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41.
本文讨论了不同测量条件对正电子素络合反应速度常数测定值的影响。实验结果表明,在稀溶液的条件下,使用我们特殊设计的盛装溶液的匣式容器能大大提高放射源的使用率并能完全避免放射性废水。 相似文献
42.
本文从各个方面介绍了目前网络上常见的、威胁网络安全的漏洞,指出了影响网络安全的主要因素,并提出了保护网络安全的一些基本措施,同时给出了一些可行的解决方案. 相似文献
43.
J A Guikema L DeBell A Paulsen B S Spooner P P Wong 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1994,14(8):173-176
The development of legume root nodules was studied as a model system for the examination of gravitational effects on plant root development. In order to examine whether rhizobial association with clover roots can be achieved in microgravity, experiments were performed aboard the KC-135 parabolic aircraft and aboard the sounding rocket mission Consort 3. Binding of rhizobia to roots and the initial stages of root nodule development successfully occurred in microgravity. Seedling germination experiments were performed in the sliding block device, the Materials Dispersion Apparatus, aboard STS-37. When significant hydration of the seeds was achieved, normal rates of germination and seedling development were observed. 相似文献
44.
45.
Diane Sonya Wong Ryan Chornock Alexei V. Filippenko 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2006,38(12):2813-2815
We present results of optical follow-up observations of candidate ultra-luminous X-ray sources (ULXs). Using Keck optical spectroscopy, 17 of the candidates from the Colbert and Ptak [Colbert, E.J.M., Ptak, A.F. A catalog of candidate intermediate-luminosity X-ray objects. ApJS 143, 25–45, 2002] catalog have been identified; this is one of the largest sets of optical identifications of such objects thus far. Fifteen are background active galactic nuclei (AGN); two are foreground stars in our Galaxy. These findings are consistent with background and foreground object expectations, as derived from log N–log S relations. Also, the results are briefly discussed in terms of the spiral-galaxy/ULX connection. 相似文献
46.
In seeking to understand the formation of the giant planets and the origin of their atmospheres, the heavy element abundance
in well-mixed atmosphere is key. However, clouds come in the way. Thus, composition and condensation are intimately intertwined
with the mystery of planetary formation and atmospheric origin. Clouds also provide important clues to dynamical processes
in the atmosphere. In this chapter we discuss the thermochemical processes that determine the composition, structure, and
characteristics of the Jovian clouds. We also discuss the significance of clouds in the big picture of the formation of giant
planets and their atmospheres. We recommend multiprobes at all four giant planets in order to break new ground. 相似文献
47.
C Chun C A Mitchell 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1997,20(10):1855-1860
A procedure for dynamic optimization of net photosynthetic rate (Pn) for crop production in Controlled Ecological Life-Support Systems (CELSS) was developed using leaf lettuce as a model crop. Canopy Pn was measured in real time and fed back for environmental control. Setpoints of photosynthetic photon flux (PPF) and CO2 concentration for each hour of the crop-growth cycle were decided by computer to reach a targeted Pn each day. Decision making was based on empirical mathematical models combined with rule sets developed from recent experimental data. Comparisons showed that dynamic control resulted in better yield per unit energy input to the growth system than did static control. With comparable productivity parameters and potential for significant energy savings, dynamic control strategies will contribute greatly to the sustainability of space-deployed CELSS. 相似文献
48.
This paper examines the planar dynamics of a wheel-and-spoke configured multi-spacecraft system, connected together by variable length tethers, near the second Sun–Earth Lagrangian point. The closed form solutions of the system under some simple tether length functions are determined and numerical results for the tether pitch librations under more complex tether length functions are obtained, along with the control effort required to maintain the desired tether librations. 相似文献
49.
Ch.-H. Chun W. Wuest 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1981,1(5):17-20
The correlation between oscillations of flow and temperature of the Marangoni convection in a cylindric floating zone are studied. Photographs of the oscillating flow patterns are taken by triggering with a thermocouple signal of the temperature oscillation to reveal the frequency and phase correlations. Whilst both frequencies coincide, phase shift between temperature and flow oscillations exists. 相似文献
50.
为研究水下超声速过膨胀燃气射流的流场特性,在压力水筒中开展了大扩张比锥形喷管的固体火箭发动机水下点火实验,并基于雷诺时均Navier-Stokes(RANS)方法和流体体积(VOF)模型进行数值求解,分析了过膨胀燃气射流与水介质的相互作用过程。研究表明:超声速过膨胀燃气建立射流通道后,射流核心区长度随喷管落压比的减少而减少;射流核心区剧烈振荡,表现为高频的膨胀和收缩,振荡频率随喷管落压比的减小而增加,范围为100~200 Hz;射流边界不断振荡,并伴随波系结构变化,当过膨胀程度较大时,激波进入喷管使其发生流动分离现象,流动分离点周期性往复移动;分离区内压力脉动没有显著的特征频率,主要集中在100~600 Hz的宽频带,锥形喷管水下流动分离的简易判据为喷管出口压力不低于环境背压的0.44倍。 相似文献