Compton Polarimetry in Gamma-Ray Astronomy

The analysis of compact astronomical objects has generally dealt with the physical properties of the source within a two-parameter space, which is defined by the spectral characteristics and time variability. This approach often leads to the situation whereby two or more very different models can explain the observations successfully. Polarimetric observations have the diagnostic potential to discriminate between the different compact source models and can offer a unique insight into the geometrical nature of the emission zones. To date, however, no polarization observation in the gamma-ray energy domain has been successfully performed, due to the difficulties in making polarimetric measurements in this high-energy region of the spectrum. In this paper the polarized gamma-ray emission mechanisms are reviewed with the emphasis on their detectable characteristics. Potential astronomical sites in which these emission mechanisms may be at work are discussed. Observational results obtained in other wavebands and theoretical predications made for some of the most likely astronomical sources of polarization are reviewed. Compton polarimetry has long been used in the field of nuclear gamma-ray spectroscopy in the laboratory. The operational principle behind all generations of nuclear gamma-ray polarimeters has been to measure the asymmetry in the azimuthal distribution of the scattered photons. However none of the polarimeters designed for laboratory experiments will be sensitive enough to observe even the strongest astronomical source. In the past few years there have been a number of innovative developments aimed at the construction of astronomical gamma-ray polarimeters, either as dedicated experiments or in missions with polarimetric capability. The designs of all the polarimeters are based on either discrete or continuous position sensitive detector planes. In this paper the data analysis techniques associated with this type of polarimeter are discussed as well as methods of removing some of the systematic effects introduced by a non-ideal detector response function and observation conditions. Laboratory tests of these new polarimetric techniques are reviewed. They demonstrate the feasibility of building a suitably sensitive astronomical gamma-ray polarimeter. Optimization of the design of pixellated detector array based polarimeters is also addressed. The INTEGRAL mission, which is to be launched by ESA in the year 2001, is the most likely telescope to perform the first successful gamma-ray polarization observation. The polarimetric characteristics of the two main instruments on board INTEGRAL are evaluated and their sensitivities to a wide range of potentially polarized gamma-ray sources are estimated.     

The atmospheric Čerenkov technique in the search for PBH

Searches for primordial black holes are reviewed.     

The High Energy Telescope for STEREO

The IMPACT investigation for the STEREO Mission includes a complement of Solar Energetic Particle instruments on each of the two STEREO spacecraft. Of these instruments, the High Energy Telescopes (HETs) provide the highest energy measurements. This paper describes the HETs in detail, including the scientific objectives, the sensors, the overall mechanical and electrical design, and the on-board software. The HETs are designed to measure the abundances and energy spectra of electrons, protons, He, and heavier nuclei up to Fe in interplanetary space. For protons and He that stop in the HET, the kinetic energy range corresponds to ～13 to 40 MeV/n. Protons that do not stop in the telescope (referred to as penetrating protons) are measured up to ～100 MeV/n, as are penetrating He. For stopping He, the individual isotopes ³He and ⁴He can be distinguished. Stopping electrons are measured in the energy range ～0.7–6 MeV.     

高温升燃烧室综合燃烧性能超大涡模拟

为了对高温升燃烧室性能进行计算分析,运用超大涡模拟方法开展数值模拟,并同步开展了雷诺平均数值模拟作为对 比。计算结果表明：旋流器设计与火焰筒开孔设计的匹配合理,Rothstein提出的射流迹线公式能够合理预测主燃孔的射流穿透。超 大涡模拟计算得到的出口径向温度分布系数的剖面曲线趋势和最大值位置均与试验结果符合较好。通过与试验结果进行定量比较 发现,在相同计算网格条件下,超大涡模拟方法预测高温升燃烧室综合燃烧性能的精度明显高于雷诺平均方法的。     

The Interstellar Boundary Explorer High Energy (IBEX-Hi) Neutral Atom Imager

The IBEX-Hi Neutral Atom Imager of the Interstellar Boundary Explorer (IBEX) mission is designed to measure energetic neutral atoms (ENAs) originating from the interaction region between the heliosphere and the local interstellar medium (LISM). These ENAs are plasma ions that have been heated in the interaction region and neutralized by charge exchange with the cold neutral atoms of the LISM that freely flow through the interaction region. IBEX-Hi is a single pixel ENA imager that covers the ENA spectral range from 0.38 to 6 keV and shares significant energy overlap and overall design philosophy with the IBEX-Lo sensor. Because of the anticipated low flux of these ENAs at 1 AU, the sensor has a large geometric factor and incorporates numerous techniques to minimize noise and backgrounds. The IBEX-Hi sensor has a field-of-view (FOV) of 6.5°×6.5° FWHM, and a 6.5°×360° swath of the sky is imaged over each spacecraft spin. IBEX-Hi utilizes an ultrathin carbon foil to ionize ENAs in order to measure their energy by subsequent electrostatic analysis. A multiple coincidence detection scheme using channel electron multiplier (CEM) detectors enables reliable detection of ENAs in the presence of substantial noise. During normal operation, the sensor steps through six energy steps every 12 spacecraft spins. Over a single IBEX orbit of about 8 days, a single 6.5°×360° swath of the sky is viewed, and re-pointing of the spin axis toward the Sun near perigee of each IBEX orbit moves the ecliptic longitude by about 8° every orbit such that a full sky map is acquired every six months. These global maps, covering the spectral range of IBEX-Hi and coupled to the IBEX-Lo maps at lower and overlapping energies, will answer fundamental questions about the structure and dynamics of the interaction region between the heliosphere and the LISM.     

高速加工技术在加工旋翼夹头中的应用

高速加工技术不但能大大缩短零件的加工周期,从而降低加工成本,而且能提高加工精度.详细介绍了应用高速加工技术制造铝制U型夹头的关键技术和测试结果.硬质合金端铣刀和定期的软件分析能够预测最佳的加工参数以确保稳定的U型夹头铝制工件的切削.通过应用该项技术,在不损失加工精度和加工质量的前提下,其加工运行时间比传统加工技术所需要的加工运行时间缩短了3-4倍.     

三角翼低速动态大攻角气动特性试验研究

对后掠角分别为X=60°、70°和80°尖前缘平板三角翼模型和一个前缘后掠角为（76° 40°）的双三角翼模型在低速风洞中作大攻角俯仰摩波运动，振幅am=30°、60°和90°，缩减频率K=0.01～0.12，基于根弦长雷诺数Re=2.76×10^5～8.23×10^5。进行了六分量动态气动载荷测量，动态流动显示和70°三角翼上翼面非定常压力测量，并分别与对应的静态试验结果比较。分析了运动参数包括缩减频率、振幅和Re数、后掠角对气流动态迟滞特性的影响。     

太阳能热动力系统吸热/蓄热器能量分析

空间太阳能热动力发电系统是一种新型的空间电力系统。吸热 /蓄热器是热动力发电系统关键部件之一。吸热 /蓄热器采用的蓄热方式是相变蓄热。通过对吸热 /蓄热器的能量分析 ,可以很好的了解吸热器的能量传递 ,以及相变材料的工作过程。建立了太阳能热动力发电系统吸热器腔体辐射模型 ,结合换热管的传热模型计算了吸热器的传热过程。得到了吸热器的能量损失、工质吸收能量、PCM的潜热储能和显热储能等重要指标 ,并且得到了换热管最大温度 ,工质出口温度等重要结果。计算结果可以用于吸热器的设计     

The Mercury Gamma-Ray and Neutron Spectrometer (MGNS) Onboard the Mercury Planetary Orbiter of the BepiColombo Mission: Design Updates and First Measurements in Space

Space Science Reviews - Volatiles and refractories represent the two end-members in the volatility range of species in any surface-bounded exosphere. Volatiles include elements that do not interact...     

高速数字电路中的信号完整性问题

主要介绍了在高速数字电路中的信号完整性问题。并讨论了如何降低电路中信号干扰的方法。     

高可靠性在高科技战争中的地位

可靠性工程是研究产品在规定的条件下和规定的时间内完成规定任务的能力的一门科学。本文以近两次世界局部战争为例,论述了可靠性在现代战争中的作用与地位。     

Cosmic Ray Isotopic Composition Studies with the Ulysses High Energy Telescope: Implications for Origin and Distribution in the Galaxy

The isotopic abundances of the Galactic cosmic radiation measured in the Heliosphere provide unique information on acceleration, propagation modes and containment times in the Galactic magnetic fields. Nuclear interactions with interstellar matter lead to observable γ-radiation production and, thus, to direct information on cosmic ray distribution throughout the Galaxy and its magnetic halo. The COSPIN High Energy Telescope (HET) has excellent isotopic resolution from hydrogen to nickel over the ten year period of Ulysses in space. Based on our recent work, we discuss the implications for modeling the acceleration and propagation of the cosmic radiation. This revised version was published online in August 2006 with corrections to the Cover Date.     

高温吸波材料研究新进展与趋势

对最近报道的耐温>1 000℃的高温吸波材料进行了回顾,主要介绍了碳和陶瓷类无机耐高温吸波材料;同时对在纳米技术、静电纺丝技术等研究中报道的新型耐高温材料应用为电磁吸收材料进行了展望。     

高性能雷达罩设计与制造关键技术分析

雷达罩作为航空武器装备的重要组成部分,对其功能性能的实现具有重要的影响。本文分析了国外航空武器装备的发展并指出了雷达罩的技术发展方向,分析了包括高隐身、宽频带、高透波、耐大功率、耐高温、透毫米波、雷达/红外双模等几种高性能雷达罩设计与制造关键技术,为高性能雷达罩的设计与制造奠定了基础。     

论《了不起的盖茨比》的叙事角度和"二元主角"技巧

<了不起的盖茨比>是美国文学中的经典之作.在小说中,菲茨杰拉德运用多元化的叙事角度和"二元主角"技巧,既讲述了杰伊·盖茨比的故事,也讲述了尼克·卡洛维的故事.因此,本文具体分析该小说中多元化的叙事角度及"二元主角"技巧的成功运用,以探讨作者在这部小说中所运用的精湛成熟的叙事技巧及其独特的艺术效果.     

合成纹影技术在内波实验研究中的应用

纹影方法是重要的密度场可视化手段。文章重点介绍实验室研究中一种新型密度场测量方法—合成纹影技术,阐述了合成纹影技术的原理。利用光源、背景模板、实验水槽、图像采集设备搭建了合成纹影系统,将合成纹影技术应用于垂直振荡圆柱和往复潮流过地形生成内波两个实验,结果验证了合成纹影技术在内波实验中定量测量密度场的可行性和准确性,为合理使用合成纹影技术进行密度场可视化测量提供借鉴和参考。     

Fe3Al高温氧化中的内氧化

用热天平、扫描电子显微镜（SEM）、能谱（EDX）和X-射线衍射（XRD）研究了Fe3Al在1000℃空气中的氧化行为。发现氧化动力学基本服从抛物线规律,氧化膜由Al2O3和少量Fe2O3组成,并产生穿晶内氧化;根据对氧化膜及基体的分析结果及有序合金扩散热力学特点,提出发生内氧化的主要原因是金属间化合物的有序结构降低了铝的活度和其在合金中的扩散系数,在高温氧化过程中,基体／氧化膜界面严重贫铝,从而发生内氧化。     

高原航线运行对航空器适航保障的特殊要求

我国西部的许多机场海拔均在2000m以上,空域复杂、气象条件多变、飞行难度大,如何保障在这些高原机场的飞行安全是所有航空公司面临的一个突出问题,本文结合我国西部地区高原机场的特点,就高原航线运行对航空器适航保障的特殊要求进行了分析.     

网格技术在高校资产协同管理系统中的应用

针对目前我国高等学校资产管理的水平及应用管理软件的开发现状,提出了一种基于网格技术的高校资产协同管理系统与模型。提出了以“协同管理,流程控制,绩效评价”为基本要求的软件开发目标。文章对实现这一系统相关问题、管理模型的建立、系统的结构与特点,特别是以网格服务为标志的新的分布式系统进行了探讨,同时对系统在高等院校的应用前景进行了展望。