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451.
Some LRS Bianchi type V viscous-fluid cosmological models are investigated, in which the coefficient of shear viscosity is
considered as proportional to the scale of expansion in the model. This leads toA=Bn, whereA andB are metric potentials,n being a constant. The coefficient of bulk viscosity is also assumed to be a power function of mass density. The cosmological
constant is found to be a decreasing function of time, which is supported by results from recent type Ia supernovae observations.
Some physical aspects of the models are also discussed. 相似文献
452.
The statistics of damage avalanches during a failure process typically follows a power law. When these avalanches are recorded only near the point at which the system fails catastrophically, one finds that the power law has an exponent which is different from that one finds if the recording of events starts away from the vicinity of catastrophic failure. We demonstrate this analytically for bundles of many fibers, with statistically distributed breakdown thresholds for the individual fibers and where the load is uniformly distributed among the surviving fibers. In this case the distribution D(Delta) of the avalanches (Delta) follows the power law Delta-xi with xi=3/2 near catastrophic failure and xi=5/2 away from it. We also study numerically square networks of electrical fuses and find xi=2.0 near catastrophic failure and xi=3.0 away from it. We propose that this crossover in xi may be used as a signal of imminent failure. 相似文献
453.
A scanning tunneling microscope was used to probe electron transport through an alkali doped C(60) monolayer crystal on Al(2)O(3) grown by the oxidation of NiAl(110). Each individual alkali atom forms a localized complex with the neighboring C(60) molecules. Charging of the complex induces a substantial rise in the current that persists outside the physical dimensions of the complex. This induction of the current rise is characterized by spatially resolved spectroscopy and mapping of the differential conductance (dI/dV) in the vicinity of the complex. 相似文献
454.
Maximizing nonlinear light-matter interactions is a primary motive for compressing laser pulses to achieve ultrashort transform limited pulses. Here we show how, by appropriately shaping the pulses, resonant multiphoton transitions can be enhanced significantly beyond the level achieved by maximizing the pulse's peak intensity. We demonstrate the counterintuitive nature of this effect with an experiment in a resonant two-photon absorption, in which, by selectively removing certain spectral bands, the peak intensity of the pulse is reduced by a factor of 40, yet the absorption rate is doubled. Furthermore, by suitably designing the spectral phase of the pulse, we increase the absorption rate by a factor of 7. 相似文献
455.
The enthalpies of mixing of four isomeric butanols with di-n-butyl ether were determined at 30°C by a Calvet type microcalorimeter. All the four systems showed endothermic behaviour.
The enthalpies of complex formation were calculated by the thermochemical cycle. The strength of H-bonding decreases in the
order l-butanol, l-methyl-1-propanol, 2-methyl-2-propanol, 2-butanol. The results are explained on the basis of a steric effect
on interaction.
NCL Communication No. 4430. 相似文献
456.
Reductive cyclization has been shown to accompany reduction on NaI/Zn/DME treatment of sulphonates of γ,δ- unsaturated alcohols. Stereoselectivity is due to FMO control with axial extension of SOMO of cyclohexyl radical playing a crucial role. 相似文献
457.
It is shown that the gauge-particle associated with local-duality transformation of Maxwell electro-magnetic equations is a massless axial vector boson which mediates universal long-range interaction between spins. Possible existence of a pure gauge field of this type in an inhomogeneous magneto-electric material is examined. 相似文献
458.
459.
Anirudh Pradhan Purnima Pandey Sunil Kumar Singh 《International Journal of Theoretical Physics》2007,46(6):1584-1595
In this paper we investigate a class of solutions of Einstein equations for the plane- symmetric perfect fluid case with shear
and vanishing acceleration. If these solutions have shear, they must necessarily be non-static. We examine the integrable
cases of the field equations systematically. Among the cases with shear we find three classes of solutions.
PACS No.: 04.20.-q. 相似文献
460.
Anirudh Pradhan Vandana Rai Kanti Jotania 《理论物理通讯》2008,50(7):279-288
Cylindrically symmetric inhomogeneous cosmological model for bulk viscous fluid distribution with electro- magnetic field is obtained. The source of the magnetic field is due to an electric current produced along the z-axis. F12 is the non-vanishing component of electromagnetic field tensor. To get the deterministic solution, it has been assumed that the expansion 0 in the model is proportional to the shear σ. The values of cosmological constant for these models are found to be small and positive at late time, which are consistent with the results from recent supernovae Ia observations. Physical and geometric aspects of the models are also discussed in presence and absence of magnetic field. 相似文献