高温超导隧道电流及旋光效应与混合配对态

给出了s+id波混合配对态前提下，有关YBa₂Cu₃O₇ Josephson隧道实验现象的分析支持了这类混合配对态提法的合理性.结合对超导体旋光现象的分析，显示了Γ₁+Γ₄表象的可取性.对分数磁通的存在性问题也展开了讨论. 关键词：     

混合配对态波函数方程的解

从群论分析角度,在C_4v点群中,讨论了高温超导混合配对态对称性问题.考虑了层间载流子库仑关联而引起的格子正交畸变,克服了以往的混合配对态分析中双相变点的困难.对s+id混合波Ginzburg-Landau方程的求解,给出了波函数的特征;而对外磁场下临界电流行为的分析,进一步揭示了“本征钉扎”的物理实质;从而对外场下高温超导体临界电流的反常行为及电阻-温度曲线展宽现象给出一种理解. 关键词：     

海森伯铁磁系统的总能量

对于海森伯铁磁系统,利用多体格林函数方法,在无规相近似下,并且考虑到关联函数〈S⁺S^-〉时,得到对于任意自旋S普遍适用的总能量的表达式.对于三维和二维的情况给出了计算结果.得到的总能量的数值低于没有考虑关联函数时的数值. 关键词： 海森伯模型 铁磁系统 总能量 关联函数     

介质阻挡均匀大气压氮气放电特性研究

基于一维流体力学模型，对介质阻挡均匀大气压氮气放电特性进行了数值计算研究.模型中考虑了氮气中主要的电离、激发过程，所包含的粒子种类为e，N₂，N⁺₂，N⁺₄，N₂(a¹∑^-_u)，N₂(A³∑⁺_u).模拟结果显示，氮中的放电具有低气压下汤生放电的特性.放电电流幅度较小，放电过程中气体电压变化缓慢，电子密度远低于离子密度，而且最大值出现在阳极，电子不能在放电间隙中被俘获，不存在中性等离子体区，气体中的电场趋于线性变化.亚稳态N₂(A³∑⁺_u)和N₂(a¹∑⁺_u)在整个放电空间都具有非常高的密度，比电子密度高三个量级以上，亚稳态密度的最大值出现在阳极，这样的分布决定了放电的空间结构.放电所需的种子电子主要由亚稳态之间潘宁电离提供，这种机理使放电的电离水平较低，导致氮气中的放电只能是汤生放电.随着放电参数的变化，多电流峰放电也可在氮气中获得. 关键词： 大气压均匀放电 介质阻挡放电 数值模拟 氮气     

类氦离子的KLL双电子复合过程的相对论理论研究

在相对论多组态Dirac-Fock理论基础上，发展了计算双电子复合截面的程序.并以类锂C³⁺，Ar¹⁵⁺，Kr³³⁺和U⁸⁹⁺等离子为例，详细计算了共振双激发态1s2l2l′的辐射衰变率、Auger衰变率及相应的双电子复合截面.对于C⁴⁺，Ar^l6+和Kr³⁴⁺离子的结果与已有的计算和实验结果都能很好地符合；对于U⁹⁰⁺离子，则重点 关键词： 双电子复合 截面 MCDF     

基于双核模型对超重元素合成机制的研究

在双核模型基础上，考虑了熔合与准裂变的竞争，通过数值法求解主方程，计算了⁵⁰Ti，⁵⁸Fe+²⁰⁸Pb，²⁰⁹Bi这4个反应系统通过冷熔合反应合成超重元素的激发函数，得到了与实验比较符合的结果.计算了不同入射能量时各角动量分波对熔合概率和超重核存活概率的影响以及对蒸发剩余截面的贡献.这些结果对进一步理解超重核的合成机制有重要意义. 关键词： 超重元素 双核模型 熔合反应 蒸发剩余截面     

指数变分方法应用于电荷交换反应

本文考虑如下的电荷交换反应:H⁺+H(1s)→H(1s)+H⁺。用指数变分方法得到类H⁺₂的波函数,并将这样的波函数用于上述的电荷交换反应。对入射H⁺的能量为60和125keV的两种情况,计算了电荷交换反应的角分布。结果表明,指数变分波函数带来明显的改进,理论结果与实验数据符合得比较好。 关键词：     

Effect of magnetic field on Mott's variable-range hopping parameters in multiwall carbon nanotube mat

We report the temperature and magnetic field dependence of the conductivity of multiwall carbon nanotube mat in the temperature range 1.4-150 K and in magnetic fields up to 10 T. It is observed that charge transport in this system is governed by Mott’s variable-range hopping of three-dimensional type in the higher temperature range and two-dimensional type in the lower temperature range. Mott’s various parameters, such as localization length, hopping length, hopping energy and density of states at the Fermi level are deduced from the variable-range hopping fit. The resistance of the sample decreases with the magnetic field applied in the direction of tube axis of the nanotubes. The magnetic field gives rise to delocalization of states with the well-known consequence of a decrease in Mott’s T0 parameter in variable-range hopping. The application of magnetic field lowers the crossover temperature at which three-dimensional variable-range hopping turns to two-dimensional variable-range hopping. The conductivity on the lower temperature side is governed by the weak localization giving rise to positive magnetoconductance. Finally, a magnetic field-temperature diagram is proposed showing different regions for different kinds of transport mechanism.     

Magnetic field induced pseudo phase transition in cadmium

Recent magnetostriction measurements in Cd showed anomalous behavior at about 25 kG. These data are shown to be consistent with a temperature and magnetic field version of Lifshitz's model for the ‘electron transitions’ associated with Fermi surface topology changes. The dependence of the model upon temperature and magnetic field direction is treated.     

基于红外光谱大型筒类锻件热处理过程中温度场检测方法研究

为了实时掌握热处理过程中锻件温度场的变化情况,提出一种基于红外光谱大型筒类锻件温度场检测方法。在传热学的基础上,运用分离变量法建立了大型筒类锻件热处理过程中的温度场检测模型;利用红外光谱构建了基于三级干涉滤光器的大型锻件红外光谱测温系统;结合红外光谱测温系统测量的温度数据和锻件温度场检测模型,实现了锻件热处理过程中温度场的检测;最后通过仿真实验验证了本文提出方法的可行性,实现了热处理过程中锻件温度场的检测,为热处理工艺的正确实施提供了理论依据。     

静电场作用下α-碘酸锂单晶中子衍射的增强(Ⅱ)

在以前工作的基础上,继续作了以下的实验:(1)在低温条件下测定了α-碘酸锂单晶在静电场中的衍射情况,观察到在～180K以下出现“冻结”现象,即加上电场并不能使衍射增强,撤去原在室温所加的电场后衍射强度也并不减弱;(2)用狭束中子探测了加静电场后晶体的不同部位,观察到衍射增强是体效应而不是表面层效应;(3)测定了低频交变电场对晶体中子衍射强度的影响,衍射束增强的程度随频率的下降而加大,频率在1500Hz时衍射束的增强已不明显。     

Coercive field vs. temperature in Fe/Ag nanogranular films

We investigate the temperature dependence of the coercive field of a nanogranular co-sputtered Fe/Ag film. The sample is superparamagnetic at room temperature and displays a 3% giant magnetoresistance. As temperature decreases from 40 to 9 K, hysteresis appears in magnetization loops. The coercive field dependence on temperature turns out to be different from the power law expected for single-domain monodispersed ferromagnetic particle ensembles. The results are analyzed in terms of a model taking into account the effect of magnetic grain size distribution on coercive field. The agreement between experiment and the model is excellent. The possibility to gain information concerning width and symmetry of the particles volume distribution from the study of coercivity's scaling with temperature is discussed.     

交变磁场作用下高温超导体温度变化研究

高温超导体在交变的磁场作用下,由于磁通的运动引起能量损耗,损耗的能量一部分通过超导体表面传递到冷却剂中,另一部分将使得超导体的温度升高。文中用数值的方法研究了外加磁场速度在0.0005T/s—5T/s变化情况下超导体的温度变化;当外磁场的速度由小到大变化时,超导板的状态会发生从稳定→不稳定(磁通跳跃)→稳定的变化;慢变磁场作用下超导体的温度在接近冷却剂温度的温区作微幅的周期性变化,当外加磁场速度比较大时,超导体发生磁通跳跃,温度也呈跳跃性变化,进一步加大外磁场速度,磁通和温度呈准周期的振荡型变化,而且振荡幅值随外磁场速度的增加逐渐减小,最后振荡消失,超导体在更高的温区稳定运行,温度呈周期性变化。     

The magnetic properties of the two-dimensional square lattice mixed-spin anisotropic Heisenberg ferromagnet with a transverse magnetic field

The two-dimensional square lattice mixed-spin anisotropic Heisenberg ferromagnet with a transverse magnetic field is studied by means of the double-time Green's function. The analytic expressions of the critical temperature, the high-temperature zero-field susceptibilities, the spin-wave velocity, spin-wave stiffness and spin-wave gap are obtained. The phase diagrams in which the critical temperature, the reorientation temperature and the reorientation magnetic field are shown as a function of single-ion anisotropic parameter are discussed.     

Breakdown threshold in the microwave field at low and high pressures in electronegative gas mixtures

The dependence of the critical value of the microwave field amplitude in electronegative mixtures, which corresponds to the local equality of the ionization frequency and the dissociation attachment frequency, is investigated theoretically in a wide range of pressures with allowance for electron temperature pulsations. The resultant values are compared with the critical value for the static field. The range of pressures in which electron temperature pulsations become significant is determined, and the excess of the critical amplitude over the value in the static field is calculated in the high-pressure limit. Simple formulas are recommended for estimating the critical value of the microwave field amplitude.     

KDP晶体微纳加工表层杂质对其激光损伤阈值影响的有限元分析

 根据KDP晶体杂质附近的温度场及热应力场理论,分析了微纳加工表层杂质影响下晶体温度场及热应力场的分布情况,发现杂质离子对激光的强吸收作用是造成KDP晶体损伤的主要原因之一,也是影响KDP晶体激光损伤阈值的最主要因素。通过分析还发现杂质半径对晶体的激光损伤阈值也有影响,并得到一个有害的杂质半径,使得杂质吸收能量最多,温度最高。另外杂质种类及杂质含量的不同也会对晶体的激光损伤阈值产生影响。     

Zeeman-driven phase transition within the superconducting state of κ-(BEDT-TTF)2Cu(NCS)2

(13)C nuclear magnetic resonance measurements were performed on κ-(BEDT-TTF)(2)Cu(NCS)(2), with the external field placed parallel to the quasi-2D conducting layers. The absorption spectrum is used to determine the electronic spin polarization M(s) as a function of external field H at a temperature T=0.35 K. A discontinuity in the derivative dM(s)/dH at an applied field of H(s)=213±3 kOe is taken as evidence for a Zeeman-driven transition within the superconducting state and stabilization of inhomogeneous superconductivity.