002081   Aggarwal P C;Sreekantan B V;Bhandari N (NO, Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai-400 012, Email: pagrawal@tifr.res.in) : Space astronomy and interplanetary exploration. Curr Sci 2007, 93(12), 1767-78.

Brief overview of Indian contributions to space astronomy and planetary studies, mainly through the satellite-borne experiments is presented. Some important results obtained in X-ray and low energy gamma-ray astronomy are summarized. Highlights of the salient results from lunar explorations are discussed. Important features of the Indian multi-wave length astronomy satellite, Astrosat and expected science from it are described. Details of the Chandrayaan-1 mission and studies initiated by the Indian Space Research Organizartion aimed at various aspects of lunar science are presented.

6 illus, 2 tables, 31 ref

001040   Santosh Kumar;Simranjit Kaur (Physics and Electronics Dep, Rani Durgawati University, Jabalpur-482 001, Email: s_kumar123@rediffmail.com) : Geo-effective transients and their solar causes during solar cycle 23. Indian J Radio Space Phys 2008, 37(6), 379-85.

During nine-year period of the current solar cycle 23 from July 1996 to January 2005, geomagnetic storms (GMSs) of Intense if (Dst < -100nT), Major if (-50nT ≥ Dst ≥ -100nT) and Minor if (-20nT ≥ Dst ≥ -50nT) have been investigated. It is observed that maximum number of GMSs are associated with coronal mass ejections (CMEs) followed by individual Hα and X-ray solar flare events. When accumulated effect of Hα and X-ray solar flare events are considered, these solar flares are better associated with GMSs than CMEs. A significant decline in the number of Intense and Minor GMSs have been observed from 1998 to 1999, however, there is an increase in Major GMSs. On the contrary, during 1997-98, Intense and Minor GMSs have increased with the ascending phase of solar activity and Major GMSs have decreased. It is observed that an overall northern bias apparently prevails for solar flares and active prominences and disappearing filaments. Hα and X-ray solar flares occurring over the western limb of the solar disk cause larger disturbances in magnetosphere leading to occurrence of Intense GMSs, whereas, solar flares occurring on eastern limb of the solar disk lead to occurrence of Major and Minor GMSs. It is observed that coronal intensity (CI) is maximum for Minor GMSs followed by Major and Intense GMSs, whereas, mean CI is maximum for Intense GMSs followed by Major and Minor GMSs. The results show that the product of solar wind velocity (Vsw) with minimum Bz component (Bz_min) of interplanetary magnetic field (Vsw.Bz_min), product of linear velocity of CMEs (Vcme) with Bz_min (Vcme.Bz_min) along with minimum Dst of the sudden storm commencement day are the reliable indicators of intensity of GMSs.

001039   Sanalkumaran Nair V;Prabhakaran Nayar S R (Physics Dep, V T M N S S College, Dhanuvachapuram, Thiruvananthapuram-695 503, Email: sanalkumar.nair@yahoo.co.in) : North-South asymmetry in solar wind & geomagnetic activity and its solar cycle evolution. Indian J Radio Space Phys 2008, 37(6), 391-5.

The unequal distribution of various aspects of solar activity between the north and south hemisphere of the Sun is well known for over a century. Analysis of solar wind data observed during 1964 - 2004 showed that solar wind velocity (V_sw), interplanetary magnetic field (IMF) B_z component and geomagnetic activity index (A_p) exhibit a clear heliospheric north-south asymmetry. In general, amplitude of the north-south asymmetry is maximum during the minimum phase of solar cycle. For V_sw and IMF B_z component, amplitude of the asymmetry is greater during even cycles 20 and 22 compared to the odd cycles 21 and 23. The phase of the asymmetry of IMF B_z reverses every cycle with a northern dominance in even cycles and southern dominance in odd cycles. The asymmetry of V_sw has a northern dominance during cycles 20 and 23 and southern dominance during cycles 21 and 22. Thus, for V_sw, the amplitude of the asymmetry and IMF B_z, both the amplitude and phase exhibit a 22-year period. The asymmetry of A_p index appears similar to that of solar wind velocity. The asymmetry in solar wind velocity and geomagnetic activity may be due to the existence of a relic solar magnetic field in the solar convection zone.

001038   Pande S;Pande B;Uddin W;Pandey K (Physics Dep, DSB Campus, Kumaun University, Nainital-263 002, Email: pandebimal@yahoo.co.in) : Hα, EUV and UV analysis of an eruptive 3B/X1.2 flare. Indian J Radio Space Phys 2008, 37(6), 386-90.

The observational results of an extremely energetic eruptive flare 3B/X1.2 from superactive region NOAA 10486. The observations were taken on 26 October 2003 with 15 cm Solar Tower Telescope at Aryabhatta Research Institute of Observational Sciences (ARIES). Hα observations of the flare show long multi ribbon eruptions along a large twisted (sigmoid) filament in a high gradient (~90°) magnetic field and shear. The evolution pattern of this flare is similar in EUV and UV. Four eruptive centers or kernels in Hα have been chosen, wherein K₁ shows two prominent peaks while K₃ exhibits only one prominent peak with gradual decay. The analysis shows that this is a classical long duration event (LDE). The results have been discussed in the light of existing theories.

000114   Senovilla J M M (Fisica Teorica, Universidad del Pais Vasco, Apartado 644, 48080 Bilbao, Spain) : A singularity theorem based on spatial averages. Pramana J Phys 2007, 69(1), 31-47.

Inspired by Raychaudhuri's work, and using the equation named after him as a basic ingredient, a new singularity theorem is proved. Open non-rotating Universes, expanding everywhere with a non-vanishing spatial average of the matter variables, show severe geodesic incompletness in the past. Another way of stating the result is that, under the same conditions, any singularity-free model must have a vanishing spatial average of the energy density (and other physical variables). This is very satisfactory and provides a clear decisive difference between singular and non-singular cosmologies.

53 ref

000113   Pandya M R;Singh R P;Chaudhari K N;Murali K R;Kirankumar A S;Dadhwal V K;Parihar J S (Space Applications Centre, Indian Space Research Organication, Ahmedabad-380 015, Email: mrpandya@sac.isro.gov.in) : Spectral characteristics of sensors onboard IRS-1D and P6 satellites: estimation and their influence on surface reflectance and NDVI. J Indian Soc Remote Sens 2007, 35(4), 333-50.

Reports the results of a modeling study carried out with two objectives, (1) to estimate and compare effective spectral characteristics (central wavelength, bandwidth and bandpass exo-atmospheric solar irradiance E₀) of various spectral channels of LISS-II1, WiFS, LISS-III*, LISS-IV and AWiFS onboard Indian Remote Sensing Satellites IRS-1D and P6 using moment method based on the laboratory measurements of sensor spectral response, and (2) to quantify the influence of varying sensor spectral response on reflectance and Normalized Difference Vegetation Index (NDVI) measurements using surface reflectance spectra corresponding to different leaf area index conditions of crop target obtained through field experiment. Significant deviation of 4 to 14 nm in central wavelength and 1.6 to 14.07 nm in spectral width was observed for the corresponding channel of IRS sensors. Coefficient of variation of the order of 0.1 to 1.11% was noticed in E₀ among various IRS sensors, which could induce a difference of 0.72 to 3.35% in the estimation of top of atmosphere reflectance for crop target. The variation in spectral response of IRS sensors implied a relative difference of the order of 0.91 to 3.38% in surface reflectance and NDVI measurements. Polynomial approximations are also provided for spectral correction that can be utilized for normalizing the artifacts introduced due to differences in spectral characteristics among IRS sensors.

9 illus, 5 tables, 28 ref

000112   Mukku C ;Mahajan S M;Bambah B A (NO, International Institute of Information Technology, Hyderabad-500 032) : On a Raychaudhuri equation for hot gravitating fluids. Pramana J Phys 2007, 69(1), 137-45.

Generalises- the Raychaudhuri equation for the evolution of a self gravitating fluid to include an Abelian and non-Abelian hybrid magneto fluid at a finite temperªature. The aim is to utilise this equation for investigating the dynamics of astrophysical high temperature Abelian and non-Abelian plasmas.

9 ref

000111   Kar S;Sengupta S (Physics and Centre for Theoretical Studies Dep, Indian Institute of Technology, Kharagpur-721 302) : Raychaudhuri equations: a brief review. Pramana J Phys 2007, 69(1), 49-76.

Bbrief review on the Raychaudhuri equations has been presented. Beginning with a summary of the essential features of the original article by Raychaudhuri and subsequent work of numerous authors, are moved on to a discussion of the equations in the context of alternate non-Riemannian space times as well as other theories of gravity, with a special mention on the equations in space times with torsion (Einstein-Cartan-Sciama-Kibble theory). Finally, gives an overview of some recent applications of these equations in general relativity, quantum field theory, string theory and the theory of relativisitic membranes.

89 ref

000110   Gupta K K;Gupta R (Instrumentation Group, B.I.T.S., Pilani-333 031, Email: kgupta@bits-pilani.ac.in) : Algorithm for road enhancement in sar images using wavelet transform. J Indian Soc Remote Sens 2007, 35(4), 361-7.

^ssc3 illus, 2 tables, 14 ref

000109   Ellis G F R (Mathematics Dep, University of Cape Town, Rondebosch, Cape Town, South Africa, Email: Ellis@MATHS.uct.ac.za) : On the raychaudhuri equation. Pramana J Phys 2007, 69(1), 15-22.

The Raychaudhuri equation is central to the understanding of gravitational attraction in astrophysics and cosmology, and in particular underlies the famous singularity theorems of general relativity theory. Reviews the derivation of the equation, and its significance in cosmology.

11 ref

000108   Dadhich N (NO, Inter-University Centre for Astronomy and Astrophysics, Post Bag 4, Pune-411 007, Email: nkd@iucaa.ernet.in) : Singularity: Raychaudhuri equation once again. Pramana J Phys 2007, 69(1), 23-9.

Recounts Raychaudhuri's deep involvement with the singularity problem in general relativity. Argues that precisely the same situation has arisen today in loop quantum cosmology as obtained when Raychaudhuri discovered his celebrated equation. A new analogue of the Raychaudhuri equation in quantum gravity is needed.

30 ref