R1-xPrxBa2Cu3O7-δ超导Tc平台的离子尺寸效应

系统地研究了Ｒ_1-xＰｒ_xＢａ₂Ｃｕ₃Ｏ_7-δ的超导Ｔ_c与Ｐｒ替代浓度ｘ的关系。发现在离子半径ｒ_i≤ｒ_i（Ｄｙ）时，在低Ｐｒ浓度范围内存在一个超导Ｔ_c平台，并且平台宽度表明一个Ｒ^３＋离子尺寸效应。我们认为，Ｔ_c平台宽度的离子尺寸效应可能起源于Ｐｒ４ｆ电子局域态的改变。提出一个临界Ｒ^３＋离子半径ｒ_ic，ｒ_i＞ｒ_ic时ＲＢａ₂Ｃｕ₃Ｏ_7-δ的超导电性消失 关键词：     

离子束-等离子体系统的电磁不稳定性

本文研究了离子束-等离子体系统的电磁不稳定性,考虑了离子-电子和离子-离子碰撞对维泊耳(Weibel)型电磁不稳定性增长率的影响。结果表明,在离子束-等离子体系统中可以激发维泊耳型电磁不稳定性,离子和电子之间的碰撞将使这类不稳定性的增长率增加。     

托卡马克中宏观束-等离子体扭曲模不稳定性研究

本文主要研究了具有单一高能离子分量的托卡马克等离子体扭曲模宏观不稳定性。它基本上模拟了中性束平行注入经过电离和电荷交换后在本底等离子体中维持一个稳恒等离子体流的物理过程。高能和本底都用无碰撞的Vlasov等离子体,并取了低频、小拉莫尔半径极限。由于主要考虑束-等离子体无耗散宏观不稳定性,故可用能量原理来分析。结果表明,高能离子束对本底等离子体的外部模没有影响,只影响内部扭曲模的增长率和扰动振幅。对适当选择的速度剖面,束能够完全稳定体系n≥2,m=1模,与Dunlap线性理论结果相反而与目前实验观测一致。m/n=1/1内部扭曲模增长率在所取得模型下随注入能量β_b,注入功率P_bw,轴上安全因子q(0)和束速度的径向剖面分布参数S的不同而出现增稳、减稳及完全稳定的行为。适当选择S,在q(0)<0.924时,高能束能够稳定m/n=1/1模。 关键词：     

C_2^+ (X^4 Σ_g^-,1^4 Σ_u^+)离子体系解析势能函数、光谱常数和振动能级研究

采用多参考组态相互作用(MRCI)方法,结合aug-cc-pV6Z(AV6Z)基组,计算了C₂⁺(X⁴Σ_g^-,1⁴Σ_u⁺)的势能曲线,计算过程中考虑了Davidson修正和相对论效应,并将结果外推至完备基组(CBS)的极限.基于得到的单点能量,用最小二乘法方法进行了Murrell-Sorbie函数拟合,得到了势能函数解析式(APEF).基于APEF,计算了C₂⁺(X⁴Σ_g^-,1⁴Σ_u⁺)离子体系的离解能D_e,平衡核间距R_e,光谱常数ω_e,ω_eχ_e,B_e,α_e,结果与实验和其他理论计算值符合...     

理论研究BeS(X~1∑~+)的光谱常数及分子常数

采用Davidson校正的内收缩多参考组态相互作用方法（MRCI+Q）结合相关一致五重基cc-pV5Z在二阶Douglas-Kroll Hamiltonian近似下,计算了BeS分子X¹∑⁺态的势能曲线.对势能曲线进行核价相关效应修正计算,得到了同时含有核价相关效应修正及相对论效应的势能曲线.拟合修正的势能曲线,获得BeS（X¹∑⁺）的光谱常数R_e,ω_e,ω_ex_e,ω_ey_e,B_e,α_e,β和D₀,分别为:0.17429 nm,997.06cm^-1,6.1056 cm^-1,0.0041 cm^-1,0.7893 cm^-1,0.006657 cm^-1,6.8002×10^-9cm^-1和4.2609 eV.与已有的实验结果及其它理论结果的比较表明,本文BeS（X¹∑⁺）的光谱常数的计算结果达到了较高的精度.通过求解双原子分子核运动的径向Schr（o|¨）nger方程,找到了非转动BeS（X¹∑⁺）的前40个振动态.针对每一振动态还分别计算了相应的振动能级、惯性转动常数和离心畸变常数等分子常数.     

磁场剪切对离子温度梯度模带状流产生的影响

对离子温度梯度模湍流非线性流体方程进行了解耦处理,得到包含磁场剪切效应的带状流与漂移波相互作用的非线性动力学方程.采用调制不稳定性的四波相互作用模型,研究了磁场剪切对带状流产生的影响.研究表明,在k_//值较小的范围内,当|k_//|增加时,带状流的增长率也呈增加的趋势. 关键词： 托卡马克等离子体 离子温度梯度模湍流 带状流 磁场剪切     

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：     

管径及气体性质对爆轰极限的影响实验研究

本文在大尺度(D=50.3 mm,63.5 mm)光滑管道内对四种预混气(2H₂+O₂+50%Ar,C₂H₂+2.5O₂+70%Ar,C₂H₂+2.5O₂+85%Ar,CH₄+2O₂)进行了爆轰实验研究;获得了爆轰极限p_c和胞格尺寸λ,分析了四种气体的不稳定性,计算了边界层位移厚度δ^*和诱导长度?_i,深入研究了管径和气体性质对爆轰极限的影响。实验结果表明：随着初始压力和管径的减小,边界层位移厚度增大,边界效应加强,热损失增多,爆轰临界压力变大;大尺度管道内,不稳定性对极限的影响占据主导,因此极限情况下不稳定气(CH₄+2O₂)符合判据λ=πD,稳定气(2H₂+O₂+50%Ar,C₂H_2<...     

荧光俘获效应对掺饵氧化物玻璃光谱性质的影响

测试了不同掺杂浓度和样品厚度下掺铒磷酸盐和碲酸盐玻璃的吸收光谱、荧光光谱和荧光寿 命，计算了Er³⁺离子在1.53 μm处的吸收截面(σ_a)、发射截面(σ _e)、自发辐射跃迁概率(A_rad)、辐射跃迁寿命(τ_rad) 、以及辐射跃迁量子效率(η)等光谱参数.讨论了荧光俘获效应对掺铒磷酸盐和碲酸盐玻璃 光谱性质及光谱参数的影响.结果表明即使在铒离子低掺杂浓度(0.1 mol% Er₂O ₃)下，荧光俘获效应也普遍存在于掺铒玻璃材料中，使得荧光寿命(τ_{f)和荧光半高宽(FWHM)随样品的厚度和铒离子掺杂浓度增加而增大，导致碲酸盐和磷酸 盐玻璃中τf分别增加11%—37％和6%—17%，FWHM分别增加15%—64%和11%—55% ，使得掺铒玻璃材料的放大品性参数(σe×FWHM) 也相应被估高.由于铒离子在 碲酸盐玻璃中在1.53 μm处吸收和发射截面重叠面积较大，加之铒离子在前者基质中的发射 截面高于后者，使得掺铒碲酸盐玻璃中的荧光俘获效应高于磷酸盐玻璃. 关键词： 荧光俘获 铒离子 碲酸盐玻璃 磷酸盐玻璃}     

HL-2A 装置中高能量捕获电子鱼骨模不稳定性研究

结合HL-2A 装置的参数,在电子回旋共振加热(ECRH)离(在)轴加热的情况下,研究高能量捕获电子驱动的鱼骨模不稳定性。数值结果表明,高能量电子极向比压β_h 大于某一个比压阈值β_h,crit 时,鱼骨模会被高能量电子激发,其频率随高能量电子极向比压的增大而缓慢增加且与高能量电子的环向进动频率一致;比压阈值β_h,crit 随着高能量电子密度剖面峰化程度的增加而减小,但当密度剖面增大到一定值时比压阈值β_h,crit 趋近于一个常数。此外,还分析了箍缩角和扰动能对鱼骨模实频和增长率的影响。发现在箍缩角α₀ =1附近增长率有一极小值,表明高能量勉强通行电子对鱼骨模具有稳定作用;而扰动能 δWˆ_c增大时,鱼骨模表现出实频变大而增长率变小的特征,这表明了本底等离子体对鱼骨模有一定的稳定效果。     

On the dynamic conductivity for an electron-impurity system

The correlation function formula for the dynamic conductivity of a system of non-interacting electrons in the field of impurities is analyzed in terms of proper connected diagrams. By selecting those diagrams appropriate in the region of weak coupling and low impurity concentration, a set of coupled equations for the energy broadening γ (ω, ε, n_s) and the energy shift Δ(ω, ε, n_s) is derived, where both γ and Δ depend on the frequency ω of a probing field, the energy ε of the electron, and the concentration, n_g, of impurities. With the assumption of a finite range potential, these equations are solved. It is found that γ (ω, n_s) is smaller than that extrapolated value which the conventional expression γ₀ for the low-concentration collision frequency would predict, in the entire region studied, that the difference γ₀-γ becomes appreciable when the ratio of the average time between scatterings, τ_c, to the average duration of a scattering, τ_d, is 100 or less, that γ (ω, n_s) decreases monotonically from its static value γ (0, n_s), and becomes vanishingly small in the region ω≈1/τ_d, and that in the static limit (ω=0), γ=γ₀[1?(2/π) (γ₀τ_d)+…], that the energy shift Δ is positive, and increases from 0 and reach a peak of magnitude γ₀ as ω is raised from 0. By using the γ and Δ obtained, the dynamic conductivity σ(ω, n_s) for degenerated electrons is calculated. The deviation, σ-σ₀, from the conventional expression σ₀=(?i) (n_ee²/M) [ω-iΓ₀]^?1, (n_e]=number density of electrons), for 0°K, is appreciable when the ratio τ_c/τ_d is 100 or less. The field-term correction, which arises from the modification of the scattering due to the probing field, is found to be negligible in the entire region studied.     

Theoretical studies on the EPR parameters of the interstitial V4+ in rutile

The electron paramagnetic resonance (EPR) parameters g-factors g _i (i=x, y, z) and the hyperfine structure constants A _i for the interstitial V⁴⁺ in rutile are theoretically studied from the perturbation formulas of these parameters for a 3d¹ ion in rhombically distorted octahedra. On the basis of the studies, the local axial distortion angle Δα′ in the impurity center is found to be about 2° smaller than the host value, characterized as stretching and contraction of the parallel and perpendicular bonding lengths by about 0.28 and 0.14 Å,respectively. This results in the less compressed ligand octahedron because of the Jahn–Teller effect and space effect arising from occupation of the impurity V⁴⁺ at the interstitial site. The theoretical EPR parameters based on the above local structural parameters of this work are in better agreement with the experimental data than those of the previous studies in the absence of the local angular distortion and the ligand orbital contributions. The two experimental optical absorption bands are also reasonably analyzed.     

The effect of Cu substitution on the A1g mode of La0.7Sr0.3MnO3 manganites

We report on the first Raman data of Cu substituted La_1−ySr_yMn_1−xCu_xO₃ (0≤x≤0.10 and 0.17≤y≤0.3, accordingly in order to have the same Mn⁴⁺/[Mn⁴⁺+Mn³⁺] ratio), collected in the frequency range 100-900 cm⁻¹ and at room temperature, with parallel (e_i∥e_s) and crossed (e_i⊥e_s) polarizations of the incident (e_i) and scattered (e_s) light. Spectra were fitted with a Drude-Lorentz model, and peaks at 190-220 and 430 cm⁻¹, together with two broad structures centered at near 500 and 670 cm⁻¹, have been found. We also have observed that the A_1g mode is substantially shifted with increasing Cu substitution. The A_1g phonon shift is a linear function of the tolerance factor t and the rhombohedral angle α_r, thus following the structural changes of the MnO₆ octahedra in the system.     

Zur Chronologie des alten Ägypten

The velocityv of the propagation of discharge along the anode of a self-quenchingG—M-counter is a function of total pressureP, pressure of the quenching gasP _D, radius of the cathoder _a and of the anoder _i andV _ü the difference between working- and starting-potential. For the mixtures argon-methylal, argon-alcohol and helium-alcohol isv=v ₀·exp[k·(V _ü/V _e)^1/2] withv ₀ the velocity at the starting potentialV _e v ₀=(a+b·P _D/P)·V _n ^1/2 ·exp [(c?d·P_D/P·V _n ^?1/2 ] andV _n=V _e·(lnr _a/r _i)^?1.k, a, b, c andd are characteristical constants of the filling gas.     

Eigenvalues of Laplacian with Constant Magnetic Field on Non-Compact Hyperbolic Surfaces with Finite Area

We consider a magnetic Laplacian −Δ _A = (id + A)^* (id + A) on a non-compact hyperbolic surface M with finite area. A is a real one-form and the magnetic field dA is constant in each cusp. When the harmonic component of A satisfies some quantified condition, the spectrum of −Δ _A is discrete. In this case, we prove that the counting function of the eigenvalues of −Δ _A satisfies the classical Weyl formula, even when dA=0.     

Spin-Hamiltonian parameters,defect model and defect structure for the tetragonal Mo5+ center in x-ray-irradiated α-ZnMoO4 crystals

ABSTRACT

The spin-Hamiltonian parameters (g factors g_i, hyperfine structure constants A_i (⁹⁵Mo⁵⁺) and A_i (⁹⁷Mo⁵⁺), i?=?// and ⊥) assigned to the tetragonal Mo⁵⁺ (4d¹) tetrahedral center in α-ZnMoO₄ crystal caused by a Mo⁶⁺(1) ion trapping an electron after x-ray irradiation are calculated from the high-order perturbation formulas resting on the two-mechanism model. The model takes account of both the effects of crystal-field (CF) mechanism concerning the CF excited states in the CF theory and that of the charge-transfer (CT) mechanism related to CT excited states. The calculated results are reasonably consistent with the experimental values, confirming this assignment (or defect model). The calculations also indicate that the effect of CT mechanism cannot be neglected. The defect structure (particularly, the angular distortion) and signs of constants A_i (⁹⁵Mo⁵⁺) and A_i (⁹⁷Mo⁵⁺) of this Mo⁵⁺ defect center are also decided from the calculations. The outcomes are discussed.     

Critical properties of high-spin Ising models on anisotropic lattices

The coordinates of the critical points of spin-S Ising models with coupling constants J and J′ are calculated for 1/2 ≤ S ≤ 13/2. The calculations are performed for several values of S and Δ ≡ J′/J independently by using the phenomenological renormalization-group method or (approximate) self-duality. Numerical results combined with a mean-field analysis show that the critical coupling strength for Δ ～ 1 (weakly anisotropic lattice) is K _c ^(S) (Δ) = K _c ^(S) (1)[1 + a(1 ? Δ)], where a = (d ? 1)/d is independent of S (d is the space dimension). Both free energy and internal energy are determined at the critical points. An extremum of the critical internal energy is found at Δ* ∈ (0, 1). The parameter Δ* can be used as a criterion that separates quasi-isotropic and quasi-one-dimensional regimes (Δ* < Δ ≤ 1 and Δ < Δ*, respectively). The finite-size scaling amplitudes A _s and A _e of the inverse spin-spin and energy-energy correlation lengths are estimated. Calculations show that the amplitudes A _s and A _e are independent of S within the accuracy of the adopted approximations. Moreover, their ratio A _e/A _s is independent of the anisotropy parameter Δ. These results support the Ising universality hypothesis.     

Power Reflection,Transmission and Absorption Coefficients for a Moving Plasma Slab

Expressions for power reflection (R), transmission (T) and absorption (A) coefficients for p-polarized wave for a warm, collisional, magnetized and moving plasma slab (with sharp boundaries and thickness d₀) are investigated. The effects of plasma slab velocity (β=v/c), electron density (ωp/ω)² and plasma temperature (K_BT) on reflection (R), transmission (T) and absorption (A) coefficients are discussed numerically. It is observed that for the value β=?0.6, reflection coefficient (R) becomes more than unity, whereas absorption coefficient (A) becomes quite negligible while transmission coefficient (T) shows oscillatory behaviour. The variation with plasma frequency (ω_p/ω)² shows that at lower plasma frequency (ω_p/ω)²=0.2 transmission (T) and absorption (A) coefficients are minimum while reflection coefficient (R) is maximum.     

Semileptonic decays of pseudoscalar particles (M→M′+ℓ+νℓ) and short-distance behaviour of quantum chromodynamics

The form factors which govern the semileptonic decays of pseudoscalar particles (M→M′+?+ν_?) are constrained by the knowledge of the two-point function Π^μν(q) = i ∫ d⁴x e^iqx〈06TV^μ(x) V^ν+ (0)60〉 in the deep euclidean region, where V^μ(x) denotes the vector current responsible for the transition M→M′. We derive the precise constraints from a QCD calculation of Π^μν which includes perturbative contributions to two loops as well as leading non-perturbative contributions. Applications to π_?3, K_?3 and $\text{D}{}^{\mathrm{+}}\text{→}\text{K}{}^0\text{e}{}^{\mathrm{+}}\text{ν}{}_{\mathrm{<mtext>e</mtext>}}$ decays are discussed.     

A test of the Lorentz structure of semi-hadronic τ decays

A method is proposed for the determination of the Lorentz structure of the electroweak interaction in semi-hadronic τ decays. Spin correlations in the process $$e^ + e^ - \to \tau ^ + \tau ^ - \to \bar v_\tau \pi ^ + \pi ^0 v_\tau \pi ^ - \pi ^0 $$ are exploited for a measurement of the normalized product, γ_AV = 2Re{g_Ag _V ^* }/(|g_V|² + |g_V|²), of the vector (g _V ) and axial vector (g _A ) coupling of the τ lepton. The contribution of scalar (g _S ) or pseudo-scalar (g _P ) couplings is also investigated. Since in the above process the direction of flight of the τ leptons can be reconstructed up to a twofold ambiguity a likelihood method using the whole kinematic information can be employed. The matrix element entering the likelihood function has been evaluated in terms of the momenta and angles of the observed pions. The sensitivity of the derived method in ane ⁺ e ^? energy region around 10 GeV has been investigated for the ARGUS experiment using Monte Carlo simulations.