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排序方式: 共有112条查询结果,搜索用时 46 毫秒
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Heilbronn L Frankel K Holabird K Zeitlin C McMahan MA Rathbun W Cronqvist M Gong W Madey R Htun M Elaasar M Anderson BD Baldwin AR Jiang J Keane D Scott A Shao Y Watson JW Zhang WM Galonsky A Ronningen R Zecher P Kruse J Wang J Cary R 《Acta Astronautica》1998,42(1-8):363-373
In order to help assess the risk to astronauts due to the long-term exposure to the natural radiation environment in space, an understanding of how the primary radiation field is changed when passing through shielding and tissue materials must be obtained. One important aspect of the change in the primary radiation field after passing through shielding materials is the production of secondary particles from the breakup of the primary. Neutrons are an important component of the secondary particle field due to their relatively high biological weighting factors, and due to their relative abundance, especially behind thick shielding scenarios. Because of the complexity of the problem, the estimation of the risk from exposure to the secondary neutron field must be handled using calculational techniques. However, those calculations will need an extensive set of neutron cross section and thicktarget neutron yield data in order to make an accurate assessment of the risk. In this paper we briefly survey the existing neutron-production data sets that are applicable to the space radiation transport problem, and we point out how neutron production from protons is different than neutron production from heavy ions. We also make comparisons of one the heavy-ion data sets with Boltzmann-Uehling-Uhlenbeck (BUU) calculations. 相似文献
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Morphological, contractile properties and myosin heavy chain (MHC) composition of rat soleus muscles were studied after 2 weeks of unloading (HS) and after 2 weeks of HS associated with selective deafferentation (HS + DEAF) at the level L4 and L5. The same significant reductions in muscle mass and tetanic tension were found after HS and HS + DEAF. However, the transformation of the slow-twitch soleus muscle towards a faster type characterized by a decrease in twitch time parameters and an increase in fast-twitch type MHC isoforms in HS did not appear in HS + DEAF conditions. Our results also showed that a pattern similar to firing rate of motoneurones innervating slow-twitch muscles inhibited the slow to fast fiber changes observed during HS. Nevertheless, neither the loss of mass or force output in the HS muscles were prevented by electrostimulation. Immobilization in a stretched position during HS maintained the muscle wet weight, mechanical and electrophoretical characteristics close to control values. We concluded that the decrease in mechanical strains imposed on the muscle during unloading was the main factor for the development of atrophy, while the kinetic changes might be predominantly modulated by the nervous command. These basic data suggested that some experimental conditions such as electrostimulation or stretching, could participate in countermeasure programmes. 相似文献
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At the 40th IAF Congress in Malaga, a nutrition system for a lunar base CELSS was presented. A lunar base with a total of eight crew members was envisaged. In this paper, four species of plants--rice, soybean, lettuce and strawberry--were introduced to the system. These plants were sufficient to satisfy fundamental nutritional needs of the crew members. The supply of nutrition from plants and the human nutritional requirements could almost be balanced. Our study revealed that the necessary plant cultivation area per crew member would be nearly 40 m3 in the lunar base. The sources of nutrition considered in the study were energy, sugar, fat, amino acids, inorganic salt and vitamins; however, calcium, vitamin B2, vitamin A and sodium were found to be lacking. Therefore, a subsystem to supply these elements is of considerable value. In this paper, we report on a study for breeding snails and utilizing meat as food. Nutrients supplied from snails are shown to compensate for the above mentioned lacking elements. We evaluate the snail breeder and the associated food supply system as a subsystem of closed ecological life support system. 相似文献
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基于CFD技术的鼻腔输药的流动特性研究 总被引:1,自引:0,他引:1
鼻腔输药作为一种新颖的输药方式,具有方便可靠的特点,不仅可以适用于局部而且适用于全身用药,已经受到广泛的重视。但由于人类的呼吸道复杂的立体结构使得鼻腔输药成为生物医药研究的一个长期的挑战。利用CFD(计算流体动力学,Computational Fluid Dynamics)技术对鼻腔输药的流动特性进行研究,对一个基于真实的人类鼻腔解剖的3D模型的输药的流动过程进行了分析,着重研究了不同的药物颗粒的流动和沉淀特性。利用CFD的商用软件FLUENT在层流情况下对不同的密度、直径和流动速率的药物颗粒在鼻腔中流动进行了数值模拟,并对计算结果进行了比较分析。CFD研究的结果为鼻腔输药这种新颖的药物输送方式的优化设计提供了依据。 相似文献
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四川省力学学会、西南结构力学研究所、四川省振动工程学会(筹)于1987年11月4日至7日在绵阳市联合召开了“四川省振动工程学术交流座谈会”。出席代表86人,他们来自中央部属(在川)、省、市20多单位。代表都是在力学、数学、机械、航空、核工程、电子、冶金、化工、电力、建筑、石油、地震等各领域从事振动工程、研究、教学、应用的 相似文献
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刘杨 濮祖荫 谢伦 郭瑞龙 王晓钢 肖池阶 史全岐 DUNLOP M BOGDANOVA Y V MOORE T E RUSSELL C T LINDQVIST P A TORBERT R B POLLOCK C ZHAO Cong 《空间科学学报》2018,38(2):147-168
利用MMS观测数据,对磁层顶通量绳内离子惯性尺度(di)的结构进行分析研究.结果发现,许多不同尺度(约1di至数十di)的通量绳内都存在具有di尺度的电流 j m,其方向在磁层顶局地坐标系的-M方向,即与磁层顶查普曼-费拉罗电流同向,由电子在+M方向的运动( v em)携带.这些电流结构具有以下特征:磁鞘与磁层成分混合,磁场为开放形态;离子去磁化,电子与磁场冻结;N方向(即垂直于磁层顶电流片方向)的电场 E n显著增大,幅度达到约20mV·m-1,并伴有明显的尖峰状起伏,该增强和尖峰状起伏的电场对应于霍尔电场.分析表明,电流、电子与离子运动的偏离以及霍尔电场之间遵从广义欧姆定律,三者密切关联.进一步对磁层顶磁重联的探测数据进行分析发现,在很多重联区内也存在与通量绳内相似的结构,其尺度约为di量级,其中霍尔电场 E N、电流 j M和电子速度 v eM均与通量绳内对应物理量的方向相同且幅度相近.基于上述观测事实,采用经典FTE通量绳模型,对通量绳内电流、电子运动和霍尔电场的起源进行了初步探讨,认为其来源于磁层顶无碰撞磁重联区内的相应结构,并且后者在离子尺度通量绳的形成过程中起到重要作用. 相似文献
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分析了2004年3月13日12:15到12:25UT期间TC-1和Cluster卫星簇的磁通门磁力计(FGM)和电子/电流试验仪(PEACE)的联合观测数据.在此期间,TC-1卫星位于日下点以南的磁层顶附近的磁鞘中,并在12:19UT左右观测到了一个典型的先正后负的磁鞘磁通量传输事件(FTE);而Cluster卫星簇位于北半球日侧高纬磁层项附近,并于12:23UT左右穿出磁层顶进入磁鞘,且在12:21 UT左右也观测到了一个典型的先正后负的磁层FTE.比较分析发现此两个FTE具有类似的磁场结构和等离子体特征,可能是同一个北向运动的FTE先后被TC-1和Cluster卫星观测到.利用Cluster 4颗卫星的多点同时观测数据,采用最小方向微分法和时空微分方法,推断Cluster卫星观测的这个FTE是尺度大小约为1.21Re的准二维结构,其运动方向为东北方向,与Cooling模型预测方向基本一致.利用Cooling模型的预测,推算了TC-1卫星在12:19UT观测的FTE的运动速度和尺度,进而得出随着通量管的极向运动,其速度和尺度均有所增加. 相似文献