Kosterlitz-Thouless transition of the quasi-two-dimensional trapped Bose gas

We use quantum Monte Carlo methods to compute the density profile, the nonclassical moment of inertia, and the condensate fraction of an interacting quasi-two-dimensional trapped Bose gas with up to N ~ 5 x 10(5) atoms and parameters closely related to recent experiments. We locate the Kosterlitz-Thouless temperature T(KT) and discuss intrinsic signatures of the onset of superfluidity in the density profile. Below T(KT), the condensate fraction is macroscopic even for our largest systems and decays only slowly with system size. We show that the thermal population of excited states in the transverse direction changes the two-dimensional density profile noticeably in both the normal and the superfluid phase.     

Fluid in contact with semipermeable vesicle: second-order integral equation approach

Secondorder Ornstein–Zernike integral equations in conjunction with the Lovett–Mou–Buff–Wertheim equation for the density profile are used to investigate a mixture of hard spheres in contact with a semipermeable membrane of spherical symmetry. Theoretical predictions are compared with grand canonical Monte Carlo simulations for several parameters, and reasonable agreement has been found. The pair functions for the systems considered are also determined and discussed.     

一种新的光纤布里渊传感散射谱拟合方法

讨论了应用于光纤分布式布里渊传感散射谱最优化拟合的Levenberg-Marquardt(L-M)非线性最小二乘算法。分析并推导了一种可较好地反映入纤脉冲宽度越来越窄所引起的光纤分布式布里渊传感散射谱形状变化的Pseu-do-Voigt分析拟合模型。由调制脉冲光和调制器泄漏连续光共同作用所产生的光纤分布式布里渊传感散射谱应为Lorentzian型谱和Gaussian型谱的线性权重组合。Gaussian型函数部分可视为Lorentzian型函数谱的近似修正处理。基于L-M算法对光纤布里渊传感散射谱采样数据进行了曲线拟合和最优化参数估计,所得到的结果与理论分析情况吻合。     

Modal analysis of a continuous gyroscopic second-order system with nonlinear constraints

A method for the modal analysis of continuous gyroscopic systems with nonlinear constraints is developed. This method assumes that the nonlinear constraint can be expressed as a piecewise linear force-deflection profile located at an arbitrary position within the domain. Using this assumption, the mode shapes and natural frequencies are first found for each state, then a mapping method based on the inner product of the mode shapes is developed to map the displacement of the system between the in-contact and out-of-contact states. To illustrate this method, a model for the vibration of a traveling string in contact with a piecewise-linear constraint is developed as an analog of the interaction between magnetic tape and a guide in data storage systems. Five design parameters of the guide are considered: flange clearance, flange stiffness, symmetry of the force-deflection profile in terms of flange stiffness and offset, and the guide's position along the length of the string. There are critical bifurcation thresholds, below which the system exhibits no chaotic behavior and is dominated by period one, symmetric behavior, and above which the system contains asymmetric, higher periodic motion with windows of chaotic behavior. These bifurcation thresholds are particularly pronounced for the transport speed, flange clearance, symmetry of the force deflection profile, and guide position. The stability of the system is sensitive to the system's velocity, and, compared to stationary systems, more mode shapes are needed to accurately model the dynamics of the system.     

Negative differential conductivity in quantum well with complex potential profile for electron–phonon scattering

The effect of phonon scattering on electrical conductivity (EC) of 2D electron gas in quantum well (QW) systems with a complicated potential profile is described. Dependence of QW electrical conductivity on QW parameters (such as QW width, Fermi level positions etc.) when phonon scattering is employed has been calculated. NDC in EC when it varies with width of the QW has been found.     

Gravity with Extra Dimensions and Dark Matter Interpretation: Phenomenological Example via Miyamoto–Nagai Galaxy

Any connection between dark matter and extra dimensions is revealed by the effective energy-momentum tensor associated with the theory. In order to investigate and test such a relationship, we examine a higher-dimensional space–time endowed with a factorizable general metric with a configuration such that its density profile coincides with the Newtonian potential for disk galaxies. An appropriate solution representing stratifications of mass in the central-bulge and disk part of galaxies, e.g., the Miyamoto–Nagai ansatz, is used to solve the Einstein equations. We compute the stable rotation curves of such systems and, with no adjustable parameters, accurately recover the observational data for flat or not asymptotically flat galaxy rotation curves. We present examples of density profiles and compare them to the profile obtained from purely Newtonian potentials.     

Lineshape analysis of the J = 3 ← 2 and J = 5 ← 4 rotational transitions of room temperature CO broadened by N2, O2, CO2 and noble gases

Collisional relaxation has been considered for millimeter lines of carbon monoxide at room temperature. Accurate measurements of carbon dioxide- and rare gases-broadened widths have been performed on the J = 3 ← 2 rotational line of ¹²CO by using a video-type spectrometer. Measurements of nitrogen-, oxygen-, and xenon-broadened widths of the J = 5 ← 4 rotational line of ¹³CO were also carried by using a frequency-modulated spectrometer. A lineshape study performed on all the investigated binary systems provide confirmation that Voigt profile is not a suitable model to analyse experimental lines in the millimeter-waves region. On one hand, using this profile in the low pressure range, i.e. in the Doppler regime, the retrieved collisional linewidths do not follow a linear variation with the perturbing gas pressure. On the other hand, regardless of the pressure, lineshapes exhibit a narrowed profile. An accurate analysis of the pressure dependence of relaxation rates show that the Galatry profile is not appropriate and that experimental lineshapes are actually Speed Dependent Voigt profiles. Accurate broadening parameters were retrieved from this profile and compared to previous reported values and predictions calculated from the Robert-Bonamy formalism. Finally a variation of the ratio of relaxation speed dependence to broadening parameters versus relative masses of the collision partners is presented.     

玻璃表面层对薄膜光学参数测量的影响

利用p偏振光在镀膜平板玻璃前后表面反射光强比γ与膜层光学参数之间的密切关系,给出了玻璃表面层的光学参数分布。对典型的薄膜系统-单面镀膜与双面镀膜两种情况,理论分析了玻璃表面层对薄膜光学参数测量的影响。实验上对PMTES和SnO₂薄膜参数进行了测量,仅当计及玻璃表面层作用时,反射光强比γ的角度调制曲线才与理论拟合结果相吻合.     

Evolution of the vortex and the asymmetrical parts of orbital angular momentum in separable first-order optical systems

We analyze the evolution of the vortex and the asymmetrical parts of orbital angular momentum during its propagation through separable first-order optical systems. We find that the evolution of the vortex part depends on only parameters a(x), a(y), b(x), and b(y) of the ray transformation matrix and that isotropic systems with the same ratio b/a produce the same change of the vortex part of the orbital angular momentum. Finally, it is shown that, when light propagates through an optical fiber with a quadratic refractive-index profile, the vortex part of the orbital angular momentum cannot change its sign more than four times per period.     

Determination of Plasma Density Profile and Other Parameters of Cylindrical Plasma Columns with an Electroacoustic Probe

A new diagnostic method based on the excitation of thermal resonances using an electroacoustic probe has been developed to determine the electron density profile and other plasma parameters of a cylindrical warm-plasma column. A coaxial electroacoustic probe is used to excite and detect the dipole and thermal resonances as the plasma density is varied. The electron density profile is expressed functionally in terms of unknown profile parameters. The profile and other parameters of the plasma column are then determined numerically based on some theoretical formulas and experimental results.     

Application of the method of smooth perturbations to the solution of problems of optical tomography of strongly scattering objects containing absorbing macroinhomogeneities

Monochromatic small-angle Fraunhofer diffraction from a spiral is studied as a function of its stretching. A simple relation between locations of the principal maxima and geometrical parameters of a spiral is obtained. Diffraction from a spiral is analyzed theoretically in the linear approximation of the boundaries of the profile of a periodic unit. An analytical expression for the light intensity at any point of a screen is derived, and analytical relations between locations of the principal maxima and geometrical parameters of a spiral, which are identical to the relations established experimentally, are obtained. The possibility for utilizing the results obtained in the development of systems of automatic control of the main geometrical parameters of spiral objects in the process of their production is demonstrated by the example of the analysis of diffraction patterns from a standard metallic screw and a twisted capron fiber.     

Approximate solutions of radiative transfer in one-dimensional non-planar systems

An approximate method is developed for the study of radiative transfer in one-dimensional, non-planar systems. While this method can be regarded as an extension of some existing approximation techniques formulated for the one-dimensional planar problem, it does yield closed-form expressions for the radiant heat flux and the temperature profile for various non-planar problems, which have not been established before. Comparisons with the available numerical results show that the heat-flux expressions are accurate throughout the entire range of the optical thickness. Results for the temperature profile. however, have the same limitation as the various closed-form approximate solutions for the planar problem. They are not very accurate at regions near the boundary, except in the optically thick limit. Based on the closed-form expressions obtained for the non-planar radiative transfer problem, the present work establishes readily the effect of the various parameters, such as the optical thickness, the surface emissivity, the radius ratio and the heat-generation rate on the heat-transfer and the temperature profile. Differences between radiative heat-transfer characteristics of the two basic non-planar systems (concentric cylinders and concentric spheres) are discussed.     

Effective method of characterization of the phase and intensity profiles of asymmetrically distorted light pulses in optical fiber systems

We address the problem of characterization of light pulses that propagate in long-haul high-bit-rate optical communication systems, under strongly perturbed conditions. We show that the conventional technique for characterization of the phase and intensity profile of such pulses becomes qualitatively inconsistent when the pulse’s profile is asymmetrically distorted with respect to its center-of-mass. We resolve these inconsistencies by partially reformulating the conventional technique by means of appropriate pulse parameters, which we call upgraded parameters, which allow a fair characterization of the intensity and phase of all types of light pulses, including those which are asymmetrically distorted. We illustrate the effectiveness of the upgraded parameters by applying them to a meticulous characterization of light pulses in a dispersion-managed optical fiber system in which third-order dispersion is acting as a strong perturbation.     

Definition and measurements of high-power laser beam parameters

Three definitions of the beam quality, characterized by waist radius and far-field divergence, of high average power laser beams are investigated. The beam parameters can be defined by their second moments, the power content profile and the power content area. The methods of measurement are described in detail and compared with respect to their suitability for two high-power laser systems: a cw Nd:YAG-rod laser and an annular system. The validity of theABCD law was checked experimentally. Additionally, third and fourth-order intensity moments were used to characterize the laser field in more detail.     

On a certain energy relationship for waves in systems having traveling parameters

A relationship is derived that couples the total energies and frequencies of quasimonochromatic wave packets that propagate in linear systems having parameters that vary in time and space according to the law governing a traveling wave having an arbitrary profile.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 15, No. 1, pp. 51–54, January, 1972.The author thanks N. S. Stepanov for raising the problem and his help with the work, and likewise M. A. Miller and L. A. Ostrovskii for their helpful comments.     

Spectral selectivity of radiation-and tunnel-coupled waveguide structures

The spectral transmission profile of systems of radiation-and tunnel-coupled waveguides is studied. It is determined how a smooth variation of the thickness of the buffer layer in a structure consisting of a pair of tunnel-coupled waveguides with strongly varying parameters will affect the spectral properties of the system as a whole. A simple physical treatment of the operation of a number of integrated and fiber-optic devices is given, and the prospects for using the proposed structure of two tunnel-coupled waveguides to realize a microlaser with waveguide output is demonstrated. Zh. Tekh. Fiz. 67, 59–65 (February 1997)     

高功率激光光学元件面形参数表征

 针对神光-Ⅲ原型装置使用的光学元件,基于国内光学元件加工现状,结合空间频段的概念,对高功率固体激光驱动器所需光学元件不同的面形评价参数进行了阐述。结合对激光远场焦斑的影响,对面形评价参数的重要性进行了举例说明。提出了面形的综合评价方式,全面界定面形各项评价参数,对光学元件的评价具有一定的参考价值。     

强烈段塞流特征参数测量方法试验研究

通过对单个液塞经过管道上某一测压点时的压力信号进行理论分析,指出了压力波动曲线上的特征点与液塞相对于测压点位置之间的对应关系。根据分析结果,采用单压力信号判断法,求得了强烈段塞流的液塞运动速度、液塞长度等特征参数。与利用双平行电导探针相关法求得的结果比较发现,单压力信号判断法具有测量结果准确、不受流动介质物性限制、不干扰流场、简便实用等优点。