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Self-assembled ordering of single-walled carbon nanotubes in a lyotropic liquid crystal system
No full textRestricted Access.We have carried out small angle X-ray scattering (SAXS) studies as a function of temperature on 0.01 wt.% single-walled carbon nanotubes (SWCNTs) dispersed lyotropic liquid crystal (LLC) system consisting of 25 wt.% cetyltrimethylammonium bromide (CTAB) in water. This LLC system exhibits crystalline surfactant + water (Cr), nematic (N), hexagonal (H) and isotropic (I) phases on heating. Our SAXS pattern revealed that in the crystalline + water phase of the LLC, the doped CNTs exhibit 1-D ordering. In the nematic and hexagonal phases of the LLC, the CNTs exhibit 2-D hexagonal ordering. In the isotropic phase, there are domains of CNTs and within each domain, the nanotubes exhibit 1-D ordering. A plot of d-spacing of the CNTs as a function of temperature showed peaks at the phase transition temperatures of the LLC. We have also carried out optical birefringence and electrical conductivity measurements of the composite as a function of temperature. Interestingly, they also showed peaks at the phase transition temperatures. This indicates a correlation between the d-spacing of the CNTs and the anomalous increase in the birefringence and conductivity of the composite at the phase transition temperatures
Thin film of palladium nanodendrites supported on graphite electrode for catalyzing the oxidation of small organic molecules
No full textRestricted Access.The present study describes the outcome of the electrocatalysis of small organic molecules methanol, ethanol and formic acid on palladium nanodendritic film on graphite electrode. Higher oxidation currents than commercial Pd/C catalyst and low activation energies are obtained for electro-oxidation of organic molecules, indicating that the nanodendrites are highly effective for the electro-oxidation of these molecules. The nanocomposite film is effective in alkaline medium for alcohols oxidation, and in acidic media for formic acid oxidation
Implementation of an F-statistic all-sky search for continuous gravitational waves in Virgo VSR1 data
No full textRestricted Access. An open-access version is available at arXiv.org (one of the alternative locations)We present an implementation of the -statistic to carry out the first search in data from the Virgo laser interferometric gravitational wave detector for periodic gravitational waves from a priori unknown, isolated rotating neutron stars. We searched a frequency f0 range from 100 Hz to 1 kHz and the frequency dependent spindown f1 range from Hz s−1 to zero. A large part of this frequency–spindown space was unexplored by any of the all-sky searches published so far. Our method consisted of a coherent search over two-day periods using the Script F-statistic, followed by a search for coincidences among the candidates from the two-day segments. We have introduced a number of novel techniques and algorithms that allow the use of the fast Fourier transform (FFT) algorithm in the coherent part of the search resulting in a fifty-fold speed-up in computation of the -statistic with respect to the algorithm used in the other pipelines. No significant gravitational wave signal was found. The sensitivity of the search was estimated by injecting signals into the data. In the most sensitive parts of the detector band more than 90% of signals would have been detected with dimensionless gravitational-wave amplitude greater than $5\times {{10}^{-24}}
Latest results of pulse phase resolved spectroscopy of cyclotron lines in accretion powered pulsars
No full textOpen Access, Proceedings of Physics at the Magnetospheric Boundary Conference held at Geneva, Switzerland, June 25-28, 2013. Edited by E. Bozzo, P. Kretschmar, M. Audard, M. Falanga and C. FerrignoWe have performed pulse phase resolved spectroscopy of the Cyclotron Resonance Scattering Features (CRSF) of some bright accretion powered X-ray pulsars like 1A 1118-61, Vela X-1, A0535+26, XTE J1946+274, 4U 1907+09, 4U 1626-67 and GX 301-2 using Suzaku observations with long exposures. We have performed the study using different spectral models for the continuum and have obtained similar patterns of variations of the CRSF in all the cases, thus demonstrating the robustness of our results. Pulse phase dependence of the CRSF in XTE J1946+274 has been obtained for the first time, and phase resolved variations of the CRSF in 4U 1907+09 has been compared at factor of ~ 2 difference in luminosity. We have also studied the pulse profiles of these objects near the CRSF energy, and have noticed an increased pulse fraction and/or a change in the pulse shape near the CRSF energy for some sources. The implications of the results are discussed
An Efficient Linear-array Imager for radio astronomy
No full textOpen AccessLarge-scale surveys are essential means to leapfrog astronomical understanding. Yet, Galaxy-wide surveys at millimetre wavelengths are rare and have not benefited much from multiple receivers that provide large instantaneous field of view. If one were to have a large number of millimetre wave receivers, how best to deploy them to maximize survey speed to measure both point and smoothly distributed emission? In this paper, we present a new cross telescope configuration, Efficient Linear-array Imager, and demonstrate that it provides an interesting alternate solution. As an interferometer element, it lends itself for close packing and thereby blends short and long spacing visibilities naturally, improving imaging
Multimessenger search for sources of gravitational waves and high-energy neutrinos: Initial results for LIGO-Virgo and IceCube
No full textOpen AccessWe report the results of a multimessenger search for coincident signals from the LIGO and Virgo gravitational-wave observatories and the partially completed IceCube high-energy neutrino detector, including periods of joint operation between 2007–2010. These include parts of the 2005–2007 run and the 2009–2010 run for LIGO-Virgo, and IceCube’s observation periods with 22, 59 and 79 strings. We find no significant coincident events, and use the search results to derive upper limits on the rate of joint sources for a range of source emission parameters. For the optimistic assumption of gravitational-wave emission energy of 10−2 M⊙c2 at ∼150 Hz with ∼60 ms duration, and high-energy neutrino emission of 1051 erg comparable to the isotropic gamma-ray energy of gamma-ray bursts, we limit the source rate below 1.6×10−2 Mpc−3 yr−1. We also examine how combining information from gravitational waves and neutrinos will aid discovery in the advanced gravitational-wave detector er
Structural and optical studies of Zn1−xCdxS quantum dots synthesized by in situ technique in PVA matrix
No full textRestricted Access.Zn1−xCdxS (x = 0.1, 0.2, 0.3, 0.4, 0.5 … 0.9) quantum dots were synthesized successfully using novel in situ technique in polyvinyl alcohol (PVA) matrix. The PVA acted as a capping agent as well as a reducing agent. The structural and optical properties of the samples were studied by X-ray diffraction (XRD), TEM analysis, UV–Visible absorption and photoluminescence spectroscopy (PL). X-ray diffraction patterns revealed cubic zinc blende phase of the samples with lattice parameter in the range 5.47–5.75 Å. Optical band gap values were calculated from the absorption spectra and observed a decreasing band gap with increasing Cd:Zn ratio. The Raman spectra were recorded using conventional Micro Raman technique. Photoluminescence spectra showed asymmetric broad emission with multiple maxima. The concentration dependent quenching of PL intensity with increasing Cd:Zn ratio was observed along with a red shift. The nonlinear optical (NLO) and limiting properties were studied using Z-scan technique
Active organization of membrane constituents in living cells
No full textRestricted Access.A search for organizing principles underlying molecular patterning at the cell surface and its regulation over different scales is necessary. This is important for understanding how the cell builds membrane bound organelles that emanate from it and for how the cell interacts with its physical and chemical milieu. This requires a broad framework to rationalize the mass of accumulated data about the spatial localization and dynamics of its constituents, and their physical and chemical environment. Lateral heterogeneities in the organization of membrane components of a living cell appear to be a hallmark of how a cell addresses sorting and signaling functions. Here we explore two classes of mechanisms of segregation of membrane components in the plasma membrane. We suggest that viewing the membrane as a passive, thermally equilibrated system is unlikely to provide an adequate framework to understand the mechanisms of membrane component segregation in vivo. Instead the surface of living cells behaves as an active membrane composite
Nonclassical paths in quantum interference experiments
No full textOpen AccessIn a double slit interference experiment, the wave function at the screen with both slits open is not exactly equal to the sum of the wave functions with the slits individually open one at a time. The three scenarios represent three different boundary conditions and as such, the superposition principle should not be applicable. However, most well-known text books in quantum mechanics implicitly and/or explicitly use this assumption that is only approximately true. In our present study, we have used the Feynman path integral formalism to quantify contributions from nonclassical paths in quantum interference experiments that provide a measurable deviation from a naive application of the superposition principle. A direct experimental demonstration for the existence of these nonclassical paths is difficult to present. We find that contributions from such paths can be significant and we propose simple three-slit interference experiments to directly confirm their existence