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81.
82.
Probhas Ray Chaudhuri 《Astrophysics and Space Science》1971,12(2):325-328
The spectroscopic determination of the helium abundance in the oldest stars of the galaxy is supported by the theory of stellar evolution when neutrino emission is considered according to the photon-neutrino coupling theory, if it is assumed that the population II stars started their life with a low surface helium content.Receipt delayed by postal strike in Great Britain. 相似文献
83.
Summary. The response of the Earth to an earthquake is a transient that is effectively zero several days after the event. A recording of the event, of finite duration in time, has a Fourier spectrum that is an entire, or integral, analytic function of frequency. We present a very simple procedure for computing the Fourier spectrum as a function of complex frequency; the analytically continued spectrum. By investigating the properties of the analytically continued spectrum we show how to extract high- Q modes, how to estimate Q either from the amplitude or from the width of a resonance function, and how to improve the resolution of splitting to the theoretical maximum. Examples of these procedures, using observed data, are presented. 相似文献
84.
A sediment quality triad (SQT) assessment was made of the impact of copper mine tailings disposal on littoral meiofaunal assemblages in the Atacama region of northern Chile. This situation is unusual in that the disposal is direct into the high-energy coastal system and not via a river estuary or other low-energy environment. This situation also allows for the examination of the impact of copper mine tailings in the absence of confounding effects from other pollutants. The three components of the SQT were: 1. an analysis of the bioavailable metals in both the sedimentary porewater and the adjacent seawater, 2. a microcosm bioassay of both sediments and seawaters using meiofaunal assemblages, and 3. quantitative field samples of the meiofaunal assemblages. Twelve study sites with varying degrees of impact were used, including three reference sites. The study identified that both the meiofaunal assemblage densities and taxa diversities decrease with increasing levels of bioavailable copper, that the Foraminifera and Harpacticoida are sensitive to copper, and that otoplanid Turbellaria are often characteristic of impacted sites; tailings also have both chemical and physical impacts on the environment. In some cases the physical impact of tailings is more important in excluding some organisms e.g. the interstitial polychaete, Saccocirrus sonomacus, from a site than is their chemical impact. 相似文献
85.
Ole B. Andersen Gary D. Egbert Svetlana Y. Erofeeva Richard D. Ray 《Ocean Dynamics》2006,56(5-6):416-429
Overtides and compound tides are generated by nonlinear mechanisms operative primarily in shallow waters. Their presence complicates
tidal analysis owing to the multitude of new constituents and their possible frequency overlap with astronomical tides. The
science of nonlinear tides was greatly advanced by the pioneering researches of Christian Le Provost who employed analytical
theory, physical modeling, and numerical modeling in many extensive studies, especially of the tides of the English Channel.
Le Provost’s complementary work with satellite altimetry motivates our attempts to merge these two interests. After a brief
review, we describe initial steps toward the assimilation of altimetry into models of nonlinear tides via generalized inverse
methods. A series of barotropic inverse solutions is computed for the M tide over the northwest European Shelf. Future applications of altimetry to regions with fewer in situ measurements will
require improved understanding of error covariance models because these control the tradeoffs between fitting hydrodynamics
and data, a delicate issue in coastal regions. While M can now be robustly determined along the Topex/Poseidon satellite ground tracks, many other compound tides face serious aliasing
problems.
In memory of Christian Le Provost 相似文献
86.
Jayanta K. Bhattacharjee Atri Bhattacharya Tapas K. Das Arnab K. Ray 《Monthly notices of the Royal Astronomical Society》2009,398(2):841-852
In a novel approach to studying viscous accretion flows, viscosity has been introduced as a perturbative effect, involving a first-order correction in the α-viscosity parameter. This method reduces the problem of solving a second-order non-linear differential equation (Navier–Stokes equation) to that of an effective first-order equation. Viscosity breaks down the invariance of the equilibrium conditions for stationary inflow and outflow solutions, and distinguishes accretion from wind. Under a dynamical systems classification, the only feasible critical points of this 'quasi-viscous' flow are saddle points and spirals. On large spatial scales of the disc, where a linearized and radially propagating time-dependent perturbation is known to cause a secular instability, the velocity evolution equation of the quasi-viscous flow has been transformed to bear a formal closeness with Schrödinger's equation with a repulsive potential. Compatible with the transport of angular momentum to the outer regions of the disc, a viscosity-limited length-scale has been defined for the full spatial extent over which the accretion process would be viable. 相似文献
87.
88.
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
89.
Bhaswati Ray 《The Professional geographer》2017,69(4):644-654
The ability of a community to withstand and recover from adversities including natural and man-made disasters has emerged as a major policy issue in recent years. This research aims to assess the role of institutional initiatives in building resilient communities and their response to natural disasters like the Gorkha earthquake in Nepal in 2015. The work is based on data collected from primary and secondary sources along with field observations. It is evident that resilient communities are equipped with greater coping capacities in the face of natural disasters and have reduced vulnerability to future hazards. Institutional capacity building and resilient construction including the School Earthquake Safety Program ensured better disaster preparedness. The traditional open spaces and building designs added to the structural resilience. There is, however, a need to build back better and to communicate earthquake-resistant designs to the affected communities. 相似文献
90.
This study examines the effectiveness of integrating geography into existing math and science curriculum to teach climate change and sea level rise. The desired outcome is to improve student performance in all three subjects. A sample of 120 fifth graders from three schools were taught the integrated curriculum over a period of two to three weeks. They were given a pretest and posttest comprised of questions measuring knowledge relevant to the lesson in terms of geography, math, science, and spatial skills. Paired-samples t-tests were conducted to determine significant differences in student performance. These t-tests indicate statistically significant improvements in all but one instance across all subjects, at all schools for both boys and girls. No statistically significant results were observed for a control group of an additional twenty-seven fifth graders. These results demonstrate the value of combining geography with math and science to improve student performance in STEM knowledge. 相似文献