Analysis of rain attenuation prediction models at Ku-band in Thailand

The performance of the existing rain attenuation models in tropical zones is still a debated issue due to the lack of measurements reported from these areas of the world to develop and validate prediction models. A three-year (2003–2005) campaign of rainfall rate and rain attenuation measurements was conducted on a satellite beacon link located in a tropical region of Thailand. The cumulative distributions of rain attenuation derived from the measured data are presented and compared with those obtained with existing prediction models.     

雄鹰亦有折翼时——航天飞机退役原因简析

虽然美国航天飞机铸就了巨大的辉煌,但是它将在2011年发射3架次后退役,这是为什么呢?千方百计难圆满为了极大提高运输能力,航天飞机当初被设计得很复杂。它里面有3500个     

Simulations of absorbed dose on the phantom surface of MATROSHKA-R experiment at the ISS

The health risks associated with exposure to various components of space radiation are of great concern when planning manned long-term interplanetary missions, such as future missions to Mars. Since it is not possible to measure the radiation environment inside of human organs in deep space, simulations based on radiation transport/interaction codes coupled to phantoms of tissue equivalent materials are used. However, the calculated results depend on the models used in the codes, and it is therefore necessary to verify their validity by comparison with measured data. The goal of this paper is to compare absorbed doses obtained in the MATROSHKA-R experiment performed at the International Space Station (ISS) with simulations performed with the three-dimensional Monte Carlo Particle and Heavy-Ion Transport code System (PHITS). The absorbed dose was measured using passive detectors (packages of thermoluminescent and plastic nuclear track detectors) placed on the surface of the spherical tissue equivalent phantom MATROSHKA-R, which was exposed aboard the ISS in the Service Zvezda Module from December 2005 to September 2006. The data calculated by PHITS assuming an ISS shielding of 3 g/cm² and 5 g/cm² aluminum mass thickness were in good agreement with the measurements. Using a simplified geometrical model of the ISS, the influence of variations in altitude and wall mass thickness of the ISS on the calculated absorbed dose was estimated. The uncertainties of the calculated data are also discussed; the relative expanded uncertainty of absorbed dose in phantom was estimated to be 44% at a 95% confidence level.     

系统级电磁兼容分析的离散技术及应用综述

介绍了一种系统级电磁兼容(EMC)分析技术—离散非线性分析(Discrete Nonlinear Analysis,DNA)的发展现状,该技术起源于线性离散EMC分析技术,后者是为开发系统内电磁兼容分析程序(IntrasystemElectromagnetic Compatibility Analysis Program,IEMCAP)所提出的方法。DNA技术可应用于以下方面:在极端恶劣电磁环境(EME)中(调制信号数目高达100 000)对无线电发射和接收建模;在一次仿真中需要综合考虑各种效应,包括线性(增益、衰减、滤波等)和非线性(互调、减敏、交调、相互混频、调幅调相转换等)效应以及高阶的非线性响应(25阶或更高);进行快速EMC分析(电磁环境越复杂,非线性效应阶数越高,DNA方法相对于传统方法的计算优势越大;自动搜寻非线性干扰源。     

Summary of the workshop on gamma-ray burst afterglows at the 34th COSPAR meeting

A summary is given of the presentations at the COSPAR workshop on γ-ray bursts with some personal commentary on the contributions, the SN/GRB connection, and on the role of magnetic fields in γ-ray bursts and their afterglows. Of special interest were the accumulated arguments for strong collimation and associated reduction in the total required energy for γ-ray bursts. Significant discussion was also devoted to the issues associated with iron and metal lines in X-ray spectra. It is important to note that some of the afterglows seem to require ambient densities 1 g cm⁻³, rather incompatible with a massive star environment. Of associated difficulty is the fact that few, if any, afterglows seem consistent with the r⁻² wind expected for a massive star model. There are reasons to think that if γ-ray bursts are associated with supernovae they are of Type Ic. This suggests that any wind present might be rich in carbon and oxygen, not hydrogen or helium. If γ-ray bursts are narrowly collimated, then the burst is only probing a small portion of any wind, perhaps just that time-dependent and isotropic structure directly along the rotation axis. The characteristics of “hypernovae” may be the result of orientation effects in a mildly inhomogeneous set of progenitors, rather than requiring an excessive total energy or luminosity. The recent event GRB 021004 provided a rich photometric and spectroscopic record and perhaps the most direct evidence yet for the association of a specific γ-ray burst with a massive star progenitor. If the magnetic field plays a significant role in launching a relativistic γ-ray burst jet from within a collapsing star, then the magnetic field may also play a role in the propagation, collimation, and stability of that jet within and beyond the star. The magneto-rotational instability (MRI) can operate under conditions of moderate rotation. This means that the MRI will be at work generating strong fields exponentially rapidly even as the disk of material begins to form and makes a transition from a non-Keplerian to quasi-Keplerian flow in the collapsar and related models.     

On the correlation of the solar wind observed at the L5 point and at the Earth

The L5 point is a promising location for forecasting co-rotating high-speed streams in the solar wind arriving at the Earth. We correlated the solar wind data obtained by the Nozomi spacecraft in interplanetary space and by the Advanced Composition Explorer (ACE) at the L1 point, and found that the correlation is significantly improved from that of the 27-day recurrence of ACE data. Based on the correlation between the two spacecraft observations, we estimated the correlation of the solar wind velocity between the L5 point and at the Earth, and found that the correlation coefficient was about 0.78 in late 1999, while that of the 27-day recurrence was 0.51. Eighty-eight percent of the velocity difference falls within 100 km/s between the L5 point and the Earth. This demonstrates the potential capability of solar wind monitoring at the L5 point to forecast the geomagnetic disturbances 4.5 days in advance.     

颠覆性技术发展及影响分析

颠覆性技术（Disruptive Technology）的概念于1995年由美国哈佛商学院工商管理教授波尔（Bower）和克里斯坦森（Christensen）提出,一经提出立刻在商业领域和学术界引发了广泛思考。该概念是相对渐进性技术提出的,区别在于,颠覆性技术更多表现为新技术的发明、应用以至超越并取代现有主流技术。     

Analysis of the solar sail deformation based on the point cloud method

The deformation of the solar-sail membrane is an important factor for causing inaccuracies in the solar-sail missions. This paper describes the solar sail under deformation by using a new modelling technique based on point cloud and triangular mesh generation. Two types of deformation, stemming from wrinkling and billowing, are modelled. The changes in the solar radiation pressure force and the moment caused by deformation are calculated and compared to the ideal non-deformed case. The heliocentric spiral trajectory and the orbital angular momentum reversal trajectory are taken as examples to quantify the influence of the deformation from an orbit point of view. Additionally, point cloud simplification, based on the normal vector and bounding box, is utilized to simplify the original deformed-sail model. It involves a reasonable reduction and renewal of the points in the model considering the variation of surface curvature. The simplification and its modelling accuracy are numerically investigated as well as computational efficiency.     

基于双因素方差分析的混响室搅拌器优化研究

针对混响室搅拌器的优化问题,建立了混响室仿真模型,分析了搅拌器叶片不同夹角和不同边长比对混响室场均匀性的影响,得到了叶片较优夹角和较优边长比。通过对仿真数据进行双因素方差分析,得到搅拌器叶片夹角和边长比对场均匀性影响的权重关系。该结论为混响室搅拌器的优化设计提供了指导依据。     

The impact of large solar events on the total electron content of the ionosphere at mid latitudes

Ionospheric disturbances associated with solar activity may occur via two basic mechanisms. The first is related to the direct impact on the ionosphere of EUV photons from a flare, and the second by prompt electric field penetration into the magnetosphere during geomagnetic storms. In this paper we examine the possibility that these two mechanisms may have an impact at mid latitudes by calculating the total electron content (TEC) from GPS stations in Mexico during several large X-ray flares. We have found that indeed large, complex flares, which are well located, may affect the mid latitude ionosphere. In fact, in the solar events of July 14, 2000 and April 2001 storms, ionospheric disturbances were observed to increase up to 138 and 150 TECu, respectively, due to the influence of EUV photons. Also, during the solar events of July 2000, April 2001, Halloween 2003, January 2005 and December 2006, there are large ionospheric disturbances (up to 393 TECu in the Halloween Storms), due to prompt penetration electric field, associated with CME producing geomagnetic storm.     

Ion signatures of reconnection at the magnetopause

For a rotational MHD discontinuity the bulk flow is Alfvénic in the de Hoffmann-Teller frame. Using AMPTE/IRM data, we present ion distribution functions during three crossings of the dayside low-latitude magnetopause. For these crossings a well defined de Hoffmann-Teller frame can be found, but the field-aligned bulk flow is always slower than the Alfvén speed. Nevertheless, we find signatures in the distribution functions that provide clear evidence for magnetic reconnection: solar wind ions reflected off the magnetopause, “D-shaped” solar wind ion distributions in the boundary layer, and counterstreaming of solar wind ions and ionospheric ions in the boundary layer.     

In situ results on the variation of neutral atmospheric hydrogen at venus

The concentrations of neutral hydrogen within the atmosphere of Venus are investigated for the period 1979–1980. During this period, the planet made nearly three orbits about the Sun, so that nearly three complete diurnal cycles were observed from the Pioneer Venus Orbiter (PVO). Values of n(H) are derived from in-situ ion and neutral composition measurements from the Orbiter Ion Mass Spectrometer (OIMS) and the Orbiter Neutral Mass Spectrometer (ONMS) using a charge exchange relationship involving O⁺, H⁺, O and CO₂. The dawn bulge in the diurnal distribution of n(H), reported from the first diurnal cycle by Brinton et al., is found to persist with n(H) peaking at levels near 2 - 5 × 10⁷/cm³ at altitudes below 165 km. At peak levels, the bulge exhibits a concentration ratio up to 400/1 relative to dayside values. Large day to day variations of up to a factor of five in n(H) are frequently encountered, and are attributed to perturbations induced by the solar wind interaction. These short term variations, plus a suggestion of some local time variation in the bulk location, make precise assessment of interannual variations in the n(H) difficult. Between the first diurnal cycle in early 1979 and the third in mid 1980, the decline in solar euv flux was of the order of 10% or less. Allowing for uncertainties due to short term variations, no clear evidence is found for an interannual variation in the hydrogen concentrations.     

Consequences of cometary aurora on the carbon chemistry at comet P/Halley.

Various experimental data acquired during the visit of Halley's comet in 1986 have shown that the amount of carbon produced due to photodissociation of parent carbon bearing species is not ample enough to explain the observations. This requires the presence of an additional source of atomic carbon. One of the possible source could be auroral-type activities resulting from the precipitation of high-energy "auroral electrons" of solar wind origin, the evidence of which have been inferred from many observations at comet Halley. We have developed a coupled chemistry-transport model to study the role of auroral and photoelectron impact as well as of chemistry on the modelling of carbon in the inner coma (< or = 10(4) km) of comet Halley. Our study suggest that electron impact dissociation of CO is the major source of carbon production in the inner coma, not the recombination of CO+ as suggested by earlier workers, while transport is the main loss process.     

拉开外空采矿竞赛的序幕？-美国行星采矿立法的法律政策分析

2015年11月25日,美国通过了《2015外空资源探索和利用法》,为私人实体进行月球及行星采矿提供了法律依据,赋予了私人实体对其开采的任何小行星资源或外空资源的各项权利,包括占有、拥有、运输、使用和出售的权利。这一规定引起了国际社会的热议。在该法案起草、论证到通过的1年多时间里,国际空间法学界对其进行了多次讨论,以质疑声居多。虽然国际法没有明确的禁止规定,但大多数学者仍认为外空属于“公有区域”,任何国家和个人不得主张对外空包括其自然资源的所有权。     

低温真空下固体界面间接触导热的实验研究

在110～325K温度范围内，对低温下两种常用接触材料-不锈钢和铝，进行了大量的接触导热试验研究，着重探讨了接触热导与界面载荷，温度和表面分形参数的关系。实验结果表明：在该实验条件下，两种材料接触热导与载荷关系的实验幂指数均在0.4～0.6之间，温度是通过材料的热导率和力学性能对接触导热发生作用的，接触热导随着表面分形维数的增加而增加。     

PTB关于实现量子计量三角的研究

PTB量子计量三角的组成部分为量子霍尔电阻标准、约瑟夫森电压标准和一个电子计数电容标准(ECCS),而电容的校准能力在量子计量三角的建立过程中起了很重要的作用。为了计算电子个数,采用了一个被称为r电子泵的低温真空电容,其电容值为1pF的十进制整数值。目前整个设备尚未正式运行,某些部件还处于研制阶段。虽然低温电容值在循环后的重复性好于10-6,但是要使量子计量三角型的不确定度达到预期的10-7以内,30 s的电子测量的停留时间还是相对较短。此外,计算电容的校准能力和量子霍尔电阻均有所改进。     

远距离准直方法探讨

准直是指保证光学轴线间的平行,或光学轴线与基面垂直的测量过程,常用于火箭发射时的瞄准和重型机械制造中平行度、垂直度等几何要求的测量。本文论述了平行光准直法、平行光自准直法、投射法、瞄标记准直法、光电法等远距离准直方法,并分析了其原理、特点、应用、测量精度及其发展趋势。     

Science at the performance limits of the Hubble Space Telescope

As with any large telescope on the ground, HST will often be used at the limits of its performance capabilities. The actual performance will only be determined once HST is i n orbit, but detailed modeling based on mirror, structure, and control system characteristics gives a reasonable assessment of the expected performance. The purpose of this paper is to present (1) selected image characteristics expected for HST, (2) performance limits for selected instrument characteristics, and (3) examples of observations for which the performance limits are approached. Among the image features noted are point spread functions, encircled energy curves, and image diameters for selected wavelengths. Performance limits discussed include expected limiting magnitude and resolution of close point sources as a function of wavelength, each for selected camera focal ratios and pixel dimensions. Examples of observations discussed include a binary in which one component is faint and the detectability of a single luminous star at large distances.     

基于热敏电阻的气体温度测量误差分析

挤压气体内部温度的精确测量对确定贮箱内推进剂剩余量和提高氧化剂和燃烧剂的混合比控制精度有重要意义.提出了一种基于热敏电阻的矢量测温方法,通过测量气瓶壁面温度推算气体内部真实温度,分析温度电阻非线性特性、温度—电压处理电路、A/D采样非线性等因素导致的温度测量误差,最终获得系统自身的温度采集误差,在此基础上分析了影响此误差的主要因素.最后分析了外界干扰引起的测量噪声对温度测量的影响,并采用小波降噪的方法对此进行降噪处理,使温度测量精度得到较大改善,并最终确定了内部气体温度的测量误差.     

Polar/TIMAS statistical results on the outflow of molecular ions from earth at solar minimum

Ion composition data from the first 22 months of operation of the Polar/TIMAS instrument, covering the 15-eV/e to 33-keV/e energy range, have been surveyed to determine the typical abundance, at solar minimum, of N₂⁺, NO⁺ and O₂⁺ ions in the auroral ion outflow, as compared to that of the better known O⁺ ions. The results indicate that molecular ions have roughly the same energy distribution as the O⁺ ions, with maximum differential flux occurring below 400 eV, but are far less abundant, by two orders of magnitude. The molecular ions also differ from the O⁺ ions in that they seem more specifically associated with enhanced geomagnetic activity.