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1
Wood, Christopher Alan. „Theoretical investigation of polar zinc oxide surface modification via phosphonic acid self-assembled monolayers“. Thesis, Georgia Institute of Technology, 2012. http://hdl.handle.net/1853/43584.
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The interface of a zinc-terminated polar zinc oxide surface (0002) with a series of chemisorbed fluorinated benzylphosphonic acids has been studied using density functional theory. The calculations indicate that there is a substantial change in the binding energies and work function modification depending on the binding motif. The results also indicate that there is a pronounced difference in the magnitude and trends of the factors determining the total change in work function. The oxygen core-level binding shifts have been calculated and compared to available experimental data.
2
Diallo, Ibrahima Castillo. „Analysis of defects in GaN using Hybrid Density Functional Theory“. VCU Scholars Compass, 2013. http://scholarscompass.vcu.edu/etd/3130.
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In this thesis, we first present a brief overview of various theoretical approaches used to examine the electronic structure of defects in GaN. Using the recently developed hybrid density functional theory (HSE06) along with the experimental measurements, we propose a new explanation of the nature of the yellow luminescence band in carbon-doped GaN. We conduct a systematic study of electronic and optical properties of defects (Carbon, Oxygen, Silicon related) that are candidates for the origin of yellow luminescence. We show that the CN-ON complex is significantly more likely to form compared to isolated carbon configurations. In contrast to the properties of the isolated carbon acceptor, calculated defect levels and optical transitions involving deep level of the CN-ON complex agree quite well with our thermal luminescence quenching data as well as with the experimentally measured C-doped GaN luminescence spectra. Hence, the CN-ON complex, rather than isolated C impurity, is more likely to resolve a long-standing problem of the yellow luminescence in GaN.
3
Li, Ben. „Müller Density-Matrix-Functional Theory: Existence of Solutions and their Properties“. Thesis, Uppsala universitet, Analys och tillämpad matematik, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-190518.
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4
Demir, Sumeyra Ummuhan. „Image Processing Algorithms for Diagnostic Analysis of Microcirculation“. VCU Scholars Compass, 2010. http://scholarscompass.vcu.edu/etd/137.
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Microcirculation has become a key factor for the study and assessment of tissue perfusion and oxygenation. Detection and assessment of the microvasculature using videomicroscopy from the oral mucosa provides a metric on the density of blood vessels in each single frame. Information pertaining to the density of these microvessels within a field of view can be used to quantitatively monitor and assess the changes occurring in tissue oxygenation and perfusion over time. Automated analysis of this information can be used for real-time diagnostic and therapeutic planning of a number of clinical applications including resuscitation. The objective of this study is to design an automated image processing system to segment microvessels, estimate the density of blood vessels in video recordings, and identify the distribution of blood flow. The proposed algorithm consists of two main stages: video processing and image segmentation. The first step of video processing is stabilization. In the video stabilization step, block matching is applied to the video frames. Similarity is measured by cross-correlation coefficients. The main technique used in the segmentation step is multi-thresholding and pixel verification based on calculated geometric and contrast parameters. Segmentation results and differences of video frames are then used to identify the capillaries with blood flow. After categorizing blood vessels as active or passive, according to the amount of blood flow, quantitative measures identifying microcirculation are calculated. The algorithm is applied to the videos obtained using Microscan Side-stream Dark Field (SDF) imaging technique captured from healthy and critically ill humans/animals. Segmentation results were compared and validated using a blind detailed inspection by experts who used a commercial semi-automated image analysis software program, AVA (Automated Vascular Analysis). The algorithm was found to extract approximately 97% of functionally active capillaries and blood vessels in every frame. The aim of this study is to eliminate the human interaction, increase accuracy and reduce the computation time. The proposed method is an entirely automated process that can perform stabilization, pre-processing, segmentation, and microvessel identification without human intervention. The method may allow for assessment of microcirculatory abnormalities occurring in critically ill and injured patients including close to real-time determination of the adequacy of resuscitation.
5
Pokhrel, Keshav Prasad. „Statistical Analysis and Modeling of Brain Tumor Data: Histology and Regional Effects“. Scholar Commons, 2013. http://scholarcommons.usf.edu/etd/4746.
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Comprehensive statistical models for non-normally distributed cancerous tumor sizes are
of prime importance in epidemiological studies, whereas a long term forecasting models
can facilitate in reducing complications and uncertainties of medical progress. The statistical
forecasting models are critical for a better understanding of the disease and supply
appropriate treatments. In addition such a model can be used for the allocations of budgets,
planning, control and evaluations of ongoing efforts of prevention and early detection of
the diseases.
In the present study, we investigate the effects of age, demography, and race on primary
brain tumor sizes using quantile regression methods to obtain a better understanding of the
malignant brain tumor sizes. The study reveals that the effects of risk factors together with
the probability distributions of the malignant brain tumor sizes, and plays significant role in
understanding the rate of change of tumor sizes. The data that our analysis and modeling is
based on was obtained from Surveillance Epidemiology and End Results (SEER) program
of the United States.
We also analyze the discretely observed brain cancer mortality rates using functional
data analysis models, a novel approach in modeling time series data, to obtain more accurate
and relevant forecast of the mortality rates for the US. We relate the cancer registries,
race, age, and gender to age-adjusted brain cancer mortality rates and compare the variations
of these rates during the period of the study that data was collected.
Finally, in the present study we have developed effective statistical model for heterogenous
and high dimensional data that forecast the hazard rates with high degree of accuracy,
that will be very helpful to address subject health problems at present and in the future.
6
Hirayama, Hiroshi. „Purification and functional analysis of cholesterol transporter ABCG1 and ABCG4“. Kyoto University, 2013. http://hdl.handle.net/2433/180522.
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Kyoto University (京都大学)0048
新制・課程博士
博士(農学)
甲第17905号
農博第2028号
新制||農||1018(附属図書館)
学位論文||H25||N4801(農学部図書室)
30725
京都大学大学院農学研究科応用生命科学専攻
(主査)教授 植田 和光, 教授 加納 健司, 教授 小川 順
学位規則第4条第1項該当
7
Brett, Constance M. „Investigation of the structure and bonding of metal complexes through the use of density functional theory“. Connect to this title online, 2005. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1118688725.
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Thesis (Ph. D.)--Ohio State University, 2005.Title from first page of PDF file. Document formatted into pages; contains xxxi, 309 p.; also includes graphics Includes bibliographical references. Available online via OhioLINK's ETD Center
8
Stasko, Anna K. „Functional Gene Analysis of Resistance QTL towards Phytophthora sojae on SoybeanChromosome 19“. The Ohio State University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=osu1524139406566913.
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9
Meng, Xiangxiang. „Spectral Bayesian Network and Spectral Connectivity Analysis for Functional Magnetic Resonance Imaging Studies“. University of Cincinnati / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1320681959.
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10
Diggs, Herman Augustus. „EFFECTS OF ACUTE THC ADMINISTRATION ON EXTINCTION OF CONDITIONED FEAR RESPONSES IN HUMANS: A FUNCTIONAL ANALYSIS OF HIGH DENSITY EEG“. OpenSIUC, 2014. https://opensiuc.lib.siu.edu/dissertations/947.
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High density electroencephalographic (EEG) measures were used to assess the effects of acute delta 9-tetrahyrdrocannabidol (THC) administration on extinction of conditioned fear responses. Fear conditioning was initiated using a differential classical conditioning paradigm that paired an aversive unconditioned stimulus (shock) with a signaling stimulus (CS+), whereas another stimulus served as a safety signal (CS-). Evoked potentials, induced event-related spectral perturbations (ERSP), and associated intertrial coherence (ITC) measures were used to quantify the acquisition and extinction of conditioned fear responses. Participants (N = 10 males) exhibited conditioning to the CS+ across fear acquisition training, as reflected by greater late positive (posterior sites) and late negative (anterior sites) potential amplitude to the CS+ relative to the CS-. Acute administration of THC facilitated extinction of the conditioned response to the CS+ relative to placebo, as reflected by greater LPP and LNP amplitude to the CS+ relative to the CS- in the placebo, but not THC condition. ERSP analyses suggest the lack of difference between CS+ and CS- ERP amplitude may be partially explained by a shifting of attention from external stimuli to internal processing in the THC condition. However, relative to placebo, THC administration also increased the amplitude of some measures of the conditioned response (LNP) to the CS-, suggesting a generalization of fear or lack of discrimination in this condition.
11
Ghosh, Aparna. „Fabrication and characterization of solid-state gas seasons“. Thesis, University of North Bengal, 2020. http://ir.nbu.ac.in/handle/123456789/4338.
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12
GALASSO, SARA. „Generalization of the Eliashberg equations and Density Functional Theory applied to the analysis of the fundamental properties of iron-based superconductors“. Doctoral thesis, Politecnico di Torino, 2015. http://hdl.handle.net/11583/2596360.
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Density Functional Theory (DFT) allows a fully ab-initio treatment of almost all the quantities that enter in the Eliashberg theory and in many other approaches used to study both the superconducting and the normal phase. A complete description from first principles of real materials is, al least in principle, possible.
Here DFT and Eliashberg theory are applied to the study of some members of the new family of superconductors discovered in 2008, the iron-compounds.
Superconductivity here is unconventional and unlikely mediated by phonons. When electronic mechanisms are involved and the properties of the compounds are more complex, as in the case of Fe-based superconductors, also the ab-initio treatment may require some reasonable ad hoc approximations, derived from experimental evidences or theoretical argumentations, introducing some phenomenological aspects in the formulation.
In this thesis, Eliashberg theory and DFT are applied to study the properties of some iron compounds, in particular the properties of LiFeAs and Co-doped Ba-122 are discussed both in the normal and in the superconducting state.
In order to unveil the the properties of the superconducting state, in particular the symmetry and the amplitude of the order parameter and the coupling mechanism, a four bands Eliashberg model is discussed for LiFeAs suggesting that the specific electronic structure of this peculiar compound may lead to the breakdown of the Migdal's theorem forcing the model to be phenomenological".
The relation between the topology of the Fermi surface and the presence of nodes
is studied in Point-contact Andreev-reflection spectra of Ba(Fe1-xCox)2As2 (both
thin fims and single crystals) and Ca(Fe1-xCox)2As2. The curves presented are fitted within the multiband 3D-BTK model that allows the inclusion of the real shape of the Fermi surface evaluated within DFT.
Thanks to the inclusion of the results obtained within the Eliashberg theory in the 2D-BTK model some additional structures due to the strong electron-boson interaction, that appear at energy higher than the amplitude of the gaps in some AR spectra, can be studied and some guesses about the nature of the superconducting mechanism can be made. This technique is here applied to the case of Ba(Fe1-xCox)2As2 thin films with x = 0.08.
Finally, as concern the normal state, the temperature dependence of resistivity is reproduced both in LiFeAs and Ba(Fe1-xCox)2As2 with a model that contains two different kind of carriers. For both compounds spin fluctuations play an important role also in the normal state in addition to being the main bosons that mediate the Cooper pairing and in both compound the transport coupling
constant results to be sensibly smaller than the superconducting one, suggesting
a way to find a unifying principle for HTCS.
13
Vastine, Benjamin Alan. „Understanding mechanisms for C-H bond activation“. [College Station, Tex. : Texas A&M University, 2008. http://hdl.handle.net/1969.1/ETD-TAMU-2679.
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Yatsyshin, Petr. „Analysis of the phase behaviour of a nano-confined Lennard-Jones fluid using a pseudo-spectral approach to classical density-functional models“. Thesis, Imperial College London, 2013. http://hdl.handle.net/10044/1/24122.
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Wetting phenomena provide a vivid manifestation of attractive intermolecular forces, putting to a test our microscopic picture of matter. Classical Density Functional (DF) theory is based on first principles of statistical mechanics and provides a way to account for various microscopic effects determining the behaviour of confined fluids. In broad terms, the thesis consists of two parts, each expanding the existing body of knowledge in the respective field. In the first part a novel numerical methodology is developed, which allows one to solve any type of non-local integral or integral-differential equations typical of equilibrium and dynamic DF theories in one- and two-dimensional problems. The approach is based on pseudo-spectral collocation method and is demonstrated to be superior in speed and accuracy to existing commonly used approaches. Novel features include an integrating matrix operator, which is calculated outside of the non-linear solver loops and then used for fast evaluation of the non-local convolution-like terms with the highly accurate Clenshaw-Curtis quadrature, and a battery of techniques based on arc-length continuation providing a systematic and efficient way to compute density profiles, find surface phase transitions and obtain full phase diagrams. The second part presents a DF study of an atomic fluid at given chemical potential and temperature spatially confined to a semi-infinite rectangular pore. Fluid-fluid and fluid-substrate interactions are with long-ranged Lennard-Jones forces. Far from the capping wall this prototypical two-dimensional system reduces to a one-dimensional slit pore. However, the broken translational symmetry dramatically changes the phenomenology of wetting from that of a slit pore. Detailed investigation reveals new phenomena related to the geometry. In particular, the existence of capillary wetting temperature, continuous capillary condensation transition, continuous planar prewetting transition, and more. Existence beyond mean-field is discussed briefly. Dynamic extension of the DF theory is used to study the relaxation of the system.
15
O'Kennedy, Sean James. „A kinetic and thermodynamic study of procyanidin oligomer conformation by 1H NMR and DFT“. Thesis, Stellenbosch : Stellenbosch University, 2015. http://hdl.handle.net/10019.1/98054.
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Schmidt, Jason M. „Adaptive Foraging in a Generalist Predator: Implications of Habitat Structure, Density, Prey Availability and Nutrients“. Miami University / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=miami1312815757.
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17
Andersson, Edvin. „Spectroelectrochemical analysis of the Li-ion battery solid electrolyte interphase using simulated Raman spectra“. Thesis, Uppsala universitet, Fasta tillståndets fysik, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-413474.
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Lithium Ion Batteries (LIBs) are important in today's society, powering cars and mobile devices. LIBs consist of a negative anode commonly made of graphite, and a positive cathode commonly made from transition metal oxides. Between these electrodes are separators and organic solvent based electrolyte. Due to the high potential of LIBs the electrolyte is reduced at the anode. The electrolyte reduction results in the formation of a layer called the Solid Electrolyte Interphase (SEI), which prohibits the further breakdown of the electrolyte. Despite being researched for over50 years, the composition formation of the SEI is still poorly understood. The aim of this project is to develop strategies for efficient identification and classification of various active and intermediate components in the SEI, to, in turn, gain an understanding of the reactions taking place, which will help find routes to stabilize and tailor the composition of the SEI layer for long-term stability and optimal battery performance. For a model gold/li-ion battery electrolyte system, Raman spectra will be obtained using Surface Enhanced Raman Spectroscopy (SERS) in a spectroelectrochemical application where the voltage of the working gold electrode is swept from high to low potentials. Spectra of common components of the SEI as well as similar compounds will be simulated using Density Functional Theory (DFT). The DFT data is also used to calculate the spontaneity of reactions speculated to form the SEI. The simulated data will be validated by comparing it to experimental spectra from pure substances. The spectroelectrochemical SERS results show a clear formation of Li-carbonate at the SERS substrate, as well as the decomposition of the electrolyte into other species, according to the simulated data. It is however shown that there are several issues when modelling spectra, that makes it harder to correlate the simulated spectra with the spectroelectrochemical spectra. These issues include limited knowledge of the structure of the compounds thought to form on the anode surface, and incorrect choices in simulational parameters. To solve these issues, more work is needed in these areas, and the spectroelectrochemical methods used in this thesis needs to be combined with other experimental methods to narrow down the amount of compounds to be modelled. More work is also needed to avoid impurities in the electrolyte. Impurities leads to a thick inorganic layer which prohibits the observation of species in the organic layer.
18
Nowroozi-Isfahani, Taraneh. „Theoretical study on the mechanism of removing nitrogen oxides using isocyanic acid“. [Johnson City, Tenn. : East Tennessee State University], 2001. http://etd-submit.etsu.edu/etd/theses/available/etd-0528101-112444/unrestricted/nowroozi0621.pdf.
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Nyberg, Borrfors André. „Energy Decomposition Analysis of Neutral and Anionic Hydrogen Bonded Dimers Using a Point-Charge Approach“. Thesis, KTH, Tillämpad fysikalisk kemi, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-288970.
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En stor samling dimolekylära vätebindningar med formen A – H … B, där AH är en alkyn, alkohol eller tiol och B = [Br–, Cl–, NH3, HCN] beräknas och utvärderas med Kohn-Sham täthetsfunktionalteori tillsammans med bassetet m062x/6-311+g(2df.2p). Dessa komplex utvärderas även med en punktladdningsmodell (som använder samma metod och basset), där atomerna i vätebindningsmottagaren B byts ut mot laddningar som passats för att återskapa laddningsfördelningen runt molekylen, med målet att separera och isolera de elektrostatiska och polariserande energikomponenterna från de totala interaktionsenergierna. Med hjälp av detta tillvägagångssätt visade det sig att vätebindningars komplexeringsenergi (i.e. interaktionsenergin med energikostnaden för att deformera atomkärnornas rymdgeometri borttagen), oberoende av karaktären hos monomeren AH eller B, till stor del består av elektrostatik och polarisation, medan laddningsutbyte, dispersion, och andra resttermer endast utgör en liten del av den totala interaktionen. Fördelningen mellan elektrostatik och polarisation varierar beroende på typen av monomerer i vätebindningen, men deras summa, den resulterande punktladdningsenergin, korrelerar linjärt (ΔECompl = 0.85ΔEPC ) med R2 = 0.995 över energiomfånget 0 < ΔECompl < 50 kcal mol–1. Detta blir ännu mer anmärkningsvärt då inkluderingen av komplexeringsenergierna från halogenbindningar i samma korrelation inte förändrar korrelationskoefficienten avsevärt, vilket indikerar att båda bindningstyperna består av samma energikomponenter även då bindningarna i sig är väldigt olika.A large set of dimeric hydrogen bonds of the type A – H … B, where AH is an alkyne, alcohol, or thiol and B = [Br–, Cl–, NH3, HCN] are computed and evaluated using Kohn-Sham density functional theory together with the m062x/6-311+g(2df.2p) basis set. These complexes are also evaluated using a point charge (PC) approach (using the same method and basis set), where the atoms of the hydrogen bond acceptor B are substituted for charges that are optimized to reproduce the charge distribution of the molecule, with the purpose of separating and isolating the electrostatics- and polarization energy components of the interaction energies. Using this approach it was discovered that the complexation energy of hydrogen bonds (i.e.the interaction energy with the energy cost of nuclear deformation corrected for), independent on the nature of either monomer AH or B, are largely made up of electrostatics and polarization, while charge transfer, dispersion, and other rest terms only make up a small fraction of the total interaction. The composition of electrostatics and polarization vary depending on the type of monomers in the hydrogen bond, but their sum, the PC interaction energy, correlates linearly (ΔECompl = 0.85ΔEPC ) with R2 = 0.995 over an energy span of 0 < ΔECompl < 50 kcal mol–1. This is made even more remarkable by the inclusion of halogen bonded complexation energies in the same correlation without changing the correlation coefficient significantly, indicating that the two bond types are comprised of the same components even though they are remarkably different in origin.
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Lontsi, Fomena Mireille. „Etude théorique de la diffusion de l’oxygène dans des oxydes diélectriques“. Thesis, Bordeaux 1, 2008. http://www.theses.fr/2008BOR13703/document.
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La miniaturisation des composants CMOS (Complementary Metal Oxide Semiconductor) impose l’emploi de matériaux diélectriques de permittivité élevée. LaAlO3 et SrTiO3 sont aujourd’hui parmi les meilleurs candidats ; toutefois, la diffusion de l’oxygène dans ces matériaux conduit à la dégradation des propriétés électriques et de l’interface avec le silicium. Ce travail théorique a pour but d’étudier les facteurs gouvernant, à l’échelle de la liaison chimique, la diffusion de l’ion oxygène. L’approche choisie repose sur la théorie de la fonctionnelle de la densité (DFT), couplée à des méthodes d’analyse de la densité électronique, et sur le développement d’un outil original : les cartes de densité d’énergie. Les régions de la densité électronique contribuant à la barrière de diffusion ont ainsi pu être identifiées; une optimisation de ces matériaux à l’échelle de la liaison chimique peut alors être envisagéeThe miniaturization of CMOS (Complementary Metal Oxide Semiconductor) components requires the use of high dielectric permittivity materials as gate oxide. LaAlO3 and SrTiO3 are among the best candidates, but the oxygen diffusion in these materials leads to the degradation of both the electrical properties and the interface with silicon. In this context, the aim of this theoretical work is to study the factors governing the oxygen ion diffusion at the chemical bonding scale. This approach is based on Density Functional Theory (DFT), coupled with electron density analysis methods, and the pioneering development of energy density cards. The regions of the electron density contributing to the diffusion barrier have been identified allowing new routes of optimization of these materials across the chemical bonding
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Drain, John Frederick. „Development of magnetic bond-order potentials for Mn and Fe-Mn“. Thesis, University of Oxford, 2013. http://ora.ox.ac.uk/objects/uuid:68a01493-4a20-4d78-ad4a-6c3c2fe072d6.
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While group VII 4d Tc and 5d Re have hexagonally close-packed (hcp) ground states, 3d Mn adopts the complex chi-phase which exhibits non-collinear magnetism. Density functional theory (DFT) calculations have shown that without magnetism the chi-phase remains the ground state of Mn implying that magnetism is not the critical factor, as is commonly believed, in driving the anomalous stability of the chi-phase over hcp. Using a tight-binding (TB) model it is found that while harder potentials stabilise close-packed hcp, a softer potential stabilises the more open chi-phase. By analogy with the structural trend from open to close-packed phases down the group IV elements, the anomalous stability of the chi-phase in Mn is shown to be due to 3d valent Mn lacking d states in the core which leads to an effectively softer atomic repulsion between the atoms than in 4d Tc and 5d Re. Subsequently an analytic Bond-Order Potential (BOP) is developed to investigate the structural and magnetic properties of elemental Mn at 0 K. It is derived within BOP theory directly from a new short-ranged orthogonal d-valent TB model of Mn, the parameters of which are fitted to reproduce the DFT binding energy curves of the five experimentally observed phases of Mn, alpha, beta, gamma, delta, and epsilon-Mn. Not only does the BOP reproduce qualitatively DFT binding energy curves of the five different structure types, it also predicts the complex collinear antiferromagnetic (AFM) ordering in alpha-Mn, the ferrimagnetic (FiM) ordering in beta-Mn and the AFM ordering in the other phases that are found by DFT. A BOP expansion including 14 moments is sufficiently converged to reproduce most of the properties of the TB model with the exception of the elastic shear constants which require further moments. Magnetic analytic BOPs are also developed for Fe and Fe-Mn. The Fe model correctly reproduces trends in the structural stabilities of the common metallic structures except that AFM hcp is overstabilised. Reproduction of the elastic constants with a 9-moment BOP is reasonable although as is found for the Mn BOP the elastic shear constants require more moments to converge. Vacancy formation energies are close to those determined by experiment and DFT and the relative stabilities of self-interstitial atom (SIA) defects in ferromagnetic bcc Fe are correctly reproduced. The SIA formation energies are found to be better than those calculated with existing BOP models. The Fe-Mn TB and BOP models were challenging to fit and nonmagnetic face-centred cubic (fcc) structures are overstabilised. Furthermore within BOP an incorrect magnetic solution is predicted for one fcc structure resulting in poor reproduction of the DFT stacking fault energies. Refitting the bond integrals might help to better reproduce the nonmagnetic hcp-fcc energy differences while an environment-dependent Stoner parameter could help provide the flexibility needed to correctly capture the magnetic energy differences.
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Khosravi, nasab Monireh. „Computational modelling of zeolite N ion exchange properties“. Thesis, Queensland University of Technology, 2020. https://eprints.qut.edu.au/200718/1/Monireh_Khosravi%20nasab_Thesis.pdf.
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Zeolites are porous alumino-silicate materials with properties that result in a wide range of industrial applications. Predictions of zeolite properties can enhance higher performance and economic value for many industries. In this research, the structure and ion exchange behaviour of synthetic zeolite N is modelled using computational chemistry techniques. Modelled outcomes are compared with experimental data that are also obtained on natural zeolites from two Australian deposits. This research shows that a precise understanding and prediction of zeolite chemical and physical properties can be achieved by correlated atomic-scale modelling and high-quality experimental techniques.
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Schory, David Henry. „Quantum Chemical Investigations of Nucleophilic Aromatic Substitution Reactions and Acid Dissociations of Aliphatic Carboxylic Acids“. Wright State University / OhioLINK, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=wright1253480264.
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Deng, Qingming. „Computational analysis of electronic properties and mechanism of formation of endohedral fullerenes and graphene with Fe atoms“. Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-203016.
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In this thesis, a series of computational studies based on density functional theory (DFT) and density functional tight-binding (DFTB) is presented to deeply understand experimental results on the synthesis of endohedral fullerenes and graphene/iron hybrids at atomic level. In the first part, a simple and efficient model is proposed to evaluate the strain experienced by clusters encapsulated in endohedral metallofullerenes (EMFs). Calculations for the sole cluster, either in the neutral or the charged state, cannot be used for this goal. However, when the effect of the carbon cage is mimicked by small organic π-systems (such as pentalene and sumanene), the cluster has sufficient freedom to adopt the optimal configuration, and therefore the energetic characteristics of the EMF-induced distortion of the cluster can be evaluated. Both nitride and sulfide clusters were found to be rather flexible. Hence, they can be encapsulated in carbon cages of different size and shape. For carbide M2C2 cluster the situation is more complex. The optimized cluster can adopt either butterfly or linear shapes, and these configurations have substantially different metal-metal distance. Whereas for Sc2C2 both structures are isoenergetic, linear form of the Y2C2 cluster is substantially less stable than the butterfly-shaped configuration. These results show that phenomenon of the “nanoscale fullerene compression” once proposed by Zhang et al. (J. AM. CHEM. SOC. (2012),134(20)) should be “nanoscale fullerene stretching”. Finally, the results also reveal that both Ti2S and Ti2C2 cluster are strained in corresponding EMF molecules, but the origin of the strain is opposite: C78-D3h(5) cage imposes too long Ti···Ti distance for the sulfide cluster and too short distance for the carbide cluster.
In the second part of the thesis, possible fullerene geometries and electronic structures have been explored theoretically for the species detected in mass spectra of the Sc-EMF extract synthesized using CH4 as a reactive gas. Two most promising candidates, namely Sc4C@C80-Ih(7) and Sc4C3@C80-Ih(7), have been identified and further studied at the DFT level. For Sc4C@C80, the tetrahedral Sc4 cluster with the central μ4-C atom was found to be 10 kJ/mol more stable than the square cluster. For Sc4C3@C80, the calculation showed that the most stable is the Sc4C3 cluster in which the triangular C3 moiety is η3- and η2-coordinated to Sc atoms. Whereas Sc4C@C80 has rather small HOMO-LUMO gap and low ionization potential, the HOMO-LUMO gap of Sc4C3@C80 is substantially higher and exceeds that of Sc4C2@C80.
In the third part, computational studies of structures and reactivity are described for a new type of EMFs with a heptagon that has been produced in the arc-discharge synthesis. DFT computations predict that LaSc2N@Cs(hept)-C80 is more stable than LaSc2N@D5h-C80, so the former should be synthesized in much higher yield than observed. This disagreement may be ascribed to the kinetic factors rather than thermodynamic stability. Because of prospective applications of this EMFs by introducing functional groups, the influence of the heptagon on the chemical properties have been further evaluated. Thermodynamically and kinetically preferred reaction sites are studied computationally for Prato and Bingel-Hirsch cycloaddition reactions. In both types of reactions the heptagon is not affected, and chemical reactivity is determined by the adjacent pentalene units. Thermodynamically controlled Prato addition is predicted to proceed regioselectively across the pentagon/pentagon edges, whereas the most reactive sites in kinetically-controlled Bingel-Hirsch reaction are the carbon atoms next to the pentagon/pentagon edge.
Fourth, although various EMFs have been successfully synthesized and characterized, the formation mechanism is still not known in details, and hence control of the synthesis products is rather poor. Therefore, EMF self-assembly process in Sc/carbon vapor in the presence and absence of cooling gas (helium) and reactive gas (NH3 and CH4) is systematically investigated using quantum chemical molecular dynamics (QM/MD) simulations based on the DFTB potentials. The cooling gas effect is that the presence of He atoms accelerates formation of pentagons and hexagons and reduces the size of formed carbon cages in comparison to the analogous He-free simulations. As a result, the Sc/C/He system yields a large number of successful trajectories (i.e. leading to the Sc-EMFs) with more realistic cage-size distribution than the Sc/C system. Encapsulation of Sc atoms within the carbon cage was found to proceed via two parallel mechanisms. The main mechanism involves nucleation of the several hexagons and pentagons with Sc atoms already at the early stages of the carbon vapor condensation. In such proto-cages, both Sc–C σ-bonds and coordination bonds between Sc atoms and the π-system of the carbon network are present. Sc atoms are thus rather labile and can move along the carbon network, but the overall bonding is sufficiently strong to prevent dissociation even at high temperatures. Further growth of the carbon cage results in encapsulation of one or two Sc atoms within the forming fullerene. Another encapsulation mechanism is observed in rare cases. In this process, the closed cage is formed with Sc being a part of the carbon network, i.e. being bonded by three or four Sc–C σ-bonds. However, such intermediates are found to be unstable, and transform into the endohedral fullerenes within few picoseconds of annealing. In perfect agreement with experimental studies, extension of the simulation to Fe and Ti showed that Fe-EMFs are not formed at all, whereas Ti is prone to form Ti-EMFs with small cage sizes, including Ti@C28-Td and Ti@C30-C2v(3).
The role of “reactive gas” in the EMF synthesis is revealed in dedicated simulations of the fullerene formation in the presence of several molecules of CH4 or NH3. When concentration of reactive gas is high, carbon vapor tends to form graphene flakes or other carbon species terminated by hydrogen atoms, whereas the yield of empty fullerenes is very low. Conversely, with additional metal atoms (Sc) and the same number of NH3 molecules, the yield of fullerenes constantly increase from 5 to 65% which is ascribed to the catalytic activity of metal atoms in the nucleation of carbon cages already at early stage. Moreover, due to the presence of hydrogen atoms from the reactive gas, the carbon cage formation requires much longer time, which provides sufficient reaction time to encapsulate 3 or 4 Sc atoms within one cage. It explains preferential formation of clusterfullerenes in experiments with reactive gas. At the same time, monometallofullerenes and dimetallofullerenes are the main products in absence of reactive gas. We also provide possible growth mechanisms of carbide and cyano-clusterfullerenes in details to elucidate how the intracluster goes into the cage. A possible growth mechanism of nitride clusterfullerenes has been proposed based on DFT results.
In the last part, a free-standing crystalline single-atom thick layer of Fe has been studied theoretically. By investigating the energy difference, ΔE, between a suspended Fe monolayer and a nanoparticle using the equivalent number of Fe atoms, one can estimate that the largest stable membrane should be ca. 12 atoms wide or 3 × 3 nm2 which is in excellent agreement with the experimental observation. Otherwise, the possibility of C, O, N atoms embedded into the Fe membrane can been fully excluded by DFTB and DFT simulations, which agrees with electron energy loss spectroscopy (EELS) measurement. A significantly enhanced magnetic moment for single atom thick Fe membranes (3.08 μB) is predicted by DFT as compared to the bulk BCC Fe (2.1 μB), which originates from the 2D nature of the Fe membrane since the dz2 orbital is out-of-plane while the dxy orbital is in-plane.
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Nguyen, Thi Ai Nhung, Thi Phuong Loan Huynh und Van Tat Pham. „Quantum chemical investigation for structures and bonding analysis of molybdenum tetracarbonyl complexes with N-heterocyclic carbene and analogues: helpful information for plant biology research“. Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-190465.
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Quantum chemical calculations at the gradient-corrected (BP86) density-functional calculations with various basis sets (SVP, TZVPP) have been carried out for Mo(CO)4 complexes of Nheterocyclic carbene and analogues-NHEMe (called tetrylenes) with E = C, Si, Ge, Sn, Pb. The equilibrium structures of complexes [Mo(CO)4-NHEMe] (Mo4-NHEMe) exhibit an interesting trend which the lightest adduct Mo4-NHCMe has a trigonal bipyramidal coordination mode where the ligand NHCMe occupies an equatorial position. In contrast, the heavier species from Mo4-NHSiMe to Mo4-NHPbMe possess a square pyramidal structure where the ligands from NHSiMe to NHPbMe occupy a basal position. The slighter complexes Mo4-NHEMe possess end-on-bonded NHEMe ligands when E = C, Si, Ge with the bending angles, α, are 180° whereas the heavier adducts Mo4-NHSnMe and Mo4-NHPbMe exhibit strongly side-on-bonded ligands which the bending angle, α become more acute. The trend of the bond dissociations energies-De [kcal/mol] (BDEs) for the Mo-E bonds is Mo4-NHCMe > Mo4-NHSiMe > Mo4-NHGeMe > Mo4-NHSnMe > Mo4-NHPbMe. Bonding analysis shows that the Mo-E bonds have a significant contribution from (CO)4Mo ← NHEMe π-donation. This is because the energy levels of the π-type donor orbitals of Mo4-NHCMe − Mo4-NHPbMe are higher lying than the σ-type donor orbitals. The NHEMe ligands in Mo4- NHEMe are strong electron donors. This review intends to provide a comprehensive data for plant biology research in the futureTính toán hóa lượng tử sử dụng lý thuyết phiếm hàm mật độ kết hợp điều chỉnh gradient (BP86) từ các bộ hàm cơ sở khác nhau (SVP, TZVPP) được thực hiện cho việc tính toán lý thuyết của phức giữa Mo(CO)4 và phối tử N-heterocyclic carbene và các phức tương tự NHEMe (gọi là tetrylenes) với E = C, Si, Ge, Sn, Pb. Cấu trúc của phức [Mo(CO)4-NHEMe] (Mo4-NHEMe) thể hiện sự khác biệt khá thú vị từ Mo4-NHCMe đến Mo4-NHPbMe, phức Mo4-NHCMe có cấu trúc phối trí lưỡng tháp tam giác trong đó phối tử NHCMe chiếm ở vị trí xích đạo. Ngược lại, những phức có phân tử khối lớn hơn từ Mo4-NHSiMe đến Mo4-NHPbMe lại có cấu trúc tháp vuông và các phối tử từ NHSiMe đến NHPbMe chiếm vị trí cạnh (basal – cạnh hướng về bốn đỉnh của đáy vuông). Các cấu trúc của phức Mo4-NHEMe cho thấy các phối tử NHEMe với E = C-Ge tạo với phân tử Mo(CO)4 một góc thẳng α =180.0°, ngược lại, các phức nặng hơn Mo4-NHEMe thì phối tử NHEMe với E = Sn, Pb liên kết với phân tử Mo(CO)4 tạo góc cong và góc cong, α, càng trở nên nhọn hơn khi nguyên tử khối của E càng lớn. Năng lượng phân ly liên kết của liên kết Mo- E giảm dần: Mo4-NHCMe > Mo4-NHSiMe > Mo4-NHGeMe > Mo4-NHSnMe > Mo4-NHPbMe. Phân tích liên kết Mo-E cho thấy có sự đóng góp đáng kể của sự cho liên kết π (CO)4Mo ← NHEMe. Điều này có thể do mức năng lượng của orbital π-cho của Mo4-NHCMe − Mo4-NHPbMe nằm cao hơn orbital σ-cho. Từ kết quả tính toán có thể kết luận rằng phối tử NHEMe trong phức Mo4- NHEMe là chất cho điện tử mạnh. Kết quả nghiên cứu lý thuyết về hệ phức Mo4-NHEMe lần đầu tiên cung cấp một cơ sở dữ liệu hoàn chỉnh cho các nghiên cứu về sinh học thực vật trong tương lai
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Rommel, Cédric. „Exploration de données pour l'optimisation de trajectoires aériennes“. Thesis, Université Paris-Saclay (ComUE), 2018. http://www.theses.fr/2018SACLX066/document.
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Cette thèse porte sur l'utilisation de données de vols pour l'optimisation de trajectoires de montée vis-à-vis de la consommation de carburant.Dans un premier temps nous nous sommes intéressé au problème d'identification de modèles de la dynamique de l'avion dans le but de les utiliser pour poser le problème d'optimisation de trajectoire à résoudre. Nous commençont par proposer une formulation statique du problème d'identification de la dynamique. Nous l'interpretons comme un problème de régression multi-tâche à structure latente, pour lequel nous proposons un modèle paramétrique. L'estimation des paramètres est faite par l'application de quelques variations de la méthode du maximum de vraisemblance.Nous suggérons également dans ce contexte d'employer des méthodes de sélection de variable pour construire une structure de modèle de régression polynomiale dépendant des données. L'approche proposée est une extension à un contexte multi-tâche structuré du bootstrap Lasso. Elle nous permet en effet de sélectionner les variables du modèle dans un contexte à fortes corrélations, tout en conservant la structure du problème inhérente à nos connaissances métier.Dans un deuxième temps, nous traitons la caractérisation des solutions du problème d'optimisation de trajectoire relativement au domaine de validité des modèles identifiés. Dans cette optique, nous proposons un critère probabiliste pour quantifier la proximité entre une courbe arbitraire et un ensemble de trajectoires échantillonnées à partir d'un même processus stochastique. Nous proposons une classe d'estimateurs de cette quantitée et nous étudions de façon plus pratique une implémentation nonparamétrique basé sur des estimateurs à noyau, et une implémentation paramétrique faisant intervenir des mélanges Gaussiens. Ce dernier est introduit comme pénalité dans le critère d'optimisation de trajectoire dans l'objectif l'intention d'obtenir directement des trajectoires consommant peu sans trop s'éloigner des régions de validitéThis thesis deals with the use of flight data for the optimization of climb trajectories with relation to fuel consumption.We first focus on methods for identifying the aircraft dynamics, in order to plug it in the trajectory optimization problem. We suggest a static formulation of the identification problem, which we interpret as a structured multi-task regression problem. In this framework, we propose parametric models and use different maximum likelihood approaches to learn the unknown parameters.Furthermore, polynomial models are considered and an extension to the structured multi-task setting of the bootstrap Lasso is used to make a consistent selection of the monomials despite the high correlations among them.Next, we consider the problem of assessing the optimized trajectories relatively to the validity region of the identified models. For this, we propose a probabilistic criterion for quantifying the closeness between an arbitrary curve and a set of trajectories sampled from the same stochastic process. We propose a class of estimators of this quantity and prove their consistency in some sense. A nonparemetric implementation based on kernel density estimators, as well as a parametric implementation based on Gaussian mixtures are presented. We introduce the later as a penalty term in the trajectory optimization problem, which allows us to control the trade-off between trajectory acceptability and consumption reduction
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Kohatsu, Higa Arturo, und Kazuhiro Yasuda. „Estimating multidimensional density functions using the Malliavin-Thalmaier formula“. Pontificia Universidad Católica del Perú, 2014. http://repositorio.pucp.edu.pe/index/handle/123456789/96672.
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The Malliavin-Thalmaier formula was introduced for simulation of high dimensional probability density functions. But when this integration by parts formula is applied directly in computer simulations, we show that it is unstable. We propose an approximation to the Malliavin-Thalmaier formula. In this paper, we find the order of the bias and the variance of the approximation error. And we obtain an explicit Malliavin-Thalmaier formula for the calculation of Greeks in finance. The weights obtained are free from the curse of dimensionality.
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Magqi, Nceba. „Studies towards the development of novel multidentate ligands“. Thesis, Rhodes University, 2007. http://eprints.ru.ac.za/867/.
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Nguyen, Thi Ai Nhung, Thi Phuong Loan Huynh und Van Tat Pham. „Quantum chemical investigation for structures and bonding analysis of molybdenum tetracarbonyl complexes with N-heterocyclic carbene and analogues: helpful information for plant biology research: Research article“. Technische Universität Dresden, 2014. https://tud.qucosa.de/id/qucosa%3A29085.
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Quantum chemical calculations at the gradient-corrected (BP86) density-functional calculations with various basis sets (SVP, TZVPP) have been carried out for Mo(CO)4 complexes of Nheterocyclic carbene and analogues-NHEMe (called tetrylenes) with E = C, Si, Ge, Sn, Pb. The equilibrium structures of complexes [Mo(CO)4-NHEMe] (Mo4-NHEMe) exhibit an interesting trend which the lightest adduct Mo4-NHCMe has a trigonal bipyramidal coordination mode where the ligand NHCMe occupies an equatorial position. In contrast, the heavier species from Mo4-NHSiMe to Mo4-NHPbMe possess a square pyramidal structure where the ligands from NHSiMe to NHPbMe occupy a basal position. The slighter complexes Mo4-NHEMe possess end-on-bonded NHEMe ligands when E = C, Si, Ge with the bending angles, α, are 180° whereas the heavier adducts Mo4-NHSnMe and Mo4-NHPbMe exhibit strongly side-on-bonded ligands which the bending angle, α become more acute. The trend of the bond dissociations energies-De [kcal/mol] (BDEs) for the Mo-E bonds is Mo4-NHCMe > Mo4-NHSiMe > Mo4-NHGeMe > Mo4-NHSnMe > Mo4-NHPbMe. Bonding analysis shows that the Mo-E bonds have a significant contribution from (CO)4Mo ← NHEMe π-donation. This is because the energy levels of the π-type donor orbitals of Mo4-NHCMe − Mo4-NHPbMe are higher lying than the σ-type donor orbitals. The NHEMe ligands in Mo4- NHEMe are strong electron donors. This review intends to provide a comprehensive data for plant biology research in the future.Tính toán hóa lượng tử sử dụng lý thuyết phiếm hàm mật độ kết hợp điều chỉnh gradient (BP86) từ các bộ hàm cơ sở khác nhau (SVP, TZVPP) được thực hiện cho việc tính toán lý thuyết của phức giữa Mo(CO)4 và phối tử N-heterocyclic carbene và các phức tương tự NHEMe (gọi là tetrylenes) với E = C, Si, Ge, Sn, Pb. Cấu trúc của phức [Mo(CO)4-NHEMe] (Mo4-NHEMe) thể hiện sự khác biệt khá thú vị từ Mo4-NHCMe đến Mo4-NHPbMe, phức Mo4-NHCMe có cấu trúc phối trí lưỡng tháp tam giác trong đó phối tử NHCMe chiếm ở vị trí xích đạo. Ngược lại, những phức có phân tử khối lớn hơn từ Mo4-NHSiMe đến Mo4-NHPbMe lại có cấu trúc tháp vuông và các phối tử từ NHSiMe đến NHPbMe chiếm vị trí cạnh (basal – cạnh hướng về bốn đỉnh của đáy vuông). Các cấu trúc của phức Mo4-NHEMe cho thấy các phối tử NHEMe với E = C-Ge tạo với phân tử Mo(CO)4 một góc thẳng α =180.0°, ngược lại, các phức nặng hơn Mo4-NHEMe thì phối tử NHEMe với E = Sn, Pb liên kết với phân tử Mo(CO)4 tạo góc cong và góc cong, α, càng trở nên nhọn hơn khi nguyên tử khối của E càng lớn. Năng lượng phân ly liên kết của liên kết Mo- E giảm dần: Mo4-NHCMe > Mo4-NHSiMe > Mo4-NHGeMe > Mo4-NHSnMe > Mo4-NHPbMe. Phân tích liên kết Mo-E cho thấy có sự đóng góp đáng kể của sự cho liên kết π (CO)4Mo ← NHEMe. Điều này có thể do mức năng lượng của orbital π-cho của Mo4-NHCMe − Mo4-NHPbMe nằm cao hơn orbital σ-cho. Từ kết quả tính toán có thể kết luận rằng phối tử NHEMe trong phức Mo4- NHEMe là chất cho điện tử mạnh. Kết quả nghiên cứu lý thuyết về hệ phức Mo4-NHEMe lần đầu tiên cung cấp một cơ sở dữ liệu hoàn chỉnh cho các nghiên cứu về sinh học thực vật trong tương lai.
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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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Joshi, Niranjan Bhaskar. „Non-parametric probability density function estimation for medical images“. Thesis, University of Oxford, 2008. http://ora.ox.ac.uk/objects/uuid:ebc6af07-770b-4fee-9dc9-5ebbe452a0c1.
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The estimation of probability density functions (PDF) of intensity values plays an important role in medical image analysis. Non-parametric PDF estimation methods have the advantage of generality in their application. The two most popular estimators in image analysis methods to perform the non-parametric PDF estimation task are the histogram and the kernel density estimator. But these popular estimators crucially need to be ‘tuned’ by setting a number of parameters and may be either computationally inefficient or need a large amount of training data. In this thesis, we critically analyse and further develop a recently proposed non-parametric PDF estimation method for signals, called the NP windows method. We propose three new algorithms to compute PDF estimates using the NP windows method. One of these algorithms, called the log-basis algorithm, provides an easier and faster way to compute the NP windows estimate, and allows us to compare the NP windows method with the two existing popular estimators. Results show that the NP windows method is fast and can estimate PDFs with a significantly smaller amount of training data. Moreover, it does not require any additional parameter settings. To demonstrate utility of the NP windows method in image analysis we consider its application to image segmentation. To do this, we first describe the distribution of intensity values in the image with a mixture of non-parametric distributions. We estimate these distributions using the NP windows method. We then use this novel mixture model to evolve curves with the well-known level set framework for image segmentation. We also take into account the partial volume effect that assumes importance in medical image analysis methods. In the final part of the thesis, we apply our non-parametric mixture model (NPMM) based level set segmentation framework to segment colorectal MR images. The segmentation of colorectal MR images is made challenging due to sparsity and ambiguity of features, presence of various artifacts, and complex anatomy of the region. We propose to use the monogenic signal (local energy, phase, and orientation) to overcome the first difficulty, and the NPMM to overcome the remaining two. Results are improved substantially on those that have been reported previously. We also present various ways to visualise clinically useful information obtained with our segmentations in a 3-dimensional manner.
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MAEDA, NANCY T. „Avaliação da neoformação óssea em tíbia de coelhos utilizando cúpula de hidroxiapatita associada a diferentes biomateriais“. reponame:Repositório Institucional do IPEN, 2013. http://repositorio.ipen.br:8080/xmlui/handle/123456789/10542.
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Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP
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Crompton, P. R. „Lee-Yang zeros analysis of finite density lattice QCD“. Thesis, University of Glasgow, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.368583.
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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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Peacock, Darren. „Parallelized multigrid applied to modeling molecular electronics“. Thesis, McGill University, 2007. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=101160.
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This thesis begins with a review on the topic of molecular electronics. The purpose of this review is to motivate the need for good theory to understand and predict molecular electronics behaviour. At present the most promising theoretical formalism for dealing with this problem is a combination of density functional theory and nonequilibrium Green's functions (NEGF-DFT). This formalism is especially attractive because it is an ab-initio technique, meaning that it is completely from first principles and does not require any empirical parameters. An implementation of this formalism has been developed by the research group of Hong Guo and is presented and explained here. A few other implementations which are similar but differ in some ways are also discussed briefly to highlight their various advantages and disadvantages.One of the difficulties of ab-initio calculations is that they can be extremely costly in terms of the computing time and memory that they require. For this reason, in addition to using appropriate approximations, sophisticated numerical analysis tech niques need to be used. One of the bottlenecks in the NEGF-DFT method is solving the Poisson equation on a large real space grid. For studying systems incorporating a gate voltage it is required to be able to solve this problem with nonperiodic boundary conditions. In order to do this a technique called multigrid is used. This thesis examines the multigrid technique and develops an efficient implementation for the purpose of use in the NEGF-DFT formalism. For large systems, where it is necessary to use especially large real space grids, it is desirable to run simulations on parallel computing clusters to handle the memory requirements and make the code run faster. For this reason a parallel implementation of multigrid is developed and tested for performance. The multigrid tool is incorporated into the NEGF-DFT formalism and tested to ensure that it is properly implemented. A few calculations are made on a benzenedithiol system with gold leads to show the effect of an applied gate voltage.
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Choi, Sujung. „On two-sample data analysis by exponential model“. Texas A&M University, 2005. http://hdl.handle.net/1969.1/2653.
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We discuss two-sample problems and the implementation of a new two-sample data
analysis procedure. The proposed procedure is based on the concepts of mid-distribution,
design of score functions, components, comparison distribution, comparison density
and exponential model. Assume that we have a random sample X1, . . . ,Xm from
a continuous distribution F(y) = P(Xi y), i = 1, . . . ,m and a random sample
Y1, . . . ,Yn from a continuous distribution G(y) = P(Yi y), i = 1, . . . ,n. Also assume
independence of the two samples. The two-sample problem tests homogeneity of
two samples and formally can be stated as H0 : F = G. To solve the two-sample problem,
a number of tests have been proposed by statisticians in various contexts. Two
typical tests are the two-sample t?test and the Wilcoxon's rank sum test. However,
since they are testing differences in locations, they do not extract more information
from the data as well as a test of the homogeneity of the distribution functions. Even
though the Kolmogorov-Smirnov test statistic or Anderson-Darling tests can be used
for the test of H0 : F = G, those statistics give no indication of the actual relation
of F to G when H0 : F = G is rejected. Our goal is to learn why it was rejected.
Our approach gives an answer using graphical tools which is a main property of our
approach. Our approach is functional in the sense that the parameters to be estimated
are probability density functions. Compared with other statistical tools for
two-sample problems such as the t-test or the Wilcoxon rank-sum test, density estimation makes us understand the data more fully, which is essential in data analysis.
Our approach to density estimation works with small sample sizes, too. Also our
methodology makes almost no assumptions on two continuous distributions F and
G. In that sense, our approach is nonparametric. Our approach gives graphical elements
in two-sample problem where exist not many graphical elements typically.
Furthermore, our procedure will help researchers to make a conclusion as to why two
populations are different when H0 is rejected and to give an explanation to describe
the relation between F and G in a graphical way.
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Signorini, David F. „Practical aspects of kernel smoothing for binary regression and density estimation“. Thesis, n.p, 1998. http://oro.open.ac.uk/19923/.
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Robbins, Andrew Campbell. „Pilot Variability During Pilot-Induced Oscillation“. Thesis, Virginia Tech, 1999. http://hdl.handle.net/10919/33681.
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Pilot Induced Oscillations (PIO) are described as pilot-aircraft dynamic couplings which can lead to instability in an otherwise stable system. Previous and ongoing research has attempted to explain, predict, and avoid such oscillations. In contrast to other research, this effort backs away from pilot models and PIO avoidance and focuses on the characteristics of the pilot before, during, and after a PIO. Often, PIO''s can be explained by limit cycles occurring in a non-linear system where the non-linearities cause a sustained, constant amplitude oscillation. The primary instigators in such a PIO are usually a non-linear element (i.e. rate limit saturation) and a trigger event (i.e. pilot mode switching or increased pilot gain). By performing analysis in the frequency domain, determining such oscillations becomes easier. Using spectrograms and power spectral density functions, the frequency content of a signal in the pilot-aircraft system can also be investigated.
An F-14 flight test was recently performed where the hydraulic system was modified to determine the feasibility of trying to recover the aircraft (land on carrier) during such an extreme hydraulic failure. During testing, a severe PIO occurred because of the tight tracking task used during aerial refueling. While performing spectrograms and power spectral analysis, an increase in power concentration at the PIO frequency was observed.
With a linear approximation of the F-14 aircraft dynamics, a closed-loop system containing the aircraft, actuator, and pilot dynamics is developed so that limit cycle analysis can be performed. With stable limit cycle solutions found possible, a pilot-in-the-loop simulation is performed to verify the pilot model used in limit cycle analysis. Using the flight test data, limit cycle analysis, and pilot-in-the-loop simulation, a connection between variation in pilot behavior and PIO predicted by the increase in power concentration is investigated.
The resulting connection showed that an increase in pilot gain along with a transition from observing pitch attitude to pitch rate are the possible trigger events causing the PIO. The use of spectrograms as a PIO predictor is shown to be possible, provided the necessary calculations can be completed in real-time.
Master of Science
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Gehrmann, Jan. „Transferable reduced TB models for elemental Si and N and binary Si-N systems“. Thesis, University of Oxford, 2013. http://ora.ox.ac.uk/objects/uuid:002b0c99-0e9d-4d8c-a0dc-ad07383f083f.
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Silicon nitride is a bulk and a coating material exhibiting excellent mechanical properties. The understanding of the complex processes at the nanometre scale gained through experimental research will be enhanced by the existence of a computationally efficient and accurate model that is able to describe the mechanical properties of silicon nitride. Such a model has yet to be proposed. In this thesis we present a transferable reduced tight-binding (TB) model for the silicon nitride system. More precisely, this model consists of a reduced TB model for elemental silicon, a reduced TB model for elemental nitrogen, and a reduced TB model for silicon nitride. These models are developed within the framework of coarse-graining the electronic structure from density functional theory (DFT) to tight binding (TB) to bond-order potentials (BOPs), and can therefore be used in the future as the stepping stone to develop BOPs for the application in large scale simulations. The bond integrals employed in the reduced TB models are obtained directly from mixed-basis DFT projections of wave functions onto a minimal basis of atom-centred orbitals. This approach reduces the number of overall parameters to be fitted and provides models which are transferable through the different coarse-graining levels. We provide an example by using the same bond integrals in the reduced TB model for silicon and the preliminary bond-based BOP for silicon. DFT binding energies of ground state and metastable crystal structures are used as the benchmark to which the TB and BOP repulsive parameters are fitted. In addition to model development, we present an improved methodology when going from TB to reduced TB. By weighting all four σ TB bond integrals equally, we provide a new parameterisation (Eqs. (2.73) and (2.74)) and show that the quality of the silicon reduced TB model can be increased by choosing one of the reduced TB parameters to be distance invariant. The ingredients, the development methodology, and the quality of each of the four models are discussed in a separate chapter. The quality of the reduced TB models and BOP is demonstrated by comparing their predictions for the binding energies, heats of formation, elastic constants, and defect energies with DFT and experimental values.
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Johnston, Karen Elizabeth. „A complementary study of perovskites : combining diffraction, solid-state NMR and first principles DFT calculations“. Thesis, University of St Andrews, 2010. http://hdl.handle.net/10023/1837.
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Perovskites, ABX₃, and their associated solid-solutions are a particularly important and attractive area of research within materials chemistry. Owing to their structural and compositional flexibility and potential physical properties they are one of the largest classes of materials currently under investigation. This thesis is concerned with the synthesis and structural characterisation of several perovskite-based materials using a combined approach of high-resolution synchrotron X-ray and neutron powder diffraction (NPD), solid-state Nuclear Magnetic Resonance (NMR) and first-principles Density Functional Theory (DFT) calculations. Initial investigations concentrated on room temperature NaNbO₃, a perovskite widely debated in the literatue. Published crystallographic data indicate NaNbO₃ possesses two crystallographically distinct Na sites in space group Pbcm. Whilst some of our materials appear in agreement with this (notably a commercially purchased sample) many of our laboratory-synthesised samples of NaNbO₃ routinely comprise of two phases, which we show to be the antiferroelectric Pbcm and polar P2₁ma polymorphs. Several different synthetic methods were utilised during this investigation and the quantity of each phase present was found to vary as a function of preparative method. ²³Na, ⁹³Nb and ¹⁷O DFT calculations were used in conjunction with experiment to aid in spectral analysis, assignment and interpretation. In addition, ab initio random structure searching (AIRSS) was utilised in an attempt to predict the most stable phases of NaNbO₃. This proved to be both successful and highly informative. A series of NaNbO₃-related solid-solutions, namely K[subscript(x)]Na[subscript(1-x)]NbO₃ (KNN), Li[subscript(x)]Na[subscript(1-x)]NbO₃ (LNN) and Na[subscript(1-x)]Sr[subscript(x/2)]□[subscript(x/2)]NbO₃ (SNN) have also been synthesised and characterised. The substitution of K⁺ , Li⁺ and Sr²⁺ cations onto the A site appears to produce the same polar P2₁ma phase initially identified in the room temperature NaNbO₃ investigation. The abrupt change in cation size in the KNN and LNN series, and the introduction of vacancies in the SNN series, is thought to result in a structural distortion which, in turn, causes the formation of the P2₁ma phase. A low temperature synchrotron X-ray powder diffraction study (12 < T < 295 K) was completed for a sample of NaNbO₁ composed of the P2₁ma polymorph (~90%) and a small quantity of the Pbcm phase (~10%). A region of phase coexistence was identified between the P2₁ma, R3c and Pbcm phases over a relatively large temperature range. Full conversion of the P2₁ma phase to the low temperature R3c phase was not possible and, consistently, the P2₁ma phase was the most abundant phase present. Factors such as structural, strain, crystallite size and morphology are thought to be crucial in determining the exact phases of NaNbO₃ produced, both at low and room temperature. The solid-solution La[subscript(1-x)]Y[subscript(x)]ScO₃ was also investigated. Compositions x = 0, 0.2, 0.4, 0.6, 0.8 and 1 were successfully synthesised and characterised. Refined high-resolution NPD data indicates that an orthorhombic structure, in space group Pbnm, was retained throughout the solid-solution. Using ⁴⁵Sc and ⁸⁹Y MAS NMR each sample was found to exhibit disorder, believed to result from both a distribution of quadrupole and chemical shifts. NMR parameters were calculated for several model Sc and Y compounds using DFT methods to determine the feasibility and accuracy of ⁴⁵Sc and ⁸⁹Y DFT calculations. These proved successful and subsequent calculations were completed for the end members LaScO₃ and YScO₃. DFT calculations were also utilised to gain insight into the disorder exhibited in the La[subscript(1-x)]Y[subscript(x)]ScO₃ solid-solution.
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Haug, Mark. „Nonparametric density estimation for univariate and bivariate distributions with applications in discriminant analysis for the bivariate case“. Thesis, Kansas State University, 1986. http://hdl.handle.net/2097/9916.
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Orlando, A. M. „NEW INSIGHT IN ELECTRON DENSITY AND ELECTRON SPIN DENSITY THROUGH TOPOLOGICAL DESCRIPTORS BASED ON BADER'S THEORY OF ATOM IN MOLECULES“. Doctoral thesis, Università degli Studi di Milano, 2016. http://hdl.handle.net/2434/374929.
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This Ph.D. thesis is focused on the application of quantum theory of atoms in molecules (QTAIM) based chemical descriptors to challenging chemical test-cases, as well as on the development of novel topological descriptors, like the Source Function for the spin density. The thesis is organized as follows: In chapter 1 the electron density (ED) of a very unusual structural feature in a synthetic beta–sultamic analogue (DTC), has been explored by both low-T single–crystal X–ray diffraction and quantum mechanical simulations to gain insights into the subtle interplay between structure, electron delocalization and crystal field polarization effects. The core chemical moiety in DTC is an uncommon 4–membered thiazete–1,1–dioxide heterocycle, where the formally single N–C bond is, on average, 0.018 Å shorter than the formally double N=C bond. Both local and non–local topological descriptors provided by QTAIM have been employed in the analysis of DTC in comparison with chemically related derivatives and possible implications from the viewpoint of the accurate in silico modelling of crystal structures are discussed. Particular attention is dedicated on such kind of issues in chemical and pharmaceutical industries, because the control of the crystal structure is really problematic in some cases; in fact different polymorphs of the same substance have different intensive physical properties, such as solubility, refraction index and conductivity and problems may arise in industrial processes related to the synthesis of chemicals and drugs on large scale. In chapter 2, we focused on the source function (SF) QTAIM based topological descriptor. The electron density (ED) at any point r within a system may be regarded as consisting of a sum of SF contributions S(r; X) representing a measure of how the various atomic basins (X) or groups of atomic basins defined through QTAIM contribute to determine the ρ(r) at r. Recently it was shown that the SF is able to reveal electron delocalization effects in planar electron conjugated systems, in terms of an increased capability of determining the ED along a given bond by the distant, though through-bonds connected, atomic basins and, at the same time, into a decreased ability to do so by the two atoms directly involved in the bond. Such an adjustment of sources then translates into a pictorial pattern of enhanced and reduced atomic SF contributions from, respectively, distant and nearby atoms, compared to the case of a partially or fully saturated network of bonds. Then we have extended such an analysis to the non planar conjugated systems, where the usual electron separation does no longer apply. Being based on the total ED, the SF analysis may be safely applied also in these less conventional electron delocalized systems. In the present Ph. D. thesis we have extended the SF reconstruction approach also to the electron density spin counterparts in vacuo. Such reconstruction was investigated both on simple (but chemically meaningful) spin-polarized molecular systems and on more complex single-molecule magnets. This investigation has showed that the difference between the two spin counterparts of electron density distribution can be reconstructed with a sufficient accuracy, analogously to the case of the total ED. Moreover, it was found that the SF for the electron spin density brings in precious chemical information, neatly distinguishing the quite different roles played by the unpaired electrons ED and the spin polarized ED due to the remaining electrons. Furthermore, quantitative answers to questions related to the transferability of the spin density in alkyl radicals or to the transmission of spin information in metal(s)-ligand systems were provided. Understanding, from a real space perspective, by which mechanisms spin information transmits, might be of relevance to interpret the fundamental magnetic interactions present in complex materials, such as for example coordination polymers or Heussler and half-Heussler alloys. As these interactions have a key role in spintronics, characterization of the chemical bond and interpretation of the electron spin density distributions in these systems through the SF analysis, could hopefully disclose structure-property relationships extremely useful for the design of materials with particular physical properties.
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Hasan, Abeer. „A Study of non-central Skew t Distributions and their Applications in Data Analysis and Change Point Detection“. Bowling Green State University / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1371055538.
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Grierson, Greg Michael Jr. „Analysis of Amur honeysuckle Stem Density as a Function of Spatial Clustering, Horizontal Distance from Streams, Trails, and Elevation in Riparian Forests, Greene County, Ohio“. Wright State University / OhioLINK, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=wright1621942350540022.
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Abdulmalic, Mohammad A. „A Tailor-Made Approach for Thin Films and Monolayer Assemblies of bis(oxamato) and bis(oxamidato) Transition Metal Complexes“. Doctoral thesis, Universitätsbibliothek Chemnitz, 2013. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-qucosa-118769.
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The present work is dealing with the synthesis and characterization of mono- to trinuclear Cu(II)- and Ni(II)-containing bis(oxamato) and bis(oxamidato) complexes, respectively. It will be derived to which extent the spin density distribution of mononuclear complexes, determined by electron paramagnetic resonance studies experimentally and calculated by quantum mechanical calculations, can be regarded as a measure of the magnitude of magnetic superexchange interactions of corresponding trinuclear complexes. The usability of tailor-made trinuclear complexes for their deposition in form of thin film by spin-coating is described as well as the magneto-optical characterization of these thin films. It is shown, that the tailor-made functionalization of mono- to trinuclear bis(oxamidato) complexes with long alkyl chains is suited to allow these complexes to assembly in monolayers on, e.g., HOPG(0001) (highly-oriented pyrolytic graphite), whereas the functionalization of the alkyl chains with S atoms allows the generation of self-assembled monolayers on metallic gold. Furthermore it is shown, that the functionalization of mono- and trinuclear Cu(II)-containing bis(oxamato) complexes with ferrocenediyle fragments allows to modify the magnetic properties by making use of the oxidation process Fe(II)/Fe(III)Die vorliegende Arbeit befasst sich mit der Darstellung und Charakterisierung ein- bis dreikerniger Cu(II)- bzw. Ni(II)-haltiger bis(oxamato) oder bis(oxamidato) Komplexe. Es wird abgeleitet, inwiefern die aus Elektronenenspinresonanz- Untersuchungen experimentell und die quantenmechanisch berechneten Spindichteverteilungen einkerniger Komplexe ein Maß für die Größe der magnetischen Superaustauschwechselwirkungen korrespondierender dreikerniger Komplexe darstellt. Die Eignung maßgeschneiderter dreikerniger Komplexe zu ihrer Überführung in dünne Filme im nm-Bereich mittels Rotationsbeschichtung auf Si/SiO2-Substraten wird beschrieben sowie die magneto-optische Charakterisierung dieser dünnen Filme. Es wird gezeigt, dass durch gezielte Funktionalisierung mit langkettigen Alkylresten ein- bis dreikernige Cu(II)-haltige bis(oxamidato) Komplexe geeignet sind, auf Substraten wie HOPG(0001) (hochorientiertes pyrolytisches Graphit) zu Monolagen zu assemblieren während die zielgerichtete Funktionalisierung der Alkylketten mit S-Atomen es ermöglicht selbst-assemblierte Monolagen auf metallischem Gold zu generieren. Zusätzlich wird beschrieben, dass durch die Funktionalisierung von ein- und dreikernigen Cu(II)-haltigen bis(oxamato) mit Ferrocendiylresten die magentischen Eigenschaften durch den Oxidationsprozess Fe(II)/Fe(III) gezielt modifiziert werden können
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Bates, Lakesha. „ANALYSIS OF TIME SYNCHRONIZATION ERRORS IN HIGH DATA RATE ULTRAWIDEBAN“. Master's thesis, University of Central Florida, 2004. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/2582.
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Emerging Ultra Wideband (UWB) Orthogonal Frequency Division Multiplexing (OFDM) systems hold the promise of delivering wireless data at high speeds, exceeding hundreds of megabits per second over typical distances of 10 meters or less. The purpose of this Thesis is to estimate the timing accuracies required with such systems in order to achieve Bit Error Rates (BER) of the order of magnitude of 10-12 and thereby avoid overloading the correction of irreducible errors due to misaligned timing errors to a small absolute number of bits in error in real-time relative to a data rate of hundreds of megabits per second. Our research approach involves managing bit error rates through identifying maximum timing synchronization errors. Thus, it became our research goal to determine the timing accuracies required to avoid operation of communication systems within the asymptotic region of BER flaring at low BERs in the resultant BER curves. We propose pushing physical layer bit error rates to below 10-12 before using forward error correction (FEC) codes. This way, the maximum reserve is maintained for the FEC hardware to correct for burst as well as recurring bit errors due to corrupt bits caused by other than timing synchronization errors.M.S.E.E.
Department of Electrical and Computer Engineering
Engineering and Computer Science
Electrical Engineering
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Ryle, Wesley Thomas. „Investigation of Fundamental Black Hole Properties of AGN through Optical Variability“. Digital Archive @ GSU, 2008. http://digitalarchive.gsu.edu/phy_astr_diss/25.
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Active galactic nuclei (AGN) are known to vary in brightness in all regions of the electromagnetic spectrum and over a wide range of timescales. Many methods have been utilized to transform this observed variability into meaningful information about the central engines of AGN. One such technique, adapted from time series analysis of galactic x-ray binary systems, has been used to detect a characteristic break timescale in the power density spectra of x-ray variability in Seyfert galaxies. This timescale, thought to be related to instabilities in the accretion disk, appears to scale with black hole mass over many orders of magnitude. This dissertation performs similar time series analyses with the optical data of eight blazars. The majority of these objects also display a characteristic break timescale. In cases where a black hole estimate is known, the timescales are in good agreement with the relationship observed for galactic x-ray binary systems and Seyfert galaxies. For objects of unknown mass, this relationship can be used to provide a mass estimate of the supermassive black hole. Comparisons are made between the structure function and power density spectrum for each object, and the implications for the connection between the accretion disk and the relativistic jet in AGN are discussed.
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Rosch, Jan, Thijs Heus, Marc Salzmann, Johannes Mülmenstädt, Linda Schlemmer und Johannes Quaas. „Analysis of diagnostic climate model cloud parameterisations using large-eddy simulations“. Universitätsbibliothek Leipzig, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-202452.
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Current climate models often predict fractional cloud cover on the basis of a diagnostic probability density function (PDF) describing the subgrid-scale variability of the total water specific humidity, qt, favouring schemes with limited complexity. Standard shapes are uniform or triangular PDFs the width of which is assumed to scale with the gridbox
mean qt or the grid-box mean saturation specific humidity, qs. In this study, the qt variability is analysed from large-eddy simulations for two stratocumulus, two shallow cumulus, and one deep convective cases. We find that in most cases, triangles are a better approximation to the simulated PDFs than uniform distributions. In two of the 24 slices examined, the actual distributions were so strongly skewed that the simple symmetric shapes could not capture the PDF at all. The distribution width for either shape scales acceptably well with both the mean value of qt and qs, the former being a slightly better choice. The qt variance is underestimated by the fitted PDFs, but overestimated by the existing parameterisations. While the cloud fraction is in general relatively well
diagnosed from fitted or parameterised uniform or triangular PDFs, it fails to capture cases with small partial cloudiness, and in 10 – 30% of the cases misdiagnoses clouds in clear skies or vice-versa. The results suggest choosing a parameterisation with a triangular shape, where the distribution width would scale with the grid-box mean qt using a scaling factor of 0.076. This, however, is subject to the caveat that the reference simulations examined here were partly for rather small domains and driven by idealised boundary conditions.
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Vo, Son [Verfasser], und Andreas [Akademischer Betreuer] Kronenburg. „DNS analysis of Large Eddy Simulation-Filtered Density Function (LES-FDF) modeling for gas phase combustion and nanoparticle flame synthesis / Son Vo ; Betreuer: Andreas Kronenburg“. Stuttgart : Universitätsbibliothek der Universität Stuttgart, 2018. http://d-nb.info/1166655237/34.
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Houwaart, Torsten. „Cobalt porphyrins on coinage metal surfaces - adsorption and template properties“. Thesis, Lyon, École normale supérieure, 2014. http://www.theses.fr/2014ENSL0927.
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Cette thèse est une étude théorique sur la interface de porphyrine de cobalt avec des surfaces métalliques avec le code VASP DFT. Le cadre DFT nécessaire a été introduit dans le chapitre 1. La structure de la jBardeen, une programme ecrit en Java, pour la simulation de la STM est expliqué dans le chapitre 2 et le code source est jointe en annexe. Une étude de l'adsorption de CoTPP sur les surfaces métalliques a été entrepris dans le chapitre 3. Différents paramètres de calcul ont été évalués: Le site d'adsorption et de la géométrie à la fois la molécule et la surface ont été étudiés par rapport à la xc-fonctionnel et correction de la dispersion utilisée. Une adsorption site le plus stable est identifié. Par conséquent, ce site plus stable a été étudiée pour sa structure électronique. Calculés images STM avec le code jBardeen ont été comparés avec une experimentation de CoTPP Cu sur une surface (111) avec une couverture sous monocouche. Dans le chapitre 4, un adatome Fe a été présenté à la CoTPP sur Ag système (111). Trois sites de liaison symétrique différentes pour l'atome Fe ont été identifiés sur le macrocycle, marqué les , bi-, brd- et bru-positions. Un moment magnétique pouvait être attestée qui a été principalement situé sur l'atome Fe. Voies possibles entre les quatre, symétriquement équivalentes, sites bi- ont été étudiées avec des méthodes différentes. Simples calculs dans le vacuum et calculs de la “Nudged Elastic Band” (NEB) de l'ensemble du système a révélé une hauteur de barrière légèrement au-dessus de 0,2 eV allant de position bi à la posititon brd. Une analyse de vibration a montré que la commutation de l'atome Fe est susceptible, lorsqu'il est perturbé hors d'équilibre dans les positions brd et bruThis thesis is a theoretical study on the cobalt porphyrin - coinage metal surface interface with the DFT code VASP. The necessary DFT framework has been introduced in chapter 1. The structure of the Java program jBardeen for STM simulation is explained in chapter 2 and the source code is attached as Appendix. A study of the adsorption of CoTPP on coinage metal surfaces has been undertaken in chapter 3. Different parameters of the calculation have been evaluated: the adsorption site and the geometry of both the molecule and surface have been investigated with respect to the xc-functional and dispersion correction used. A most stable adsorption site -bridge down- is identified. Consequently, this most stable site was investigated for its electronic structure. Calculated STM images with the jBardeen code were compared with an experiment of CoTPP on a Cu(111) surface with sub monolayer coverage. In chapter 4 an Fe adatom was introduced to the CoTPP on Ag(111) system. Three symmetrically different binding sites for the Fe atom were identified on the macrocycle, labelled the bi-, brd- and bru-positions for bisector, bridge down and bridge up respectively. A magnetic moment could be evidenced which was mainly located on the Fe atom. Possible pathways between the four symmetrically equivalent bisector sites were investigated with different methods. Single point calculations in vacuum and Nudged Elastic Band (NEB) of the whole system revealed a barrier height of slightly above 0.2 eV going from bi- to the brd-position. A vibrational analysis showed that switching of the Fe atom is likely, when perturbed out of equilibrium in the brd- and bru- positions