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41.
H. Thiemann R. W. Schunk 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1992,12(12):143-146
Heavy emission caused by impacting plasma ions results in a fast discharging effect of the initially large surface potentials on the dielectric solar cells. This eventually counteracts the energization process of the plasma ions to the cover glasses and leaves no significant electric fields. Thus, with an existing thermal plasma, electrons are again able to reach dielectric surfaces. Strong localized electric fields of the order of several 10 kV/cm form near the interconnector-cover glass interface. 相似文献
42.
J H Bieging 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1995,15(3):3-14
Stars in their late stages of evolution often shed matter in the form of a cool wind which is molecular in composition. These winds are a major source of replenishment of the interstellar gas and dust, so they furnish a large part of the raw materials for new generations of stars and planets. The chemistry of the circumstellar envelope depends strongly on the photospheric abundances of the elements, especially C and O. If C/O > 1, a rich organic chemistry is observable in the microwave and mm-wavelength emission lines of the reactions products. This paper reviews the observational evidence for the presence of organic molecules and their formation pathways in circumstellar envelopes, with special emphasis on rotational spectra at microwave and millimeter wavelengths. 相似文献
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44.
M. F. Kessler H. J. Habing 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1993,13(12):485-494
The INFRARED SPACE OBSERVATORY (ISO), a project of the European Space Agency (ESA), will make various astronomical observations in the wavelength range of 2 to 200 μm. Two-thirds of its observing time will be available to guest observers via the traditional route of proposal submission. ISO will be launched in 1995 by an Ariane 4 from Kourou (Guyana) and be brought into a very elongated orbit with a 24hr period of which 16 hr can be used for astronomical observations. The payload module is essentially a large cryostat with a tank that will be filled with over 2000 litres of superfluid helium to keep the instruments cold (2 to 4 K) during an expected lifetime of 18 months. Inside the dewar, there is a Ritchey-Chretien telescope with a primary mirror of diameter 60cm. Four instruments, each provided by a different PI consortium, share the ISO focal plane. These instruments are : a photometer, a camera and two spectrometers — one for the wavelength range 2–45 μm and the other for 45–180 μm. 相似文献
45.
Senrad: an advanced wideband air-surveillance radar 总被引:1,自引:0,他引:1
Skolnik M. Linde G. Meads K. 《IEEE transactions on aerospace and electronic systems》2001,37(4):1163-1175
The generic characteristics and performance of an experimental long-range air-surveillance radar, known at the Naval Research Laboratory as Senrad, is described. Its distinguishing feature is that it can operate with simultaneous transmissions over a very wide bandwidth-from 850 to 1400 MHz. The technology and type of experimental radar equipment employed are discussed and examples are given of its performance capabilities obtained by means of very wideband operation. The unusually wide bandwidth of this radar allows 1) improved detection and tracking performance because of the absence of the nulls that are common in the antenna elevation radiation-pattern of a single-frequency radar; 2) moving target indication (MTI) without loss of targets due to blind speeds and without the need for multiple PRFs (pulse repetition frequencies); 3) accurate height finding with a fan-beam radar by taking advantage of the multipath time difference as a function of target height; 4) a form of limited target recognition based on high range-resolution; and 5) a reduction of the effectiveness of electronic countermeasures that can seriously degrade more narrowband radars 相似文献
46.
Dong-Wook Lee McClellan J.H. 《IEEE transactions on aerospace and electronic systems》1997,33(3):795-801
The problem of extracting multiple frequencies from phase-only data is addressed. Multiple frequency estimation is accomplished by reconstructing the Fourier transform of the complex-valued time signal and then finding peaks in the frequency domain. We present a set of conditions under which a discrete-time complex sequence can be completely specified by its phase-only information. Two candidate multiple frequency estimation schemes are introduced, one based on a closed-form least-squares inverse, the other an iterative reconstruction algorithm. The uniqueness of the closed-form solution and the convergence of the iterative scheme have been proven under certain conditions. Several examples are given, including the case where the phase is quantized as would happen in an analog-to-digital (A/D) converter. Extensions to the multidimensional case, and to the case of real-part only reconstruction are straightforward. 相似文献
47.
H J Durand-Manterola B Mendoza R Diaz-Sandoval 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2001,28(4):679-684
An increasing number of studies have appeared in the last ten years indicating that some pathologies may correlate with geomagnetic activity and cosmic rays. However a physical mechanism binding both phenomena has not been proposed. In the present work we obtain the amplitude of the magnetic fields at different frequencies, that may induce inside biological cells currents of the same magnitude of the currents generated by the cells themselves. We compare these values with the wave amplitudes produced in geomagnetic and atmospheric phenomena, and found that micropulsations, whistlers and lightning are capable of produce the same or larger values. 相似文献
48.
A representative switched-capacitor DC-DC converter topology is presented, circuit operation is explained, and control strategies are identified. State-space averaging is used to analyze steady-state performance and to develop control criteria and design equations. The analytical results are verified by SPICE simulation 相似文献
49.
The Freja ultraviolet imager 总被引:2,自引:0,他引:2
J. S. Murphree R A. King T. Payne K. Smith D. Reid J. Adema B. Gordon R. Wlochowicz 《Space Science Reviews》1994,70(3-4):421-446
Auroral images acquired by satellite instrumentation have proven to be a crucial component of the scientific equiry into the physical processes of the Earth's magnetosphere. TheFreja mission provided an opportunity to extend these measurements into the temporal and spatial regime commonly associated with ground-based optical imagers. Employing the basic procedure used successfully in theViking program allowed image repetition rates of 6 s to be achieved with simultaneous exposure of all pixels within the field-of-view. Typical exposure times of 0.3 s required development of an improved image intensifier system and operational requirements resulted in image formats covering approximately one-third of a spin. Simultaneously exposing two broad-band UV cameras, the instrument generates in its normal operational mode 264.6 kbytes per image pair. Results from initial operations confirm the design approach and suggest such imagers can be routinely included on challenging low cost missions such asFreja. 相似文献
50.