The Influence of the Sun and Moon on the Observation of Very High Energy Gamma-ray Sources Using EAS Arrays

With great advance of ground-based extensive air shower arrays,such as LHAASO and HAWC,many very high energy(VHE)gamma-ray sources have been discovered and are being monitored regardless of the day and the night.Hence,the Sun and Moon would have some impacts on the observation of gamma-ray sources,which have not been taken into account in previous analysis.In this paper,the influence of the Sun and Moon on the observation of very high energy gamma-ray sources when they are near the line of sight of the Sun or Moon is estimated.The tracks of all the known VHE sources are scanned and several VHE sources are found to be very close to the line of sight of the Sun or Moon during some period.The absorption of very high energy gamma rays by sunlight is estimated with detailed method and some useful conclusions are achieved.The main influence is the block of the Sun and Moon on gamma rays and the shadow on the cosmic ray background.The influence is investigated considering the detector angular resolution and some strategies on data analysis are proposed to avoid the underestimation of the gamma-ray emission.

Simulation and Performance Analysis of Six Types of Sun Tracker Approaches:A Comparative Analysis for Solar Concentrating Technology Application at Burkina Faso

Modelization equations of six approaches for tracking the sun are recalled and used to evaluate the constraints and performances to which they lead to.The geographical study case is taken for the specific latitude of 12 North that is a good matching with the location of the country of Burkina Faso.Three decisive periods were locally established in order to consider the different travels of the sun on sky during one year.This work presents some technical data which facilitates the choice of sun tracking approaches with concern of a concentrator limits such as its angle of acceptance,its motion control card interpolation model,or its minimum irradiation level for energy conversion effectiveness.

The Science of Radio Astronomy: An Investigation of Crab Nebula

The science of radio astronomy focuses on the observation and study of celestial objects by reading their radio waves. The 5 meter radio-telescope is able to observe different radio sources using a C-band LNB. This research was essentially focused on Crab Nebula, also known as Taurus A. The study led to interesting observations, which were validated numerically using various scientific computing software. The radio waves emitted by Taurus A are readable by the RTL-SDR, a software defined radio receiver. This device is capable of reading radio frequencies in the range of 0.5 MHZ to 1700 MHZ.

Impact of atmospheric ionization by delayed radiation from highaltitude nuclear explosions on radio communication

In this study,we investigated the motion,shape,and delayed radiation intensity of a radioactive cloud by establishing a volume-source model of delayed radiation after high-altitude nuclear explosions.Then,the spatial distribution of electron number density at different moments on the north side of the explosion point generated by delayed γ-rays and delayed β-rays from the radioactive cloud under the influence of the geomagnetic field was calculated by solving chemical reaction kinetics equations.The impact of radio communication in the different frequency bands on the process of atmospheric ionization was also studied.The numerical results of the high-altitude nuclear explosion (120 km high and with a 1 megaton equivalent at 40°N latitude) indicated that the peak of electron number density ionized delayed γ-rays is located at a height of approximately 100 km and that of electron number density ionized delayed β-rays is about 90 km high.After 1 min of explosion,the radio communication in the medium frequency (MF) and high-frequency (HF)bands was completely interrupted,and the energy attenuation of the radio wave in the very high-frequency (VHF)band was extremely high.Five minutes later,the VHF radio communication was basically restored,but the energy attenuation in the HF band was still high.After 30 min,theVHF radio communication returned to normal,but its influence on the HF and MF radio communication continued.

DSC based Dual-Resunet for radio frequency interference identification

Radio frequency interference(RFI)will pollute the weak astronomical signals received by radio telescopes,which in return will seriously affect the time-domain astronomical observation and research.In this paper,we use a deep learning method to identify RFI in frequency spectrum data,and propose a neural network based on Unet that combines the principles of depthwise separable convolution and residual,named DSC Based Dual-Resunet.Compared with the existing Unet network,DSC Based Dual-Resunet performs better in terms of accuracy,F1 score,and MIoU,and is also better in terms of computation cost where the model size and parameter amount are 12.5%of Unet and the amount of computation is 38%of Unet.The experimental results show that the proposed network is a high-performance and lightweight network,and it is hopeful to be applied to RFI identification of radio telescopes on a large scale.

Knowledge and Practices of Health Professionals on the Optimization of Radiation Protection in Diagnostic Radiology in Children and Adults in the General Referral Hospitals of Bukavu in South Kivu, DRC

The aim of this research was to assess the knowledge and practices of radiological versus non-radiological health professionals on the optimisation of radiation protection in paediatric and adult radiology in BUKAVU hospitals. To achieve this, we surveyed a convenience sample of 73 health professionals including 23 radiologists working in the hospitals surveyed to assess knowledge and level of implementation of radiation protection principles. Also, physical parameters were taken for the calculation of entry doses in paediatric and adult radiology units for comparison with the International Commission on Radiological Protection (ICRP) diagnostic reference levels. After analysis of the data, the following was found: although radiologists have sufficient knowledge of radiation protection standards, technical constraints do not allow them to observe the dose limitation principle recommended by the ICRP. This is why several radiology departments, including those of the HPGRB, the MWANZI clinic and CIRIRI hospital, have proved to be very irradiating for children. However, radiologists and non-radiologists alike do not contribute positively to the optimisation of radiation protection in the diagnostic use of X-rays. Therefore, support in the implementation of radiation protection principles and regular monitoring of the units as well as replacement of non-standard equipment is necessary to promote patient and environmental safety by optimising radiation protection.

Non-uniform temperature distribution of the main reflector of a large radio telescope under solar radiation

The non-uniform temperature distribution of the main reflector of a large radio telescope may cause serious deformation of the main reflector,which will dramatically reduce the aperture efficiency of a radio telescope.To study the non-uniform temperature field of the main reflector of a large radio telescope,numerical calculations including thermal environment factors,the coefficients on convection and radiation,and the shadow boundary of the main reflector are first discussed.In addition,the shadow coverage and the non-uniform temperature field of the main reflector of a 70-m radio telescope under solar radiation are simulated by finite element analysis.The simulation results show that the temperature distribution of the main reflector under solar radiation is very uneven,and the maximum of the root mean square temperature is 12.3℃.To verify the simulation results,an optical camera and a thermal imaging camera are used to measure the shadow coverage and the non-uniform temperature distribution of the main reflector on a clear day.At the same time,some temperature sensors are used to measure the temperature at some points close to the main reflector on the backup structure.It has been verified that the simulation and measurement results of the shadow coverage on the main reflector are in good agreement,and the cosine similarity between the simulation and the measurement is above 90%.Despite the inevitable thermal imaging errors caused by large viewing angles,the simulated temperature field is similar to the measured temperature distribution of the main reflector to a large extent.The temperature trend measured at the test points on the backup structure close to the main reflector without direct solar radiation is consistent with the simulated temperature trend of the corresponding points on the main reflector with the solar radiation.It is credible to calculate the temperature field of the main reflector through the finite element method.This work can provide valuable references for studying the thermal deformation and the surface accuracy of the main reflector of a large radio telescope.

Investigation on the Formation of Herringbone Structure in TypeⅡSolar Radio Bursts

We report detailed observation of the“herringbone”of a Type II solar radio burst that occurred on 2010 November 3rd.Data from the Space Weather Prediction Center,National Oceanic and Atmospheric Administration,e-CALLISTO,and Nan?ay Radio Heliograph are analyzed.We determine the brightness temperature and degree of circular polarization of the“herringbone”burst.Correlations between the physical parameters and the“herringbone”are examined.Based on the relationship,this is the first study that suggested this“herringbone”was generated through fundamental plasma.

Estimation of Solar Observations with the Five-hundred-meter Aperture Spherical Radio Telescope(FAST)

We present the estimation of solar observation with the Five-hundred-meter Aperture Spherical radio Telescope(FAST).For both the quiet Sun and the Sun with radio bursts,when pointing directly to the Sun,the total power received by FAST would be out of the safe operational range of the signal chain,even resulting in damage to the receiver.As a conclusion,the Sun should be kept at least~2°away from the main beam during observations at~1.25 GHz.The separation for lower frequency should be larger.For simplicity,the angular separation between the FAST beam and the Sun is suggested to be~5°for observations at 200 MHz or higher bands.

Radiation pattern analyses of circular aperture antenna to generate radio orbital angular momentum

圆形口径天线近来被认为是在毫米波频段产生具有高功率电磁轨道角动量的自然方式之一。但是,目前的研究并没有给出该种天线的辐射特性分析。本文从理论角度推导了产生轨道角动量的圆形口径天线的辐射特性,并通过仿真实验验证了理论结果的准确性。正交横电模(TE)和横磁模(TM)激励的圆形口径天线的仿真实验表明,TE_(g1)可以产生纯净g–1模态的轨道角动量,更适合在实际应用中使用。本文对该类天线的分析有助于毫米波电磁波涡旋的产生的研究和分析。

卫星微波高层探测通道定标精度评估

全球/区域数值预报同化系统所需要的重要资料来源之一是卫星微波遥感的亮温数据。微波遥感仪器的高层大气(平流层中上部)探测通道亮温的定标精度,受多种因素影响,存在一定的偏差。由于高层大气高精度探测资料相对比较匮乏,因此对微波遥感的高层大气亮温的精度检验评估成为重要研究内容。本文对在轨运行的微波温度遥感器AMSU-A、ATMS和FY-3D MWTS-2在2020年观测数据进行了定标精度检验评估,综合使用了三种评估方法进行了较为全面的分析,即基于掩星资料、再分析资料的辐射传输模拟比较和同类仪器交叉定标比较。三种检验评估方法从不同角度揭示了各仪器高层大气探测通道观测资料的误差特征,分析了对比误差的可能来源。三种评估方案给出的高层通道亮温的偏差存在差异,但基本结果变化趋势是一致的,即高层通道相比中低层通道,存在较大的噪音。除了交叉定标方法,其它两种方法都检验出了高层资料偏差的季节变化;整体而言,AMSU-A表现要优于MWTS-2和ATMS。本研究评估的高层亮温偏差的时间、空间变化特征可为微波高层大气资料的同化、气候应用提供参考。

DSRT三轴低频天线指向误差批量测量和校正方法

稻城圆环阵太阳射电望远镜(Daocheng Solar Radio Telescope, DSRT)作为子午工程二期太阳-行星际探测子系统的重要部分,工作在150–450 MHz频段,可提供高空间、高时间分辨率的太阳爆发亮温图像.针对DSRT天线的高精度指向测量以及对指向误差批量标定和校正的需求,首先根据DSRT独有的三轴座架系统,通过四元数旋转变换法建立了天线3参数编码器零点误差模型;然后提出了基于射电源的漂移扫描法获得16个单元天线功率方向图,并根据2维方向图确定波束中心的方法精确测量了DSRT天线指向误差;最后用最小二乘法拟合得到模型参数,并通过天线控制软件重新调整各个轴的零点,后对调整结果进行验证.结果表明指向校正方法可靠有效,校正后16个天线的指向精度为0.5°之内,明显优于校正前3.5°的指向误差,满足误差小于DSRT天线最高工作频率下的1/10波束范围内的要求.

基于增强积分双谱的轨道交通辐射源识别方法

[目的]城市轨道交通无线通信系统中存在大量外部干扰信号,对行车安全构成重大隐患。针对辐射源射频特征易受噪声与干扰影响,导致识别准确率低的问题,须提出一种基于增强对角积分双谱的通信辐射源个体识别方法,为轨道交通无线通信系统安全保障提供有效新途径。[方法]分析了对角相关局部积分双谱(DCLIB)的数据处理过程及原理,阐述了双谱变换的计算、增强对角积分双谱的计算、自适应双谱积分区间的划分,以及基于残差网络的辐射源识别方法。基于实际Wi-Fi(无线保真)设备进行仿真试验,对DCLIB方法和其他辐射源识别方法的识别效果进行分析对比。[结果及结论]DCLIB方法先估计通信辐射源信号的双谱,并利用次对角线各平行线的自相关特性形成新的谱信息以增强信号的细微特征;然后依据谱信号强度自适应选取合理的谱信号积分区间,在降低噪声影响的同时降低算法的计算复杂度,从而获得增强的对角积分双谱;进而将所提DCLIB信号作为辐射源的射频指纹特征,采用深度残差网络实现辐射源个体识别。基于实际Wi-Fi设备的仿真识别试验结果表明,DCLIB方法的识别准确率最优,并具有良好的抗噪声性能。

科研成果进“天线与电波传播”课堂的探索——以天线辐射与散射一体化控制的科研成果为例

“天线与电波传播”是电子信息类本科专业的核心课程,是注重基础理论与实际应用相结合的课程。为了提高该课程的教学效果,提升课程知识与科研实际联系程度,在课程教学中采用科研成果进课堂的教学方法。利用科研中已解决的关键问题,让学生带着问题去学习,提升对本门课程学习的兴趣和主动性。以天线辐射与散射一体化控制的科研成果进课堂为例,将此成果引入《微带天线》章节,从天线辐射与散射控制的矛盾出发,综合运用课程知识点,对天线辐射控制和散射控制的影响因素进行剖析,结合科研实践开展启发性教学,启发学生思考如何通过天线结构的巧妙设计实现辐射与散射一体化控制,培养学生的创新思维和综合分析能力,使学生走出课堂就能走向科研和工程实践。

基于RCS不同海况双基雷达最优角度分析

雷达散射截面(RCS,Radar Cross Section)用于表征雷达目标对照射电磁波反射特性,在被动雷达系统中,雷达散射截面是判断能否检测到目标的一个重要参数。针对以广播电视卫星为外辐射源的被动雷达系统对海面目标进行检测的问题,仿真了目标和海面的双基地雷达散射截面(RCS),分析外辐射源-仿真对象-接收机位置关系对雷达散射截面(RCS)的影响,讨论了目标和海面的雷达散射截面(RCS)与角度的关系,对被动雷达系统如何选择外辐射源具有一定参考价值。

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。

A review of solar type Ⅲ radio bursts

Solar type III radio bursts are an important diagnostic tool in the understanding of solar accelerated electron beams. They are a signature of propagating beams of nonthermal electrons in the solar atmosphere and the solar system. Consequently, they provide information on electron acceleration and transport, and the conditions of the background ambient plasma they travel through. We review the observational properties of type III bursts with an emphasis on recent results and how each property can help identify attributes of electron beams and the ambient background plasma. We also review some of the theoretical aspects of type III radio bursts and cover a number of numerical efforts that simulate electron beam transport through the solar corona and the heliosphere.

Recent results of zebra patterns in solar radio bursts

This review covers the most recent experimental results and theoretical research on zebra patterns （ZPs） in solar radio bursts. The basic attention is given to events with new peculiar elements of zebra patterns received over the last few years. All new properties are considered in light of both what was known earlier and new theoretical models. Large-scale ZPs consisting of small-scale fiber bursts could be explained by simultaneous inclusion of two mechanisms when whistler waves ＂high- light＂ the levels of double plasma resonance （DPR）. A unique fine structure was observed in the event on 2006 December 13： spikes in absorption formed dark ZP stripes against the absorptive type Ⅲ-like bursts. The spikes in absorption can appear in accordance with well known mechanisms of absorptive bursts. The additional injection of fast particles filled the loss-cone （breaking the loss-cone distribution）, and the generation of the continuum was quenched at these moments. The maximum absorptive effect occurs at the DPR levels. The parameters of millisecond spikes are determined by small dimensions of the particle beams and local scale heights in the radio source. Thus, the DPR model helps to understand severai aspects of unusual elements of ZPs. However, the simultaneous existence of several tens of the DPR levels in the corona is impossible for any realistic profile of the plasma density and magnetic field. Three new theories of ZPs are examined. The formation of eigenmodes of transparency and opac- ity during the propagation of radio waves through regular coronal inhomogeneities is the most natural and promising mechanism. Two other models （nonlinear periodic space - charge waves and scattering of fast protons on ion-sound harmonics） could happen in large radio bursts.

BoxCox multi-output linear regression for 10.7 cm solar radio flux prediction

We consider the problem of predicting the mid-term daily 10.7 cm solar radio flux(F10.7),a widely-used solar activity index.A novel approach is proposed for this task,in which BoxCox transformation with a proper parameter is first applied to make the data satisfy the property of homoscedasticity that is a basic assumption of regression models,and then a multi-output linear regression model is used to predict future F10.7 values.The experiment shows that the BoxCox transformation significantly improves the predictive performance and our new approach works substantially better than the prediction from the US Airforce and other alternative methods like Auto-regressive Model,Multi-layer Perceptron,and Support Vector Regression.

Tuning control system of a third harmonic superconducting cavity in the Shanghai Synchrotron Radiation Facility

Beam lifetime is dominated by Touschek scattering at the Shanghai Synchrotron Radiation Facility(SSRF).Touschek loss rate is affected by probability for scattering beyond the RF acceptance and the volume charge density of the bench.In the phaseⅡupgrade of the SSRF,a third harmonic superconducting cavity will be used to enhance the Touschek lifetime by lengthening the bunches.The Touschek lifetime improvement factor is affected by the voltage of a harmonic cavity.To stabilize the cavity voltage,a tuning control system was designed to control it.The design of the tuning control system was based on the SSRF third-generation low-level RF control system.Some hardware and specialized algorithms were redesigned to fit the harmonic cavity control.The design of the tuning control system is complete,and the control system has been tested.The test result shows that the fluctuation of amplitude is<±0.34%within 1.5 h,which satisfies the stability requirement.