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991.
Merging neutron stars (NSs) are hot candidates for the still enigmatic sources of short gamma-ray bursts (GRBs). If the central engines of the huge energy release are accreting relic black holes (BHs) of such mergers, it is important to understand how the properties of the BH–torus systems, in particular disc masses and mass and rotation rate of the compact remnant, are linked to the characterizing parameters of the NS binaries. For this purpose, we present relativistic smoothed particle hydrodynamic simulations with conformally flat approximation of the Einstein field equations and a physical, non-zero temperature equation of state. Thick disc formation is highlighted as a dynamical process caused by angular momentum transfer through tidal torques during the merging process of asymmetric systems or in the rapidly spinning triaxial post-merger object. Our simulations support the possibility that the first well-localized short and hard GRBs 050509b, 050709, 050724, 050813 have originated from NS merger events and are powered by neutrino-antineutrino annihilation around a relic BH–torus system. Using model parameters based on this assumption, we show that the measured GRB energies and durations lead to estimates for the accreted masses and BH mass accretion rates which are compatible with theoretical expectations. In particular, the low-energy output and short duration of GRB 050509b set a very strict upper limit of less than 100 ms for the time interval after the merging until the merger remnant has collapsed to a BH, leaving an accretion torus with a small mass of only ∼0.01 M⊙ . This favours a (nearly) symmetric NS+NS binary with a typical mass as progenitor system. 相似文献
992.
N. P. Abel 《Monthly notices of the Royal Astronomical Society》2006,368(4):1949-1958
The [C ii ] 158-μm line is an important emission-line diagnostic in photodissociation regions (PDRs), but this emission line can also emerge from ionized gas. This work calculates the contribution of [C ii ] emission from ionized gas over a wide range of parameter space by considering the simplified case of an H+ region and PDR in pressure equilibrium. Additionally, these calculations also predict the strong correlation observed between [N ii ] 205-μm emission and [C ii ] discussed by previous authors. Overall, the results of these calculations have wide-ranging applications to the interpretation of [C ii ] emission in astrophysical environments. 相似文献
993.
994.
QI Jianfeng LUAN Maotian FENG Xiuli MA Tailei NIE Ying 《中国海洋大学学报(英文版)》2007,6(4):413-420
The apparatus for static and dynamic universal triaxial and torsional shear soil testing is employed to perform stress-controlled cyclic single-direction torsional shear tests and two-direction coupled shear tests under unconsolidated-undrained conditions. Through a series of tests on saturated clay, the effects of initial shear stress and stress reversal on the clay’s strain-stress behavior are examined, and the behavior of pore water pressure is studied. The experimental results indicate that the patterns of stress-strain relations are distinctly influenced by the initial shear stress in the cyclic single-direction shear tests. When the initial shear stress is large and no stress reversal occurs, the predominant deformation behavior is characterized by an accumulative effect. When the initial shear stress is zero and symmetrical cyclic stress occurs, the predominant deformation behavior is characterized by a cyclic effect. The pore water pressure fluctuates around the confining pressure with the increase of cycle number. It seems that the fluctuating amplitude increases with the increase of the cyclic stress. But a buildup of pore water pressure does not occur. The de- formations of clay samples under the complex initial and the cyclic coupled stress conditions include the normal deviatoric deforma- tion and horizontal shear deformation, the average deformation and cyclic deformation. A general strain failure criterion taking into account these deformations is recommended and is proved more stable and suitable compared to the strain failure criteria currently used. 相似文献
995.
In an earlier analysis it was demonstrated that general relativity gives higher values of surface tension in strange stars
with quark matter than neutron stars. We generate the modified Tolman-Oppenheimer-Volkoff equation to incorporate anisotropic
matter and use this to show that pressure anisotropy provides for a wide range of behaviour in the surface tension than is
the case with isotropic pressures. In particular, it is possible that anisotropy drastically decreases the value of the surface
tension. 相似文献
996.
We propose a novel mathematical method to construct an exact polytropic sphere in self-gravitating hydrostatic equilibrium, improving the non-linear Poisson equation. The central boundary condition for the present equation requires a ratio of gas pressure to total one at the centre, which is uniquely identified by the whole mass and molecular weight of the system. The special solution derived from the Lane–Emden equation can be reproduced. This scheme is now available for modelling the molecular cloud cores in interstellar media. The mass–radius relation of the first core is found to be consistent with the recent results of radiation hydrodynamic simulations. 相似文献
997.
We study possible impact of a softening of the equation of state by a phase transition, or appearance of hyperons, on the
spin evolution of isolated pulsars. Numerical simulations are performed using exact 2-D simulations in general relativity.
The equation of state of dense matter at supranuclear densities is poorly known. Therefore, the accent is put on the general
correlations between evolution and equation of state, and mathematical strictness. General conjectures referring to the structure
of the one-parameter families of stationary configurations are formulated. The interplay of the back bending phenomenon and
stability with respect to axisymmetric perturbations is described. Changes of pulsar parameters in a corequake following instability
are discussed, for a broad choice of phase transitions predicted by different theories of dense matter. The energy release
in a corequake, at a given initial pressure, is shown to be independent of the angular momentum of collapsing configuration.
This result holds for various types of phases transition, with and without metastability. We critically review observations
of pulsars that could be relevant for the detection of the signatures of the phase transition in neutron star cores.
This work was partially supported by the Polish MNiI Grant no. 1P03D-008-27. 相似文献
998.
1 INTRODUCTIONRecently ,thepollutionoftracemetalinseawaterhasbecomeincreasinglyevident.Researchershavefo cusedattentiontotracemetalpresentinvariousexistenceforms ,especiallyorganiccomplexingphases.Theexistencestatesandtransportmechanismofbaytracemetalswerethesubjectofstudybysomere searchers(Gu ,1 991 ;Florence ,1 998;Guo ,1 998;Wells,1 991 ,1 998a ,b ;Wellsetal.,1 998) .Whetherinfreshwaterorseawater,colloidsareclearlydominantfactorsaffectingtheexistencestatesandtransportmechanismoftrac… 相似文献
999.
The problem of the symmetric quasi‐static large‐strain expansion of a cavity in an infinite granular body is studied. The body is assumed to be dry or fully drained so that the presence of the pore water can be disregarded. Both spherical and cylindrical cavities are considered. Numerical solutions to the boundary value problem are obtained with the use of the hypoplastic constitutive relation calibrated for a series of granular soils. As the radius of the cavity increases, the stresses and the density on the cavity surface asymptotically approach limit values corresponding to a so‐called critical state. For a given soil, the limit values depend on the initial stresses and the initial density. A comparison is made between the solutions for different initial states and different soils. Applications to geotechnical problems such as cone penetration test and pressuremeter test are discussed. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
1000.
本文在综合国内外有关文献的基础上,评述了火成岩自组织结构成因研究的新进展;指出了今后研究时应注意的问题。 相似文献