Experimental Study of Current Loss of Stainless Steel Magnetically Insulated Transmission Line with Current Density at MA/cm Level

A magnetically insulated transmission line （MITL） is used to transmit high power electric pulses in large pulse power systems. However, current loss is unavoidable, especially when the current density is up to 1 MA/cm. In the paper, the current loss of an MITL made of stainless steel, which is usually used in large pulse power generators, is experimentally studied, and possible mechanisms to explain the current loss of the MITL are analyzed and discussed. From the experimental results, the relationship between loss current density and input current density follows approximately a power law. The loss is also related to the configuration of the MITL.

Determinations of plasma density and decay time in the hollow cathode discharge by microwave transmission

The microwave （MW） transmission method is employed to measure both the plasma density and the plasma decay time in the hollow cathode discharge （HCD） in argon at low pressure. The plasma density in DC-driven or pulsed HCD is on the order of 1012 cm-3, which can block the X-band MW effectively. In the case of pulsed HCD, the MW transmittance shows the same waveform as the pulsed current during the rising edge if the driving frequency is low, but with a longer delay during the falling edge. The MW transmittance reaches a constant low level when the driving frequency is high enough. The plasma decay time in the HCD system is measured to be about 100 μs around a pressure of 120 Pa. The ambipolar diffusion is considered to be the major mechanism in the decay process.

Analysis of vibration and frequency transmission of high speed EMU with flexible model

When the operation speed of the high-speed train increases and the weight of the carbody becomes lighter,not only does the sensitivity of the wheel/rail contact get higher,but also the vibration frequency range of the vehicle system gets enlarged and more frequencies are transmitted from the wheelset to the carbody.It is important to investigate the vibration characteristics and the dynamic frequency transmission from the wheel/rail interface to the carbody of the high-speed electric multi-uint（EMU）.An elastic highspeed vehicle dynamics model is established in which the carbody,bogieframes,and wheelsets are all dealt with as flexible body.A rigid high-speed vehicle dynamics model is set up to compare with the simulation results of the elastic model.In the rigid vehicle model,the carbody,bogieframes and wheelsets are treated as rigid component while the suspension and structure parameters are the same as used in the elastic model.The dynamic characteristic of the elastic high speed vehicle is investigated in time and frequency domains and the di ff erence of the acceleration,frequency distribution and transmission of the two types of models are presented.The results show that the spectrum power density of the vehicle decreases from the wheelset to the carbody and the acceleration transmission ratio is approximately from 1%to 10%for each suspension system.The frequency of the wheelset rotation is evident in the vibration of the flexible model and is transmitted from the wheelset to the bogieframe and to thecarbody.The results of the flexible model are more reasonable than that of the rigid model.A field test data of the high speed train are presented to verify the simulation results.It shows that the simulation results are coincident with the field test data.

INTERNAL STRESS MECHANISM OF CARBON TRANSMISSION UNDER HIGH TEMPERATURE AND HIGH PRESSURE

The problem was found that the nucleation and growth of diamond are different on each side of flaky catalyst in the cubic high pressure diamond synthesis system. Some theories explainning this difference were introduced in the paper. The synthesis cavity and the forces on flaky ctalyst were analysed. The results show that the stress makes the transmission velocity of carbon different on each side of catalyst slice, which causes the difference of nucleation density of diamond between two sides of the slice.

Simulation of x-ray transmission through an ellipsoidal capillary

This paper develops a simulation program for x-ray transmission in an ellipsoidal capillary based on a ray-tracing method. The influence of the parameters of ellipsoidal capillary and x-ray energy on transmission efficiency, full width at half maximum and power density gain of x-ray beams through an ellipsoidal capillary was analysed by this program. It shows that the particular rules of the ellipsoidai capillary x-ray lens are different from the polycapillary lens. Furthermore, this analysis method can be applied to the optimized design of ellipsoidal capillary.

Irregular and regular LDPC codes with high spectrum efficiency modulation in image transmission over fading channel

If the degree distribution is chosen carefully, the irregular low-density parity-check (LDPC) codes can outperform the regular ones. An image transmission system is proposed by combining regular and irregular LDPC codes with 16QAM/64QAM modulation to improve both efficiency and reliability. Simulaton results show that LDPC codes are good coding schemes over fading channel in image communication with lower system complexity. More over, irregular codes can obtain a code gain of about 0.7 dB compared with regular ones when BER is 10 -4. So the irregular LDPC codes are more suitable for image transmission than the regular codes.

Research on corona discharge suppression of high-voltage direct-current transmission lines based on dielectric-film-covered conductor

Corona discharge suppression for high-voltage direct-current(HVDC)transmission lines at line terminals such as converter stations is a subject that requires attention.In this paper,a method based on a conductor covered with dielectric film is proposed and implemented through a bench-scale setup.Compared with the bare conductor,the corona discharge suppression effect of the dielectric-film-covered conductor under positive polarity is studied from the composite field strength and ion current density using a line-plate experimental device.The influences of film thickness and film material on the corona discharge suppression effect are investigated.The charge accumulation and dissipation characteristics of different film materials are also studied.The results show that the conductor covered with dielectric film has excellent ability to inhibit corona discharge.The ground-level composite field strength of the conductor covered with dielectric film is lower than its nominal field strength,and its ion current density is at the nA m^(−2) level.The corona threshold voltage can be promoted by increasing the film thickness,but the ability to inhibit corona discharge becomes weak.The larger the surface electric field strength,the more charge accumulated,but the faster the charge dissipation rate.Compared with polyvinyl chloride film,cross-linked polyethylene film has stronger charge accumulation ability and slower charge dissipation rate,which can better restrain the corona discharge of HVDC transmission lines.

Imaging internal density structure of the Laoheishan volcanic cone with cosmic ray muon radiography

Muon radiography is a promising technique for imaging the internal density structures of targets such as tunnels,pyramids,and volcanoes up to a scale of a few hundred meters by measuring the flux attenuation of cosmic ray muons after they have traveled through these targets.In this study,we conducted experimental muon radiography of one of the volcanoes in the Wudalianchi area in Northeast China to image its internal density structure.The muon detector used in this study was composed of plastic scintillators and silicon photomultipliers.After approximately one and a half months of observing the crater and conduit of the Laoheishan volcano cone in Wudalianchi from September 23^(rd) to November 10^(th) 2019,more than 3 million muon tracks fulfilling the data selection criteria were collected.Based on the muon samples and high-resolution topography obtained through aerial photogrammetry using an unmanned aerial vehicle,a density image of the Laoheishan volcano cone was constructed.The results obtained in this experiment demonstrate the feasibility of using a radiography technique based on plastic scintillator detectors.To obtain the density distribution,we performed a detailed background analysis and found that low-energy charged particles dominated the background noise.Relatively higher densities were found near the surface of the volcanic cone,whereas relatively lower densities were found near the center of the volcanic cone.The experiment in this study is the first volcano muon tomography study performed in China.Our work provides an important reference for future research.

Expected density of progress for wireless ad hoc networks with Nakagami-m fading

This paper presents the closed-form expression to the expected density of progress for wireless ad hoc networks with Nakagami-m fading. The expected density of progress is defined as the expectation of a product between the number of simultaneous successful transmission per unit area and the distance towards the destination. Numerical results show that the expected density of progress is determined by two factors, terminal density and the probability that a terminal attempts to transmit.

Two-coupled structural modulations in charge-density-wave state of SrPt_2As_2 superconductor

Transmission electron microscopy （TEM） study of SrPt2As2 reveals two incommensurate modulations appearing in the charge-density-wave （CDW） state below TCDW ≈ 470 K. These two structural modulations can be well explained in terms of condensations of two-coupled phonon modes with wave vectors of q1=0.62a＊ on the a＊-b＊ plane and q2 = 0.23a＊ on the a＊-c＊ plane. The atomic displacements occur along the b-axis direction for q1 and along the c-axis direction for q2, respectively. Moreover, the correlation between ql and q2 can be generally written as q1 = （q2 ＋ a＊）/2 in the CDW state, suggesting the presence of essential coupling between q1 and q2. A small fraction of Ir doping on the Pt site in Sr（Pt1-xIrx）2As2 （x ≤ 0.06） could moderately change these CDW modulations and also affect their superconductivities.

Design and Implementation of Distributed Broadcast Algorithm Based on Vehicle Density for VANET Safety-Related Messages

Vehicle ad hoc network (VANET) is a research hotspot in industrial and academic fields now and after. Dedicated short-range communication (DSRC) is a key technology of vehicular safety services and most research adhere to IEEE 802.11p standard. The safety-related services face channel congestion, message collision, and hidden tinal problem in different traffic conditions. This paper focuses on the broadcast of safety-related message under different vehicle densities. In this paper, we firstly divide the safety-related messages into three categories and assign them different broadcast priorities. Secondly, we design different distributed broadcast algorithms for the three type messages. Then,we propose a method used to evaluate the vehicle density and present the relationship between the vehicle density and the transmit power. Then the safety module selects proper transmit power according to the relationship before the message is sent. Finally, we conduct the simulation experiment using NS3 software in the Linux environment. Simulation results show that the broadcast scheme can effectively ensure that the emergency message is correctly received in the 200m range for high vehicle density. Compared with the algorithm without considering the vehicle density, the performance has been greatly improved.

天气雷达站电磁环境影响监测研究

天气雷达站产生的超标电磁辐射会对人体造成严重的损伤。为此,提出天气雷达站电磁环境影响监测与分析。分析天气雷达站电磁影响因素,结合发射天线的方向函数,构建雷达功率密度模型。测试结果表明,对于S波、C波段、X波段,真实值与计算值呈现随距离增加而降低的趋势。对于三个波的频段,当接近天线的远场区时,计算值与真实值逐渐接近,相对误差均较小,说明模型在远场区的适用性更强;研究算法与实测值的拟合程度较高;在模型的应用中,真实反映了某市区的电磁辐射情况。

基于概率密度演化的大跨越导线铝部风振疲劳可靠度分析

为了掌握微风作用下大跨越架空输电导线铝股疲劳特性及其可靠度,提出了基于概率密度演化的大跨越输电导线铝部疲劳可靠度计算方法.首先建立了大跨越塔线体系有限元模型,研究了微风激振下导线悬挂点处振动位移时程,然后构建了导线节段有限元实体模型,以微风激振作用下导线位移时程为激励,研究了大跨越导线内外层铝股风振疲劳应力时程响应,最后采用概率密度演化方法,考虑线路风速风向概率分布,分析了大跨越导线疲劳可靠度,并与Miner线性累积损伤结果进行比较.结果表明:微风风速越大,大跨越导线振幅越大;微风作用下大跨越导线的外层铝股应力大于内层铝股,外层的钢股应力亦大于内层;大跨越导线运行年限越大,导线内外层铝股可靠度越小,但内层铝股可靠度大于外层铝股可靠度;基于Miner原理计算的铝股疲劳可靠度偏大,建议开展大跨越输电导线疲劳设计时考虑分层特性.

电力通信网络敏感信息传输路由安全优化设计

优化电力通信网络敏感信息传输节点选取过程,可避免链路拥挤,高消耗的传输能量导致簇首分布不合理的问题。因此,为了提高敏感信息传输安全性和网络覆盖率,设计电力通信网络敏感信息传输路由安全优化方案。结合PageRank算法迭代更新连接节点,构建路由连接函数,综合考虑节点负荷容量和等级选取节点。构建路由安全优化协议整体框架,依据链路ETX值改善电力通信网络中能量损耗。计算目标节点分布概率密度,设计路由优化数据分发机制,实现敏感信息传输路由安全优化。由实验结果可知,所设计方法簇1、2、3、4的簇首中心坐标分别为(-1,2)、(1,1.8)、(0.95,-2.2)、(-1,-2),与实际簇首所在中心一致;最高网络覆盖率为96%,有效提高了网络连接安全性。

基于缪子成像技术对浅层与深层地质结构的模拟研究

缪子透射成像技术是一种基于物体密度差的新型成像技术,利用穿透物体前后的通量变化实现目标物的远距离无损成像。矿产资源勘查与地质结构的勘探对于经济、社会和环境的可持续发展具有重要意义,缪子透射成像技术可以作为现有勘探手段的有力补充。基于Geant4软件模拟研究宇宙射线缪子在不同地质结构中的物理过程,首先研究了该技术区分两个物体时需要存在的密度差大小,其次在地面结构的模拟中构建了火山模型并对其进行宇宙射线缪子透射成像研究,最后模拟在地下600 m深处对矿洞上方未探明的不同规模矿体使用缪子探测器进行扩展勘探。研究结果表明:使用缪子透射成像技术能够区分密度差大于5%的地质结构,并反演出火山的密度分布;在地下600 m深处,当射线穿透矿体的路径不透明度与周围岩石的路径不透明度差值大于4%时,缪子透射成像技术便能够识别深层岩石中的矿体。因此,当存在合理的密度差时,将缪子透射成像技术应用于地质勘探能够实现无损勘探并获得较高的成像精度。

基于计算流体力学-离散元耦合的相对密实度对断级配土体渗蚀效应的影响研究

土体几何因素(粒径比、细粒含量、相对密实度等)不仅影响土体内部稳定性,同时对侵蚀进程有着重要影响。基于离散单元法(discrete element method,简称DEM)与计算流体动力学(computational fluid dynamics,简称CFD)耦合方法,建立了内部不稳定土渗流-侵蚀三维计算模型。考虑细粒含量及相对密实度对内部侵蚀过程的耦合影响,对细观变量:土体孔径分布曲线、颗粒接触数目以及内部传力机制进行分析,以揭示细粒含量与相对密实度的影响的细观机制。研究结果表明:相对密实度的增加降低了侵蚀质量比,且该影响程度与细粒含量相关,细粒含量越高,相对密实度的影响更加明显;内部不稳定土体渗蚀后沿渗流方向可分为上游侵蚀区、中部稳定区及下游侵蚀区。土体渗透性在侵蚀过程中的增长幅度随相对密实度的降低而逐渐增加,随细粒含量的增加而增加;相对密实度对渗蚀过程的影响可归因于三方面:相同水力梯度下渗流流量不同,内部孔隙尺寸分布存在差异,以及细颗粒对土体内部应力传递的贡献不同。研究结果加深了土体几何因素对内部渗蚀过程影响的理解,并为宏观侵蚀本构的建立提供了参考。

8号液力传动油低温表观黏度的相关性研究

为满足8号液力传动油精益生产的需要,实现调合中控室对8号液力传动油低温表观黏度的预测与把控,通过不同原材料制备的8号液力传动油的物理性能与低温表观黏度的相关性研究,利用响应曲面法和Design-expert 12.0软件进一步研究密度、黏度指数、运动黏度与低温表观黏度的相关性,掌握低温表观黏度的变化规律,建立低温表观黏度预测模型。结果表明:8号液力传动油的运动黏度(A)、黏度指数(B)、20℃密度(C)与低温表观黏度(Y)的相关性高,拟合得到低温表观黏度回归方程:Y=2032.74+123.28 A-1142.98 B+574.01 C+680.72 AB-1294.84 AC-1091.62 BC,经过8个批次不同原材料生产的8号液力传动油的应用验证,低温表观黏度预测值与实测值基本一致,回归方程模型的可靠性高。

基于分形曲线近零密度声学超材料的声波调控研究

结合空间卷曲理念和分形自相似原理,提出了一种具有“之”字型特征的空间卷曲型声学超材料,利用等效参数法提取了该分形声学超材料结构单元的等效质量密度,结果表明,在特定的频率范围内该分形结构单元具有近零密度特性。有限元法分析结果表明,利用该近零密度分形结构单元进行特定的周期性排列后组成的声学超材料,可以在特定频率范围内实现高效调控声波的目的,例如实现声隐身、声隧穿、弯曲狭缝传输和波前整形,同时分析了这些声特殊现象的出现与近零密度声学超材料透射系数峰值频率的对应关系。最后进行了试验验证,利用3D打印技术加工制得1阶、2阶近零密度声学超材料单元样品,并测试其透射系数,通过对比可知,实测结果和有限元分析结果符合良好,证明了结果的准确性和所设计结构的有效性。