高能束流焊接技术在航空发动机耐热材料中的应用

我国高能束流焊接技术经过半个世纪,特别是近20年的迅速发展,逐渐形成了自己的研发体系.国内众多研究者进行的一系列基础理论和应用研究为高能束流焊接技术的发展奠定了基础.     

Comparison of self-healing ionomer to aluminium-alloy bumpers for protecting spacecraft equipment from space debris impacts

This paper discusses the impact behavior of a self-healing ionomeric polymer and compares its protection capability against space debris impacts to that of simple aluminium-alloy bumpers. To this end, 14 impact experiments on both ionomer and Al-7075-T6 thin plates with similar surface density were made with 1.5 mm aluminium spheres at velocity between 1 and 4 km/s.     

Cosmogenic Radionuclides as an Extension of the Neutron Monitor Era into the Past: Potential and Limitations

The cosmogenic radionuclides, ¹⁰Be, ¹⁴C and others, provide a record of the paleo-cosmic radiation that extends >10,000 years into the past. They are the only quantitative means at our disposal to study the heliosphere prior to the commencement of routine sunspot observations in the 17th century. The cosmogenic radionuclides are primarily produced by secondary neutrons generated by the galactic cosmic radiation, and can be regarded, in a sense, as providing an extrapolation of the neutron monitor era into the past. However, their characteristics are quite different from the man-made neutron monitor in several important respects: (1) they are sensitive to somewhat lower cosmic ray energies; (2) their temporal resolution is ～1 to 2 years, being determined by the rapidity with which they are sequestered in ice, biological, or other archives; (3) the statistical precision for annual data is very poor (～19%); however it is quite adequate (～5% for 22-year averages) to study the large variations (±40%) that have occurred in the paleo-cosmic ray record in the past between grand solar minima and maxima. The data contains “noise” caused by local meteorological effects, and longer-term climate effects, and the use of principal component analysis to separate these “system” effects from production effects is outlined. The concentrations of ¹⁰Be decreased by a factor of two at the commencement of Holocene, the present-day “interglacial”, due to a 100% increase in the ice accumulation rates in polar regions. The use of the ¹⁰Be flux to study heliospheric properties during the last glacial is discussed briefly.     

Planetary Dynamos from a Solar Perspective

Direct numerical simulations of the geodynamo and other planetary dynamos have been successful in reproducing the observed magnetic fields. We first give an overview on the fundamental properties of planetary magnetism. We review the concepts and main results of planetary dynamo modeling, contrasting them with the solar dynamo. In planetary dynamos the density stratification plays no major role and the magnetic Reynolds number is low enough to allow a direct simulation of the magnetic induction process using microscopic values of the magnetic diffusivity. The small-scale turbulence of the flow cannot be resolved and is suppressed by assuming a viscosity far in excess of the microscopic value. Systematic parameter studies lead to scaling laws for the magnetic field strength or the flow velocity that are independent of viscosity, indicating that the models are in the same dynamical regime as the flow in planetary cores. Helical flow in convection columns that are aligned with the rotation axis play an important role for magnetic field generation and forms the basis for a macroscopic α-effect. Depending on the importance of inertial forces relative to rotational forces, either dynamos with a dominant axial dipole or with a small-scale multipolar magnetic field are found. Earth is predicted to lie close to the transition point between both classes, which may explain why the dipole undergoes reversals. Some models fit the properties of the geomagnetic field in terms of spatial power spectra, magnetic field morphology and details of the reversal behavior remarkably well. Magnetic field strength in the dipolar dynamo regime is controlled by the available power and found to be independent of rotation rate. Predictions for the dipole moment agree well with the observed field strength of Earth and Jupiter and moderately well for other planets. Dedicated dynamo models for Mercury, Saturn, Uranus and Neptune, which assume stably stratified layers above or below the dynamo region, can explain some of the unusual field properties of these planets.     

DLR-TUBSAT, qualification of high precision attitude control in orbit

DLR-TUBSAT is a joint project of the DLR Institute of Space Sensor Technology and the Institute of Aeronautics and Astronautics at the Technical University of Berlin. Based on the experience gained with TUBSAT-A and TUBSAT-B an attitude control unit of minimal dimensions has been developed for the DLR-TUBSAT microsatellite. The DLR-TUBSAT microsatellite is mainly used to carry out tests involving exact three axes attitude control and to qualify the different subsystems with regard to their tasks in target pointing and high-resolution earth observation.     

Double strand breaks in the DNA of Bacillus subtilis cells irradiated by heavy ions.

Cells of Bacillus subtilis strain TKJ 8431 in stationary phase were irradiated with X-rays (150 kV at DLR) or heavy ions (Ne, Ar, Pb with residual energies between 3 and 15 MeV/u at GSI). The action cross section for the formation of double strand breaks in the DNA of the irradiated cells follows a similar dependence on mass and energy of the ions as has been found for various biological endpoints, e.g. inactivation, mutagenesis and repair efficacy.     

Glossary

Space Science Reviews -     

Nonlinear Optimal Feedback Regulation of Satellite Angular Monenta

Some important regulation properties of satellite angular momentum dynamics are investigated using a combination of reaction jets and flywheels. The optimal feedback controller is designed in such a way that system regulation, under large perturbations, to a proper bounded subset in Rn, is achieved by using reaction jets. Thereafter, flywheels are activated to bring the system to the rest (desired) state. The domain and the size over which reaction jets are active, as well as the corresponding fuel cost, are discussed. Further, the effect of linear as well as nonlinear optimal feedback regulators on system behavior is indicated. Finally, the range (in the state space Rn) over which the flywheels are capable of regulating the system is also studied.     

A holistic approach to the monitoring of land cover changes in Sri Lanka using intermediate remote sensing techniques

Heavy social and economic pressure on the available land resources in Sri Lanka are causing major land-cover changes. They need to be assessed to serve as input data for decision-making processes e.g. in agricultural or ecological planning.The Sri Lanka/Swiss Satellite Imagery Interpretation Project has developed a holistic approach to the mapping and monitoring of the land-use and the land-cover changes. The method applies intermediate level technology and is based on a benchmark/masking technique using satellite images, aerial photography and field surveys.The regular monitoring of changes of land-use types as a whole, e.g. forests, is part of the approach as well as the periodic assessment of changes within a specific land category, e.g. the seasonally cultivated riceland.The activities have to be transferred from the level of scientific research to the actual application within a reasonable time frame using the local resources. Discussed are also some of the problems inherent in the implementation of remote sensing activities in a so-called Third World country.