Showing papers by "Government College published in 1974"

Annealing studies on radiation damages in biotite, apatite and sphene and corrections to fission track ages

Abstract: Fission track ages need to be corrected for the loss of fossil tracks due to geological and thermal annealing. The range distribution of full-length tracks can yield such corrections if calibration curves translating length reductions into density reductions are available. The study of the annealing characteristics of the three terrestrial minerals, i.e. biotite, apatite and sphene, as functions of temperature and time, has been completed from this point of view. A linear relation has been observed between etchable track length and track density, but slopes and intercepts of the curves tend to vary from mineral to mineral. Over-etching shows significant effect in retrieving partially faded tracks in the case of biotite only, and track density reduction always lags behind track length reduction. In apatite and sphene track density is reduced in the same proportion as track length when length reduction is ∼30 to 50%. For length reductions 50% the density reduction progressively outweighs the former. The possible reasons for such variations and the usefulness of the calibration curves are briefly discussed.

Physical activity and efficiency of mental work.

Abstract: To investigate the influence of physical activity on the efficiency of mental work 50 Ss between 19 and 21 yr. of age did step-ups (for physical activity) and added, subtracted, multiplied, and divided simple sums of one digit (for mental work). Analysis disclosed a significant (p < .01) increase in mental work when the physical activity was of 2 and 5 min. duration and significant (p < .01) decrease when the physical activity was of 10 and 15 min. duration.

Fission track ages of cogenetic minerals of the Nellore mica belt of India

Abstract: Fission track ages of three cogenetic minerals, i.e. muscovite, apatite and biotite, from the Nellore mica belt of India have been determined. Corrections to the observed ages due to geological annealing of fossil tracks have been computed by comparative study of the track lengths of fossil as well as induced fission tracks. An attempt has been made to infer the thermal history of the region in the light of different annealing behaviours of minerals and the discordance in their ages. The muscovite age of 632±15 m.y. corresponds to the occurrence of major metamorphic event and the apatite age of 446±10 m.y. appears to coincide with the time when the thermal conditions in the region became stable. The muscovite age can be reconciled with the biotite age (487±17 m.y.) when its track length distribution curve is interpreted on a two-stage thermal annealing model and the necessary corrections are applied for the decrease of fossil track density.

Studies on the nocturnal periodicity of six species of black flies (Diptera: Simuliidae) at Darjeeling, West Bengal

Abstract: The nocturnal periodicity of six species of black flies (Diptera : Simuliidae) of Darjeeling was found out from the data of light trapping made in three equal shifts for each of the five nights selected in 1969. The incidence of these flies was marked by hourly variation. Each ofpraelargum, gracilis, himalayense, grisescens andtenuistylum showed its peak abundance in the middle of night, whilerufibasis was at its peak at the end of night. The percentage composition ofgracilis andgrisescens in the last shift was higher than that in the first shift, and this was the general trend of the species of these flies taken together. The incidence ofpraelargum andtenuistylum in the first shift was higher than that in the last shift. Inhimalayense the distribution was similar in any of the two shifts, while inrufibasis it was found to rise gradually, thereby attaining itself to its peak at the end of night. The incidence shown by the two sexes of a species did not always obey the general trend and this is discussed in detail in this communication.

Propagation of waves in warm plasma with anisotropic pressure

Abstract: The effect of the thermal electron pressure on the propagation characteristics of arbitrarily directed waves travelling in a homogeneous warm electron magneto-plasma is dealt with in this paper. It is noted that, in general, thermal pressure does not affect the propagation characteristics of those waves which are electro-magnetic in nature but it excites another wave known as the electron plasma mode. In the case of the isotropic pressure, only ono electron plasma mode propagates in all possible directions. But when the thermal electron pressure is considered to be anisotropic, two electron plasma waves propagate in any arbitrary direction other than the directions along and perpendicular to the external magnetic field, in which directions only one electron plasma wave propagates. The phase velocities of these waves are discussed in detail for several particular cases.