Transition region line-shifts in the rebound shock spicule model

Spectral emission lines created in the solar chromosphere — corona transition region show net red-shifts. It has been proposed that this may be the result of the return of spicular material. We simulate a spicule numerically using the rebound shock model and find that the resulting hydrodynamic evolution leads to a perceived up-flow in transition region spectral lines even though the average velocity in the line forming region is directed downward. The explanation for this apparent paradox is found in the correlation between density and velocity in the waves generated by the rebound shock spicule.     

Radiative and hybrid cooling of infrared space telescopes

The designs of cold space telescopes, cryogenic and radiatively cooled, are similar in most elements and both benefit from orbits distant from the Earth. In particular such orbits allow the anti-sunward side of radiatively-cooled spacecraft to be used to provide large cooling radiators for the individual radiation shields. Designs incorporating these features have predictedT _tel near 20 K. The attainability of such temperatures is supported by limited practical experience (IRAS, COBE). Supplementary cooling systems (cryogens, mechanical coolers) can be advantageously combined with radiative cooling in hybrid designs to provide robustness against deterioration and yet lower temperatures for detectors, instruments, and even the whole telescope. The possibility of such major additional gains is illustrated by the Very Cold Telescope option under study forEdison, which should offerT _tel5 K for a little extra mechanical cooling capacity.     

Biological responses to space: results of the experiment "Exobiological Unit" of ERA on EURECA I.

Spores of different strains of Bacillus subtilis and the Escherichia coli plasmid pUC19 were exposed to selected conditions of space (space vacuum and/or defined wavebands and intensities of solar ultraviolet radiation) in the experiment ER 161 "Exobiological Unit" of the Exobiology Radiation Assembly (ERA) on board of the European Retrievable Carrier (EURECA). After the approximately 11 months lasting mission, their responses were studied in terms of survival, mutagenesis in the his (B. subtilis) or lac locus (pUC19), induction of DNA strand breaks, efficiency of DNA repair systems, and the role of external protective agents. The data were compared with those of a simultaneously running ground control experiment. The survival of spores treated with the vacuum of space, however shielded against solar radiation, is substantially increased, if they are exposed in multilayers and/or in the presence of glucose as protective, whereas all spores in "artificial meteorites", i.e. embedded in clays or simulated Martian soil, are killed. Vacuum treatment leads to an increase of mutation frequency in spores, but not in plasmid DNA. Extraterrestrial solar ultraviolet radiation is mutagenic, induces strand breaks in the DNA and reduces survival substantially; however, even at the highest fluences, i.e. 3 x 10(8) J m-2, a small but significant fraction of spores survives the insolation. Action spectroscopy confirms results of previous space experiments of a synergistic action of space vacuum and solar UV radiation with DNA being the critical target.     

Human productivity in space and systems costs

Human productivity during assembly operations in-orbit is dependent on limits set by fatigue, metabolic rates, learning, and assembly techniques. In order to quantify these effects, tests were conducted in the NASA MSFC Neutral Buoyancy Simulator, in the NASA KC-135 in parabolic flight, and in space with the EASE program during the Shuttle Atlantis mission 61-B. A separate program attempted to relate productivity to system costs. Because of the surprisingly high productivity which had been demonstrated in orbit, it was shown that assembly operations would have only a small effect on system costs at the present level of launch costs. The results of these continuing studies have been reported in a recent paper(1). They will be briefly summarized here and the results updated to include additional cost elements and to examine the effects of reductions in transportation costs, resulting from advances in technology and from increased demand, on system costs. It is shown that, as launch costs are reduced, the assembly costs could become an increasingly important component of the total system costs.     

Experimental Aspects of Mid-Frequency Pulsations (f≈10–100 mHz) in the Southern Polar Cap

We review the results obtained in the frequency range of Pc3 (22-100 mHz) and Pc4 (7-22 mHz) pulsations at Italian Antarctic stations in the southern polar cap (“Mario Zucchelli”, at Terra Nova Bay, TNB, 80^˚.S; “Concordia”, the Italian/French base at Dome C, DMC, 89^˚.S). The absence of a midnight enhancement in the pulsation power suggests a negligible substorm influence at extreme latitudes, while the sharp noon enhancement, which appears only at TNB, is determined by the closer proximity of the station to cusp related phenomena. The relationship between the frequency of the band-limited signals and the interplanetary magnetic field strength, the cone angle influence, and the higher correlation of the Pc3 power with the solar wind speed in the morning hours suggest a global scenario in which upstream waves would be mainly responsible for the mid-frequency activity in the polar cap. However, the polarization pattern is odd with respect to the predictions for tailward propagating modes.     

C/SiC复合材料超声振动钻孔评估

在分析碳纤维增强碳化硅复合材料的力学性能、密度、孔隙率和弯曲强度的基础上 ,进行了超声钻孔工艺试验 ,检测并研究了材料去除率、孔径差、孔边质量和工具损耗情况 ,得出了超声钻孔是一种好的加工方法的结论。     

Analysis of Multimodal Systems

The estimation of a multimodal linear system whose mode-to-mode transitions are described by a finite-state Markov chain is described. The problem has application in studying separation standards in an air traffic control environment. An optimal solution is formulated which is computationally infeasible. A suboptimal estimator is then derived which closely approximates the optimal estimator. An example is presented to illustrate the technique.     

Instability and unsteadiness of aircraft wake vortices

This paper presents a review of theoretical and experimental results on stability and other unsteady properties of aircraft wakes. The basic mechanisms responsible for the propagation and the amplification of perturbation along vortices, namely the Kelvin waves and the cooperative instabilities, are first detailed. These two generic unsteady mechanisms are described by considering asymptotic linear stability analysis of model flows such as vortex filaments or Lamb–Oseen vortices. Extension of the linear analysis to more representative flows, using a biglobal stability approach, is also described. Experimental results obtained using LDV, hot wire and PIV in wind tunnels are presented and they are commented upon the light of theory.