A massive binary black-hole system in OJ 287 and a test of general relativity

Tests of Einstein's general theory of relativity have mostly been carried out in weak gravitational fields where the space-time curvature effects are first-order deviations from Newton's theory. Binary pulsars provide a means of probing the strong gravitational field around a neutron star, but strong-field effects may be best tested in systems containing black holes. Here we report such a test in a close binary system of two candidate black holes in the quasar OJ 287. This quasar shows quasi-periodic optical outbursts at 12-year intervals, with two outburst peaks per interval. The latest outburst occurred in September 2007, within a day of the time predicted by the binary black-hole model and general relativity. The observations confirm the binary nature of the system and also provide evidence for the loss of orbital energy in agreement (within 10 per cent) with the emission of gravitational waves from the system. In the absence of gravitational wave emission the outburst would have happened 20 days later.     

A test of general relativity using radio links with the Cassini spacecraft

According to general relativity, photons are deflected and delayed by the curvature of space-time produced by any mass. The bending and delay are proportional to gamma + 1, where the parameter gamma is unity in general relativity but zero in the newtonian model of gravity. The quantity gamma - 1 measures the degree to which gravity is not a purely geometric effect and is affected by other fields; such fields may have strongly influenced the early Universe, but would have now weakened so as to produce tiny--but still detectable--effects. Several experiments have confirmed to an accuracy of approximately 0.1% the predictions for the deflection and delay of photons produced by the Sun. Here we report a measurement of the frequency shift of radio photons to and from the Cassini spacecraft as they passed near the Sun. Our result, gamma = 1 + (2.1 +/- 2.3) x 10(-5), agrees with the predictions of standard general relativity with a sensitivity that approaches the level at which, theoretically, deviations are expected in some cosmological models.     

三维通用特征函数研究

提出n=2时m级内能的球面型构造。将六个状态参量均匀有序地分布在球面上,每三个状态参量构成的球面三角形组成了以顶点参量为自变量的特征函数。利用该球面可直接得到8个特征函数的微分方程、24个偏导数与状态参量的关系和24个偏导数间的关系。     

普通物理相对论教学的几点思考

X相对论作为前沿内容已引入了高中物理新教材。基于这一现实,重新思考了普通物理相对论的教学——认为普通物理相对论教学应强调科学哲学、渗透科学方法、联系物理学史、了解前沿进展、关注多元理解。     

时空背景的微分几何表征

文章从近代微分几何及其核心概念微分流形着手，阐释了流形及相关问题与物理背景空间的关系，重新认识张量场和剖析相对论背景时空。     

Abrupt acceleration of a 'cold' ultrarelativistic wind from the Crab pulsar

Pulsars are thought to eject electron-positron winds that energize the surrounding environment, with the formation of a pulsar wind nebula. The pulsar wind originates close to the light cylinder, the surface at which the pulsar co-rotation velocity equals the speed of light, and carries away much of the rotational energy lost by the pulsar. Initially the wind is dominated by electromagnetic energy (Poynting flux) but later this is converted to the kinetic energy of bulk motion. It is unclear exactly where this takes place and to what speed the wind is accelerated. Although some preferred models imply a gradual acceleration over the entire distance from the magnetosphere to the point at which the wind terminates, a rapid acceleration close to the light cylinder cannot be excluded. Here we report that the recent observations of pulsed, very high-energy γ-ray emission from the Crab pulsar are explained by the presence of a cold (in the sense of the low energy of the electrons in the frame of the moving plasma) ultrarelativistic wind dominated by kinetic energy. The conversion of the Poynting flux to kinetic energy should take place abruptly in the narrow cylindrical zone of radius between 20 and 50 light-cylinder radii centred on the axis of rotation of the pulsar, and should accelerate the wind to a Lorentz factor of (0.5-1.0)?×?10(6). Although the ultrarelativistic nature of the wind does support the general model of pulsars, the requirement of the very high acceleration of the wind in a narrow zone not far from the light cylinder challenges current models.     

Absolute time-of-arrival measurements of optical pulses from the Crab pulsar

An attempt is made to understand the characteristics of pulsar slowdown in terms of various possible emission mechanisms. Though magnetic-dipole radiation seems to be dominant, the deviations from a pure dipolar decay are large compared with errors in measurement and indicate the presence of more complicated braking mechanisms, small fluctuations, and major "jumps", or period discontinuities. Some rapid-relaxation effect is evident following the discontinuous jump in period in September 1969, but there is no evidence of the quasi-sinusoidal behaviour reported before the jump by Arecibo. An alternative interpretation of the Arecibo data is given.     

有限域上辛几何中一类Cartesian认证码的构作

利用有限域上的辛几何构造了一类Cartesian认证码，并且计算了其参数及模仿攻击成功的概率PI和替换攻击成功的概率PS。     

中心有脉冲星的γ暴970228火球模型

重点讨论了中心有脉冲量生的γ射线暴火球模型，假定在火球的中心有一强磁场的毫秒级脉冲星，改革以往文献中的能量转化方程，计算出GRB970228的辐射流，与观测结果符合的很好，自然解释了GRB970228余辉的光变曲线特征。     

中心有脉冲星的︽暴970228火球模型

重点讨论了中心有脉冲星的γ射线暴火球模型,假定在火球的中心有一强磁场的毫秒级脉冲星,改变以往文献中的能量转化方程,计算出GRB970228的辐射流,与观测结果符合的很好.自然解释了GRB970228余辉的光变曲线特征.     

Correlation of subpulse structure in a sequence of pulses from pulsar PSR 1919+21

The fluctuation power spectrum of a sequence of momentary pulse energies formed using an integration gate narrower than the pulse width displays features not visible with a wider gate. The analysis indicates that the class two period is a function of phase within the pulse profile. The statistical constitution of the mean pulse is discussed.     

黏弹性材料纳米压痕测试及接触形貌的影响

利用纳米硬度计测量聚氯乙烯(PVC)的力学性能,用有限元软件仿真了实测过程,比对实验和仿真数据,得出有限元法研究黏弹性材料纳米压痕实验的可行性结论.据此针对不同尖端曲率半径的圆锥形压头,模拟纳米压痕测量过程,结果显示:在黏弹性材料纳米压痕实验中硬度测量值随压入深度的增加而减小,随尖端曲率半径的增加而增大.最后引入压头表征尺寸概念,针对表征尺寸与表面粗糙度参数在同一数量级以及表征尺寸远小于表面粗糙度参数这两种情况分别进行仿真,结果表明:接触零点在峰顶或谷底时的硬度测量值会相应地偏小或偏大,并且硬度测量值的偏差随纹波间距和轮廓最大高度的增加而增大.     

A large age for the pulsar B1757-24 from an upper limit on its proper motion

The 'characteristic age' of a pulsar is usually considered to approximate its true age, but this assumption has led to some puzzling results, including the fact that many pulsars with small characteristic ages have no associated supernova remnants. The pulsar B1757-24 is located just outside the edge of a supernova remnant; the properties of the system indicate that the pulsar was born at the centre of the remnant with a substantial velocity, and that it has subsequently overtaken the expanding blast wave. With a characteristic age of 16,000 yr, the pulsar is expected to have a proper motion of 63-80 milliarcseconds (mas) per year. Here we report observations of the nebula surrounding the pulsar, which limit its proper motion to less than 25 mas yr(-1), implying a minimum age of 39,000 yr. A more detailed analysis argues that the true age may be as great as 170,000 yr, which is significantly larger than the characteristic age. We conclude from this result and other discrepancies associated with pulsars that characteristic ages greatly underestimate the true ages of pulsars.     

有限域上特征为奇数的正交空间中一类Cartesian认证码的构作

利用有限域上特征为奇数的正交几何构造了一类Cartesian认证码,并且计算了其参数及模仿攻击成功的概率PI和替换攻击成功的概率PS,这类Cartesian认证码对PI是最优的。     

由伽利略相对性原理推导动量守恒定律

作为一种教学研讨 ,在大学低年级物理教学中 ,应用对称性、不变性、相对性原理等新的物理概念、思想和方法推导动量守恒定律。     

Prediction of the structure of a receptor-protein complex using a binary docking method.

To validate procedures of rational drug design, it is important to develop computational methods that predict binding sites between a protein and a ligand molecule. Many small molecules have been tested using such programs, but examination of protein-protein and peptide-protein interactions has been sparse. We were able to test such applications once the structures of both the maltose-binding protein (MBP) and the ligand-binding domain of the aspartate receptor, which binds MBP, became available. Here we predict the binding site of MBP to its receptor using a 'binary docking' technique in which two MBP octapeptide sequences containing mutations that eliminate maltose chemotaxis are independently docked to the receptor. The peptides in the docked solutions superimpose on their original positions in the structure of MBP and allow the formation of an MBP-receptor complex. The consistency of the computational and biological results supports this approach for predicting protein-protein and peptide-protein interactions.