Assessing exposure to cosmic radiation on board aircraft.

The assessment of exposure to cosmic radiation on board aircraft is one of the preoccupations of organizations responsible for radiation protection. The cosmic radiation particle flux increases with altitude and latitude and depends on the solar activity. The radiation exposure has been estimated on several airlines using transatlantic, Siberian and transequatorial routes on board subsonic and supersonic aircraft, to illustrate the effect of these parameters. Measurements have been obtained with a tissue equivalent proportional counter using the microdosimetric technique. Data have been collected at maximum solar activity in 1991-92 and at minimum in 1996-98. The lowest mean dose rate measured was 3 microSv/h during a Paris-Buenos Aires flight in 1991; the highest was 6.6 microSv/h during a Paris-Tokyo flight using a Siberian route and 9.7 microSv/h on Concorde in 1996-97. The mean quality factor is around 1.8. The corresponding annual effective dose, based on 700 hours of flight for subsonic aircraft and 300 hours for Concorde, can be estimated between 2 mSv for least-exposed routes and 5 mSv for more exposed routes.     

Information Support for Space Experiments Based on a Numerical-Analytical Theory of Satellite Motion

A software tool for application in calculations of the position and velocity vectors of spacecraft is presented. These vectors are necessary at the stage of processing the data of space experiments and analyzing the results of ground-based observations. A new theory of satellite motion, in a numerical-analytical form, is the basis of this software application. The model of disturbing forces corresponds to recommendations of the International Laser Ranging Service. The reliability of the software tool is confirmed by the results of processing of high-precision laser satellite observations.     

Galactic cosmic ray transport methods: past, present, and future.

The development of the theory of high charge and energy (HZE) ion transport is reviewed. The basic solution behavior and approximation techniques will be described. An overview of the HZE transport codes currently available at the Langley Research Center will be given. The near term goal of the Langley program is to produce a complete set of one-dimensional transport codes. The ultimate goal is to produce a set of complete three-dimensional codes which have been validated in the laboratory and can be applied in the engineering design environment. Recent progress toward completing these goals is discussed.     

Cognitive deficits induced by 56Fe radiation exposure.

Exposing rats to particles of high energy and charge (e.g., 56Fe) disrupts neuronal systems and the behaviors mediated by them; these adverse behavioral and neuronal effects are similar to those seen in aged animals. Because cognition declines with age, and our previous study showed that radiation disrupted Morris water maze spatial learning and memory performance, the present study used an 8-arm radial maze (RAM) to further test the cognitive behavioral consequences of radiation exposure. Control rats or rats exposed to whole-body irradiation with 1.0 Gy of 1 GeV/n high-energy 56Fe particles (delivered at the alternating gradient synchrotron at Brookhaven National Laboratory) were tested nine months following exposure. Radiation adversely affected RAM performance, and the changes seen parallel those of aging. Irradiated animals entered baited arms during the first 4 choices significantly less than did controls, produced their first error sooner, and also tended to make more errors as measured by re-entries into non-baited arms. These results show that irradiation with high-energy particles produces age-like decrements in cognitive behavior that may impair the ability of astronauts to perform critical tasks during long-term space travel beyond the magnetosphere.     

Oscillations of axial plant organs.

The tips of roots and shoots commonly show lateral movements as they grow forwards. These occur as both circumnutations (with long periods and large amplitudes) and micronutations (with short periods and small amplitudes). Their properties are reviewed, with emphasis on roots, and possible ways in which they could be regulated are discussed. The mechanisms could include long-range controls (for circumnutations) that depend on transmissible signals using steps common to gravitropism, and short-range controls (for micronutations) that operate within the elongation zone. The former are a property of the apex as a whole, while the latter may be confined to localized groups of cells. Simulation of nutations is presented with a view to isolating key physiological processes. However, this approach is limited by the current inadequate understanding of the growth mechanisms involved.     

A program to measure new energetic particle nuclear interaction cross sections.

The Transport Collaboration, consisting of researchers from institutions in France, Germany, Italy and the USA, has established a program to make new measurements of nuclear interaction cross sections for heavy projectiles (Z > or = 2) in targets of liquid H2, He and heavier materials. Such cross sections directly affect calculations of galactic and solar cosmic ray transport through matter and are needed for accurate radiation hazard assessment. To date, the collaboration has obtained data using the LBL Bevalac HISS facility with 20 projectiles from 4He to 58Ni in the energy range 393-910 MeV/nucleon. Preliminary results from the analysis of these data are presented here and compared to other measurements and to cross section prediction formulae.     

Suboptimal joint probabilistic data association

A significant problem in multiple target tracking is the hit-to-track data association. A hit is a received signal from a target or background clutter which provides positional information. If an incorrect hit is associated with a track, that track could diverge and terminate. Prior methods for this data association problem include various optimal and suboptimal two-dimensional assignment algorithms which make hit-to-track associations. Another method is to assign a weight for the reasonable hits and use a weighted centroid of those hits to update the track. The method of weighting the hits is known as joint probabilistic data association (JPDA). The authors review the JPDA approach and a simple ad hoc approximation and then introduce a new suboptimal JPDA algorithm. Examples which compare an optimal two-dimensional assignment algorithm with the ad hoc and the new suboptimal JPDA formulation are given     

Kinetic cyclotron and synchrotron maser instabilities: Radio emission processes by direct amplification of radiation

This article reviews the theory of the kinetic (cyclotron an synchroton) maser instabilities. The subject has been extensively developed in recent years by many authors, who have been incited by the research of the auroral kilometric radiation and other applications. The maser mechanism is appealing because it is simple and efficient, and can lead to direct amplification of radiation. Two types of electron distribution functions have been investigated so far. These are the loss-cone and hollow-beam distributions which may exist pervasively in many regions within and beyond the solar system. It is likely that the maser instabilities can have many potentially important applications to numerous radio emission processes observed in astrophysical research.     

Design study for a three-meter balloon-borne telescope for far infrared and submillimeter astronomy

A NASA supported design study is being carried out for a three-meter balloon-borne far infrared and submillimeter telescope. The goal of this project is to provide a facility for frequent flights for photometry, spectroscopy, and imaging in the spectral region 30 micrometers to 1 millimeter. It is intended to provide a scientific and technical step on the way to a large submillimeter telescope in space in the future. The study is concentrating on areas where technical advances are required: materials and fabrication techniques for lightweight primary mirrors, telescope and gondola structure, and pointing and stabilization. We are carrying out a design optimization and environmental test program of state-of-the-art carbon fiber reinforced plastic sandwich panels in collaboration with Dornier Systems. Similar efforts are being pursued for very lightweight molded glass mirrors. Innovative approaches to the telescope support and stabilization are being explored for achieving the required 1 arcsecond pointing stability.     

Preliminary results of Cytos 2 experiment.

Cytos 2 experiment, carried out during the French-Soviet manned flight (July 1982), has studied the antibiotics sensitivity of bacteria cultivated in vitro during the orbital flight. The results show an increase of the antibiotics resistance and a larger thickness of the cellular envelope for the inflight cells. The increase of antibiotics resistance can be related to a stimulating effect of space on the cell growth rate or to changes of the cellular envelope structure.