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Apraiz, Jose Manuel Redondo. "The structure of density interfaces." Thesis, University of Cambridge, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.317855.
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Sowers, Gerald Wayne. "Structure of high-density wall plasmas." Diss., The University of Arizona, 1993. http://hdl.handle.net/10150/186244.
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Wall plasmas, plasmas in contact with a solid wall, are studied in two basic cases. The first is a linear theta-pinch. In this geometry the motion of the plasma along the field lines and the transfer of heat along the field lines is investigated using a transient hydrodynamic heat flow model and a steady state heat flow model. Good agreement is found with experimental results on the Scylla IV-P linear theta pinch. Results of the stationary model are used to estimate linear fusion reactor lengths. Results are that linear fusion reactors would be shorter for low atomic number (Z) end walls, but have higher linear power levels (power per unit length) for high Z end walls. The second case is a stationary solution of the structure of a plasma in contact with a diverter or limiter in a tokamak. This geometry is investigated to determine relationships between plasma density, temperature and the velocity of plasma flow toward the diverter. Solutions are found and sensitivities are presented.
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Dansik, Fevzi. "Force density method and configuration processing." Thesis, University of Surrey, 1999. http://epubs.surrey.ac.uk/812913/.
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May, Andrew James. "Density fitting in explicitly correlated electronic structure theory." Thesis, University of Bristol, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.432962.
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McConaha, Matthew. "Graded Lattice Structure Density Optimization for Additive Manufacturing." University of Cincinnati / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1523634949822303.
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Nagata, Koji. "TURBULENCE STRUCTURE AND TRANSPORT PHENOMENA IN DENSITY STRATIFICATION." Kyoto University, 2000. http://hdl.handle.net/2433/151546.
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Nigussa, Kenate Nemera. "Density Functional Theory Investigations of Surface Structure and Reactivity." Doctoral thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for fysikk, 2011. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-14345.
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The Cr2O3(0001) surface is assumed to terminate by chromium atoms, chromyl groups, and oxygen atoms. This essentially models the industrial surface when subjected to different oxygen chemical potentials. The issue of high temperature surface states is also of particular importance concerning various effects such as corrosion. The investigation of the interaction of selected atomic adsorbates, paper I, has not only been important from a fundamental physics point of view, but also offered useful insight on applied subjects such as corrosion. Various diatomic molecules, paper II, are found to show different reactivities to the Cr2O3(0001) surface. The different terminations provide insight on the reactivity of the surface to the molecules under varying oxygen chemical potential as background environment. Various chemical complexes have been investigated, each having applications in chemical catalysis, including the growth of an H2O layer in a hexagonal 2D lattice and an array of Cl atoms in a honeycomb lattice. Poisoning of materials by sulfuric acid is among the daily problems worldwide, with significant loss of resources. A mechanistic design on how to avert the problem is at the heart of scientific activities. This study, paper III, investigates the interaction of molecular, intermediately decomposed, and fully decomposed states of H2S with the Cr2O3(0001) surface, allowing for the possibility of a varying oxygen chemical potential as background environment. Based on the difference in reactivity of the adsorbate species with the differently terminated surfaces, we have suggested that a higher oxygen chemical potential as background environment has a potential to be unreactive to the adsorbate species or at least minimize the surface poisoning. Titanium-nickelide is an important biomaterial with various applications in medical technology. However, it is still a matter of a continued research effort on how to establish the best biocompatible version of the material. Existence of nickel atoms at contact points of the biomaterial has been reported to hamper the quality of the biomaterial. As a consequence, several experimental activities have been carried out to remedy a surface treatment of the material, mostly by oxidation. This study, paper IV, characterizes the oxidation of various low indexes of the biomaterial surface. Based on this characterization, a conclusion is reached that doping the material with potassium atoms improves the performance quality of the biomaterial and a method of achieving the doping is suggested. The use of two or more DFT packages, with different basis sets, may be motivated for consistency verification of results obtained so as to make quality conclusions, or to take advantage of a reduced computational time. In this report, paper V, we have shown that the Dacapo DFT package and the BAND DFT package with very different basis sets, i.e., plane waves and atomic orbitals, respectively, can be used together in a single study by satisfying the above motivation points. We have reported that the pseudopotentials (frozen cores) used in the calculations play a crucial role for the outcome of calculations and computation time demand, and suggested a possible discrepancy in the magnitudes of energy differences. The alloy between rare earths and novel transition metals Pt and Pd is of renewed research interest. This is in part motivated by the desire to tailor some of the properties of these widely applied transition metals or the rare earths. To be able to have control over the quantitative changes in the properties, a clear establishment of the alloy structures is crucial. There have been considerable experimental research efforts carried out reporting the investigated alloy structures. However, a consistent conclusion has not been obtained. This study, paper VI, is based on the various experimentally predicted structures and systematically suggests the most stable structure.
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Louca, P. "From X-ray structure factors to electron-density distributions." Thesis, University of Bristol, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.374638.
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Van, Caillie Carole. "Electronic structure calculations using time-dependent density functional theory." Thesis, University of Cambridge, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.621205.
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Augousti, A. T. "Density functional theories and the structure of fluids near walls." Thesis, University of Kent, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.353815.
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Zhang, Botao. "Design of Variable-Density Structures for Additive Manufacturing Using Gyroid Lattices." University of Cincinnati / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1535374427634743.
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Tabbernor, Mark Adrian. "A charge density study of Cu, Al, Zn and beta'NiAl." Thesis, University of Wolverhampton, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.277872.
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Long, Wenhui. "Relativistic Hartree-Fock approach with density-dependent meson-nucleon couplings." Paris 11, 2005. http://www.theses.fr/2005PA112056.
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Le travail de cette thèse porte sur la détermination de nouvelles interactions effectives capables de donner une description microscopique et quantitative des noyaux stables et instables, dans une approche relativiste. Dans une première partie, on se place dans le cadre du champ moyen relativiste (RMF). Trois nouvelles interactions sont proposées, l’une, PKDD, avec couplages méson-nucléon dépendants de la densité et deux, PK1 et PK1R, avec des couplages mésoniques non-linéaires et ce même pour les mésons rho dans le cas de PK1R. Les résultats obtenus dans la matière nucléaire sont comparables avec ceux d’interactions existantes telles que TM1 ou NL3, mais avec une densité de saturation baryonique plus raisonnable. Il s’ensuit une meilleure description des rayons de charge. Les résultats pour les énergies de séparation à deux neutrons et l’épaisseur de la peau de neutrons dans des chaînes d’isotopes permettent des extrapolations raisonnables pour comprendre la structure des noyaux à halos. La deuxième partie de ce travail se fait dans le cadre de l’approche Hartree-Fock relativiste avec des constantes de couplage méson-nucléon dépendant de la densité(DDRHF). Trois nouvelles interactions sont présentées dans ce travail, RHF1, RHF2 et RHF3. Il est intéressant de voir que l’on retrouve, outre un comportement comparable à celui de RMF dans la matière nucléaire, le bon comportement concernant les masses effectives des neutrons et des protons dans la matière nucléaire asymétrique, ce qui n’était pas le cas avec la théorie RMF. La description des noyaux finis est très bonne, avec une nette amélioration des dépendances en isospin des masses des noyaux<br>The work of this thesis deals with the determination of new effective interactions aiming at a microscopic, quantitative description of stable and unstable nuclei, within a relativistic framework. In the first part, one adopts the relativistic mean field (RMF) approach. Three new interactions are proposed, PKDD with density-dependent meson-nucleon couplings, PK1 and PK1R with non-linear mesonic self-energies. The predicted results in nuclear matter are comparable with those obtained with existing effective interactions like TM1 or NL3. However, the baryonic saturation density has more reasonable values, and hence the calculated charge radii are better described. Results for two-neutron separation energies and neutron skin thickness in isotopic chains allow for reasonable extrapolations towards halo nuclei. In the second part of this work, one examines the relativistic Hartree-Fock approach with density-dependant meson-nucleon coupling constants (DDRHF). Three new interactions are proposed, RHF1, RHF2 and RHF3. The general results in nuclear matter are similar to those of the RMF approach, but it is interesting to see that the predicted neutron and proton effective masses in asymmetric nuclear matter have now the correct behaviour while this was not the case with the RMF approach. The description of finite nuclei is quite good, with a clear improvement over RMF in the isospin dependence of nuclear masses
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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.
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Harrison, Michael James. "Density functional theory investigations of surface stress and surface structure." Thesis, University of Warwick, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.429720.
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Lehman, Theodore Welby. "complexity form order structure." Thesis, Virginia Tech, 2008. http://hdl.handle.net/10919/42808.
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This thesis project is complex because of its crystalline form. It is ordered through structural hierarchy and modularity. The presence of both complexity and order gives articulation to all scales of the project, allows for variety without chaos, and repetition without monotony. All of these characteristics are essential for the program of a high-rise residential building that accommodates 1,500 people.<br>Master of Architecture
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Percival, Will. "Cosmological structure formation and its link to quasar evolution." Thesis, University of Oxford, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.325786.
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Kolokotronis, Evaggelos. "Modelling large-scale structure and the value of the density parameter." Thesis, Queen Mary, University of London, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.288012.
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O'Kane, Maurice J. "The assay, structure and metabolism of pre-beta high density lipoprotein." Thesis, Queen's University Belfast, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.282043.
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Jones, Daniel Oliver Brée. "Ecological controls on density, diversity and community structure of Polar Megabenthos." Thesis, University of Southampton, 2005. https://eprints.soton.ac.uk/25131/.
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Polar deep water environments are poorly studied. This thesis investigates fundamental questions as to the nature of controlling factors on megabenthic communities as well as the diversity, densities and distributions of organisms present. The deep (1000-1660m) Faroe-Shetland Channel harbours an Arctic fauna owing to cold deepwater intrusions from the Norwegian Sea. Despite the relatively low species richness of the megabenthos, variation in faunal composition with depth is apparent. Two distinct communities were identified in the north and south of the channel. Epibenthic megafauna in the south are dominantly filter feeders and in the north deposit feeders. Megabenthic diversity and density decreased to the northeast of the channel. Lebensspuren number and area increase northwards in the Channel. The increase in bioturbation and deposit feeder abundance is concurrent with an increase in fine sediment quantity. The response of a deep, Arctic benthic community to physical disturbance was investigated in the Faroe-Shetland Channel. High levels of physical disturbance, characterised by smothering of the seabed resulted in significant but variable reductions in megafaunal abundance (up to 92.3%). Reductions in diversity, particularly in species richness, were apparent between disturbed (ES(500) = 12.9) and undisturbed areas (ES(500) = 20.6). The implications of selective removal of taxa on ecosystem function and recovery are discussed. Low level disturbance had comparatively little effect on the communities. The effects varied in nature depending on motility and functional group (e.g. motile scavenger abundances were maximal at intermediate distances from disturbance). Effects of physical factors on the megabenthos of Kangerdlugssuaq Fjord mouth in Arctic Greenland were investigated. Large reductions in faunal density (1881 to 60,132 individuals ha-1) and increases in diversity (H´ = 0.93-2.54), through increases in richness (ES(220) = 7.6-18.8) and reductions in dominance (Berger-Parker Index = 0.77-0.38), were found from 270 to 720m depth. Distinct shallow, intermediate and deep communities were identified. Shallower stations had high levels of iceberg disturbance, directly reducing diversity and creating a complex, patchy environment. Responses to disturbance were taxa specific (e.g. mobile suspension feeders aggregate on disturbed areas), but the shallow area has higher densities of suspension feeding epifauna. Deeper areas experience small scale disturbance from deposition of drop stones but its relatively low frequency and magnitude allows increased diversity. Deposit feeding epifaunal and infaunal taxa increase with depth indicated by increased Lebensspuren. Density decreases result from decreased food supply with depth. Benthic megafauna were investigated from the NE Weddell Sea (250 to 500m depth), close to the Fimbul Ice Shelf. Faunal density decreased with depth; diversity was variable but not related to depth. Two distinct communities were found, a shallow community with dense patches of suspension feeders in undisturbed areas and a deep community where these were not present. Disturbance from icebergs was very important in controlling faunal distribution. In shallow waters direct effects of disturbance were observed. In deeper waters habitat changes, caused by past disturbance, controlled faunal distributions. Ice ploughing created a mosaic landscape of fine and coarse sediments. Megafaunal density was highest in coarse sediment and diversity highest in intermediate areas. Quantitative data on benthic megafaunal abundance and diversity obtained using the same method allowed valid comparisons to be made between these polar areas. Megafaunal abundance was comparable between the Arctic and Antarctic stations, although in both areas abundance decreased with increased depth. Diversity was higher in the Antarctic stations, but species richness and evenness in both areas changed with depth. Iceberg disturbance was found to be very important in structuring megabenthic communities, particularly in the Antarctic. The results of this study are used to assess the utility of towed camera sleds, remotely operated vehicles and autonomous underwater vehicles as a method for obtaining ecological information in remote environments.
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Shinko, Andrew. "Structure and Morphology Control in Polymer Aerogels with Low Crosslink Density." University of Akron / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=akron1430399529.
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Zelaya, Carlos. "X-Ray Structure Analysis and Topological Charge Density Studies of Gossypol Derivatives." ScholarWorks@UNO, 2014. http://scholarworks.uno.edu/td/1841.
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Gossypol and gossypol derivatives are natural byproducts of a variety of cotton plant species that poses interesting chemical, biological, and medicinal properties that are currently heavily researched. Supporting evidence suggest that gossypol and gossypol derivatives act on the Bcl-2 proteins that have been linked to certain cancers. Gossypol amine derivatives, specifically, are actively researched and a variety of amine derivatives have already been synthesized. However, gossypol and its derivatives are challenging compounds to work with because many of its derivatives tend to exist in various tautomeric forms. When analyzing gossypol and its derivatives it is the complex electron configuration that dictates the chemical mechanism and biological activity. The following research provides a charge density study that describes in detail the electronic configuration via Bader's topological analysis of di(methoxy)gossypol and di(propylamino) gossypol. In addition, a series of crystallographic studies of gossypol amine derivatives and di(methoxy)gossypol are also analyzed.
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Wood, Hayley Marie. "Density functional studies of relativistic effects on molecular properties." Thesis, University of Manchester, 2013. https://www.research.manchester.ac.uk/portal/en/theses/density-functional-studies-of-relativistic-effects-on-molecular-properties(9f362361-5c09-4b35-a296-dec927ce7b7b).html.
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Relativistic effects are extremely important for heavy atoms and heavy atom containing molecules. Therefore, a relativistic treatment is needed when calculating molecular properties of these species. The fully- relativistic Dirac treatment involves electronic and positronic wavefunctions and a very large basis set is required. This leads to calculations that are too costly and time-consuming for larger molecules. The Zeroth-Order Regular Approximation (ZORA) is an approximation to the Dirac approach, which only deals with the electronic wavefunction. However, unfortunately this method is plagued by the gauge-dependence problem. The gauge-independent ZORA (ZORA-GI) and strictly atomic ZORA approaches provide solutions to this problem.In this work, the ZORA-GI and strictly atomic ZORA codes have been successfully implemented into the Gaussian 09 program. They have been used to calculate the bond lengths, harmonic vibrational frequencies and dissociation energies of the I2, Au2 and Pt2 diatomic molecules. The results show good agreement with experiment and previous theoretical studies. The non-relativistic, ZORA-GI, strictly atomic ZORA and pseudopotential approximations have been used to investigate the electronic structure of the actinide monoxides, AnO, and actinide monoxide cations, AnO+ (An = Th – Cm). It was found that the ground state configurations were dependent on the relativistic approximation chosen. The bond lengths, harmonic vibrational frequencies and dissociation energies were also calculated, with the ZORA methods generally outperforming the pseudopotential approximation. The first theoretical g-tensor study of the organouranium(V) complexes [U(C7H7)2]-, [U(η8-C8H8)(NEt2)(THF)]+, [U(η5-C5H5)(NMe2)3(THF)]+, [U(η8-C8H8)(NEt2)3], [U(η5-C5H5)2(NEt2)2]+ and [U(η8-C8H8)(η5-C5H5)(NEt2)2] has been carried out. It was demonstrated that the choice of density functional affects the way in which the g-tensor axes are assigned. The ground state spin density and SOMO are also sensitive to the choice of density functional. It is these factors that determine the value of the g-tensor.
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Östlin, Andreas. "Electronic structure studies and method development for complex materials." Doctoral thesis, KTH, Tillämpad materialfysik, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-167109.
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Over the years electronic structure theory has proven to be a powerful method with which one can probe the behaviour of materials, making it possible to describe and predict material properties. The numerical tools needed for these methods are always in need of development, since the desire to calculate more complex materials pushes this field forward. This thesis contains work on both this implementational and developmental aspects. It begins by reviewing density functional theory and dynamical mean field theory, with the aim of merging these two methods. We point out theoretical and technical issues that may occur while doing this. One issue is the Padé approximant, which is used for analytical continuation. We assess the approximant and point out difficulties that can occur, and propose and evaluate methods for their solution. The virial theorem is assessed within the framework of density functional theory merged with many-body methods. We find that the virial theorem is extended from its usual form, and confirm this by performing practical calculations. The unified theory of crystal structure for transition metals has been established a long time ago using early electronic structure calculations. Here we implement the first- principles exact muffin-tin orbitals method to investigate the structural properties of the 6d transition metals. The goal of our study is to verify the existing theory for the mostly unknown 6d series and the performance of the current state-of-the art in the case of heavy d metals. It is found that these elements behave similarly to their lighter counterparts, except for a few deviations. In these cases we argue that it is relativistic effects that cause this anomalous behaviour. Palladium is then studied, taking many-body effects into account. We find that we can reproduce experimental photoemission spectra by these methods, as well as the Fermi surface. The thesis ends with an investigation of the stacking fault energies of the strongly correlated metal cerium. In addition to providing the first ab-initio stacking fault data for the two cubic phases of Ce, we discuss how these results could have an impact on the interpretation of the phase diagram of cerium<br><p>QC 20150522</p>
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Bodin, Simon, and William Karlsson. "Network Structure and Economic Performance." Thesis, Mittuniversitetet, Avdelningen för ekonomivetenskap och juridik, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:miun:diva-21834.
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Purpose - The purpose of this study is to examine and map out the network innovative companies and to calculate values of the network structure in order to compare them to different performance measures. Furthermore, we aim to investigate the trade-off efficiency of innovations in a particular network structure, more specifically to investigate if the same elements generating more innovations have a relationship with economic performance that originates from innovations. Methodology - This study give emphasis to map and illustrate the Swedish companies on NASDAQ OMX First North network through direct and indirect connection and to compare the centrality, density and size of the companies ego network in our population with the performance measures which are logically connected with the launch of an innovation; average EBITDA (earnings before interest, taxes, depreciation and amortization) and average annual turnover. Findings - First we noticed that there was a significant connection between a negative average EBITDA and positive average annual turnover for our population, as we foretold would occur during the launch of an innovation. Secondly, the paper suggests that there is a weak or near non-existent connection between the elements that generates more innovations and the result of innovations, e.g. the economic performance of innovative firms. This might indicate that the focus of recent studies in the subject might have been mistaken focusing on the quantity of innovation, when the basic assumption of an innovation is that it is qualitative and thereby generates money for the company. This study suggests that more innovations do not necessarily lead to better economic performance for the companies within our population.
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Norman, Dennis. "Comparison of structure and function of lipoprotein receptors." Thesis, Imperial College London, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.340596.
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Engelhardt, Ilka A. D. "Plasma Structures at the Enceladus Plume." Thesis, Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-211996.
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Cassini-RPWS high resolution (20 Hz) Langmuir probe data was analyzed to find the source of fast variations in the electron density especially in the Enceladus plume region. The spatial scale on the variations is between 1 and 10 km in size. The approaches were to check for correlations between the plasma density and its variations on one hand, and boundary conditions such as the cracks on Enceladus surface as well as dust and single jets on the other hand. None of these mechanisms could be identified as the only or dominating source of observed fine structure, though partial correlation can sometimes be found and the comparison to dust presence is qualitative more than quantitative. Along the way the charging mechanism in the plume was found to be most likely due to solar UV ionization since the maximum electron density was found to be around 200km altitude. Also the deformation of the plume in the corotation direction is visible in the 20 Hz data.
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Paiboonvorachat, Nattapong. "Density matrix renormalisation group calculations of the electronic structure of conjugated molecules." Thesis, University of Oxford, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.606304.
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With many interesting electronic and optical properties, conjugated molecules have long been a subject for both theoretical and experimental studies, especially in recent applications in optoelectronics. Most of the properties are controlled by their electronic structures, with the low-lying states predominantly characterised by the 7!'-electrons. We have thus employed the semi-empirical Pariser-Parr-Pople model, whose Hamiltonian parameters are optimised against the excited states, in this study. Despite only considering the π-delocalised system, the model has been widely and successfully applied to study such molecules, giving fairly accurate results. The calculation of these strongly correlated systems requires an accurate computational method, which is usually limited to small molecules due to an enormous amount of resources demanded, as in ab initio calculations. Density Matrix Renormalisation Group (DMRG) provides a systematic way to truncate the size of the Hilbert space while being able to reasonably capture the correlation effect. We have compared three different approaches using both localised and delocalised basis states in the DMRG calculations. First, in the real-space method, atomic sites are aligned on the one-dimensional DMRG lattice as originally developed to study the fermionic systems in condensed matter physics. Alternatively, a collection of atoms, e.g. a monomer unit in conjugated polymers, can be used where an in situ optimisation technique is employed to pre-select the important states. Last, the correlation effect between the Hartree-Fock (HF) molecular orbitals on the lattice sites is calculated in the HF -DMRG scheme. In this post-HF method, the energy converges more slowly than the first but the implementation of t he codes is generic to any geometric structures. In addition to the spin-flip and particle-hole symmetries, which are available in the real-space method, the spatial symmetries can also be applied to target specific states when working in HF space. Calculations have been made on conjugated polymers, i.e. polyacetylene and poly(parophenylene), and aromatic compounds, i.e. pentacene and porphin. The results are compared to other methods, e.g. exact diagonalisation and Configurational Interaction Singles, as well as other theoretical and experimental results in the literature
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Kurniawan, Nyoman Dana. "Dissection of the human low-density lipoprotein receptor structure using NMR spectroscopy /." [St. Luica, Qld.], 2002. http://www.library.uq.edu.au/pdfserve.php?image=thesisabs/absthe16824.pdf.
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Lutton, R. "The effect of Maleic Anhydride-grafted-high density polyethylene combatibilisers on the structure and properties of high density polyethylene/montmorillonite nanocomposities." Thesis, Queen's University Belfast, 2014. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.679044.
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Nanocomposites have received a great deal of attention in recent years; particularly polymer layered silicate nanocomposites such as montmorillonite, where the surface to volume ratio is exceptionally high. As a result of their ultrafine phase dimensions, these layered silicate nanocomposites possess unique properties typically not shared by more conventional microcomposites and, therefore, offer new technology and business opportunities. However, despite the attention, the influence of compatibilisers on the nanocomposites is not well understood; more critically, the literature exposes a large degree of disagreement as to the required compatibiliser type for optimal function. This study examines the effect of Maleic Anhydride grafted HDPE compatibilisers, with differing MFls and grafting contents, on the mechanical, thermal an.d rheological properties of HDPE. The materials were compounded in a twin screw extruder before being compression moulded into plaques for characterisation and analysis; this consisted of structural analysis utilising XRD and tensile testing; thermal and rheological characterisation using power compensated DSC, DMTA and a rotational rheometer. The results confirm organo-modification of MMT as sufficient in producing a miscible polymer system; however addition of compatibiliser is best. In an unfilled system, the incorporation of MAH groups cause axis distortion and rearrangement of chain conformation and lattice structure, crosslin king and increase RAF. With the addition of MMT, the MAH groups preferentially interact with the clay changing the crystal type to transcrystalline layers, lowering the Tg whilst simultaneously increasing the modulus. The most effective compatibilisers have a characteristic enabling a more dominant exfoliation mechanism. Intercalated nanocomposites presented the more improved systems, with 4:1 and 5:1, plus 5% clay, being the optimal due to crystallisation between layers. Changes in MFI and grafting are a complicated matrix but higher mobility and grafting is preferred: as opportunity for interaction increases, the likelihood of formation of nanocomposites, and improvement in material properties, increases.
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Li, Zheng. "Assessing Structure–Property Relationships of Crystal Materials using Deep Learning." Thesis, Virginia Tech, 2020. http://hdl.handle.net/10919/99488.
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In recent years, deep learning technologies have received huge attention and interest in the field of high-performance material design. This is primarily because deep learning algorithms in nature have huge advantages over the conventional machine learning models in processing massive amounts of unstructured data with high performance. Besides, deep learning models are capable of recognizing the hidden patterns among unstructured data in an automatic fashion without relying on excessive human domain knowledge. Nevertheless, constructing a robust deep learning model for assessing materials' structure-property relationships remains a non-trivial task due to highly flexible model architecture and the challenge of selecting appropriate material representation methods. In this regard, we develop advanced deep-learning models and implement them for predicting the quantum-chemical calculated properties (i.e., formation energy) for an enormous number of crystal systems. Chapter 1 briefly introduces some fundamental theory of deep learning models (i.e., CNN, GNN) and advanced analysis methods (i.e., saliency map). In Chapter 2, the convolutional neural network (CNN) model is established to find the correlation between the physically intuitive partial electronic density of state (PDOS) and the formation energies of crystals. Importantly, advanced machine learning analysis methods (i.e., salience mapping analysis) are utilized to shed light on underlying physical factors governing the energy properties. In Chapter 3, we introduce the methodology of implementing the cutting-edge graph neural networks (GNN) models for learning an enormous number of crystal structures for the desired properties.<br>Master of Science<br>Machine learning technologies, particularly deep learning, have demonstrated remarkable progress in facilitating the high-throughput materials discovery process. In essence, machine learning algorithms have the ability to uncover the hidden patterns of data and make appropriate decisions without being explicitly programmed. Nevertheless, implementing machine learning models in the field of material design remains a challenging task. One of the biggest limitations is our insufficient knowledge about the structure-property relationships for material systems. As the performance of machine learning models is to a large degree determined by the underlying material representation method, which typically requires the experts to have in-depth knowledge of the material systems. Thus, designing effective feature representation methods is always the most crucial aspect for machine learning model development and the process takes a significant amount of manual effort. Even though tremendous efforts have been made in recent years, the research process for robust feature representation methods is still slow. In this regard, we attempt to automate the feature engineering process with the assistance of advanced deep learning algorithms. Unlike the conventional machine learning models, our deep learning models (i.e., convolutional neural networks, graph neural networks) are capable of processing massive amounts of structured data such as spectrum and crystal graphs. Specifically, the deep learning models are explicitly designed to learn the hidden latent variables that are contained in crystal structures in an automatic fashion and provide accurate prediction results. We believe the deep learning models have huge potential to simplify the machine learning modeling process and facilitate the discovery of promising functional materials.
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Guo, Zhen. "Density functional theory studies of selected hydrogen bond assisted chemical reactions." Click to view the E-thesis via HKUTO, 2009. http://sunzi.lib.hku.hk/hkuto/record/B42182335.
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Widany, Joerg. "Density-Functional Tight-Binding Calculations on the Structure of Complex Boron Nitride Systems." Doctoral thesis, Universitätsbibliothek Chemnitz, 1997. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-199700412.
Full textAbstract:
Die vorliegende Arbeit befasst sich mit theoretischen
Untersuchungen struktureller Eigenschaften komplexer
Bornitrid-Systeme.
Die Rechnungen basieren auf einem Dichtefunktional-
Tight-Binding-Verfahren. Die interatomaren Potentiale fuer
das heteronukleare System sowie die Wechselwirkung mit
Wasserstoff werden in Anpassung an ab-initio-Daten
abgeleitet. Mit ausfuehrlichen Testrechnungen
an theoretisch wie experimentell gut charakterisierten
Systemen wird gezeigt, dass die Tight-Binding-Potentiale
die mannigfaltigen Bindungstypen in BN-Systemen richtig
beschreiben.
Im Hauptteil der Arbeit werden in Anwendung der Methode
experimentell relevante Fragestellungen untersucht.
Zunaechst werden die Rekonstruktionen verschiedener
Kristalloberflaechen des kubischen Bornitrid (c-BN)
berechnet. In Anlehnung an experimentelle Ergebnisse
wird die Grenzflaeche zwischen kubischem und hexagonalem
BN hinsichtlich ihres atomaren Aufbaues und ihrer
energetischen Stabilitaet untersucht.
Eine ausfuehrliche Diskussion struktureller Eigenschaften
von amorphen Bornitrid-Modellen folgt im Anschluss. Die
Betrachtung von Modellen unterschiedlicher Massendichte
ermoeglicht es, Rueckschluesse auf grundlegende Mechanismen
der Strukturbildung kristalliner Phasen zu ziehen.
Der Einbau atomaren Wasserstoffs in verschiedene
Bornitrid-Kristallgitter wird im abschliessenden Abschnitt
untersucht.
Weiterhin wendet sich die Arbeit ternaeren Materialien
(Bor-Kohlenstoff-Stickstoff) zu. Es werden Stabilitaet und
strukturelle Eigenschaften von kubischen BC2N-Kristallen
diskutiert. Die gezeigte Anwendbarkeit der Methode auf
derartige Materialien eroeffnet zugleich Perspektiven
fuer kuenftige Arbeiten.
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Yao, Wenlong. "Structure, ionic conductivity and mobile carrier density in fast ionic conducting chalcogenide glasses." [Ames, Iowa : Iowa State University], 2006.
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Brandt, Erika [Verfasser], and Bernd [Akademischer Betreuer] Möbius. "Information density and phonetic structure : Explaining segmental variability / Erika Brandt ; Betreuer: Bernd Möbius." Saarbrücken : Saarländische Universitäts- und Landesbibliothek, 2019. http://d-nb.info/1184878218/34.
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Bang, Jung Woong. "An Empirical Comparison of Random Number Generators: Period, Structure, Correlation, Density, and Efficiency." Thesis, University of North Texas, 1995. https://digital.library.unt.edu/ark:/67531/metadc277807/.
Full textAbstract:
Random number generators (RNGs) are widely used in conducting Monte Carlo simulation studies, which are important in the field of statistics for comparing power, mean differences, or distribution shapes between statistical approaches. Statistical results, however, may differ when different random number generators are used. Often older methods have been blindly used with no understanding of their limitations. Many random functions supplied with computers today have been found to be comparatively unsatisfactory. In this study, five multiplicative linear congruential generators (MLCGs) were chosen which are provided in the following statistical packages: RANDU (IBM), RNUN (IMSL), RANUNI (SAS), UNIFORM(SPSS), and RANDOM (BMDP). Using a personal computer (PC), an empirical investigation was performed using five criteria: period length before repeating random numbers, distribution shape, correlation between adjacent numbers, density of distributions and normal approach of random number generator (RNG) in a normal function. All RNG FORTRAN programs were rewritten into Pascal which is more efficient language for the PC. Sets of random numbers were generated using different starting values. A good RNG should have the following properties: a long enough period; a well-structured pattern in distribution; independence between random number sequences; random and uniform distribution; and a good normal approach in the normal distribution. Findings in this study suggested that the above five criteria need to be examined when conducting a simulation study with large enough sample sizes and various starting values because the RNG selected can affect the statistical results. Furthermore, a study for purposes of indicating reproducibility and validity should indicate the source of the RNG, the type of RNG used, evaluation results of the RNG, and any pertinent information related to the computer used in the study. Recommendations for future research are suggested in the area of other RNGs and methods not used in this study, such as additive, combined, mixed and shifted RNGs.
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Tang, Miru. "DENSITY FUNCTIONAL THEORY STUDIES ON THE STRUCTURE AND CATALYTIC ACTIVITY OF METAL OXIDES." OpenSIUC, 2018. https://opensiuc.lib.siu.edu/dissertations/1602.
Full textAbstract:
In this dissertation, I present four projects on the fundamental study of the surface configurations and reactivity of the metal oxides using density functional theory computational method. In the first project, we studied the formaldehyde adsorption and diffusion on rutile TiO2 (110) surface. By comparing the adsorption of formaldehyde on stoichiometric and defective TiO2 surfaces under the same condition, we evaluated the effect of surface oxygen vacancy on their interaction with formaldehyde. The project involved close collaboration with Dr. Zhenrong Zhang’s group of Baylor University who studied the formaldehyde chemistry on rutile TiO2(110) surface using a combination of STM and other surface science techniques. In the second project, we compared the surface chemistries of formaldehyde and formic acid on rutile TiO2 and SnO2, two structurally similar but chemically different oxides. We analyzed the oxidation of formaldehyde to formic acid on two oxides and assessed the role of surface oxygen in the oxidation. In the third project, we studied the oxygen evolution reaction (OER) catalyzed by γ-FeOOH (010) under the alkaline condition. The OER process was divided into four elementary steps and the potential energy profiles of these steps on three terminations of the γ-FeOOH (010) surface were mapped out. Based on the computed reaction energies, we determined the most probable OER reaction pathway on each surface termination. We found that partially exposed surface Fe sites were the active sites for the OER process. In the fourth project, we studied the potential of iron oxides (FeOx) and iron-titanium mixed oxides (FeTiOx) as solid oxygen carriers for the chemical looping combustion (CLC) process. As oxygen carriers for CLC, FeOx and FeTiOx in fully oxidized forms went through a series of reduction steps by reacting with the fuel molecules. The reduced oxides were then re-oxidized in an air reactor to restore their oxygen. By studying the surface oxygen vacancy formation and oxygen diffusion, we gained insights into the initial stage of reduction process and activities of FeOx and FeTiOx as well as the effect of Ti on oxygen carrying properties of FeTiOx for CLC.
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Stoltzfus, Matthew W. "Structure-property relationships in solid state materials a computational approach emphasizing chemical bonding /." Columbus, Ohio : Ohio State University, 2007. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1190087366.
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PETRETTO, GUIDO. "Density functional simulation of chalcogen doped silicon nanowires." Doctoral thesis, Università degli Studi di Milano-Bicocca, 2012. http://hdl.handle.net/10281/28938.
Full textAbstract:
In this thesis we report about the first principle investigation of silicon nanowires. Density functional theory has been used to study the electronic properties of pristine and chalcogen doped nanowires. Nanowires with different surface structures and orientations have been considered. We show that substitutional chalcogen atoms have
favorable configurations for positions close to the surface of the nanowire. We also show that hyperfine interactions increase
at small diameters, as long as the nanowire is large enough to prevent surface
distortion which modifies the symmetry of the donor wave function. Moreover,
surface effects lead to strong differences in the hyperfine parameters depending on
the Se location inside the nanowire, allowing the identification of an impurity site on
the basis of EPR spectra.
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Arehart, Eric. "Dioxin Alters Human Low-Density and Very Low-Density Lipoprotein Structure with Evidence for Specific Quenching of TRP-48 in Apolipoprotein C-H." Fogler Library, University of Maine, 2003. http://www.library.umaine.edu/theses/pdf/ArehartES2003.pdf.
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Iusan, Diana Mihaela. "Density Functional Theory Applied to Materials for Spintronics." Doctoral thesis, Uppsala universitet, Materialteori, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-119887.
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The properties of dilute magnetic semiconductors have been studied by combined ab initio, Monte Carlo, and experimental techniques. This class of materials could be very important for future spintronic devices, that offer enriched functionality by making use of both the spin and the charge of the electrons. The main part of the thesis concerns the transition metal doped ZnO. The role of defects on the magnetic interactions in Mn-doped ZnO was investigated. In the presence of acceptor defects such as zinc vacancies and oxygen substitution by nitrogen, the magnetic interactions are ferromagnetic. For dilute concentrations of Mn (~ 5%) the ordering temperature of the system is low, due to the short ranged character of the exchange interactions and disorder effects. The clustering tendency of the Co atoms in a ZnO matrix was also studied. The electronic structure, and in turn the magnetic interactions among the Co atoms, is strongly dependent on the exchange-correlation functional used. It is found that Co impurities tend to form nanoclusters and that the interactions among these atoms are antiferromagnetic within the local spin density approximation + Hubbard U approach. The electronic structure, as well as the chemical and magnetic interactions in Co and (Co,Al)-doped ZnO, was investigated by joined experimental and theoretical techniques. For a good agreement between the two, approximations beyond the local density approximation must be used. It is found that the Co atoms prefer to cluster within the semiconducting matrix, a tendency which is increased with Al co-doping. We envision that it is best to describe the system as superparamagnetic due to the formation of Co nanoclusters within which the interactions are antiferromagnetic. The magnetic anisotropy and evolution of magnetic domains in Fe81Ni19/Co(001) superlattices were investigated both experimentally, as well as using model spin dynamics. A magnetic reorientation transition was found.
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Guo, Zhen, and 郭臻. "Density functional theory studies of selected hydrogen bond assisted chemical reactions." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2009. http://hub.hku.hk/bib/B42182335.
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Vauhkonen, Matti. "Surface structure of human low density lipoproteins carbohydrate structure of apolipoprotein B-100 and properties of the surface lipid layer /." Helsinki : Finnish Society of Sciences and Letters, 1990. http://catalog.hathitrust.org/api/volumes/oclc/22137261.html.
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Giusca, Cristina Elena. "Scanning tunnelling microscopy studies of carbon nanotubes : from atomic structure to density of states." Thesis, University of Surrey, 2006. http://epubs.surrey.ac.uk/842847/.
Full textAbstract:
Recent years have witnessed an increased demand for more powerful computers and continuous miniaturization of electronics. As the drive toward miniaturisation of electronic devices continues, the utilization of the one-dimensional electronic properties would facilitate very fast and functional devices. A system that provides a unique template for studying the one-dimensional electronic behaviour is present in carbon nanotubes, which have been proposed as nanoscale building blocks because of their exceptional physical properties, making them an ideal candidate for future solid-state nanoelectronic devices. For the nanotubes to be part of a larger assembly, their properties, together with their response to different environments need to be examined. An ideal tool for probing tiny structures such as carbon nanotubes is the scanning tunnelling microscope, which has the ability to obtain a direct real space image with extremely high spatial resolution, allowing also investigations of the electron distribution in a material. Measurements performed with the scanning tunnelling microscope of the electronic states of carbon nanotubes are reported and several key electronic phenomena are demonstrated in this study. The explicit relationship between the atomically resolved structure and the corresponding electronic behaviour of carbon nanotubes, as predicted by theory for carbon nanotubes, is revealed by our measurements, which are further validated by calculations. Evidence indicative of interlayer interaction between the two constituent shells of double walled carbon nanotubes is found and the chirality of the inner tube determined, based on a detailed analysis of the tunnelling spectra. Our experiments indicate that the overall electronic structure is dependent on the interlayer interaction and not only on the chirality pairs as was previously suggested. Radial deformations of carbon nanotubes have been studied and found to drastically affect the electronic properties of carbon nanotubes, hi particular, the effect on the electronic properties of a twist-induced deformation was observed to be reversed by the radial collapse of the tube. Due to their dimensions and geometry, carbon nanotubes also provide a unique opportunity of engineering novel one-dimensional structures within their cores. Once successfully introduced into the nanotubes, the effect that the encapsulated filling material (AgNO3, AgI and HgTe) exerts on the encasing nanotube was investigated by scanning tunnelling microscopy. The results are discussed in connection with some of the encountered difficulties that sometimes precluded reliable measurements.
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Aryal, Sita Ram Ching Wai-Yim. "Density functional calculations of the electronic structure of aluminosilicate polymorphs (Al₂SiO₅) and mullite." Diss., UMK access, 2007.
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Thesis (M.S.)--Dept. of Physics. University of Missouri--Kansas City, 2007.<br>"A thesis in physics." Typescript. Advisor: Wai-Yim Ching. Vita. Title from "catalog record" of the print edition Description based on contents viewed Sept. 12, 2008. Includes bibliographical references (leaves 53-58). Online version of the print edition.
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Aebischer, Danille P. "Basic density and shrinkage of oak in relation to wood structure and cambial age." Thesis, Bangor University, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.285465.
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Barnard, L. "The structure and properties of low density polyurethane foam with particular reference to ageing." Thesis, University of Strathclyde, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.371957.
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Campbell, Rory M. "Relationships between stability, structure, and energy density of nitrogen-rich Group 14 coordination compounds." Thesis, University of Sheffield, 2017. http://etheses.whiterose.ac.uk/16269/.
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Palmer, Prem. "Structure, Energetics and Reactions of Bisketenes: An Ab Initio and Density Functional Theory Study." Thesis, University of North Texas, 1997. https://digital.library.unt.edu/ark:/67531/metadc501272/.
Full textAbstract:
The effect of varying substituents on structure and energies of bisketenes was studied using ab initio methods. Effect of substituents on ring closing reaction of bisketenes to the corresponding cyclobutenediones was also studied using ab initio methods. One or two of the following substituents were used to study the effect of varying substituents: BH2, CH3, NH2, OH, F, AlH2, SiH3, PH2, SH, Cl. Studies were done at the Hartree-Fock (HF), Møller-Plesset (MP2), and Density Functional Theory (B3LYP) levels of theory using the 6-31G* basis set.
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Sun, Yurong. "Ultrasound characterization of structure and density of coral as a model for trabecular bone." Link to electronic version, 2000. http://www.wpi.edu/Pubs/ETD/Available/etd-0808100-001812/.
Full textAbstract:
Thesis (M.S.)--Worcester Polytechnic Institute.<br>Keywords: angular decorrelation function; impulse response; BUA; BMD; ultrasound; coral; trabecular bone; osteoporosis. Includes bibliographical references (p. 189-191).