No abstract

The collision frequency of electrons in the F region of the ionosphere has been measured at Delhi (geographical latitude 28°38′ N, geographical longitude 77°13′ E) using a method similar to that suggested by Appleton. The amplitude and group path of short radio waves vertically incident on the F region of the ionosphere have been measured simultaneously at a suitable frequency (for both the ordinary and extraordinary wave modes) in early morning and late evening hours, corresponding to times of appearance and disappearance of the echo, respectively. Simultaneous changes in amplitude and group path are related to deduce the collision frequency. Some selected records taken near the time of sunrise have been analyzed and the values of collision frequency are found to be (4.2 ± 0.5) × 103 and (3.5 ± 0.5) × 103 s−1 for the ordinary and extraordinary waves, respectively, in the true-height range of 270–310 km.

Coronary heart disease (CUD) is the major cause of sudden death amongst adults throughout the globe. Though the prevalence of CUD Is increasing steadily all over, CUD amongst Indians Is peculiar in the sense that it Is more prevalent. more severe and appears at younger age. Development of CUD depends upon the status of various coronary risk factors in one's body. It bas been observed that to measure the impact of risk factors for the cardiac health of a person, coUective impact of aU the known risk factors taken together should be calculated rather than individual risk factors. DEBEL (Defence Bio-Engineering and Electro-Medical Laboratory) is developing a cardiac risk analyser to calculate the absolute coronary risk of an individual in next 2.,5 or 10 years and help in managing his coronary risk status.

A comprehensive clinical study on the effects of various aviation stresses on soft and semisoft contact lenses was carried out to find out their compatibility in aviation environment. Twenty subjects (11 aircrew and 9 non air-crew) participated in the study. Twelve of them were given soft lenses of water contents of 38%, 50% and 78% and rest 8 were given semisoft lenses of daily wear and extended wear type. The environmental trial consisted of exposure to hypoxia, rapid decompression, acceleration, pressure breathing, vibration and high temperature. On successful completion of environmental trials on ground simulators, the inflight trials on high performance aircraft, transport aircraft, passenger aircraft and helicopters were conducted. The soft lenses with low, medium and high water contents and extended wear semisoft lenses (large diameter) were found compatible with all types of aircraft flying.