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Molecular mechanisms underlying the regulation of brain-derived neurotrophic factor (BDNF) translation in dendrites

Pinheiro, Vera Lúcia Margarido
Fonte: Universidade de Coimbra Publicador: Universidade de Coimbra
Tipo: Dissertação de Mestrado
Português
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A especificidade espacial e temporal subjacente à diversidade de processos de plasticidade sináptica que ocorrem no sistema nervoso central está profundamente relacionada com a disponibilidade da proteína brain-derived neurotrophic factor (BDNF) em domínios sub-celulares distintos, especialmente na área pós-sináptica. Contudo, os mecanismos moleculares que regulam a síntese proteica de BDNF nas dendrites estão ainda por desvendar. Assim, o principal objectivo deste trabalho foi investigar alguns dos mecanismos de regulação da síntese de BDNF em diferentes regiões das dendrites. Em particular, foram estudados os mecanismos envolvidos na regulação dos níveis de BDNF em resposta à estimulação eléctrica in vitro e a um estímulo epileptogénico in vivo, e a contribuição da maquinaria de síntese proteica para essas alterações. Usando imunocitoquímica demonstrámos que o aumento dos níveis da proteína BDNF resultante da actividade neuronal está dependente da acção de alguns elementos no processo de síntese proteica. Em particular, a proteína ribossomal S6 parece ter um papel preponderante nas fases iniciais da tradução, enquanto a cinase de proteínas Aurora A, envolvida em mecanismos de tradução dependentes de 3’UTR...

Simulação numérica da influência dos fluxos de superfície em ciclones na costa leste do sul do Brasil; Numerical simulation of the role of surface heat and moisture fluxes in cyclones at the southeastern coast of Brasil.

Gozzo, Luiz Felippe
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 12/05/2010 Português
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O papel dos fluxos de superfície de calor sensível e latente (FCSL) em dois ciclones extratropicais com desenvolvimento distinto na costa do sul do Brasil foi avaliado a partir de simulações numéricas utilizando o modelo de área limitada WRF versão 2.2. Em um dos ciclones, a circulação se originou em baixos níveis e propagou-se para a média troposfera (ciclone 1). No outro ciclone (ciclone 2) a circulação originou-se em níveis médios e propagou-se até a superfície. Foram realizadas simulações numéricas com e sem FCSL para cada um dos ciclones. A trajetória do ciclone 1 foi fortemente alterada na ausência de FCSL, exibindo deslocamento incorreto (para nordeste) e menor tempo de vida. Este comportamento esteve associado às mudanças no padrão de advecção de temperatura em baixos níveis e à diminuição da convergência de massa induzida pelo calor sensível, na ausência de FCSL. No experimento sem FCSL, ocorre também desacoplamento entre o ciclone em superfície e a onda em níveis médios e altos, com consequente enfraquecimento do sistema. O aumento da estabilidade estática e o mecanismo de convergência de Ekman são responsáveis por menor convergência nas regiões frontais na ausência de FCSL. A relação de fase entre os campos de altura geopotencial e temperatura em baixos níveis e o perfil vertical de aquecimento diabático também mostram condições mais favoráveis ao desenvolvimento do ciclone na presença dos FCSL. O ciclone 2 não teve a trajetória alterada entre as duas simulações. A advecção de temperatura e a convergência em baixos níveis devido ao calor sensível foram semelhantes...

Simulações de sistemas em nanoescala : membranas de grafeno e espectroscopia fora do equilíbrio; Simulations of nanoscale systems : from graphene membranes to non equilibrium spectroscopy

Gustavo Brunetto
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 26/02/2014 Português
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Nas últimas décadas, sucessivas descobertas em materiais baseados em carbono abriram uma nova era na ciência dos materiais. Exemplos destas descobertas são os fulerenos, nanotubos de carbono e, mais recentemente, o grafeno. O grafeno é uma rede bi-dimensional de unidades hexagonais de carbono com ligações do tipo sp2. Grafeno apresenta propriedades mecânicas e eletrônicas não usuais e muito interessantes e devido a estas propriedades é um dos materiais mais promissores para aplicações em diversas áreas da tecnologia tais como eletrônica, militar, aeroespa- cial, dispositivos e outras. Entretanto, há algumas barreiras que devem ser superadas a fim de utilizar o grafeno em aplicações práticas. O grafeno, em sua forma pura, é um semicondutor com gap zero. Esta característica impõe sérias limitações em algumas aplicações em eletrônica, tal como, transistores. Além do mais, é muito difícil a síntese de grandes porções de grafeno que possuam poucos ou nenhum defeito estrutural. Através de simulações de primeiros princípios, propomos uma rota de síntese a partir da de-hidrogenação completa do grafeno poroso para a obtenção de um alótropo de carbono conhecido como BPC. Cálculos de estrutura eletrônica mostraram que o BPC possui um gap da ordem de 0...

Unfolding of cardosin A in organic solvents and detection of intermediaries

Sarmento, Ana Cristina; Oliveira, Cláudia S.; Pereira, Anabela; Esteves, Valdemar I.; Moir, Arthur J.G. Moir; Saraiva, Jorge; Pires, Euclides; Barros, Marlene
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
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In the present study the relationship between conformational stability and enzymatic activity in the presence of organic solvents (OS) was investigated. We have found that cardosin A, the model protease investigated in this work, inactivates through a biphasic mechanism, which is incipient in aqueous buffer and becomes visible in the presence of hydrophilic OS. In fact, in OS this inactivation originates stable intermediaries thatwere detected in acetonitrile. This biphasic mechanism can be described in two phases: an initial one, where OS induce alterations that affect the active site cleft and global mobility, but with little interference on the global protein conformation, and, a second phase, where there is a global change in protein conformation with concomitant activity loss. It is shown that in the presence of hydrophilic OS there is a larger mobility of the enzyme, revealed by limited proteolysis, probably due to a weakening of hydrophobic interactions within the protein core.

Análise do fluxo polimérico em micro cavidades revestidas com diamante

Santos, Cátia Sofia Castanheira dos
Fonte: Universidade de Aveiro Publicador: Universidade de Aveiro
Tipo: Dissertação de Mestrado
Português
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Com o aumento da produção de micro-componentes é necessário vencer vários desafios tecnológicos presentes na adaptação do processo de moldação por injeção: desgaste da ferramenta moldante, elevada influência do mecanismo de transferência de calor, razão de aspeto das cavidades a preencher, reologia do material à escala micrométrica, entre outros. Uma possível solução passa por aplicar sistemas de revestimento avançados que contenham elevada dureza, elevada condutividade térmica, elevada capacidade de resistência ao choque térmico e baixo coeficiente de atrito. Neste trabalho, um postiço microestruturado foi revestido com nitreto de crómio (comercial) numa das vias de moldacão e revestido com nanodiamante na via oposta, através de uma metodologia adequada e da tecnologia deposição química a partir da fase de vapor por filamento quente (HFCVD). Este postiço foi posteriormente utilizado para a produção de micro-peças de polipropileno, com o objetivo de se analisar a posição relativa da linha de soldadura e, assim, avaliar o fluxo do polímero semicristalino fundido nas micro-cavidades. Numa primeira fase, analisaram-se através das técnicas de caracterização SEM e espetroscopia de Raman, a morfologia...

Force production by depolymerizing microtubules: A theoretical study

Molodtsov, M. I.; Grishchuk, E. L.; Efremov, A. K.; McIntosh, J. R.; Ataullakhanov, F. I.
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
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Chromosome movement during mitosis is powered in part by energy released through the depolymerization of kinetochore microtubules (MTs). Strong but indirect evidence suggests the existence of a specialized coupling between kinetochores and MT plus ends that enables this transduction of chemical energy into mechanical work. Analysis of this phenomenon is important for learning how energy is stored within the MT lattice, how it is transduced, and how efficient the process can be, given coupling devices of different designs. Here we use a recently developed molecular-mechanical model of MTs to examine the mechanism of disassembly dependent force generation. Our approach is based on changes in tubulin dimer conformation that occur during MT disassembly. We find that all of the energy of polymerization-associated GTP hydrolysis can be stored as deformations of the longitudinal bonds between tubulin dimers, and its optimal use does not require the weakening of lateral bonds between dimers. Maximum utilization of this stored energy and, hence, the generation of the strongest possible force, is achieved by a protofilament power-stroke mechanism, so long as the coupling device does not restrict full dissociation of the lateral bonds between tubulin dimers.

Structure and function of the globin and globin gene from the Antarctic mollusc Yoldia eightsi.

Dewilde, Sylvia; Angelini, Elisa; Kiger, Laurent; Marden, Michael C; Beltramini, Mariano; Salvato, Benedetto; Moens, Luc
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 15/02/2003 Português
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The mechanism of adaptation of haemoglobin from the Antarctic mollusc Yoldia eightsi to its low-temperature environment is a decrease in the oxygen affinity via an increased ligand-dissociation rate. At 2 degrees C this haemoglobin has an oxygen affinity similar to other haemoglobins at 25 degrees C. At 25 degrees C, Yoldia haemoglobin shows a low oxygen affinity, resembling that of human deoxyhaemoglobin. The mechanism involves a lower binding energy to oxygen, suggesting a loss or weakening of the usual hydrogen bond, leading to a higher oxygen-dissociation rate. However, Yoldia haemoglobin has the usual distal and proximal histidines, so the primary structure alone does not provide an obvious explanation for the low affinity. The CO-binding kinetics are biphasic, with the fraction of slow phase increasing at higher protein concentrations, indicating the formation of dimers or a higher level of polymerization. The protein-protein interaction appears to be of hydrophobic nature, since it can be partially reversed by addition of ethylene glycol as co-solvent. While the CO-association rates differ by a factor of 10, the oxygen equilibrium data could be simulated with a single affinity. The Yoldia haemoglobin gene contains three introns...

Failure of Elastic Fiber Homeostasis Leads to Pelvic Floor Disorders

Liu, Xiaoqing; Zhao, Yun; Pawlyk, Basil; Damaser, Margot; Li, Tiansen
Fonte: American Society for Investigative Pathology Publicador: American Society for Investigative Pathology
Tipo: Artigo de Revista Científica
Publicado em /02/2006 Português
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Pelvic floor disorders, a group of conditions affecting adult women, include pelvic organ prolapse and urinary incontinence. Vaginal childbirth and aging are risk factors, and weakening of the pelvic support structures is a major aspect of the pathology. However, the underlying molecular mechanism remains unknown. Female reproductive organs are rich in elastic fibers that turn over slowly in most adult tissues but undergo massive remodeling in the reproductive organs through pregnancy and birth. Here we show that a failure to maintain elastic fiber homeostasis in mice causes pelvic floor disorders. Lysyl oxidase-like-1 (LOXL1), a protein essential for the postnatal deposition of elastic fibers, was highly expressed and regulated in the reproductive tract of the mouse, and its expression was diminished during aging. LOXL1 deficiency caused an inability of reproductive tissues to replenish elastic fibers after parturition, leading to pelvic organ prolapse, weakening of the vaginal wall, paraurethral pathology, and lower urinary tract dysfunction. These data demonstrate the importance of elastic fibers for maintaining structural and functional integrity of the female pelvic floor. Our findings raise the possibility that a failure of elastic fiber homeostasis...

Latency-Related Development of Functional Connections in Cultured Cortical Networks

le Feber, J.; van Pelt, J.; Rutten, W.L.C.
Fonte: The Biophysical Society Publicador: The Biophysical Society
Tipo: Artigo de Revista Científica
Publicado em 22/04/2009 Português
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To study plasticity, we cultured cortical networks on multielectrode arrays, enabling simultaneous recording from multiple neurons. We used conditional firing probabilities to describe functional network connections by their strength and latency. These are abstract representations of neuronal pathways and may arise from direct pathways between two neurons or from a common input. Functional connections based on direct pathways should reflect synaptic properties. Therefore, we searched for long-term potentiation (this mechanism occurs in vivo when presynaptic action potentials precede postsynaptic ones with interspike intervals up to ∼20 ms) in vitro. To investigate if the strength of functional connections showed a similar latency-related development, we selected periods of monotonously increasing or decreasing strength. We observed increased incidence of short latencies (5–30 ms) during strengthening, whereas these rarely occurred during weakening. Furthermore, we saw an increased incidence of 40–65 ms latencies during weakening. Conversely, functional connections tended to strengthen in periods with short latency, whereas strengthening was significantly less than average during long latency. Our data suggest that functional connections contain information about synaptic connections...

Ethylene Interacts with Abscisic Acid to Regulate Endosperm Rupture during Germination: A Comparative Approach Using Lepidium sativum and Arabidopsis thaliana[W][OA]

Linkies, Ada; Müller, Kerstin; Morris, Karl; Turečková, Veronika; Wenk, Meike; Cadman, Cassandra S.C.; Corbineau, Françoise; Strnad, Miroslav; Lynn, James R.; Finch-Savage, William E.; Leubner-Metzger, Gerhard
Fonte: American Society of Plant Biologists Publicador: American Society of Plant Biologists
Tipo: Artigo de Revista Científica
Publicado em /12/2009 Português
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The micropylar endosperm cap covering the radicle in the mature seeds of most angiosperms acts as a constraint that regulates seed germination. Here, we report on a comparative seed biology study with the close Brassicaceae relatives Lepidium sativum and Arabidopsis thaliana showing that ethylene biosynthesis and signaling regulate seed germination by a mechanism that requires the coordinated action of the radicle and the endosperm cap. The larger seed size of Lepidium allows direct tissue-specific biomechanical, biochemical, and transcriptome analyses. We show that ethylene promotes endosperm cap weakening of Lepidium and endosperm rupture of both species and that it counteracts the inhibitory action of abscisic acid (ABA) on these two processes. Cross-species microarrays of the Lepidium micropylar endosperm cap and the radicle show that the ethylene-ABA antagonism involves both tissues and has the micropylar endosperm cap as a major target. Ethylene counteracts the ABA-induced inhibition without affecting seed ABA levels. The Arabidopsis loss-of-function mutants ACC oxidase2 (aco2; ethylene biosynthesis) and constitutive triple response1 (ethylene signaling) are impaired in the 1-aminocyclopropane-1-carboxylic acid (ACC)-mediated reversion of the ABA-induced inhibition of seed germination. Ethylene production by the ACC oxidase orthologs Lepidium ACO2 and Arabidopsis ACO2 appears to be a key regulatory step. Endosperm cap weakening and rupture are promoted by ethylene and inhibited by ABA to regulate germination in a process conserved across the Brassicaceae.

Interaction of CarD with RNA Polymerase Mediates Mycobacterium tuberculosis Viability, Rifampin Resistance, and Pathogenesis

Weiss, Leslie A.; Harrison, Phillip G.; Nickels, Bryce E.; Glickman, Michael S.; Campbell, Elizabeth A.; Darst, Seth A.; Stallings, Christina L.
Fonte: American Society for Microbiology Publicador: American Society for Microbiology
Tipo: Artigo de Revista Científica
Publicado em /10/2012 Português
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Mycobacterium tuberculosis infection continues to cause substantial human suffering. New chemotherapeutic strategies, which require insight into the pathways essential for M. tuberculosis pathogenesis, are imperative. We previously reported that depletion of the CarD protein in mycobacteria compromises viability, resistance to oxidative stress and fluoroquinolones, and pathogenesis. CarD associates with the RNA polymerase (RNAP), but it has been unknown which of the diverse functions of CarD are mediated through the RNAP; this question must be answered to understand the CarD mechanism of action. Herein, we describe the interaction between the M. tuberculosis CarD and the RNAP β subunit and identify point mutations that weaken this interaction. The characterization of mycobacterial strains with attenuated CarD/RNAP β interactions demonstrates that the CarD/RNAP β association is required for viability and resistance to oxidative stress but not for fluoroquinolone resistance. Weakening the CarD/RNAP β interaction also increases the sensitivity of mycobacteria to rifampin and streptomycin. Surprisingly, depletion of the CarD protein did not affect sensitivity to rifampin. These findings define the CarD/RNAP interaction as a new target for chemotherapeutic intervention that could also improve the efficacy of rifampin treatment of tuberculosis. In addition...

The Digital Commons: Tragedy or Opportunity? The Effect of Crowdsourced Digital Goods on Innovation and Economic Growth

Nagle, Francis
Fonte: Harvard University Publicador: Harvard University
Tipo: Thesis or Dissertation; text Formato: application/pdf
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The classic economic concept of the tragedy of the commons occurs when individuals overuse a public good, resulting in the complete depletion of the good. Comparatively, in the digital world public goods are non-rival and essentially infinitely abundant. However, the nearly infinite supply of a public digital good can still be tragic, albeit in a different manner. For example, the rise of the free crowdsourced digital good Wikipedia essentially destroyed billions of dollars of economic value in the encyclopedia industry. Despite this apparent destruction of value, the reduction in prices for many digital goods also represents a great opportunity. Firms are increasingly relying on the crowd to help shape future products, provide value for their customers, and build software crucial to the firm’s production process. This phenomenon is leading to a weakening of firm boundaries and a change in the nature of the firm’s innovative processes. My dissertation is comprised of four studies that explore this phenomenon to better understand the transformative nature of the digital commons. The first chapter, “Innovating Without Information Constraints: Organizations, Communities, and Innovation When Information Costs Approach Zero” (w/ Elizabeth Altman...

Fast software transactions

Spear, Michael F. (1977 - ); Scott, Michael L. (1959 - )
Fonte: University of Rochester Publicador: University of Rochester
Tipo: Tese de Doutorado Formato: Number of Pages:xxi, 266 leaves
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Thesis (Ph. D.)--University of Rochester. Dept. of Computer Science, 2009.; In the past, only a small group of highly-skilled programmers were expected to write programs that used multiple processors simultaneously. However, microprocessor vendors have recently turned to multi-core chip designs as the most profitable way to increase performance. We are now seeing multi-core processors in desktops, laptops, handheld computers, and even embedded devices. As a result, parallel programming is becoming a core competency for all programmers. When concurrent threads of a parallel program share data, they must ensure that certain sets of accesses to shared memory execute as indivisible operations (that is, the regions must appear to execute atomically). The dominant mechanism for providing atomicity is mutual exclusion locks. Unfortunately, locks are a very low-level mechanism, widely regarded as too difficult for the average programmer to use correctly. Fortunately, locks are not the only mechanism that provides atomicity. Database transactions (used by millions of programmers to write highly concurrent e-commerce code) also ensure that regions of code execute atomically. Many efforts are underway to employ transactions to implement atomicity within general-purpose programming languages...

Multiscale modeling of upper mantle plasticity: From single-crystal rheology to multiphase aggregate deformation

RATERON, Paul; DETREZ, Fabrice; CASTELNAU, Olivier; BOLLINGER, Caroline; CORDIER, Patrick; MERKEL, Sébastien
Fonte: ELSEVIER Publicador: ELSEVIER
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We report a first application of an improved second-order (SO) viscoplastic self-consistent model for multiphase aggregates, applied to an olivine + diopside aggregate as analogue for a dry upper mantle peridotite deformed at 10 15 s 1 shear strain rate along a 20-Ma ocean geotherm. Beside known dislocation slip systems, this SO-model version accounts for an isotropic relaxation mechanism representing ‘diffusionrelated’ creep mechanisms in olivine. Slip-system critical resolved shear stress (CRSS) are evaluated in both phases – as functions of P, T, oxygen fugacity (fO2) and strain rate – from previously reported experimental data obtained on single crystals and first-principle calculations coupled with the Peierls–Nabarro model for crystal plasticity; and the isotropic-mechanism dependence on T and P matches that of Si selfdiffusion in olivine, while its relative activity is constrained by reported data. The model reproduces well the olivine and diopside lattice preferred orientations (LPO) produced experimentally and observed in naturally deformed rocks, as well as observed sensitivities of multiphase aggregate strength to the volume fraction of the hard phase (here diopside). It shows a significant weakening of olivine LPO with increasing depth...

Theoretical insight into the catalytic cycle of cobalamin-glutamate mutase complex

Miranda Rojas, Sebastián Esteban
Fonte: Universidad de Chile; CyberDocs Publicador: Universidad de Chile; CyberDocs
Tipo: Tesis
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Tesis para optar al grado de Doctor en Química; Las enzimas son capaces de acelerar reacciones químicas con una gran selectividad, permitiendo que la vida sea posible como la conocemos. Glutamato mutasa (GM) es una enzima dependiente de adenosilcobalamina (AdoCbl), la cual cataliza la isomerización reversible de glutamato (glm) a metilaspartato (masp). AdoCbl es un cofactor que consiste en un macrociclo ubicado en el plano ecuatorial denominado corrina, el cual tiene como átomo central un Co+3. Este metal está axialmente coordinado por un ligando desoxiadenosina e intramolecularmente por un grupo 5,6-dimetilbenzimidazol. El mecanismo propuesto para la reacción de isomerización comienza con la unión del sustrato al sitio catalítico, la cual induce la ruptura homolítica del enlace cobalto-carbono (Co-C) del cofactor. Como producto de esta disociación homolítica se forma el radical desoxiadenosilo (Ado•) que luego abstrae un hidrógeno desde el sustrato, formando un radical derivado del sustrato y AdoH. Este radical sufre un reordenamiento que da origen al radical relacionado con el producto, el cual reabstrae el hidrógeno desde AdoH, regenerando Ado•. El ciclo catalítico termina con la formación del enlace Co-C. La generación de intermediarios radicalarios altamente reactivos hace que esta reacción sea muy difícil de llevar a cabo sin reacciones secundarias. Es así que la necesidad de una maquinaria catalítica capaz de controlar los caminos de reacción sea indispensable. Una interesante pregunta en química bioinorgánica es cómo luego de la unión del sustrato...

On the velocity-strengthening behavior of dry friction

Bar-Sinai, Yohai; Spatschek, Robert; Brener, Efim A.; Bouchbinder, Eran
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
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The onset of frictional instabilities, e.g. earthquakes nucleation, is intimately related to velocity-weakening friction, in which the frictional resistance of interfaces decreases with increasing slip velocity. While this frictional response has been studied extensively, less attention has been given to steady-state velocity-strengthening friction, in spite of its potential importance for various aspects of frictional phenomena such as the propagation speed of interfacial rupture fronts and the amount of stored energy released by them. In this note we suggest that a crossover from steady-state velocity-weakening friction at small slip velocities to steady-state velocity-strengthening friction at higher velocities might be a generic feature of dry friction. We further argue that while thermally activated rheology naturally gives rise to logarithmic steady-state velocity-strengthening friction, a crossover to stronger-than-logarithmic strengthening might take place at higher slip velocities, possibly accompanied by a change in the dominant dissipation mechanism. We sketch a few physical mechanisms that may account for the crossover to stronger-than-logarithmic steady-state velocity-strengthening and compile a rather extensive set of experimental data available in the literature...

Auto-Concealment of Supersymmetry in Extra Dimensions

Dimopoulos, Savas; Howe, Kiel; March-Russell, John; Scoville, James
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
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In supersymmetric (SUSY) theories with extra dimensions the visible energy in sparticle decays can be significantly reduced and its energy distribution broadened, thus significantly weakening the present collider limits on SUSY. The mechanism applies when the lightest supersymmetric particle (LSP) is a bulk state-- e.g. a bulk modulino, axino, or gravitino-- the size of the extra dimensions larger than ~$10^{-14}$ cm, and for a broad variety of visible sparticle spectra. In such cases the lightest ordinary supersymmetric particle (LOSP), necessarily a brane-localised state, decays to the Kaluza-Klein (KK) discretuum of the LSP. This dynamically realises the compression mechanism for hiding SUSY as decays into the more numerous heavier KK LSP states are favored. We find LHC limits on right-handed slepton LOSPs evaporate, while LHC limits on stop LOSPs weaken to ~350-410 GeV compared to ~700 GeV for a stop decaying to a massless LSP. Similarly, for the searches we consider, present limits on direct production of degenerate first and second generation squarks drop to ~450 GeV compared to ~800 GeV for a squark decaying to a massless LSP. Auto-concealment typically works for a fundamental gravitational scale of $M_*$~10-100 TeV, a scale sufficiently high that traditional searches for signatures of extra dimensions are mostly avoided. If superpartners are discovered...

Are Aftershocks of Large Californian Earthquakes Diffusing?

Helmstetter, Agnes; Ouillon, Guy; Sornette, Didier
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
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We analyze 21 aftershock sequences of California to test for evidence of space-time diffusion. Aftershock diffusion may result from stress diffusion and is also predicted by any mechanism of stress weakening. Here, we test an alternative mechanism to explain aftershock diffusion, based on multiple cascades of triggering. In order to characterize aftershock diffusion, we develop two methods, one based on a suitable time and space windowing, the other using a wavelet transform adapted to the removal of background seismicity. Both methods confirm that diffusion of seismic activity is very weak, much weaker than reported in previous studies. A possible mechanism explaining the weakness of observed diffusion is the effect of geometry, including the localization of aftershocks on a fractal fault network and the impact of extended rupture lengths which control the typical distances of interaction between earthquakes.; Comment: latex file of 34 pages, 15 postscript figures, minor revision. In press in J. Geophys. Res

Simulating the quartic Galileon gravity model on adaptively refined meshes

Li, Baojiu; Barreira, Alexandre; Baugh, Carlton M.; Hellwing, Wojciech A.; Koyama, Kazuya; Pascoli, Silvia; Zhao, Gong-Bo
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
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We develop a numerical algorithm to solve the high-order nonlinear derivative-coupling equation associated with the quartic Galileon model, and implement it in a modified version of the RAMSES N-body code to study the effect of the Galileon field on the large-scale matter clustering. The algorithm is tested for several matter field configurations with different symmetries, and works very well. This enables us to perform the first simulations for a quartic Galileon model which provides a good fit to the cosmic microwave background (CMB) anisotropy, supernovae and baryonic acoustic oscillations (BAO) data. Our result shows that the Vainshtein mechanism in this model is very efficient in suppressing the spatial variations of the scalar field. However, the time variation of the effective Newtonian constant caused by the curvature coupling of the Galileon field cannot be suppressed by the Vainshtein mechanism. This leads to a significant weakening of the strength of gravity in high-density regions at late times, and therefore a weaker matter clustering on small scales. We also find that without the Vainshtein mechanism the model would have behaved in a completely different way, which shows the crucial role played by nonlinearities in modified gravity theories and the importance of performing self-consistent N-body simulations for these theories.; Comment: 22.15 pages...

Historical sociology and great power vulnerability: The end of the Cold War and the collapse of the Soviet Union.

Bisley, Nicholas Lyon
Fonte: London School of Economics and Political Science Thesis Publicador: London School of Economics and Political Science Thesis
Tipo: Thesis; NonPeerReviewed Formato: application/pdf
Publicado em //2001 Português
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This thesis examines the collapse of Soviet state power from an international perspective. It assesses the extent to which the Soviet Union's international confrontation with the capitalist West, and the end of that confrontation, contributed to the strengthening and weakening of the Soviet state. It shows that the state's international stance of hostility, in both social-systemic and geopolitical terms, became a central component of Soviet state power. Central to this study is the assumption that the continuation of state power is contingent on the successful reproduction of the institutions of political rule. To this end, the thesis develops a historical sociological theory of the state which builds on a critique of neo-Weberian institutional-functional theories of the modem state. Using this theory, the thesis examines the development of Soviet state power and draws out the ways in which the international confrontation with the West reinforced the Soviet state and came to develop and shape its structures and institutions. Following an examination of the end of the Cold War, the thesis considers the way in which the change in international policy undermined elements of Soviet power, particularly in terms of ideology, legitimacy and material-organisational structures. The retreat from this posture...