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1.
Summary This paper presents a theory of the transient Bernoulli-Euler beam problem on an elastic foundation which takes into account the effects of axial load and linear damping. An analytical solution of the steady state and the transient components has been obtained due to physically realistic load distributions. With a view to extend its practical applicability, the characteristic features of the solution are explored. Several limiting situations are investigated as special cases. It is shown that the steady state vibration can be achieved as the limit of the solution of the transient problem. 相似文献
2.
Summary An investigation is carried out on the unsteady boundary layer induced in an incompressible, homogeneous, viscous fluid bounded by (i) an infinite horizontal porous plate aty=0, or (ii) two parallel horizontal rigid porous plates aty=0 andy=d. The unsteady motion is generated in the above fluid configurations by moving the plate(s) impulsively in its (their) own plane with a prescribed time-dependent velocity. Solutions for the unsteady velocity field are exactly solved by the Laplace transform treatment combined with the theory of residues. The structures of the associated boundary layers are determined. The effects of suction on the solutions and the boundary layers are investigated in detail, the limiting behaviour of the unsteady solution as timet is examined and Physical interpretations of the mathematical results are given. Finally, the frictional stresses on the plates are stated without detailed calculation. 相似文献
3.
Summary Unsteady boundary layer flows generated in a homogeneous, non-rotating viscous fluid are considered. The method of Laplace transform is used to obtain exact solutions of the unsteady boundary layer equations in a more general situation. The structures of the unsteady velocity field and the associated boundary layers are determined. Several particular solutions are recovered as special cases of the present general theory. The physical implications of the mathematical results are investigated. 相似文献
4.
Tilak B. Kotoch Anuj Nandi D. Debnath J. P. Malkar A. R. Rao M. K. Hingar Vaibhav P. Madhav S. Sreekumar Sandip K. Chakrabarti 《Experimental Astronomy》2011,29(1-2):27-54
Cadmium Zinc Telluride (CZT) detectors are high sensitivity and high resolution devices for hard X-ray imaging and spectroscopic studies. The new series of CZT detector modules (OMS40G256) manufactured by Orbotech Medical Solutions (OMS), Israel, are used in the RT-2/CZT payload onboard the CORONAS-PHOTON satellite. The CZT detectors, sensitive in the energy range of 20 to 150 keV, are used to image solar flares in hard X-rays. Since these modules are essentially manufactured for commercial applications, we have carried out a series of comprehensive tests on these modules so that they can be confidently used in space-borne systems. These tests lead us to select the best three pieces of the ??Gold?? modules for the RT-2/CZT payload. This paper presents the characterization of CZT modules and the criteria followed for selecting the ones for the RT-2/CZT payload. The RT-2/CZT payload carries, along with three CZT modules, a high spatial resolution CMOS detector for high resolution imaging of transient X-ray events. Therefore, we discuss the characterization of the CMOS detector as well. 相似文献
5.
Bijaya B. Karki Dipesh Bhattarai Mainak Mookherjee Lars Stixrude 《Physics and Chemistry of Minerals》2010,37(2):103-117
We have explored first-principles molecular dynamics simulation data for hydrous MgSiO3 liquid (with 10 wt% water) to gain insight into its structural and dynamical behavior as a function of pressure (0–150 GPa)
and temperature (2,000–6,000 K). By visualizing/analyzing a number of parameters associated with short- and mid-range orders,
we have shown that the melt structure changes substantially on compression. The speciation of the water component at low pressures
is dominated by the isolated structures (with over 90% hydrogen participated) consisting of hydroxyls, water molecules, O–H–O
bridging and four-atom (O–H–O–H and H–O–H–O) groups, where every oxygen atom may be a part of polyhedron or free (i.e., bound
to only magnesium atom). Hydroxyls favor polyhedral sites over magnesium sites whereas molecular water is almost entirely
bound to magnesium sites, and also interpolyhedral bridging (Si–O–H–O–Si) dominates other types of bridging. Water content
is shown to enhance and suppress, respectively, the proportions of hydroxyls and molecular water. As compression increases,
these isolated structures increasingly combine with each other to form extended structures involving a total of five or more
O and H atoms and also containing threefold coordination species, which together consume over 80% hydrogen at the highest
compression studied. Our results show that water lowers the mean coordination numbers of different types including all cation–anion
environments. The hydrous melt tends to be more tetrahedrally coordinated but with the Si–Si network being more disrupted
compared to the anhydrous melt. Protons increase the content of non-bridging oxygen and decrease the contents of bridging
oxygen as well as oxygen triclusters (present at pressures above 10 GPa). The calculated self-diffusion coefficients of all
atomic species are enhanced in the presence of water compared to those of the anhydrous melt. This is consistent with the
prediction that water depolymerizes the melt structure at all pressures. Our analysis also suggests that proton diffusion
involves two processes—the transfer of H atoms (requiring the rupture and formation of O–H bonds) and the motion of hydroxyls
as hydrogen carriers (requiring the rupture and formation of Si–O and/or Mg–O bonds). Both the processes are operative at
low compression whereas only the first process is operative at high compression. 相似文献
6.
Ujjal Debnath Soma Nath Subenoy Chakraborty 《Monthly notices of the Royal Astronomical Society》2006,369(4):1961-1964
The junction conditions between static and non-static space–times are studied for analysing gravitational collapse in the presence of a cosmological constant. We have discussed about the apparent horizon and their physical significance. We also show the effect of cosmological constant in the collapse and it has been shown that cosmological constant slows down the collapse of matter. 相似文献
7.
In this paper, we have considered a model of our universe containing five components as its constituents. Then, we have done
here the statefinder diagnostics for this model. This model can successfully explain the accelerated expansion of the universe
given that it satisfies a certain condition. Here we have considered the modified Chaplygin gas as the dynamically changing
part of the dark energy component of our universe. Chaplygin gas provides early deceleration and late time acceleration of
the universe. The graphical representation of statefinder parameters shows that the total evolution of the universe starts
from radiation era to phantom model. 相似文献
8.
In this work, we have studied the model of modified Chaplygin gas and its role in accelerating phase of the universe for anisotropic
model. We have assumed that the equation of state of this modified model is valid from the radiation era to ΛCDM model. We
have obtained the possible relation between the hessence and the modified Chaplygin gas. We have also use the statefinder
parameters for characterize different phase of the universe diagrammatically. 相似文献
9.
In this letter, we have considered that the universe is filled with normal matter and variable modified Chaplygin gas. Also we have considered the interaction between normal matter and variable modified Chaplygin gas in FRW universe. Then we have considered a correspondence between the holographic dark energy density and interacting variable modified Chaplygin gas energy density. Then we have reconstructed the potential of the scalar field which describes the variable modified Chaplygin cosmology. 相似文献
10.
We investigate the background dynamics when dark energy is coupled to dark matter in the universe described by loop quantum
cosmology. We consider dark energy of the form modified Chaplygin gas. The dynamical system of equations is solved numerically
and a stable scaling solution is obtained. It henceforth resolves the famous cosmic coincidence problem in modern cosmology.
The statefinder parameters are also calculated to classify this dark energy model. 相似文献