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81.
White Oran R. Fox Peter A. Meisner Randy Rast Mark P. Yasukawa Eric Koon Darryl Rice Crystal Lin Haosheng Kuhn Jeff Coulter Roy 《Space Science Reviews》2000,94(1-2):75-82
Two Precision Solar Photometric Telescopes (PSPT) designed and built at the U.S. National Solar Observatory (NSO) are in operation in Rome and Hawaii. A third PSPT is now in operation the NSO at Sunspot, NM. The PSPT system records full disk solar images at three wavelengths: K line at 393.3 nm and two continua at 409 nm and 607 nm throughout the observing day. We currently study properties of limb darkening, sunspots, and network in these images with particular emphasis on data taken in July and September 1998. During this period, the number of observations per month was high enough to show directional properties of the radiation field surrounding sunspots. We show examples of our PSPT images and describe our study of bright rings around sunspots. 相似文献
82.
White B.A. Zbikowski R. Tsourdos A. 《IEEE transactions on aerospace and electronic systems》2007,43(3):899-919
This paper examines the application of differential geometry to the engagement of both nonmanoeuvring and manoeuvring targets. The kinematics of the engagement for both manoeuvring and nonmanoeuvring target are developed and expressed in differential geometric terms. Two-dimensional geometry is then used to determine the intercept conditions for a straight line target and a constant manoeuvre target. The intercept conditions for both targets are developed for the case when the interceptor missile guides onto a straight line interception. These two cases are shown to have a common set of core conditions such that it enables a unified guidance law to be developed. The guidance law is shown to be globally stable using Lyapunov theory, so that guidance capture is assured for any initial condition. The analysis and guidance law design does not rely on local linearisation and can be shown to produce guidance trajectories that mirror proportional navigation for the straight line interception of a nonmanoeuvring target for which proportional navigation was originally developed. The paper finishes with simulation in two dimensions, illustrating the convergence and solution properties of the approach. 相似文献
83.
84.
L. A. Frank J. B. Sigwarth J. D. Craven J. P. Cravens J. S. Dolan M. R. Dvorsky P. K. Hardebeck J. D. Harvey D. W. Muller 《Space Science Reviews》1995,71(1-4):297-328
The Visible Imaging System (VIS) is a set of three low-light-level cameras to be flown on the POLAR spacecraft of the Global Geospace Science (GGS) program which is an element of the International Solar-Terrestrial Physics (ISTP) campaign. Two of these cameras share primary and some secondary optics and are designed to provide images of the nighttime auroral oval at visible wavelengths. A third camera is used to monitor the directions of the fields-of-view of these sensitive auroral cameras with respect to sunlit Earth. The auroral emissions of interest include those from N
2
+
at 391.4 nm, Oi at 557.7 and 630.0 nm, Hi at 656.3 nm, and Oii at 732.0 nm. The two auroral cameras have different spatial resolutions. These resolutions are about 10 and 20 km from a spacecraft altitude of 8R
e
. The time to acquire and telemeter a 256×256-pixel image is about 12 s. The primary scientific objectives of this imaging instrumentation, together with thein-situ observations from the ensemble of ISTP spacecraft, are (1) quantitative assessment of the dissipation of magnetospheric energy into the auroral ionosphere, (2) an instantaneous reference system for thein-situ measurements, (3) development of a substantial model for energy flow within the magnetosphere, (4) investigation of the topology of the magnetosphere, and (5) delineation of the responses of the magnetosphere to substorms and variable solar wind conditions. 相似文献
85.
A. C. Brinkman R. Mewe T. Langerwerf J. Heise A. Peacock N. White 《Space Science Reviews》1985,40(1-2):201-206
EXOSAT measurements of Sco X-1 have been carried out with the 500 l/mm and 1000 l/mm grating spectrometers and simultaneously with the gas scintillation proportional counter (GSPC) on two occasions in August 1983. The first observing period, part of the instrument performance verification phase, on August 7 and 8, 1983, lasted for about twenty two hours and showed the source flaring during the first six hours. During the second observing period, August 29 and 30, 1983, the source was again active during part of the time. The lightcurves of the spectrometers and the GSPC show some correlation during the flaring activity. The grating spectra show clear emission features between 12 and 20 Å, which vary with time. When fitting the observed spectra to a thermal bremsstrahlungs model (exponential with gaunt factor) together with absorption by neutral matter, a reduced abundance of oxygen in the absorbing matter with respect to Solar is required. 相似文献
86.
"Artificial noise," or the connection of feedback paths around the the integrators, is shown to be an effective method of dealing with the problem of multiplier offsets in adaptive antennas. This probl which was analyzed by Compton [1] is particularly troubles when the covariance matrix is singular or nearly so. Like added real noise, the artificial noise improves the condition number of the underlying matrix. The artificial noise, however, avoids the obvious disadvantage of adding to the real noise level. As a result the output-signal-to-interference ratio is much less degraded. 相似文献
87.
This paper presents numerical results from a study of sidelobe cancellers operating against wideband interfering signals. The study was designed to provide information that would be useful to system designers. Among other things, we address the question of whether it is best to enhance the bandwidth capability of the canceller by using tapped delay lines or simply by using more auxiliary elements. We also develop guidance rules to help the designer determine the number of adaptive loops required for a given environment. 相似文献
88.
One of the big surprises of the Infrared Space Observatory (ISO) has been discovery of crystalline silicates outside our own
Solar system. It was generally assumed before that all cosmic silicates in space were of amorphous structure. Thanks to ISO
we know now that crystalline silicates are ubiquitous in the Galaxy (except for the diffuse ISM) and sometimes even in very
large quantities (> 50% of the small dust particles). The evolution of the crystalline silicates is still not completely clarified,
but the combination of theoretical modeling and observations have already shed light on their life-cycle. The absence of crystalline
silicates in the diffuse ISM provides us with information about the dust amorphization rate in the ISM. 相似文献
89.
Inhibition of denitrification by ultraviolet radiation. 总被引:1,自引:0,他引:1
R L Mancinelli M R White 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2000,26(12):2041-2046
It has been shown that UV-A (lambda=320-400 nm) and UV-B (lambda=280-320 nm) inhibit photosynthesis, nitrogen fixation and nitrification. The purpose of this study was to determine the effects, if any, on denitrification in a microbial community inhabiting the intertidal. The community studied is the microbial mat consisting primarily of Lyngbya that inhabits the Pacific marine intertidal, Baja California, Mexico. Rates of denitrification were determined using the acetylene blockage technique. Pseudomonas fluorescens (ATCC #17400) was used as a control organism, and treated similarly to the mat samples. Samples were incubated either beneath a PAR transparent, UV opaque screen (OP3), or a mylar screen to block UV-B, or a UV transparent screen (UVT) for 2 to 3 hours. Sets of samples were also treated with nitrapyrin to inhibit nitrification, or DCMU to inhibit photosynthesis and treated similarly. Denitrification rates were greater in the UV protected samples than in the UV exposed samples the mat samples as well as for the Ps fluorescens cultures. Killed controls exhibited no activity. In the DCMU and nitrapyrin treated samples denitrification rates were the same as in the untreated samples. These data indicate that denitrification is directly inhibited by UV radiation. 相似文献
90.
Marc Studer Gesine Bradacs Andre Hilliger Eva Hürlimann Stephanie Engeli Cora S. Thiel Peter Zeitner Beat Denier Markus Binggeli Thomas Syburra Marcel Egli Frank Engelmann Oliver Ullrich 《Acta Astronautica》2011,68(11-12):1729-1741
Long-term sensitivity of human cells to reduced gravity has been supposed since the first Apollo missions and was demonstrated during several space missions in the past. However, little information is available on primary and rapid gravi-responsive elements in mammalian cells. In search of rapid-responsive molecular alterations in mammalian cells, short-term microgravity provided by parabolic flight maneuvers is an ideal way to elucidate such initial and primary effects. Modern biomedical research at the cellular and molecular level requires frequent repetition of experiments that are usually performed in sequences of experiments and analyses. Therefore, a research platform on Earth providing frequent, easy and repeated access to real microgravity for cell culture experiments is strongly desired. For this reason, we developed a research platform onboard the military fighter jet aircraft Northrop F-5E “Tiger II”. The experimental system consists of a programmable and automatically operated system composed of six individual experiment modules, placed in the front compartment, which work completely independent of the aircraft systems. Signal transduction pathways in cultured human cells can be investigated after the addition of an activator solution at the onset of microgravity and a fixative or lysis buffer after termination of microgravity. Before the beginning of a regular military training flight, a parabolic maneuver was executed. After a 1 g control phase, the parabolic maneuver starts at 13,000 ft and at Mach 0.99 airspeed, where a 22 s climb with an acceleration of 2.5g is initiated, following a free-fall ballistic Keplerian trajectory lasting 45 s with an apogee of 27,000 ft at Mach 0.4 airspeed. Temperature, pressure and acceleration are monitored constantly during the entire flight. Cells and activator solutions are kept at 37 °C during the entire experiment until the fixative has been added. The parabolic flight profile provides up to 45 s of microgravity at a quality of 0.05g in all axes. Access time is 30 min before take-off; retrieval time is 30 min after landing. We conclude that using military fighter jets for microgravity research is a valuable tool for frequent and repeated cell culture experiments and therefore for state-of-the art method of biomedical research. 相似文献