辐射输运菱形差分SN方程的扩散综合加速方法

讨论辐射输运菱形差分S_N方程的源迭代加速方法,在一维情形下给出与输运算子离散相容的线性多频灰体加速计算格式.数值算例表明该加速算法是健壮有效的.     

δ函数SN方法求解含各向异性散射输运方程的本征值问题

将角通量分解成一个δ函数和一个低阶函数,分别采用解析方法和求积组来计算源项.利用δ函数S_N方法,计算了平几何条件下含各向异性散射单速输运方程的临界问题.分析和数值结果表明,采用数量较少的离散方向,能够达到较高计算精度.     

RfN小波及其在气象资料分析中的应用

讨论了分式滤波器小波的一个子类Rf_N小波,并从理论与应用两个方面将其与Db_N小波进行比较,得出Rf_N小波在理论与应用上均明显优于Db_N.应用方面的比较是通过分析哈尔滨地区从1881年到2000年的几项气象资料进行的.     

Fibonacci链的电子结构特性

对由递推关系S_m+1={S_m|S_m-1}生成的Fibonacci链,从Anderson紧束缚模型出发,用负本征值理论及三对角高阶厄米矩阵本征值理论,对电子的态密度和能级结构进行数值研究,直观简洁地论证其三分叉的能带结构.用重整化群方法,结合散射理论,研究链中电子的局域长度和输运系数,发现具有不同局域属性的能态.一些特定的能量区间值存在扩展态,其相应的输运系数接近1.绝大部分能量对应的电子具有很小或几乎为零的局域长度,说明链中存在相当数量的局域态.定性得出电子输运系数随Fibonacci链参数变化的规律.     

基于蒙特卡罗正算输运的全局减方差方法

蒙特卡罗方法是当前形势下辐射屏蔽计算的首选分析工具。小概率深穿透问题则是屏蔽计算的关键与亟待解决的核心问题,需要使用有效的减方差技巧。针对全局问题,利用蒙特卡罗正算输运得到的粒子通量或探测响应来构建权重窗参数,将现有的粒子位置偏移拓展到位置和能量偏倚。利用国际屏蔽基准题进行测试验证,通过使用该方法,粒子被引导到模型的所有位置。平均相对误差降低到10%以下,几乎所有网格区域都有粒子统计。结果表明,基于蒙特卡罗正算输运的输运偏倚参数构建方法能够实现全局减方差。     

基于共轭离散纵标的减方差方法

对于深穿透类型的屏蔽计算,为了得到较为可信的统计结果,蒙特卡罗方法(MC方法)需要模拟大量的粒子,巨大的计算时间是其存在的主要问题。源偏倚和权窗技巧能够有效降低深穿透问题的计数误差。开展了基于共轭离散纵标(SN)的MC减方差方法研究,根据SN方法的共轭注量率计算并生成了源偏倚和权窗参数,编写了JMCT程序的源抽样子程序,并且在秦山一期测量值基础上进行了验证,成功应用到CAP1400压力容器快中子注量率和堆腔中子和光子剂量率计算中。数值结果表明,对于深穿透屏蔽计算问题,和无偏的MC方法相比,基于共轭SN的MC减方差方法能够在保证结果精度的前提下,提高计算效率1~2个量级。     

CeO2热力学性质的第一原理研究

使用第一性原理方法结合准谐德拜模型研究压力0~30 GPa,温度0~2 000 K,二氧化铈立方结构的热力学性质,包括常压下平衡体积V、体弹模量B₀、热容c_p和熵S随温度的变化以及不同压强下热容c_p、熵S、德拜温度Θ,体膨胀系数α与温度的关系.常压下计算的热容c_p和熵S随温度的变化与实验数据符合很好.     

氮杂环化合物中1JCH与电荷密度的关系

本文用EHMO程序计算了氮杂环化合物中N-CH₂-R基团上C和H原子的S电子密度S_C^(o)和S_H^(o),对于吡啶盐系列S_C^(o)S_H^(o)等于1.172±0.006,对于咔唑系列S_C^(o)S_H^(o)等于1.162±0.015。实验指出,这两个系列化合物的NMR耦合常数¹J_CH分别为144±2Hz_o和135±2Hz对比计算结果和实验数据可以很好地解释¹J_CH不随取代基的改变而变化。     

AlxGa1-xN/GaN双量子阱的结构和掺杂浓度对子带间跃迁波长和吸收系数的影响

用薛定谔方程和泊松方程自洽计算的方法研究了Al_0.75Ga_0.25N/GaN对称双量子阱(DQWs)中子带间跃迁(ISBT)的波长和吸收系数对中间耦合势垒高度、中间耦合势垒宽度、势阱宽度和势垒掺杂浓度的依赖关系.研究发现,第一奇序子带S_1ood与第二偶序子带S_2even ISBT波长随着中间耦合势垒高度的降低而变短.当中间耦合势垒高度高于0.62 eV时,S_{1odd< 关键词： 自洽 x}Ga_1-xN/GaN双量子阱')" href="#">Al_xGa_1-xN/GaN双量子阱 子带间跃迁     

宽脉冲中子注入下中子裂变链统计涨落的数值计算

研究了裂变系统在宽脉冲外中子源注入驱动下裂变链统计涨落问题.提出了概率分布W_n方程的分解-合成数值模拟计算方法,使裂变系统注入中子源数值模拟计算扩展到一般广义条件(具有任意时间分布、注入时间零点t₀概率分布函数P(t₀)和数概率分布S(n)等).同时讨论了应用物理模型的等效条件.将基本前提等效条件从单介质区模型扩展到多介质区模型.为解概率分布W_n方程必备参数提供了计算平均公式.     

From Planck to GUT via dimensional transmutation

Consider a gauge singlet superfield S coupled to a pair of adjoint fields in a SUSY-GUT. If the tree-level vacuum is flat in S, the vev S which defines the GUT scale will be determined via dimensional transmutation at a scale M where the soft-breaking (mass)² vanishes as a result of running from M_P = (8πG_N)^−1/2. Because of the large number of adjoint fields N_A coupled to S, one finds that M can be generically close to M_GUT = 2 × 10¹⁶GeV:

, where λ is a Yukawa 0.7. This work examines the symmetries and dynamical constraints required in a SUSY-GUT in order that the desired flatness in S is achieved, and that this flatness may survive in a supergravity framework.     

Duality and quantum-algebra symmetry of the AN−1 open spin chain with diagonal boundary fields

We show that the transfer matrix of the A_N−1⁽¹⁾ open spin chair with diagonal boundary fields has the symmetry U_q(SU(l)) × U_q(SU(N−l)) × U(1), as well as a “duality” symmetry which maps l ↔ N − l. We exploit these symmetries to compute exact boundary S-matrices in the regime with q real.     

A new upper bound formula for the ground state energies of N-boson systems

The energy E_N of an N-body system of pairwise interacting bosons is shown to satisfy the inequality, E_N < [N(N − 1)/n(n − 1)] E_n, where N > n 2. This inequality generalizes the Bruch-Sawada result, E₃ < 3E₂, and is superior in its predictive ability to Lim et al.'s .     

Magnetic behavior of the two-dimensional antiferromagnet RbFeF4

RbFeF₄ shows anomalous magnetic susceptibility behavior rather similar to that of KFeF₄, in which the existence of two-dimensional antiferromagnetic ordering has recently been clearly demonstrated. A neutron diffraction study of powder samples reveals that RbFeF₄ orders antiferromagnetically in three dimensions at T_N = 134 K. In addition around T_N, the diffraction patterns indicate a magnetic ridge, thus giving, in accordance with KFeF₄, the evidence of the two-dimensional nature of the magnetism in RbFeF₄.     

Disruption of antiferromagnetic order in Zn-doped La2CuO4

The magnetic phase diagram of La₂(Cu_1−xZn_x)O₄ has been determined from zero-field muon-spin-rotation (ZF-μSR) data taken at LAMPF for 0 ≤ x ≤ 0.10. Antiferromagnetic onset temperatures follow T_N(x) from susceptibility measurements on the same samples. However, the order becomes long range, as evidenced by a well-defined internal magnetic field, only at temperatures well below T_N. Extrapolation of our results yields T_N → 0 K at x = 0.11 for a single (Cu_1−xZn_x)O₂ plane, and comparison with YBa₂(Cu_1−xZn_x)₃O₆ implies identical disruption of magnetism by Zn doping in the single- and double-plane systems.     

Elastic proton-proton scattering: Excitation functions from 0.45 to 2.5 GeV

Excitation functions of the differential cross sections dσ/dgw, analyzing powers A_N and spin correlation parameters A_NN, A_SS and A_SL have been measured with internal targets at the Cooler Synchrotron COSY. Data were taken continously during the acceleration and deceleration of the internal beam for kinetic energies between 450 and 2500 MeV and scattering angles 30° σ_cm 90°. Details of the experimental method are presented. The results provide excitation functions and angular distributions of high precision and internal consistency. No evidence for narrow structures are found. Upper limits on the coupling of narrow resonances to elastic scattering in the mass range √s = 2.2…2.8 GeV are deduced. The data have significant impact on phase shift solutions.     

Thermoelectric power of antiferromagnetic RIn3 compounds

The thermoelectric power (TEP) has been measured from 2.2 to 300 K for antiferromagnetic compounds, CeIn₃, NdIn₃, SmIn₃, GdIn₃ and (Ce_1−xLa_x)In₃ with x = 0.1 and 0.2. The effects of the antiferromagnetic order were observed on the TEP of these compounds below T_N. The observations are explained by the antiferromagnetic band gap formation theory proposed by Abel'skii.     

Entanglement measures of a new type pseudo-pure state in accelerated frames

In this work we analyze the characteristics of quantum entanglement of the Dirac field in noninertial reference frames in the context of a new type pseudo-pure state, which is composed of the Bell states. This will help us to understand the relationship between the relativity and quantum information theory. Some states will be changed from entangled states into separable ones around the critical value F = 1/4, but there is no such a critical value for the variable y related to acceleration a. We find that the negativity N_ABI (ρ^TA_ABI) increases with F but decreases with the variable y, while the variation of the negativity N_BIBII(ρ^TA_ABI) is opposite to that of the negativity N_ABI (ρ^TA_ABI). We also study the von Neumann entropies S(ρ_ABI) and S(ρ_BIBII). We find that the S(ρ_ABI) increases with variable y but S(ρ_BIBII) is independent of it. However, both S(ρ_ABI) and S(ρ_BIBII) first decreases with F and then increases with it. The concurrences C(ρ_ABI) and C(ρ_BIBII) are also discussed. We find that the former decreases with y while the latter increases with y but both of them first increase with F and then decrease with it.     

A large NMR lineshift due to induced-staggered magnetization in paramagnetic state

Antiferromagnetic staggered susceptibility is studied in a new way by the examination of the proton NMR lineshift above T_N in a crystallographic two-sublattice system with different g-tensors. The lineshift has a large contribution from the staggered magnetization which is induced in the paramagnetic state by the action of a uniform external field. A large value of the staggered susceptibility derived from the experiment in a nearly two-dimensional Heisenberg antiferromagnet, Cu(HCOO)₂.4D₂O, can be ascribed to the existence of a highly developed short-range order above T_N in this crystal.