystal structure prediction : a molecular modellling study of the solid state behaviour of small organic compounds." Thesis, University of Bradford, 2010. http://hdl.handle.net/10454/4441.

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The knowledge of the packing behaviour of small organic compounds in crystal lattices is of great importance for industries dealing with solid state materials. The properties of materials depend on how the molecules arrange themselves in a crystalline environment. Crystal structure prediction provides a theoretical approach through the application of computational strategies to seek possible crystal packing arrangements (or polymorphs) a compound may adopt. Based on the chemical diagrams, this thesis investigates polymorphism of several small organic compounds. Plausible crystal packings of those compounds are generated, and their lattice energies are minimised using molecular mechanics and/or quantum mechanics methods. Most of the work presented here is conducted using two software packages commercially available in this field, Polymorph Predictor of Materials Studio 4.0 and GRACE 1.0. In general, the computational techniques implemented in GRACE are very good at reproducing the geometries of the crystal structures corresponding to the experimental observations of the compounds, in addition to describing their solid state energetics correctly. Complementing the CSP results obtained using GRACE with isostructurality offers a route by which new potential polymorphs of the targeted compounds might be crystallised using the existing experimental data. Based on all calculations in this thesis, four new potential polymorphs for four different compounds, which have not yet been determined experimentally, are predicted to exist and may be obtained under the right crystallisation conditions. One polymorph is expected to crystallise under pressure. The remaining three polymorphs might be obtained by using a seeding technique or the utilisation of suitable tailor made additives.

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Kassebaum, Paul Gregory. "The Adiabatic Bond Charge Model of Phonons." Digital WPI, 2012. https://digitalcommons.wpi.edu/etd-dissertations/180.

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The dispersion relation between frequency and wavevector of atomic vibrations, or phonons, can be succinctly described by the adiabatic bond charge model, first developed by Weber. The model employs as few as four parameters to fit experiment. We investigated this model in order to better unify the description of the technologically relevant group IV elemental semiconductors (e.g. diamond, silicon, germanium, and gray tin) by replacing an ad hoc parameter introduced by Weber with one arising from quadrupolar interactions between the bond charges, and by fitting the parameters to density functional theory calculations. We also illustrate constant frequency surfaces embedded in wavevector space for the various modes of vibration for the first time. The bond charge model allows for rapid calculation of various quantities related to the interaction of phonons with electrons and photons as compared to density functional theory, especially in structures with little symmetry and for macroscopic structures, thus enabling the design of complicated electronic and photonic devices much more accurately.

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Lechner, Ruep Ekkehard, Goetz Schuck, and Klaus Langer. "Mechanism of proton conduction in solid-state protonic conductors: method and results from investigations by QENS techniques." Diffusion fundamentals 12 (2010) 3, 2010. https://ul.qucosa.de/id/qucosa%3A13865.

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Boulfelfel, Salah Eddine. "Atomic Scale Investigation of Pressure Induced Phase Transitions in the solid State." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2009. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-25283.

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In this work, atomic scale investigation of pressure-induced transformations in the solid state have been carried out. A series of compounds including GaN, ZnO, CaF2, and AgI, in addition to elemental phosphorus have been studied. The corresponding transition mechanisms have been elucidated with a clear description of atomic displacements and intermediate structures involved therein. In the first group of compounds, the long standing debate on the transition path of the wurtzite(WZ)-to-rocksalt(RS) transition in semiconductors, GaN and ZnO was resolved using geometrical modeling combined with molecular dynamics (MD) simulations conducted in the frame of transition path sampling (TPS) method. In GaN, a two-step mechanism through a metastable intermediate phase with a tetragonal structure iT has been revealed from simulations. In ZnO, the tetragonal intermediate structure was kinetically less stable, although still part of the real transition mechanism. It appeared at the interface between WZ and RS as consequence of a layers shearing. The transition regime in ZnO was characterized by a competition between iT structure and another hexagonal intermediate with hexagonal symmetry iH. Although possible, the latter is not functional for the transition. In both cases, GaN and ZnO, two points of agreement with experiments have been revealed. The tilting of structures after transition, and the phonon mode softening associated with atomic displacements leading to the tetragonal structure iT In the second group of compounds, the investigation of transitions in superionic conductors, CaF2 and AgI, demonstrated a different and particular behavior of atomic motion under pressure. The solid-solid reconstruction of CaF2 structure was shown to be initiated and precedented by high disorder of the anionic sublattice. The percolation of fluoride ions through voids in the fluorite structure created a thin interface of liquid like state. The sparce regions caused by the departure of anions facilitates the cation sublattice reconstruction. In AgI, ion diffusion during the wurtzite/zincnlende(ZB)$rocksalt transition was more pronounced due to the extended stacking disorder WZ/ZB. The Ag+ ions profited not only from the structure of the interface but used the combination of interstitial voids offered by both phases, WZ and ZB, to achieve long diffusion paths and cause the cation sublattice to melt. Clearly, a proper account for such phenomena cannot be provided by geometry-designed mechanisms based on symmetry arguments. In phosphorus, the question of how the stereochemically active lone pairs are reorganized during the orthorhombic (PI) to trigonal (PV) structural transition was answered by means of simulations. Computation was performed at different levels theory. First, the mechanism of the transition was obtained from TPS MD simulations. MD runs were performed within density functional tight binding method (DFTB). The analysis of atomic displacements along the real transformation path indicated a fast bond switching mechanism. In a second step, the nature of the interplay between orbitals of phosphorus during the bond switching was investigated. A simultaneous deformation of lone pair and P−P bond showed a mutual switching of roles during the transformation. This interplay caused a low dimensional polymerization of phosphorus under pressure. The corresponding structure formed as zigzag linear chain of fourfold coordinated phosphorus atoms (· · ·(P(P2))n · · ·) at the interface between PI and PV phases. A further result of this work was the development of a simulation strategy to incorporate defects and chemical doping to structural transformations. On top of the transition path sampling iterations, a Monte Carlo like procedure is added to stepwise substitute atoms in the transforming system. Introducing a chemically different dopant to a pure system represents a perturbation to the energy landscape where the walk between different phases is performed. Therefore, any change in the transition regime reflects the kinetic preference of a given structural motif at times of phase formation. This method was applied to the elucidation of WZ-RS transition mechanism in the series of semiconducting compounds AlN, GaN, and InN. Simulations showed that In atoms adopt the same transformation mechanism as in GaN and favor it, while Al atoms demonstrated a significant reluctance to the path going through tetragonal intermediate iT. The difference between transition regime in mixed systems InxGa1−xN and AlxGa1−xN is in agreement with experiments on high pressure behavior of AlN, GaN, and InN. While transitions in GaN and InN are reversible down to ambient conditions, AlN is stable. The work presented in this thesis constitutes the seed of new perspectives in the understanding of pressure-induced phase transformations in the solid state, where the physics and the chemistry are brought together by means of computer simulations.

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45

Sarkar, Sujan K. "Reaction Mechanism and Detection of Elusive C, N, and O Centered Radicals and Intermediates in Solution and Solid State." University of Cincinnati / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1448037904.

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46

Nagy, Péter. "Formation and Decomposition of Platinum–Thallium Bond, Kinetics and Mechanism. Structural Characterization of Some Metal Cyanides in the Solid State." Doctoral thesis, KTH, Chemistry, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3803.

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The kinetic and mechanistic features of a new series ofplatinum-thallium cyano compounds containing a direct andunsupported by ligands metal-metal bond have been studied insolution, using standard mixandmeasurespectrophotometric technique and stoppedflow method.These reactions are interpreted as oxidative addition of the cspecies to the square planar Pt(CN)₄^2-complex. Each of these processes was found to befirst-order in Pt(CN)₄^2-, the corresponding TI^IIIcomplex and a cyanide ion donating species whichacts as a catalyst. Both di- and trinuclear complexes werestudied, and the kinetically significant thallium complexes intheir formation and the catalytically active cyanide sourcesare as follows: [(CN)₅PtTl(CN)₃]^3-: Tl(CN)₄(alkaline region), Tl(CN)₃(slightly acidic region) and CN; [(CN)₅PtTl(CN)]: Tl(CN)₂⁺and Tl(CN)₂⁺; [(CN)₅PtTlPt(CN)₅]^3-: [(CN)₅PtTl(CN)]and HCN. Appropriatemechanisms were postulated for the overall reactions in allcases, which include i) metalmetal bond formation stepand ii) coordination of an axial cyanide ion to the platinumcenter. Two experimentally indistinguishable kinetic modelswere proposed for the formation of the dinuclear complexeswhich are different in the sequence of the two steps. In thecase of the trinuclear complex, experimental evidence isavailable to exclude one of the alternative reaction paths, andit was proven that the metalmetal bond formation precedesthe axial cyanide coordination.

The cyanide ligands coordinated to TI^IIIin the PtTl complexes could be replacedsuccessfully with aminopolycarboxylates e.g.: mimda^2-, nta^3-, edta^4-. The [(CN)₅PtTl(edta)]^4-complex, with a direct metalmetal bond hasbeen prepared in solution by two different reactions: a)dissolution of [(CN)₅PtTl](s) in an aqueous solution of edta, b)directly from Pt(CN)₄^2-and Tl(edta)(CN)^2-. The decomposition reaction is greatlyaccelerated by cyanide and significantly inhibited by edta. Itproceeds through the [(CN)₅PtTl(CN)₃]^3-intermediate. The formation of [(CN)₅PtTl(edta)]^4-can proceed via two different pathways dependingon the ratio of the cyanide to the edta ligand concentrations.Thedirect pathat excess of edta means theformation of intermediate[(CN)4Pt···Tl(CN)(edta)]^4-, followed by a release of the cyanide from theTlcentre followed by coordination of a cyanide from thebulk to the Ptcentre of the intermediate. Theindirect pathdominates in the absence of extraedta and the formation of the PtTl bond occours betweenPt(CN)₄^2-and Tl(CN)4.

Homoligand MTl(CN)₄(M = Tl^I, K, Na) and, for the first time, Tl(CN)₃species have been synthesized in the solid stateand their structures solved by single crystal Xraydiffraction method. Interesting redox processes have been foundbetween TI^IIIand CNin nonaqueous solution and in Tl₂O₃-CNaqueous suspension. In the crystal structureof Tl(CN)₃·H₂O, the thallium(III) ion has a trigonal bypiramidalcoordination geometry with three cyanides in the trigonalplane, while an oxygen atom of the water molecule and anitrogen atom from a cyanide ligand attached to a neighboringthallium complex, form a linear OTlN fragment.Cyanide ligand bridges thallium units forming an infinitezigzag chain structure. Among the thallium(III) tetracyanocompounds, the isostructural M[Tl(CN)₄](M = Tl and K) and Na[Tl(CN)₄]·3H₂O crystallize in different crystal systems, but thethallium(III) ion has in all cases the same tetrahedralgeometry in the [Tl(CN)₄]unit.

Three adducts of mercury(II) (isoelectronic with TI^III) (K₂PtHg(CN)₆·2H₂O, Na₂PdHg(CN)₆·2H₂O and K₂NiHg(CN)₆·2H₂O) have been prepared from Hg(CN)₂and square planar transition metal cyanides M^II(CN)₄^2-and their structure have been studied by singlecrystal Xray diffraction, XPS and Raman spectroscopy inthe solid state. The structure of (K₂PtHg(CN)₆·2H₂O consists of strictly linear one dimensional wireswith Pt^IIand Hg^IIcenters located alternately, d_HgPt= 3.460 Å. The structure of Na₂PdHg(CN)₆·2H₂O and K₂NiHg(CN)₆·2H₂O can be considered as double salts, the lack ofheterometallophilic interaction between both the Hg^IIand Pd^IIatoms, d_HgPd= 4.92 Å, and Hg^IIand Ni^IIatoms, d_NiPd= 4.60 Å, seems obvious. Electronbinding energy values of the metallic centers measured by XPSshow that there is no electron transfer between the metal ionsin all three adducts. In solution, experimental findingsclearly indicate the lack of metalmetal bond formation inall studied Hg^IICN^-M^II(CN)4^2-systems (M = Pt, Pd and Ni). It is in contrary tothe platinumthallium bonded cyanides.

KEYWORDS:metalmetal bond, platinum, thallium,kinetics, mechanism, stopped flow, oxidative addition, cyanocomplexes, edta, redox reaction, metal cyanides, Xraydiffraction, Raman, NMR, mercury, palladium, nickel, onedimensional wire

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Rusanova-Naydenova, Daniela. "³¹P- and ⁶⁵Cu- solid state NMR studies of Cu(I) di-alkyl-dithiophosphates : complex formation mechanism on synthetic chalcocite surfaces /." Luleå, 2004. http://epubl.luth.se/1402-1757/2004/04.

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Xiao, Yao. "Analysis for reaction mechanism of cathode materials for lithium-sulfur batteries." Doctoral thesis, Kyoto University, 2021. http://hdl.handle.net/2433/263747.

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京都大学
新制・課程博士
博士(人間・環境学)
甲第23286号
人博第1001号
京都大学大学院人間・環境学研究科相関環境学専攻
(主査)教授内本喜晴, 教授田部勢津久, 教授高木紀明
学位規則第4条第1項該当
Doctor of Human and Environmental Studies
Kyoto University
DFAM

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49

Satulovsky, Javier Eduardo. "Modelo estocástico para um sistema predador-presa." Universidade de São Paulo, 1995. http://www.teses.usp.br/teses/disponiveis/43/43133/tde-28022014-111840/.

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Neste trabalho introduzimos e estudamos um modelo estocástico de gás de rede para descrever a evolução de um sistema de partículas interagentes que representam duas espécies: presas e predadores. As presas se reproduzem autocataliticamente ocupando sítios vazios de uma rede. Os predadores também se reproduzem autocataliticamente mas às expensas das presas, e morrem via aniquilação espontânea. As regras locais e irreversíveis do modelo, de dois parâmetros, são inspiradas no modelo de Lotka-Volterra e no processo de contato. No regime estacionário o modelo apresenta três fases. A primeira corresponde a um estado absorvente em que as presas cobrem toda a rede. A segunda é caracterizada por valores médios não nulos das densidades de cada espécie. Á medida que variamos os parâmetros dentro dessa fase surgem oscilações locais nas densidades. A segunda fase está separada da primeira através de uma linha de transição de fases cinética contínua. Essa linha crítica encontra-se na classe de universalidade da percolação dirigida em d+1 dimensões, com exceção de um ponto terminal que pertence à classe de universalidade da percolação ordinária. A terceira fase corresponde a um outro estado absorvente em que as duas espécies foram exterminadas. A transição da segunda para a terceira fase é contínua e também pertence à classe de universalidade da percolação dirigida em d+1 dimensões. Os resultados foram obtidos por meio de simulações computacionais bem como através de métodos analíticos aproximados
In this work, we introduce and study a stochastic lattice gas model for the evolution of an interacting particle system describing two species: prey and predators. Prey undergo autocatalytic reproduction on empty sites of a lattice. Predators also reproduce autocatalytically at the expense of prey, as well as suffer spontaneous annihilations. The irreversible local rules of the model, involving two parameters, are inspired both in the Lotka-Volterra model and the contact process. In the stationary regime, the model shows three phases. The first one is associated to an absorbing state in which the lattice is completely covered by prey. The second one is characterized by finite values of the density of each species. As we tune the parameters values inside that phase, local oscillations in the population densities start to appear. The second phase is reached from the first one through a line of continuous kinetic phase transitions. The line belongs to the universality class of directed percolation in d+1 dimensions, except for its terminal point, which belongs to the universality class of ordinary percolation. The third phase corresponds to another absorbing state completely devoided of particles. The transition from the second to the third phase is continuous and also belongs to universality class of directed percolation in d+1 dimensions. The model has been studied by means of computer simulations as well as by using approximate analytical technics.

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Thomson, Stuart. "Mathematical modelling of elastoplasticity at high stress." Thesis, University of Oxford, 2017. http://ora.ox.ac.uk/objects/uuid:a7d565c6-abeb-4932-8c1e-aebc38da7584.

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This thesis is concerned with the mathematical modelling of elastic-plastic deformation in regimes of stress far exceeding the yield stress. Such scenarios are typically encountered in violent impact testing, where millimetre-thick samples of metal are subjected to pressures on the order of the bulk modulus of the material. We begin with an overview of violent impact testing, with particular attention paid to a specific class of experiments known as isentropic compression experiments (ICEs), which will provide motivation for the mathematical modelling and analysis in subsequent chapters. In chapter 2, by appealing to sound notions from rational mechanics and thermodynamics, we construct a mathematical model which aims to encapsulate the essential phenomena involved in violent elastic-plastic deformation. This is followed in chapter 3 with a numerical analysis of the mathematical model in uniaxial strain, which is the geometry relevant ICEs. In chapters 4 and 5, we corroborate the observations made in chapter 3 via a systematic mathematical analysis. In particular, our focus will be on the elastic and plastic waves that can propagate through finite metal samples during isentropic compression. Finally, in chapter 6, we explore the applicability of our model to other geometries, specifically the radially axisymmetric expansion of a circular cavity embedded in an infinite elastic-plastic medium. We conclude with a summary of our findings and suggest some avenues for future investigation.

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