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).     

垂直载荷下湿玻璃珠样品的声速和衰减测量及非线性声学响应

为了分析垂直载荷下颗粒物质的声速、声衰减系数、谐波非线性等特性,本工作采用飞行时间法测量了不同含水量下声速随压强的变化规律,并利用傅里叶变换法分析了干、湿玻璃珠样品的声衰减和非线性声学特性。结果表明:干、湿玻璃珠样品中的声速、声衰减系数以及谐波非线性均随压强呈幂律变化;湿颗粒样品中随着液体含量增多,声速逐渐增加,超声波透过湿颗粒样品时的能量耗散和非线性逐渐减小。分析原因表明,压强和孔隙流体改变了颗粒之间的接触分布,使得颗粒体系的声速、声衰减以及谐波非线性等特性都随之发生变化。     

多晶Tl2Ba2Ca2Cu3Oy超导体钉扎研究

我们测量了高温超导体 Tl_2Ba_2Ca_2Cu_3O_y 多晶样品的磁化强度弛豫及在小场,高场情形下的磁滞回线,并推出了该样品的钉扎势 U_0 在77K 的温度下随外加磁场的变化关系:当20mT<μ_0H<106mT 时,U_0∝H~(-0.1),当230mT>μ_0H>106mT,U_0∝H~(-0.8).我们认为这是由于随着外场增加,起主要作用的钉扎中心从样品中超导颗粒间钉扎转向超导颗粒内部钉扎.小场下的磁滞回线及扫描电镜形貌相表明该样品具有颗粒性质.     

关于一级近似T_c级数解的收敛问题

本文通过一个实例说明:μ~* =0时,一级近似T_c级数解的收敛半径既不是由z_(ph)=-integral from n=0 to (ω_(ph)) (dωg(ω)·ω＇/ω_(ph)~2-ω~2),也不是由z_(ph)=integral from n=0 to (ω_(ph)) (dωg(ω)ω~2/ω_(ph)~2 ω~2)决定的。     

水平激励下颗粒物质的有效质量及耗散功率的研究

对颗粒物质的有效质量谱及耗散功率进行了数值研究,发现水平和垂直激励下颗粒体系的共振频率f_g与体积模量k均随压强P呈分段幂律变化,在高压强下遵循fg∝P~(1/6),k∝P~(1/3)的规律,在低压强下遵循fg∝P~(1/4),k∝P~(1/2)的规律.同时,在水平和垂直振动下,颗粒体系品质因子的倒数1/Q随P的变化呈指数衰减.在特定频率和压强下,颗粒体系的平均耗散功率p随振动强度Γ的变化曲线上存在一个特征振动强度Γ*,当ΓΓ*时,颗粒体系表现出类固态行为,平均耗散功率p随振动强度Γ呈幂律标度,p∝Γ~α(2α5);当ΓΓ*时,颗粒体系表现出类液态行为,体系的平均耗散功率p随振动强度Γ呈线性变化.由此得到了水平激励下颗粒体系类固体类流体转变的Γ-P相图.     

钠玻璃与钛玻璃在静水压下的弹性性能

用超声脉冲重叠法测量了钠玻璃(float glass)和钛玻璃(SiO₂+8.4wt%TiO₂)从大气压到2GPa静水压条件下的纵波声速和横波声速.发现两种玻璃有不同的变化规律.钛玻璃的纵波声速和横波声速,与钠玻璃的横波声速都随压力的增加而减小;而钠玻璃的纵波声速随压力的增加先增大,后减小.这一现象不同于别的氧化硅玻璃.对实验结果进行了讨论,并计算了弹性模量在压力下的变化和Murnaghan状态方程参数. 关键词： 高压 超声 玻璃     

非晶态快离子导体(AgI)_x(Ag_4P_2O_7)_(1-x)的声学性质

用液氮骤冷方法制备了(AgI)_x(Ag_4P_2O_r)_(1-x)系列非晶态快离子导体。对AgI摩尔浓度x=0.50,0.60,0.67,0.75,0.80的样品,在77—300K温度范围及2,5,10,15MHz的频率上测量了纵波和横波的超声衰减和声速。发现在200—240K附近存在一个异常强的弛豫型超声吸收峰,随AgI含量的增加,该峰的位置向低温方向移动,且峰的高度增大。在实验的温度范围内,观察到纵波和横波的内耗Q_M~(-1)基本相等。由声速与AgI浓度关系的实验结果,计算了样品的弹性常数,并分析了玻璃态结构的变化。 用Ngai提出的低频涨落、耗散和弛豫过程的统一理论(即红外发散响应(IDR)理论),对实验结果进行了较满意的解释,给出了样品的表观激活能和红外发散指数。     

LaCoO3中自旋态转变现象的超声研究

测量了LaCoO3单相多晶样品的纵波与横波超声声速和衰减随温度的变化关系, 在材料的自旋态转变温度附近(≈90K),纵波声速出现明显的软化并伴随一个尖锐的衰减峰,但是在横波的测量中却没有出现类似的超声异常,分析认为LaCoO3在90K附近的自旋态转变是由于Co3+离子是从低自旋态(LS,t62ge0g)转变到中等自旋态(IS,t52ge1g ),而不是高等自旋态(HS,t42ge2g).随着温度的升高,在200K附近纵波和横波测量上都观察到一个伴随着微小声速软化的宽大的衰减峰,这可能是随机分布的IS态Co3+离子的Jahn-Teller效应导致的局域晶格扭曲所造成的.     

McMillan T_c公式的解析推导(Ⅱ) μ~*≠0情形

本文把文献[1]的理论以及所得到的T_c公式推广到μ≠0情形,得到 T_c=2r/πω_(log)·(ω_(log)/ω_c)~μ/(λ-μ)·exp{-(1 λ)/(λ-μ)}.nγ=C=0.5772是Euler常数。     

聚四氟乙烯F-C-F弯曲振动二维红外光谱研究

在303~393K的温度范围内,分别测定聚四氟乙烯F-C-F弯曲振动模式(δ_(CF2(PTFE)))的一维红外光谱、二阶导数红外光谱、四阶导数红外光谱和去卷积红外光谱。研究发现:640和620cm~(-1)附近的吸收峰归属于F-C-F面外摇摆振动模式(ω_(CF2-A)和ω_(CF2-B)),550cm~(-1)附近的吸收峰归属于F-C-F剪式振动模式(δ_(CF2)),而500cm~(-1)附近的吸收峰则归属于F-C-F面内摇摆振动模式(ρ_(CF2))。最后研究了聚四氟乙烯二维红外光谱。研究发现:随着测定温度的升高,δ_(CF2(PTFE))吸收强度变化快慢的顺序为:550cm~(-1)(δ_(CF2))500cm~(-1)(ρ_(CF2))620cm~(-1)(ω_(CF2-B))640cm~(-1)(ω_(CF2-A))。本项研究拓展了二维红外光谱技术在聚四氟乙烯材料热变性的方面的研究范围。     

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.     

Rashba自旋-轨道相互作用影响下量子盘中强耦合磁极化子性质的研究

本文基于Lee-Low-Pines幺正变换法,采用Tokuda改进的线性组合算符法研究了Rashba自旋-轨道相互作用效应下量子盘中强耦合磁极化子的性质.结果表明,磁极化子的相互作用能Eint的取值随量子盘横向受限强度ω0、外磁场的回旋频率ωc、电子-LO声子耦合强度α和量子盘厚度L的变化均与磁极化子的状态性质密切相关;磁极化子的平均声子数N随ωc,ω0和α的增加而增大,随L的增加而振荡减小;在Rashba自旋-轨道相互作用效应影响下磁极化子的有效质量将劈裂为m*+,m*-两种,它们随ωc,ω0和α的增加而增大,随L的增加而振荡减小;在研究量子盘中磁极化子问题时,电子-LO声子耦合和Rashba自旋-轨道相互作用效应的影响不可忽略,但Rashba自旋-轨道相互作用和极化子效应对磁极化子的影响只有在电子运动的速率较慢时显著.     

Energy Spectra and g Factors of α-A1203:Cr3+ and α-A1203:Mn4+

By diagonalizing the complete d³ energy matrix in a trigonally distorted cubicfield and using the wavefunctions from it, unified calculations of the whole energy spectrum as well as the g factors of the ground state and t₂^{3 2} E excited states for α-A1₂0₃:Cr³⁺ and α-A1₂0₃:Mn⁴⁺ have been carried out respectively. A11 the calculated results are in very good agreement with the experimental data. The comparison between the results of the two crystals has been made, which demonstrates that the covalency of α-A1₂0₃:Mn⁴⁺ is stronger than the one of α-A1₂0₃:Cr³⁺. For the zero-field splittings of the ground state and t₂^{3 2} E , their physical origins are revealed; the comparison and analysis of their values of the two crystals have been made.     

Tunable two-axis spin model and spin squeezing in two cavities

Multi-mode cavities have now attracted much attention both experimentally and theoretically. In this paper, inspired by recent experiments of cavity-assisted Raman transitions, we realize a two-axis spin Hamiltonian H = q(J_x~2+ χJ_y~2) + ω_0J_z in two cavities. This realized Hamiltonian has a distinct property that all parameters can be tuned independently. For proper parameters, the well-studied one- and two-axis twisting Hamiltonians are recovered, and the scaling of N~(-1) of the maximal squeezing factor can occur naturally. On the other hand, in the two-axis twisting Hamiltonian, spin squeezing is usually reduced when increasing the atomic resonant frequency ω_0. Surprisingly, we find that by combining with the dimensionless parameter χ(-1), this atomic resonant frequency ω_0 can enhance spin squeezing greatly. These results are beneficial for achieving the required spin squeezing in experiments.     

Theoretical Study on the Low-Lying Electronic States of He2, He2+, and He2++

The equilibrium geometries, potential energy curves, spectroscopic dissociation energies of the ground and low-lying electronic states of He₂, He₂⁺ and He₂⁺⁺ are calculated using symmetry adapted cluster/symmetry adapted cluster-configuration interaction (SAC/SAC-CI) method with the basis sets CC-PV5Z. The corresponding dissociation limits for all states are derived based on atomic and molecular reaction statics. The analytical potential energy functions of these states are fitted with Murrell--Sorbie potential energy function from our calculation results. The spectroscopic constants B_e, α _e, ω _e, and ω _e χ _e of these states are calculated through the relationship between spectroscopic data and analytical energy function, which are in well agreement with the experimental data. In addition, the origin of the energy barrier in the ground state X¹Σ_g⁺ of He₂⁺⁺ energy curve are explained using the avoided crossing rules of valence bond model.     

二维有摩擦颗粒体系振动态密度与玻色峰的研究

利用颗粒离散元方法,研究了由2048个有摩擦的单分散圆盘颗粒组成的体系在各向同性压缩条件下,颗粒摩擦系数μ对颗粒体系结构与振动特性的影响.结果表明:固定压强下,随μ的增大,区分德拜标度与态密度平台的过渡频率ω*与玻色峰频率ωBP均向低频移动,玻色峰高度D(ωBP)/ωBP逐渐增加.主要原因是μ增大导致颗粒体系无序程度增加(平均配位数减小)而在ωω*处出现了大量额外模式.模式分析表明:低频(ω1.0)模式主要是以平动为主的混合模式,中频(1.0ω4.0)模式主要是以平动为主的混合局域化模式,高频(ω4.0)振动模式几乎为纯转动的局域化模式;并且随μ的增大,低频下平动模式更加局域化,同时低频转动模式的贡献也逐渐增加,暗示在高摩擦系数下低频转动模式产生更重要的影响.     

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.     

Dynamical Behavior of the Quant um Periodically Kicked Harmonic Oscillator

We explore the properties of the quantum kicked harmonic osciUation governed by the Hamiltonian H=1/2p²+1/2ω₀²x²-K cos x∑_n=-∞^∞δ(t/T - n): The classical version of this model is known to exhibit certain type of stochastic behavior. We reduce the quantum equation of the model td quantum mapping equations. Numerical results of the mappings show that the behavior of the average energy as a function of time depends on the ration of the frequency of the external (2π/T) and that of the unperturbed system wo. The energy increases first very rapidly and then the energy growth saturates for irrational ω₀T/2π. The break time is independent of the strength of the external force, but is roughly proportional to 1/ω₀T.For a fixed rational ω₀T/2πt,h e energy is damped oscillation for smaller T , a nd it is seemingly recurrent with time in the sense of Hogg and Huberman. In both cases, these behaviors of energy are independent of the strength of the external force and differ from the behavior of the quantum kicked rotator.     

矢量介子及其激发态的讨论

在Regge唯象下, 首先研究自旋-宇称多重态中六个介子质量间的关系式. 运用验证后的关系式, 重点计算基态矢量介子多重态(1³S₁)中尚未观测到的双重粲-底介子 B_c^*的质量. 还计算了径向激发态2³S₁多重态的介子质量和轨道激发态1³G₅介子九重态的质量. 根据计算结果结合实验数据和其他理论进行讨论, 建议在6355 MeV附近寻找和研究 B_c^*介子, 将 D(2600)和 D_s1(2700)分别作为主要成分为 nc(2³S₁)和 sc(2³S₁)的态进行研究; 分别在5812, 5917, 6896 MeV附近寻找矢量介子第一径向激发态 B^*(2S), B_s^*(2S)和 B_c^*(2S). 建议将 ω₅(2250)安排在1³G₅介子九重态的同位旋标量态, 实验上在2259 MeV附近进一步研究 ρ₅(2350)的性质, 在2438 MeV附近寻找和研究 φ₅(1³G₅). 研究结果对于相关介子的自旋-宇称安排和通过实 验寻找新的介子激发态具有重要的参考价值. 关键词： Regge唯象 矢量介子 质量谱     

极化检测型铷原子磁力仪的研究

针对交变弱磁场的检测,研制了一种基于极化-检测双光束结构的激光抽运铷原子磁力仪.为了获得该磁力仪对磁场的响应特性,通过数值仿真分析了信号幅度随极化磁场强度、弛豫时间的变化关系,并进行了实验验证.最后通过选择合适的极化磁场使磁力仪对待测磁场的灵敏度最大.实验结果表明,优化后磁力仪灵敏度为0.2pT/(Hz)~(1/2),响应带宽3.5kHz,可用于弱磁场磁共振、高频异常物理现象等信号的检测.