Review of primary spaceflight-induced and secondary reloading-induced changes in slow antigravity muscles of rats.

We have examined the light and electron microscopic properties of hindlimb muscles of rats flown in space for 1-2 weeks on Cosmos biosatellite flights 1887 and 2044 and Space Shuttle missions Spacelab-3, Spacelab Life Sciences-1 and Spacelab Life Sciences-2. Tissues were obtained both inflight and postflight permitting definition of primary microgravity-induced changes and secondary reentry and gravity reloading-induced alterations. Spaceflight causes atrophy and expression of fast fiber characteristics in slow antigravity muscles. The stresses of reentry and reloading reveal that atrophic muscles show increased susceptibility to interstitial edema and ischemic-anoxic necrosis as well as muscle fiber tearing with disruption of contractile proteins. These results demonstrate that the effects of spaceflight on skeletal muscle are multifaceted, and major changes occur both inflight and following return to Earth's gravity.     

Changes of contractile responses due to simulated weightlessness in rat soleus muscle.

Some contractile and electrophysiological properties of muscle fibers isolated from the slow-twitch soleus (SOL) and fast-twitch extensor digitorum longus (EDL) muscles of rats were compared with those measured in SOL muscles from suspended rats. In suspended SOL (21 days of tail-suspension) membrane potential (Em), intracellular sodium activity (aiNa) and the slope of the relationship between Em and log [K]o were typical of fast-twitch muscles. The relation between the maximal amplitude of K-contractures vs Em was steeper for control SOL than for EDL and suspended SOL muscles. After suspension, in SOL muscles the contractile threshold and the inactivation curves for K-contractures were shifted to more positive Em. Repriming of K-contractures was unaffected by suspension. The exposure of isolated fibers to perchlorate (ClO4-)-containing (6-40 mM) solutions resulted in a similar concentration-dependent shift to more negative Em of activation curves for EDL and suspended SOL muscles. On exposure to a Na-free TEA solution, SOL from control and suspended rats, in contrast to EDL muscles, generated slow contractile responses. Suspended SOL showed a reduced sensitivity to the contracture-producing effect of caffeine compared to control muscles. These results suggested that the modifications observed due to suspension could be encounted by changes in the characteristics of muscle fibers from slow to fast-twitch type.     

Crustaceans as a model for microgravity-induced muscle atrophy.

Atrophy of skeletal muscles is a serious problem in a microgravity environment. It is hypothesized that the unloading of postural muscles, which no longer must resist gravity force, causes an accelerated breakdown of contractile proteins, resulting in a reduction in muscle mass and strength. A crustacean model using the land crab, Gecarcinus lateralis, to assess the effects of spaceflight on protein metabolism is presented. The model is compared to a developmentally-regulated atrophy in which a premolt reduction in muscle mass allows the withdrawal of the large claws at molt. The biochemical mechanisms underlying protein breakdown involves both Ca(2+)-dependent and multicatalytic proteolytic enzymes. Crustacean claw muscle can be used to determine the interactions between shortening and unloading at the molecular level.     

Alterations in glucose and protein metabolism in animals subjected to simulated microgravity.

Reduction of physical activity due to disease or environmental restraints, such as total bed rest or exposure to spaceflight, leads to atrophy of skeletal muscle and is frequently accompanied by alterations in food intake and the concentration of metabolic regulatory hormones such as insulin. Hindlimb suspension of laboratory rats, as a model for microgravity, also shows marked atrophy of gravity dependent muscles along with a reduced gain in body weight. Suspended rats exhibit enhanced sensitivity to insulin-induced glucose uptake when compared with normal control rats and resistance to insulin action when compared with control rats matched similarly for reduced body weight gain. These changes are accompanied by decreased insulin binding and tyrosine kinase activity in soleus but not plantaris muscle, unchanged glucose uptake by perfused hindlimb and decreased sensitivity but not responsiveness to insulin-induced suppression of net proteolysis in hindlimb skeletal muscle. These findings suggest that loss of insulin sensitivity during muscle atrophy is associated with decreased insulin binding and tyrosine kinase activity in atrophied soleus muscle along with decreased sensitivity to the effects of insulin on suppressing net protein breakdown but not on enhancing glucose uptake by perfused hindlimb.     

Animal models for the study of the effects of spaceflight on the immune system.

Animal models have been used to determine the effects of spaceflight on the immune system. Rats and rhesus monkeys have been the primary animals used for actual space flight studies, but mice have also been utilized for studies in ground-based models. The primary ground based model used has been hindlimb unloading of rodents, which is similar to the chronic bed-rest model for humans. A variety of immune responses have been shown to be modified when animals are hindlimb unloaded. These results parallel those observed when animals are flown in space. In general, immune responses are depressed in animals maintained in the hindlimb unloading model or flown in space. These results raise the possibility that spaceflight could result in decreased resistance to infection in animals.     

Effects of microgravity on muscle and cerebral cortex: a suggested interaction.

The "slow" antigravity muscle adductor longus was studied in rats after 14 days of spaceflight (SF). The techniques employed included standard methods for light microscopy, neural cell adhesion molecule (N-CAM) immunocytochemistry and electron microscopy. Light and electron microscopy revealed myofiber atrophy, segmental necrosis and regenerative myofibers. Regenerative myofibers were N-CAM immunoreactive (N-CAM-IR). The neuromuscular junctions showed axon terminals with a decrease or absence of synaptic vesicles, degenerative changes, vacant axonal spaces and changes suggestive of axonal sprouting. No alterations of muscle spindles was seen either by light or electron microscopy. These observations suggest that muscle regeneration and denervation and synaptic remodeling at the level of the neuromuscular junction may take place during spaceflight. In a separate study, GABA immunoreactivity (GABA-IR) was evaluated at the level of the hindlimb representation of the rat somatosensory cortex after 14 days of hindlimb unloading by tail suspension ("simulated" microgravity). A reduction in number of GABA-immunoreactive cells with respect to the control animals was observed in layer Va and Vb. GABA-IR terminals were also reduced in the same layers, particularly those terminals surrounding the soma and apical dendrites of pyramidal cells in layer Vb. On the basis of previous morphological and behavioral studies of the neuromuscular system after spaceflight and hindlimb suspension it is suggested that after limb unloading there are alterations of afferent signaling and feedback information from intramuscular receptors to the cerebral cortex due to modifications in the reflex organization of hindlimb muscle groups. We propose that the changes observed in GABA immunoreactivity of cells and terminals is an expression of changes in their modulatory activity to compensate for the alterations in the afferent information.     

基于神经网络的重力卸载系统控制器设计

吊挂系统是地面模拟空间机械臂重力卸载试验的重要方法之一.针对传统PID控制方式动作响应慢、鲁棒性差等缺点,提出了一种基于径向基函数(RBF)神经网络的智能控制方式.该方式有很强的非线性拟合能力,且学习规则简单,可映射任意复杂的非线性关系,便于计算机实现.利用该特性,设计了一种重力卸载精度较PID控制方式更高的控制器.该...     

磁流体斜激波的碰撞

讨论了磁流体斜激波之间的碰撞及其与接触间断的相互作用规律,主要结论如下:(1)两个快激波碰撞后交换位置,同时出现一接触间断和一慢稀疏波对。(2)两个慢激波碰撞后交换位置且强度减弱,同时出现一接触间断和一块激波对。(3)一前向快激波与一后向慢激波碰撞后交换位置,快激波强度增加,慢激波强度减弱,同时出现一后向快激波、一负接触间断和一前向慢稀疏波。(4)一前向快激波与一正(负)接触间断相互作用后交换位置,快激波减弱,同时出现一后向快稀疏波(快激波)、一后向慢激波和一前向慢激波(慢稀疏波).(5)一前向慢激波与一正(负)接触间断相互作用后交换位置,慢激波减弱,同时出现一后向慢稀疏波(慢激波)和一快稀疏波(快激波)对。      

磁流体中间激波的相互作用

本文讨论磁流体中间激波的相互作用规律．主要结论：中间激波汇合的产物为后向快简单波、后向慢简单波或慢激波、接触间断、前向慢激波和前向快激波，其中后向波成份和接触间断很弱．当左（右）激波较强时，中国激波碰撞产物为后（前）向快激波、后（前）向慢简单波或慢激波、负（正）切向间断、前（后）向慢简单波和前（后）向快激波．     

磁流体斜激波的汇合

本文讨论磁流体快、慢激波的汇合作用规律,主要结论如下:(1)两个前向快激波汇合之后,形成一更强的前向快激波,尾随一前向慢稀疏波、一正接触间断(后侧密度大于前侧)、一后向慢激波和一后向快稀疏浚。(2)两个前向慢激波汇合之后,形成一更强的前向慢激波,尾随一正接触间断、一后向慢稀疏波和一后向快激波2在前向慢激波前方出现一前向快波,它或为稀疏浚(中、小激波角情况),或为激波(大激波角情况).(3)前向快激波会追上前向慢激波而发生汇合,之后互换位置且强度减弱,尾随一正接触间断和一后向稀疏波对。      

The declined phosphorylation of Heat shock protein 27 in rat cardiac muscle after hindlimb unloading

Hindlimb unloading can induce the cardiac atrophy and diminished cardiac function, however, the mechanisms responsible for which remain elusive. The chronic volume unloading of heart, which decreases the local mechanical stress, may lead to cardiac atrophy after hindlimb unloading. Many studies showed that integrin signaling, p38 MAPK, Heat shock protein 27 and cytoskeleton involved in the hypertrophic growth induced by mechanical stress. However, the mechanisms responsible for cardiac atrophy after hindlimb unloading are still unclear. In this study, we used the tail-suspended, hindlimb unloading rat model to simulate the effects of microgravity. Western blot analysis was used to detect the protein expression of Heat shock protein 27, focal adhesion kinase, p38 MAPK and their phosphorylation levels in rat cardiac muscle after 14d hindlimb unloading. The results showed that the phosphorylation levels of both Heat shock protein 27 and p38 MAPK were decreased significantly in rat cardiac muscle after hindlimb unloading. However, the phosphorylation level of focal adhesion kinase was not decreased significantly. The results suggested that Heat shock protein 27, the downstream of p38 MAPK, might play a critical role in the cardiac atrophy in response to simulated microgravity induced by hindlimb unloading.     

Research on the adaptation of skeletal muscle to hypogravity: past and future directions.

Our current understanding of hypogravity-induced atrophy of skeletal muscles is based primarily on studies comparing pre- and post-flight properties of muscles. Interpretations are necessarily qualified by the assumption that the stress of reentry and readjustment to terrestrial gravity do not alter the parameters being analyzed. The neuromuscular system is highly responsive to changes in functional demands and capable of rapid adaptation, making this assumption questionable. A reexamination of the changes in the connective tissue and synaptic terminals of soleus muscles from rats orbited in biosatellites and sampled postflight indicates that these structural alterations represent adaptative responses of the atrophic muscles to the increased workload of returning to 1 G, rather than hypogravity per se. The atrophy of weightlessness is postulated to result because muscles are both underloaded and used less often. Proper testing of this hypothesis requires quantitation of muscle function by monitoring electromyography, force output and length changes during the flight. Experiments conducted in space laboratories, like those being developed for the Space Shuttle, will avoid the complications of reentry before tissue sampling and allow time course atudies of the rate of development of adaptive changes to zero gravity. Another area of great importance for future studies of muscle atrophy is inflight measurement of plasma levels of hormones and tissue receptor levels. Glucocorticoids, thyroid hormone and insulin exert dramatic regulatory influences on muscle structure. Prevention of neuromuscular atrophy becomes increasingly more important as spaceflights increase in duration. Definition of the atrophic mechanism is essential to developing means of preventing neuromuscular atrophy.     

不等径纤维混杂复合材料混杂原理

对碳化硅-碳(SiCF-CF)/环氧和硼-碳(BF-CF)/环氧2种不等径纤维混杂复合材料的混杂模型和机理进行了初步研究.建立了三角形和四边形阵列的混杂模型;分析了材料制备工艺对混杂阵列、纤维体积含量的影响.      

复合材料的冲击吸能与动态黏弹特性

考察了玻璃纤维、炭纤维、芳纶和UHMWPE纤维复合材料(分别称为GFRP,CFRP,AFRP和DFRP)层板的低速冲击吸能,并采用高载动态热机械分析仪EPLEXOR500分析了其纤维复丝的动态黏弹性的载荷敏感性.结果表明:冲击吸能明显受纤维性能及层板破坏模式的影响,呈韧性破坏的AFRP和DFRP的冲击吸能明显高于呈脆性破坏的GFRP和CFRP.在动态热机械分析中,静载增大使得储能模量升高但损耗角正切减小,动载增大时正好相反,且在这些影响中有机纤维复丝动态黏弹性较无机纤维复丝表现出更显著的载荷敏感性和非线性.4种层板的吸能大小与其纤维复丝储能模量载荷敏感性的强弱以及损耗角正切大小的顺序相同:DFRP>AFRP>GFRP>CFRP,反映出材料宏观冲击性能与表征其微观结构特征的黏弹性能的相关性.      

一种考虑过滤的短纤维增强复合材料RVE建模方法

代表性体积单元（RVE）法是短纤维增强复合材料性能预测的常用方法,其RVE生成效率是预测效率的重要影响因素。针对现有的随机顺序吸附（RSA）方法生成RVE时,布尔运算次数多、效率低的问题,通过在布尔运算前加入对纤维形心距的判断,过滤掉一部分随机生成的且与已有纤维相交的纤维,以减少布尔运算次数,提出了一种考虑过滤的随机顺序吸附（FRSA）方法。通过将改进后的FRSA方法在不同RVE参数和方法参数下生成RVE所需布尔运算次数和所需时间与基于布尔运算的随机顺序吸附（BORSA）方法进行比较,证明了FRSA方法的先进性。      

单向纤维集束的树脂浸润影响因素

运用自行研制的浸润特性测试系统,研究了环氧树脂对单向纤维集束的浸润行为,分析了纤维体积含量、树脂温度、纤维种类及纤维表面浸润剂等因素对浸润的影响规律.研究表明,增加纤维体积含量、升高树脂温度、去除纤维表面浸润剂均可加快环氧树脂对纤维集束的平均浸润速率.研究结果对指导复合材料成型工艺的合理设计、开发浸润特性表征新方法具有重要的意义.      

接触角法测玄武岩及玻璃纤维表面能实验

通过Wilhelmy吊片法测试液体与玄武岩、玻璃纤维单丝的前进接触角,应用OWRK理论计算得到纤维表面能及其色散与极性分量.实验研究表明:未经表面处理的玄武岩纤维表面能高于S-2玻璃纤维,去除浸润剂后2种纤维表面能的极性分量均明显降低,并且测试液体的极性分量对纤维表面能的测试结果影响甚大.分析结果为纤维与树脂的表面张力合理匹配、形成良好界面浸润和粘接提供了理论依据.      

光纤陀螺分形噪声的预白化滤波方法

光纤陀螺分形噪声往往具有长相关特性,导致陀螺输出信号慢漂移.为了滤除这类分形噪声,提出了一种分数阶预白化差分方法,通过该方法可以将分形噪声转化为高斯白噪声;利用小波变换,在小波变换域中采用Bayes软阈值去噪方法去除该白化噪声,从而形成了一种光纤陀螺分形噪声的预白化滤波方法.对VG949p型光纤陀螺实测数据处理结果表明,该方法能够有效地去除其中的分形噪声,抑制了陀螺低频漂移,同时也滤掉了其高频噪声项.      

超机动飞机的非线性飞行控制研究

介绍了应用非线性动态逆理论进行战斗机过失速机动条件下飞行控制律设计的具体过程,首先根据奇异摄动理论将受控状态变量分为快变量和慢变量两个层次,快变量为三个角速率,慢变量为迎角、侧滑角和速度滚转角,然后根据非线性动态逆理论分别对内环和外环进行设计,其中外环控制器的输出作为内环控制器的输入指令.最后对所设计的飞行控制律利用过失速机动仿真来加以验证,结果表明本文设计的飞行控制律完全能够在过失速机动条件下控制飞机跟踪指令飞行.     

Comparison of hindlimb unloading and partial weight suspension models for spaceflight-type condition induced effects on white blood cells

Animal models are frequently used to assist in the determination of the long- and short-term effects of space flight. The space environment, including microgravity, can impact many physiological and immunological system parameters. It has been found that ground based models of microgravity produce changes in white blood cell counts, which negatively affects immunologic function. As part of the Center of Acute Radiation Research (CARR), we compared the acute effects on white blood cell parameters induced by the more traditionally used animal model of hindlimb unloading (HU) with a recently developed reduced weightbearing analog known as partial weight suspension (PWS). Female ICR mice were either hindlimb unloaded or placed in the PWS system at 16% quadrupedal weightbearing for 4 h, 1, 2, 7 or 10 days, at which point complete blood counts were obtained. Control animals (jacketed and non-jacketed) were exposed to identical conditions without reduced weightbearing. Results indicate that significant changes in total white blood cell (WBC), neutrophil, lymphocyte, monocyte and eosinophil counts were observed within the first 2 days of exposure to each system. These differences in blood cell counts normalized by day 7 in both systems. The results of these studies indicate that there are some statistically significant changes observed in the blood cell counts for animals exposed to both the PWS and HU simulated microgravity systems.