Helium-3 adsorption refrigerator cooled with a closed-cycle cryocooler

A helium-3 adsorption refrigerator cooled with a pulse-tube cryocooler is developed. The refrigerator has two stages of adsorption pumping. The first stage is designed for the condensing and pumping of helium-4, whose cooling capacity is used for the condensation of helium-3. The second stage is designed for pumping helium-3. The final temperature reached by the refrigerator is 0.305 K. This temperature is retained for at least 24 h. The time required for helium recondensation and the obtainment of low temperature is 1.5 h. The cryostat is a self-contained instrument, as it contains no external gas-supply pipelines and the working gas is stored directly within the working volume of the refrigerator. The work is performed in the Frank Laboratory of Neutron Physics of the Joint Institute for Nuclear Research.     

基于复合干涉的光纤低相干干涉传感系统研究

研究一种能够进行远程及绝对测量的光纤低相干干涉传感系统。该系统包含两个光纤干涉仪,其中一个光纤干涉仪置于被测场中感应被测量的变化,可实现远程测量;另一个光纤干涉仪解调被测量的值。运用波分复用技术,使用于解调的光纤干涉仪同时工作于低相干干涉和高相干干涉状态。用低相干干涉信号决定被测量的幅值,对被测量实现绝对测量,并使测量量程不受波长限制;同时,用高相干干涉信号对被测量进行高精度的测量。系统的测量量程为6mm,测量分辨率小于1nm,位移实验结果的线性相关系数R为0.99。     

氢化物发生ICP-AES法同时测定纯净水中的砷和汞

本文建立了氢化物发生ICP－AES法同时测定纯净水中砷和汞的方法,检出限分别为As1.7ug/L-Hg0.1ug/L,方法精密度（RSD）为As 3.46%,Hg2.85%,回收率为As92%-110%,Hg90-113%。     

INHOMOGENEOUS WAVES IN ANISOTROPIC POROUS LAYER OVERLYING SOLID BEDROCK

The problem of propagation of inhomogeneous waves in anisotropic porous layered medium is studied using transfer matrix. Firstly, transfer matrix for an anisotropic porous layer is derived. Biot's poro-elastic theory is incorporated to model the acoustics of anisotropic porous layer. The interface between porous layer and elastic half-space is considered as imperfect and modified boundary conditions are applied for this more realistic situation. The theory of transfer matrix is used to derive the analytical expression for the surface impedance. Numerical computation of results is done for different degrees of bonding in the low as well as high-frequency range. In the first case, which is relevant to geophysical studies, the surface impedance is predicted for low-frequency range and surface impedance for second model is computed in high-frequency range. It is observed that loose bondedness is accompanied by the loss of energy at the interface. The technique of transfer matrix is utilized to compute the surface impedance in both cases. The role of surface impedance in seismological studies and in the study of composites is discussed.     

自治广义Birkhoff系统的平衡稳定性

研究广义Birkhoff系统的平衡稳定性问题.建立了自治广义Birkhoff系统的平衡方程;给出了自治广义Birkhoff系统的一次近似方程,利用Lyapunov一次近似理论,建立了系统平衡状态稳定性的判据;构建了Lyapunov函数,利用Lyapunov直接法,建立了自治广义Birkhoff系统平衡状态稳定性的判据.给出了若干算例以说明结果的应用.     

Optimization of self-frequency doubling in periodically and quasi-periodically poled nonlinear crystals

The theory of self-frequency doubling in a periodically poled nonlinear crystal is generalized to the case of varied domain thickness (quasi-periodically poled crystals). A particular statistical model of quasi-periodicity is considered. The effect of quasi-periodicity on the output emission intensity is calculated. The degree of quasi-periodicity allowable for practical applications is estimated, and the advantages of quasi-periodically poled crystals are discussed. The problem of maximization of the output emission intensity for periodically and quasi-periodically poled crystals is considered. The dependence of the output emission intensity on the crystal length is investigated, and an upper estimate for the maximum intensity is obtained. A formula for the optimal reflection coefficient of the output mirror as a function of the crystal length is derived.     

Microscopic derivation of fluctuation formulas for calculating dielectric constants by simulation

A microscopic derivation using the average Maxwell electric field is given for fluctuation formulas for the dielectric constant of a simulation sample for both periodic and reaction field boundary conditions. The reaction field case is for a spherical cavity reaction field. The derivations put both boundary conditions on an equal footing of microscopic theory and the only nonrigorous part of the derivation is the assumption that the region used to average the electric field is large enough. The fluctuation formula for reaction field boundary conditions is rather different from that used heretofore. The method is applied to a subregion of an isolated spherical system.     

Beyond Einstein's radiation theory

Einstein's radiation mechanism is generalized to account for the possibility of population inversion by placing a nonlinear bound on the growth of an unstable perturbation. The nonstationary linear mechanism of relaxation to blackbody radiation below threshold is studied. The nonstationary photon distribution is the negative binomial distribution, and casting it as a law of error, for which the most probable value is the mean value, gives the expression for the statistical entropy. The second law yields a nonequilibrium generalization of Planck's radiation law. The nonlinear mechanism leading to the transformation from the negative binomial probability distribution, for chaotic light, to a Poisson probability distribution, for coherent light, is then analyzed. A criterion for lasing is given in terms of the chemical potential of radiation which is compared to the inequality for the transition from quantum to classical statistics.     

Optical conductivity of solitons in polyacetylene

The soliton lattice solution of the continuum model for polyacetylene is used to derive the frequency dependent conductivity of charged solitons. The limit of low soliton density is explicitly evaluated and shown to be free of singularities. The conductivity sum rule is proven for the model Hamiltonian, and is shown to be satisfied by the explicit solution. Implications for polyacetylene and for TTF-TCNQ are discussed.     

Influence of periodie and random two-dimensional nuclei distribution on the recrystallization kinetics

The recrystallization process is modeled by using both a periodic lattice and a random array of nuclei for the two-dimensional, instantaneous nucleation case. Recrystallization kinetics is obtained with analytical expressions for the periodic model and computer-generated results for the random situation. The resulting kinetics shows some disagreement with the classical Johnson-Mehl-Avrami-Kolmorogav kinetics, and stresses the fact that there is a finite time for the completion of the whole process. The time for completion is calculated for the two-dimensional and three-dimensional cases.     

Solvability condition in multi-scale analysis of gyroscopic continua

The solvability condition is investigated for the method of multiple scales applied to gyroscopic continua. The general framework of the multi-scale analysis is proposed for a linear gyroscopic continuous system under small nonlinear time-dependent disturbances. The solvability condition is derived from the properties of the systems. The condition holds only for appropriate boundary conditions. The appropriateness of the boundary conditions can be examined for unperturbed linear systems. An example is presented to highlight the requirements on the boundary conditions.     

耦合双原子Jaynes-Cummings模型的腔场谱H

研究了处于激发态的两原子与高Q腔场相互作用单光子过程的腔场谱,给出了初始光场为光子数态、相干态、压缩真空态时的腔场谱数值计算结果,分析了原子间偶极-偶极相互作用强度gα对腔场谱结构的影响.发现真空场Rabi峰,当gα较弱时为4峰,gα较强时为3峰结构;弱场数态(n＞0)时为5峰,强场时为3峰结构.相干态和压缩真空态时,谱结构与光子数分布有关,一般为复杂的多峰结构.结果表明,gα对峰位峰高都有影响,破坏了谱结构的对称性,但这种影响只在真空场和弱场时才较明显.     

The quantum electrodynamics of the nucleon

The Nuclear Force between a statistical assemblage of nucleon pairs is calculated directly for pseudo-scalar meson exchange. The Nucleon (proton) is treated as a particle with an extended structure. The model of the proton used is the one determined by high energy electron-proton scattering experiments.The self-energy process for such a proton is examined first for the emission and re-absorption of a photon. An appropriate photon propagator is derived for such a system using variational techniques. It is shown that the integrals that occur in the self-energy process converge without any of the difficulties associated with the point charge model. This shows the divergences in Quantum Electrodynamics (for nucleons) do not exist when nucleons are treated as particles with a structure.The pseudo-scalar meson propagator is derived using similar methods and the exchange force is calculated. It is shown that only certain diagrams need be considered when a stable nuclear bond is being calculated. The corrections to the Nuclear Force, which are self-energy processes involving emission and re-absorption of Virtual pseudoscalar mesons, are shown to converge for strong coupling.     

KBA显微镜成像系统的成像模拟及X光成像实验的研究

KBA显微镜是一种非轴对称、非共轴的掠入射成像系统。其结构复杂,调节精度要求很高,在实际成像实验操作中难以掌握其成像特性。利用光学设计软件模拟其成像,对系统的调节和成像分析提供有益的参考。利用光学设计软件ZEMAX模拟了KBA显微镜对点源的成像过程,给出了KBA显微镜成像系统的焦深约为1 mm,景深为50 mm左右。并且由模拟可知,掠入射角对成像的影响很大。对像素尺寸约10μm的探测设备,模拟得出KBA成像系统的空间分辨力上限为3μm左右。基于星光Ⅱ装置对周期为20μm的网格靶成像,获得了KBA显微镜较为清晰的X光图像。该项工作为进一步开展掠入射成像系统的研究奠定了基础。     

Rigid piston approximation for computing the transfer function and angular response of a fiber-optic hydrophone

The transfer function of a fiber-optic hydrophone (FOH) is computed for various fiber core radii. The hydrophone is modeled as a rigid disk, with plane waves impinging at normal or oblique incidence. The total sound field is written as the sum of the incident field and the field diffracted from the hydrophone. The diffracted field is approximated by the field generated by a vibrating planar piston in an infinite rigid baffle. For normal incidence and a pointlike fiber core, an analytical solution is presented. For finite fiber core radii, and for oblique incidence, the transfer functions are computed numerically. The calculated transfer functions exhibit an oscillatory frequency dependency that is most pronounced for small fiber cores. The solution for a core radius of 2.5 microm can be very well approximated by the analytical solution for a pointlike core at frequencies of up to 30 MHz. The results for normal incidence can be directly employed to deconvolute ultrasonic pressure signals measured with an FOH. From the transfer functions for oblique incidence, the angular response of the hydrophone is calculated. The angular response obtained here differs significantly from the model commonly used for piezoelectric hydrophones. The effective hydrophone radius derived from the angular response shows a strong frequency dependency. For low frequencies, it is found to be larger than the outer fiber radius, whereas it generally lies between the outer radius and the fiber core radius for frequencies above 10 MHz.     

Propagation of a spatial soliton in a system of tunneling-coupled optical waveguides with a variable coupling coefficient

The problem of the propagation of a spatial soliton in a system of tunneling-coupled optical waveguides is studied. The tunneling coupling coefficient is assumed to be modulated in a transverse direction. The adiabatic dynamics is studied for the case of periodic modulation of the tunneling coupling coefficient. The stationary points for the beam parameters are found. The effective potential is calculated for the center of the beam in the equivalent-particle model. The condition for resonance emission of waves by a soliton is obtained. Zh. Tekh. Fiz. 68, 1–4 (June 1998)     

Exact formulae for the electrical resistivity

The theory of exact formulae for the electrical resistivity is reviewed. The derivation of an exact formula for the resistivity and the proof of the equivalence of this formula with the linear response formula for the electrical conductivity are presented. One form of the resistivity formula is evaluated in the limit of weak scattering. The model for this calculation is a system of non-interacting free electrons scattered by random fixed impurities. It is shown that the evidence which suggested that the resistivity formula is simpler to evaluate than the conductivity formula is misleading.     

1H pulse NMR analysis of silane-treated layers on glass fiber surfaces

The surface treatment of a glass fiber using mercapto-functional silane coupling agent having a di- or trialkoxy group has been studied. The surface of silane-treated fiber is observed by scanning electron microscopy. The treated layer looks hard like glass for the trialkoxy silane-treated, whereas it looks soft for the dialkoxy silane-treated. Molecular mobility of the treated layer is analyzed by ¹H pulse nuclear magnetic resonance spectroscopy. The amount of silane loading increases with increased silane concentration in the treatment solution. The relaxation time for the surface layer is longer for the dialkoxy structure than for the trialkoxy structure. The silane chain is flexible in the dialkoxy structure, but is rigid for the trialkoxy structure, independent of the loading amount of silane. The relaxation behavior for the mixture of the di- and trialkoxy structures is between those of the pure dialkoxy and trialkoxy structures and depends on the mixing ratio. The network density of silane chains on the glass fiber can be controlled by varying the mixing ratio of the di- and trialkoxy compounds.