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Using the standard reductive perturbation technique, nonlinear cylindrical and spherical Kadomtsev-Petviashvili (KP) equations are derived for the propagation of ion acoustic solitary waves in an unmagnetized collisionless plasma with nonthermal electrons and warm ions. The influence of nonthermally distributed electrons and the effects caused by the transverse perturbation on cylindrical and spherical ion acoustic waves (IAWs) are investigated. It is observed that the presence of nonthermally distributed electrons has a significant role in the nature of ion acoustic waves. In particular, when the nonthermal distribution parameter ?? takes certain values the usual cylindrical KP equation (CKPE) and spherical KP equation (SKPE) become invalid. One then has to have recourse to the modified CKPE or SKPE. Analytical solutions of both CKPE and SKPE and their modified versions are discussed in the present paper. The present investigation may have relevance in the study of propagation of IAWs in space and laboratory plasmas. 相似文献
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We present here results from our search for X-ray pulsations of the neutron star in the low mass X-ray binary EXO 0748-676 at a frequency near the burstoscillation frequency of 44.7Hz.Using the observations made with the Proportional Counter Array onboard the Rossi X-ray Timing Explorer,we did not find any pulsations in the frequency band of 44.4Hz to 45.0Hz and obtained a 3σ upper limit of 0.47% on the pulsed fraction for any possible underlying pulsation in this frequency band.We also discuss the importan... 相似文献
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Prasanta Chatterjee Deb Kumar Ghosh Biswajit Sahu 《Astrophysics and Space Science》2012,339(2):261-267
The nonlinear propagation of ion acoustic shock waves (IASWs) are studied in an unmagnetized plasma consisting of nonthermal
electrons, nonthermal positrons, and singly charged adiabatically hot positive ions, whose dynamics is governed by the two
dimensional nonplanar Kadomstev-Petviashvili-Burgers (KPB) equation. The shock solution of the KPB equations is obtained numerically.
The effects of several parameters and ion kinematic viscosities on the properties of ion acoustic shock waves are discussed
in planar and nonplanar geometry. It is shown that the ion acoustic shock wave propagating in cylindrical/spherical geometry
with transverse perturbation will be deformed as time goes on. Also, it is seen that the strength and the steepness of the
IASWs increases with increasing β, the nonthermal parameter. 相似文献
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Uday Narayan Ghosh Deb Kumar Ghosh Prasanta Chatterjee Biswajit Sahu 《Astrophysics and Space Science》2012,342(2):449-456
The basic features of planar and nonplanar time-dependent dust-ion-acoustic (DIA) solitary waves (SWs) and double layers (DLs) have been studied in an unmagnetized dusty plasma system consisting of positively and negatively charged dust, Boltzmann distributed ions and superthermal electrons (represented by kappa distribution). Using the reductive perturbation technique (RPT) we have derived modified Gardner (MG) equation, which gives information beyond the Korteweg-de Vries (KdV) limits (corresponding to the vanishing of nonlinear coefficient of the KdV equation). It is seen that the properties of nonplanar DIA SWs and DLs are significantly differs as the value of spectral index kappa (κ) changes. The present investigation may have relevance in the study of propagation of DIA waves in space and laboratory plasmas. 相似文献
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Biswajit Pandey Somnath Bharadwaj 《Monthly notices of the Royal Astronomical Society》2008,387(2):767-771
We have quantified the average filamentarity of the galaxy distribution in seven nearly two-dimensional strips from the Sloan Digital Sky Survey Data Release Five (SDSS DR5) using a volume-limited sample in the absolute magnitude range −21 ≤ M r ≤−20 . The average filamentarity of star-forming (SF) galaxies, which are predominantly blue, is found to be more than that of other galaxies which are predominantly red. This difference is possibly an outcome of the fact that blue galaxies have a more filamentary distribution. Comparing the SF galaxies with only the other blue galaxies, we find that the two show nearly equal filamentarity. Separately analyzing the galaxies with high star formation rates (SFR) and low SFR, we find that the latter has a more filamentary distribution. We interpret this in terms of two effects. (i) A correlation between the SFR and individual galaxy properties like luminosity with the high-SFR galaxies being more luminous. (ii) A relation between the SFR and environmental effects like the density with the high-SFR galaxies preferentially occurring in high-density regions. These two effects are possibly not independent and are operating simultaneously. We do not find any difference in the filamentarity of SF galaxies and active galactic nuclei. 相似文献
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We have investigated the long-term flux variation in Cen X-3 using orbital modulation and pulsed fraction in different flux states using observations made with the All-Sky Monitor and the Proportional Counter Array on board the Rossi X-ray Timing Explorer . In the high state, the eclipse ingress and egress are found to be sharp whereas in the intermediate state the transitions are more gradual. In the low state, instead of eclipse ingress and egress, the light curve shows a smooth flux variation with orbital phase. The orbital modulation of the X-ray light curve in the low state shows that the X-ray emission observed in this state is from an extended object. The flux-dependent orbital modulations indicate that the different flux states of Cen X-3 are primarily due to varying degree of obscuration. Measurement of the pulsed fraction in different flux states is consistent with the X-ray emission of Cen X-3 having one highly varying component with a constant pulsed fraction and an unpulsed component and in the low state, the unpulsed component becomes dominant. The observed X-ray emission in the low state is likely to be due to scattering of X-rays from the stellar wind of the companion star. Though we cannot ascertain the origin and nature of the obscuring material that causes the aperiodic long-term flux variation, we point out that a precessing accretion disc driven by radiative forces is a distinct possibility. 相似文献
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Located adjacent to the Banded Gneissic Complex, Rampura–Agucha is the only sulfide ore deposit discovered to date within
the Precambrian basement gneisses of Rajasthan. The massive Zn–(Pb) sulfide orebody occurs within graphite–biotite–sillimanite
schist along with garnet–biotite–sillimanite gneiss, calc–silicate gneisses, amphibolites, and garnet-bearing leucosomes.
Plagioclase–hornblende thermometry in amphibolites yielded a peak metamorphic temperature of 720–780°C, whereas temperatures
obtained from Fe–Mg exchange between garnet and biotite (580–610°C) in the pelites correspond to postpeak resetting. Thermodynamic
considerations of pertinent silicate equilibria, coupled with sphalerite geobarometry, furnished part of a clockwise P–T–t path with peak P–T of ∼6.2 kbar and 780°C, attained during granulite grade metamorphism of the major Zn-rich stratiform sedimentary exhalative
deposits orebody and its host rocks. Arsenopyrite composition in the metamorphosed ore yielded a temperature [and log f(S
2)] range of 352°C (−8.2) to 490°C (−4.64), thus indicating its retrograde nature. Contrary to earlier research on the retrogressed
nature of graphite, Raman spectroscopic studies on graphite in the metamorphosed ore reveal variable degree of preservation
of prograde graphite crystals (490 ± 43°C with a maximum at 593°C). The main orebody is mineralogically simple (sphalerite,
pyrite, pyrrhotite, arsenopyrite, galena), deformed and metamorphosed while the Pb–Ag-rich sulfosalt-bearing veins and pods
that are irregularly distributed within the hanging wall calc–silicate gneisses show no evidence of deformation and metamorphism.
The sulfosalt minerals identified include freibergite, boulangerite, pyrargyrite, stephanite, diaphorite, Mn–jamesonite, Cu-free
meneghinite, and semseyite; the last three are reported from Agucha for the first time. Stability relations of Cu-free meneghinite
and semseyite in the Pb–Ag-rich ores constrain temperatures at >550°C and <300°C, respectively. Features such as (1) low galena–sphalerite
interfacial angles, (2) presence of multiphase sulfide–sulfosalt inclusions, (3) microcracks filled with galena (±pyrargyrite)
without any hydrothermal alteration, and (4) high contents of Zn, Ag (and Sb) in galena, indicate partial melting in the PbS–Fe0.96S–ZnS–(1% Ag2S ± CuFeS2) system, which was critical for metamorphic remobilization of the Rampura–Agucha deposit. 相似文献