Dissertations / Theses: '"Functional structure principle"'

1

Paglia, Gianluca. "Determination of the structure of y-alumina using empirical and first principle calculations combined with supporting experiments." Thesis, Curtin University, 2004. http://hdl.handle.net/20.500.11937/2341.

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Aluminas have had some form of chemical and industrial use throughout history. For little over a century corundum (α-Al2O3) has been the most widely used and known of the aluminas. The emerging metastable aluminas, including the γ, δ, η, θ, κ, β, and χ polymorphs, have been growing in importance. In particular, γ-Al2O3 has received wide attention, with established use as a catalyst and catalyst support, and growing application in wear abrasives, structural composites, and as part of burner systems in miniature power supplies. It is also growing in importance as part of the feedstock for aluminium production in order to affect both the adsorption of hydrogen fluoride and the feedstock solubility in the electrolytic solution. However, much ambiguity surrounds the precise structure of γ-Al2O3. Without proper knowledge of the structure, understanding the properties, dynamics and applications will always be less than optimal. The aim of this research was to contribute towards settling this ambiguity. This work was achieved through extensive computer simulations of the structure, based on interatomic potentials with refinements of promising structures using density functional theory (DFT), and a wide range of supporting experiments. In addition to providing a more realistic representation of the structure, this research has also served to advance knowledge of the evolution of the structure with changing temperature and make new insights regarding the location of hydrogen in γ-Al2O3.Both the molecular modelling and Rietveld refinements of neutron diffraction data showed that the traditional cubic spinel-based structure models, based on m Fd3 space group symmetry, do not accurately describe the defect structure of γ-Al2O3. A more accurate description of the structure was provided using supercells of the cubic and tetragonal unit cells with a significant number of cations on c symmetry positions. These c symmetry based structures exhibited diffraction patterns that were characteristic of γ-Al2O3. The first three chapters of this Thesis provide a review of the literature. Chapter One provides a general introduction, describing the uses and importance of the aluminas and the problems associated with determining the structure of γ-Al2O3. Chapter Two details the research that has been conducted on the structure of vi γ-Al2O3 historically. Chapter Three describes the major principles behind the computational methods employed in this research. In Chapter Four, the specific experimental and computational techniques used to investigate the structure of γ-Al2O3 are described. All preparation conditions and parameters used are provided. Chapter Five describes the methodology employed in computational and experimental research. The examination of the ~ 1.47 billion spinel-based structural possibilities of γ-Al2O3, described using supercells, and the selection of ~ 122,000 candidates for computer simulation, is detailed. This chapter also contains a case study of the structure of κ-Al2O3, used to investigate the applicability of applying interatomic potentials to solving complex structures, where many possibilities are involved, and to develop a systematic procedure of computational investigation that could be applied to γ-Al2O3. Chapters Six to Nine present and discuss the results from the experimental studies.Preliminary heating trials, performed to determine the appropriate preparation conditions for obtaining a highly crystalline boehmite precursor and an appropriate calcination procedure for the systematic study of γ-Al2O3, were presented in Chapter Six. Chapter Seven details the investigation of the structure from a singletemperature case. Several known structural models were investigated, including the possibility of a dual-phase model and the inclusion of hydrogen in the structure. It was demonstrated that an accurate structural model cannot be achieved for γ-Al2O3 if the cations are restricted to spinel positions. It was also found that electron diffraction patterns, typical for γ-Al2O3, could be indexed according to the I41/amd space group, which is a maximal subgroup of m Fd3 . Two models were presented which describe the structure more accurately; Cubic-16c, which describes cubic γ-Al2O3 and Tetragonal-8c, which describes tetragonal γ-Al2O3. The latter model was found to be a better description for the γ-Al2O3 samples studied. Chapter Eight describes the evolution of the structure with changing calcination temperature. Tetragonal γ-Al2O3 was found to be present between 450 and 750 °C. The structure showed a reduction in the tetragonal distortion with increasing temperature but at no stage was cubic γ-Al2O3 obtained. Examination of the progress of cation migration indicates the reduction in the tetragonal nature is due to ordering within inter-skeletal oxygen layers of the unit cell, left over from the breakdown of the hydroxide layers of boehmite when the transformation to γ-Al2O3 occurred. Above 750 °C, δ-Al2O3 was not observed, but a new phase was identified and designated γ.-Al2O3.The structure of this phase was determined to be a triple cell of γ-Al2O3 and is herein described using the 2 4m P space group. Chapter Nine investigates the presence of hydrogen in the structure of γ-Al2O3. It was concluded that γ-Al2O3 derived from highly crystalline boehmite has a relatively well ordered bulk crystalline structure which contains no interstitial hydrogen and that hydrogen-containing species are located at the surface and within amorphous regions, which are located in the vicinity of pores. Expectedly, the specific surface area was found to decrease with increasing calcination temperature. This trend occurred concurrently with an increase in the mean pore and crystallite size and a reduction in the amount of hydrogen-containing species within the structure. It was also demonstrated that γ-Al2O3 derived from highly crystalline boehmite has a significantly higher surface area than expected, attributed to the presence of nano-pores and closed porosity. The results from the computational study are presented and discussed in Chapter Ten. Optimisation of the spinel-based structural models showed that structures with some non-spinel site occupancy were more energetically favourable. However, none of the structural models exhibited a configuration close to those determined from the experimental studies. Nor did any of the theoretical structures yield a diffraction pattern that was characteristic of γ-Al2O3. This discrepancy between the simulated and real structures means that the spinel-based starting structure models are not close enough to the true structure of γ-Al2O3 to facilitate the derivation of its representative configuration.Large numbers of structures demonstrate migration of cations to c symmetry positions, providing strong evidence that c symmetry positions are inherent in the structure. This supports the Cubic-16c and Tetragonal-8c structure models presented in Chapter Seven and suggests that these models are universal for crystalline γ-Al2O3. Optimisation of c symmetry based structures, with starting configurations based on the experimental findings, resulted in simulated diffraction patterns that were characteristic of γ-Al2O3.

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2

Paglia, Gianluca. "Determination of the structure of y-alumina using empirical and first principle calculations combined with supporting experiments." Curtin University of Technology, Department of Applied Physics & Department of Applied Chemistry, 2004. http://espace.library.curtin.edu.au:80/R/?func=dbin-jump-full&object_id=14992.

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Aluminas have had some form of chemical and industrial use throughout history. For little over a century corundum (α-Al2O3) has been the most widely used and known of the aluminas. The emerging metastable aluminas, including the γ, δ, η, θ, κ, β, and χ polymorphs, have been growing in importance. In particular, γ-Al2O3 has received wide attention, with established use as a catalyst and catalyst support, and growing application in wear abrasives, structural composites, and as part of burner systems in miniature power supplies. It is also growing in importance as part of the feedstock for aluminium production in order to affect both the adsorption of hydrogen fluoride and the feedstock solubility in the electrolytic solution. However, much ambiguity surrounds the precise structure of γ-Al2O3. Without proper knowledge of the structure, understanding the properties, dynamics and applications will always be less than optimal. The aim of this research was to contribute towards settling this ambiguity. This work was achieved through extensive computer simulations of the structure, based on interatomic potentials with refinements of promising structures using density functional theory (DFT), and a wide range of supporting experiments. In addition to providing a more realistic representation of the structure, this research has also served to advance knowledge of the evolution of the structure with changing temperature and make new insights regarding the location of hydrogen in γ-Al2O3. Both the molecular modelling and Rietveld refinements of neutron diffraction data showed that the traditional cubic spinel-based structure models, based on m Fd3 space group symmetry, do not accurately describe the defect structure of γ-Al2O3. A more accurate description of the structure was provided using supercells of the cubic and tetragonal unit cells with a significant number of cations on c symmetry positions. These c symmetry based structures exhibited diffraction patterns that were characteristic of γ-Al2O3. The first three chapters of this Thesis provide a review of the literature. Chapter One provides a general introduction, describing the uses and importance of the aluminas and the problems associated with determining the structure of γ-Al2O3. Chapter Two details the research that has been conducted on the structure of vi γ-Al2O3 historically. Chapter Three describes the major principles behind the computational methods employed in this research. In Chapter Four, the specific experimental and computational techniques used to investigate the structure of γ-Al2O3 are described. All preparation conditions and parameters used are provided. Chapter Five describes the methodology employed in computational and experimental research. The examination of the ~ 1.47 billion spinel-based structural possibilities of γ-Al2O3, described using supercells, and the selection of ~ 122,000 candidates for computer simulation, is detailed. This chapter also contains a case study of the structure of κ-Al2O3, used to investigate the applicability of applying interatomic potentials to solving complex structures, where many possibilities are involved, and to develop a systematic procedure of computational investigation that could be applied to γ-Al2O3. Chapters Six to Nine present and discuss the results from the experimental studies. Preliminary heating trials, performed to determine the appropriate preparation conditions for obtaining a highly crystalline boehmite precursor and an appropriate calcination procedure for the systematic study of γ-Al2O3, were presented in Chapter Six. Chapter Seven details the investigation of the structure from a singletemperature case. Several known structural models were investigated, including the possibility of a dual-phase model and the inclusion of hydrogen in the structure. It was demonstrated that an accurate structural model cannot be achieved for γ-Al2O3 if the cations are restricted to spinel positions. It was also found that electron diffraction patterns, typical for γ-Al2O3, could be indexed according to the I41/amd space group, which is a maximal subgroup of m Fd3 . Two models were presented which describe the structure more accurately; Cubic-16c, which describes cubic γ-Al2O3 and Tetragonal-8c, which describes tetragonal γ-Al2O3. The latter model was found to be a better description for the γ-Al2O3 samples studied. Chapter Eight describes the evolution of the structure with changing calcination temperature. Tetragonal γ-Al2O3 was found to be present between 450 and 750 °C. The structure showed a reduction in the tetragonal distortion with increasing temperature but at no stage was cubic γ-Al2O3 obtained. Examination of the progress of cation migration indicates the reduction in the tetragonal nature is due to ordering within inter-skeletal oxygen layers of the unit cell, left over from the breakdown of the hydroxide layers of boehmite when the transformation to γ-Al2O3 occurred. Above 750 °C, δ-Al2O3 was not observed, but a new phase was identified and designated γ.-Al2O3. The structure of this phase was determined to be a triple cell of γ-Al2O3 and is herein described using the 2 4m P space group. Chapter Nine investigates the presence of hydrogen in the structure of γ-Al2O3. It was concluded that γ-Al2O3 derived from highly crystalline boehmite has a relatively well ordered bulk crystalline structure which contains no interstitial hydrogen and that hydrogen-containing species are located at the surface and within amorphous regions, which are located in the vicinity of pores. Expectedly, the specific surface area was found to decrease with increasing calcination temperature. This trend occurred concurrently with an increase in the mean pore and crystallite size and a reduction in the amount of hydrogen-containing species within the structure. It was also demonstrated that γ-Al2O3 derived from highly crystalline boehmite has a significantly higher surface area than expected, attributed to the presence of nano-pores and closed porosity. The results from the computational study are presented and discussed in Chapter Ten. Optimisation of the spinel-based structural models showed that structures with some non-spinel site occupancy were more energetically favourable. However, none of the structural models exhibited a configuration close to those determined from the experimental studies. Nor did any of the theoretical structures yield a diffraction pattern that was characteristic of γ-Al2O3. This discrepancy between the simulated and real structures means that the spinel-based starting structure models are not close enough to the true structure of γ-Al2O3 to facilitate the derivation of its representative configuration. Large numbers of structures demonstrate migration of cations to c symmetry positions, providing strong evidence that c symmetry positions are inherent in the structure. This supports the Cubic-16c and Tetragonal-8c structure models presented in Chapter Seven and suggests that these models are universal for crystalline γ-Al2O3. Optimisation of c symmetry based structures, with starting configurations based on the experimental findings, resulted in simulated diffraction patterns that were characteristic of γ-Al2O3.

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3

Afaneh, Akef. "Computational investigations of the electronic structure of molecular mercury compounds: ion-selective sensors." Springer International Publishing AG, 2012. http://hdl.handle.net/1993/30661.

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This thesis presents the basic concepts of electronic structure theory and the chemical properties of mercury. The theoretical foundation of DFT and the consequences of relativity are also introduced. The electronic structure of Hg(II) ions, [Hg(L)n(H2O)m]q (L = HO-, Cl-, HS-, S2-) has been studied. We show, in this thesis, that the charge transfer (that is calculated from the hard-soft-acid-base principle (Pearson’s principle)), the total NBO charge and the interaction energies are strongly correlated. Our studies indicate the effect of the solvent on the global electrophilicity, the charge transfer and consequently the interaction strength between Hg(II) and ligand L. The formation constants, logK, of Hg2+−complexes are calculated. The procedure that we follow in this thesis to calculate the formation constants, logK’s, are in good agreement with the extrapolated experimental values. We introduce and explain why it is important adding water molecules explicitly during the calculations of the logK. The recommended logK value of HgS is 27.2. We examined two different types of organic compounds as sensors for heavy metal ions: lumazine (Lm) and 6-thienyllumazine (TLm). We found that the simple calculation of pKa values using DFT methods and implicit solvent models failed to reproduce the experimental values. However, calculated orbital energies and gas phase acidities both indicate that the compound TLm is inherently more acidic than the parent species Lm. We demonstrate that: (1) we need to take in our consideration the population of each tautomer and conformer during the calculations of the pKa values, and (2) thienyl group has indirect effect on the acidity of the proton on N1 in the uracil ring. Last but not least, the fluorescence spectrum of the sensors (L) and their [(L)nM(H2O)m]2+ complexes (L = Lumazine (Lm) and 6-thienyllumazine (TLm) and M = Cd2+and Hg2+) are calculated using time dependent DFT (TDDFT). The results show that TDDFT is in good agreement with experimental results. This chapter provides a new concept in the design of fluorescence turn-on/off sensors that has wider applicability for other systems. Finally, we provide a summary of the works compiled in this thesis and an outlook on potential future work. October 2015

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4

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.

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5

Daghighi, Abtin. "The Maximum Principle for Cauchy-Riemann Functions and Hypocomplexity." Licentiate thesis, Mittuniversitetet, Institutionen för tillämpad naturvetenskap och design, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:miun:diva-17701.

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This licentiate thesis contains results on the maximum principle forCauchy–Riemann functions (CR functions) on weakly 1-concave CRmanifolds and hypocomplexity of locally integrable structures. Themaximum principle does not hold true in general for smooth CR functions,and basic counterexamples can be constructed in the presenceof strictly pseudoconvex points. We prove a maximum principle forcontinuous CR functions on smooth weakly 1-concave CR submanifolds.Because weak 1-concavity is also necessary for the maximumprinciple, a consequence is that a smooth generic CR submanifold ofCn obeys the maximum principle for continuous CR functions if andonly if it is weakly 1-concave. The proof is then generalized to embeddedweakly p-concave CR submanifolds of p-complete complexmanifolds. The second part concerns hypocomplexity and hypoanalyticstructures. We give a generalization of a known result regardingautomatic smoothness of solutions to the homogeneous problemfor the tangential CR vector fields given local holomorphic extension.This generalization ensures that a given locally integrable structureis hypocomplex at the origin if and only if it does not allow solutionsnear the origin which cannot be represented by a smooth function nearthe origin. Uppsatsen innehåller resultat om maximumprincipen för kontinuerligaCauchy–Riemann funktioner (CR-funktioner) på svagt 1-konkava CRmångfalder,samt hypokomplexitet för lokalt integrerbara strukturer.Maximumprincipen gäller inte generellt för släta CR funktioner ochmotexempel kan konstrueras givet strängt pseudokonvexa punkter.Vi bevisar en maximumprincip för kontinuerliga CR-funktioner påsläta inbäddade svagt 1-konkava CR-mångfalder. Eftersom svagt 1-konkavitet också är nödvändigt får vi som konsekvens att för slätageneriska inbäddade CR-mångfalder i Cn gäller att maximum-principenför kontinuerliga CR-funktioner håller om och endast om CR-mångfaldenär svagt 1-konkav. Vi generaliserar satsen till svagt p-konkava CRmångfalderi p-kompletta mångfalder. Den andra delen behandlarhypokomplexitet och hypoanalytiska strukturer. Vi generaliserar enkänd sats om automatisk släthet för lösningar till de tangentiella CRekvationerna,givet existensen av lokal holomorf utvidgning. Generaliseringenger att en lokalt integrerbar struktur är hypokomplex iorigo om och endast om den inte tillåter lösningar nära origo som inteär släta nära origo. Forskning finansierad av Forskarskolan i Matematik och Beräkningsvetenskap (FMB), baserad i Uppsala.

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Chen, Rongzhen. "First-Principles Study on Electronic and Optical Properties of Copper-Based Chalcogenide Photovoltaic Materials." Doctoral thesis, KTH, Materialvetenskap, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-207626.

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To accelerate environmentally friendly thin film photovoltaic (PV) technologies, copper-based chalcogenides are attractive as absorber materials. Chalcopyrite copper indium gallium selenide (CIGS ≡ CuIn1–xGaxSe2) is today a commercially important PV material, and it is also in many aspects a very interesting material from a scientific point of view. Copper zinc tin sulfide selenide (CZTSSe ≡ Cu2ZnSn(S1–xSex)4) is considered as an emerging alternative thin film absorber material. Ternary Cu2SnS3 (CTS) is a potential absorber material, thus its related alloys Cu2Sn1–xGexS3 (CTGS) and Cu2Sn1–xSixS3 (CTSS) are attractive due to the tunable band gap energies. CuSb(Se1–xTex)2 and CuBi(S1–xSex)2 can be potential as ultra-thin (≤ 100 nm) film absorber materials in the future. In the thesis, analyses of these Cu-based chalcogenides are based on first-principles calculations performed by means of the projector augmented wave method and the full-potential linearized augmented plane wave formalisms within the density functional theory as implemented in the VASP and WIEN2k program packages, respectively. The electronic and optical properties of CIGS (x = 0, 0.5, and 1) are studied, where the lowest conduction band (CB) and the three uppermost valence bands (VBs) are parameterized and analyzed in detail. The parameterization demonstrates that the corresponding energy dispersions of the topmost VBs are strongly anisotropic and non-parabolic even very close to the Γ-point. Moreover, the density-of-states and constant energy surfaces are calculated utilizing the parameterization, and the Fermi energy level and the carrier concentration are modeled for p-type CIGS. We conclude that the parameterization is more accurate than the commonly used parabolic approximation. The calculated dielectric function of CuIn0.5Ga0.5Se2 is also compared with measured dielectric function of CuIn0.7Ga0.3Se2 collaborating with experimentalists. We found that the overall shapes of the calculated and measured dielectric function spectra are in good agreement. The transitions in the Brillouin zone edge from the topmost and the second topmost VBs to the lowest CB are responsible for the main absorption peaks. However, also the energetically lower VBs contribute significantly to the high absorption coefficient. CTS and its related alloys are explored and investigated. For a perfectly crystalline CTS, reported experimental double absorption onset in dielectric function is for the first time confirmed by our calculations. We also found that the band gap energies of CTGS and CTSS vary almost linearly with composition over the entire range of x. Moreover, those alloys have comparable absorption coefficients with CZTSSe. Cu2XSnS4 (X = Be, Mg, Ca, Mn, Fe, Ni, and Zn) are also studied, revealing rather similar crystalline, electronic, and optical properties. Despite difficulties to avoid high concentration of anti-site pairs disordering in all compounds, the concentration is reduced in Cu2BeSnS4 partly due to larger relaxation effects. CuSb(Se1–xTex)2 and CuBi(S1–xSex)2 are suggested as alternative ultra-thin film absorber materials. Their maximum efficiencies considering the Auger effect are ~25% even when the thicknesses of the materials are between 50 and 300 nm. QC 20170523

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7

Shenton, John Kane. "First-principles investigations of structure-function relationships in bismuth ferrite." Thesis, University College London (University of London), 2018. http://discovery.ucl.ac.uk/10057684/.

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The simplicity of the basic perovskite structure belies a seemingly boundless potential for novel phenomena and technological applications. The ferroelectric perovskites, in particular, can have complex and subtle relationships between their crystal structures and functional properties. Understanding such structure-function relationships is a central theme of this work. In this work, advanced computational approaches are used to gain insight into key structure-function relationships in the multiferroic perovskite, bismuth ferrite (BFO). Density functional theory (DFT) has proven to be an immensely valuable tool in the study of condensed matter. However, techniques beyond standard DFT are often required to deal with the strongly localised electronic states in materials like BFO. In the first part of this thesis, we conduct a systematic study of a commonly used correction to DFT: DFT+U. We focus on the effect of the U parameter on the conduction band minimum (CBM) and valence band maximum (VBM). We find drastic changes to the location and curvature of the CBM in particular. Specifically, we find a surprising inversion in the ordering of the Fe t2g and eg manifolds at the CBM when U exceeds 4 eV. We therefore suggest caution when employing large values of U to calculate optoelectronic properties. In the second part of this work, motivated by the prospects of BFO-based photovoltaics, we investigate the influence of crystal structure on charge carrier effective masses. We begin by comparing the effective masses of several known phases of BFO, finding orders of magnitude differences between them. The strain-induced tetragonal phase emerged from this comparison as having the promising combination of a large spontaneous polarisation and relatively light charge carriers. Through a systematic decomposition of geometric relationships between different phases of BFO, we identify key physical influences on effective masses. We suggest that these insights could be exploited to improve photovoltaic efficiency. In the final part of this thesis, we enter the realm of designer materials. The creation and characterisation of atomically sharp interfaces between different complex oxides has proven to be an exciting and fruitful area of research in recent years. We investigate superlattices made up of repeating lanthanum aluminate (LAO) and BFO layers. By simply varying the thickness of the BFO layer, we found that one could tune the tetragonality, spontaneous polarisation and band gap of the superlattices. We also predict the formation of two-dimensional (2D) electron and hole gases at opposing interfaces above a critical thickness of BFO. The ferroelectric origin of the 2D gases, together with an emergent magnetism, suggests that this system may be a promising source of novel multiferroic functionality. In particular, we suggest the possibility of switching the 2D electron and hole gases via an external electric field.

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8

Anderson, Joel Edmund. "Isaiah 7:14 : identity and function within the bookend structure of Proto-Isaiah." Thesis, Pretoria : [s.n.], 2008. http://upetd.up.ac.za/thesis/available/etd-01152009-090940.

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9

Hu, Wenhao. "First principles investigations of single dopants in diamond and silicon carbide." Diss., University of Iowa, 2016. https://ir.uiowa.edu/etd/2092.

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In the most recent two decades, the development of impurity controls with ultra-high precision in semiconductors motivates people to put more and more attentions on the solotronic devices, whose properties depend on one or a few dopants. One of the most promising applications of solotronic device is the qubit in quantum computing. In the procedure of exploring qubit candidates, the most straightforward challenges we need face include that the qubit must be highly isolated and can be initialized/manipulated efficiently with high fidelities. It has been proved that qubits based on single defects have excellent performances as quits. For instance, the NV center in diamond forms a ground spin triplet which can be manipulated at room temperature with electromagnetic fields. This work focuses on searching for new single defects as qubit candidates with density functional theory. Lanthanides element possesses excellent optical characteristics and extremely long nuclear coherence time. Therefore, combining it into the diamond platform can be possible design for integrated quantum information processing devices in the future. To investigate the stability of lanthanides dopants in the diamond matrix, the formation energies of charge states of complexes are calculated. The broadening of Eu(III) peak in the photoluminescence spectrum can be verified according to the existence of more than stable configuration and steady 4f electron occupation. In the case of transition-metal dopant in the silicon carbide, it is found that both silicon and carbon substituted nickels in 3C-SiC shows a magnetic-antimagnetic transition under applied strains. The virtual hopping rate of electrons strongly depends on the distance between the spin pair residing in the nickel and dangling bonds. Therefore, the Heisenberg exchange coupling between them can be adjusted subtly by controlling the external strain. According to the the spin Hamiltonian of the defect, the spin state can be manipulated universally with strain and electromagnetic fields. In contrast, the nickel dopant in 4H-SiC exhibits a very stable magnetic property. Other than that, the electronic structure of Cr in 4H-SiC implies that optical manipulations of spin states might be realized in the excited state.

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10

Huang, Jianqiu. "First-Principles Study of Band Alignment and Electronic Structure at Metal/Oxide Interfaces: An Investigation of Dielectric Breakdown." Diss., Virginia Tech, 2018. http://hdl.handle.net/10919/95967.

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Oxide dielectric breakdown is an old problem that has been studied over decades. It causes power dissipations and irreversible damage to the electronic devices. The aggressive downscaling of the device size exponentially increases the leakage current density, which also raises the risk of dielectric breakdown. It has been proposed that point defects, current leakages, impurity diffusions, etc. all contribute to the change of oxide chemical composition and ultimately lead to the dielectric breakdown. However, the conclusive cause and a clear understanding of the entire process of dielectric breakdown are still under debate. In this research, the electronic structure at metal/oxide interfaces is studied using first-principle calculations within the framework of Density Functional Theory (DFT) to investigate any possible key signature that would trigger the dielectric breakdown. A classical band alignment method, the Van de Walle method, is applied to the case study of the Al/crystal-SiO2 (Al/c-SiO2) interface. Point defects, such as oxygen vacancy (VO) and hydrogen impurity (IH), are introduced into the Al/c-SiO2 interface to study the effects on band offset and electronic structure caused by point defects at metal/oxide interfaces. It is shown that the bonding chemistry at metal/oxide interfaces, which is mainly ionic bond, polarizes the interface. It results in many interface effects such as the interface dipole, built-in voltage, band bending, etc. Charge density analysis also indicates that the interface can localize charge due to such ionic bonding. It is also found that VO at the interface traps metal electrons which closes the open -sp3 orbital. The analysis on local potential shows that the metal potential penetrates through a few layers of oxide starting from the interface, which metalizes the interfacial region and induces unoccupied states in the oxide band gap. In addition, it is shown that higher oxygen content at metal/oxide interfaces minimizes such metal potential invasion. In addition, an oxygen vacancy is created at multiple sites through the Al/c-SiO2 and Al/a-SiO2 interface systems, separately. The oxygen local pressure is also calculated before its removal using Quantum Stress Density theory. Correlations among electronic structure, stress density, and vacancy formation energy are found, which provide informative insights into the defect generation controlling and dielectric breakdown analysis. A new band alignment approach based on the projection of plane-waves (PWs) into the space-dependent atomic orbital (LCAO) basis is presented and tested against classical band offset methods -- the Van de Walle method. It is found that the new band alignment approach can provide a quantitative and reliable band alignment and can be applied to the heterojunctions consisting of amorphous materials. The new band alignment approach reveals the real-space dependency of the electronic structure at interfaces. In addition, it includes all interface effects, such as the interface dipole, built-in voltage, virtual oxide thinning, and band deformation, which cannot be derived using classical band offset methods. This new band alignment approach is applied to the case study of both the Al/amorphous-SiO2 (Al/a-SiO2) interface and the Al/c-SiO2. We have found that at extremely low dimensions, the reduction of the insulator character due to the virtual oxide thinning is a pure quantum effect. I highlight that the quantum tunneling current leakage is more critical than the decrease of the potential barrier height on the failure of the devices. PHD

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11

Dai, Xianqi, and 戴憲起. "A study of the structural properties of SiC and GaN surfaces and theirinterfaces by first principle total energy calculation." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2003. http://hub.hku.hk/bib/B31244130.

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12

Ball, Molly R. "First Principles Study of Electronic and Magnetic Structures in Double Perovskites." The Ohio State University, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=osu1483702986122186.

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13

Kaewmaraya, Thanayut. "First-Principles Studies of Materials Properties : Pressure-Induced Phase Transitions & Functional Materials." Doctoral thesis, Uppsala universitet, Institutionen för fysik och astronomi, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-251343.

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This thesis presents the first-principles studies of materials properties within the framework of the density functional theory (DFT). The thesis constitutes three main parts, i. e., pressure-induced phase transitions in solids, data-storage and clean-energy materials. The first part focuses on the predictions of crystal structures and the determinations of electronic properties of Xe-H2, FeB4 and Co3O4. Pressurizing Xe-H2 compound yields the formation of H-rich Xe(H2)8, which can exhibit a metallic feature at comparatively lower pressure than pure hydrogen. Hard superconducting FeB4 gets transformed into a novel transparent phase under pressure owing to the enhanced overlap of atomic cores. Spinel Co3O4 undergoes the phase transition from a cubic to a monoclinic because of the charge transfer between cations via the increased 3d-3d interactions. The second part involves the study of structural and electronic properties of phase-change memory materials (PCMs), i. e., Ge2Sb2Te5 (GST) and Ga-doped In2O3. Van der Waals (vdW) interaction must be considered to obtain accurate crystal structure of layered GST. For Ga-doped In2O3 (GIO), the local structure of amorphous GIO is found to resemble that of amorphous In2O3, except the vicinity of doping atoms. The electronic property of a-GIO is metallic, which considerably differs from the semiconducting feature of the crystalline GIO. This emphasizes the contrast in the conductivity of the crystalline and amorphous upon phase switching of GIO. The third part associates with the search for clean-energy materials, viz., hydrogen production, hydrogen storage and green Mg-ion batteries. For hydrogen production, the role of intrinsic point defects to water adsorption on ZnO(10-10) surface is investigated. The findings show that the Zn and O defect-sites are energetically not favorable for the water adsorption and dissociation. For the purpose of storing hydrogen in a solid phase, silicene, doped by alkaline and alkaline earth metals, is investigated. We find that Li-doped and Na-doped silicene can attain the superior storage capacity. For cathode material of Mg-ion batteries, Mg2Mo6S8, the diffusivity of Mg ions occurs through an available channel in the bulk with the onset temperature of 200 K.

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14

Daghighi, Abtin. "Regularity and uniqueness-related properties of solutions with respect to locally integrable structures." Doctoral thesis, Mittuniversitetet, Avdelningen för ämnesdidaktik och matematik, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:miun:diva-21641.

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We prove that a smooth generic embedded CR submanifold of C^n obeys the maximum principle for continuous CR functions if and only if it is weakly 1-concave. The proof of the maximum principle in the original manuscript has later been generalized to embedded weakly q-concave CR submanifolds of certain complex manifolds. We give a generalization of a known result regarding automatic smoothness of solutions to the homogeneous problem for the tangential CR vector fields given local holomorphic extension. This generalization ensures that a given locally integrable structure is hypocomplex at the origin if and only if it does not allow solutions near the origin which cannot be represented by a smooth function near the origin. We give a sufficient condition under which it holds true that if a smooth CR function f on a smooth generic embedded CR submanifold, M, of C^n, vanishes to infinite order along a C^infty-smooth curve \gamma in M, then f vanishes on an M-neighborhood of \gamma. We prove a local maximum principle for certain locally integrable structures. Funding by FMB, based at Uppsala University.

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Alumasa, John N. "New insights on the structure-function principles and design of quinoline antimalarial drugs." Connect to Electronic Thesis (CONTENTdm), 2010. http://worldcat.org/oclc/642829236/viewonline.

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Cheng, Lei. "FIRST-PRINCIPLES DENSITY FUNCTIONAL THEORY STUDIES OF REACTIVITIES OF HETEROGENEOUS CATALYSTS DETERMINED BY STRUCTURE AND SUBSTRATE." OpenSIUC, 2009. https://opensiuc.lib.siu.edu/dissertations/99.

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In this dissertation, density functional theory (DFT) calculations were used to investigate (1)NO2 adsorption on BaO in NOx Storage Reduction (NSR) catalyst affected by the morphology of BaO and the γ-Al2O3 support, (2) energy barrier of H2 dissociative adsorption over Mg clusters affected by its electronic structure, and (3) comparison of the activities of CeO2 clusters affected by two different supports--monoclinic ZrO2 and non-spinel γ-Al2O3. Our results showed that the electronic effect caused by the non-stoichiometry of the bare BaO clusters and surfaces improves their reactivities toward NO2 adsorption greatly, whereas the geometric structure of the catalyst has only minor effect on the activity; we also found that the γ-Al2O3 substrate improves the reactivities of the supported BaO clusters and at the same time the interface between BaO and γ-Al2O3 provided a unique and highly reactive environment for NO2 adsorption. Hydrogen dissociation barrier over pure Mg clusters is greatly affected by the electronic structure of the clusters--closed shell clusters such as Mg10 and Mg92- have higher energy barrier toward H2 dissociation; however, H2 dissociation over clusters that are two electrons shy from the closed electronic shell are relatively easier. As substrates, neither ZrO2(111) nor γ-Al2O3(100) affects the reactivity of the supported Ce2O4 toward CO2 adsorption and CO physisorption significantly; whereas the reactivity of Ce2O4 toward CO reactive adsorption were found to be affected by the two substrates very differently.

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Allemang, Matthew R. "Comparison of Automotive Structures Using Transmissibility Functions and Principal Component Analysis." University of Cincinnati / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1367944783.

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Sheppard, Therese. "Extending covariance structure analysis for multivariate and functional data." Thesis, University of Manchester, 2010. https://www.research.manchester.ac.uk/portal/en/theses/extending-covariance-structure-analysis-for-multivariate-and-functional-data(e2ad7f12-3783-48cf-b83c-0ca26ef77633).html.

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For multivariate data, when testing homogeneity of covariance matrices arising from two or more groups, Bartlett's (1937) modified likelihood ratio test statistic is appropriate to use under the null hypothesis of equal covariance matrices where the null distribution of the test statistic is based on the restrictive assumption of normality. Zhang and Boos (1992) provide a pooled bootstrap approach when the data cannot be assumed to be normally distributed. We give three alternative bootstrap techniques to testing homogeneity of covariance matrices when it is both inappropriate to pool the data into one single population as in the pooled bootstrap procedure and when the data are not normally distributed. We further show that our alternative bootstrap methodology can be extended to testing Flury's (1988) hierarchy of covariance structure models. Where deviations from normality exist, we show, by simulation, that the normal theory log-likelihood ratio test statistic is less viable compared with our bootstrap methodology. For functional data, Ramsay and Silverman (2005) and Lee et al (2002) together provide four computational techniques for functional principal component analysis (PCA) followed by covariance structure estimation. When the smoothing method for smoothing individual profiles is based on using least squares cubic B-splines or regression splines, we find that the ensuing covariance matrix estimate suffers from loss of dimensionality. We show that ridge regression can be used to resolve this problem, but only for the discretisation and numerical quadrature approaches to estimation, and that choice of a suitable ridge parameter is not arbitrary. We further show the unsuitability of regression splines when deciding on the optimal degree of smoothing to apply to individual profiles. To gain insight into smoothing parameter choice for functional data, we compare kernel and spline approaches to smoothing individual profiles in a nonparametric regression context. Our simulation results justify a kernel approach using a new criterion based on predicted squared error. We also show by simulation that, when taking account of correlation, a kernel approach using a generalized cross validatory type criterion performs well. These data-based methods for selecting the smoothing parameter are illustrated prior to a functional PCA on a real data set.

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19

Schusteritsch, Georg. "First-Principles Multiscale Investigation of Structural and Chemical Defects in Metals." Thesis, Harvard University, 2012. http://dissertations.umi.com/gsas.harvard:10586.

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This thesis explores multiscale approaches to describe structural and chemical defects in metals. Particular emphasis is placed on investigating processes involving grain boundaries (GBs) in combination with impurity and vacancy defects. The defects and their interactions are calculated to very high accuracy using density functional theory (DFT) and connected to the macroscopic behavior within the two multiscale formalisms presented here. We begin with a sequential approach to address chemical embrittlement of nickel by sulfur impurities. Effects at both a \(\Sigma 5 (012)\) symmetric tilt GB and in the bulk are studied by considering competing mechanisms for ductile and brittle behavior. For the bulk, this takes the form of Rice’s theory, where the ratio of the surface and unstable stacking energy is used as a measure of ductility. This is generalized to the GB by considering GB sliding (GBS) and intergranular decohesion. Clear evidence that chemical embrittlement of nickel by sulfur is a GB driven effect is found. Next, a concurrent multiscale approach is described. A small region, containing the defects, is treated with Kohn-Sham DFT and coupled to the bulk, described with the embedded atom method. We apply this novel method to elucidate the chemical embrittlement of a copper \(\Sigma 5 (012)\) symmetric tilt GB. Intergranular decohesion for three substitutional impurities, bismuth, lead and silver, is investigated by considering the work of separation \((W_s)\) and the tensile strength \((\sigma_t)\). Bismuth and lead show a significant decrease in \(W_s\) and \(\sigma_t\), consistent with embrittlement, whilst silver has only a minor effect. Then, the concurrent multiscale method is applied to the process of GBS in copper. It is found that the resistance against sliding increases significantly for bismuth, lead and silver impurities. The underlying mechanisms for this increase are found to be dominated by size effects for bismuth and lead. For silver, chemical effects are of greater importance. Similar results are found for the underlying mechanisms of intergranular decohesion. The effect of a mono-vacancy on GBS is studied for copper. The multiscale approach enables improved decoupling of the mono-vacancy. It is found that the monovacancy enhances GBS by 22%. Engineering and Applied Sciences

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20

Ortiz, Carlos. "First Principles Calculations of Electron Transport and Structural Damage by Intense Irradiation." Doctoral thesis, Uppsala : Acta Universitatis Upsaliensis, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-102376.

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21

Guest, Jason Michael [Verfasser]. "Structural and functional principles of long-range connectivity in the rat vibrissal system / Jason Michael Guest." Bonn : Universitäts- und Landesbibliothek Bonn, 2020. http://d-nb.info/1222588773/34.

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22

Andersson, David. "From the Electronic Structure of Point Defects to Functional Properties of Metals and Ceramics." Doctoral thesis, Stockholm : Materialvetenskap, Materials Science and Engineering, KTH, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4309.

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23

Pinto, Leandro Moreira de Campos [UNESP]. "A teoria do funcional da densidade na caracterização de fases intermetálicas ordenadas." Universidade Estadual Paulista (UNESP), 2009. http://hdl.handle.net/11449/99693.

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Made available in DSpace on 2014-06-11T19:30:19Z (GMT). No. of bitstreams: 0 Previous issue date: 2009-11-03Bitstream added on 2014-06-13T19:39:43Z : No. of bitstreams: 1 pinto_lmc_me_bauru.pdf: 3368770 bytes, checksum: 3eea6b86b88292db626794855037e7c0 (MD5) Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) A utilização das fases intermetálicas ordenadas como eletrocatalisadores em células a combustível já pode ser considerada como uma solução iminente para os problemas que envolvem a eficiência e as questões econoômicas. Para assegurar que as propriedades geométricas e eletrônicas destes materiais sejam realmente as almejadas para atender a todas as exigências na eletrocatálise das reações de oxidação das moléculas é necessário um estudo aprofundado de caracterização das fases intermetálicas, comumente realizado por criteriosas técnicas experimentais. Entretanto, experimentalmente, a caracterização destes materiais não fornece informações precisas que permitam correlacionar as propriedades dos materiais com o seu desempenho frente a uma dada reação eletrostática. Desta forma, uma estratégia metodológica para se obter um conhecimento mais adequado no estudo das fases intermetálicas é a utilização de métodos computacionais, baseados na Teoria do Funcional da Densidade (DFT). A metodologia empregada neste trabalho aborda uma sistemática para a otimização das propriedades geométricas através da minimização da energia total do sistema, bem como uma avaliação da estrutura eletrônica para estes materiais por meio de projeções sobre os orbitais atômicos na densidade de estados e de mapas de densidade de carga. O processo de otimização é feito por cálculos de campo auto-consistente sucessivos que variam o parâmetro de rede até encontrar uma estrutura que possua energia mínima, este processo pode ser realizado de duas formas, manual e automaticamente pelo código computacional, os resultados obtidos mostram que ambas as formas possuem a mesma precisão, levando a valores quase idênticos e que permitem reproduzir bem os cristais para os materiais estudados. A análise comparativa entre os dados cristalográficos da literatura e os resultados... The use of ordered intermetallic phases as electrocatalysts in fuel cells can now be regarded as an imminent solution for the problems concerning the efficiency of the device and for economic issue. To ensure that the geometric and electronic properties of these materials are actually suitable for the requirements in the electrocatalysis of melecules oxidation reactions need a meticulous characterization of the intermetallic phases, in general done by standard experimental techniques. However, the characterization of these materials performed solely experimentally does not provide accurate information to enable correlation of the properties of the materials with their performance against a given electrocatalytic reaction. Thus, a methodological strategy for obtaining a better knowledge in the study of ordered intermetallic phases is the use of computational methods, based on the Density Functional Theory. The methodology used in in thius research presents a sytematic optimization of the geometric properties by minimizing the total energy of the system and an evaluation of the electronic structure for these materials by means of the density of states projected onto atomic orbital and charge density maps. The optimization process is done by successively self-consistent field calculations that very the lattice parameter to find a structure that has a minimum energy, this process can be accomplished in two ways, manually and automatically by the computer code, the results show that both forms have the same precision, leading to almost identical identical values and allow to reproduce well the crystals of the studied materials. A comparative analysis of the crystallographic data from the literature and the results presented here show very small errors (in the order of 2-3% for most of the materials), which can be attributed exclusively to the various mathematical approaches applied... (Complete abstract click electronic access below)

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24

Trippett, Fran. "Towards a broad-based precautionary principle in law and policy, a functional role for indigenous knowledge systems (TEK) within decision-making structures." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp03/MQ62360.pdf.

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25

Verstraete, Matthieu. "Ab initio calculation of the structural, electronic, and superconducting properties of nanotubes and nanowires." Université catholique de Louvain, 2005. http://edoc.bib.ucl.ac.be:81/ETD-db/collection/available/BelnUcetd-06282005-114313/.

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The structural, electronic, and superconducting properties of one dimensional materials are calculated from first principles, using the density functional theory. Nanotubes and nanowires are important building blocks in nanotechnology, in particular for nanoelectronics. In this manuscript, the growth of carbon nanotubes is studied through the interaction between carbon and the transition metal atoms used as growth catalysts. The accepted model for a new phase of nanotube-like molybdenum disulfide is critically examined using comparisons of energetic stability and types of chemical bonding in different candidate structures which have similar compositions. The epitaxial growth of diamond carbon on (100) iridium is exceptionally favorable. The differences between various substrates used experimentally are studied, and the specificity of Ir is shown. Finally, the characteristics of the electron-phonon interaction in aluminium nanowires are determined. The structural instabilities and the differences in the electron-phonon coupling are calculated for straight monoatomic wires, zigzag wires, and thicker straight wires. The constrained geometry of the wires generates a coupling which can be very strong or almost vanish, depending on the structural details, but which is concentrated in the longitudinal high-frequency phonons.

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26

Youssef, Srour Juliana. "Structure électronique et compétition de phases dans les semi-conducteurs Cu-(In,Ga)-Se, Ga-Se et In-Se : calculs premiers principes basés sur divers potentiels d'échange-corrélation." Thesis, Université de Lorraine, 2016. http://www.theses.fr/2016LORR0238/document.

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Afin de pouvoir utiliser les nouveaux matériaux semi-conducteurs dans les domaines de l’électronique et de l’optique, il faut parvenir à comprendre leur «structure électronique», ou plus précisément le positionnement des niveaux d’énergie des électrons impliqués dans l’absorption / émission d’un photon. Les propriétés électroniques, sensibles à la composition chimique et à la structure du matériau, sont théoriquement accessibles en résolvant les équations de la mécanique quantique sur ordinateur. Ce travail porte sur des simulations théoriques de la structure électronique de semi-conducteurs binaires constitués d'indium (ou du gallium) et de sélénium, ainsi que de leurs "dérivés" à base de cuivre. La stabilité relative des phases cristallographiques de certains composés In-Se et Ga-Se a été évaluée, ce qui a permis d’expliquer certaines tendances connues et de formuler des prédictions. Les résultats obtenus seront particulièrement utiles dans le domaine du photovoltaïque. Les simulations numériques ont été réalisées dans le cadre de la théorie de la fonctionnelle de la densité (DFT), visant les structures cristallines d'équilibre et les propriétés électroniques de quelques semi-conducteurs binaires ou (pseudo)ternaires à base de Cu, In, Ga et Se. Les systèmes étudiés possèdent la même structure à courte portée (environnement tétraédrique des cations et anions) mais diffèrent à longue portée. Les composés binaires (Ga/In)Se, (Ga/In)2Se3 constituent des références importantes dans les diagrammes de phases des systèmes à base de (Cu, In, Se) et (Cu, Ga, Se), au sein desquels figurent les phases potentiellement utiles dans le domaine du photovoltaïque. Le travail comprend deux chapitres d'introduction et trois chapitres exposant des résultats nouveaux In order to optimally use new semiconductor materials in electronics or optics, one needs to understand their “electronic structure”, that is, the mutual placement of the electron energy levels concerned by the processes of absorption / emission of a photon. The electronic properties, which depend on the material’s chemical composition and crystal structure, may be assessed by theory via solving quantum-mechanical equations on a computer. The present work deals with theory simulations of electronic structure done for several binary semiconductors consisting of indium (or gallium) and selenium, moreover for their “derivatives” containing copper. As a result, the relative stability of crystallographic phases of some Ga-Se and In-Se compounds has been assessed, explaining the known trends and making predictions. The results are expected to be useful for current works in photovoltaics. The numerical simulations have been performed within the density functional theory (DFT), aimed at the equilibrium crystal structures and electronic characteristics of several binary or (pseudo)ternary semiconductors based on Cu, In, Ga and Se. The compounds under study share similar short-range order features (tetrahedral environment of both cations and anions), differently assembled on a long-range scale. The binary compounds (Ga/In)Se, (Ga/In)2Se3 mark important end points at the phase diagrams of the (Cu,In,Se) and (Cu,Ga,Se) systems that cover a number of phases relevant, e.g., for applications in photovoltaics. The work comprises two chapters of introduction and three outlining novel results

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Cankurtaran, Burak O. "Linear-scaling techniques for first principles calculations of stationary and dynamic systems." Thesis, Curtin University, 2010. http://hdl.handle.net/20.500.11937/24.

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First principles calculations can be a computationally intensive task when studying large systems. Linear-scaling methods must be employed to find the electronic structure of systems consisting of thousands of atoms and greater. The goal of this thesis is to combine the linear-scaling divide-and-conquer (D&C) method with the linear-scaling capabilities of the SIESTA (Spanish Initiative for Electronic Simulations with Thousands of Atoms) density functional theory (DFT) methodology and present this union as a viable approach to large-scale first principles calculations. In particular, the density matrix version of the D&C method is implemented into the SIESTA package. This implementation can accommodate high quality calculations consisting of atom numbers in the tens of thousands using moderate computing resources. Low quality calculations have been tested up to half million atoms using reasonably sized computing resources.The D&C method is extended to better handle atomic dynamics simulations. First, by alleviating issues caused by discontinuities in the potential energy surface, with the application of a switching function on the Hamiltonian and overlap matrices. This allows for a smooth potential energy surface to be generated. The switching function has the additional benefit of accelerating the self-consistent field (SCF) process. Secondly, the D&C frozen density matrix (FDM) is modified to allow for improved charge transfer between the active and constrained regions of the system. This modification is found to reduce both the number of SCF iterations required for self-consistency and the number of relaxation steps in a local geometry optimisation. The D&C paradigm is applied to the real-time approach of time-dependent density functional theory (TDDFT). The method is tested on a linear alkane molecule with varying levels of success.Divergences in the induced dipole moment occur when the external excitation field is aligned parallel to the axis of the molecule. The method succeeds in producing accurate dipole moments when the external field is aligned perpendicular to the molecule. Various techniques are tested to improve the proposed method. Finally, the performance and effectiveness of the current D&C implementation is evaluated by studying three current systems. The first two systems consist of two different DNA sequences and the last system is the large ZIF-100 zeolitic imidazolate framework (ZIF).

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Bandara, Arachchillage Rupika Priyadarshani. "Damage identification and condition assessment of building structures using frequency response functions and neural networks." Thesis, Queensland University of Technology, 2013. https://eprints.qut.edu.au/61196/4/Rupika_Bandara_Thesis.pdf.

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This thesis investigated the viability of using Frequency Response Functions in combination with Artificial Neural Network technique in damage assessment of building structures. The proposed approach can help overcome some of limitations associated with previously developed vibration based methods and assist in delivering more accurate and robust damage identification results. Excellent results are obtained for damage identification of the case studies proving that the proposed approach has been developed successfully.

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Baykov, Vitaly. "Point defect interactions and structural stability of compounds." Doctoral thesis, Stockholm Stockholm : Materialvetenskap, Kungliga Tekniska högskolan, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4605.

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30

Lizárraga, Jurado Raquel. "Non-collinear Magnetism in d- and f-electron Systems." Doctoral thesis, Uppsala universitet, Fysiska institutionen, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-6812.

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In this thesis, non-collinear magnetism has been studied by using density functional theory and the augmented plane wave method with local orbitals (APW+lo). Two conditions for non-collinear instabilities have been identified in this thesis. First, the Fermi energy should cut through both spin up and down states. Secondly, strong nesting between the spin up and spin down Fermi surfaces is needed. The two criteria described here can be fulfilled by tuning the exchange-splitting and/or by modifying the volume. Calculations on several elements; bcc V, bcc and fcc Mn, bcc Fe, bcc and fcc Co, and bcc and fcc Ni show that a non-collinear state can be stabilized provided that the criteria discussed above are met. More complex materials have also been analyzed in terms of these two criteria. The substitutional alloys TlCo2Se2-xSx are found in experiments to possess spin spiral structures for x = {0-1.5} and at a concentration x = 1.75 the alloys become ferromagnetic. As S takes the place of Se in the crystal structure the distance between the Co layers is reduced and the turn angle of the spin spiral becomes smaller until it totally vanishes at x = 1.75. This thesis show that the evolution of the magnetic structure in these alloys is the consequence of a modification of the distance between Co layers, which induces a change in the interlayer exchange coupling. Fermi surfaces have been analyzed in TbNi5 in order to determine nesting features which would be responsible for the magnetic spin spiral observed in this material. The electronic structure of CeRhIn5 is also reported in this thesis. Furthermore, the 3-k magnetic structure of UO2 was investigated and the crystal field levels were calculated. Transition metal systems such as Fe in the superconducting high-pressure hcp phase and in the fcc crystal structure were also studied. The results obtained for fcc Fe are in accordance with previous reports. However the paramagnetic state in hcp Fe is found to be more stable than the antiferromagnetic configurations discussed earlier in the literature as being favored in the volume range where the hcp phase is stable and superconductivity appears (~ 15 GPa). The complex non-collinear magnetic structure in Mn3IrSi was calculated and the results are found to be in good agreement with experiments.

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31

Pinto, Leandro Moreira de Campos. "A teoria do funcional da densidade na caracterização de fases intermetálicas ordenadas /." Bauru, 2009. http://hdl.handle.net/11449/99693.

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Orientador: Antonio Carlos Dias Angelo Banca: Hamilton Brandão Varela de Albuquerque Banca: Nelson Henrique Morgon O Programa de Pós-Graduação em Ciência e Tecnologia de Materiais, PosMat, tem caráter institucional e integra as atividades de pesquisa em materiais de diversos campi da Unesp Resumo: A utilização das fases intermetálicas ordenadas como eletrocatalisadores em células a combustível já pode ser considerada como uma solução iminente para os problemas que envolvem a eficiência e as questões econoômicas. Para assegurar que as propriedades geométricas e eletrônicas destes materiais sejam realmente as almejadas para atender a todas as exigências na eletrocatálise das reações de oxidação das moléculas é necessário um estudo aprofundado de caracterização das fases intermetálicas, comumente realizado por criteriosas técnicas experimentais. Entretanto, experimentalmente, a caracterização destes materiais não fornece informações precisas que permitam correlacionar as propriedades dos materiais com o seu desempenho frente a uma dada reação eletrostática. Desta forma, uma estratégia metodológica para se obter um conhecimento mais adequado no estudo das fases intermetálicas é a utilização de métodos computacionais, baseados na Teoria do Funcional da Densidade (DFT). A metodologia empregada neste trabalho aborda uma sistemática para a otimização das propriedades geométricas através da minimização da energia total do sistema, bem como uma avaliação da estrutura eletrônica para estes materiais por meio de projeções sobre os orbitais atômicos na densidade de estados e de mapas de densidade de carga. O processo de otimização é feito por cálculos de campo auto-consistente sucessivos que variam o parâmetro de rede até encontrar uma estrutura que possua energia mínima, este processo pode ser realizado de duas formas, manual e automaticamente pelo código computacional, os resultados obtidos mostram que ambas as formas possuem a mesma precisão, levando a valores quase idênticos e que permitem reproduzir bem os cristais para os materiais estudados. A análise comparativa entre os dados cristalográficos da literatura e os resultados... (Resumo completo, clicar acesso eletrônico abaixo) Abstract: The use of ordered intermetallic phases as electrocatalysts in fuel cells can now be regarded as an imminent solution for the problems concerning the efficiency of the device and for economic issue. To ensure that the geometric and electronic properties of these materials are actually suitable for the requirements in the electrocatalysis of melecules oxidation reactions need a meticulous characterization of the intermetallic phases, in general done by standard experimental techniques. However, the characterization of these materials performed solely experimentally does not provide accurate information to enable correlation of the properties of the materials with their performance against a given electrocatalytic reaction. Thus, a methodological strategy for obtaining a better knowledge in the study of ordered intermetallic phases is the use of computational methods, based on the Density Functional Theory. The methodology used in in thius research presents a sytematic optimization of the geometric properties by minimizing the total energy of the system and an evaluation of the electronic structure for these materials by means of the density of states projected onto atomic orbital and charge density maps. The optimization process is done by successively self-consistent field calculations that very the lattice parameter to find a structure that has a minimum energy, this process can be accomplished in two ways, manually and automatically by the computer code, the results show that both forms have the same precision, leading to almost identical identical values and allow to reproduce well the crystals of the studied materials. A comparative analysis of the crystallographic data from the literature and the results presented here show very small errors (in the order of 2-3% for most of the materials), which can be attributed exclusively to the various mathematical approaches applied... (Complete abstract click electronic access below) Mestre

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32

Westin, Lars. "Vintage models of spatial structural change." Doctoral thesis, Umeå universitet, Institutionen för nationalekonomi, 1990. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-73665.

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In the study a class of multisector network models, suitable for simulation of the interaction between production, demand, trade, and infrastructure, is presented. A characteristic feature of the class is a vintage model of the production system. Hence, the rigidities in existing capacities and the temporary monopolies obtainable from investments in new capacity at favourable locations are emphasized.As special cases, the class contains models in the modelling traditions of "interregional computable general equilibriunT, Hspatial price equilibrium**, "interregional input-output" and transportation networks.On the demand side, a multihousehold spatial linear expenditure system is introduced. This allows for an endogenous representation of income effects of skill-differentiated labour.The models are represented by a set of complementarity problems. This facilitates a comparison of model properties and the choice of an appropriate solution algorithm.The study is mainly devoted to single period models. Such equilibrium models are interpreted as adiabatic approximations of processes in continuous time. A separation by the time scale of the processes and an application of the slaving principle should thus govern the choice of endogenous variables in the equilibrium formulation. digitalisering@umu

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Gao, Huanhuan. "Categorical structural optimization : methods and applications." Thesis, Compiègne, 2019. http://www.theses.fr/2019COMP2471/document.

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La thèse se concentre sur une recherche méthodologique sur l'optimisation structurelle catégorielle au moyen d'un apprentissage multiple. Dans cette thèse, les variables catégorielles non ordinales sont traitées comme des variables discrètes multidimensionnelles. Afin de réduire la dimensionnalité, les nombreuses techniques d'apprentissage sont introduites pour trouver la dimensionnalité intrinsèque et mapper l'espace de conception d'origine sur un espace d'ordre réduit. Les mécanismes des techniques d'apprentissage à la fois linéaires et non linéaires sont d'abord étudiés. Ensuite, des exemples numériques sont testés pour comparer les performances de nombreuses techniques d’apprentissage. Sur la base de la représentation d'ordre réduit obtenue par Isomap, les opérateurs de mutation et de croisement évolutifs basés sur les graphes sont proposés pour traiter des problèmes d'optimisation structurelle catégoriels, notamment la conception du dôme, du cadre rigide de six étages et des structures en forme de dame. Ensuite, la méthode de recherche continue consistant à déplacer des asymptotes est exécutée et fournit une solution compétitive, mais inadmissible, en quelques rares itérations. Ensuite, lors de la deuxième étape, une stratégie de recherche discrète est proposée pour rechercher de meilleures solutions basées sur la recherche de voisins. Afin de traiter le cas dans lequel les instances de conception catégorielles sont réparties sur plusieurs variétés, nous proposons une méthode d'apprentissage des variétés k-variétés basée sur l'analyse en composantes principales pondérées The thesis concentrates on a methodological research on categorical structural optimizationby means of manifold learning. The main difficulty of handling the categorical optimization problems lies in the description of the categorical variables: they are presented in a category and do not have any orders. Thus the treatment of the design space is a key issue. In this thesis, the non-ordinal categorical variables are treated as multi-dimensional discrete variables, thus the dimensionality of corresponding design space becomes high. In order to reduce the dimensionality, the manifold learning techniques are introduced to find the intrinsic dimensionality and map the original design space to a reduced-order space. The mechanisms of both linear and non-linear manifold learning techniques are firstly studied. Then numerical examples are tested to compare the performance of manifold learning techniques mentioned above. It is found that the PCA and MDS can only deal with linear or globally approximately linear cases. Isomap preserves the geodesic distances for non-linear manifold however, its time consuming is the most. LLE preserves the neighbour weights and can yield good results in a short time. KPCA works like a non-linear classifier and we proves why it cannot preserve distances or angles in some cases. Based on the reduced-order representation obtained by Isomap, the graph-based evolutionary crossover and mutation operators are proposed to deal with categorical structural optimization problems, including the design of dome, six-story rigid frame and dame-like structures. The results show that the proposed graph-based evolutionary approach constructed on the reduced-order space performs more efficiently than traditional methods including simplex approach or evolutionary approach without reduced-order space. In chapter 5, the LLE is applied to reduce the data dimensionality and a polynomial interpolation helps to construct the responding surface from lower dimensional representation to original data. Then the continuous search method of moving asymptotes is executed and yields a competitively good but inadmissible solution within only a few of iteration numbers. Then in the second stage, a discrete search strategy is proposed to find out better solutions based on a neighbour search. The ten-bar truss and dome structural design problems are tested to show the validity of the method. In the end, this method is compared to the Simulated Annealing algorithm and Covariance Matrix Adaptation Evolutionary Strategy, showing its better optimization efficiency. In chapter 6, in order to deal with the case in which the categorical design instances are distributed on several manifolds, we propose a k-manifolds learning method based on the Weighted Principal Component Analysis. And the obtained manifolds are integrated in the lower dimensional design space. Then the method introduced in chapter 4 is applied to solve the ten-bar truss, the dome and the dame-like structural design problems

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Guzmán, García Dany Julian, and Clavijo Javier Francisco Ulloa. "Evaluación estructural, superficial y funcional del pavimento de la pista principal aeropuerto de Pisco: Renan Elias Olivera." Bachelor's thesis, Universidad Ricardo Palma, 2015. http://cybertesis.urp.edu.pe/handle/urp/1333.

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La presente tesis para optar el grado de Ingeniero Civil se titula “Evaluación estructural, superficial y funcional del pavimento de la pista principal aeropuerto de Pisco: Renán Elías Olivera”. El objetivo de la investigación ha sido explicar los elementos de la evaluación estructural, superficial y funcional del pavimento de la pista principal del Aeropuerto de Pisco “Renán Elías Olivera” para cumplir con la Norma establecida por las FAA. La metodología utilizada es de tipo descriptivo – aplicada y de diseño cualitativo – cuantitativo. La hipótesis general ha comprobado lo siguiente: “existe una relación significativa entre los elementos de la evaluación estructural, superficial y funcional del pavimento de la pista principal del Aeropuerto de Pisco “Renán Elías Olivera” y el cumplimiento con la Norma establecida por las FAA para llegar a ser admitido como aeropuerto alterno del Jorge Chávez. La validación de la Hipótesis ha quedado comprobada y demostrada a través del análisis de los diferentes estratos del suelo, espesores característicos del suelo de fundación por medio de calicatas y las características de la pista asfáltica del Aeropuerto Renán Elías Olivera y el cumplimiento de la Norma establecida por la Federal Aviation Administration (FAA), generando la conclusión general, como resultado de la comprobación de la hipótesis global mediante el siguiente enunciado: “…Se ha podido determinar que la evaluación estructural, superficial y funcional del pavimento de la pista principal aeropuerto de Pisco: Renán Elías Olivera cumple con los requerimientos de la FAA para ser un aeropuerto alterno al Jorge Chávez”. This thesis for the degree of Civil Engineer is entitled "Structural evaluation, functional surface and the floor of the main runway airport in Pisco: Renan Elias Olivera". The aim of the research was to explain the elements of structural, surface and functional assessment of the main runway pavement Airport Pisco "Renan Elias Olivera" to meet the standard set by the FAA. The methodology is descriptive - applied design and qualitative - quantitative. The general assumption has proven that: "there is a significant relationship between structural elements, surface and functional assessment of the main runway pavement Airport Pisco" Renan Elias Olivera "and compliance with the standard set by the FAA become accepted as an alternate airport Jorge Chavez. Validation of the hypothesis has been tested and demonstrated through the analysis of different soil layers, soil thickness characteristic foundation through pits and characteristics of the asphalt airport runway Renan Elias Olivera and compliance with the standard set by the Federal Aviation Administration (FAA), generating the overall conclusion as a result of the verification of the overall hypothesis by the following statement: "... It has been determined that the structural, surface and functional evaluation of pavement from the main runway airport Pisco: Renan Elias Olivera meets the requirements of the FAA to be an alternate airport Jorge Chavez".

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Peschek, Jirka [Verfasser], Johannes [Akademischer Betreuer] Buchner, Matthias [Akademischer Betreuer] Rief, Sevil [Akademischer Betreuer] Weinkauf, and Bernd [Akademischer Betreuer] Reif. "Structural and Functional Principles of the Small Heat Shock Protein alpha-Crystallin / Jirka Peschek. Gutachter: Matthias Rief ; Sevil Weinkauf ; Bernd Reif ; Johannes Buchner. Betreuer: Johannes Buchner." München : Universitätsbibliothek der TU München, 2012. http://d-nb.info/104594548X/34.

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Tagwireyi, Paradzayi. "Ant and spider dynamics in complex riverine landscapes of the Scioto River basin, Ohio: implications for riparian ecosystem structure and function." The Ohio State University, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=osu1398983906.

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Bauer, David Siegfried Georg [Verfasser]. "Development of a relativistic full-potential first-principles multiple scattering Green function method applied to complex magnetic textures ofnano structures at surfaces / David Siegfried Georg Bauer." Aachen : Hochschulbibliothek der Rheinisch-Westfälischen Technischen Hochschule Aachen, 2014. http://d-nb.info/1049572882/34.

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38

Zhuo, Keenan. "Electronic, thermoelectric and vibrational properties of silicon nanowires and copper chalcogenides." Diss., Georgia Institute of Technology, 2015. http://hdl.handle.net/1853/54878.

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Silicon nanowires (SiNWs) and the copper chalcogenides, namely copper sulfide (Cu2S) and selenide Cu2Se, have diverse applications in renewable energy technology. For example, SiNWs which have direct band gaps unlike bulk Si, have the potential to radically reduce the cost of Si based photovoltaic cells. However, they degrade quickly under ambient conditions. Various surface passivations have therefore been investigated for enhancing their stability but it is not yet well understood how they affect the electronic structure of SiNWs at a fundamental level. Here, we will explore, from first-principles simulation, how fluorine, methyl and hydrogen surface passivations alter the electronic structures of [111] and [110] SiNWs via strain and quantum confinement. We also show how electronic charge states in [111] and [110] SiNWs can be effectively modelled by simple quantum wells. In addition, we address the issue of why [111] SiNWs are less influenced by their surface passivation than [110] SiNWs. Like SiNWs, Cu2S and Cu2Se also make excellent photovoltaic cells. However, they are most well known for their exceptional thermoelectric performance. This is by virtue of their even more unique solid-liquid hybrid nature which combines the low thermal conductivity and good electrical characteristics required for a high thermoelectric efficiency. We use first-principles molecular dynamics simulations to show that Cu diffusion rates in Cu2S and Cu2Se can be as high as 10-5cm2s-1. We also relate their phonon power spectra to their low thermal conductivities. Furthermore, we evaluate the thermoelectric properties of Cu2S and Cu2Se using a combination of Boltzmann transport theory and first-principles electronic structure calculations. Our results show that both Cu2S and Cu2Se are capable of maintaining high Seebeck coefficients in excess of 200μVK-1 for hole concentrations as high as 3x1020cm-3.

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Picat, Marie-Quitterie. "Analyses intégratives de biomarqueurs immunologiques dans les études épidémiologiques. Applications à trois études cliniques." Thesis, Bordeaux, 2015. http://www.theses.fr/2015BORD0144/document.

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Les processus biologiques sont nombreux et leurs interactions complexes. Les mesures de cesphénomènes génèrent des biomarqueurs multiples. Ainsi, l’épidémiologie doit évoluer dans cecontexte de données complexes et de nature multidimensionnelle. Les maladies du systèmeimmunitaire et les troubles immunologiques qui leur sont associés constituent un bon exemplede pathologies où les questions clinico-épidémiologiques sont de plus en plus complexes,nécessitant des méthodes biostatistiques et épidémiologiques adaptées. Dans cette thèsed’Université, des méthodes permettant de prendre en compte les difficultés méthodologiquesgénérées par les données d’immunologie sont présentées autour de trois applicationscliniques. Notre approche consiste en l’utilisation de méthodes intégratives qui prennent encompte l’ensemble des mesures concernant une pathologie donnée. Nous montrons l’intérêtde l’analyse en composantes principales et de la classification hiérarchique ascendante pourrésumer et extraire l’information de données multiples de cytométrie en flux et celui desmodèles d’équations structurelles pour l’étude de relations complexes entre variables lors deprocessus multifactoriels. Enfin, via l’exemple d’un modèle de reconstitution immunitaireasymptotique utilisant une fonction exponentielle, nous illustrons l’importance de s’appuyersur la structure même des données et sur la compréhension des mécanismes biologiques quisous-tendent la variabilité de ces données dans la réflexion qui concourt au choix d’un modèlestatistique. Les méthodes et la réflexion proposées dans cette thèse sont transposables àd’autres domaines d’application avec des données multiples complexes Numerous biological processes with potentially complex interactions exist. Measurements ofthese processes allow to produce multiple biomarkers. Thus, there is a need for epidemiologyto evolve within the context of complex and multidimensional data. Immune system diseasesand associated immune disorders are an example of a field where clinical and epidemiologicalissues are increasingly complex, requiring appropriate statistical and epidemiologicalmethods. In this thesis, methods taking into account methodological difficulties generated byimmunology data are presented through three motivating examples. The general paradigm ofour approach is to take into account all measurements on a given pathology using integrativemethods. We propose principal component analysis and hierarchical clustering to summarizemultidimensional cytometry data and structural equation modelling for dealing with complexrelationships between variables in multifactorial processes. Then, through the example of anasymptotic model of immune reconstitution using an exponential function, we illustrate theimportance about the data’s structure and the biological mechanisms underlying its variabilitywhen building a mathematical model. The methods and the thinking advocated in this thesisare transposable to other research domains with complex data

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Кульбаба, Мар’яна Василівна, та Kulbaba Mariana. "Удосконалення механізмів забезпечення ефективного управління інноваційним розвитком підприємства (на прикладі ПАТ “Тернопільський радіозавод “Оріон”)". Thesis, Тернопільський національний технічний університет імені Івана Пулюя, 2013. http://elartu.tntu.edu.ua/handle/123456789/2598.

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Магістерська робота присвячена науковому обґрунтуванню та оптимізації теоретичних та методичних положень, а також практичних рекомендацій щодо удосконалення механізмів забезпечення ефективного управління інноваційним розвитком підприємства. У роботі подано загальну характеристику управління інноваційним розвитком підприємств, принципи формування та структуру організаційно-економічного механізму управління інноваційним розвитком підприємств; здійснено комплексний аналіз інноваційної та фінансової діяльності ПАТ “ТРЗ “Оріон”; визначено інноваційний потенціал та стратегічні напрями інноваційного розвитку досліджуваного підприємства. Запропоновано шляхи підвищення продуктивності праці інноваційними засобами, що передбачають реалізацію інноваційного проекту з модернізації обладнання Master's thesis is devoted to the scientific substantiation and optimization of theoretical and methodological positions, as well as practical recommendations for improving mechanisms to ensure the effective management of innovative enterprise development. The paper presents a general description of the development of innovative enterprises, the principles of the formation and structure of the organizational and economic mechanism of development of innovative enterprises, a comprehensive analysis of innovation and financial activity of the open joint-stock company “The Ternopol radio factory “Orion”, defined innovation potential and strategic directions for the development of the innovative enterprise. The ways of increasing productivity with innovative tools that provides realization of innovative projects to modernize equipment

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Martínez, Brito Izacar Jesús. "Quantitative structure fate relationships for multimedia environmental analysis." Doctoral thesis, Universitat Rovira i Virgili, 2010. http://hdl.handle.net/10803/8590.

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Key physicochemical properties for a wide spectrum of chemical pollutants are unknown. This thesis analyses the prospect of assessing the environmental distribution of chemicals directly from supervised learning algorithms using molecular descriptors, rather than from multimedia environmental models (MEMs) using several physicochemical properties estimated from QSARs. Dimensionless compartmental mass ratios of 468 validation chemicals were compared, in logarithmic units, between: a) SimpleBox 3, a Level III MEM, propagating random property values within statistical distributions of widely recommended QSARs; and, b) Support Vector Regressions (SVRs), acting as Quantitative Structure-Fate Relationships (QSFRs), linking mass ratios to molecular weight and constituent counts (atoms, bonds, functional groups and rings) for training chemicals. Best predictions were obtained for test and validation chemicals optimally found to be within the domain of applicability of the QSFRs, evidenced by low MAE and high q2 values (in air, MAE≤0.54 and q2≥0.92; in water, MAE≤0.27 and q2≥0.92). Las propiedades fisicoquímicas de un gran espectro de contaminantes químicos son desconocidas. Esta tesis analiza la posibilidad de evaluar la distribución ambiental de compuestos utilizando algoritmos de aprendizaje supervisados alimentados con descriptores moleculares, en vez de modelos ambientales multimedia alimentados con propiedades estimadas por QSARs. Se han comparado fracciones másicas adimensionales, en unidades logarítmicas, de 468 compuestos entre: a) SimpleBox 3, un modelo de nivel III, propagando valores aleatorios de propiedades dentro de distribuciones estadísticas de QSARs recomendados; y, b) regresiones de vectores soporte (SVRs) actuando como relaciones cuantitativas de estructura y destino (QSFRs), relacionando fracciones másicas con pesos moleculares y cuentas de constituyentes (átomos, enlaces, grupos funcionales y anillos) para compuestos de entrenamiento. Las mejores predicciones resultaron para compuestos de test y validación correctamente localizados dentro del dominio de aplicabilidad de los QSFRs, evidenciado por valores bajos de MAE y valores altos de q2 (en aire, MAE≤0.54 y q2≥0.92; en agua, MAE≤0.27 y q2≥0.92).

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Casero, Cañas Ramón. "Left ventricle functional analysis in 2D+t contrast echocardiography within an atlas-based deformable template model framework." Thesis, University of Oxford, 2008. http://ora.ox.ac.uk/objects/uuid:b17b3670-551d-4549-8f10-d977295c1857.

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This biomedical engineering thesis explores the opportunities and challenges of 2D+t contrast echocardiography for left ventricle functional analysis, both clinically and within a computer vision atlas-based deformable template model framework. A database was created for the experiments in this thesis, with 21 studies of contrast Dobutamine Stress Echo, in all 4 principal planes. The database includes clinical variables, human expert hand-traced myocardial contours and visual scoring. First the problem is studied from a clinical perspective. Quantification of endocardial global and local function using standard measures shows expected values and agreement with human expert visual scoring, but the results are less reliable for myocardial thickening. Next, the problem of segmenting the endocardium with a computer is posed in a standard landmark and atlas-based deformable template model framework. The underlying assumption is that these models can emulate human experts in terms of integrating previous knowledge about the anatomy and physiology with three sources of information from the image: texture, geometry and kinetics. Probabilistic atlases of contrast echocardiography are computed, while noting from histograms at selected anatomical locations that modelling texture with just mean intensity values may be too naive. Intensity analysis together with the clinical results above suggest that lack of external boundary definition may preclude this imaging technique for appropriate measuring of myocardial thickening, while endocardial boundary definition is appropriate for evaluation of wall motion. Geometry is presented in a Principal Component Analysis (PCA) context, highlighting issues about Gaussianity, the correlation and covariance matrices with respect to physiology, and analysing different measures of dimensionality. A popular extension of deformable models ---Active Appearance Models (AAMs)--- is then studied in depth. Contrary to common wisdom, it is contended that using a PCA texture space instead of a fixed atlas is detrimental to segmentation, and that PCA models are not convenient for texture modelling. To integrate kinetics, a novel spatio-temporal model of cardiac contours is proposed. The new explicit model does not require frame interpolation, and it is compared to previous implicit models in terms of approximation error when the shape vector changes from frame to frame or remains constant throughout the cardiac cycle. Finally, the 2D+t atlas-based deformable model segmentation problem is formulated and solved with a gradient descent approach. Experiments using the similarity transformation suggest that segmentation of the whole cardiac volume outperforms segmentation of individual frames. A relatively new approach ---the inverse compositional algorithm--- is shown to decrease running times of the classic Lucas-Kanade algorithm by a factor of 20 to 25, to values that are within real-time processing reach.

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Andersson, David. "Multivariate design of molecular docking experiments : An investigation of protein-ligand interactions." Doctoral thesis, Umeå universitet, Kemiska institutionen, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-35736.

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To be able to make informed descicions regarding the research of new drug molecules (ligands), it is crucial to have access to information regarding the chemical interaction between the drug and its biological target (protein). Computer-based methods have a given role in drug research today and, by using methods such as molecular docking, it is possible to investigate the way in which ligands and proteins interact. Despite the acceleration in computer power experienced in the last decades many problems persist in modelling these complicated interactions. The main objective of this thesis was to investigate and improve molecular modelling methods aimed to estimate protein-ligand binding. In order to do so, we have utilised chemometric tools, e.g. design of experiments (DoE) and principal component analysis (PCA), in the field of molecular modelling. More specifically, molecular docking was investigated as a tool for reproduction of ligand poses in protein 3D structures and for virtual screening. Adjustable parameters in two docking software were varied using DoE and parameter settings were identified which lead to improved results. In an additional study, we explored the nature of ligand-binding cavities in proteins since they are important factors in protein-ligand interactions, especially in the prediction of the function of newly found proteins. We developed a strategy, comprising a new set of descriptors and PCA, to map proteins based on their cavity physicochemical properties. Finally, we applied our developed strategies to design a set of glycopeptides which were used to study autoimmune arthritis. A combination of docking and statistical molecular design, synthesis and biological evaluation led to new binders for two different class II MHC proteins and recognition by a panel of T-cell hybridomas. New and interesting SAR conclusions could be drawn and the results will serve as a basis for selection of peptides to include in in vivo studies.

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Шурко, О. І. "Адміністративно-правове забезпечення охорони та підтримання громадського порядку в судах". Thesis, Сумський державний університет, 2020. https://essuir.sumdu.edu.ua/handle/123456789/77937.

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Визначається поняття громадського порядку як об’єкта адміністративно- правової охорони. Окреслюються особливості забезпечення охорони та підтримання громадського порядку в судах. Надається характеристика правовим засадам забезпечення охорони та підтримання громадського порядку в судах та визначається місце серед них адміністративно-правового регулювання. Встановлюються завдання та функції Служби судової охорони. Визначаються компетенція і повноваження Служби судової охорони. З’ясовуються особливості юридичної відповідальності працівників Служби судової охорони. Розглядається організаційно-штатна структура Служби судової охорони. Узагальнюється зарубіжний досвід охорони та підтримання громадського порядку в судах та визначаються можливості його використання в Україні. Окреслюються перспективні напрямки вдосконалення адміністративного законодавства, яке регламентує здійснення охорони та підтримання громадського порядку в судах. Визначаються напрямки удосконалення організаційних засад здійснення охорони та підтримання громадського порядку в судах. В диссертации приведено теоретическое обобщение и новое решение научной задачи, которая заключается в решении комплекса теоретических и практических проблем административно-правового обеспечения охраны и поддержания общественного порядка в судах. В результате проведенного исследования сформулирован ряд выводов, предложений и рекомендаций, направленных на совершенствование соответствующего законодательства. Определяется понятие общественного порядка как объекта административно-правовой охраны, под которым предлагается понимать состояние общественных отношений, сложившееся в результате регулятивного воздействия на них правовых и иных социальных норм, определяющее режим поведения субъектов в общественных местах с целью обеспечения безопасности жизни и здоровья людей, уважения их чести и достоинства, нормального функционирования государственных и общественных институтов, сохранения собственности и поддержания общественного порядка. Отмечается, что общественный порядок является необходимым условием для: а) нормального общения людей, безопасной и беспрепятственной реализации ими своих прав и обязанностей; б) надлежащего выполнения органами публичной власти и их должностными лицами своих задач и функций. Определяются особенности обеспечения охраны и поддержания общественного порядка в судах. Дается характеристика правовым основам обеспечения охраны и поддержания общественного порядка в судах и определяется место среди них административно-правового регулирования. Устанавливаются задачи и функции Службы судебной охраны. Определяются компетенция и полномочия Службы судебной охраны. Доказано, что компетенция и полномочия Службы судебной охраны формируют фундамент ее правового статуса. Отмечается, что ни компетенция, ни полномочия не являются постоянными категориями, а зависят от развития общественных отношений, возникающих в ходе осуществления правосудия, а также характера и объема задач, которые возлагаются на Службу судебной охраны. Под компетенцией Службы судебной охраны предложено понимать определенный объем задач, которые возлагаются на эту Службу и реализуются с учетом предоставленных ей прав и обязанностей. Полномочия Службы судебной охраны, в свою очередь, определены как совокупность предоставленных государством и закрепленных в установленном законом порядке прав и обязанностей, необходимых и достаточных для надлежащего выполнения возложенных на нее задач и функций. Выясняются особенности юридической ответственности работников Службы судебной охраны. Рассматривается организационно-штатная структура Службы судебной охраны. Определено, что организационно- штатная структура территориальных органов Службы судебной охраны окончательно сформирована не во всех регионах. Она находится на стадии своего становления. В краткосрочной перспективе будут доукомплектованы органы управления, продлено обучение и повышение квалификации сотрудников, укомплектованы подразделения оперативно-внезапного действия и личной безопасности судей. Предложено в ближайшее время разработать и утвердить приказом Государственной судебной администрации Положение об организационно-штатной структуре Службы судебной охраны. Обобщается зарубежный опыт охраны и поддержания общественного порядка в судах и определяются возможности его использования в Украине. Определяются перспективные направления совершенствования административного законодательства, регламентирующего осуществление охраны и поддержания общественного порядка в судах. Определяются направления совершенствования организационных основ осуществления охраны и поддержания общественного порядка в судах. The concept of public order as an object of administrative and legal protection has been determined. Specific features of ensuring the protection of public order in the courts have been outlined. The author has provided characteristics of legal principles of ensuring the protection of public order in the courts and has determined the place of administrative and legal regulation among them. The tasks and functions of the Judicial Protection Service have been established. The competences and powers of the Judicial Protection Service have been determined. Specific features of legal liability of the employees of the Judicial Protection Service have been clarified. The organizational structure of the Judicial Protection Service has been considered. International experience for protecting and keeping public order in the courts has been generalized; and opportunities for its application in Ukraine have been determined. The perspective directions for improving administrative legislation regulating the protection of public order in the courts have been outlined. The directions for improving organizational principles of protecting and keeping public order in the courts have beendetermined.

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Singh, Vijay Ramdin. "First Principles Study of Electronic Structure and Magnetism in Functional Materials." Thesis, 2019. http://hdl.handle.net/10821/8310.

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In the present thesis work, we have employed rst principles calculations based on density functional theory (DFT) to understand the electronic structure and magnetism of several functional materials. We have studied the magnetic property of the rare-earth based intermetallic compound Gd2In which is a rather unique system where both localized 4f electrons as well as itinerant 5d electrons all originating from Gd are responsible for its novel magnetic property with hardly any role of In s, p electrons. In particular, analysing the response of Gd 4f and 5d moments in a magnetic eld using xed spin moment method we have conclusively established the important role of Gd 5d electrons in the metamagnetic property of Gd2In. Next we have considered, local cationic order and its impact on magnetism in the double perovskite LaSrVMoO6. Experiments reveal unusual atomic scale chemical fluctuation in LaSrVMoO6 where there are narrow patches of La-V and Sr-Mo rich phases. Our electronic structure calculations reveal that the La-O covalency play a key role that leads to the preferential La, V and Sr, Mo ionic proximity and therefore the resulting patchy structure in LaSrVMoO6. In contrast to the suggestion that LaSrVMoO6 may be a half-metallic antiferromagnet, our calculations on the experimentally realized patchy structure suggest that the system is metallic (not a half metal) and does not exhibit long range magnetic order. Finally, we have studied the magnetic and phononic properties of non-stoichiometric full Heusler alloys Ni2+xMn1 xIn and Ni2Mn1+xSn1 x. Our study of the non-stoichiometric full Heusler alloy Ni2+xMn1 xIn reveal that these systems do not exhibit martensitic transition like the Ni2+xMn1 xGa alloys. The magnetic properties of the In samples however are very similar to the Ga counterpart. The reduction of the total magnetic moment as a function of excess Ni concentration is attributed to the progressive lling up of the Ni-d minority states with the availability of excess electrons upon Ni doping. The reduction in the ferromagnetic Curie temperature observed experimentally is argued to be due to the decrease in tion of the conduction (In s+p) electrons with excess Ni concentration leading to the weakening of the RKKY like interactions. Finally, we have investigated the origin of martensitic transition in Ni2Mn1:5Sn0:5 alloy. The phonon dispersion relation calculated for Ni2Mn1:5Sn0:5 alloy with parallel alignment of the moment of the excess Mn at the Sn site with the Mn already existing in the unit cell reveal softening of the TA2 mode analogous to Ni2MnGa and is responsible for the martensitic transition. Thorigin of the martensitic transition is traced back to the nesting of the Fermi surface in the minority spin channel. Research was conducted under the supervision of Prof. Indra Dasgupta of the Solid State Physics division under SPS [School of Physical Sciences] Research was carried out from DST grant and IACS fellowship

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"Prediction of structures and properties of high-pressure solid materials using first principles methods." Thesis, 2016. http://hdl.handle.net/10388/ETD-2016-02-2441.

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The purpose of the research contained in this thesis is to allow for the prediction of new structures and properties of crystalline structures due to the application of external pressure by using first-principles numerical computations. The body of the thesis is separated into two primary research projects. The properties of cupric oxide (CuO) have been studied at pressures below 70 GPa, and it has been suggested that it may show room-temperature multiferroics at pressure of 20 to 40 GPa. However, at pressures above these ranges, the properties of CuO have yet to be examined thoroughly. The changes in crystal structure of CuO were examined in these high-pressure ranges. It was predicted that the ambient pressure monoclinic structure changes to a rocksalt structure and CsCl structure at high pressure. Changes in the magnetic ordering were also suggested to occur due to superexchange interactions and Jahn-Teller instabilities arising from the d-orbital electrons. Barium chloride (BaCl) has also been observed, which undergoes a similar structural change due to an s – d transition, and whose structural changes can offer further insight into the transitions observed in CuO. Ammonia borane (NH3BH3) is known to have a crystal structure which contains the molecules in staggered conformation at low pressure. The crystalline structure of NH3BH3 was examined at high pressure, which revealed that the staggered configuration transforms to an eclipsed conformation stabilized by homopolar B–Hδ-∙∙∙ δ-H–B dihydrogen bonds. These bonds are shown to be covalent in nature, comparable in bond strength to conventional hydrogen bonds, and may allow for easier molecular hydrogen formation in hydrogen fuel storage.

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Slepko, Alexander. "Theory of biomineral hydroxyapatite." 2013. http://hdl.handle.net/2152/20794.

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Hydroxyapatite (HA, Ca₁₀(PO₄)₆(OH)₂) is one of the most abundant materials in mammal bone. It crystallizes in an aqueous environment within spaces between tropocollagen protein chains. However, despite its abundance and possible usefulness in the medical field this complex physical system remains poorly understood to date. We present a theoretical study of the energetics of hydroxyapatite, its electronic, mechanical and thermodynamic properties. Our mechanical and thermodynamic properties from first principles are in excellent agreement with the rare available experimental data. The monoclinic and hexagonal phases are lowest in energy. A comparison of the phonon dispersions of these two phases reveals that a phase transition occurs due to a difference in vibrational free energy. The transition is of order-disorder type. Our calculated phase transition temperature is 680 K, in decent agreement with the experimentally determined 470 K. An alternative theoretical model yields 882 K. The phase transition is mediated by OH libration modes. We also report for the first time on a peculiarity in the phonon spectrum of hexagonal and monoclinic HA. When studying the Lyddane-Sachs-Teller shifts in the spectrum close to the [Gamma]-point we identify two vibration modes showing a systematically increasing Lyddane-Sachs-Teller shift in frequency with decreasing dielectric constant. In experiment, the dielectric constant varies between 5 and 20 depending on the Ca/P ratio in the sample. The frequency shifts in the affected modes are as large as 20 cm⁻¹ as one spans the range of the dielectric constant. Thus, a simple spectroscopic analysis of a sample of bone may determine the quality of the sample in a physiological sense. We also identify the chemically stable low energy surface configurations as function of the OH, PO₄ and Ca concentration. In the experimentally relevant OH-rich regime we find only two surfaces competing for lowest energy. The surface most stable over almost the entire OH-rich regime is OH-terminated, and is currently being investigated in the presence of water and atomic substitutions on the HA surface. text

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Malaj, Naim, Bartolo Gabriele, Giovanni Sindona, and Roberto Bartolino. "Modern mass spectrometric applications in the structure and function evaluation of active principles." Thesis, 2011. http://hdl.handle.net/10955/1055.

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Luo, Heng. "Phase stability and electronic structures of perovskite and organic optoelectronic materials via first-principle calculations." Thesis, 2015. https://hdl.handle.net/2144/15184.

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Mixed ionic and electronic conductor oxides, in particular La1-xSrxCoyFe1-yO3-d (LSCF), have been widely used as the cathode materials in solid oxide fuel cells for high-temperature energy applications. The focus of this thesis is primarily on constructing the instability phase diagram of Sr segregations on LSCF surfaces at the experimentally relevant temperatures and oxygen partial pressures using the first-principles density functional theory (DFT). A generic first-principles free-energy functional is developed to obtain the nonstoichiometric oxygen vacancy concentrations for the bulk and surface phases. These results agree well with the corresponding thermo-gravimetry measurements, and furthermore suggest that the oxygen vacancies are energetically stabilized at surfaces for all temperatures and oxygen partial pressures, while such surface stabilization effects become stronger at higher temperatures and lower oxygen partial pressures. Based on these nonstoichiometric oxygen vacancy predictions, we construct the free-energy phase diagrams of the Sr-segregation reaction as a function of temperature, oxygen partial pressure, and CO2 partial pressure for both the bulk and surface LSCF phases. Our results suggest that Sr segregations strongly accumulate towards the LSCF surface phase where the oxygen vacancy nonstoichiometries are abundant. Our results also indicate that the Sr segregation reactions are significantly enhanced at high temperatures, low oxygen partial pressures, and high CO2 partial pressures. The computed reaction temperature ranges are consistent with the total reflection X-ray fluorescence (TXRF) measurements.

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Roberts, Mokone Joseph. "The molecular structure of selected South African coal-chars to elucidate fundamental principles of coal gasification / Mokone Joseph Roberts." Thesis, 2015. http://hdl.handle.net/10394/16014.

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Advances in the knowledge of chemical structure of coal and development of high performance computational techniques led to more than hundred and thirty four proposed molecular level representations (models) of coal between 1942 and 2010. These models were virtually on the carboniferous coals from the northern hemisphere. There are only two molecular models based on the inertinite- and vitrinite-rich coals from the southern hemisphere. The current investigation is based on the chars derived from the Permian-aged coals in two major South African coalfields, Witbank #4 seam and Waterberg Upper Ecca. The two coals were upgraded to 85 and 93% inertinite- and vitrinite-rich concentrates, on visible mineral matter free basis. The coals were slow heated in inert atmosphere at 20 ℃ min-1 to 450, 700 and 1000 ℃ and held at that temperature for an hour. After the HCl-HF treatment technique at ambient temperatures, the characteristics of the coals and chars were examined with proximate, ultimate, helium density, porosity, surface area, petrographic, solid-state 13C NMR, XRD and HRTEM analytical techniques. The results largely showed that substantial transitions occurred at 700-1000 ℃, where the chars became physically different but chemically similar. Consequently, the chars at the highest temperature (1000 ℃) drew attention to the detailed study of the atomistic properties that may give rise to different reactivity behaviours with CO2 gas. The H/C atomic ratios for the inertinite- and vitrinite-rich chars were respectively 0.31 and 0.49 at 450 ℃ and 0.10 and 0.12 at 1000 ℃. The true density was respectively 1.48 and 1.38 g.cm-3 at 450 ℃ and 1.87 and 1.81 g.cm-3 at 1000 ℃. The char form results from the petrographic analysis technique indicated that the 700-1000 ℃ inertinite-rich chars have lower proportions of thick-walled isotropic coke derived from pure vitrinites (5-8%) compared with the vitrinite-rich chars (91-95%). This property leads to the creation of pores and increases of volume and surface area as the softening walls expand. It was found that the average crystallite diameter, La, and the mean length of the aromatic carbon fringes from the XRD and HRTEM techniques, respectively, were in good agreement and made a definite distinction between the 1000 ℃ inertinite- and vitrinite-rich chars. The crystallite diameter on peak (10) approximations, La(10), of 37.6Å for the 1000 ℃ inertinite-rich chars fell within the HRTEM’s range of minimummaximum length boundary of 11x11 aromatic fringes (27-45Å). The La (10) of 30.7Å for the vitrinite-rich chars fell nearly on the minimum-maximum length range of 7x7 aromatic fringes (17-28Å.) The HRTEM results showed that the 1000 ℃ inertinite-rich chars comprised a higher distribution of larger aromatic fringes (11x11 parallelogram catenations) compared with a higher distribution of smaller aromatic fringes (7x7 parallelogram catenations). The mechanism for the similarity between the 700-1000 ℃ inertinite- and vitrinite-rich chars was the greater transition occurring in the vitrinite-rich coal to match the more resistant inertinite-rich coal. This emphasised that the transitions in the properties of vitrinite-rich coals were more thermally accelerated than those of the inertinite-rich coals. The similarity between the inertinite- and vitrinite-rich chars was shown by the total maceral reflectance, proximate, ultimate, skeletal density and aromaticity results. Evidence for this was the carbon content by mass for the inertinite- and vitrinite-rich chars of respectively 90.5 and 85.3% at 450 ℃ and 95.9 and 94.1% at 1000 ℃. The aromaticity from the XRD technique was respectively 87 and 77% at 450 ℃ and 98 and 96% at 1000 ℃. A similar pattern was found in the hydrogen and oxygen contents, the atomic O/C ratios and the aromaticity from the NMR technique. The subsequent construction of large-scale molecular structures for the 1000 ℃ inertinite-rich chars comprised 106 molecules constructed from a total of 42929 atoms, while the vitrinite-rich char model was made up of 185 molecules consisting of a total of 44315 atoms. The difference between the number of molecules was due to the inertinite-rich char model comprising a higher distribution of larger molecules compared with the vitrinite-rich char model, in agreement with the XRD and HRTEM results. These char structures were used to examine the behaviour on the basis of gasification reactivity with CO2. The density functional theory (DFT) was used to evaluate the interactions between CO2 and the atomistic representations of coal char derived from the inertinite- and vitrinite rich South African coals. The construction of char models used the modal aromatic fringes (fringes of highest frequencies in size distributions) from the HRTEM, for the inertinite- and vitrinite-rich chars, respectively (11x11 and 7x7 parallelogram-shaped aromatic carbon rings). The structures were DFT geometrically optimized and used to measure reactivity with the Fukui function, f+(r) and to depict a representative reactive carbon edge for the simulations of coal gasification reaction mechanism with CO2 gas. The f+(r) reactivity indices of the reactive edge follows the sequence: zigzag C remote from the tip C (Czi = 0.266) > first armchair C (Cr1 = 0.087) > tip C (Ct = 0.075) > second armchair C (Cr2 = 0.029) > zigzag C proximate to the tip C (Cz = 0.027). The DFT simulated mean activation energy, ΔEb, for the gasification reaction mechanism (formation of second CO gas molecule) was 233 kJ mol-1. The reaction for the formation of second CO molecule is defines gasification in essence. The experimental activation energy determined with the TGA and random pore model to account essentially for the pore variation in addition to the gasification chemical reaction were found to be very similar: 191 ± 25 kJ mol-1 and 210 ± 8 kJ mol-1; and in good agreement with the atomistic results. The investigation gave promise towards the utility of molecular representations of coal char within the context of fundamental coal gasification reaction mechanism with CO2. PhD (Chemical Engineering), North-West University, Potchefstroom Campus, 2015

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