Дисертації з теми "Stability of the structure"
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1
Fernier, Alexandre. "Couplage multi-échelle pour l'intéraction fluide structure en dynamique rapide." Thesis, Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLY001/document.
Анотація:
Dans l’industrie nucléaire, la simulation de transitoires accidentels à l’échelle d’un réacteur devient une composante d’importance croissante de la démonstration de sûreté à destination des agences de surveillance nationales. Elle permet ainsi de limiter le recours à des expériences complexes et coûteuses tout en facilitant l’évaluation des stratégies de mitigation. Cependant, les modèles mis en jeu sont inévitablement volumineux et construits avec une finesse de modélisation rendant difficile la prise en compte de détails géométriques locaux pourtant susceptibles d’influencer significativement la solution globale. Dans ce travail de thèse, on propose ainsi des approches multi-modèles pour l’intégration de tels détails dans un modèle global sans modification du maillage initial (on parle aussi de zoom numérique). Des techniques sont proposées aussi bien pour les structures que pour les fluides, avec un souci de démontrer la précision et la stabilité de la solution multi-modèles couplée comparée à une solution de référence à une seule échelle. Ce travail intègre deux spécificités propres, à savoir son adéquation avec les contraintes de la dynamique rapide avec intégration temporelle explicite et l’objectif de traiter simultanément la superposition de modèles et l’interaction fluide-structureIn nuclear industry, simulating accidental transient sequences at full reactor scale is becoming an increasingly important feature of the safety demonstration towards national agencies. It thus allows limiting the number of complex and costly experiments, while simplifying and accelerating the evaluation of mitigation strategies. However, the implemented numerical models are inevitably heavy to build and maintain, with a global modelling scale making it difficult to account for local geometric details yet able to significantly influence the physical solution. To provide an answer to these problems, this PhD work is dedicated to multi-model approaches designed to integrate such details into bigger models with no modification at the global level (techniques often designated as numerical zoom techniques). Some methods are proposed for both structures and fluids, with special care given to the accuracy and stability of the coupled multi-scale solution compared to a single-scale reference solution. This work handles two very specific topics, namely its compatibility with numerical features imposed by fast transient dynamics with explicit time integration, and the general objective of simultaneously dealing with superimposed models and fluid-structure interaction
2
Raii, Mohamed. "Formulation, caractérisation et mise en œuvre des barrières perméables réactives à base de phosphate de calcium, utilisation pour la fixation de polluants." Phd thesis, Toulouse, INPT, 2012. http://oatao.univ-toulouse.fr/9123/1/raii.pdf.
Анотація:
L'objectif principal de cette thèse est la formulation des mélanges stables contenant l'hydroxyapatite gel synthétisée (Ca-HAGel). Le comportement rhéologique des mélanges Eau/(sulfate de calcium) et hydroxyapatite/(sulfate de calcium) a été étudié. Les résultats ont montré que tout les mélanges sont caractérisés par un comportement rhéologique rhefluidifiant et thixotrope. Le potentiel zeta a été utilisé dans cette étude pour mieux appréhender les interactions entre les particules et leur effet sur le comportement des mélanges. La fixation de sulfate sur la surface de Ca- HA favorise la stabilité de la structure du Ca-HAGel. Les analyses de caractérisation effectuées sur les formulations ont montré la formation de nouveaux composés tels que le sulfate-phosphate de calcium hydrate et l'Ardealite. Les tests de lixiviation et de percolation ont révélé que le taux de relargage de soufre et strontium à partir des sous-produits de gypse était négligeable pour les mélanges contenant Ca-HAGel. Ca- HAGel stabilise les métaux lourds relargués à partir du gypse et plâtre. Les particules du gypse améliorent les performances hydrauliques de Ca-HAGel et le plâtre hydraté stabilise la structure de Ca-HAGel par la formation des particules agglomérées. Le test colonne effectué sur la formulation AWPG2 a montré une grande performance à retenir le plomb et le cadmium avec des capacités de rétention de plus de 99% et 88% respectivement. Le traitement des métaux lourds était lié aux particules de Ca-HA et aux phosphate et calcium libres. La formulation AWPG2 peut être utilisée dans les barrières perméables réactives pour traiter les eaux souterraines contaminées.
3
Moosavian, Mohammad Ali. "The structure and stability of liquid foam." Thesis, University of Manchester, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.332024.
4
Chan, Chau Ping. "Stability and structure of suspo-emulsion components." Thesis, University of Bristol, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.440050.
5
Magyari-Köpe, Blanka. "Structural stability of solids from first principles theory." Doctoral thesis, KTH, Physics, 2002. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3366.
6
Hu, Bin. "Stability analysis of linear thin shells." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2014. http://amslaurea.unibo.it/7360/.
Анотація:
Shell structure is widely used in engineering area. The purpose of this dissertation is to show the behavior of a thin shell under external load, especially for long cylindrical shell under compressive load, I analyzed not only for linear elastic problem and also for buckling problem, and by using finite element analysis it shows that the imperfection of a cylinder could affect the critical load which means the buckling capability of this cylinder.
For linear elastic problem, I compared the theoretical results with the results got from Straus7 and Abaqus, and the results are really close. For the buckling problem I did the same: compared the theoretical and Abaqus results, the error is less than 1%, but in reality, it’s not possible to reach the theoretical buckling capability due to the imperfection of the cylinder, so I put different imperfection for the cylinder in Abaqus, and found out that with the increasing of the percentage of imperfection, the buckling capability decreases, for example 10% imperfection could decrease 40% of the buckling capability, and the outcome meet the buckling behavior in reality.
7
Zhu, Jian. "The stabilities of RNA and DNA structural elements." Diss., Georgia Institute of Technology, 1998. http://hdl.handle.net/1853/25194.
8
Konstantopoulos, G. P. "A unified treatment of semisubmersible stability." Thesis, University of Strathclyde, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.382306.
9
Plotka, Hanna. "The structure, stability and interaction of geophysical vortices." Thesis, University of St Andrews, 2013. http://hdl.handle.net/10023/3729.
Анотація:
This thesis examines the structure, stability and interaction of geophysical vortices. We do so by restricting our attention to relative vortex equilibria, or states which appear stationary in a co-rotating frame of reference. We approach the problem from three different perspectives, namely by first studying the single-vortex, quasi-geostrophic shallow-water problem, next by generalising it to an (asymmetric) two-vortex problem, and finally by re-visiting the single-vortex problem, making use of the more realistic, although more complicated, shallow-water model. We find that in all of the systems studied, small vortices (compared to the Rossby deformation length) are more likely to be unstable than large ones. For the single-vortex problem, this means that large vortices can sustain much greater deformations before destabilising than small vortices, and for the two-vortex problem this means that vortices are able to come closer together before destabilising. Additionally, we find that for large vortices, the degree of asymmetry of a vortex pair does not affect its stability, although it does affect the underlying steady state into which an unstable state transitions. Lastly, by carefully defining the "equivalence" between cyclones and anticyclones which appear in the shallow-water system, we find that cyclones are more stable than anticyclones. This is contrary to what is generally reported in the literature.
10
Ayed, Ayeda. "Stability and structure of Escherichia coli citrate synthase." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp02/NQ31962.pdf.
11
Alhummiany, Haya A. "The structure and stability of colloidal nanoparticle assemblies." Thesis, University of Nottingham, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.604308.
Анотація:
Thiol-passivated gold nanoparticies deposited onto a silicon substrate from an organic solvent form a remarkable variety of self-organised nanostructured and microstructured patterns. The work in this thesis focuses on three key aspects of these systems: (i) their environmental stability, (ii) the formation of nanoparticie rings via condensation of water droplets, and (iii) the morphology of nanoparticie mono layers formed at the water-air interface and transferred to silicon substrates using the Langmuir-Blodgett technique. The nanoparticie structures were studied by combined atomic force microscopy (A FM) and contrast-enhanced optical microscopy. Striking changes in the morphology of self-organised nanoparticie patterns are observed during exposure to high humidity or high temperature environment. Annealing the sample at 1200 C leads to a high degree of nanoparticie sintering promoted by break-up of the initial assembly. Conversely, exposing the sample to a high relative humidity (80%) environment induces layer-by-layer assembly of 3D aggregates with no evidence of sintering. We focus also on the formation of rings of thiol-passivated Au nanoparticies, addressing the controversy in the literature regarding the formation of these structures. We provide compelling evidence that nanoparticie rings formed via the adsorption of droplets of condensed water. This so-called "breath figure" effect plays the dominant role in the dynamics of ring formation via iii evaporative dewetting. Different sizes and size distributions of nanoparticle rings have been created under controlled relative humidity environments ranging from ~50% to 80%. Fmthermore, the dynamic behaviour of water droplets on surface has been examined using a contrast-enhanced optical mIcroscope. Analysis of the observed droplet dynamics shows significant differences between the behaviour of droplets formed on top of a silicon substrate and the nanoparticle films. Finally, the formation of gold nanoparticle assemblies at the water-air interface using the Langmuir-Blodgett deposition technique has also been studied. The LB films were transferred to a solid substrate (silicon) and the nanoparticle assemblies fOlmed close to the contact line imaged by AFM and contrastenhanced optical microscopy. The experimental control parameters resulted in the emergence of variety of nanoparticie morphologies. We propose formation mechanisms for a number of these morphologies.
12
Hartsel, Scott Clifton. "Effect of membrane supramolecular structure on the photoresponse and structural stability of bacteriorhodopsin /." The Ohio State University, 1985. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487260531954914.
13
Rasmussen, Kim J. R. "Stability of thin-walled structural members and systems." Thesis, The University of Sydney, 2017. http://hdl.handle.net/2123/18194.
Анотація:
This DEng thesis consists of 83 articles containing research material on the stability of thin-walled structural members and systems with emphasis on metal structures. Metal structures are used widely in the construction industry. They include structural members and frames made from rolled and fabricated steel, cold-formed steel, stainless steel and aluminium. Common to these products is the desire to minimise the cross-sectional area to reduce weight and cost. Structural cross-sections are therefore thin-walled and prone to buckling, and an overriding consideration in the design of metal structures is to account for buckling in determining the strength of sections, members and frames. Specifically, the thesis is concerned with determining the reduction in buckling capacity and strength of structural members and frames caused by cross-sectional buckling and material softening. The thesis presents research under the headings Stainless Steel Structures - Hollow Sections, covering tubular columns, beams and welded connections; Stainless Steel Structures - Open Sections, addressing the effect of distortional buckling and interaction buckling on the design of stainless steel columns and beams; Analysis of Locally Buckled Members and Frames, describing a theory to determine the buckling loads of locally and/or distortionally buckled members and frames; Behaviour and Design of Members and Sections Composed Solely or Predominantly from Unstiffened Elements, outlining analytical, numerical and experimental research to advance the understanding of the behaviour and design of singly symmetric cross-sections made up entirely or predominantly from plate elements, including angle sections, T-sections and plain channel sections; Cold-formed Steel Structural Systems, describing numerical and experimental investigations of steel storage racks including selective and drive-in racking systems; and System-based Design of Steel Structures, developing a general framework for designing steel structural framing systems by advanced analysis, termed the Direct Design Method. The thesis also highlights the implementation of the research outcomes in national and international specifications for the design of steel, cold-formed steel and stainless steel structures.
14
Blanchon, Guillaume. "Reaction and structure models for nuclei far from stability." Paris 11, 2008. http://www.theses.fr/2008PA112350.
Анотація:
Cette these traite de l'etude spectroscopique des noyaux exotiques. Nous nous concentrons plus Particulierement sur la structure et les reactions impliquant les systemes a halo de deux neutrons. Notre but principal est d'etablir l'ordre des single particules dans differents noyaux en utilisant la random phase approximation particule-particule (pp-rpa) et des modeles de reaction adaptes. La premiere partie traite du transfert au continu que nous appliquons a l'etude du 10li. Dans la seconde partie, nous developpons un modele de fragmentation des noyaux halo. Nous etudions ainsi les noyaux: 13be et 10li. Dans une troisieme partie nous etudions une serie d'isotopes du beryllium avec la pp-rpa. L'ordre des niveaux dans le 13be est etabli. Finalement dans la derniere partie, nous presentons des calculs en voies couplees pour l'etude de reactions de transfert envisageables avec la facilite a venir eurisolThis thesis is concerned with sprectroscopic studies of exotic nuclei. We concentrate on the Structure and reactions of two-neutron halo systems. Our main goal is to establish the single Particle shell ordering in a series of cases through the use of the particle-particle random approximation (pp-rpa) structure calculations, appropriate reaction mechanism models and comparison with data. In a first part, we study transfer to the continuum reaction. By studying neutron transfer from a series of targets (d, 9be, 12c) to a 9li beam, we show that theory of transfer reaction from bound to Continuum states is well suited to extract structure information on 10li from experiment. The next chapter deals with a fragmentation model. We study 13be and 10li. In the third part the nuclear structure of halo nuclei is studied by applying the pp-rpa to a range of beryllium isotopes from 8be to 14be. Results obtained with our method for different observables are compared with available experiemental data With success. The level oredering in 13be is established on a firm basis. Finally in the fourth part, we present coupled-channels calculations related to transfer experiments for the forthcoming Facility eurisol
15
Shehan, Joe Michael. "Stability analysis of a 2-D acoustic/structure model." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1995. http://handle.dtic.mil/100.2/ADA303097.
16
Jokela, Slade Joseph. "Stability and structure of hydrogen defects in zinc oxide." Online access for everyone, 2006. http://www.dissertations.wsu.edu/Dissertations/Fall2006/s_jokela_122106.pdf.
17
Gatkowski, Mateusz. "Financial network stability and structure : econometric and network analysis." Thesis, University of Essex, 2015. http://repository.essex.ac.uk/17090/.
Анотація:
Since the Global Financial Crisis, the literature of financial networks analysis has been trying to investigate the changes in the financial networks structure, that led to the instability of the financial system. The Global Financial Crisis followed by the Great Recession costed taxpayers an unprecedented $14 trillion (Alessandri and Haldane, 2009), austerity and downturns in GDP. The dynamics of the financial networks transferred the collapse of a US housing market bubble into a large meltdown of the financial systems globally. The study of systemic risk and macro-prudential policy has come to the forefront to model and manage the negative externalities of monetary, fiscal and financial sector activities that can lead to system wide instabilities and failure. The dimensions of crisis propagation have been modelled as those that can spread cross-sectionally in domino like failures with global scope, or build up over time, as in asset bubbles. The cross sectional propagation of shocks that occur due to non-payment of debt or other financial obligations with the failure of a financial intermediary or a sovereign leading to the failure of other economic entities, is called financial contagion. Cross sectional analysis of financial contagion can be done using statistical methods or by network analysis. The latter gives a structural model of the interconnections in terms of financial obligations. This dissertation uses both approaches to model financial contagion. The applications include the study of systemic risk in Eurozone Sovereign crisis, the US CDS market and the global banking network. This is organized in three self-contained chapters Our contribution to the literature begins with the study of the dynamics of the market of the Credit Default Swap (CDS) contracts for selected Eurozone sovereigns and the UK. The EWMA correlation analysis and the Granger-causality test demonstrate that there was contagion effect since correlations and cross-county interdependencies increased after August 2007. Furthermore, the IRF analysis shows that among PIIGS, the CDS spreads of Spain and Ireland have the biggest impact on the European CDS spreads, whereas the UK is found not be a source of sovereign contagion to the Eurozone. Next we perform the empirical reconstruction of the US CDS network based on the real-world data obtained from the FDIC Call Reports, and study the propagation of contagion, assuming different network structures. The financial network shows a highly tiered core-periphery structure. We find that network topology matters for the stability of the financial system. The “too interconnected to fail” phenomenon is discussed and shown to be the result of highly tiered network with central core of so called super-spreaders. In this type of network the contagion is found to be short, without multiple waves, but with very high losses brought by the core of the network. Finally we study a global banking network (GBN) model based on the Markose (2012) eigen-pair approach and propose a systemic risk indices (SRI) which provide early warning signals for systemic instability and also the rank order of the systemic importance and vulnerability of the banking systems. The empirical model is based on BIS Consolidated Banking Statistics for the exposures of 19 national banking systems to the same number of debtor countries and the data obtained from Bankscope for the equity capital of these 19 national banking systems. The SRI is based on the ratio of the netted cross-border exposures of the national banking systems to their respective equity capital. The eigen-pair method stipulates that if the maximum eigenvalue of the network exceeds the capital threshold, there is cause for concern of a contagion. This is compared with the loss multiplier SRI proposed by Castrén and Rancan (2012). The latter is found to have no early warning capabilities and peaks well after the onset of the crisis in 2009 while the eigen-pair SRI gives ample warning by late 2006 that the cross border liabilities was unsustainable in respect of the equity capital of the national banking systems. We contribute to the literature by highlighting the efficacy of the network approach to systemic stability analysis of GBNs. In particular we develop an eigen-pair approach for GBNs and prove its usefulness in an early warning context.
18
Railton, Anna Dorothy. "The structure and stability of vortices in astrophysical discs." Thesis, University of Cambridge, 2015. https://www.repository.cam.ac.uk/handle/1810/252700.
Анотація:
This thesis finds that vortex instabilities are not necessarily a barrier to their potential as sites for planetesimal formation. It is challenging to build planetesimals from dust within the lifetime of a protoplanetary disc and before such bodies spiral into the central star. Collecting matter in vortices is a promising mechanism for planetesimal growth, but little is known about their stability under these conditions. We therefore aim to produce a more complete understanding of the stability of these objects. Previous work primarily focusses on 2D vortices with elliptical streamlines, which we generalise. We investigate how non?constant vorticity and density power law profiles affect stability by applying linear perturbations to equilibrium solutions. We find that non?elliptical streamlines are associated with a shearing flow inside the vortex. A ?saddle point instability? is seen for elliptical?streamline vortices with small aspect ratios and we also find that this is true in general. However, only higher aspect ratio vortices act as dust traps. For constant?density vortices with a concentrated vorticity source we find parametric instability bands at these aspect ratios. Models with a density excess show many narrow bands, though with less strongly growing modes than the constant?density solutions. This implies that dust particles attracted to a vortex core may well encounter parametric instabilities, but this does not necessarily prevent dust?trapping. We also study the stability and lifetime of vortex models with a 2D flow in three dimensions. Producing nearly?incompressible 3D models of columnar vortices, we find that weaker vortices persist for longer times in both stratified and unstratified shearing boxes, and stratification is destabilising. The long survival time for weak, elongated vortices makes it easier for processes to create and maintain the vortex. This means that vortices with a large enough aspect ratio have a good chance of surviving and trapping dust for sufficient time in order to build planetesimals.
19
Schleer, Matthias. "Flow structure and stability of a turbocharger centrifugal compressor /." Düsseldorf : VDI-Verl, 2006. http://bvbr.bib-bvb.de:8991/F?func=service&doc_library=BVB01&doc_number=015054634&line_number=0001&func_code=DB_RECORDS&service_type=MEDIA.
20
Söderberg, Karin. "Structure and stability of Bi₁₋xSbx and CaAl₂₋xZnx /." Stockholm : Department of Structural Chemistry, Stockholm University, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-624.
21
Acharya, Ananta R. "Indium Nitride Surface Structure, Desorption Kinetics and Thermal Stability." Digital Archive @ GSU, 2013. http://digitalarchive.gsu.edu/phy_astr_diss/62.
Анотація:
Unique physical properties such as small effective mass, high electron drift velocities, high electron mobility and small band gap energy make InN a candidate for applications in high-speed microelectronic and optoelectronic devices. The aim of this research is to understand the surface properties, desorption kinetics and thermal stability of InN epilayers that affect the growth processes and determine film quality as well as device performance and life time. We have investigated the structural properties, the surface desorption kinetics, and the thermal stability using Auger electron spectroscopy (AES), x-ray diffraction (XRD), Raman spectroscopy, atomic force microscopy (AFM), high resolution electron energy loss spectroscopy (HREELS), and temperature programmed desorption (TPD). Investigations on high pressure chemical vapor deposition (HPCVD)-grown InN samples revealed the presence of tilted crystallites, which were attributed to high group V/III flux ratio and lattice mismatch. A study of the thermal stability of HPCVD-grown InN epilayers revealed that the activation energy for nitrogen desorption was 1.6±0.2 eV, independent of the group V/III flux ratio. Initial investigations on the ternary alloy In0.96Ga0.04N showed single-phase, N-polar epilayers using XRD and HREELS, while a thermal desorption study revealed an activation energy for nitrogen desorption of 1.14 ± 0.06 eV.
HREELS investigations of atomic layer epitaxy (ALE)-grown InN revealed vibrational modes assigned to N-N vibrations. The atomic hydrogen cleaned InN surface also exhibited modes assigned to surface N-H without showing In-H species, which indicated N-polar InN. Complete desorption of hydrogen from the InN surface was best described by the first-order desorption kinetics with an activation energy of 0.88 ± 0.06 eV and pre-exponential factor of (1.5 ± 0.5) ×105 s-1.
Overall, we have used a number of techniques to characterize the structure, surface bonding configuration, thermal stability and hydrogen desorption kinetics of InN and In0.96Ga0.04N epilayers grown by HPCVD and ALE. High group V/III precursors ratio and lattice mismatch have a crucial influence on the film orientation. The effects of hydrogen on the decomposition add to the wide variation in the activation energy of nitrogen desorption. Presence of surface defects lowers the activation energy for hydrogen desorption from the surface.
22
Dunn, Carolyn M. "Phase behavior, structure and stability of surfactant organised assemblies." Thesis, University of East Anglia, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.236841.
23
Bayeh, Joseph N. "Systemic effects on the structure and stability of Lebanon." Thesis, University of Exeter, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.426162.
24
Sharpe, Timothy David. "Structure, stability and folding kinetics of small protein domains." Thesis, University of Cambridge, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.616265.
25
Radford, Matthew. "Purification structure and stability of voltage-gated sodium channels." Thesis, Birkbeck (University of London), 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.535845.
Анотація:
Voltage gated sodium channels (VGSC) are integral membrane proteins that selectively transport sodium ions across cellular membranes in response to changes in membrane potential. In vertebrates sodium channels are composed of a pore forming alpha subunit and one or more auxiliary beta subunit. There are a total of nine different alpha subunit isoforms and four known beta subunits. In higher eukaryotes VGSCs are responsible for fast electrical signalling through the propagation of action potentials in excitable cells such as neurons and muscle. Voltage gated sodium channels due to their physiological importance are established drug targets for anticonvulsants, local anaesthetics and antiarrhythmics. They are also the target of a number of naturally produced neurotoxins that form a diverse group of compounds including polypeptides such as scorpion toxins, alkaloids such as veratridine and others such as heterocyclic guanidines. The work of this thesis has been to isolate and purify firstly a higher eukaryotic sodium channel sourced from the electroplax tissue of the eel Electrophorus electricus and secondly a prokaryotic channel (NaChBac) that was over expressed in an E. Coli cell system. Purified channels were biophysically characterised using circular dichroism spectroscopy to analyse secondary structure content. Purified NaChBac was chemically and thermally unfolded using SDS and monitored using CD. The drug mibefradil was able to bind NaChBac and increase its Tm by 4°C. Ligand binding to the Eel channel was also investigated using CD and tryptophan fluorescence to establish if secondary or tertiary structural changes could be observed upon ligand binding.
26
Uye, U. O. "Stability, structure, and formulation of antibody fragments during bioprocessing." Thesis, University College London (University of London), 2014. http://discovery.ucl.ac.uk/1451193/.
Анотація:
Despite their huge potential as therapeutic agents, protein molecules are not naturally optimised for stability and are susceptible to aggregation during bioprocessing. A good understanding the mechanisms that drive protein aggregation is therefore important to enable the development of strategies for eliminating protein aggregation bioprocessing. To better understand the factors affecting aggregation, a detailed kinetic and biophysical analysis of the Af-X molecule when subjected to a range of pH and NaCl concentrations was carried out. At pH 4.0, a salt-induced dimer was found to accumulate at low NaCl concentrations, but less so at higher salt where the rate of protein precipitation increased. Kinetic studies showed that this salt-induced dimer is not an intermediate on the Af-X precipitation pathway. Surface plasmon resonance, circular dichroism, and fluorescence spectroscopy highlighted the biological inactivity of the salt-induced dimer and confirmed its structural and functional similarity to a previously observed cell culture dimer. Analysis of the crystal structures of both dimers confirmed the biophysical characterisation. The post induction time and cellular location of Af-X dimer formation, as well as the effect of IPTG concentration, temperature, and post-induction feed rate on the propensity for dimerisation of the Af-X molecule, were investigated using fed-batch fermentation. While a decrease in both the IPTG concentration and the post-induction feed rate resulted in a 2% increase and a 5% decrease (respectively) in dimer content of the total Af-X yield, a reduction in the post-induction temperature resulted in a 12% increase in the dimer content of the total Af-X yield. This unexpected increase in dimer concentration was found to agree with the proposed effect of temperature on the Af-X mechanism of aggregation. Site-directed mutagenesis was used to generate L-XX-KVRST single and H-XX-Y/L-XX-KVRST double mutants that were evaluated for their propensity for aggregation both in solution and during E. coli cell culture. While the L-XX-K single mutant was found to be destabilising to the Af-X molecule, the L-XX-R single mutant was found to be stabilising. These contrasting observations can be explained by taking into account possible physical distance limitations or angular orientation of the lysine side chain that is less than optimal for salt bridge formation with the aspartic acid residue at position XX. Finally, samples of Af-X were incubated for 8 weeks at 25 °C without shaking, and compared to samples incubated for 6 days at 25 °C with shaking in order to establish a correlation between agitation and the long term stability studies commonly used in formulation development. The effect of ultrasonication on the propensity for aggregation of the Af-X molecule was also assessed using a time-course experiment. Both agitation and sonication had negligible effects on the propensity for Af-X dimerisation. In addition to providing useful insights into aggregation in the Af-X molecule, this work will serve as a starting point for future investigation of aggregation in antibody fragments in general. A number of potential future directions that build on these insights are also discussed.
27
Silwana, Nothemba. "Structure and thermal stability of selected organic inclusion compounds." Thesis, Cape Peninsula University of Technology, 2012. http://hdl.handle.net/20.500.11838/2618.
Анотація:
Thesis (MTech (Chemistry))--Cape Peninsula University of Technology, 2012.Crystal engineering is the synthesis of new crystalline materials with specific chemical and physical properties which allows the comprehensive understanding of the non covalent interactions that occur between molecules in the crystalline state. This has lead to extensive work being done in terms of host design. The study of non-covalent interactions formed by - these materials is crucial to understanding many biological processes. This study focuses on the inclusion compounds of 1, 4-bis (diphenylhydroxymethyl) benzene H, a host compound engineered by EWeber, that conforms to Weber's rules for host design as it is bulky, rigid, and has hydroxyl moieties that act as hydrogen-bonding donors. A Cambridge Structural Database (CSDversion 5.33) search has revealed that no research has been conducted on this host compound. Characterization of the compounds were conducted using thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), hot stage microscopy (HS), gas chromatography (GC), powder X-ray diffraction(PXRD) and single X -ray diffraction. Host: guest ratios determined from TG analysis were correlated with structural analysis results. We have successfully prepared inclusion compounds with N, N- dimethylformamide(DMF) N, N- dimethylacetamide (DMA), N-methylformamide (NMF) and N-methylacetamide (NMA), 2-picoline, 3-picoline, 4-picoline, pyridine and morpholine. Following which a series of competition experiments were conducted to establish the selectivity profile of the host by dissolving the host in an excess of two guests pairs, between DMF: DMA, DMF: NMF, DMF: NMA, DMA: NMF, DMA: NMA and NMF: NMA. The results of the competition experiment showed that the host had high selectivity for DMF and the selectivity profile follows a trend as follows DMF>NMA>NMF>DMA. The results for the competition experiments between the picolines, pyridine and morpholine were inconclusive.
28
Tsiamantas, Christos. "Synthesis and structure-stability relationship of aromatic helical foldamers." Thesis, Bordeaux, 2015. http://www.theses.fr/2015BORD0029/document.
Анотація:
Au niveau moléculaire, les fonctions des motifs hélicoïdaux sont souvent associées à la stabilité de cesarchitectures. Par exemple, lorsqu’une hélice α est isolée de la structure tertiaire des protéines, celle-cidevient alors flexible et perd son activité. Afin de contrôler la rigidité de ces architectures, différentesapproches ont été proposées dont la construction d’édifices moléculaires repliés de façon contrôlée : lesfoldamères. Notre équipe s’intéresse aux foldamères d’oligoamide aromatique hélicoïdaux et à l’heureactuelle plusieurs études ont déjà été menées afin de comprendre les facteurs influant la stabilité de telleshélices: la longueur de l’oligomère, le solvant et l’effet de l’introduction d’un espaceur aliphatique dans laséquence. Lors de ce travail nous nous sommes tout d’abord intéressés à la capacité de repliement de cinqmonomères aromatiques couramment utilisés pour la préparation de foldamères. Leur contribution dans lastabilité hélicoïdale du système a été évaluée par RMN, diffraction des rayons-X et HPLC chirale dynamique.Inspirés par le rôle des ponts disulfure dans les protéines, nous avons décidé d’explorer l’effet d’une telleliaison sur la stabilité des hélices d’oligoamide aromatique. Deux composés contenant une liaison disulfureintramoléculaire ou deux liaisons intermoléculaires ont été synthétisés et leur stabilité étudiée par RMN, HPLCChiral et Dichroïsme circulaire.Enfin, la synthèse d’hélices moléculaires de grandes dimensions (assimilables à celles de polymèresmonodisperses) a été réalisée par une approche convergente de triplement de longueur de segment via laformation de liaisons anhydrides entre blocs oligomériquesAt the molecular level, the functions of helical patterns are often directly associated with the stability of thesearchitectures, (in α-helices). For example, upon removal of such an entity from the protein’s tertiary structure,the peptidic helix becomes flexible and thus inactive. In order to control the rigidity of these architectures,several strategies have been used and the construction of completely artificial well folded molecules known asfoldamers is one them. Our group mainly focuses on helical aromatic oligoamide foldamers and to dateseveral studies have been carried out to investigate factors affecting the helical stability; the influence ofoligomer length, solvent effects and the effect of aliphatic linkers within a helical aromatic sequence.In the present study we investigate the helical propensity of five commonly used aromatic monomers infoldamer synthesis and by using NMR spectroscopy, X-ray crystallography and dynamic chiral HPLC weevaluate their contribution in helical stability. Additionally, inspired by the role of disulfide bonds in proteins wedecided to explore their effect on helical stability. For this reason intra- and inter-molecularly disulfide bondedcompounds were designed and synthesized. Their stability was studied using NMR spectroscopy, chiral HPLCand CD experiments.Finally, the synthesis of mono-disperse helical strings of polymeric dimensions through a convergent, segmenttripling strategy has been developed. This protection/deprotection free synthesis was carried out byconnecting oligomeric blocks via a labile anhydride functionality
29
Astudillo, Ariel. "Nebulisation effects on the structure stability of bacteriophage PEV44." Thesis, The University of Sydney, 2016. http://hdl.handle.net/2123/17955.
Анотація:
With the present concern of widespread appearance of multi-drug resistant bacteria, bacteriophage therapy is currently being considered as a suitable alternative for bacterial infections. In the area of respiratory infections, inhalation by nebulisation is a preferred method for the delivery of phage formulations into the lung. However, the process of nebulisation is known to reduce infectivity levels (expressed by the tire loss) of phage preparations. It is unknown if any structural or morphological changes occur to the phage during nebulisation, and if any of such changes contribute to the titre loss. In this study, three different types of nebulisers were used relying on air-jet, vibrating mesh and static mesh mechanisms (SideStream, Aeroneb Go and Omron NE22, respectively) for aerosol generation. PEV44 was used as a bacteriophage model and nebulisation effects on its structure were assessed by transmission electron microscopy (TEM). Samples were negatively stained with 1% Phosphotungstic acid (PTA). Aerosol characteristics were measured by laser diffraction and phage viability by the plaque assay method. The viability within the aerosol respirable fraction was determined by particle size deposition using a multi-stage liquid impactor (MSLI). Air-jet and vibrating mesh nebulisations (SideStream and Aeroneb Go) caused a larger change on the phage morphology than static mesh nebulisation, with 50% of phages having their tail lost. In contrast, static mesh nebulisation (Omron NE22) caused only 15% tail detachment. Among the phages that conserved the tail, further observations showed that air-jet and vibrating mesh nebulisations caused tail contraction on almost 100% of phages while nebulisation by the static mesh mechanism affected about 80% of the phages. Moreover, the air-jet nebuliser caused the production of significantly more empty capsids compared with the other two nebulisers. All three nebulisers produced a similar reduction in phage viability of up to 80% (< 1 log reduction) from the initial titer. In terms of a viable respirable fraction (VRF), the Omron showed a better delivery of viable phages and had a lesser effect on the phage structure than the SideStream air-jet and Aeroneb Go vibrating mesh nebulisers.
30
Rabayda, Daniel P. "The Structure and Stability of Cationic Metal-Benzene Clusters." VCU Scholars Compass, 2019. https://scholarscompass.vcu.edu/etd/5823.
Анотація:
We have investigated the size-dependent stability and structure of benzene, aluminum-benzene, and vanadium-benzene clusters. Motivated by gas-phase experimental studies performed by an experimental collaborator, we have used first-principle electronic structure methods to identify the structure of Al+(Bz)n, V+(Bz)n, and Bzn clusters. Our studies reveal that cationic aluminum-benzene clusters have a magic number of 13, and that its high stability may be understood by analyzing the structure of the cluster. We also investigate the structure of vanadium-benzene clusters which have a magic number of 2. Here I examine the benzene-cation and benzene-benzene interactions that lead to these magic numbers, as well as their geometric shell structures and their formation/solvation.
31
ZHANG, Jingyao. "STRUCTURAL MORPHOLOGY AND STABILITY OF TENSEGRITY STRUCTURES." 京都大学 (Kyoto University), 2007. http://hdl.handle.net/2433/49132.
Анотація:
学位授与大学：京都大学 ; 取得学位: 博士(工学) ; 学位授与年月日: 2007-09-25 ; 学位の種類: 新制・課程博士 ; 学位記番号: 工博第2856号 ; 請求記号: 新制/工/1420 ; 整理番号: 25541Kyoto University (京都大学)
0048
新制・課程博士
博士(工学)
甲第13385号
工博第2856号
新制||工||1420(附属図書館)
25541
UT51-2007-Q786
京都大学大学院工学研究科建築学専攻
(主査)教授 加藤 直樹, 教授 上谷 宏二, 准教授 大﨑 純
学位規則第4条第1項該当
32
Neumann, Michael Landon. "A method for the spatial functionalization of the dynamic response of a structure with structural stability considerations." Thesis, This resource online, 1993. http://scholar.lib.vt.edu/theses/available/etd-06112009-063931/.
33
Wang, Chaomin [Verfasser], Horst [Akademischer Betreuer] Hahn, and Karsten [Akademischer Betreuer] Albe. "Atomic structure and structural stability of Fe90Sc10 nanoglasses / Chaomin Wang ; Horst Hahn, Karsten Albe." Darmstadt : Universitäts- und Landesbibliothek Darmstadt, 2017. http://d-nb.info/1147968446/34.
34
Maccallum, Peter Hugh. "Hydrogen bonding and the stability of the polypeptide backbone." Thesis, University of Glasgow, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.360133.
35
Nanayakkara, Masarachige A. "Finite element analysis for the elastic stability of thin walled open section columns under generalized loading." Thesis, Loughborough University, 1986. https://dspace.lboro.ac.uk/2134/7501.
Анотація:
The current interest in collapse characteristics brought about by crashworthiness requirements ýas shown the need for a better understanding and predictive capability for the thin walled open section structures. In general three possible modes exist in which a loaded thin walled open section column can buckle: 1) they can bend in the plane of one of the principal axes; 2) they can twist about the shear. centre; 3) or they can bend and twist simultaneously. The following study was undertaken to investigate the general failure of thin walled open section structures. A literature survey was conducted and it prevailed that a basic fundamental theoretical study was vital in describing the behaviour of thin walled structural members. The following stages of theoretical study have been completed: 1) Formulation of the stiffness matrix to predict the generalised force-displacement relationships assuming the small displacement theory in the linear elastic range. 2) Formulation of the geometric stiffness matrix to predict the buckling criteria under generalised loading and end constraints in the linear elastic range. 3) Formulation of the compound coordinate transformation matrix to relate local and global displacements or forces. 4) Preparation of the associated finite element computer program to solve general thin walled open sections structural problems.
36
Hashimoto, Ryota. "Development of Stability Evaluation Methods for Soil-Masonry Structure Interactive Problems and Application to Historic Structures." 京都大学 (Kyoto University), 2017. http://hdl.handle.net/2433/225552.
37
Tournebize, Aurélien. "Structure électronique et stabilité de matériaux pour le photovoltaïque organique." Thesis, Clermont-Ferrand 2, 2015. http://www.theses.fr/2015CLF22654/document.
Анотація:
Ce travail de thèse a été consacré à l’étude de la stabilité dans différents milieux des matériaux constitutifs de la couche active des cellules solaires organiques. Les deux objectifs principaux étaient premièrement d’approfondir la compréhension sur certains mécanismes complexes intervenant dans la couche active, et deuxièmement d’étudier les processus de dégradation intervenant spécifiquement aux interfaces de la couche active au sein de la cellule. La première partie de ce mémoire est consacrée à l’étude de la dégradation photochimique et thermique de la couche active des cellules solaires en faisant varier le matériau polymère qui la constitue. La deuxième partie est dédiée au rôle d’un troisième composant de la couche active que peut être la présence d’additifs résiduels provenant de la mise en forme, ou d’un additif stabilisant ajouté à dessein. La troisième partie est consacrée au processus de délamination susceptible d’intervenir à l’interface couche active / couche transporteuse de trous. Enfin, une dernière partie concerne l’étude de l’alignement des niveaux énergétiques entre la molécule de C60 et divers substrats transporteurs d’électrons. L’influence de la lumière et de la température sur les propriétés d’interface couche active / couche transporteuse d’électrons est également reportéeThis word was devoted to the stability in various conditions of materials used in the active layer of organic solar cells. The main goals of this work were first to provide deeper understanding about complex mechanisms occurring in the active layer and second to investigate interfacial degradation pathways involving the active layer. A first part was dedicated to the photo and thermal stability of the polymer blend materials which constitute the active layer of the solar cells. A second section focused on the role of the third component of the active layer which can be undesired residual additives coming from the processing or the desired insertion of a stabilizer additive. A third part concerned the delamination issue which takes place at the active layer / hole transporting layer interface. Finally, a last section was devoted to the energy level alignment between the C60 molecules and various electron transporting substrates. The photo and thermal stability of the active layer / electron transporting layer interface was also studied in this section
38
Janko, Marek. "Structure and stability of biological materials – characterisation at the nanoscale." Diss., lmu, 2012. http://nbn-resolving.de/urn:nbn:de:bvb:19-143453.
39
Motaung, David Edmond. "Structure property relationship and thermal stability of organic photovoltaic cells." Thesis, University of the Western Cape, 2010. http://etd.uwc.ac.za/index.php?module=etd&action=viewtitle&id=gen8Srv25Nme4_6331_1307942460.
Анотація:
In this thesis, regioregularpoly( 3-hexylthiophene) (rr-P3HT) polymer was used as a light absorption and electron donating material, while the C60 fullerene and its derivative [6,6]-phenyl C61-butyric acid methyl ester (PCBM) were used as electron acceptor materials. The effect of solvent to control the degree of mixing of the polymer and fullerene components, as well as the domain size and charge transport properties of the blends were investigated in detail using P3HT:C60 films. The photo-physical, structural and electrical transport properties of the polymer blends were carried out according to their ratios. A distinctive photoluminescence (PL) quenching effect was observed indicating a photo-induced electron transfer. In this thesis, the effect of solvents on the crystallization and interchain interaction of P3HT and C60 fullerene films were studied using XRD, UV-vis, PL, Raman and FTIR spectroscopy. The polymer blends formed with non-aromatic solvents exhibited an improved crystallinity and polymer morphology than that formed with aromatic solvents. An improved ordering was demonstrated in the polymer films spin coated from non-aromatic solvents. This indicates that the limited solubility of rr P3HT in a marginal solvent such as non-aromatic solvents can offer a strategy to obtain highly ordered crystal structures and lead directly to optimal morphologies on the films.
40
Tworzecki, Hubert. "Measuring the structure and stability of opinion in mass publics." Thesis, University of British Columbia, 1989. http://hdl.handle.net/2429/28555.
Анотація:
This thesis examines the structure and stability of public opinion in a sample of Canadian respondents. The data consist of a three-wave panel of 1790 cases; the interviews were conducted in 1977, 1979 and 1980 as part of the Social Change in Canada project of the Institute for Behavioral Research of York University. In the first part of the thesis various theoretical and methodological issues pertinent to the study of mass political attitudes are discussed and a research strategy is proposed. In the second part, factor analysis is used to extract structural information from the data. It is found that the opinions of English-speaking respondents can be described in terms of four fundamental dimensions which are given the tentative labels of "welfare liberalism," "nostalgic conservatism," "pro-business," and "provincial rights." For French-speaking respondents, two dimensions are found: "welfare liberalism" and "protection of French-Canadian society." Finally, regression analysis is performed on factor-based scales to obtain more information about the opinion structures. The central finding is that it is indeed possible to use mass survey data to identify a simple structure of political beliefs of the Canadian public, and to tie this structure to the political and social makeup of the country.Arts, Faculty of
Political Science, Department of
Graduate
41
Welsh, Francis Paul. "Shock structure and stability in low density under-expanded jets." Thesis, University of Oxford, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.302489.
42
Eastoe, Julian. "Influence of pressure on the structure and stability of microemulsions." Thesis, University of East Anglia, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.236911.
43
SANTEE, DONALD MARK. "NONLINEAR VIBRATION AND STRUCTURE STABILITY ANALYSIS OF IMPERFECTION SENSITIVE ELEMENTS." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 1999. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=1897@1.
Анотація:
COORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIORO objetivo desta tese é estudar os mecanismos de escape em sistemas estruturais sensíveis a imperfeições quando submetidos a certas classes de carregamentos dinâmicos, identificar os parâmetros que controlam o escape e criar critérios capazes de prever a fronteira de escape e a perda de estabilidade da estrutura no espaço dos parâmetros de controle. Isto permitirá um melhor entendimento dos processos de perda de estabilidade e servirá de base para o cálculo e controle da integridade dessas estruturas. Após a descrição dos fenômenos que podem ocorrer na dinâmica dessa classe de estruturas, são testados e adaptados alguns critérios existentes na literatura, que verificam a estabilidade de uma estrutura a partir do conhecimento dos parâmetros de controle. Em seguida estuda-se a evolução da estabilidade global do conjunto das soluções medida pela área da bacia de atração, e pelas características de sua fronteira. Desenvolvem-se expressões gerais para o critério de Melnikov, e mostra-se, a partir de perturbações aleatórias nos parâmetros de controle e na força externa, que essas expressões podem ser tomadas como um limite inferior para o carregamento de escape e conseqüentemente como uma contribuição para o desenvolvimento de critérios de projeto. Verifica-se também que os valores obtidos pelos critérios de escape podem ser tomados como limites superiores para o valor da força de escape.
The purpose of this thesis is to study the escape mechanisms in imperfection sensitive structural systems under certain dynamical loading conditions. Other objectives are to identify the parameters that control the escape phenomenon and to create some criteria capable of predicting the escape boundary and the structures stability in the control parameters space. This will allow a better understanding of the stability loss process and can serve as a basis to the integrity control and design of these structures. After a description of the phenomena that can occur in the dynamics of this class of structures, some predictive criteria, found in literature, that verify the structure stability based on the control parameters knowledge, are adapted and tested. Following is a study of the evolution of the global stability of the set of solutions measured by the basin of attraction area, and by the characteristics of its boundary. Some general expressions for the Melnikov criterion are developed, and it is shown by randomly perturbing the control parameters and the external force, that these expressions can be taken as a lower bound for the escape load, and consequently as a contribution to the development of design criteria. It is also observed that the values obtained by the escape criteria can be taken as an upper bound for the values of the escape force.
EL objetivo de esta tesis es estudiar los mecanismos de escape en sistemas extructurales que son sensibles a imperfecciones cuando son sometidos a ciertas clases de cargas dinámicas. Outro objetivo es identificar los parámetros que controlan el escape y crear criterios capaces de preveer la frontera de escape y la pérdida de estabilidad de la extructura en el espacio de los parámetros de control. Esto permitirá una mejor comprensión de los procesos de pérdida de estabilidad y servirá de base para el cálculo y control de la integridad de esas extructuras. Después de describir los fenómenos que pueden ocurrir en la dinámica de esta clase de extructuras, se prueban y adaptan algunos criterios existentes en la literatura, que verifican la estabilidad de una extructura a partir del conocimiento de los parámetros de control. Seguidamente, se estudia la evolución de la estabilidad global del conjunto de las soluciones, se dearrollan expresiones generales para el criterio de Melnikov, y se muestra, a partir de perturbaciones aleatorias en los parámetros de control y en la fuerza externa, que esas expresiones pueden ser tomadas como límite inferior para la carga de escape y conseqüentemente como una contribución para el desarrollo de criterios de proyecto. Se verifica también que los valores obtenidos por los criterios de escape pueden ser tomados como límites superiores para el valor de la fuerza de escape.
44
Nelson, Joseph Richard. "Crystal structure prediction at high pressures : stability, superconductivity and superionicity." Thesis, University of Cambridge, 2017. https://www.repository.cam.ac.uk/handle/1810/268482.
Анотація:
The physical and chemical properties of materials are intimately related to their underlying crystal structure: the detailed arrangement of atoms and chemical bonds within. This thesis uses computational methods to predict crystal structure, with a particular focus on structures and stable phases that emerge at high pressure. We explore three distinct systems. We first apply the ab initio random structure searching (AIRSS) technique and density functional theory (DFT) calculations to investigate the high-pressure behaviour of beryllium, magnesium and calcium difluorides. We find that beryllium fluoride is extensively polymorphic at low pressures, and predict two new phases for this compound - the silica moganite and CaCl$_2$ structures - to be stable over the wide pressure range 12-57 GPa. For magnesium fluoride, our results show that the orthorhombic `O-I' TiO$_2$ structure ($Pbca$, $Z=8$) is stable for this compound between 40 and 44 GPa. Our searches find no new phases at the static-lattice level for calcium difluoride between 0 and 70 GPa; however, a phase with $P\overline{6}2m$ symmetry is energetically close to stability over this pressure range, and our calculations predict that this phase is stabilised at high temperature. The $P\overline{6}2m$ structure exhibits an unstable phonon mode at large volumes which may signal a transition to a superionic state at high temperatures. The Group-II difluorides are isoelectronic to a number of other AB$_2$-type compounds such as SiO$_2$ and TiO$_2$, and we discuss our results in light of these similarities. Compressed hydrogen sulfide (H$_2$S) has recently attracted experimental and theoretical interest due to the observation of high-temperature superconductivity in this compound ($T_c$ = 203 K) at high pressure (155 GPa). We use the AIRSS technique and DFT calculations to determine the stable phases and chemical stoichiometries formed in the hydrogen-sulfur system as a function of pressure. We find that this system supports numerous stable compounds: H$_3$S, H$_7$S$_3$, H$_2$S, H$_3$S$_2$, H$_4$S$_3$, H$_2$S$_3$ and HS$_2$, at various pressures. Working as part of a collaboration, our predicted H$_3$S and H$_4$S$_3$ structures are shown to be consistent with XRD data for this system, with H$_4$S$_3$ identified as a major decomposition product of H$_2$S in the lead-up to the superconducting state. Calcium and oxygen are two elements of generally high terrestrial and cosmic abundance, and we explore structures of calcium peroxide (CaO$_2$) in the pressure range 0-200 GPa. Stable structures for CaO$_2$ with $C2/c$, $I4/mcm$ and $P2_1/c$ symmetries emerge at pressures below 40 GPa, which we find are thermodynamically stable against decomposition into CaO and O$_2$. The stability of CaO$_2$ with respect to decomposition increases with pressure, with peak stability occurring at the CaO B1-B2 phase transition at 65 GPa. Phonon calculations using the quasiharmonic approximation show that CaO$_2$ is a stable oxide of calcium at mantle temperatures and pressures, highlighting a possible role for CaO$_2$ in planetary geochemistry, as a mineral redox buffer. We sketch the phase diagram for CaO$_2$, and find at least five new stable phases in the pressure/temperature ranges 0 $\leq P\leq$ 60 GPa, 0 $\leq T\leq$ 600 K, including two new candidates for the zero-pressure ground state structure.
45
Chyi, Kwo-Ling. "Relationships between crystal structure, bonding and thermal stability of amphiboles." Diss., Virginia Polytechnic Institute and State University, 1987. http://hdl.handle.net/10919/87181.
Анотація:
The complexities in structure and chemical composition of the amphiboles and the wide range of their occurrence suggest that the amphiboles are potential index minerals for the physical conditions of their formation. Hydrothermal stability studies of several amphibole endmembers have demonstrated that the FeMg₋₁ substitution produces a wide spread in thermal stability. The crystal structure, upon substitution, responds to the differences in cation size and site occupancy, but the changes are small.
In order to correlate the observed stability variation with the observed differences in crystal structure of amphiboles, structure parameters as well as calculated bond strengths, Madelung site energies, and average bond overlap populations obtained from Extended Hückel Molecular Orbital (EHMO) calculation for different cation sites, were examined. Among the examined structural parameters, calculated Madelung site potentials, and bond strength, only the parameters involving bonds between the M(1)- and M(3)-cations with OH show higher correlations with the thermal stability as compared to those of the M(2)- and M(4)-cations. This reflects the dehydration nature of the amphibole break-down reaction, since the OH bonding with seems important in controlling the thermal stability.
Infrared absorption spectra of amphiboles show the fine structure of the hydroxyl group. The frequency of the absorption band is related directly to the strength of the OH bond. Positive correlations exist between thermal stability and OH-stretching frequency for different amphibole end-members at different temperatures. For epidote minerals, as well as for muscovite and phlogopite, high OH-stretching frequencies also correlated with the minerals having higher thermal stability. These correlations indicate that the thermal stability of many hydrous minerals may be significantly related to the localized force field around the OH bond.
The crystal structure of grunerite Klein No. 9A has been refined and compared with grunerite Klein No. 1 (Finger, 1969) and cummingtonite (Ghose, 1961; Fisher, 1966). The results show that the substitution of Fe for Mg into the cummingtonite-grunerite structure not only enlarges the octahedral layer but also affects the size of the T(1) and T(2) tetrahedra and thus increases strain on the octahedral and tetrahedral linkage. The high thermal expansion of the octahedral layer and the negligible effect of heating on the tetrahedral layer substantially increase the strain on the structure. This may also explain why the Fe-rich end member decomposes at a lower temperature than its Mg-analogue, the structure of which can accommodate the build-up of strain with increasing temperature.Ph. D.
46
Blades, William H. "Electronic Structure and Stability of Ligated Superatoms and Bimetallic Clusters." VCU Scholars Compass, 2016. http://scholarscompass.vcu.edu/etd/4292.
Анотація:
Quantum confinement in small metal clusters leads to a bunching of states into electronic shells reminiscent of shells in atoms. The addition of ligands can tune the valence electron count and electron distribution in metal clusters. A combined experimental and theoretical study of the reactivity of methanol with AlnIm− clusters reveals that ligands can enhance the stability of clusters. In some cases the electronegative ligand may perturb the charge density of the metallic core generating active sites that can lead to the etching of the cluster. Also, an investigation is conducted to understand how the bonding scheme of a magnetic dopant evolves as the electronic structure of the host material is varied. By considering VCun+, VAgn+, and VAun+ clusters, we find that the electronic and atomic structure of the cluster plays a major role in determining how an impurity will couple to its surroundings.
47
Molina, Manon. "Exploration of the molecular determinants involved in alternansucrase specificity and stability." Thesis, Toulouse, INSA, 2019. http://www.theses.fr/2019ISAT0010.
Анотація:
L’alternane-saccharase (ASR) de Leuconostoc citreum NRRL B-1355 est une glucane-saccharase appartenant à la famille 70 des glycoside hydrolases (GH70). Cette α-transglucosylase utilise le saccharose, substrat peu coûteux et abondant, pour catalyser la formation d’un polymère d’α-glucane composé de liaisons osidiques α-1,6 et α-1,3 alternées dans la chaîne principale et appelé alternane. Avec une température optimale de 45°C, l’ASR est parmi les glucane-saccharases les plus stables. Afin d’avoir une meilleure compréhension des déterminants de la spécificité de liaison, de la polymérisation et de la plus haute stabilité de l’ASR, nous avons résolu la structure de cette enzyme. Notre étude par mutagénèse dirigée combinée à du docking moléculaire suggère que la spécificité de liaison est contrôlée par le positionnement de l’accepteur dans l’un ou l’autre des sous-sites +2 ou +2’. Des complexes de l’ASR avec différents ligands ont également mis en évidence un site signature de l’enzyme. Ce site est impliqué dans la formation du polymère d’alternane et pourrait servir de pont facilitant l’élongation processive de l’alternane. Enfin, nos travaux préliminaires indiquent que le domaine C pourrait être impliqué dans la stabilité de ces enzymes. Nos résultats ouvrent des nouvelles pistes d’investigation concernant l’étude des relations structure-fonction des glucane-saccharases et la conception de polymères de structure et propriétés physico-chimiques contrôléesThe alternansucrase (ASR) from Leuconostoc citreum NRRL B-1355 is a glucansucrase belonging to the family 70 of glycoside hydrolases (GH70). This α-transglucosylase uses a cheap and abundant molecule, sucrose, to catalyze the formation of a unique α-glucan polymer made of alternating α-1,6 and α-1,3 linkages in the main chain, called alternan. With a 45°C optimum temperature, ASR is among the most stable glucansucrases to date. To get a deeper insight in ASR determinants involved in linkage specificity, polymerization and stability, we have solved the unliganded 3D structure of this enzyme at 2.8 Å. Coupled to mutagenesis and molecular docking, our results suggest the alternance to be governed by the acceptor positioning in either +2 or +2’ subsite, and the key contributions of Trp675 or Asp772 residue, respectively. Complexes of ASR with various sugar ligands were also obtained and highlighted a site never identified in any other GH70 enzymes. This site is uniquely found in alternansucrase and could act as a bridge between the domain V and the active site facilitating alternan processive elongation. Finally, the construction and characterization of chimera enzymes suggested domain C to be involved in enzyme stability. Overall, our results improved our knowledge on the structure-function relationship of ASR and open new paths for the conception of polymers with controlled structures and physicochemical properties
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Eaglesham, Archie. "Factors influencing emulsion and foam stability : a study of the stability and structure of thin liquid films." Thesis, University of Reading, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.254024.
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Baxant, Radek. "Řešení stability prutových konstrukcí." Master's thesis, Vysoké učení technické v Brně. Fakulta stavební, 2015. http://www.nusl.cz/ntk/nusl-227507.
Анотація:
This diploma thesis deals with the subject of slenderness bars’ stability assessment, especially in the steel structures. Before the assessment of bars in the frame constructions, we search for the influence of the computational model’s settings on the final result. The initial geometrical imperfections are examined on the model of Euler’s bar. The influence of the rigidity of girders on the poles’ buckling length is examined on the basic frame construction. The buckling lengths are assessed in the comparison with the figures we got from the statistical tables and the computational software. The influence of construction’s initial tilt and its replacement by the system of outer forces is examined on the frame structure. Three-hinged frame structure with variable cross-section member is designed then and the influence of non-linear calculations on the inner forces is studied. In the complex frame assessment, the influence of the number of parts of variable cross-section member on the bars’ buckling length is examined.
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Karamertzanis, P. G., G. M. Day, G. W. A. Welch, John Kendrick, Frank J. J. Leusen, M. A. Neumann, and S. L. Price. "Modeling the interplay of inter- and intramolecular hydrogen bonding in conformational polymorphs." American Institute of Physics, 2011. http://hdl.handle.net/10454/4734.
Анотація:
noThe predicted stability differences of the conformational polymorphs of oxalyl dihydrazide and ortho-acetamidobenzamide are unrealistically large when the modeling of intermolecular energies is solely based on the isolated-molecule charge density, neglecting charge density polarization. Ab initio calculated crystal electron densities showed qualitative differences depending on the spatial arrangement of molecules in the lattice with the greatest variations observed for polymorphs that differ in the extent of inter- and intramolecular hydrogen bonding. We show that accounting for induction dramatically alters the calculated stability order of the polymorphs and reduces their predicted stability differences to be in better agreement with experiment. Given the challenges in modeling conformational polymorphs with marked differences in hydrogen bonding geometries, we performed an extensive periodic density functional study with a range of exchange-correlation functionals using both atomic and plane wave basis sets. Although such electronic structure methods model the electrostatic and polarization contributions well, the underestimation of dispersion interactions by current exchange-correlation functionals limits their applicability. The use of an empirical dispersion-corrected density functional method consistently reduces the structural deviations between the experimental and energy minimized crystal structures and achieves plausible stability differences. Thus, we have established which types of models may give worthwhile relative energies for crystal structures and other condensed phases of flexible molecules with intra- and intermolecular hydrogen bonding capabilities, advancing the possibility of simulation studies on polymorphic pharmaceuticals.