Cosmic string in the NUT-Kerr-Newman spacetime

We study the equilibrium configurations of a cosmic string described by the Nambu action in the NUT-Kerr-Newman spacetime which includes as special cases the Kerr-Newman black hole spacetime as well as the NUT spacetime which is considered as a cosmological model. In this study it is interesting to note that one can obtain parallel results for the Kerr-Newman black hole as well as the NUT spacetime.     

500 kV全固态Marx发生器

500 kV全固态Marx发生器采用Z型电路结构,以28个最大工作电压达22 kV、满载最高连续重复运行频率达200 Hz的绝缘栅双极型晶体管组件作为脉冲控制开关,采用以金属化膜电容器和线绕电感构成的梯形脉冲形成网络作为储能和脉冲形成器件。目前已实现500 kV脉冲输出,在50 Hz的重复频率下实现数十个脉冲的猝发输出。该发生器的输出脉冲电压峰值与已有文献报道的最高功率固态Marx发生器技术指标相近,输出脉冲电流峰值提高1倍,达到1000 A,发生器输出脉冲功率峰值达到500 MW。在采用电容器作为储能元件时,此Marx发生器输出脉冲宽度可在3～10 s范围内连续调整。     

Exploding wires in air and vacuum

An apparatus for studies of wire explosions in air at atmospheric as well as reduced pressures is described. A theoretical treatment of the discharge circuit is presented. In this treatment the external resistance and inductance as well as the wire inductance (all as functions of time) have been taken into consideration. It is then possible to calculate the wire variables — current, resistance, resistive voltage drop, effect, and energy input — as functions of time from thedI/dt waveform experimentally obtained. Wire variables of Ni- and W-wires exploded both in air and vacuum are presented as well as a discussion of these.     

Facile fabrication of a lotus-effect composite coating via wrapping silica with polyurethane

A lotus-effect coating was fabricated by wrapping micro-silica and nano-silica with polyurethane (PU) and subsequent spraying. The coating shows the similar self-cleaning property as lotus leaves: the contact angle is as large as 168° and the sliding angle is as low as 0.5°. Surface morphology of the coating was studied with scanning electron microscopy and atomic force microscopy. The composite coating shows the similar structure as lotus leaves.     

Multiple pure tone noise prediction

This paper presents a fully numerical method for predicting multiple pure tones, also known as “Buzzsaw” noise. It consists of three steps that account for noise source generation, nonlinear acoustic propagation with hard as well as lined walls inside the nacelle, and linear acoustic propagation outside the engine. Noise generation is modeled by steady, part-annulus computational fluid dynamics (CFD) simulations. A linear superposition algorithm is used to construct full-annulus shock/pressure pattern just upstream of the fan from part-annulus CFD results. Nonlinear wave propagation is carried out inside the duct using a pseudo-two-dimensional solution of Burgers? equation. Scattering from nacelle lip as well as radiation to farfield is performed using the commercial solver ACTRAN/TM. The proposed prediction process is verified by comparing against full-annulus CFD simulations as well as against static engine test data for a typical high bypass ratio aircraft engine with hardwall as well as lined inlets. Comparisons are drawn against nacelle unsteady pressure transducer measurements at two axial locations as well as against near- and far-field microphone array measurements outside the duct.     

Multivariate analysis of dynamical processes

The analysis of multi-dimensional biomedical systems requires analysis techniques, which are able to deal with multivariate data consisting of both time series as well as point processes. Univariate and bivariate analysis techniques in the frequency domain for time series and point processes are established and investigated, although the number of investigations is strongly biased towards time series. Actual multivariate techniques for time series or hybrids of time series and point processes are scarcely addressed. Here, we present spectral analysis techniques which are able to analyse point processes as well as time series. Thereby, univariate, bivariate as well as multivariate techniques are discussed. Applications to simulated as well as real-world data reveal the abilities of the proposed techniques.     

Hypergeometric solution of the Stark-ladder effect in crystals

The motion of electrons in a crystal subjected to a linear electric field is studied by means of the molecular orbital method. The field perturbation of the resonance integrals, as well as the Coulomb ones, results in the Schroedinger equation being expressed as a hypergeometric difference equation, whose solution gives rise to the well-known Stark-ladder picture of the tilted energy band. It is found that the part played by the resonance integral perturbation is just as important as that of the Coulomb integral perturbation and, therefore, cannot be neglected as in earlier investigations.     

Femtosecond self mode locking of Yb:fluoride phosphate glass laser

Passive cw mode locking of an ytterbium-doped fluoride phosphate glass laser is demonstrated, for what we believe to be the first time, based solely on the Kerr effect in the active medium in a resonator with dispersion compensation. Nearly bandwidth-limited pulses as short as 160fs are generated at ~1040 nm. We obtain average output powers as high as 250mW at 170-MHz repetition rate with absorbed pump power as low as 1.2W.     

基于LVQ神经网络的目标识别技术

通过对目标特征的分析比较,选取不变矩作为识别特征.为了达到很好的识别效果,对不变矩做了优化处理.采用LVQ神经网络技术建立了识别模型,提高了识别速度.运用有限的样本对目标识别技术进行了测试,结果表明采用此技术后的识别成功率较高,平均约为98%,识别速度快,每幅二值目标图像的识别时间约为16 ms.