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Plasmonic and nonlinear optical absorption properties of Ag:Zro2 nanocomposite thin films
No full textRestricted Access.Ag nanoparticles (NPs) embedded in a zirconium oxide matrix in the form of Ag:ZrO2 nanocomposite (NC) thin films were synthesized by using the sol–gel technique followed by thermal annealing. With the varying of the concentration of Ag precursor and annealing conditions, average sizes (diameters) of Ag nanoparticles (NPs) in the nanocomposite film have been varied from 7 to 20 nm. UV–VIS absorption studies reveal the surface plasmon resonance (SPR)-induced absorption in the visible region, and the SPR peak intensity increases with the increasing of the Ag precursor as well as with the annealing duration. A red shift in SPR peak position with the increase in the Ag precursor concentration confirms the growth of Ag NPs. Surface topographies of these NC films showed that deposited films are dense, uniform, and intact during the variation in annealing conditions. The magnitude and sign of absorptive nonlinearities were measured near the SPR of the Ag NPs with an open-aperture z-scan technique using a nanosecond-pulsed laser. Saturable optical absorption in NC films was identified having saturation intensities in the order of 1012 W/m2. Such values of saturation intensities with the possibility of size-dependent tuning could enable these NC films to be used in nanophotonic applications
A survey for transients and variables with the Murchison Widefield Array 32-tile prototype at 154 MHz
No full textRestricted Access. An open-access version is available at arXiv.org (one of the alternative locations)We present a search for transient and variable radio sources at 154 MHz with the Murchison Widefield Array 32-tile prototype. 51 images were obtained that cover a field of view of 1430 deg2 centred on Hydra A. The observations were obtained over three days in 2010 March and three days in 2011 April and May. The mean cadence of the observations was 26 min and there was additional temporal information on day and year time-scales. We explore the variability of a sample of 105 low-frequency radio sources within the field. Four bright (S > 6 Jy) candidate variable radio sources were identified that displayed low levels of short time-scale variability (26 min). We conclude that this variability is likely caused by simplifications in the calibration strategy or ionospheric effects. On the time-scale of 1 yr we find two sources that show significant variability. We attribute this variability to either refractive scintillation or intrinsic variability. No radio transients were identified and we place an upper limit on the surface density of sources ρ < 7.5 × 10−5 deg−2 with flux densities >5.5 Jy, and characteristic time-scales of both 26 min and 1 yr
Tomographic studies of pulsar radio emission cones and searches for radio counterparts of gamma-ray pulsars
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Synthesis of some novel aromatic alkynyl silanes: mesomorphic characterization of ethynyl-substituted rod-shaped molecules
No full textRestricted Access.The synthesis and characterization of 10 new rod-shaped substituted benzoates possessing the 4-(2-trimethylsilyl)ethynyl group in terminal phenyl position is reported employing the simple and efficient Sonogashira cross-coupling and DCC esterification. 4′-Dodecylbiphenyl-4-carboxylic(2-trimethylsilylethynyl)-phenyl ester (3i), 4-(4′-hexadecyloxybenzyloxy) carboxylic-4-trimethylsilanylethynyl-phenyl ester (3j), and 1,4-bis(4-(pentyloxy)phenyl)buta-1,3-diyne (7) compounds were evaluated for liquid crystal property
Role of surface states and defects in the ultrafast nonlinear optical properties of CuS quantum dots
No full textOpen AccessWe report facile preparation of water dispersible CuS quantum dots (2–4 nm) and nanoparticles (5–11 nm) through a nontoxic, green, one-pot synthesis method. Optical and microstructural studies indicate the presence of surface states and defects (dislocations, stacking faults, and twins) in the quantum dots. The smaller crystallite size and quantum dot formation have significant effects on the high energy excitonic and low energy plasmonic absorption bands. Effective two-photon absorption coefficients measured using 100 fs laser pulses employing open-aperture Z-scan in the plasmonic region of 800 nm reveal that CuS quantum dots are better ultrafast optical limiters compared to CuS nanoparticles
Cosmic backgrounds due to the formation of the first generation of supermassive black holes
No full textOpen AccessThe statistics of black holes and their masses strongly suggests that their mass distribution has a cut-off towards lower masses near 3 × 106 M&sun;. This is consistent with a classical formation mechanism from the agglomeration of the first massive stars in the universe. However, when the masses of the stars approach 106 M&sun;, the stars become unstable and collapse, possibly forming the first generation of cosmological black holes. Here, we speculate that the claimed detection of an isotropic radio background may constitute evidence of the formation of these first supermassive black holes, since their data are compatible in spectrum and intensity with synchrotron emission from the remnants. The model proposed fulfils all observational conditions for the background, in terms of single-source strength, number of sources, far-infrared and gamma-ray emission. The observed high-energy neutrino flux is consistent with our calculations in flux and spectrum. The proposal described in this paper may also explain the early formation and growth of massive bulge-less disc galaxies as derived from the massive, gaseous shell formed during the explosion prior to the formation of a supermassive black hole
Estimating the anti-symmetric and symmetric part of the circular polarization in pulsar profiles using simple modeling
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Synthesis and photoswitching properties of liquid crystals derived from myo-inositol
No full textRestricted Access.A new series of unconventional liquid crystal molecules derived from myo-inositol core were synthesized by linking six azobenzene units having terminal double bonds as polymerizable functional groups to myo-inositol. Differential scanning calorimetry, polarizing optical microscopy and X-ray diffraction studies were carried out to determine mesomorphism in these materials. Thus, all compounds showed stable enantiotropic SmA phase which was independent of the chain length and chain parity. The photoswitching behaviour of these molecules in solutions showed E to Z isomerization in 8–10 s, whereas the reverse process took about 270–305 min. In solid film, the E–Z photoisomerization took 5 s, while the reverse transformation from Z to E state took 120 min. The photoswitching behaviour of these materials represents one of the fastest switching times so far observed in such materials and, therefore, they are good candidates for molecular switches