On singularity-free spacetimes

We consider here the metric for the singularity-free family of fluid models. The metric is unique for cylindrically symmetric space-time with metric potentials being separable functions of radial and time coordinates in the comoving coordinates. It turns out that fluid models separate out into two classes, withρ ≠μp in general butρ = 3p in particular andp =ρ. It is shown that in both the cases radial heat flow can be incorporated without disturbing the singularity-free character of the spacetime. The geodesics of the singularity-free metric are studied and the geodesic completeness is established. Several previously known solutions are derived as particular cases.     

一类无奇点宇宙模型

按照Penrose-Hawking的奇点定理,在场源物质无旋、无加速且能量密度满足条件ρ+3p≥0的宇宙模型中一定存在奇点.本文研究了场源物质有旋时的无奇点宇宙模型,获得了几种无奇点的宇宙解.     

Space-time microstructure and singularity-free quantum field theory

It is shown that the dynamical consistency requirements of quantum field theory and the Lorentz-invariant character of particle kinematics and wave equations are compatible with the postulate that physical space is a complex manifold with Euclidean-Gaussian measure in the small. Such a postulate for the microstructure of space introduces a fundamental length(10^–16 cm) and leads to-functions that are analytic on the light-cone for a free field, and hence to self-energies and renormaiization constants that are finite for interacting fields.Work supported by a National Science Foundation grant.     

Quantum vacuum energy and singularity-free Kaluza-Klein cosmology

We present a class of cosmological models in which vacuum collapse to curvature singularity is prevented by the generalized gravitational Casimir energy. The mechanism works in higher dimensions, and gives rise to Kaluza-Klein cosmologies free from singularity.     

A non-diagonal singularity-free model in torsion gravity

In the context of torsion (teleparallel) gravity, we focus on discussing the spin effects of Dirac particles associated with the non-diagonal singularity-free model (Mars space-time). We see that the vector part depends on the radial r and z directions and the axial-vector will be along the radial direction, that is, it will be symmetric about radial direction. Furthermore, the t = 0 case of the Mars metric is considered, thence it is seen that the axial-vector vanishes.     

A singularity-free cosmological model in ECSK theory

In the framework of the ECSK [Einstein-Cartan-Sciama-Kibble] theory of cosmology, a scalar field nonminimally coupled to the gravitational field is considered. For a Robertson-Walker open universe (k=0) in the radiation era, the field equations admit a singularity-free solution for the scale factor. In theory, the torsion is generated through nonminimal coupling of a scalar field to the gravitation field. The nonsingular nature of the cosmological model automatically solves the flatness problem. Further absence of event horizon and particle horizon explains the high degree of isotropy, especially of 2.7-K background radiation.     

On spherically symmetric singularity-free models in relativistic cosmology

The introduction of time dependence through a scale factor in a non-conformally flat static cosmological model whose spacetime can be embedded in a five demensional flat spacetime is shown to give rise to two spherical models of universe filled with perfect fluid acompannied with radial heat flux without any Big Bang type singularity. The first model describes an ever existing universe which witnesses a transition from state of contraction to that of ever expansion. The second model represents a universe oscillating between two regular states.     

Fundamental constants in singularity-free five-dimensional Kaluza-Klein cosmological model

Expressions for the time dependence of the fundamental constants are derived through dimensional reduction and one-loop quantum corrections to scalar fields. Moreover, singularity-free solutions of Einstein's field equations are obtained. Using these solutions, we discuss the time dependence of fundamental constants. It is interesting to see that the fine structure constant asymptotically approaches to 1/137,G _eff (effective four-dimensional constant) approachesG _N (Newtonian gravitational constant), and _eff vanishes. Graphical representations of these results are also given for a special case.     

Solution of dirac equation in a singularity-free Kaluza-Klein cosmological model

The singularity-free solution of (4 + D) -dimensional Einstein field equations for the Kaluza-Klein cosmological model is obtained. Then the Dirac equations are solved in this model.     

离散时空中的奇性自由的Friedmann宇宙解

由尘埃物质粒子的集合来形成一个理想的离散时空的Friedmann宇宙模型并证明了它是奇性 自由的. 关键词： 离散时空 尘埃物质 Friedmann宇宙 奇性自由     

An angular singularity-free method for the dynamics of the rovibrational motion of diatomic molecules

An angular singularity-free method for the dynamics of the rovibrational motion of diatomic molecules has been proposed. The present method is based on a formulation that the orientation of a diatomic molecule is expressed by the Cartesian coordinates of the unit vector parallel to the molecular axis. In this light, the present method can be considered as a modification of a method proposed for the rigid rotational motion to the rovibrational motion. Illustrations of the present method have been performed for the classical dynamics of the rovibrational motion of a diatomic molecule, and for the semiclassical dynamics of the collision between an atom and a diatomic molecule, including comparisons with other conventional methods. It is concluded that the present method is free from angular singularity, and that the present method is superior to other conventional methods in view of computational efficiency.     

Gravity waves, chaos, and spinning compact binaries

Spinning compact binaries are shown to be chaotic in the post-Newtonian expansion of the two-body system. Chaos by definition is the extreme sensitivity to initial conditions and a consequent inability to predict the outcome of the evolution. As a result, the spinning pair will have unpredictable gravitational waveforms during coalescence. This poses a challenge to future gravity wave observatories which rely on a match between the data and a theoretical template.     

Development of medium power, compact, all-solid-state lasers

Conclusions  We have briefly reviewed some of the applications of diode-pumping to solid-state laser systems. The potential of this combination is already well demonstrated in these few examples which only consider medium-power applications. New highly efficient laser crystals like Yb:YAG, and new pumping schemes like that employed in newly developed thin-disk lasers also appear promising as an alternative approach to medium-high power all-solid-state lasers [44]. High-power systems have also been developed for industrial, medical and environmental applications [45]; their massive use, however, largely depends on diode-bar cost drop, by this time being well-established that the more efficient pumping solution for these high power bulk systems is side-pumping. An increasingly attractive alternative to diode-pumped medium power infrared cw lasers is currently represented by diode-pumped fibre lasers, which generate as much as 35 W in a diffraction-limited beam. This technology offers superior ruggedness and compactness, but is presently limited to cw operation or very low-energyQ-switching. In conclusion, we strongly believe that an improved technology for more reliable and low-cost diode bar production could accelerate the power scale up of DPSS laser systems and quickly push them to fully replace all the other laser competitors.     

Smectic shells

Confining a smectic liquid crystal between two spherical surfaces results in the formation of a complex defect structure characterized by a set of curvature walls that divide the sphere into crescent domains, causing the undulation of the smectic layers. In this paper, we examine in detail these smectic textures and discuss the various possible origins of the observed patterns.     

Energy conditions,traversable wormholes and dust shells

Firstly, we review the pointwise and averaged energy conditions, the quantum inequality and the notion of the “volume integral quantifier,” which provides a measure of the “total amount” of energy condition violating matter. Secondly, we present a specific metric of a spherically symmetric traversable wormhole in the presence of a generic cosmological constant, verifying that the null and the averaged null energy conditions are violated, as was to be expected. Thirdly, a pressureless dust shell is constructed around the interior wormhole spacetime by matching the latter geometry to a unique vacuum exterior solution. In order to further minimize the usage of exotic matter, we then find regions where the surface energy density is positive, thereby satisfying all of the energy conditions at the junction surface. An equation governing the behavior of the radial pressure across the junction surface is also deduced. Lastly, taking advantage of the construction, specific dimensions of the wormhole, namely, the throat radius and the junction interface radius, and estimates of the total traversal time and maximum velocity of an observer journeying through the wormhole, are also found by imposing the traversability conditions.     

GYRAC: a compact, cyclic electron accelerator

The concept of the gyro-resonant accelerator (GYRAC), which is based on cyclotron resonance in a magnetic field that is increasing slowly in time, is presented. Previously published work shows that this results in an autoresonance in which the wave provides a synchronous acceleration of the electrons. Using a simple model makes it possible to design a particularly compact, cyclic electron accelerator; in a cavity with a 1-m radius and final magnetic field of 5 T, electron energy reaches 680 MeV, giving rise to synchrotron radiation of 1 keV. Assuming uniform fields and rescaling time, a Hamiltonian system is arrived at which has one degree of freedom and which, in first-order approximation is time independent. In a second-order approximation, a slow damping of the autoresonant oscillation is found. A paraxial model for beam and fields allows evaluation of the charge effects-the GYRAC then resembles the betatron. These results are illustrated by numerical three-dimensional simulations     

On geometric quantization of compact,complex manifolds

A modified Kostant-Souriau geometric quantization procedure in a case of purely complex polarization is described. It is proved that each algebraic manifold admits such a quantization. The cases of a C-homogeneous manifold and a manifold covered with a bounded complex domain are studied.     

Large-field-of-view, high-gain, compact diode-pumped Nd:YAG amplifier

We present a compact diode-end-pumped Nd:YAG amplifier with a FWHM angular bandwidth of 100 degrees . Using a 1.064-microm probe beam, we measured a 2-pass gain of 23 (13.6dB) and a 4-pass gain of 420 (26.2dB). High-gain image amplification with such a laser amplifier is also demonstrated.     

High repetition rate, compact micro-pulse all-solid-state laser

A high repetition rate, compact micro-pulse all-solid-state laser is designed. The diffusion bonded crystal of YAG, Nd:YAG, and Cr4+:YAG is taken as a monolithic cavity. The optimized initial transmission,output coupling, and pumping size of Cr4+:YAG are calculated. The experimental results show that the laser satisfies the requirement of a spaceborne laser range finder.