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本文概述了高质量消色差波片(水晶+MgF_2)的设计原理,晶体材料的光学质量检查,延迟量的误差控制以及波片胶合等方面的问题. 相似文献
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详细地介绍了VLBI系统的地面单元中电缆延迟变化的测量方法,这种基于相位的测量方法,为相关领域的高精度延迟测量提供了借鉴。概要介绍了地面单元中电缆测量、反射调制以及相位比较器的工作原理,对各个环节作了数学上的推导分析。给出了一个电缆相对延迟值随温度变化的测试样本。 相似文献
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2.16m望远镜红外自适应光学系统的误差和性能分析 总被引:9,自引:0,他引:9
在自适应光学系统中,波前探测器的噪声,未完全补偿湍流所引起的误差以及变形镜的拟合误差是主要的误差源,本针对已经建立2.16m望远镜红外自适应光学系统,从伺服控制系统的角度分析了该系统的闭环噪声,大气湍流引起的误差以及该系统的闭环总体误差,该系统的闭环总体误差是光强及系统闭环带宽的函数,本还分析了该系统的有效性以及对大气湍流不同改善程度情况下的光强与闭环带宽的关系,并在此基础上给出了该系统的最佳 相似文献
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纪志浩 《中国科学院上海天文台年刊》1989,(10):183-188
在射电干涉仪中,单边带系统和双边带系统都有广泛的作用。本主要讨论了单、双边带系统中相关器输出中的条纹相位与本振相位、延迟、仪器相位的关系。特别对多资频率变换系统的相位关系作了论述。并指出了它们的优缺点。 相似文献
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文章详细介绍了VLBI电缆延迟测量的改进设计,针对在电缆延迟校正器研制和使用中遇到的问题,重新设计了反射调制、电缆测量和相位比较模块,并作了详细的推导分析。在校正器设计中还增加了数据自动采集模块,将计数、串口通信、实时控制功能集成到FPGA(Field Programmable Gate Array)芯片,提高了延迟校正器的使用灵活性,使数据采集实现完全自动化,降低了研制成本。 相似文献
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特征提取是对光谱测量数据成分的分解、重组和选择的过程,它是光谱数据挖掘中的一个关键环节,不仅决定着后续处理的质量、效率、系统复杂度和稳健性,也关系到能够挖掘到什么知识和处理结果物理意义的可解释性。按照特征表达方式将已有方法分为3类:统计约简法,特征谱法和谱线法,并对这些方法的基本原理、适用性、优缺点及其在光谱数据挖掘中的应用作了综述和分析。另外,亦从方法的"时"、"频"分析能力方面探讨了不同方法的特点,例如,物理意义的易解释性、对波长定标畸变和流量定标畸变的敏感性等。 相似文献
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High-speed plasma streams identified in the solar wind measurements can be separated into two categories: coronal-hole-associated streams and flare-generated streams. Effects of these plasma streams on cosmic-ray intensity are studied for the period of 1991–1996. It is investigated that both of these high-speed solar wind plasma streams (CS and FGS) are found equally effective in producing the cosmic-ray intensity decrease on short-term basis. 相似文献
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We used two methods to investigate the periodic behavior of sunspot counts in four categories for the time period January 1986?–?October 2013. These categories include the counts from simple (A and B), medium (C), large (D, E, and F), and final (final-stage; H) sunspot groups. We used i) the multitaper method with red noise approximation, and ii) the Morlet wavelet transform for periodicity analysis. Our main findings are that 1) the solar rotation periodicity of about 25 to 37 days, which is of obvious significance, is found in all groups with at least a 95 % significance level; 2) the periodic behavior of a cycle is strongly related to its amplitude and group distribution during the cycle; 3) the appearance of periods follows the amplitude of the investigated solar cycles; and that 4) meaningful periods do not appear during the minimum phases of the investigated cycles. We would like to underline that the cyclic behavior of all categories is not exactly the same; there are some differences between these groups. This result can provide a clue for the better understanding of solar cycles. 相似文献
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A new approach is presented for the problem of planar optimal impulsive rendezvous of a spacecraft in an inertial frame near
a circular orbit in a Newtonian gravitational field. The total characteristic velocity to be minimized is replaced by a related
characteristic-value function and this related optimization problem can be solved in closed form. The solution of this problem
is shown to approach the solution of the original problem in the limit as the boundary conditions approach those of a circular
orbit. Using a form of primer-vector theory the problem is formulated in a way that leads to relatively easy calculation of
the optimal velocity increments. A certain vector that can easily be calculated from the boundary conditions determines the
number of impulses required for solution of the optimization problem and also is useful in the computation of these velocity
increments. Necessary and sufficient conditions for boundary conditions to require exactly three nonsingular non-degenerate
impulses for solution of the related optimal rendezvous problem, and a means of calculating these velocity increments are
presented. A simple example of a three-impulse rendezvous problem is solved and the resulting trajectory is depicted. Optimal
non-degenerate nonsingular two-impulse rendezvous for the related problem is found to consist of four categories of solutions
depending on the four ways the primer vector locus intersects the unit circle. Necessary and sufficient conditions for each
category of solutions are presented. The region of the boundary values that admit each category of solutions of the related
problem are found, and in each case a closed-form solution of the optimal velocity increments is presented. Similar results
are presented for the simpler optimal rendezvous that require only one-impulse. For brevity degenerate and singular solutions
are not discussed in detail, but should be presented in a following study. Although this approach is thought to provide simpler
computations than existing methods, its main contribution may be in establishing a new approach to the more general problem. 相似文献
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L.L. Cogger J.S. Murphree C.A. Tepley J.W. Meriwether 《Planetary and Space Science》1985,33(4):373-379
The neutral E-region wind field was measured at Calgary, Canada (51°N, 114°W) during 75 nights in 1982. Observations of the Doppler shift of the 5577-Å emission line of atomic oxygen using a Fabry-Perot interferometer were converted to horizontal wind vectors. From the analysis of the data, four categories of wind characteristics were identified. In order of increasing magnetic activity these categories are (a) wind field mostly variable in space and time, (b) predominantly equatorward flow throughout the night, (c) predominantly poleward flow throughout the night and (d) north-westward flow before midnight and southward after midnight. The wind magnitude was also variable and on some disturbed days exceeded 200 m s?1. 相似文献
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《天文和天体物理学研究(英文版)》2014,(8)
The emission sources of umbral flashes(UFs) are believed to be closely related to running umbral and penumbral waves,and are concluded to be associated with umbral dots in the solar photosphere. Accurate identification of emission sources of UFs is crucial for investigating these physical phenomena and their inherent relationships. A relatively novel model of shape perception,namely phase congruency(PC),uses phase information in the Fourier domain to identify the geometrical shape of the region of interest in different intensity levels,rather than intensity or gradient.Previous studies indicate that the model is suitable for identifying features with low contrast and low luminance. In the present paper,we applied the PC model to identify the emission sources of UFs and to locate their positions. For illustrating the high performance of our proposed method,two time sequences of Ca II H images derived from the Hinode/SOT on 2010 August 10 and 2013 August 20 were used. Furthermore,we also compared these results with the analysis results that are identified by the traditional/classical identification methods,including the gray-scale adjusted technique and the running difference technique. The result of our analysis demonstrates that our proposed method is more accurate and effective than the traditional identification methods when applied to identifying the emission sources of UFs and to locating their positions. 相似文献
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Hikmet Çakmak 《Solar physics》2017,292(12):186
Determining the relative brightness of the solar corona is one of the most critical stages in solar eclipse studies. For this purpose, images taken with different exposures and polarization angles in white-light observations are used. The composite image of each polarization angle is produced by combining the images of different exposures. With the help of the intensity calibration function of these images, the relative intensity of the corona can be calculated. The total brightness of the solar corona is calculated using Stokes parameters obtained from intensity values of three polarization angles. In this study, two methods are presented: the first is used to obtain the intensity calibration function of the photographic material using calibration images, and the second is used to calculate the combined intensity values of images taken with different polarization angles. 相似文献
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High-speed solar wind streams (HSWS) were identified for solar cycles 22 and 23 (up to 2004). Preliminarily, HSWS were classified
in three groups according to their continuous period of occurrence. In the declining phase of solar cycle 23, 2003 is found
to be anomalous, showing a very large number of HSWS events of long duration (> ten days). We have studied the effect of HSWS
on the cosmic-ray intensity as well as their relationship with geomagnetic disturbance index Ap on yearly, daily, and hourly bases. The yearly average of solar-wind speed was also found to be maximum in 2003. Being within
the declining phase of solar activity, the occurrence of solar flares in 2003 is quite low. In particular during HSWS, no
solar flares have been observed. Associations with cosmic-ray changes do not support the notion that the HSWS are usually
effective in producing significant cosmic-ray decreases. Out of 12 HSWS events observed during the period 2002 (December)
to 2003, four events of significant cosmic-ray decreases at all the stations have been selected for further analysis. The
cosmic-ray intensity has been found to decrease during the first phase of the event (first five days of HSWS) at all three
neutron-monitor stations situated at different latitudes with different cutoff rigidities. The rigidity spectra of observed
decreases in cosmic-ray intensity for these four cases have been found to be significantly different than that of Fds (Forbush
decrease). In two cases the spectra are softer, whereas in the other two they are harder than that of Fds. However, if the
average of all four events is considered together then the spectra of the decrease in cosmic rays during HSWS exactly match
that of Fds. Such a result implies that initially individual events should be considered, instead of combining them together,
as was done earlier. The Ap index is also found to generally increase in the first phase of the event. However, the four events selected on the basis
of cosmic-ray decrease are not always associated with enhanced values of the Ap index. As such, the significance of our study is that further detailed investigations for much longer periods and on an event-by-event
basis is required to understand the effect of coronal-hole-associated HSWS. 相似文献