On the fluctuation enhanced conductivity of a superconductor: The correct evaluation of the Maki graph

According to Maki, a particular diagram—the Maki graph—gives a contribution to the fluctuation enhanced conductivity of a superconductor which is infinite in the case of a thin film. It is shown that this result is spurious and that it is due to a breakdown of the standard Green function impurity technique. A new method is developed which is strictly based on the Boltzmann equation. It is shown that the temperature dependent contribution of the Maki graph to the conductivity is negligibly small in a dirty metal.     

A Dynamic Anomaly Detection Approach Based on Permutation Entropy for Predicting Aging-Related Failures

Software aging is a phenomenon referring to the performance degradation of a long-running software system. This phenomenon is an accumulative process during execution, which will gradually lead the system from a normal state to a failure-prone state. It is a crucial challenge for system reliability to predict the Aging-Related Failures (ARFs) accurately. In this paper, permutation entropy (PE) is modified to Multidimensional Multi-scale Permutation Entropy (MMPE) as a novel aging indicator to detect performance anomalies, since MMPE is sensitive to dynamic state changes. An experiment is set on the distributed database system Voldemort, and MMPE is calculated based on the collected performance metrics during execution. Finally, based on MMPE, a failure prediction model using the machine learning method to reveal the anomalies is presented, which can predict failures with high accuracy.     

The shape gradient of the least-squares objective functional in optimal shape design problems of radiative heat transfer

Optimal shape design problems of steady-state radiative heat transfer are considered. The optimal shape design problem (in the three-dimensional space) is formulated as an inverse one, i.e., in the form of an operator equation of the first kind with respect to a surface to be optimized. The operator equation is reduced to a minimization problem via a least-squares objective functional. The minimization problem has to be solved numerically. Gradient minimization methods need the gradient of a functional to be minimized. In this paper the shape gradient of the least-squares objective functional is derived with the help of the shape sensitivity analysis and adjoint problem method. In practice a surface to be optimized may be (or, most likely, is to be) given in a parametric form by a finite number of parameters. In this case the objective functional is, in fact, a function in a finite-dimensional space and the shape gradient becomes an ordinary gradient. The gradient of the objective functional, in the case that the surface to be optimized is given in a finite-parametric form, is derived from the shape gradient. A particular case, that a surface to be optimized is a “two-dimensional” polyhedral one, is considered. The technique, developed in the paper, is applied to a synthetic problem of designing a “two-dimensional” radiant enclosure.     

The precision improvement of the scanner in optical scanning imaging system

A disadvantage of using a galvanometer as the horizontal scanner in CSOM and OCT is its nonlinear distortion caused by the rotational inertial. This is inevitable even if a closed loop is equipped. Here, a second closed loop is introduced to provide pixel clocks to reduce the pincushion distortion of the images. A subdivided step motor is employed to be the vertical scanner as the result of price consideration. Nonetheless, the conventional linearity model of the peck torque with a winding current relationship is no longer in agreement with the experiment when the winding current is low, while a parabolic model is more likely to be reasonable. Relational treatment is proposed in the paper. Both methods have proved to be good enough to meet the requirement of a super resolution scanning imaging.     

On the width of a ray

Consistent with earlier work by Kravtsov and Orlov, a simple general expression for the width of a Fresnel zone deltar(F) in a smooth inhomogeneous environment is derived; this is the diffractive contribution to the width of a ray. In a stratified environment at long range, the general Fresnel zone width expression is shown to reduce approximately to one that is proportional to [equation in text] where alpha is the ray stability parameter, sigma is the acoustic frequency, r is the range from the source to the field point of interest, and R is the source to receiver range. In a stratified environment on which a weak small-scale perturbation is superimposed, deterministic rays in the background environment that connect fixed end points break up into bundles of micromultipaths at moderate to long range and a second, scattering-induced, contribution deltar(s) to the width of a ray must be considered. It is shown that deltar(s) is proportional to /alpha/r(R-r) and argued that in a micromultipathing environment the total effective width of a background ray is deltar(tot)= [equation in text] . Theoretical predictions are shown to agree well with travel-time sensitivity kernel calculations.     

Limit of hanger linearity in suspension footbridge dynamics: A new section model

The mechanical behaviour of suspension bridges is characterised by nonlinearities due to the main cables geometric effects and to the inability of the hangers to sustain compressive loads. The nonlinear effects due to hanger slackening are expected to increase in suspension footbridges due to lightweight decks, that is, low dead to live load ratio, and to shallow plate-girder decks with very low flexural and torsional stiffness. In this paper a new section model is proposed to study the limit of hanger linearity in lightweight suspension footbridges. The model is inspired to a four degrees-of-freedom model already proposed in the literature, but is expressed with a new formalism that allows some interesting properties to be outlined. Specifically, the expression of a particular frequency, herein called relative antiresonance frequency, as a function of the model generalised properties is derived: if the system is loaded with a harmonic force having that frequency, the linear behaviour of the hangers is assured for every value of the force amplitude. The proposed section model is applied to a footbridge benchmark subject to the pedestrian harmonic load and results are compared with those obtained through a nonlinear dynamic analysis on a 3D Finite Element model of the bridge.     

̀Spatial impulse response of a rectangular double curved transducer

Calculation of the pressure field from transducers with both a convex and a concave surface geometry is a complicated assignment that often is accomplished by subdividing the transducer surface into smaller flat elements of which the spatial impulse response is known. This method is often applied to curved transducers because an analytical solution is unknown. In this work a semi-analytical algorithm for the exact solution to a first order in diffraction effect of the spatial impulse response of rectangular-shaped double curved transducers is presented. The solution and an approximation to it are investigated. The approximation reformulates the solution to an analytically integrable expression, which is computationally efficient to solve. Simulation results are compared to FIELD II simulations. Calculating the response from 200 different points yields a mean error for the different approximations ranging from 0.03% to 0.8% relative to a numerical solution for the spatial impulse response. It is also shown that the presented algorithm gives consistent results with FIELD II for a linear flat, a linear focused, and a convex nonfocused element. The solution involved a three-point Taylor expansion and gave an accuracy of 0.01%.     

A TB-Mode Accelerator

An accelerator is proposed in which a TE-mode wave is used to drive charged particles in contrast to the usual linear accelerators in which longitudinal electric fields or TM-mode waves are supposed to be utilized. The principle of the acceleration is based on the Vp × B acceleration of a dynamo force acceleration. That is, a charged particle trapped in a transverse wave feels a constant electric field (Faraday induction field) and subsequently is accelerated when an appropriate magnetic field is externally applied in the direction perpendicular to the wave propagation. A pair of dielectric plates is used to produce a slow TE mode. Discussions will be given on what the conditions of the particle trapping are and how to stabilize the particle orbit.     

Cosmological transition periods

A method is given for continuously following a model of a universe that in its evolution makes a transition from one type of universe to another. As an illustration, a universe is considered that initially is radiation-dominated and then makes a transition to a final matter-dominated Einstein-de Sitter universe. The epoch when the universe changes from being radiation-dominated to being matter-dominated is found and is related to the epoch when radiation decouples from matter.     

Reduction of turbulent boundary layer induced interior noise through active impedance control

The use of a single actuator tuned to an optimum impedance to control the sound power radiated from a turbulent boundary layer (TBL) excited aircraft panel into the aircraft interior is examined. An approach to calculating the optimum impedance is defined and the limitations on the reduction in radiated power by a single actuator tuned to that impedance are examined. It is shown that there are too many degrees of freedom in the TBL and in the radiation modes of the panel to allow a single actuator to control the radiated power. However, if the panel modes are lightly damped and well separated in frequency, significant reductions are possible. The implementation of a controller that presents a desired impedance to a structure is demonstrated in a laboratory experiment, in which the structure is a mass. The performance of such a controller on an aircraft panel is shown to be effective, if the actuator impedance is similar to but not the same as the desired impedance, provided the panel resonances are well separated in frequency and lightly damped.     

弯曲光纤针尖及其法向力压电探测技术

本文介绍一种弯曲光纤针尖及其法向力压电探测的新技术.与目前普遍采用的方法不同,弯曲针尖的制作是先利用电阻丝加热,将光纤弯曲成所需的角度,然后再在缓冲氢氟酸中腐蚀成针尖,得到曲率半径为300μm,弯曲角度为120°,长度为500μm的弯曲针尖.同激光或电弧熔拉、弯曲的方法相比,这种方法工艺简单,成本低廉.由弯曲针尖与蜂鸣器压电片组成的悬臂,利用压电片的正、逆压电效应实现弯曲针尖法向力的非光学法探测.实验表明,这种弯尖法向力的探测较直尖切变力具有更高灵敏度,探测距离提高了一倍以上,给实际应用带来很大的便利.     

Integrability of Characteristic Hamiltonian Systems on Simple Lie Groups with Standard Poisson Lie Structure

Phase space of a characteristic Hamiltonian system is a symplectic leaf of a factorizable Poisson Lie group. Its Hamiltonian is a restriction to the symplectic leaf of a function on the group which is invariant with respect to conjugations. It is shown in this paper that such a system is always integrable.     

Experiments to study the confinement of a target plasma in a magnetic trap with inverse plugs and circular multipole walls

In order to neutralize beams of high-energy negative ions, it is convenient to use a plasma target. It is necessary to confine a target plasma within a magnetic trap. It is of importance to restrict the escape of a plasma from the inlet and outlet holes in the target. It is proposed to confine a target plasma in a magnetic trap with a weak longitudinal field with circular multipole walls and with inverse plugs (with an inverse field). Experiments in which a plasma is confined in an axisymmetric trap of this type with one double inverse plug, which restricts longitudinal plasma outflow, are described. A cathode pellet emitting accelerated electrons for plasma production by gas ionization is installed at the opposite end face of the trap on the axis. The experiment shows that inverse plugs suppress strongly the plasma outflow into the end-face hole. The mechanism of this suppression is revealed. It is found that electrons are confined within a trap predominantly by magnetic fields.     

Background-independence

Intuitively speaking, a classical field theory is background-independent if the structure required to make sense of its equations is itself subject to dynamical evolution, rather than being imposed ab initio. The aim of this paper is to provide an explication of this intuitive notion. Background-independence is not a not formal property of theories: the question whether a theory is background-independent depends upon how the theory is interpreted. Under the approach proposed here, a theory is fully background-independent relative to an interpretation if each physical possibility corresponds to a distinct spacetime geometry; and it falls short of full background-independence to the extent that this condition fails.     

含有大位移动边界的复杂流场的数值模拟

含有运动弹丸的膛口流场是典型的大位移动边界问题,同时弹丸在出膛过程中,流场的结构也会发生变化,增加了流场的复杂程度.在对该流场的数值模拟中,将它分为两个区:弹丸运动区和普通流场区,它们之间用一个特殊的分区边界联系,同时运用网格局部重构技术处理弹丸运动造成的网格变形问题,并将对称轴定义为网格变形边界,使得弹丸在对称轴上运动过程中不会导致对称轴上的网格体积为负.从计算结果可以看出整个膛口波系结构变化过程和弹丸先加速后减速的过程,从而表明该动网格处理方法是成功的.     

Quantitative estimation of ultrasonic attenuation in a solid in the immersion case with correction of diffraction effects

This paper presents a method of diffraction correction for the log-spectral difference method to estimate quantitatively attenuation of a solid in the immersion case. The correction method is established based on the angular spectrum approach that is used to calculate the echoes from the front and back surfaces of the immersed solid. An example is given of a copper plate submerged in water and inspected by a linear array with a cylindrically curved surface. The correction method is first applied to a theoretical estimation of attenuation which is linearly dependent on frequency. The results have shown that the evaluated attenuation coefficient is in excellent agreement with the exact value. Then the method is applied to a real situation, in which the results have shown that the method yields reasonable evaluated attenuation values. This work has demonstrated that the method is able to correct effectively the diffraction effect so as to achieve a quantitative estimation of attenuation.     

Transmission of structure-borne sound from a beam into an infinite plate

An analytical study of transmission of structure-borne sound from a semi-infinite beam into an infinite, isotropic plate is presented. The beam is assumed to carry a torsional, a quasi-longitudinal and bending wave and the transmission is obtained with the help of the admittances of the beam and the plate. The analysis is restricted to the case of low frequencies but is otherwise general; thus due regard is given not only to the bending wave of the plate but also to the other propagating waves and to the local reactions. An interesting result from the study is that a bending wave on the beam will transfer a substantial part of its power into quasi-longitudinal and transverse waves in the plate, especially if the plate is thin compared with the beam. This is thought to be a factor that is important and not so easily quantifiable in the analysis of a complex structure. The local reactions on the other hand are of small importance for the power transmission from a torsional and quasi-longitudinal wave on the beam but may be important for the transmission of a bending wave, especially if the Young's modulus of the beam is larger than that of the plate.     

Infrared catastrophe in a two-quasiparticle collision integral

Relaxation of a nonequilibrium state in a disordered metal with a spin-dependent electron energy distribution is considered. The collision integral due to the electron-electron interaction is computed within the approximation of a two-quasiparticle scattering. It is shown that the spin-flip scattering processes with a small energy transfer may lead to the divergence of the collision integral for a quasi one-dimensional wire. This divergence is present only for a spin-dependent electron energy distribution that corresponds to the total electron spin magnetization M = 0 and only for nonzero interaction in the triplet channel. In this case, a nonperturbative treatment of the electron-electron interaction is needed to provide an effective infrared cutoff. The text was submitted by the authors in English. An erratum to this article is available at .     

含单排线缺陷锯齿型石墨烯纳米带的电磁性质

基于密度泛函理论的第一性原理方法,研究了含单排线缺陷锯齿型石墨烯纳米带(ZGNR)的电磁性质,主要计算了该缺陷处于不同位置时的能带结构、透射谱、自旋极化电荷密度、总能以及布洛赫态.研究表明,含单排线缺陷的ZGNR和无缺陷的ZGNR在非磁性态和铁磁态下都为金属.虽然都为金属,但其呈金属性的成因有差异.在反铁磁态下,单排线缺陷越靠近ZGNR的边缘,对ZGNR电磁性质的影响越明显,缺陷由ZGNR对称轴线向边缘移动过程中,含单排线缺陷的ZGNR有一个半导体-半金属-金属的相变过程.虽然线缺陷靠近中线的ZGNR为半导体,但由于缺陷引入新的能带,导致含单排线缺陷的ZGNR的带隙小于无缺陷ZGNR的带隙.单排线缺陷紧邻边界时,含缺陷ZGNR最稳定;单排线缺陷位于次近邻边界位置时,含缺陷ZGNR最不稳定.在反铁磁态下,对单排线缺陷位于对称轴线的ZGNR施加适当的横向电场,可以实现半导体到半金属的转变.这些研究结果对于发展基于石墨烯的纳米电子器件有重要的意义.