http://dspace.rri.res.in:8080/jspui The DSpace digital repository system captures, stores, indexes, preserves, and distributes digital research material. Search the Channel search http://dspace.rri.res.in:8080/jspui/simple-search http://hdl.handle.net/2289/3889 Title: Recombination emissions and spectral blueshift of pump radiation from ultrafast laser induced plasma in a planar water microjet<br/><br/>Authors: Anija, M.; Philip, Reji<br/><br/>Abstract: We report spectroscopic investigations of an ultrafast laser induced plasma generated in a planar water microjet. Plasma recombination emissions along with the spectral blueshift and broadening of the pump laser pulse contribute to the total emission. The laser pulses are of 100 fs duration, and the incident intensity is around 1015 W/cm2. The dominant mechanisms leading to plasma formation are optical tunnel ionization and collisional ionization. Spectrally resolved polarization measurements show that the high frequency region of the emission is unpolarized whereas the low frequency region is polarized. Results indicate that at lower input intensities the emission arises mainly from plasma recombinations, which is accompanied by a weak blueshift of the incident laser pulse. At higher input intensities strong recombination emissions are seen, along with a broadening and asymmetric spectral blueshift of the pump laser pulse. From the nature of the blueshifted laser pulse it is possible to deduce whether the rate of change of free electron density is a constant or variable within the pulse lifetime. Two input laser intensity regimes, in which collisional and tunnel ionizations are dominant respectively, have been thus identified.<br/><br/>Description: Restricted Access. http://hdl.handle.net/2289/3888 Title: Re-entrant phase behavior of a concentrated anionic surfactant system with strongly binding counterions<br/><br/>Authors: Ghosh, Sajal Kumar; Rathee, Vikram; Krishnaswamy, Rema; Raghunathan, V.A.<br/><br/>Abstract: The phase behavior of the anionic surfactant sodium dodecyl sulfate (SDS) in the presence of the strongly binding counterion p-toluidine hydrochloride (PTHC) has been examined using small-angle X-ray diffraction and polarizing microscopy. A hexagonal-to-lamellar transition on varying the PTHC to SDS molar ratio (α) occurs through a nematic phase of rodlike micelles (NC) → isotropic (I) → nematic of disklike micelles (ND) at a fixed surfactant concentration (). The lamellar phase is found to coexist with an isotropic phase (I′) over a large region of the phase diagram. Deuterium nuclear magnetic resonance investigations of the phase behavior at = 0.4 confirm the transition from NC to ND on varying α. The viscoelastic and flow behaviors of the different phases were examined. A decrease in the steady shear viscosity across the different phases with increasing α suggests a decrease in the aspect ratio of the micellar aggregates. From the transient shear stress response of the NC and ND nematic phases in step shear experiments, they were characterized to be tumbling and flow aligning, respectively. Our studies reveal that by tuning the morphology of the surfactant micelles strongly binding counterions modify the phase behavior and rheological properties of concentrated surfactant solutions.<br/><br/>Description: Restricted Access. http://hdl.handle.net/2289/3887 Title: Spacelike distance from discrete causal order<br/><br/>Authors: Rideout, David; Wallden, Petros<br/><br/>Abstract: Any discrete approach to quantum gravity must provide some prescription as to how to deduce continuum properties from the discrete substructure. In the causal set approach it is straightforward to deduce timelike distances, but surprisingly difficult to extract spacelike distances, because of the unique combination of discreteness with local Lorentz invariance in that approach. We propose a number of methods to overcome this difficulty, one of which reproduces the spatial distance between two points in a finite region of Minkowski space. We provide numerical evidence that this definition can be used to define a 'spatial nearest neighbor' relation on a causal set, and conjecture that this can be exploited to define the length of 'continuous curves' in causal sets which are approximated by curved spacetime. This provides some evidence in support of the 'Hauptvermutung' of causal sets.<br/><br/>Description: Restricted Access. An open-access version is available at arXiv.org (one of the alternative locations) http://hdl.handle.net/2289/3886 Title: Optical and nonlinear absorption properties of Na doped ZnO nanoparticle dispersions<br/><br/>Authors: Karthikeyan, B.; Suchand Sandeep, C.S.; Pandiyarajan, T.; Venkatesan, P.; Philip, Reji<br/><br/>Abstract: We report linear and nonlinear optical properties of the biologically important Na doped ZnO nanoparticle dispersions. Interesting morphological changes involving a spherical to flowerlike transition have been observed with Na doping. Optical absorption measurements show an exciton absorption around 368 nm. Photoluminescence measurements reveal exciton recombination emission, along with shallow and deep trap emissions. The increased intensity of shallow trap emission with Na doping is attributed to oxygen deficiency and shape changes associated with doping. Nonlinear optical measurements show a predominantly two-photon induced, excited state absorption, when excited with 532 nm, 5 ns laser pulses, indicating potential optical limiting applications<br/><br/>Description: Restricted Access. An open-access version is available at arXiv.org (one of the alternative locations)