Classification of gravity effects on “free” cells

When cell physiologists detect gravity related reactions of their objects it is often difficult to decide where the receptors for the observed effects are located. Answering this question is necessary for any further analysis of a detected gravity effect on cells. In previous papers we have discussed direct and indirect gravity effects in relation to the smallest functional units where the primary receptor, which interacts with gravity, is positioned inside and outside of such a unit, respectively. So, in a first approximation we can conclude that in a multicellular aquatic organism, which changes its metabolism in weightlessness, the primary receptors of gravity are located inside the cells of that organism. A special approach is necessary when free living cells, the density of which may be higher than the one of the (liquid) medium, or even cells living on a free surface are observed. In these two cases also indirect effects have to be taken into account, which will be demonstrated with the aid of the slime mold . Additionally the environment of the organisms can be changed directly and indirectly by gravity.     

Magnetic levitation-based Martian and Lunar gravity simulator.

Missions to Mars will subject living specimens to a range of low gravity environments. Deleterious biological effects of prolonged exposure to Martian gravity (0.38 g), Lunar gravity (0.17 g), and microgravity are expected, but the mechanisms involved and potential for remedies are unknown. We are proposing the development of a facility that provides a simulated Martian and Lunar gravity environment for experiments on biological systems in a well controlled laboratory setting. The magnetic adjustable gravity simulator will employ intense, inhomogeneous magnetic fields to exert magnetic body forces on a specimen that oppose the body force of gravity. By adjusting the magnetic field, it is possible to continuously adjust the total body force acting on a specimen. The simulator system considered consists of a superconducting solenoid with a room temperature bore sufficiently large to accommodate small whole organisms, cell cultures, and gravity sensitive bio-molecular solutions. It will have good optical access so that the organisms can be viewed in situ. This facility will be valuable for experimental observations and public demonstrations of systems in simulated reduced gravity.     

Microgravity effects on sea urchin fertilization and development.

Gravity has been a pervasive influence on all living systems and there is convincing evidence to suggest that it alters fertilization and embryogenesis in several developmental systems. Notwithstanding the global importance of gravity on development, it has only been recently possible to begin to design experiments which might directly investigate the specific effects of this vector. The goal of this research program is to explore and understand the effects of gravity on fertilization and early development using sea urchins as a model system. Sea urchin development has several advantages for this project including the feasibility of maintaining and manipulating these cells during spaceflight, the high percentage of normal fertilization and early development, and the abundant knowledge about molecular, biochemical, and cellular events during embryogenesis which permits detailed insights into the mechanism by which gravity might interfere with development. Furthermore, skeletal calcium is deposited into the embryonic spicules within a day of fertilization permitting studies of the effects of gravity on bone calcium deposition.     

The influence of gravity on structure and function of animals

Gravity is the only environmental parameter that has remained constant during the period of evolution of living matter on Earth. Thus, it must have been a major force in shaping livimg things. The influence of gravitational loading on evolution of the vertebrate skeleton is well recognized, and scale effects have been studied. This paper, however, considers in addition four pivotal events in early evolution that would seem to have been significant for the later success and diversification of animal life. These are evolution of the cytoskeleton, cell motility (flagellae and cilia), gravity detecting devices (accelerometers), and biomineralization. All are functionally calcium dependent in eukaryotes and all occurred or were foreshadowed in prokaryotes. A major question is why calcium was selected as an ion of great importance to the structure and function of living matter; another is whether gravity played a role in its selection.     

A theory of gravikinesis in Paramecium.

The archaic eukaryote unicellular microorganism, Paramecium, is propelled by thousands of cilia, which are regulated by modulation of the membrane potential. Ciliates can successfully cope with gravity, which is the phylogenetically oldest stimulus for living things. One mechanism for overcoming sedimentation is negative gravitaxis, an orientational response antiparallel to the gravity vector. We have postulated the existence of a negative gravikinesis in Paramecium, i.e. a modulation of swimming speed as a function of cellular orientation in space. With negative gravikinesis, an upward oriented cell actively augments the rate of forward swimming and depresses active locomotion during downward orientation. A brief outline of the gravikinesis hypothesis is given on a quantitative basis and experimental data are presented which have confirmed the major assumptions.     

Possible actions of gravity on the cellular machinery.

Since the first flight of the ESA Biorack on the German Spacelab Mission D1 in 1985 evidence has been obtained that biological cells and small unicellular organisms function differently under conditions of microgravity. However, there is still lack of scientific proof that these effects are caused by a direct influence on the cells in the weightlessness condition. The question how normal gravity may play a role in cellular activity is being addressed and the results show that gravity may provide important signals during certain state transitions in the cell. These would be gravity-sensitive windows in the biological process. Also, by amplification mechanisms inside the cell, the cell may assume a state that is typical for normal gravity conditions and would change in microgravity. Experimental tools are discussed that would provide the conditions to obtain evidence for direct action of gravity and for the possible existence of gravity-sensitive windows.     

基于计算力矩法的眼内手术机器人的重力补偿

为了提高一种具有远程运动中心(RCM)机构的眼内手术机器人的定位精度和稳定性,在建立机器人坐标系的基础上,通过动力学等效,对机器人各构件质心瞬态位置进行分析。根据拉格朗日方程建立机器人动力学模型。提出基于计算力矩法的重力补偿方法。在此基础上,通过MATLAB/Simulink软件对重力补偿模型进行仿真。比较独立比例微分(PD)控制方法及重力补偿方法的各关节运动响应曲线,表明重力补偿模型可有效补偿重力项;同时,分析重力补偿模型响应曲线与期望曲线的误差,证明重力补偿模型具有较高的补偿精度和可行性。     

Microtubule self-organisation depends upon gravity.

The molecular processes by which gravity is transduced into biological systems are poorly, if at all, understood. Under equilibrium conditions, chemical and biochemical structures do not depend upon gravity. It has been proposed that biological systems might show a gravity dependence by way of the bifurcation properties of certain types of non-linear chemical reactions that are far-from-equilibrium. We have found that in-vitro preparations of microtubules, an important element of the cellular cytoskeleton, show this type of behaviour. On earth, the solutions show macroscopic self-ordering, and the morphology of the structures that form depend upon the orientation of the sample with respect to gravity at a critical moment at an early stage in the development of the self-organised state. An experiment carried out in a sounding rocket, showed that as predicted by theories of this type, no self-organisation occurs when the microtubules are assembled under low gravity conditions. This is an experimental demonstration of how a very simple biochemical system, containing only two molecules, can be gravity sensitive. At a molecular level this behaviour results from an interaction of gravity with macroscopic concentration and density fluctuations that arise from the processes of microtubule contraction and elongation.     

Experimental concept for examination of biological effects of magnetic field concealed by gravity.

Space is not only a place to study biological effects of gravity, but also provides unique opportunities to examine other environmental factors, where the biological actions are masked by gravity on the ground. Even the earth's magnetic field is steadily acting on living systems, and is known to influence many biological processes. A systematic survey and assessment of its action are difficult to conduct in the presence of dominant factors, such as gravity. Investigation of responses of biological systems against the combined environment of zero-gravity and zero-magnetic field might establish the baseline for the analysis of biological effects of magnetic factors. We propose, in this paper, an experimental concept in this context, together with a practical approach of the experiments, both in orbit and on the ground, with a thin magnetic shielding film. Plant epicotyl growth was taken as an exemplar index to evaluate technical and scientific feasibility of the proposed system concept.     

北京地区大气温度及重力波活动的季节变化

利用瑞利激光雷达观测数据,分析了北京地区35~70km高度范围内大气温度和重力波活动的季节变化.发现北京地区30~70km高度范围内的大气温度有明显的年周期变化:平流层顶最高温度出现在6,7月份,大约为270K;中间层70km高度最低温度也出现在6,7月份,大约为200K.以2014年10月14日晚数据为例,分析重力波势能密度,发现50km以下重力波势能存在耗散,而在50km以上重力波近乎无耗散地向上传播.通过对比35~50km高度范围内的平均势能密度,对北京地区重力波活动强弱的季节变化进行了研究.研究结果表明,北京上空重力波活动强度具有明显的年周期变化,冬季平均势能密度为18J·kg-1,夏季为8J·kg-1,且冬季重力波活动强度约为夏季的两倍.此外,还分析了春夏秋冬四个季节重力波势能密度随高度的变化.结果表明,不同季节和不同高度的重力波势能密度不同.      

Activity of the sympathetic-adrenomedullary system in rats after space flight on the COSMOS biosatellites

The indicators of adrenomedullary activity (catecholamine content (CA) and the activity of the catecholamine-synthesizing enzymes tyrosine hydroxylase (TH) and dopamine-β-hydroxylase (DBH)) were measured in the adrenal glands of rats living in a state of weightlessness for 18.5–19.5 days on board the biosatellites COSMOS 936 and COSMOS 1129. None of these indicators was significantly changed by space flight, neither in the group living in a state of weightlessness nor in the group living in a centrifuge on board the spacecraft and exposed to artificial gravity of 1 g (COSMOS 936). Animals exposed after space flight to repeated immobilization stress on Earth showed a significant decrease of adrenal adrenaline and an appreciable increase in adrenal TH activity compared to stressed animals which were not in space. These results suggest that a prolonged state of weightlessness during space flight does not by itself represent an intensive stressful stimulus for the adrenomedullary system but potentiates the response of cosmonauts to stress after return to Earth.     

Introduction: an overview of gravity sensing, perception, and signal transduction in animals and plants.

The antiquity of biological sensitivity and response to gravity can be traced through the ubiquity of morphology, mechanisms, and cellular events in gravity sensing biological systems in the most diverse species of both plants and animals. Further, when we examine organisms at the cellular level to elucidate the molecular mechanism by which a gravitational signal is transduced into a biochemical response, the distinction between plants and animals becomes blurred.     

Gravity and developmental plasticity.

Living organisms, especially plants, show some plasticity in their overall development, usually as a response to the external environment. Plasticity may apply not only to the external form of organisms but also to their physiology as well as to the detailed structure of their genome. A further example of plasticity may be developmental instability, where anomalous development seems to appear spontaneously, probably as a result of some transient environmental perturbation. Whether the absence of gravity would have sufficient impact on any living process to evoke a specific course of plastic development is unknown, though it is possible that in certain circumstances special forms, or 'agravimorphs', could be produced. Through such new forms, it should be possible to identify processes required for development in which 1 x g gravity is a necessary participant.     

The relation of gravity waves and turbulence in the mesosphere

VHF radar observations of the mesosphere generally reveal that the structure of turbulence is intermittent in space and time. Some examples of such turbulence layers and the concurrent gravity wave oscillations, observed in the low latitude mesosphere over the Arecibo Observatory/Puerto Rico are discussed. This turbulence structures which are intermittent on short time scales but persistently recur over periods of many hours at almost the same height are evidently not related to the simultaneously occurring short period gravity waves. These kinds of persistent turbulence structures are assumed to be related to very long period (inertia-) gravity waves, where instability takes place only by the wave induced shear in a narrow critical level. However, the short period gravity waves occasionally break into turbulence by overturning and convective instability. These interpretations offer a way to understand the generation mechanisms of the different kinds of turbulence structures, namely blobs, sheets and layers, which were reported in the early days of mesospheric VHF radar observations.     

Molecular developmental neurobiology of formation, guidance and survival of primary vestibular neurons.

Untangling the molecular and physiological interactions that generate the proper connections of the primary vestibular neurons in normal gravity requires two parallel approaches. One approach needs to use mutant mice to delineate the molecular basis of developmental mechanisms that govern ear development, including formation and differentiation of neurons and establishment of their peripheral and central connections. Beyond that and in addition to it, we need physiological investigations using microgravity and/or hypergravity, as well as absence of otoconia, to understand the role played by vestibular stimuli to fine tune connections of primary and secondary vestibular neurons. This paper provides an overview of some of the molecular mechanisms uncovered over the last few years that guide development, differentiation and survival of primary vestibular neurons of the mammalian ear. Briefly, several genes that are essential for primary neuron formation have been identified, all genes that govern embryonic survival are known and the first genes and mechanisms that guide formation of proper connections are being revealed. While still incomplete, the progress has been astounding and the completion of the mouse genome project will further accelerate the pace. Such data pave the way to put the research on the influence of altered gravity stimulation within a molecular framework.     

Evaluation of experiments involving the study of plant orientation and growth under different gravitational conditions.

The manifestation of gravitropic reaction in plants has been considered from the phylogenetic point of view. A chart has been suggested according to which it is supposed that the first indications of the ability to identify the direction of the gravitational vector were inherent in the most ancient eukaryotes, which gave rise to green, brown, yellow-green, golden and diatomaceous algae as well as fungi. The experiments on the role of gravity in plant ontogenesis are being continued. The sum total of the data obtained in a number of experiments in space shows that under these conditions a structurally modified but normally functioning gravireceptive apparatus is formed. The data confirming the modification, under changed gravity, of the processes of integral and cellullar growth of the axial organs of seedlings as well as of the anatomo-morphological structure and developmental rates of plants during their prolonged growth in space are presented. It is assumed that this fact testifies to the presence of systems interacting with gravity during plant ontogenesis. At the same time the necessity for further experiments in order to differentiate an immediate biological effect of gravity from the ones conditioned by it indirectly due to the changes in the behavior of liquids and gases is pointed out. The methodological aspects of biological experiments in space as the main source of reliable information on the biological role of gravity are discussed.     

Theory and experimental results on gravitational effects on monocellular algae.

The orientation of a body which has an anisotropic distribution of mass and which is suspended in water is biased by gravitational torque, so that the center of gravity lies below the center of buoyancy. Many species of unicellular swimming algae are gravitationally oriented in this manner. Their axis of propulsion is essentially fixed within their bodies, so that when the cells swim, they swim upwards. Gravitaxis is an exotaxis, which requires no sensory processing. Nevertheless, gravity affects the lives of these cells both individually and collectively. For single cells, gravity intervenes in the execution and mechanism of sense-dependent taxes, such as phototaxis, it provides for fail-safe locomotion toward the upper interface of their habitat, the source of light and air, and it may cause up-accumulation. Populations of single cells, swimming in the presence of gravity, are coupled through fluid-mechanical interactions which cause spatial and temporal patterns of fluid convection and cell concentration. These patterns modify the cell's environmental interactions, by facilitating downward migrations of cell populations, by mixing the embedding fluid and its contents, and by providing a collective mechanism for controlling light intensity at the individual cell level. Summarizing, gravity modulates the interaction of algal cells with each other and with their environment.     

Influence of different natural physical fields on biological processes.

In space flight conditions gravity, magnetic, and electrical fields as well as ionizing radiation change both in size, and in direction. This causes disruptions in the conduct of some physical processes, chemical reactions, and metabolism in living organisms. In these conditions organisms of different phylogenetic level change their metabolic reactions undergo changes such as disturbances in ionic exchange both in lower and in higher plants, changes in cell morphology for example, gyrosity in Proteus (Proteus vulgaris), spatial disorientation in coleoptiles of Wheat (Triticum aestivum) and Pea (Pisum sativum) seedlings, mutational changes in Crepis (Crepis capillaris) and Arabidopsis (Arabidopsis thaliana) seedling. It has been found that even in the absence of gravity, gravireceptors determining spatial orientation in higher plants under terrestrial conditions are formed in the course of ontogenesis. Under weightlessness this system does not function and spatial orientation is determined by the light flux gradient or by the action of some other factors. Peculiarities of the formation of the gravireceptor apparatus in higher plants, amphibians, fish, and birds under space flight conditions have been observed. It has been found that the system in which responses were accompanied by phase transition have proven to be gravity-sensitive under microgravity conditions. Such reactions include also the process of photosynthesis which is the main energy production process in plants. In view of the established effects of microgravity and different natural physical fields on biological processes, it has been shown that these processes change due to the absence of initially rigid determination. The established biological effect of physical fields influence on biological processes in organisms is the starting point for elucidating the role of gravity and evolutionary development of various organisms on Earth.     

基于线性重力差模型的拦截弹中制导技术

针对机载动能拦截弹的中制导段气动力作用可忽略且存在无法实时精确计算重力偏差等特点,提出了一种基于线性重力差模型的预测制导方法。通过线性模型逼近中制导过程中拦截弹与目标之间的重力偏差,以此为依据调整拦截弹的推力矢量并将重力偏差值消除。在此基础上采用延迟点火的策略使得拦截弹的拦截器助推级更好地修正预测模型与实际情况的偏差,经过仿真验证可以将整个中制导段的脱靶量限制在一个较小数值,从而为末制导段提供良好的初始条件。