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1.
Manjari Bagchi Rachid Ouyed Jan Staff Subharthi Ray Mira Dey † Jishnu Dey ‡ 《Monthly notices of the Royal Astronomical Society》2008,387(1):115-120
We study the effects of temperature on strange stars. It is found that the maximum mass of the star decreases with the increase of temperature, as at high temperatures the equations of state become softer. Moreover, if the temperature of a strange star increases, keeping its baryon number fixed, its gravitational mass increases and its radius decreases. This leads to a limiting temperature, where it turns into a black hole. These features are the result of a combined effect of the change of gluon mass and the quark distribution with temperature. We report on a new type of radial oscillation of strange stars, driven by what we call 'chromothermal' instability. We also discuss the relevance of our findings in the astrophysics of core collapse supernovae and gamma-ray bursts. 相似文献
2.
Site response studies in Agartala Urban agglomeration 总被引：1，自引：0，他引：1
A systematic investigation using digital microearthquake recorders with short period SS-1 seismometers, covering 76 sites
in and around Agartala city, has been carried out for site response (SR) studies in the area. In the northern part of the
area, SR varies from 1.15 to 1.85 corresponding to peak frequency 0.76 to 0.93 Hz where soil is mostly semi-consolidated and
stiffer than recent Quaternary deposits (Haora River formation). In the southern part of the area, SR varies from 1.12 to
2.42 corresponding to peak frequency from 0.71 to 0.85 Hz within the Dupitila formation (early Quaternary). It is observed
that estimated SR from H/V increases from edges to middle of the Haora River valley and impedance contrast fallows the similar
trend. This reflects that site response by H/V is influenced by impedance contrast, whereas computed amplification from 1-D
model shows opposite trend. The maximum amplification at fundamental frequency of resonance, 1.04 Hz estimated from H/V by
near to BH-7, is 2.5 times greater than the impedance contrast/ratio derived from 1-D model for same location. Relationship
between resonance frequency and depth was obtained by applying quarter wavelength and Bard (2000) methodologies, which shows linearity, whereas H/V shows its nonlinearity characteristic in soil across the valley part of
Haora River. Shear wave velocities, and subsequently, SPT index and factor of safety (by cyclic stress approach) were estimated
from geotechnical parameters. Vs30 and site response data were used in this study for getting a first hand information about
soil stiffness condition in the area. The estimation of SPT index and factor of safety could be a useful tool for delineating
liquefied and none liquefied zones at various depth levels, especially where water table exists at a very shallow level. The
expected liquefiable zone was observed at depths varying from 6–25 m beneath the soil bearing zones where percentage of fines
is estimated to be more than 35% for the area. This knowledge about subsurface soil characteristics will be useful for the
civil engineers/city planners, which can be taken into account at the time of constructing earthquake-resistant structures
in the area. 相似文献
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Tarun Souradeep Sanjit Mitra Anand Sengupta Subharthi Ray Rajib Saha 《New Astronomy Reviews》2006,50(11-12):1030
In the era of high precision CMB measurements, systematic effects are beginning to limit the ability to extract subtler cosmological information. The non-circularity of the experimental beam has become progressively important as CMB experiments strive to attain higher angular resolution and sensitivity. The effect of non-circular beam on the power spectrum is important at multipoles larger than the beam-width. For recent experiments with high angular resolution, optimal methods of power spectrum estimation are computationally prohibitive and sub-optimal approaches, such as the Pseudo-Cl method are used. We provide an analytic framework for correcting the power spectrum for the effect of beam non-circularity and non-uniform sky coverage (including incomplete/masked sky maps). The approach is perturbative in the distortion of the beam from non-circularity allowing for rapid computations when the beam is mildly non-circular. We advocate that when the non-circular beams are important, it is computationally advantageous to employ ‘soft’ azimuthally apodized masks whose spherical harmonic transforms die down fast with m. 相似文献
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Pal Subodh Chandra Chakrabortty Rabin Arabameri Alireza Santosh M. Saha Asish Chowdhuri Indrajit Roy Paramita Shit Manisa 《Natural Hazards》2022,110(2):847-879
Hot and humid subtropical plateau regions are susceptible to land degradation in the form of weathering and gully erosion. Here, we investigate chemical weathering, gully erosion and cohesiveness through field-based measurements with a view to understand the controlling factors of potential land degradation, in complex river basin of the Chotanagpur plateau region in Eastern India. The layers of controlling factors of gully erosion were developed and prioritized considering boosted regression tree (BRT), alternative decision tree (ADT), particle swarm optimization (PSO) and random forest (RF) algorithms in the R software, and the results of these methods were also validated using receiver operating characteristic (ROC) curves. The spectroscopic analysis was carried out of collected soil samples to measure the degree of chemical weathering and cohesiveness. Furthermore, the climatic elements like temperature and rainfall were also considered for estimating the chemical weathering. The results of the gully erosion models (i.e., BRT, ADT, PSO and RF) show remarkable accuracy with ROC values of 0.93, 0.89, 0.91 and 0.84, respectively. An advanced decision tree model was integrated with the results of degree of chemical weathering and cohesiveness in geographical information system platform. The land degradation map developed from this approach shows that 10.53% of the study area is highly affected, whereas 17.36% area is moderately affected and the rest of the 73.85% area is less affected by land degradation. Our results provide essential information for policy makers in adopting measures for minimizing and controlling the land degradation. Our novel approach is significant to assess land degradation to a large scale.
相似文献7.
We perform a detailed physical analysis for a class of exact solutions for the Einstein–Maxwell equations. The linear equation of state consistent with quark stars has been incorporated in the model. The physical analysis of the exact solutions is performed by considering the charged anisotropic stars for the particular nonsingular exact model obtained by Maharaj, Sunzu and Ray. In performing such an analysis we regain masses obtained by previous researchers for isotropic and anisotropic matter. It is also indicated that other masses and radii may be generated which are in acceptable ranges consistent with observed values of stellar objects. A study of the mass-radius relation indicates the effect of the electromagnetic field and anisotropy on the mass of the relativistic star. 相似文献
8.
Manjari Bagchi Subharthi Ray Mira Dey † Jishnu Dey 《Monthly notices of the Royal Astronomical Society》2006,368(2):971-975
From recent reports on terrestrial heavy ion collision experiments it appears that one may not obtain information about the existence of asymptotic freedom (AF) and chiral symmetry restoration (CSR) for quarks of QCD at high density. This information may still be obtained from compact stars – if they are made up of strange quark matter (SQM).
Very high gravitational redshift lines (GRL), seen from some compact stars, seem to suggest high ratios of mass and radius ( M / R ) for them. This is suggestive of strange stars (SS) and can in fact be fitted very well with SQM equation of state (EOS) deduced with built in AF and CSR. In some other stars broad absorption bands (BAB) appear at about ∼0.3 keV and multiples thereof, that may fit in very well with resonance with harmonic compressional breathing mode frequencies of these SS. Emission at these frequencies are also observed in six stars.
If these two features of large GRL and BAB were observed together in a single star, it would strengthen the possibility for the existence of SS in nature and would vindicate the current dogma of AF and CSR that we believe in QCD. Recently, in 4U 1700 − 24 , both features appear to be detected, which may well be interpreted as observation of SS – although the group that analyzed the data did not observe this possibility. We predict that if the shifted lines, that has been observed, are from neon with GRL shift z = 0.4 – then the compact object emitting it is a SS of mass 1.2 M⊙ and radius 7 km. In addition the fit to the spectrum leaves a residual with broad dips at 0.35 keV and multiples thereof, as in 1E 1207 − 5209 which is again suggestive of SS. 相似文献
Very high gravitational redshift lines (GRL), seen from some compact stars, seem to suggest high ratios of mass and radius ( M / R ) for them. This is suggestive of strange stars (SS) and can in fact be fitted very well with SQM equation of state (EOS) deduced with built in AF and CSR. In some other stars broad absorption bands (BAB) appear at about ∼0.3 keV and multiples thereof, that may fit in very well with resonance with harmonic compressional breathing mode frequencies of these SS. Emission at these frequencies are also observed in six stars.
If these two features of large GRL and BAB were observed together in a single star, it would strengthen the possibility for the existence of SS in nature and would vindicate the current dogma of AF and CSR that we believe in QCD. Recently, in 4U 1700 − 24 , both features appear to be detected, which may well be interpreted as observation of SS – although the group that analyzed the data did not observe this possibility. We predict that if the shifted lines, that has been observed, are from neon with GRL shift z = 0.4 – then the compact object emitting it is a SS of mass 1.2 M
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We suggest that the mass of four compact stars SAX J1808.4-3658, KS 1731-260, SAX J1750.8-2900 and IGR J17191-2821 can be determined from the difference in the observed kiloHertz quasi periodic oscillations (kHz QPO-s) of these stars. The stellar radius is very close to the marginally stable orbit Rms as predicted by Einstein’s general relativity. It may be noted that the first of these stars was suggested to be a strange star more than a decade back by Li et al. (1999a) from the unique millisecond X-ray pulsations with an accurate determination of its rotation period. It showed kHz QPO-s eight years back and so far it is the only set that has been observed. This is the first time we give an estimate of the mass of the star and of three other compact stars in low-mass X-ray binaries using their observed kHz QPO-s. 相似文献