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Rad, M. Goshtasbi. "Electronic structure and reactions at some tetrahedral semiconductor surfaces /." Stockholm : Tekniska högsk, 2000. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3069.
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Zimmermann, Iwan. "The Role of Tetrahedral Building Blocks in Low-Dimensional Oxohalide Materials." Doctoral thesis, Stockholms universitet, Institutionen för material- och miljökemi (MMK), 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-108160.
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The structural architecture found in low-dimensional materials can lead to a number of interesting physical properties including anisotropic conductivity, magnetic frustration and non-linear optical properties. There is no standard synthesis concept described thus far to apply when searching for new low-dimensional compounds, and therefore control on the design of the new materials is of great importance.This thesis describes the synthesis, crystal structure and characterization of some new transition metal oxohalide compounds containing p-elements having a stereochemically active lone-pair. First row transition metal cations have been used in combination with SeIV, SbIII and TeIV ions as lone-pair elements and Cl- and Br- as halide ions. The lone-pairs do not participate in covalent bonding and are responsible for an asymmetric one-sided coordination. Lone-pair elements in combination with halide ions have shown to be powerful structural spacers that can confine transition metal building blocks into low-dimensional arrangements. The halide ions and lone-pairs reside in non-bonded crystal volumes where they interact through weak van der Waals forces. The transition metal atoms are most often arranged to form sheets, chains or small clusters; most commonly layered compounds are formed.To further explore the chemical system and to separate the transition metal entities even more the possibility to include tetrahedral building blocks such as phosphate-, silicate-, sulphate- and vanadate building blocks into this class of compounds has been investigated. Tetrahedral building blocks are well known for their ability of segmenting structural arrangements by corner sharing, which often leads to the formation of open framework structures. The inclusion of tetrahedral building blocks led to the discovery of interesting structural features such as complex hydrogen bonding, formation of unusual solid solutions or faulted stacking of layers.Compounds for which phase pure material could be synthesized have been characterized in terms of their magnetic properties. Most compounds were found to have antiferromagnetic spin interactions and indications of magnetic frustration could be observed in some of them.<br><p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 6: Manuscript. Paper 9: Manuscript. Paper 10: Manuscript.</p>
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Alshahrani, Sahar. "A Theoretical Study of the Electronic Structures of Tetrahedral Boron-Halogen Complexes." DigitalCommons@Robert W. Woodruff Library, Atlanta University Center, 2019. http://digitalcommons.auctr.edu/cauetds/180.
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This study addresses the structure and the bonding in the family of tetrahedral boranes. The specific molecules studied are the series B4X4 (X=H, F, Br, Cl, I), the series B4BrCl3, B4Br2Cl2, and B4Br3Cl and tetra-tert-butyl-tetraborane, t-Bu4B4. The research presented herein employs the Hartree-Fock Self Consistent Field (HFSCF), the Moller-Plesset second-order perturbation theory (MP2), and the Density Function Theory (DFT). A variety of basis sets was employed. Our calculations are the first theoretical studies of B4Br4, B4I4, B4BrCl3, B4Br2Cl2, and B4Br3Cl, and are also the first calculations for the D4h structures of any of these molecules, except for B4H4. These results were compared with experimental results, where such comparisons can be made. The most energetically stable structure for all the B4X4 and B4BrnClm molecules has symmetry Td.
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Liu, Ping. "Structural, Kinetic and Mutational Analysis of Two Bacterial Carboxylesterases." Digital Archive @ GSU, 2007. http://digitalarchive.gsu.edu/biology_diss/26.
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The crystal structures of two thermostable carboxylesterase Est30 and Est55 from Geobacillus stearothermophilus were determined to help understand their functions and applications in industry or medicine. The crystal structure of Est30 was determined at 1.63 Å resolution by the multiple anomalous dispersion method. The two-domain Est30 structure showed a large domain with a modified alpha/beta hydrolase core including a seven, rather than an eight-stranded beta sheet, and a smaller cap domain comprising three alpha helices. A 100 Da tetrahedral ligand, propyl acetate, was observed to be covalently bound to the side chain of Ser94 in the catalytic triad. This ligand complex represents the first tetrahedral intermediate in the reaction mechanism. Therefore, this Est30 crystal structure will help understand the mode of action of all enzymes in the serine hydrolase superfamily. Est55 is a bacterial homologue of the mammalian carboxylesterases involved in hydrolysis and detoxification of numerous peptides and drugs and in prodrug activation. Est55 crystals were grown at pH 6.2 and pH 6.8 and the structures were determined at resolutions of 2.0 and 1.58 Å respectively. Est55 folds into three domains, a catalytic domain, an α/β domain and a regulatory domain. This structure is in an inactive form; the side chain of His409, one of the catalytic triad residues, is pointing away from the active site. Moreover, the adjacent Cys408 is triply oxidized and lies in the oxyanion hole, which would block the entry of substrate to its binding site. This structure suggested a self-inactivation mechanism, however, Cys408 is not essential for enzyme activity. Mutation of Cys408 showed that hydrophobic side chains at this position were favorable, while polar serine was unfavorable for enzyme activity. Both Est30 and Est55 were shown to hydrolyze the prodrug CPT-11 into the active form SN-38. Therefore, Est30 and Est55 are potential candidates for use with irinotecan in cancer therapy. The catalytic efficiency (kcat/Km) of Est30 is about 10-fold lower than that of Est55. The effects of the Cys408 substitutions on Est55 activity differed for the two substrates, p-NP butyrate and CPT-11. Mutant C408V may provide a more stable form of Est55.
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Basbous, Hind. "Etudes structurales et propriétés enzymatiques de deux nouvelles aminopeptidases TETs auto-compartimentées chez les archées." Thesis, Université Grenoble Alpes (ComUE), 2016. http://www.theses.fr/2016GREAV016/document.
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Les aminopeptidases représentent un groupe d’enzymes qui possèdent une fonction cellulaire clef dans les mécanismes physiologiques et pathologiques. Elles interviennent dans la cascade enzymatique après l’action des endoprotéases, dans l’homéostasie au travers le renouvellement du pool d’acides aminés, dans le métabolisme énergétique, la régulation de l’activité des peptides bioactifs, la présentation antigénique ainsi dans une diversité de mécanismes pathologiques tels que les maladies neurologiques et les infections virales et parasitaires. Les aminopeptidases TETs sont capables de former des macro-assemblages tétraédriques comprenant douze sous-unités. En vue de mieux comprendre leur fonction biologique et leur mode d'action, nous avons étudié les propriétés fonctionnelles et structurales de deux nouveaux complexes TETs issus d'archées hyperthermophiles. L'archée hyperthermophile Methanocaldococcus jannaschii ne possède qu'une version de TET (MjTET) qui a été produite dans Escherichia coli et purifiée sous forme de dodécamère. La recherche de son activité enzymatique et de ses substrats peptidiques par des tests chromogéniques et fluorogéniques, ainsi que des études par HPLC en phase inverse, montre que cette enzyme est une leucine aminopeptidase activée par le cobalt se distinguant des autres aminopeptidases M42 par son très large spectre d'action qui s'étend aux résidus aromatiques. Une structure complète de cette aminopeptidase a été résolue en combinant la cristallographie (2.4 Å) et la cryo-EM (4,1 Å). L'analyse de la poche de spécificité de MjTET permet de mieux comprendre les bases structurales de la discrimination de substrat chez les TETs. De plus, l'analyse de la structure interne de la particule permet de proposer un nouveau mécanisme de navigation des peptides à l’intérieur des particules tétraédriques de la famille TET.L'archée hyperthermophile Pyrococcus horikoshii comporte trois types de complexes TETs. L'étude d'une protéine présentant ~20 % d'identité avec ces systèmes, nous a permis d'identifier une quatrième version du système TET dans cet organisme : PhTET4. La protéine recombinante a été purifiée. Elle forme un complexe dodécamérique tétraédrique. Les études biochimiques révèlent que l'enzyme possède une spécificité très étroite dirigée exclusivement vers l'hydrolyse des résidus glycines de l'extrémité N-terminale des peptides. De plus, elle estactivée par le nickel. Ces caractéristiques permettent de proposer que, chez les archées, la multiplication et la spécialisation des enzymes TETs seraient associées au caractère hétérotrophes alors que le système des archées autotrophes se réduirait à une TET unique apte à assurer une fonction de « ménage »<br>Aminopeptidases represent a group of enzymes displaying key cellular function inphysiological and pathological mechanisms. They are involved in the enzymatic cascade beyond the action of endoproteases, in homeostasis through the renewal of the amino acid pool, in the energy metabolism, in the regulation of bioactive peptide activities, in the antigen presentation and in a diversity of pathological mechanisms such as neurological diseases as well as viral and parasitic infections. Aminopeptidases TET are able of forming tetrahedral macro-assemblies built by twelve subunits. In order to better understand their biological function and their mode of action, we studied the functional and structural properties of two novel TET complexes derived from hyperthermophilic archaea. The hyperthermophilic archaeon Methanocaldococcus jannaschii has only one version of TET (MjTET) that was produced in Escherichia coli and purified as dodecameric macromolecule. The search for its enzymatic activity and peptide substrates by using chromogenic/fluorogenic assays and reverse phase HPLC studies, demonstrated that this enzyme is a cobalt-activated leucine aminopeptidase, discriminated from other M42 aminopeptidases by its very broad activity spectrum, that extends to aromatic residues. Complete structure of this aminopeptidase was determined by combining X-ray crystallography (2.4 Å) and cryo-electron microscopy (4.1 Å). Analysis of MjTET specificity pocket indicated possible molecular bases for substrate discrimination in TET peptidases. In depth investigation of the particle internal structure allowed to propose a novel peptide trafficking mechanism for the TET family tetrahedral particles. Three types of TET complexes are present in the hyperthermophilic archaea, Pyrococcus horikoshii. The study of an unassigned protein displaying ~20% identity with the PhTETs systems allowed us to identify a fourth version of TET complex in this organism: PhTET4. The recombinant protein was purified. It formed tetrahedral dodecameric complex. Biochemical studies indicated that the enzyme has a very narrow hydrolytic specificity directed exclusively toward the peptide N-terminal glycine residues. In addition, this enzyme is activated by nickel ions. These features allowed proposing that, in archaea, the multiplicity of specialized TET systems could be associated with heterotrophy while unique TET system displaying “housekeeping” function is present in autotrophic organisms
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Vancraeyenest, Aurélie. "Résultats et simulation en spectroscopie γ des noyaux déformés : cas des noyaux isomériques et tétraédriques". Phd thesis, Université Claude Bernard - Lyon I, 2010. http://tel.archives-ouvertes.fr/tel-00639798.
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Le travail présenté dans ce manuscrit regroupe deux études de spectroscopie γ. La première concerne les isomères des noyaux de néodyme autour de N=82. Ces noyaux, lorsqu'ils sont étudiés par des modèles de type Cranked-Nilsson-Strutinsky, présentent des états énergétiquement favorisés. Ils sont autant de candidats pour la recherche d'isomères de spin. Expérimentalement, un certain nombre d'états isomériques ont déjà été observés dans les noyaux de 138,139,140Nd sur lesquels porte cette étude. Afin de mieux caractériser ces états, une expérience a été menée en août 2009 à Jyväskylä auprès de l'ensemble de détection JUROGAM-RITU-GREAT. La réaction de fusion-évaporation 48Ca + 76Zr 144Nd* réalisée avec une cible mince a permis de produire majoritairement les noyaux 139,140Nd. Les noyaux produits, transportés au plan focal par le spectromètre RITU, sont implantés et le rayonnement émis par la décroissance des isomères est ensuite recueilli par l'ensemble de détection GREAT. Nous développerons l'analyse complète de cette expérience et nous montrerons les résultats émergents. Nous avons, par exemple, pu montrer l'alimentation du niveau 20+ de 140Nd ainsi que le placement énergétique du niveau isomérique du noyau 139Nd. La deuxième partie de ce travail s'articule autour de la recherche de la symétrie tétraédrique dans le noyau 156Gd. Cela a consisté à la fois en un travail de spectroscopie γ des bandes de parité positive de ce noyau, laquelle a fait émerger un certain nombre de nouvelles transitions. Le deuxième volet de cette étude consistait à simuler dans l'environnement ROOT - GEANT4 le seuil d'observation des signaux faibles avec le détecteur de rayonnements γ de nouvelle génération AGATA
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Clark, Stewart. "Complex structures in tetrahedrally bonded semiconductors." Thesis, University of Edinburgh, 1994. http://hdl.handle.net/1842/13420.
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Complex tetrahedral structures form good models for amorphous Group IV and III-V semiconductors. With a view of working towards examining non-crystalline materials, the structural, electronic and vibrational properties of complex tetrahedrally bonded semiconductors are investigated by various molecular dynamics techniques. First principles quantum mechanical molecular dynamics calculations are performed on two such structures and the effects of pressure on their behaviour is reported. A full free energy calculation using this method remains unfeasible and therefore an empirical bond charge model is used to calculate the full pressure-temperature phase diagram of the structures. Several surface reconstructions of a complex phase of silicon are then examined and the lowest energy surface of any silicon structure so far is found. Point defects in the diamond phase of silicon and carbon also give insight into various unusual bonding topologies that could be found in their amorphous phase. Structural and vibrational properties of several defects are considered. Finally, calculations on amorphous carbon and silicon at several densities are done and a comparison between the structural and electronic properties made. New bonding topologies are found in the structures including three centre bonding orbitals in the amorphous carbon models.
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Wilson, Janet Kirsten. "Procedures for sequential and parallel automatic adaptive tetrahedral mesh generation." Thesis, Heriot-Watt University, 1997. http://hdl.handle.net/10399/1171.
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Jesurum, Caroline Esther 1969. "Local-rules based topological modeling of tetrahedral ceramic network structures." Thesis, Massachusetts Institute of Technology, 1998. http://hdl.handle.net/1721.1/49622.
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Touileb, Yazid. "Four-dimensional dose calculation using deformable tetrahedral geometries for hadron therapy." Thesis, Lyon, 2019. http://www.theses.fr/2019LYSE1179.
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L’estimation de la distribution de dose et d’énergie en présence du mouvement des tissus induit par la respiration, constitue un défi technologique important dans la planification du traitement en hadronthérapie. Notamment pour le cancer pulmonaire, dans lequel de nombreuses difficultés apparaissent comme la variation de densité des tissues, le changement de la forme des organes ainsi que le décalage de la position de la tumeur pendant la respiration. Tous ces paramètres affectent la portée du faisceau d’ions utilisés pendant le traitement, et, par conséquent entraînent une distribution de dose inattendue. L’objectif principal de cette thèse est de proposer une méthode de calcul de dose basée sur les structures tétraédriques, qui permet d’estimer les distributions de dose des organes en mouvement en utilisant les simulations Monte Carlo. Ces distributions de dose sont calculées en utilisant une carte de densité tétraédrique dépendante du temps, décrivant l’anatomie interne du corps humain. De plus, le mouvement interne peut être représenté à l'aide d'une modélisation biomécanique résolue par la méthode des éléments finis (MEF) ou d'une carte de déplacement issue d’un recalage d’images déformable. Contrairement aux méthodes basées sur les structures classiques à base de voxels, la dose déposée s’accumule à l’intérieur de chaque tétraèdre au cours de la déformation, surmontant ainsi le problème du suivi tissulaire puisque le tétraèdre est défini comme une partie d’un tissu dont la composition chimique et la topologie ne changent pas. Dans la première partie de la thèse, nous avons développé une méthode de calcul de dose qui génère une carte de dose 4D en utilisant un modèle tétraédrique spécifique au patient. En outre, nous étudions l’effet du niveau de détail des maillages tétraédriques sur la précision de la distribution de la dose obtenue. Dans la deuxième partie, nous nous concentrons sur l’optimisation de la géométrie tétraédrique pour réduire le temps de simulation, sachant que l’obtention d’une distribution de dose précise peut être coûteux en termes de temps. Pour surmonter ce problème, nous avons proposé une nouvelle approche qui prend en compte la direction du faisceau afin de minimiser l'erreur de l’épaisseur équivalent eau des tétraèdres avant le volume de la tumeur. Cette méthode permet d'obtenir un maillage tétraédrique grossier et, par conséquent, d'améliorer les performances de calcul dans les simulations de Monte Carlo, tout en conservant une distribution de dose précise dans le volume cible<br>The estimation of energy and dose distribution patterns in respiratory-induced organ motion constitutes a significant challenge in hadron therapy treatment planning and dosimetry. Notably for lung cancer in which many difficulties arise, like tissue densities variation and the tumor position shifting during respiration. All these parameters affect the ranges of protons or ions used in treatment when passing through different tissues and can easily result in unexpected dose distribution. The present work consists of calculating the dose distributions of moving organs by means of Monte Carlo simulations and patient-specific modeling tools. The dose distributions are calculated using a time-dependent tetrahedral density map, describing the internal anatomy of the human body. Additionally, the internal motion can be described using either a biomechanical modeling based on Finite Element Analysis (FEA) or deformable image registration displacement map. Unlike methods based on the conventional voxel-based structures, the deposited energy is accumulated inside each tetrahedron during deformation, thus overcoming the problem of tissue tracking since that the tetrahedron is defined as a part of a tissue whose chemical composition and topology do not change. The first part of the Ph.D. project proposes a dose calculation method that generates a 4D dose map using a patient-specific tetrahedral model. Besides, we study the effect of the level of detail of tetrahedral meshes on the accuracy of the resulted dose distribution. In the second part, we focus on the optimization of the tetrahedral geometry to address the problem of time simulation, since obtaining a precise dose distribution can be very time-consuming. To overcome this issue, we've defined a new approach that takes into account the direction of the beam to minimize the error of the water equivalent thickness of the tetrahedrons before the tumor volume. This method allows for a coarsened tetrahedral mesh and as a result, improved computational performance in Monte Carlo simulations while guaranteeing a precise dose distribution in the target volume
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Russo, Santina. "Structural and functional studies on the dodecameric tetrahedral-shaped aminopeptidase FrvX from Pyrococcus horikoshii /." [S.l.] : [s.n.], 2005. http://www.zb.unibe.ch/download/eldiss/05russo_s.pdf.
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Champion, Daniel James. "Mobius Structures, Einstein Metrics, and Discrete Conformal Variations on Piecewise Flat Two and Three Dimensional Manifolds." Diss., The University of Arizona, 2011. http://hdl.handle.net/10150/145313.
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Spherical, Euclidean, and hyperbolic simplices can be characterized by the dihedral angles on their codimension-two faces. These characterizations analyze the Gram matrix, a matrix with entries given by cosines of dihedral angles. Hyperideal hyperbolic simplices are non-compact generalizations of hyperbolic simplices wherein the vertices lie outside hyperbolic space. We extend recent characterization results to include fully general hyperideal simplices. Our analysis utilizes the Gram matrix, however we use inversive distances instead of dihedral angles to accommodate fully general hyperideal simplices.For two-dimensional triangulations, an angle structure is an assignment of three face angles to each triangle. An angle structure permits a globally consistent scaling provided the faces can be simultaneously scaled so that any two contiguous faces assign the same length to their common edge. We show that a class of symmetric Euclidean angle structures permits globally consistent scalings. We develop a notion of virtual scaling to accommodate spherical and hyperbolic triangles of differing curvatures and show that a class of symmetric spherical and hyperbolic angle structures permit globally consistent virtual scalings.The double tetrahedron is a triangulation of the three-sphere obtained by gluing two congruent tetrahedra along their boundaries. The pentachoron is a triangulation of the three-sphere obtained from the boundary of the 4-simplex. As piecewise flat manifolds, the geometries of the double tetrahedron and pentachoron are determined by edge lengths that gives rise to a notion of a metric. We study notions of Einstein metrics on the double tetrahedron and pentachoron. Our analysis utilizes Regge's Einstein-Hilbert functional, a piecewise flat analogue of the Einstein-Hilbert (or total scalar curvature) functional on Riemannian manifolds.A notion of conformal structure on a two dimensional piecewise flat manifold is given by a set of edge constants wherein edge lengths are calculated from the edge constants and vertex based parameters. A conformal variation is a smooth one parameter family of the vertex parameters. The analysis of conformal variations often involves the study of degenerating triangles, where a face angle approaches zero. We show for a conformal variation that remains weighted Delaunay, if the conformal parameters are bounded then no triangle degenerations can occur.
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Anand, Nagarajan. "A Conforming to Interface Structured Adaptive Mesh Refinement for Modeling Complex Morphologies." The Ohio State University, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=osu1574436067401755.
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Neudecker, Max Verfasser], Matthias [Akademischer Betreuer] Schröter, Annette [Akademischer Betreuer] Zippelius, and Stephan [Akademischer Betreuer] [Herminghaus. "Geometric structure and mechanical stability of disordered tetrahedra packings : An experimental X-ray computed tomography study / Max Neudecker. Gutachter: Annette Zippelius ; Stephan Herminghaus. Betreuer: Matthias Schröter." Göttingen : Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2013. http://d-nb.info/1045776211/34.
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Lussier, Aaron J. "Zonation in tourmaline from granitic pegmatites & the occurrence of tetrahedrally coordinated aluminum and boron in tourmaline." Mineralogical Society of Great Britan and Ireland, 2008. http://hdl.handle.net/1993/5043.
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[1] Four specimens of zoned tourmaline from granitic pegmatites are characterised in detail, each having unusual compositional and/or morphologic features: (1) a crystal from Black Rapids Glacier, Alaska, showing a central pink zone of elbaite mantled by a thin rim of green liddicoatite; (2) a large (~25 cm) slab of Madagascar liddicoatite cut along (001) showing complex patterns of oscillatory zoning; and (3) a wheatsheaf and (4) a mushroom elbaite from Mogok, Myanmar, both showing extensive bifurcation of fibrous crystals originating from a central core crystal, and showing pronounced discontinuous colour zoning. Crystal chemistry and crystal structure of these samples are characterised by SREF, EMPA, and 11B and 27Al MAS NMR and Mössbauer spectroscopies. For each sample, compositional change, as a function of crystal growth, is characterised by EMPA traverses, and the total chemical variation is reduced to a series of linear substitution mechanisms. Of particular interest are substitutions accommodating the variation in [4]B: (1) TB + YAl ↔ TSi + Y(Fe, Mn)2+, where transition metals are present, and (2) TB2 + YAl ↔ TSi2 + YLi, where transition metals are absent. Integration of all data sets delineates constraints on melt evolution and crystal growth mechanisms.
[2] Uncertainty has surrounded the occurrence of [4]Al and [4]B at the T-site in tourmaline, because B is difficult to quantify by EMPA and Al is typically assigned to the octahedral Y- and Z-sites. Although both [4]Al and [4]B have been shown to occur in natural tourmalines, it is not currently known how common these substituents are. Using 11B and 27Al MAS NMR spectroscopy, the presence of [4]B and [4]Al is determined in fifty inclusion-free tourmalines of low transition-metal content with compositions corresponding to five different species. Chemical shifts of [4]B and [3]B in 11B spectra, and [4]Al and [6]Al in 27Al spectra, are well-resolved, allowing detection of very small (< ~0.1 apfu) amounts of T-site constituents. Results show that contents of 0.0 < [4]B, [4]Al < 0.5 apfu are common in tourmalines containing low amounts of paramagnetic species, and that all combinations of Si, Al and B occur in natural tourmalines.
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Ramezani-Dakhel, Hadi. "Bioengineered Metal Nanoparticles: Shape Control, Structure, and Catalytic Functionality." University of Akron / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=akron1426184509.
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Li, Iila Jingjiao. "Flexible polyhedra : exploring finite mechanisms of triangulated polyhedra." Thesis, University of Cambridge, 2018. https://www.repository.cam.ac.uk/handle/1810/271806.
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In a quest to design novel deployable structures, flexible polyhedra provide interesting insights. This work follows the discovery of flexible polyhedra and aims to make flexible polyhedra more useful. The dissertation describes how flexible polyhedra can be made. The flexible polyhedra first considered in this dissertation have a rotational degree of freedom. The range of this rotational movement is measured and maximised in this work by numerical maximisation. All polyhedra are established computationally: an iterative solution method is used to find vertex coordinates; several clash detecting methods are described to define whether each rotational position of a flexible polyhedron is physically possible; then a range of motion is defined between occurrences of clashes at the two ends; finally, an optimisation tool is used to maximise the range of motion. By using these tools, the range of motion of two types of simplest flexible polyhedra are maximised. The first type is a series of flexible polyhedra generalised from the Steffen flexible polyhedron. The range of motion of this type is improved to double that of Steffen’s original, from 27° to 59°. Another type of flexible polyhedron is expanded from a model provided by Tachi. Based on the understanding of Steffen’s flexible polyhedron, optimisation parameters are carefully given. This new type has achieved a wider range of motion, so now the range of motion of flexible polyhedron is tripled to 80°. After enlarging the range of motion of the degree of freedom in the 1-dof systems, the dissertation found multiple degrees of freedom in one polyhedron. The multiple mechanisms can be even repetitive, so that an n-dof polyhedron is found. A polyhedron of two degrees of freedom is first presented. Then, a unit cell for any number of mechanisms is found. As a repetitive structure, a 3-dof polyhedron is presented. Finally, this work presents the possibility of configuring a flexible polyhedral torus and a closed polyhedral surface that is able to flex without the need to stop.
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Walton, Kirk S. "Sculpting: An Improved Inside-out Scheme for All Hexahedral Meshing." BYU ScholarsArchive, 2003. https://scholarsarchive.byu.edu/etd/3451.
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Generating all hexahedral meshes on arbitrary geometries has been an area of important research in recent history. Hexahedral meshes have advantages over tetrahedral meshes in structural mechanics because they provide more accurate results with fewer degrees of freedom. Many different approaches have been used to create all-hexahedral meshes. Grid-based, inside-out, or superposition meshing all refer to a similar meshing approach that is a very common mesh generation technique. Grid-based algorithms provide the ability to generate all hexahedral meshes by introducing a structured mesh that bounds the complete body modeled, marking hexahedra to define an interior and exterior mesh, manipulating the boundary region between interior and exterior regions of the structured mesh to fit the specific boundary of the body, and finally, discarding the exterior hexahedra from the given body. Such algorithms generally provide high quality meshes on the interior of the body yet distort element at the boundary in order to fill voids and match surfaces along these regions. The sculpting algorithm as presented here, addresses the difficulty in forming quality elements near boundary regions in two ways. The algorithm first finds more intelligent methods to define a structured mesh that conforms to the body to lessen large distortions to the boundary elements. Second, the algorithm uses collapsing templates to adjust the position of boundary elements to mimic the topology of the body prior to capturing the geometric boundary.
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Sengele, Loic. "Etude des modes octupolaires dans le noyau atomique de 156Gd : recherche expérimentale de la symétrie tétraédrique." Thesis, Strasbourg, 2014. http://www.theses.fr/2014STRAE038/document.
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Les symétries géométriques jouent un rôle important dans la compréhension de la stabilité de tout système physique. En structure nucléaire, elles sont reliées à la forme du champ moyen utilisé pour décrire les propriétés des noyaux atomiques. Dans le cadre de cette thèse, nous avons utilisé les prédictions obtenues avec l'aide du Hamiltonien du champ moyen nucléaire avec le potentiel de Woods-Saxon Universel pour étudier les effets des symétries dites de « Haut-Rang ». Ces symétries ponctuelles mènent à des dégénérescences des états nucléaires d’ordre 4. Il est prédit que la symétrie tétraédrique influence la stabilité des noyaux proches des nombres magiques tétraédriques [Z,N]=[32,40,56,64,70,90-94,136]. Nous avons sélectionné la région des Terres-Rares proche du noyau doublement magique tétraédrique 154Gd pour notre étude. Dans cette région, il existe des structures de parité négative qui sont mal comprises. Or la symétrie tétraédrique, en tant que déformation octupolaire non-axiale, brise la symétrie par réflexion et doit produire des états de parité négative. Après une étude systématique des propriétés expérimentales des noyaux de la région, nous avons sélectionné le 156Gd comme objet de notre étude des modes d’excitation octupolaire. Nous avons utilisé les probabilités réduites de transition gamma pour discerner ces différents modes. Pour atteindre cet objectif, nous avons réalisé trois expériences de spectroscopie gamma à l’ILL de Grenoble avec les détecteurs EXILL et GAMS afin de mesurer les durées de vie et les intensités des transitions gamma des états candidats. L'analyse de nos résultats montre que notamment la forme tétraédrique aide à comprendre les probabilités des transitions dipolaires. Ce résultat ouvre de nouvelles perspectives expérimentales et théoriques<br>Geometrical symmetries play an important role in the understanding of all physical systems. In nuclear structure they are linked to the shape of the mean-field used to describe the atomic nuclei properties. In the framework of this thesis, we have used the predictions obtained with the help of the nuclear mean-field Hamiltonian with the Universal Woods-Saxon potential to study the effects of the so-called “High-Rank” symmetries. These point-group symmetries lead to a nuclear state degeneracy of the order of 4. It is predicted that the tetrahedral symmetry affects the stability of nuclei close to the tetrahedral magic numbers [Z,N]=[32,40,56,64,70,90-94,136]. We have selected the Rare-Earth region close to the tetrahedral doubly magic nucleus 154Gd for our study. In this region, there exists negative parity structures poorly understood. Yet the tetrahedral symmetry, as related to a non-axial octupole deformation, breaks the reflection symmetry and leads to the negative parity states. Following a systematics of experimental properties of the nuclei in this region, we have selected 156Gd as the object of our study for the octupole excitation modes. We have used the reduced transitions probabilities to discriminate between these modes. To achieve this goal, we have performed three gamma spectroscopy experiments at the ILL in Grenoble with the EXILL and GAMS detectors to measure the lifetimes and the gamma transition intensities from the candidate states. The analysis of our results shows that including the tetrahedral shape helps to understand the dipole transition probabilities. This result will open new experimental and theoretical perspectives
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Burger, Matthew S. "Evidence for the 3-D network of P-centered Pyramidal P(Se1/2)3 and Quasi-tetrahedral Se=P(Se1/2)3 Local Structures and their 3-membered Ring Counterparts Decoupled from the Quasi-1-D Ethylene-like P2Se2+x (x= 2,1,0) Chains in Bulk PxSe100-x Glasses." University of Cincinnati / OhioLINK, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1627664642854937.
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Trovalet, Lionel. "Résolution numérique des transferts par rayonnement et conduction au sein d'un milieu semi-transparent pour une géométrie 3D de forme complexe." Thesis, Nancy 1, 2011. http://www.theses.fr/2011NAN10142/document.
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Ce travail porte sur la résolution numérique des transferts couplés par rayonnement et conduction au sein d'un milieu semi-transparent pour une géométrie 3D de forme complexe. Le rayonnement thermique est simulé par un code de calcul développé durant cette thèse. Ce code résout l'équation du transfert radiatif (ETR) par une méthode aux volumes finis (MVF) avec une formulation " cell-vertex " s'appliquant à des maillages tétraédriques non structurés. Il utilise un schéma de fermeture de type exponentiel, un ordre de parcours ainsi qu'une résolution matricielle innovante pour la MVF appliquée à l'ETR. Le modèle mis en place traite des milieux absorbants, émettants, gris ou non-gris bordés par des surfaces noires ou opaques à réflexion diffuse. Le couplage rayonnement-conduction s'effectue sur le même maillage avec un code d'éléments finis pour la conduction. La validation du code de rayonnement et du couplage passe par de nombreux cas tests issus de la littérature. Il aborde les milieux gris, isotherme avec différentes géométries où les effets de la discrétisation spatiale et angulaire sont observés au travers d'une étude de sensibilité. Trois schémas de fermeture ont été étudiés sur un milieu transparent pour montrer leurs influences sur la précision et la diffusion numérique. Les études des transferts de chaleur couplés traitent le problème de l'équilibre radiatif et du couplage conduction-rayonnement en régime stationnaire ou instationnaire avec les équations adimensionnées. La dernière étude porte sur un milieu non-gris tel que le verre en considérant la conduction et le rayonnement en régime stationnaire avec une méthode spectrale par bande pour la partie radiative<br>This work deals with the numerical solution of coupled radiative and conductive heat transfer in participating media in complex 3D geometries. Thermal radiation is simulated by a numerical code developed during this thesis. This code solves the radiative transfer equation (RTE) by a modified finite volume method (FVM) with a cell-vertex formulation applied to unstructured tetrahedral meshes. It uses a closure relation based on an exponential scheme, a marching order map and an innovative matrix solution for the FVM applied to the RTE. The model is applied to absorbing-emitting, grey or non-grey media bounded by black or opaque walls with diffuse reflection. The mesh used for the radiation-conduction coupling is the one used by the finite element code for the conduction. The validation of the radiative code and the coupling are carried out through several test cases taken from the literature. Grey and isothermal media with different geometries are considered, and the effects of the spatial and angular discretizations are observed through a sensitivity study. Three closure schemes have been studied on a transparent medium in order to show their influence on the accuracy and false scattering. Studies of coupled heat transfer are carried out on radiative equilibrium problems and coupled radiation-conduction problems in steady or transient states with the dimensionless equations. Finally a non-grey medium such glass is also studied, considering conduction and radiation in steady state with a spectral band model for radiation
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Wiedeking, Mathis Tabor Samuel L. Wiedenhoever Ingo L. "Nuclear structure of 86Zr and 20O and beam pulsing techniques." Diss., 2004. http://etd.lib.fsu.edu/theses/available/etd-12142004-163314/.
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Thesis (Ph. D.)--Florida State University, 2004.<br>Advisor: Dr. Samuel L. Tabor and Dr. Ingo L. Wiedenhoever, Florida State University, College of Arts and Sciences, Dept. of Physics. Title and description from dissertation home page (viewed June 6, 2005). Document formatted into pages; contains xv, 143 pages. Includes bibliographical references (p. 138-142).
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Chagnon-Lessard, Sophie. "Structure of 152Sm with (d,d') reactions in search of a tetrahedral symmetry signature." Thesis, 2012. http://hdl.handle.net/10214/3842.
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Nuclei near N=90 and Z=64 have recently been suggested to be `tetrahedral-magic'. One of the main signatures for tetrahedral symmetry is a vanishing quadrupole moment in low-lying negative-parity bands, resulting in very weak or even vanishing E2 matrix elements. With N=90 and Z=62, the transitional nucleus 152Sm is a potential candidate for relatively stable tetrahedral symmetry. Its structure was investigated using deuteron inelastic scattering with a 22 MeV polarized beam at the MP tandem Van de Graaff accelerator of the TU/LMU Munich. The scattered deuterons were momentum analyzed using the Q3D spectrometer. The experimental spectra obtained have allowed the extraction of high-quality differential cross-sections and analyzing powers for levels up to 1.8 MeV. The low-lying negative-parity bands are observed to be strongly populated and the angular distributions associated to their levels exhibit several structural features. The overall agreement is relatively good when considering strong intra-band E2 transitions, but further calculations must be performed to allow precise matrix element extraction. In particular, a simple population pathway test on the 1- state has demonstrated that calculations with vanishing E2 transitions in the negative-parity band are also capable of reproducing its experimental angular distributions. Therefore, the presence of tetrahedral symmetry signature in 152Sm is not excluded.<br>This work has been supported in part by the Natural Sciences and Engineering Research Council of Canada.
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Heard, Damian. "Computation of hyperbolic structures on 3-dimensional orbifolds." 2006. http://repository.unimelb.edu.au/10187/691.
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The computer programs SnapPea by Weeks and Geo by Casson have proven to be powerful tools in the study of hyperbolic 3-manifolds. Manifolds are special examples of spaces called orbifolds, which are modelled locally on R^n modulo finite groups of symmetries. SnapPea can also be used to study orbifolds but it is restricted to those whose singular set is a link.One goal of this thesis is to lay down the theory for a computer program that can work on a much larger class of 3-orbifolds. The work of Casson is generalized and implemented in a computer program Orb which should provide new insight into hyperbolic 3-orbifolds.The other main focus of this work is the study of 2-handle additions. Given a compact 3-manifold M and an essential simple closed curve α on ∂M, then we define M[α] to be the manifold obtained by gluing a 2-handle to ∂M along α. If α lies on a torus boundary component, we cap off the spherical boundary component created and the result is just Dehn filling.The case when α lies on a boundary surface of genus ≥ 2 is examined and conditions on α guaranteeing that M[α] is hyperbolic are found. This uses a lemma of Scharlemann and Wu, an argument of Lackenby, and a theorem of Marshall and Martin on the density of strip packings. A method for performing 2-handle additions is then described and employed to study two examples in detail.This thesis concludes by illustrating applications of Orb in studying orbifoldsand in the classification of knotted graphs. Hyperbolic invariants are used to distinguish the graphs in Litherland’s table of 90 prime θ-curves and provide access to new topological information including symmetry groups. Then by prescribing cone angles along the edges of knotted graphs, tables of low volume orbifolds are produced.
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Neudecker, Max. "Geometric structure and mechanical stability of disordered tetrahedra packings." Doctoral thesis, 2013. http://hdl.handle.net/11858/00-1735-0000-0022-609B-9.
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"DNA Tetrahedra as Structural Frameworks for Catalytic Centers." Doctoral diss., 2012. http://hdl.handle.net/2286/R.I.16022.
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abstract: The need for a renewable and sustainable light-driven energy source is the motivation for this work, which utilizes a challenging, yet practical and attainable bio-inspired approach to develop an artificial oxygen evolving complex, which builds upon the principles of the natural water splitting mechanism in oxygenic photosynthesis. In this work, a stable framework consisting of a three-dimensional DNA tetrahedron has been used for the design of a bio-mimic of the Oxygen-Evolving Complex (OEC) found in natural Photosystem II (PSII). PSII is a large protein complex that evolves all the oxygen in the atmosphere, but it cannot be used directly in artificial systems, as the light reactions lead to damage of one of Photosystem II's core proteins, D1, which has to be replaced every half hour in the presence of sunlight. The final goal of the project aims to build the catalytic center of the OEC, including the Mn4CaCl metal cluster and its protein environment in the stable DNA framework of a tetrahedron, which can subsequently be connected to a photo-stable artificial reaction center that performs light-induced charge separation. Regions of the peptide sequences containing Mn4CaCl ligation sites are implemented in the design of the aOEC (artificial oxygen-evolving complex) and are attached to sites within the tetrahedron to facilitate assembly. Crystals of the tetrahedron have been obtained, and X-ray crystallography has been used for characterization. As a proof of concept, metal-binding peptides have been coupled to the DNA tetrahedron which allowed metal-containing porphyrins, specifically Fe(III) meso-Tetra(4-sulfonatophenyl) porphyrin chloride, to be encapsulated inside the DNA-tetrahedron. The porphyrins were successfully assembled inside the tetrahedron through coordination of two terminal histidines from the orthogonally oriented peptides covalently attached to the DNA. The assembly has been characterized using Electron Paramagnetic Resonance (EPR), optical spectroscopy, Dynamic Light Scattering (DLS), and x-ray crystallography. The results reveal that the spin state of the metal, iron (III), switches during assembly from the high-spin state to low-spin state.<br>Dissertation/Thesis<br>Ph.D. Biochemistry 2012
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Ho, Shu-Chun, and 何淑君. "Protection of scour downstream of a grade control structure using tetrahedron frames." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/52482523124477385181.
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碩士<br>國立中興大學<br>土木工程學系所<br>97<br>In the west of Taiwan, bed elevations of many rivers lowered down seriously. River and bridge management bureaus often construct grade-control structures to stabilize the riverbeds and reduce the scouring of the pier foundations.
This research is mainly aimed at the edge failures downstream of the grade-control structures. Firstly, a series of experiment was conducted under the limit condition of clear-water with sand and gravel, two riverbed slopes, two ramp slopes for the grade-control structures, and three flow discharges. Based on the measured lengths of the scour holes for the non-protected conditions, the tetrahedron frames were covered on the sand bed downstream of the grade-control structures. Indoor experiments were then carried out to investigate the scour hole shapes and the effectiveness of this type of scour reduction device.
The results of the non-protected experiments show that under a given flow discharge, the shape of scour hole could reach the equilibrium state in a short time. In addition, generally the scour depth increases with an increase of the flow intensity or the riverbed slpoe. Moreover, the maximum equilibrium scour depth usually occurs very close to the upstream grade-control structure, which is a threat to the grade-control structure.
With protection of tetrahedron frame downstream of the grade-control structure, the scour depth is obviously lower than that without protection. The results indicate that the tetrahedron frames could reduce the flow velocities, trap the sediment particles within the protected region, and effectively reduce the scour depth.
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Jen, I.-Hsuan, та 任怡瑄. "Edge-Sharing BO4 Tetrahedra in the Structure of Hydrothermally Synthesized Barium Borate: α-Ba3[B10O17(OH)2]". Thesis, 2019. http://ndltd.ncl.edu.tw/handle/6dvk77.
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碩士<br>國立中央大學<br>化學學系<br>107<br>A new barium borate, α-Ba3[B10O17(OH)2](α-form), has been synthesized through hydrothermal reaction at 500 °C and 1000 bar and the structure determined by single-crystal X-ray diffraction. The 3D framework structure of the α-form is formed of two different fundamental building blocks (FBB) with the descriptors 4Δ6□:[⧄⧅]−<3□>−<2Δ□>|−<3□>−<2Δ□>| (FBB1) and 2Δ3□:<Δ2□>−<Δ2□> (FBB2). FBB1 is unique and contains unusual edge-sharing BO4 tetrahedra. The 3D framework of α-form consists of alternating sheets of FBB1 and FBB2 in ac plane. There are two kinds of narrow channels parallel to the a axis where the Ba2+ cations are located.
The structure of α-form is very interesting and it is one of the few compounds with es-BO4. All of the other compounds were synthesized through solid state reactions at high temperature under high pressure or ambient pressure. α-Ba3[B10O17(OH)2] is the first compound with edge-sharing BO4 tetrahedra synthesized in aqueous solution under hydrothermal conditions.
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Timofte, Tudor Lucian [Verfasser]. "Structural and physical properties of salts containing tetrahedral anions with group 13 metals (aluminates and halogenidogallates) / vorgelegt von Tudor Lucian Timofte." 2008. http://d-nb.info/995827524/34.
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