Dynamics of scalar fields in an expanding/contracting cosmos at finite temperature

This study extends the investigation of quantum dissipative effects of a cosmological scalar field by taking into account cosmic expansion and contraction.Cheung,Drewes,Kang,and Kim calculated the effective action and quantum dissipative effects of a cosmological scalar field in a recent work,where analytical expressions for the effective potential and damping coefficient were presented using a simple scalar model with quartic interactions,and the work was conducted using Minkowski-space propagators in loop diagrams.In this work,we incorporate the Hubble expansion and contraction of the cosmic background and focus on the thermal dynamics of a scalar field in a regime where the effective potential changes slowly.Given that the Hubble parameter,H,attains a small but non-zero value,we carry out calculations to the first order in H.If we set H=0,all results match those in flat spacetime.Interestingly,we must integrate over the resonances,which in turn leads to an amplification of the effects of a non-zero H.This is an intriguing phenomenon,which cannot be uncovered in flat spacetime.The implications on particle creations in the early universe will be studied in a forthcoming study.     

混合纤芯光子晶体光纤超平坦色散的研究

利用平面波展开法,系统地研究了一种具有混合纤芯结构的光子晶体光纤的色散特性. 数值计算结果表明,通过优化结构参量,这种新型结构的光子晶体光纤在通信窗口1.55 μm 附近可以获得带宽超过800 nm的超平坦色散区域（色散曲线的变化范围不超过 ±0.6 ps·km－1·nm－1）.     

以研促教：新型荧光探针检测铜离子的研究应用于分析化学拓展实验教学中

将新型荧光探针用于铜离子分析的科研成果转化为本科分析化学拓展实验教学,涵盖了结构分析、定性分析、定量分析等教学内容。通过荧光的“开-关-开”实验让学生直观地理解荧光探针与铜离子之间的配位反应,提升学生的研究兴趣;引导学生以研究者的角色设计和执行新的分析方法的建立程序并将建立的方法应用于实际样品分析中;探究荧光探针与铜离子的络合比;最后将荧光探针技术应用到快速分析领域中,鼓励学生活学活用。     

基于波动模态耦合的铝电解槽磁流体稳定性傅立叶级数法分析

铝电解槽内磁流体稳定性对铝电解生产有重要影响。本文结合铝电解槽实体仿真的电磁场计算结果,应用傅立叶级数法对槽内磁流体波动稳定性进行数值计算,并对波动的模态耦合问题进行了重点分析。在此基础上,本文以某320kA铝电解槽为研究载体分析了槽长宽比设计对磁流体稳定性的影响,结果表明:波动的不稳定分量集中分布在频谱图中重力波模态密集的低频区域;不考虑母线对体系的影响,增大槽的长宽比,有利于提高磁流体的稳定性。     

非定常膨胀过程中水蒸汽凝结对流场影响的数值分析

采用数值目的对激波管非定常膨胀过程中,汽液相变与流场的相互作用进行了模拟.主要研究了含有水蒸汽的混合气体在激波管中的非平衡凝结过程以及其对流场的作用.结果表明由于水蒸气的凝结释放热量对流场局部进行加热,使流场参数发生扰动而产生凝结激波.经过与凝结激波的相互作用后,流场参数和结构将发生明显的变化.     

基于平面通量展开的三维Pin by Pin输运SP3计算

基于Pin by Pin输运SP3计算是下一代反应堆物理计算方法中一个重要的研究方向.节块法一般采用高阶通量和中子源展开以适应较大的节块尺寸,因此对于Pin by Pin计算来说效率偏低.由于反应堆堆芯不均匀性更多发生在径向,本文提出一种径向基于二维平面通量展开结合轴向常规节块法的综合方法进行三维Pin by Pin输...     

Transition from decelerated to accelerated cosmic expansion in braneworld universes

Braneworld theory provides a natural setting to treat, at a classical level, the cosmological effects of vacuum energy. Non-static extra dimensions can generally lead to a variable vacuum energy, which in turn may explain the present accelerated cosmic expansion. We concentrate our attention in models where the vacuum energy decreases as an inverse power law of the scale factor. These models agree with the observed accelerating universe, while fitting simultaneously the observational data for the density and deceleration parameter. The redshift at which the vacuum energy can start to dominate depends on the mass density of ordinary matter. For _m = 0.3, the transition from decelerated to accelerated cosmic expansion occurs at z _T ≈ 0.48 ± 0.20, which is compatible with SNe data. We set a lower bound on the deceleration parameter today, namely > − 1 + 3 _m /2, i.e., > − 0.55 for _m = 0.3. The future evolution of the universe crucially depends on the time when vacuum starts to dominate over ordinary matter. If it dominates only recently, at an epoch z < 0.64, then the universe is accelerating today and will continue that way forever. If vacuum dominates earlier, at z > 0.64, then the deceleration comes back and the universe recollapses at some point in the distant future. In the first case, quintessence and Cardassian expansion can be formally interpreted as the low energy limit of our model, although they are entirely different in philosophy. In the second case there is no correspondence between these models and ours.     

直接膨胀供液制冷系统性能可视化研究

对直接膨胀供液制冷系统的传热性能进行了理论分析,建立了相应的数学模型.在保温体内对-5℃、0℃、5℃、10℃、15℃、20℃的工况进行了实验.分别测得制冷系统的压力、风量、制冷量、及功耗等技术参数,得到在环境温度一定的情况下的传热系数和制冷量的变化关系.并对蒸发器内制冷剂流动状态进行观察.实验表明:直接膨胀供液制冷系统...     

The nucleon wave function at the origin

We calculate the next-to-leading order perturbative corrections to the SVZ sum rules for the coupling fN$f_N$, the nucleon leading twist wave function at the origin. The results are compared to the established Ioffe sum rules and also to lattice QCD simulations.     

High‐pressure studies of the micro‐Raman spectra of iron cyanide complexes: Prussian blue (Fe4[Fe(CN)6]3), potassium ferricyanide (K3[Fe(CN)6]), and sodium nitroprusside (Na2[Fe(CN)5(NO)]·2H2O)

The pressure dependences of the peaks observed in the micro‐Raman spectra of Prussian blue (Fe₄[Fe(CN)₆]₃), potassium ferricyanide (K₃[Fe(CN)₆]), and sodium nitroprusside (Na₂[Fe(CN)₅(NO)]·2H₂O) have been measured up to 5.0 GPa. The vibrational modes of Prussian blue appearing at 201 and 365 cm⁻¹ show negative dν/dP values and Grüneisen parameters and are assigned to the transverse bending modes of the Fe C N Fe linkage which can contribute to a negative thermal expansion behavior. A phase transition occurring between 2.0 and 2.8 GPa in potassium ferricyanide is shown by changes in the spectral region 150–700 cm⁻¹. In the spectra of the nitroprusside ion, there are strong interactions between the FeN stretching mode and the FeNO bending and the axial CN stretching modes. The pressure dependence of the NO stretching vibration is positive, 5.6 cm⁻¹ GPa⁻¹, in contrast to the negative behavior in the iron(II)‐meso‐tetraphenyl porphyrinate complex. Copyright © 2011 John Wiley & Sons, Ltd.