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991.
F. Di Capua L. Campajola P. Casolaro M. Campajola A. Aloisio A. Lucaroni G. Furano A. Menicucci S. Di Mascio F. Malatesta M. Ottavi 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2019,63(10):3249-3257
A new methodology for Total Ionizing Dose (TID) tests is proposed. It is based on the employment of an on-chip 90Sr/90Y beta source as alternative to standard methods such as 60Co gamma rays and electrons from LINAC. The use of a compact beta source for TID tests has several advantages. In particular, the irradiation of devices with more than one radiation source results in a better representation of the complex space radiation environment composed of several types, energies and dose-rates. In addition, the use of an easy handling beta source allows the irradiation of electronic devices without any damage to other auxiliary circuit. In this work, 90Sr/90Y beta source dosimetry and related radiation field characteristics are discussed in depth.In order to validate the proposed source for TID tests, a rather complex device such as the “SPC56EL70L5” microcontroller from ST-Microelectronics was exposed to 90Sr/90Y beta rays. The results of this test were compared to that of a previous test of another sample from the same lot with a standard gamma 60Co source. The electronic performances following the two irradiations have been found to be in excellent agreement, by demonstrating therefore the validity of the proposed beta source for TID tests. 相似文献
992.
The techniques of forming the mobile sliding manifolds and vector controls, which bring these systems into the sliding modes under continuous action of uncertain factors, namely limited disturbances and total errors in measurements, are developed for dynamic systems with discontinuous control. The techniques are applicable for effective control of complex aerospace objects. 相似文献
993.
994.
Structures for radar detection in compound Gaussian clutter 总被引:1,自引:0,他引:1
Sangston K.J. Gini F. Greco M.V. Farina A. 《IEEE transactions on aerospace and electronic systems》1999,35(2):445-458
The problem of coherent radar target detection in a background of non-Gaussian clutter modeled by a compound Gaussian distribution is studied here. We show how the likelihood ratio may be recast into an estimator-correlator form that shows that an essential feature of the optimal detector is to compute an optimum estimate of the reciprocal of the unknown random local power level. We then proceed to show that the optimal detector may be recast into yet another form, namely a matched filter compared with a data-dependent threshold. With these reformulations of the optimal detector, the problem of obtaining suboptimal detectors may be systematically studied by either approximating the likelihood ratio directly, utilizing a suboptimal estimate in the estimator-correlator structure or utilizing a suboptimal function to model the data-dependent threshold in the matched filter interpretation. Each of these approaches is studied to obtain suboptimal detectors. The results indicate that for processing small numbers of pulses, a suboptimal detector that utilizes information about the nature of the non-Gaussian clutter can be implemented to obtain quasi-optimal performance. As the number of pulses to be processed increases, a suboptimal detector that does not require information about the specific nature of the non-Gaussian clutter may be implemented to obtain quasi-optimal performance 相似文献
995.
Interplanetary origin of geomagnetic storms 总被引:8,自引:0,他引:8
Gonzalez Walter D. Tsurutani Bruce T. Clúa de Gonzalez Alicia L. 《Space Science Reviews》1999,88(3-4):529-562
Around solar maximum, the dominant interplanetary phenomena causing intense magnetic storms (Dst<−100 nT) are the interplanetary
manifestations of fast coronal mass ejections (CMEs). Two interplanetary structures are important for the development of storms,
involving intense southward IMFs: the sheath region just behind the forward shock, and the CME ejecta itself. Whereas the
initial phase of a storm is caused by the increase in plasma ram pressure associated with the increase in density and speed
at and behind the shock (accompanied by a sudden impulse [SI] at Earth), the storm main phase is due to southward IMFs. If
the fields are southward in both of the sheath and solar ejecta, two-step main phase storms can result and the storm intensity
can be higher. The storm recovery phase begins when the IMF turns less southward, with delays of ≈1–2 hours, and has typically
a decay time of 10 hours. For CMEs involving clouds the intensity of the core magnetic field and the amplitude of the speed
of the cloud seems to be related, with a tendency that clouds which move at higher speeds also posses higher core magnetic
field strengths, thus both contributing to the development of intense storms since those two parameters are important factors
in genering the solar wind-magnetosphere coupling via the reconnection process.
During solar minimum, high speed streams from coronal holes dominate the interplanetary medium activity. The high-density,
low-speed streams associated with the heliospheric current sheet (HCS) plasma impinging upon the Earth's magnetosphere cause
positive Dst values (storm initial phases if followed by main phases). In the absence of shocks, SIs are infrequent during
this phase of the solar cycle. High-field regions called Corotating Interaction Regions (CIRs) are mainly created by the fast
stream (emanating from a coronal hole) interaction with the HCS plasma sheet. However, because the Bz component is typically highly fluctuating within the CIRs, the main phases of the resultant magnetic storms typically have
highly irregular profiles and are weaker. Storm recovery phases during this phase of the solar cycle are also quite different
in that they can last from many days to weeks. The southward magnetic field (Bs) component of Alfvén waves in the high speed stream proper cause intermittent reconnection, intermittent substorm activity,
and sporadic injections of plasma sheet energy into the outer portion of the ring current, prolonging its final decay to quiet
day values. This continuous auroral activity is called High Intensity Long Duration Continuous AE Activity (HILDCAAs).
Possible interplanetary mechanisms for the creation of very intense magnetic storms are discussed. We examine the effects
of a combination of a long-duration southward sheath magnetic field, followed by a magnetic cloud Bs event. We also consider the effects of interplanetary shock events on the sheath plasma. Examination of profiles of very
intense storms from 1957 to the present indicate that double, and sometimes triple, IMF Bs events are important causes of such events. We also discuss evidence that magnetic clouds with very intense core magnetic
fields tend to have large velocities, thus implying large amplitude interplanetary electric fields that can drive very intense
storms. Finally, we argue that a combination of complex interplanetary structures, involving in rare occasions the interplanetary
manifestations of subsequent CMEs, can lead to extremely intense storms.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
996.
From magnetic fields and coronal heating observed in flares, active regions, quiet regions, and coronal holes, we propose
that exploding sheared core magnetic fields are the drivers of most of the dynamics and heating of the solar atmosphere, ranging
from the largest and most powerful coronal mass ejections and flares, to the vigorous microflaring and coronal heating in
active regions, to a multitude of fine-scale explosive events in the magnetic network, driving microflares, spicules, global
coronal heating, and, consequently, the solar wind.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
997.
M R Sims C T Pillinger I P Wright J Dowson S Whitehead A Wells J E Spragg G Fraser L Richter H Hamacher A Johnstone N P Meredith C de la Nougerede B Hancock R Turner S Peskett A Brack J Hobbs M Newns A Senior M Humphries H U Keller N Thomas J S Lingard T C Ng 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1999,23(11):1925-1928
The aim of the proposed Beagle 2 small lander for ESA's 2003 Mars Express mission is to search for organic material on and below the surface of Mars and to study the inorganic chemistry and mineralogy of the landing site. The lander will have a total mass of 60kg including entry, descent, and landing system. Experiments will be deployed on the surface using a robotic arm. It will use a mechanical mole and grinder to obtain samples from below the surface, under rocks, and inside rocks. Sample analysis by a mass spectrometer will include isotopic analysis. An optical microscope, an X-ray spectrometer and a Mossbauer spectrometer will conduct in-situ rock studies. 相似文献
998.
从工程实践角度,探讨了在目前广泛采用的偏置动量轮三轴姿态稳定卫星上,进行大尺寸(3~5m)和高指向精度(0.05°)的挠性天性指向控制问题。在建立具有挠性天线的星体动力学模型,以及在借鉴和改进有关抑制挠性天线振动研究的基础上,设计了三轴稳定卫星平台上的挠性天线指向控制系统的方案。最后,根据数值仿真结果,给出了影响挠性天线指向精度的主要因素。 相似文献
999.
利用前缘旋转控制边条翼外翼分离 总被引:1,自引:0,他引:1
边条翼在边条较小时中等迎角以上外翼就会出现分离,现提出用转动前缘表面来控制边条翼外翼分离。通过测力、油流和烟丝实验研究了转动前缘对机翼气动特性的影响。结果表明,在这种机翼上转动前缘对控制分离是有效的,升力增量最大可达30%。可以预期,转动前缘与边条的综合作用,机翼的分离特性将有较大的改善 相似文献
1000.