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991.
M Andre P Chagvardieff 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1999,24(3):265-269
During the past 10 years, the main part of CELSS studies has concerned the exploration of limits of plant productivity. Very high yields were obtained in continuous and high lighting, without reaching any limit. Concepts of mineral nutrition were renewed. CELSS activities now induce a development in the techniques of image processing applied to plants in order to follow the growth, to detect stresses or diseases or to pilot harvesting robots. Notable efforts concern the development of sensors, the study of trace contaminants and the micro-organisms monitoring. In parallel, several instruments for plant culture in closed Systems were developed. The advantages of closure are emphasised in comparison with open flow systems. The concept of Artificial Ecosystems developed for space research is more and more taken into account by the scientific community. It is considered as a new tool to study basic and applied problems related to ecology and not especially concerned with space research. 相似文献
992.
The 1999 Radar Conference banquet address, in which an attempt is made to predict future developments in radar, is presented 相似文献
993.
The Ultra Low Maintenance (ULM) battery technology and its historical performance validation programs are reviewed. Recent military flight test programs are discussed and the growing lists of both military and commercial aircraft flying ULM batteries are presented 相似文献
994.
In this paper, the results of calculating the processes of two fuel mixture combustion in different proportions are presented.
The values of temperature, thermal capacity, specific gas constant and isentropic expansion ratio of combustion products are
given. Also shown is the distinction of thermodynamic properties from the additivity law. 相似文献
995.
996.
A finite element statement of solving problems on stability of reinforced elliptic cylindrical shells taking into account
momentness and nonlinearity of their subcritical stress strain state is presented. The explicit expressions for displacements
of noncircular cylindrical shell elements as rigid bodies are determined by integrating the equations obtained by equating
the components of linear strains to zero. These expressions were used to construct the form functions for an efficient quadrilateral
finite element of natural curvature. An efficient numerical algorithm of nonlinear deformation and stability of shells was
developed. The stability of reinforced elliptic cylindrical shells under combined loading by bending moment, transverse boundary
force and internal pressure is analyzed. We also examine how the critical loads are affected by the strain nonlinearity and
ellipticity of shell deformation at the subcritical stage. 相似文献
997.
In this paper, a process of flanging to create thin-walled axisymmetrical shells with the shape of truncated cone is analyzed. Also presented are some dependences that make it possible to determine the relative depth of a formed piece at the given piece-blank thickness ratio. 相似文献
998.
Current projects of manned missions to Mars are aimed to their realization in the second-third decades of this century. The purpose of this paper is to determine and review the main biomedical problems, that require a first and foremost decision for safety support of extravehicular activity (EVA) carried out by crewmembers of the Mars expedition. To a number of such problems the authors of the paper attribute a creation of adequate EVA equipment intended, first, for assembly of interplanetary spacecraft on the Earth orbit, performance of maintenance operations and scientific researches on the external surface of spacecraft during interplanetary flight and, secondly, for work on the Mars surface. New generation of space suits with low weight, high mobility and acceptable risk of decompression sickness must be as a central component of EVA equipment. The program for preparation to a Mars expedition also has to include special investigations in order to design the means and methods for a reliable protection of crew against space radiation, to elaborate the approach to medical monitoring and primary medical care during autonomous space mission, to maintain good health condition of crewmembers during EVA under the Mars gravity (0.38 g) after super long-term flight in weightlessness. 相似文献
999.
温度对液体中超声速度的影响 总被引:4,自引:0,他引:4
本文导出了超声波速度同液体压缩系数及密度关系,研究了压缩系数及密度与温度的关系,进而研究了温度对声速及声时的影响,用实验测量了不同的液体成份下的声时同温度的关系,从而提出了进行液体成份分析所必需的参量,对用超声波分析液体成份提供了理论依据,对提高产品质量及实现工业在线检测有一定的实用价值。 相似文献
1000.
The problem of bearings-only target localization is to estimate the location of a fixed target from a sequence of noisy bearing measurements. Although, in theory, this process is observable even without an observer maneuver, estimation performance (i.e., accuracy, stability and convergence rate) can be greatly enhanced by properly exploiting observer motion to increase observability. This work addresses the optimization of observer trajectories for bearings-only fixed-target localization. The approach presented herein is based on maximizing the determinant of the Fisher information matrix (FIM), subject to state constraints imposed on the observer trajectory (e.g., by the target defense system). Direct optimal control numerical schemes, including the recently introduced differential inclusion (DI) method, are used to solve the resulting optimal control problem. Computer simulations, utilizing the familiar Stansfield and maximum likelihood (ML) estimators, demonstrate the enhancement to target position estimability using the optimal observer trajectories 相似文献