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991.
S. Roose Y. Stockman P. Rochus T. Kuhn M. Lang H. Baier S. Langlois G. Casarosa 《Acta Astronautica》2009,65(9-10):1317-1329
Structures for space applications very often suffer stringent mass constraints. Lightweight structures are developed for this purpose, through the use of deployable and/or inflatable beams, and thin-film membranes. Their inherent properties (low mass and small thickness) preclude the use of conventional measurement methods (accelerometers and displacement transducers for example) during on-ground testing. In this context, innovative non-contact measurement methods need to be investigated for these stretched membranes.The object of the present project is to review existing measurement systems capable of measuring characteristics of membrane space-structures such as: dot-projection videogrammetry (static measurements), stereo-correlation (dynamic and static measurements), fringe projection (wrinkles) and 3D laser scanning vibrometry (dynamic measurements).Therefore, minimum requirements were given for the study in order to have representative test articles covering a wide range of applications. We present test results obtained with the different methods on our test articles. 相似文献
992.
Morphological and molecular changes of maize plants after seeds been flown on recoverablf satellite 总被引:1,自引:0,他引:1
M Mei Y Qiu Y Sun R Huang J Yao Q Zhang M Hong J Ye 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1998,22(12):1691-1697
Dry seeds of Zea mays, heterozygous for Lw1/lw1 alleles, sandwiched between nuclear track detectors aboard Chinese satellite for 15 days, were recovered and mutations in morphological characters on plants developed from these seeds, as well as their selected progenies, were investigated. The dosimetric results indicated that 85% of the seeds received at least 1 hit with Z≥20. About 10% of plants developed from flown seeds and 40% of observed selfed lines from the first generation plants showed some morphological changes, such as yellow stripes displayed on leaves, dwarf, anomogensis of floral organs and yellow-green seedlings, when compared with those from ground control. Using yellow stripes on leaves as the main endpoint for evaluating mutation induced in space environment, the frequency of stripe occurrence was 4.6% in the first generation plants, comparable with the results obtained from Long Duration Exposure Facility (LDEF) mission (Mei et al., 1994), but much lower than those from ground based 60 Co-gamma treatment at a dose of 100 Gy, which reached 35.5% in the selfed lines of the second generation. One hundred and ten random primers were screened in RAPD analysis to detect the variation on genomic DNA of plants with stripes on leaves. Of these primers, 10.9% were able to generate polymorphic bands between mutated plants and control, also, common band patterns in several progenies with the same mutation phenotype were observed. These results demonstrated that space radiation environment could induce inheritable mutagenic effects on plant seeds, and verified the change in genetic material in the mutants. Further study will be needed for a better understand of the nature and mechanism of this induction of mutation. 相似文献
993.
An approach to detection and diagnosis of multiple failures in a dynamic system is proposed. It is based on the interacting multiple-model (IMM) estimation algorithm, which is one of the most cost-effective adaptive estimation techniques for systems involving structural as well as parametric changes. The proposed approach provides an integrated framework for fault detection, diagnosis, and state estimation. It is able to detect and isolate multiple faults substantially more quickly and more reliably than many existing approaches. Its superiority is illustrated in two aircraft examples for single and double faults of both sensors and actuators, in the forms of “total”, “partial”, and simultaneous failures. Both deterministic and random fault scenarios are designed and used for testing and comparing the performance fairly. Some new performance indices are presented. The robustness of the proposed approach to the design of model transition probabilities, fault modeling errors, and the uncertainties of noise statistics are also evaluated 相似文献
994.
Muraviev V.V. Rubanic A.V. Vorobiev Y.P. Choban Y.M. Fedosuk P.V. 《Aerospace and Electronic Systems Magazine, IEEE》1999,14(7):23-25
This article is about the development of a 3 mm wave range pulse radar designed for short-range navigation and collision avoidance. The basic technical specifications of the radar are given, and the functional scheme and construction features are described 相似文献
995.
G.M. Mason R. Von Steiger R.B. Decker M.I. Desai J.R. Dwyer L.A. Fisk G. Gloeckler J.T. Gosling M. Hilchenbach R. Kallenbach E. Keppler B. Klecker H. Kunow G. Mann I.G. Richardson T.R. Sanderson G.M. Simnett Y.-M. Wang R.F. Wimmer-Schweingruber M. Fränz J.E. Mazur 《Space Science Reviews》1999,89(1-2):327-367
This report emphasizes new observational aspects of CIR ions revealed by advanced instruments launched on the Ulysses, WIND,
SOHO, and ACE spacecraft, and by the unique vantage point of Ulysses which carried out the first survey of Corotating Interaction
Region (CIR) properties over a very wide range of heliolatitudes. With this more complete observational picture established,
this review is the basis to consider the status of theoretical models on origin, injection, and acceleration of CIR particles
reported by Scholer, Mann et al. (1999) in this volume.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
996.
Y. Nakamura A. Aoki 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008,41(5):777-782
Effects of sub-atmospheric ambient pressure and oxygen content on irradiated ignition characteristics of solid combustibles were examined experimentally in order to elucidate the flammability and chance of fire in depressurized systems and give ideas for the fire safety and fire fighting strategies for such environments. Thin cellulosic paper was used as the solid combustible since cellulose is one of major organic compounds and flammables in the nature. Applied atmospheres consisted of inert gases (either CO2 or N2) and oxygen at various mixture ratios. Total ambient pressure (P) was varied from 101 kPa (standard atmospheric pressure, P0) to 20 kPa. Ignition was initiated by external thermal radiation with CO2 laser (10 W total; 21.3 W/cm2 of the corresponding peak flux) onto the solid surface. Thermal degradation of the solid produced combustible gaseous products (e.g. CO, H2, or other low weight of HCs) and these products mixed with ambient oxygen to form the combustible mixture over the solid. Heat transfer from the irradiated surface into the mixture accelerated the exothermic reaction in the gas phase and finally thermal runaway (ignition) was achieved. A digital video camera was used to analyze the ignition characteristics. Flammability maps in partial pressure of oxygen (ppO2) and normalized ambient pressure (P/P0) plane were made to reveal the fire hazard in depressurized environments. Results showed that a wider flammable range was obtained in sub-atmospherics conditions. In middle pressure range (101–40 kPa), the required ppO2 for ignition decreased almost linearly as the total pressure decreased, indicating that higher fire risk is expected. In lower pressure range (<40 kPa), the required partial pressure of oxygen increased dramatically, then ignition was eventually not achieved at pressures less than 20 kPa under the conditions studied here. The findings suggest that it might be difficult to satisfy safety in space agriculture since it has been reported that higher oxygen concentrations are preferable for plant growth in depressurized environments. Our results imply that there is an optimum pressure level to achieve less fire chance with acceptable plant growth. An increase of the flammable range in middle pressure level might be explained by following two effects: one is a physical effect, such as a weak convective thermal removal from ignitable domain (near the hot surface) to the ambient of atmosphere, and the other is chemical effect which causes so-called “explosion peninsula” as a result of depleting radical consumption due to third-body recombination reaction. Further studies are necessary to determine the controlling factor on the observed flammable trend in depressurized conditions. 相似文献
997.
Abramovich Y.I. Spencer N.K. Anderson S.J. Gorokhov A.Y. 《IEEE transactions on aerospace and electronic systems》1998,34(4):1271-1292
This paper considers the use of spatio-temporal adaptive array processing in over-the-horizon radar (OTHR) and airborne radar applications in order to remove nonstationary multipath interference, known as “hot clutter”. Since the spatio-temporal properties of hot clutter cannot be assumed constant over the coherent processing interval (CPI), conventional adaptive techniques fail to provide effective hot-clutter mitigation without simultaneously degrading the properties of the backscattered radar signals, known as “cold clutter”. The approach presented incorporates multiple “stochastic” (data-dependent) constraints to achieve effective hot-clutter suppression, while maintaining distortionless output cold-clutter post-processing stationarity 相似文献
998.
B V Lambert ChANusgens 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1998,21(8-9):1081-1091
One main function of the connective tissues is to provide cells with a mechanically resistant attachment support required for survival, division and differentiation. All cells contain membrane-anchored attachment proteins able to recognize specific chemical motifs in the extracellular macromolecules forming the supporting scaffold, made of various types of collagen, adhesive glycoproteins, elastin, proteoglycans, etc... These cell-matrix interactions are mainly mediated by receptors of the integrins family, heterodimeric molecules made of an extracellular domain connected through a transmembrane sequence to an intracytoplasmic tail. Upon recognition of the extracellular ligand, the clustering and activation of the integrins result in the recruitment of a complex of proteins and formation of the focal adhesion plaque, containing both cytoskeletal and catalytic signaling molecules. Activation results in polymerization of actin and formation of stress fibers. These structures establish a physical link between the extracellular matrix components and the cytoskeleton through the integrins providing a continuous path acting as a mechanotransducer. This connection is used by the cells to perform their mechanical functions as adhesion, migration and traction. In vitro experimental models using fibroblasts in a collagen gel demonstrate that cells are in mechanical equilibrium with their support which regulates their replicative and biosynthetic phenotype. The present review discusses the molecular structures operating in the transmission of the mechanical messages from the support to the connective tissue cells, and their effect on the cellular machinery. We present arguments for investigating these mechanisms in understanding the perception of reduced gravity and the resulting reaction leading to microgravity induced pathologies. 相似文献
999.
Y. Suzuki 《Space Science Reviews》1998,85(1-2):91-104
The current status of solar neutrino experiments is reviewed. All the experimental measurements show deficits of solar neutrinos.
Non monotonic suppression indicates that the problem may naturally be explained by neutrino oscillations, but not by modifying
solar models. A new experiment shows very promising results. We hope that a definite answer to the question of whether solar
neutrinos are oscillating will be obtained in the very near future.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
1000.
T Hoson S Kamisaka M Yamashita Y Masuda 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1998,21(8-9):1229-1238
On a three-dimensional (3-D) clinostat, various plant organs developed statocytes capable of responding to the gravity vector. The graviresponse of primary roots of garden cress and maize grown on the clinostat was the same as the control roots, whereas that of maize coleoptiles was reduced. When maize seedlings were grown in the presence of 10(-4) M gibberellic acid and kinetin, the graviresponse of both roots and shoots was suppressed. The corresponding suppression of amyloplast development was observed in the clinostatted and the hormone-treated seedlings. Maize roots and shoots showed spontaneous curvatures in different portions on the 3-D clinostat. The hormone treatment did not significantly influence such an automorphic curvature. When the root cap was removed, maize roots did not curve gravitropically. However, the removal suppressed the automorphic curvatures only slightly. On the other hand, the removal of coleoptile tip did not influence its graviresponse, whereas the spontaneous curvature of decapitated coleoptiles on the clinostat was strongly suppressed. Also, cytochalasin B differently affected the gravitropic and the automorphic curvatures of maize roots and shoots. From these results it is concluded that the graviperception and the early processes of signal transmission are unnecessary for automorphoses under simulated microgravity conditions. Moreover, the results support the view that the amyloplasts act as statoliths probably via an interaction with microfilaments. 相似文献