The pulse-period distribution of binary X-ray pulsars

The pulse-period distribution of binary X-ray pulsars has been considered. A gap in this distribution, in the period rangeP10 s toP100s has been explained in terms of the character of mass transfer in the X-ray binary systems. It is shown that this gap arises because the rotating magnetised neutron stars in these systems are slowed down by accretion torques, either toP10 s when the mass transfer is by means of Roche-lobe overflow in low mass binaries, or toP100 s by stellar winds in massive binaries. The gap is maintained as the slow pulsars (P>100 s) in their spin-up phase cross the gap in a time short compared to their life-time, because of the increase in mass transfer with the evolution of the normal star.     

Movement of theSq foci in 1958

Summary Latitudinal locations of the foci of theSq ionospheric current systems are estimated for each month using geomagnetic data for five international quiet days of each month of the year 1958. It is found that: 1) The pattern of the monthly movement is different in the three sectors chosen for this investigation (North-South American Sector, European-African Sector and Asian-Australian Sector). 2) Regardless of the sector the foci generally seem to move together in the same direction like a rigid system; during the northern summer they shift towards a more northerly latitude than during the northern winter. 3) The positions of the foci differ considerably in adjacent months. 4) The largest movements of the foci are noted in the American sector where the magnetic dip equator is farthest south.Contribution from the Earth Physics Branch No. 453.     

Uplift capacity of pile group anchors

Experimental investigations on model single pile anchor and pile group anchors of configuration 2 × 2 subjected to uplift loads were conducted on dry Ennore sand, obtained from Madras, India. The embedment length to shaft width ratios, L/d = 20 and L/d = 30, and enlarged base width to shaft width ratios, B/d = 1,2,3, center to center spacing of pile anchors in the groups, 3d, 4d, 6d and 8d were used. The load displacement response, ultimate resistance and variation of group efficiency with L/d, B/d and spacing have been studied quantitatively and qualitatively. For short pile group anchors (L/d = 20), the isolation spacing appears to be at a spacing of about 4d to 6d and 8d for B/d = 1 and B/d = 2 and 3, respectively. For long pile group anchors (L/d = 30), the isolation spacing appears to be at a spacing of about 4d, 6d and 8d for B/d = 1, 2 and 3, respectively. The analytical model of limit equilibrium method has been proposed to predict the net uplift capacity of pile group anchors. The predicted results compare reasonably well with the experimental results.     

Remote probing ofD-region irregularities

The nature of theD-region irregularities responsible for partial reflections is studied using amplitude, phase and range information taken at Buckland Park, South Australia, utilising a 178-dipole receiving array. Stratifications with distinct layer type structures below 80 km are noticed. A major part of the echo amplitude consists of specularly reflected signals.     

Daily variations ofE andF region drifts over Tiruchirapalli

Daily variations of the E-W and N-S components of ionospheric drifts, measured using closely spaced receiver method over Tiruchirapalli near magnetic equator, are described for the periods 1973–75 forE region and 1974–75 forF region. N-S component is not observed except for a few occasions during summer months for theE region. E-W component is generally eastward during night hours and westward during day hours. There is a large day-to-day variability in the magnitude as well as in the evening reversal time. Daily variations primarily consist of the diurnal component with average amplitude of about 90 m/sec forF region and of about 80 m/sec forE region. The drift speeds are found to decrease with magnetic activity. It is concluded that the abnormal electrojet region extends upto north of Tiruchirapalli in the Indian zone and drifts here can be used as a monitor of electric field.     

Geomagnetic disturbance effects on equatorial spreadF

Geomagnetic disturbance effects on the occurrence of range and frequency spread at Huancayo are studied for the period 1957–74. The occurrence of frequency spread is decreased on disturbed days forD-months andE-months while duringJ-months an increase is noted in the post-midnight period. The occurrence of range spread is decreased on disturbed days in the pre-midnight hours duringD andE-months. Post-midnight hours ofD andE-months and all hours of night duringJ-months show an increase of range spread on disturbed days, which is most prominent during low sunspot years. The mean occurrence of frequency spread (2300–0100 LT) and range spread (2000–2300 LT) decrease with increasing ΣKp. On the other hand, occurrence of range spread (0300–0500 LT) increases with increasing ΣKp, and is suggested as the consequence of the changes of the horizontal electric field in theF-region associated with the geomagnetic storms.     

Diffraction ofSH-waves originating from a moving point source by a rigid quarter space

Summary ApplyingWiener-Hopf techniques the diffraction ofSH-waves originating from a moving point source due to the presence of a step change in the elevation of the surface of a homogeneous half-space have been obtained. An interesting feature of resonance associated with the motion of a load at a velocityv ₀ ^–1 approachingv ₀ ^–1 has been observed.     

Thermal stresses in a finite cylinder having temperature varying linearly along the length prescribed on the curved surface

Summary The problem of a finite cylinder of isotropic material in which the temperature on the curved surface varies linearly along its length and has its ends in contact with smooth rigid insulating plates has been investigated in this paper.     

Characterisation of malaria vector habitats using Remote sensing and GIS

As per the World Health Organisation, about 260 million people worldwide are infected with malaria and 1.5 to 2.7 million patients die annually due to this most significant infectious parasite. In this study two important species,Anopheles dints andAnopheles minimus, have been studied in North Lakhimpur and Dibrugarh districts of Assam in the North-Eastern India. Remote sensing has certainly provided a clue in identifying the symptoms of mosquito habitat and Geographical Information System (GIS) has helped us to analyse and identify two species with several environmental parameters. Remote sensing inputs have made a difference in understanding the presence of these species in two districts which are having similar meteorological conditions. It has been found that the nature of the breeding ground for mosquitoes and their spreading patterns are not so complex as generally expected.     

Effect of filtering on drift and anisotropy parameters determined by full correlation analysis

The effect of low-pass filtering on the various drift and anisotropy parameters obtained by full correlation analysis of spaced receiver records is studied theoretically, assuming Gaussian correlation functions. A decrease in the characteristic velocityV _cis shown with increasing filtering, unlessV ≫ V _v, whenV _cincreases with filtering. The ratioV _c/V however shows an increase as the decrease in the true drift velocityV is steeper thanV _c. An increase in the size of the ground pattern with increasing filtering is also shown, while the axial ratio for anisotropic patterns shows a decrease. The results are verified with experimental data recorded earlier at Tiruchirapalli.