Bianchi Type Ⅲ String Cosmological Model with Bulk Viscosity

The Bianchi type Ⅲ cosmological model for a cloud string with bulk viscosity are presented. To obtaina determinate model, an equation of state p = κλ and a relation between metric potentials B = Cn are assumed. Thephysical and geometric aspects of the model are also discussed. The model describes a shearing non-rotating continuouslyexpanding universe with a big-bang start, and the relation between the coefficient of bulk viscosity and the energy densityis ζ∝1 p1/2.     

Bianchi Type-Ⅲ String Cosmological Model With Bulk Viscosity and Magnetic Field

The Bianchi type-Ⅲ cosmological model for a cloud string in the presence of bulk viscosity and magnetic field are presented. To obtain the determinate model it is assumed that there is an equation of state ρ = kA and the scalar of expansion is proportional to the shear scalar θ ∝ σ, which leads to a relation between metric potentials B = mC^n. The physical and geometric aspects of the model are also discussed. The model describes a shearing non-rotating continuously expanding universe with a big-bang start. In the absence of magnetic field, it reduces to the string model with bulk viscosity that was previously given in the literature.     

Locally Rotationally Symmetric Bianchi Type-ⅠString Cosmological Model with Bulk Viscosity

A locally rotationally symmetric (LRS) Bianchi type-I string cosmological model with bulk viscosity is investigated. To obtain a determinate solution, it is assumed that the coefficient of bulk viscosity is a power function of the energy density ζ= ζop^m and the scalar of expansion is proportional to the shear scalar θ σ or, which leadsto a relation between metric potentials R=AS^n, where R and S are only the functions of time. The physicaland geometrical aspects of the model are also discussed. The solution includes some results previously given inthe literature as special cases.     

Bianchi Type-I Cosmology with Cosmic String and Bulk Viscosity

Some locally rotationally symmetric Bianchi type=I cosmological solutions for a cloud string with bulk viscosity are presented. In the first case, an equation of state ρ = κλ and the relation between metric potentials R = AS^m are considered, and the solution represents shearing non-rotating model with the bulk viscosity ζ∝ρ^1/2, where ρ is the rest energy density of the cloud of strings with particles attached to them, λ is the tension density of the cloud of strings, ζ is the coefficient of the bulk viscosity, R and S are only the functions of time t, while A and κ are constant. In the second case, the constant coefficient of bulk viscosity is considered.     

Bianchi Type-Ⅲ String Cosmological Models with Time Dependent Bulk Viscosity

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.     

Structure and property of metal melt Ⅲ—Relationship between kinematic viscosity and size of atomic clusters

The method of crucible rotating oscillation damping was employed to measure the kinematic viscosity of aluminum melt,and the curve of viscosity v versus temperature T from 935 to 1383 K was obtained.Besides,based on the calculation model of the evolution behavior of atomic clusters in liquid structure,the curve of atomic clusters size d versus temperature was obtained,and the calculated results are in good agreement with the experimental values.By analyzing experimental data,it was found that both the viscosity and the size of atomic clusters of aluminum melt are monodrome functions of temperature,and the relation between v(T) and d(T) is a linear function,i.e.,v = v 0 + K·d(T).This relation indirectly verifies the calculation model of the structural information of metal melt,which is of great significance for studying the relation between melt microstructure and macro-physical properties.     

Transport coefficients of a massive pion gas

We review our main results concerning the transport coefficients of a light meson gas,in particular we focus on the case of a massive pion gas.Leading order results according to the chiral power-counting are presented for the DC electrical conductivity,thermal conductivity,shear viscosity,and bulk viscosity.We also comment on the possible correlation between the bulk viscosity and the trace anomaly in QCD,as well as the relation between unitarity and a minimum of the quotient η/s near the phase transition.     

Transport coefficients of a massive pion gas

We review our main results concerning the transport coefficients of a light meson gas,in particular we focus on the case of a massive pion gas.Leading order results according to the chiral power-counting are presented for the DC electrical conductivity,thermal conductivity,shear viscosity,and bulk viscosity.We also comment on the possible correlation between the bulk viscosity and the trace anomaly in QCD,as well as the relation between unitarity and a minimum of the quotient η/s near the phase transition.     

Viscous Dark Energy Models with Variable G and Λ

We consider a cosmological model with bulk viscosity η and variable cosmological A ∝p^-α, alpha = const and gravitational G constants. The model exhibits many interesting cosmological features. Inflation proceeds du to the presence of bulk viscosity and dark energy without requiring the equation of state p =-p. During the inflationary era the energy density p does not remain constant, as in the de-Sitter type. Moreover, the cosmological and gravitational constants increase exponentially with time, whereas the energy density and viscosity decrease exponentially with time. The rate of mass creation during inflation is found to be very huge suggesting that all matter in the universe is created during inflation.     

Bulk Modulus and Electronic Band Structure of ZnGa2Xa （X=S,Se）： a First-Principles Study

First-principles local density functional calculations are presented for the compounds ZnGa2X4 （X = S, Se）. We investigate the bulk moduli and electronic band structures in a defect chalcopyrite structure. The lattice constants and internal parameters are optimized. The electronic structures are analysed with the help of total and partial density of states. The relation between the cohesive energy and the unit cell volume is obtained by fully relaxed structures. We derive the bulk modulus of ZnGa2Xa by fitting the Birch-Murnaghan＇s equation of state. The extended Cohen＇s empirical formula agrees well with our ab initio results.     

Singularities and Entropy in Bulk Viscosity Dark Energy Model

In this paper bulk viscosity is introduced to describe the effects of cosmic non-perfect fluid on the cosmos evolution and to build the unified dark energy (DE) with (dark) matter models. Also we derive a general relation between the bulk viscosity form and Hubble parameter that can provide a procedure for the viscosity DE model building. Especially, a redshift dependent viscosity parameterζ∝λ₀ +λ₁(1+z)ⁿ proposed in the previous work [X.H. Meng and X. Dou, Commun. Theor. Phys. 52 (2009) 377] is investigated extensively in this present work. Further more we use the recently released supernova dataset
(the Constitution dataset) to constrain the model parameters. In order to differentiate the proposed concrete dark energy models from the well known $\Lambda$CDM model, statefinder diagnostic method is applied to this bulk viscosity model, as a complementary to the Om parameter diagnostic and the deceleration parameter analysis performed by us before. The DE model evolution behavior and tendency are shown in the plane of the statefinder diagnostic parameter pair {r,s} as axes where the fixed point represents theΛCDM model. The possible singularity property in this bulk viscosity
cosmology is also discussed to which we can conclude that in the different parameter regions chosen properly, this concrete viscosity DE model can have various late evolution behaviors and the late time singularity could be avoided. We also calculate the cosmic entropy in the bulk viscosity dark energy frame, and find that the total entropy in the viscosity DE model increases monotonously with respect to the scale factor evolution, thus this monotonous
increasing property can indicate an arrow of time in the universe evolution, though the quantum version of the arrow of time is still very puzzling.     

A spatio-temporal study of rheo-oscillations in a sheared lamellar phase using ultrasound

We present an experimental study of the flow dynamics of a lamellar phase sheared in the Couette geometry. High-frequency ultrasonic pulses at 36 MHz are used to measure time-resolved velocity profiles. Oscillations of the viscosity occur in the vicinity of a shear-induced transition between a high-viscosity disordered fluid and a low-viscosity ordered fluid. The phase coexistence shows up as shear bands on the velocity profiles. We show that the dynamics of the rheological data result from two different processes: (i) fluctuations of slip velocities at the two walls and (ii) flow dynamics in the bulk of the lamellar phase. The bulk dynamics are shown to be related to the displacement of the interface between the two differently sheared regions in the gap of the Couette cell. Two different dynamical regimes are investigated under applied shear stress: one of small amplitude oscillations of the viscosity ( %) and one of large oscillations ( %). A phenomenological model is proposed that may account for the observed spatio-temporal dynamics.Received: 2 December 2003, Published online: 9 March 2004PACS: 83.10.Tv Structural and phase changes - 43.58. + z Acoustical measurements and instrumentation - 47.50. + d Non-Newtonian fluid flows     

Fluctuations and pseudo long range dependence in network flows: A non-stationary Poisson process model

In the study of complex networks (systems), the scaling phenomenon of flow fluctuations refers to a certain power-law between the mean flux (activity) < F_i> of the i-th node and its variance σ_i as F_{i ∝ <Fi^α. Such scaling laws are found to be prevalent both in natural and man-made network systems, but the understanding of their origins still remains limited. This paper proposes a non-stationary Poisson process model to give an analytical explanation of the non-universal scaling phenomenon: the exponent α varies between 1/2 and 1 depending on the size of sampling time window and the relative strength of the external/internal driven forces of the systems. The crossover behaviour and the relation of fluctuation scaling with pseudo long range dependence are also accounted for by the model. Numerical experiments show that the proposed model can recover the multi-scaling phenomenon.}     

Holographic Dark Energy Model is Consistent with Pantheon SN Ia Data

We constrain three cosmological models,i.e.,ACDM model, holographic dark energy(HDE) model and R_h = ct model by using the recent Pantheon compilation of type la supernovae(SN la), the direction measurements of Hubble parameter H(z), and the baryon acoustic oscillations(BAO). The spatial curvature is considered in the ACDM model and the HDE model. We show that the HDE model in a spatially flat and HDE dominate universe has the same behavior as Rh = ct model if the characteristic parameter of the HDE model C_0 approaches to infinity. Numerical results show that the ACDM model is the best favoured one among the three models. The HDE model is consistent with observational data, the best fitting value of C_0 is around 0.8, which implies that the Rh = ct model should be modified to be compatible with the present cosmological observational data. Combing all the datasets, we give strict constraint on the Hubble constant,where h_0=0.694 ± 0.020 for the ACDM model and h_0= 0.689 ±0.019 for the HDE model.Our results imply that the tension of Hubble constant between Planck collaborations and Riess et al. has been partially relaxed. The constraint on the spatial curvature is also given,where Ω_(k0) =-0.066 ± 0.165 for the ACDM model andΩ_(k0)=0.029 ± 0.067 for the HDE model.     

SUPERCONDUCTING TRANSITION TEMPERATURES AND NORMAL-STATE ELECTRICAL RESISTIVITIES OF Tm1-xPrxBa2Cu3O7-δ

Superconducting transition temperature T_c and normal-state electrical resistivities ρ of the Tm_1-xPr_xBa₂Cu₃O_7-δ system have been measured. The results indicate that T_c remains constant for x = 0 to 0.08 before it drops steadily with higher x. Following the Abrikosov-Gor'kov model, a total suppression of superconductivity occurs at a critical Pr concentration x_cr≈0.56. It is found for the first time, as far as we know, that the logarithmic resistivity at 270 K increases linearly with increasing x, yielding ρ= ρ₀e^ax. Judging from the relation between dρ/dT and x, a metal to insulator transition occurs just beyond x_cr.     

Critical behaviour of the ferromagnetic Ising model on a triangular lattice

We use a new updated algorithm scheme to investigate the critical behaviour of the two-dimensional ferromagnetic Ising model on a triangular lattice with the nearest neighbour interactions. The transition is examined by generating accurate data for lattices with L= 8, 10, 12, 15, 20, 25, 30, 40 and 50. The updated spin algorithm we employ has the advantages of both a Metropolis algorithm and a single-update method. Our study indicates that the transition is continuous at T_c= 3.6403({2}). A convincing finite-size scaling analysis of the model yields υ=0.9995(21), β / υ = 0.12400({17}), γ / υ = 1.75223(22), γ '/υ=1.7555(22), α/υ= 0.00077(420) (scaling) and α / υ = 0.0010(42) (hyperscaling). The present scheme yields more accurate estimates for all the critical exponents than the Monte Carlo method, and our estimates are shown to be in excellent agreement with their predicted values.     

Electrostatic interaction of a spherical particle in the vicinity of a circular orifice

The electrostatic interaction of a charged spherical particle in the vicinity of an orifice plane has been investigated in this paper.The particle can creep along the axis of the orifice and is immersed in a bulk electrolyte.By solving the Poisson-Boltzmann problem,we have obtained the effective electrostatic interaction for several values of reduced orifice radius h,including the cases of h > 1,h = 1 and h < 1.Two kinds of boundary conditions of the orifice plane are considered.One is the constant potential model corresponding to a conducting plane,the other is the constant charge model.In the constant potential model,there is an electrostatic attraction between the particle and the orifice plane when they get close to each other,while there is a pure electrostatic repulsion in the constant charge model.The interactions in both boundary models are sensitive to the parameters of the reduced orifice radius,the reduced particle-orifice distance,surface charge densities of the particle and orifice plane,and the reduced Debye screen constant corresponding to the salt-ion concentration and ion valence.     

Superconducting properties of the C15-type Laves phase ZrIr2 with an Ir-based kagome lattice

We report systematic studies on superconducting properties of the Laves phase superconductor ZrIr$_2$. It crystallizes in a C15-type (cubic MgCu$_2$-type, space group $Fd\overline{3}m$) structure in which the Ir atoms form a kagome lattice, with cell parameters $a=b=c=7.3596(1)$ Å. Resistivity and magnetic susceptibility measurements indicate that ZrIr$_2$ is a type-II superconductor with a transition temperature of 4.0 K. The estimated lower and upper critical fields are 12.8 mT and 4.78 T, respectively. Heat capacity measurements confirm the bulk superconductivity in ZrIr$_2$. ZrIr$_2$ is found to possibly host strong-coupled s-wave superconductivity with the normalized specific heat change $\Delta C_{\rm e}/\gamma T_{\rm c} \sim 1.86$ and the coupling strength $\Delta_0/k_{\rm B}T_{\rm c} \sim 1.92$. First-principles calculations suggest that ZrIr$_2$ has three-dimensional Fermi surfaces with simple topologies, and the states at Fermi level mainly originate from the Ir-5d and Zr-4d orbitals. Similar to SrIr$_2$ and ThIr$_2$, spin--orbit coupling has dramatic influences on the band structure in ZrIr$_2$.     

Growth and characterization of superconducting Ca1-xNaxFe2As2 single crystals by NaAs-flux method

High-quality superconducting Ca$_{1-x}$Na$_x$Fe$_2$As$_2$ single crystals have been successfully grown by the NaAs-flux method, with sodium doping level $x = 0.4$-0.64. The typical sizes of these crystals are more than 10 mm in $ab$-plane and $\sim 0.1$ mm along $c$-axis in thickness. X-ray diffraction, resistance and magnetization measurements are carried out to characterize the quality of these crystals. While no signature of magnetic phase transitions is detected in the normal state, bulk superconductivity is found for these samples, with a sharp transition at $T_{\rm c}$ ranging from 19.8 K ($x = 0.4$) to 34.8 K ($x = 0.64$). The doping dependences of the $c$-axis parameter and $T_{\rm c}$ are consistent with previous reports, suggesting a possible connection between the lattice parameters and superconductivity.     

Effect of local structure on electron paramagnetic resonance spectra for trigonal [Cr(H2O)6]3+coordination complex in the sulfate alums series: a ligand field theory study

A simple theoretical method is introduced for studying the interrelation between electronic and molecular structures.By diagonalizing the 120 × 120 complete energy matrices,the relationships between zero-field splitting(ZFS) parameter D and local distortion parameter △θ for Cr 3+ ions doped,separately,in α-and β-alums are investigated.Our results indicate that there exists an approximately linear relationship between D and △θ in a temperature range 4.2-297 K and the signs of D and △θ are opposite to each other.Moreover,in order to understand the contribution of spin-orbit coupling coefficient ζ to ZFS parameter D,the relation between D and ζ is also discussed.