arXiv subjects

S. Hassan

Publications and source records attributed to S. Hassan.

7 recordsLinked to original sources

arXiv2024

Depth resolved study of annealing in IrMn/(Fe, Co, CoFe) exchange bias systems

Depth resolved study of structural and magnetic profiles of antiferromagnetic/ferromagnetic (AFM/FM) system upon annealing was performed in this work. We studied systems comprising of AFM IrMn and FM (Co, Fe, Co$_{70}$Fe$_{30}$) structures using polarized neutron and soft X-ray scattering, secondary neutral spectrometry, and magnetometry. Structural depth profiles obtained from neutron reflectometry indicate non-homogeneity of the AFM layer even before annealing, which is associated with the migration of manganese to the surface of the sample. Annealing of samples with CoFe and Co layers leads to a slight increase ($\sim$ 5 %) in the migration of manganese, which, however, does not lead to significant degradation of the exchange coupling at the AFM/FM interface. A significantly different picture was observed in the Fe/IrMn systems where a strong migration of iron into the AFM layer was observed upon annealing of the sample, leading to erosion of the magnetic profile, the formation of a non-magnetic alloy and degradation of the pinning strength. This study can be useful in the design of AF/FM systems in different spintronics devices, including HDD read heads, where thermal annealing is applied at different stages of the device manufacturing process.

cond-mat.mtrl-sci↗

arXiv2024

Stabilization of Multi Fractional Order Differential Equation with Delay Time and Feedback Control

The purpose of this article is to introduce the original results which devoted with the nonlinear control system problems involves of nonlinear differential equations of fractional orders. Thus, this system is described with a mixed of ordinary derivatives in the first and second order that, are unstable before feedback gain. More precisely, we investigate and analysis the nonlinear control system in related to feedback gain matrix. In addition, we prove that the considered system is locally asymptotically stabilizable via certain conditions. Then, this work reinforce through some application examples that programmed for illustrating and showing the stabilizability of the current systems with high efficiency and accuracy.

math.OC↗

arXiv2022

Model studies of V0 production ratios in $pp$ collisions at $\sqrt{\mathrm{s}}$ = 0.2, 0.9, and 7 TeV

A comparative study of $V^0$ ratios has been performed between HIJING, Sibyll and QGSJET model-based event generators in this paper. The ratios under study are {\alam}/{\lam}, {\alam}/{\ks} and {\xim}/{\lam} as a function of rapidity $y$, rapidity loss ($Δy$) and {\ppt} from $pp$ collisions at \sqrts~= 0.2, 0.9, and 7 TeV and these simulations are then compared with the STAR and LHCb fiducial phase spaces in different {\ppt} regions. Although the models could produce some of the ratios in a limited {\ppt} and/or $y$ region, none of them completely predicts the experimental results. The QGSJET has good predictions with the data in most of the cases but since the model does not include the $Ξ$ particle definition, therefore it does not give any predictions for $Ξ$/{\lam} ratios. The extrapolation to the highest possible energies can be studied by re-tune some of the basic parameters based on current and previous measurements. These kinds of systematic comparison studies are also useful to apply certain constraints on the pQCD and non-pQCD-based hadronic event generators to significantly improve the predictions of Standard Model physics at the RHIC and LHC experimental data for the understanding of underlying physics mechanisms in high energy collisions.

hep-ph↗

arXiv2021

The upgrade of the ALICE TPC with GEMs and continuous readout

The upgrade of the ALICE TPC will allow the experiment to cope with the high interaction rates foreseen for the forthcoming Run 3 and Run 4 at the CERN LHC. In this article, we describe the design of new readout chambers and front-end electronics, which are driven by the goals of the experiment. Gas Electron Multiplier (GEM) detectors arranged in stacks containing four GEMs each, and continuous readout electronics based on the SAMPA chip, an ALICE development, are replacing the previous elements. The construction of these new elements, together with their associated quality control procedures, is explained in detail. Finally, the readout chamber and front-end electronics cards replacement, together with the commissioning of the detector prior to installation in the experimental cavern, are presented. After a nine-year period of R&D, construction, and assembly, the upgrade of the TPC was completed in 2020.

physics.ins-det↗

arXiv2019

Secondary discharge studies in single and multi GEM structures

Secondary discharges, which consist of the breakdown of a gap near a GEM foil upon a primary discharge across that GEM, are studied in this work. Their main characteristics are the occurrence a few $10\,μ\textrm{s}$ after the primary, the relatively sharp onset at moderate electric fields across the gap, the absence of increased fields in the system, and their occurrence under both field directions. They can be mitigated using series resistors in the high-voltage connection to the GEM electrode facing towards an anode. The electric field at which the onset of secondary discharges occurs indeed increases with increasing resistance. Discharge propagation form GEM to GEM in a multi-GEM system affects the occurrence probability of secondary discharges in the gaps between neighbouring GEMs. Furthermore, evidence of charges flowing through the gap after the primary discharge are reported. Such currents may or may not lead to a secondary discharge. A characteristic charge, of the order of $10^{10}\,\textrm{electrons}$, has been measured as the threshold for a primary discharge to be followed by a secondary discharge, and this number slightly depends on the gas composition. A mechanism involving the heating of the cathode surface as trigger for secondary discharges is proposed.

physics.ins-det↗

arXiv2015

Four-Terminal Mechanically Stacked GaAs/Si Tandem Solar Cells

This study investigates a four-terminal mechanically stacked double junction photovoltaic device based on GaAs as a top subcell and Si as a bottom subcell. Unlike two terminal monolithically series connected double junction photovoltaics, four-terminal mechanically stacked devices benefit from the ability to choose a combination of materials that are not constrained to lattice matching condition. GaAs top subcell is the best sensitive to visible light and Si bottom subcell is chosen to be grown on Si substrate which has relatively low cost. Moreover, the carriers generated by each subcell is collected independently to the external circuit. This electrical isolation of the subcells ensures higher efficiency, where no current matching nor tunnel junctions and related losses exist. A conversion efficiency of the device with a thickness in the order of 10 microns surpassed 27%.

physics.optics↗

arXiv2001

An optical and near IR study of the old open cluster NGC 2141

We report on CCD optical (B and V passbands) and near IR (J and K bands) observations in the region of the old open cluster NGC 2141. By combining the two sets of photometry (500 stars in common) we derive new estimates of the cluster fundamental parameters. We confirm that the cluster is 2.5 Gyrs old, but, with respect to previous investigations, we obtain a slightly larger reddening (E(B-V)=0.40), and a slightly shorter distance (3.8 kpc) from the Sun. Finally we present Luminosity Function (LF) in the V band, which is another age indicator. We provide a good fit for the age range inferred from isochrones by assuming the Kroupa et al. (1993) IMF up to $M_V$=5.0. We interpret the disagreemt at fainter magnitudes as an evidence of mass segregation.

astro-ph↗