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.     

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.     

Correlation between the cosmic noise absorption calculated from the SARINET data and the energetic particles measured by MEPED: Simultaneous observations over SAMA region

The cosmic noise absorption is presented in terms of two-dimensional images obtained from the imaging riometers operated at the Southern Space Observatory (geographic coordinate: 29.4° S, 53.1° W), in São Martinho da Serra, Brazil, Concepcion (geographic coordinate: 36.5° S, 73.0° W) and Punta Arenas (geographic coordinate: 53.0° S, 70.5° W) in Chile, which belong to the South American Riometer Network and are located at the central and periphery regions of the South American Magnetic Anomaly. Correlations are performed between the maximum cosmic noise absorption observed at these stations and the energetic electron flux in two energy channels (>30 and >300 keV) and the proton flux in three energy channels (80–240, 800–2500 and >6900 keV) as measured by the Medium Energy Proton and Electron Detector, during a moderate geomagnetic storm that occurred on September 3, 2008. The results show high correlations between the cosmic noise absorption detected at São Martinho da Serra and the flux of protons with energy between 80 and 240 keV, and the flux of electrons with energies higher than 300 keV, while an additional ionization at Concepcion was correlated with electrons of energies higher than 30 keV. The cosmic noise absorption detected at Punta Arenas was probably caused by the increase of the protons flux with energy between 80 and 240 keV.     

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.     

基于粒子群算法的石英挠性加速度计温度补偿方法研究

由于使用环境的需求,需要光纤惯组具有较宽的工作温度范围,一般在-40℃~60℃温度范围内有稳定且准确的输出。而实际情况下温度变化会使惯性器件输出产生温度漂移,制约惯组的输出精度。以工程实例为依托,以光纤惯组中低精度石英挠性加速度计作为研究对象,首先分析了石英加速度计的温度特性,然后设计了一种基于粒子群算法的石英加速度计温度补偿方法,并以温补后器件的零偏特性为依据,利用试验平台对温补效果进行了试验验证。试验结果表明,该温补方法能够有效补偿石英加速度计的温度漂移,补偿后的零偏稳定性较补偿前有数量级上的提升。     

Energy release in double layers

A Double layer (DL) in a current carrying plasma sustains a localised net potential difference and acts as an impedance converting electrical energy to directed particle energy determined by the DL potential. DL's accelerate equal numbers of ions and electrons for relativistic energies, otherwise electron energisation predominates. Their time independent structure may be described as a BGK (Bernstein-Greene-Kruskal) state analogous to that for laminar shocks, and certain existence criteria must be satisfied. The generalised Langmuir criterion requires total particle pressure balance over the DL and may imply propagation in the plasma reference frame. The Bohm criteria require sufficiently large current densities and are closely related to the local stability condition at the edges of the DL. The DL potential must be sustained externally, for example by the release of stored magnetic energy. A steady state is also possible where (externally maintained) mass motions drive a dynamo region connected by currents to the DL which acts as an electrical load.     

新型含能材料──CL－20

综述了ＣＬ－２０结构特征、合成方法及热分解性能，并对其作为固体推进剂氧化剂的能量特性进行了计算分析。结果显示ＣＬ－２０具有能量密度高、感度适中等特点，同时具有较好热稳定性和不同于ＨＭＸ的热分解特性，是一种有潜力的高能量密度材料。     

Some non-linear effects in diffusive shock acceleration

I briefly describe nonlinear effects that result when shock acceleration is efficient and present some examples where these effects may be required to explain observations.     

Direct thrust control for multivariable turbofan engine based on affine linear parameter-varying approach

A novel turbofan Direct Thrust Control(DTC) architecture based on Linear ParameterVarying(LPV) approach for a two-spool turbofan engine thrust control is proposed in this paper.Instead of transforming thrust command to shaft speed command and pressure ratio command, the thrust will be directly controlled by an optimal controller with two control variables. LPV model of the engine is established for the designing of thrust estimator and controller. A robust LPV H∞filter is introduced to estimate ...