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961.
The status of computational tests for establishing matrix positive semidefiniteness and positive definiteness is reviewed. Two pervasive real-time tests that have been used for many years in varied applications to ensure that computed covariances encountered in Kalman filter applications are positive definite and discussed. Structural representations of covariance matrices are reviewed as a prelude to constructing a counterexample and demonstrating that it refutes these real-time tests. It is maintained that the latter are bogus approaches despite the fact that they are pervasive. It is suggested that such bogus tests arose as an attempt to fill the need for a quick check (over the entire mission time) of the massive number of matrices computationally encountered in real-time applications 相似文献
962.
The possible benefits of using ground power to accelerate the airplane on a launch ramp are quantified. A passenger-carrying hypersonic airplane leaving its loading ramp carries fuel for acceleration, cruise and landing. For example, a 230-passenger plane starting a Mach 5 trans-Pacific flight will be loaded with 80 metric tons of liquid hydrogen, up to 40% of which is burned in generating kinetic energy. Catapulting this airplane to cruise speed with ground power would reduce weight and liquid-hydrogen volume. However, there are limits. A ramp for launching a 150-metric-ton vehicle to Mach 5 with 4 g acceleration would be 38 km long and require up to 10 GW of power. In the final second, 2.8 MWh of energy is consumed along 1720 m of ramp. Possible scenarios and acceleration mechanisms are evaluated 相似文献
963.
Yamamoto H. Sugita K. Kanzaki N. Johja I. Hiraki Y. Kuwahara M. 《Aerospace and Electronic Systems Magazine, IEEE》1990,5(6):31-35
A method for enhancing the boundaries of magnetic resonance images (MRIs) using a V-filter (a spatial nonlinear filter) is presented. By iterated V-filtering the signal-to-noise ratio of the MRI can be increased while preserving edge sharpness. A simulation experiment was carried out to evaluate the filter, using clinical brain images. The boundaries of the brain tumor and edematous region were precisely extracted by the region segmentation techniques 相似文献
964.
R Hilbig R H Anken G Sonntag S Hohne J Henneberg N Kretschmer H Rahmann 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2002,30(4):835-841
Humans taking part in parabolic aircraft flights (PAFs) may suffer from space motion sickness-phenomena (SMS, a kinetosis). It has been argued that SMS during PAFs might not be based on microgravity alone but rather on changing accelerations from 0 g to 2 g. We test here the hypothesis that PAF-induced kinetosis is based on asymmetric statoliths (i.e., differently weighed statoliths on the right and the left side of the head), with asymmetric inputs to the brain being disclosed at microgravity. Since fish frequently reveal kinetotic behaviour during PAFs (especially so-called spinning movements and looping responses), we investigated (1) whether or not kinetotically swimming fish at microgravity would have a pronounced inner ear otolith asymmetry and (2) whether or not slow translational and continuously changing linear (vertical) acceleration on ground induced kinetosis. These latter accelerations were applied using a specially developed parabel-animal-container (PAC) to stimulate the cupular organs. The results suggest that the fish tested on ground can counter changing accelerations successfully without revealing kinetotic swimming patterns. Kinetosis could only be induced by PAFs. This finding suggests that it is indeed microgravity rather than changing accelerations, which induces kinetosis. Moreover, we demonstrate that fish swimming kinetotically during PAFs correlates with a higher otolith asymmetry in comparison to normally behaving animals in PAFs. 相似文献
965.
R H Anken K Werner H Rahmann 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2002,30(4):849-853
Larval cichlid fish (Oreochromis mossambicus) siblings were subjected to 3 g hypergravity (hg) and total darkness for 21 days during development and subsequently processed for conventional histology. Further siblings reared at 1 g and alternating light/dark (12h:12h) conditions served as controls. Cell number counts of the visual Nucleus isthmi (Ni) versus the vestibular Nucleus magnocellularis (Nm) revealed that in experimental animals total cell number was decreased in the Ni, possibly due to retarded growth as a result of the lack of visual input whereas no effect was observed in the Nm. Calculating the percentual asymmetry in cell number (i.e., right vs. the left side of the brain), no effects of hg/darkness were seen in the Ni, whereas asymmetry was slightly increased in the Nm. Since the asymmetry of inner ear otoliths is decreased under hg, this finding may indicate efferent vestibular action of the CNS on the level of the Nm by means of a feedback mechanism. 相似文献
966.
Ts Dachev B Tomov Yu Matviichuk Pl Dimitrov J Lemaire Gh Gregoire M Cyamukungu H Schmitz K Fujitaka Y Uchihori H Kitamura G Reitz R Beaujean V Petrov V Shurshakov V Benghin F Spurny 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2002,30(4):917-925
The Mobile Radiation Exposure Control System's (Liulin-4 type) main purpose is to monitor simultaneously the doses and fluxes at 4 independent places. It can also be used for personnel dosimetry. The system consists of 4 battery-operated 256-channel dosimeters-spectrometers. We describe results obtained during the calibrations of the spectrometers at the Cyclotron facilities of the University of Louvain, Belgium and of the National Institute of Radiological Sciences-STA, Chiba, Japan with protons of energies up to 70 MeV. The angular sensitivities of the devices are studied and compared with Monte-Carlo predictions. We also present the results obtained at the HIMAC accelerator with 500 MeV/u Fe ions and at the CERN high energy radiation reference fields. Records made during airplane flights are shown and compared with the predictions of the CARI-6 model. 相似文献
967.
A low-dimensional test problem with a known solution is used to verify various computer implementations of F.C. Schweppe's likelihood detector (1965). In this case a closed-form solution is provided for a Schweppe likelihood detector in terms of an intermediate Kalman filter, as utilized in its implementation, for detecting the presence of a two-state signal model in Gaussian white noise. The associated error probabilities are also evaluated following a procedure that utilizes optimized Chernoff-like bounds for a tight approximation. A methodology is demonstrated for appropriately setting the decision threshold for this example as a tradeoff against allowable observation time. By using this or similar examples, certain qualitative and quantitative aspects of the software implementation can be checked for conformance to anticipated behavior as an intermediate benchmark, prior to modular replacement of the various high-order matrices appropriate to the particular application 相似文献
968.
H Rahmann R H Anken 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2002,30(4):697-710
During the entire evolution of life on Earth, the development of all organisms took place under constant gravity conditions, against which they achieved specific countermeasures for compensation and adaptation. On this background, it is still an open question to which extent altered gravity such as hypergravity (centrifuge) or microgravity (spaceflight) affects the normal individual development, either on the systemic level of the whole organism or on the level of individual organs or even single cells. The present review provides information on these questions, comprising gravistimulated effects on invertebrates and vertebrates (with the exception of mammals, since respective biomedically oriented reviews abound), focusing on developing fish as model systems, with special emphasis on the effect of altered gravity on the developing brain and vestibular system, comprising investigations on behaviour and plastic reactivities of the brain and inner ear. Clues and insights into the possible basic causes of space motion sickness-phenomena (SMS; a kinetosis) are provided as well as perspectives in regard to future work to be done including studies on the ISS concerning the analysis of gravistimulated effects on developmental issues (imprinting phase for graviperception?). 相似文献
969.
H. Tanabe S. Isobe H. Akiyama Y. Koma T. Okabe J. Nishimura T. Maihara K. Mizutani J. Soegijo T.E. Hariadi S. Indrawan S. Slamet P. Anondo T. Tatang S. Agus W. Mulyana V.R. Suroto 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1985,5(1):69-72
A balloon observation of the total solar eclipse on 11 June 1983 was carried out as a cooperative work between Japanese and Indonesian teams. The observation was a photo-polarimetry of the F corona in both visual and near-infrared regions.The balloon of 15,000-m3 with a payload of 150-kg was launched at 7h13m on 11 June from Watukosek Balloon Base in East Java. Observation at an altitude of 30.5-km was successfully made during the totality (11h28~32m) at a position of ~40-km east-south-east from Jogjakarta.As a preliminary result, an excess in infrared brightness has been found near the position of 3.8R⊙ west from the sun, which may be due to thermal emission from a high-temperature dust cloud located around the sun. 相似文献
970.
H. Okuda 《Space Science Reviews》1985,42(1-2):41-52
Several numerical plasma simulation models using particles are described which are appropriate for low frequency electrostatic
and electromagnetic microinstabilities in a strong magnetic field. The model makes use of the guiding center drift approximations
for the electrons while the ions are represented either as particles obeying the equation of motion with the full Lorentz
force or a fluid which includes finite-Larmor-radius effects. These models are particularly useful for studying low frequency
microinstabilities (ω ≲ ωpi, Ωi) propagating nearly perpendicular to an external magnetic field (k⊥ ≫ k∥). 相似文献