排序方式： 共有69条查询结果，搜索用时 15 毫秒
61.
Biswajit Sahu Swarup Poria Rajkumar Roychoudhury 《Astrophysics and Space Science》2012,341(2):567-572
In the present paper we investigate the nonlinear wave structures of electron acoustic waves (EAWs) in an unmagnetized quantum plasma consisting of cold and hot electrons and ions. The one-dimensional quantum hydrodynamic model is used to study the quantum correction of the well known EAWs. Computational investigations have been performed to examine the effects of quantum diffraction and Mach number on nonlinear waves. It is shown that for Mach number M<1, soliton solution exist and for M>1, quasi-periodic and periodic type solution exist. The effects of other several parameters on the properties of EAWs are also discussed. 相似文献
62.
The properties of dust acoustic double-layers (DA-DLs) in an unmagnetized electron depleted dusty plasma consisting of inertial dust fluid and ions featuring Tsallis statistics are investigated. It is found that our plasma model can admit compressive as well as rarefactive DA-DLs depending on the value of nonextensive parameter q. As the value of q increases, the negative DA-DL shrinks and, beyond a certain critical value, develops into a positive structure allowing therefore the existence of compressive DA-DLs. 相似文献
63.
Biswajit Mukhopadhyay 《水文科学杂志》2013,58(12):2062-2085
AbstractField observations and geodetic measurements suggest that in the Karakoram Mountains, glaciers are either stable or have expanded since 1990, in sharp contrast to glacier retreats that are prevalently observed in the Himalayas and adjoining high-altitude terrains of central Asia. Decreased discharge in the rivers originating from this region is cited as a supporting evidence for this somewhat anomalous phenomenon. Here, we show that river discharge during the melting season of the glaciers in the eastern and western Karakoram, respectively, exhibits rising and falling trends. We have implemented a statistical procedure involving non-parametric tests combined with a benchmark smoothing technique that has proven to be a powerful method for separating the stochastic component from the trend component in a time series. Precipitation patterns determined from ERA-40 and GPCP data indicate that summer-monsoonal precipitation has increased over the Karakoram Mountains in recent decades. Increasing flows in June and July in the eastern Karakoram are due to an increase in summer-monsoonal precipitation. The rising trend of August discharge is due to an increase in the loss of glacier storage at an approximate average rate of 0.186–0.217 mm d-1 year-1 during the period 1973–2010. Moreover, this rate is higher than the rate of increase in monsoonal snowfall during the months of August and September. Therefore, most plausibly, glacier mass balance in the eastern Karakoram is negative. In the western Karakoram, river flows show declining trends for all summer months for the period 1966–2010, corresponding to a rate of increase of glacier storage by approximately 0.552–0.644 mm d-1 year-1, which is also higher than the rate of increase in summer-monsoonal precipitation. The gain of the cryospheric mass in the western Karakoram is in the form of increased thickness of the glaciers and perennial snowpacks instead of areal expansion. This investigation shows two contrasting patterns of trends of river flows that signify both negative and positive mass balance of the Karakoram glaciers. Trends of river flows are spatially and temporally integrated responses of a watershed to changing climate and thereby are important signals of the conditions of the cryospheric component of a watershed where it is highly significant. However, they cannot unequivocally provide indications of the state and fate of the glaciers in the complex hydrometeorological setting of the Karakoram. Extreme caution and care must be exercised in interpreting trends of river discharge in conjunction with climatic data. 相似文献
64.
We present results from a pulse timing analysis of the accretion-powered millisecond X-ray pulsar SAX J1808.4-3658 using X-ray
data obtained during four outbursts of this source. Extensive observations were made with the proportional counter array of
the Rossi X-ray Timing Explorer (RXTE) during the four outbursts that occurred in 1998, 2000, 2002 and 2005. Instead of measuring
the arrival times of individual pulses or the pulse arrival time delay measurement that is commonly used to determine the
orbital parameters of binary pulsars, we have determined the orbital ephemeris during each observation by optimizing the pulse
detection against a range of trial ephemeris values. The source exhibits a significant pulse shape variability during the
outbursts. The technique used by us does not depend on the pulse profile evolution, and is therefore, different from the standard
pulse timing analysis. Using 27 measurements of orbital ephemerides during the four outbursts spread over more than 7 years
and more than 31,000 binary orbits, we have derived an accurate value of the orbital period of 7249.156862(5) s (MJD = 50915)
and detected an orbital period derivative of (3.14 ± 0.21) × 10−12 s s−1. We have included a table of the 27 mid-eclipse time measurements of this source that will be valuable for further studies
of the orbital evolution of the source, especially with ASTROSAT. We point out that the measured rate of orbital period evolution
is considerably faster than the most commonly discussed mechanisms of orbital period evolution like mass transfer, mass loss
from the companion star and gravitational wave radiation. The present time scale of orbital period change, 73 Myr is therefore
likely to be a transient high value of period evolution and similar measurements during subsequent outbursts of SAX J1808.4-3658
will help us to resolve this. 相似文献
65.
Zn-bearing minerals that act as indicator minerals for base metal sulphide mineralization from the Proterozoic Betul Belt,
central India with special emphasis on their genetic significance have been discussed. Sulphide mineralisation is hosted by
the felsic volcanic rocks and has similarities with volcanic-hosted massive sulphide deposits in other parts of the world.
Synvolcanic hydrothermal alteration is crudely zoned with an inner high Mg-Ca core and an outer wider envelop of Al-Fe rich
mineral assemblage. Most of the prospects have strata bound, moderately to steeply dipping, multiple, sub-parallel sheet like
ore bodies composed of disseminated and semi-massive to massive ores. Zn-bearing spinel, staurolite, biotite and ilmenite
typically occur within the foot-wall alteration zones in close proximity to the sulphide mineralization. Zincian spinel is
ubiquitous irrespective of the nature of alteration zone. Zincian staurolite is nearly absent in Mg-Ca alteration zones but
commonly present in Al-Fe alteration zone along with zincian ilmenite. Zn-bearing biotite in intimate association with zincian
spinel is generally found in Mg-Ca alteration zone and in the transition to Al-Fe alteration zone. Most of these indicator
minerals can be considered as products of desulphidation of sphalerite during metamorphism. Mechanisms other than desulphidation
like formation of gahnite by overstepping of the zinc saturation limit of biotite during retrogression to chlorite and formation
of zincian staurolite at the expense of gahnite is also recorded. Field presence of these minerals has immense significance
in exploration in Betul Belt as they occur in close spatial relationship with the sulphide rich zones and therefore act as
direct vectors to ore. 相似文献
66.
The nonlinear wave structure of arbitrary amplitude ion acoustic solitary waves (IASWs) are studied in the Sagdeev’s pseudopotential framework for an ultra-relativistic degenerate dense plasma comprising cold and hot electrons and inertial ultra-cold ions. By employing standard normal-mode analysis the dispersion relation for linear waves is studied. The numerical results are presented to understand the features of ion acoustic solitary wave structures. It is shown that the present plasma model supports IASWs having positive potential well. Also, it is found that the small amplitude rarefactive double layer solution can exist in such a plasma system in some parametric region. It is shown that solitary structures and double layers are affected by relevant plasma parameters. 相似文献
67.
The propagation of nonlinear waves in a quantum plasma is studied. A quantum magnetohydrodynamic (QHD) model is used to take into account the effects of quantum force associated with the Bohm potential. Using the standard reductive perturbation technique, nonlinear Kadomtsev-Petviashvili (KP) equation is obtained to study the properties of ion acoustic waves (IAWs). For such waves the amplitude of the solitary waves is independent of the quantum parameter H (the ratio of the electron plasmon to electron Fermi energy), whereas the width and energy of the soliton increases with H. 相似文献
68.
Black sands rich in chromian spinel commonly occur in pockets along the eastern shoreline of Andaman Island where various types of peridotites and volcanics belonging to the Andaman ophiolite suite are exposed in close vicinity. The chemistry of these detrital chromian spinels has been extensively used here in identifying the source rocks vis-à-vis deciphering the source characteristics. The composition of the chromian spinels (Cr#: 0.20–0.88, Mg#: 0.26–0.77, Al 2 O 3: 5.04–48.21 wt.%, TiO 2: up to 1.39 wt.% and Fe 2+/Fe 3+: 1.73–9.12) varies widely signifying multiple sources, of which mantle peridotites and volcanic rocks are relevant in an ophiolitic terrain. The volcanic chromian spinels are relatively fresh, commonly euhedral, sometimes with compositional variations, and contain inclusions in contrast to the mantle peridotitic chromian spinels which are rounded, extensively fractured, and altered. We used a number of geochemical bivariate plots in order to know the provenance protoliths. The volcanic chromian spinels show geochemical characters of MORB, related to spreading centers (either MOR or back-arc) and also boninites/arc-tholeiites, related to active subduction. On the other hand, the peridotitic spinels indicate partially depleted lherzolite and depleted harzburgite source of the ophiolite suite. 相似文献
69.
Mainak?ThakurEmail authorView author&#;s OrcID profile Biswajit?Samanta Debashish?Chakravarty 《Stochastic Environmental Research and Risk Assessment (SERRA)》2018,32(8):2381-2404
Multigaussian kriging technique has many applications in mining, soil science, environmental science and other fields. Particularly, in the local reserve estimation of a mineral deposit, multigaussian kriging is employed to derive panel-wise tonnages by predicting conditional probability of block grades. Additionally, integration of a suitable change of support model is also required to estimate the functions of the variables with larger support than that of the samples. However, under the assumption of strict stationarity, the grade distributions and important recovery functions are estimated by multigaussian kriging using samples within a supposedly spatial homogeneous domain. Conventionally, the underlying random function model is required to be stationary in order to carry out the inference on ore grade distribution and relevant statistics. In reality, conventional stationary model often fails to represent complicated geological structure. Traditionally, the simple stationary model neither considers the obvious changes in local means and variances, nor is it able to replicate spatial continuity of the deposit and hence produces unreliable outcomes. This study deals with the theoretical design of a non-stationary multigaussian kriging model allowing change of support and its application in the mineral reserve estimation scenario. Local multivariate distributions are assumed here to be strictly stationary in the neighborhood of the panels. The local cumulative distribution function and related statistics with respect to the panels are estimated using a distance kernel approach. A rigorous investigation through simulation experiments is performed to analyze the relevance of the developed model followed by a case study on a copper deposit. 相似文献