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931.
A numerical analysis was performed to compare natural convection velocities in two-dimensional enclosures of various shape. The following shapes were investigated: circle, square, horizontal and upright 2 × 1 aspect ratio rectangles, horizontal and upright half-circles, diamond (square oriented with diagonal vertical) and triangle (equilateral and horizontal base). In all cases, the length scale in the various dimensionless parameters, such as Rayleigh number, is defined as the diameter of the equal area circle. Natural convection velocities were calculated for Rayleigh numbers of 100 and 500 with the temperature difference taken to be across (a) the maximum horizontal dimension, (b) the median horizontal line (line through centroid) and (c) the horizontal distance such that the temperature gradient is the same for shapes of equal area. A Rayleigh number of 1000 is within the “low Rayleigh number” range for agreement with first order theory for circular enclosures. A Rayleigh number of 5000 is slightly out of this range. For the class of shapes including the square, upright half-circle and upright rectangle, the computed velocities were found to agree very closely with that of the equal area circle when the temperature difference is taken to be across the maximum horizontal dimension [condition (a)]. The velocities for the horizontal rectangle and half circle were found to be approximately one-half that of the equal area circle for the same condition. Better overall agreement among all shapes was obtained by setting the temperature difference across a distance such that the temperature gradients were equal for shapes of equal area. 相似文献
932.
The design and implementation of a switching regulator incorporating a high-frequency series-resonant converter and a combined FM and on-off feedback control is presented. The combined FM and on-off control results in a better conversion efficiency and a wider range of operational input voltage and output current. A 22.5 V, 50 W experimental regulator has been built to demonstrate the practicality of the circuit and its high efficiency, typically 92 to 96 percent, depending on the input and loading conditions. 相似文献
933.
C.S. Leyman 《Progress in Aerospace Sciences》1986,23(3):185-238
The technical problems encountered during the development and certification of Concorde are reviewed. The topics covered are mainly associated with aerodynamics, but other areas are discussed where they interact with the aerodynamic design or if there were conditions peculiar to supersonic transportation which had to be considered. 相似文献
934.
J.S. Kaastra 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1984,4(7):209-210
A semi-analytical model for the electrodynamic development of two-ribbon flares is presented. A current filament above a bipolar active region starts rising according to the model of Van Tend and Kuperus. Due to this motion large induced electric fields arise at a magnetic neutral line far below the filament, resulting in and associated with magnetic reconnection and the formation of a current sheet. The interaction of this current sheet with the original current filament, the background magnetic field and the boundary layer of the photosphere determine the further electrodynamic development of the flare. The model predicts the energy release, the time of maximum, the height of the energy source and other quantities reasonably well. 相似文献
935.
Kuo-Chu Chang Mori S. Chee-Yee Chong 《IEEE transactions on aerospace and electronic systems》1994,30(1):213-219
This paper describes an analysis of track initiation performance in very high target density environments. The analysis of tracking performance performed previously by S. Mori et al. (1992) yielded very simple expressions to predict average track purity in terms of tracking parameters. These results were, however, obtained mainly for the track continuation phase in which tracks are more or less well established. We extend these results to the track initiation phase 相似文献
936.
S. Drapatz L. Haser R. Hofmann N. Oda R. Wilczek 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1985,5(3):7-10
Far-infrared observations of the Galactic Center have been carried through with the MPE Im balloon-borne telescope “Golden Dragon”. The measurements are composed of photometric scanning (33–95 μm) of the inner 4′×4′ and low resolution spectroscopy (δν = 10 cm?1) of the center and of a position approximately 1.5′ to the north. A Mars spectrum has been obtained for calibration. The spatial resolution of the photometry map is increased using the Maximum Entropy Method and the resulting map is compared to other observations in the same and other spectral regions. A clear asymmetry in the ring-like structure around the center indicates the presence of noncircular motions. The shape of the spectra is fairly smooth with at least no prominent dust features. A simple modelling shows a drastic increase of column density within 2 pc from the center and a modest drop over the next 3 pc to the north. 相似文献
937.
E.S. Kazimirovsky E.I. Zhovty 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1984,4(1):149-151
Methods for constructing a dynamical part of the IRI model are described. 相似文献
938.
Martha S. Hanner 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1984,4(9):189-196
Measurements of the thermal emission from the cometary dust coma can be used to derive the rate of dust production from the nucleus as well as the size distribution of absorbing grains. More than ten short-period comets have now been observed in the infrared over a wide range in heliocentric distance. Dust production rates are derived for these comets based on theoretical models of the thermal emission from small absorbing grains and calculations of dust grain velocities. The mean size and albedo of the dust grains is similar in these comets, with the exception of Comet Crommelin, which seems to have had larger, darker grains. 相似文献
939.
N. V. Stoichev S. B. Yaneva L. L. Regel I. V. Videnskiy 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1988,8(12):171-174
Directional solidification of eutectic Al-Cu alloys has been studied to demonstrate the influence of both impurity concentration and convective conditions. The λ/R relations show that higher iron concentration and intensive stirring coarsen the microstructure. The formation and growth of new iron-containing phases at the solidification front restrict impurity influence. Kinetic data follow a dependence λ.Rn=const with n-value close to 0,5. 相似文献
940.
P.N. Bhat S.K. Gupta P.V.Ramana Murthy B.V. Sreekantan S.C. Tonwar P.R. Vishwanath 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1984,3(10-12)
In a further study of sporadic emission from pulsars we find evidence for short lived intense emission from the Crab pulsar. 相似文献