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561.
The measured D/H ratios in interstellar environments and in the solar system are reviewed. The two extreme D/H ratios in solar
system water - (720±120)×10−6 in clay minerals and (88±11)×10−6 in chondrules, both from LL3 chondritic meteorites - are interpreted as the result of a progressive isotopic exchange in
the solar nebula between deuterium-rich interstellar water and protosolar H2. According to a turbulent model describing the evolution of the nebula (Drouart et al., 1999), water in the solar system cannot be a product of thermal (neutral) reactions occurring in the solar nebula. Taking
720×10−6 as a face value for the isotopic composition of the interstellar water that predates the formation of the solar nebula, numerical
simulations show that the water D/H ratio decreases via an isotopic exchange with H2. During the course of this process, a D/H gradient was established in the nebula. This gradient was smoothed with time and
the isotopic homogenization of the solar nebula was completed in 106 years, reaching a D/H ratio of 88×10−6. In this model, cometary water should have also suffered a partial isotopic re-equilibration with H2. The isotopic heterogeneity observed in chondrites result from the turbulent mixing of grains, condensed at different epochs
and locations in the solar nebula. Recent isotopic determinations of water ice in cold interstellar clouds are in agreement
with these chondritic data and their interpretation (Texeira et al., 1999).
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
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563.
This article presents an innovative time-domain nonlinear mapping-based identification method. The method reported is applied to identify the unknown parameters of multivariable dynamic systems which are mapped by nonlinear differential equations. A systematic identification method is introduced, and a novel algorithm is developed using nonlinear error maps. An analysis of parameter convergence is provided and the regions of convergence can be found using the second method of Lyapunov. Innovative nonquadratic Lyapunov functions are designed and used. Analytical and numerical studies are performed to illustrate and validate the identification concept. The unsteady flight of a high-alpha aircraft in the longitudinal axis is chosen as a nonlinear case study. The unknown parameters are identified. Simulation results show that the model dynamics match the experimental data. The reported example demonstrates that the time-domain nonlinear mapping-based identification method ensures robustness and reduces major shortcomings in stability, convergence, and computational efficiency compared with other algorithms available 相似文献
564.
Metallic Power has demonstrated a regenerative zinc air fuel cell for applications in industrial and specialty vehicles. The fuel cell uses zinc pellets and atmospheric oxygen to generate electric current; the reaction product is zinc oxide, which is collected in a tank. In its present stage of development the 36 V fuel cell will deliver approximately 6 kWh, with a maximum power of 4 kW. The device is refueled at a zinc recycling/refueling station where zinc pellets are pumped into each cell; ZnO is pumped from the tank and replaced with KOH electrolyte. The recycling/refueling unit uses an electrolytic process to convert zinc oxide powder into zinc pellets 相似文献
565.
566.
Lobanov V.S. Tarasenko N.V. Shulga D.N. Zboroshenko V.N. Fedotov V.P. 《Aerospace and Electronic Systems Magazine, IEEE》2007,22(4):23-29
In article the opportunity of use strapdown inertial navigation system (SINS) on the base of fiber-optic gyroscopes and quartz accelerometers corrected from star sensors and satellite navigation equipment (SNE) for perspective interplanetary spacecrafts motion control on phases of interplanetary trajectory insertion, trajectory correction, and braking during transition to Mars orbit is investigated. Results of onboard control complex accuracy characteristics estimation are presented at the given dynamic spacecraft scheme which is taking into account the liquid oscillations in tanks and structure elements elasticity. At modelling the errors of measuring devices installation, errors of SINS initial alignment and instrumental errors of SINS sensitive elements, variation of control engines parameters were taken into account. The structure of the developed complex of imitation modelling of interplanetary spacecraft controlled motion is resulted. Estimations of active flight legs realization accuracy were received by a method of statistical modelling of spacecraft controlled motion 相似文献
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569.
Barrett A. Rabideau G. Estlin T. Chien S. 《Aerospace and Electronic Systems Magazine, IEEE》2007,22(2):27-33
Eight evaluation metrics are used to compare and contrast three coordination schemes for a system that continuously plans to control collections of rovers (or spacecraft) using collective mission goals instead of goals or command sequences for each spacecraft. These schemes use a central coordinator to either: 1) micromanage rovers one activity at a time; 2) assign mission goals to rovers; or 3) arbitrate mission goal auctions among rovers. A self-commanding collection of rovers would autonomously coordinate itself to satisfy high-level science and engineering goals in a changing partially understood environment - making the operation of tens or even a hundred spacecraft feasible 相似文献
570.
A.H. Manson C.E. Meek M. Massebeuf J.L. Fellous W.G. Elford R.A. Vincent R.L. Craig R.G. Roper S. Avery B.B. Balsley G.J. Fraser M.J. Smith R.R. Clark S. Kato T. Tsuda A. Ebel 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1985,5(7):135-144
During the last decade a large number of radars (~12) have been developed, which have produced substantial quantities of tidally-corrected mean winds data. The distribution of the radars is not global, but many areas are well covered: the Americas with Poker Flat (65°N), Saskatoon (52°N), Durham (43°N), Atlanta (34°N), Puerto Rico (18°N); Europe with Kiruna (68°), Garchy (47°N) and Monpazier (44°N); and Oceania with Christchurch (44°S), Adelaide (35°S), Townsville (20°S), and Kyoto (35°N). Zonal and meridional wind height-time cross-sections from km (MF/Meteor Radar) to ~110 km have been prepared for the last 5–6 years. They are compared with cross-sections from CIRA-72 for zonal winds, and Groves (1969) for meridional winds.It is shown that while CIRA-72 is still a useful model for many purposes, significant differences exist between it and the new radar data. The latter demonstrate important seasonal, latitudinal, longitudinal and hemispheric variations. The new meridional cross-sections are of great value. The common features with Groves (1969) are the equatorward cells in summer near 85 km; however their strength (~10 ms?1) and size are less. Systematic and somewhat different variations emerge at higher (?52°N) and middle (35–44°) latitudes. 相似文献