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Stacking of ultra-thin reduced graphene oxide nanoparticles in supramolecular structures for optoelectronic applications
No full textRestricted Access.Octadecylamine functionalized ultra-thin reduced graphene oxide nanoparticles were synthesized and dispersed in the supramolecular order of discotic liquid crystals for the first time. The insertion and properties of the graphene nanoparticles in the columnar mesophase were studied using field emission scanning electron microscopy, atomic force microscopy, Raman spectroscopy, UV-vis spectroscopy, photoluminescence spectroscopy, polarized optical microscopy, differential scanning calorimetry, X-ray diffraction and DC conductivity. Experimental studies indicate the stacking of two-dimensional graphene nanoparticles in the supramolecular order of the columnar mesophase. The dispersion of graphene nanoparticles improves the order in the columnar phase and thus enhances the conductivity of the syste
Nanosecond and ultrafast optical power limiting in luminescent Fe2O3 hexagonal nanomorphotype
No full textOpen Access.Nonlinear optical absorption and optical power limiting properties of Fe2O3 hexagonal nanomorphotype are investigated using open aperture Z-scan technique with the 5 ns and 100 fs laser pulses, at 532 nm and 800 nm excitation domains. At relatively low pulse energies (below 5 μJ), sample shows saturable absorption (SA), but on going to the higher energies an interesting switchover from saturable absorption to effective two photon absorption is observed in both excitation domains. The magnitude of effective two photon absorption coefficients is calculated to be in the range of 10−10 m/W for nanosecond and 10−15 m/W for femtosecond laser pulse energies, respectively. XRD and TEM study reveals the polycrystalline nature, hexagonal morphology, and size of the nanostructure. The luminescence emission property is examined by photoluminescence spectroscopy (PL). It is found that some strange features exist in the luminescence spectra that are consistent with the nanoparticles size distribution. The PL emission lines are explained as originated from various optical band edges due to the size induced quantum confinement and band gap resonant PL absorption/emission behavior of semiconductor nanostructures
A quantum kinematics for asymptotically flat gravity
No full textOpen AccessWe construct a quantum kinematics for asymptotically flat gravity based on the Koslowski–Sahlmann (KS) representation. The KS representation is a generalization of the representation underlying loop quantum gravity (LQG) which supports, in addition to the usual LQG operators, the action of 'background exponential operators', which are connection dependent operators labelled by 'background' su(2) electric fields. KS states have, in addition to the LQG state label corresponding to one dimensional excitations of the triad, a label corresponding to a 'background' electric field that describes three dimensional excitations of the triad. Asymptotic behaviour in quantum theory is controlled through asymptotic conditions on the background electric fields that label the states and the background electric fields that label the operators. Asymptotic conditions on the triad are imposed as conditions on the background electric field state label while confining the LQG spin net graph labels to compact sets. We show that KS states can be realised as wave functions on a quantum configuration space of generalized connections and that the asymptotic behaviour of each such generalized connection is determined by that of the background electric fields which label the background exponential operators. Similar to the spatially compact case, the Gauss law and diffeomorphism constraints are then imposed through group averaging techniques to obtain a large sector of gauge invariant states. It is shown that this sector supports a unitary action of the group of asymptotic rotations and translations and that, as anticipated by Friedman and Sorkin, for appropriate spatial topology, this sector contains states that display fermionic behaviour under rotation
Promoting Usage of E-resources with special reference to NKRC at DST Institutes
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Narrow-band search of continuous gravitational-wave signals from Crab and Vela pulsars in Virgo VSR4 data
No full textOpen AccessIn this paper we present the results of a coherent narrow-band search for continuous gravitational-wave signals from the Crab and Vela pulsars conducted on Virgo VSR4 data. In order to take into account a possible small mismatch between the gravitational-wave frequency and two times the star rotation frequency, inferred from measurement of the electromagnetic pulse rate, a range of 0.02 Hz around two times the star rotational frequency has been searched for both the pulsars. No evidence for a signal has been found and 95% confidence level upper limits have been computed assuming both that polarization parameters are completely unknown and that they are known with some uncertainty, as derived from x-ray observations of the pulsar wind torii. For Vela the upper limits are comparable to the spin-down limit, computed assuming that all the observed spin-down is due to the emission of gravitational waves. For Crab the upper limits are about a factor of 2 below the spin-down limit, and represent a significant improvement with respect to past analysis. This is the first time the spin-down limit is significantly overcome in a narrow-band search
Spectral, thermal and optical properties of N, N′-Bis (4-chlorobenzylidene)-3, 3′-dimethoxybiphenyl-4, 4′-diamine
No full textRestricted Access.One of the novel organic Schiff base materials, N,N′-Bis(4-chlorobenzylidene)-3,3′-dimethoxybiphenyl-4,4′-diamine (CBMPA), was synthesized and molecular structure of CBMPA was confirmed from nuclear magnetic resonance spectral analysis. Functional groups present in the compound were identified using Fourier transform infrared spectroscopy. Thermal studies show that the melting point of the material is at ~189 °C and it has a single-stage weight loss. Optical properties of CBMPA were studied using UV–vis–NIR and fluorescence spectral analyses. Optical nonlinearity of CBMPA was investigated at 532 nm using 5 ns laser pulses, employing an open aperture Z-scan technique. An optical limiting response which arises mostly from reverse saturable absorption was observed, and the effective two-photon absorption coefficient was calculated
Effect of octadecylamine-functionalised SWCNTs on the elastic constants and electro-optic response of a liquid crystal
No full textRestricted Access.For efficient and high-performance liquid crystal (LC) devices, the physical properties of the LC materials can be suitably altered by incorporating nanomaterials like carbon nanotubes (CNTs), graphene and quantum dots. In the present work, the effect of incorporation of octadecylamine-functionalised single-walled carbon nanotubes (ODA-SWCNT) in a LC exhibiting nematic and smectic phases on its physical properties is investigated. The electro-optic threshold voltage in the nematic phase of ODA-SWCNT nanocomposite of LC is enhanced as compared to that of pure LC. The dielectric anisotropy as a function of reduced temperature decreases with an increase in the concentration of ODA-SWCNT. The ratio of bend to splay elastic constants of ODA-SWCNT nanocomposite of LC is enhanced considerably as compared to that of pure LC at low temperature. The electro-optic response rise time decreased and decay time increased at higher concentrations of ODA-SWCNT. The temperature range of smectic phase is increased with an increase in the concentration of ODA-SWCNT. At the lower concentration of ODA-SWCNTs (0.05 wt%), the anchoring of the nanotubes at the LC–electrode interface is favoured. At higher concentration of the ODA-SWCNTs, in addition to the anchoring at the interface, the nanotubes that are dispersed in the LC medium increases the orientational ordering
Characterization of quantum dynamics using quantum error correction
No full textOpen Access.Characterizing noisy quantum processes is important to quantum computation and communication (QCC), since quantum systems are generally open. To date, all methods of characterization of quantum dynamics (CQD), typically implemented by quantum process tomography, are off-line, i.e., QCC and CQD are not concurrent, as they require distinct state preparations. Here we introduce a method, “quantum error correction based characterization of dynamics,” in which the initial state is any element from the code space of a quantum error correcting code that can protect the state from arbitrary errors acting on the subsytem subjected to unknown dynamics. The statistics of stabilizer measurements, with possible unitary preprocessing operations, are used to characterize the noise, while the observed syndrome can be used to correct the noisy state. Our method requires at most 2(4n−1) configurations to characterize arbitrary noise acting on n qubits
Dynamics of membrane tethers reveal novel aspects of cytoskeleton-membrane interactions in axons.
No full textRestricted Access.Mechanical properties of cell membranes are known to be significantly influenced by the underlying cortical cytoskeleton. The technique of pulling membrane tethers from cells is one of the most effective ways of studying the membrane mechanics and the membrane-cortex interaction. In this article, we show that axon membranes make an interesting system to explore as they exhibit both free membrane-like behavior where the tether-membrane junction is movable on the surface of the axons (unlike many other cell membranes) as well as cell-like behavior where there are transient and spontaneous eruptions in the tether force that vanish when F-actin is depolymerized. We analyze the passive and spontaneous responses of axonal membrane tethers and propose theoretical models to explain the observed behavio