Radio Interference Characteristic of Ultra-high Voltage AC Transmission Lines by Using Stochastic Modeling

For developing ultra-high voltage(UHV) AC power transmission systems,it is important to precisely estimate and to limit the radio interference(RI) level of power lines.Based on the stochastic characteristics in amplitude and repetition rate of induced corona current,by using the probability theory and mathematical statistics,we establish a stochastic model for the wide-sense stationary random process of corona discharges.Then combining the stochastic model with model-propagation-analysis method,the RI levels under three-phase UHV AC transmission lines are calculated.The results of the calculation based on stochastic model method and International Council on Large Electric Systems(CIGRE) excitation function are compared with that based on semi-empirical method and some other excitation functions.The stochastic model based on different excitation functions is also adopted to simulate the RI levels under finite test lines with two opened terminations.The results indicate that with the same average maximum gradient on conductor surface and the same conductor type,the number of corona discharge per unit length is one of the main reasons that causes the difference between different excitation functions.It is also concluded that for a long test line,the effect of standing wave on RI field strength is negligible in the middle of the line,but obvious near both terminations: for a 10-km line,the maximum difference in RI field strength is 2.78 dB,between the peak value of the standing wave near the ends and the steady value near the middle of the line.

Balmer H_α,H_β and H_γ Spectral Lines Intensities in High-Power RF Hydrogen Plasmas

Hα（Balmer-alpha）, Hβ （Balmer-beta） and Hγ （Balmer-gamma） spectral line inten- sities in atomic hydrogen plasma are investigated by using a high-power RF source. The intensities of the Hα, Hβ and Hγ spectral lines are detected by increasing the input power （0-6 kW） of ICPs （inductively coupled plasmas）. With the increase of net input power, the intensity of Hα im- proves rapidly （0-2 kW）, and then reaches its dynamic equilibrium; the intensities of Hβ can be divided into three processes： obvious increase （0-2 kW）, rapid increase （2-4 kW）, almost constant （4-6 kW）; while the intensities of Hγ increase very slowly. The energy levels of the excited hydro- gen atoms and the splitting energy levels produced by an obvious Stark effect play an important role in the results.

Alternative kind of hydrogen atoms as a possible explanation for the latest puzzling observation of the 21 cm radio line from the early Universe

There is a puzzling astrophysical result concerning the latest observation of the absorption profile of the redshifted radio line 21 cm from the early Universe(as described in Bowman et al.). The amplitude of the profile was more than a factor of two greater than the largest predictions. This could mean that the primordial hydrogen gas was much cooler than expected. Some explanations in the literature suggested a possible cooling of baryons either by unspecified dark matter particles or by some exotic dark matter particles with a charge a million times smaller than the electron charge. Other explanations required an additional radio background. In the present paper, we entertain a possible different explanation for the above puzzling observational result: the explanation is based on the alternative kind of hydrogen atoms(AKHA),whose existence was previously demonstrated theoretically, as well as by the analysis of atomic experiments. Namely, the AKHA are expected to decouple from the cosmic microwave background(CMB) much earlier(in the course of the Universe expansion) than usual hydrogen atoms, so that the AKHA temperature is significantly lower than that of usual hydrogen atoms. This seems to lower the excitation(spin) temperature of the hyperfine doublet(responsible for the 21 cm line) sufficiently enough for explaining the above puzzling observational result. This possible explanation appears to be more specific and natural than the previous possible explanations. Further observational studies of the redshifted 21 cm radio line from the early Universe could help to verify which explanation is the most relevant.

Radio recombination line observations at 1.0-1.5 GHz with FAST

H Ⅱ regions made of gas ionized by radiations from young massive stars,are widely distributed in the Milky Way.They are tracers for star formation,and their distributions are correlated with the Galactic spiral structure.Radio recombination lines(RRLs) of hydrogen and other atoms allow for the most precise determination of physical parameters such as temperature and density.However,RRLs at around 1.4 GHz from HⅡ regions are weak and their detections are difficult.As a result,only a limited number of detections have been obtained yet.The 19-beam receiver on board of the Five-hundred-meter Aperture Spherical radio Telescope(FAST) can simultaneously cover 23 RRLs for Hnα,Henα,and Cnα(n=164-186),respectively.This,combined with its unparalleled collecting area,makes FAST the most powerful telescope to detect weak RRLs.In this pilot survey,we use FAST to observe nine HⅡ regions at L band.We allocate20 minutes pointing time for each source to achieve a sensitivity of around 9 mK in a velocity resolution of2.0 km s^(-1).In total,21 RRLs for Hnα and Cnα at 1.0-1.5 GHz have been simultaneously detected with strong emission signals.Overall,the detection rates for the H167α and C167α RRLs are 100%,while that for the He167α RRL is 33.3%.Using hydrogen and helium RRLs,we measure the electron density,electron temperature,and pressure for three HⅡ regions.This pilot survey demonstrates the capability of FAST in RRL measurements,and a statistically meaningful sample with RRL detection,through which knowledge about Galactic spiral structure and evolution can be obtained,is expected in the future.

基于FPGA的射频腔体系统数学模型在线辨识算法

射频系统的数学模型包含了射频腔体的关键特征参数(如腔体半带宽、谐振频率和洛伦兹力失谐系数等),数学模型对腔体性能检测、控制系统仿真及低电平控制算法优化具有重要意义。网络分析仪通常用于测量射频系统的散射参数,进而构建射频系统的数学模型,但其测量步骤繁琐且无法实现系统模型的在线自动辨识。本文通过模拟网络分析仪的工作原理,在数字低电平系统内部构建了基于数控振荡器的扫频算法,实现了射频腔体系统的在线辨识。该算法的有效性已在加速器驱动嬗变研究装置前端示范样机的超导腔上验证,其测量结果与网络分析仪测量结果吻合。此外,本文利用该辨识算法还成功测得了由洛伦兹力失谐引起的超导腔频率响应畸变曲线,并讨论了洛伦兹力失谐量的大小对腔体关键特征参数测量的影响。

面向环境射频能量收集的宽频整流电路

整流电路是射频能量回收系统的核心,能够将射频能量转换为直流。但由于整流电路中使用的二极管具有非线性特性,导致整流效率会随频率变化而降低。为解决这一问题,本文提出一种具有宽频带的整流电路,它通过采用与二极管串联的短路线、与二极管并联的开路线以及多级微带线结构来调整阻抗匹配,实现了在宽频带范围内的高转换效率。设计的整流电路在0 dBm的输入功率下,从1.7~2.7 GHz,均达到50%的整流转换效率,最高整流转换效率为63.3%。该宽带整流电路可以运用在无线能量收集系统中。

基于复合左右手理论的双模态低损耗宽带毫米波片上传输线

本文提出了一种基于复合左右手(Composite Right-/Left-Handed,CRLH)理论的双模态毫米波片上传输线(Transmission Line,TL),有效兼顾了宽频段和低损耗特性,并且同时包含支持前向波的右手频段和支持后向波的左手频段.为解决毫米波半导体衬底高损耗、高寄生干扰的问题,本文首先提出T型片上CRLH单元,通过研究CRLH传输线的电路拓扑与结构实现,减小了传输损耗并展宽带宽.此外,文章通过研究色散特性实现左手和右手通带两种模态.基于砷化镓(GaAs)基集成无源器件(Integrated Passive Device,IPD)工艺,加工并实测了一款工作频段覆盖18~44.5 GHz的3阶周期CRLH TL.本文提出的传输线尺寸紧凑,为1.3 mm×0.55 mm,带有GSG(Ground Signal Ground)焊盘,最小插入损耗为1.18 dB,3 dB相对带宽超过90%.该测试结果表明所提出的片上传输线可广泛应用于实现独特电磁相位特性的片上功能电路和系统.

HI in High Gas-phase Metallicity Dwarf Galaxy WISEA J230615.06+143927.9

We present resolved Giant Metrewave Radio Telescope H I observations of the high gas-phase metallicity dwarf galaxy WISEA J230615.06+143927.9(z = 0.005)(hereafter J2306) and investigate whether it could be a Tidal Dwarf Galaxy(TDG) candidate. TDGs are observed to have higher metallicities than normal dwarfs. J2306 has an unusual combination of a blue g-r color of 0.23 mag, irregular optical morphology and high-metallicity(12 +log(O/H) = 8.68 ± 0.14), making it an interesting galaxy to study in more detail. We find J2306 to be an H I rich galaxy with a large extended, unperturbed rotating H I disk. Using our H I data we estimated its dynamical mass and found the galaxy to be dark matter(DM) dominated within its H I radius. The quantity of DM, inferred from its dynamical mass, appears to rule out J2306 as an evolved TDG. A wide area environment search reveals J2306 to be isolated from any larger galaxies which could have been the source of its high gas metallicity. Additionally, the H I morphology and kinematics of the galaxy show no indication of a recent merger to explain the high-metallicity.Further detailed optical spectroscopic observations of J2306 might provide an answer to how a seemingly ordinary irregular dwarf galaxy achieved such a high level of metal enrichment.

城市高压交流输电线路对电磁环境的影响研究

电磁环境承载无线电通信、广播和观测等业务,支撑移动互联网、物联网、卫星电视和射电望远镜等新型基础设施,保护电磁环境成为交流输变电系统设计运行的关键。该研究选取城市常见的架空220 kV交流输电线路为研究对象,测量某线路附近地面及居民楼内电场和磁场强度,分析电磁干扰的来源、产生机理、频域特征和空间衰减过程,比照城市常见无线电业务的频段和调制方式,得到典型工况下输电线路对无线电信号信噪比的影响规律,提出输电系统影响下,电磁环境保护和通信增益措施。

基于GPRS技术的输电线路状态数据通信系统设计

在现代电力系统管理中,实时监测输电线路的状态至关重要,这不仅有助于提前预防故障,而且能优化能源分配和增强系统的可靠性。通用分组无线业务(General Packet Radio Service,GPRS)技术作为一种成熟的无线数据传输手段,为远程输电线路监测提供了一种有效的通信解决方案。文章设计基于GPRS技术的输电线路状态数据通信系统,重点分析系统的总体架构、GPRS通信模块的设计、数据管理与传输策略以及安全性与容错机制的构建,并阐述测试系统的方法及其效果。

基于接地线电流法的电力电缆绝缘在线监测

为提高电力系统的安全性,将接地线电流法作为核心方法,设计电力电缆绝缘在线监测系统。采用通用分组无线业务/码分多址(General Packet Radio Service/Code Division Multiple Access,GPRS/CDMA)通信方式作为电力电缆绝缘在线监测系统的核心,建立电缆各条线路之间的通信连接。利用电流互感器(Current Transformer,CT)检测电缆电流变化情况,有利于提高绝缘在线监测系统的检测精度。将绝缘在线监测应用于电力系统,可为电力系统的后续发展提供依据。

Efficiency Effect of Obstacle Margin on Line-of-Sight in Wireless Networks

Line-of-sight clarity and assurance are essential because they are considered the golden rule in wireless network planning,allowing the direct propagation path to connect the transmitter and receiver and retain the strength of the signal to be received.Despite the increasing literature on the line of sight with different scenarios,no comprehensive study focuses on the multiplicity of parameters and basic concepts that must be taken into account when studying such a topic as it affects the results and their accuracy.Therefore,this research aims to find limited values that ensure that the signal reaches the future efficiently and enhances the accuracy of these values’results.We have designed MATLAB simulation and programming programs by Visual Basic.NET for a semi-realistic communication system.It includes all the basic parameters of this system,taking into account the environment’s diversity and the characteristics of the obstacle between the transmitting station and the receiving station.Then we verified the correctness of the system’s work.Moreover,we begin by analyzing and studying multiple and branching cases to achieve the goal.We get several values from the results,which are finite values,which are a useful reference for engineers and designers of wireless networks.

SMA molecular line survey towards the massive star-forming region G10.6-0.4in W31complex

Line surveys of complex molecules with millimeter and sub-millimeter telescopes are important for probing the physical and chemical environments of massive star forming regions(MSFRs).We present a molecular line survey with the Submillimeter Array(SMA) in the frequency ranges of 220.3–222.3 GHz and 230.3–232.3 GHz toward G10.6-0.4, the brightest star forming core in the W31 complex. Ninety-nine transitions from 22 molecular species and their isotopologues are identified. The moment 0 images of typical molecules show a compact core which is concentrated at the continuum peak position. Based on the local thermodynamic equilibrium assumption, the molecular line data are modeled. The rotational temperatures of those molecular species range from 96 to 178 K and their column densities range from 2.0×1014to 3.7×1017cm-2. The observational data suggest that all complex molecules are located in a warm environment. Chemical environments of the molecules are discussed. We compared molecular abundances and gas temperatures in G10.6-0.4 with those in other MSFRs, and found that gas temperatures and fractional abundances of specific molecules in G10.6-0.4 are similar to the typical MSFR W51 North, suggesting that there are similar physical and chemical environments in these two MSFRs.

Balmer-alpha and Balmer-beta Stark line intensity profiles for high-power hydrogen inductively coupled plasmas

We compare Balmer-alpha （Ha） and Balmer-beta （Hβ） emissions from high-power （1.0-6.0 kW） hydrogen inductively coupled plasmas （ICPs）, and propose region Ⅰ （0.0-2.0 kW）, region Ⅱ （2.0-5.0 kW）, and region Ⅲ （5.0-6.0 kW）. In region Ⅰ, both Ha emission intensity （la） and Hβ emission intensity （1β） increase with radio frequency （RF） power, which is explained by the corona model and Boltzmann＇s law, etc. However, in region II, la almost remains constant while 1β rapidly achieves its maximum value. In region Ⅲ, 1α slightly increases with RF power, while 1β decreases with RF power, which deviates significantly from the theoretical explanation for the Ha and Hβ emissions in region I. It is suggested that two strong electric fields are generated in high-power （2.0-6.0 kW） hydrogen ICPs： one is due to the external electric field of high-power RF discharge, and the other one is due to the micro electric field of the ions and electrons around the exited state hydrogen atoms in ICPs. Therefore, the strong Stark effect can play an important role in explaining the experimental results.

Simulational Investigation of a High-Efficiency X-Band Magnetically Insulated Line Oscillator

Abstract The magnetically insulated line oscillator （MILO） is a gigawatt-class, coaxial crossed-field microwave tube, which is at present a major hotspot in the field of high-power mi- crowaves （HPM） research. In order to improve the power conversion efficiency and eliminate or at least minimize anode plasma formation in the load region and radio frequency （RF） breakdown in the slow wave structure （SWS） section, an X-band MILO is presented and inyestigated nu- merically with KARAT code. The design idea is briefly presented and the simulation results are given and discussed. In the simulation, HPM is generated with peak power of 3.4 GW, maximum electric field of about 1 MV/cm, and peak power conversion efficiency of 14.0%, when the voltage is 559.1 kV and the current is 43.2 kA. The microwave frequency is pure and falls in the X-band of 9.0 GHz. The theoretical investigation and the simulation results are given to prove that the anode plasma formation and the RF breakdown can be effectively avoided or at least minimized, respectively.

Search for H I emission from superdisk candidates associated with radio galaxies

Giant gaseous layers(termed “superdisks”) have been hypothesized in the past to account for the strip-like radio emission gap(or straight-edged central brightness depression) observed between twin radio lobes, in over a dozen relatively nearby powerful Fanaroff-Riley Class II radio galaxies. They could also provide a plausible alternative explanation for a range of observations. Although a number of explanations have been proposed for the origin of the superdisks, little is known about their material content. Some X-ray observations of superdisk candidates indicate the presence of hot gas, but a cool dusty medium also seems to be common. If they are entirely or partly composed of neutral gas, then it may be directly detectable and we report here a first attempt to detect/image any neutral hydrogen gas present in the superdisks that are inferred to be present in four nearby radio galaxies. We have not found a positive H I signal in any of the four sources, resulting in tight upper limits on the H I number density in the postulated superdisks,estimated directly from the central rms noise values of the final radio continuum subtracted image. The estimated ranges of the upper limit on neutral hydrogen number density and column density are 10^-4-10^-3 atoms per cm3 and 10^19-10^20 atoms per cm^2, respectively. No positive H I signal is detected even after combining all the four available H I images(with inverse variance weighting). This clearly rules out an H I dominated superdisk as a viable model to explain these structures, however, the possibility of a superdisk being composed of warm/hot gas still remains open.

A Simulation Experiment of a Pipeline Based on Machine Learning for Neutral Hydrogen Intensity Mapping Surveys

We present a simulation experiment of a pipeline based on machine learning algorithms for neutral hydrogen(H I)intensity mapping(IM)surveys with different telescopes.The simulation is conducted on H I signals,foreground emission,thermal noise from instruments,strong radio frequency interference(s RFI),and mild RFI(m RFI).We apply the Mini-Batch K-Means algorithm to identify s RFI,and Adam algorithm to remove foregrounds and m RFI.Results show that there exists a threshold of the s RFI amplitudes above which the performance of our pipeline enhances greatly.In removing foregrounds and m RFI,the performance of our pipeline is shown to have little dependence on the apertures of telescopes.In addition,the results show that there are thresholds of the signal amplitudes from which the performance of our pipeline begins to change rapidly.We consider all these thresholds as the edges of the signal amplitude ranges in which our pipeline can function well.Our work,for the first time,explores the feasibility of applying machine learning algorithms in the pipeline of IM surveys,especially for large surveys with the next-generation telescopes.

HI detection of J030417.78+002827.4 by the Five-hundred-meter Aperture Spherical Radio Telescope

We present the first HI 21 cm spectroscopy detection of J030417.78+002827.4,which is an active galactic nucleus(AGN)with an intermediate-mass black hole(IMBH)in the center.The observations were carried out with the Five-hundred-meter Aperture Spherical Radio Telescope(FAST)last year.We relied on the ON-OFF observing approach with the 19-beam receiver covering 1.05-1.45 GHz.Within a total integration time of about 20 min,the root mean square(RMS)of our data reaches 1.2 mJy beam-1,at a velocity resolution of 1.6 km s^(-1).Radio frequency interference(RFI)is checked and excluded during the data analysis.The detected HI spectroscopy shows a dual-horned profile with a line width of 223.5 km s^(-1),indicating gas rotation around this AGN.The redshift of this galaxy derived from our HI observation is0.0447.We calculate the atomic gas mass by the integrated flux of the HI emission line.The total gas mass in this galaxy is estimated to be 1.8×10^(10)M☉.We find the fraction of gas-to-stellar mass ratio in J030417.78+002827.4 is more than 50%.This ratio is much higher than the typical value found in other AGNs with supermassive black holes(SMBHs),and is comparable to some star-forming galaxies recently observed by FAST.