Incremental planning to control time-constrained blackboard-basedproblem solver [vehicle monitoring]

A planner that improves the control decisions made by a blackboard-based problem solver is described. This planner interleaves planning and execution. It sketches out major plan steps but incrementally details actions for only the next step since earlier actions influence how (and whether) to pursue a plan. The planner also reasons about time constraints, revising plans to meet problem-solving deadlines and deciding when it has done enough work on a problem. Implementation of these mechanisms is outlined, and experiments are discussed showing how they reduce overall computation and improve problem solving     

The role of antiprotons in cosmic-ray physics

Though success eluded experimentalists from detecting cosmic-ray antiprotons over a long period of time, the study of cosmic-ray antiprotons has now become a fascinating field of research. In this review, we have attempted to elucidate the excitement in this area of research since the discovery of antiprotons in the laboratory. We have described the experiments carried out so far to measure the energy spectrum of antiprotons, from about 200 MeV to about 15 GeV, and summarised the results. The observed spectrum, with the limited data, appears to be very hard and is different from other components of cosmic radiation. Upper limits to the fraction of antiprotons in cosmic-rays have also been derived at higher energies, using the observed spectra of cosmic-ray primary and secondary particles at different depths in the atmosphere. We have described various physical processes by which antiprotons could be produced, such as high-energy interactions, neutron oscillations, evaporation of Mini Black Holes, decay of super symmetric particles, etc. The energy spectrum of antiprotons, which are produced through the above processes, undergoes modifications during propagation in the Galaxy. We have examined in detail the propagation models which have been employed to explain the observed data. It is shown that no single model could predict correctly the observed energy spectrum of antiprotons over the entire energy region. However, many models are able to explain the data at relativistic energies. It is difficult at this stage to make a choice among these models. The implications of these models for other components of cosmic-rays, such as positrons, deuterium, and He, have been discussed. We have examined the production of gamma rays in the Galaxy from sources, which produce the observed antiprotons through high-energy interactions. We have also briefly indicated the effect of possible re-acceleration during their confinement in the Galaxy. We finally emphasized the need for more detailed measurements of the spectral shape of cosmic-ray antiprotons to further refine speculations of their origin. Similarly, we have shown that detailed observation of the energy spectra of positrons, deuterium, and He at relativistic energies are crucial to test various propagation models.     

Signatures of troposphere-stratosphere momentum coupling: Implications for global atmospheric angular momentum and earth rotation budgets

During January–August 1978, the global atmospheric angular momentum (M) exhibits distinct patterns of short term momentum interchange across latitudes. In the northern hemisphere winter-spring season, 30–50 day modulations of M are present in which momentum $\text{enhancements}$ at mid-latitudes (20–30°) are closely matched by momentum $\text{depressions}$ at high latitudes (50–60°). During the same interval there are no corresponding variations in M evident in the southern hemisphere. Conversely, during southern hemisphere fall-winter, similar anticorrelations in monthly scale momentum excursions are evident between mid and high latitudes. In the northern hemisphere, the winter-spring momentum signatures are detected throughout the atmosphere, from the lower troposphere to the stratosphere. During the southern hemisphere fall-winter, the modulation patterns are not evident at the higher altitudes. Structural details of the momentum signatures indicate that the coupling is sometimes effective on very short time scales, e.g. 1–2 days, or less. The evidence of distinct anti-correlation between large regions has interesting implications for studies of global atmospheric circulation, and also for studies of the excitation of variations in earth rotation in response to short term modulations of M.     

Dust environment models for comet P/Halley: Support for targeting of the GIOTTO S/C

In March 1985 ESA's GIOTTO spacecraft will fly by P/Halley's nucleus at a distance of a few hundred kilometres. The near nucleus dust environment the probe will traverse poses a hazard with respect to physical damage as well as to attitude disturbance with the possible loss of ground station contact. To predict S/C survivability and dust impact rates for the experiments, a model of the spatial distribution of the dust in the nucleus' vicinity is required. In the ‘dynamic’ model, the local spatial dust density is derived from exact expressions for the dust particle dynamic motion. The model has been implemented in a software system which allows for fast simulations of a cometary fly-by.     

Status of space science and technology — An Australian perspective

The “Tyranny of Distance” has had a profound influence on Australian history and reaction to it has been an important factor in determining national scientific and technological goals. Because of its size and geographical remoteness, Australia is one of the countries to have gained substantially from the applications of space technology particularly in the fields of communications, meteorology and remote sensing. Australia is the fifth largest investor in INTELSAT which carries a major fraction of the nation's overseas telecommunications. A domestic satellite system, AUSSAT, is being acquired to improve telecommunications within the country. Australia is heavily dependent on satellite data for routine meteorological forecasting. Data from the Australian Landsat Station are in strong demand, particularly for mineral exploration. In the field of space science, Australia is collaborating with Canada and the United States in feasibility studies for STARLAB, a free-flying UV-optical one metre telescope proposed for launch by the US Space Shuttle beginning in 1989. These scientific and technological programs in which Australia is participating are all dependent upon the space programs of other nations and in describing the status of space science and technology from an Australian perspective some comments will be made on particular aspects of the space programs of the United States and Japan.     

Properties of the neutral density and composition in the thermosphere

Measurements of the density and composition of the thermosphere between 150 and 500 km, which were obtained by the S3-1 satellite, have been compared with the Jacchia and MSIS models. The measurements of the densities of O, N₂, N and Ar show some differences from the current models which should be considered during the preparation of the next CIRA model. The Ar measurements are particularly useful in examining the response of the neutral atmosphere to geomagnetic heating. These results are useful in establishing the appropriate lower boundary conditions for modeling of the thermosphere.     

Experiences of the GDR in space sciences and technology

Following a historical review of the first activities of GDR scientists in the fields of space research, especially on astronomical and geodetical satellite-observations and in atmospheric and magnetospheric research, the growing scientific and increasingly efficient technological and economic benefits of the cooperation of the Academy of sciences and other scientific and technological institutions of the GDR within the Intercosmos-programme are described. Especially, the experiences in connection with remote sensing, of the cooperation with countries as Cuba and the Peoples Republic of Vietnam and of the common USSR - GDR manned spaceflight are discussed under the viewpoint of the mutual interests of developing and developed countries in the fields of space science and technology.     

Prebiotic synthesis and reactions of nucleosides and nucleotides.

Diiminosuccinonitrile (DISN) has been investigated as a potential prebiotic phosphorylating agent. It is formed readily by the oxidation of diaminomaleonitrile (DAMN), a tetramer of HCN. DISN effects the cyclization of 3'-adenosine monophosphate to adenosine 2',3'-cyclic phosphace in up to 40% yield. The DISN-mediated phosphorylation of uridine to uridine mono-phosphate does not proceed efficiently in aqueous solution. The reaction of DISN and BrCN with uridine-5'-phosphate and uridine results in the formation of 2,2'-anhydronucleotides and 2,2'-anhydronucleosides respectively, and other reaction products resulting from an initial reaction at the 2'- and 3'-hydroxyl groups. The clay mineral catalysis of the cyclization of adenosine-3'-phosphate was investigated using homoionic montmorillonites.     

Measurements of the earth radiation budget from satellites during the first garp global experiment

Two special measurements of the energy exchange between earth and space were made in connection with the FGGE. A global monitoring program using wide-field-of-view and scanner detectors from NASA's NIMBUS-7 satellite successfully returned measurements during the entire FGGE. This experiment system also used a black cavity detector to measure the total energy output of the sun to very high precision. A second set of high frequency time and space estimates of the radiation budget were determined from selected geostationary satellite data. Preliminary results from both radiation budget data sets and the solar “constant” measurements will be presented.