关于引力场的能量问题

本文讨论引力场中局部区域的能量问题。这里提出了一个新的引力场总能量-动量赝张量密度,它所表示的引力场局部空间区域中的能量对纯空间坐标变换是不变量,因而引力场的局部区域能量具有确定的物理意义。关于Schwarzschild场的能量和动量,新的赝张量给出的结果要比现有广义相对论文献中的其他形式的赝张量所给出的结果较为合理。文中还讨论了在引力理论中质量与能量的关系问题。 关键词：     

广义相对论中能量的定域性

本文就文献[1]中的主要论点作了考核。指出推论中的疏忽;表明文献[1]提出的引力场总能量-动量综量以及由它所表示的引力场有限空间区域中的能量对纯空间坐标变换来说不是唯一的,因而不具有确定的物理意义。 关键词：     

Mφller的引力场能量公式的另一推导

一、引言 几年前,Mφller曾经讨论过引力场的能量问题,他指出:爱因斯坦的能量—动量准张量密度是值得商榷的,因为在有限空间区域Ω内的积分     

矢引力子场度规场引力理论的共形平直静止解及引力场的能量动量赝张量的正常性

本文求出了VGM引力理论的共形平直静止解。文中把胡宁表达式引入VGM,它同样是守恒的能量动量表达式。对于单个集中质量的引力场,与GR一样,可证实引力质量与惯性质量相等。但Einstein的等效原理在这理论中并不成立。利用所求得的解,可知当n<1/4时,引力场的能量动量赝张量就是正常的。 关键词：     

等离子体二维密度重建的影响因素

利用超强超短激光脉冲产生的高能质子束的库仑能量损失可以重建稠密等离子体的二维密度分布，使用同时迭代重建算法（SIRT算法）研究等离子体二维密度重建的影响因素.研究等离子体密度梯度、密度量级和质子束入射能量对重建误差的影响，分析质子束成像探测等离子体密度之前获得等离子体大概方位的重要性，通过数据拟合确定了能量噪声和重建误差之间的解析关系式.     

引力场约化理论中的Virasoro代数

我们在引力场约化理论中找到了一种新的变换关系, 并且发现这种变换所对应的代数结构是没有中心项的Virasoro代数. 同Geroch群相比较, 不难确定在引力场约化理论中Virasoro代数与Kac-Moody代数之间的关系. 最后, 我们指出了这种变换可用来产生Ernst场方程的新解.     

利用"万有引力场的高斯定理"计算 地球表面某处的重力加速度

通过量子理论推导及类比电场来建立引力场高斯定理的概念,并根据布伦地球密度分布模型及受力情况分析得出地球表面某处的重力加速度计算公式,为重力加速度的理论计算提供了一种全新的思路和方法,对误差可能产生的来源也做了相关分析和探讨。     

用CCD相机测量中性束的空间密度分布

利用CCD(电荷耦合装置)相机所成象的光强度峰值拟合中性束中三种能量成分的空间密度分布。本文给出象光强度的峰值坐标,滤光片中心波长与束能量和束的观察方向夹角的关系,束能量与束的观察方向夹角的关系及实验结果。     

能流密度概念不适用于静场情形吗?

根据麦克斯韦方程组,可将电磁现象的能量守恒定律具体表述为[1]式中　是电磁场的场能密度, 　是电磁场的能流密度矢量(坡印亭矢量),记为S,则式(1)表明,空间任意体积V内产生的电功率,等于单位时间内体积V中电磁能的减少与通过体积V的界面S流入的能量之和。根据麦克斯韦方程组还可得到动量守恒定律的具体表示,电磁场的动量密度为这表明电磁场的动量密度矢量与能流密度矢量方向相同。 由于任意矢量A满足因此,在能流密度　中可附加任意矢量A的旋度　,而不影响式(1)成立。这似乎说明能流密度并非单值,可以有一附加项　的不确定度。但是这只是…     

引力透镜效应研究的历史与现状

在七十年代末,有文章报道说[1],在宇宙空间发现了一对极为相象的“孪生类星体”,发现者们认为,这极可能是六十多年来人们所谈论的“引力透镜效应”. 一、什么是引力透镜效应? 引力场能偏转光线传播的方向.在广义相对论中,有引力场存在的空间不再是平直空间,而是弯曲空间.光线在引力场中传播时偏转的角α=4GM/c2b.式中,G是引力常数,M是引力场源的质量,c是光速,b是光线离引力源最短的距离.对于掠过太阳表面的光线来讲,α=1.75角秒.从1919年以来,这个数值已多次为观测所证实.由此,引力场有可能使远处光源射来的光线会聚起来,起类似光学透镜的…     

On the intrinsic entropy of the gravitational field

I show that in linearized general relativity it is impossible to construct a detector by the use of which the quantum state of the linearized gravitational field could be reliably determined. This is because there is no material satisfying the positive energy condition which can serve as a good conductor or absorber of gravitational radiation over a finite range of frequencies. If this property is true of the full theory then one can conclude that a certain proportion of both the energy and information carried by a gravitational wave is irreversibly lost, and that there is a correspondingintrinsic entropy associated with any distribution of gravitational radiation.     

Sparling Two-Forms, the Conformal Factor and the Gravitational Energy Density of the Teleparallel Equivalent of General Relativity

It has been shown recently that within the framework of the teleparallel equivalent of general relativity (TEGR) it is possible to define the energy density of the gravitational field in a unique way. The tegr amounts to an alternative formulation of Einstein's general relativity, not to an alternative gravity theory. The localizability of the gravitational energy has been investigated in a number of spacetimes with distinct topologies, and the outcome of these analyses agree with previously known results regarding the exact expression of the gravitational energy, and/or with the specific properties of the spacetime manifold. In this article we establish a relationship between the expression of the gravitational energy density of the TEGR and the Sparling two-forms, which are known to be closely connected with the gravitational energy. We will also show that our expression of energy yields the correct value of gravitational mass contained in the conformal factor of the metric field.     

Freely Falling 2-Surfaces and the Effective Gravitational Mass

We derive an expression for the effectivegravitational mass for any closed spacelike 2-surface.This effective gravitational energy is defined directlythrough the geometrical quantity of the freely falling 2-surface and thus is well adapted to intuitiveexpectation that the gravitational mass should bedetermined by the motion of a test body moving freely inthe gravitational field. We find that this effective gravitational mass has a reasonable positivevalue for a small sphere in the non-vacuum space-timesand can be negative for the vacuum case. Further, thiseffective gravitational energy is compared with the quasi-local energy based on the (2 + 2)formalism of General Relativity. Although some gaugefreedoms exist, analytic expressions of the quasi-localenergy for vacuum cases are the same as the effective gravitational mass. Especially, we see that thecontribution from the cosmological constant is the samein general cases.     

Energy of Gravitational Field of Static Spherically Symmetric Neutron Stars

By using the Einstein-Tolman expression of the energy-momentum pseudo-tensor, the energy density of the gravitational field of the static spherically symmetric neutron stars is calculated in the Cartesian coordinate system.It is exciting that the energy density of gravitational field is positive and rational The xmmerical results of the energy density of gravitational field of neutron stars are calculated. For neutron stars with M=2M, the ratio of the energy density of gravitational field to the energy density of pure matters would be up to 0.54 at the surface.     

Energy of Gravitational Field of Static Spherically Symmetric Neutron Stars

By using the Einstein-Tolman expression of the energy-momentum pseudo-tensor, the energy density ofthe gravitational field of the static spherically symmetric neutron stars is calculated in the Cartesian coordinate system.It is exciting that the energy density of gravitational field is positive and rational. The numerical results ot the energydensity of gravitational field of neutron stars are calculated. For neutron stars with M = 2M , the ratio of the energydensity of gravitational field to the energy density of pure matters would be up to 0.54 at the surface.     

Mechanism of Gravity Impulse

It is well known that energy-momentum is the source of gravitational field. For a long time, it is generally believed that only stars with huge masses can generate strong gravitational field. Based on the unified theory of gravitational interactions and electromagnetic interactions, a new mechanism of the generation of gravitational field is studied. According to this mechanism, in some special conditions, electromagnetic energy can be directly converted into gravitational energy, and strong gravitational field can be generated without massive stars. Gravity impulse found in experiments is generated by this mechanism.     

Deviation of the Earth’s crust and upper mantle from isostatic equilibrium

The isostatically unbalanced crust and upper mantle structures conforming to the external gravitational field and minimizing deviation of the internal gravitational field from the isostatic equilibrium field, are determined. A dipole-type distribution of these structures associated with the motion of anomalous masses toward the potential energy minimum is revealed. On the basis of seismic data, it is inferred that the compensation of isostatically unbalanced masses is possible at the core-mantle boundary.     

Rydberg states of hydrogenlike ions in a braneworld model

Precise measurements of optical transition frequencies between Rydberg states of hydrogen-like ions could be used to obtain an improved value of the Rydberg constant, by avoiding the uncertainties about the proton radius. Motivated by this perspective, we investigate the influence of the gravitational interaction on the energy levels of Hydrogen-like ions in Rydberg states in a braneworld model. As it is known, in this scenario, the gravitational interaction is amplified in short distances. We show that, for Rydberg states, the main contribution for the gravitational potential energy does not come from the rest energy concentrated on the nucleus but from the energy of the electromagnetic field created by its electric charge. The reason is connected to the fact that, when the ion is in a Rydberg state with high angular momentum, the gravitational potential is not computable in zero-width brane approximation due to the gravitational influence of the electrovacuum in which the lepton is moving. Considering a thick brane scenario, we calculate the gravitational potential energy associated to the nucleus charge in terms of the confinement parameter of the electric field in the brane. We show that the gravitational effects on the energy levels of a Rydberg state can be amplified by hidden dimensions even when the compactification scale is shorter than the Bohr radius.     

Gravitational energy of a magnetized Schwarzschild black hole: a teleparallel approach

We investigate the distribution of gravitational energy in the spacetime of a Schwarzschild black hole immersed in a cosmic magnetic field. This is done in the context of the teleparallel equivalent of general relativity, which is an alternative geometrical formulation of general relativity, where gravity is described by a spacetime endowed with torsion rather than curvature, whose fundamental field variables are tetrad fields. We calculate the energy enclosed by a two-surface of constant radius—in particular, the energy enclosed by the event horizon of the black hole. In this case we find that the magnetic field has the effect of increasing the gravitational energy as compared to the vacuum Schwarzschild case. We also compute the energy (i) in the weak magnetic field limit, (ii) in the limit of vanishing magnetic field, and (iii) in the absence of the black hole. In all cases our results are consistent with what should be expected on physical grounds.