Remote Sensing of H from Ulysses and Galileo

We model interplanetary H Lyman-α (Lα) observations from Galileo UVS (Ultraviolet Spectrometer) and EUVS (Extreme Ultraviolet Spectrometer) (Hord et al., 1992) and the Ulysses interstellar neutral gas (GAS) instrument (Witte et al., 1992). EUVS measurements near solar maximum (max) in 1990–1992 have a peaked brightness maximum upwind due to a rather isotropic solar wind charge-exchange ionization pattern (A=0–0.25). GAS measurements from solar minimum (min) in 1997 have a plateau in the upwind direction that we model using Ulysses SWOOPS (solar wind plasma experiment) solar min data on solar wind density and velocity at different heliographic latitudes. The isotropic ionization pattern deduced from EUVS at solar max may be consistent with recent SWOOPS results (McComas et al., 2000b, c) that high speed solar wind is absent at high latitudes during solar max. Galileo and Ulysses Lα data favor higher H temperatures (15 000–18 000 K) than previous models. This revised version was published online in August 2006 with corrections to the Cover Date.     

Radio science investigations with Voyager

The planned radio science investigations during the Voyager missions to the outer planets involve: (1) the use of the radio links to and from the spacecraft for occultation measurements of planetary and satellite atmospheres and ionospheres, the rings of Saturn, the solar corona, and the general-relativistic time delay for radiowave propagation through the Sun's gravity field; (2) radio link measurements of true or apparent spacecraft motion caused by the gravity fields of the planets, the masses of their larger satellites, and characteristics of the interplanetary medium; and (3) related measurements which could provide results in other areas, including the possible detection of long-wavelength gravitational radiation propagating through the Solar System. The measurements will be used to study: atmospheric and ionospheric structure, constituents, and dynamics; the sizes, radial distribution, total mass, and other characteristics of the particles in the rings of Saturn; interior models for the major planets and the mean density and bulk composition of a number of their satellites; the plasma density and dynamics of the solar corona and interplanetary medium; and certain fundamental questions involving gravitation and relativity. The instrumentation for these experiments is the same ground-based and spacecraft radio systems as will be used for tracking and communicating with the Voyager spacecraft, although several important features of these systems have been provided primarily for the radio science investigations.     

Coronal investigations with occulted spacecraft signals

The radio telemetry links between Earth and a spacecraft near superior conjunction penetrate the corona at ranges well within the acceleration regime of the solar wind. Occultation experiments in the solar corona have been performed on many interplanetary missions beginning with the Mariner and Pioneer series and extending up to the more recent data on Helios, Viking, and Voyager. The changes in group and phase velocity of the radio signal are measured to determine the total electron content of the corona and its fluctuations. The broadening of the carrier signal may be used in combination with the electron content data to derive a solar wind velocity profile. The wave number spectrum of electron density fluctuations in the corona may be inferred from amplitude and phase scintillations of the received signal. Linearly polarized signals, which are rotated along the propagation path by the Faraday effect, can provide information on the coronal magnetic field and its variations.Paper presented at the IX-th Lindau Workshop The Source Region of the Solar Wind.     

BOC信号的相关跟踪研究及GALILEO接收机设计初探

Galileo卫星导航系统是欧盟组织研发的新一代完全面向民用的卫星导航系统,使用了BOC(二进制副载波)这一独特的调制方式,研究BOC信号的相关峰特性,对设计接收机捕获跟踪通道是至关重要的。本文简要介绍了Galileo系统导航信号的特征和频率规划,对多种BOC信号的自相关性能、码跟踪方法进行了仿真,并探讨了接收机开发中的关键问题。     

Radio Frequency Fluctuation Spectra During the Solar Conjunctions of the Ulysses and Galileo Spacecraft

Temporal power spectra have been computed from recordings of the downlink frequency fluctuations of the Galileo and Ulysses radio signals during their solar conjunctions. Both the equatorial streamer belt and the polar coronal holes were investigated over a range of ray path solar offset distances from 4 to 80 R_⊙. By combining gapless data from successive tracking passes, Doppler scintillation power spectra could be computed down to extremely low frequencies. Some spectra feature a low-frequency turnover at frequencies around 0.1 mHz that could be interpreted as an outer scale of density turbulence in the coronal plasma. This revised version was published online in August 2006 with corrections to the Cover Date.     

Ulysses/Galileo observations of type III radio bursts and associated in-situ electrons and Langmuir waves

Both the Ulysses and Galileo spacecraft detected energetic electrons and Langmuir waves that were associated with a type III radio burst on 10 December 1990. At the time of these observations, these spacecraft were in the ecliptic plane and separated by 0.4 AU, with Galileo near the Earth at 1 AU and Ulysses at 1.36 AU. From the measured electron arrival times, the propagation path lengths of the electrons to both Ulysses and Galileo were estimated to be significantly longer than the length of the Parker spiral. These long path lengths are interpreted as due to draping of the interplanetary magnetic field lines around a CME. The onset times of the Langmuir waves at Ulysses and Galileo coincided with the estimated arrival time of the 9 keV and 14 keV electrons, respectively.     

Galileo Probe Measurements of D/H and 3He/4He in Jupiter's Atmosphere

The Galileo Probe Mass Spectrometer measurements in the atmosphere of Jupiter give D/H = (2.6 ± 0.7) × 10-5 3He/4He = (1.66 ± 0.05) × 10-4These ratios supercede earlier results by Niemann et al. (1996) and are based on a reevaluation of the instrument response at high count rates and a more detailed study of the contributions of different species to the mass peak at 3 amu. The D/H ratio is consistent with Voyager and ground based data and recent spectroscopic and solar wind (SW) values obtained from the Infrared Spectroscopic Observatory (ISO) and Ulysses. The 3He/4He ratio is higher than that found in meteoritic gases (1.5 ± 0.3) × 10-4. The Galileo result for D/H when compared with that for hydrogen in the local interstellar medium (1.6 ± 0.12) × 10-5 implies a small decrease in D/H in this part of the universe during the past 4.55 billion years. Thus, it tends to support small values of primordial D/H - in the range of several times 10-5 rather than several times 10-4. These results are also quite consistent with no change in (D+3He)/H during the past 4.55 billion years in this part of our galaxy.     

The interaction between a magnetized plasma flow and a magnetized celestial body: A review of magnetospheric studies

Through an intensive study of the magnetospheres of the Earth, Mercury, and Jupiter, we have begun to understand how a magnetized celestial body interacts with a magnetized plasma flow. Some of the important findings are:Some of these findings may have significant implications in interpreting a variety of astrophysical processes associated with the magnetosphere of magnetic stars, pulsars and head-tail galaxies and also with transient processes, such as solar flares and flarings of particular types of variable stars, etc.     

The Global Geospace Science Program and its investigations

The detailed study of the solar-terrestrial energy chain will be greatly enhanced with the launch and simultaneous operation of several spacecraft during the current decade. These programs are being coordinates in the United States under the umbrella of the International Solar Terrestrial Physics Program (ISTP) and include fundamental contributions from Japan (GEOTAIL Program) and Europe (SOHO and CLUSTER Programs). The principal United States contribution to this effort is the Global Geospace Science Program (GGS) described in this overview paper. Two spacecraft, WIND and POLAR, carrying an advanced complement of field, particle and imaging instruments, will conduct investigations of several key regions of geospace. This paper provides a general overview of the science objectives of the missions, the spacecraft orbits and the ground elements that have been developed to process and analyze the instrument observations.     

Codes cross-correlation analysis and data/pilot code pairs optimization for Galileo E1 OS and GPS L1C

The Galileo E1 open service (OS) and the global positioning system (GPS) L1C are intending to use the multiplexed binary offset carrier (MBOC) modulation in E1/L1 band, including both pilot and data components. The impact of data and pilot codes cross-correlation on the distortion of the discriminator function (i.e., the S-curve) is investigated, when only the pilot (or data) components of MBOC signals are tracked. It is shown that the modulation schemes and the receiver configuration (e.g., the correlator spacing) strongly affect the S-curve bias. In this paper, two methods are proposed to optimize the data/pilot code pairs of Galileo E1 OS and GPS L1C. The optimization goal is to obtain the minimum average S-curve bias when tracking only the pilot components a the specific correlator spacing. Figures of merit, such as S-curve bias, correlation loss and code tracking variance have been adopted for analyzing and comparing the un-optimized and optimized code pairs. Simulation results show that the optimized data/pilot code pairs could significantly mitigate the intra-channel codes cross-correlation, and then improve the code tracking performance of MBOC signals.     

离散力学与最优控制理论在谐波减速器控制中的应用研究

为解决谐波减速器内部非线性干扰,基于离散力学理论,考虑谐波减速器固有的粘性摩擦与柔性关节特性,建立了全时域下谐波减速器的离散动力学与控制的数学模型,并针对离散时域下谐波减速器的最优时间控制问题与最优轨迹跟踪控制问题进行了研究。跟踪误差和运动轨迹分析表明:离散控制方法实现了误差为10-8rad量级的谐波减速器轨迹跟踪控制,并在具有运动约束的同时实现了最短时间到达的控制目标。     

On the computation of instabilities and symmetry-breaking in fluid mechanics

A review on the implementation of modern computational fluid dynamics (CFD) methods for simulating low- and high-speed flows featuring turbulent mixing, instabilities and symmetry-breaking is presented. Results are reviewed for several complex flows including turbulent mixing associated with Richtmyer–Meshkov and Rayleigh–Taylor instabilities, incompressible flows in suddenly expanded geometries, shock-induced instabilities, free-shear instabilities and complex vortex dynamics. Many of the results presented in this review have been obtained by large eddy simulation (LES), monotone integrated LES (MILES) in particular. The computational challenges associated with complex flow physics and nonlinear behaviour of the numerics are discussed.     

不同机翼优化构型的轻质F4模型气动特性实验研究

采用光固化快速成型技术（SL）加工基于气动/结构耦合分析的六套不同机翼优化构型的轻质F4模型,在0.6m跨超声速风洞完成了马赫数0.6-0.85范围内的气动力测量试验。试验结果表明,采用气动/结构耦合优化设计的代号为6#的轻质F4模型升力特性与国外结果较接近,与机翼三维变形的事实吻合,验证了采用的气动/结构耦合优化设计方法基本可行,为探索模型静气动弹性风洞试验数据修正方法提供了参考。     

Experimental and theoretical investigations of vibration characteristics for GTE compressor blade

The tables of vibration modes for a blade obtained by the experimental method of holographic interferometry and systematized according to the number of nodal lines are presented. The graphical dependences of resonant frequencies that allow eliminating the vibration mode miss are presented. The vibration modes for a rectangular plate and a blade are compared. A technique of determining the resonant frequency for a missed harmonics is proposed.     

The Contributions of Comets to Planets, Atmospheres, and Life: Insights from Cassini-Huygens, Galileo, Giotto, and Inner Planet Missions

Comets belong to a group of small bodies generally known as icy planetesimals. Today the most primitive icy planetesimals are the Kuiper Belt objects (KBOs) occupying a roughly planar domain beyond Neptune. KBOs may be scattered inward, allowing them to collide with planets. Others may move outward, some all the way into the Oort cloud. This is a spherical distribution of comet nuclei at a mean distance of ～50,000 AU. These nuclei are occasionally perturbed into orbits that intersect the paths of the planets, again allowing collisions. The composition of the atmosphere of Jupiter—and thus possibly all outer planets—shows the effects of massive early contributions from extremely primitive icy bodies that must have been close relatives of the KBOs. Titan may itself have a composition similar to that of Oort cloud comets. The origin and early evolution of its atmosphere invites comparison with that of the early Earth. Impacts of comets must have brought water and other volatile compounds to the Earth and the other inner planets, contributing to the reservoir of key ingredients for the origin of life. The magnitude of these contributions remains unknown but should be accessible to measurements by instruments on spacecraft.     

原子氧对Kapton侵蚀及ZnO-有机硅涂层防护效应研究

在原子氧(AO)侵蚀地面模拟试验设备中对聚酰亚胺(Kapton)和涂ZnO-有机硅防护层的样品进行原子氧剥蚀效应试验。用LAMBDA-9分光度计、光电子能谱(XPS)、红外光谱(FTIR)和扫描电镜(SEM)等对试验前后试样的表面形貌、质量及化学结构进行表征研究。AO对Kapton表现了较严重的侵蚀作用,其化学结构、元素百分含量和表面形貌都发生明显变化。而所施用的ZnO-有机硅涂层对AO辐照有较强的防护效果,并具有较好的空间稳定性。因腐蚀产物为SiO2,这对抑制AO的进一步侵蚀起到了关键作用。     

Combustion mechanism of fluorinated organic compound-modified nano-aluminum composite particles: Towards experimental and theoretical investigations

Fluorinated Organic Compounds (FOCs) are commonly used as modifiers for Aluminum (Al) powder to improve its ignition, combustion, and agglomeration characteristics. However, the effects of FOCs on combustion and inhibition mechanisms of agglomeration of Al powder are not well understood. In this paper, based on the experimental study of Fluorinated Graphite (FG)-modified Al matrix composite particles, the combustion and aggregation inhibition mechanisms of FOCs on Al particles were studied by the quantum chemical calculation at B3LYP/6-311+G(d,P) and G3//B3LYP/6-311+G(d,p) levels. The flame behavior and single particle burning behavior of FG-modified samples were compared through ignition experiments, and the characteristic spectra of Al related oxides of different samples in the initial ignition stage were captured. It is found that FG increases the burning intensity of Al composite samples significantly, while it decreases the emission intensity of Al secondary oxides. Quantum chemical calculation results show that the thermal decomposition intermediates of FOCs, namely C₂F₄, can react with AlO and Al₂O, which weakens the characteristic emission intensity of AlO and Al₂O in the sample, and thus inhibits the formation of Al₂O₃ in the combustion process. These results contribute to enriching the combustion dynamics model of Al-FOCs reaction system.     

Experimental investigations of the spray structure and interactions between sectors of a double-swirl low-emission combustor

In this paper,the spray characteristics of a double-swirl low-emission combustor are analyzed by using Particle Imaging Velocimetry (PIV) and Planar Laser Induced Fluorescence(PLIF) technologies in an optical three-sector combustor test rig.Interactions between sectors and the influence of main stage swirl intensity on spray structure are explained.The results illustrate that the swirl intensity has great effect on the flow field and spray structure.The spray cone angle is bigger when the swirl number is 0.7,0.9 than that when the swirl number is 0.5.The fuel distribution zone is larger and the distribution is more uniform when the swirl number is 0.5.The fuel concentration in the center area of the center plane of side sector (Plane 5) is larger than that of the center plane of middle sector (Plane 1).The spray cone angle in Plane 5 is larger than that in Plane 1.The width of spray cone becomes larger with the increase of Fuel-Air Ratio (FAR),whereas the spray cone angle under different fuel-air ratios are absolutely the same.The results of the mechanism of spray organization in this study can be used to support the design of new low-emission combustor.