光学湍流的强弱和分布是描述天文台址优劣的重要参数.介绍了利用大气模式WRF(Weather Research and Forecasting Model)计算高美古站周围大气光学湍流参数的方法,这些参数包括C_n^2(大气光学湍流强度)廓线、大气相干长度、大气相干时间...光学湍流的强弱和分布是描述天文台址优劣的重要参数.介绍了利用大气模式WRF(Weather Research and Forecasting Model)计算高美古站周围大气光学湍流参数的方法,这些参数包括C_n^2(大气光学湍流强度)廓线、大气相干长度、大气相干时间、视宁度、等晕角和闪烁率等.包括模型计算方法的实现过程、模型的设置和模拟结果的验证.计算结果与云南高美古观测站DIMM(Differential Image Motion Monitor)的实测数据进行了对比.展开更多
Active surface technique is one of the key technologies to ensure the reflector accuracy of the millimeter/submillimeter wave large reflector antenna.The antenna is complex,large-scale,and high-precision equipment,and...Active surface technique is one of the key technologies to ensure the reflector accuracy of the millimeter/submillimeter wave large reflector antenna.The antenna is complex,large-scale,and high-precision equipment,and its active surfaces are affected by various factors that are difficult to comprehensively deal with.In this paper,based on the advantage of the deep learning method that can be improved through data learning,we propose the active adjustment value analysis method of large reflector antenna based on deep learning.This method constructs a neural network model for antenna active adjustment analysis in view of the fact that a large reflector antenna consists of multiple panels spliced together.Based on the constraint that a single actuator has to support multiple panels(usually 4),an autonomously learned neural network emphasis layer module is designed to enhance the adaptability of the active adjustment neural network model.The classical 8-meter antenna is used as a case study,the actuators have a mean adjustment error of 0.00252 mm,and the corresponding antenna surface error is0.00523 mm.This active adjustment result shows the effectiveness of the method in this paper.展开更多
Leighton Chajnantor Telescope(LCT), i.e., the former Caltech Submillimeter Observatory telescope, will be refurbished at the new site in Chajnantor Plateau, Chile in 2023. The environment of LCT will change significan...Leighton Chajnantor Telescope(LCT), i.e., the former Caltech Submillimeter Observatory telescope, will be refurbished at the new site in Chajnantor Plateau, Chile in 2023. The environment of LCT will change significantly after its relocation, and the telescope will be exposed to large wind disturbances directly because its enclosure will be completely open during observation. The wind disturbance is expected to be a challenge for LCT's pointing control since the existing control method cannot reject this disturbance very well. Therefore, it is very necessary to develop a new pointing control method with good capability of disturbance rejection. In this research, a disturbance observer—based composite position controller(DOB-CPC) is designed, in which an H∞feedback controller is employed to compress the disturbance, and a feedforward linear quadratic regulator is employed to compensate the disturbance precisely based on the estimated disturbance signal. Moreover, a controller switching policy is adopted, which applies the proportional controller to the transient process to achieve a quick response and applies the DOB-CPC to the steady state to achieve a small position error. Numerical experiments are conducted to verify the good performance of the proposed pointing controller(i.e., DOB-CPC) for rejecting the disturbance acting on LCT.展开更多
We introduce a new code for cosmological simulations, PHo To Ns, which incorporates features for performing massive cosmological simulations on heterogeneous high performance computer(HPC) systems and threads oriented...We introduce a new code for cosmological simulations, PHo To Ns, which incorporates features for performing massive cosmological simulations on heterogeneous high performance computer(HPC) systems and threads oriented programming. PHo To Ns adopts a hybrid scheme to compute gravitational force, with the conventional Particle-Mesh(PM) algorithm to compute the long-range force,the Tree algorithm to compute the short range force and the direct summation Particle-Particle(PP) algorithm to compute gravity from very close particles. A self-similar space filling a Peano-Hilbert curve is used to decompose the computing domain. Threads programming is advantageously used to more flexibly manage the domain communication, PM calculation and synchronization, as well as Dual Tree Traversal on the CPU+MIC platform. PHo To Ns scales well and efficiency of the PP kernel achieves68.6% of peak performance on MIC and 74.4% on CPU platforms. We also test the accuracy of the code against the much used Gadget-2 in the community and found excellent agreement.展开更多
AT2021lfa,also known as ZTF21aayokph,was detected by the Zwicky Transient Facility on 2021 May 4,a 05:34:48 UTC.Follow-up observations were conducted using a range of ground-based optical telescopes,as wel as Swift/XR...AT2021lfa,also known as ZTF21aayokph,was detected by the Zwicky Transient Facility on 2021 May 4,a 05:34:48 UTC.Follow-up observations were conducted using a range of ground-based optical telescopes,as wel as Swift/XRT and VLA instruments.AT2021lfa is classified as an“orphan afterglow”candidate due to its rapid flux decline and its reddened color(g-r=0.17±0.14 mag).For an optical transient source without promp gamma-ray detection,one key point is to determine its burst time.Here we measure the burst time through fitting the initial bump feature of AT2021lfa and obtain its burst time as 2021 May 3,at 22:09:50 UTC.Using afterglowpy,we model the multi-band afterglow of AT2021lfa and find that the standard model canno reproduce the late radio observations well.Considering that the microphysical parameters ε_(e),ε_(B)(the energy fraction given to electrons and magnetic field),andξN(the fraction of accelerated electrons)may vary with time we then model the afterglow of AT2021lfa taking into account the temporal evolution of the physical parameters ε_(e),ε^(B),and ξ_(N) and find in this case the multi-wavelength observations can be reproduced well.The initial Lorentz factor of AT2021lfa can be estimated from the peak time of the early afterglow,which yields a value of about 18 suggesting that AT2021lfa should be classified as a“dirty fireball.”From the upper limit for the prompt emission energy of AT2021lfa,we obtain that the radiation efficiency is less than 0.02%,which is much smaller than that of ordinary gamma-ray bursts(GRBs).It is also interesting that the fitted values of jet angle and viewing angle are very large,θ_(c)~0.66 rad,θ_(v)~0.53 rad,which may lead to the low Lorentz factor and radiation efficiency.When compared with GRB afterglow samples,it is evident that the onset bump timescale of AT2021lfa satisfies the empirical relationships observed in GRB samples.Additionally,the luminosity of AT2021lfa falls within the range of observations for GRB samples;however,approximately 1 day after the展开更多
Using an effective adiabatic index γ_(eff) to mimic the feedback of efficient shock acceleration,we simulate the temporal evolution of a young type Ia supernova remnant (SNR) with two different background magnetic fi...Using an effective adiabatic index γ_(eff) to mimic the feedback of efficient shock acceleration,we simulate the temporal evolution of a young type Ia supernova remnant (SNR) with two different background magnetic field(BMF) topologies:a uniform and a turbulent BMF.The density distribution and magnetic-field characteristics of our benchmark SNR are studied with two-dimensional cylindrical magnetohydrodynamic simulations.When γ_(eff)is considered,we find that:(1) the two-shock structure shrinks and the downstream magnetic-field orientation is dominated by the Rayleigh–Taylor instability structures;(2) there exists more quasi-radial magnetic fields inside the shocked region;and (3) inside the intershock region,both the quasi-radial magnetic energy density and the total magnetic energy density are enhanced:in the radial direction,with γ_(eff)=1.1,they are amplified about 10–26 times more than those with γ_(eff)=5/3.While in the angular direction,the total magnetic energy densities could be amplified about 350 times more than those with γ_(eff)=5/3,and there are more grid cells within the intershock region where the magnetic energy density is amplified by a factor greater than 100.展开更多
随着射电望远镜口径增大、观测频率提高,对其指向精度的要求也越来越高.然而,望远镜服役于野外台站,台址风扰对天线指向精度的影响在高频段观测时已不能忽略.由于风扰的时变性,现有的抗风方法无法保障大口径高指向精度望远镜在高频段的...随着射电望远镜口径增大、观测频率提高,对其指向精度的要求也越来越高.然而,望远镜服役于野外台站,台址风扰对天线指向精度的影响在高频段观测时已不能忽略.由于风扰的时变性,现有的抗风方法无法保障大口径高指向精度望远镜在高频段的有效观测时长.因此,提出了一种基于风障精确布置改善台址风环境的方法.通过数值模拟构建了风障仿真模型,并将仿真结果与风洞实测数据比较,两种孔隙率风障的平均误差分别为3.7%和6.1%,保证了风障模型的可靠性.以新疆奇台射电望远镜(QiTai radio Telescope,QTT)台址为例,基于QTT台址斜坡地形构建了计算域模型,开展单风障不同高度、不同孔隙率的系列风场仿真试验,得到了风障参量与下游挡风效果的关系.基于单风障合理高度和最优孔隙率设置南北风障,仿真结果表明在确定高度下最优孔隙率可以组合,孔隙率0.1-0.1组合的风障挡风效果最优,南方向来风在天线区域可以有效降低75%以上的风速.展开更多
以ASTRODI(Astrodynamical Space Test of Relativity using Optical DevicesI,单航天器天文激光动力学)为例介绍无拖曳卫星的结构及其工作原理.推导了其动力学方程,并在此基础上建立了卫星的动力学数值仿真器.将H_2最优控制理论运用于...以ASTRODI(Astrodynamical Space Test of Relativity using Optical DevicesI,单航天器天文激光动力学)为例介绍无拖曳卫星的结构及其工作原理.推导了其动力学方程,并在此基础上建立了卫星的动力学数值仿真器.将H_2最优控制理论运用于以噪声压制为主要目的的无拖曳卫星控制系统的设计,通过传递函数法及数值法双重分析表明所设计的控制器能符合卫星的控制要求,同时表明在控制器没计过程中采用的线性化假设是适当的.展开更多
Determining asteroid properties provides valuable physical insights but inverting them from photometric lightcurves remains computationally intensive.This paper presents a new approach that combines a simplified Celli...Determining asteroid properties provides valuable physical insights but inverting them from photometric lightcurves remains computationally intensive.This paper presents a new approach that combines a simplified Cellinoid shape model with the Parallel Differential Evolution(PDE)algorithm to accelerate inversion.The PDE algorithm is more efficient than the Differential Evolution algorithm,achieving an extraordinary speedup of 37.983 with 64 workers on multicore CPUs.The PDE algorithm accurately derives period and pole values from simulated data.The analysis of real asteroid lightcurves validates the method’s reliability:in comparison with results published elsewhere,the PDE algorithm accurately recovers the rotational periods and,given adequate viewing geometries,closely matches the pole orientations.The PDE approach converges to solutions within 20,000 iterations and under one hour,demonstrating its potential for large-scale data analysis.This work provides a promising new tool for unveiling asteroid physical properties by overcoming key computational bottlenecks.展开更多
小天体探测是当今太阳系探测的一大热点,对小行星演化的研究有助于人们了解太阳系的起源.演化研究的一项重要内容是小天体结构的演化,即小天体在多种力学机制作用下自身形状与结构的演化.在小天体碎石堆结构的假设之下,一种比较常见的...小天体探测是当今太阳系探测的一大热点,对小行星演化的研究有助于人们了解太阳系的起源.演化研究的一项重要内容是小天体结构的演化,即小天体在多种力学机制作用下自身形状与结构的演化.在小天体碎石堆结构的假设之下,一种比较常见的模拟小天体结构演化的方法是离散元仿真算法(Discrete Element Method, DEM),目前国内外有数个团队开发了相关算法软件.本文介绍了团队开发的《基于DEM仿真算法的多粒子系统模拟软件》的基础理论、实现方法以及加速算法,并使用二体接触模型、声速传播仿真、小行星内部压强、小行星旋转稳定性仿真算例验证了算法的可靠性.展开更多
A new method based on the parameters iteration technique has been developed to determine the optimal subreflector position for shaped Cassegrain antennas, that are distorted by gravity, to improve their electromagneti...A new method based on the parameters iteration technique has been developed to determine the optimal subreflector position for shaped Cassegrain antennas, that are distorted by gravity, to improve their electromagnetic(EM) performance. Both the features of shaped surface and the relationship between optical path difference(OPD) and far field beam pattern are employed. By describing the shaped dualreflector surface as a standard discrete parabola set, we can utilize the optical features of the standard Cassegrain system in the classical OPD relationship. Then, the actual far field beam pattern is expressed as the synthesis of ideal beam and error beam by decomposing subreflector adjustment parameters using a mechanical-electromagnetic-field-coupling-model(MEFCM). Furthermore, a numerical method for determining optimal subreflector position is presented. The proposed method is based on the iteration technique of subreflector adjustment parameters, and the optimal far field pattern is used for the iteration. The numerical solution of optimal adjustment parameters can be obtained rapidly. Results for a 25 m shaped Cassegrain antenna demonstrate that the adjustment of the subreflector to the optimal position as determined by the proposed method can improve the EM performance effectively.展开更多
文摘光学湍流的强弱和分布是描述天文台址优劣的重要参数.介绍了利用大气模式WRF(Weather Research and Forecasting Model)计算高美古站周围大气光学湍流参数的方法,这些参数包括C_n^2(大气光学湍流强度)廓线、大气相干长度、大气相干时间、视宁度、等晕角和闪烁率等.包括模型计算方法的实现过程、模型的设置和模拟结果的验证.计算结果与云南高美古观测站DIMM(Differential Image Motion Monitor)的实测数据进行了对比.
基金supported by the National Key R&D Program of China No.2021YFC220350the National Natural Science Foundation of China Nos.12303094&52165053+2 种基金the Natural Science Foundation of Xinjiang Uygur Autonomous Region Nos.2022D01C683the China Postdoctoral Science Foundation Nos.2023T160549&2021M702751in part by Guangdong Basic and Applied Basic Research Foundation Nos.2020A1515111043&2023A1515010703。
文摘Active surface technique is one of the key technologies to ensure the reflector accuracy of the millimeter/submillimeter wave large reflector antenna.The antenna is complex,large-scale,and high-precision equipment,and its active surfaces are affected by various factors that are difficult to comprehensively deal with.In this paper,based on the advantage of the deep learning method that can be improved through data learning,we propose the active adjustment value analysis method of large reflector antenna based on deep learning.This method constructs a neural network model for antenna active adjustment analysis in view of the fact that a large reflector antenna consists of multiple panels spliced together.Based on the constraint that a single actuator has to support multiple panels(usually 4),an autonomously learned neural network emphasis layer module is designed to enhance the adaptability of the active adjustment neural network model.The classical 8-meter antenna is used as a case study,the actuators have a mean adjustment error of 0.00252 mm,and the corresponding antenna surface error is0.00523 mm.This active adjustment result shows the effectiveness of the method in this paper.
文摘Leighton Chajnantor Telescope(LCT), i.e., the former Caltech Submillimeter Observatory telescope, will be refurbished at the new site in Chajnantor Plateau, Chile in 2023. The environment of LCT will change significantly after its relocation, and the telescope will be exposed to large wind disturbances directly because its enclosure will be completely open during observation. The wind disturbance is expected to be a challenge for LCT's pointing control since the existing control method cannot reject this disturbance very well. Therefore, it is very necessary to develop a new pointing control method with good capability of disturbance rejection. In this research, a disturbance observer—based composite position controller(DOB-CPC) is designed, in which an H∞feedback controller is employed to compress the disturbance, and a feedforward linear quadratic regulator is employed to compensate the disturbance precisely based on the estimated disturbance signal. Moreover, a controller switching policy is adopted, which applies the proportional controller to the transient process to achieve a quick response and applies the DOB-CPC to the steady state to achieve a small position error. Numerical experiments are conducted to verify the good performance of the proposed pointing controller(i.e., DOB-CPC) for rejecting the disturbance acting on LCT.
基金support from the National Key Program for Science and Technology Research and Development (2017YFB0203300)the National Natural Science Foundation of China (Grant Nos. 11403035, 11425312 and 11573030)support from Royal Society Newton advanced Fellowships
文摘We introduce a new code for cosmological simulations, PHo To Ns, which incorporates features for performing massive cosmological simulations on heterogeneous high performance computer(HPC) systems and threads oriented programming. PHo To Ns adopts a hybrid scheme to compute gravitational force, with the conventional Particle-Mesh(PM) algorithm to compute the long-range force,the Tree algorithm to compute the short range force and the direct summation Particle-Particle(PP) algorithm to compute gravity from very close particles. A self-similar space filling a Peano-Hilbert curve is used to decompose the computing domain. Threads programming is advantageously used to more flexibly manage the domain communication, PM calculation and synchronization, as well as Dual Tree Traversal on the CPU+MIC platform. PHo To Ns scales well and efficiency of the PP kernel achieves68.6% of peak performance on MIC and 74.4% on CPU platforms. We also test the accuracy of the code against the much used Gadget-2 in the community and found excellent agreement.
基金supported by the National Natural Science Foundation of China(NSFC,grant Nos.12073080,11933010,11921003,12233011,and 12225305)。
文摘AT2021lfa,also known as ZTF21aayokph,was detected by the Zwicky Transient Facility on 2021 May 4,a 05:34:48 UTC.Follow-up observations were conducted using a range of ground-based optical telescopes,as wel as Swift/XRT and VLA instruments.AT2021lfa is classified as an“orphan afterglow”candidate due to its rapid flux decline and its reddened color(g-r=0.17±0.14 mag).For an optical transient source without promp gamma-ray detection,one key point is to determine its burst time.Here we measure the burst time through fitting the initial bump feature of AT2021lfa and obtain its burst time as 2021 May 3,at 22:09:50 UTC.Using afterglowpy,we model the multi-band afterglow of AT2021lfa and find that the standard model canno reproduce the late radio observations well.Considering that the microphysical parameters ε_(e),ε_(B)(the energy fraction given to electrons and magnetic field),andξN(the fraction of accelerated electrons)may vary with time we then model the afterglow of AT2021lfa taking into account the temporal evolution of the physical parameters ε_(e),ε^(B),and ξ_(N) and find in this case the multi-wavelength observations can be reproduced well.The initial Lorentz factor of AT2021lfa can be estimated from the peak time of the early afterglow,which yields a value of about 18 suggesting that AT2021lfa should be classified as a“dirty fireball.”From the upper limit for the prompt emission energy of AT2021lfa,we obtain that the radiation efficiency is less than 0.02%,which is much smaller than that of ordinary gamma-ray bursts(GRBs).It is also interesting that the fitted values of jet angle and viewing angle are very large,θ_(c)~0.66 rad,θ_(v)~0.53 rad,which may lead to the low Lorentz factor and radiation efficiency.When compared with GRB afterglow samples,it is evident that the onset bump timescale of AT2021lfa satisfies the empirical relationships observed in GRB samples.Additionally,the luminosity of AT2021lfa falls within the range of observations for GRB samples;however,approximately 1 day after the
基金supported by the National Natural Science Foundation of China 12233006partially supported by the National Natural Science Foundation of China 12203042the Foundations of Yunnan Province 202301AU070009。
文摘Using an effective adiabatic index γ_(eff) to mimic the feedback of efficient shock acceleration,we simulate the temporal evolution of a young type Ia supernova remnant (SNR) with two different background magnetic field(BMF) topologies:a uniform and a turbulent BMF.The density distribution and magnetic-field characteristics of our benchmark SNR are studied with two-dimensional cylindrical magnetohydrodynamic simulations.When γ_(eff)is considered,we find that:(1) the two-shock structure shrinks and the downstream magnetic-field orientation is dominated by the Rayleigh–Taylor instability structures;(2) there exists more quasi-radial magnetic fields inside the shocked region;and (3) inside the intershock region,both the quasi-radial magnetic energy density and the total magnetic energy density are enhanced:in the radial direction,with γ_(eff)=1.1,they are amplified about 10–26 times more than those with γ_(eff)=5/3.While in the angular direction,the total magnetic energy densities could be amplified about 350 times more than those with γ_(eff)=5/3,and there are more grid cells within the intershock region where the magnetic energy density is amplified by a factor greater than 100.
文摘随着射电望远镜口径增大、观测频率提高,对其指向精度的要求也越来越高.然而,望远镜服役于野外台站,台址风扰对天线指向精度的影响在高频段观测时已不能忽略.由于风扰的时变性,现有的抗风方法无法保障大口径高指向精度望远镜在高频段的有效观测时长.因此,提出了一种基于风障精确布置改善台址风环境的方法.通过数值模拟构建了风障仿真模型,并将仿真结果与风洞实测数据比较,两种孔隙率风障的平均误差分别为3.7%和6.1%,保证了风障模型的可靠性.以新疆奇台射电望远镜(QiTai radio Telescope,QTT)台址为例,基于QTT台址斜坡地形构建了计算域模型,开展单风障不同高度、不同孔隙率的系列风场仿真试验,得到了风障参量与下游挡风效果的关系.基于单风障合理高度和最优孔隙率设置南北风障,仿真结果表明在确定高度下最优孔隙率可以组合,孔隙率0.1-0.1组合的风障挡风效果最优,南方向来风在天线区域可以有效降低75%以上的风速.
文摘以ASTRODI(Astrodynamical Space Test of Relativity using Optical DevicesI,单航天器天文激光动力学)为例介绍无拖曳卫星的结构及其工作原理.推导了其动力学方程,并在此基础上建立了卫星的动力学数值仿真器.将H_2最优控制理论运用于以噪声压制为主要目的的无拖曳卫星控制系统的设计,通过传递函数法及数值法双重分析表明所设计的控制器能符合卫星的控制要求,同时表明在控制器没计过程中采用的线性化假设是适当的.
基金supported by the Characteristic innovation project of Guangdong Provincial Department of Education(No.2023KTSCX195)Scientific Computing Research Innovation Team of Guangdong Province(No.2021KCXTD052)+2 种基金Guangdong Key Construction Discipline Research Capacity Enhancement Project(No.2022ZD JS049)Technology Planning Project of Shaoguan(No.230330108034184)Science and Technology Development Fund,Macao SAR(No.0096/2022/A)。
文摘Determining asteroid properties provides valuable physical insights but inverting them from photometric lightcurves remains computationally intensive.This paper presents a new approach that combines a simplified Cellinoid shape model with the Parallel Differential Evolution(PDE)algorithm to accelerate inversion.The PDE algorithm is more efficient than the Differential Evolution algorithm,achieving an extraordinary speedup of 37.983 with 64 workers on multicore CPUs.The PDE algorithm accurately derives period and pole values from simulated data.The analysis of real asteroid lightcurves validates the method’s reliability:in comparison with results published elsewhere,the PDE algorithm accurately recovers the rotational periods and,given adequate viewing geometries,closely matches the pole orientations.The PDE approach converges to solutions within 20,000 iterations and under one hour,demonstrating its potential for large-scale data analysis.This work provides a promising new tool for unveiling asteroid physical properties by overcoming key computational bottlenecks.
文摘小天体探测是当今太阳系探测的一大热点,对小行星演化的研究有助于人们了解太阳系的起源.演化研究的一项重要内容是小天体结构的演化,即小天体在多种力学机制作用下自身形状与结构的演化.在小天体碎石堆结构的假设之下,一种比较常见的模拟小天体结构演化的方法是离散元仿真算法(Discrete Element Method, DEM),目前国内外有数个团队开发了相关算法软件.本文介绍了团队开发的《基于DEM仿真算法的多粒子系统模拟软件》的基础理论、实现方法以及加速算法,并使用二体接触模型、声速传播仿真、小行星内部压强、小行星旋转稳定性仿真算例验证了算法的可靠性.
基金supported by the National Key Basic Research Program of China (2015CB857100)the Chinese Academy of Sciences (CAS) "Light of West China" Program (2017-XBQNXZB-021)+2 种基金the National Natural Science Foundation of China (Nos. 51805399 and U1737211)the Natural Science Foundation of Shanxi Province (No. 2018JZ500)supported by the Operation, Maintenance and Upgrading Fund for Astronomical Telescopes and Facility Instruments, budgeted from the Ministry of Finance of China (MOF) and administrated by CAS
文摘A new method based on the parameters iteration technique has been developed to determine the optimal subreflector position for shaped Cassegrain antennas, that are distorted by gravity, to improve their electromagnetic(EM) performance. Both the features of shaped surface and the relationship between optical path difference(OPD) and far field beam pattern are employed. By describing the shaped dualreflector surface as a standard discrete parabola set, we can utilize the optical features of the standard Cassegrain system in the classical OPD relationship. Then, the actual far field beam pattern is expressed as the synthesis of ideal beam and error beam by decomposing subreflector adjustment parameters using a mechanical-electromagnetic-field-coupling-model(MEFCM). Furthermore, a numerical method for determining optimal subreflector position is presented. The proposed method is based on the iteration technique of subreflector adjustment parameters, and the optimal far field pattern is used for the iteration. The numerical solution of optimal adjustment parameters can be obtained rapidly. Results for a 25 m shaped Cassegrain antenna demonstrate that the adjustment of the subreflector to the optimal position as determined by the proposed method can improve the EM performance effectively.
