Determination of <Emphasis Type="Italic">Foton M-2</Emphasis> satellite attitude motion by the data of microacceleration measurements

The results of reconstruction of uncontrolled attitude motion of the Foton M-2 satellite using measurements with the accelerometer TAS-3 are presented. The attitude motion of this satellite has been previously determined by the measurement data of the Earth’s magnetic field and the angular velocity. The TAS-3 data for this purpose are used for the first time. These data contain a well-pronounced additional component which made impossible their direct employment for the reconstruction of the attitude motion and whose origin was unknown several years ago. Later it has become known that the additional component is caused by the influence of the Earth’s magnetic field. The disclosure of this fact allowed us to take into account a necessary correction in processing of TAS-3 data and to use them for the reconstruction of the attitude motion of Foton M-2. Here, a modified method of processing TAS-3 data is described, as well as results of its testing and employing. The testing consisted in the direct comparison of the motion reconstructed by the new method with the motion constructed by the magnetic measurements. The new method allowed us to find the actual motion of Foton M-2 in the period June 9, 2005–June 14, 2005, when no magnetic measurements were carried out.     

An analysis of low-frequency component in microacceleration measurements made onboard the <Emphasis Type="Italic">Foton M-2</Emphasis> satellite

The low-frequency component is investigated in the data of measurements performed onboard the Foton M-2 satellite with the three-component accelerometer TAS-3. Investigations consisted in comparison of this component with its calculated analog found from a reconstruction of the satellite’s attitude motion. The influence of the Earth’s magnetic field on the accelerometer readings is discovered by way of spectral analysis of the functions representing the results of determining the low-frequency microacceleration by two methods. After making correction for this influence, the results obtained by these two methods coincided within a root-mean-square error of less than 10^?6 m/s².     

Ranging airport pseudolite for local area augmentation

This paper discusses the integration of an airport pseudolite (APL) into a local area augmented differential GPS based precision approach system. A prototype architecture is described that is being used to develop requirements for the local area augmentation system. Key features of this prototype system are presented along with its current performance. Key features discussed include the use of a multipath limiting antenna, APL signal structure factors, a unique APL automatic gain control, and GPS blanking technique to maximize APL tracking performance, while minimizing the electromagnetic interference to nominal DGPS performance     

ISO Observations of Pre-Stellar Cores and Young Stellar Objects

We summarize the observations of the Infrared Space Observatory (ISO) concerning the earliest stages of the stellar formation. The observations of samples of sources in different evolutionary stages are reviewed, addressing in particular how the physical and chemical properties of the protostellar environments change from the pre-stellar cores to the protostars at the end of their accretion phase. In addition, the mid-IR surveys in nearby star-forming regions are discussed, showing their implications for the understanding of the stellar initial mass function. Based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries: France, Germany, The Netherlands, and the United Kingdom), and with the participation of ISAS and NASA.     

A perspective on the importance of reproductive mode in astrobiology

Reproduction is a vital characteristic of life, and sex is the most common reproductive mode in the eukaryotic world. Sex and reproduction are not necessarily linked mechanisms: Sexuality without reproduction exists, while several forms of asexual reproduction are known. The occurrence of sexuality itself is paradoxical, as it is very costly in evolutionary terms. Most of the hypotheses (more than 20) attempting to explain the prevalence of sex fall into two categories: Sex either creates good gene combinations for adaptation to environments or eliminates bad gene combinations counteracting the accumulation of mutations. In spite of this apparent wealth of beneficial effects of sex, asexuality is not rare. Most eukaryotic, asexual lineages are short-lived and can only persist through the presence of sexual roots, but at least two animal groups, bdelloid rotifers and darwinulid ostracods, seem to claim the status of ancient asexuals. Research on (a)sexuality is relevant to astrobiology in a number of ways. First, strong relationships between the origin and persistence of life in extreme environments and reproductive mode are known. Second, the "habitability" of nonterrestrial environments to life greatly depends on reproductive mode. Whereas asexuals can do equally well or better in harsh environments, they fail to adapt fast enough to changing abiotic and biotic environments. Third, it has been shown that plants reproduce mainly asexually in space, and sperm production and motility in some vertebrates are hampered. Both findings indicate that extraterrestrial life under conditions different from Earth might be dominated by asexual reproduction. Finally, for exchange of biological material between planets, the choice of reproductive mode will be important.     

盘形锥齿轮的横向振动特性分析

本文分析了盘形锥齿轮的横向振动特性,分析指出此种齿轮小端齿槽底横向振动周向拉应力最大,故易在此处首先出现疲劳源。对此种齿轮振动的共振条件提出了新的理论。理论分析和试验实例表明两者结果十分一致。     

Microgravity and bone cell mechanosensitivity.

The capacity of bone tissue to alter its mass and structure in response to mechanical demands has long been recognized but the cellular mechanisms involved remained poorly understood. Bone not only develops as a structure designed specifically for mechanical tasks, but it can adapt during life toward more efficient mechanical performance. Mechanical adaptation of bone is a cellular process and needs a biological system that senses the mechanical loading. The loading information must then be communicated to the effector cells that form new bone or destroy old bone. The in vivo operating cell stress derived from bone loading is likely the flow of interstitial fluid along the surface of osteocytes and lining cells. The response of bone cells in culture to fluid flow includes prostaglandin (PG) synthesis and expression of prostaglandin G/H synthase inducible cyclooxygenase (COX-2). Cultured bone cells also rapidly produce nitric oxide (NO) in response to fluid flow as a result of activation of endothelial nitric oxide synthase (ecNOS), which enzyme also mediates the adaptive response of bone tissue to mechanical loading. Earlier studies have shown that the disruption of the actin-cytoskeleton abolishes the response to stress, suggesting that the cytoskeleton is involved in cellular mechanotransduction. Microgravity, or better near weightlessness, is associated with the loss of bone in astronauts, and has catabolic effects on mineral metabolism in bone organ cultures. This might be explained as resulting from an exceptional form of disuse under near weightlessness conditions. However, under near weightlessness conditions the assembly of cytoskeletal elements may be altered since it has been shown that the direction of the gravity vector determines microtubular pattern formation in vivo. We found earlier that the transduction of mechanical signals in bone cells also involves the cytoskeleton and is related to PGE2 production. Therefore it is possible that the mechanosensitivity of bone cells is altered under near weightlessness conditions, and that this abnormal mechanosensation contributes to disturbed bone metabolism observed in astronauts. In our current project for the International Space Station, we wish to test this hypothesis experimentally using an in vitro model. The specific aim of our research project is to test whether near weightlessness decreases the sensitivity of bone cells for mechanical stress through a decrease in early signaling molecules (NO, PGs) that are involved in the mechanical loading-induced osteogenic response. Bone cells are cultured with or without gravity prior to and during mechanical loading, using our modified in vitro oscillating fluid flow apparatus. In this "FlowSpace" project we are developing a cell culture module that is used to provide further insight in the mechanism of mechanotransduction in bone.