Department of Physics

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IIT Jodhpur

A Ni0.8Zn0.2Fe2O4 reduced graphene oxide nanocomposite has been synthesized by a simple 'in situ co-precipitation' technique. This composite exhibited an ability to act as an excellent magnetically separable catalyst towards the degradation of various dyes as well as a toxic herbicide (trifluralin). It also demonstrated very good microwave absorption properties. © The Royal Society of Chemistry 2016.

World University root node

RSC Advances

Synthesis of a Ni0.8Zn0.2Fe2O4-RGO nanocomposite: An excellent magnetically separable catalyst for dye degradation and microwave absorber

We report a numerical study on formation and stability of parabolic pulses during their propagation through highly nonlinear specialty optical fibers. Here, we have formed a parabolic pulse at wavelength of 2.1 μm from a Gaussian input pulse with 1.9 ps FWHM and 75 W peak power after traveling through only 20 cm length from the input end of a 1 m long chalcogenide glass based microstructured optical fiber (MOF). Dependence on input pulse shapes towards most efficient conversion into self-similar states is reported. The stability in terms of any deviation from dissipative self-similar nature of such pulses has been analyzed by introducing a variable longitudinal loss profile within the spectral loss window of the MOF, and detailed pulse shapes are captured. Moreover, three different dispersion regimes of propagation have been considered to study the suitability to support most stable propagation of the pulse. © 2016 Elsevier B.V. All rights reserved.

Fulltext

Optics Communications

Formation and stability analysis of parabolic pulses through specialty microstructured optical fibers at 2.1 μm

We have fabricated an organic non-volatile memory device wherein the ON/OFF current ratio has been controlled by varying the concentration of a small organic molecule, 2,3-Dichloro-5,6-dicyano-p-benzoquinone (DDQ), in an insulating matrix of a polymer Poly(4-vinylphenol) (PVP). A maximum ON-OFF ratio of 106 is obtained when the concentration of DDQ is half or 10 wt. % of PVP. In this process, the switching direction for the devices has also been altered, indicating the disparity in conduction mechanism. Conduction due to metal filament formation through the active material and the voltage dependent conformational change of the organic molecule seem to be the motivation behind the gradual change in the switching direction. © 2016 Author(s).

Applied Physics Letters

A complementary switching mechanism for organic memory devices to regulate the conductance of binary states

Neutrino oscillations provide evidence for the mode entanglement of neutrino mass eigenstates in a given flavour eigenstate. Given this mode entanglement, it is pertinent to consider the relation between the oscillation probabilities and other quantum correlations. In this work, we show that all the well-known quantum correlations, such as the Bell's inequality, are directly related to the neutrino oscillation probabilities. The results of the neutrino oscillation experiments, which measure the neutrino survival probability to be less than unity, imply Bell's inequality violation. © 2016 The Authors.

Nuclear Physics B

Quantum correlations in terms of neutrino oscillation probabilities

We make use of the tools of quantum information theory to shed light on the Unruh effect. A modal qubit appears as if subjected to quantum noise that degrades quantum information, as observed in the accelerated reference frame. The Unruh effect experienced by a mode of a free Dirac field, as seen by a relativistically accelerated observer, is treated as a noise channel, which we term the Unruh channel. We characterize this channel by providing its operator-sum representation, and study various facets of quantum correlations, such as, Bell inequality violations, entanglement, teleportation and measurement-induced decoherence under the effect. We compare and contrast this channel from conventional noise due to environmental decoherence. We show that the Unruh effect produces an amplitude-damping-like channel, associated with zero temperature, even though the Unruh effect is associated with a non-zero temperature. Asymptotically, the Bloch sphere subjected to the channel does not converge to a point, as would be expected by fluctuation-dissipation arguments, but contracts by a finite factor. We construct for the Unruh effect the inverse channel, a non-completely-positive map, that formally reverses the effect, and offer some physical interpretation. © Rinton Press.

Quantum Information and Computation

The unruh effect interpreted as a quantum noise channel

We consider a model where the standard model is extended by the addition of a vector-like isosinglet down-type quark b'. We perform a χ2 fit to the flavor physics data and obtain the preferred central values along with errors of all the elements of the measurable 3×4 quark mixing matrix. The fit indicates that all the new-physics parameters are consistent with zero and the mixing of the b' quark with the other three is constrained to be small. The current flavor physics data rules out possibility of detectable new physics signals in most of the flavor physics observables. We also investigate possible deviations in the standard model Wtb couplings and bottom quark coupling to Higgs boson. We find that these deviations are less than a percent level which is too small to be observed at the LHC with current precision. © 2016 The Authors.

Flavor signatures of isosinglet vector-like down quark model

High-energy neutrinos (HEN) and gravitational waves (GW) can probe astrophysical sources in addition to electromagnetic observations. Multimessenger studies can reveal the nature of the sources, which may not be discerned from one type of signal alone. We discuss HEN emission in connection with the Advanced Laser Interferometer Gravitational-Wave Observatory event GW150914, which could be associated with a short gamma-ray burst detected by the Fermi Gamma-Ray Burst Monitor 0.4 s after the GW event and within localization uncertainty of the GW event. We calculate HEN flux from this short gamma-ray burst, GW150914-GBM, and show that nondetection of a high-energy starting event by the IceCube Neutrino Observatory can constrain the total isotropic-equivalent jet energy of this short burst to be less than 3×1052 erg. © 2016 American Physical Society.

Physical Review D

High-energy neutrinos from the gravitational wave event GW150914 possibly associated with a short gamma-ray burst

Detection of ~0.1-70 GeV prompt γ-ray emission from the exceptionally bright gamma-ray burst (GRB) 130427A by the Fermi-Large Area Telescope provides an opportunity to explore the physical processes of GeV γ-ray emission from the GRB jets. In this work, we discuss interactions of Iron and Oxygen nuclei with observed keV-MeV photons in the jet of GRB 130427A in order to explain an additional, hard spectral component observed during 11.5-33 s after trigger. The photodisintegration time-scale for Iron nuclei is comparable to or shorter than this duration.We find that γ rays resulting from the Iron nuclei disintegration can account for the hard power-law component of the spectra in the ~1-70 GeV range, before the γγ →e± pair production with low-energy photons severely attenuates emission of higher energy photons. Electron antineutrinos from the secondary neutron decay, on the other hand, can be emitted with energies up to ~2 TeV. The flux of these neutrinos is low and consistent with non-detection of GRB 130427A by the IceCube Neutrino Observatory. The required total energy in the Iron nuclei for this hadronic model for GeV emission is ≲10 times the observed total energy released in the prompt keV-MeV emission. © 2016 The Authors.

Monthly Notices of the Royal Astronomical Society: Letters

Photodisintegrated gamma rays and neutrinos from heavy nuclei in the gamma-ray burst jet of GRB 130427A

In order to interpret recent experimental studies of the dependence of conductance of ds-DNA as the DNA is pulled from the 3′end1-3′end2 ends, which find a sharp conductance jump for a very short (4.5%) stretching length, we carried out multiscale modeling to predict the conductance of dsDNA as it is mechanically stretched to promote various structural polymorphisms. We calculate the current along the stretched DNA using a combination of molecular dynamics simulations, non-equilibrium pulling simulations, quantum mechanics calculations, and kinetic Monte Carlo simulations. For 5′end1-5′end2 attachments we find an abrupt jump in the current within a very short stretching length (6 Å or 17%) leading to a melted DNA state. In contrast, for 3′end1-3′end2 pulling it takes almost 32 Å (84%) of stretching to cause a similar jump in the current. Thus, we demonstrate that charge transport in DNA can occur over stretching lengths of several nanometers. We find that this unexpected behaviour in the B to S conformational DNA transition arises from highly inclined base pair geometries that result from this pulling protocol. We found that the dramatically different conductance behaviors for two different pulling protocols arise from how the hydrogen bonds of DNA base pairs break. © 2016 The Royal Society of Chemistry.

Nanoscale

Dramatic changes in DNA conductance with stretching: Structural polymorphism at a critical extension

We report a coarse-grained molecular dynamics simulation study of a bundle of parallelactin filaments under supercritical conditions pressing against a loaded mobile wall using aparticle-based approach where each particle represents an actin unit. The filaments are graftedto a fixed wall at one end and are reactive at the other end, where they can perform singlemonomer (de)polymerization steps and push on a mobile obstacle. We simulate a reactive grandcanonical ensemble in a box of fixed transverse area A, with a fixed number of grafted filaments Nf ,at temperature T and monomer chemical potential μ1. For a single filament case (Nf=1) and fora bundle of Nf = 8 filaments, we analyze the structural and dynamical properties at equilibriumwhere the external load compensates the average force exerted by the bundle. The dynamics of thebundle-moving-wall unit are characteristic of an over-damped Brownian oscillator in agreementwith recent in vitro experiments by an optical trap setup. We analyze the influence of thepressing wall on the kinetic rates of (de)polymerization events for the filaments. Both static anddynamic results compare reasonably well with recent theoretical treatments of the same system.Thus, we consider the proposed model as a good tool to investigate the properties of a bundle ofliving filaments. © 2016 by the authors.