Effects of coarse riblets on air flow structures over a slender delta wing using particle image velocimetry

This research investigates the aerodynamic performance and flow characteristics of a delta wing with 65° sweep angle and with coarse axial riblets,and then compares with that of a smooth-surface delta wing.Particle Image Velocimetry(PIV)were utilized to visualize the flow over the wing at 6 cross-sections upright to the wing surface and parallel to the wing span,as well as 3 longitudinal sections on the leading edge,symmetry plane,and a plane between them at Angles of Attack(AOA)=20°and 30°and Re=1.2×10~5,2.4×10~5,and 3.6×10~5.The effects of the riblets were studied on the vortices diameter,vortex breakdown location,vortices distance from the wing surface,flow lines pattern nearby the wing,circulation distribution,and separation.The results show that the textured model has a positive effect on some of the parameters related to drag reduction and lift increase.The riblets increase the flow momentum near the wing’s upper surface except near the apex.They also increase the flow momentum behind the wing.     

The Rosetta Alpha Particle X-Ray Spectrometer (APXS)

The Alpha Particle X-Ray Spectrometer (APXS) is a small instrument to determine the elemental composition of a given sample. For the ESA Rosetta mission, the periodical comet 67P/Churyumov-Gerasimenko was selected as the target comet, where the lander PHILAE (after landing) will carry out in-situ observations. One of the instruments onboard is the APXS to make measurements on the landing site. The APXS science goal is to provide basic compositional data of the comet surface. As comets consist of a mixture of ice and dust, the dust component can be characterized and compared with known meteoritic compositions. Various element ratios can be used to evaluate whether chemical fractionations occurred in cometary material by comparing them with known chondritic material. To enable observations of the local environment, APXS measurements of several spots on the surface and one spot as function of temperature can be made. Repetitive measurements as function of heliocentric distance can elucidate thermal processes at work. By measuring samples that were obtained by drilling subsurface material can be analyzed. The accumulated APXS data can be used to shed light on state, evolution, and origin of 67P/Churyumov- Gerasimenko.     

X-ray, γ-ray and neutron detector development for future space instrumentation

An overview of the material developments currently being pursued by the European Space Agency (ESA) with respect to X-ray, γ-ray and neutron detection media is given. The benefits underlying the selection of specific materials are discussed. In the X-ray regime the basic microphysics behind degraded spectral performance caused by the polarization effect and Te inclusions, have been investigated. We have found that both effects degrade the spectra by producing a localised distortion of the electric field. The underlying cause for the distortion does however differ. For the γ-ray regime, a low-noise equivalent scintillator to LaBr₃ has been developed in the form of CeBr₃. Three inch crystals with a FWHM energy resolution of 4.4% at 662 keV have successfully been produced. For neutron detection, a boron compound based solid state neutron detector has been developed that is sensitive to neutrons, alpha particles and 60 keV X-rays. The measured detection efficiency in detection for thermal neutrons was found to be in the order of a few per cent.     

Processes that Promote and Deplete the Exosphere of Mercury

It has been speculated that the composition of the exosphere is related to the composition of Mercury’s crustal materials. If this relationship is true, then inferences regarding the bulk chemistry of the planet might be made from a thorough exospheric study. The most vexing of all unsolved problems is the uncertainty in the source of each component. Historically, it has been believed that H and He come primarily from the solar wind (Goldstein, B.E., et al. in J. Geophys. Res. 86:5485–5499, 1981), Na and K come from volatilized materials partitioned between Mercury’s crust and meteoritic impactors (Hunten, D.M., et al. in Mercury, pp. 562–612, 1988; Morgan, T.H., et al. in Icarus 74:156–170, 1988; Killen, R.M., et al. in Icarus 171:1–19, 2004b). The processes that eject atoms and molecules into the exosphere of Mercury are generally considered to be thermal vaporization, photon-stimulated desorption (PSD), impact vaporization, and ion sputtering. Each of these processes has its own temporal and spatial dependence. The exosphere is strongly influenced by Mercury’s highly elliptical orbit and rapid orbital speed. As a consequence the surface undergoes large fluctuations in temperature and experiences differences of insolation with longitude. Because there is no inclination of the orbital axis, there are regions at extreme northern and southern latitudes that are never exposed to direct sunlight. These cold regions may serve as traps for exospheric constituents or for material that is brought in by exogenic sources such as comets, interplanetary dust, or solar wind, etc. The source rates are dependent not only on temperature and composition of the surface, but also on such factors as porosity, mineralogy, and space weathering. They are not independent of each other. For instance, ion impact may create crystal defects which enhance diffusion of atoms through the grain, and in turn enhance the efficiency of PSD. The impact flux and the size distribution of impactors affects regolith turnover rates (gardening) and the depth dependence of vaporization rates. Gardening serves both as a sink for material and as a source for fresh material. This is extremely important in bounding the rates of the other processes. Space weathering effects, such as the creation of needle-like structures in the regolith, will limit the ejection of atoms by such processes as PSD and ion-sputtering. Therefore, the use of laboratory rates in estimates of exospheric source rates can be helpful but also are often inaccurate if not modified appropriately. Porosity effects may reduce yields by a factor of three (Cassidy, T.A., and Johnson, R.E. in Icarus 176:499–507, 2005). The loss of all atomic species from Mercury’s exosphere other than H and He must be by non-thermal escape. The relative rates of photo-ionization, loss of photo-ions to the solar wind, entrainment of ions in the magnetosphere and direct impact of photo-ions to the surface are an area of active research. These source and loss processes will be discussed in this chapter.     

SOFTWARE SERVO COURSE(ATTITUDE) SYSTEMS

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The gamma-ray observatory mission objectives and its significance for gamma-ray astronomy

The Gamma Ray Observatory (GRO) is an approved NASA mission, programmed for launch in 1988. Its complement of four detectors has established goals: 1) to study the nature of compact γ-ray sources such as neutron stars and black holes, or objects whose nature is yet to be understood; 2) to search for evidence of nucleosynthesis especially in the regions of supernovae; 3) to study structural features and dynamical properties of our galaxy; 4) to explore other galaxies, especially the extraordinary types such as radio, Seyferts, and quasars; and 5) to study cosmological effects by examining the diffuse radiation in detail. This paper discusses the design, objectives, and expected scientific results of each of the GRO instruments in view of the GRO mission goals.     

正电子素的络合作用

本文介绍了正电子素及其络合作用。讨论了正电子素络合反应速度常数的测量方法。比较了几种线性自由能的表达式。     

颗粒增强金属基复合材料凝固过程中的颗粒推移效应

归纳了颗粒增强金属基复合材料凝固过程中颗粒推移效应的各判据,分析了各自的适用范围,提出了实际复合材料铸件中抑制颗粒推移的途径。     

Dynamic particle accumulation structure (PAS) in half-zone liquid bridge – Reconstruction of particle motion by 3-D PTV

Three-dimensional (3-D) velocity field reconstruction of oscillatory thermocapillary convections in a half-zone liquid bridge with a radius of O (1 mm) was carried out by applying 3-D particle tracking velocimetry (PTV). Simultaneous observation of the particles suspended in the bridge by two CCD cameras was carried out by placing a small cubic beam splitter above a transparent top rod. The reconstruction of the 3-D trajectories and the velocity fields of the particles in the several types of oscillatory-flow regimes were conducted successfully for sufficiently long period without losing particle tracking. With this application the present authors conducted a series of experiments focusing upon the collapse and re-formation process of the PAS by mechanically disturbing fully developed PAS.     

An adaptive-order particle filter for remaining useful life prediction of aviation piston pumps

An accurate estimation of the remaining useful life (RUL) not only contributes to an effective application of an aviation piston pump, but also meets the necessity of condition based maintenance (CBM). For the current RUL evaluation methods, a model-based method is inappropriate for the degradation process of an aviation piston pump due to difficulties of modeling, while a data-based method rarely presents high-accuracy prediction in a long period of time. In this work, an adaptive-order particle filter (AOPF) prognostic process is proposed aiming at improving long-term prediction accuracy of RUL by combining both kinds of methods. A dynamic model is initialized by a data-driven or empirical method. When a new observation comes, the prior state distribution is approximated by a current model. The order of the current model is updated adaptively by fusing the information of the observation. Monte Carlo simulation is employed for estimating the posterior probability density function of future states of the pump’s degradation. With updating the order number adaptively, the method presents a higher precision in contrast with those of traditional methods. In a case study, the proposed AOPF method is adopted to forecast the degradation status of an aviation piston pump with experimental return oil flow data, and the analytical results show the effectiveness of the proposed AOPF method.