The structure of polar caps and the equatorial belt of pulsars

The self-consistent balanced pulsar magnetosphere of a magnetic neutron star with aligned magnetic and rotational axes is considered. It is shown that the magnetosphere consists of electron polar caps separated by empty space from a positron equatorial belt. The shape of the cold polar caps at a large distance from the star is calculated. It is shown that the cap shape at a large distance is independent of the magnetospheric structure near the neutron star. The shape of the equatorial belt is calculated. It is shown that a part of the equatorial belt rotates differentially, and its angular velocity is larger than that of the star (superrotation). It is shown that under certain conditions the space charge density of the belt can be very large. In principle, the formation of a surface charge placed in vacuum on a magnetic surface is possible. Magnetospheric vibrations are considered. A connection is established between drifting subpulses and the equatorial belt superrotation and also between drifting subpulses and cap vibrations. The characteristic frequency of vibrations and the angular velocity of superrotation are estimated.     

Some physical properties and stability of an exact model of a relativistic star

An exact solution of Einstein's field equations for an isentropic fluid sphere is examined. It turns out that the crucial factor for the physical properties and the stability of this model is the degree of incompressibility. Necessary and sufficient conditions are given for the weak and the strong energy conditions to be fulfilled and for the speed of sound to be less than the speed of light. The speed of sound always has a minimum at the center of the fluid sphere. But two possibilities exist: either the speed of sound is increasing all the way outwards to the surface of the sphere, or the speed of sound is first increasing, then reaching a maximum when still inside the fluid sphere, and thereafter decreasing outwards to the surface. The adiabatic index is investigated and is found to be increasing outwards for the actual degrees of compressibility. This adiabatic index is always greater than unity, and the temperature is thus decreasing throughout the sphere. The necessary and sufficient condition for the adiabatic index to be greater than 4/3 is also given. (This is a necessary condition for the fluid sphere to be stable.) Chandrasekhar's pulsation equation with boundary conditions is investigated, and the fluid sphere is found to bestable if and only if the degree of incompressibility is greater than a certain value.Dedicated to the memory of the late Bronislaw Kuchowicz.     

应用于射电天文的低噪声温度测量方法

噪声温度是接收机和低噪声放大器最重要的性能指标,是了解设备性能好坏的关键因素。随着电子技术的快速发展,接收机和低噪声放大器的噪声温度变得越来越低,准确而快速地测量接收机和低噪声放大器的噪声温度变得非常困难。介绍了6种在射电天文中经常使用的测量低噪声温度的方法,这些测量方法具有准确可靠、简单易行的优点。叙述了测量原理并给出了一些测量方法的测量结果,对影响测量噪声温度精度并且易被忽视的因素也做了详细讨论。     

Time-dependent heating of the solar corona

The problem of how the corona is heated is of central importance in solar physics research. Here it is assumed that the heating occurs in a regular time-dependent manner and the response of the plasma is investigated. If the magnetic field is strong then the dynamics reduces to a one-dimensional problem along the field. In addition if the radiative time in the corona is much longer than the sound travel time then the plasma evolvesisobarically. The frequency with which heat is deposited in the corona is investigated and it is shown that there is a critical frequency above which a hot corona can be maintained and below which the plasma temperature cools to chromospheric values. An evaluation of the isobaric assumption to the solar corona and the implications of time-dependent heating upon the forthcoming SOHO observations are also presented.     

On the interpretation of the photometry of irregular variable stars observed intermittently

This note is concerned with the inherent possibilities and limitations in the characterisation of irregular variables when, as is almost inevitably the case, the observations are not effectively continuous. The historical tendency to interpret almost everything in terms of strict periodicity is criticised. The basic logic of the situation is discussed, and it is emphasised that intermittency of observation inevitably blunts our knowledge of the spectrum of the variation. This can be restored to only a limited extent, depending on how reliably it is possible to presume missing observations by interpolation. Some applcation is made to a recent publication on 3C 345.A knowledge of formal Fourier theory is assumed, and the aim is to discuss critical principles rather than to recommend any fixed procedures of interpretation.     

Mathematical Model of Unit Vector Method (MMUVM) and Convergence of Its Iteration Method in Simplified Form (PUVM1)

The unit vector method (PUVM1) by which the observed data of artificial satellites are used to determine the perturbed initial orbits has been widely applied. In order to further perfect and improve this method, first, a mathematical model (MMUVM) corresponding to this method is constructed on the basis of measuring errors. In essence, the MMUVM is a nonlinear optimization problem. In the light of the MMUVM, simulated and observed data of multiple circuits are taken to form specific objective functions, which are then processed by means of a direct search method and with of a tri-diagonal quadratic interpolation model for solving optimization problems. The calculated results show that the optimization model MMUVM is right and reasonable and the adopted direct method is practical and effective. Secondly, the relation between PUVM1 and MMUVM is further clarified: PUVM1 is essentially a simplified form of the MMUVM, and the primary reason is found from mathematical principles, why it is that PUVM1 can only be applied to short-arc data within one circuit and not to long-arc or multi-circuit data. Finally, a preliminary theoretical analysis of the convergence of the iteration algorithm of PUVM1 is carried out and instancesof numerical verification given. It is pointed out that the iterative scheme of PUVM1 is conditionally convergent. This means that sometimes, even though the quasi-normalization equation is reasonable, the iteration diverges.     

近距离罗兰-C信号周期识别的数字化方法初探

对判断罗兰-C脉冲峰值的算法作了改进。对加有噪声的近距离罗兰- C脉冲仿真信号的采样值用改进的算法进行计算后,可识别信号周期并给出相位编码信息。对改进后的算法的有效性用MATLAB进行了验证,并用MODELSIM对改进的算法进行了仿真实现。结果表明：在一定的信噪比条件下,改进后的算法初步实现了对近距离罗兰-C信号周期识别的数字化,具有一定的实用性。     

Numerical treatment of hydromagnetic thermal boundary-layer flow of an infinite porous limiting surface

The finite difference approximation technique using the explicit method is used for solving the unsteady flow of an electrically conducting viscous and incompressible fluid, subjected to a normal homogenous magnetic field. The flow is confined on one side of a non-magnetic infinite limiting surface (wall) which is initially at rest and then is suddenly accelerated in its own plane with a velocity which is a general function of time. The wall is porous and we assume that the Prandtl number of the fluid corresponds to the case of water and that the magnetic Prandtl number is equal to one. Quantitative discussion of the results is presented for the case of uniformly accelerated motion of the wall.     

Active Optics in LAMOST

Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) is one of the major national projects under construction in China. Active optics is one of the most important technologies for new large telescopes. It is used for correcting telescope errors generated by gravitational and thermal changes. Here, however, we use this technology to realize the configuration of LAMOST, -a task that cannot be done in the traditional way. A comprehensive and intensive research on the active optics used in LAMOST is also reported, including an open-loop control method and an auxiliary closed-loop control method. Another important development is in our pre-calibration method of open-loop control, which is with some new features: simultaneous calculation of the forces and displacements of force actuators and displacement actuators; the profile of mirror can be arbitrary; the mirror surface shape is not expressed by a fitting polynomial, but is derived from the mirror surface shape formula which is highly accurat     

原太阳吸积盘结构

计算了粘滞演化阶段原太阳吸积盘结构。采用稳态标准吸积盘模型来描述盘中湍动粘滞；忽略其径向能量传输，将垂直结构作为一维问题处理。假设盘作Keplerian较差旋转，处于流体力学平衡和局域热平衡，盘由粘滞耗散加热，能量通过对流和辐射向外传输。结果表明，对温度敏感的不透明度是决定盘结构的重要因素；原太阳吸积盘为冷的薄盘，盘中热对流不稳定性由外而内，由上而下地终结；行星的形成应首先开始于对流终结的区域。     

Kinetic equilibrium of nonlinear electromagnetic waves in electron-positron-ion magnetoplasmas

The problem of a one-dimensional, nonlinear, circularly polarized wave in a collisionless plasma is solved for the case in which the group velocity of the localized wave is zero relative to the plasma frame.For an electron-positron plasma the ponderomotive potential is repulsive, and both small and large amplitude waves in the presence of reflected and transmitted particles is discussed.The inclusion of an external magnetic field such that the cyclotron frequency is smaller than the wave frequency does not alter qualitatively the results of the fieldless case, except for the fact that an electrostatic potential is generated.For the case in which the cyclotron frequency is larger than the wave frequency, the resulting potential is attractive, and it is shown that no localized waves can coexist with confined and transmitted particles. If, however, an ionic component is presnt in the electron-positron plasma, such as may be the case in pulsar magnetospheres, localized waves may again be possible.     

The possible compatibility of Einstein's general theory of relativity,Mach's principle,and Rosen's bimetric theory,in relation to Horák's cosmic potential

Mach's principle is formulated in two different ways, heuristic and mathematical. Known problems of the principle are listed and two of them, the problem of its validity in the case the Universe is open and the boundary condition problem, are analyzed separately. Moreover, the history of the cosmic potential is outlined and a short modification of Horák's deduction of the potential is presented together with a discussion on the conditions of the solution. The conclusions are drawn that the Universe is closed and that Mach's principle is compatible with the general theory of relativity, provided that the Big Bang did not start from a singularity but from finite volume and density. In the last section it is shown that Rosen's bimetric theory is compatible with our picture of the Universe.     

网络时延对网上高时间约束业务影响的讨论

给出了一系列的网络测量结果。通过对实测结果的分析，结合图表形象地揭示了网络时延的严重性、随机性和信息路径的不确定性，指出了这种网络现象对具有高时间约束的网络通信业务的严重影响，并阐述了测量和改正网络时延的重要意义。     

The Friedmann universe and the world potential

In Section 1 of the paper the energy equation of the Friedmann universe, when matter dominates over radiation, is discussed. It is known that the value of the world potential is constant everywhere in the Universe, despite the pulsation motion of the Universe or a possible transformation of pulsation energy into matter or vice versa. The condition for the Universe being closed is deduced. Furthermore, the possibility to define the mass-energy of the Universe is discussed; and the conclusion is arrived at that the mass-energy of the Universe relative to an observer in the non-metric space outside the Universe is equal to zero; i.e. the Universe originated as a vacuum fluctuation. Finally, the view-point of an external observer is described. Such an observer can claim that our closed Universe is a black hole in a non-metric empty space. Besides, the differences between such a black hole and the astrophysical black holes are indicated.In Section 2 the origin of the gravitational force retarding the expansion is discussed, using the properties of the relativistic gravitational potential. In contradiction to Section 1, the view-point of an inner observer (inside the Universe) is used here. It is concluded that the boundary of the closed Universe is an unlocalizable potential barrier.In Section 3 of the paper the apparent discrepancy between Mach's principle and the general theory of relativity is resolved. The solution is based on the fact that, for the Euclidean open universe, the concept of mass is related to the potential of the background equal to –1, but the concept of the mass-energy is related to the zero-potential of the non-metric background. Because the universe is open and a potential barrier (a boundary of the universe) can be localized-i.e. is geometrically existing — by solution of the field equation, we have to refer to the background with zero-potential. The principal idea of the solution is then that the zero-density means the density of mass-energy, when simultaneously the mass density is equal to the critical value for which the Robertson-Walker metric becomes the Euclidean metric of the Minkowski (i.e., flat) space-time. Further a generalization of Newton's law of inertia is formulated, and the properties of nullgeodesics are touched upon. As a conclusion it is stated that this paper and the two previous ones (see Voráek, 1979a, b)de facto express Mach's principle.     

Atmospheric effect on the upwelling radiation at the top of the atmosphere over a stream

A new version is adopted for the evaluation of the upwelling radiation from atmosphere bounded by the surface, where the surface is composed of two half semi-infinite Lambert surfaces and a stream is inserted between them. The contrast of the stream is discussed with respect to the atmospheric effect. The width of the stream is considered to be 0.5, 1, and 3km; The solar and observational direction is located in the normal plane to the stream. The observational site is located at altitude 30km. The horizontal distance of observational site to the stream is fixed to 6.28 . The atmosphere is assumed to be homogeneous, which is composed of aerosol and molecules, where the model aerosol is of the oceanic type.In the computational procedure, a probability of radiation interacting with respective half surfaces and the stream are calculated based on the assumption of single scattering in the atmosphere, where isotropic scattering is undertaken. By use of this probability, the emergent radiation at the top of the atmosphere is calculated approximately by considering the radiative interactions between atmosphere and surfaces up to twice. The numerical simulation exhibits the extraordinary effect near the stream. The contrast of the stream depends upon the albedo of the surrounding surfaces. It increases with the increase of the stream width and decreases with the optical thickness.     

Stability of the equilibrium distributions of interstellar gas,cosmic rays,and magnetic field in an external gravitational field

An interstellar medium consisting of regular and turbulent magnetic fields, thermal gas and cosmic rays is tested for stability in a stellar gravitational field. Cosmic rays are described by the diffusion-convection equation and the stability region of the system is determined. It is shown that the presence of cosmic rays is a stabilizing factor if the cosmic-ray diffusion coefficient is sufficiently small. The dependence of the maximum growth rate of instability on the cosmic-ray diffusion coefficient is qualitatively determined.     

Nonsingular cosmological model with background field in flat space-time theory of gravitation

A previously studied theory of gravitation in flat space-time is applied to homogeneous, isotropic cosmological models. In addition to radiation a two-component fluid model consisting of dust and of a background field is studied. This universe starts from a nonsingular state and expands for ever. The energy of radiation, of dust and of the background are emerged from the gravitational energy. Entropy is produced. The age of the universe is infinite measured in units of absolute time whereas the proper-time of the universe is finite. The sum of the density parameters of dust, of radiation and of the background field is about one. There is no flatness and no monopole problem.     

基于单目视觉的天线副面并联调整机构相对位姿测量方法

为测量天线副面并联调整机构的相对位姿,研究了一种基于单目视觉的位姿测量系统.采用光源照射固定于动平台上的合作目标,结合滤光片等控制手段,利用单目相机采集非共面特征点的图像,获得高对比度的准理想图像.经过图像处理和平方加权质心法,提取出特征点的图像坐标,使用EPnP (Efficient Perspective-n-Point)算法进行位姿解算,最终可以得到并联调整机构的相对位姿测量方法.最后通过实验进行了精度验证,结果表明平移精度为0.1 mm,旋转精度为0.05°,满足了实验要求,为并联机构的位姿检测提供了可行性思路.     

Zonal winds near Venus' cloud top level: An analytic model of the equatorial wind speed

It is proposed that the equatorial wind speed near Venus' cloud top level is maintained by a balance between the pumping effect of the semidiurnal tide and vertical advection by the Hadley circulation, both integrated across the thermal driving region. A consequence of this hypothesis is that the maximum equatorial zonal wind speed is proportional to Nh where N is buoyancy frequency and h is a measure of the thickness of the driving region. The proportionality constant is a weakly increasing function of the heating rate and a decreasing function of λh, where λ is an inverse length characterizing the mean zonal wind shear. The equilibrium solution considered is shown to be stable. For the class of solutions investigated, there is a threshold value of heating rate below which there is no equilibrium satisfying the hypothesized balance, but this result depends on the assumption that the shape of the zonal wind profile is invariant with thermal forcing amplitude.     

A new regularization of the restricted three-body problem and an application

A new regularizing transformation for the three-dimensional restricted three-body problem is constructed. It is explicitly derived and is equivalent to a simple rational map. Geometrically it is equivalent to a rotation of the 3-sphere. Unlike the KS map it is dimension preserving and is valid inn dimensions. This regularizing map is applied to the restricted problem in order to prove the existence of a family of periodic orbits which continue from a family of collision orbits.