The effects of microgravity on induced mutation in Escherichia coli and Saccharomyces cerevisiae.

We examined whether microgravity influences the induced-mutation frequencies through in vivo experiments during space flight aboard the space shuttle Discovery (STS-91). We prepared dried samples of repair-deficient strains and parental strains of Escherichia (E.) coli and Saccharomyces (S.) cerevisiae given DNA damage treatment. After culture in space, we measured the induced-mutation frequencies and SOS-responses under microgravity. The experimental findings indicate that almost the same induced-mutation frequencies and SOS-responses of space samples were observed in both strains compared with the ground control samples. It is suggested that microgravity might not influence induced-mutation frequencies and SOS-responses at the stages of DNA replication and/or DNA repair. In addition, we developed a new experimental apparatus for space experiments to culture and freeze stocks of E. coli and S. cerevisiae cells.     

惩罚函数法在发动机性能计算中的应用

按照涡喷发动机工作时遵守的气动热力学定律，建立了发动机的稳定数学模型，并针对双轴涡轮发动机性能计算的非线性数学模型，利用优化和最优控制理论中的惩罚函数法，对发动机性能进行了基于约束的最优求解程序设计，利用程序对某型发动机的稳定飞行特性进行了计算，计算结果表明，使用惩罚函数法求出的特性曲线变化规律正确，发动机平衡方程的解的精度更高，在此基础上得出的发动机飞行特性也更准确。另外惩罚函数法对初值的要求很低，迭代运算不易发散。     

Plasma production by secondary impacts: Implications for velocity measurements by in-situ dust detectors

A number of in-situ cosmic dust detectors derive the dust particle velocities from measurement of the risetimes of the impact plasma signal. Extensive calibration of these instruments has established a reliable empirical relationship but a quantitative explanation has not been available, with the result that confidence in flight data outside the range of the calibration data is hard to assess. Recent measurements taken at the dust accelerator facilities at the University of Kent (UK) and at MPI-K (Germany), supported by a theoretical analysis, have demonstrated that the relationship results from the time-spread of secondary impacts coupled with the mobility of ions in the impact plasma cloud, which is in turn determined by the magnitude and geometry of the applied electric field and on the ion species present. Results of the current investigations are presented, and the implications of measurements based on this principle at high particle velocities, at masses unobtainable in calibration studies, and for other instrument geometries, are considered.     

Calibration techniques for magnetometers implementing on-board de-spinning algorithms

The Fluxgate Magnetometer experiments on-board the European Space Agency’s four spacecraft Cluster Mission have the capability to store sampled magnetic field vectors in the instrument memory, either as a full resolution ‘event capture’ or as spin-resolution vectors transformed into a non-spinning co-ordinate system (de-spun). The latter capability has ensured a dataset is available which extends the partial orbital coverage achieved during nominal operations in the first years of operation. The on-board de-spin is achieved using a Walsh function with Haar coefficients and allows for up to 27 h additional data per non-coverage interval. A number of commissioning orbits were used to verify the accuracy of data collected by the de-spin mode, whereby individual spacecraft were operated separately in a number of standard normal sampling and de-spin mode combinations. Up to the present time, this data has not been available to the Cluster community. We present results here comparing the performance of the on-board de-spin algorithm versus the normal sampling modes over a number of boundary layer crossings, describe the techniques used for calibration and timeline recovery, and outline the context in which the data may be usable in future studies.     

Exercise response to simulated weightlessness

Two bed rest analog studies of space flight were performed; one 14 d and the other 28 d in duration. Exercise response was studied in detail during the 28 d study and following both the 14 d and 28 d studies. This paper relates the results of these studies to physiologic changes noted during and following space flight. The most consistent change noted after both bed rest and space flight is an elevated heart rate during exercise. A second consistent finding is a postflight or postbed rest reduction in cardiac stroke volume. Cardiac output changes were variable. The inability to simulate inflight activity levels and personal exercise makes a direct comparison between bed rest and the results from specific space flights difficult.     

Track-While-Scan Algorithm in a Clutter Environment

A track-while scan (TWS) algorithm is developed for targets in a clutter environment. The problem has been studied using only the position measurements [1, 5-8], but the simulation results have not been satisfactory. Modern processing techniques (FFT processor) ) in air traffic control and surveillance radar receivers provide both position and radial velocity. The radial velocity measurement may be conveniently used in the target-track correlation process, which will reduce the association ambiguity in the clutter environment. t. In the clear environment the algorithm using the position and radial velocity measurements has been treated in [3, 4]. A TWS algorithm, using both position and radial velocity measurements for targets in a clutter environment, is presented here. The algorithm obtained is nonlinear and adaptive. In order to evaluate the improvement due to radial velocity measurement a simulation has been performed on a digital computer. The algorithm was run with and without radial velocity measurements to compare its performances. An improvement was noted especially when the target path included an accelerated portion.     

The scientific case for renewed human activities on the Moon

It is over 30 years since the last human being stood on the lunar surface and this long hiatus in human exploration has been to the detriment of lunar and planetary science. The primary scientific importance of the Moon lies in the record it preserves of the early evolution of a terrestrial planet, and of the near-Earth cosmic environment in the first billion years or so of Solar System history. This record may not be preserved anywhere else; gaining proper access to it will require a human presence. Moreover, while this will primarily be a task for the geosciences, the astronomical and biological sciences would also benefit from a renewed human presence on the Moon, and especially from the establishment of a permanently occupied scientific outpost.     

A Study of the Reflection of Radio Waves from the Plasma Region on the Track behind an Axisymmetric Body Moving in the Earth’s Atmosphere

The results of numerical calculation of the dependences of the electron density, the eigenfrequency and the dielectric plasma permeability on the geometric parameters and the altitude of body motion in the near and far wake behind a thin conical body with a spherical nose blunting have been presented. The electron density maximum has been shown to be located in the region of the neck of the near wake behind the body, which determines the type of this region (supercritical or subcritical). This in turn affects the propagation of radio waves through this plasma region. A comparative analysis was performed for two different bodies with the same ballistic coefficient values. No characteristic distinctions were revealed in the values of electron density or the plasma eigenfrequency in the near and far wake behind these bodies. However, it has been shown that there are differences in the values of the distance from the bottom cross section to the neck of the near wake behind these bodies.