Vikram Sarabhai Space Centre

About: Vikram Sarabhai Space Centre is a facility organization based out in Thiruvananthapuram, India. It is known for research contribution in the topics: Aerosol & Ultimate tensile strength. The organization has 2092 authors who have published 3058 publications receiving 47975 citations. The organization is also known as: VSSC.

Tropical connection to the polar stratospheric sudden warming through quasi 16-day planetary wave

Abstract: . The Planetary Waves (PWs) are believed to have significant role in generating the wintertime warming over the polar stratosphere, known as Stratospheric Sudden Warming (SSW). However, the origin, characteristics and evolution of these waves are still speculative. The possibility that the PWs over the polar stratosphere, which play an important role in the generation of SSW, could also have contribution from the tropics has been indicated through many numerical simulations in the past, but due to the paucity of global measurements it could not be established unequivocally. The earlier numerical studies also indicated the presence of a zero-wind line (more general the critical layer, where the zonal wind amplitude becomes zero) whose real counterparts were not observed in the atmosphere. The present study based on the NCEP/NCAR reanalysis of stratospheric wind and temperatures of recent years clearly shows that (i) the zero-wind line appears over the tropics ~60 days prior to the major SSWs and progresses towards the Pole and (ii) an enhanced PW activity of quasi periodicity 16-days, which is also seen almost simultaneously with the zero-wind line, shows a propagation from equator to the Pole. This result is significant as it presents for the first time the connection between the tropics during the SSW events and the pole, through the quasi 16-day wave.

Vibrational spectral studies and the non-linear optical properties of a novel NLO material L-prolinium tartrate

Abstract: Vibrational spectral analysis of the novel non-linear optical (NLO) material, L-prolinium tartrate (LPT) was carried out using NIR-FT-Raman and FT-IR spectroscopy. The density functional theoretical (DFT) computations have been performed at B3LYP/6–31G (d) level to derive equilibrium geometry, vibrational wavenumbers, intensities and first hyperpolarizability. The reasonable NLO efficiency, predicted for the first time in this novel compound, has been confirmed by Kurtz–Perry powder second-harmonic generation (SHG) experiments. The charge-transfer interaction between the pyrrolidine ring and the carbonyl group of the tartrate anion through the intramolecular ionic hydrogen bonds is confirmed by the simultaneous activation of ring modes in IR and Raman spectra. The splitting of the ring-breathing mode, pseudo-rotational ring puckering modes and the NH2 modes of the pyrrolidine ring lead to the conclusion that the pyrrolidine ring adopts a conformation intermediate between the envelope (bent) form and the half-chair (twisted) form, resulting in the lowering of symmetry from C2 to Cs. The lowering of the methylenic stretching wavenumbers and the enhancement of the stretching intensities suggest the existence of the electronic effects of back-donation in LPT. The positional disorder of the pyrrolidine ring, the presence of blue-shifting H-bonds as well as other non-bonded interactions in LPT, low frequency H-bond vibrations and the role of intramolecular charge transfer and the hydrogen bonds in making the molecule NLO active have been analysed on the basis of the vibrational spectral features. Copyright © 2006 John Wiley & Sons, Ltd.

Durable Superhydrophobic Particles Mimicking Leafhopper Surface: Superoleophilicity and Very Low Surface Energy

Abstract: The powder coating on brochosomes of leafhopper can repel water, diiodomethane (DM), and ethylene glycol (EG) droplets with contact angle >150°. This is attributed to the very low surface energy as low as <1.0 mN m–1 and their porous honeycomb structure. In this work, grafted silica nanoparticles with properties similar to leafhopper (LH) particle coating is synthesized in a single step by catalytic grafting of stearic acid on nonporous silica nanoparticles. The particles repel water, diiodomethane, and ethylene glycol with contact angle 167°, 161°, and 157°, respectively. The surface energy is also found as <1.0 mN m–1. The particle coating shows sliding angle <10° with these probe liquids. The superhydrophobic particles are resistant to pH = 1 to 13, boiling water conditions and preserves super-repelling nature to reference liquids after the treatments. In a mixture of hexane/water or kerosene/water, the particles completely wet the oleophilic part and repel water layer due to superoleophilic–superhydro...

Solar system X-rays from charge exchange processes

Abstract: Summary of the spectral results obtained with Chandrafor all the comets (denoted by A–H) which were observed from2000 to 2006: a ) the 0.3–1.0 keV pulse height distributions, b )theecliptic latitudes and c ) phases in the solar cycle of the observedcomets,and d )thededuced informationaboutthesolarwindheavyion content. Fig.3a,c,d were adapted from Bodewits et al. (2007). rienced a spectacular outburst, which increased its dust andgasoutflowandopticalbrightnessbyalmostamilliontimeswithin hours,from under17 magto 3 mag, makingit by farthe optically brightest comet observable by Chandra sinceits launch. At the time, comet 17P/Holmes was located at asufficiently high heliographic latitude (19 ◦ ) to be exposedto the polar wind at solar minimum. It was thus expectedthat this comet would exhibit considerably different X-rayproperties, and in fact this was observed: 17P/Holmes be-came the first comet where Chandra did not detect any sig-nificant X-ray emission at all (Christian et al. 2010). Themost likely explanation for this dramatic X-ray faintness isthat the polar wind was so diluted and its ionization so lowthat only very little X-ray flux was generated by charge ex-change at energies above∼300eV. An instrumental effect,i.e., a loss of sensitivity, can definitively be ruled out, be-cause only two months later, another comet, 8P/Tuttle, wasobservedwith Chandra,andthiscomet,at lowlatitude (3