Dynamical spin susceptibility of the d–p model in the over doping region

Dynamical spin susceptibility χ^s(q,ω) of the d–p model in the over doping region is investigated by using the auxiliary boson technique. It includes higher order terms of the 1/N-expansion within the random phase approximation (RPA) of the local vertex, where frequency dependence of the quasi-particle interaction is taken into account. The incommensurate spin fluctuation is obtained due to the nesting effect in the low energy region (ωω^*), whereas the commensurate one in the high energy region (ωω^*), the characteristic energy ω^* is estimated to be about 30 meV. Both of the spin–lattice relaxation rate 1/T₁ and the spin–spin relaxation rate 1/T_g monotonically increase as T decreases, while the spin Knight shift K is almost independent of T.     

镁基合金自由枝晶生长的相场模拟研究

利用定量相场模型, 以Mg-0.5 wt.%Al合金为例模拟了基面((0001)面)内镁基合金的等温自由枝晶生长过程. 通过研究该合金体系数值模拟的收敛性, 获得了最优化值耦合参数λ = 5.5及网格宽度Δx/W₀ = 0.4, 并在该参数下系统研究了各向异性强度和过饱和度对枝晶尖端生长速度、尖端曲率半径、Péclet数及稳定性常数σ^* 的影响. 结果表明, 由微观可解性理论得到的稳定性系数σ^* 与ε₆ 拟合值σ^*≅ ε₆ ^1.81905, 更接近理想值σ ^* (ε₆) ≅ε₆ ^1.75. 此外, 当过饱和度Ω < 0.6时, 稳定性系数σ ^* 不随ε₆ 的变化而变化, 而当Ω > 0.6时, 稳定性系数σ ^* 随着ε₆ 的增加而减小. 这反映了枝晶的生长由扩散控制向动力学控制的转变. 随着过饱和度的增加, 枝晶形貌由雪花状枝晶向圆状枝晶转变.     

Excitation energy and angular momentum dependence of nuclear level densities and spin cut-off factor in SPA and SPA + RPA approaches

We investigate the excitation energy (E^*) and angular momentum (J) dependence of nuclear level density and spin cut-off factor (σ) within microscopic approaches based on SPA and its extension SPA + RPA representation of the grand partition function for quadrupole-quadrupole interaction model Hamiltonian. For ¹¹⁰Sn, we find that excitation energy dependence of the total level density obtained within these approaches is significantly different. On the other hand, these approaches yield similar behaviour for J-dependence of the level density at fixed values of E^*. Values of σ_{SPA + RPA} at low E^* are found to be slightly smaller than σ_SPA but they tend to become almost the same at higher E^* (> 30 MeV). We also find that Bethe's formula for fixed-J level density based on the spin cut-off approximation can be used to compute (E^*, J) near the yrast line provided one uses an appropriate value of the spin cut-off factor.     

Flux creep and flux flow for thallium ceramics in a pulsed magnetic field

The resistive properties of Tl-ceramics with T_c|=0=114 K were investigated in a pulsed magnetic field (B) up to 30 T and in the temperature range of 4.2 K<T<140 K. It was shown that the character of the field dependence of the resistance differs qualitatively in high-and low-temperature regions. At low (T80K) temperatures the dynamic magnetoresistance arising in the sample is analogous to that observed earlier in LaSrCuO [1] and YBaCuO [2] ceramics. This magnetoresistance is defined by the magnetic field variation rate and leads to the appearance of a minimum at the maximum of the magnetic field pulse, i.e. at . In the region of high temperatures (80 K T<T_c) or magnetic fields (at T60K) the sample resistance rises monotonically with B increase, and dynamic resistance is not observed. In this temperature range the existence of a scaling relation is shown (here B^* and T^* meet the condition k=(B^*, T^*)/ _n(T^*)=const) for the ceramics resistance (B,T), which can be represented as . An estimate for the upper critical field B_c2(0)B_o=1030±40 T is obtained.     

简单金属固液界面固化过程生长机制的分子动力学研究

采用分子动力学方法,研究两种简单金属Ni、Al固液界面的动力学过程.结果表明：两种金属表现出相同的特征,即界面温度存在某个特征值（T^*）,生长速度在这个特征温度附近达到最大值.高于这个温度时,随着过冷温度（熔点温度与界面温度差）的增加生长速度单调增加,低于这个温度时,Ni的生长速度几乎不变,而Al的生长速度随过冷温度的增加而快速减小到零.在此基础上,基于高温BGJ碰撞约束模型和低温W-F扩散模型分析界面的生长机制,发现在小过冷温区和深过冷温区存在碰撞机制和扩散机制的渐变过程,不同温区二者所起的主导作用不同,生长机制的转变是T^*存在的原因.     

The ΔNγ electromagnetic transition form factors GM(q) and GE(q)

A parameter-free, nonperturbative calculation of the ΔNγ electromagnetic transition amplitudes GM*(q2), GE*(q2), and the resonant multipole ratio REM(q2)≡E1+3/2(q2)/M1+3/2(q2) is performed in terms of the well-known nucleon isovector Sachs form factor GMV. Our methods are fully relativistic with conservation of the electromagnetic current guaranteed. We find that GM*(q2) decreases more rapidly than the nucleon dipole form factor when −q21 GeV2/c2 and that REM(q2) remains small even for very high four-momentum transfer implying that the perturbative QCD prediction REM(q2)→1 is purely asymptotic and is valid only for extremely high |q2|.     

层流圆管潜射流生成蘑菇形涡结构特性数值研究

基于不可压Navier-Stokes方程, 采用计算流体力学方法, 数值模拟与分析了层流圆管潜射流在密度均匀黏性流体中的演化机理及其表现特征, 定量研究了蘑菇形涡结构无量纲射流长度L^*、螺旋型涡环半径R^*及其包络外形长度d^*等几 何特征参数随无量纲时间t^*的变化规律. 数值结果表明, 蘑菇形涡结构的形成与演化过程可分为三个不同的阶段: 启动阶段、发展阶段和衰退阶段. 在启动阶段, L^*和d^*随t^* 线性变化, 而R^*则近似为一个常数; 在发展阶段, 蘑菇形涡结构的演化具有自相似性, L^*, R^*和d^*与t^*1/2均为同一正比关系, 而且雷诺数和无量纲射流时间不影响该正比关系; 在衰退阶段, L^* 和R^* 正比于t^*1/5, 而d^*则近似为一个常数. 此外, 还对蘑菇形涡结构二次回流点、 动量源作用中心及其几何中心的速度变化规律、垂向涡量分布特征和 涡量-流函数关系进行了分析. 关键词： 圆管潜射流 蘑菇形涡结构 演化机理     

Conductivity relaxation in zirconium fluoride glasses: effect of substitution of Zr by Y ions

The electrical conductivity and the conductivity relaxation of (55−x)ZrF₄–15BaF₂–xYF₃–30LiF glasses were studied in the temperature range from 300 K to just below the glass transition temperature and in the frequency range from 10 Hz to 2 MHz. No large changes in the conductivity were observed with the substitution of Zr⁴⁺ by the Y³⁺ ions. The activation energy remained almost constant up to 20 mol.% YF₃ content and increased for higher YF₃ content in the glass compositions. The frequency dependent conductivity was analyzed in terms of modulus formalism. The distribution parameter for the conductivity relaxation times remained almost unchanged with the substitution of YF₃ with an increase for 40 mol.% YF₃ content. The distribution of relaxation times of the present glasses was much broader than that for the YF₃-free zirconium fluoride glasses. The glass decoupling index decreased and the modulus relaxation rate increased with the increase of YF₃ content in the glass compositions with an anomaly for the composition having 20 mol.% YF₃ content.     

Probing the EOS and nn cross section by analyzing the collective flow at high and intermediate energy in the RVUU approach

We have studied the collective flow at high and intermediate energy in a relativistic Vlasov-Uehling-Uhlenbeck (RVUU) approach based on Walecka's QHD-I model, with the aim to probe the nuclear-matter equation of state (EOS) and the in-medium nucleon-nucleon cross section σ. At high energy (1.2 GeV/u), the out-of-plane azimuthal correlation function C(Ψ) is only sensitive to the effective mass m^* and insensitive to the nuclear compressibility K and the effective nucleon-nucleon cross section σ within a reasonable range. We have found that the preferred value of m^* is about 0.85 m. With this value of m^*, from the in-plane mean transverse momentum P_x(Y) which is sensitive to both m^* and σ we have drawn an effective nn cross section σ, namely σ 0.8σ_f where σ_f is the free nucleon-nucleon cross section in Cugnon's parametrization. Taking advantage of the fact that the energy of vanishing flow (EVF) at intermediate energy (around 100 MeV/u) is only sensitive to the nucleon-nucleon cross section σ, we have drawn some information on the nucleon-nucleon cross section σ, namely σ = (1.4±0.2)σ_f.     

二维圆盘颗粒体系声学行为的数值研究

数值测量了卸载过程中二维单分散圆盘颗粒系统的横波、纵波声速、声衰减系数、非线性系数随压强的变化以及声衰减系数随频率的变化.结果表明,二维(2D)圆盘颗粒体系的横波、纵波声速均随压强呈分段幂律标度:当压强P10~(-4)时,横波、纵波声速随压强的增大而减小;当P10~(-4)时,有v_t~P~(0.202),v_l~P~(0.338).进一步得到其剪切模量和体积模量的比值G/B也随压强呈幂律标度,G/B~P~(-0.502),暗示在低压强下,与三维(3D)球形颗粒体系类似,2D圆盘颗粒体系也处于L玻璃态.水平激励和垂直激励下2D圆盘颗粒系统的衰减系数随频率变化也呈现分段行为:当频率f0.05时,衰减系数不随f变化;当f0.05时,横波纵波的衰减系数α~f;当f0.35时,横波衰减系数α_T~f~2,纵波衰减系数α_L~f~(1.5).此外,竖直水平激励下的2D圆盘颗粒系统的非线性系数和衰减系数随压强也呈现与声速类似的分段规律:当P10~(-4)时,横波非线性系数β_T~P~(-0.230),其余都不随压强变化.当P10~(-4)时,两者均随压强增大呈幂律减小:β_T~P~(-0.703),β_L~P~(-0.684),α_T~P~(-0.099),α_L~P~(-0.105).进而得到2D圆盘颗粒系统中散射相关的特征长度?~*随压强呈幂律标度,当P10~(-4)时,?~*~P~(-0.595);当P10~(-4)时,?~*~P~(0.236).     

Elastic electron scattering with formamide-(H2O)n complexes (n=1, 2): Influence of microsolvation on the π* and σ* resonances

We report elastic cross sections for low-energy electron scattering with formamide-(H₂O)_n complexes (n=1, 2) in the energy region of 0.01-8 eV. The scattering calculations are performed using the R-matrix method in the static-exchange (SE) approximation. We consider three structures of formamide-H₂O and six structures of formamide-(H₂O)₂ in the present work. Our purpose is to investigate effects of water molecules hydrogen-bonding to formamide. We focus on the influence of microsolvation on the π^* and σ^* resonances of formamide. The scattering result for complexes shows that the position of π^* resonance appears at lower or higher energies in the cluster than in the isolated formamide depending on the complex structure and the water role in the hydrogen bonding. We explain this behavior according to the net charge of the solute. It is found that the microsolvation environment has a substantial effect on the width of π^* resonance. Our results indicate that surrounding water molecules may affect the lifetime of the resonances, and hence the process is driven by the anion state, such as the dissociative electron attachment.     

Eu3+掺杂Bi2O3-PbO-B2O3-ZnO玻璃光谱性质

用高温融熔法制备了Eu³⁺掺杂浓度为1%的(60-x)Bi₂O₃xPbO30B₂O₃10ZnO(x=0,10,30,摩尔分数)玻璃.测定了玻璃的差热分析曲线、吸收光谱、声子边带谱、发射光谱与激发光谱.由发射光谱与稀土Eu³⁺离子光学跃迁矩阵元的特点,计算了Eu³⁺光学跃迁的J-O参数Ω₂与Ω₄.结果显示强度参数Ω₂随着PbO量的增加而略减少,表明材料的对称性略增加,Eu—O键强减弱,共价性降低.PbO组分的增加,使玻璃的结晶起始温度与软化温度差降低,导致玻璃的热温度性变差.随着PbO的增加,电-声子耦合减弱.     

Anomalous temperature dependence of magnetization in polycrystalline Fe65Ni35 alloy

Magnetization at 0.3 and 140 Hz (0–10 Oe) and magnetic relaxation measurements were carried out in detail in the temperature range between 4.2 and 300 K for a polycrystalline Fe₆₅Ni₃₅ alloy. The typical temperature T_g and the magnetic field H_g which correspond to the anomalous temperature in χ-T curves and inflection field in σ-H curves, respectively, are summarized and a H-T diagram is obtained. A strong magnetic relaxation is observed along the H_g-T line. The temperature dependence of H_g is discussed by the thermal activation of 180° domain wall which is pinned strongly by the antiferromagnetic-like clusters below T_g. It is find that H _g is a linear function of T .     

微波低温制备Mg2Si0.4Sn0.6-yBiy热电材料的传输机理

德拜弛豫理论表明, 在频率为2.45 GHz的外加交变电磁场的作用下, 微波对极性分子的极化过程约为10^-10 s, 因此利用微波固相反应可以在短时低温条件下制备出纳米粉体材料. 本文以MgH₂代替Mg粉, 利用微波固相反应在低温下制备了Mg₂Si_0.4Sn_0.6-yBi_y (0 ≤y ≤q 0.03)固溶体, 并结合单带抛物线计算模型对其热电传输机理进行了分析. 研究结果表明: 利用该工艺可以有效抑制Mg的挥发和MgO 的生成, 在400 ℃保温15 min内即可完成MgH₂与Si粉和Sn粉的固相反应, 获得片层间距为100 nm的超细化学计量比产物; 杂质Bi的引入可以有效增加载流子浓度, 并引起晶格畸变, 在晶格畸变和样品特有的纳米片层结构的协同作用下, 声子得到有效散射, 样品具有最低的热导率1.36 W·m^-1·K^-1. 较低的有效掺杂率和复杂的能带结构具有降低能带态密度有效质量和减小载流子弛豫时间的双刃效应, 使得本征激发提前, 在600 K样品取得最大ZT值为0.66.     

Field-induced parameters of re-entrant magnets and concentrated spin glasses

We have used electron spin resonance measurements to derive the temperature and frequency dependences of the field-induced magnetization [M(T, f)] and anisotropy field [H_an (T)] in a number of amorphous alloys belonging to the series (Fe_pNi_1−p)₇₅P₁₆B₆Al₃. In re-entrant (p > p_c, the critical concentration for ferromagnetism) alloys at hi gh frequencies (f = 35 GHz, field ≈ 12 kOe) M reduces as T^3/2 at high T and as T below ≈ 40 K, the deviation from T^3/2 becoming more marked as p → p⁺_c. For p close to p_c, lowering the frequency first causes the T term to increase and ultimately ( ≈ 4 GHz) changes the variation of M with T to that discovered previously for concentrated spin glasses, namely M is constant at low T and drops linearly at high temperatures. For the re-entrants, the results are interpreted on the basis of a model which invokes an energy gap in the spin-wave spectrum, introduces a non-zero density of states of the gap energy and takes into consideration a low-q cut-off in the spin-wave integral in thelow-T (T) regime.In the concentrated spin glasses [M (0) - M (T)]/ M (0) is well represented by the function [exp (Δ / T) - 1]^-1, where Δ has values close to the corresponding Curie-Weiss temperatures θ_p but much larger than the respective spin glass transition temperatures T_SG. The temperature dependence of H_an is largely given by the function (1 - T/T^*), where T^* is equal to the zero-field freezing temperature for the re-entrants and T_SG for the spin glasses, respectively.     

Remarks on stochastic non-linear birth and death models

The first part of this paper is an attempt to formulate and motivate additional work on the important problem of obtaining global bounds applicable to the controlled truncation of the paper relates specifically to the linear birth, quadratic death model. Asymptotic results are given for the first finite difference ΔT_m where T_m is the exactly known mean time to extinction starting from state m (m= 0,1,…). These results are in terms of the environmental carrying capacity n^* taken to be large. For m near zero ΔT_me^n*/(n^*)²; whereas, for m near n^*ΔT_m ≈ (π/2)^1/2/(n^*)^3/2. This indicates the vastly different time scales in those two regions of state space - with considerably slower action near extinction than near n^*.     

Measurement and analysis of the infrared reflection spectrum of semiconducting SnS

The infrared reflection spectrum of p-type SnS single crystals was measured between 2 and 25μ. The observed dispersion was ascribed to the combined effects of lattice vibrations and free holes. An analysis gave for the index of refraction n₀ = 3.6 ± 0.1, the dielectric constant = 19.5 ± 2, and the effective charge on the atoms e^* = 0.7e₀.

The effective mass of holes is isotropic in the plane perpendicular to the c-axis, with m^* = 0.20m₀; the effective mass parallel to the c-axis is much larger: m^* m₀.     

The mechanism of diffusion and ionic transport of alkali metal ions in the particles of tin (IV) antimonate

The kinetics of exchange of Li⁺, Na⁺, K⁺ and Cs⁺ ions on tin (IV) antimonate with H⁺ form was studied particle-diffusion-control conditions at different temperatures. The values of activation energy, diffusion coefficient and entropy of activation increase with the ionic mobilities and radii, and decrease with the hydration energy of the alkali metal ions. On the basis of the kinetic parameters, the exchange of alkali metal ions occurs in the unhydrated form.     

潮湿空气对碘化铯薄膜结构和性质的影响

采用热蒸发法在普通载玻片上制备了碘化铯(CsI)多晶薄膜,采用扫描电子显微镜(SEM)、X射线衍射仪(XRD)、高阻仪、红外分光光度计研究了暴露于潮湿空气对CsI薄膜结构、电阻率及红外透过率的影响.SEM结果表明,薄膜中颗粒平均尺寸由0.36μm变为1.25μm.吸附水沿颗粒间界扩散,间界发生弯曲和移动,大颗粒吸收小颗粒质量长大.XRD分析表明,(110)晶面衍射峰强度增加,峰位向高角度移动,半高宽减少,薄膜张应力减小,趋于形成(110/220)织构,晶粒平均尺寸为25.6,28.4,45.1 nm.受潮后薄膜电阻率由1010?·cm量级减少为108?·cm量级.在3675—3750 cm-1和3560—3640 cm-1位置出现接近游离水而非液态水的红外吸收峰,观察到吸收峰的精细结构,峰分裂源于受离子偶极键影响的羟基与吸附水气液界面处悬键的伸缩振动.     

Union of chiral and heavy quark symmetries

We describe the chiral symmetric couplings of pions to heavy mesons (B or D), valid in the portion of phase space where the pions have low momentum. In order to include consistently all low energy excitations, the vector mesons (B^* or D^*) must appear explicitly in the effective lagrangian. The result is then invariant under both the chiral and heavy quark symmetries. We include matrix elements relevant for various weak decays.