Time filter

Source Type

Thiruvananthapuram, India

The Vikram Sarabhai Space Centre is a major space research centre of the Indian Space Research Organisation , focusing on rocket and space vehicles for India's satellite programme. It is located in Thiruvananthapuram, in the Indian state of Kerala.The centre had its beginnings as the Thumba Equatorial Rocket Launching Station in 1962. It was renamed in honour of Dr. Vikram Sarabhai, the father of the Indian space program.The Vikram Sarabhai Space Centre is one of the main Research & Development establishments within ISRO. VSSC is an entirely indigenous facility working on the development of sounding rockets; Rohini and Menaka launchers; ASLV, PSLV GSLV and the GSLV Mk III.VSSC's current director is S. Ramakrishnan. He took over from P.S. Veeraraghavan on December 31, 2012. Wikipedia.

Karmalkar S.,Indian Institute of Technology Madras | Saleem H.,Vikram Sarabhai Space Center
Solar Energy Materials and Solar Cells | Year: 2011

We have earlier introduced the power law equation, j=1-(1-γ)v- γvm, where j=J/Jsc and v=V/V∝, to simplify determination of the JV curve, fill-factor and peak power point of an illuminated solar cell from a few measurements as well as physical parameters. However, the validity of the various formulae and parameter extraction procedure was established for a limited class of cells, having moderately convex JV curves with fill-factors of 0.560.77 and obeying single exponential theory with bias independent photocurrent. This paper presents a thorough validation of the model proposed earlier. New formulae and parameter extraction procedure are presented to extend the applicability of the power law equation to a much wider variety of cells. The JV curves considered in this paper range from concave (fill-factor<0.25) to highly convex (fill-factor>0.85), and their theoretical expressions contain bias dependent photocurrent and double exponential terms. It is shown that the power law equation also simplifies the calculation of the cell bias point for an arbitrary load. © 2010 Elsevier B.V. All rights reserved. Source

The crosslink density (CLD) for polyurethane elastomeric networks based on hydroxyl terminated polybutadiene and isophorone-diisocyanate was theoretically calculated with α-model equations the employing the functionality distribution and extent of reaction as input parameters. The theoretical crosslink density (vt) was compared with the CLD values computed from stress-strain data evaluated at various strain rates. The methods for the calculation of the CLD from stress- strain data were based on the Mooney-Rivlin and Young's modulus approaches. Theoretical stress-strain curves were generated on the basis of vt conforming to both phantom and affine model calculations. The experimental stress- strain plots aligned more closely to the affine model line. The deviation of the experimentally derived stress-strain curves from the theoretical affine curve was probably due to the presence of temporarily trapped physical entanglements. From the stress-strain data, the concentrations of true chemical crosslinks and physical entanglements were estimated individually. © 2010 Wiley Periodicals, Inc. Source

Hegde P.,Hokkaido University | Hegde P.,Vikram Sarabhai Space Center | Kawamura K.,Hokkaido University
Atmospheric Chemistry and Physics | Year: 2012

Aerosol samples were collected from a high elevation mountain site (Nainital, India; 1958 m a.s.l.) in the central Himalayas, a location that provides an isolated platform above the planetary boundary layer to better understand the composition of the remote continental troposphere. The samples were analyzed for water-soluble dicarboxylic acids (C2-C 12) and related compounds (ketocarboxylic acids and α-dicarbonyls), as well as organic carbon, elemental carbon and water soluble organic carbon. The contributions of total dicarboxylic acids to total aerosol carbon during wintertime were 1.7% and 1.8%, for day and night, respectively whereas they were significantly smaller during summer. Molecular distributions of diacids revealed that oxalic (C2) acid was the most abundant species followed by succinic (C4) and malonic (C 3) acids. The average concentrations of total diacids (433±108 ng m-3), ketoacids (48±23 ng m-3), and α-dicarbonyls (9±4 ng m-3) were similar to those from large Asian cities such as Tokyo, Beijing and Hong Kong. During summer most of the organic species were several times more abundant than in winter. Phthalic acid, which originates from oxidation of polycyclic aromatic hydrocarbons such as naphthalene, was found to be 7 times higher in summer than winter. This feature has not been reported before in atmospheric aerosols. Based on molecular distributions and air mass backward trajectories, we conclude that dicarboxylic acids and related compounds in Himalayan aerosols are derived from anthropogenic activities in the highly populated Indo-Gangetic plain areas. © 2012 Author(s). CC Attribution 3.0 License. Source

Bhardwaj A.,Vikram Sarabhai Space Center | Jain S.K.,Vikram Sarabhai Space Center
Icarus | Year: 2012

A model for N 2 triplet states band emissions in the venusian dayglow has been developed for low and high solar activity conditions. Steady state photoelectron fluxes and volume excitation rates for N 2 triplet states have been calculated using the Analytical Yield Spectra (AYS) technique. Model calculated photoelectron flux is in good agreement with Pioneer Venus Orbiter-observed electron flux. Since inter-state cascading is important for the triplet states of N 2, populations of different levels of N 2 triplet states are calculated under statistical equilibrium considering direct electron impact excitation, and cascading and quenching effects. Densities of all vibrational levels of each triplet state are calculated in the model. Height-integrated overhead intensities of N 2 triplet band emissions are calculated, the values for Vegard-Kaplan (A3Σu+-X1Σg+), First Positive (B3Πg-A3Σu+), Second Positive (C 3Π u-B 3Π g), and Wu-Benesch (W 3Δ u-B 3Π g) bands of N 2, are 1.9 (3.2), 3 (6), 0.4 (0.8), and 0.5 (1.1)kR, respectively, for solar minimum (maximum) conditions. The intensities of the three strong Vegard-Kaplan bands (0,5), (0,6), and (0,7) are 94 (160), 120 (204), and 114 (194) R, respectively, for solar minimum (maximum) conditions. Limb profiles are calculated for VK(0,4),(0,5),(0,6) and (0,7) bands. The calculated intensities on Venus are about a factor 10 higher than those on Mars. The present study provides a motivation for a search of N 2 triplet band emissions in the dayglow of Venus. © 2011 Elsevier Inc. Source

Bhardwaj A.,Vikram Sarabhai Space Center | Raghuram S.,Vikram Sarabhai Space Center
Astrophysical Journal | Year: 2012

The green (5577 Å) and red-doublet (6300, 6364 Å) lines are prompt emissions of metastable oxygen atoms in the 1 S and 1 D states, respectively, that have been observed in several comets. The value of the intensity ratio of green to red-doublet (G/R ratio) of 0.1 has been used as a benchmark to identify the parent molecule of oxygen lines as H2O. A coupled chemistry-emission model is developed to study the production and loss mechanisms of the O(1 S) and O(1 D) atoms and the generation of red and green lines in the coma of C/1996 B2 Hyakutake. The G/R ratio depends not only on photochemistry, but also on the projected area observed for cometary coma, which is a function of the dimension of the slit used and the geocentric distance of the comet. Calculations show that the contribution of photodissociation of H2O to the green (red) line emission is 30%-70% (60%-90%), while CO2 and CO are the next potential sources contributing 25%-50% (<5%). The ratio of the photoproduction rate of O(1 S) to O(1 D) would be around 0.03 (0.01) if H2O is the main source of oxygen lines, whereas it is 0.6 if the parent is CO2. Our calculations suggest that the yield of O(1 S) production in the photodissociation of H2O cannot be larger than 1%. The model-calculated radial brightness profiles of the red and green lines and G/R ratios are in good agreement with the observations made on the comet Hyakutake in 1996 March. © 2012 The American Astronomical Society. All rights reserved. Source

Discover hidden collaborations