NanoSIMS analysis of organic carbon from the Tissint Martian meteorite: Evidence for the past existence of subsurface organic‐bearing fluids on Mars

Two petrographic settings of carbonaceous components, mainly filling open fractures and occasionally enclosed in shock‐melt veins, were found in the recently fallen Tissint Martian meteorite. The presence in shock‐melt veins and the deuterium enrichments (δD up to +1183‰) of these components clearly indicate a pristine Martian origin. The carbonaceous components are kerogen‐like, based on micro‐Raman spectra and multielemental ratios, and were probably deposited from fluids in shock‐induced fractures in the parent rock of Tissint. After precipitation of the organic matter, the rock experienced another severe shock event, producing the melt veins that encapsulated a part of the organic matter. The C isotopic compositions of the organic matter (δ¹³C = ?12.8 to ?33.1‰) are significantly lighter than Martian atmospheric CO₂ and carbonate, providing a tantalizing hint for a possible biotic process. Alternatively, the organic matter could be derived from carbonaceous chondrites, as insoluble organic matter from the latter has similar chemical and isotopic compositions. The presence of organic‐rich fluids that infiltrated rocks near the surface of Mars has significant implications for the study of Martian paleoenvironment and perhaps to search for possible ancient biological activities on Mars.     

Detection of large color variation in the potentially hazardousasteroid （297274） 1996 SK

Low-inclination near-earth asteroid(NEA)(297274) 1996 SK,which is also classified as a potentially hazardous asteroid,has a highly eccentric orbit.It was studied by multi-wavelength photometry within the framework of an NEA color survey at Lulin Observatory.Here,we report the finding of large color variation across the surface of(297274) 1996 SK within one asteroidal rotation period of4.656 ± 0.122 hours and classify it as an S-type asteroid according to its average colors of B- V = 0.767 ± 0.033,V- R = 0.482 ± 0.021,V- I = 0.801 ± 0.025and the corresponding relative reflectance spectrum.These results might be indicative of differential space weathering or compositional inhomogeneity in the surface materials.     

A Disconnection Event of Comet Lulin†

The cometary disconnection event (DE) is the separation of the entire cometary tail or a part of it from the cometary head. It is one of the most spectacular phenomena of comets. The driving mechanism remains unclear, and at present there are many competitive theories to explain the onset of DE. However, the variable solar wind is suspected to play a major role. Comet Lulin exhibited a DE on 4th Feb. 2009. The data around this date are analyzed, and it is found that the comet Lulin had already endured a DE on 3rd Feb. 2009. By comparing the morphologies of the plasma tails in these two DEs, it is concluded that the DE which occurred on 3rd Feb. 2009 is another DE, which is distinct from that of 4th Feb. 2009. In this paper, we describe the results of analysis on the DE dated 3rd Feb. 2009. The measured velocity of disconnection motion is about 68 km/s, and the calculated onset time of this DE is 3.635 ± 0.215 Feb. 2009 in UT decimal date. Combining the orbital characteristics of Comet Lulin before and after the DE occurrence and the solar-wind data measured by the STEREO-A spacecraft, it is concluded that the DE which occurred on 3rd Feb. 2009 was probably caused by the magnetic reconnection due to the interaction between the comet and a coronal mass ejection (CME).     

Spectral energy distributions for TeV blazars

In this work, we collected a sample of 69 TeV blazars from TeVCat, obtained their multiwavelength observations, and fitted their spectral energy distributions by using a second degree polynomial function. The structure parameters of synchrotron bumps for 68 blazars and those of inverseCompton bumps for 56 blazars were derived. Then, we conducted statistical analysis on the parameters(curvature, peak frequency, peak luminosity, bolometric luminosity and X/γ-ray spectral indexes).From our analysis and discussions, we can conclude the following:(1) There is a clear positive correlation between the synchrotron peak frequency, log ν_p~s, and the inverse-Compton peak frequency, log ν_p~(IC),and between the synchrotron peak luminosity, log ν_p~sL_(νp)~s, and the inverse-Compton peak luminosity,log ν_p~(IC)L_(νp)~(IC).(2) The correlation between the peak frequency and the curvature of synchrotron bump is clearly different from that of the inverse-Compton bump, which further indicates that there are different emission mechanisms between them.(3) There is a correlation between log νIC pand γ-ray spectral index, α_γ, for the TeV blazars: log ν_p~(IC)=-(4.59 ± 0.30)α_γ+(32.67 ± 0.59), which is consistent with previous work.(4) An "L-shape" relation is found between log ν_p~s and α_X for both TeV blazars and Fermi blazars. A significant correlation between log νs pand X-ray photon index(α_X) is found for the TeV blazars with high synchrotron peak frequency: log ν_p~s=-(3.20 ± 0.34)α_X+(24.33 ± 0.79),while the correlation is positive for low synchrotron peaked TeV sources.(5) In the αX-αγdiagram,there is also an "L-shape." The anti-correlation is consistent with results available in the literature, and we also find a positive correlation between them.(6) Inverse-Compton dominant sources have luminous bolometric luminosities.     

Swift时代伽马暴的观测及研究进展

Swift卫星从2004年11月20日升空开始运转到现在已有2年多时间.到目前为止,它-共观测到了200多个伽马暴及其余辉现象.由于Swift观测到了早期X射线余辉、短暴余辉和高红移伽马暴等新的重要现象,伽马暴研究进入了新的时代.该文首先对伽马暴的研究历史做简短回顾,然后简要介绍伽马暴的物理图像和Swift卫星的构成及特点,最后全面评述Swift的观测成就及由此引起的理论挑战.     

一种基于FPGA的多种波形发生器的设计

简要介绍了直接数字频率合成技术的基本原理,重点给出了直接数字频率合成技术的FPGA硬件实现.实验表明,基于FPGA的直接数字频率合成技术不仅可以产生任意波形,而且波形的频率、相位、幅度任意可调.     

灰色-自回归动态模型用于原子时尺度计算

由于各种噪声和其他因素的影响,原子钟运行情况十分复杂.为了准确地预测其确切的频率变化或钟速,有必要研究建立一个可靠的预测模型,通过模型预测原子钟的钟速,以便在地方协调时的监控和地方原子时计算中采用.讨论了如何利用灰色模型与自回归模型对原子钟钟速进行预测,研究并提出了二者的综合模型,结合国家授时中心原子钟实际数据进行了验证,并给出了不同原子钟对应模型的预测精度计算方法.     

卫星轨道偏心率的变化特征及其对轨道寿命的影响

轨道偏心率的变化极其重要,它是制约各类(不同高度)空间飞行体轨道寿命的关键因素之一.对于地球低轨卫星,主要受大气耗散作用的影响,而对环月(或环火星)低轨卫星,主要受非球形引力位中奇次带谐项的影响,会出现变幅较大的长周期变化,从而导致近星点高度hp在一段时间内有明显的下降趋势.对大偏心率轨道和高轨道,第三体的引力作用也会使e出现变幅较大的长周期变化,近星点高度hp也会有明显下降的现象,这都会影响卫星的轨道寿命,但这一动力学机制与大气耗散机制和非球形引力机制都不相同.即对轨道偏心率的变化特征及其对轨道寿命的影响作一综述.     

基于不等式约束的磁共振信号T2谱多指数分解法及算法改进

磁共振地下水探测信号的弛豫时间T₂和振幅与地下岩石孔隙大小和地下水的含水量直接相关。目前,磁共振地下水探测方法中,信号的衰减特性由平均弛豫时间T^*₂来描述。然而,对于复杂的多孔介质组成的岩石结构,仅由T^*₂无法准确描述地下孔隙情况。详细研究了基于不等式约束的多指数分解法,进行了信号T₂谱的提取,并重新计算多指数形式下的信号初始振幅。结果表明：对比信号在不同采集时间下的T₂谱提取结果,延长信号的采集时间有助于T₂谱的准确提取;通过磁共振仿真信号计算并分析不同信噪比下的T₂谱提取结果,信噪比大于30 dB时相对误差平均值小于5%;进行算法改进,得到信噪比大于10 dB时相对误差平均值小于5%的结果,且幅值和T₂的相对误差平均值降低了约1/3。由此可知:采用多指数分解法能够获得磁共振信号的T₂谱,正则化技术和加权修正能够提高T₂谱的准确度和抗干扰能力;与单指数方式相比,采用多指数拟合能够更准确地恢复信号初始振幅。     

西北干旱区SG-SPAC系统水力模型的建立

文章论述了西北干旱区水资源的特点，利用现代农田水分研究方法研究了干旱区地表水、地下水、土壤、植物、大气连续体（SG－SPAC）系统的水分转化规律，建立了地表水、地下水和土壤水之间的水力耦合模型，为干旱区的水资源规划、开发和生态环境保护奠定了科学的基础。