Propagation of a magnetic insulation wave in a vacuum line with a bias current

An analytic model is developed and numerical simulation is performed for the operation of a vacuum coaxial line with a bias current. The results of computations make it possible to determine the bias current preventing electron leakage at the front of an incident voltage wave and to predict the ??hot?? line impedance. This model forms the basis of the method for determining the voltage across a vacuum load with the help of a short-circuited coaxial line with a bias current.     

Dynamics of a single vortex line in a Bose-Einstein condensate

We study experimentally the line of a single quantized vortex in a rotating prolate Bose-Einstein condensate confined by a harmonic potential. In agreement with predictions, we find that the vortex line is in most cases curved at the ends. We monitor the vortex line leaving the condensate. Its length is measured as a function of time and temperature. For a low temperature, the survival time can be as large as 10 sec. The length of the line and its deviation from the center of the trap are related to the angular momentum per particle along the condensate axis.     

Graphene valley filter using a line defect

With its two degenerate valleys at the Fermi level, the band structure of graphene provides the opportunity to develop unconventional electronic applications. Herein, we show that electron and hole quasiparticles in graphene can be filtered according to which valley they occupy without the need to introduce confinement. The proposed valley filter is based on scattering off a recently observed line defect in graphene. Quantum transport calculations show that the line defect is semitransparent and that quasiparticles arriving at the line defect with a high angle of incidence are transmitted with a valley polarization near 100%.     

微液滴在超疏水表面的受迫振动及其接触线的固着-移动转变

利用高速摄影技术对超疏水表面液滴振动的动态行为进行观测,研究液滴在不同频率下的振动特性. 实验发现,液滴的共振频率满足Rayleigh方程,微液滴在超疏水表面具有自由液滴的振动性质. 在80–200 Hz的驱动频率范围内,接触线出现了明显的固着-移动现象,液滴的振动频率是驱动频率的一半,液滴振动时的形变较大. 当驱动频率大于200 Hz时,接触线基本固着,液滴的振动频率近似等于驱动频率,液滴共振时的形态边缘始终有节点存在. 分析表明,液滴对外界驱动的不同响应与接触线的振荡行为和变形程度密切相关 关键词： 超疏水表面 受迫振动 共振 接触线     

Generation of a uniform line source using a binary filter

A uniform or nearly uniform 10 mm long line source has been generated from a gaussian laser beam using a binary filter. This is done by processing the binary filter throughout a well corrected optical system, so that the equivalent of a continuous inverse gaussian filter is obtained at the final image plane. This equivalent continuous filter generates a uniform line source with maximum conversion efficiency of 50%.     

A Lattice Model for the Line Tension of a Sessile Drop

Within a semi-infinite three-dimensional lattice gas model describing the coexistence of two phases on a substrate, we study, by cluster expansion techniques, the free energy (line tension) associated with the contact line between the two phases and the substrate. We show that this line tension, is given at low temperature by a convergent series whose leading term is negative, and equals 0 at zero temperature.     

Dynamics of arrays of legs powered by a discrete electrical model of nerve

This paper studies the dynamics of an array of legs connected through magnetic coupling at nodes of a discrete electrical model of nerve fibre or a linear electric line. Considering legs fixed on spring, it is found that they exhibit pulse like behavior when the electrical signal propagates in the array. The amplitude of the pulse like motion increases with the magnitude of magnetic field. Legs without spring undergo a step motion at the passage of the electrical signal, advancing in a given distance before they stop. The magnitude of the step also increases with the magnetic coupling. Considering a linear electrical line excited at a single node, it is found that the legs oscillate with decreasing amplitude till the center of the line and increasing amplitude from the center to the first node of the linear line.     

线条属性对文本感知清晰度的影响模型研究

对数字硬拷贝成像ISO13660标准的线条客观属性量与其形成文本的感知清晰度的相关性进行了研究。实验针对6.5 磅和10.5磅简单笔划的黑体汉字、Times New Roman西文字符,以及等价宽度的线条组成的等宽度明暗条纹,进行了清晰度感知质量的主观测评和相应单线条客观质量属性的测量,并建立了两者间的相关模型。结果表明,线条的对比度、粗糙度、相对模糊度及线宽与文字的感知清晰度具有线性相关性,且感知清晰度与线条的对比度正相关,与粗糙度和相对模糊度负相关;对少笔划或多笔划但间距较大的情况,感知清晰度与线宽正相关,反之,负相关。此外,各线属性量对感知清晰度的影响权重相互间至少有1倍的差距。     

线电荷串产生的史密斯-帕塞尔辐射

采用积分方法分析了线电荷串,沿周期性理想金属光栅表面平行移动时产生的史密斯帕塞尔辐射。分别对短周期光栅、低能量线电荷串与长周期光栅、高能量线电荷串的辐射情况进行了数值计算。相对单个线电荷而言,N个线电荷与反射光栅作用产生的辐射场密度,在频率是线电荷串调制频率的整数倍处出现最大,辐射谱宽变窄;随电荷能量增高,辐射能量向高频方向移动,并具有强烈的定向性;可以通过调节线电荷调制频率等参量实现辐射电磁波频率锁定。研究结果表明,对高能量与低能量的电荷参量,适当选择光栅尺寸与线电荷串间隔周期,都可使辐射波工作于太赫兹波段。     

狭缝微等离子体的光谱线形研究

在狭缝微等离子体中,研究了Ar Ⅰ(2P2→1S5)光谱线的展宽和频移随放电参数的变化.为了测量谱线频移,采用低气压(10 Pa左右)氩气放电发射的Ar Ⅰ光谱线作为参考线.实验在氩气含量为99.92%的氩气/空气放电中,测量了气压从1×104Pa增大到6×104 Pa时Ar Ⅰ谱线的频移和展宽.结果表明随着气压的升高...     

Relaxation of a dislocation in a nanocrystallite

Experimental studies of dislocations in nanoparticles are just beginning. The corresponding theoretical models are still lacking. In this context, the author analyzes relaxation of a dislocation in a nanoparticle. Mechanistically, this process is considered to occur primarily via dislocation drift induced by the stress-related image forces. Elementary dislocation displacements include the formation of a kink at one of the sides of the dislocation line, its diffusion along this line, and annihilation at the opposite side. For this mechanism, the dependence of the time of dislocation disappearance on the nanoparticle size has been identified.     

Interference of a pair of symmetric Collett-Wolf beams

We present a study of the interference of light produced by a pair of mutually correlated Gaussian Schell-model sources. The spatial distributions of the fields produced by these sources are symmetric with respect to a plane through their common center and differ by a phase factor exp(i phi). When phi = 0, the resulting radiation is a beam with an intensity distribution that displays a narrow bright line at its center. When the sources can be regarded as Collett-Wolf sources, the resulting bright line diverges much more slowly than the beam itself. When phi = pi the radiated beam has an intensity distribution with a narrow dark line at its center. The theoretical results are supported by experimental results obtained by use of a modified Michelson interferometer and suggest that the interference of a pair of correlated Collett-Wolf beams can be used to produce a pseudo-nondiffracting beam.     

Bose-Einstein condensates with a bent vortex in rotating traps

We consider a 3D dilute Bose-Einstein condensate at thermal equilibrium in a rotating harmonic trap. The condensate wavefunction is a local minimum of the Gross-Pitaevskii energy functional and we determine it numerically with the very efficient conjugate gradient method. For single vortex configurations in a cigar-shaped harmonic trap we find that the vortex line is bent, in agreement with the numerical prediction of Garcia-Ripoll and Perez-Garcia [Phys. Rev. A 63, 041603 (2001)]. We derive a simple energy functional for the vortex line in a cigar-shaped condensate which allows to understand physically why the vortex line bends and to predict analytically the minimal rotation frequency required to stabilize the bent vortex line. This analytical prediction is in excellent agreement with the numerical results. It also allows to find in a simple way a saddle point of the energy, where the vortex line is in a stationary configuration in the rotating frame but not a local minimum of energy. Finally we investigate numerically the effect of thermal fluctuations on the vortex line for a condensate with a straight vortex: we can predict what happens in a single realization of the experiment by a Monte Carlo sampling of an atomic field quasi-distribution function of the density operator of the gas at thermal equilibrium in the Bogoliubov approximation. Received 28 March 2002 / Received in final form 13 September 2002 Published online 21 January 2003 RID="a" ID="a"e-mail: yvan.castin@lkb.ens.fr     

Tomographic rf spectroscopy of a trapped Fermi gas at unitarity

We present spatially resolved radio-frequency spectroscopy of a trapped Fermi gas with resonant interactions and observe a spectral gap at low temperatures. The spatial distribution of the spectral response of the trapped gas is obtained using in situ phase-contrast imaging and 3D image reconstruction. At the lowest temperature, the homogeneous rf spectrum shows an asymmetric excitation line shape with a peak at 0.48(4)epsilonF with respect to the free atomic line, where epsilonF is the local Fermi energy.     

Bound states of 3He at the edge of a 4He drop on a cesium surface

We show that small amounts of 3He atoms, added to a 4He drop deposited on a flat cesium surface at zero temperature, populate bound states localized at the contact line. These edge states show up for drops large enough to develop well defined surface and bulk regions together with a contact line, and they are structurally different from the well-known Andreev states that appear at the free surface and at the liquid-solid interface of films. We illustrate the one-body density of 3He in a drop with 1000 4He atoms, and show that for a sufficiently large number of impurities the density profiles spread beyond the edge, coating both the curved drop surface and its flat base and eventually isolating it from the substrate.     

有界波电磁脉冲模拟器下短线缆效应的理论和实验研究

 研究了有界波电磁脉冲模拟器下短线缆效应的理论建模和实验方法。基于传输线模型计算了线缆在有界波电磁脉冲模拟器辐照下的电流响应。建立了有界波电磁脉冲模拟试验环境,其前沿时间小于5 ns,脉冲半高宽约200 ns。开展了短线缆的效应实验验证研究,短线缆负载端响应电流的测量和计算结果吻合得很好,表明应用改型有界波电磁脉冲模拟器开展短线缆效应实验在理论和实验上都是可行的。这种线缆实验方法具有效应实验空间电磁场分布规范均匀、参数指标可控、监测技术成熟等优点。     

Line thermodynamics: adsorption at a membrane edge

We report a novel experimental study of line thermodynamics. Our system consists of detergent molecules adsorbing at the edges of freestanding lipid bilayers. Adsorption reduces the line tension T of the membrane edges. Measuring T as a function of the bulk detergent concentration C, we obtain a line adsorption isotherm. Using an extension of Gibbs's surface thermodynamics to lines, we estimate the "line excess density" of adsorbants and the energy of adsorption per site.     

Structure of the surface microrelief of a droplet evaporating from a rough substrate as a possible cause of contact angle hysteresis

Based on the refraction images of a droplet evaporating on a rough substrate, we simultaneously observed the dynamics of its surface microrelief, contact angle, and contact line deformations along the entire perimeter of the contact line. This has led us conclude that the microrelief structure is directly related to the phenomenon of contact angle hysteresis and the jump-like pattern of contact line deformation. We suggest a possible mechanism for the occurrence of contact angle hysteresis during droplet evaporation and derive the relations that specify the range of possible contact angles at known microrelief parameters.     

Electromagnetically induced transparency in a molecular gas

The dynamic Stark effect on the as Q(5,4) transition of the 0 → 1 vibrational band of the ν₂ mode of ammonia ¹⁵NH₃ was studied by the method of copropagating waves of radiation of two ¹³CO₂ lasers operating at the R(18)_I line. For waves with mutually orthogonal polarizations, which propagated in a waveguide cell, the intensity of the saturating radiation reached 225 W/cm², and the absorption line of the probing radiation had the form of a two-hump curve with a splitting that was consistent with the Rabi frequency for the ammonia transition being investigated. At the maximum intensity of the saturating radiation, complete transparency was observed at the center of the absorption line of ¹⁵NH₃. When identically polarized saturating and probing waves propagating in a cell at a small angle with respect to each other were used, the splitting was more weakly manifested. The effect of a spatial inhomogeneity of the optical fields on the shape of the line of saturated absorption is discussed.     

Recognition of a light line pattern by Hu moments for 3-D reconstruction of a rotated object

A simple technique of a light line projection for 3-D shape detection of rotated objects is presented. In this technique, an object is rotated around its symmetrical axis four times at an angle by using an electromechanical device and scanned by a light line. Four views of the object surface are extracted from each one of these rotations by processing a set of light line images. These views are connected using rotation angle and origin coordinates to obtain the complete 3-D shape. Angle and origin are calculated by recognition of a light line pattern. Light line pattern is recognized by Hu moments. In this manner, measurement errors on setup are avoided. It is an advantage over common methods, where these two parameters are measured directly on the setup to obtain the 3-D shape. Local profilometric method is based on the perturbation that the light line suffers when it is projected on the object surface. This perturbation is observed on an image plane due to the different direction between light line projector and viewer. These perturbations are measured by using Gaussian functions. In this technique the light line images are processed in very fast form. The technique and processing time are presented in detail. This technique is tested with objects, which have little information and its experimental results are also presented.