共查询到20条相似文献，搜索用时 62 毫秒
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提出了一种加工离轴非球面的预应力环抛方法,基于预应力加工方法的基本原理,利用环抛机来磨制离轴非球面.设计了一套专门的加载装置,将拼接镜面中具有不同离轴量的非球面子镜转化成曲率半径相同的球面子镜进行磨制,可以在同一台环抛机上进行抛光.利用这种方法,花费连续40 h的时间,磨制了一块按照中国30 m极大口径望远镜(CFGT)主镜参数比例缩小的离轴抛物面,顶点曲率半径21.6 m,离轴量3.6 m,离轴口径为330 mm,最大非球面度为16μm.试验表明该方法效率高,适用于批量加工,特别是极大口径天文望远镜拼接主镜的大批量非球面子镜研制. 相似文献
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李凤云 韩智洁 刘明旭 淳于波 徐亚军 陈余 李双虎 闫秋浩 包铁威 郭王伟 李义成 李新南 王晋峰 田杰 乔撩云 陈亮 吕金虎 陈超 刘承 张勇 侯永辉 王跃飞 葛群 左恒 姜方华 李烨平 陆启帅 胡守伟 王佑 李爱华 倪季君 张超 倪小康 许静 李浩 李晓飞 张昊彤 白仲瑞 胡天柱 王丹 崔向群 赵永恒 李国平 《天文学报》2022,63(1):12-126
对大口径光学/红外天文望远镜而言,为保障其稳定高效运行,镜面镀膜是重要的维护环节之一.镀膜质量的好坏直接影响镜面光学反射率的高低,也严重影响到天文望远镜的成像质量、观测效率.国家重大科技基础设施—大天区面积多目标光纤光谱天文望远镜(Large Sky Area Multi-Object Fiber Spectroscopic Telescope, LAMOST,又名郭守敬望远镜)自2009年6月通过国家竣工验收并逐步投入巡天观测,目前已进入第2个5 yr巡天计划阶段,取得近两千万的光谱产出和大批高显示度的科学成果. LAMOST共拥有24块施密特改正镜子镜和37块球面主镜子镜,为了确保在野外恶劣观测环境下镜面反射率维持在较高水平,每年要对大批子镜进行镀膜.主要介绍了镀膜需求、镀膜设备,并基于大量实验和多年的完善探索出一套可行的镀膜工艺流程,确保了LAMOST子镜极高的镀膜质量.镀膜后子镜平均反射率高达90%以上,满足了LAMOST光谱巡天的镜面反射率要求. 相似文献
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大型光学望远镜扇形子镜拼接设计及仿真分析 总被引：1，自引：0，他引：1
《天文研究与技术》2010,(4)
目前,国际上大型望远镜拼接镜面采用的拼接子镜几乎都是六边形而没有采用扇形。比较六边形子镜和扇形子镜各方面的优缺点,建立六边形和扇形子镜的有限元模型,均采用18点轴向支撑,优化支撑方式,计算各子镜在自重作用下,镜面在水平位置,倾斜45°和垂直位置时的变形参数RMS值。结果表明在面积和支撑点数目均相同的条件下,扇形子镜在理论上可以获得与六边形子镜近似的镜面RMS值,但是在实际应用中扇形子镜的支撑,镜面调控与六边形子镜相比将更加复杂困难。 相似文献
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自从400 yr前伽利略第1次使用望远镜观测天空以来,人类为了探索更深的宇宙,望远镜的口径越做越大,拼接镜面望远镜成为趋势.本世纪初一批大口径拼接望远镜先后被研制出来,这其中包括我国的大天区面积多目标光纤光谱天文望远镜LAMOST.随着望远镜口径增大,子镜单元增多,子镜单元的装卸问题日益突出.本文试图对这一问题进行探讨,设计了一套用于LAMOST球面主镜的子镜单元装卸装置,希望为大口径望远镜的子镜装卸提供一些思路和借鉴. 相似文献
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基于对大型光学望远镜子镜的要求,比较六边形和扇形两种子镜的优缺点.用有限元法分析扇形子镜在自重下的变形,确定扇形子镜的支撑点数和排列方式.并具体分析了通过18点、24点、27点三种支撑点的排列方式,分别计算不同支撑点下的子镜变形.通过计算表明,27点的支撑方式可以满足子镜的镜面RMS小于10nm的技术要求,并讨论子镜的轴向和侧向支撑方案.计算了在轴向和侧向支撑的条件下,各子镜在水平,垂直以及45°三个极限位置的镜面RMS值. 相似文献
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地基光学天文望远镜是人类探索与研究宇宙的重要手段, 对已有地基光学台址的光学观测环境进行监测分析, 可以为后期设备针对性改造以及观测者调整观测策略提供参考依据, 对提升地基光学设备的观测效能具有重要的意义. 吉林天文观测基地(简称``基地'')隶属于中国科学院国家天文台长春人造卫星观测站, 位于吉林省吉林市大绥河镇小绥河村南沟约5 km处(东经126.3\circ, 北纬43.8\circ, 海拔高度313m). 基地大气视宁度均值范围约为1.3$''$--1.4$''$、天顶附近V波段的天光背景亮度为20.64magcdotarcsec-2、年晴夜数最高可达270余天, 具有良好的天文观测条件. 吉林天文观测基地于2016年投入运行, 现有1.2m光电望远镜、迷你光电阵列望远镜、大视场光电望远镜阵列、新型多功能阵列结构光电探测平台等多台(套)光电望远镜设备. 利用上述设备, 主要围绕空间目标探测与识别、精密轨道确定、光电探测新方法以及变源天体的多色测光等开展相关研究工作, 与多家国内高校及科研院所保持着良好的合作关系. 相似文献
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骄傲地矗立在夏威夷岛莫纳克亚顶峰的著名凯克双子有了一个新邻居。宿魃奴,即日语晶星团,是日本国家天文台的骄傲财富。凯克的10米主镜是由36块子镜拼接而成。与凯克不同,宿魃奴使用单块巨大的直径8.3米的主镜收集来自宇宙的光线,实际上它是目前世界上最大的单镜面望远镜。 造价为3.7亿美元的宿魃奴帮助日本跃入光学和红外天文学的前沿。望远镜于1999年1月开始试观测并于2000年底部分地投入科学观测。 相似文献
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云南天文台1m红外太阳望远镜是多功能、多波段的太阳望远镜,望远镜使用过程中主镜的热变形直接关系这系统的光学精度,建立光学系统的光机热结合的分析方法,可以直观的得到热辐射对光学系统的影响结果,使得望远镜的设计阶段就能评估热变形对系统的精度影响,确定光学元件是否满足要求. 相似文献
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Stéphane Colombi rew Jaffe Dmitri Novikov Christophe Pichon 《Monthly notices of the Royal Astronomical Society》2009,393(2):511-526
A method to rapidly estimate the Fourier power spectrum of a point distribution is presented. This method relies on a Taylor expansion of the trigonometric functions. It yields the Fourier modes from a number of fast Fourier transforms (FFTs), which is controlled by the order N of the expansion and by the dimension D of the system. In three dimensions, for the practical value N = 3 , the number of FFTs required is 20.
We apply the method to the measurement of the power spectrum of a periodic point distribution that is a local Poisson realization of an underlying stationary field. We derive an explicit analytic expression for the spectrum, which allows us to quantify – and correct for – the biases induced by discreteness and by the truncation of the Taylor expansion, and to bound the unknown effects of aliasing of the power spectrum. We show that these aliasing effects decrease rapidly with the order N . For N = 3 , they are expected to be, respectively, smaller than ∼10−4 and 0.02 at half the Nyquist frequency and at the Nyquist frequency of the grid used to perform the FFTs. The only remaining significant source of errors is reduced to the unavoidable cosmic/sample variance due to the finite size of the sample.
The analytical calculations are successfully checked against a cosmological N -body experiment. We also consider the initial conditions of this simulation, which correspond to a perturbed grid. This allows us to test a case where the local Poisson assumption is incorrect. Even in that extreme situation, the third-order Fourier–Taylor estimator behaves well, with aliasing effects restrained to at most the per cent level at half the Nyquist frequency.
We also show how to reach arbitrarily large dynamic range in Fourier space (i.e. high wavenumber), while keeping statistical errors in control, by appropriately 'folding' the particle distribution. 相似文献
We apply the method to the measurement of the power spectrum of a periodic point distribution that is a local Poisson realization of an underlying stationary field. We derive an explicit analytic expression for the spectrum, which allows us to quantify – and correct for – the biases induced by discreteness and by the truncation of the Taylor expansion, and to bound the unknown effects of aliasing of the power spectrum. We show that these aliasing effects decrease rapidly with the order N . For N = 3 , they are expected to be, respectively, smaller than ∼10
The analytical calculations are successfully checked against a cosmological N -body experiment. We also consider the initial conditions of this simulation, which correspond to a perturbed grid. This allows us to test a case where the local Poisson assumption is incorrect. Even in that extreme situation, the third-order Fourier–Taylor estimator behaves well, with aliasing effects restrained to at most the per cent level at half the Nyquist frequency.
We also show how to reach arbitrarily large dynamic range in Fourier space (i.e. high wavenumber), while keeping statistical errors in control, by appropriately 'folding' the particle distribution. 相似文献
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针对包含饱和样本数据的频数幂律分布拟合,提出一个新的幂律分布指数的极大似然估计方法的修正公式.对比研究显示,修正公式适用于剔除异常饱和值的幂律频数拟合.如果不剔除饱和值,幂律指数的估计只能使用修正前的公式,其误差随幂律指数变化,指数较小时误差较大.由此建议,对于包含饱和样本的频数分布拟合,首先剔除异常的饱和值,然后对剩余不含饱和值的子集使用修正公式进行参数估计. 相似文献
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Chris Koen 《Monthly notices of the Royal Astronomical Society》2005,361(3):887-896
The theory of low-order linear stochastic differential equations is reviewed. Solutions to these equations give the continuous time analogues of discrete time autoregressive time-series. Explicit forms for the power spectra and covariance functions of first- and second-order forms are given. A conceptually simple method is described for fitting continuous time autoregressive models to data. Formulae giving the standard errors of the parameter estimates are derived. Simulated data are used to verify the performance of the methods. Irregularly spaced observations of the two hydrogen-deficient stars FQ Aqr and NO Ser are analysed. In the case of FQ Aqr the best-fitting model is of second order, and describes a quasi-periodicity of about 20 d with an e-folding time of 3.7 d. The NO Ser data are best fitted by a first-order model with an e-folding time of 7.2 d. 相似文献
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多任务学习方法在机器学习、计算机视觉、人工智能领域已得到广泛关注,利用任务间的相关性,将多个任务同时学习的效果优于每个任务单独学习的情况.采用多任务Lasso回归法(Multi-task Lasso Regression)用于恒星光谱物理参量的估计,不仅可以获取不同物理参量间的共同的特征信息,而且也可以很好地保留不同物理参量的特有的补充信息.使用恒星大气模拟模型合成光谱库ELODIE中的光谱数据和美国大型巡天项目Sloan发布的SDSS实测光谱数据进行实验,模型估算精度优于相关文献中的方法,特别是对重力加速度(lg g)和化学丰度([Fe/H])的估计.实验中通过改变光谱的分辨率,施加不同信噪比(SNR)的噪声,来说明模型的稳定性强.结果表明,模型精度受光谱分辨率和噪声的影响,但噪声对其影响更大,可见,多任务Lasso回归法不仅操作简便,稳定性强,而且也提高了模型的整体预测精度. 相似文献
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Chris Koen 《Monthly notices of the Royal Astronomical Society》2001,325(4):1335-1340
The observation of flux sources near the limit of detection requires a careful evaluation of possible biases in magnitude determination. Both the traditional logarithmic magnitudes and the recently proposed inverse hyperbolic sine (asinh) magnitudes are considered. Formulae are derived for three different biasing mechanisms: the statistical spread of the observed flux values arising from e.g. measurement error; the dependence of these errors on the true flux; and the dependence of the observing probability on the true flux. As an example of the results, it is noted that biases at large signal-to-noise ratios R , at which the two types of magnitude are similar, are of the order of −( p +1)/ R 2 , where the exponent p parametrizes a power-law dependence of the probability of observation on the true flux. 相似文献
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Chris Koen 《Monthly notices of the Royal Astronomical Society》1999,309(3):769-802
The estimation of the frequency, amplitude and phase of a sinusoid from observations contaminated by correlated noise is considered. It is assumed that the observations are regularly spaced, but may suffer missing values or long time stretches with no data. The typical astronomical source of such data is high-speed photoelectric photometry of pulsating stars. The study of the observational noise properties of nearly 200 real data sets is reported: noise can almost always be characterized as a random walk with superposed white noise. A scheme for obtaining weighted non-linear least-squares estimates of the parameters of interest, as well as standard errors of these estimates, is described. Simulation results are presented for both complete and incomplete data. It is shown that, in finite data sets, results are sensitive to the initial phase of the sinusoid. 相似文献