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1.
J Sch?nleber R H Anken 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2004,33(8):1416-1420
Previous investigations revealed that the growth of fish inner ear otoliths depends on the amplitude and the direction of gravity, thus suggesting the existence of a (negative) feedback mechanism. In the course of these experiments, it was shown that altered gravity both affected otolith size (and thus the provision of the proteinacious matrix) as well as the incorporation of calcium. It is hitherto unknown, as of whether sensory hair cells are involved either in the regulation of otolith growth or in the provision of otolithic material (such as protein or inorganic components) or even both. The ototoxic aminoglycoside gentamicin (GM) damages hair cells in many vertebrates (and is therefore used for the treatment of Meniere's disease in humans). The present study was thus designed to determine as of whether vestibular sensory cells are needed for otolith growth by applying GM in order to induce a (functionally relevant) loss of these cells. Developing cichlid fish Oreochromis mossambicus were therefore immersed in 120 mg/l GM for 10 or 21 days. At the beginning and at the end of the experimental periods, the fish were incubated in the calcium-tracer alizarin complexone (AC). After the experiment, otoliths were dissected and the area grown during GM-exposure (i.e., the area enclosed by the two AC labellings) was determined planimetrically. The results showed that incubating the animals in a GM-solution had no effect on otolith growth, but the development of otolith asymmetry was affected. Ultrastructural examinations of the sensory hair cells revealed that they had obviously not been affected by GM-treatment (no degenerative morphological features observed). Overall, the present results suggest that hair cells are not affected by GM concerning their possible role in (general) otolith growth, but that these cells indeed might have transitionally been impaired by GM resulting in a decreased capacity of regulating otolith symmetry. 相似文献
整流罩设计对基于分布式动力的翼身融合(BWB)飞机气动特性会产生显著影响。为了揭示在边界层吸入(BLI)效应下整流罩的设计参数对飞机气动特性的影响及其原因,采用计算流体力学(CFD)方法和Morris敏感度分析法对此布局飞机气动特性进行了详细研究,得到了整流罩主要设计参数对飞机气动特性影响的敏感度和耦合关系,并对典型设计参数下的流动特性进行分析。结果表明:对飞机气动特性影响较大的参数是整流罩特征截面2和3的最大厚度,这是因为其增大了当地截面的厚度和弯度,进而影响了整流罩表面的压力分布;在流量系数减小和进气边界弦向位置前移时,最大厚度增大会造成背风面发生局部分离;整流罩特征截面2和3的最大厚度对气动特性具有较强的耦合影响。 相似文献
3.
BLI效应下整流罩设计对翼型气动特性的影响 总被引:1,自引:0,他引:1
边界层吸入(BLI)效应对飞行器气动特性的影响比较显著,而整流罩的设计会进一步影响BLI效应下的翼型气动特性。为了揭示BLI效应下整流罩的主要设计参数对翼型气动特性的影响及其原因,本文采用计算流体力学(CFD)和Morris敏感度分析相结合的方法对该问题进行了详细研究,得到了整流罩主要设计参数对翼型气动特性的敏感度排序和耦合影响程度排序;对敏感度较高和耦合影响较大的参数进行了流动分析。结果表明:在巡航和起飞2种状态下,对气动系数影响相对较大的设计参数是整流罩最大厚度和进气边界弦向位置,整流罩最大厚度对翼型气动特性影响的主要原因是整流罩背风面会发生局部分离,且其还会改变阻力-流量系数曲线的趋势;整流罩最大厚度和进气边界弦向位置对翼型气动特性的耦合影响作用较强。 相似文献
4.
三维充液航天器的位置和姿态联合控制 《空间控制技术与应用》2017,43(3):15-20
考虑充液月球着陆器悬停避障阶段的控制问题,采用三维球摆作为液体晃动部分的等效模型.针对球摆与刚体耦合的三维动力学模型,给出动力学模型的矢量方程及各矢量在本体系的投影坐标,设计位置和姿态联合控制器.所设计的控制器可以稳定航天器刚体的位置和姿态,且只依赖刚体的位置和姿态,不依赖晃动角或者动力学方程,利于工程应用.利用LaSalle不变原理分析闭环系统的稳定性,给出期望姿态为竖直时系统渐近稳定的控制器参数选择依据.最后数值仿真验证控制方法的有效性. 相似文献
5.
A V Kondrachuk 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2002,30(4):745-750
This paper analyzes experimental data related to the reaction of otolith afferents in response to acceleration (Fernandez and Goldberg, 1976). It considers the assumptions that were the basis of the interpretation of the stimulus-response characteristics of afferents proposed by Fernandez and Goldberg. Comparing these experimental data with the results of modeling the otolith structures of vertebrates indicates that some peculiarities of the neural responses may be explained by the spatial dependence of the material parameters of the otolithic membrane across its thickness and within the volume of the membrane corresponding to the terminal field. The importance of the spatial dependence of the material parameters of the otolithic membrane for otolith functioning is discussed. 相似文献
6.
M Beier R H Anken H Rahmann 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2004,33(8):1386-1389
It has been shown earlier that hypergravity slows down inner ear otolith growth in developing fish. Otolith growth in terms of mineralization mainly depends on the enzyme carboanhydrase (CA), which is responsible for the provision of the pH-value necessary for calcium carbonate deposition. Larval siblings of cichlid fish (Oreochromis mossambicus) were subjected to hypergravity (3 g, hg; 6 h) during development and separated into normally and kinetotically swimming individuals following the transfer to 1 g (i.e., stopping the centrifuge; kinetotically behaving fish performed spinning movements). Subsequently, CA was histochemically demonstrated in inner ear ionocytes (cells involved in the endolymphatic ion exchange) and enzyme reactivity was determined densitometrically. It was found that both the total macular CA-reactivity as well as the difference in reactivities between the left and the right maculae (asymmetry) were significantly lower (1) in experimental animals as compared to the 1 g controls and (2) in normally swimming hg-animals as compared to the kinetotically behaving hg-fish. The results are in complete agreement with earlier studies, according to which hypergravity induces a decrease of otolith growth and the otolithic calcium incorporation (visualized using the calcium-tracer alizarin complexone) of kinetotically swimming hg-fish was higher as compared to normally behaving hyper-g animals. The present study thus strongly supports the concept that a regulatory mechanism, which adjusts otolith size and asymmetry as well as otolithic calcium carbonate incorporation towards the gravity vector, acts via activation/deactivation of macular CA. 相似文献
7.
E Edelmann R H Anken H Rahmann 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2004,33(8):1390-1394
Previous investigations on neonate swordtail fish (Xiphophorus helleri) revealed that otolithic calcium incorporation (visualized using the calcium tracer alizarin complexone) and thus otolith growth had ceased after nerve transection, supporting a hypothesis according to which the gravity-dependent otolith growth is regulated neuronally. Subsequent investigations on larval cichlid fish (Oreochromis mossambicus) yielded contrasting results, repeatedly depending on the particular batch of cichlids investigated. Like most neonate swordtails, Type I cichlids revealed a stop of calcium incorporation after unilateral vestibular nerve transection. Their behaviour after transection was normal, and the otolithic calcium incorporation in controls of the same batch was symmetric. In Type II cichlids, however, vestibular nerve transection had no effect on otolithic calcium incorporation. They behaved kinetotically after transection (this kind of kinetosis was qualitatively similar to the swimming behaviour exhibited by larval cichlids during microgravity in the course of parabolic aircraft flights). The otolithic calcium incorporation in control animals was asymmetric. These results show that the effects of vestibular nerve transection as well as the efficacy of the mechanism, which regulates otolith growth/otolithic calcium incorporation, are--depending on the particular batch of animals--genetically predispositioned. In conclusion, the regulation of otolithic calcium incorporation is guided neuronally, in part via the vestibular nerve and, in part, via a further pathway, which remains to be addressed in the course of future investigations. 相似文献
8.
M L Wiederhold M Yamashita K Larsen M Asashima 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1994,14(8):327-330
Pre-mated adult female newts and fertilized eggs will be flown on the International Microgravity Laboratory-2 flight, in 1994. One objective of the flight will be to observe the influence of microgravity on the development of the gravity-sensing organs in the inner ear. These organs contain sensory hair cells covered by a layer of dense stones (otoconia). Gravity and linear acceleration exert forces on these masses, leading to excitation of the nerve fibers innervating the hair cells. If the production of the otoliths is regulated to reach an optimal weight, their development might be abnormal in microgravity. Ground-based control experiments are reported describing the developmental sequence in which both the otoliths and their associated sensory epithelium and the semicircular canals appear and develop. Three-dimensional reconstruction of serial sections through the otic vesicle of newt embryos at stages 31 through 58 demonstrate the first appearance, relative position and growth of the otoliths. Reports of experiments in which fertilized frog eggs were flown on a Russian Cosmos mission conclude that the utricular otolith is increased in volume, whereas the saccular otolith maintains normal size, suggesting that at least in the utricle, the weight of the otolith might be regulated. 相似文献
9.
对于在零重力环境下受到横向控制力和俯仰控制力矩作用的带球形贮液箱的航天器模型,研究了其在平面运动的动力学特性.将晃动液体等效为单摆模型,利用Lagrange方法建立了系统动力学方程并且将其转化为状态变量方程形式;应用微分几何原理,以单输入—单输出系统(SISO)为例,研究了系统的非线性动力学特性,并进一步针对目标跟踪问题设计了SISO系统基于线性化模型的控制策略.研究结果表明:对于液体晃动-航天器姿态耦合动力学系统采用极点配置间接自校正控制策略能够实现姿态角的镇定及跟踪. 相似文献
10.
C A Mitchell 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1992,12(1):219-225
Growth, development, and orientation of higher plants is altered by physical disturbances such as shaking, touching, or vibration. Plant growth responses to thigmic (contact rubbing) forces are almost always negative, whereas growth responses to periodic seismic (shaking) or vibric (vibrational) disturbances may be positive or negative, depending on intensity and duration of force, and prevailing environmental conditions. Seedlings are most sensitive to mechanical stress when grown in darkness or under the low-light conditions typically available in plant flight hardware. Brief exposure to physical perturbation causes immediate growth inhibition of dark-grown seedlings followed by gradual recovery of growth rate beginning 10-12 minutes later. For mild vibration, growth rate may overshoot that of undisturbed control plants within an hour of a stress episode, whereas for thigmic stress recovery may remain incomplete for 24 hours or longer. Lack of physical stimulation by gravity should make plants even more responsive to random physical perturbation. Threshold growth response of seedlings to vibrational parameters needs to be determined under real spaceflight conditions. 相似文献
11.
T型尾翼构型复杂,操纵面多,在动气动弹性的有限元建模和颤振特性设计中,需要修改的参数多,颤振分析复杂,设计人员面临很大的困难.通过在设计过程中引入优化方法,能够有效的解决这些问题.依据遗传算法和敏度优化算法的特点,针对固有振动和颤振优化设计的不同要求,将两种优化方法进行混合和递进应用,形成不同的优化设计方法.建立固有振动频率和颤振阻尼对结构参数的敏度公式,设计两种不同优化问题的数学模型.将优化方法应用于某T型尾翼的结构动力学优化设计,提高了设计速度,保证了设计精度,固有振动频率误差保证在3%以内.在保证质量最小的要求下,使颤振速度得到提高,并为实际结构的设计提供一定指导. 相似文献
12.
研究了充液航天器储箱内液体晃动与全星姿态运动的耦合动力学建模方法.分别基于单摆等效力学模型和质心面等效力学模型建立了全星姿态耦合动力学方程,并分别针对2个储箱串联布局、3个储箱并联布局的充液航天器在不同工况下的液体晃动问题进行了数值仿真研究;同时比较分析了两种储箱布局方案下液体晃动对航天器姿态运动的影响,为工程应用提供参考. 相似文献