Energy dissipation in wave propagation in general-relativistic plasma     

Ajanta Das  S. Chatterjee 《Astrophysics and Space Science》2010,330(2):329-336

Based on a recent communication by the present authors the question of energy dissipation in magnetohydrodynamical waves in an inflating background in general relativity is examined. It is found that the expanding background introduces a sort of dragging force on the propagating wave such that, unlike the Newtonian case, energy gets dissipated as it progresses. This loss in energy having no special-relativistic analogue is, however, not mechanical in nature as in case of an elastic wave. It is also found that the energy loss is model dependent and also depends on the number of dimensions.  相似文献   

Radiation condensation instability in a plasma with ionization and recombination     

Manasi Buzar Baruah  Samiran Chatterjee  Madhurjya P. Bora 《Astrophysics and Space Science》2010,325(2):217-225

In this work, we consider radiation (thermal) instability in a weakly ionized plasma with continuous ionization and recombination. The situation can be visualized in the case of envelopes of planetary nebulae, which are envelopes of ionized plasmas surrounding red giant stars. Various observations report continuous photoionization of these plasmas by the highly energetic streams of photons emanating from the parent star. Recently, it has been shown that thermal instability can be a probable candidate in such plasmas for the existence of small scale structures (viz., striations) whose kinematic age is much smaller than that of the parent nebula. We therefore report a systematic study of these plasmas with photoionization and determine the instability domain. We have shown that the continuous ionization and recombination may lead to modification of the underlying instability, which may limit the size of the small structures that are believed to form from these instabilities, and may thus provide an explanation of the physical processes responsible for the existence of these structures. We further show that in many cases the system bifurcates to an ovserstable (growing wave) state from a condensation instability (monotonic) and vice versa.  相似文献   

Lead isotope and trace element composition of K-feldspars from peraluminous granitoids of the Late Devonian South Mountain Batholith (Nova Scotia, Canada): implications for petrogenesis and tectonic reconstruction     

Jaroslav Dostal  A. K. Chatterjee 《Contributions to Mineralogy and Petrology》2010,159(4):563-578

The South Mountain Batholith (SMB) of southwestern Nova Scotia (Canada) is a Late Devonian (~375 Ma) composite intrusion, which crops over an area of about 7,300 km². This peraluminous granitoid body consists of rocks ranging from granodiorite through monzogranite and leucomonzogranite to leucogranite that locally host greisen tin-base metal mineralization. K-feldspar displays large compositional variations of trace elements and Pb isotopic ratios, particularly in the highly fractionated rocks. Many variations are consistent with processes of fractional crystallization, but a distinct enrichment of Rb, Li and Cs accompanied by low K/Rb, Ba/Rb, Eu/Eu* and K/Cs ratios point to the role of fluids during the late stages of magmatic evolution. The correlation of Pb isotopic ratios with the enriched elements and their ratios implies that the isotopic variations are an integral part of the evolution of the SMB. Together with well-defined isochronal relationships of Pb systems in the feldspars, the correlation suggests that fractional crystallization accompanied in the late stages by fluid fractionation led to the formation of Li–F-rich leucogranites. Internally derived U-rich fluids fractionated U/Pb ratios, which in turn produced distinct variations of ²⁰⁶Pb/²⁰⁴Pb and ²³⁸U/²⁰⁴Pb ratios in K-feldspars. This implies that the Pb isotopic values of K-feldspar, which have traditionally been used for tectonic reconstructions, might have been modified in many granitic rocks. Thus, only early magmatic K-feldspars, which show no discernible effects of fluid fractionation yield the initial Pb isotopic compositions of the parental granitic magmas and their sources. The data also show that the geochemical characteristics of the leucogranites are the results of magmatic evolution rather than a distinctive source.  相似文献   

Distribution of stars perpendicular to the plane of the galaxy     

S. Chatterjee 《Journal of Astrophysics and Astronomy》1991,12(4):269-280

We present here rigorous analytical solutions for the Boltzmann-Poisson equation concerning the distribution of stars above the galactic plane. The number density of stars is considered to follow a behaviour n(m,0) ∼H(m - m₀)m^−x, wherem is the mass of a star andx an arbitrary exponent greater than 2 and also the velocity dispersion of the stars is assumed to behave as < v²(m)> ∼ m^−θ the exponent θ being arbitrary and positive. It is shown that an analytic expression can be found for the gravitational field K_z, in terms of confluent hypergeometric functions, the limiting trends being K_z∼z for z →0, while K_z → constant for z → infinity. We also study the behaviour of < |z(m)|²>,i.e. the dispersion of the distance from the galactic disc for the stars of massm. It is seen that the quantity < |z(m)|²>∼ m^t-θ, for m→ t, while it departs significantly from this harmonic oscillator behaviour for stars of lighter masses. It is suggested that observation of < |z(m)|²> can be used as a probe to findx and hence obtain information about the mass spectrum.  相似文献   

Multi-technique Analysis of the Solar 10.7 cm Radio Flux Time-Series in Relation to Predictability     

Oindrilla Ghosh  Tanushree Ghosh  T. N. Chatterjee 《Solar physics》2014,289(6):2297-2315

We studied the predictability of the 10.7 cm solar radio flux by using stationary and non-stationary time-series analysis techniques of fractal theory to find the correlation exponent, the spectral exponent, the Hurst exponent, and the fluctuation exponent of the time series. The Hurst exponent was determined, from which the fractal dimension and consequently the predictability was evaluated. The results suggest that stationary methods of analysis yield inconsistent result, that is, amongst the four techniques used, the values of the exponents show great disparity. While two of the techniques, namely the auto-correlation function analysis and the spectral analysis, indicate long-term positive correlation, the other two methods, specifically the Hurst rescaled range-analysis and the fluctuation analysis, clearly exhibit the anti-correlated nature of the time series. The two non-stationary methods, that is, the discrete wavelet transform and the centered moving-average analysis, yielded values of the Hurst exponent that are indicative of positive correlation, of persistent behavior, and also showed that the time series is predictable to a certain extent.  相似文献   

Head-on collisions of two types of dust-acoustic solitons in a magnetized quantum plasma     

M. K. Ghorui  U. K. Samanta  T. K. Maji  P. Chatterjee 《Astrophysics and Space Science》2014,352(1):159-169

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Unilateral extension of a two-dimensional shear crack under the influence of cohesive forces     

L. Knopoff  A. K. Chatterjee 《Geophysical Journal International》1982,68(1):7-25

Summary. We consider the problem of the unilateral extension of a two-dimensional anti-plane crack that initiates spontaneously at a point. The crack extends under the influence of cohesive resistance at the edge and dynamical friction along the crack walls. The stresses in the region beyond the edge of the crack are approximated so that they are exactly equal to the cohesive stresses near the edge of the crack, and are zero on the wavefront. An exact method of solving such problems is also given and can be used to determine the validity of the approximation. We find that the crack will not grow if the cohesion exceeds some critical value; this is consistent with an earlier result obtained by Knopoff, Mouton & Burridge for a similar one-dimensional model of crack propagation.  相似文献   

A dynamical study of the frequency of merging galaxies     

Tapan K. Chatterjee 《Astrophysics and Space Science》1992,196(2):283-297

A study of the expected frequency of merging galaxies, for mergers taking place in several orbital periods, is conducted on the basis of the collisional theory of their formation, using galaxy models without halos. The results indicate that the expected frequency of such mergers is an order of magnitude below the observed value for the present epoch. The need for halos to hasten mergers is highlighted. In the light of current observational evidence and the results obtained, the formation of ellipticals by dissipative collapse followed by secular evolution by the mergers is favoured.  相似文献   

A dynamical study of the frequency of ring galaxies     

Tapan K. Chatterjee 《Astrophysics and Space Science》1987,132(1):177-189

An investigation of the expected frequency of ring galaxies is conducted in the light of the theory of their formation by the collision process involving a disk and a spherical galaxy, using the impulsive approximation. It is found that very favourable collision parametrs (in terms of the impact parameter, orientation, and energy changes) are required for the formation of ring galaxies.Results indicate that if the expected frequency of fairly well-defined ring galaxies is measured with respect to regions of high density (in terms of population of galaxies) and using the average distance between galaxies corresponding to these regions for its determination, then it comes out to be of the order of 0.01% of spirals. An even higher frequency is obtained if we take the messy and ill-defined rings into account. The results obtained are quite compatible with the observational values.But, however, if we consider a region of normal density (where collisions are rare) for frequency determinations, the expected frequency goes down by few orders of magnitude. Thus stray-hyperbolic encounters are too scarce to explain the formation of ring galaxies. This indicates that most of these interacting pairs must have already been bound doubles, whose orbits are such as to have brought about only now the interpenetrating encounters leading to ring formation.  相似文献   

In-cloud and below-cloud scavenging of aerosol ionic species over a tropical rural atmosphere in India     

Abhijit Chatterjee  Achutan Jayaraman  T. Narayana Rao  Sibaji Raha 《Journal of Atmospheric Chemistry》2010,66(1-2):27-40

The temporal variation in concentrations of major water soluble ionic species has been studied from several rain events occurred over Gadanki (13.5 °N, 79.2 °E), located in tropical semi arid region in southern India. The contribution from rain-out (in cloud) and wash-out (below cloud) processes to the total removal of ionic species by rain events is also estimated using the pattern of variations of ionic species within an individual event. A number of rain samples were collected from each rain event during June–November in 2006, 2007 and 2008. On average, nearly 20% of the total NH ₄ ⁺ and non-sea SO ₄ ^2? is removed by in-cloud scavenging, suggesting that their removal by “below cloud” washout is relatively dominant. In contrast Na⁺, Ca²⁺, Mg²⁺, NO ₃ ^? and sea-SO ₄ ^2? are mainly removed by below-cloud scavenging or wash-out process. A significant variation in the acidity was observed within rain events with successive precipitation showing higher acidity at the final stage of the precipitation due to partial neutralization of non-sea SO ₄ ^2? . Overall, greater influence of both terrestrial and anthropogenic sources is recorded in the rain events compared to that from marine sources.  相似文献