Exothermic Supercooled Liquid-Liquid Transition in Amorphous Sulfur

Amorphous sulfur （a-S） is prepared by rapidly compressing molten sulfur to high pressure. From differential scanning calorimeter measurements, a large exothermic peak has been observed around 396K. Online wide-angled x-ray scattering spectra indicate that no crystallization occurs in the temperature range 295-453K, suggesting that the exothermal process corresponds to an amorphous-to-amorphous transition. The transition from amor- phous sulfur to liquid sulfur is further verified by the direct observation of sulfur melt at the temperature of the associated transition. This is the first time of reporting that a-S transforms to liquid sulfur directly, which has avoided a crystallization process. What is more, the transition is an exothermic and a volume expansion process.     

Dissipative Future Universe Without Big Rip

The present study deals with dissipative future universe without big rip in context of Eckart formalism. The generalised Chaplygin gas, characterised by equation of state p=-\fracAr^\frac1ap=-\frac{A}{\rho^{\frac{1}{\alpha}}}, has been considered as a model for dark energy due to its dark-energy-like evolution at late time. It is demonstrated that, if the cosmic dark energy behaves like a fluid with equation of state p=ωρ; ω<−1 as well as Chaplygin gas simultaneously then the big rip problem does not arise and the scale factor is found to be regular for all time.     

Comment on the Transition Amplitude for Toy Universe Models

The parametrized system called the idealclock is turned into an ordinary gauge system andquantized by means of a path integral in which canonicalgauges are admissible. Then the possibility of applying the results to obtain the transition amplitudefor empty minisuperspaces, and the restrictions arisingfrom the topology of the constraint surface, are studiedby matching the models with the ideal clock. A generalization to minisuperspaces with truedegrees of freedom is also discussed.     

Non-Violation of Energy Conditions in the Future Accelerated Universe Due to Quantum Effects

Here, an accelerated phantom model for the late universe is explored, which is free from future singularity. It is interesting to see that this model exhibits strong curvature for all time in future, unlike models with ‘big-rip singularity’ showing high curvature near singularity time only. So, quantum gravity effects grow dominant as time increases in late universe too. More importantly, it is demonstrated that quantum corrections to FRW equations lead to non-violation of ‘cosmic energy conditions’ of general relativity, which are violated for accelerating universe without these corrections.     

Future Destiny of Quintessential Universe and Constraint on Model from Deceleration Parameter

The evolution of the quintessence in various stages of the universe, i.e., the radiation-, matter-, andquintessence-dominated stages, is closely related with the tracking behavior and the deceleration parameter of theuniverse. We gave the explicit relation between the equation-of-state of the quintessence in the epoch of the matter-quintessence equality and the inverse power index of the quintessence potential, obtained the constraint on this potentialparameter comingfrom the present deceleration parameter, i.e., a low inverse power index.We point out that the lowinverse power-law potential with a single term cannot work for the tracking solution. In order to have both of the trackerand the suitable deceleration parameter it is necessary to introduce at least two terms in the quintessence potential. Wegive the future evolution of the quintessential universe.     

Future Destiny of Quintessential Universe and Constraint on Model from Deceleration Parameter

The evolution of the quintessence in various stages of the universe, i.e., the radiation-, matter-, and quintessence-dominated stages, is closely related with the tracking behavior and the deceleration parameter of the universe. We gave the explicit relation between the equation-of-state of the quintessence in the epoch of the matter-quintessence equality and the inverse power index of the quintessence potential, obtained the constraint on this potential parameter coming from the present deceleration parameter, i.e., a low inverse power index. We point out that the low inverse power-law potential with a single term cannot work for the tracking solution. In order to have both of the tracker and the suitable deceleration parameter it is necessary to introduce at least two terms in the quintessence potential. We give the future evolution of the quintessential universe.     

Zitterbewegung of a Model Universe

We investigate the quantum evolution of the metric operators for Bianchi-Type I model universes in the Heisenberg picture in order to remove the need to consider the wave function of the universe and interpret its “spin” variables. The calculation is analogous to that of the Zitterbewegung of the Dirac electron. We consider the behavior of the metric near the classical singularity, and consider the curvature there. Although factor ordering questions preclude the presentation of an unambiguous result for the curvature invariants, it does seem that the classical t ⁻⁴ divergence of the Kretschmann scalar is not removed by quantization.     

Models for a Finite Universe

A method of constructing 3-dimensional hyperbolic manifolds is described. Because of their high degree of symmetry, these may be suitable models for a finite universe. Because their group of symmetries is different from any in the list of manifolds given in Hodgeson and Weeks (available at ftp://ftp.northnet.org/pub/weeks/snappea/closedcensus), it is claimed that these are new.     

The Universe Without a Singularity

A rigorous solution of the field equations with a finite density of matter in the Universe is obtained in the context of classical gravitation theory.     

Wormholes in a Brane Universe

In this work, wormholes are discussed for the case where the classical brane action contains a 4-curvature. Equations of motion are obtained for R = 0 and R 0. Numerical solutions of these equations are found for special boundary conditions.     

Holographic considerations on a Machian Universe

MOND theory explains the rotation curves of the galaxies. Verlinde’s ideas establish an entropic origin for gravitational forces and Tsallis principle generalizes the theory of Boltzmann–Gibbs. In this work we have promoted a connection between these recent approaches, that at first sight seemed to have few or no points in common, using the Mach’s principle as the background. In this way we have used Tsallis formalism to calculate the main parameters of the Machian Universe including the Hubble parameter and the age of the Universe. After that, we have also obtained a new value for the Tsallis parameter via Mach’s principle. Using Verlinde’s entropic gravity we have obtained new forms for MOND’s well established ingredients. Finally, based on the relations between particles and bits obtained here, we have discussed the idea of bits entanglement in the holographic screen.     

反物质稀缺之谜有望被揭开

一般认为,约在140亿年前宇宙诞生时,应该产生同等数量的粒子和反粒子,两者的质量相同,但电荷的正、负相反,按理说两者相遇就会湮灭生成光而消失.     

Is a Spatially Closed Universe Possible?

The present speculation shows that a spatially closed geometry might be an alternative to Inflation scenario.     

A point mass in a Einstein Universe

An exact solution of Einstein's equations is presented for a perfect fluid representing a point mass in a Einstein Universe.     

Essay: Initial Conditions for a Universe

In physical theories, boundary or initial conditions play the role of selecting special situations which can be described by a theory with its general laws. Cosmology has long been suspected to be different in that its fundamental theory should explain the fact that we can observe only one particular realization. This is not realized, however, in the classical formulation and in its conventional quantization; the situation is even worse due to the singularity problem. In recent years, a new formulation of quantum cosmology has been developed which is based on quantum geometry, a candidate for a theory of quantum gravity. Here, the dynamical law and initial conditions turn out to be linked intimately, in combination with a solution of the singularity problem.     

Transition to turbulence in a shear flow

We analyze the properties of a 19-dimensional Galerkin approximation to a parallel shear flow. The laminar flow with a sinusoidal shape is stable for all Reynolds numbers Re. For sufficiently large Re additional stationary flows occur; they are all unstable. The lifetimes of finite amplitude perturbations shows a fractal dependence on amplitude and Reynolds number. These findings are in accord with observations on plane Couette flow and suggest a universality of this transition scenario in shear flows.     

Exact Solutions for the Fluctuations in a Flat FRW Universe Coupled to a Scalar Field

Some exact solutions for the small-first-order perturbations of an FRW metric minimally coupled to a neutral massive scalar field are presented.