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591.
T.K. Yeoman H.C. Scoffield D.M. Wright L.J. Baddeley A.N. Vasilyev N.V. Semenova 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008
A brief review is provided of recent progress in understanding the ionospheric Alfvén resonator (IAR) at high latitude. Firstly, naturally occurring resonances of the IAR as detected by pulsation magnetometers in the auroral zone at Sodankylä and in the polar cap at Barentsburg are considered. The characteristics of the IAR in the two regions are broadly similar, although the effects of solar illumination are less clear at the higher latitudes. Secondly we review recent attempts to stimulate the IAR through high-power radio frequency experiments both in the auroral zone at Tromsø with the European Incoherent SCATter (EISCAT) heater, and within the polar cap at Longyearbyen with the Space Plasma Exploration by Active Radar (SPEAR) facility. In the auroral zone at, Tromsø the stimulated IAR has been observed by ground-based magnetometers, and through electron acceleration observed on the FAST spacecraft. At SPEAR in the polar cap, the stimulated IAR has been investigated, with ground magnetometers, with the first results indicative of a positive detection. 相似文献
592.
S. Azouggagh-McBride L.A. Roe M.A. Franzen J.A. Buffington D.W.G. Sears 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008
Laboratory impact tests have been performed on experimental versions of a proposed robotic sample collector for extraterrestrial samples. The collector consists of a retractable aluminum ring containing an impregnable silicone compound that is pressed into the surface of the body to be sampled. As part of a comprehensive program to evaluate this idea, we have performed tests to determine if the samples embedded in the collector medium can survive the impact forces experienced during direct reentry, such as that of the recent Genesis sample return mission. For the present study, samples of sand, rock, glass, and chalk were subjected to decelerations of 1440–2880 g using drop tests. We found that even the most fragile samples, chosen to be representative of a wide range of the types of materials found on the surface of asteroids that have currently been studied, can withstand impacts of the intensity experienced by a sample return capsule during direct reentry. 相似文献
593.
J.S. Halekas D.A. BrainR.P. Lin J.G. LuhmannD.L. Mitchell 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008,41(9):1347-1352
We investigate accelerated electrons observed by Mars Global Surveyor (MGS), using data from the Electron Reflectometer (ER) instrument. We find three different types of accelerated electron events. Current sheet events occur over regions with weak or no crustal fields, have the highest electron energy fluxes, and are likely located on draped magnetotail fields. Extended events occur over regions with moderate crustal magnetic fields, and are most often observed on closed magnetic field lines. Localized events have the lowest energy fluxes, occur in strong magnetic cusp regions, and are the most likely kind of event to be found on open magnetic field lines. Some localized events have clear signatures of field-aligned currents; these events have much higher electron fluxes, and are preferentially observed on radially oriented open magnetic field lines. Electron acceleration events, especially localized events, are similar in many ways to events observed in the terrestrial auroral zone. However, physical processes related to those found in the terrestrial cusp and/or plasmasheet could also be responsible for accelerating electrons at Mars. 相似文献
594.
Hardware-in-the-loop testing technology for automatic control, condition monitoring and diagnostics systems of gas turbine engines is described. The technology proposed makes it possible to simulate combinations and chains of unexpected and gradual failures of engines, transducers and actuators. 相似文献
595.
V. A. Olaev 《Russian Aeronautics (Iz VUZ)》2009,52(2):214-220
The algorithmic support of a small-sized navigation system on the basis of the magnetoinertial course transmitter is considered; the support makes it possible to significantly reduce accumulating errors that are due to incomplete data on wind parameters and decrease requirements for random errors of initial data sensors. 相似文献
596.
I. Sh. Sharafeev 《Russian Aeronautics (Iz VUZ)》2009,52(2):255-258
A set of systems for labor standard computer-aided design is described, namely, initial developments, advance and state-of-the art. 相似文献
597.
Yu. G. Kutsenko 《Russian Aeronautics (Iz VUZ)》2009,52(2):208-213
A modification of the Zimont turbulent combustion model is presented; the modification makes it possible to describe processes in diffusion and homogeneous flame fronts as well as to take into account the influence of different factors that cause flame destabilization. The model is based on the equation for a reaction completeness extent (completeness of combustion). The model realization to simulate the premixed combustion is described and the modification of the turbulent combustion model is applied to simulate a process of flameout downstream of the flameholder. 相似文献
598.
D. H. Wooden 《Space Science Reviews》2008,138(1-4):75-108
Comets are heterogeneous mixtures of interstellar and nebular materials. The degree of mixing of interstellar sources and nebular sources at different nuclear size scales holds the promise of revealing how cometary particles, cometesimals, and cometary nuclei accreted. We can ascribe cometary materials to interstellar and nebular sources and see how comets probe planet-forming process in our protoplanetary disk. Comets and cometary IDPs contain carbonaceous matter that appears to be either similar to poorly-graphitized (amorphous) carbon, a likely ISM source, or highly labile complex organics, with possible ISM or outer disk heritage. The oxygen fugacity of the solar nebula depends on the dynamical interplay between the inward migration of carbon-rich grains and of icy (water-rich) grains. Inside the water dissociation line, OH? reacts with carbon to form CO or CO2, consuming available oxygen and contributing to the canonical low oxygen fugacity. Alternatively, the influx of water vapor and/or oxygen rich dust grains from outer (cooler) disk regions can raise the oxygen fugacity. Low oxygen fugacity of the canonical solar nebula favors the condensation of Mg-rich crystalline silicates and Fe-metal, or the annealing of Fe-Mg amorphous silicates into Mg-rich crystals and Fe-metal via Fe-reduction. High oxygen fugacity nebular conditions favors the condensation of Fe-bearing to Fe-rich crystalline silicates. In the ISM, Fe-Mg amorphous silicates are prevalent, in stark contrast to Mg-rich crystalline silicates that are rare. Hence, cometary Mg-rich crystalline silicates formed in the hot, inner regions of the canonical solar nebula and they are the touchstone for models of the outward radial transport of nebular grains to the comet-forming zone. Stardust samples are dominated by Mg-rich crystalline silicates but also contain abundant Fe-bearing and Fe-rich crystalline silicates that are too large (?0.1 μm) to be annealed Fe-Mg amorphous silicates. By comparison with asteroids, the Stardust Fe-bearing and Fe-rich crystalline silicates suggests partial aqueous alteration in comet nuclei. However, aqueous alteration transforms Fe-rich olivine to phyllosilicates before Mg-rich olivine, and Stardust has Mg-rich and Fe-rich olivine and no phyllosilicates. Hence, we look to a nebular source for the moderately Fe-rich to nearly pure-Fe crystalline silicates. Primitive matrices have Mg-Fe silicates but no phyllosilicates, supporting the idea that Mg-Fe silicates but not phyllosilicates are products of water-rich shocks. Chondrule-formation is a late stage process in our protoplanetary disk. Stardust samples show comet 81P/Wild 2 formed at least as late to incorporate a few chondrules, requiring radial transport of chondrules out to perhaps >20 AU. By similar radial transport mechanisms, collisional fragments of aqueously altered asteroids, in particular achondrites that formed earlier than chondrules, might reach the comet-forming zones. However, Stardust samples do not have phyllosilicates and chondrules are rare. Hence, the nebular refractory grains in comet 81P/Wild 2, as well as other comets, appear to be pre-accretionary with respect to asteroid parent bodies. By discussing nebular pathways for the formation of Fe-rich crystalline silicates, and also phyllosilicates and carbonates, we put forth the view that comets contain both the interstellar ingredients for and the products of nebular transmutation. 相似文献
599.
Some experimental data on the process of impulsive ultrasonic machining are presented. Also given are the data on variations in the impulsive vibration frequency of a workpiece and a tool. 相似文献
600.
Miller D.L. Wolfman G.J. Volanth A.J. Mullins R.T. 《Aerospace and Electronic Systems Magazine, IEEE》1996,11(4):22-26
Tower air traffic control is currently performed using several unintegrated systems. While each of these systems supports performing an isolated task, the compilation of tools presents a number of challenges. This paper reports ways in which the Tower Control Computer Complex (TCCC) will support and enhance user management of numerous systems. Areas that will be notably improved include the consistency in the user interface of the air traffic control toolset, the task of manually integrating tools and information, toolset alert management, and toolset organization and administration 相似文献