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31.
A self consistent formulation of the Jeans instability of a dusty plasma with proper inclusion of charge dynamics is described.
It is shown that charge fluctuations significantly affect the Jeans as well as the Buneman mode. For plasma particles (electrons
and ions) in local thermal equilibrium, the Jeans lengthλ
J is given byλ
J≈λ
g
F(R, ε, β/η), whereλ
g is the Debye length of the charged grains,R is the square of the ratio of the Jeans to the plasma frequency of the grains,ε is the square of the ratio of the Debye length of the grains and the plasma particles andβ/η is the ratio of the attachment to the decay frequency of the electronic charges to the grain surface. The functional form
ofF is given in the text. Numerical investigation of the Jeans-Buneman mode for a two and three component plasma shows that the
Jeans mode dominates atkλ
D≪1 (wherek is the wave number andλ
D is the Debye length of plasma particles), whereas atkλ
D≫1 only the Buneman mode operates. Charge fluctuations reduce the area of overlap of the two modes. Furthermore, in the absence
of gravity, there exists a new, charge fluctuation induced unstable mode in a streaming dusty plasma. Astrophysical applications
of the results are discussed. 相似文献
32.
V. Yamakov A. Milchev G.M. Foo R.B. Pandey D. Stauffer 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,9(4):659-667
A coarse-grained off-lattice bead-spring model is used to reveal the complex dynamics of a polymer chain in a quenched porous
medium in the presence of an external field B. The behavior of the mean square displacement (MSD) of the center chain bead and that of the center of mass of the chain
as a function of time is studied at different values of the barrier concentration C, the field strength B and the chain length N. In a field, important information on the way in which chains move between obstacles and overcome them is gained from the
MSD vs. time analysis in the directions parallel and perpendicular to the flow. Instead of a steady approach to uniform drift-like
motion at low C, for sufficiently strong field B we observe logarithmic oscillations in the effective exponents describing the time dependence of the MSD along and perpendicular to field. A common nature of
this phenomenon with oscillatory behavior, observed earlier for biased diffusion of tracers on random lattices, is suggested.
Received 7 August 1998 相似文献
33.
Journal of Applied Spectroscopy - The elemental composition of one- and two-rupee coins issued in different years by the Reserve Bank of India (RBI) was investigated using laser-induced breakdown... 相似文献
34.
35.
Vibhav Pandey R.P. Aloysius V.P.S. Awana R.K. Kotnala 《Journal of magnetism and magnetic materials》2009,321(14):2239-2244
The structural magnetic and magneto-transport properties of double perovskite system Ba2−xSrxFeMoO6 (0?x?1.0) prepared in bulk polycrystalline form are reported in this paper. X-ray diffraction analysis showed that samples are single phase and the lattice constants decreases with increase in the Sr content. The degree of Fe-Mo ordering has been found decreasing in the series with an increase in the Sr content. Parent compound Ba2FeMoO6 exhibits saturation magnetic moment value of 3.54 μB/f.u. at 85 K in a magnetic field of 6000 Oe. Temperature dependence of resistivity shows metallic behavior for all the samples. The magneto-resistance (MR) of the compound with x=0.4 is higher than that of the other samples. At room temperature this system shows a saturation magnetization value of 1.73 μB/f.u. and MR value of 7.08% (1 T). The observed variations in the structural and magnetic properties are attributed to the change of chemical pressure due to the substitution of Sr in place of Ba. The effect of antisite disorder (ASD) defects on magneto-transport properties is studied in more detail. 相似文献
36.
K.K.M. Pandey G.M. Chow B.C. Lim 《Journal of magnetism and magnetic materials》2009,321(19):3236-3240
The effects of interface roughness of Ta seedlayer on the structural and magnetic properties of Co72Pt28(20 nm)/Ru(30 nm)/Pt(2 nm)/Ta(5 nm)/glass were investigated. Uniaxial perpendicular magnetic anisotropy (8.6×106 ergs/cc), coercivity (5.5 kOe) and nucleation field (−2.8 kOe) in the Co72Pt28 thin film sputter-deposited on relatively smooth surface of Ta seedlayer were achieved. The results showed that relatively smoother interface roughness of Ta seedlayer improved the CoPt/Ru (0 0 0 2) texture and magnetic properties. 相似文献
37.
Temperature dependent ultrasonic properties of aluminium nitride 总被引:1,自引:0,他引:1
Hexagonal wurtzite structured aluminium nitride has been characterized by the theoretical calculation of ultrasonic attenuation, ultrasonic velocity, higher order elastic constants, thermal relaxation time, acoustic coupling constants and other related parameters in temperature range 200-800 K for wave propagation along the unique axis of the crystal. Higher order elastic constants of AlN at different temperatures are calculated using Lennard-Jones potential for the determination of ultrasonic attenuation. A decrease in ultrasonic velocity with temperature has been predicted, which is caused by reduction in higher order elastic constants with temperature. The temperature dependent ultrasonic properties have been discussed in correlation with higher order elastic constants, thermal relaxation time, thermal conductivity, acoustic coupling constants and thermal energy density. Anomalous behaviour of the attenuation is found at 400 K. On the basis of attenuation, the ductility and performance of AlN have been studied. 相似文献
38.
P.?Bhargava M.?Kumar H.?Kumar P.?Pandit R.?Pandey A.?K.?NathEmail author 《Pramana》2004,62(4):923-932
We have studied about the thrust imparted to targets of different materials by pulsed TEA CO2 laser and chopped CW CO2 laser in air and its dependence on different parameters such as laser intensity and pulse duration. We estimated the impulse-coupling
coefficient and compared it with the published results. The mechanism of generation of thrust by laser incident on targets
in air is, in effect, combination of those involved in laser ablation in vacuum and laser-induced air detonation. 相似文献
39.
In this review article, we discuss a class of biosensors that exploit the change in the colorimetric properties of noble metal nanoparticles in response to biomolecular binding at their surface. Several sensor fabrication techniques as well as sensor configurations are discussed with an emphasis on their strengths and limitations. We conclude by presenting the future prospects and challenges for the successful transition of this technology from the laboratory to a commercial product. 相似文献
40.
R. B. Pandey 《Journal of statistical physics》1989,54(3-4):997-1010
Immune response in a retrovirus system is modeled by a network of three binary cell elements to take into account some of the main functional features of T4 cells, T8 cells, and viruses. Two different intercell interactions are introduced, one of which leads to three fixed points while the other yields bistable fixed points oscillating between a healthy state and a sick state in a mean field treatment. Evolution of these cells is studied for quenched and annealed random interactions on a simple cubic lattice with a nearest neighbor interaction using inhomogenous cellular automata. Populations of T4 cells and viral cells oscillate together with damping (with constant amplitude) for annealed (quenched) interaction on increasing the value of mixing probabilityB from zero to a characteristic valueB
ca (B
cq). For higherB, the average number of T4 cells increases while that of the viral infected cells decreases monotonically on increasingB, suggesting a phase transition atB
ca (B
cq). 相似文献