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101.
Mubasher Jamil Farook Rahaman 《The European Physical Journal C - Particles and Fields》2009,64(1):97-105
We here investigate a cosmological model in which three fluids interact with each other, involving certain coupling parameters
and energy exchange rates. The motivation of the problem stems from the puzzling ‘triple coincidence problem’ which naively
asks why the cosmic energy densities of matter, radiation and dark energy are almost of the same order of magnitude at the
present time. In our model, we determine the conditions under which triple interacting fluids will cross the phantom divide. 相似文献
102.
F. Rahaman Saibal Ray M. Kalam M. Sarker 《International Journal of Theoretical Physics》2009,48(11):3124-3138
We perform a survey whether higher dimensional Schwarzschild space-time is compatible with some of the solar system phenomena.
As a test we examine four well known solar system effects, viz., (1) Perihelion shift, (2) Bending of light, (3) Gravitational
redshift, and (4) Gravitational time delay. It is shown, under a N-dimensional solutions of Schwarzschild type very narrow class of metrics, that the results related to all these physical
phenomena are mostly incompatible with the higher dimensional version of general relativity. We compare all these restricted
results with the available data in the literature. 相似文献
103.
H. Penttil? P. Karvonen T. Eronen V. -V. Elomaa U. Hager J. Hakala A. Jokinen A. Kankainen I. D. Moore K. Per?j?rvi S. Rahaman S. Rinta-Antila V. Rubchenya A. Saastamoinen T. Sonoda J. ?yst? 《The European Physical Journal A - Hadrons and Nuclei》2010,44(1):147-168
A novel method to determine independent yields in particle-induced fission employing the ion guide technique and ion counting after a Penning trap has been developed. The method takes advantage of the fact that a Penning trap can be used as a precision mass filter, which allows an unambiguous identification of the fission fragments. The method was tested with 25MeV and 50MeV proton-induced fission of 238U . The data is internally reproducible with an accuracy of a few per cent. A satisfactory agreement was obtained with older ion guide yield measurements in 25MeV proton-induced fission. The results for Rb and Cs yields in 50MeV proton-induced fission agree with previous measurements performed at an isotope separator equipped with a chemically selective ion source. 相似文献
104.
I. Obrusník O. Skřivánek M. Umlaufová V. Hovorka 《Journal of Radioanalytical and Nuclear Chemistry》1985,89(2):561-570
Instrumental neutron activation analysis has been performed on human head hair of newborns and mothers sampled in two areas with a different level of environmental exposure. The group of neonates from the exposed area (polluted by thermal power plants burning brown coal and by chemical industry) has exhibited higher levels of several trace elements in hair, e.g. Se, Zn, Hg and Sb in comparison with the control group. Moreover, the mean concentrations of Se, Hg, Zn and Br in neonate hair have been found to be higher than in mothers hair. Although the study revealed statistically significant differences in the composition of neonate hair sampled in areas with different levels of environmental exposure, the differences are relatively small. Only a thorough long-term study both with environmental and medical observations can prove a direct connection of the elevated levels of some trace elements in neonate hair with the higher frequency of mental diseases of children living in the exposed area. 相似文献
105.
Nanocrystalline Cr2O3 and NiO are prepared using high-energy ball milling. Average sizes of the particles obtained from Scanning Electron Microscopy and crystallite sizes obtained from X-ray diffraction are larger for Cr2O3 than NiO particles. At low temperature, large high-field magnetization and small coercivity lead to a weak exchange bias for Cr2O3, whereas small high-field magnetization and large coercivity lead to a considerable exchange bias for NiO. The training effect is observed for NiO at 4 K which could be described with a recursive formula constructed in the framework of the spin configurational relaxation model. The results suggest that the pinning mechanism at the interface between the antiferromagnetic and the weak ferromagnetic component ascribed to uncompensated spins leads to the exchange bias effect. 相似文献
106.
Dr. J. Hostomský Dr. J. Rathouský Jr. Prof. Dr. J. Skřivánek 《Crystal Research and Technology》1981,16(7):759-765
The growth rate of barium sulphate seed crystals from stirred solutions was studied conductometrically at 25°C by a stopped-flow technique. The supersaturation ranged from 3 × 10−7 to 3 × 10−8 mol BaSO4/cm3. The seed crystals were grown in the system during the initial (steady-state) period of the experiment. Crystal size distributions were determined by optical microscopy. The growth rate of barium sulphate under the conditions of the experiments can be expressed by a quadratic function of supersaturation. The results, which suggest an interface rate-controlling mechanism, are discussed with respect to published data. 相似文献
107.
Sk.Khadeer Pasha V.S.V.Satyanarayana A.Sivakumar K.Chidambaram L.John Kennedy 《中国化学快报》2011,22(8):891-894
Several 2,5-dimethyl-N-substituted pyrroles were prepared by the condensation of different substituted anilines with 2,5- hexanedione using nano lead oxide as an efficient and recyclable catalyst.All the synthesized compounds are confirmed through IR, 1H NMR,13C NMR and mass spectral data.Nano lead oxide β-PbO(P85) was prepared by dissolving lead acetate dihydrate in 1- propanol at a pH 9.0 under stirring at 85℃.The structural study and surface morphology of the lead oxide(PbO) were characterized using X-ray diffraction(XRD),Scanning electron microscopy(SEM) and the functional groups of the PbO sample were investigated using infrared spectrophotometer. 相似文献
108.
In this paper we have considered a spherically symmetric domain wall with non vanishing stress component in the direction perpendicular to the plane of the wall. The exact solutions are obtained using functional separability of metric coefficients. Also we have studied the motion of the test particles in different situations. 相似文献
109.
Moumita Majumdar Arup Sinha Tapas Ghatak Sanjib K. Patra Nabanita Sadhukhan S. M. Wahidur Rahaman Jitendra K. Bera Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(8):2574-2585
The complete sequence of reactions in the base‐promoted reduction of [{RuII(CO)3Cl2}2] to [RuI2(CO)4]2+ has been unraveled. Several μ‐OH, μ:κ2‐CO2H‐bridged diruthenium(II) complexes have been synthesized; they are the direct results of the nucleophilic activation of metal‐coordinated carbonyls by hydroxides. The isolated compounds are [Ru2(CO)4(μ:κ2‐C,O‐CO2H)2(μ‐OH)(NPF‐Am)2][PF6] ( 1 ; NPF‐Am=2‐amino‐5,7‐trifluoromethyl‐1,8‐naphthyridine) and [Ru2(CO)4(μ:κ2‐C,O‐CO2H)(μ‐OH)(NP‐Me2)2][BF4]2 ( 2 ), secured by the applications of naphthyridine derivatives. In the absence of any capping ligand, a tetranuclear complex [Ru4(CO)8(H2O)2(μ3‐OH)2(μ:κ2‐C,O‐CO2H)4][CF3SO3]2 ( 3 ) is isolated. The bridging hydroxido ligand in 1 is readily replaced by a π‐donor chlorido ligand, which results in [Ru2(CO)4(μ:κ2‐C,O‐CO2H)2(μ‐Cl)(NP‐PhOMe)2][BF4] ( 4 ). The production of [Ru2(CO)4]2+ has been attributed to the thermally induced decarboxylation of a bis(hydroxycarbonyl)–diruthenium(II) complex to a dihydrido–diruthenium(II) species, followed by dinuclear reductive elimination of molecular hydrogen with the concomitant formation of the RuI? RuI single bond. This work was originally instituted to find a reliable synthetic protocol for the [Ru2(CO)4(CH3CN)6]2+ precursor. It is herein prescribed that at least four equivalents of base, complete removal of chlorido ligands by TlI salts, and heating at reflux in acetonitrile for a period of four hours are the conditions for the optimal conversion. Premature quenching of the reaction resulted in the isolation of a trinuclear RuI2RuII complex [{Ru(NP‐Am)2(CO)}{Ru2(NP‐Am)2(CO)2(μ‐CO)2}(μ3:κ3‐C,O,O′‐CO2)][BF4]2 ( 6 ). These unprecedented diruthenium compounds are the dinuclear congeners of the water–gas shift (WGS) intermediates. The possibility of a dinuclear pathway eliminates the inherent contradiction of pH demands in the WGS catalytic cycle in an alkaline medium. A cooperative binuclear elimination could be a viable route for hydrogen production in WGS chemistry. 相似文献
110.