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931.
As aerospace vehicles travel in a hellish environment, the reliability of the measuring and controlling systems has played a critical role in the credibility of a whole airborne system. Embryo-electronic system is a bionic hardware capable of self-diag- nosing and self-healing. This article presents a new approach to design embryo-electronic systems and introduces their bionic principles, system structures and fault-tolerant mechanism. As the current methods cannot meet the requirements for large-scale embryo-electronic systems, this article advances a new shift-register-based configuration memory of embryonic system to solve the problem by using the inter-cell communication to reduce the gene storage capacity of a single cell. The article designs an overall structure of the shift-register-based configuration memories of the embryonic system and connects them into a chain structure. The article also designs an inner circuit of the cell, the control of shift-register-based configuration memory and the way of runtime dynamic configuration. The simulation of field programmable gate array (FPGA) evidences the realizability of the proposed design. Compared to the SRAM-based one, this memory can save 90% of the area when constructing embryonic systems larger than 128 × 128 under the same condition.  相似文献   
932.
Plant lighting is a critical issue for cost effectiveness of bioregenerative systems. A plant lighting system using sunlight has been investigated and compared to systems using electrical lighting. Co-generation of electricity and use of in situ resource utilization (ISRU) were also considered. The fixed part of equivalent system mass was found to be reduced by factors of from 3.1 to 3.9, according to the mission assumptions. The time-dependent part of equivalent system mass was reduced by a smaller value, of about 1.05. Cost effectiveness of bioregeneration has been compared to the cost of shipping food. Break-even times for different Lunar and Mars missions were generally in the order of 2–10 years, and were quite sensitive to the assumptions. There is significant scope for future refinement of these values, and work is ongoing.  相似文献   
933.
The James Webb Space Telescope   总被引:4,自引:0,他引:4  
The James Webb Space Telescope (JWST) is a large (6.6 m), cold (<50 K), infrared (IR)-optimized space observatory that will be launched early in the next decade into orbit around the second Earth–Sun Lagrange point. The observatory will have four instruments: a near-IR camera, a near-IR multiobject spectrograph, and a tunable filter imager will cover the wavelength range, 0.6 < ; < 5.0 μ m, while the mid-IR instrument will do both imaging and spectroscopy from 5.0 < ; < 29 μ m.The JWST science goals are divided into four themes. The key objective of The End of the Dark Ages: First Light and Reionization theme is to identify the first luminous sources to form and to determine the ionization history of the early universe. The key objective of The Assembly of Galaxies theme is to determine how galaxies and the dark matter, gas, stars, metals, morphological structures, and active nuclei within them evolved from the epoch of reionization to the present day. The key objective of The Birth of Stars and Protoplanetary Systems theme is to unravel the birth and early evolution of stars, from infall on to dust-enshrouded protostars to the genesis of planetary systems. The key objective of the Planetary Systems and the Origins of Life theme is to determine the physical and chemical properties of planetary systems including our own, and investigate the potential for the origins of life in those systems. Within these themes and objectives, we have derived representative astronomical observations.To enable these observations, JWST consists of a telescope, an instrument package, a spacecraft, and a sunshield. The telescope consists of 18 beryllium segments, some of which are deployed. The segments will be brought into optical alignment on-orbit through a process of periodic wavefront sensing and control. The instrument package contains the four science instruments and a fine guidance sensor. The spacecraft provides pointing, orbit maintenance, and communications. The sunshield provides passive thermal control. The JWST operations plan is based on that used for previous space observatories, and the majority of JWST observing time will be allocated to the international astronomical community through annual peer-reviewed proposal opportunities.  相似文献   
934.
935.
Robustness of transportation networks is one of the major challenges of the 21st century. This paper investigates the resilience of global air transportation from a complex network point of view, with focus on attacking strategies in the airport network, i.e., to remove airports from the sys-tem and see what could affect the air traffic system from a passenger's perspective. Specifically, we identify commonalities and differences between several robustness measures and attacking strate-gies, proposing a novel notion of functional robustness: unaffected passengers with rerouting. We apply twelve attacking strategies to the worldwide airport network with three weights, and eval-uate three robustness measures. We find that degree and Bonacich based attacks harm passenger weighted network most. Our evaluation is geared toward a unified view on air transportation net-work attack and serves as a foundation on how to develop effective mitigation strategies.  相似文献   
936.
Vibrations represent one of the most important topics of the engineering design relevant to flexible structures. The importance of this problem increases when a very flexible system is considered, and this is often the case of space structures. In order to identify the modal characteristics, in terms of natural frequencies and relevant modal parameters, ground tests are performed. However, these parameters could vary due to the operative conditions of the system. In order to continuously monitor the modal characteristics during the satellite lifetime, an operational modal analysis is mandatory. This kind of analysis is usually performed by using classical accelerometers or strain gauges and by properly analyzing the acquired output. In this paper a different approach for the vibrations data acquisition will be performed via image-based technique. In order to simulate a flexible satellite, a free flying platform is used; the problem is furthermore complicated by the fact that the overall system, constituted by a highly rigid bus and very flexible panels, must necessarily be modeled as a multibody system. In the experimental campaign, the camera, placed on the bus, will be used to identify the eigenfrequencies of the vibrating structure; in this case aluminum thin plates simulate very flexible solar panels. The structure is excited by a hammer or studied during a fast attitude maneuver. The results of the experimental activity will be investigated and compared with respect to the numerical simulation obtained via a FEM-multibody software and the relevant results will be proposed and discussed.  相似文献   
937.
为满足空-空导弹火控系统解算攻击区的实时性要求,提出一种新的快速仿真方案。在六自由度弹道模型基础上进行合理有效地简化,基于瞬时平衡假设建立了导弹质心运动方程。采用时域离散相似法将导弹质心运动方程进行了离散化处理。通过传统模型、变步长积分模型、气动系数拟合模型和离散模型的仿真结果比较,表明气动系数拟合模型虽然运算速度最快但仿真精度最差,而离散模型不仅能大幅提高仿真速度,还能保证较高的计算精度,从而为空-空导弹攻击区快速解算提供了一种合理可行的方案。  相似文献   
938.
We have shown in several recent publications that it is necessary to group the meteorological data according to the phase of the Quasi-Biennial Oscillation (QBO) throughout the year, in order to find a clear signal of the 11-year sunspot cycle (SSC). This work is summarized here. It is the purpose of this paper (1) to update earlier results of the solar cycle – QBO relationship for the northern winter, (2) to stress the interaction between the hemispheres and (3) to summarize the influence of the QBO on the solar variability signal, as well as the influence of the solar variability signal on the QBO throughout the year. For this, the constructed annual mean of the solar cycle – QBO relationship is introduced.  相似文献   
939.
Temperature increases in plant reproductive organs such as anthers and stigmas could cause fertility impediments and thus produce sterile seeds under artificial lighting conditions without adequately controlled environments in closed plant growth facilities. There is a possibility such a situation could occur in Bioregenerative Life Support Systems under microgravity conditions in space because there will be little natural convective or thermal mixing. This study was conducted to determine the temperature of the plant reproductive organs as affected by illumination and air movement under normal gravitational forces on the earth and to make an estimation of the temperature increase in reproductive organs in closed plant growth facilities under microgravity in space. Thermal images of reproductive organs of rice and strawberry were captured using infrared thermography at air temperatures of 10–11 °C. Compared to the air temperature, temperatures of petals, stigmas and anthers of strawberry increased by 24, 22 and 14 °C, respectively, after 5 min of lighting at an irradiance of 160 W m−2 from incandescent lamps. Temperatures of reproductive organs and leaves of strawberry were significantly higher than those of rice. The temperatures of petals, stigmas, anthers and leaves of strawberry decreased by 13, 12, 13 and 14 °C, respectively, when the air velocity was increased from 0.1 to 1.0 ms−1. These results show that air movement is necessary to reduce the temperatures of plant reproductive organs in plant growth facilities.  相似文献   
940.
综合火力/飞行控制系统的一种自调整因子模糊控制   总被引:2,自引:1,他引:1  
研究了综合火力/飞行控制系统(IFFCS)模糊控制器因子的自调整问题。本文用降半凸函数和指数函数来描述量化因子及比例因子与误差e的关系,提出了自调整因子模糊控制的一种设计方法,并进行了计算机仿真验证。仿真结果表明,这一方法的控制效果是较满意的。  相似文献   
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