Physical interpretation of interdisciplinary solar/interplanetary observations relevant to the 27–29 June 1980 SMY/STIP event no. 5

A sequence of six well defined interplanetary structures (magnetic clouds) was identified in the solar wind and magnetic field measurements of Helios-1 from 29 June-01 July, 1980. (location 0.64–0.67 AU, C. Long. ～165°, C. Lat. ～5.8°). These structures were characterized by a large northward directed solar wind flow; by well defined directional discontinuities of mainly the ‘tangential-type’ at their beginnings and ends; by some increase in proton and by very pronounced increases in alpha particle number densities - each accompanied by sudden temperature decreases (or in one case by an increase); by some times an increase in magnetic field strength and by values of Nα/Np typical of the inner solar atmosphere. These structures are suggested to have been ejections from a succession (27–29 June, 1980) of Type II producing flares in Hale Region 16923 which coronagraph and X-ray (GOES) data indicate constituted a family of transient producing events. Only two interplanetary shocks were identified in the relevant Helios-1 records. It is suggested on the basis of observations of the directionality of certain of the flare related Type II bursts that some of these shocks could have been missed by the spacecraft. This implies that, in the absence of directional information, correlation of an observed interplanetary shock wave with a solar Type II burst may not always lead to a unique result.     

Evaluating the economic impact of design alternatives on domestic communication satellite ventures

What are the economic consequences of establishing a domestic communication satellite venture? Has the best design alternative been selected? Should investments be made to develop new technology? How much should be invested? These are but some of the questions facing those concerned with providing domestic communication satellite services. Because of the demand, performance and cost uncertainties and the unpredictability of the need for and timing of large capital expenditures (due to less than perfect reliability of transportation systems and satellites) providing answers to these and other related questions is a complex process.This paper describes a methodology for providing answers to the above questions. The methodology, by explicitly considering demand, performance and cost uncertainties and satellite and transportation system reliability, develops probabilistic pro forma financial analyses of domestic communication satellite system ventures. In so doing, the risk dimension is quantified and alternative courses of action can be evaluated and compared taking into account expected values, risk and risk aversion preferences. It is also important to quantify and consider the risk dimension since many R &; D projects are specifically aimed at risk reduction.     

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.     

Radiation environments and absorbed dose estimations on manned space missions.

In order to make an assessment of radiation risk during manned missions in space, it is necessary first to have as accurate an estimation as possible of the radiation environment within the spacecraft to which the astronauts will be exposed. Then, with this knowledge and the inclusion of body self-shielding, estimations can be made of absorbed doses for various body organs (skin, eye, blood-forming organs, etc.). A review is presented of our present knowledge of the radiation environments and absorbed doses expected for several space mission scenarios selected for our development of the new radiation protection guidelines. The scenarios selected are a 90-day mission at an altitude (450 km) and orbital inclinations (28.5 degrees, 57 degrees and 90 degrees) appropriate for NASA's Space Station, a 15-day sortie to geosynchronous orbit and a 90-day lunar mission. All scenarios chosen yielded dose equivalents between five and ten rem to the blood forming organs if no large solar particle event were encountered. Such particle events could add considerable exposure particularly to the skin and eye for all scenarios except the one at 28.5 degrees orbital inclination.     

Signal-to-Noise Ratio of Arbitrary Power-Series Nonlinear Amplifier

A general analysis of the effect of an arbitrary power-series nonlinear amplifier followed by a coherent mixing device on signal-to-noise ratio (SNR) is performed. An expression is derived for the improvement factor which is defined as the logarithm of the ratio of the output SNR to the input SNR. This expression is applicable to the coherent amplitude detector and phase locked loop as well as noncoherent amplifier by appropriate selections of the detection angle. Moreover, the improvement factor can be obtained for noise with an arbitrary amplitude distribution. To demonstrate the applicability of this analysis, the improvement factors of the nonlinear amplifiers such as a power-law amplifier and a power-series amplifier with positive and negative discriminations are numerically calculated for the cases where the input noise amplitude distributions are Rician and triangular.     

Dependence of ESP intensity on collisionless shock wave characteristics

Flux variations of 1 – 5 MeV protons are studied in energetic storm particle events with respect to the preshock solar wind plasma parameters and to the thickness of the collisionless interplanetary shock wave. It is found that the peak intensity in ESP events depends on pre-shock plasma density and on the thickness of the transition region. These relations predict, in agreement with recent observations, the increase of ESP events at larger heliocentric distances.     

Equatorial F-region ionization differences between March and September, 1979

Ionospheric total electron content and the F-region maximum electron density at a number of stations in the equatorial region, during the recent solar activity maximum period 1979 to 1980, show significant differences between the two equinoctial periods. Ionization during the month of March is higher than in September, irrespective of the station location both in northern and southern hemispheres, and in different longitude sectors. The observed pattern is compared with those predicted by different models, in particular with one of the authors which includes processes such as ionization production, loss, electrodynamic drifts, winds and global composition changes involved in the equatorial ionosphere. It is found that a change in the neutral composition is primarily responsible for the observed F-region density differences between March and September.     

Cometary habitats for primitive life.

Comet Halley studies indicate most of the nucleus is covered by an insulating crust, presumed of pyrolysed organic material. The subcrust is warmed and percolated by gases within 2AU, so provides one habitat for primitive replicating organisms. Cracks and crevices within contaminated ice in the craters provides a habitat for photosynthesising organisms. Subsurface lakes on the Europa model, though insulated by some metres of ice, would require a trigger (perhaps meteorite impact and energy source (chemical or metabolic energy) to initiate and maintain a suitable-habitat on short period comets. Constraints on transfer between comets and other planetary bodies implies that radiation-resistant species with lengthy hibernation potential would be expected.     

The low energy gamma-ray experiments on GRO in perspective

The NASA Gamma-Ray Observatory, GRO, will carry two instruments for low energy gamma-ray astronomy. The ‘Oriented Scintillation Spectrometer Experiment - OSSE’ represents the latest step in the evolution of collimated detectors. A large detection area, simultaneous source and background observation and rigorous control over systematic errors yield significant improvements in sensitivity over earlier instruments. The ‘Imaging Compton Telescope - COMPTEL’ brings the proven concept of the Compton telescope to the state of the art level. Position sensitive scintillation detectors make it possible to generate sky images with a resolution of about 2° over a f.o.v. of about 1 sr. The complementary nature of these two experiments promises a first in-depth exploration of the sky in a wavelength range which covers the transition from the X-ray sky to the apparently unrelated high energy gamma-ray sky. Possible directions of further evolution of these experiments will be discussed.     

Discrete-time state estimation of analog double integrators

The problem of minimum variance discrete-time state estimation of a continuous-time double integrator via noisy continuous-time measurements is considered. The error covariance matrices of this estimation are calculated and analyzed. The relations between these covariance matrices and the error covariance matrix of the optimal continuous-time filter are obtained, and a way for determining the required sampling period is proposed. A commonly used approximated model is investigated; it is shown to be inappropriate unless a specific improvement is introduced in the model