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国家重点基础研究发展计划(2006CB806302)

作品数:11 被引量:16H指数:3
相关作者:韩钢李友平甘为群李瑛许春更多>>
相关机构:中国科学院国家天文台云南大学中国科学院云南天文台更多>>
发文基金:国家重点基础研究发展计划国家自然科学基金更多>>
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11 条 记 录,以下是 1-10
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Statistical study of EUV and X-ray transient brightenings被引量:3
2010年
Using the visual inspection and base difference method and data from the X-ray Telescope (XRT) onboard Hinode and TRACE with improved spatial and temporal resolution, we selected 48 X-ray transient brightenings (XTBs) and 237 EUV transient brightenings (ETBs) to study the connection between these two types of transient brightenings (TBs). These ETBs and XTBs have smaller areas (8.42 Mm^2 and 36.3 Mm^2, respectively, on average) and shorter durations (9.0 min and 6.9 min, respectively, on average) than previous studies. These XTBs show three types of morphological structure: point-like, single-loop and multiple-loop. We find only 20% of the ETBs have corresponding XTBs while the other 80% have no X-ray signatures at all. This is presumably due to the small amount of released energy, which is not enough to heat the plasma to coronal temperatures which produce X-ray emission rather than being due to the limitation of spatial resolution and temperature sensitivity of the X-ray instrument. These small ETBs may significantly contribute to the coronal heating.
Jing-Wei Li Hui Li
关键词:SUNCORONA
太阳耀斑色球蒸发现象的研究进展
2010年
色球蒸发是耀斑能量释放后所导致的一种动力学现象。耀斑发生时,太阳大气被加热,形成的高压驱动等离子体物质向上运动,在观测上表现为高温谱线的多普勒蓝移,有时出现硬X射线足点源逐渐向环顶源的并合过程。数值模拟在理论上验证了色球蒸发理论。色球蒸发的加热机制主要包括热传导和非热粒子束加热。回顾了色球蒸发的研究进展,介绍了不同时期空间仪器对色球蒸发的观测结果,以及数值模拟方面的研究进展,并概括了目前存在的一些主要问题,最后给出简短的总结和展望。
李瑛丁明德
关键词:耀斑软X射线紫外辐射
Effects of inelastic collisions on Alfvn waves in partially ionized plasmas被引量:1
2014年
Based on a three-component description of partially ionized plasmas(i.e.,electrons,ions,and neutral atoms),effects of inelastic collisions between ions(neutrals)and electrons on Alfve′n waves(AWs)in a partially ionized plasma are studied.It is shown that for a fixed ionizability(i)or a fixed inelastic collision parameter(v,i.e.,the ratio of the inelastic to elastic collision frequency),the damping rate of AWs has a peak value round kz vA/min*1,where kz is the parallel wavenumber of AWs,vA is the Alfve′n velocity,and min is the elastic collision frequency between ions and neutrals.On the other hand,the damping rate of AWs decreases monotonously with the ionizabilityi for a fixed inelastic collision parameter,but has a peak value when the inelastic collision parameter varies for sufficiently small ionizability(i\0:1).For sufficiently large ionizability(i[0:1),it is found that the damping rate decreases with the inelastic collision parameter.The results may help us to understand the physics of AWs in partially ionized plasmas.
Bing LiLing ChenDejin Wu
关键词:非弹性碰撞电离度中性原子
RHESSI耀斑中非热电子低能截止的研究被引量:1
2008年
太阳耀斑中硬X射线(HXR)光子谱的低能变平过去一般认为是由于耀斑中非热电子的低能截止造成的,但现在也有作者认为耀斑光子与下层大气的逆康普顿散射(albedo效应)或者其他作用也能够使得HXR光子谱出现低能变平的情形.采用Gan et al.(2001,2002)中提出的求非热电子低能截止的方法,统计分析了Ramaty High Energy Solar Spectroscopy Imager(RHESSI)卫星在2002—2005年间观测的100个耀斑,发现经albedo校正,有18个耀斑的HXR光子谱可以利用单幂律谱来拟合,在80个可以用双幂律谱来拟合HXR光子谱的耀斑中,有21个耀斑可以直接用单幂律电子谱加一个低能截止来解释.低能截止范围为20—50keV,平均值约为30keV.同时也分析了耀斑光子谱特征的其他可能解释.
韩钢李友平甘为群
Double hard X-ray peaks in RHESSI flares as evidence of chromospheric evaporation and implications for modifying the Neupert effect被引量:2
2009年
Among the RHESSI flare samples, we concentrated on a kind of flare that presents two successive peaks (that is, it presents both an impulsive phase and a gradual phase) in 12 - 25 keV light curves. Taking the C1.4 flare on 2002 August 12 as an example, we studied the light curves, spectra, and images in detail. Making full use of the capabilities of RHESSI, we showed some evidence to support the expected causal relationship between these two peaks; the first peak is mainly nonthermal, while the second peak is mainly thermal; the energy carried by nonthermal electrons during the first peak seems to be comparable to the thermal energy of the second peak. The morphologies of X-ray images and their evolutions provide additional evidence for this causality. We conclude that two such peaks in the 12 - 25 keV light curve are good evidence for the chromospheric evaporation. However, the maximum time of the second peak is later than the end time of the first peak, suggesting that for some events, a modification of the traditional Neupert effect could be necessary by inclusion of a time delay, which might be partly related to the filling of the loop by evaporated material.
You-Ping Li Wei-Qun Gan Yang Su
关键词:SUN
基于窗函数数字预滤波处理系统的研究
2010年
由于在FPGA中能够通过FIRIPCore很方便地实现FIR滤波器组。在此,从FIR滤波器组的各种窗函数特性分析入手,分析了各种窗函数在频域内的各种性质,提出了在合理使用FPGA内部资源的前提下,设计适用于不同天文观测的预处理DFB系统中FIR滤波器的设计。通过设计观测具有频率分裂特征的太阳Ⅱ型爆发的DFB,详细论证了该种设计的可行性。
董亮柏正尧汪敏许春施硕彪
关键词:FPGAFIR窗函数DFB
Properties of the He I 10830 Line in Solar Flares
2008年
We study the properties of the He I 10830 A line in nine selected solar flares, using spectral data obtained with the Multi-channel Infrared Solar Spectrograph (MISS) at Purple Mountain Observatory (PMO) and photospheric images from the Michelson Doppler Imager (MDI) onboard the Solar and Heliospheric Observatory (SOHO). Our results indicate that, over an area of 3″- 8″, the He I 10830 A line shows emission exceeding the continuum in nearby quiet region when the Geostationary Operations Environmental Satellite (GOES) X- ray class of the flare reaches a threshold value (C4.5). The He I 10830 A line emission is detected only in the kernels of the Ha brightenings, but is not associated with the size of the flare. It is found that, whenever the He I 10830 Aline shows excess emission over the nearby continuum both the Ha and the Ca Ⅱ 8542 A lines display enhanced intensities exceeding their preflare intensities. The He I 10830A line emission can occasionally extend into the umbra of the involved sunspot, which is inconsistent with previous studies. The weak com- ponent of He I 10830A line changes from emission to absorption earlier than does the main component. Our results favor the photoionization-reconnection mechanism for the excitation of the He I 10830fi, line.
Qiu-Sheng Du Hui Li
电子回旋脉泽不稳定性驱动的太阳射电辐射机制
2010年
在解释天体爆发过程中的短时标相干射电辐射现象方面,非热电子驱动的回旋脉泽辐射得到了广泛应用。在以往的研究中,一个关键条件是非热电子具有各向异性速度分布,从而有效激发回旋脉泽不稳定性。然而,观测显示太阳和其他天体的非热电子经常呈现负幂律谱形式的能量分布。非热电子的这种负幂律能谱特征会严重抑制回旋脉泽不稳定性放大率,因此,进一步研究非热电子的负幂律能谱分布行为,能拓宽电子回旋脉泽辐射机制的适用性,很好地发展天体射电辐射机制理论。最近研究结果显示,负幂律谱电子的低能截止行为可以有效地激发电子回旋脉泽辐射,从而拓宽了其在天体物理研究中的应用范围。
唐建飞吴德金
VLBI observations with the Kunming 40-meter radio telescope被引量:5
2010年
The Kunming 40-meter radio telescope is situated in the yard of the Yunnan Astronomical Observatory (Longitude: 102.8° East, Latitude: 25.0° North) and saw its first light in 2006 May. The Kunming station successfully joined the VLBI tracking of China's first lunar probe "Chang'E-1" together with the other Chinese telescopes: the Beijing Miyun 50-meter radio telescope, Urumqi Nanshan 25-meter radio telescope, and Shanghai Sheshan 25-meter radio telescope, and received the downlinked scientific data together with the Miyun station from October of 2007 to March of 2009. We give an introduction to the new Chinese VLBI facility and investigate its potential applications. Due to its location, the Kunming station can significantly improve the u - v coverage of the European VLBI Network (EVN), in particular, in long baseline observations. We also report the results of the first EVN fringe-test experiment of N09SX1 with the Kunming station. The first fringes in the European telescopes were successfully detected at 2.3 GHz with the ftp-transferred data on 2009 June 17. From scheduling the observations to performing the post correlations, the Kunming station shows its good compatibility to work with the EVN. The imaging result of the extended source 1156+295 further demonstrates that the Kunming station greatly enhances the EVN performance.
Long-Fei HaoMin WangJun Yang
关键词:INTERFEROMETERSVLBI
EIT waves and coronal magnetic field diagnostics被引量:3
2009年
Magnetic field in the solar lower atmosphere can be measured by the use of the Zeeman and Hanle effects. By contrast, the coronal magnetic field well above the solar surface, which directly controls various eruptive phenomena, can not be precisely measured with the traditional techniques. Several attempts are being made to probe the coronal magnetic field, such as force-free extrapolation based on the photospheric magnetograms, gyroresonance radio emissions, and coronal seismology based on MHD waves in the corona. Compared to the waves trapped in the localized coronal loops, EIT waves are the only global-scale wave phenomenon, and thus are the ideal tool for the coronal global seismology. In this paper, we review the observations and modelings of EIT waves, and illustrate how they can be applied to probe the global magnetic field in the corona.
CHEN PengFei Department of Astronomy, Nanjing University, Nanjing 210093, China
关键词:CORONALDIAGNOSTICSMAGNETOHYDRODYNAMICS
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