Heavy-ion effects on cellular and subcellular systems: inactivation, chromosome aberrations and strand breaks induced by iron and nickel ions.

A broad spectrum of particles and energies has been used in the last years to study the influence of the radiation quality i.e. of the physical parameters of the particle beam on the biological effectiveness ?2?12?. In these measurements a common structure of the functional dependence of the induction probability per particle (cross section) from the linear energy transfer is observed for different biological endpoints. Because of the relevance for space research, we present in this report our data from experiments with iron and nickel particles, in particular. Our experiments were designed to investigate the relationship between the inactivation and chromosome aberration in mammalian cells and the induction of single and double strand breaks in SV40 DNA in respect to the parameters of the track formation like LET and particle energy.     

Recent advances in lunar base simulation

This article reports about the results of the latest computer runs of a lunar base simulation model. The lunar base consists of 20 facilities for lunar mining, processing and fabrication. The infrastructure includes solar and nuclear power plants, a central workshop, habitat and farm. Lunar products can be used for construction of solar power systems (SPS) or other spacecraft at several space locations. The simulation model evaluates the mass, energy and manpower flows between the elements of the system as well as system cost and cost of products on an annual basis for a given operational period. The 1983 standard model run over a fifty-years life cycle (beginning about the year 2000) was accomplished for a mean annual production volume of 78 180 Mg of hardware products for export resulting in average specific manufacturing cost of 8.4 $/kg and total annual cost of 1.25 billion dollars during the life cycle. The reference space transportation system uses LOX/LH₂ propulsion for which at the average 210 500 Mg LOX per year is produced on the moon. The sensitivity analysis indicates the importance of bootstrapping as well as the influence of market size, space transportation cost and specific resources demand on the mean lunar manufacturing cost. The option using lunar resources turns out to be quite attractive from the economical viewpoint. Systems analysis by this lunar base model and further trade-offs will be a useful tool to confirm this.     

Aeroelastic stability of cascades in turbomachinery

State-of-the-art prediction of the aeroelastic stability of cascades in axial-flow turbomachines is reviewed. The first main chapter of the article presents a comprehensive formulation of the two- and three-dimensional classical (unstalled) flutter problem of tuned and mistuned rotor blade rows and bladed disc assemblies. Within the framework of linearized analysis, a complete and generalized theory in modal form is outlined, comprising the various formulations of the cascade flutter problem distributed in fragments throughout the literature. Brief outlines are also made of recent advances in unsteady aero-dynamic methods for turbomachinery aeroelastic applications. The second main chapter contains a parametric study of the classical flutter stability characteristics of compressor and turbine cascades in subsonic and supersonic flow. Stability boundaries and dominant trends in flutter behaviour are outlined, and the significant effects of blade mistuning on the aeroelastic stability of turbomachine bladings are highlighted.     

Protein crystal growth aboard the U.S. space shuttle flights STS-31 and STS-32.

The first microgravity protein crystal growth experiments were performed on Spacelab I by Littke and John. These experiments indicated that the space grown crystals, which were obtained using a liquid-liquid diffusion system, were larger than crystals obtained by the same experimental system on earth. Subsequent experiments were performed by other investigators on a series of space shuttle missions from 1985 through 1990. The results from two of these shuttle flights (STS-26 and STS-29) have been described previously. The results from these missions indicated that the microgravity grown crystals for a number of different proteins were larger, displayed more uniform morphologies, and yielded diffraction data to significantly higher resolutions than the best crystals of these proteins grown on earth. This paper presents the results obtained from shuttle flight STS-32 (flown in January, 1990) and preliminary results from the most recent shuttle flight, STS-31 (flown in April, 1990).     

Heavy ion measurement on LDEF.

A stack of CR-39 track detectors was exposed on the NASA satellite LDEF and recovered after almost 6 years in space. The quick look analysis yielded heavy ion tracks on a background of low energy secondaries from proton interactions. The detected heavy ions show a steep energy spectrum which indicates a radiation belt origin.     

Precision orbit determination for TOPEX/Poseidon using TDRSS doppler tracking data

Precision orbit determination on the TOPEX/Poseidon (T/P) altimeter satellite is now being routinely achieved with sub-5cm radial and sub-15 cm total positioning accuracy using state-of-the-art modeling with precision tracking provided by a combination of: (a) global Satellite Laser Ranging (SLR) and Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS), or (b) the Global Positioning System (GPS) Constellation which provides pseudo-range and carrier phase observations. The geostationary Tracking and Data Relay Satellite System (TDRSS) satellites are providing the operational tracking and communication support for this mission. The TDRSS Doppler data are of high precision (0.3 mm/s nominal noise levels). Unlike other satellite missions supported operationally by TDRSS, T/P has high quality independent tracking which enables absolute orbit accuracy assessments. In addition, the T/P satellite provides extensive geometry for positioning a satellite at geostationary altitude, and thus the TDRSS-T/P data provides an excellent means for determining the TDRS orbits. Arc lengths of 7 and 10 days with varying degrees of T/P spacecraft attitude complexity are studied. Sub-meter T/P total positioning error is achieved when using the TDRSS range-rate data, with radial orbit errors of 10.6 cm and 15.5 cm RMS for the two arcs studied. Current limitations in the TDRSS precision orbit determination capability include mismodeling of numerous TDRSS satellite-specific dynamic and electronic effects, and in the inadequate treatment of the propagation delay and bending arising from the wet troposphere and ionosphere.     

Modelling mesoscale processes in the global geospace system

Intermediate or mesoscale processes mediate the transfer of mass, momentum, and energy across the dynamic solar wind-magnetosphere interface, and the propagation of this input through the system to the ionosphere and atmosphere. The Dartmouth-Berkeley-Minnesota theory team has identified a number of mesoscale phenomena to be investigated as part of the GGS program, including: (1) effects of upstream density fluctuations on magnetopause dynamics, (2) three-dimensional reconnection, (3) magnetopause depletion layer studies, (4) ring current interaction with Pc 1 and Pc 5 waves, (5) generation of ion Larmor-scale current layers in the near Earth plasmasheet, (6) test particle studies in the magnetotail, (7) simulation of magnetosphere- ionosphere coupling including effects of kinetic Alfvén waves and (8) auroral acceleration region studies of the effects of kinetic Alfvén waves on particle distribution functions. A broad range of techniques will be implemented including ideal and reduced MHD, two fluid, hybrid, particle-in-cell and test particle simulations. Detailed comparison of simulation results with GGS satellite and ground based data will be undertaken.     

Solar cycle effects upon the relationship of Ne and Te in the F-region

Employing Atmsophere Explorer-C measurements made in 1974, just prior to solar minimum, Brace and Theis /1/ demonstrated that a remarkably consistent inverse relationship existed between the electron density N_e and temperature T_e in the F-region. In this paper we use later data from AE-C, taken when solar activity was rising (1975–1978), and Dynamics Explorer-2 data taken at solar maximum (1981), to examine how the temperature and density relationship changes with solar activity. We find that the solar maximum T_e is a factor of two larger than the solar minimum T_e for the same values of N_e. T_e does not necessarily increase with solar activity, however, because N_e increases enough to approximately cancel the effect of higher solar extreme ultraviolet heating. We find that the effect of solar activity can be accounted for by a simple function of the F_10.7 cm index that multiplies the solar minimum equation of Brace and Theis /1/.     

The stability of magnetic fields relevant to two-ribbon flares

The preflare structure, prior to two-ribbon flares, is thought to consist of magnetic field arcades. As a first approximation, the magnetic field is assumed to be invariant along the length of the arcade. The ideal MHD stability of such structures is studied using the energy method. The dense photosphere is simulated by line-typing the magnetic field and a discussion of boundary conditions is presented. Using the energy method, sufficient conditions for stability are obtained for certain magnetohydrostatic fields that also include the effect of gravity. Under certain circumstances, these conditions become necessary and sufficient. Some comments on resistive effects are mentioned.     

Thermal and nonthermal flare emission observed with the Nobeyama Radio Heliograph

The early phases of three flares, observed by the Nobeyama Radio Heliograph, are studied. Nonthermal and thermal radio sources are identified by comparison with soft X-ray images taken by the Soft X-ray Telescope onboard the Yohkoh satellite. Two of the flares are mainly of nonthermal origin and their location coincides with one of the footpoints of soft X-ray loops. Another flare has both thermal and nonthermal components which start to brighten simultaneously. This suggests that particle acceleration and plasma compression develop simultaneously.