快前沿直线脉冲变压器驱动源模块中开关同步对放电电流的影响

介绍了4支路并联快前沿直线脉冲变压器驱动源(FLTD)模块的初步实验结果,在工作电压160 kV时,次级短路放电电流幅值达到103.4 kA,电流前沿为78 ns(10%~90%)。利用微分环测量了4只开关在工作电压120 kV时的同步情况,研究分析了开关同步对放电电流幅值和波形的影响。开关同步小于15ns时,放电电流幅值变化不明显,电流幅值的标准偏差约3.62 kA,电流波形没有明显畸变;开关同步15~25ns时,放电电流幅值略有下降,电流幅值的标准偏差约8.59 kA,电流波形有一定程度畸变;开关同步大于25ns时,放电电流幅值明显降低,电流的标准偏差显著增大,电流波形发生严重畸变。     

超导装置电流引线的研究进展

电流引线是连接室温端电源和低温端超导装置的重要部件,也是超导装置热损耗的主要热源之一。选择合适的电流引线形式,并进行引线结构优化设计,可以提高超导装置的可靠性和经济性。概述了电流引线的优化设计目标和分类形式,介绍了全金属电流引线、高温超导电流引线和珀尔帖电流引线的研究进展,分析比较了三类电流引线的工作特点和适用场景,可为超导装置的电流引线选型和优化设计提供参考。     

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介绍了EAST装置新型离子回旋加热(ICRH)天线电流带的设计结构。通过对电流带实际工况的计算得出电流带的工作温度分布,以此来模拟实际工作条件下电流带的热载荷承受能力以及对电流带结构的影响。论证了在实际工况热载荷条件(0.2MW)下,电流带辐射面温度及电流带整体结构强度满足设计要求。     

Z箍缩丝阵负载区域的似稳态磁场分布

 将负载区域的电流（丝阵电流、阴极板电流、阳极板电流和回流柱电流）离散成电流线或电流面等电流微元,根据毕奥-萨伐尔定律,计算所有电流微元在指定场点的磁场,再通过叠加给出该点的总磁场。研究结果发现:在丝阵外围区域,仅由丝阵电流所产生的磁场偏离无限长直导线磁场公式的值,但全部电流所产生的总磁场与公式给出的值很接近。同时,研究了不同负载结构参数下的磁场分布,结果表明：增加丝根数有助于减小单根丝表面的局部磁场,改善丝阵外围磁场分布的均匀性。     

不同排布和通流下高温超导电缆交流损耗研究

运用实验的方法,系统研究了在堆叠与并列两种排布方式下YBCO和Bi2223两种高温超导电缆关于电流方向的交流损耗特性,并进行了分析比较。研究表明,在堆叠的情况下,反向电流的交流损耗大于同向电流的交流损耗,两者保持一定的比列;并列的情况下,同向电流的交流损耗大于反向电流的交流损耗,且随着电流的增大,两者的差异在逐渐减小。在堆叠的情况下,YBCO同向电流的交流损耗和反向电流交流损耗的差异远大于Bi2223。     

EAST装置离子回旋加热天线电流带热结构分析

介绍了EAST装置新型离子回旋加热(ICRH)天线电流带的设计结构。通过对电流带实际工况的计算得出电流带的工作温度分布,以此来模拟实际工作条件下电流带的热载荷承受能力以及对电流带结构的影响。论证了在实际工况热载荷条件(0.2MW)下,电流带辐射面温度及电流带整体结构强度满足设计要求。     

脉冲功率晶闸管反向恢复特性

为建立有效的晶闸管模型来仿真晶闸管关断时过电压,减小晶闸管过压损坏的概率,以最大通流150 kA、耐压5.2 kV的脉冲晶闸管为研究对象,将其前置于脉冲形成单元回路中作为大功率开关使用,记录放电过程中晶闸管两端电压及电流。实验数据表明:恢复过程中的电流下降率、反向恢复电荷、反向恢复电流峰值随通态电流峰值的增大而增大,晶闸管关断时间随通态电流峰值的增大而减小。此外,在关断过程中,当电流下降率在-50~1000 A/s时,电流下降率与电流峰值为线性关系。因此,在大脉冲电流条件下,推导反向恢复过程参数与通态电流参数的关系时电流下降率可用与电流峰值的线性关系代替。基于Matlab仿真平台,建立了具有反向恢复过程的脉冲晶闸管模型。该模型仿真得到的晶闸管反向恢复电流峰值与实测结果较为吻合,反向恢复电压尚待进一步修正。     

全光纤电子电流互感器技术探讨

随着输电电压升高到超高压、特高压,传统的基于电磁感应机理的电流互感器技术已暴露出越来越多的内在的、难以克服的缺点。因此,用电子电流互感器取代传统的电流互感器已是大势所趋。特别是目前在电力系统大力推进智能电网技术的形势下,电力系统对全光纤电子电流互感器技术的需求日趋增长。此外,在高频电流及微弱电流测量方面全光纤电流传感技术也有重要应用。在简要介绍全光纤电流传感技术的概念、基本分类之后,阐述了目前全光纤电流互感器技术实用化过程中遇到的主要技术障碍,探讨了可能的解决办法,介绍了光纤Bragg光栅、量子点掺杂光纤及光纤纳米线/微米线等新兴技术在光纤电流传感器中的应用。     

具有电流阻挡层的不同GaN基LED的光电特性(英文)

研究对比了InGaN/GaN多量子阱发光二极管中p电极下的不同SiO2电流阻挡层的光电特性。6种样品被分为3组:普通表面、表面粗化、表面粗化+边墙腐蚀。每组都有两种结构,一种具有电流阻挡层,另一种没有电流阻挡层。每组中,具有电流阻挡层的LED在20 mA下的正向电压分别为3.156,3.282,3.284 V,略高于不含电流阻挡层的样品(Vf=3.105,3.205,3.210 V).但是,具有电流阻挡层的LED的光效和光功率要优于无电流阻挡层的器件,在20 mA下的光功率分别提高了10.20%、12.19%和11.49%。这些性能的提升都要归功于电流阻挡层良好的电流扩展效应,同时电流阻挡层还可以减小p电极下的寄生光吸收。     

趋肤效应的一种解释

福里斯、季莫列娃的《普通物理学》对趋肤效应的解释是不正确的.如图1所示:i表示通过导体的交变电流.ib表示如图所示的闭合回路里的感应电流.图1中所表示的是交变电流i正在增长时的情况.结果,在导体中心处i和ib这两个电流方向相反,电流被减弱.在导体表面处两个电流方向相同,电流得到加强.表面处的电流大于中心处的电流. 按照这种解释,则当导体中的交变电流i衰减时,导体中心处的电流将得到加强,而表面处的电流将被减弱.这样,在交变电流的一个全周期内,无论在导体的表面或中心,电流加强和减弱的机会均等,效果相同,也就无所谓趋肤了.可见福里斯…     

First experimental observations of neutron bursts under thunderstorm clouds near sea level

The connection of short-term neutron bursts near sea level with the electric and geomagnetic atmospheric fields during thunderstorms in 2009–2011 has been experimentally studied. The data from the cosmic-ray spectrograph named after Kuzmin, an electrostatic fluxmeter, and a three-component fluxgate magnetometer in Yakutsk have been analyzed. It has been shown that short-term (no longer than 4 min) neutron bursts are due to negative lightning discharges. The bursts are detected at the ground level 1–3 km below thunderstorm clouds. In this case, the neutron flux is about 4 × 10⁻³ cm⁻² s⁻¹. The minimum energy of the neutrons that are efficiently detected by the monitor is about 10 MeV. It has been found that short-term neutron bursts are detected when the electric field strength reaches a threshold value of −16 kV/m.     

Neutron bursts during cloud-to-ground discharges of lightning

Neutron bursts of up to 30% per minute resolution are recorded by the Yakutsk cosmic ray spectrograph during jumps of an electric field undergoing changes in the vicinity of the neutron monitor upon cloud-to-ground discharges of lightning. The electric field variations are recorded with an electrostatic fluxmeter (±50 keV m^?1).     

A study of the assessment of air temperature, and sensible-and latent-heat fluxes from sonic-anemometer observations

Summary In the past ten years, use of sonic anemometers to provide fast-response wind sensing in the atmospheric surface layer became more and more intensive, due to their increasing availability, decreasing cost and increasing number of publications regarding their data treatment. In this paper, we present an algorithm we have developed in order to analyse the data of one of the most diffused types of sonic anemometer,i.e. the Gill sonic anemometer. Our software allows to evaluate the air temperature and the sensible- and latent-heat fluxes if also low-response measurements of air humidity at the same level of sonic anemometer, and of net radiation and ground surface flux are available. We let our software the option of evaluating the fluxes along the mean local streamline (thus the turbulent fluxes are associated with transport across mean streamline surfaces). By using the data gathered in two field experiments, we discuss the applications of the proposed formulations and check the accuracy of our method by comparing the evaluated fluxes with those measured by fluxmeter.     

Deflagration-to-detonation transition in spiral channels

The deflagration-to-detonation transition in hydrogen–air mixtures that fill spiral channels has been studied. A spiral channel has been produced in a cylindrical detonation tube with a twisted ribbon inside. The gas mixture has been ignited by means of a spark gap switch. The predetonation distance versus the twisted ribbon configuration and molar ratio between the gas mixture components has been determined. A pulling force exerted by the detonation tube after a single event of hydrogen–air mixture burnout has been found for four configurations of the twisted ribbon. Conditions under which the use of a spiral tube can be more effective (increase the pulling force) have been formulated.     

稀土和锕系化合物中重费密子行为

本文采用周期Anderson哈密顿量研究了稀土和锕系化合物中的重费密子行为。对f电子间库仑关联项做了平均场近似并引入自能项反映多体作用的效应。对自能项采用了单格位近似,在准粒子表象中讨论了系统的性质,通过对f电子平均占据数的自洽计算,得到了准粒子有效质量,讨论了形成重费密子的条件,以及相应的磁性的变化,并做了数值计算。所得结果与最近的实验进行了比较。 关键词：     

Observation of bistability in a CO2 laser exhibiting passive Q-switching

Optical bistability has been investigated experimentally in a CO₂ laser containing CF₃Br as a saturable absorber. The frequency dependence of the hysteresis cycle of this laser containing a saturable absorber (LSA) has been studied. It has also been shown that the LSA may undergo simultaneously hysteresis cycles and Q-switching. The phase diagram of the LSA has been extended towards regions where this behavior has been observed.     

Bistability of a “chevron” smectic C* liquid crystal in an external electric field

The system of nonlinear equations describing a surface-stabilized ferroelectric smectic C* liquid crystal in the chevron geometry has been investigated by numerical methods in the framework of the continuum model of liquid crystals. Stable orientational and structural configurations have been studied, and the results obtained have been compared with those derived using simplified models. The height of the potential barrier separating two stable configurations has been determined, and the transition between them under the action of the external electric field has been examined. It has been demonstrated that this effect has a threshold character. The dependence of the threshold field on the film thickness has been analyzed.     

Spatial Temporal Analysis of Electrically-Addressable Phase-Only Spatial Light Modulator

An optically addressed parallel-aligned nematic-liquid-crystal spatial light modulator (PAL-SLM) has been studied as a dynamic phase-only modulation device. A computer control feature of the spatial light modulator is strongly desired for practical applications. For those demands, an electrically-addressable phase-only spatial light modulator has been developed to combine a liquid crystal display (LCD) with a PAL-SLM (LCD-coupled PAL-SLM) and its performance has been reported. However, a temporal characteristic especially two-dimensional (2D) response has not been discussed before. In this paper, 2D response analysis system has been constructed by using a high-speed complementary Metal-Oxide-Semiconductor (CMOS) camera (1000 frames/sec) and the 2D-modulation characteristic of the LCD-coupled PAL-SLM has been observed. As a result, the LCD has a spatially non-uniform modulation characteristic due to a scanning addressing. It has the potential to cause problems in high speed switching for a computer generated hologram. On the other hand, the spatial non-uniformity has not been observed with the LCD-coupled PAL-SLM.     

Approximate radiative solutions of the Einstein equations

In this paper the external field of a bounded source emitting gravitational radiation has been considered. A successive approximation method has been used to integrate the Einstein equations in Bondi's coordinates. A method of separation of angular variables has been worked out and the approximate Einstein equations have been reduced to the key equations (3.8)–(3.10). The losses of mass, momentum, and angular momentum due to gravitational multipole radiation have been found. It has been demonstrated that in the case of proper treatment a real mass occurs instead of a mass aspect in a solution of the Einstein equations. In Appendix C Bondi's news function has been given in terms of sources.     

Magnetization and transport characteristics of layered high-temperature superconductors with different anisotropy parameters

The magnetization of a layered high-temperature superconductor with different anisotropy parameters has been calculated using the Monte Carlo method in the framework of a modified three-dimensional Lawrence–Doniach model with actual boundary conditions. The penetration of a magnetic flux into a bulk sample from the boundary has been simulated, and the curves of magnetization reversal of a high-temperature superconductor by an external magnetic field have been calculated for different anisotropy parameters γ and types of defects in the sample. It has been found that there are significant differences in the magnetization curves and transport properties of superconductors with different anisotropy parameters γ. The influence of tilted columnar defects on the critical current has been analyzed. A decreasing dependence of the critical current on the tilt angle of defects with respect to the c axis has been obtained. It has been shown that, as the anisotropy parameter increases, this dependence weakens and, for a specific value of γ, disappears. An explanation of the mechanism responsible for the disappearance of the dependence has been proposed.