Equilibrium dynamics of the sub-Ohmic spin-boson model under bias

Using the bosonic numerical renormalization group method, we studied the equilibrium dynamical correlation function C(ω) of the spin operator σ_z for the biased sub-Ohmic spin-boson model. The small-ω behavior C(ω) ∝ω~s is found to be universal and independent of the bias ε and the coupling strength α(except at the quantum critical point α = αc and ε = 0). Our NRG data also show C(ω) ∝χ~2ω~s for a wide range of parameters, including the biased strong coupling regime(ε = 0 and α α_c), supporting the general validity of the Shiba relation. Close to the quantum critical point αc,the dependence of C(ω) on α and ε is understood in terms of the competition between ε and the crossover energy scale ω_0~*of the unbiased case. C(ω) is stable with respect to ε for ε《ε~*. For ε》ε~*, it is suppressed by ε in the low frequency regime. We establish that ε~*∝(ω_0~*)~(1/θ)holds for all sub-Ohmic regime 0≤s 1, with θ = 2/(3s) for 0 s≤1/2 and θ = 2/(1 + s) for 1/2 s 1. The variation of C(ω) with α and ε is summarized into a crossover phase diagram on the α–ε plane.     

Soliton Excitations in the Compressible Heisenberg Spin Chain: A General Approach

A general approach is given for the nonlinear excitations in the compressible Heisenberg ferromagnetic chain in coherent-state representation. It is shown that the relative ratio of ε to δ is very important for determining the nonlinear modified terms of the equations of motion. ε = 1√S (S is the spin length) and δ = α/λ₀ (α is the lattice constant and λ₀ is the characteristic wavelength of the excitations) are two small dimensionless parameters used in the semiclassical approximation and in the long wavelength approximation, respectively. In the case of δ = O(ε), the reduced equations of motion are solved exactly and spin soliton and elastic kink solutions are obtained. The other cases of the relation between δ and ε are also discussed and the solitary wave solutions are also given. The result obtained by Ferrer, as a special case, has been included in our approach.     

Alternating-current relaxation of a rotating metallic particle

Based on a first-principles approach,we establish an alternating-current(AC) relaxation theory for a rotating metallic particle with complex dielectric constant ε_α=ε_α-iσ_α/ω_0.Here εα is the real part,σ_α the conductivity,ω_0 the angular frequency of an AC electric field,and i=-1~(1/2).Our theory yields an accurate interparticle force,which is in good agreement with the existing experiment.The agreement helps to show that the relaxations of two kinds of charges,namely,surface polarized charges(described by ε_α) and free charges(corresponding to σ_α),contribute to the unusually large reduction in the attracting interparticle force.This theory can be adopted to determine the relaxation time of dynamic particles in various fields.     

Electronic,optical, and mechanical properties of BN,AlN, and InN with zinc-blende structure under pressure

In this work, the electronic, optical, and mechanical properties of BN, AlN, and InN under the action of pressure are calculated. For each of these compounds, the energy band structure, band gaps(E~L_g, E~Γ_g, E~X_g), refractive index(n),dielectric constants(ε_∞, ε_0), elastic constants(C_11, C_12, C_44), and relevant parameters such as bulk(B_u), shear(S_h), and Young's(Y_0) moduli are studied, and other important parameters such as bond-stretching(α), bond-bending(β) force constant, internal-strain parameter(ζ), effective charges(e~*_T, Z~*), anisotropy factor(I_s), Poisson's ratio(P_o), Cauchy ratio(C_a), the ductility index(μ_D), and linear compressibility(C0_) are also calculated. The effects of pressure on all studied properties are investigated. Our results are in good agreement with the available experimental and theoretical data for BN,AlN, and InN.     

Nonlinear Response of Granular Composite Mediurn

In this paper, the linear and nonlinear responses of granular composite medium consisting of spherical grains with coating shells embedded in a host medium are studied. We assume that the shell and the host medium are linear (the dielectric constants of which are ε⁰ and ε_m⁰ respectively), while the spherical grain is nonlinear (the diektric constant of which is ε_c = ε_c⁰ + χ_c|E_c|^β). Starting from the definition (D) = ε_eff and taking in to account the corrections to the local field within the spherical grains, expressions for the linear and high-order nonlinear susceptibilities are presented.     

Upper Bounds on Top Quark Mass,Z Boson Decay Widths and Mass Ratio MW/MZ

In this paper we made a comprehensive analysis of some latest esperimental data-the Z boson decay widths, the mass ratio M_W/M_Z and effective vector coupling constant g_v, within the framework of standard model. We considered the 0(α_s²), order QCD corrections in tlte calculation of T_h and T_z. The analysis shows that the mass ratio (M_W/M_Z)² is rather sensitive to the change of the strong coupling constant α_s(M_Z), and the smaller value α_s(M_Z)≤0.128 is preferred. The upper bounds on top quark Inass M_t are obtained from different analyses. The final averaged result is M_t= 102 37 GeV, or M_t< 186 GeV at 95% C.L. for Higgs boson mass M_H in the range of 50～1000 GeV.     

铁冲击相变的晶向效应

采用基于火炮加载的三样品精细波剖面对比测量,研究了晶向效应对铁弹-塑性转变及体心立方结构(bcc,α相)至六角密排结构(hcp,ε相)相变特性的影响.观测到单晶铁异常的弹-塑性转变行为,这与基于位错密度描述的黏塑性本构模型计算结果相符,对应的Hugoniot弹性极限δ_(HEL)均大于6 GPa,且具有晶向相关性,即δ(111)/(HEL)δ(110)/(HEL)δ(100)/(HEL);系统获取了相变起始压力P_(PT)晶向相关性的实验数据,[100],[110]和[111]晶向的PPT实测值分别为13.89±0.57 GPa,14.53±0.53 GPa,16.05±0.67 GPa,其变化规律与非平衡分子动力学计算结果相符.上述结果揭示出冲击压缩下单晶铁存在塑性与相变微观机理的强耦合,为完善用于冲击实验描述的相场动力学模型提供了重要的实验支撑.     

河南省清凉寺窑址出土富铁釉瓷的无损分析研究

富铁釉瓷在中国古陶瓷史上具有重要地位，综合利用光学相干层析成像技术(OCT)、光学显微镜(OM)、激光拉曼光谱技术(LRS)和X射线荧光光谱分析技术(XRF) 对河南省宝丰清凉寺窑址出土宋金时期富铁釉瓷样品进行无损分析研究，获取了富铁釉瓷的釉层结构、釉面析晶的物相信息及胎釉化学成分等信息，探讨了釉层断面OCT灰度图像特征与其显微结构之间的关系以及富铁釉瓷的烧制工艺。结果表明，酱釉瓷和柿叶红釉瓷表面及黑釉红斑区存在富铁析晶层，黑釉瓷釉层表面未发现富铁析晶层的存在。酱釉瓷釉层富铁析晶层中铁的氧化物以ε-Fe₂O₃晶体为主，而柿叶红釉层则主要是α-Fe₂O₃晶体，黑釉红斑层同时存在ε-Fe₂O₃，α-Fe₂O₃晶体以及磁铁矿。上述差异形成的原因与釉层化学成和烧制工艺存在联系。釉层中高含量碱土金属氧化物及氧化铁区域更容易析出氧化铁晶体。黑釉瓷烧成气氛以还原气氛为主，而酱釉瓷和柿叶红釉瓷则倾向于氧化烧成气氛，且柿叶红釉瓷的烧成温度高于酱釉瓷。该研究将OCT，OM，LRS与XRF相结合，有助于加强对富铁釉瓷的整体认知，为富铁釉瓷的断源断代提供更为丰富的线索。     

KM Matrix Parametrizatidn Convenient for Both Bd Study and Data Analysis

The value of the ε parameter of a pseudoscalar mixing system is phase-conventiondependent. We prove that one can make two of the three ε parameters, ε_K, ε_Bd and ε_Bd, small but not all of them simultaneously by adjusting the phase convention of the Kobayashi-Maskawa (KM) matrix. We give corresponding KM matrices based on the Wolfenstein parametrization, which are also suitable for ahalyzing the values of KM parameters. The transformation from one matrix to the other is extremely simple.     

各向异性表面张力对定向凝固中共晶生长形态稳定性的影响

研究各向异性表面张力对定向凝固中共晶生长形态稳定性的影响.应用多重变量展开法导出了共晶界面表达式和扰动振幅的变化率满足的色散关系.结果表明,共晶生长系统有两种整体不稳定性机理:由非震荡导致的"交换稳定性"机理和由震荡导致的"整体波动不稳定性"机理.震荡有四种典型模式,即:反对称-反对称(AA-),对称-反对称(SA-)、反对称-对称(AS-)和对称-对称(SS-)模式.稳定性分析表明:共晶界面形态稳定性取决于Peclet数ε的某一个临界值ε_*,当ε大于临界值ε_*时,共晶界面形态不稳定;当ε小于临界值ε_*时,共晶界面形态稳定.随着各向异性表面张力增大,对应于AA-,SA-和SS-模式的临界值ε_(aa*),ε_(sa*)和ε_(ss*)随之减小,表明各向异性表面张力减小这三种模式的稳定性区域;然而,随着各向异性表面张力增大,对应于AS-模式的临界值ε_(as*)随之增大,表明各向异性表面张力增大AS-模式的稳定性区域.     

非简谐振动对石墨烯杨氏模量与声子频率的影响

在哈里森键联轨道法框架下, 考虑到原子的短程相互作用和原子的非简谐振动, 应用固体物理理论和方法, 得到了石墨烯的力常数、杨氏模量、扭曲模量、泊松系数以及声子频率随温度的变化关系, 探讨了非简谐振动对它们的影响. 结果表明: 1)杨氏模量与声子频率等随温度变化并遵从一定的规律, 其中力常数、杨氏模量、扭曲模量随温度升高而增大, 但变化较小; 声子频率随温度升高而增大但变化较快; 泊松系数随温度升高而较快地减小; 2)石墨烯原子具有沿键长方向的纵振动和垂直键长方向的横振动, 但以纵振动为主, 纵振动的非简谐效应远大于横振动, 横振动的简谐系数ε₀' 和第二非谐系数ε₂' 均小于纵振动的相应值ε₀,ε₂; 比值为ε₀/ε₀' ≈ 8.477,ε₂/ε₂' ≈ 156; 3)若不考虑非简谐振动项, 则石墨烯的力常数、杨氏模量和扭曲模量、泊松系数、声子频率均为常量, 与实验不符合; 同时考虑到原子的第一、二非简谐振动项后, 它们均随温度升高而变化, 而且温度愈高, 原子振动的非简谐效应愈显著. 本文的结果与文献的实验结果符合较好.     

Topological Insulators in α-Graphyne

In this paper, we investigate topological phases of α-graphyne with tight-binding method. By calculating the topological invariant Z2 and the edge states, we identify topological insulators. We present the phase diagrams of α-graphyne with different filling fractions as a function of spin-orbit interaction and the nearest-neighbor hopping energy. We find there exist topological insulators in α-graphyne. We analyze and discuss the characteristics of topological phases of α-graphyne.     

The Optical Properties of (C59N)2

Using the extended Hubbard model and sum-over-state method, we have calculated the linear polarizability α and the third-order nonlinear polarizability γ for (C₅₉N)₂. We find that (C₅₉N)₂ has very big γ value (around esu), and its α and γ values are bigger than those of C₅₉N. In particular, when 1.2 eV≤3ω, (C₅₉N)₂ as much larger γ values than C₅₉N.     

核磁共振的差谱在天然产物研究中的应用（Ⅰ）

提出应用核磁共振差谱研究天然产物混合物的方法. 在对黄海繁茂膜海绵天然产物的研究中，通过柱分离的溶剂强度连续变化，获得连续洗脱物，对这几个连续洗脱物的核磁共振谱图进行比较得出差谱，实现核磁共振谱峰的分类、归属，从而解析出各个化合物. 在此过程中也可以获得被分离物与溶剂强度之间的关系.     

Quantization of Space in the Presence of a Minimal Length

In this article,we apply the Generalized Uncertainty Principle(GUP),which is consistent with quantum gravity theories to an elementary particle in a finite potential well,and study the quantum behavior in this system.The generalized Hamiltonian contains two additional terms,which are proportional to αp~3(the result of the maximum momentum assumption) and α~2p~4(the result of the minimum length assumption),where α ~ 1/M_(PIC) is the GUP parameter.On the basis of the work by Ali et al.,we solve the generalized Schrodinger equation which is extended to include the α~2 correction term,and find that the length L of the finite potential well must be quantized.Then a generalization to the double-square-well potential is discussed.The result shows that all the measurable lengths especially the distance between the two potential wells are quantized in units of α_0l_(PI) in GUP scenario.     

High-pressure dynamic,thermodynamic properties,and hardness of CdP_2

Using a pseudopotential plane-waves method,we calculate the phonon dispersion curves,thermodynamic properties,and hardness values of α-CdP_2 and β-CdP_2 under high pressure.From the studies of the phonon property and enthalpy difference curves,we discuss a phase transform from β-CdP_2 to a-CdP_2 in a pressure range between 20 GPa and 25 GPa.Then,the thermodynamic properties,Debye temperatures,and heat capacities are investigated at high pressures.What is more,we employ a semiempirical method to evaluate the pressure effects on the hardness for these two crystals.The results show that the hardness values of both α-CdP_2 and β-CdP_2 increase as pressure is increased.The influence mechanism of the pressure effect on the hardness of CdP_2 is also briefly discussed.     

具有p波超流的一维非公度晶格中迁移率边研究

研究了具有p波超流的一维非公度晶格中迁移率边的性质. 发现适当的p波超流可以增加体系中的迁移率边的数目, 并且通过多分形分析确定了迁移率边所在的位置.     

Alternating current characterization of nano-Pt(Ⅱ)octaethylporphyrin(PtOEP) thin film as a new organic semiconductor

Alternating current(AC) conductivity and dielectric properties of thermally evaporated Au/Pt OEP/Au thin films are investigated each as a function of temperature(303 K–473 K) and frequency(50 Hz–5 MHz).The frequency dependence of AC conductivity follows the Jonscher universal dynamic law.The AC-activation energies are determined at different frequencies.It is found that the correlated barrier hopping(CBH) model is the dominant conduction mechanism.The variation of the frequency exponent s with temperature is analyzed in terms of the CBH model.Coulombic barrier height Wm,hopping distance Rω,and the density of localized states N(EF) are valued at different frequencies.Dielectric constant ε_1(ω,T) and dielectric loss ε_2(ω,T) are discussed in terms of the dielectric polarization process.The dielectric modulus shows the non-Debye relaxation in the material.The extracted relaxation time by using the imaginary part of modulus(M')is found to follow the Arrhenius law.     

The low-temperature sintering and microwave dielectric properties of (Zn_(0.7)Mg_(0.3))TiO_3 ceramics with H_3BO_3

The effects of the addition of H 3 BO 3 on the microstructure, phase formation, and microwave dielectric properties of (Zn 0.7 Mg 0.3 )TiO 3 ceramics sintered at temperatures ranging from 890 ℃ to 950 ℃ are investigated. H 3 BO 3 as a sintering agent can effectively lower the sintering temperature of ZMT ceramics below 950 ℃ due to the liquid-phase effect. The microwave dielectric properties are found to strongly correlate with the amount of H 3 BO 3 . With the increase in H 3 BO 3 content, the dielectric constant (ε r ) monotonically increases, but the quality factor (Q × f ) reaches a maximum at 1 wt% H 3 BO 3 , and the apparent density of ZMT ceramics with H 3 BO 3 ≥ 1 wt% gradually decreases. At 950 ℃, the ZMT ceramics with 1% H 3 BO 3 exhibit excellent microwave dielectric properties: ε r = 19.8, and Q × f = 43800 GHz (8.94 GHz).     

伸缩-剪切模式自偏置铌酸锂基复合材料的磁电性能和高频谐振响应

选用多种切型铌酸锂(LiNbO_3)单晶,研究了铁基非晶合金(Metglas)/LiNbO_3叠层复合材料基于伸缩-剪切模式的磁电耦合性能,揭示了铌酸锂单晶压电系数与复合材料剪切磁电耦合系数的对应关系,在使用铌酸锂xzt/30~?切型时得到了最优化剪切磁电系数.通过SrFe12O19薄磁带提供偏置磁场,Metglas/LiNbO_3磁电复合材料可在没有外加直流磁场时实现剪切磁电响应,并在0.991 MHz和3.51 MHz频率时分别测出了谐振磁电系数,有望将铌酸锂基剪切磁电复合材料用于高频磁场探测.