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The development of missing transverse momentum reconstruction with the ATLAS detector using the PUfit algorithm in pp collisions at 13 TeVLi, Zhelun 19 August 2019 (has links)
Many interesting physical processes produce non-interacting particles that could only be measured using the missing transverse momentum. The increase of the proton beam intensity in the Large Hadron Collider (LHC) provides sensitivity to rare physics processes while inevitably increasing the number of simultaneous proton collisions in each event. The missing transverse momentum (MET) is a variable of great interest, defined as the negative sum of the transverse momentum of all visible particles. The precision of the MET determination deteriorates as the complexity of the recorded data escalates. Given the current complexity of data analysis, a new algorithm is developed to effectively determine the MET. Several well-understood physics processes were used to test the effectiveness of the newly designed algorithm. The performance of the new algorithm is also compared to that of the standard algorithm used in the ATLAS experiment. / Graduate
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Contribuição da rigidez transversal à flexão das lajes na distribuição dos esforços em estruturas de edifícios de andares múltiplos, em teoria de segunda ordem / Contribution of bending stiffness transverse of slabs in the forces distribution in structures of multistory buildings, in second order theoryMartins, Carlos Humberto 10 August 1998 (has links)
O principal objetivo deste trabalho é calcular esforços e deslocamentos de estruturas tridimensionais de edifícios de andares múltiplos, sujeitos às ações verticais e laterais, considerando a rigidez transversal à flexão das lajes, em teoria de 2ª ordem. O elemento finito de placa adotado na discretização do pavimento, responsável pela consideração da rigidez transversal das lajes na análise do edifício é o DKT (Discrete Kirchhoff Theory). Para os pilares o equilíbrio de forças é verificado na sua posição deformada, ou como é conhecido da literatura técnica, análise em teoria de 2ª ordem, considerando a não linearidade geométrica. Para o cálculo dos esforços e deslocamentos na estrutura são aplicadas as técnicas de subestruturação em série e paralelo na matriz de rigidez global da estrutura. Elaborou-se um programa de computador para o processo de cálculo, utilizando a linguagem computacional Fortran Power Station 90 e pré e pós processadores em Visual Basic 4.0 para ambiente Windows. Finalmente são apresentados alguns exemplos para comprovar a validade do processo de cálculo utilizado / The main aim of this work is to calculate stresses and displacements of threedimensional structures of multistory buildings, subjected to vertical and lateral loads, considering the transverse bending stiffness of slabs, in second order theory. The plate finite element adopted in floor discretization, responsible for considering the bending stiffness contribution of slabs in the analysis of buildings, is the DKT (Discrete Kirchhoff Theory). For columns the forces equilibrium is verified for the columns in their deformed position, which is known in the technical literature as 2nd order analysis, considering the geometric non-linearity. The techniques of serial and parallel analysis of substructures are applied to the global stiffness matrix for the calculus of forces and displacements in the strucuture. A computer program was developed for the calculation process, using the computer language Fortran Power Station 90 and pre and post-processors in Visual Basic 4.0 for a Windows environment. Finally, some examples are presented to check the validity of the employed calculus process
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Juntas em pavimentos de concreto: dispositivos de transferência de carga / Joints in concrete pavements: load transfer devicesRodrigues, Lezzir Ferreira 25 February 2008 (has links)
Este trabalho apresenta um estudo experimental do comportamento de juntas transversais em placas de concreto simples, apoiadas sobre fundação elástica. Uma vez sujeita a tensões, provocadas tanto pelo carregamento como por empenamentos e variações volumétricas da placa, as juntas podem provocar uma redução sensível na vida do pavimento, caso não estejam devidamente dimensionadas para suportar as cargas impostas. Devido a isto, a conexão mecânica entre as placas do pavimento é fundamental para garantir uma melhor eficiência na transferência desses esforços e, consequentemente, um aumento na vida útil do pavimento. No trabalho, faixas de concreto, com dimensões de 220 cm x 60 cm e espessuras de 12 cm e 16 cm, foram ensaiadas com força monotônica até a ruína, considerando força em um dos lados da junta. O estudo analisou o comportamento do sistema placa-junta para diferentes dispositivos metálicos de transferência, sendo eles: barras de seções circulares e quadradas, placas e discos, adotando dois dispositivos por modelo ensaiado. Dois diferentes tipos de juntas foram analisados, segundo sua tipologia, como juntas serradas e juntas moldadas. Os resultados experimentais mostram que o aumento na espessura do pavimento aumenta sua capacidade resistente, para os dois tipos de junta. Já a tipologia da junta pode influenciar na força de ruína da peça, uma vez que a presença de concreto abaixo do dispositivo causa variação na rigidez vertical do conjunto, conhecida como interação concreto-barra, levando o modelo serrado a romper com uma carga superior. Os ciclos de carregamento aumentaram a propagação de fissuras sob o lado carregado, reduziram a força de fissuração em parte dos modelos, mas não reduziram sua força de ruína. O disco metálico, em função dos dados coletados, apresentou o melhor desempenho em relação aos demais, e é sugerido como o dispositivo de transferência de carga preferencial para se obter uma maior eficiência do sistema. / This paper presents an experimental study of the behavior of transverse joints in slabs of plain concrete, under elastic support. Once it subjects to tensions, caused so much by the loading as for warped and volumetric variations of the slap, the joints can cause a sensitive reduction in the life of the pavement, in case they are not properly design to support the loads forced. Due to this, the mechanical connection among the slabs of the pavement is fundamental to guarantee a better efficiency in the transfer of those efforts and, consequently, a prolongation in the useful life of the pavement. In the paper, concrete areas, with dimensions of 220 cm x 60 cm and thickness of 12 cm and 16 cm were loading frame monotonic until the rupture, in one on the sides of the joint. The study analyzed the behavior of the system slab/joint for different metallic devices of transfer, being them: dowels of circular and square sections, plates and disks, adopting two devices for model. Two different types of joints were analyzed, according to the typology, as sawed and molded joints. The tests data show that the increase in the thickness of the pavement increases in resistant capacity, for the two types of joints. Already the typology of the joints can influence in the maximum load of the model, once the concrete presence below the device causes variation in the vertical rigidity of the group, known as interaction concrete-dowel, taking the sawed model rupture with a superior load. The loading cycles increased the cracks propagation under the load side, they reduced the load crack partly of the models, but they didn\'t reduce ultimate force. The disk plate, in function of the collected data, presented the best performance in relation to the others, and it is suggested as the preferential transfer device of load to obtain a larger efficiency of the system.
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Ligações e armaduras de lajes em vigas mistas de aço e de concreto. / Connections and slab reinforcement of concrete-steel composite beams.Fuzihara, Marisa Aparecida Leonel da Silva 24 November 2006 (has links)
As vigas mistas de aço-concreto vêm ganhando espaço no mundo e no Brasil. Sua grande vantagem é o aproveitamento das melhores propriedades que cada material apresenta. O aço possui excelente resposta para esforços tanto de tração como os de compressão e o concreto para esforços de compressão. As vigas mistas envolvem basicamente o perfil de aço, a laje de concreto, os conectores e as armaduras. Na interface destes materiais ocorrem fenômenos que merecem destaque, como grau de interação, cisalhamento na superfície de contato e separação vertical. Os procedimentos normalmente empregados em projetos de estruturas convencionais de concreto armado e de aço fornecem muitas respostas para questões semelhantes nas estruturas mistas, porém, no geral, não abordam a questão mais relevante que é a ligação entre o aço e o concreto. Na vizinhança dos conectores de cisalhamento, a laje da viga mista de aço e concreto está sujeita a uma combinação de cisalhamento longitudinal e momento fletor transversal, por isso a interface é a região que necessita de uma análise cuidadosa. Esses aspectos são os objetos principais da pesquisa. Adicionalmente são discutidos os procedimentos de projetos adotados pelas normas brasileira (NBR 8800-86), americana (AISC) e européia (EUROCODE 4): nas regiões de ligações entre os materiais por meio de conectores em perfis de aço sob lajes de concreto, no controle da fissuração em seções solicitadas por momentos negativos e nas armaduras transversais de costura. / The use of composite steel-concrete beams is increasing in Brazil and in the world, because this is to take advantage of the best properties of each material. Steel has an excellent response to compression and tension and concrete has to compression. Composite beams include basically the steel beam, concrete slab, connectors and reinforcement. Some phenomena in the interface of these materials must be considered, like the degree of interaction, shear in contact surface and uplift. The procedures normally taken in design of conventional structures of reinforced concrete and steel structures supply many answers to similar questions in composite structures, but, in general, they do not approach the most relevant question which is the bond between steel and concrete. The slab of composite steel-concrete beam is affected by a combination of longitudinal shear and transverse flexure, in the neighborhood of the shear connector. The analysis of the behavior of the slab and the reinforcement are main aspect of the work. In addition, some design procedures adopted by Brazilian Standard (NBR 8800-86), American Standard (AISC-2005) and European standard (EUROCODE 4) are discussed, in especial the related to connects, the crack control in sections with hogging moment and in transverse reinforcement.
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Diferenciação entre microRNAs expressos na hipertrofia cardíaca fisiológica e patológicaMartinelli, Nidiane Carla January 2016 (has links)
A hipertrofia cardíaca é uma adaptação do coração frente a estímulos de crescimento, sejam eles patológicos e irreversíveis como a sobrecarga de pressão ou de volume, ou fisiológicos e reversíveis como a gravidez e o exercício físico. A hipertrofia derivada de estímulos patológicos é conhecida como mal adaptativa enquanto que a hipertrofia proveniente de estímulos ditos fisiológicos é conhecida como benéfica ou adaptativa. Embora ambas hipertrofias tenham fatores em comum no que diz respeito ao crescimento do cardiomiócito e adaptações moleculares, elas acabam divergindo para desfechos completamente diferentes. A hipertrofia patológica evolui para um quadro de disfunção cardíaca ao passo que a hipertrofia fisiológica não acarreta nenhum dano funcional ao miocárdio. Essa linha tênue entre um fenótipo e outro envolve mecanismos celulares complexos que ainda precisam ser esclarecidos. Dentro deste cenário, os microRNAs aparecem como reguladores de diversos processos celulares, e têm sido associados ao crescimento miocárdico. Portanto, nosso objetivo foi comparar o padrão de expressão de microRNAs entre os modelos de hipertrofia fisiológica, induzido por natação (SWIM), e o modelo de hipertrofia patológica, induzida por bandeamento aórtico transtorácico (TAC). As análises foram realizadas após 28 dias para o modelo de natação, e 35 dias para o modelo de TAC. A comparação foi realizada através da técnica de microarranjo de microRNAs (Affymetrix). Interessantemente, apenas 20 microRNAs apresentaram níveis de expressão distinta entre os dois modelos de hipertrofia. Destes, 12 microRNAs apresentaram aumento de expressão (miR-193a-3p, miR-299a-5p, miR- 127-5p, miR-214-5p, miR-188-5p, miR-326-3p, miR-6395, miR-547-3p, miR-199a-5p, miR-381-3p, miR-223-3p e miR-199b-5p) e 8 estavam com seus níveis diminuídos (miR11 708-5p, miR-30c-1-3p, miR-22-5p, miR-6921-5p, miR-30a-3p, miR-30e-3p, miR-27a-5p and miR-6975-5p) no grupo TAC em relação ao grupo SWIM. Além disso, apenas 3 microRNAs, miR-21a-5p, miR-206-3p e miR-1983, apresentaram aumento de expressão tanto no grupo TAC quanto no grupo SWIM em comparação aos grupos SHAM e Sedentário, respectivamente. Após isso, foi realizada uma busca por possíveis alvos destes microRNAs na base de dados KEGG Pathway que identificou 4 rotas enriquecidas (665 genes) entre os alvos dos microRNAs reduzidos, e 80 rotas (3394 genes) fortemente associadas aos microRNAs que estavam aumentados no grupo TAC comparado ao SWIM. Conclui-se que existem microRNAs específicos para o desenvolvimento da hipertrofia cardíaca fisiológica, bem como patológica conforme os dados obtidos na análise de microarranjo. Além disso, os possíveis alvos destes microRNAs parecem estar envolvidos em rotas bastante envolvidas no crescimento celular, sobrevivência e adaptação cardíaca. / Cardiac hypertrophy is a heart adaptation in response to growth stimuli whether pathological and irreversible such as pressure overload or physiological and reversible as pregnancy and exercise. Hypertrophy because of pathological stimuli is known as mal adaptive while the one that comes from physiological triggers is known as beneficial or adaptive. Although both have similarities about cardiomyocyte growth and molecular adaptations, they diverge to distinct outcomes. The pathological hypertrophy evolves to a pattern of cardiac dysfunction while the physiological one does not cause any damage to the heart. This tenuous line between those phenotypes involves complex cellular mechanisms that need to be clarified. In this context, microRNAs are considered as regulators of many biological processes, and have been associated to myocardial growth. Therefore, our aim was to compare microRNA expression between physiological (swiminduced) and pathological (TAC-induced) hypertrophy. The analysis was performed after 28 days for SWIM protocol and 35 days for TAC model. The comparison was done using microRNA microarray technology (Affymetrix). Interestingly, only 20 microRNAs were differential expressed between both models. Out of those, 12 were up regulated (miR- 193a-3p, miR-299a-5p, miR-127-5p, miR-214-5p, miR-188-5p, miR-326-3p, miR-6395, miR-547-3p, miR-199a-5p, miR-381-3p, miR-223-3p and miR-199b-5p) while 8 were down regulated in TAC group compared to SWIM group. Besides, only 3 microRNAs, miR-21a-5p, miR-206-3p and miR-1983, were upregulated in TAC and SWIM model compared to SHAM and SED groups. After that, a search at KEGG Pathway database retrieved 4 pathways (665 genes) enriched with targets from microRNAs downregulated and 80 pathways (3394 genes) enriched with targets from up-regulated microRNAs in in 13 TAC group compared to SWIM group. In conclusion, there are microRNAs specific committed to the physiological cardiac hypertrophy development as well to the pathological cardiac growth as observed in our microarray data. Furthermore, the possible targets of those microRNAs could be involved in pathways associated with cellular growth, survival and cardiac adaptation.
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Search for a heavy scalar boson in the ZZ->2l2v channel with the CMS experiment at the LHC using 2016 data at 13 TeVDelannoy, Hugo 05 April 2019 (has links) (PDF)
Les premières années d’opération du LHC à 7 et 8 TeV ont permis de tester de nombreux aspects du modèle standard (MS) de la physique des particules avec comme point d’orgue la découverte d’un boson scalaire compatible avec celui du MS. Cependant, malgré son succès, le MS n’explique pas tout. De nombreux modèles essayent donc de combler les manques du MS et certains requièrent un secteur scalaire étendu. Cette thèse étudie ce secteur scalaire et présente en particulier la recherche d’un nouveau boson scalaire massif en utilisant les 35,9 fb-1 de données récoltées au LHC à 13 TeV en 2016. Cette recherche se concentre sur le processus H→ZZ→2l2ν où l est un electron ou un muon, et ν un neutrino. Une analyse statistique des distributions de masse transverse du boson (Z→l^+ l^-) reconstruit et de l’énergie transverse manquante est réalisée en catégories de jets et de saveurs de lepton après une sélection des événements dans le but de faire sortir un signal potentiel par rapport aux bruits de fond. Divers scenarios de masse, largeur et de mode de productions sont testés pour un boson scalaire H et aucun excès significatif n’est observé dans les données pour une gamme de masses allant de 300 GeV à 3 TeV. Des limites supérieures à 95% de niveau de confiance sur la section efficace σ(pp→H→ZZ) sont établies. Ces résultats sont combinés avec deux autres canaux étudiés par la collaboration CMS :H→ZZ→4l et H→ZZ→2l2q, où q représente un quark. Cette combinaison est publiée (CMS Collaboration, « Search for a new scalar resonance decaying to a pair of Zbosons in proton-proton collisions at √s=13 TeV », JHEP, vol. 06, pp. 127,2018) et aucun excès significatif n’est observé dans les données pour des masses entre 130 GeV et 3 TeV. Un bruit de fond majeur pour cette analyse est le bruit de fond instrumental Z+jets. Son estimation est faite non pas par simulation mais en utilisant les données récoltées par CMS. Un chapitre entier est dédié à l’étude de ce bruit de fond et les incertitudes sur celui-ci sont estimées en détails pour la première fois. En particulier les sources d’incertitudes sont divisées en celles d’origine statistique, systématique et celles inhérentes à la méthode d’estimation de ce bruit de fond. Elles sont respectivement de l’ordre de 50%, 50% et 10%. / The first years of operation of the LHC at 7 and 8TeV (run 1) allowed to probemany aspects of the Standard Model (SM) of particle physics, confirming many predictions up to a high level of precision. An awaited event was the discovery of a scalar boson compatible with the SM in 2012. However, despite its success, the SM cannot explain everything on its own. Models going beyond the SM try to address such issues, and in particular classes of BSM theories require an extended scalar sector.The scope of this thesis falls within the direct search for heavy BSM scalar boson(H) using 35,9 fb-1 of data taken at LHC at 13TeV during 2016 operations. Inparticular, the thesis focuses on H→ZZ→2l2ν where l is an electron or a muon, and ν a neutrino.A statistical analysis of the transversemass distributions of the reconstructed Z boson and the missing transverse energy isperformed in categories of jet and lepton flavour after selecting events in order to enhancethe number of potential signal events in comparison to background events. Variousscenarii of masses, widths and production mechanisms (gluon fusion and vector boson fusion) are tested and no excess is observed in data compared to backgroundestimations for a scalar mass between 300 GeV and 3TeV. Upper exclusion limits onthe cross section of a potential signal are set using the CLs method.The results of this analysis are combined with two other channels studied by theCMS collaboration: H→ZZ→4l and H→ZZ→2l2q, where q is a quark.This combinationhas been published (CMS Collaboration, « Search for a new scalar resonance decaying to a pair of Zbosons in proton-proton collisions at √s=13 TeV », JHEP, vol. 06, pp. 127,2018) and no significanthint for BSM physics is observed for a scalar mass between 130 GeV and 3TeV.A critical background to control for this analysis is the Z+jet background. Its estimation is done using a data-driven method.A full chapter is dedicated to the study of this background. The present thesis is the first time that the uncertainties on the data-driven estimationof the Z+jet background are estimated in detail. Uncertainties are dividedinto statistical uncertainties, systematic uncertainties and uncertainties inherent to themethod, the latter being computed from a closure test of the method and evaluated to10%. The relative statistical and systematic uncertainties are both of the order of 50%. / Option Physique du Doctorat en Sciences / info:eu-repo/semantics/nonPublished
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Estudo da energia transversal eletromagnética em colisões Pb-Pb a √SNN = 2.76 TeV com o experimento ALICE / Study of electromagnetic transverse energy in Pb-Pb collisions at √SNN = 2.76 TeV with ALICELima, Caio Eduardo Ferreira 15 May 2017 (has links)
A física de altas energias, mais especificamente o estudo de colisões entre de íons pesados relativísticos tem como objetivo o estudo do comportamento de quarks e glúons em condições extremas de temperatura, pressão e densidade. Tais condições levam à formação de um novo estado da matéria chamado Plasma de Quarks e Glúons (QGP, do inglês Quark-Gluon Plasma). Medidas de observáveis globais tem sido usadas como uma importante ferramenta para a caracterização desse novo estado. Entre esses observáveis, a energia transversal por unidade de rapidez (dET/dy) das partículas emitidas em uma colisão entre íons pesados pode ser usada como evidência da formação do QGP. Este trabalho propõe um procedimento para obtenção da energia transversal eletromagnética, que é um importante componente da energia transversal total, em colisões Pb-Pb no experimento ALICE no LHC. O estudo foi feito através de simulações de Monte Carlo e validou o procedimento proposto com uma diferença sistemática em função da centralidade em torno de 2%. / High energy physics with heavy ion collisions studies quarks and gluons under extreme conditions of temperature, pressure and density. Such conditions lead to the formation of a new state of matter called the Quark-Gluon Plasma (QGP). The measurement of global observables have been used as an important tool for the characterization of this new state. Among these observables, the transverse energy per unit of rapidity (dET/dy) from particles emitted in a heavy ion collision can be used as evidence of QGP formation. The work proposes a procedure to obtain the transverse electromagnetic energy, an important component of total transverse energy, in Pb-Pb collisions measured by the LHC-ALICE experiment. The study was done using Monte Carlo simulations, and validated the proposed procedure with a systematic difference as function of the centrality around 2%.
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Structural behaviour of concrete segmental lining tunnels : towards design optimisationGil Lorenzo, Saleta January 2018 (has links)
The deployment of engineering models and design methods divorced from the effect that mechanised shield tunnelling with tunnel boring machines (TBMs) has on concrete segmental linings (CSLs) can lead to either material waste or structural damage within the tunnel design life. Most research to date on CSL behaviour during construction neglects the sequential ring loading and TBM-lining transverse interactions, which this thesis proved to be key in the short and long term behaviour of CSLs and whose study is essential if the design and maintenance of CSL structures is ever to be optimised. This thesis investigates the longitudinal and transverse behaviour of CSL structures simultaneously backfilled with bicomponent grouts (BGs) during tunnelling, and how this early response influences long term behaviour. The research work is drawn on three pillars that enable cross-validation of conclusions: analytical models, three-dimensional numerical simulations and the interpretation of the Crossrail's Thames tunnel (CTT) field data, which included distributed fibre optic strain (DFOS) data. A theoretical framework ranging from construction loading scenarios to the mechanisms underlying structural damage is described for the future development of limit state design methods. Analytical models of longitudinal behaviour are also proposed. The study of joint geometries, temporary spear bolts and DFOS sensing in CSL construction monitoring is included as ancillary research. The solution developed for a sequential elastic rod subjected to a trilinear temperature profile and in shear interaction with the elastic ground predicts accurately the early tunnel pre-stressing relaxation caused by grout hardening, e.g. ≈50% in the CTT. The proposed sequential elastic beam model, which incorporates the effects of stage-varying net TBM moments, transverse loads and lining pressure gradients within the tunnel unsupported length, estimates satisfactorily the history of tunnel beam response during construction for a realistic expression of the lining stiffness. A potential damage assessment method for the early detection of tunnel sections prone to ring joint damage was proposed. The TBM-lining transverse interaction determines the CSL ring behaviour at the early stages of tunnelling. The ring response resultant from this interaction is irrecoverable and contributes to the long term total deformations and internal forces; in tunnels excavated in grounds with Ko≈1, it becomes the major source of ring distortion. The main transverse actions are the sealing pressures, which are inversely related to the tail clearance, and the transverse load of oblique hydraulic jacks. When the non-bedded rings are eccentric with respect to the shield tail, the ring distortion increases the risk of cracking near the rear corners and spalling at the ram pad interspaces of constrained segments. The ring distortion is directly related to the pressure gradients, the unsupported length and the ring flexibility. When individual segments rotate outwards under the action of transverse ram loads, e.g. the outer springline segment during pronounced TBM steering around a horizontal curve, the localised action of the sealing pressures can result in longitudinal cracking at the intrados of the segment front. This study represents a qualitative leap towards the optimisation of CSL design, shifting the attention of researchers and designers to TBM-lining transverse interactions as the most determinant factor of structural response during construction in CSLs simultaneously backfilled with BGs.
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New insight into models of cardiac caveolae and arrhythmiaZhu, Chenhong 01 July 2015 (has links)
Recent studies suggest that cardiomyocyte membrane microdomains, caveolae and transverse tubules, play a key role in cardiac arrhythmia. Mutation of caveolin-encoding genes CAV3, co-expressed with genes of caveolae ion channels, leads to a late persistent sodium currents and delayed repolarization stage, called LQT9 disease. A simplified three-current model is created to largely reduce the well-known Pandit rat ventricular myocyte model. The mathematical tractability of the three-current model allows us to conduct asymptotic analysis and efficiently estimate action potential duration. Improvement in the description of the mechanism for caveolae sodium current is incorporated into the three-current model utilizing a probability density approach for the four-state caveolae neck-channel coupling. The prolongation of action potentials and the formation of potential arrhythmia are shown to arise if caveolae neck open probability varies. A minimal model of the Ca2+ spatial distribution of CICR units illustrates the transverse tubule remodeling in failing myocyte causes dysfunction in the Ca2+ profile. With regards to discrimination of protein localization, which is widely used in biological experiments, the bagging pruned decision tree algorithm is tested to be one of the algorithms with best performance on the large data set, and it succeeds in extracting information to be highly predictive on test data. Parallel computation technique is applied to accelerate the speed of implementation in K-nearest neighbor learning algorithms on big data sets.
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Surface and Interface Magnetism in Nanostructures and Thin FilmsFrey, Natalie A 03 April 2008 (has links)
Nanostructured systems composed of two or more technologically important materials are useful for device applications and intriguing for the new fundamental physics they may display. Magnetism at the nanoscale is dominated by size and surface effects which combined with other media lead to new spin dynamics and interfacial coupling phenomena. These new properties may prove to be useful for optimizing sensors and devices, increasing storage density for magnetic media, as well as for biomedical applications such as drug delivery, MRI contrast enhancement, and hyperthermia treatment for cancer. In this project we have examined the surface and interface magnetism of composite nanoparticles and multilayer thin films by using conventional DC magnetization and AC susceptibility as well as transverse susceptibility, a method for directly probing the magnetic anisotropy of materials. Au and Fe3O4 synthesized together into three different nanoparticle configurations and ranging in size for 60 nm down to 9nm are used to study how the size, shape, and interfaces affect the most fundamental properties of magnetism in the Au-Fe3O4 system. The findings have revealed ways in which the magnetic properties can be enhanced by tuning these parameters. We have shown that by changing the configurations of the Au and Fe3O4 particles, exotic behavior can be observed such as a large increase in anisotropy field (H[subscript]K ranging from 435 Oe to 1650 Oe) and the presence of exchange bias. Multilayer thin films have been studied as well which combine the important classes of ferromagnetic and ferroelectric materials. In one case, barium hexaferrite/barium strontium titanate thin films, the anisotropic behavior of the ferromagnet is shown to change due to the introduction of the secondary material. In the other example, CrO2/Cr2O3 bilayers, exchange coupling is observed as Cr2O3 is an antiferromagnet as well as a ferroelectric. This coupling is manifest as a uniaxial anisotropy rather than the unidirectional anisotropy associated with exchange biased bilayers. Not only will such multifunctional structures will be useful for technological applications, but the materials properties and configurations can be chosen and tuned to further enhance the desired functional properties.
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