5,311 research outputs found
Spatial structures and dynamics of kinetically constrained models for glasses
Kob and Andersen's simple lattice models for the dynamics of structural
glasses are analyzed. Although the particles have only hard core interactions,
the imposed constraint that they cannot move if surrounded by too many others
causes slow dynamics. On Bethe lattices a dynamical transition to a partially
frozen phase occurs. In finite dimensions there exist rare mobile elements that
destroy the transition. At low vacancy density, , the spacing, ,
between mobile elements diverges exponentially or faster in . Within the
mobile elements, the dynamics is intrinsically cooperative and the
characteristic time scale diverges faster than any power of (although
slower than ). The tagged-particle diffusion coefficient vanishes roughly
as .Comment: 4 pages. Accepted for pub. in Phys. Rev. Let
Lattice Glass Models
Motivated by the concept of geometrical frustration, we introduce a class of
statistical mechanics lattice models for the glass transition. Monte Carlo
simulations in three dimensions show that they display a dynamical glass
transition which is very similar to that observed in other off-lattice systems
and which does not depend on a specific dynamical rule. Whereas their analytic
solution within the Bethe approximation shows that they do have a discontinuous
glass transition compatible with the numerical observations.Comment: 4 pages, 2 figures; minor change
Neutralization of IFN-γ reverts clinical and laboratory features in a mouse model of macrophage activation syndrome.
BACKGROUND: The pathogenesis of macrophage activation syndrome (MAS) is not clearly understood: a large body of evidence supports the involvement of mechanisms similar to those implicated in the setting of primary hemophagocytic lymphohistiocytosis.
OBJECTIVE: We sought to investigate the pathogenic role of IFN-γ and the therapeutic efficacy of IFN-γ neutralization in an animal model of MAS.
METHODS: We used an MAS model established in mice transgenic for human IL-6 (IL-6TG mice) challenged with LPS (MAS mice). Levels of IFN-γ and IFN-γ-inducible chemokines were evaluated by using real-time PCR in the liver and spleen and by means of ELISA in plasma. IFN-γ neutralization was achieved by using the anti-IFN-γ antibody XMG1.2 in vivo.
RESULTS: Mice with MAS showed a significant upregulation of the IFN-γ pathway, as demonstrated by increased mRNA levels of Ifng and higher levels of phospho-signal transducer and activator of transcription 1 in the liver and spleen and increased expression of the IFN-γ-inducible chemokines Cxcl9 and Cxcl10 in the liver and spleen, as well as in plasma. A marked increase in Il12a and Il12b expression was also found in livers and spleens of mice with MAS. In addition, mice with MAS had a significant increase in numbers of liver CD68+ macrophages. Mice with MAS treated with an anti-IFN-γ antibody showed a significant improvement in survival and body weight recovery associated with a significant amelioration of ferritin, fibrinogen, and alanine aminotransferase levels. In mice with MAS, treatment with the anti-IFN-γ antibody significantly decreased circulating levels of CXCL9, CXCL10, and downstream proinflammatory cytokines. The decrease in CXCL9 and CXCL10 levels paralleled the decrease in serum levels of proinflammatory cytokines and ferritin.
CONCLUSION: These results provide evidence for a pathogenic role of IFN-γ in the setting of MAS
Boro no crescimento de mudas de erva-mate em solução nutritiva.
A maioria das soluções nutritivas indicam a dose de 0,5 mg L-1 de boro (B) como ideal, mas para erva-mate não há informações sobre sua necessidade em B. Avaliou-se o crescimento de mudas clonais de erva-mate em solução nutritiva, submetidas a doses de: 0,0; 1,0; 2,5 e 5,0 mg L-1 de B. O experimento foi conduzido em Viçosa-MG e após 80 dias, através de análise de regressão, avaliou-se características de crescimento das mudas onde obteve-se que doses de B próximas de 2,90 mg L-1 favoreceram o melhor crescimento em altura, diâmetro do colo e comprimento do sistema radicular. Já para maximizar a produção de matéria seca, volume do sistema radicular, área foliar e espessura foliar a erva-mate necessita de doses próximas a 3,00 mg L-1 de B. Conclui-se que mudas de erva-mate, conduzidas em solução nutritiva, necessitam de 2,5 a 3,1 mg L-1 de B para um bom crescimento
Real-time monitoring of protein conformational changes using a nano-mechanical sensor.
Proteins can switch between different conformations in response to stimuli, such as pH or temperature variations, or to the binding of ligands. Such plasticity and its kinetics can have a crucial functional role, and their characterization has taken center stage in protein research. As an example, Topoisomerases are particularly interesting enzymes capable of managing tangled and supercoiled double-stranded DNA, thus facilitating many physiological processes. In this work, we describe the use of a cantilever-based nanomotion sensor to characterize the dynamics of human topoisomerase II (Topo II) enzymes and their response to different kinds of ligands, such as ATP, which enhance the conformational dynamics. The sensitivity and time resolution of this sensor allow determining quantitatively the correlation between the ATP concentration and the rate of Topo II conformational changes. Furthermore, we show how to rationalize the experimental results in a comprehensive model that takes into account both the physics of the cantilever and the dynamics of the ATPase cycle of the enzyme, shedding light on the kinetics of the process. Finally, we study the effect of aclarubicin, an anticancer drug, demonstrating that it affects directly the Topo II molecule inhibiting its conformational changes. These results pave the way to a new way of studying the intrinsic dynamics of proteins and of protein complexes allowing new applications ranging from fundamental proteomics to drug discovery and development and possibly to clinical practice
Ubiquity of metastable-to-stable crossover in weakly chaotic dynamical systems
We present a comparative study of several dynamical systems of increasing
complexity, namely, the logistic map with additive noise, one, two and many
globally-coupled standard maps, and the Hamiltonian Mean Field model (i.e., the
classical inertial infinitely-ranged ferromagnetically coupled XY spin model).
We emphasize the appearance, in all of these systems, of metastable states and
their ultimate crossover to the equilibrium state. We comment on the underlying
mechanisms responsible for these phenomena (weak chaos) and compare common
characteristics. We point out that this ubiquitous behavior appears to be
associated to the features of the nonextensive generalization of the
Boltzmann-Gibbs statistical mechanics.Comment: Communication at next2003, Second Sardinian International Conference
on News and Expectations in Thermostatistics, Villasimius (Cagliari) Italy,
21st-28th September 2003. Submitted to Physica A. Elsevier Latex, 17 pages, 8
figure
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