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11.
Anirudh Pradhan Hassan Amirhashchi Rekha Jaiswal 《Astrophysics and Space Science》2011,334(2):249-260
A new class of dark energy models in a Locally Rotationally Symmetric Bianchi type-II (LRS B-II) space-time with variable
equation of state (EoS) parameter and constant deceleration parameter have been investigated in the present paper. The Einstein’s
field equations have been solved by applying a variation law for generalized Hubble’s parameter given by Berman: Nuovo Cimento
74:182 (1983) which generates two types of solutions for the average scale factor, one is of power-law type and other is of the exponential-law
form. Using these two forms, Einstein’s field equations are solved separately that correspond to expanding singular and non-singular
models of the universe respectively. The dark energy EoS parameter ω is found to be time dependent and its existing range for both models is in good agreement with the three recent observations
of (i) SNe Ia data (Knop et al.: Astrophys. J. 598:102 (2003)), (ii) SNe Ia data collaborated with CMBR anisotropy and galaxy clustering statistics (Tegmark et al.: Astrophys. J. 606:702 (2004)) and latest (iii) a combination of cosmological datasets coming from CMB anisotropies, luminosity distances of high redshift
type Ia supernovae and galaxy clustering (Hinshaw et al.: Astrophys. J. Suppl. 180:225 (2009); Komatsu et al. Astrophys. J. Suppl. 180:330 (2009)). The cosmological constant Λ is found to be a positive decreasing function of time and it approaches a small positive value
at late time (i.e. the present epoch) which is corroborated by results from recent supernovae Ia observations. The physical
and geometric behaviour of the universe have also been discussed in detail. 相似文献
12.
Anirudh Pradhan Rekha Jaiswal Kanti Jotania Rajeev Kumar Khare 《Astrophysics and Space Science》2012,337(1):401-413
We present two dark energy (DE) models with an anisotropic fluid in Bianchi type-VI
0 space-time by considering time dependent deceleration parameter (DP). The equation of state (EoS) for dark energy ω is found to be time dependent and its existing range for derived models is in good agreement with the recent observations.
Under the suitable condition, the anisotropic models approach to isotropic scenario. We also find that during the evolution
of the universe, the EoS parameter for DE changes from ω>−1 to ω=−1 in first model whereas from ω>−1 to ω<−1 in second model which is consistent with recent observations. The cosmological constant Λ is found to be a positive decreasing
function of time and it approaches a small positive value at late time (i.e. the present epoch) which is corroborated by results
from recent type Ia supernovae observations. The cosmic jerk parameter in our derived models is also found to be in good agreement
with the recent data of astrophysical observations. The physical and geometric aspects of both the models are also discussed
in detail. 相似文献
13.
R. R. Yadav Dilip Kumar Jaiswal Hareesh Kumar Yadav Gulrana 《Environmental Earth Sciences》2012,65(3):849-859
A three-dimensional model for non-reactive solute transport in physically homogeneous subsurface porous media is presented.
The model involves solution of the advection-dispersion equation, which additionally considered temporally dependent dispersion.
The model also account for a uniform flow field, first-order decay which is inversely proportional to the dispersion coefficient
and retardation factor. Porous media with semi-infinite domain is considered. Initially, the space domain is not solute free.
Analytical solutions are obtained for uniform and varying pulse-type input source conditions. The governing solute transport
equation is solved analytically by employing Laplace transformation technique (LTT). The solutions are illustrated and the
behavior of solute transport may be observed for different values of retardation factor, for which simpler models that account
for solute adsorption through a retardation factor may yield a misleading assessment of solute transport in ‘‘hydrologically
sensitive’’ subsurface environments. 相似文献
14.
Spatial aspects of building and population exposure data and their implications for global earthquake exposure modeling 总被引：1，自引：1，他引：0
This paper discusses spatial aspects of the global exposure dataset and mapping needs for earthquake risk assessment. We discuss this in the context of development of a Global Exposure Database for the Global Earthquake Model (GED4GEM), which requires compilation of a multi-scale inventory of assets at risk, for example, buildings, populations, and economic exposure. After defining the relevant spatial and geographic scales of interest, different procedures are proposed to disaggregate coarse-resolution data, to map them, and if necessary to infer missing data by using proxies. We discuss the advantages and limitations of these methodologies and detail the potentials of utilizing remote-sensing data. The latter is used especially to homogenize an existing coarser dataset and, where possible, replace it with detailed information extracted from remote sensing using the built-up indicators for different environments. Present research shows that the spatial aspects of earthquake risk computation are tightly connected with the availability of datasets of the resolution necessary for producing sufficiently detailed exposure. The global exposure database designed by the GED4GEM project is able to manage datasets and queries of multiple spatial scales. 相似文献
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17.
The probability of landslide volume, V
L
, is a key parameter in the quantitative hazard analysis. Several studies have demonstrated that the non-cumulative probability
density, p(V
L
), of landslide volumes obeys almost invariably a negative power law scaling of p(V
L
) for landslides exceeding a threshold volume and a roll-over of small landslides. Some researchers attributed the observed
roll-over to under-sampling of data, while others relate it to a geo-morphological (physical) property of landslides. We analyzed
15 sets of a complete landslide inventory containing shallow debris slides (2 ≤ V
L
≤ 3.6 × 103 m3) with sources located on cut slopes along a 17-km-long railroad corridor. The 15 datasets belong to individual years from
1992 to 2007. We obtained the non-cumulative probability densities of landslide volumes for each dataset and analyzed the
distribution pattern. The results indicate that for some datasets the probability density exhibits a negative power law distribution
for all ranges of volume, while for others, the negative power scaling exists only for a volume greater than 10 m3, with scaling exponent β varying between 0.96 and 2.4. When the spatial distribution of landslides were analyzed in relation to the terrain condition
and triggering rainfall, we observed that the number of landslides and the range and the frequency of volumes vary according
to the changes in local terrain condition and the amount of rainfall that trigger landslides. We conclude that the probability
density distribution of landslide volumes has a dependency on the local morphology and rainfall intensity and the deviation
of small landslides from power law, i.e., the roll-over is a “real effect” and not an artifact due to sampling discrepancies. 相似文献
18.
Geosynthetic is widely used to reinforce the weak rock mass, mine waste dump, soil slopes road cut slopes, etc. The present
paper discusses the effect of geogrids on the stability of mine waste dump. The stability of mine waste dump has been done
by Fast Langrage Analysis of Continua (FLAC) slope software, which is based on finite difference method. Reinforcement by
geogrids mainly depends on the tensile strength, aperture size of geogrids, and particle size distribution of dump rock mass.
Different permutations and combinations of spacing between two geogrid sheets have been taken into consideration to study
the stability of mine waste dump. The factor of safety is calculated to quantify the effect of geogrids on waste dump slope.
It has been observed from numerical modeling that the maximum slope angle is 45° at a height of 10 m. The scope of increasing
slope angle from 45 to 60° is evaluated using geogrids. It has been found from the study that the factor of safety increases
as the spacing between geogrids decreases. Maximum strain is also plotted of each case to identify the slip circle. The positions
of geogrids modify the probable slip circle or failure plane of mine waste dump. Using ten geogrids at a spacing of 1 m, the
slope angle can be increased up to 60° with factor of safety of 1.4. 相似文献
19.
Shao-Yi Huang Yue-Gau Chen George S. Burr Manoj K. Jaiswal Yunung Nina Lin Gongming Yin Jingwei Liu Shujun Zhao Zhongquan Cao 《Quaternary Research》2014
We present a reconstructed lithologic column compiled from a series of lacustrine outcrops along a tributary of the Nyang River, a major tributary of the Yarlung-Tsangpo in southeast Tibet. The deposits were preserved between terraces at altitudes of 2950–3100 m asl. The stratigraphic record features at least two sets of coarsening-upward sequences depicting episodic aggradation and progradation of a glacially dammed lake related delta. Recognized facies changes illustrate the evolution cycles of depositional environments from pro-delta, delta front, to delta plain. Radiocarbon and optically stimulated luminescence dates reveal an aging-downward trend in stratigraphic order and provide an approximate timeline for the formation of glacially dammed lakes in late Pleistocene. This result reflects that the Zelunglung Glacier had progressively advanced to block the Yarlung-Tsangpo river and the dam materials had stepwise stacked up to an altitude of 3095 m asl during Marine Oxygen Isotope Stages 4 to 2. 相似文献
20.
India’s polar orbiting satellite Oceansat-2 was launched by Indian Space Research Organisation on 23 September 2009 for applications pertaining to ocean studies and meteorology. The wind scatterometer aboard the Oceansat-2 satellite (OSCAT) covers 90 % of the global ocean within a day. In the present study, the OSCAT-derived wind fields are used to predict the genesis of tropical cyclones over the North Indian Ocean using a new technique based on data mining. The technique is based on the premise that there is some degree of similarity in low-level wind circulation among developing systems, which can be utilized to distinguish them from non-developing systems. This similarity of wind patterns has been measured quantitatively by computing the “matching index” between the given wind pattern and the wind signatures of developing systems available from the past observations. The algorithm is used to predict the tropical cyclogenesis of cyclones formed during the period 2009–11 in the North Indian Ocean. All the tropical disturbances that developed into tropical storms during the above period (2009–11), viz. PHYAN, WARD, LAILA, BANDU, PHET, GIRI, JAL, KEILA, FOUR, FIVE and THANE were predicted using the proposed method. The mean prediction lead time of the technique was 63 h. Probability of detection of the technique was 100 %, while the false alarm ratio was 2 %. 相似文献