Superradiance of dyonic black holes

The Klein-Gordon equation is applied to investigate superradiance around a dilatonic variant of dyonic black holes, a type of black holes whose extremal limits are justified for the S-wave approximation. The result is: The dilaton field boosts the superradiance.     

On static spherically symmetric solutions of the vacuum Brans-Dicke theory

It is shown that among the four classes of the static spherically symmetric solutions of the vacuum Brans-Dicke theory of gravity only two are really independent. Further, by matching exterior and interior (due to physically reasonable spherically symmetric matter source) scalar fields it is found that only the Brans class I solution with a certain restriction on the solution parameters may represent an exterior metric for a nonsingular massive object. The physical viability of the black hole nature of the solution is investigated. It is concluded that no physical black hole solution different from the Schwarzschild black hole is available in the Brans-Dicke theory.     

A class of generalised Robinson-Trautman solutions in non-comoving coordinates

A new class of algebraically special solutions is found for Einstein's equations based on the generalised Robinson-Trautman formulation introduced by Wainwright. The solution metrics depend on all four spacetime coordinates t,x,y and r, and in the x,y subspace are either spherically symmetric (parameter K ₀ > 0) or spatially flat (K ₀ = 0). The inhomogeneous spacetimes, of Petrov type II, have singularities at t = 0 and r = 0. The source is a stiff perfect fluid that expands with shear and acceleration but without rotation. The dynamical configuration in the era t ∼ 0 depends directly on a function h(x,y) of the metric. Trapped surfaces are found, associated with the singularity r = 0, which is shown to be censored.     

Black holes in which the electrostatic or scalar equation is solvable in closed form

We show that the method used in the Schwarzschild black hole for finding the elementary solution of the electrostatic equation in closed form cannot extend in higher dimensions. By contrast, we prove the existence of static, spherically symmetric geometries with a non-degenerate horizon in which the static scalar equation can be solved in closed form. We give the explicit results in 6 dimensions. We determine moreover the expressions of the electrostatic potential and of the static scalar field for a point source in the extremal Reissner-Nordström black holes in higher dimensions.     

The dynamical model and quantization of the Schwarzschild black hole

The mass of the Schwarzschild black hole, an observable quantity, is defined as a dynamical variable, while the corresponding conjugate is considered as a generalized momentum. Then a two-dimensional phase space is composed of the two variables. In the two-dimensional phase space, a harmonic oscillator model of the Schwarzschild black hole is obtained by a canonical transformation. By this model, the mass spectrum of the Schwarzschild black hole is firstly obtained. Further the horizon area operator, quantum area spectrum and entropy are obtained in the Fock representation. Lastly, the wave function of the horizon area is derived also. Supported by the National Natural Science Foundation of China (Grant No. 10773002) and the Natural Research Foundation of Heze University (Grant No. XY05WL02)     

NON-OCCURRENCE OF TRAPPED SURFACES AND BLACK HOLES IN SPHERICAL GRAVITATIONAL COLLAPSE

By using the most general form of Einstein equations for General Relativistic (GTR) spherical collapse of an isolated fluid having arbitrary equation of state and radiation transport properties, we show that they obey a Global Constraint, 2GM(r, t)/R(r, t)c ²1, where R is the invariant circumference radius, t is the comoving time, and M(r, t) is the gravitational mass enclosed within a comoving shell r. This inequality specifically shows that, contrary to the traditional intuitive Newtonian idea, which equates the total gravitational mass (M _b) with the fixed baryonic mass (M ₀), the trapped surfaces are not allowed in general theory of relativity (GTR), and therefore, for continued collapse, the final gravitational mass M _f0 as R0. This result should be valid for all spherical collapse scenarios including that of collapse of a spherical homogeneous dust as enunciated by Oppenheimer and Snyder (OS). Since the argument of a logarithmic function cannot be negative, the Eq. (36) of the O–S paper (TIn ) categorically demands that y _b=R _b/R _gb1, or 2GM _b/R _b c ²1, where R _b referes to the invariant radius at the outer boundary. Unfortunately, OS worked with an approximate form of Eq. (36) [Eq. 37], where this fundamentalconstraint got obfuscated. And although OS noted that for a finite value of M(r, t) the spatial metric coefficient for an internal point fails to blow up even when the collapse is complete for R0, they, nevertheless, ignored it, and, failed to realize that such a problem was occurring because they were assuming a finite value ofM _f, where M _f is the value of the finite gravitational mass, in violation of their Eq. (36).Additionally, irrespective of the gravitational collapse problem, by analyzing the properties of the Kruskal transformations we show that in order that the actual radial geodesics remain timelike, finite mass Schwarzschild Black Holes can not exist at all.Our work shows that as one attempts to arrive at the singularity, R0, the proper radial length l= dr (even though r and R are finite), and the collapse process continues indefinitely. During this indefinite journey, naturally, the system radiates out all available energy, QM _i c ², because trapped surfaces are not formed. And this categorically shows that GTR is not only the most beautiful physical theory, but also, is the only, naturally, singularity free theory (atleast for isolated bodies), as intended by its founder, Einstein. However, this derivation need not rule out the initial singularity of big bang cosmology because the universe may not be treated as an isolated body.There is a widespread misconception, that recent astrophysical observations have proved the existence of Black Holes. Actually, observations suggest existence of compact objects having masses greater than the upper limit of static Neutron Stars. The present work also allows to have such massive compact objects. It is also argued that there is evidence that part of the mass-energy accreting onto several stellar mass (binary) compact objects or massive Active Galactic Nuclei is getting lost, indicating the presence of an Event Horizon. Since, we are showing here that the collapse process continues indefinitely with local 3-speed Vc, accretion onto such Eternally Collapsing Objects (ECO) may generate little collisional energy out put. But, in the frame work of existence of static central compact objects, this small output of accretion energy would be misinterpreted as an evidence for Event Horizons. Thus the supposed BHs are actually massive compact ECOs.     

Estimation of the Tensile Strength Reduction of a Composite Laminate with a Hole

The strength problem for a body with an artificial defect in the form of a hole is considered. To solve this problem, an approach is suggested according to which the local strength of a material in the area of stress concentration is assumed to depend on the size of this area. The scale of the problem is introduced via the ratio between the characteristic sizes of the deformed area and the characteristic length of the material. This approach is used to estimate the strength of composite laminates weakened by holes and notches. Expressions for the failure stress are obtained, which can be applied to isotropic and orthotropic laminates both in quasi-brittle failure and in failure associated with significant inelastic deformations. A comparison between the calculated _c values and the known experimental data for glass/epoxy and graphite/epoxy laminates is presented.     

一个平面对称黑洞的霍金隧穿辐射

在Anti—de Sitter时空中，采用Parikh的半经典量子隧穿模型，研究了一个平面对称黑洞的霍金隧穿辐射，考虑到自引力作用和能量守恒，得出的隧穿率与Bekensten—Hawking熵有关，且隧穿辐射谱不是纯热谱，并满足么正性理论．     

动态Vaidya黑洞的Hawking隧穿辐射

采用Hamilton-Jacobi方法对动态Vaidya黑洞的Hawking隧穿辐射进行研究，结果表明该黑洞的辐射谱不是纯热谱，且出射粒子的隧穿率与Bekenstein-Hawking熵变有关．本文不仅提出了一种研究动态黑洞Hawking隧穿辐射的新方法，而且得出了有意义的结果．     

强抑制性多元醇海水钻井液研究及应用

胜利浅海埕岛油田沙河街组地层粘土含量高，粘土组成以伊像混层和伊利石为主，地层水敏性较弱，微裂缝及层理较发育。钻井液及滤液沿层理和微裂缝渗入地层内部，引起硬脆性泥页岩剥落坍塌。针对沙河街组地层特点，研制出一种强抑制性多元醇海水钻井液体系，并对其进行了性能评价及防塌机理分析。室内试验结果表明，该钻井液体系具有较好的抑制性能和流变性，抗海水和劣质土污染的能力较强，环境可接受性好。现场实践证明，该钻井液性能稳定，维护处理简单，能有效解决沙河街组地层钻进中出现的技术难题，避免复杂情况的发生。