一类宇宙模型的稳定性

研究了一类Einstein-Kartan宇宙模型的稳定性.分别讨论了宇宙模型对于参量λ和k的变化.在λ=0附近,宇宙模型相对于λ的变化是不稳定的;在λ=β=0附近,宇宙对于k的变化也是不稳定的.因此,在考虑合理的宇宙模型时必须考虑非零的宇宙项. 关键词： 宇宙 模型 广义相对论     

γ吸收实验的改进

γ射线吸收是近代物理实验中重要内容之一。各校在做实验时,一般都是采用铅准直器将γ射线变为平行的窄束射线,以满足公式I=I_0e~(-μ~x) (1)的要求。然后测量γ射线穿过物质前后的强度I_0和I,由吸收物质的厚度x,用公式(1)求得物质的吸收系数μ,进而求得γ射     

取代基效应对脂肪醇13C NMR化学位移的影响

用原子电负性、静电作用、极化度作为基本参数,并结合表征原子空间连接方式的立体效应参数,对醇分子中不同环境碳原子的化学位移进行关联, 将120个模型化合物(91个脂肪一元醇, 29个二元醇)中747个碳原子相关参数值和化学位移值带入模型中得到如下估算方程:  δ_C=42.947 9 + 63.064 0Q_i-3.628 6F+5.121 3Σα_x-6.584 8Q_iΣα_x -4.842 7N^α_H-0.585 5N^γ_H-4.104 6N^γ_OH (R=0.998 1 R²=0.996 1 S=1.14 F=27 125.2 n=747)  方程中各参数物理意义比较明确. 通过用“留一法”(LOO)检验(R_cv=0.998 0,R²_cv = 0.996 0,S_cv=1.16)及对样本外5个化合物69个碳原子化学位移的预测值和实验值比较, 结果表明模型方程具有很好的稳定性和预测精度, 该模型的提出为以后计算更加复杂化合物的¹³C NMR化学位移奠定了良好的基础.     

一种具有次近邻相互作用的Transverse XY模型

本文推广Transverse XY模型量子链至次近邻相互作用情况,考虑哈密顿量 H=g∑_nσ_n²-∑_n ((1+γ)/2σ_n^xσ_n+1^x+(1-γ)/2σ_n^yσ_n+1^y)-λ∑_n ((1+β)/2σ_n^xσ_n+2^x+(1-β)/2σ_n^yσ_n+2^y)。当β=0以及γ≠0时,证明在临界点附近它对应于一自由费密场,从而属伊辛普适类。 关键词：     

非晶态Fe13Ni67.2P4.5B15.3合金的临界现象

本文报道非晶态Fe₁₃Ni_67.2P_4.5B_15.3合金的磁化强度与温度和磁场关系的测量结果。在居里温度附近样品的磁特性符合二级相变规律,得到临界指数β=0.39±0.02,γ=1.56±0.06,δ=5.20±0.1,样品的居里温度T_c=(180.4±0.2)K。在实验误差范围内,临界指数β,γ,δ满足γ=β(δ-1)关系,在168—192K温度范围,实验数据满足二级相变的磁状态方程。当T>270K时,样品顺磁磁化率服从居里-外斯定律,由居里-外斯常数c计算出有效顺磁磁矩P_eff=3.19 μ_B。 关键词：     

分离压作用下波纹状基底上含活性剂液滴铺展稳定性

针对波纹状基底上含不溶性活性剂液滴的铺展过程,引入受活性剂浓度影响的分离压模型,应用非模态稳定性理论分析液滴铺展稳定性.研究表明:与不计及分离压情形相比,分离压作用下的液滴铺展前沿高度明显下降,液滴铺展速率加快;长波扰动有利于增强液滴的演化稳定性,且随扰动波数增大稳定性增强;然而随短波波数增加,液滴演化稳定性逐渐减弱甚至转变为不稳定;较小波数下(k=3)减小引力强度系数α₁和提高斥力强度系数α₂液滴铺展稳定性增强;而较大波数下(k=30)增大α₁和减小α₂有利于液滴铺展稳定性.     

非晶态Co70Cr20Zr10合金在居里温度附近的磁性

本文研究非晶态Co₇₀Cr₂₀Zr₁₀合金在居里温度附近的磁性,样品的磁特性符合二级相变规律。得到临界指数β=0.45±0.02,γ=1.9±0.1,δ=5.13±0.05。Co₇₀Cr₂₀Zr₁₀合金的居里温度为T_c=(186.7±0.2)K。临界指数β,γ,δ满足γ=β(δ-1)关系,但临界指数值都偏离三维Heisenberg模型的理论值,这种行为可能起源于非晶态合金磁的不均匀性。讨论了Kouvel-Fisher(K-F)参数γ(T)对温度T的依赖关系。 关键词：     

McMillan Tc公式的解析推导(Ⅱ)——μ*≠0情形

本文把文献[1]的理论以及所得到的T_c公式推广到μ^*≠0情形,得到T_c=(2γ)/πω_log·(ω_log/ω_c)^{(μ*/(λ-μ*))}·exp{-(1+λ)/(λ-μ^*)}. Inγ=C=0.5772是Euler常数。 关键词：     

难熔金属钒熔化行为的局域原子结构模拟与分析

采用经典分子动力学(molecular dynamics,MD)方法,模拟了16000个钒原子在5种不同熔化速率(γ₁=1×1011 K/s,γ₂=1×1012 K/s,γ₃=1×1013 K/s,γ₄=1×10¹⁴ K/s与γ₅=1×10¹⁵ K/s)下原子结构的熔化行为.结果表明:不同熔化速率对难熔金属钒的熔点影响明显,不过随着温度升高,体系特征原子结构诸如体心立方(BCC)、六角密堆(HCP)、面心立方(FCC)、简单立方(SC)以及二十面体(ICO)的相对分布次序并不随熔化速率的改变而改变,温度仍然是影响原子结构分布的主要因素.通过从头算分子动力学(ab initio MD)与热力学分析发现,ICO能够在液态金属区域稳定存在,一方面是因为其孤立团簇的相对稳定性和团簇寿命要优于晶体型原子团簇,另一方面是因为其拥有相对较高的团簇熵与相对较低的自由能.     

轮烯衍生物电子结构及三阶非线性光学性质的理论研究

苯轮烯衍生物具有良好的非线性光学性质. 运用密度泛函理论在不同理论水平和不同基组下计算了轮烯衍生物的静态极化率α和静态第二超极化率γ. 采用含时密度泛函TD-B3LYP方法计算了轮烯分子的紫外吸收光谱. 结果发现: 弥散函数对静态线性极化率α和第二超极化率γ 的计算结果都有显著的影响; 共轭体系的大小和引入的推拉电子基团可以调节轮烯衍生物的第二超极化率. 添加推拉电子基团后不仅能得到更高的非线性光学系数, 也能保证有较好的透光性能, 表明轮稀分子兼具有较高的三阶非线性光学响应和在可见光波段具有良好的透光性的特性. 此外, 采用CAM-B3LYP方法计算了分子1-1和分子2-2的动态(超)极化率. 计算结果表明: 在近红外区, 随着入射光频率的增大, α (ω; ω), γ (-ω; ω, 0, 0) 和γ (-2ω; ω, ω, 0) 都随之增大, 出现近共振增强效应; 在远离共振条件下, α (ω; ω), γ (-ω; ω, 0, 0) 和γ (-2ω; ω, ω, 0) 变化平缓.     

Friedmann Cosmology with a Generalized Equation of State and Bulk Viscosity

The universe content is considered as a non-perfect fluid with bulk viscosity and is described by a more general equation of state (endowed some deviation from the conventionally assuned cosmic perfect fluid model).We assume the bulk viscosity is a linear combination of two termsone is constant,and the other is proportional to the scalar expansion θ = 3a/a.The equation of state is described as p = (γ - 1)p p0,where p0 is a parameter.In this framework we demonstrate that this model can be used to explain the dark energy dominated universe,and different proper choices of the parameters may lead to three kinds of fates of the cosmological evolutionno future singularity,big rip,or Type-Ⅲ singularity as presented in [S.Nojiri,S.D.Odintsov,and S.Tsujikawa,Phys.Rev.D 71 (2005) 063004].     

Phantom Appearance of Non-phantom Matter in Bianchi Type-I Cosmological Model

Two cosmological models with non-phantom matter having the same expansion of the universe as phantom cosmologies are constructed in Bianchi type-I universe. The exact solutions to the corresponding Einstein field equations have been obtained. The cosmological parameters have been obtained in two interesting cases (i) γ=0 and (ii) γ=1/3. We have also discussed the well-known astrophysical phenomena, namely the look-back time, luminosity distance and event horizon with redshift.     

C-Field Cosmological Model for Barotropic Fluid Distribution with Varying Λ in FRW Space Time

A cosmological model for barotropic fluid distribution in creation field cosmology with varying cosmological constant (Λ) in FRW space-time is investigated. To get the deterministic model satisfying conservation equation, we have assumed $\varLambda = \frac{1}{R^{2}}$ as considered by Chen and Wu (in Phys. Rev. D 41:695, 1990) where R is scale factor. We find that creation field (C) increases with time, which matches with the result of HN Theory (in Hoyle and Narlikar, Proc. R. Astron. Soc. A 282:178, 1964), $\varLambda\sim\frac{1}{t^{2}}$ , the spatial volume increases with time and deceleration parameter q<0 which shows that universe is accelerating. This result matches with recent observations. The inflationary scenario exists in the models and the results so obtained match with astronomical observations. The various special cases of the model (21) viz. dust filled universe (γ=0) and radiation dominated era (ρ=3p), ρ=p (stiff fluid universe) are also discussed. The models are free from horizon.     

Viscous fluid in static spherically symmetric space-time

The paper presents a static spherically symmetric viscous fluid solution of Einstein field equation, assuming an equation of statep=(γ?1)ρ. Though static, the solution has expansion, shear, and acceleration and can explain cosmological red shift. Also it has a particle horizon. The singularity at the origin and larger viscosity make it unfit to represent a real universe.     

Study of the decayf 1(1285)→ρ0(770)γ

The decayf ₁(1285)→ρ⁰(770)γ was studied at VES spectrometer of IHEP. Clear signal off ₁(1285) is seen in the effective mass spectrum of the π⁺π^?γ system in the reaction π^?γN→π⁺π^?π^?γN at the momentum $P_{\pi ^ - } = 37 GeV/c$ . The branching fraction of decayf ₁(1285)→ρ⁰(770)γ has been found to be $$BR(f_1 (1285) \to \rho ^0 (770)\gamma ) = (2.8 \pm 0.7(stat) \pm 0.6(syst)) \cdot 10^{ - 2} .$$ The ratio of the helicity amplitudes for ρ⁰ meson in its rest frame was determined by the analysis of angular distributions: $$\rho _{00} /\rho _{11} = 3.9 \pm 0.9(stat) \pm 1.0(syst).$$      

Reconstructing Equation of State for Dark Energy in Double Complex Symmetric Gravitational Theory

We propose to study the accelerating expansion of the universe in the double complex symmetric gravitational theory (DCSGT). The universe we live in is taken as the real part of the whole spacetime M4C(J), which is double complex. By introducing the spatially flat FRW metric, not only the double Friedmann equations but also the two constraint conditions pJ = 0 and J2 = 1 are obtained. Furthermore, using parametric DL(z) ansatz, we reconstruct the ω′(z) and V(φ) for dark energy from real observational data. We find that in the two cases of J = i, pJ = 0, and J = ε, pJ ≠ 0, the corresponding equations of state ω′(z) remain close to -1 at present (z = 0) and change from below -1 to above -1. The results illustrate that the whole spacetime, i.e. the double complex spacetime M4C(J), may be either ordinary complex (J = i, pJ = 0) or hyperbolic complex (J = ε, pJ ≠ 0). And the fate of the universe would be Big Rip in the future.     

Symmetry energy from elliptic flow in Au + Au

The elliptic-flow ratio of neutrons with respect to protons or light complex particles in reactions of neutron-rich systems at relativistic energies is proposed as an observable sensitive to the strength of the symmetry term in the equation of state at supra-normal densities. The results obtained from the existing FOPI/LAND data for ¹⁹⁷Au + ¹⁹⁷Au collisions at 400 MeV/nucleon in comparison with the UrQMD model favor a moderately soft symmetry term with a density dependence of the potential term proportional to γ(ρ/ρ₀)${(\rho /{\rho }_0)}^{\gamma }$ with γ=0.9±0.4$\gamma =0.9\pm 0.4$.     

Universe Described by Variable Modified Chaplygin Gas with Statefinder Diagnostic in General Relativity

The universe filled with variable modified Chaplygin gas having the equation of state p=Aρ?B/ρ ^α , where 0≤α≤1, A is a positive constant and B is a positive function of the average scale factor a(t) of the universe (i.e. B=B(a)) is studied within the framework of general relativity. The new class of exact solutions of Einstein’s field equations is derived by using a time dependent deceleration parameter. The cosmic jerk parameter in our derived model is in good agreement with the recent data of astrophysical observations under appropriate condition. It is observed that the universe starts from an asymptotic Einstein static era and reaches to the ΛCDM model. So from recently developed statefinder parameters, the behavior of different stages of the universe is studied. The physical and kinematical properties of cosmological models are also discussed.     

A Few Remarks on Milburn Equation

After presenting the infinite operator-sum form solution to the Milburnequation d ρ/dt=γ (Uρ U⁺-ρ ) =γU[ρ,U⁺], where U=exp(-i H/\hbar{γ}), and verifying that this equation preserves the three necessary conditions of density operators during time evolution, we prove that the von Neumann entropy increases with time. We also point out that if A and B both obey the Milburn equation, then the product AB obeys (d/dt)( AB) =γ U[ AB,U⁺] -(1/γ) (dA/dt)(dB/dt), which violates the Milburn equation, this reflects that a pure state will evolve to a mixture in general.     

Anisotropic Viscous Fluid Cosmological Models from Deceleration to Acceleration in String Cosmology

In the present study, anisotropic locally rotationally symmetric (LRS) Bianchi type II models representing massive strings have been presented with variable mean deceleration parameter. The field equations in scalar-tensor theory with energy momentum tensor proposed by Letelier (Phys. Rev. D 28: 2414, 1983), have been solved for the bulk viscous fluid and perfect fluid under the following physically relevant assumptions: (a) scale factor varies with time as $a(t) = (\sinh(\alpha t))^{\frac{1}{n}}$ , (b) Expansion (θ) in the model is proportional to shear (σ), (c) p=γρ, where γ (0≤γ≤1) is a constant, (d) ξ(t)=ξ ₀ ρ ^η . It has been observed that the presented universe has a phase transition from the early decelerating phase to the accelerating phase at present epoch which is in good agreement with the recent astronomical observations. Moreover, some physical and geometric properties of the models have been discussed in detail.