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101.
Polycrystalline samples of ternary rare-earth germanides R2Co3Ge5 (R=La, Ce and Pr) have been prepared and investigated by means of magnetic susceptibility, isothermal magnetization, electrical resistivity and specific heat measurements. All these compounds crystallize in orthorhombic U2Co3Si5 structure (space group Ibam). No evidence of magnetic or superconducting transition is observed in any of these compounds down to 2 K. The unit cell volume of Ce2Co3Ge5 deviates from the expected lanthanide contraction, indicating non trivalent state of Ce ions in this compound. The reduced value of effective moment (μeff≈0.95 μB) compared to that expected for trivalent Ce ions further supports valence-fluctuating nature of Ce in Ce2Co3Ge5. The observed temperature dependence of magnetic susceptibility is consistent with the ionic interconfiguration fluctuation (ICF) model. Although no sharp anomaly due to a phase transition is seen, a broad Schottky-type anomaly is observed in the magnetic part of specific heat of Pr2Co3Ge5. An analysis of Cmag data suggests a singlet ground state in Pr2Co3Ge5 separated from the singlet first excited state by 22 K and a doublet second excited state at 73 K. 相似文献
102.
We investigate transverse electromagnetic waves propagating in a plasma influenced by the gravitational field of the Schwarzschild-de
Sitter black hole. Applying 3+1 spacetime split we derive the relativistic two-fluid equations to take account of gravitational
effects due to the event horizon and describe the set of simultaneous linear equations for the perturbations. We use a local
approximation to investigate the one-dimensional radial propagation of Alfvén and high frequency electromagnetic waves. We
derive the dispersion relation for these waves and solve it for the wave number k numerically. 相似文献
103.
104.
Arindam Sarkar Paltu Banerjee Sk. Ugir Hossain Sudin Bhattacharya Subhash Chandra Bhattacharya 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2009,72(5):1097-1102
In this work, three newly synthesized derivatives of thiazolidinediones, with potential for application as drugs in pharmaceutical industry and free radical scavenging activity, have been taken up to investigate their behaviour in different homogeneous solvents. The purpose of this work is to study the solvation characteristics in ground and excited states of the derivatives by monitoring the absorbance and fluorescence band maxima. The steady state and time resolved fluorescence studies in protic and aprotic solvents have been rationalized on the basis of solute–solvent interaction and substituent effect on these photophysical processes have been analyzed. Substituents at different positions of the aryl moiety affect the hydrogen bond formation ability of the probes. 相似文献
105.
We have developed a convenient two-step procedure for the synthesis of 3-ethoxycarbonyl indoles from commercially available materials. The two-step procedure involves the synthesis of 2-aryl-3-hydroxypropenoic acid ester, followed by a catalytic reduction. This method is efficient, simple, and selective. 相似文献
106.
Diaryliodonium triflates have been directly prepared by reaction of arenes with elemental iodine in good yields by using K2S2O8 and TFA, followed by treatment with NaOTf. This procedure avoids the use of high temperature and severe reaction conditions. 相似文献
107.
This paper discusses the effect of thermophoretic particle deposition on the transient natural convection laminar flow along a vertical flat surface,which is immersed in an optically dense gray fluid in the presence of thermal radiation.In the analysis,the radiative heat flux term is expressed by adopting the Rosseland diffusion approximation.The governing equations are reduced to a set of parabolic partial differential equations.Then,these equations are solved numerically with a finite-difference scheme in the entire time regime.The asymptotic solutions are also obtained for sufficiently small and large time.The obtained asymptotic solutions are then compared with the numerical solutions,and they are found in excellent agreement.Moreover,the effects of different physical parameters,i.e.,the thermal radiation parameter,the surface temperature parameter,and the thermophoretic parameter,on the transient surface shear stress,the rate of surface heat transfer,and the rate of species concentration,as well as the transient velocity,temperature,and concentration profiles are shown graphically for a fluid(i.e.,air) with the Prandtl number of 0.7 at 20 C and 1.013 × 10 5 Pa. 相似文献
108.
A. Asgarian M. Z. Hossain J. M. Floryan 《Theoretical and Computational Fluid Dynamics》2016,30(4):313-337
Natural convection in a two-dimensional horizontal layer has been investigated. The layer is confined between two parallel horizontal plates. The upper plate is kept isothermal, while the lower plate has an externally imposed, long wavelength, spatially sinusoidal heating with the amplitude expressed in terms of the Rayleigh number Ra and the wavelength characterized by the wave number α. Only steady-state flow structures and their bifurcations have been considered. The detailed analysis has been carried out for two Prandtl numbers, i.e. Pr = 0.7 and Pr = 7, and only small differences in the bifurcation diagrams have been observed. When Ra < Ra cr = 427, convection has a simple topology consisting of one pair of counter-rotating rolls per heating period. Secondary motion in the form of rolls aligned in the direction of the primary rolls and concentrated around the hot spots occurs for Ra > 427. When 427 < Ra < ~470 and α < ~0.14, the secondary motion is described by the supercritical pitchfork bifurcation. One of the branches of this bifurcation is associated with an odd number of secondary rolls per half wavelength, with rolls above the hot spots rotating in the direction opposite to the primary rolls. The other branch is associated with an even number of secondary rolls per half wavelength, with the rolls above the hot spots co-rotating with the primary rolls. The new rolls are pinched off in pairs when α decreases. When Ra > ~470 and α > ~0.14, bifurcation assumes the form of “bifurcation from infinity”. The main branch is associated with one pair of rolls per heating period for α > 0.25. Decrease in α along this branch results in the formation of secondary rolls, with the rolls at the hot spot co-rotating with the primary rolls. The lower part of the other branch is associated with one pair of rolls per heating period in the limit α → 0. Increase in α results in pinching off a single roll which counter-rotates with respect to the primary roll at the hot spot. 相似文献
109.
Melissa officinalis contains various secondary metabolites that have health benefits. Generally, irradiating plants with ultraviolet (UV)-B induces the accumulation of secondary metabolites in plants. To understand the effect of UV-B irradiation on the metabolism of M. officinalis, metabolomics based on gas chromatography-mass spectrometry (GC-MS) was used in this study. The GC-MS analysis revealed 37 identified metabolites from various chemical classes, including alcohols, amino acids, inorganic acids, organic acids, and sugars. The metabolite profiles of the groups of M. officinalis irradiated with UV-B were separated and differentiated according to their irradiation times (i.e., 0, 1, and 2 h), using principal component analysis (PCA) and hierarchical clustering analysis (HCA), respectively. The PCA score plots of PC1 and PC2 showed that the three groups with different irradiation times followed a certain trajectory with increasing UV-B irradiation. HCA revealed that metabolic patterns differed among the three groups, and the 1 h-irradiated group was more similar to the control group (0 h) than the 2 h-irradiated group. In particular, UV-B irradiation of plants led to a decrease in sugars such as fructose, galactose, sucrose, and trehalose and an increase in metabolites in the tricarboxylic acid cycle, the proline-linked pentose phosphate pathway, and the phenylpropanoid pathway. This study demonstrated that metabolite profiling with GC-MS is useful for gaining a holistic understanding of UV-induced changes in plant metabolism. 相似文献
110.
Mohammad A Hossain Sereyrath Ngeth Teddy Chan Michael N Oda Gordon A Francis 《BMC biochemistry》2012,13(1):1