三轴椭球体模型下转动双星系统的演化

采用三轴椭球体模型和非均匀的星风物质损失的理论计算,数值模拟并分析了转动双星系统的演化.结果表明子星间物质交换和氢开始燃烧提前,主序带变宽,演化更大幅度地向蓝方向运动并形成较大回绕,演化轨迹向低光度偏转,子星半径在慢速物质交换过程中出现周期性的膨胀和收缩,角动量损失率变小.     

基于势流理论的回转体并联入水双空泡演化动力学研究

两回转体并联入水过程中,双空泡在空间上相互干扰,使得单个入水空泡呈现非对称特性.本文基于势流理论,在现有二维轴对称入水空泡计算模型的基础上,对空泡干涉区域的三维流动进行简化,将相对流动对空泡发展的约束简化为约束势,分析了两回转体轴线内外两侧的空泡形态变化;基于非线性假设,引入影响函数,给出了空泡在三维空间演化的计算模型,并分析了同步并联入水过程空泡的三维演化特性.结果表明：回转体入水过程流场速度势可以看作由一个随回转体运动的点源和位于空泡轴线处的线源叠加产生;在并联入水过程中,双空泡演化在空间呈镜面对称,空泡间的相互扰动可以通过引入有势壁面进行分析;并联入水空泡半径随极角的变化与空泡截面所处深度有关,在靠近闭合点附近的抑制演化区空泡截面半径随极角的增大而逐渐减小,远离闭合点处的抑制演化区空泡截面半径随极角的增大而增大,空泡加权半径规律相反.     

双孤子非线性干涉中的狄拉克磁单极势

本文深入研究了孤子干涉过程中的相位演化特性及其背后的拓扑矢势.基于一维非线性薛定谔方程的双孤子解,发现波函数密度零点广泛存在于拓展的复平面内,并且每一个密度零点对应狄拉克磁单极的矢势场.矢势场是由周期排布的具有相反磁荷的狄拉克磁单极对组成.通过观察磁单极子的运动,可以方便地理解干涉过程中的相位演化特征.特别发现,一对正负磁单极对在实轴上的碰撞恰好对应波函数相位在节点处的π跃变.此外,还对比讨论了线性波包干涉动力学中的狄拉克磁单极.结果表明狄拉克磁单极势广泛存在于波场的干涉现象之中,并且磁单极在拓展的复平面内分布特征可用于区分线性干涉和非线性干涉过程背后的拓扑性质.     

用落体法测重力加速度的实验方案选择

重力加速度是物理学中一个重要的参量.地球上各地区的重力加速度的数值随地理纬度、海拔高度和地质结构的不同而不同.重力加速度的测量不仅在物理中具有重要意义,而且对于研究地层结构和探查地下资源都有实用价值,因此,细致地测量和准确地计算重力加速度是十分必要的.测量重力加速度的方法多种多样,本文利用自由落体原理,借助光电门测重力加速度.为减小误差对具体实验操作及数据处理方法的选择进行深入探讨.     

多模式原子干涉仪的相位研究

在本文中,我们研究了谐振子势阱(频率为ω)中多模式原子干涉仪相位演化的动力学特性.第一次Kapitza-Dirac脉冲产生出了具有不同相位的模式.外场的作用使这些模式的相位演化相对于没有外场下的演化发生了偏离.Kapitza-Dirac脉冲的强度不会对相位演化产生任何影响.在第二次Kapitza-Dirac脉冲后,外场作用使t=π/(2ω)之前已经存在的非零模式相位发生突变.对于外场是重力场,测量时刻相邻两模式之间的相位差和重力加速度成线性关系.     

辐射压对非同步转动双星系统洛希势函数的影响

辐射压是影响大质量恒星结构和演化不可忽视的重要物理因素. 根据辐射压对非同步转动的洛希势函数的影响, 数值计算了洛希瓣的大小和3个拉格朗日点的位置和相应的势函数, 并与同步转动的洛希模型计算的结果做了对比. 结果发现: 辐射压可以整体地减小大质量恒星表面的重力加速度, 而转动离心力能最大减少赤道附近的重力加速度. 辐射压和非同步转动均可以明显地改变洛希瓣的大小和3个拉格朗日点的位置和势函数, 影响双星系统物质交换的时间. 因此, 研究辐射压, 非同步转动等物理因素对大质量双星系统洛希势函数的影响, 对密近双星的演化具有重要意义. 关键词： 恒星结构与演化 转动 辐射压     

转动潮汐变形双星理论模型研究

转动和潮汐效应是影响双星系统结构和演化不可忽略的重要物理因素. 根据大质量双星系统V478 Cyg的观测结果, 检验了提出的转动潮汐变形的理论模型. 将转动潮汐变形的模型与传统的双星演化模型对比发现: 转动和潮汐效应使恒星外层(低于平均密度区)发生的形变远大于内层; 恒星两极点重力加速度变大, 赤道面上重力加速度变小; 转动潮汐变形模型具有较大的半径、赤道速度和中心集中度, 较低的氢核能产生率, 恒星向低温和低光度端演化. 此外, 大质量双星系统V478 Cyg由潮汐形变造成的拱线运动速率大于转动形变造成的拱线运动速率, 广义相对论效应造成的拱线运动最小. 由于主星具有较高的中心集中度, 次星潮汐、转动形变造成的拱线运动速率均大于主星相应的拱线运动速率.     

纳米铜薄膜塑性变形中空位型缺陷形核与演化的分子动力学研究

本文采用分子动力学方法模拟了纳米单晶铜薄膜在单向拉伸载荷作用下的塑性变形过程, 重点分析了空位型缺陷的形核过程和演化机理. 在模拟过程中, 采用镶嵌原子势描述原子间的相互作用. 模拟结果表明纳米铜薄膜中塑性变形起源于位错的表面形核, 而空位型缺陷的形核及演化都与晶体内部的位错运动密切相关. 空位型缺陷通常从位错割阶及层错交截处开始形核, 以单空位、层错四面体和不规则空位团等形式存在. 关键词： 纳米薄膜 塑性变形 空位 层错四面体     

重力加速度的新探索

简要介绍了重力加速度在理论和实验上的新探索，即“引力常数Ｇ”的可变性对重力加速度的影响，阐述了在广义相对论等引力理论基础上重力加速度的后牛顿效应．     

基于演化博弈的社交网络模型演化研究

社会网络研究的兴起,为网络演化规律研究提供了有效工具,但大多数研究集中从宏观机制评估网络演化的动态过程. 本文基于公共品博弈,通过演化博弈与网络拓扑共演化方式,从微观角度提出了多社区动态网络演化模型（dMCPGG）. 即以节点间演化博弈为动力,修改节点间边的关系,驱动网络拓扑演化. 考虑到网络异质性,采用基于拓扑势的偏好规则更准确全面的描述节点影响力. 通过数值模拟和仿真实验,验证了本模型的合理性,不仅重现了无标度网络及随机网络的节点度、聚类系数及平均路径长度的结构特性,还准确捕捉到真实社交网络的演化过程. 关键词： 公共品博弈 拓扑势 偏好选择 共演化     

Acceleration Field of a Universe Modeled as a Mixture of Scalar and Matter Fields

A model of the Universe as a mixture of a scalar (inflaton or rolling tachyon from the string theory) and a matter field (classical particles) is analyzed. The particles are created at the expense of the gravitational energy through an irreversible process whereas the scalar field is supposed to interact only with itself and to be minimally coupled with the gravitational field. The irreversible processes of particle creation are related to the non-equilibrium pressure within the framework of the extended (causal or second-order) thermodynamic theory. The scalar field (inflaton or tachyon) is described by an exponential potential density added by a parameter which represents its asymptotic value and can be interpreted as the vacuum energy. This model can simulate three phases of the acceleration field of the Universe, namely, (a) an inflationary epoch with a positive acceleration followed by a decrease of the acceleration field towards zero, (b) a past decelerated period where the acceleration field decreases to a maximum negative value followed by an increase towards zero, and (c) a present accelerated epoch. For the energy densities there exist also three distinct epochs which begin with a scalar field dominated period followed by a matter field dominated epoch and coming back to a scalar field dominated phase.     

Liquid-Droplet as a model for the rotation curve problem

The dynamics of large scale gravitational structures like galaxies, local groups and clusters is studied based on the so-called Liquid-Droplet model describing the saturation property of the nuclear force. Using the assumption that the gravitational force is also saturated over large scale structures, it is argued that the Newtonian gravitational potential may be replaced by an effective Machian gravitational potential. Application of this new potential at these large scale structures may give the rotation curves in good agreement with observations. Then, the virial theorem for this kind of gravitational interaction is developed and also the Tully-Fisher relation is obtained. A physical explanation is given for the so-called constant acceleration in the MOND as the effective gravitational strength of these structures. Finally, a brief argument is given for comparison with dark matter models.     

Free fall of a spin-zero quantum particle

The acceleration operators are derived for a spin-zero quantum particle near an observation point which is at rest in a static, spherically symmetric gravitational field. The expectation value of the acceleration of the center of gravity of an arbitrary wave packet is found.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 36–41, June, 1976.     

Precision measurement of gravity with cold atoms in an optical lattice and comparison with a classical gravimeter

We report on a precision measurement of gravitational acceleration using ultracold strontium atoms confined in an amplitude-modulated vertical optical lattice. An uncertainty Δg/g ≈ 10(-7) is reached by measuring at the 5th harmonic of the Bloch frequency. The value obtained with this microscopic quantum system is consistent with the one measured with a classical gravimeter. Using lattice modulation to prepare the atomic sample, we also achieve high visibility of Bloch oscillations for ～ 20 s. These results can be of relevance for testing gravitational redshift and Newtonian law at micrometer scale.     

斜轨法测量重力加速度影响因素的探讨

斜轨法是测量重力加速度的一种常用方法,但光电门挡光片的形状和宽度以及导轨的倾斜角度对测量结果有着直接的影响。本文从实验角度探讨上述几个因素对测量结果的影响并与当地重力加速度的标称值(广州9.788 m/s2)进行对比。测量结果表明:在导轨的垫片高度为2 cm时,使用条形挡光片的测量值均大于标称值;而U型挡光片宽度大于13 cm时测量值大于标称值,而小于13 cm时测量值则均小于标称值。在相同的导轨倾斜角下用U型挡光片时,两挡光片间距越大,测量值越大;而使用条形挡光片时,挡光片宽度越大,测量值就越小。     

The gravitational acceleration of antiprotons

We review the theoretical arguments and experimental evidence (both direct and indirect) for the conventional view that the gravitational acceleration of antimatter must be the same as that of matter. We find there is no compelling support for such a belief. Therefore, we propose to measure the gravitational acceleration of antiprotons using a beam extracted from the low-energy antiproton ring (LEAR) at CERN.This essay received the fifth award from the Gravity Research Foundation for the year 1985-Ed.     

What if gravity becomes really repulsive in the future?

The current acceleration of the Universe is one of the most puzzling issues in theoretical physics nowadays. We are far from giving an answer in this letter to the question of its nature. Yet, with the observations we have at hand, we analyse the different patterns that the gravitational potential can show in the future. Surprisingly, gravity not only can get weaker in the near future, it can even become repulsive; or equivalently, the gravitational potential may become negative. We show this remark by using one of the simplest phenomenological model we can imagine for dark energy. We have also reviewed the statefinder approach of these models. For completeness, we have also showed the behaviour of the density contrast of dark matter and dark energy for these simple (yet illustrative models). Our results are displayed and we see how they shall evolve in the future.     

Experimental study of the dynamic Newtonian field with a cryogenic gravitational wave antenna

We present an experiment performed to study the behaviour of the dynamic gravitational interaction at laboratory scale. We used as field generator a mass quadrupole rotating in the range of 460 Hz and we detected the acceleration field with the cryogenic gravitational wave antenna Explorer of the Rome group. We report the measurements of this interaction as a function of the distance between the field source and the detector. An upper limit on the parameters of a Yukawa-like potential, modeling an hypotetic deviation from the Newtonian law of gravity, is derived. Received: 14 June 1998 / Published online: 16 September 1998     

Quantum information paradox: Real or fictitious?

One of the outstanding puzzles of theoretical physics is whether quantum information indeed gets lost in the case of black hole (BH) evaporation or accretion. Let us recall that quantum mechanics (QM) demands an upper limit on the acceleration of a test particle. On the other hand, it is pointed out here that, if a Schwarzschild BH exists, the acceleration of the test particle would blow up at the event horizon in violation of QM. Thus the concept of an exact BH is in contradiction with QM and quantum gravity (QG). It is also reminded that the mass of a BH actually appears as an integration constant of Einstein equations. And it has been shown that the value of this integration constant is actually zero! Thus even classically, there cannot be finite mass BHs though zero mass BH is allowed. It has been further shown that during continued gravitational collapse, radiation emanating from the contracting object gets trapped within it by the runaway gravitational field. As a consequence, the contracting body attains a quasi-static state where outward trapped radiation pressure gets balanced by inward gravitational pull and the ideal classical BH state is never formed in a finite proper time. In other words, continued gravitational collapse results in an ‘eternally collapsing object’ which is a ball of hot plasma and which is asymptotically approaching the true BH state with M = 0 after radiating away its entire mass energy. And if we include QM, this contraction must halt at a radius suggested by the highest QM acceleration. In any case no event horizon (EH) is ever formed and in reality, there is no quantum information paradox.