Department of Physics

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IIT Jodhpur

Gamma Ray Bursts (GRBs) are the explosions which take place in the universe with the emission of extraordinarily high energies of the order of 1055 erg. These explosions were detected at redshift up to z = 9.4. Many theoretical models were used to explain the mechanism of GRBs. Here we have done the synchrotron modeling of the spectral energy distribution of the GRBs in the fast cooling and slow cooling regimes for the adiabatic blastwaves in Interstellar Medium (ISM) and wind environment. We have modeled the spectral energy distribution at different time intervals for GRB 130427A. GRBs help us to learn about the processes that cannot be studied under laboratory conditions and also enable us to understand the physics behind the formation and structure of matter in the Universe. GRBs are candidate sources of ultra high energy cosmic rays (UHECRs). High energy neutrinos can be produced by the interaction of these UHECRs with the GRB afterglow photons, which are produced in the blastwave.

World University root node

Proceedings of Science

Gamma-Ray bursts and its afterglow modeling

Cosmic neutrino events detected by the IceCube Neutrino Observatory with energy 0 3 TeV have poor angular resolutions to reveal their origin. Ultrahigh-energy cosmic rays (UHECRs), with better angular resolutions at 0>6 EeV energies, can be used to check if the same astrophysical sources are responsible for producing both neutrinos and UHECRs. We test this hypothesis, with statistical methods which emphasize invariant quantities, by using data from the Pierre Auger Observatory, Telescope Array and past cosmic-ray experiments. We find that the arrival directions of the cosmic neutrinos are correlated with 0≥ 10 EeV UHECR arrival directions at confidence level 90%. The strength of the correlation decreases with decreasing UHECR energy and no correlation exists at energy 0∼ 6 EeV . A search in astrophysical databases within 3 of the arrival directions of UHECRs with energy 0≥ 10 EeV, that are correlated with the IceCube cosmic neutrinos, resulted in 18 sources from the Swift-BAT X-ray catalog with redshift z≤ 0.06. We also found 3 objects in the Kühr catalog of radio sources using the same criteria. The sources are dominantly Seyfert galaxies with Cygnus A being the most prominent member. We calculate the required neutrino and UHECR fluxes to produce the observed correlated events, and estimate the corresponding neutrino luminosity (25 TeV-2.2 PeV) and cosmic-ray luminosity (500 TeV-180 EeV), assuming the sources are the ones we found in the Swift-BAT and Kühr catalogs. We compare these luminosities with the X-ray luminosity of the corresponding sources and discuss possibilities of accelerating protons to 0 10 EeV and produce neutrinos in these sources. © 2015 IOP Publishing Ltd and Sissa Medialab srl .

Fulltext

Journal of Cosmology and Astroparticle Physics

Angular correlation of cosmic neutrinos with ultrahigh-energy cosmic rays and implications for their sources

Long-ranged dipole-dipole interactions in magnetic glasses give rise to magnetic domains having labyrinthine patterns on the scale of about 1 micron. Barkhausen Noise then results from the movement of domain boundaries which is modeled by the motion of elastic membranes with random pinning. Here we propose that on the nanoscale new sources of Barkhausen Noise can arise. We propose an atomistic model of magnetic glasses in which we measure the Barkhausen Noise which results from the creation of new domains and the movement of domain boundaries on the nanoscale. The statistics of the Barkhausen Noise found in our simulations is in striking disagreement with the expectations in the literature. In fact we find exponential statistics without any power law, stressing the fact that Barkhausen Noise can belong to very different universality classes. In the present model the essence of the phenomenon is the fact that the spin response Green's function is decaying too rapidly for having sufficiently large magnetic jumps. A theory is offered in excellent agreement with the measured data without any free parameter. © EPLA, 2015.

Modeling Barkhausen Noise in magnetic glasses with dipole-dipole interactions

The concept of a Shear Transformation Zone (STZ) refers to a region in an amorphous solid that undergoes a plastic event when the material is put under an external mechanical load. An important question that had accompanied the development of the theory of plasticity in amorphous solids for many years now is whether an STZ is a region existing in the material (which can be predicted by analyzing the unloaded material), or it is an event that depends on the loading protocol (i.e., the event cannot be predicted without following the protocol itself). In this letter we present strong evidence that the latter is the case. Infinitesimal changes of protocol result in macroscopically big jumps in the positions of plastic events, meaning that these can never be predicted from considering the unloaded material. Copyright © EPLA, 2015.

Shear Transformation Zones: State determined or protocol dependent?

A modular double gap pseudospark discharge based switch has been recently designed and developed for various pulsed power applications. The modular pseudospark geometry has two gaps that are separated by a cavity drift space region. It employs a single trigger unit in the cathode region to initiate discharge for the rapid breakdown of both the gaps. Successful experiments for the double gap pseudospark with typical coaxial arrangement of multichannel discharges were performed. The peak discharge currents at breakdown voltage of about 40 kV were 5 and 10 kA through resistive loads of 5.25 and 2.7 Ω, respectively. The design of the double gap pseudospark along with switching results is presented in this paper. © 2015 IEEE.

IEEE Transactions on Dielectrics and Electrical Insulation

Switching behavior of a double gap pseudospark discharge

ICOPS/BEAMS 2014 - 41st IEEE International Conference on Plasma Science and the 20th International Conference on High-Power Particle Beams

Development of PIC-FDTD code for beam-wave interaction study in 'PASOTRON'

Large volume penning plasma discharge source: An efficient light emitting source for the visible and VUV radiations simultaneously

Pseudospark (PS) discharge is promising source for high brightness and high intensity electron beam pulses. In the present paper, an effort has been made to analyse the temporal behaviour of discharge current, applied voltage, plasma density in the PS discharge based PCE-Gun at different hollow cathode aperture sizes using 3-D particle-in-cell (PIC) simulation code "VORPAL". The peak discharge current in the PS discharge is a function of hollow cathode dimensions. The plasma generation process by self ionization discharge is examined at different operating conditions. Argon is taken as the background neutral gas. It has been observed that the decrease in the aperture size from 8 mm to 3 mm increases the discharge current, the electron confinement time and the plasma density. © 2015, National Institute of Science Communication and Information Resources (NISCAIR). All rights reserved.

Indian Journal of Pure and Applied Physics

Particle-in-cell simulation study of PCE-gun for different hollow cathode aperture sizes

Zirconium carbide-nitride absorber (ZrC-ZrN) and zirconium reflector tandem structures were prepared on glass and aluminum substrate, in conjunction with zirconium oxide (ZrOx) anti-reflection coatings, using DC/RF magnetron sputtering system. The solar absorption properties of zirconium carbide-nitride absorber layers were optimized by controlling nitrogen flow during synthesis process for optimal solar thermal response. X-ray diffraction (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM) measurements were carried out on fabricated absorber-reflector tandem structures to understand the structure-property correlation. We absorbed strong dependence of zirconium nitride fraction on solar thermal performance. We observed enhanced solar absorptance α ∼ 0.86 and thermal emittance ϵ ∼ 0.05 at room temperature for structures fabricated with optimized synthesis parameters. The optimized structures are stable up to 150 °C in the air without any significant degradation in their solar performance. © 2016. The Authors.

Department of Mechanical Engineering

ISES Solar World Congress 2015, Conference Proceedings

Zirconium carbide-nitride composite matrix based solar absorber structures on glass and aluminum substrates for solar thermal applications

Alloy composition (Co94Fe6)72.75Si12.25B13.25Cr1.75 was designed to develop nearly zero-magnetostrictive materials in the form of ribbons and wires to obtain suitable magnetic properties for use as giant magnetoimpedance (GMI) and low-noise fluxgate sensor cores. During the development of magnetic sensing core using amorphous wires of diameter 80 μ m for GMI sensing, we observed a maximum impedance change (GMI ratio) of 430% with as-cast wires, which further enhanced to 650% when annealed at 300 °C for 5 min. The effect of annealing temperature and stress on the magnetic properties of fluxgate sensing core materials has been studied. Magnetic hysteresis loops were measured with 3-mm-wide and 45-μm-thick amorphous ribbons on a toroidal ring of 50 mm diameter for fluxgate sensor core. A coercivity of 10.57 A/m and saturation field of ∼ 150 A/m were observed with as-quenched ribbon, which improved to a coercivity of 2.16 A/m and saturation field ∼ 100 A/m when annealed without stress just above its Curie temperature. An induced anisotropy transverse to excitation direction was achieved by applying temperature with stress and time (300 °C/100 MPa/20 min) to use it for fluxgate sensor core. © 2015 IEEE.