Tidal dynamics of relativistic flows near black holes

We point out novel consequences of general relativity involving tidal dynamics of ultrarelativistic relative motion. Specifically, we use the generalized Jacobi equation and its extension to study the force‐free dynamics of relativistic flows near a massive rotating source. We show that along the rotation axis of the gravitational source, relativistic tidal effects strongly decelerate an initially ultrarelativistic flow with respect to the ambient medium, contrary to Newtonian expectations. Moreover, an initially ultrarelativistic flow perpendicular to the axis of rotation is strongly accelerated by the relativistic tidal forces. The astrophysical implications of these results for jets and ultrahigh energy cosmic rays are briefly mentioned.     

Future Destiny of Quintessential Universe and Constraint on Model from Deceleration Parameter

The evolution of the quintessence in various stages of the universe, i.e., the radiation-, matter-, andquintessence-dominated stages, is closely related with the tracking behavior and the deceleration parameter of theuniverse. We gave the explicit relation between the equation-of-state of the quintessence in the epoch of the matter-quintessence equality and the inverse power index of the quintessence potential, obtained the constraint on this potentialparameter comingfrom the present deceleration parameter, i.e., a low inverse power index.We point out that the lowinverse power-law potential with a single term cannot work for the tracking solution. In order to have both of the trackerand the suitable deceleration parameter it is necessary to introduce at least two terms in the quintessence potential. Wegive the future evolution of the quintessential universe.     

基于微段插补模型的数控刀具运动优化控制

针对直线段与圆弧连接处的过渡,采用微小线段插补进行处理;通过前瞻分析的方法,控制直线段与圆弧段过渡处的进给速度提前减速,有效地减少了直线与圆弧过渡处的加工误差,建立混合S型双向加减速曲线模型,实现了圆弧段拐角处速度的控制.为了更好地优化数控刀具的加工时间,改进S型加速曲线原来加速缓慢耗时的前半部分,建立非零启动S型曲线加减速模型,从而减少启动时间,这种改进极大地优化刀具在走圆弧时的时间及平稳性.     

弹体高过载硬回收测量技术的实验探讨

为提供引信服役的力学参数,达到引战配合目的,弹体过载(减速度)的测量十分必要。采用硬回 收法测量了高速侵彻混凝土的先进钻地弹缩比弹过载时间历程。实验弹最大直径48mm,计及过载测量装 置,弹体质量约1.8kg,撞击速度1142m/s。过载测试系统模块化和集成化设计,包括过载测量模块、电路模 块、信号存储模块、电源模块和外部计算机模块,传感器为压阻式。量程在(-8~21)104g,可测量过载幅值 约20104g。     

基于调制光晶格的中性分子束光学Stark减速与囚禁的理论研究

本文基于分子束光学Stark减速理论,提出采用调制的红失谐光晶格来减速和囚禁任意脉冲超声分子束方案,并予以理论研究.以CH₄超声分子束为例,利用Monte-Carlo方法模拟了调制光晶格中的分子减速与囚禁的动力学过程,给出减速级数、同步分子初始位相角与减速效果的关系.研究结果表明：随着减速级数的增加,被减速的分子波包逐渐从原来的分子速度分布的大波包中分离开来,且减速级数越高,减速后的分子速度越小.在其他条件相同时同步分子初始位相角越大,减速波包内的分子数目越少,同时位相空间被压缩.与未调制的光晶格减速方案相比,本方案中无分子自由飞行过程,在相同的光晶格长度内完成了双倍的减速级数.当光晶格长度取3.71 mm时,模拟结果显示CH₄分子从280 m/s减速至172 m/s,而未调制光晶格只能将CH₄分子从280 m/s减速至232 m/s,减速效果提高了26%.本方案可以集分子的减速、囚禁于一体,是一种新型的分子光学功能器件,在冷分子光学、量子信息、冷化学等前沿研究领域中有潜在的应用.     

Observational constraints on the accelerating universe in the framework of a 5D bounce cosmological model

In the framework of a five-dimensional (5D) bounce cosmological model, a useful function f(z) is obtained by giving a concrete expression of deceleration parameter q(z)=q₁+{q₂}/{1+ln (1+ z)}. Then using the obtained Hubble parameter H(z) according to the function f(z), we constrain the accelerating universe from recent cosmic observations: the 192 ESSENCE SNe Ia and the 9 observational H(z) data. The best fitting values of transition redshift z_T and current deceleration parameter q₀ are given as z_T= 0.65_-0.12^0.25 and q₀ = - 0.76_-0.15^+0.15 (1σ). Furthermore, in the 5D bounce model it can be seen that the evolution of equation of state (EOS) for dark energy w_de can cross over -1 at about z=0.23 and the current value w_0de= - 1.15<- 1. On the other hand, by giving a concrete expression of model-independent EOS of dark energy w_de, in the 5D bounce model we obtain the best fitting values z_T= 0.66_0.08^+0.11 and q₀ = - 0.69_0.10^+0.10 (1σ) from the recently observed data: the 192 ESSENCE SNe Ia, the observational H(z) data, the 3-year Wilkinson Microwave Anisotropy Probe (WMAP), the Sloan Digital Sky Survey (SDSS) baryon acoustic peak and the x-ray gas mass fraction in clusters.     

激光尾波场中光子加速研究

在SILEX-Ⅰ激光装置上,测量了超短超强激光脉冲与稀薄等离子体相互作用之后的透射谱. 实验中发现,激光尾波场产生的密度扰动导致等离子体折射率随时间空间不断变化,导致光子的加速/减速. 透射谱上主要表现为激光频率谱峰的劈裂和随密度变化的展宽,没有发现与前向受激拉曼散射或自调制不稳定性相联系的边频波. 同时,利用LPIC++无碰撞粒子模拟程序模拟了超短超强激光与稀薄等离子体相互作用后的透射谱,模拟结果也发现了明显的光子加速过程. 关键词： 超短超强激光脉冲 透射谱 光子加速/减速     

弹丸低速垂直侵彻无钢筋混凝土的实验研究

提出了一种在钢弹侵彻素混凝土的全尺寸试验中测量弹丸减速度时间曲线的测试方法,该方法通过安装在弹丸上的加速度传感器测量弹丸减速度并把数据同步传递给地面记录系统。用这种测试方法,在空气炮上进行了一系列半球形头部钢弹以１５０ ～４００ｍ／ｓ 速度垂直侵彻素混凝土目标的试验,成功地测量了弹丸的减速度时间历程曲线。对减速度曲线中的高频成分进行了分析,第一次用试验证实了高频成分可能是弹体结构响应的推测。并对减速度曲线的一些特性进行了讨论。     

Periodic cosmic evolution in f(Q) gravity formalism

We study the periodic cosmic transit behavior of the accelerated universe in the framework of symmetric teleparallelism. The exact solution of field equations is obtained by employing a well-known deceleration parameter (DP) called periodic varying DP, $q=m\cos {kt}-1$. The viability and physical reliability of the DP are studied by using observational constraints. The dynamics of periodicity and singularity are addressed in detail with respect to time and redshift parameter. Several energy conditions are discussed in this setting.