掺磷纳米硅薄膜的微结构

采用喇曼(Raman)散射谱、高分辨率电子显微镜(HRTEM)和原子力显微镜(AFM)对掺磷纳米硅薄膜的微结构进行了分析,并对纳米硅薄膜的传导机制进行了探讨.结果表明:掺磷纳米硅薄膜由尺寸为2～4*#nm的晶粒和2～3个原子层厚的非晶界面构成,计算得到薄膜的晶态比为40%～55%.与本征纳米硅薄膜相比,掺磷纳米硅薄膜晶粒尺寸和晶态比没有明显变化,电导率却提高了2个数量级.随着掺磷浓度增加,纳米硅薄膜的晶粒尺寸、晶态比及电导率逐渐增大.AFM观察表明掺磷纳米硅薄膜由尺寸介于15～20*#nm的团簇构成,团簇排列具有带状特征.     

Spatial variation of the supersonic thermal plasma flow downstream of the termination shock

In this paper we start from the most recently observed fact that the solar wind plasma after passage over the termination shock is still supersonic with a Mach number of about 2. To explain this unexpected phenomenon and to predict the evolution of properties of the downstream plasma flow we here consider a two-fluid proton plasma with pick-up protons as a separate suprathermal, second proton fluid. We then formulate a self-consistent system of hydrodynamical conservation equations coupling the two fluids by dynamical and thermodynamical coupling terms and taking into account the effects of newly incorporated protons due to charge exchange with the H-atoms in the heliosheath. This then allows us to predict that in the most probable case the solar wind protons will become subsonic over a distance of about 30 AU downstream of the shock. As we can also show, it may, however, happen that the plasma mixture later again reconverts to a supersonic signature and has to undergo a second shock before meeting the heliopause.     

单层钎焊砂盘磨粒分布有序性研究

对亲型非砂轮磨削工具－－单层钎焊砂盘的硬质合金磨粒在基体上的分布进行了初步研究,砂盘作为一种手握粗磨削工具,降低磨削力是最重要的,文中借鉴砂带及单层高温钎焊超硬磨料砂轮的一些研究,提出了砂盘的磨粒在基体上有序性分布的概念,将此概念应用于砂盘钎焊制造工艺上,在相同的制造工艺和磨洵深度条件下,对得到的磨粒有序性及无序性分布的砂盘进行了磨削对比实验。结果表明,砂盘磨粒的有序性分布能显著降低其磨削力。此概     

日球层内外能量中性原子的探测

能量中性原子(Energetic Neutral Atoms, ENA, 简称能原子)是指在日球层内外空间, 拥有>0.1keV动能的原子.在此空间领域并没有温度>106K的中性气体, 但却充满动能>0.1keV的正离子.因此能原子A应该是A+离子与原地稀薄气体B原子或分子交换电荷所产生的, 即A++B→A+B+. 电荷交换涉及极小的动能变化, 新生的能原子A和离子B+基本上各自保持原有动能. 离子B+随即被当地磁场俘获, 能原子A则脱离磁场约束并携带其原属离子群的成分和能量信息而直线运动, 成为遥测空间等离子体的有效媒介. 美国人造卫星 IBEX (Interstellar Boundary Explorer) 直接探测得到来自日球层以外星际空间的能原子, 大幅延伸了利用能原子遥测空间等离子体的领域. 本文据此论述了空间能原子的发现, 综述了探测空间能原子的基本概念与实例、取得的主要成果、仪器设计和研制进展以及未来空间利用能原子遥测的发展趋势.      

Search for high-proper motion objects with infrared excess

The possibility of interstellar migration has been theorized during the past thirty years in the form of “Dysonships” that, using non-relativistic propulsion systems, are able to colonize the Galaxy in a relatively short time compared to the age of the Galaxy and consequently penetrate inside our solar system too. Observational evidence of this can be potentially obtained using the present state of the art of telescopes and related sensors, by following aimed searches and an expanded SETI protocol. Some transient and unrepeated radio signals recorded during standard SETI observations might be due to the transit of high-proper motion artificial sources of extraterrestrial origin, which are expected to show a very weak optical emission, a strong infrared excess and occasional high-energy bursts in the X and Gamma-ray wavelength ranges. Such artificial sources might show an interest to Earth by sending probes to visit it: such a possibility can be investigated scientifically as well.     

Design and Optimization of 3D Radial Slot Grain Configuration

Upper stage solid rocket motors (SRMS) for launch vehicles require a highly efficient propulsion system. Grain design proves to be vital in terms of minimizing inert mass by adopting a high volumetric efficiency with minimum possible sliver. In this article, a methodology has been presented for designing three-dimensional (3D) grain configuration of radial slot for upper stage solid rocket motors. The design process involves parametric modeling of the geometry in computer aided design (CAD) software through...     

Interstellar planetary protection

In the coming decades the detection of Earth-like extrasolar planets, either apparently lifeless or exhibiting spectral signatures of life, will encourage design studies for craft to visit them. These missions will require the elaboration of an interstellar planetary protection protocol. Given a specific dose required to sterilize microorganisms on a spacecraft, a critical mean velocity can be determined below which a craft becomes self-sterilizing. This velocity is calculated to be below velocities previously projected for interstellar missions, suggesting that an active sterilization protocol prior to launch might be required. Given uncertainties in the surface conditions of a destination extrasolar planet, particularly at microscopic scales, the potential for unknown biochemistries and biologies elsewhere, or the possible inoculation of a lifeless planet that is habitable, then both lander and orbiter interstellar missions should be completely free of all viable organisms, necessitating a planetary protection approach applied to orbiters and landers bound for star systems with unknown local conditions for habitability. I discuss the case of existing craft on interstellar trajectories – Pioneer 10, 11 and Voyager 1 and 2.     

一种双基站低轨道区域覆盖δ星座设计

在双基站理论研究基础上 ,进行了定倾角区域性覆盖双基站δ星座设计 ,采用倾角为 41°的回归轨道 ,用点覆盖数值仿真的方法设计了对地面站与空间站的一重覆盖与二重覆盖下的星座构型。且星座中各星之间 ,各星与空间站之间均可建立星际链路 ,保证数据在空间站、地面站及星座之间连续传递     

Ⅱ类甲醇脉泽的红外抽运研究

本文研究了Ⅱ类甲醇脉泽与周围红外源的关系,发现它们有很强的相关性。分析认为红外源很可能是Ⅱ类甲醇脉泽的抽运源。     

适用于固体推进剂药柱应力分析的一种粘弹性有限元法

本文根据Ｈｅｒｒｍａｎｎ变分原理导出一种适用于不可压缩和近似不可压粘弹性的新的本构关系和相应的有限元公式，开发了用于平面问题分析的计算机程序ＶＦＡＰＩＮＰ。计算结果表明，本方法和程序可用于所有泊松比的粘弹性问题的计算，尤其适用于推进剂药柱的应力分析。