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Is there an unaccounted for excess in the extragalactic cosmic radio background?
No full textRestricted AccessAnalyses of the distribution of absolute brightness temperature over the radio sky have recently led to suggestions that there exists a substantial unexplained extragalactic radio background. Consequently, there have been numerous attempts to place constraints on plausible origins of this "excess." We suggest here that this expectation of a large extragalactic background, over and above that contributed by the sources observed in the surveys, is based on an extremely simple geometry adopted to model the Galactic emission and the procedure adopted in the estimation of the extragalactic contribution. In this paper, we derive the extragalactic radio background from wide-field radio images using a more realistic modeling of the Galactic emission and decompose the sky maps at 150, 408, and 1420 MHz into anisotropic Galactic and isotropic extragalactic components. The anisotropic Galactic component is assumed to arise from a highly flattened spheroid representing the thick disk, embedded in a spherical halo, both centered at the Galactic center, along with Galactic sources, filamentary structures, and Galactic loops and spurs. All components are constrained to be positive and the optimization scheme minimizes the sky area occupied by the complex filaments. We show that in contrast with simple modeling of Galactic emission as a plane parallel slab, the more realistic modeling yields estimates for the uniform extragalactic brightness that are consistent with expectations from known extragalactic radio source populations
Spectral dispersion of ultrafast optical limiting in Coumarin-120 by white-light continuum Z-scan
No full textOpen AccessMeasurement of the wavelength dispersion of optical limiting in materials can provide invaluable information useful for laser safety device applications. However, it can be a tedious task when conventional tunable laser sources like the optical parametric amplifier are employed for excitation. Here we report the spectral dispersion of ultrafast optical limiting in the laser dye Coumarin-120 in the wavelength region 630 to 900 nm, measured in a single Z-scan, using the white-light continuum as the excitation source. Optical limiting is found to arise from two-photon absorption, and its spectrum agrees very well in shape with the linear absorption spectrum
These IDLIs are food for the brain
No full textOpen AccessReport on 15th International conference of Asia-Pecific Digital libraries held at Bangalor
Modulated phase of liquid crystals: Covariant elasticity in the context of soft, achiral smectic-C materials
No full textRestricted Access.Ginzburg-Landau–de Gennes-type covariant theories are extensively used in connection with twist grain boundary phases of chiral smectogens. We analyze the stability conditions for the linear, covariant elasticity theory of smectic-C liquid crystals in the context of achiral materials, and predict an equilibrium modulated structure with an oblique wave vector. We suggest that a previous experimental observation of stripes in smectic-C is consistent with the predicted structure
Unusual displacement of HI due to tidal interaction in Arp 181
No full textRestricted Access. An open-access version is available at arXiv.org (one of the alternative locations)We present results from Giant Metrewave Radio Telescope H i 21 cm line observations of the interacting galaxy pair Arp 181 (NGC 3212 and NGC 3215) at z = 0.032. We find almost all of the detected H i (90 per cent) is displaced well beyond the optical discs of the pair with the highest density H i located ∼70 kpc west of the pair. An H i bridge extending between the optical pair and the bulk of H i together with their H i deficiencies provide strong evidence that the interaction between the pair has removed most of their H i to the current projected position. H i to the west of the pair has two approximately equal intensity peaks. The H i intensity maximum furthest to the west coincides with a small spiral companion SDSS J102726.32+794911.9 which shows enhanced mid-infrared (Spitzer), ultraviolet (UV; GALEX) and Hα emission indicating intense star-forming activity. The H i intensity maximum close to the Arp 181 pair, coincides with a diffuse optical cloud detected in UV (GALEX) at the end of the stellar and H i tidal tails originating at NGC 3212 and, previously proposed to be a tidal dwarf galaxy in formation. Future sensitive H i surveys by telescopes like Australian Square Kilometre Array Pathfinder should prove to be powerful tools for identifying tidal dwarfs at moderate to large redshifts to explore in detail the evolution of dwarf galaxies in the Universe
Synthesis and Liquid crystal property of new fluoro coumarin carboxylates
No full textRestricted Access.New liquid crystalline 4-alkoxyphenyl-coumarin-3-carboxylates 6a–e, 7a–g, 8a–e, and 9a–e were prepared by reacting various coumarin-3-carboxylic acids 5a–d with 4-(alkoxy) phenols 4a–g in the presence of 1(3-dimethylaminopropyl-3-ethylcarbodiimide/dimethyl amino pyridine (EDCI/DMAP) as a coupling agent. The structures of the new coumarin derivatives were confirmed by spectral analysis and the liquid crystalline property was established by polarizing optical microscope and by differential scanning calorimetric techniques. The diethyl amine and morpholine were taken as electron-donating and –CF3 as electron-withdrawing groups at the seventh position of the coumarin-3-carboxylic acids to check the mesomorphic property in all new 4-alkoxyphenyl-coumarin-3-carboxylates. Among them, only 4-alkoxyphenyl-7-triflouromethyl-coumarin-3-carboxylates 7a–g exhibited liquid crystalline SmA phas
CdSe quantum dot-dispersed DOBAMBC : an electro-optical study
No full textRestricted Access.Cadmium selenide quantum dot (CdSe QD) has been used as a dopant in ferroelectric liquid crystal (FLC) 2-methylbutyl 4-(4-decyloxybenzylideneamino) cinnamate (DOBAMBC). Effect of CdSe QD in DOBAMBC on its different electro-optical (E-O) properties has been studied in the SmC* phase. The optical micrographs recorded for the pure and composite material are showing good dispersion of QDs in the FLC matrix. Micrographs of unaligned sample cell revealed that CdSe QDs induce homeotropic alignment of FLC molecules. An appreciable change in the value of E-O parameters like tilt angle, spontaneous polarisation and response time with shifting of SmA–SmC* phase transition temperature has been observed for CdSe QD–DOBAMBC composite. The observed properties of composite system have been discussed on the basis of surface properties of QDs in FLC system
Synthesis of reduced graphene oxide–ZnO hybrid with enhanced optical limiting properties
No full textRestricted Access.Reduced graphene oxide–ZnO (rGO–ZnO) is synthesized by in situ growth of ZnO on the surface of graphene oxide (GO) by facile solution methods; namely, a solution precipitation method and a hydrothermal method. The characterization shows that GO is reduced and exfoliated to graphene sheets and ZnO is partially covered by graphene layers. A formation mechanism of rGO–ZnO hybrid proposed is well suited to the experimental results. Structural analysis indicates that the graphene possesses a greater extent of π-conjugation in the hydrothermally prepared rGO–ZnO hybrid. These hybrids exhibit an intense and broad absorption in the visible region, in addition to the sharp UV absorption peak. These rGO–ZnO hybrids also show fluorescence quenching properties. The nonlinear absorption coefficient and optical limiting properties of rGO–ZnO hybrid is evaluated using an open aperture Z-scan technique. More interestingly, we found that there is a 15 times enhancement in the nonlinear absorption coefficient of the rGO–ZnO hybrid compared to the bare ZnO. The hybrid shows excellent optical limiting properties compared to its individual counterparts, implying the usability of these hybrids in optoelectronics
Planetarium in Shimoga
No full textOpen AccessJnanadeepa School has established a Planetarium in Shimoga in Collaboration with Raman Research Institute, Bangalore
Pulse-phase-dependent variations of the Cyclotron absorption features of the accreting pulsars A0535+26, XTE J1946+274, and 4U 1907+09 with Suzaku
No full textRestricted Access. An open-access version is available at arXiv.org (one of the alternative locations)We have performed a detailed pulse-phase-resolved spectral analysis of cyclotron resonant scattering features (CRSFs) of the two Be/X-ray pulsars A0535+26 and XTE J1946+274 and the wind accreting HMXB pulsar 4U 1907+09 using Suzaku observations. The CRSF parameters vary strongly over the pulse phase and can be used to map the magnetic field, and a possible deviation forms the dipole geometry in these sources. It also reflects the conditions at the accretion column and the local environment over the changing viewing angles. The pattern of variation with pulse phase is obtained with more than one continuum spectral model for each source, all of which give consistent results. Care is also taken in performing the analysis over a stretch of data having constant spectral characteristics and luminosity in order to ensure that the results reflect the variations due to the changing viewing angle alone. For A0535+26 and XTE J1946+274, which show energy-dependent dips in their pulse profiles, a partial covering absorber is added in the continuum spectral models to take into account an additional absorption at those phases by the accretion stream/column blocking our line of sight