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941.
While the microbial diversity of a spacecraft assembly facility at the Jet Propulsion Laboratory (Pasadena, CA) was being monitored, H2O2-resistant bacterial strains were repeatedly isolated from various surface locations. H2O2 is a possible sterilant for spacecraft hardware because it is a low-temperature process and compatible with various modern-day spacecraft materials, electronics, and components. Both conventional biochemical testing and molecular analyses identified these strains as Bacillus pumilus. This Bacillus species was found in both unclassified (entrance floors, anteroom, and air-lock) and classified (floors, cabinet tops, and air) locations. Both vegetative cells and spores of several B. pumilus isolates were exposed to 5% liquid H2O2 for 60 min. Spores of each strain exhibited higher resistance than their respective vegetative cells to liquid H2O2. Results indicate that the H2O2 resistance observed in both vegetative cells and spores is strain-specific, as certain B. pumilus strains were two to three times more resistant than a standard Bacillus subtilis dosimetry strain. An example of this trend was observed when the type strain of B. pumilus, ATCC 7061, proved sensitive, whereas several environmental strains exhibited varying degrees of resistance, to H2O2. Repeated isolation of H2O2-resistant strains of B. pumilus in a clean-room is a concern because their persistence might potentially compromise life-detection missions, which have very strict cleanliness and sterility requirements for spacecraft hardware. 相似文献
942.
943.
The electric field transported by charged aircraft during free flight can be observed quantitatively in distances of up to some 100 m. A system of three plane sensors arranged in the corners of a triangle or the Earth surface is described, by which the flight path of aircraft is detected in the range of 40 to 500 m with velocities of approximately 50 m/s. The theory and typical experimental results are discussed. 相似文献
944.
Powers E.J. Hong J.Y. Kim Y.C. 《IEEE transactions on aerospace and electronic systems》1981,(4):602-605
The nonlinear system concepts of nonlinear transfer functions are extended to nonlinear cross sections which may be used to quantitatively describe the characteristics of a nonlinear scatter. The concept of nonlinear cross sections is used to generalize the radar equation for nonlinear scattering objects. 相似文献
945.
An analysis is made of the errors in the determination of the position of an emergency transmitter in a satellite-aided search and rescue system. The satellite is assumed to be at a height of 820 km in a near-circular near polar orbit. Short data spans of four minutes or less are used. The error sources considered are measurement noise, transmitter frequency drift, ionospheric effects, and error in the assumed height of the transmitter. The errors are calculated for several different transmitter positions, data rates, and data spans. The only transmitter frequency used was 406 MHz, but the result can be scaled to different frequencies. 相似文献
946.
Edward J. Smith 《Space Science Reviews》1976,19(4-5):661-686
A review is presented of the interplanetary magnetic field observations acquired in early August 1972 when four solar flares erupted in McMath Plage region 11976. Measurements of the interplanetary field were obtained by Earth satellites, HEOS-2 and Explorer 41, and by Pioneers 9 and 10 which, by good fortune, were radially aligned and only 45° east of the Earth-Sun direction. In response to the four flares, four interplanetary shocks were seen at Earth and at Pioneer 9, which was then at a heliocentric distance of 0.78 AU. However, at Pioneer 10, which was 2.2 AU from the Sun, only two forward shocks and one reverse shock were seen. The available magnetic field data acquired in the vicinity of the shocks are presented. Efforts to identify corresponding shocks at the several locations and to deduce their velocities of propagation between 0.8 and 2.2 AU are reviewed. The early studies were based on average velocities between the Sun and Pioneer 9, the Sun and Earth and the Sun and Pioneer 10. A large deceleration of the shocks between the Sun and 0.8 AU as well as between 0.8 and 2.2 AU was inferred. More recently the local velocities of the shocks at Pioneers 9 and 10 have become available. A comparison of these velocities shows little, if any, deceleration between 0.8 and 2.2 AU and implies that most or all of the deceleration actually occurred nearer the Sun. Evidence is also presented that shows a significant departure of the flare-generated shock fronts from spherical symmetry. 相似文献
947.
Summary From the extensive set of numerical calculations briefly described above, it seems apparent that rotating, isothermal gas clouds are unstable to fragmentation under a wide range of conditions. (Caution: This result for isothermal clouds cannot be generalized to all clouds, as is shown, for example, by Boss's analysis [these proceedings] of the stability of collapsing, adiabatic clouds.) It is of importance to note, however, that no fragmentation is apparent during a cloud's initial dynamic collapse toward a disk structure; rather it is the rotationally flattened disk/ring configuration that undergoes fragmentation. This is a considerably different picture of fragmentation than has been presented, for example, by Hoyle (1953).The degree of instability and the mode (ring vs. blob) of fragmentation is sensitive to , but insensitive to . The initial amplitude of a perturbation does not appear to be crucial--fragmentation should occur eventually even for low amplitude initial NAPs.Finally, it is of some interest to know what the properties are of the fragments that break out of these isothermal clouds. Before outlining these properties we emphasize that in this set of calculations we have specifically excited the m = 2 (binary) non-axisymmetric mode; hence we have in some sense suppressed the development of other modes and we have promoted the development of equal mass components in the binary systems. In these evolutions, a typical fragment contained 15% of the initial cloud mass; had a specific angular momentum 25–30% that of the original cloud; had a ratio of spin angular momentum to orbital angular momentum 0.2; and itself had a ratio of thermal to gravitational energy frag < 0.1. The formation of a binary system has therefore resulted in a conversion of some of the original cloud's spin angular momentum into orbital angular momentum, and has produced protostars with reduced specific angular momenta. It is also evident that each fragment is unstable to further collapse (having low ) under the isothermal assumptions imposed here. 相似文献
948.
The extended Kalman-Bucy filtering algorithm is applied to the problem of estimating the system parameters of a single-channel missile attitude control system. In particular, noisy observations of body angular rate, normal acceleration, and control surface deflec tion are used in the algorithm to obtain estimates of body angular rate, angle of attack, control surface deflection, air density, and missile velocity. Computational results obtained for this problem are presented. These results are evaluated to determine the applicapility of this estimator as a part of an adaptive control scheme. In addition, a general approach to the formulation of practical nonlinear estimation problems is suggested. 相似文献
949.
A measure of analog correlator performance is considered and interpreted reted as an output signl-to-noise ratio. This quantity is shown to depend on the fourth-order expectation of the input signals and the characteristics of the integrating system. Based on the output signal-to-noise ratio, figures of merit are established for correlators utilizing an ideal low-pass filter, an RC filter, and a finite time integrator. These figures of merit indicate to what degree the correlators reject noise components. For jointly Gaussian inputs, the variation of the output signal-to-noise ratio with the input signal-to-noise ratio is shown to be independent of the integrating system. Finally, a graphical comparison indicates the characteristics of the three systems for several different parameters. This comparison shows that the finite time integrator is superior to the other two systems considered. 相似文献
950.
Space radiation dosimetry with active detections for the scientific program of the second Bulgarian cosmonaut on board the Mir space station. 总被引:1,自引:0,他引:1
J V Dachev TsPMatviichuk YuN Semkova R T Koleva B Boichev P Baynov N A Kanchev P Lakov P T Ivanov YaJTomo V M Petrov V I Redko V I Kojarinov R Tykva 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1989,9(10):247-251
A dosimetry-radiometry system has been developed at the Space Research Institute of the Bulgarian Academy of Science to measure the fluxes and dose rates on the flight of the second Bulgarian cosmonaut. The dosimetry system is designed for monitoring the different space radiations, such as solar cosmic rays, galactic cosmic rays and trapped particles in the earth radiation belts. The system consists of a battery operated small size detector unit and a "read-write" and telemetry microcomputer unit. The sensitivity of the instrument (3.67 x 10(-8) rad/pulse) permits high resolution measurements of the flux and dose rate along the track of the Mir space station. We report our initial results for the period of the flight between the 7th and 17th June 1988. 相似文献