Prolonged weightlessness and calcium loss in man

Data have been accumulated from a series of studies in which men have been subjected to weightlessness in orbital space flight for periods of up to 12 weeks. These data are used to predict the long term consequences of weightlessness upon the skeletal system. Space flight induced a loss of calcium which accelerated exponentially from about 50 mg/d at the end of 1 week to approx. 300 mg/d at the end of 12 weeks. The hypercalciuria reached a constant level within 4 weeks while fecal calcium losses continued to increase throughout the period of exposure. This apparent diminution of gastrointestinal absorptive efficiency was accompanied by a slight decline in the plasma level of parathyroid hormone and a slight elevation in the plasma level of calcium and phosphorus. Although losses in mineral from the calcaneus were closely correlated with the calcium imbalance, no changes were detected in the mineral mass of the ulna and radius. From the data presented it is concluded that the process of demineralization observed in space flight is more severe than would be predicted on the basis of observations in immobilized, bed rested, or paralyzed subjects. It is, moreover, suggested that the process may not be totally reversible.     

Altitude Damping of Space-Stable Inertial Navigation Systems

In order to stabilize the altitude calculation in an inertial navigation system, an altimeter is commonly used. In a conventional local-level mechanization, this is generally accomplished by correcting the vertical channel integrators with the difference between the inertial system and altimeter indication of vertical position. However, in a space-stable system the procedure is not as clear since a vertical channel is not physically present. Three altitude damping mechanizations for a space-stable inertial navigation system are proposed. The equivalent local-level mechanizations are then found by comparing error propagation equations in a common coordinate frame.     

Corrections of Satellite Positions in Near-Real Time

The influence of sudden increases of electron content on the accurate determination of the position of a satellite is investigated based on a spherically stratified ionospheric model. Using the total electron content information from Faraday rotation measurements, a procedure is presented whereby the corrections of satellite position due to the unpredicted electron increase can be accounted for without the need to know the spatial distribution of the additional electrons.     

Constant-False-Alarm-Rate Processors for Locally Nonstationary Clutter

A technique for designing normalizing processors for locally non-stationary clutter is discussed. The design procedure assumes the logarithm of the clutter power varies as a polynomial with range. When the actual environment matches the design environment, the false-alarm rate is a constant that is independent of the polynomial coefficients. A measure of the relative target detection capability as a function of the number of normalization cells and the degree of the design-environment polynomial is given. The applicability of the processors to non-Rayleigh clutter is discussed.     

Performance Degradation Due to Specular Multipath Intersymbol Interference

Plots of performance degradation are used to compare the effects of fading and intersymbol interference in a two- component specular multipath digital communications channel. Similar plots are then used to compare two practical receivers designed to combat the interference. Degradation plots are shown to allow easy identification of each receiver's range of usefulness, as well as identification of variance bounds demanded of channel parameter estimates which the receivers require.     

Biological effects of heavy ions from the standpoint of target theory.

The biological effect of heavy ions is best described through the action cross section, as a function of the end-point of interest and the charge and speed of the ion. In track theory this is called the "ion-kill" cross section, for it is the effect produced by a single heavy ion and its delta rays. As with nuclear emulsions the biological track structure passes from the grain count regime to the track width regime to the thindown region with an increase in LET. With biological cells, as with any detector capable of storing sublethal damage, with low LET irradiation the action cross section (in the ion-kill mode) is increasingly obscured by the effect of "gamma-kill", by the influence of overlapping delta rays from neighboring heavy ions. Thus at low LET response is dominated by the gamma-kill mode, so that the RBE approaches 1. The theory requires 4 radiosensitivity parameters for biological detectors, extracted from survival curves at several high LET bombardments passing through the grain count regime, and at high doses. Once these are known the systematic response of biological detectors to all high LET bombardments can be unfolded separating ion kill from gamma kill, predicting the response to a mixed radiation environment, and predicting low dose response even at the level of a single heavy ion. Cell killing parameters are now available for a variety of cell lines. Newly added is a set of parameters for cell transformation.     

Formation and evolution of low-mass Algols

We discuss the origin, evolution and fate of low-mass Algols (LMA) that have components with initial masses less than 2.5 M₀. The semi-major axes of orbits of pre-LMA do not exceed 20–25 R₀. The rate of formation of Algol-type stars is 0.01/year. Magnetic stellar winds may be the factor that determines the evolution of LMA. Most LMA end their lives as double helium degenerate dwarfs with M₁/M₂ 0.88 (like L870-2). Some of them even merge through angular momentum loss caused by gravitational waves.     

An Electrooptical Automatic Gain Control

The laser beam affords a valuable carrier medium for an optical calmunication system, but such a system for transmission through the atmosphere is subjected to wide fluctuations in received signal strength because of turbulence. An electrooptical automatic gain control system em has been studied and built which can substantially reduce the effect of these fluctuations. The effect of system parameters on the control characteristics are considered.     

Conjugate features of magnetospheric electron dynamics observed at balloon altitudes

Analysis of recent observations (from balloons, spacecraft, and surface observatories) demonstrate regional, shell, and nearpoint conjugacy at L ～ 7 during precipitative events which were characterized by local acceleration as well as release of gradient-drifted electrons injected during substorms. A number of new features of magnetospheric dynamics relating to substorm development and sudden-commencement effects, have been brought to light which, though poorly understood at present, may prove of considerable importance and are worthy of further investigation.

1. During the initial period of instability in substorm evolution, preceding the slower magnetotail convective injection, precipitation of waves of electrons in rapid polewards motion exhibit L-shell conjugacy near midnight.
2. Transient, large scale expansions of the magnetospheric electron population accompanied by temporally imbedded substorms display large scale regional conjugacy and are simultaneously observed as similarly transient intensity dropouts at balloon altitudes.
3. Precipitation from gradient-drifting electrons in the dayside magnetosphere exhibits near point-conjugacy, at least down to the order of 50 km and quite probably less.

Similarly tight conjugacy applies to the release of electrons showing a specific local response to sudden commencements.

1. Analysis of the approach to and attainment of spectral equilibrium in the precipitation observed from drifting electrons may provide information about either, or both, the source spectrum at injection and the process of local release.
2. The specific precipitation effect sometimes observed at the time of an SC remains a rather puzzling feature, although it seems clear now that the acceleration and/or release process responsible is of a highly local nature and works selectively at small pitch angles well within the magnetospheric boundary. Coupling of the interplanetary shock with the magnetosphere must be an important aspect, but the details are not clear as yet.
3. On at least one occasion, a large part (perhaps all) of the magnetospheric electron population varied in a nearly synchronous manner in response to solar wind induced distortions during the variable compressive phase of a sudden commencement geomagnetic storm.

In the ongoing effort to identify and understand acceleration and release mechanisms involved in magnetospheric dynamics, balloon-borne experiments will continue to be useful, providing essential information presently unattainable by other means.