关于超导临界温度级数收敛半径的一个注记

本文指出,对于实际的归一化有效声子谱函数g(ω),一般来说,z_ph≡F(-ω_ph^-2是函数z=F(y)≡∫₀^(ω_ph)(ω²y)/(ω²y+1)g(ω)dω的反函数的分支点。因此,在估算超导T_c级数的收敛半径时,应当予以考虑。 关键词：     

n+1维双sine-Gordon模型的Coleman相变

本文计算了n+1维双sinc-Gordon模型的高斯有效势,在高斯有效势近似下,证明:n≥3的模型是平凡的,n<3的模型存在一个Coleman相交点,临界耦合参数为β_cr=(2ⁿ⁺²π^(n+1)/2(α_1R+α_2R/4)^(3-n)/2)/(Γ(1/2(3-n))(α_1R+α_2R/16)). 关键词：     

Si中S0对、Se0对和Te0对的电子结构

利用紧束缚近似下的格林函数方法,讨论了Si中(S⁰)₂,(Se⁰)₂及(Te⁰)₂基态的能级和波函数。分析了几种不同的观点。(S⁰)₂,(Se⁰)₂及(Te⁰)₂均在禁带中引入一个对称性的A_1g能级和一个反对称性的A_2u能级,二者都是填满的。现有实验观测到的是较高的A_1g能级。从理论上指出了对称性的A_1g能级反而高于反对称性的能级的原因。而Si中(Se₂)⁺的g因子测量值和(S₂)⁺,(Se₂)⁺的ESR实验结果也支持本文的观点。 关键词：     

非晶态超导体的2△0/(kBTc)和声子谱参量

提出了能够很好地描述非过渡金属无序和非晶态超导体的2Δ₀/(k_BT_c)与声子谱参量之间关系的一个公式:2Δ₀(k_BT_c=4.95[1-(T₀<ω>^1/2)/A(1/(λω₀)+1/(20λ<ω>)+1/(20<ω>))]。计算了大量已知声子谱的非晶和无序超导体的能隙2Δ₀对T_c的比,结果表明在百分之几的范围内与实验值符合。指出了非过渡金属和合金的非晶态超导体,既可以是一个2Δ₀/(k_BT_c)值远大于BCS理论值(3.53)的强耦合超导体,也可以是一个2Δ₀/(k_BT_c)值比BCS理论值还要小得多的弱耦合超导体。 关键词：     

倾转晶体电子衍射图的自动标定

用电子计算机标定倾转晶体电子衍射斑点指数的计算公式如下:[hkl]=[xy0]Γ^(θ)Γ^(ω₀-ω)Γ^(θ₀)P^-1H,其中θ,ω为倾转角,θ₀,ω₀为初始倾转角。一个适合于任意晶系的计算机程序已经编写出来。与极图法比较起来,用计算机标定既简便又迅速。 关键词：     

有磁辫等离子体的双撕裂模研究

在电磁流体力学范围内研究了与磁辫相联系的反常电子粘滞性效应所驱动的双撕裂模的线性行为。采用分区处理方法得到了该模式的一个近似色散关系。如果在x=±x_s处的两个有理面间的距离足够小[x_s/α《(k_yα)^-11/15R^-11/15],则所得增长率的变化规律为τ_v^-1/5,随着该距离的增大,增长率过渡为τ_r^-1/3定标。τ_v^-1/5定标被证明为与撕裂层中不变φ近似的失效有关。 关键词：     

无扩散相变中界面动力学的唯象理论及其应用

固态相变中相界面或畴界面的平均运动速度V与有效相变驱动力△G＇(相变驱动力△G与相界面运动阻力△G_R之差)之间的关系可表示为V=φ(△G—△G_R)。当有单向变化的外场(场强为ξ,变化速率为ξ)作用于相变系统并能诱导相界面运动时,就会产生母相/新相间的转变。在相变过程中同时叠加一个交变应力时,则可计算得界面动力学关系V=φ(△G—△G_R)与相变过程内耗Q^-1、相关的模量亏损(△M/M)、相变速率dF/dξ、相变应变ε₀间的关系为 [d lnφ(△G-△G_R)/d(△G-△G_R)]= Q^-1ω/n²M(dF/dξ)ξ = (△M/M)ω/nMε₀(dF/dξ)ξ, 以及 (△M/M)/Q^-1=ε₀/n。此处ω为交变应力的圆频率,M为与振动模式有关的弹性模量,n为应力与界面运动的耦合因子。因此,界面动力学关系式的通解为 V = ∑(±n)/(α≠-1) A_α exp{[(△G-△G_R)/△G_α^*]^{α+ 1}/(α+ 1)} +∑(m)/(β₀) A_β[(△G-△G_R)/△G_β^*]^β 此处n,m为正整数。上式中的各项参数可由实验数据确定。此外,(△M/M)/Q^-1的等式还可用于判别相变过程的模量亏损中有无声子模软化的贡献。 关键词：     

新型白光LED的光谱特性和相关结温特性

利用蓝光LED芯片激发[Ru(dtb-bpy)₃]²⁺(PF₆^-)₂和YAG混合荧光粉的方法制备了新型白光LED,研究了随着[Ru(dtb-bpy)₃]²⁺(PF₆^-)₂含量的增加而引起的白光LED光谱特性的变化。当[Ru(dtb-bpy)₃]²⁺(PF₆^-)₂的质量分数为1.5%时,白光LED的显色指数达到83.2,效率相对于其含量为0%时下降了约20%。另外,研究了结温对于一体化封装的该新型白光LED发光特性的影响,结果表明:高显色LED的结温从30 ℃上升到130 ℃的过程中,芯片的蓝光辐射出现了较大幅度的减少,共降低了27.73%,随之也导致该白光LED总发光强度的衰减,而且其发光效率出现了大幅度的下降,共衰减了31.76%,但是其显色性没有明显的变化。     

H2(X1∑g+)—H2(E1∑g+)系统的相互作用

采用显含电子对相关坐标的波函数,在微扰论的框架下计算了E^l∑_g⁺态氢分子与基态氢分子取cross构型时的中长程相互作用。结果表明,该相互作用在分子间距6.5α₀附近存在着一个活化能势垒,在4.5α₀附近显示出较强的化学键行为。 关键词：     

阈值附近撕裂模的非线性行为

电阻率型m≥2的撕裂模在线性不稳定性阈值附近的非线性演化方程可以表示为 ?-Q²A+K²/2A²à-Q²(δ△_1e)/(△_1e)A³=0。这里A为模的幅值,Q为线性增长率,K为模的波矢,△_e为线性模匹配计算中的外区解的对数微分差,δ△_1e为非线性效应对于对数微分差的贡献。本文除在拟线性近似下推导出该方程外,还仔细讨论了该模的非线性行为。在对称电流分布sheet pinch模型的特例下,可以证明δ△_1e=0,不存在新的平衡点。 关键词：     

A calorimetric study of the dimerized phase of C60 fullerene

The temperature dependence of the heat capacity at a constant pressure C _p ⁰ = f(T) for the dimerized phase of the C₆₀ fullerene in the temperature range 300–575 K and the thermodynamic characteristics for depolymerization of this phase under normal pressure are investigated using precision differential scanning calorimetry. It is established that thermal depolymerization is a kinetically hindered process. The final products of thermal depolymerization are identified as a partially crystalline monomer face-centered cubic phase of C₆₀ with a degree of crystallinity α = 67 mol %. The results obtained in this study and our previous experimental data on the low-temperature heat capacity are used in the calculations of standard thermodynamic functions for the (C₆₀)₂ crystalline dimer, namely, the heat capacity C _p ⁰ (T), the enthalpy H ⁰(T) ? H ⁰(0), the entropy S ⁰(T), and the Gibbs function G ⁰(T) ? H ⁰(0) in the temperature range from T → 0 to 394 K.     

代位合金中的空穴扩散和有序化

本文根据空穴扩散促使有序化的观点导出决定恒温有序化几率的一个公式。这个公式中包括扩散系数,柯诺库夫温度及其他实验都可以直接测定的数量。引用了现有的这些数量的实验数据,证明所提出的有序化几率公式和实验结果是符合的。     

The local potential approximation for the Brueckner G-matrix and a simple model of the scalar-isoscalar Landau-Migdal amplitude

The Brueckner G-matrix for a slab of nuclear matter is analyzed in the singlet ^1S and triplet ³ S + ³ D channels. The complete Hilbert space is split into two domains, the model subspace S₀, in which the two-particle propagator is calculated explicitly, and the complementary one, S', in which the local potential approximation is used. This kind of local approximation was previously found to be quite accurate for the ^1S pairing problem. A set of model spaces S ₀(E ₀) with different values of the energy E₀ is considered, E₀ being the upper limit for the single-particle energies of the states belonging to S₀. The independence of the G-matrix on E₀ is assumed as a criterion for the validity of the local potential approximation. It turns out that such an independence holds within few percents for E ₀ = 10-20 MeV, for both channels under consideration. The G-matrix within the local potential approximation is used for justifying a simple microscopic model for the coordinate-dependent scalar-isoscalar component f (r) of the Landau-Migdal amplitude in terms of the free T-matrix. Received: 2 November 2001 / Accepted: 4 January 2002     

Pilgrim dark energy in f(T) gravity

We discuss the interacting f(T) gravity with pressureless matter in an FRW spacetime. We construct an f(T) model by following the correspondence scheme incorporating a recently developed pilgrim dark energy model and taking the Hubble horizon as the IR cutoff. We use constructed model to discuss the evolution trajectories of the equation-of-state parameter, the ω _T -ω′ _T phase plane, and state-finder parameters in the evolving universe. It is found that the equation-of-state parameter gives a phantom era of the accelerated universe for some particular range of the pilgrim parameter. The ω _T -ω′ _T plane represents freezing regions only for an interacting framework, while the ΛCDM limit is attained in the state-finder plane. We also investigate the first and second laws of thermodynamics assuming equal temperatures at and inside the horizon in this scenario. Due to the violation of the first law of thermodynamics in f(T) gravity, we explore the behavior of the entropy production term. The validity of a generalized second law of thermodynamics depends on the present-day value of the Hubble parameter.     

On the beauty of the f xyz orbital in T,T d,D2d and D2 symmetries

This paper focuses on the properties of the tesseral harmonic S³ ₂ which describes the f_xyz orbital. In a few symmetry groups: T, T_d, D_2d and D₂ f_xyz is a basis for the total symmetric representation Γ₁ as well as R which denotes a function going into itself under all proper and improper rotations. The f_xyz, tesseral harmonic is also the only function transforming into itself under a cyclic permutation × → y → z → x. This very unique property is discussed in the framework of the Judd-Ofelt theory. It is shown that the absorption or fluorescence intensity of the J = 2 ? J = 0 transitions in Eu³⁺ are concentrated in one, two or three lines with ratios 3; 2:1; 1:1:1 respectively for T, T_d; D_2d and D₂ because the only tesseral harmonic acting in the induced electric-dipole mechanism is S³ ₂ (without J mixing of course). Two notes are added with respect to the f_xyz, properties in applications as lasers and high-temperature superconductors (HTS).     

Diffusion activation energy versus the favourable energy in two-order-parameter model:A molecular dynamics study of liquid Al

In the present work, we find that both diffusion activation energy E_a(D) and E_a(S^ex) increase linearly with pressure and have the same slope (0.022±0.001 eV/GPa) for liquid Al. The temperature and pressure dependence of excess entropy is well fitted by the expression -S^ex(T,P)/k_B=a(P)+b(P)T+c(P)exp(E_f/k_BT), which together with the small ratio of E_f/k_BT leads to the relationship of excess entropy to temperature and pressure, i.e. S^ex≈-cE_f/T, where c is about 12 and E_f (=Δ E-PΔV) is the favourable energy. Therefore, there exists a simple relation between E_a(S^ex) and E_f, i.e. E_a(S^ex)≈cE_f.     

The Squeezing Effect of Three-Mode Operator as an Extension from Two-Mode Squeezing Operator

We theoretically study the squeezing effect in a 3-wave mixing process, generated by the operator S₃ o exp[m(a₁a₂-a₁^fa₂^f)+n(a₁a₃-a₁^fa₃^f)]S_{3}\equiv \exp[\mu(a_{1}a_{2}-a_{1}^{\dagger}a_{2}^{\dagger})+\nu(a_{1}a_{3}-a_{1}^{\dagger}a_{3}^{\dagger})]. The corresponding 3-mode squeezed vacuum state in Fock space and its uncertainty relation are presented. It turns out that S ₃ may exhibit enhanced squeezing. By virtue of integration within an ordered product (IWOP) of operators, we also give the S ₃’s normally ordered expansion. Finally, we calculate the Wigner function of 3-mode squeezed vacuum state by using the Weyl ordering invariance under similar transformations.     

Thermodynamic and dilatometric properties of the dimerized phase of a C<Subscript>60</Subscript> fullerene

This paper reports on the results of complex investigations into the structural, thermodynamic, and dilatometric properties of the C₆₀ dimerized phase prepared under compression of a C₆₀ fullerite at a pressure up to 8 GPa and a temperature of 290 K. It is demonstrated that the dimerized phase has a face-centered cubic structure with a lattice parameter a=14.02±0.05 Å. The dimeric structure of the studied sample is confirmed by x-ray diffraction analysis. According to the dilatometric data, the volume jump observed in the vicinity of the orientational transition for the dimerized phase is estimated to be approximately 30 times less than that for the C₆₀ fullerite. The temperature dependence of the heat capacity of the (C₆₀)₂ crystalline dimer is examined using precision adiabatic vacuum calorimetry under normal pressure in the temperature range from T → 0 K to 340 K. The results obtained are used in the calculations of thermodynamic functions, namely, the heat capacity C _p ⁰ (T), the enthalpy H⁰(T)-H⁰(0), the entropy S⁰(T), and the Gibbs function G⁰(T)-H⁰(0). The fractal dimension D is determined as a function of the heat capacity. The standard entropy of the formation of the (C₆₀)₂ crystalline dimer from a simple compound (graphite) at T=298.15 K and normal pressure is calculated.     

Field-induced structural transition and the related magnetic entropy change in Ni43Mn43Co3Sn11 alloy

Magnetic properties and magnetic entropy change ΔS were investigated in Heusler alloy Ni₄₃Mn₄₃Co₃Sn₁₁. With decreasing temperature this alloy undergoes a martensitic structural transition at T_M=188 K. The incorporation of Co atoms enhances ferromagnetic exchange for parent phases. Austenitic phase with cubic structure shows strong ferromagnetic behaviors with Curie temperature T_C^A at 346 K, while martensitic phase shows weak ferromagnetic properties. An external magnetic field can shift T_M to a lower temperature at a rate of 4.4 K/T, and a field-induced structural transition from martensitic to austenitic state takes place at temperatures near but below T_M. As a result, a great magnetic entropy change with positive sign appears. The size of ΔS reaches 33 J/kg K under 5 T magnetic field. More important is that the ΔS displays a table-like peak under 5 T, which is favorable for Ericsson-type refrigerators.     

Chiral symmetry amplitudes in the S-wave isoscalar and isovector channels and the σ, f0(980), a0(980) scalar mesons

We use a non-perturbative approach which combines coupled channel Lippmann-Schwinger equations with meson-meson potentials provided by the lowest order chiral Lagrangian. By means of one parameter, a cut off in the momentum of the loop integrals, which results of the order of 1 GeV, we obtain singularities in the S-wave amplitudes corresponding to the σ, f₀ and a₀ resonances. The ππ → ππ, phase shifts and inelasticities in the T = 0 scalar channel are well reproduced as well as the π⁰η and mass distributions in the T = 1 channel. Furthermore, the total and partial strong decay widths of the f₀ and a₀ resonances are properly reproduced. The results seem to indicate that chiral symmetry constraints at low energy and unitarity in coupled channels is the basic information contained in the meson-meson interaction below GeV.