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641.
Ahmad Rami El-Nabulsi 《Astrophysics and Space Science》2010,325(2):163-175
We processed the data on radial velocities and HI line widths for 1678 flat edge-on spirals from the Revised Flat Galaxy Catalogue.
We obtained the parameters of the multipole components of the large-scale velocity field of collective non-Hubble galaxy motion
as well as the parameters of the generalized Tully–Fisher relation in the “HI line width—linear diameter” version. All the
calculations were performed independently in the framework of three models, where the multipole decomposition of the galaxy
velocity field was limited to a dipole, a quadrupole, and an octopole term. We showed that both the quadrupole and the octopole
components are statistically significant.
On the basis of the compiled list of peculiar velocities of 1623 galaxies we obtained estimations of cosmological parameters
Ω
m
and σ
8. These estimations were obtained in both graphical form and as a constraint of the value S
8=(Ω
m
/0.3)0.35
σ
8=0.91±0.05. 相似文献
642.
We examine cosmic energy equation for extended galaxy structures on the basis of different models of universe. We also extend the power spectrum and density fluctuations for extended structure by introducing softening parameter both for linear and non-linear regimes. The results are compared with earlier results of point mass structures. It is found that softening parameters introduced in the theory influence the thermodynamic fluctuation theory. Results obtained with spectrum analysis are also compared with Riemannian geometric approach (Ruppeiner in Rev. Mod. Phys. 67:605, 1995) to the galaxy clustering. The singular solutions of thermodynamic fluctuation results can be interpreted on the basis of power spectrum analysis in terms of power index law of two point correlation function. 相似文献
643.
The Kachchh Basin is a pericratonic rift basin situated at the western margin of the Indian plate. The Habo Dome embodies
an important exposure of Bathonian to Kimmergian sediments among the Kachchh Mainland exposures. Based on vertical facies
transitions, facies associations were documented: mixed shallow marine (Facies association 1), shoreface and lagoon deposits
(Facies association II) and subtidal innershelf below fair weather wave base (Facies association III). The documented facies
associations reflect that Habo Dome sediments deposited in a variety of environments from shallow marine to fluvio-deltaic
and were strongly influenced by fluctuation of relative sea level. The dominance of floating grains and point contacts in
the sandstone indicate that detrital grains do not show much pressure effects as a result of either shallow burial or early
cementation. The sandstones were cemented by iron oxide, carbonate and silica in order of abundance. Three types of cements,
blocky, rim and fibrous cement occur in the studied limestone representing phreatic, fresh water phreatic and deep burial
diagenetic stages. Neomorphism and micritization are common. Both primary and secondary porosity exists in these sediments.
Different graphs of porosity versus depth suggest a depth of burial in the range of 615–769 m. 相似文献
644.
Naoki Ikegaya Aya Hagishima Jun Tanimoto Yudai Tanaka Ken-ichi Narita Sheikh Ahmad Zaki 《Boundary-Layer Meteorology》2012,143(2):357-377
We performed a series of wind-tunnel experiments under neutral conditions in order to create a comprehensive database of scalar
transfer coefficients for street surfaces using regular block arrays representing an urban environment. The objective is to
clarify the geometric dependence of scalar transfer phenomena on rough surfaces. In addition, the datasets we have obtained
are necessary to improve the modelling of scalar transfer used for computational simulations of urban environments; further,
we can validate the results obtained by numerical simulations. We estimated the scalar transfer coefficients using the salinity
method. The various configurations of the block arrays were designed to be similar to those used in a previous experiment
to determine the total drag force acting on arrays. Our results are summarized as follows: first, the results for cubical
arrays showed that the transfer coefficients for staggered and square layouts varied with the roughness packing density. The
results for the staggered layout showed the possibility that the mixing effect of air can be enhanced for the mid-range values
of the packing density. Secondly, the transfer coefficients for arrays with blocks of non-uniform heights were smaller than
those for arrays with blocks of uniform height under conditions of low packing density; however, as the packing density increased,
the opposite tendency was observed. Thirdly, the randomness of rotation angles of the blocks in the array led to increasing
values of the transfer coefficients under sparse packing density conditions when compared with those for cubical arrays. 相似文献
645.
Bivariate drought frequency analysis using the copula method 总被引:7,自引:2,他引:5
Rasoul Mirabbasi Ahmad Fakheri-Fard Yagob Dinpashoh 《Theoretical and Applied Climatology》2012,108(1-2):191-206
Droughts are major natural hazards with significant environmental and economic impacts. In this study, two-dimensional copulas were applied to the analysis of the meteorological drought characteristics of the Sharafkhaneh gauge station, located in the northwest of Iran. Two major drought characteristics, duration and severity, as defined by the standardized precipitation index, were abstracted from observed drought events. Since drought duration and severity exhibited a significant correlation and since they were modeled using different distributions, copulas were used to construct the joint distribution function of the drought characteristics. The parameter of copulas was estimated using the method of the Inference Function for Margins. Several copulas were tested in order to determine the best data fit. According to the error analysis and the tail dependence coefficient, the Galambos copula provided the best fit for the observed drought data. Some bivariate probabilistic properties of droughts, based on the derived copula-based joint distribution, were also investigated. These probabilistic properties can provide useful information for water resource planning and management. 相似文献
646.
647.
China Ocean Engineering - The breakwaters have experienced many changes during their construction history. These changes have been considered to improve their performance, depending on their... 相似文献
648.
Gravitational instabilities with respect to warp modes of vertical oscillations are examined for nonlinearly nonequilibrium
disk models with isotropic and anisotropic velocity diagrams. Nonstationary analogs of the dispersion relations for vertical
oscillations in these models are derived in a general form. A detailed study is made of the major large scale oscillatory
modes, which correspond primarily to the most common type of warp in the form of an integral sign, as well as to dome-shaped,
U-shaped, and precessional warps. Critical diagrams showing the initial virial relation as a function of the rotation parameter
for the nonstationary model are constructed for each of these vertical oscillation modes. A comparative analysis is made of
the growth rates of the instabilities for these modes in order to determine the dependence of the characteristic times for
their appearance on the basic physical parameters of the two models. 相似文献
649.
Ahmad Rami El-Nabulsi 《Astrophysics and Space Science》2009,324(1):71-75
The recent observational available data for an accelerated expansion state of the present universe, obtained from distant
SNeIa gave strong support to the search of alternative cosmologies. Recently, there have been a number of different attempts
to modify Einstein’s gravity to yield accelerated expansion at late times. Unfortunately, many of the theoretical models discussed
in the literature are plagued with theoretical problems, in particular the singularity problem at the origin of time. In the
present work we have analyzed a multidimensional spacetime Friedmann–Robertson–Walker (FRW) model with a decaying cosmological
constant and a varying gravitational constant. Many interesting consequences are revealed, in particular the behavior of the
scale factor and the shape of the universe in terms of the number of extra dimensions. 相似文献
650.
In this work, the Direct and Indirect Boundary Element Methods as applied to dynamic soil structure interaction problems, are compared. Both the methods are used to find the dynamic stiffnesses of rigid surface and embedded foundations. For surface foundations, the results obtained by the two methods were very close for the frequency range considered, but for embedded foundations at higher frequencies, the Indirect Boundary Element Method produced erroneous values for the real part of vertical compliance. The possible reasons for this discrepancy are also studied in this paper. 相似文献