共查询到20条相似文献，搜索用时 52 毫秒
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The problem of thermal convection instability of a horizontal layer of magnetized fluid has been studied to occur crystal growing under the effect of horizontal temperature gradient. In the study, the problem has been reduced to an eigen-value problem for a stream function. The dispersion relations for low viscosity fluid and high viscosity fluid respectively have been discussed analytically and some numerical results have been obtained. It is shown that the critical Rayleigh number and other its related constants for low viscosity fluid (i.e., mercury) are much differ than the high viscosity fluid (i.e., glycerol). 相似文献
3.
In two earlier papers (BRÄUER and RÄDLER 1986, 1987) the evolution of a magnetic field was considered which pervades an electrically conducting fluid and its non-conducting surroundings. A construction principle for Green's functions of the corresponding initial value problem was proposed, and worked out for the case in which the fluid fills a spherical region. Now the principle is applied to the case of a fluid body occupying a half-space. Green's functions are constructed for arbitrary motions of the fluid. More concrete results are derived for shear flow, and explicit expressions of Green's functions are given for rigid body motion. 相似文献
4.
O. V. Kravtsov 《Astrophysics and Space Science》1991,180(1):19-37
It is shown that the velocity distribution and equilibrium conditions of the self-gravitating configurations from an ideal fluid are closely related with the presence of freezing-in vector fields determined by means of scalar potentials, whose total derivative is equal to zero. Ignorance of integrals of motion connected with the existence of freezing-in fields did not allow one to obtain the complete equilibrium conditions by variational method and, especially, led to the divergence in Lyapunov's and Riemann's results. This defect is eliminated in the paper and the equilibrium conditions and velocity distribution are considered by a single approach in the models of: (1) homogeneous fluid; (2) compressible fluid; (3) fluid with a magnetic field; (4) ideal fluid in the PNA of GR. 相似文献
5.
The evolutionary excitation dynamics of the gravitational instability in a self-gravitating viscoelastic non-thermal polytropic complex fluid is semi-analytically explored on the astro-scales of space and time. The polytropic equation of state is well validated for the hydrostatic equilibrium established by a perfect heating-cooling balancing in the uni-component complex fluid. We apply a generalized gravitating hydrodynamic model in the concurrent presence of buoyancy, thermal fluctuations, volumetric expansion, and so forth. A normal mode (local) analysis yields a quadratic linear dispersion relation with a unique set of multi-parametric coefficients. The analytical reliability is checked by comparing with the existing reports on purely ideal inviscid nebular fluids and non-ideal viscoelastic fluids in isolation. It is seen that, unlike the normal instability mechanisms, the instability here remains unaffected due to the thermo-mechanical diffusion processes. The stabilizing (destabilizing) and accelerating (decelerating) factors of the instability are illustratively explored. The instability features are judged in the light of both impure non-ideal viscoelastic fluid and pure ideal inviscid nebular fluid scenarios. The relevancy of our exploration in superdense compact viscoelastic astro-objects and their surrounding atmospheres is summarily outlined. 相似文献
6.
A. A. Raptis 《Astrophysics and Space Science》1982,86(1):43-53
An analysis of the two-dimensional flow of an incompressible, viscous binary fluid past an infinite, porous, vertical plate is presented under the following conditions: (i) the suction velocity is constant; (ii) the free stream oscillates in time about a constant mean; (iii) the plate moves in the upward direction in its own plane; (iv) the temperature of the plate is constant; (v) there are heat generation (absorption) in the fluid.Approximate solutions for the coupled non-linear equations are obtained for the velocity, temperature and their related quantities and the influence of the various parameters entering into the problem is discussed. 相似文献
7.
Marina Martínez Charles K. Shearer Adrian J. Brearley 《Meteoritics & planetary science》2023,58(9):1229-1245
Secondary minerals in martian nakhlites provide a powerful tool for investigating the nature, composition, and duration of aqueous activity in the martian crust. Northwest Africa (NWA) 998 crystallized early from the nakhlite magmatic source and has evidence of minimal signatures of the late hydrothermal alteration event that altered the nakhlites. Using FIB-TEM techniques to study a cumulus apatite grain in NWA 998, we report the first evidence of a submicron-scale vein consisting of fluorapatite and an SiO2-rich phase. Fluorapatite grew epitaxially on the walls of an opened cleavage plane of host F-bearing chlorapatite and the SiO2-rich phase filled the center of the vein. The presence of nanoporosity and nanometer-scale amorphous material and the sharp interface between the vein and the host apatite indicate the vein represents a coupled dissolution–reprecipitation process that generated apatite of a different composition that was more stable with the fluid. Using experimental data and diffusion coefficients of Cl in apatite from the literature, we conclude that the vein was caused by a low temperature (~300°C), slightly acidic, F-, Si-rich, aqueous fluid that acted as a closed system. Based on the characteristics of the vein (formation by rapid injection of fluid) and the fluid (composition, temperature, pH), and the lack of terrestrial weathering products in our SEM and TEM images, we infer that the vein is pre-terrestrial in origin. Our observations support the hypothesis that the heat source triggering a hydrothermal system was a low-shock velocity impact and rule out a magmatic origin. Finally, the vein could have formed from a late-stage fluid different from that reported in other nakhlites, but formation during the same magmatic event by, for example, a less evolved fluid might also be plausible. 相似文献
8.
A. Satya Narayanan 《Astrophysics and Space Science》1994,222(1-2):205-212
The formation of structures in the universe is one of the most challenging problems of cosmology. In this paper, an attempt to explain the formation of galaxies through the generation of vortices (with dissipation) in an uniformly expanding perfect fluid is made. The equation governing the mean square vorticity for a turbulent (isotropic and homogeneous) fluid is derived. It is shown that the mechanism of stretching vortices could enhance the mean square vorticity as a function of time. However, ultimately expansion and dissipation dominate and the solution for the mean square vorticity reaches the prediction by linear theory. 相似文献
9.
Irreversible matter creation is investigated in a two-component (scalar field and ordinary matter) cosmological fluid in a
homogeneous spatially flat and isotropic Friedmann-Robertson-Walker (FRW) inflationary Universe during its reheating era.
The thermodynamics of open systems as applied together with the gravitational field equations to the two-component cosmological
fluid leads to a generalisation of the elementary reheating theory in which the decay (creation) pressures are explicitly
considered as parts of the fluid stress-energy tensor. Particular models describing coherently oscillating scalar waves and
leading to a high particle production at the beginning of the oscillatory period are considered too.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
10.
In this paper, we have constructed a five dimensional LRS Bianchi type I cosmological model with wet dark fluid (WDF) in general relativity with the matter field described as bulk viscosity. It is found that in presence of bulk viscosity an inflationary effective stiff fluid cosmological model is obtained, whereas in absence of bulk viscosity the wet dark fluid degenerate to stiff fluid. Some physical and geometrical properties of the model are also discussed. 相似文献
11.
In FRW space time Brans-Dicke theory is developed for two cases: (i) the vacuum and (ii) the perfect fluid model. The field equations are transformed into a much simpler form under a change of time co-ordinates and then the solutions are determined for the above cases. An equation of statep =/3 (radiation) is assumed in the case of perfect fluid. 相似文献
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Some features of the Bianchi type-I universes in the presence of a fluid that wields an anisotropic equation of state (EoS)
parameter are discussed in the context of general relativity. The models that exhibit de Sitter volumetric expansion due to
the constant effective energy density (the sum of the energy density of the fluid and the anisotropy energy density) are of
particular interest. We also introduce two locally rotationally symmetric models, which exhibit de Sitter volumetric expansion
in the presence of a hypothetical fluid that has been obtained by minimally altering the conventional vacuum energy. In the
first model, the directional EoS parameter on the x axis is assumed to be −1, while the ones on the other axes and the energy density of the fluid are allowed to be functions
of time. In the second model, the energy density of the fluid is assumed to be constant, while the directional EoS parameters
are allowed to be functions of time. 相似文献
14.
Field equations in a scalar-tensor theory of gravitation proposed by Saezand Ballester (1985) are obtained with the aid of
(i) Friedmann-type metric (ii) a non static plane symmetric metric and (iii) spatially homogeneous Bianchi type – III metric.
Some cosmological models corresponding to perfect fluid and bulk viscous fluid are presented. Physical and kinematical properties
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
15.
D. R. K. Reddy CH. C. S. V. V. R. Murthy R. Venkateswarlu 《Astrophysics and Space Science》2006,301(1-4):79-82
Field equations in the presence of a perfect fluid distribution are obtained in a scalar-tensor theory of gravitation proposed
by Saez and Ballester (Phys. Lett. 113, 1985, 467) with the aid of Einstein–Rosen cylindrically symmetric metric. A static vacuum model and a non-static stiff fluid
model are presented. The physical and geometrical properties of the stiff fluid model are studied. 相似文献
16.
N.H. Bian 《Astronomische Nachrichten》2007,328(8):756-759
The resistive tearing instability of a sheet pinch, first investigated by Kuang & Roberts (1990) for the case of a rapidly rotating inviscid fluid, is studied for arbitrary rotation rate in a visco‐resistive fluid. Altogether there are three regimes of the resistive tearing instability which correspond to the particular parameter domain in the (Ω, Pm) plane. Here Ω is the angular velocity of the medium which is normalized to the Alfvén time and Pm is the magnetic Prandtl number. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
17.
The occurrence of oscillatory mode for magnetized fluid in the presence of vertical and horizontal temperature gradients has been studied. In both the cases (highly viscous and low-viscosity fluids) the occurrence of oscillatory solutions to the Bénard problem has been investigated as a function of Prandtl number, magnetic number, resistivity number and the ratio of applied temperature gradients. It is clear that the high Prandtl numbers completely change the character of instability and of the solutions as compared to those appropriate for low Prandtl-number fluids. It has also been shown that small horizontal temperature gradient readily generate oscillatory modes only for real frequencies. The critical Rayleigh number is higher than the critical Rayleigh number of non-magnetized fluid in both the cases-i.e., highly viscous fluid and one of moderate viscosity. 相似文献
18.
I. A. Hassanien 《Astrophysics and Space Science》1989,151(1):73-80
Unsteady two-dimensional hydromagnetic free convection and mass transfer flow of an electrically-conducting viscous-incompressible fluid, through a highly porous medium bounded by a vertical plane surface of constant temperature is considered. The free-stream velocity of the fluid vibrates about a mean constant value and the surface absorbs the fluid with constant velocity. Expressions for the velocity, temperature, concentration are obtained. Effects of Gr (Grashof number), Gm (modified Grashof number),K (permeability of the porous medium), (frequency parameter), andM (magnetic parameter) upon the velocity field are discussed. 相似文献
19.
In this paper, we study the evolution of the dark energy parameter in the spatially homogeneous and isotropic Friedmann-Robertson-Walker (FRW) model filled with barotropic fluid and dark energy in the scalar-tensor theory of gravitation proposed by Brans and Dicke (Phys. Rev. 24:925, 1961). A determinate solution is presented using (i) the special law of variation for Hubble’s parameter proposed by Berman (Nuovo Cimento B 74:183, 1983) and (ii) trace free energy momentum tensor of the two fluid. Two cases of interacting and non-interacting fluid (barotropic and dark energy) scenario is considered and general results are obtained. The physical aspects of the results obtained are, also, discussed. 相似文献
20.
The nonlinear properties of solitary waves structure in a hot magnetized dusty plasma consisting of a negatively charged,
extremely massive hot dust fluid, positively charged hot ion fluid and vortex-like distributed electrons, are reported. A
modified Korteweg de Vries equation (mKdV) which admits a solitary wave solution for small but finite amplitude is derived
using a reductive perturbation theory. The modifications in the amplitude and width of the solitary wave structures due to
the inclusion of an external magnetic field and dust and ions temperature are investigated.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献