共查询到20条相似文献,搜索用时 15 毫秒
1.
K. S. Adhav M. V. Dawande V. B. Raut 《International Journal of Theoretical Physics》2009,48(3):700-705
Bianchi type III space time is considered in the presence of cosmic strings in Einstein’s general theory of relativity. Exact
cosmological models are presented with the help of relation C=B
n
between metric coefficients C and B. Some physical properties of the model in each cases are discussed. 相似文献
2.
We discuss whether an appropriately defined dimensionless scalar function might be an acceptable candidate for the gravitational entropy, by explicitly considering Szekeres and Bianchi type VI
h
models that admit an isotropic singularity. We also briefly discuss other possible gravitational entropy functions, including an appropriate measure of the velocity dependent Bel-Robinson tensor.
PACS: 04.20.-q 95.30.Sf 98.80.Jk 相似文献
3.
4.
The spatially homogeneous and totally anisotropic Bianchi type-II cosmological solutions of massive strings have been investigated in the presence of the magnetic field in the framework of scale-covariant theory of gravitation formulated by Canuto et al. (Phys. Rev. Lett. 39, 429, 1977). With the help of special law of variation for Hubble’s parameter proposed by Berman (Nuovo Cimento 74, 182, 1983) string cosmological model is obtained in this theory. We use the power law relation between scalar field ? and scale factor R to find the solutions. Some physical and kinematical properties of the model are also discussed. 相似文献
5.
6.
BALI Raj PRADHAN Anirudh 《中国物理快报》2007,24(2):585-588
Bianchi type-Ⅲ string cosmological models with bulk viscous fluid for massive string are investigated. To obtain the determinate model of the universe, we assume that the coeffcient of bulk viscosity ξ is inversely proportional to the expansion θ in the model and expansion θ in the model is proportional to the shear g. This leads to B =lC^n, where l and n are constants. Behaviour of the model in the presence and absence of bulk viscosity is discussed. The physical implications of the models are also discussed in detail. 相似文献
7.
The LRS Bianchi type-I and type-II string cosmological models are studied when the source for the energy momentum tensor is a bulk viscous stiff fluid containing one dimensional strings together with zero-mass scalar field. We have obtained the solutions of the field equations assuming a functional relationship between metric coefficients when the metric is Bianchi type-I and constant deceleration parameter in case of Bianchi type-II metric. The physical and kinematical properties of the models are discussed in each case. The effects of Viscosity on the physical and kinematical properties are also studied. 相似文献
8.
The spatially homogeneous and totally anisotropic Bianchi type-II cosmological solutions of massive strings have been investigated in the presence of the magnetic field in the framework of f(R,T) gravity proposed by Harko et al. (Phys Rev D 84:024020, 2011). With the help of special law of variation for Hubble’s parameter proposed by Berman (Nuovo Cimento B 74:182, 1983) cosmological model is obtained in this theory. We consider f(R,T) model and investigate the modification R+f(T) in Bianchi type-II cosmology with an appropriate choice of a function f(T)=μ T. We use the power law relation between average Hubble parameter H and average scale factor R to find the solution. The assumption of constant deceleration parameter leads to two models of universe, i.e. power law model and exponential model. Some physical and kinematical properties of the model are also discussed. 相似文献
9.
Bulk viscous fluid distribution with massive strings in LRS Bianchi type-1 space time is studied. The exact solutions of the
field equations are obtained by using the equation of state ρ=−λ and ρ=λ. We observed that the bulk viscous fluid does not survive for ρ=−λ whereas it survives for ρ=λ. Some physical and geometrical properties of the models are discussed. 相似文献
10.
Mahesh Kumar Yadav Anju Rai Anirudh Pradhan 《International Journal of Theoretical Physics》2007,46(11):2677-2687
We investigate the integrability of cosmic strings in Bianchi III space-time in presence of a bulk viscous fluid by applying
a new technique. The behavior of the model is reduced to the solution of a single second order nonlinear differential equation.
We show that this equation admits an infinite family of solutions. Some physical consequences from these results are also
discussed. 相似文献
11.
Noriko Nakagawa Takafumi Yamada Koji Akioka Susumu Okubo Shojiro Kimura Hitoshi Ohta 《International Journal of Infrared and Millimeter Waves》1998,19(2):167-176
New systems for millimeter and submillimeter wave ESR have been developed in Kobe University. In the previous system the pulsed magnetic field was limited up to 17 T in the temperature range from 1.8 to 86 K. Using the new systems, we can measure in the field range up to 30 T in the temperature range from 1.8 K to 4.2 K and from 18 K to room temperature. The resolution of the magnetic field has been also improved in the new ESR system. The details of our new ESR systems are presented. In addition, the measurements of Yb2Cu2O5 using these new systems are presented. 相似文献
12.
Y.R. DaiQingyu Xu Xiaohong ZhengShijun Yuan Ya ZhaiMingxiang Xu 《Physica B: Condensed Matter》2012,407(3):560-563
BiFe1−xNixO3 ceramic powders with x up to 0.10 have been prepared by the sol-gel technique. The band gap of BiFeO3 is 2.23 eV, and decreases to 2.09 eV for BiFe0.95Ni0.05O3 and BiFe0.90Ni0.10O3. The Mössbauer spectra show sextet at room temperature, indicating the magnetic ordering and the presence of only Fe3+ ions. Superparamagnetism with blocking temperature of 31 K for BiFe0.95Ni0.05O3 and 100 K for BiFe0.90Ni0.10O3 was observed. Enhanced magnetization at room temperature have been observed (1.0 emu/g for BiFe0.95Ni0.05O3 and 2.9 emu/g for BiFe0.90Ni0.10O3 under magnetic field of 10,000 Oe), which is one order larger than that of BiFeO3 (0.1 emu/g under magnetic field of 10,000 Oe). The enhanced magnetization was attributed to the suppression of the cycloidal spin structure by Ni3+ substitution and the ferrimagnetic interaction between Fe3+ and Ni3+ ions. 相似文献
13.
The effect of three metal oxides on the magnetic properties of polymer bonded magnets (PBMs) was studied. The three PBMs, using polycarbonate (PC) as binder and 5 wt% of Fe3O4, Fe2O3, or CuO nanoparticles, were prepared by melt extrusion in a twin screw extruder followed by compression molding. Transmission electron microscopic (TEM) images showed a better dispersion for the PC/Fe3O4 nanocomposite compared with that of the other nanocomposites. The dynamic intersection frequency (ωc), which is related to the crossing of the G′ and G″ curves, showed that there was more homogeneity in the PC/Fe3O4 and PC/Fe2O3 nanocomposites. The curves of saturation magnetization for the three nanocomposites showed that there was a relationship between the magnetic properties and the homogeneity of the nanoparticles studied by rheometry. Because the magnetic strength of PC/Fe3O4 was greater than that of the other nanocomposites, it was concluded that not only the intrinsic magnetic property of the filler was an important factor to increase the magnetic property, but also the homogeneity of the filler within the matrix had an important role. 相似文献
14.
Raj Bali 《International Journal of Theoretical Physics》2009,48(2):476-486
Bianchi Type V magnetized string dust bulk viscous fluid cosmological model with variable magnetic permeability, is investigated.
The magnetic field is due to an electric current produced along x-axis. Thus the magnetic fields is in yz-plane and F
23 is the only non-vanishing component of electromagnetic field tensor F
ij
. To get the deterministic model in terms of cosmic time t, we have also assumed the condition ζ
θ=constant where ζ the coefficient of bulk viscosity and θ the expansion in the model. The behaviour of the model in presence and absence of magnetic field and bulk viscosity and singularities
in the model are also discussed.
相似文献
15.
16.
The magnetic properties of trigonal Nd0.9Dy0.1Fe3(BO3)4 substituted compound with the competitive Nd-Fe and Dy-Fe exchange interactions have been investigated. It has been shown that in Nd0.9Dy0.1Fe3(BO3)4 a spontaneous spin-reorientation transition from an ease-axis state to an easy-plane occurs near 8 K. Anomalies of the magnetization curves are observed in a spin-flop transition induced by the magnetic field B‖c. The calculations were performed using a molecular-field approximation and a crystal-field model for the rare-earth subsystem. Extensive experimental data on the magnetic properties of Nd0.9Dy0.1Fe3(BO3)4 have been interpreted and good agreement between theory and experiment has been achieved using the obtained theoretical dependences. 相似文献
17.
The results of ac and dc magnetic susceptibility, thermopower and Hall effect measurements of a compound, Gd2PdSi3, establish that this compound orders magnetically below Tn = 20 K. Though the ordering appears to be of an antiferromagnetic-type, the paramagnetic Curie temperature is positive with
the magnitude being nearly the same as that of TN, suggestive of the existence of ferromagnetic correlations. The thermopower at 300 K is large, apparently due to Pd 4d electrons,
decreasing monotonically with temperature. There is a change in the sign of Hall constant well below TN Also considering the observation of Kondo-like characteristics above 21K earlier by us, the overall thermal, transport and
magnetic behaviour of this compound is interesting. 相似文献
18.
Magnetic phase transitions in rare earth intermetallic compound Nd7Rh3 have been investigated using a single crystal. Measurement results of magnetization, magnetic susceptibility, specific heat, and electrical resistivity reveal that Nd7Rh3 has two magnetic phase transitions at TN=34 K, Tt2=9.1 K and a change of the magnetic feature at Tt1=6.8 K in the absence of an external magnetic field. Antiferromagnetic orderings exist in all the three magnetic states; a large magnetic anisotropy between the c-axis and the c-plane is observed. In the magnetic phase below Tt2, an irreversible field-induced magnetic phase transition takes place in the c-plane; after removing external magnetic field, a coexistence state of ferro- and antiferromagnetic ordering or a ferrimagnetic state having a remanent magnetization MR is stabilized. The MR decays to a certain value for several hours after the first process; a magnetic field cooling effect was also observed in the c-plane below Tt2. In the antiferromagentic state above Tt2, the irreversibility disappears and an ordinary antiferromagnetic state takes place. As the origin of this phenomenon, a kind of martensitic structural transition that is observed in Gd5Ge4 can be considered. 相似文献
19.
As prominent characteristics of magnetic metal cluster found in vanadium sulfides, we point out marked separation and compensation
of the hyperfine field at the nuclear site; these are in somewhat discordance with the common sense for 3d transition-metal
magnets, where the on-site isotropic field, scaling the ordered moment magnitude, is dominant. 相似文献
20.
Magnetic properties and magnetocaloric effects of
Tb6Co1.67Si3 have been investigated by magnetization
measurement. This compound is of a hexagonal
Ce$_{6}$Ni$_{2}$Si$_{3}$-type structure with a saturation
magnetization of 187\,emu/g at 5\,K and a reversible second-order
magnetic transition at Curie temperature $T_{\rm C} = 186$\,K. A
magnetic entropy change $\Delta S =
7$\,J\,$\cdot$\,kg$^{-1}$\,$\cdot$\,K$^{-1}$ is observed for a
magnetic field change from 0 to 5\,T. A large value of refrigerant
capacity (RC) is found to be 330\,J/kg for fields ranging from 0 to
5\,T. The large RC, the reversible magnetization around $T_{\rm C}$
and the easy fabrication make the Tb6Co1.67Si3
compound a suitable candidate for magnetic refrigerants in a
corresponding temperature range. 相似文献