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41.
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We present an exact solution of Einstein's equations for cosmological models of Bianchi type-II filled with string dust as the source for the gravitational field. The solution represents an expanding and anisotropic universe which would give essentially an empty universe for large time. Some kinematical properties of the solution are discussed. 相似文献
44.
For the general plane symmetric metric, some exact solutions of Einstein field equations in the scalar tensor theory developed
by Saez and Ballestev are presented in vaccum and in the presence of stiff fluid. The physical and kinematical features of
the models are also discussed.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
45.
Einstein field equations are considered for zero-curvature Robertson-Walker models in the case of a viscous fluid distribution interacting with zero-rest-mass scalar fields. Exact solutions are obtained for two different phases of the early universe viz. the inflationary phase and the radiation-dominated phase, by using the 'gamma-law' equation of state p = (-1). The index describing the material content varies continuously with cosmological time. The gravitational 'constant' and bulk viscosity are both allowed to depend on the cosmic time. Some physical properties of the cosmological models are also discussed. 相似文献
46.
Kant S 《Population geography : a journal of the Association of Population Geographers of India》1990,12(1-2):11-26
"The paper attempts to analyse the patterns of and trends in demographic development in Rajasthan state [India] by employing the indices of urbanization, literacy and occupational diversification.... An effort has also been made to define the concept of demographic development...." Demographic development is defined as improvement in the quality of the population in a given area. 相似文献
47.
48.
Rupendra Babu Veeru Kant Singh Naresh Chandra Mehrotra 《Journal of the Geological Society of India》2014,84(4):442-448
An assemblage of structurally preserved organic-walled microfossils (OWMs) from the macerated residue of black carbonaceous shale belonging to Saradih Formation, the youngest carbonate horizon of the Raipur Group, Chhattisgarh Supergroup exposed at on the right bank of Mahanadi River, NE of Sarangarh township in Raigarh district, Chhattisgarh is being reported for the first time. The assemblage is comprised of 19 taxa of 13 genera belong to eukaryotes and prokaryotes viz. Leiosphaeridia, Stictosphaeridium, Dictyotidium, Synsphaeridium, Symplassosphaeridium, Satka, Trachysphaeridium, Goniosphaeridium, Trachyhystrichosphaera, Vandalosphaeridium, Siphonophycus, Oscillatoriopsis and Polythrichoides. The comprehensive account of recovered microbiotic assemblage can be correlated with globally known Neoproterozoic (early Cryogenian) assemblages, deposited in tidal complexes of shallow sea. 相似文献
49.
WANG Xinfeng WANG Tao Ravi Kant PATHAK Mattias HALLQUIST GAO Xiaomei NIE Wei XUE Likun GAO Jian GAO Rui ZHANG Qingzhu WANG Wenxing WANG Shulan CHAI Fahe CHEN Yizhen 《大气科学进展》2013,30(2):341-353
For the 2008 Olympic Games, drastic control measures were implemented on
industrial and urban emissions of sulfur dioxide (SO2), nitrogen oxides
(NOx) and other pollutants to address the issues of poor air quality in
Beijing. To investigate the effects of SO2 and NOx reductions on
the particulate sulfate and nitrate concentrations as well as their size
distributions, size-segregated aerosol samples were collected using
micro-orifice uniform deposit impactors (MOUDIs) at urban and downwind rural
sites in Beijing before and after full-scale controls. During the sampling
period, the mass concentrations of fine particles (PM1.8) at the urban
and rural sites were 94.0 and 85.9 μg m-3, respectively. More than
90% of the sulfates and ~60% of nitrates formed as fine
particles. Benefiting from the advantageous meteorological conditions and
the source controls, sulfates were observed in rather low concentrations and
primarily in condensation mode during the Olympics. The effects of the
control measures were separately analyzed for the northerly and the
southerly air-mass-dominated days to account for any bias. After the control
measures were implemented, PM, sulfates, and nitrates were significantly
reduced when the northerly air masses prevailed, with a higher percentage of
reduction in larger particles. The droplet mode particles, which dominated
the sulfates and nitrates before the controls were implemented, were
remarkably reduced in mass concentration after the control measures were
implemented. Nevertheless, when the polluted southerly air masses prevailed,
the local source control measures in Beijing did not effectively reduce the
ambient sulfate concentration due to the enormous regional contribution from
the North China Plain. 相似文献
50.
N. BHANDARI S. V. S. MURTY P. N. SHUKLA R. R. MAHAJAN A. D. SHUKLA G. LASHKARI M. S. SISODIA R. P. TRIPATHI G. PARTHASARATHY H. C. VERMA I. A. FRANCHI 《Meteoritics & planetary science》2008,43(4):761-770
Abstract— We report here a chance find of a meteorite in the sand dunes of Ararki village of Hanumangarh district in the Rajasthan desert of northwest India. Chemical and petrological evidence in conjunction with isotopic composition of oxygen indicate that it is an L5 chondrite. The fayalite content of olivines is 26.3 mol%. The meteorite has some serpentinized olivines and 0.3% carbon having a terrestrial isotopic composition, indicating that it is moderately weathered. The absence of 22Na indicate that the meteorite fell to Earth more than a decade ago. The cosmic‐ray exposure age based on cosmogenic 21Ne is 7.2 Ma. Low density of cosmic‐ray heavy nuclei tracks, low 26A1 activity, the shielding parameter [(22Ne/21Ne)C = 1.094] and absence of neutron capture effects indicate cosmic‐ray shielding in a meteoroid having radius of about 16 cm, implying a meteoroid mass of about 60 kg and ablation of about 93%. The gas retention ages, based on U/Th‐4He and K‐40Ar are 1.1 and 0.58 Ga, respectively, suggesting a heating and degassing event late in the history of this meteorite. 相似文献