分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-05-08
摘要: We use the stochastic approach to investigate a measure for slow roll eternal inflation. The probability for the universe to have a given Hubble radius can be calculated in this framework. In a solvable model, it is shown that the probability for the universe to evolve from a state with a smaller Hubble radius to one with a larger Hubble radius is dominated by the classical probability without the stochastic source, while the probability for the universe to evolve from a state with a larger Hubble radius to one with a smaller one is suppressed by exp(-Delta S), where the de Sitter entropy S arises naturally in this stochasticapproach.
分类: 物理学 >> 交叉学科物理及相关领域的科学与技术 提交时间: 2016-05-08
摘要: Small regulatory RNA (sRNA) that acts by an antisense mechanism is critical for gene regulation at the posttranscriptional level. Recently, an Hfq-dependent sRNA named MicM, which is related to the regulation of outer membrane protein, was verified as a novel antisense sRNA due to its catalytic mode of regulation. Here we propose a simple kinetic model for the enzyme-like regulation mode of sRNA and study in detail the noise properties of the target gene under various recycling rates of the regulator. We predict that the recycling rate of sRNA and other relative parameters have significant influence on the noise strength of target expression. In comparison with the stoichiometric regulatory mode, a lesser fluctuation of target expression was observed near the threshold at which the transcription rates of both sRNA and target mRNA equal each other. We also found that the new mode is better in terms of rapid response to external signals. However, it needs more time to achieve target recovery if the stimulating signal disappears. Additionally, the obtained time evolution results of the MicM-ybfM interaction system based on our model are consistent with previous experimental results, serving as experimental evidence to back up our theoretical analysis. (C) 2010 Elsevier Ltd. All rights reserved.
分类: 物理学 >> 凝聚态:结构、力学和热性能 提交时间: 2016-05-08
摘要: By including the contribution of the thermal cloud in the Lagrangian of the condensate of a Bose gas, we extend the time-dependent variational method at zero temperature to study temperature-dependent low collective excitation modes. A Gaussian trial wave function of the condensate and a static distribution density of the thermal cloud are used and analytical expressions for temperature-dependent excitation frequencies obtained. Theoretical results are compared with measurements in the JILA and MIT experiments.
分类: 物理学 >> 凝聚态:结构、力学和热性能 提交时间: 2016-05-08
摘要: A Bose gas in an external potential is studied by means of the local density approximation. Analytical results are derived for the thermodynamic properties of an ideal Bose gas in a generic power-law trapping potential, and their dependence on the mutual interaction of atoms in the case of a non-ideal Bose gas.
分类: 物理学 >> 凝聚态:结构、力学和热性能 提交时间: 2016-05-08
摘要: A Bose gas in an external potential is studied by means of the semiclassical approximation. Analytical results are derived for the energy of an interacting Bose gas in a generic power-law trapping potential. An expression for the chemical potential below the critical temperature is also obtained. The theoretical results are in agreement with a recent energy measurement.
分类: 物理学 >> 凝聚态:结构、力学和热性能 提交时间: 2016-05-08
摘要: A Bose gas in an external potential is studied by means of the semiclassical approximation. Analytical results are derived for the energy of an interacting Bose gas in a generic power-law trapping potential. An expression for the chemical potential below the critical temperature is also obtained. The theoretical results are in agreement with a recent energy measurement.