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Asymptotic flatness and quantum geometry
No full textOpen Access IOPSelectWe construct a canonical quantization of the two dimensional theory of a parametrized scalar field on noncompact spatial slices. The kinematics is built upon generalized charge-network states which are labelled by smooth embedding spacetimes, unlike the standard basis states carrying only discrete labels. The resulting quantum geometry corresponds to a nondegenerate vacuum metric, which allows a consistent realization of the asymptotic conditions on the canonical fields. Although the quantum counterpart of the classical symmetry group of conformal isometries consists only of continuous global translations, Lorentz invariance can still be recovered in an effective sense. The quantum spacetime as characterized by a gauge invariant state is shown to be made up of discrete strips at the interior, and smooth at asymptotia. The analysis here is expected to be particularly relevant for a canonical quantization of asymptotically flat gravity using kinematical states labelled by smooth geometries
Electro-optical and dielectric properties of CdSe quantum dots and 6CHBT liquid crystals composites
No full textOpen AccessWe have prepared the composites of a room temperature nematic liquid crystal namely 4-(trans-4-n-hexylcyclohexyl) isothiocyanatobenzoate (6CHBT) and Cadmium Selenide Quantum Dots (CdSe-QDs) and investigated their electro-optical and dielectric properties. Effect of dispersion of CdSe-QDs on various electro-optical and display parameters of host liquid crystalline material have been studied. Physical parameters, such as switching threshold voltage and splay elastic constant have been altered drastically for composites. Dispersion of QDs in a liquid crystals medium destabilizes nematic ordering of the host and decreases the nematic-to-isotropic transition temperature
Formation of deeply bound ultracold LiRb molecules via photoassociation near the Li 2S1/2+Rb 5P3/2 asymptote
No full textOpen AccessWe present spectra of ultracold Li7Rb85 molecules in their electronic ground state formed by spontaneous decay of weakly bound photoassociated molecules. Beginning with atoms in a dual-species magneto-optical trap, weakly bound molecules are formed in the 4(1) electronic state, which corresponds to the B1Π state at short range. These molecules spontaneously decay to the electronic ground state and we use resonantly enhanced multiphoton ionization to determine the vibrational population distribution in the electronic ground states after spontaneous emission. Many of the observed lines from the spectra are consistent with transitions from the X1Σ+ ground electronic state to either the B1Π or the D1Π electronic state that has been previously observed, with levels possibly as low as X1Σ+(v''=2) being populated. We do not observe decay to weakly bound vibrational levels of the X1Σ+ or a3Σ+ electronic state in the spectra. We also deduce a lower bound of 3900 cm−1 for the dissociation energy of the LiRb+ molecular ion
Driven inelastic Maxwell gases
No full textOpen AccessWe consider the inelastic Maxwell model, which consists of a collection of particles that are characterized by only their velocities and evolving through binary collisions and external driving. At any instant, a particle is equally likely to collide with any of the remaining particles. The system evolves in continuous time with mutual collisions and driving taken to be point processes with rates τ−1c and τ−1w, respectively. The mutual collisions conserve momentum and are inelastic, with a coefficient of restitution r. The velocity change of a particle with velocity v, due to driving, is taken to be Δv=−(1+rw)v+η, where rw∈[−1,1] and η is Gaussian white noise. For rw∈(0,1], this driving mechanism mimics the collision with a randomly moving wall, where rw is the coefficient of restitution. Another special limit of this driving is the so-called Ornstein-Uhlenbeck process given by dvdt=−Γv+η. We show that while the equations for the n-particle velocity distribution functions (n=1,2,...) do not close, the joint evolution equations of the variance and the two-particle velocity correlation functions close. With the exact formula for the variance we find that, for rw≠−1, the system goes to a steady state. Also we obtain the exact tail of the velocity distribution in the steady state. On the other hand, for rw=−1, the system does not have a steady state. Similarly, the system goes to a steady state for the Ornstein-Uhlenbeck driving with Γ≠0, whereas for the purely diffusive driving (Γ=0), the system does not have a steady state
Enhanced fluorescence and optical power limiting in Ag-nanocomposite glasses
No full textRestricted Access.In this letter, we prepared and studied the plasmon, fluorescence and optical limiting properties of silver ion-exchanged glasses followed by an external thermal treatment for clusterization inside the glass matrix. TEM (Transmission electron microscopy) studies of the prepared samples provides information about the size of the nanoclusters, their size enhancement after TA (Thermal annealing) and supports the SPR band shape variations from the UV–Vis. absorption studies. Enhancement in fluorescence and optical-limiting (with excitation near to resonant value of the SPR) is ascribed to the amplified local field after metal nanocluster growth by thermal annealing
How many of the observed neutrino events can be described by cosmic ray interactions in the Milky Way?
No full textRestricted Access. An open-access version is available at arXiv.org (one of the alternative locations)Cosmic rays diffuse through the interstellar medium and interact with matter and radiations as long as they are trapped in the Galactic magnetic field. The IceCube experiment has detected some TeV–PeV neutrino events whose origin is yet unknown. We study if all or a fraction of these events can be described by the interactions of cosmic rays with matter. We consider the average target density needed to explain them for different halo sizes and shapes, the effect of the chemical composition of the cosmic rays, the impact of the directional information of the neutrino events, and the constraints from gamma-ray bounds and their direction. We do not require knowledge of the cosmic ray escape time or injection for our approach. We find that, given all constraints, at most 0.1 of the observed neutrino events in IceCube can be described by cosmic ray interactions with matter. In addition, we demonstrate that the currently established chemical composition of the cosmic rays contradicts a peak of the neutrino spectrum at PeV energies
Enhanced optical limiting in polystyrene-ZnO nanotop composite films
No full textRestricted Access.In this work we investigate the optical limiting property of polystyrene–zinc-oxide (ZnO) nanotop composite films, using an open aperture Z-scan technique. The nanocomposites are prepared for different loading concentrations of ZnO and are fabricated using spin and dip coating techniques. On exposing the films to a pulsed nanosecond laser at 532 nm, the nonlinear absorption (NLA) coefficient is found to be greater for spin-coated films compared to dip-coated films. The measured NLA coefficient is found to be enhanced with an increase in loading concentration of ZnO in the monomer for both spin- and dip-coated films
Open access initiatives in physics literature : Exploratory study
No full textRestricted Access. Proceedings of DEMICT Conference - 2014, held at DLIS, Mangalore University, Mangalore. from 24th-25th January 2014. Eds, Khaisar Muneebulla Khan et alThe major barrier for scholars and researchers in physics or any other subject is lack of access to the current literature in their field of study. Due to multidisciplinary research, there has been growth of literature and proliferation of e-products resulting in increase in number of e-journals. Simultaneously, there was an escalation of costs of annual subscription of journals, with impact on shrinking library budgets. At the same time due to tremendous developments in ICT, which led to emergence of open access (OA) movement as an alternative to access to scientific information .This paper discusses the development of the open access Initiative in the field of physics. This includes OA journals and Institutional repositories (IR). Special attention is given to most important information tools in physics, viz. The NASA Astrophysics Data Systems (ADS) and the arXiv electronic e-prints repositor
Quantum which-way information and fringe visibility when the detector is entangled with an ancilla
No full textOpen AccessQuantum-mechanical wave-particle duality is quantified in terms of a trade-off relation between the fringe visibility and the which-way distinguishability in an interference experiment. This relation was recently generalized by Banaszek et al. [Nat. Commun. 4, 2594 (2013)] when the particle is equipped with an internal degree of freedom such as spin. Here, we extend the visibility-distinguishability trade-off relation to quantum interference of a particle possessing an internal degree of freedom, when the which-way detector state is entangled with an ancillary system. We introduce an extended which-way distinguishability DE and the associated extended fringe visibility VE, satisfying the inequality D2E+V2E≤1 in this scenario. We illustrate, with the help of three specific examples, that while the which-way information inferred solely from the detector state (without ancilla) vanishes, the extended distinguishability retrievable via measurements on the detector-ancilla entangled state is nonzero. Furthermore, in all the three examples, the extended visibility and the generalized visibility (which was introduced by Banaszek et al.) match identically with each other