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D. Ibrahim

Publications and source records attributed to D. Ibrahim.

3 recordsLinked to original sources

The second Arcminute Microkelvin Imager - Large Array Gamma-ray burst radio afterglow catalog

Radio observations of gamma-ray burst afterglows provide insight in to the different emitting regions within the jet, its hydrodynamics and burst environment. In this paper, we present the second iteration of the Arcminute Microkelvin Imager - Large Array (AMI-LA) Gamma-ray burst (GRB) radio afterglow catalog. The catalog consists of 1035 observations of 210 bursts. Our observations range from 0.04 to 900days post-burst. We detect radio emission associated with 19 events with flux densities spanning 0.1-40mJy, and present a detailed analysis of six events whose light curves have not been published elsewhere. In our individual afterglow analyses, we find that our radio counterparts show evidence of reverse shock emission 60% of the time. Two of the detected afterglows show evidence of scintillation which we use to place source size limits at tens of days. Of the whole catalog, 50 events have redshift measurements which we use to find the radio afterglow luminosity distribution for our sample. Our luminosity distribution spans five orders of magnitude, a larger range than seen in optical and X-ray bands, indicative of the strong dependence of the radio counterparts on the GRB's physical parameters.

astro-ph.HE

Pulsed discharge plasma for graphite exfoliation in liquid nitrogen

Highly Oriented Pyrolytic Graphite was exfoliated via pulsed discharge plasma in liquid nitrogen. The potential mechanisms involved were investigated by observing the treated surface of the graphitic material and the obtained particles. Non-exfoliating defects from the plasma treatment were observed and experimental parameter were modified to counteract those. One experiment was performed without exposing the HOPG directly to the discharges so as to better understand the plasma role. The exfoliated particles were observed via TEM and SEM to evaluate the defects, the size, the purity and the crystallinity but no quantitative characterization of their thickness was possible so the actual number of layer of each particle is unknown. Nonetheless, few layers graphene (FLG) was successfully exfoliated through this process. The proposed mechanisms were extrapolated from the observation of the damaged HOPG surface and the obtained particles but the correlation found does not prove causation.

physics.app-ph

Study of the exfoliation and functionalization of graphene from graphite flakes with plasma discharge in solution

Graphene flakes were produced by nanosecond plasma discharge at atmospheric pressure between an electrode and the surface of distilled water, in which were placed graphite flakes. The discharge ionizes the gas and forms free radicals on the surface of the water, functionalizing the graphite flakes in solution. The plasma also gives enough energy to break the Van der Waals bonds between the graphene layers but not enough to break the covalent C-C bonds within the layers. Transmission electron microscopy confirmed the hexagonal structure of graphene sheets, and showed that they were monocrystalline. No contamination was found in the obtained nanomaterial. An unknown phenomenon has been found in the activated distilled water, making its electrical conductivity decrease with an increasing temperature. An acidification of the water is observed. The gas in which the discharge takes place plays a major role on the process, no exfoliation is observed if plasmogen argon gas is used.

physics.app-ph