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[en] The perovskite type oxide SrHfO had a huge scientist interest for the past few years thanks to its properties, which allowed it to be applied in different area, in our case we focused on the photovoltaic field application and it is known that this technology has been based on the use of semiconductors with a specific gap value since its birth, which indicates that the gap value is an important element who influences on the efficiency of panels. The aim of our work is based on reducing the gap value by applying different percentage of doping SrHfOS (x = 0%, 8% and 16%) and the determination of electronic and optical properties of all percentage of S using density functional theory (DFT). As a result we reduced the gap value from 5.60 eV corresponding to 0% of S to 2.09 eV corresponding to 16% of S and the band gap is changed from an indirect band gap equivalent to 0% of S to a direct band gap for 8% and 16% of S.
[en] Gamma-ray bursts (GRBs) are the most powerful explosions in the universe. They have remained the object of intense research ever since their discovery was declassified in the early 1970s. Several space-borne missions have been dedicated to their study, including the Compton Gamma-Ray Burst Observatory (CGRO) in the 1990s and the current Swift and Fermi satellites. However, despite several decades of focused research, the precise mechanisms behind these enigmatic explosions have not been fully established. In the first part of this paper, we review what is currently known about GRBs. This includes: GRB light-curves and spectra; the different progenitor models, i.e., the 'collapsar' and 'merger' models; and the afterglow characteristics, including external shocks and the surrounding medium. In the second part of the paper, we present our work, which focuses on utilizing GRBs as cosmological probes. GRBs are ideal cosmological tools, because they have been observed to great distances (redshifts up to z = 9.4) and their radiation is unencumbered by any intervening dust. Although GRBs are not standard candles, the discovery of several energy and luminosity correlations, like the Amati relation which correlates the intrinsic spectral peak energy, Ep,i to the equivalent isotropic energy, Eiso , has ushered in a new era in which GRBs are used to investigate cosmological issues like the star formation rate and the value of the matter-density parameter, ΩM. (paper)
[en] We have undertaken a literature search for associations of gamma-ray bursts (GRBs) with supernovae (SNe), and we have constructed a much larger table of cases than has been published until now. The table contains a suite of physical properties for the GRBs (and the SNe when available), which will allow us and others to infer valuable knowledge about the GRBs and their physical mechanisms. From this basic table, we have undertaken a very preliminary examination, looking at the intrinsic GRB properties at hand, i.e. duration, isotropic energy output, peak spectrum energy, fluence, spectral index, redshift etc., and we present initial results. Future analyses will be performed to try to determine whether GRBs with no associated SNe constitute a subclass or category of bursts with particular characterizing properties. (paper)
[en] Ever since the insightful analysis of the durations of gamma-ray bursts (GRBs) by Kouveliotou et al. (Astrophys. J. Lett. 413:101, 1993), GRBs have most often been classified into two populations: “short bursts” (shorter than 2.0 seconds) and “long bursts” (longer than 2.0 seconds). However, recent works have suggested the existence of an intermediate population in the bursts observed by the Swift satellite. Moreover, some researchers have questioned the universality of the 2.0-second dividing line between short and long bursts: some bursts may be short but actually result from collapsars, the physical mechanism behind normally long bursts, and some long ones may originate from mergers, the usual progenitors of short GRBs.In this work, we focus on GRBs detected by the Fermi satellite (which has a much higher detection rate than Swift and other burst-detecting satellites) and study the distribution of their durations measured in the observer’s reference frame and, for those with known redshifts, in the bursts’ reference frames. However, there are relatively few bursts with measured redshifts, and this makes an accurate study difficult. To overcome this problem, we follow Zhang and Wang (Astrophys. J. 852:1, 2018) and determine a “pseudo-redshift” from the correlation relation between the luminosity and the energy , both of which are calculated at the peak of the flux. Interestingly, we find that the uncertainties in the quantities observed and used in the determination of pseudo-redshifts, do affect the precision of the individual results significantly, but they keep the distribution of pseudo-redshifts very similar to that of the actual ones and thus allow us to use pseudo-redshifts for our statistical study. We briefly present the advantages and disadvantages of using pseudo-redshifts in this context.We use the reduced chi-square and the maximization of the log-likelihood to statistically analyze the distribution of Fermi GRB durations. Both methods show that the distribution of the observed (measured) and the intrinsic (source/rest frame) bursts durations are better represented by two groups/populations, rather than three.
[en] We compute the expected GRB luminosity function in the internal shock model. We find that if the population of GRB central engines produces all kind of relativistic outflows, from very smooth to highly variable, the luminosity function has to branchs: at low luminosity, the distribution is dominated by low efficiency GRBs and is close to a power law of slope -0.5, whereas at high luminosity, the luminosity function follows the distribution of injected kinetic power. Using Monte Carlo simulations and several observational constrains (BATSE logN-logP diagram, peak energy distribution of bright BATSE bursts, fraction of XRFs in the HETE2 sample), we show that it is currently impossible to distinguish between a single power law or a broken power law luminosity function. However, when the second case is considered, the low-luminosity slope is found to be -0.6±0.2, which is compatible with the prediction of the internal shock model
[en] We investigate the interface between Au catalysts and a Ge(1 1 1) substrate. This system is achieved by dewetting an Au layer above the Au–Ge eutectic temperature. We show by high resolution transmission electron microscopy that a large amount of Ge can be moved over a surface of Ge(1 1 1) by using assistance of eutectic Au–Ge droplets. This localization is achieved thanks to the ability of nano Au–Ge droplets to incorporate a large amount of Ge and to release it by cooling down the sample at room temperature. This makes the localization process irreversible with respect to annealing at a very high temperature. The extra Ge supplied by precipitation is in epitaxy with the Ge(1 1 1) substrate. This reflects in macroscopic I(V) measurements