二氧化硅气凝胶的防爆震性能及机理研究

利用聚偏二氟乙烯压电传感器研究了爆炸加载下冲击波在二氧化硅气凝胶中的传播特性,并对冲击波在二氧化硅气凝胶和泡沫铝中的传播特性进行了比较.结果表明:在二氧化硅气凝胶中冲击波的强度随传播距离的增加呈现指数衰减的趋势.冲击波在二氧化硅气凝胶中衰减比在泡沫铝中衰减明显.由于二氧化硅气凝胶内部特殊的纳米多孔网状结构,导致冲击波在二氧化硅气凝胶中的衰减效果较好.冲击波在二氧化硅气凝胶中的传播速度极低,因此冲击波在二氧化硅气凝胶中传播时卸载波的追赶卸载效应非常明显,这又进一步促进了冲击波的衰减.     

Belousov-Zhabotinsky反应体系中的波与稳定性

我们在Oregonator模型的基础上,取速率常数k₆、理想配比系数f及波数k为参变量,首先讨论了B-Z反应体系的稳定性,并得到了下列各量的表达式:空间周期结构的临界速率常数k₆^c、短波临界波数k_s^c与长波临界波数k_L^c,时空周期结构的临界速率常数k₆^c及临界波数k_c等。而后,我们给出了B-Z反应体系的临界频率λ_c,讨论了体系在临界状态附近的行为,并得到了触发波速度u_T及相位波速度u_P的表达式。本文的结论是,在一定条件下,不搅拌的B-Z反应体系能在临界状态附近呈现稳定的波群或者波包,触发波是均匀体系中的波包,相位波是有微小梯度的非均匀体系中的波包。u_T=2ηDk_c,D为HBrO₂的扩散系数,η为[H⁺]的缓变函数(在实验观测范围内,η≈0.1);u_P=v,v为相速度。 关键词：     

Vector soliton of self-induced transparency of a generalized love wave

A theory of acoustic self-induced transparency of a two-component vector soliton for a generalized Love wave is constructed. The three-layer system contains a resonance transition layer with paramagnetic impurity atoms or quantum dots. It is shown that, under these conditions, a vector soliton of the generalized Love wave can be formed. It oscillates at the sum and difference frequencies in the vicinity of the carrier wave frequency. Explicit analytical expressions for the parameters of a nonlinear surface acoustic wave are presented. The parameters depend on the elastic properties of the contacting media, the resonance transition layer, and the transverse structure of the wave. Numerical calculations are carried out for the three-layer Al₂O₃/ZnO/SiO₂ system. The significant difference between the two-component vector soliton and singlecomponent soliton is shown.     

等离子体波在喇曼自由电子激光中的作用

本文用参量放大器模型,分析了喇曼型自由电子激光中等离子体波的作用。结果表明,在忽略电子束初始横向速度的情况下,慢等离子体波与散射波耦合的必要条件为k_wv₂₀>ω_c,即电子的平衡态运动应处于第一组轨道。文中还求出散射波的色散特性和增益公式,以及散射波与等离子体波的相位匹配关系。 关键词：     

神经元网络中分布式电流诱导靶波机理研究

以四变量的Hodgkin-Huxley神经元模型构建规则网络来研究分布式电流刺激诱导靶波问题. 在一个二维规则网络的局部方形区域输入恒定刺激电流I₁, 其余区域结点上的神经元输入刺激电流I₂ 来刻画分布式电流. 分别研究了耦合强度、刺激电流I₁作用区域(受控神经元个数)、 分布式电流梯度(ΔI=I₁-I₂)对靶波形成的影响. 研究发现: 刺激的区域越小, 需要的电流梯度(ΔI)越大; 耦合强度越大, 诱导靶波所需要的电流梯度(ΔI)也越大. 最后讨论了分布式电流作用和靶波的形成机理. 进一步研究发现, 诱导的靶波对通道噪声有较强的抗干扰性. 关键词： 靶波 神经元网络 分布式电流     

Selective Alignment of D2 Induced by Two Ultrashort Laser Pulses

通过求解D₂分子在飞秒激光场中的含时薛定谔方程,研究了室温下D₂分子在超快飞秒激光驱动下的的转动波包动力学. 选择用第一束超短飞秒脉冲与温度为300 K的D₂分子系综相互作用产生一个相干转动波包,用第二束超短飞秒脉冲在波包的1/4和3/4恢复周期选择操纵D₂分子取向. 研究结果表明,通过选择两束超短飞秒脉冲的延迟时间,可以有效控制D₂分子转动波包中奇偶态的相对布居,从而选择性的控制D₂分子取向.     

Coexistence of superconductivity and magnetic order

The microscopic theory of simple antiferromagnetic superconductors is extended to structures where the magnetic order is described by a spin-density wave. For the case where the magnetic system is inherently ferromagnetic, the free energy of the combined system is minimized with respect to the amplitude and the wave vector of the spin-density wave. It is found that the wave vector depends very weakly on temperature. We apply the theory to the coexistence region in ErRh₄B₄, finding a first-order re-entry transition.     

Si中深能级T2对称波函数理论

木文在文献[5,6]所发展的在位缺陷势格林函数方法基础上,进一步讨论Si中短程缺陷势引入的T₂对称深能级波函数性质。第一次给出了Si禁带中部很宽能量范围之内T_2对称波函数的完整数据。波函数在缺陷最近邻四个格点的占据几率P₁有一高达50％以上峰值。该部分相当于四个最近邻格点指向缺陷的杂化轨道准悬键的T₂组合。第0,1,2三个格点壳层波函数占据几率之和约为70％。波函数其余部分较平缓地分布在一相当大空间。波函数的以上特征与禁带中部能量位置关系不灵敏。但在靠近导带E_c和满带E_v的浅能量区,以上P₁峰趋于消失,整个波函数在空间的分布趋于平坦。Si空位在禁带引入一个T₂对称深能级,位于E_v以上0.51eV处。 关键词：     

Quantum spin dynamics of the bilayer ferromagnet La Sr Mn O

We construct a theory of spin wave excitations in the bilayer manganite La_1.2Sr_1.8Mn₂O₇ based on the simplest possible double-exchange model, but including leading quantum corrections to the spin wave dispersion and damping. Comparison is made with recent inelastic neutron scattering experiments. We find that quantum effects account for some part of the measured damping of spin waves, but cannot by themselves explain the observed softening of spin waves at the zone boundary. Furthermore a doping dependence of the total spin wave dispersion and the optical spin wave gap is predicted. Received 15 January 2002 Published online 6 June 2002     

Growth of discontinuities in chemically reacting relativistic fluids

A relativistic theory is developed to study the growth of weak discontinuities propagating in a chemically reacting fluid mixture. The velocity of propagation is determined, which fully agrees with classical results in the nonrelativistic limit. The growth equation for the wave propagation in relativistic fluid flows with nonequilibrium effects is obtained and solved. The wave amplitude is determined as a function of time. The relativistic and relaxation effects on the global behavior of the wave amplitude are studied analytically. It is concluded that if the wave is of a compressive nature and its initial amplitude is greater than a critical value, then the discontinuity grows until it develops into a shock wave after a finite critical timet _c . But on the other hand if the initial wave amplitude is less than the critical one, the wave decays and damps out ultimately. It is shown that both relativistic and relaxation effects help in stabilizing the wave propagation by increasing the critical timet _c for the breakdown of the wave due to nonlinear steepening.     

Complex singularity of a stokes wave

Two-dimensional potential flow of the ideal incompressible fluid with free surface and infinite depth can be described by a conformal map of the fluid domain into the complex lower half-plane. Stokes wave is the fully nonlinear gravity wave propagating with the constant velocity. The increase in the scaled wave height H/λ from the linear limit H/λ = 0 to the critical value H _max/λ marks the transition from the limit of almost linear wave to a strongly nonlinear limiting Stokes wave. Here, H is the wave height and λ is the wavelength. We simulated fully nonlinear Euler equations, reformulated in terms of conformal variables, to find Stokes waves for different wave heights. Analyzing spectra of these solutions we found in conformal variables, at each Stokes wave height, the distance ν _c from the lowest singularity in the upper half-plane to the real line which corresponds to the fluid free surface. We also identified that this singularity is the square-root branch point. The limiting Stokes wave emerges as the singularity reaches the fluid surface. From the analysis of data for ν _c → 0 we suggest a new power law scaling ν _c ∝ (H _max ? H)^3/2 as well as new estimate H _max/λ ? 0.1410633.     

Temperature-electric field hysteresis loop of multicaloric effects in PbZr0.8Ti0.2O3 thin films

The Multicaloric effect in the PbZr_0.8Ti_0.2O₃ thin films is investigated with the application of sine wave electric field, dc electric field and stress using a phase field method combined with the thermodynamic analysis. The simulation results show that the adiabatic temperature change-electric field curve presents a shape of butterfly in the presence of the sine wave electric field. In order to detect the effect of the sine wave electric field, the multicaloric effect and the domain structures under the direct electric field and the sine wave electric field are compared. It is found that the domain switching behaviors are quite different under the different applied electric fields. And the negative multicaloric effect in the PbZr_0.8Ti_0.2O₃ thin film is attribute to the domain switching under the external field.     

Determination of spatial characteristics of the chain reaction wave in silver azide

The paper presents the methodology and results of determination of the spatiotemporal characteristics of the solid-state chain reaction wave in silver azide, initiated by a neodymium laser pulsed. The wave’s leading front width at half maximum is l ₁ = (110 ± 10) μm, the wave’s rear front width at half maximum is l ₂ = (120 ± 20) μm. The spatiotemporal parameters of the reaction wave in silver azide whiskers are calculated using a phenomenological model of the process previously proposed by the authors. It is shown that the calculated values of the velocity and the wave front width are consistent with the available experimental data.     

Mode selection of Lamb waves for the evaluation of solid plates with liquid loading

This paper studies the mode selection of Lamb waves for evaluating solid plates with liquid loading. For this purpose, the Lamb wave selected should have the features such as zero normal displacement components at the plate surface in contact with liquid, small dispersion, and maximum group velocity. It is found that when the phase velocity of Lamb wave is equal to the longitudinal wave velocity of the plate material, its normal displacement at the plate surface is always zero. Through the numerical analyses, the specific S₂ Lamb wave that has zero normal displacement component at the plate surface, small dispersion and maximum group velocity compared with the other Lamb waves has been found. With respect to the specific S₂ Lamb wave, some experimental examinations have been carried out. It is found that the liquid loading on the plate surface has less influence on the specific S₂ Lamb wave signal but it can effectively eliminate the other signals. Moreover, the specific S₂ Lamb wave selected exhibits the capability of detecting multiple defects in the solid plate with the liquid loading. It can be concluded that the specific S₂ Lamb wave selected is suitable for the evaluation of solid plates with liquid loading.     

对SU3波函数的讨论

本文详细地讨论了Elliott引入的SU₃波函数Ψ(α(λμ)KLM)=(2L+1)/(C(λμKL))∫x_Ω(a(λμ)K)×D_MK^L(Ω)dΩ的若干性质。利用SU₃群的无穷小算子的对易关系,可以较容易地求出“内部态”波函数x(α(λμ)K)的表达式,并由此求出了波函数Ψ(α(λμ)KLM)的母分数系数(f·p·c.)。作为例子,本文还计算出了sd壳中有两或三个核子的SU₃波函数Ψ(α(λμ)KLM)。     

Spontaneous initiation and development of hydrogen–oxygen detonation with ozone sensitization

This work studies numerically the spontaneous initiation and sustenance of a detonation wave from a hot spot with a nonuniform initial temperature embedded within an H₂O₂ mixture with and without O₃ addition. For the case with either no or just a small amount of O₃ addition, a weak reaction wave is auto-ignited at the hot spot, accelerates and then transitions to a pulsating detonation, which propagates along the temperature gradient and quenches as it runs into the cold fresh mixture. However, with increasing O₃ addition, the possibility of sustenance of a developing detonation within the gradient is significantly enhanced as it enters the cold mixture. Furthermore, the reduced induction time by O₃ addition leads to earlier appearance of the spontaneous reaction wave and detonation formation in the cold mixture, demonstrating that quenching of the detonation is largely related to the instability property of the mixture because the shortened induction time reduces substantially the instability. It is also noted that, for 5%O₃ addition, a low-temperature flame produced by the O₃ reactions is present in front of the spontaneous reaction wave, inducing a local pressure wave, which facilitates spontaneous initiation and sustains the detonation entering the cold mixture. Moreover, O₃ addition renders the critical temperature to induce the minimum spontaneous wave speed higher than the crossover temperature, while they are very close for the case without O₃.     

Effect of a liquid on the characteristics of antisymmetric lamb waves in thin piezoelectric plates

The effect of a perfectly elastic nonviscous nonconducting liquid on the characteristics of a zero-order antisymmetric Lamb wave (the A ₀ wave) in a 128YX LiNbO₃ plate, whose thickness is small compared to the wavelength, is studied both theoretically and experimentally. A method for calculating the velocity and attenuation of this wave depending on the value of the parameter hf (h is the plate thickness and f is the wave frequency) is proposed. In addition, the characteristics of an A ₀ wave in a piezoelectric plate that is in contact with two different perfectly elastic nonviscous nonconducting liquids on its two sides are investigated. A possibility for the development of a proximate analyzer of liquids on the basis of such a structure is indicated.     

MAPW calculation of the anisotropic positron annihilation in copper

The wave function ψ_? of a positron in Cu is calculated using the MAPW (modified augmented plane wave) method. This method, taking into account the correct symmetry of ψ_? inside the atomic polyhedron and yielding the appropriate behaviour near the nucleus, leads to rapidly converging results. The Hartree potential seen by the positron is constructed from the electronic wave functions determined by the MAPW method. It is found that the lowest eigenstate of the positron is a Γ₁ state. In a provisional calculation, the matrix elements describing the two-quantum angular distribution of positron annihilation radiation are computed using recent MAPW electron wave functions. Good agreement with the measured anisotropic positron annihilation is found.     

激波作用下SF6气泡界面演化和射流发展的数值模拟

 数值研究了平面激波冲击氮气环境中SF₆气泡界面的Richtmyer-Meshkov不稳定性,重点关注其中的激波聚焦及射流的产生和发展过程。在入射激波马赫数为1.23的情况下,给出了压力、密度、数值纹影和涡量等物理量的演化图像,定量分析了流场中压力最大值、密度最大值、射流速度、环量和斜压力矩随时间的变化关系。计算结果表明,平面激波冲击SF₆气泡过程有很强的聚能效应,在气泡内部靠近下游极点处发生激波近似理想聚焦和点爆炸现象,直接导致出现二次波系以及向下游运动的细长射流结构。相比入射激波,二次波系产生斜压力矩和涡量的能力要弱得多。     

Interaction of a Defect Density Wave With a Modulated Structure in Incommensurate-Phase Crystals

Experimental and theoretical studies of the optical birefringence increment in the transition and metastable states of the incommensurate phase of Rb₂ZnBr₄, [N(CH₃)4]₂MeCl₄ (Me = Zn, Cu, Fe) crystals have been made. It has been established that in the modulated structure field a defect density wave is formed. It has been shown that when the period of the defect density wave coincides with the period of the modulation wave, the region of existence of the metastable state expands; when the periods of these waves do not coincide, their superposition occurs, with the formation of a wave with a difference value of the modulation vector. The presence of defect density waves in the incommensurate phase leads to a temperature hysteresis and kinetics of the physical quantities in the vicinity of T_c. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 5, pp. 632–639, September–October, 2005.