Antiorthostatic hypokinesia as a method of weightlessness simulation

Physiological effects seen in eight test subjects during a 5-d bedrest experiment in the head-down position (0,-4,-8,-12degrees) were studied. It was shown that the antiorthostatic hypokinesia at -12degrees could reproduce physiological responses shown by space crewmembers more closely than recumbent bedrest. Our observations help to stimulate an acute stage of human adaptation to the weightless state and to assess the part played by gravity-induced blood redistribution in the development of physiological changes.     

Role of digitalis-like substance in the hypertension of streptozotocin-induced diabetes and simulated weightlessness in rats

We have examined the role of plasma Na+-K+ pump inhibitor (SPI) in the hypertension of streptozotocin induced insulin dependent diabetes (IDDM) in reduced renal mass rats. The increase in blood pressure (BP) was associated with an increase in extracellular fluid volume (ECFV), and SPI and a decrease in myocardial Na+,K+ATPase (NKA) activity, suggesting that increased SPI, which inhibits cardiovascular muscle (CVM) cell NKA activity, may be involved in the mechanism of IDDM-hypertension. In a second study, using prolonged suspension resulted in a decrease in cardiac NKA activity, suggesting that cardiovascular deconditioning following space flight might in part result from insufficient SPI.     

Shape of liquid current-carrying conductor under conditions of weightlessness

Translated from Poroshkovaya Metallurgiya, No. 10(334), pp. 26–28, October, 1990.     

Effect of penetrating radiation on skeletal muscles of rats in weightlessness

The isoenzyme composition of lactate dehydrogenase of soleus and plantaris muscles of rats flown for 20.5 d aboard the biosatellite Cosmos-690 and irradiated with a dose of 800 rad was investigated. The muscles exposed to weightlessness per se and weightlessness combined with radiation showed similar changes in their carbohydrate metabolism. On return to 1 G, readaptation of irradiated rats developed less rapidly than of animals exposed to weightlessness alone.     

Postnatal development under conditions of simulated weightlessness and space flight

The axial structures, the notochord and the neural tube, play an essential role in the dorsoventral patterning of somites and in the differentiation of their many cell lineages. Here, we investigated the role of the axial structures in the mediolateral patterning of the somite by using a newly identified murine homeobox gene, Nkx-3.1, as a medial somitic marker in explant in vitro assays. Nkx-3.1 is dynamically expressed during somitogenesis only in the youngest, most newly-formed somites at the caudal end of the embryo. We found that the expression of Nkx-3.1 in pre-somitic tissue explants is induced by the notochord and maintained in newly-differentiated somites by the notochord and both ventral and dorsal parts of the neural tube. We showed that Sonic hedgehog (Shh) is one of the signaling molecules that can reproduce the effect of the axial structures by exposing explants to either COS cells transfected with a Shh expression construct or to recombinant SHH. Shh could induce and maintain Nkx-3.1 expression in pre-somitic mesoderm and young somites but not in more mature, differentiated ones. The effects of Shh on Nkr-3.1 expression were antagonized by a forskolin-induced increase in the activity of cyclic AMP-dependent protein kinase A. Additionally, we confirmed that the expression of the earliest expressed murine myogenic marker, myf 5, is also regulated by the axial structures but that Shh by itself is not capable of inducing or maintaining it. We suggest that the establishment of somitic medial and lateral compartments and the early events in myogenesis are governed by a combination of positive and inhibitory signals derived from the neighboring structures, as has previously been proposed for the dorsoventral patterning of somites.     

Voluntary head stabilization in space during oscillatory trunk movements in the frontal plane performed in weightlessness

The ability voluntarily to stabilize the head in space during lateral rhythmic oscillations (0.59+/-0.09 Hz) of the trunk has been investigated during microgravity (microG) and normal gravity (nG) conditions (parabolic flights). Five healthy young subjects, who gave informed consent, were examined. The movements were performed with eyes open or eyes closed, during phases of either microG or nG. The main result was that head orientation with respect to vertical may be stabilized about the roll axis under microG with, as well as without vision, despite the reduction in vestibular afferent and muscle proprioceptive inputs. Moreover, the absence of head stabilization about the yaw axis confirms that the degrees of freedom of the neck can be independently controlled, as was previously reported. These results seem to indicate that voluntary head stabilization does not depend crucially upon static vestibular afferents. Head stabilization in space may in fact be organized on the basis of either dynamic vestibular afferents or a short-term memorized postural body schema.     

Exoelectron emission from torsional fatigue damage in hardened steels

Exoelectron emission associated with surface fatigue damage in two types of steel was measured by means of an ultraviolet laser scanning system. The localized emission from damage areas in quenched and tempered 1541 steel increased systematically with continued fatigue cycling. Plots of emissionvs cycles were in good agreement with earlier results for 1018 steel. Much of this emission resulted from the accumulation of plastic deformation during the crack initiation stage. In the case of relatively brittle 1144 steel, the dominant source of exoelectrons was a fatigue crack with little associated plasticity. However, shot peening of the 1144 steels completely changed the character of the surface layers. While the core material still cracked in a rather brittle manner, the shot peened layer accumulated a broad distribution of plastic deformation as revealed by the systematic development of exoelectron emission. These results indicate that the accumulation of surface fatigue deformation during the crack initiation stage is a systematic and perhaps universal process when viewed on the appropriate microscale.     

Signs of surface torsion and torsional dioptric power

Although there is agreement in the literature over the magnitude of torsion and torsional dioptric power, there is ambiguity over the signs of those quantities. The purpose of this paper is to define terms in such a way that the ambiguity is removed. Explicit equations are presented for torsion and torsional power along a meridian of a surface. In keeping with common practice in other disciplines, right-handed torsion is chosen to be positive. The components of the dioptric power matrix of thin systems and of the reduced vergence matrix are reinterpreted in terms of curvital and torsional power. In this reinterpretation the off-diagonal components of the matrices remain the torsional power and the reduced torsion along the meridian orthogonal to the reference meridian. However, they become the negatives of those quantities along the reference meridian. In particular, the top-right component can be interpreted as the reduced torsion or the torsional power along the meridian orthogonal to the reference meridian and the bottom-left as the negative of those quantities along the reference meridian. Torsion and torsional power along a meridian, as well as curvature and curvital power, are invariant under change of reference meridian and under spherocylindrical transposition.     

Functional activity of rat pancreatic endocrine cells in weightlessness and in a suspended state]

Molecular dynamics calculations have been carried out on a model of the LS3 synthetic ion channel in a membrane mimetic environment. In the absence of an external electrostatic field, the LS3 channel, which consists of a bundle of six alpha-helices with sequence Ac-(LSSLLSL)3-CONH2, exhibits large structural fluctuations. However, in the presence of the field, the bundle adopts a well defined coiled-coil structure with an inner pore of water. The observed structural changes induced by the applied field are consistent with the proposed gating mechanism of the ion channel.     

Comparison of the torsional forces at failure for seven endodontic post systems

Resistance to torsional forces is critical in restoration of endodontically treated teeth. Seven post designs (Flexi-Post, Flexi-Flange, Para-Post, AccessPost, World Post, Vlock, and Dentatus posts) were cemented in roots of natural teeth with zinc phosphate and Flexi-Flow cements, which resulted in 11 different groupings that were subjected to torsional forces in a clockwise direction. In addition, clockwise and counterclockwise torque was applied to the Flexi-Post and Flexi-Flange systems cemented with zinc phosphate and Flexi-Flow cements. A total of 150 samples were prepared, and groups for this study were: group 1, Flexi-Post/zinc phosphate clockwise and counterclockwise; group 2, Flexi-Post/Flexi-Flow clockwise and counterclockwise; group 3, Flexi-Flange/zinc phosphate clockwise and counterclockwise; group 4, Flexi-Flange/Flexi-Flow clockwise and counterclockwise; group 5, Para-Post/zinc phosphate clockwise; group 6, AccessPost/zinc phosphate clockwise; group 7, AccessPost/Flexi-Flow with grooved dentin clockwise; group 8, World Post/zinc phosphate clockwise; group 9, World Post/Flexi-Flow with grooved dentin clockwise; group 10, Vlock Post/zinc phosphate clockwise; and group 11, Dentatus post/zinc phosphate clockwise. Torsional forces for the groups ranged from 17 ounce-inches (Dentatus/zinc phosphate) to 81 ounce-inches (Flexi-Post/zinc phosphate). Flexi-Post and Flexi-Flange threaded posts exhibited statistically greater resistance to torsional forces. Analyses were computed with one-way and three-way analysis of variance followed by Duncan's multiple range test. Duncan's multiple range test indicated that Flexi-Post/zinc phosphate/clockwise was similar to Flexi-Post/Flexi-Flow/clockwise and that both had significantly higher torque levels than the other treatment conditions in the clockwise direction (p 0.0001). Dentatus/zinc phosphate/clockwise had significantly lower torque levels than the other treatment conditions (p 0.031).     

The influence of alveolar structures on the torsional strain field in a gorilla corporeal cross-section

Anthropologists have often used mandibular torsional properties to make inferences about primate dietary adaptations. Most of the methods employed are based on assumptions related to periodontal and alveolar properties. This study uses the finite element method to evaluate some of these assumptions with a cross-section through the third molar of a gorilla. Results indicate that the properties of alveolar bone play an important role in determining the strain field. In comparison, the exact stiffness values of the periodontal ligaments seem to have a much smaller impact. Replacing the dental roots and periodontal ligaments with alveolar bone, however, has a significant influence on the strain field. It underestimates the maximum shear strain by about 28% along its periosteal aspect when alveoli are modeled as cortical bone. It overestimates the strain by a smaller amount when alveoli are modeled as trabecular bone. This study supports the assumption that primate mandibles behave like a closed-section under torsion under the limiting condition that the alveolar bone stiffness is more than half of the value of cortical bone; alveolar bone can then be modeled as cortical bone with a minimal loss of accuracy. In addition, this study suggests that the minimum cortical thickness should be considered for torsional strength. Finally, modeling accuracy can be significantly increased if both dental and periodontal structures can be realistically incorporated into mandibular biomechanical models. However, this may not be always feasible in studies of fossil mandibles. This is due mainly to the difficulties involved in estimating alveolar bone densities and in distinguishing boundaries between cortical bone, alveolar bone, periodontal ligaments, and dental roots in fossil specimens.     

Changes in central and peripheral hemodynamics during prolonged anti-orthostatic hypokinesia as a model of weightlessness

Central and peripheral circulation was studied rheographically in 6 test subjects during a 30-day bed rest experiment and in 9 test subjects during a 49-day bed rest. The bed rested subjects were kept in a head-down position at an angle of --4 degrees. At an early stage of the experiments the cardiac output and stroke volume increased, the total peripheral resistance decreased, the tone of major regional vessels decreased and that of small vessels increased. During the 3rd-7th weeks the changes were just the opposite: cardiac output and stroke volume decreased, the total peripheral resistance increased the tone of major regional vessels increased and that of small vessels decreased. At the end of the bed rest experiment the cardiac output and stroke volume increased and the tone of regional vessels changed accordingly. Circulation parameters returned to the pretest level, at least, 3-4 weeks after the end of the best rest experiments.     

Effect of weightlessness and centrifugation on red cell survival in rats subjected to space flight

Rats were flown aboard the Soviet biosatellite Cosmos 936 for 18.5 d during August, 1977. Five rats were subjected to near-weightless space flight, as with Cosmos 782, and five rats were subjected to a 1-G force via an on-board centrifuge. These rats and three control groups were injected with 2-14C glycine 19 d preflight. The flight rats were recovered from orbit after 18.5 d of space flight. Erythrocyte hemolysis and lifespan were evaluated in the five groups of rats by quantitation of radioactive carbon monoxide exhaled in the breath which arises from the breakdown of the previously labeled hemoglobin. The results support our previous findings wherein hemolysis was found to increase as a result of weightless space flight. A comparison to the centrifuged animals indicates that artificial gravity attenuates the effect of weightlessness on hemolysis and appears to normalize the hemolytic rate in the early postflight period.     

CSP轧机万向接轴弯扭耦合振动

以连续分布质量的轧机万向接轴为研究对象,考虑了万向接轴的倾角、自重、质量偏心以及阻尼的影响,从动力学角度建立了万向接轴的弯扭耦合振动方程,并对实测的数据给出了理论解释.从所得到的微分方程可以看出:当轴系存在不平衡时,扭转振动与弯曲振动之间存在着很明显的相互耦合关系;当轴系没有不平衡时,扭转振动会对弯曲振动产生影响,而弯曲振动对扭转振动没有影响.