Distributed computation for a tree network with communicationdelays

Tree networks of communicating processors are examined with the objective of solving a computational problem in a minimal amount of time. The processors in the networks may be equipped either with or without front-end processors for communicating of loading. The determination of the optimal division of processing load is discussed for the network with and the network without front-end processors. The inclusion of solution time, the time taken for sensors to report the solution back to originator, is discussed     

A comparison of semi-empirical models in the lower thermosphere

Semi-empirical models are derived predominantly from satellite-borne observations. The nature of these observations restricts the applicability of the models mainly to the atmospheric regions sampled, i.e. the upper thermosphere. Current models are only capable of reproducing a zero-order approximation of the structure of the lower thermosphere. Based on selected examples, the progress in atmospheric research since CIRA-72 as well as the continuing deficiencies are demonstrated.     

Travelling heater growth of GaSb under reduced gravity during the first spacelab-mission

Single crystals of binary III-V-semiconductors, e.g. GaAs or InP, are important basic materials for optoelectronic devices, e.g. LED's and lasers. Device production needs highly perfect substrate crystals with low defect densities and homogeneous dopant distributions. In our experiment we applied the Travelling-Heater-Method to grow the III-V compound GaSb. The aim of this research project was to improve the crystal quality by investigating convective transport phenomena and the origins of dopant inhomogeneities under earth and space conditions. Earth grown crystals show strong dopant variations mainly due to convective flow phenomena. The preliminary result of our SPACELAB 1 experiment reveals an increase of dopant homogeneity in the space grown crystal because of the absence of natural convection under reduced gravity.     

Mesospheric ozone densities deduced from solar occultation measurements

Quartz-UV occultation measurements by the satellite Interkosmos-16 have been used to calculate ozone densities at altitudes between 50 and 90 km for the period August to October 1976. Below 65 km densities agree well with the Krueger-Minzner-model. Mesopause densities have been studied in some detail. A certain percentage of the profiles show close correlation with the model of Shimazaki and Laird (with a pronounced minimum below the mesopause) while others fit better to the Park and London model (no minimum). This variability of the ozone density may be caused by different processes in the photo-chemistry of ozone. Two possible causes, the temperature dependent rate coefficients and the odd hydrogen processes are discussed in greater detail.     

Extraction of mineral elements from inedible wastes of biological components of a life-support system and their utilization for plant nutrition.

Two methods of extracting mineral elements from otherwise deadlock products of a life-support system are presented. We describe first optimum conditions for recovering elements by water extraction from dry wastes of plants, biomass ash, and solid human wastes after passing them through the catalytic furnace; and, second, we describe acid extracts of biogenous elements by 1N and 2N HNO3 from these products. Ways to use the extracts of elements in plant nutrition are considered in order to increase the extent to which the mineral loop of a life-support system can be closed.     

Consideration in selecting crops for the human-rated life support system: a Linear Programming model.

A Linear Programming model has been constructed which aids in selecting appropriate crops for CELSS (Controlled Environment Life Support System) food production. A team of Controlled Environment Agriculture (CEA) faculty, staff, graduate students and invited experts representing more than a dozen disciplines, provided a wide range of expertise in developing the model and the crop production program. The model incorporates nutritional content and controlled-environment based production yields of carefully chosen crops into a framework where a crop mix can be constructed to suit the astronauts' needs. The crew's nutritional requirements can be adequately satisfied with only a few crops (assuming vitamin mineral supplements are provided) but this will not be satisfactory from a culinary standpoint. This model is flexible enough that taste and variety driven food choices can be built into the model.     

Decay rate of the second radiation belt.

Variations in the Earth's trapped (Van Allen) belts produced by solar flare particle events are not well understood. Few observations of increases in particle populations have been reported. This is particularly true for effects in low Earth orbit, where manned spaceflights are conducted. This paper reports the existence of a second proton belt and it's subsequent decay as measured by a tissue-equivalent proportional counter and a particle spectrometer on five Space Shuttle flights covering an eighteen-month period. The creation of this second belt is attributed to the injection of particles from a solar particle event which occurred at 2246 UT, March 22, 1991. Comparisons with observations onboard the Russian Mir space station and other unmanned satellites are made. Shuttle measurements and data from other spacecraft are used to determine that the e-folding time of the peak of the second proton belt. It was ten months. Proton populations in the second belt returned to values of quiescent times within eighteen months. The increase in absorbed dose attributed to protons in the second belt was approximately 20%. Passive dosimeter measurements were in good agreement with this value.