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Hard X-ray emitting symbiotic stars are candidates for SN Ia progenitors. The importance of Type Ia SNe as standard candles for cosmology makes the study of their progenitor systems particularly important. Additionally, they provide one of the most promising laboratories for the study of astrophysical jets. Typically, the X-ray emission in these systems is modeled with a collisional plasma model, sometimes with an emission measure distribution taken from a cooling flow model. The lack of any coherent periods in both X-rays and optical wave band strongly suggests that the accreting white dwarfs in the hard X-ray symbiotic stars are non-magnetic. Although relatively few have been discovered to date, but we believe that there are very many of them in our galaxy and could be possible candidates for the Galactic Ridge X-ray Emissions (GRXE).  相似文献   
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压电主动杆Maxwell动力学建模与鲁棒H∞控制研究   总被引:1,自引:0,他引:1  
未来高性能航天器迫切需要基于压电作动的主动减振控制.针对压电作动器和检波器组成的主动杆系统,基于控制目的,推导了作动器Maxwell动力学模型,为了更好的反映检波器噪声和低频较差性能带来的影响,采用同价的SUITE动杆的系统辨识模型设计了H∞控制器,仿真结果表明H∞控制器对100Hz的正弦扰动有效隔离73%(11.4dB),对频带250Hz的白噪声有效隔离70%(10.5dB).  相似文献   
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原子钟的五种噪声反映了它在一定时间间隔内的性能。当取样间隔小于1h,原子钟主要表现为调相白噪声。在地方协调时UTC(NTSC)的实时监控中,不仅要求参考原子时(RTA,用于地方协调时控制的参考)具有很高的长期稳定度,而且要求其短期稳定度亦很高。影响RTA短期稳定度的主要是个台原子钟的调相白噪声。首先讨论了确定原子钟短期噪声的方法,进而利用小波分析方法研究了原子钟凋相白噪声分离与降噪的方法。  相似文献   
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调相白噪声对频率传递短期稳定度的影响分析   总被引:1,自引:0,他引:1  
详细分析了调相白噪声对频率稳定度的影响。经过理论分析,得出了频率传递系统信噪比的开方与稳定度成正比,调制信号频率与稳定度成正比。经过分析得到,在一定范围内,提高激光器光功率可以提高频标传递的稳定度;调制频率和传递系统信噪比是影响短期稳定度的两个重要因素;通过增加EDFA的方法不能提高传递系统短期稳定度,反而每增加4到5个EDFA,稳定度下降1个数量级。  相似文献   
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Several important issues are open in the field of solar variability and they wait their solution which up to now was attempted using critical ground-based instrumentations. However, accurate photometric data are attainable only from space. New observational material should be collected with high enough spatial and spectral resolution, covering the whole visible range of the electromagnetic spectrum as well infrared and ultraviolet to reconstruct the total solar irradiance: (1) the absolute contributions of different small-scale structural entities of the solar atmosphere from the white light flares and from micro-flares are still poorly known; (2) we do not know the absolute contributions of different structural elements of the solar atmosphere to the long-term and to the cyclic variations of the solar irradiance, including features of the polar regions of the Sun; (3) the variations of the chromospheric magnetic network are still poorly evaluated; (4) only scarce information is available about the spectral variations of different small-scale features in the high photosphere. Variability of the Sun in white light can be studied with higher spectral, spatial and time resolution using space-born telescopes, which are more appropriate for this purpose than ground based observatories because of better seeing conditions, no interference of the terrestrial atmosphere and a more precise calibration procedure. Scientific requirements for such observations and the possible experimental tools proposed for their solution. Suggested solar studies have broader astrophysical importance.  相似文献   
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This paper proposes a novel ship wake detection algorithm based on the White Top-hat Transform (WTHT) and the Radon transform, which aims to improve the contrast between the ship wake and the background so as to improve the detection performance on Synthetic Aperture Radar (SAR) images. The proposed algorithm includes two major processes, and one is to improve the contrast and another one is to locate the ship wake. In high sea state conditions, the contrast of ship wake and background can be very low, which makes it difficult to detect. In the first step, the proposed contrast improvement algorithm is applied to improving the contrast which helps for improving the detection performance. An attribute filter based on edge detection result is adopted here. In the second step the contrast improved image is transformed into the Radon domain followed by peak extraction process to find the wake, the WTHT is used once more in this step. Finally, in the last step, the wake is overlapped on the original image. Experimental results on Tiangong-2 Interferometric Imaging Radar Altimeter (InIRA) images are presented and compared with that obtained by using the classical algorithm, and in this way, the better performance of our algorithm is demonstrated.   相似文献   
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随着现代制造业的飞速发展,电子元器件的体积将变得越来越小,于是测试功率受到了很大的限制,都需要降低测试电流,这就对系统测试小电压信号时的噪声抑制能力提出了极大的挑战,本文在经典偏置补偿测量电阻方法的基础上,介绍了基于直流电流换向方法的电阻测量技术,并对这两种方法进行了比较,得出基于直流电流换向方法在抑制噪声能力上的优越性。  相似文献   
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