一种求解二次约束二次规划问题的自适应全局优化算法

为了更好地解决二次约束二次规划问题(QCQP), 本文基于分支定界算法框架提出了自适应线性松弛技术, 在理论上证明了这种新的定界技术对于解决(QCQP)是可观的。文中分支操作采用条件二分法便于对矩形进行有效剖分; 通过缩减技术删除不包含全局最优解的部分区域, 以加快算法的收敛速度。最后, 通过数值结果表明提出的算法是有效可行的。     

EPR of Cu2+-doped tris-sarcosine calcium chloride

The EPR study of the Cu²⁺-doped tris-sarcosine calcium chloride (TSCC) at room temperature is reported. Two magnetically inequivalent sites for Cu²⁺ were observed. The rhombic spin Hamiltonian parameters are determined by fitting the EPR spectra for two centres: Cu²⁺(I) g₁ = 2.0276, g₂ = 2.0517, g₃ = 2.4019, A₁ = 82, A₂ = 128, A₃ = 152 [G] and Cu²⁺(II) g₁ = 2.0231, g₂ = 2.0368, g₃ = 2.5294, A₁ = 76, A₂ = 92, A₃ = 156 [G]. The ground state wave function is also determined. The g-anisotropy is evaluated and compared with the experimental value. Further, the optical study of the crystal at room temperature is carried out and the nature of bonding in the complex is discussed.     

LiV2O4: electronic,magnetic structure and heavy-fermion behaviour from first principles

First principles studies based on density functional theory (DFT) calculations within the generalized gradient approximations (GGA) and GGA + U approach using the full-potential, augmented plane wave + local orbitals (APW + lo) method, as implemented in the WIEN2k code, have been used to investigate the structural, electronic and magnetic properties of spinel-structure LiV₂O₄, in particular regarding the heavy fermion (HF) behaviour. The calculations were performed for ferromagnetic, anti-ferromagnetic, and ferrimagnetic configurations using two kinds of magnetic structures (tetragonal and rhombohedral). The GGA results showed that the Fermi energy lies in the V 3d (t_2g) bands with 1.5 electrons per V atom occupying this band, and the V 3d bands are separated by a ～1.9 eV energy gap from the O 2p bands and further split into t_2g and e_g bands with a ～1.0 eV energy gap, which are in good agreement with the photoelectron spectra. The GGA + U method indicates that the ground state of LiV₂O₄ is the tetragonal anti-ferromagnetic configuration with metallic character, and ferromagnetic order character at slightly higher energy, which is consistent with experimental result. The geometric frustration and hybridization between 3d (V) and 2p (O) could induce spin fluctuation and help to explain the instability of specific heat, susceptibility and HF behaviour.     

Nuclear spin–spin constants,rotational g factor and susceptibility of sulphur hexafluoride

Following our previous study on spin–rotation and shielding constants of the SF₆ molecule, the rotational g factor and the magnetic susceptibility are calculated here, using ab initio methods to evaluate the electronic contribution to the nuclear hyperfine constants, and compared with experimental results. It is shown, for the first time, that the electronic component of the rotational g factor is proportional to a constant, which is given by a sum over electronic states. We also evaluate for the SF₆ molecule the indirect, or electron-coupled spin–spin interaction, theoretically described by Ramsey, and show that it gives non-negligible corrections to direct coupling constants d ₁ and d ₂. The contributions of the terms included in this interaction (DSO, PSO, SD and FC) are also analysed.     

Low-temperature magnetization relaxation in magnetic molecular solids

The low temperature relaxation of the magnetization in molecular magnetic solids such as Fe₈ is studied using Monte Carlo simulations. A set of rate equations is then developed to understand the simulations, and the results are compared. The simulations show that the magnetization of an initially saturated sample deviates as a square-root in time at short times, as observed experimentally, and this law is derived from the rate equations analytically.     

Frontiers in frustrated magnetism

This article discusses at a qualitative level a number of issues at the forefront of current understanding and developments in frustrated quantum magnetism. The focal point of the presentation is the spin liquid, which is introduced in terms of (un)broken spin and lattice symmetries. An overview of the full spectrum of research activity in the field is obtained by considering selected examples from experimental approaches to realising spin-liquid states, from theoretical efforts which seek both to classify spin liquids according to their physical properties and to broaden the search for spin-liquid behaviour, and from numerical techniques which offer the prospect of qualitatively new insight into frustrated spin systems.     

Body Temperature Mapping by Magnetic Resonance Imaging

Abstract

There are numerous clinical situations, such as hyperthermia cancer therapy, under which body temperature has to be accurately evaluated. Magnetic Resonance Imaging presently offers the best set of non-invasive methods for body temperature mapping, including diffusion imaging, relaxation time measurement, magnetization transfer contrast and chemical shift spectroscopic imaging. The basic NMR parameters involved in each are first analyzed. The role of temperature in their physical variation is then presented and finally the different practical MRI methods are briefly discussed. In the present slate of available technology and for basic physical reasons, the T 1 method appears the best compromise at low and medium magnetic field in a limited temperature range. Chemical shift could be theoretically more promising but strictly depends from the homogeneity and stability of the magnet and will be available only at high or very high field.

     

Small-Angle and Wide-Angle X-Ray Scattering Study of Slow Relaxation Following Phase Transitions of New Bolaamphiphiles Based on N-(12-Betainylamino-Dodecane)-octyl β-D-Glucofuranosiduronamide Chloride

In the present study, we investigated the polymorphism and its time-dependence of a new series of bolaamphiphile molecules based on N-(12-Betainylamino-dodecane)-octyl β-D-Glucofuranosiduronamide Chloride. To obtain six members of this series, the length of the main bridging chain and the lateral chain were varied in order to modify the hydrophilic–lipophilic balance. Another chemical modification was to introduce a diacetylenic unit in the middle of the bridging chain to study the influence of the π–π stacking on the supramolecular organization of these molecules. Dry bolaamphiphiles self-organize in supramolecular structures such as lamellar crystalline structure, L_c; lamellar gel structure, L_β′; lamellar fluid structure, L_α; and lamellar isotropic structure, L. Thermal hysteresis of these structures, following phase transitions, are investigated by small-angle and wide-angle X-ray scattering. Once the thermal cycle is accomplished, the system remains in the kinetically stabilized undercooled high-temperature phase at the temperature of 20°C. Subsequently, the time-dependence of the relaxation to the thermodynamically stable phase is followed, and very slow relaxation for a period on the order of hours or days is observed. The study of the polymorphism and the stability of various phases of this new series of bolaamphiphiles—which are issued from natural primary resources (sugar beet and wheat) and thus interesting for potential application in pharmaceutical, cosmetics, or food industry—was undertaken in this work.     

BN链掺杂的石墨烯纳米带的电学及磁学特性

基于密度泛函理论第一性原理系统研究了BN链掺杂石墨烯纳米带(GNRs)的电学及磁学特性, 对锯齿型石墨烯纳米带(ZGNRs)分非磁态(NM)、反铁磁态(AFM)及铁磁性(FM)三种情况分别进行考虑. 重点研究了单个BN链掺杂的位置效应. 计算发现: BN链掺杂扶手椅型石墨烯纳米带(AGNRs) 能使带隙增加, 不同位置的掺杂, 能使其成为带隙丰富的半导体. BN链掺杂非磁态ZGNR的不同位置, 其金属性均降低, 并能出现准金属的情况; BN链掺杂反铁磁态ZGNR, 能使其从半导体变为金属或半金属(half-metal), 这取决于掺杂的位置; BN链掺杂铁磁态ZGNR, 其金属性保持不变, 与掺杂位置无关. 这些结果表明: BN链掺杂能有效调控石墨烯纳米带的电子结构, 并形成丰富的电学及磁学特性, 这对于发展各种类型的石墨烯基纳米电子器件有重要意义. 关键词： 石墨烯纳米带 BN链掺杂 输运性质 自旋极化     

{Cu3}单分子磁体在磁场中的热纠缠

本文研究单分子磁体Na₉[Cu₃Na₃(H₂O)₉ (α-AsW₉O₃₃)₂]·26H₂O中三角自旋 环在磁场作用下的热纠缠性质, 利用数值计算求出任意两个Cu²⁺离子量子比特之间的配对纠缠度, 分别记为C₁₂, C₂₃和C₁₃. 研究结果表明, 磁场的方向和大小以及温度对配对纠缠度具有重要影响, 而且参数的变化对C₁₂, C₂₃和C₁₃的影响也是各不相同. 给出外加三个不同方向的磁场时, 配对纠缠度C₁₂, C₂₃和C₁₃各自对应的临界温度T_c随磁场强度的变化图, 由此可以得到单分子磁体三角自旋环中存在纠缠态的参数范围. 通过选择适当的磁场方向和大小以及温度等实验参数, 可以有效地调节和提高单分子磁体中的配对纠缠度. 关键词： 配对纠缠 单分子磁体 三角自旋环