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Torsional instanton effects in quantum gravity
No full textOpen AccessWe show that in the first-order gravity theory coupled to axions the instanton number of the Giddings-Strominger wormhole can be interpreted as the Nieh-Yan topological index. The axion charge of the baby universes is quantized in terms of the Nieh-Yan integers. Tunneling between universes of different Nieh-Yan charges implies a nonperturbative vacuum state. The associated topological vacuum angle can be identified with the Barbero-Immirzi parameter
Birefringence of a normal human red blood cell and related optomechanics in an optical trap
No full textRestricted Access.A normal human red blood cell (RBC) when trapped with a linearly polarized laser, reorients about the electric polarization direction and then remains rotationally bound to this direction. This behavior is expected for a birefringent object. We have measured the birefringence of distortion-free RBCs in an isotonic medium using a polarizing microscope. The birefringence is confined to the cell’s dimple region and the slow axis is along a diameter. We report an average retardation of 3.5±1.5 nm for linearly polarized green light (λ=546 nm). We also estimate a retardation of 1.87±0.09 nm from the optomechanical response of the RBC in an optical trap. We reason that the birefringence is a property of the cell membrane and propose a simple model attributing the origin of birefringence to the phospholipid molecules in the lipid bilayer and the variation to the membrane curvature. We observe that RBCs reconstituted in shape subsequent to crenation show diminished birefringence along with a sluggish optomechanical response in a trap. As the arrangement of phospholipid molecules in the cell membrane is disrupted on crenation, this lends credence to our conjecture on the origin of birefringence. Dependence of the birefringence on membrane contours is further illustrated through studies on chicken RBCs
First order transition for the optimal search time of lévy flights with resetting
No full textOpen AccessWe study analytically an intermittent search process in one dimension. There is an immobile target at the origin and a searcher undergoes a discrete time jump process starting at x0≥0, where successive jumps are drawn independently from an arbitrary jump distribution f(η). In addition, with a probability 0≤r<1, the position of the searcher is reset to its initial position x0. The efficiency of the search strategy is characterized by the mean time to find the target, i.e., the mean first passage time (MFPT) to the origin. For arbitrary jump distribution f(η), initial position x0 and resetting probability r, we compute analytically the MFPT. For the heavy-tailed Lévy stable jump distribution characterized by the Lévy index 0<μ<2, we show that, for any given x0, the MFPT has a global minimum in the (μ,r) plane at (μ∗(x0),r∗(x0)). We find a remarkable first-order phase transition as x0 crosses a critical value x∗0 at which the optimal parameters change discontinuously. Our analytical results are in good agreement with numerical simulations
A quick electrochemical approach for synthesizing the metal nanostructures stabilized with conducting polymers
No full textRestricted Access.We demonstrate a simple technique to produce gold nanoparticles (GNPs) stabilized with polyaniline (PANI) in the aqueous solution. The method is extremely efficient yet an uncomplicated process, which involves the in situ electrochemical-cum-chemical polymerization of aniline to yield the metal nanoparticles. The nanosize particles were examined with the help of UV–vis and HRTEM. The proposed method although combines electrochemical and chemical synthesis events, however it is essentially a single step process. The method can also be extended for various other combinations of metals and conducting polymers
Effects of chain branching and lateral fluorine substitution on mesomorphism of cholesteryl benzoates
No full textRestricted Access.The mesogenic cholesteryl 4′-alkoxyphenyl-4-carboxylates possessing terminal normal/branched/saturated/unsaturated alkyl chains with laterally ortho/meta substituted electronegative fluorine atom are described. All the homologues exhibited enantiotropic mesomorphism. Smectic A phase, chiral nematic, blue phase (BP) and TGBA phases were observed in different homologues. All the novel compounds were characterised by spectroscopic and elemental analysis. Thermal investigations and mesophase characterisations for all the compounds were carried out by the combination of DSC, POM and X-ray analysis. The effects of the various terminal normal/branched/saturated/unsaturated alkyl chains and the position of the substituted fluorine atom with its structurally related compounds have been discussed
Heat conduction in the α-β-Fermi-Pasta-Ulam chain
No full textRestricted Access. An open-access version is available at arXiv.org (one of the alternative locations)Recent simulation results on heat conduction in a one-dimensional chain with an asymmetric inter-particle interaction potential and no onsite potential found non-anomalous heat transport in accordance to Fourier’s law. This is a surprising result since it was long believed that heat conduction in one-dimensional systems is in general anomalous in the sense that the thermal conductivity diverges as the system size goes to infinity. In this paper we report on detailed numerical simulations of this problem to investigate the possibility of a finite temperature phase transition in this system. Our results indicate that the unexpected results for asymmetric potentials is a result of insufficient chain length, and does not represent the asymptotic behavior
A thin wire ion trap to study ion-atom collisions built within a Fabry-Perot cavity
No full textRestricted Access.We report on the implementation of a thin wire Paul trap with tungsten wire electrodes for trapping ions. The ion trap geometry, though compact, allows large optical access enabling a moderate finesse Fabry–Perot cavity to be built along the ion trap axis. The design allows a vapor-loaded magneto-optical trap of alkali atoms to be overlapped with trapped atomic or molecular ions. The construction and design of the trap are discussed, and its operating parameters are determined, both experimentally and numerically, for Rb+. The macromotion frequencies of the ion trap for 85Rb+ are determined to be f r = 43 kHz for the radial and f z = 54 kHz for the axial frequencies, for the experimentally determined optimal operating parameters. The destructive off axis ion extraction and detection by ion counting is demonstrated. Finally, evidence for the stabilization and cooling of trapped ions, due to ion–atom interactions, is presented by studying the ion-atom mixture as a function of interaction time. The utility and flexibility of the whole apparatus, for a variety of atomic physics experiments, are discussed in conclusion
The quantum cryptographic switch
No full textRestricted Access. An open-access version is available at arXiv.org (one of the alternative locations)We illustrate the principle of a cryptographic switch for a quantum scenario, in which a third party (Charlie) can control to a continuously varying degree the amount of information the receiver (Bob) receives, after the sender (Alice) has sent her information through a quantum channel. Suppose Charlie transmits a Bell state to Alice and Bob. Alice uses dense coding to transmit two bits to Bob. Only if the 2-bit information corresponding to the choice of the Bell state is made available by Charlie to Bob can the latter recover Alice’s information. By varying the amount of information Charlie gives, he can continuously alter the information recovered by Bob. The performance of the protocol as subjected to the squeezed generalized amplitude damping channel is considered. We also present a number of practical situations where a cryptographic switch would be of use
