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Xu, Liang. "Simulating electronic-structure properties of atomic clusters by Ab-initio calculations, and inter-nuclear quantum-statistical effects of molecules from an integration-free path-integral method /Xu Liang." HKBU Institutional Repository, 2016. https://repository.hkbu.edu.hk/etd_oa/344.
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In this dissertation, we have employed some well-established electronic-structure methods [e.g., density functional theory (DFT) and time-dependent DFT (TD-DFT)] to investigate the potential energy surfaces for 2s 2p excitation of beryllium atomic clusters, attempting to provide direct computational support for the mechanism of a newly invented laser spectroscopy. The computing time of single-point energy calculations for a series of beryllium clusters from using TD-DFT has been compared with that from a higher-level coupled-cluster method, in order to demonstrate the computational practicality of TD-DFT methods. Meanwhile, to benchmark the accuracy of TD-DFT methods, the state properties such as the equilibrium inter-atomic distance and dissociation energy of beryllium clusters calculated by us are compared with experimental results and other computational values where available. Furthermore, we have defined the fork intersections to characterize the position where the excited states can be treated as degenerate = Moreover, to shed some light on the reaction mechanism of a Diels-Alder reaction between isoprene and maleic anhydride, we have investigated the kinetic isotope effects (KIE) of the reaction. To further include inter-nuclear quantum-statistical effects (i.e., the quantum tunneling effect and anharmonicity), an automated integration-free path-integral (AIF-PI) method developed by our group in recent years based on Kleinert's variational perturbation theory has been used. The KIE values produced by the AIF-PI method can be used to clearly distinguish between the two isomeric transition-state structures, and determine the actual rate-limiting transition state. By virtue of the AIF-PI method, we have also analyzed the quantum tunneling effects and anharmonicity separately, which are excluded in conventional Bigeleisen equation. Furthermore, the influence of different numbers of quantized nuclei on the KIE values using base-catalyzed RNA 2'-O-transphosphorylation models as examples are explored, by systematically increasing the number of quantized nuclei from 1 to 16 (fully quantized)
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Wang, Leiming. "Photoelectron spectroscopy studies on novel doped clusters." Pullman, Wash. : Washington State University, 2009. http://www.dissertations.wsu.edu/Dissertations/Fall2009/l_wang_111309.pdf.
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Thesis (Ph. D.)--Washington State University, December 2009.Title from PDF title page (viewed on Dec. 11, 2009). "Department of Physics and Astronomy." Includes bibliographical references (p. 156-176).
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SANTOS, RICHARD BRYAN MAGALHAES. "AN IMAGE ANALYSIS SYSTEM FOR THE CHARACTERIZATION OF SINTER FEED MICROCLUSTERS." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2018. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=36029@1.
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PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIROOs minérios, uma vez extraídos, passam por diversas etapas de beneficiamento antes que possam ser devidamente utilizados. Os finos de minérios que, ao final dessa etapa, não possuem a granulometria necessária para alimentar os fornos de redução, passam por processos de aglomeração para alcançá-la, como a pelotização e a sinterização, cujo material produzido em uma das etapas deste último processo é o foco do presente trabalho. Esses finos passam primeiramente por uma etapa de microaglomeração, que é fundamental para o processo, pois muitas das características e propriedades do sínter são função da estrutura do microaglomerado pré-tratamento térmico. Ela consiste numa mistura do sinter feed com água, fundentes e combustível sólido (coque). Existem 3 estruturas típicas para um microaglomerado: quasipartícula, micropelota e partícula não aglomerada. A presente dissertação desenvolveu uma rotina automática no programa de processamento e análise de imagens FIJI, baseada em processamento e análise de imagens do microaglomerado obtidas por microscópio ótico, que é capaz de identificar as partículas de diferentes granulometrias que compõem a amostra, e classificá-las quanto às 3 classes supramencionadas. Após a classificação, a rotina é capaz de extrair atributos dos objetos identificados (percentual de cada classe, circularidade média, espessura média), e analisar os núcleos das quasipartículas, classificando-os quanto à fase (hematita, magnetita, goethita e outros). Ademais, a rotina apresenta todos os dados já citados na forma de um relatório em pdf, que contém também uma listagem das quasipartículas e micropelotas em ordem crescente de tamanho. Essa rotina elimina a imprecisão e a subjetividade do operador humano, obtém medidas não realizáveis manualmente, permitindo prever características futuras do sínter de forma totalmente automática.
The ores, once extracted, undergo several stages of processing before they can be properly used. The fines of ores that, at the end of this stage, do not have the granulometry required to feed the reduction furnaces, pass through agglomeration processes to reach it, such as pelletizing and sintering. The material produced in one of the stages of the latter process is the focus of this work. These fines first go through a micro-agglomeration stage, which is fundamental to the process because many of the characteristics and properties of the sinter are function of the structure of the pre-heat treatment microcluster. It consists of a mixture of the sinter feed, water, fluxes and solid fuel (coke). There are 3 typical structures for a microcluster: quasiparticle, micropellet, and non-agglomerated particles. The present dissertation has developed an automatic routine in the FIJI image-processing program, based on optical microscope image processing and analysis, which is able to identify the particles of different granulometry that compose the sample, and classify them in the 3 classes mentioned above. After classification, the routine is able to extract attributes of the identified objects (percentage of each class, average circularity, average thickness), and to analyze the quasiparticle nuclei, classifying them as to the phase (hematite, magnetite, goethite and others). In addition, the routine presents all the data in the form of a pdf report, which also contains a listing of quasiparticles and micropellets in increasing order of size. This automatic classification eliminates the lack of reproducibility and subjectivity of the human operator, provides measures that would be untenable manually, allowing the forecast of the future characteristics of the sinter in a fully automatic fashion.
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Cui, Lifeng. "Photoelectron spectroscopy studies on group IV semiconductor clusters and novel binary clusters." Online access for everyone, 2007. http://www.dissertations.wsu.edu/Dissertations/Spring2007/l_cui_050107.pdf.
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Eljack, Fadwa Tahra. "A property based approach to integrated process and molecular design." Auburn, Ala., 2007. http://repo.lib.auburn.edu/2007%20Spring%20Dissertations/ELJACK_FADWA_14.pdf.
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黃柄榕 and Ping-yung Wong. "Molecular clusters on surfaces: a Monte Carlostudy." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1999. http://hub.hku.hk/bib/B31221956.
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Wong, Ping-yung. "Molecular clusters on surfaces : a Monte Carlo study /." Hong Kong : University of Hong Kong, 1999. http://sunzi.lib.hku.hk/hkuto/record.jsp?B20566694.
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Paukstis, Sarah Joan. "The spectroscopy of small silicon clusters Si₂X(X = N,O)." Diss., Georgia Institute of Technology, 2000. http://hdl.handle.net/1853/30309.
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Liu, Haichuan. "Reactions in gaseous metal-organic complexes induced by the photoexcitation of the metal chromaphores /." View abstract or full-text, 2004. http://library.ust.hk/cgi/db/thesis.pl?CHEM%202004%20LIU.
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Spraggins, Jeffrey M. "Environmental applications of ESI FT-ICR mass spectrometry oxidized peptides and metal sulfide clusters /." Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file, 231 p, 2010. http://proquest.umi.com/pqdweb?did=1993336521&sid=11&Fmt=2&clientId=8331&RQT=309&VName=PQD.
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Johnston, Roy Luigi. "Theoretical investigations of polyhedral inorganic molecules." Thesis, University of Oxford, 1986. http://ora.ox.ac.uk/objects/uuid:810da917-8aff-44f4-b539-3212254d7642.
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This Thesis describes some theoretical studies on cluster compounds of the main group and transition metal elements. Chapter 1 presents a review of the theoretical aspects of cluster chemistry. Three major theoretical approaches are identified, namely the localised, delocalised and free electron models and their historical development is described. The research described in this Thesis is based on extensions of Stone's Tensor Surface Harmonic (TSH) methodology, supported by Extended Huckel molecular orbital calculations. In Chapter 2, the TSH approach is used to describe the skeletal bonding in 3- and 4-connected polyhedral clusters. Like the deltahedral clusters, 4-connected molecules are generally characterised by (n+1) Skeletal Electron Pairs (SEP's). 3- connected clusters, however, possess 3n/2 SEP's. This difference is attributed to the occurrence of additional non-bonding orbitals in the 3-connected case. In Chapter 3, the bonding in a novel class of deltahedral metallaborane clusters is discussed. These hyper-closo or iso-closo species are studied from a fragment orbital viewpoint, regarding the structures as metal-capped fragments of a borane icosahedron. In this way, the problem of whether these clusters possess n or (n+1) SEP's is studied for n=9, 10 and 11. Although most deltahedral clusters conform to the (n+1) SEP rule, there are a significant number which do not. In Chapter 4, these deviations are rationalised from a group theoretical/topological viewpoint. A group theoretical paradigm is developed which simplifies the derivation of the frontier orbitals for these molecules. Chapter 5 extends the TSH methodology to clusters with bispherical topologies. To discuss these clusters, the TSH wavefunctions are modified to include radial, as well as angular nodes. The methodology is also applied to clusters with toroidal topologies, where the capping atoms form a ring around the equator of the inner cluster sphere. The bonding in π-donor- and π-acceptor-bridged clusters of the transition metals are compared in Chapter 6. Although the symmetry aspects are identical and lead to similar bonding patterns, the ir-donor clusters are characterised by a number of unoccupied dδ-based orbitals. The bonding in a series of closo, nido and arachno π-donor clusters, based on edge- and face-bridged octahedral molecules is considered and a relationship between the cluster electron count and the number of unavailable dδ-based orbitals is identified.
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Chaganti, Venkata R. "Study of the structural and spectroscopic properties of small ZnS clusters by DFT." To access this resource online via ProQuest Dissertations and Theses @ UTEP, 2008. http://0-proquest.umi.com.lib.utep.edu/login?COPT=REJTPTU0YmImSU5UPTAmVkVSPTI=&clientId=2515.
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Raparla, Mrudula. "Study of the structural and electronic properties of aluminum nano clusters by DFT." To access this resource online via ProQuest Dissertations and Theses @ UTEP, 2009. http://0-proquest.umi.com.lib.utep.edu/login?COPT=REJTPTU0YmImSU5UPTAmVkVSPTI=&clientId=2515.
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Young, Teresa Marie. "Statistical thermodynamics of cluster formation in dilute colloidal and coarse-grained protein solutions." Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file, 206 p, 2010. http://proquest.umi.com/pqdweb?did=1997524011&sid=2&Fmt=2&clientId=8331&RQT=309&VName=PQD.
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Lin, Zhenyang. "Theoretical studies on cluster compounds." Thesis, University of Oxford, 1989. http://ora.ox.ac.uk/objects/uuid:4afef76e-df5f-4357-9072-f20cb5a3b5d8.
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This Thesis describes some theoretical studies on ligated and bare clusters. Chapter 1 gives a review of the two theoretical models, Tensor Surface Harmonic Theory (TSH) and Jellium Model, accounting for the electronic structures of ligated and bare clusters. The Polyhedral Skeletal Electron Pair Theory (PSEPT), which correlates the structures and electron counts (total number of valence electrons) of main group and transition metal ligated clusters, is briefly described. A structural jellium model is developed in Chapter 2 which accounts for the electronic structures of clusters using a crystal-field perturbation. The zero-order potential we derive is of central-field form, depends on the geometry of the cluster, and has a well-defined relationship to the full nuclear-electron potential. Qualitative arguments suggest that this potential produces different energy level orderings for clusters with a nucleus with large positive charge at the centre of the cluster, enabling the spherical jellium model to be applied to alkali metal clusters seeded with magnesium and zinc. Analysis of the effects of the non-spherical perturbation on the spherical jellium shell structures leads to the conclusion that for a cluster with a closed shell electronic structure a high symmetry arrangement which is approximately or precisely close packed will be preferred. It also provides a basis for rationalising those structures, which have been predicted using ab initio calculations, of clusters with incomplete shell electronic configurations In Chapter 3, the geometric conclusions derived in the structural jellium model are developed in more detail. Alkali metal clusters with closed shell electronic configurations according to the jellium model adopt geometries of high symmetry and based on the Td , Oh and Ih point groups. For high nuclearity clusters alternative high symmetry structures can occur and those which are either the most close packed or spherical are predicted to be the most stable. When the jellium closed shell "magic numbers" coincides with one of these high symmetry structures then the cluster will be particularly stable. The group theoretical consequences of the Tensor Surface Harmonic Theory are developed in Chapter 4 for[ML2]n, [ML4]n and [ML5]n clusters where either the xz and yz or x2-y2 and xy components to Lπd and Lδd do not contribute equally to the bonding. The closed shell requirements for such clusters are defined and the orbital symmetry constraints pertaining to the interconversion of conformers of these clusters are described. In Chapter 5 Stone's Tensor Surface Harmonic methodology is applied to high nuclearity transition metal carbonyl cluster compounds with 13-44 metal atoms. Two limiting bonding situations are identified and represented in terms of general electron counting rules. If the radial bonding effects predominate the clusters are characterised by 12ns+Δi valence electrons, where Δi is the characteristic electron count of the interstitial moiety. If radial and tangential bonding effects are important then the total number of valence electrons is 12ns+2(ss+si-l), where ss and si are the number of skeletal bonding molecular orbitals associated with surface (ss) and interstitial (si) moieties. Chapter 6 develops a new theoretical framework to account for the bonding in the high nuclearity ligated clusters with columnar topologies. The wave functions of columnar metal clusters can be expressed as an expansion based on the particle on the cylinder problem. This bonding analysis is applied to clusters containing columns of triangles and squares. In Chapter 7 the origin of non-bonding orbitals in molecular compounds is reviewed and analysed using general quantum mechanical considerations. A combination of the pairing theorem and a group theoretical analysis leads to a definition of the number of the non-bonding molecular orbitals in co-ordination, polyene and cluster compounds. The non-bonding molecular orbitals have been generated by defining the nodal characteristics of the relevant orbitals and evaluating the solutions under the appropriate boundary conditions. The stereochemical role of nonbonding molecular orbitals in co-ordination compounds is also discussed.
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Amon, Lynn. "Methods for calculating the free energy of atomic clusters /." Thesis, Connect to this title online; UW restricted, 2000. http://hdl.handle.net/1773/8595.
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Wallace, William Todd. "Selective molecular adsorption on gold clusters." Diss., Georgia Institute of Technology, 2003. http://hdl.handle.net/1853/27045.
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Liang, Anthony. "Electric deflection measurements of sodium clusters in a molecular beam." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2009. http://hdl.handle.net/1853/31750.
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Thesis (Ph.D)--Physics, Georgia Institute of Technology, 2010.Committee Chair: de Heer, Walter; Committee Member: Chou, Mei-Yin; Committee Member: First, Phillip; Committee Member: Whetten, Robert; Committee Member: Zangwill, Andrew. Part of the SMARTech Electronic Thesis and Dissertation Collection.
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López, José G. "Theoretical studies of the dynamics and spectroscopy of weakly bound systems." Connect to resource, 2005. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1127220592.
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Thesis (Ph. D.)--Ohio State University, 2005.Title from first page of PDF file. Document formatted into pages; contains xv, 99 p.; also includes graphics (some col.). Includes bibliographical references (p. 95-99). Available online via OhioLINK's ETD Center
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Zhang, Jiapu. "Derivative-free hybrid methods in global optimization and their applications." Thesis, University of Ballarat, 2005. http://researchonline.federation.edu.au/vital/access/HandleResolver/1959.17/34054.
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In recent years large-scale global optimization (GO) problems have drawn considerable attention. These problems have many applications, in particular in data mining and biochemistry. Numerical methods for GO are often very time consuming and could not be applied for high-dimensional non-convex and / or non-smooth optimization problems. The thesis explores reasons why we need to develop and study new algorithms for solving large-scale GO problems .... The thesis presents several derivative-free hybrid methods for large scale GO problems. These methods do not guarantee the calculation of a global solution; however, results of numerical experiments presented in this thesis demonstrate that they, as a rule, calculate a solution which is a global one or close to it. Their applications to data mining problems and the protein folding problem are demonstrated.Doctor of Philosophy
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Beck, Douglas R. "Theoretical investigations in vibrational spectroscopy /." Thesis, Connect to this title online; UW restricted, 1996. http://hdl.handle.net/1773/8675.
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Scholl, Peter. "Modellieren von Microclustern." [S.l. : s.n.], 2002. http://deposit.ddb.de/cgi-bin/dokserv?idn=964250705.
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Batista, Enrique R. "Development of a new water-water interaction potential and application to molecular processes in ice /." Thesis, Connect to this title online; UW restricted, 1999. http://hdl.handle.net/1773/9733.
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Rives, Molina Vicente José. "Study of b-hadron decays into two hadrons and a photon at LHCb and first observation of b-baryon radiative decays." Doctoral thesis, Universitat de Barcelona, 2016. http://hdl.handle.net/10803/400528.
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This thesis is divided in different sections. After a short introduction about the thesis contents, the theory chapter presents the Standard Model of Particle Physics (SM), with an emphasis on those properties of flavour physics, such as oscillations. In this chapter a brief comment on radiative decays, the main topic through the thesis, is given, to present the specific theoretical description of these processes.
The European Centre of Nuclear Research (CERN) is introduced in the second chapter, where the nature of such organization and the different experiments it holds are explained. Special emphasis is given for the LHCb experiment, which is the one that collected the data used in the analysis.
The third chapter describes the monitorization and re-calibration of the SPD sub- detector, which is the one in charge of the discrimination between photons and other electromagnetic particles. During the Run 1 (2011-2012), this sub-detector suffered from ageing due to the presence of radiation inside the LHCb cavern. This ageing led to a drop in the SPD cell efficiencies, which could imply a loss in the data quality. The SPD is key in the context of radiative decays due to the presence of photons in the radiative final states and due to the fact that the main sources of background for radiative decays are related to the mis-identification of other particles as photons. With the work presented in this thesis, the performance of the SPD sub-detector reached the same status than it did for the beginning of Run 1, which corresponds to an almost flat cell efficiency around 95%. This recovery in efficiencies was performed by applying a correction factor calculated through the study of cosmic ray data and collision data from 2015.
The fourth chapter describes a software tool developed within the radiative decays context. This tool is aimed for a better description of the photon/neutral pion separation variable, which is built making use of the electromagnetic clusters that these particles leave in the LHCb electromagnetic calorimeter (ECAL). This tool builds a variable that separates between the two particles but discrepancies between the data and the simulation distributions are observed. Because of this, two additional tools were developed to improve the agreement between them. These tools trust that the separation variable can be binned in terms of the particle transverse momentum and pseudorapidity. The first of the tools, “efficiency table tool”, assigns the efficiency for a certain 2-dimensional bin as a weight to the simulation sample, so the distribution is corrected and matches the one for data. The “resampling tool”, however, creates a new variable from calibration histograms built from background- subtracted distributions, trusting all radiative decays to have a similar behaviour in the 2-dimensional bins. The two tools can also be applied to neutral pions selection.
The main chapter of the thesis is related to the measurement of the ratio of branching fractions for Bs decaying into phi (which decays into two kaons) and a photon and Lambda_b, decay into a Lambda bayron (which decays into a kaon and a proton) and a photon with respect to the best controlled radiative decay, Bd decaying into a K* (which decays into a kaon and a pion) and a photon, as well as the measurement of the direct CP asymmetry for the Lambda_b and Bd decays. This analysis also implies the first observation of a b-baryon radiative decay and constitutes the best measurement of the observables presented above. The analysis is performed over the whole Run 1 LHCb dataset (3 inverse fb). Special care is applied to the Lambda_b decay since it had never been done before; taking into account the different resonances that may
intervene (that cannot be distinguished since they overlap and interfere). A 2- dimensional binning (on the resonance mass and on the proton angle) is defined for the study of the efficiencies, as recommended by the theory approaches to this decay and trusting (and confirmed afterwards) the different resonance decays to give a similar efficiency for the offline selection for a given bin.
The thesis concludes with an overview of the whole work presented, given the calculated results for the physical observables and comparing them to the previously measured ones in the LHCb.Esta tesis está dividida en varias partes. Después de una breve introducción sobre el contenido de la tesis, las dos primeras de ellas presentan el Modelo Estándard de la Física de Partículas (ME), el contexto teórico que describe la naturaleza de las partículas y sus interacciones; y el CERN, el laboratorio de física de partículas más grande del mundo. Se dedica especial énfasis a la física de las “desintegraciones radiativas”, que son aquellas en las que un fotón forma parte del estado final de la desintegración. La tercera de las secciones de la tesis describe la toma de datos por parte del sub- detector SPD así como el proceso de recuperación del funcionamiento posterior a la observación de pérdida de eficiencia debida a la presencia de radiación en la caverna del LHCb. Este sub-detector es el encargado de proporcionar la información necesaria que permita la diferenciación entre fotones y piones neutros y por tanto muy importante en procesos radiativos. La cuarta sección explica el desarrollo y funcionamiento de una herramienta de software destinada a una mejor descripción de la variable de separación entre fotones y piones neutros a partir de la forma de los clusters que estas partículas dejan en el calorímetro electromagnético del LHCb. La quinta sección explica el análisis de datos recogidos por el experimento LHCb durante los años 2011 y 2012 en términos de la medida de frecuencia de desintegración de procesos radiativos. En particular, se estudia la relación entre la frecuencia de desintegración entre el proceso de desintegración de un mesón Bs decayendo a una partícula phi (que a su vez se desintegra en dos kaones) y un fotón y un barión Lambda_b decayendo a una partícula Lambda* (que a su vez se desintegra en un protón y un kaón) y un fotón respecto de la desintegración de un mesón Bd a un K* (que a su vez se desintegra en un kaón y un pión) y un fotón así como la medida de asimetría de CP-paridad para las dos últimas desintegraciones. Este análisis supone la medida más precisa para estas magnitudes hasta la fecha y la primera observación de una desintegración radiativa de un barión con un quark b. La tesis termina con un capítulo de conclusiones donde se detallan los valores encontrados para las magnitudes físicas y el impacto del trabajo presentado en esta tesis, comparando los valores hallados con los existentes anteriormente y recordando que este trabajo supone la primera observación de una desintegración radiativa de un barión cuyo contenido de quarks incluye un quark b.
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Bradley, Colin Bueth. "Microclustered optimistic simulation." Thesis, McGill University, 2008. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=19273.
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Software-driven simulation as a design and verification tool has become almost ubiquitous in today's industrial and technology-based society. As systems grow in scale and complexity, often on a non-linear basis, demands on simulation change accordingly. Distributed simulation is one approach to deal with such growth. As distributed simulation becomes the norm in various contexts, focus has shifted to the efficiencies of such simulations. A popular approach has been to partition a given problem into sub-units in such a manner as to increase the efficiency of the simulation run. Further, efforts have been made to dynamically re-partition the problem units using run-time metrics. Noting the limitations of static partitioning and contrasting dynamic re-partitioning, this thesis approaches simulation efficiency by proposing an initial over-partitioning of the problem. Using run-time data, we hope to discover potential efficiencies and exploit them by dynamically amalgamating these ''micro-clusters'' as suggested by run-time analysis.La simulation menée par logiciel comme outil de conception et de vérification est devenue presque omniprésente dans la société industrielle et basée sur la technologe d'aujourd'hui. Comme les systèmes se développent en éechelle et en complexité, souvent sur une base non linéaire, les exigences sur la simulation changent en conséquence. La simulation distribuée est une approche pour traiter d'une telle croissance. Alors que la simulation distribuée devient la norme dans divers contextes, le centre d'intérêt s'est porté sur l'efficacité de telles simulations. Une approche populaire a été de diviser un problème donné dans des sous-unités de manière à optimiser l'efficacité de la simulation. De plus, des efforts ont été faits pour répartir les unités de problème en utilisant des données d'exécution. Prenant en compte les limitations de la division statique des partitions et contraste dynamique, cette thèse approche l'efficacité de simulation en proposant une répartition de niveau supérieur du problème. En utilisant des données d'exécution, nous espérons découvrir des efficacités potentielles et les exploiter en amalgamant dynamiquement ces ''microamas'' comme suggérés par l'analyse d'exécution.
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Watson, Thomas Francis. "Tin Oxide Cluster Assembled Films: Morphology and Gas Sensors." Thesis, University of Canterbury. Physics and Astronomy, 2009. http://hdl.handle.net/10092/3160.
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In this thesis, investigations into fabricating tin oxide hydrogen gas sensors from films assembled by the deposition of tin clusters are reported. The tin clusters were formed in a UHV compatible cluster apparatus by DC magnetron sputtering and inert gas aggregation. Through SEM imaging, it was found that the morphology of tin cluster assembled films deposited onto silicon nitride substrates was highly coalesced. The coalescence between the clusters was significantly reduced by reacting the clusters with nitrogen before they were deposited. This resulted in granular films with a grain size close to that of the deposited clusters. The coalesced and granular tin films were used to fabricate tin oxide conducti-metric gas sensors. This was done by depositing the tin films onto gold contacts and then oxidising them by baking them at 250°C for 24 hours. The sensors were tested using a purpose built gas test rig. It was found that the sensors with the granular film morphology were much more sensitive to 500 ppm, 1000 ppm, and 5000 ppm of hydrogen at 200°C in ambient air with zero humidity. This was attributed to the smaller grain size and the larger surface area of the granular films.
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Jonke, Alex P. "Atomic metal/polyaniline composites." Diss., Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/49070.
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It is ideal to theoretically predict the activity of a catalyst. It has been recognized that not only the type of metal, but also its atomic size plays an important role in catalysis. In the past, atomic clusters have been created by sputtering from a sacrificial metal plate and then using a mass selector to choose cluster sizes from 1-233 atoms of gold. This approach has practical limitations. In this thesis, I describe a procedure by which atomic clusters of gold containing 1-8 atoms are deposited in polyaniline as an isolation matrix. My atomic deposition follows a cyclic pathway. Atomic clusters of palladium and atomic alloys of gold and palladium are also deposited in polyaniline using the same process. It is to show that this method will also work for other metals. These composite materials are characterized, and the catalytic activity for alcohol oxidation is evaluated.
This thesis is divided into seven chapters. The first chapter discusses the chemistry of polyaniline for using gold and palladium as catalysts. The technique developed to deposit the atomic clusters is discussed in the second chapter. This technique deposits one atom of metal per imine site on polyaniline, per cycle. The cycle is repeated n-times until a cluster of specified size, Mn, and composition has been synthesized. It is known that polyaniline plays an important role in stabilization of the formed clusters which prevents their aggregation. The optimization of this technique is the topic of the third chapter along with the description of how these composite films are produced. To end this chapter, the composite films are characterized by cyclic voltammetry, Kelvin probe, and X-ray photoelectron spectroscopy.
In chapters 4 and 5, the catalytic activity of the polyaniline/gold composites for the oxidation of alcohols in alkaline media using cyclic voltammetry is evaluated. In chapter 4, the correlation of the electrochemical activity for the oxidation of n-PrOH with the odd-even pattern from the calculated HOMO-LUMO gap energies for the same size clusters is shown. It is shown that the infrared spectrum of polyaniline with different sizes of atomic gold clusters also follows the odd-even pattern. Chapter 5 expands on the discussion of the catalytic oxidation of alcohols. The oxidation of methanol, ethanol, propanol, and butanol is surveyed. The peak currents are again dominated by the odd-even pattern.
In chapter 6, the versatility of the atomic deposition cycle is shown by depositing atomic palladium clusters. The peak currents for the oxidation of n-PrOH by these palladium composite films again follows the predicted pattern of the calculated HOMO-LUMO gap energies for atomic palladium clusters. This chapter also explores bimetallic atomic clusters of gold and palladium. The results indicate that the catalytic activity depends on the orientation of the cluster in the polyaniline matrix. Chapter 7 discusses the oxidation of methanol, ethanol, and isopropanol on AunPd1 bimetallic atomic clusters. The addition of palladium in the cluster increases the peak current densities for the oxidation of both alcohols except for the most stable of the atomic gold clusters, while it inactivated the electrodes for isopropanol. The possible future work for this project is discussed in chapter 8.
Overall, this thesis has developed a novel and unique technique for depositing atomic metal clusters into a polyaniline matrix. The technique is versatile enough to deposit atomic metal clusters other than gold, as shown by creating atomic palladium clusters and atomic bimetallic clusters of gold and palladium. This is extremely useful, since this single technique can produce many different types of atomic catalysts. The composite materials have been shown to be catalytically active for the oxidation of alcohols in alkaline media. This indicates a significant improvement to conserve precious metals while still retaining a high catalytic activity.
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Neaime, Chrystelle. "Nanoparticules et colloïdes multifonctionnels à base de clusters d’éléments de transition et complexes de lanthanides." Thesis, Rennes, INSA, 2015. http://www.theses.fr/2015ISAR0017/document.
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La première partie de ce travail porte sur l’élaboration et la caractérisation de nouvelles nanoparticules (NPs) multifonctionnelles de silice à architectures complexes. L’enjeu est de répondre à la demande croissante d’élaboration de nouveaux systèmes colloïdaux non toxiques, magnétiques et/ou luminescents dans la région NIR pour des applications potentielles en biotechnologie. Cet objectif a été atteint en associant intimement des composés à clusters de molybdène avec des nanocristaux de maghémite et/ou d’or dans une NPs de silice de 50 nm. Une évaluation de la cytotoxicité des NPs contenant des clusters d’éléments de transition Cs2Mo6Br14 ainsi qu’un suivi par microscopie de fluorescence en temps retardé des NPs Cs2Mo6I8(C2F5COO)6@SiO2 incorporées dans des cellules cancéreuses sont présentés. Dans la deuxième partie, des poudres microcristallines de composés hétéronucléaires de polymères de coordination à base de terres rares de formule chimique générale [Ln2-2xLn’2x(bdc)3,4H2O]∞ avec 0 ≤ x ≤ 1 ont été nanométrisées dans du glycérol. Ces NPs présentent des propriétés luminescentes identiques à celles du matériau massif. Une étude détaillée de cette nouvelle voie de synthèse répondant aux principes de la chimie verte ainsi qu’une étude de la stabilité en fonction du temps et de la dilution des colloïdes obtenus ont été réaliséesThe first part of this work involves the development and characterization ofnovel nanoparticles (NPs) of multifunctional silica with complex architectures.The challenge is to meet the increasing demand for development of newnon-toxic colloidal systems, magnetic and/or luminescent in the NIR regionfor potential applications in biotechnology. This objective was achievedby closely associating molybdenum clusters compounds with maghemitenanocrystals and/or gold in 50 nm silica NPs. An evaluation of thecytotoxicity of NPs containing clusters of transition elements of Cs2Mo6Br14and a time-gated fluorescence microscopy of Cs2Mo6I8(C2F5COO)6@SiO2NPs incorporated in cancer cells are presented.In the second part, microcrystalline powders of heteronuclear lanthanidebasedcoordination polymers with general chemical formula [Ln2-2xLn’2x(bdc)3,4H2O] ∞ 0 ≤ x ≤ 1 were dissolved in glycerol . These NPsexhibit luminescent properties identical to that of the bulk material.A detailed study of this new green synthetic route and a study of thestability over time and a dilution of the obtained colloids were performed
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Bilal, Mahmood. "The role of the GRB2 family of adaptor proteins in T cell receptor-mediated signaling." Diss., University of Iowa, 2015. https://ir.uiowa.edu/etd/1548.
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CD4+ T cells are critical in the fight against parasitic, bacterial, and viral infections, but are also involved in many autoimmune and pathological disorders. Ligation of the T Cell Receptor (TCR) is the primary signal required for T cell activation proliferation, differentiation and cytokine release. Upon TCR activation, several kinases and adaptor proteins are assembled at the TCR/linker for activation of T cells (LAT) signaling complexes, a process indispensable for optimal signal transduction. One important group of proteins recruited to the TCR/LAT complexes is the GRB2 family of adaptors.
Due to their role in mediating signaling complexes, the GRB2 family of adaptors are critical for development, proliferation, and survival of diverse cell types. These proteins have been linked to the initiation and progression of numerous pathological conditions including diabetes, asthma/allergy, and solid and hematopoietic malignancies. Therefore, it is essential to characterize and understand the complete functions of these proteins for the generation of safe and efficient targeting treatments for diseases mediated by these proteins. In T cells, GRB2 and its homologs, GADS and GRAP, are crucial for the propagation of signaling pathways through the TCR and adaptor protein LAT. These proteins recruit distinct sets of proline-rich ligands to LAT thereby inducing multiple signaling pathways such as MAP kinase activation, calcium influx and cellular adhesion. However, the role of GRB2 family members in controlling TCR and LAT mediated signaling in mature human T cells is not completely understood. Moreover, the relative role of GRB2 family members in the extent and timing of the recruitment of SH3 domain ligands to the LAT complex is unknown. Our hypothesis is that these proteins recruit distinct sets of ligands to the LAT complex that can drive differential downstream signaling events.
As presented in CHAPTER III, we developed microRNA and shRNA targeting viral vectors to effectively inhibit the expression of GRB2 and GADS in human CD4+ T cells to examine the role of these adaptors in mature human T cells. We also established optimized protocols for high efficacy retro or lentiviral transduction of human T cell lines, activated and "hard-to-transduce" non-activated primary human CD4+ T cells. In CHAPTER IV, we demonstrate the requirement for GRB2 in TCR-induced IL-2 and IFN-γ release. The defects in cytokine release in the absence of GRB2 were attributed to diminished formation of LAT signaling microclusters, which resulted in reduced MAP kinase activation, calcium flux and PLC-γ1 recruitment to LAT signaling clusters. Overall, the data presented in this chapter demonstrate that the ability of GRB2 to facilitate protein clustering is as important in regulating TCR-mediated functions as its capacity to recruit effector proteins. This highlights that GRB2 regulates signaling downstream of adaptors and receptors by both recruiting effector proteins and regulating the formation of signaling complexes. In CHAPTER V, we describe the role for GADS in mediating TCR-induced IL-2 and IFN-γ production. GADS was critical for the recruitment of SLP-76 and PLC-γ1 to the LAT complex and subsequent calcium influx. We also show, in contrast to the current paradigm, that recruitment of GADS/SLP-76 complexes to LAT is not required for TCR-mediated adhesion and cytoskeletal arrangement.
Overall, our studies reveal novel mechanisms for the role of GRB2 family members in TCR-mediated signaling. They also provide insight into the mechanisms that regulate growth factor, cytokine and insulin receptors. Importantly, studies presented in this thesis will help us understand the mechanisms of T cell activation and highlight potential new therapies for T cell-mediated diseases, including leukemia, lymphomas, autoimmune disorders and cardiovascular disease.
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Kaufmann, Martin. "Electron Diffraction Studies of Unsupported Antimony Clusters." Thesis, University of Canterbury. Physics and Astronomy, 2006. http://hdl.handle.net/10092/1269.
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This thesis contains two main parts: the first part focusses on an electron diffraction study on unsupported antimony (Sb) clusters, while in the second part the design and development of a time-of-flight mass spectrometer (TOFMS) is discussed. Electron diffraction is an ideal tool to study the structure of clusters entrained in a beam. The main advantage of this technique is the ability to study the clusters in situ and in an interaction-free environment. It is therefore not necessary to remove the particles from the vacuum system which would lead to oxidation. Since the particles do not have to be deposited on a sample for further investigation, there is also no substrate which could influence the cluster structure. An additional advantage is the short exposure to the electron beam, thereby minimising the likelihood of damaging the particles. Sb clusters were produced using an inert-gas aggregation source. To control the cluster properties the source temperature, pressure and type of cooling gas can be adjusted. In the range of source parameters tested, Sb clusters with three different structures were observed: a crystalline structure corresponding to the rhombohedral structure of bulk Sb, an amorphous structure equivalent to the structure of amorphous Sb thin films, and a structure with the same diffraction signature as Sb4 (Sb evaporates mainly as Sb4). This last structure was found to belong to large particles consisting of randomly oriented Sb4 units. In order to study the size distributions and morphologies of the Sb clusters, the clusters were deposited onto substrates and studied under an electron microscope. The crystalline particles showed a wide variety of strongly faceted shapes. Depending on source conditions, the average cluster diameters ranged from 15 to 130 nm. There was a considerable disagreement between these values and the size estimates from the diffraction results with the latter being smaller by an order of magnitude. This might be due to the existence of domains inside the clusters. The amorphous particles were all found to be spherical with mean sizes between 27 and 45 nm. The Sb4 particles showed a liquid-like morphology and tended to coalesce easily. Their sizes ranged from 18 to 35 nm. To obtain an independent method for determining the cluster size, a TOFMS was designed and developed in collaboration with Dr Bernhard Kaiser. However, the TOFMS failed to detect a cluster signal in the original set-up which is most likely due to a defective ioniser and underestimated cluster energies. Further tests were performed in a new vacuum system and mass spectra for palladium clusters were successfully recorded.
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Macià, Escatllar Antoni. "Computational Modelling of TiO2 and Mg-silicate nanoclusters and nanoparticles - Crystallinity and Astrophysical Implications." Doctoral thesis, Universitat de Barcelona, 2020. http://hdl.handle.net/10803/669508.
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The research presented in this thesis contributes to the understanding of both titania and silicate nanosystems by providing new information on energetic stability and properties of nanometer sized particles using computational modelling. Particular emphasis is placed on the importance of two nanosized regimes: i) tens of atoms, and ii) several hundred up to thousands of atoms. We differentiate these two size regimes by naming nanoclusters the structures containing between tens up to a hundred of atoms, and using the term nanoparticles (NPs) for the structures containing hundreds to thousands of atoms.
Titania (TiO2) is the most studied photocatalyst, and thus research is mostly focused on understanding the electronic properties of different morphologies of TiO2 NPs. In detail, for TiO2 the present thesis benchmarks the ability of several interatomic potentials (IPs) to reduce the computational cost of Density Functional Theory (DFT) calculations, as well as a detailed analysis of the energetic stability of three different morphologies of NPs together with an analysis of their band-gap. We show that the Anatase crystal structure becomes the most stable for particle sizes of ~2-3 nm in diameter, while for smaller sizes amorphous particles are the most stable. Within the Anatase structure, we see that Wulff construction is the most stable for large sizes (above 2 nm), but amorphous shell-crystalline core nanoparticles are within the same energy range below a radius of 2 nm. We also find that spherical particles have a band-gap consistent with the so-called black TiO2.
On the other hand, research on silicates is mainly focused on calculating the properties of nanoclusters and NPs, with the objective of obtaining a better understanding of the relevance of such species in interstellar space. In detail, we propose global minima (GM) candidates for numerous nanoclusters based on extensive global optimization (GO) searches and compare their spectroscopic and chemical properties with literature values, where the later values are mostly derived from extrapolation using macroscale laboratory samples. The GO searches were done with a reparameterization of the FFSiOH where we included the Mg element. We also evaluate whether silicate nanoclusters can be the origin of the anomalous microwave emission (AME), a foreground emission in the microwave (MW) region of the spectra from an unknown source and find that indeed nano silicates have the appropriate dipole moments in order to be a strong source of the AME. We indicate that the amount of nano silicates in the interstellar medium is constrained by the AME emission. Finally, the IR spectra of large NPs of around 4 nm in diameter is compared on the basis of their crystallinity. We find that for such sizes, the IR spectra of the crystalline particle corresponds to a broad band similar to the amorphous material, which we ascribe to the large fraction of surface atoms. We conclude that the IR spectra is not sufficient to characterize the crystallinity of astronomical silicates with sizes of several nanometers in diameter. We also show that amorphous silicate nano particles with sizes of ~1 nm in diameter are more stable than their crystalline counterparts. We extrapolate the tendency and propose that the crystalline nanoparticles become more stable than amorphous particles at particle sizes of ~12 nm in diameter.En la presente tesis se estudian la estructura y propiedades de nano partículas de TiO2 y de silicatos de magnesio. Mediante cálculos de teoría del funcional de la densidad y cálculos de potenciales interatómicos se muestra, para TiO2, cómo la estructura de la nano partícula tiene un factor clave para entender la diferencia de energía entre la banda de conducción y la banda de valencia. Además, Comparamos la estabilidad energética de nano partículas de Anatasa con diferente geometría respecto a nano partículas y nano clúster amorfos, mostrando como la geometría de Wulff es energéticamente la más estable a partir de 2nm, pero para tamaños inferiores los clúster amorfos son más estables. Para silicatos de magnesio, se describe la estructura, espectro infra-rojo y microondas de clúster de MgSiO3 y Mg2SiO4, así como la similitud del espectro infra-rojo en materiales cristalinos y amorfos de tamaños ~4 nm. Los resultados se comparan con los modelos usados para entender las propiedades del medio interestelar. Se muestra que para nano partículas de hasta algunos nanómetros de radio no es posible diferenciar el material cristalino del amorfo en base a espectroscopia infrarroja. Finalmente, se calcula la intensidad de emisión en microondas (10-60 GHz) de nano clústers de silicatos de ~100 átomos y se demuestra a nivel teórico la capacidad de los silicatos como fuente viable de la emisión anómala de microondas.
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Minarik, Philip R. "Coherent anti-Stokes Raman studies of acetylene nanoclusters." Thesis, 1996. http://hdl.handle.net/1957/34369.
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Zhang, Min. "Theoretical studies of metal clusters with empirical and ab-initio methods /." 2009. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&res_dat=xri:pqdiss&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&rft_dat=xri:pqdiss:NR51495.
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Thesis (Ph.D.)--York University, 2009. Graduate Programme in Physics & Astronomy.Typescript. Includes bibliographical references (leaves 179-198). Also available on the Internet. MODE OF ACCESS via web browser by entering the following URL: http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&res_dat=xri:pqdiss&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&rft_dat=xri:pqdiss:NR51495
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Choi, Boyeon Bonnie. "Assembly of Multifunctional Materials Using Molecular Cluster Building Blocks." Thesis, 2018. https://doi.org/10.7916/D8RV255J.
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This thesis explores the synthesis, properties, and potential applications of molecular clusters and the hierarchical solids that form when complementary clusters are combined. Chapter 1 introduces the diverse set of molecular clusters that I employ as nanoscale building blocks in the assembly of multifunctional materials. The core structure of the molecular clusters is closely related to the superconducting Chevrel phases. In discrete clusters, however, the core is passivated by organic ligands, which add stability and important functionalities. The molecular clusters have rich physical and chemical properties of their own, and I present some of the techniques used to investigate their intrinsic electronic properties. Finally, I review some of the modes by which the molecular clusters interact with another to assemble into hierarchical solids. The structural tunability and complexity embedded in the molecular clusters will enable the design of modular, well-defined, multifunctional materials with desirable electronic and magnetic properties.
Chapter 2 details the synthesis and characterization of a family of manganese telluride molecular clusters. By varying the ligands that decorate the surface of the inorganic core, I show that the core structures can be tuned. The study of molecular clusters provides insight into how extended solids form. As such, I make structural comparisons of the clusters to known solid-state compounds. Being structurally varied and chemically flexible, the clusters reported in this chapter present an exciting new class of building blocks for the assembly of solid-state compounds.
In Chapters 3-4, I present a nanoscale approach to investigate the electronic behaviors of individual molecular clusters. By using a scanning tunneling microscope-based break-junction technique and density-functional theory calculations, I study the effects of the junction environment and the redox properties of the molecular clusters on the conductance of single-cluster junction. Importantly, current blockade effect is observed at room temperature in the single-cluster junctions, allowing for the conductance to be turned on or off by varying the bias potential.
Chapters 5-7 explore the synthesis and properties of the hierarchical solids comprised of molecular cluster building blocks. Chapter 5 unveils an approach to create a three-dimensional (3D) coordination network of molecular clusters by using a bifunctional cyanide ligand. The cyanide ligand is appended to the metal sites of the cluster through the carbon terminus, leaving the nitrogen end available for coordination by a divalent metal cation. Whereas the molecular cluster itself is paramagnetic across a temperature range of 3-300 K, the 3D coordination compound shows a ferromagnetic transition at ~25 K. In Chapter 6, I describe the importance of a molecular recognition feature on the molecular cluster that contributes to the assembly of a layered, van der Waals solid. The bulk material contains monolayers of fullerene and can be mechanically exfoliated to thinner layers, providing a key templated strategy to isolate free monolayers of fullerene. Lastly, Chapter 7 details layered, van der Waals solids of rhenium and molybdenum synthesized using traditional solid-state reactions. Because the neighboring cluster units are covalently bound together, the inter-cluster coupling is much stronger in the plane of these materials than that of the self-assembled solid described in Chapter 6. The strong two-dimensional (2D) character in these layered materials allows for the exfoliation of bulk crystals into robust, low-defect monolayers. The surfaces of these monolayers are covered with substitutionally labile ligands, which is an atypical yet valuable feature among 2D materials. I demonstrate that the electronic properties of the monolayers can be tuned by exchanging the surface ligands.
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Pinkard, Andrew. "Architecting Superatomic Metal Chalcogenide Clusters for Materials Design." Thesis, 2018. https://doi.org/10.7916/D8RB8NGG.
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This dissertation describes and summarizes the research I performed as a member of the Roy group. The Roy group uses molecular clusters as nanoscale building blocks for new materials, in addition to several other topics of related interest including the design and synthesis of molecular wires to study the movement of electrons (conductance) at the molecular level.
Chapter 1 introduces molecular clusters as superatomic nanoscale building blocks and describes how superatomic crystals, analogous to ionic crystals, can be controllably assembled from these building blocks. Next, Chapter 2 examines how the atomic properties of ionization energy and electron affinity can be extended to superatoms by investigating the Co6S8(PEt3)6(CO)6-x family of clusters. As the degree of cabonylation increases, the superatom moves from alkali-like to halogen-like behavior; i.e., it becomes harder to ionize and easier to add an electron to the superatom as PEt3 ligands are replaced with CO ligands while still maintaining the overall electron count of the cluster. Chapter 3 then moves to discuss how the related building blocks, Co6Te8(PEt3)6 and its derivatives, can be assembled into superatomic crystals using the electron-accepting Fe8O4pz12Cl4 cluster. Chapter 4 then uses this same Fe8O4pz12Cl4 cluster as a probe for singlet fission triplet dynamics by functionalizing this cluster with a singlet fission chromophore. Chapter 5 continues the idea of ligand design by exploring a series of oligophenylenediamine molecules capable of binding to gold (and presumably other metals), and it is observed that the conductance dramatically increases by applying a high positive bias to the molecules when they are bound to the tips of two gold electrodes. This dissertation concludes with Chapter 6, which discusses how new cobalt chalcogenide materials prepared from superatomic precursors can be deployed as new battery electrode materials for lithium and sodium ion batteries. Each of these chapters help illustrate how synthetic chemistry can be used to both elucidate interesting chemical phenomena and to design new materials with tailored properties.
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Fomytsʹkyi, Mykhailo. "Numerical simulation of high intensity laser-plasma interaction." Thesis, 2004. http://hdl.handle.net/2152/1165.
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Fomytsʹkyi, Mykhailo Chiu Charles Breizman Boris N. "Numerical simulation of high intensity laser-plasma interaction." 2004. http://wwwlib.umi.com/cr/utexas/fullcit?p3142720.
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Zhong, Xinjue. "Exploring two-dimensional superatomic semiconductors." Thesis, 2019. https://doi.org/10.7916/d8-mtzn-sd45.
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Two-dimensional (2D) van der Waals materials have received widespread attention due to their novel 2D properties that are distinct from their bulk counterparts. These unique properties offer new possibilities for fundamental research and for diverse applications in electronics, optoelectronics, and valleytronics. It is therefore of great interest to design 2D materials from complex, hierarchical and/or tunable building blocks. Atomic and molecular clusters are attractive target due to their atomic precision, structural and compositional diversity and synthetic flexibility. In this thesis, we report two novel quasi-2D superatomic semiconductors: Re6Se8Cl2 and Mo6S3Br6, whose building blocks are atomic clusters rather than simple atoms. In Chapter 3, we determine the electronic bandgap (1.58 eV), optical bandgap (indirect, 1.48 eV), and exciton binding energy (100 meV) of Re6Se8Cl2 crystals by using scanning tunneling spectroscopy, photoluminescence and ultraviolet photoelectron spectroscopy, and first principles calculations. The exciton binding energy is consistent with the partially 2D nature of the exciton. In Chapter 4, the layered van der Waals material Mo6S3Br6 possesses a robust 2D character with a direct gap of 1.64 eV, as determined by scanning tunneling spectroscopy. By using polarization dependent Raman spectroscopy and DFT calculations, we determine its strong in-plane electronic anisotropy. The complex, hierarchical structures with 2D characters of these two materials thus suggest an effective strategy to expand the design space for 2D materials research with multi-functionality and novel physical properties.
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"Ab initio molecular dynamics studies on the thermal properties of small silver clusters and the thermal decomposition channels of 5-nitro-2,4-dihydro-3H-1,2,4-triazol-3-one." 1999. http://library.cuhk.edu.hk/record=b5890000.
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Yim Wai-leung.Thesis (M.Phil.)--Chinese University of Hong Kong, 1999.
Includes bibliographical references (leaves 73-77).
Abstracts in English and Chinese.
THESIS COMMITTEE --- p.ii
ABSTRACT (English version) --- p.iii
ABSTRACT (Chinese version) --- p.v
ACKNOWLEDGEMENTS --- p.vi
TABLE OF CONTENTS --- p.vii
LIST OF FIGURES --- p.ix
LIST OF TABLES --- p.xi
Chapter CHAPTER 1. --- General Introduction
Chapter Section 1.1 --- Introduction --- p.1
Chapter Section 1.2 --- Electronic Structure Calculation
Chapter 1.2.1 --- Density Functional Theory --- p.2
Chapter 1.2.2 --- "Exchange, Correlation and the Local Density Approximation" --- p.4
Chapter 1.2.3 --- Bloch's Theorem and Plane Wave Basis Set --- p.6
Chapter 1.2.4 --- The Pseudopotential Approximation --- p.10
Chapter Section 1.3 --- Molecular Dynamics
Chapter 1.3.1 --- Molecular Dynamics --- p.12
Chapter 1.3.2 --- Nose Thermostat
Chapter 1.3.2.1 --- Introduction --- p.14
Chapter 1.3.2.2 --- Feedback Method --- p.15
Chapter Section 1.4 --- Case Studies
Chapter 1.4.1 --- Thermal properties of small silver clusters --- p.18
Chapter 1.4.2 --- Thermal decomposition channels of NTO --- p.20
Chapter CHAPTER 2. --- Ab Initio Molecular Dynamics Study on Agn (n=4-6)
Chapter Section 2.1 --- Introduction --- p.22
Chapter Section 2.2 --- Computational Method --- p.24
Chapter Section 2.3 --- Results and Discussion
Chapter 2.3.1 --- Ag2 --- p.26
Chapter 2.3.2 --- Ag4 --- p.30
Chapter 2.3.3 --- Ag5 --- p.36
Chapter 2.3.4 --- Ag6 --- p.45
Chapter Section 2.4 --- Summary --- p.49
Chapter CHAPTER 3. --- Ab Initio Molecular Dynamics Study on Thermal Decomposition of NTO
Chapter Section 3.1 --- Introduction --- p.52
Chapter Section 3.2 --- Computation Details --- p.55
Chapter Section 3.3 --- Results and Discussion
Chapter 3.3.1 --- Comparison of the Quantum Calculations by VASP and Gaussian98 --- p.56
Chapter 3.3.2 --- Exploring the Reaction Channels --- p.62
Chapter 3.3.2.1 --- Hydrogen-transfer Activation --- p.62
Chapter 3.3.2.2 --- Homolytic Cleavage of C-N02 Bond --- p.63
Chapter 3.3.2.3 --- Nitro-nitrite Rearrangement --- p.64
Chapter 3.3.2.4 --- Direct Ring Rupture --- p.64
Chapter 3.3.3 --- Energetic Consideration --- p.65
Chapter 3.3.4 --- Activation Barriers --- p.70
Chapter 3.3.5 --- Summary --- p.72
REFERENCES --- p.73
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Beecher, Alexander Nathaniel. "Using atomically precise clusters to model materials." Thesis, 2016. https://doi.org/10.7916/D8XK8FTF.
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Using two different model systems, this thesis considers the old, but fascinating question: how do atoms or particles possessing a particular set of individual characteristics combine to form assemblies with quite distinct, ensemble characteristics, and how do those characteristics evolve as a function of the size of the assembly? For the last thirty years, numerous experiments studying the emergence of collective material properties have focused on a class of semiconducting, colloidal nanocrystals commonly known as quantum dots, which are notable for the size-dependence of their optical properties. Despite years of effort, even the most uniform quantum dot samples possess some heterogeneity in size, shape, and composition, which has prevented complete structure determination and hindered understanding of structure-property relationships. Chapter 1 of this thesis presents an approach to overcoming this challenge and reports the synthesis of a set of four, new, atomically precise cadmium selenide nanocrystal samples, which we call CdSe(350 nm), CdSe(380 nm), CdSe(408 nm), and CdSe(435 nm) after their lowest energy absorption features. We determine their structures and formulas through a combination of single crystal and powder X-ray diffraction measurements, elemental analysis, and spectroscopy. We also describe the optical properties of these samples and their sensitivity to ligand coverage, compare them to other previously reported cadmium selenide nanomaterials, and discuss ongoing experiments.
Because CdSe(350 nm), CdSe(380 nm), CdSe(408 nm), and CdSe(435 nm) are atomically precise, they allow us to correlate specific structural features with material properties, which is the focus Chapter 2. Here we present a series of Raman scattering experiments designed to probe the evolution of vibrational structure with size. We find that the Cd-Se stretching region of the Raman spectra exhibits two peaks, which are assigned to primarily surface-derived and interior-derived atomic motions using density functional theory calculations. By performing variable temperature measurements, we discover that the smallest sample, CdSe(350 nm), exhibits behavior that can be well-described using a model developed for small molecules while the vibrations of the largest measured cluster, CdSe(408 nm), are better described by a model developed for bulk materials. This observation is evidence that the transition to a more bulk-like vibrational structure occurs relatively rapidly when cadmium selenide materials are approximately 2 nm in size.
The emergence of collective material properties is also the subject of Chapter 3, but the topic is approached from a different perspective. Instead of focusing on a series of atomically precise clusters that differ in size, Chapter 3 presents a series of molecules composed of atomically precise clusters. We prepare octahedral hexaruthenium carbonyl clusters, [Ru₆C(CO)₁₆]²⁻, and use them as building blocks to assemble oligomers linked by single metal atom bridges. We synthesize and structurally characterize a set of compounds varying in length (from monomer to trimer) and linker atom identity (cadmium and mercury) and study the effect on electronic structure using infrared and UV-Visible absorption spectroscopies and density functional theory calculations. With increasing oligomer length, the UV-Vis absorption profile changes and shifts to lower energy, which we attribute in part to the development of coupling between neighboring clusters. Our calculations show that the infinite polymer composed of [Ru₆C(CO)₁₆]²⁻ linked by Hg²⁺ would be a one-dimensional semiconductor with a 1.5 eV direct band-gap.
More detailed abstracts can be found at the beginning of each chapter.
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Scholl, Peter [Verfasser]. "Modellieren von Microclustern / vorgelegt von Peter Scholl." 2002. http://d-nb.info/964250705/34.
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