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Hamid Ez-Zahraouy

Publications and source records attributed to Hamid Ez-Zahraouy.

14 recordsLinked to original sources
arXiv2022

Theoretical Investigation of Structural, Electronic Properties and Half-Metallic Ferromagnetism in Ti doped CaS

In this research paper, we investigated the structural, electronic, and magnetic features of titanium atom substituting calciumatom in rock salt structure of CaS to explore the new dilute magnetic semiconductor compounds. The calculations are carried out using the full potential linearized augmented plane wave (FP-LAPW) method based on spin-polarized density functional theory, implemented in WIEN2k code. The generalized gradient approximation and Tran-Balaha modified Becke-Johnson exchange potential. The stability of Ti doped CaS in ferromagnetic state is provided by the total energy released from the optimized structures and defect formation energies. The classical model of Heisenberg is employed to estimate Curie temperature of these compounds. It is found that the room temperature ferromagnetism is achieved at low concentrations. The studied materials exhibit half metallic ferromagnetic demeanor. The half metallic gaps (GHM) are the extremely significant factors to consider for spintronic applications. The insertion of impurity significantly decreased the value of GHM due the broadening of 3d Ti states in the gap of the minority spin. Furthermore, to evaluate the effects of the exchange splitting process, the pd exchange splitting and the exchange constants are predicted.

cond-mat.mtrl-sci↗
arXiv2022

Theoretical investigation of electronic, optical and thermoelectric properties of tellurium doped barium titanate (BTO) through modified Becke Johnson exchange potential

The stability, electronic structure, optical and thermoelectric properties of Te-doped BaTiO3 are investigated by first-principal calculation based on the density functional theory and Boltzmann transport theory implemented in WIEN2K and BoltzTraP simulation program. This study is carried out by applying LDA + TB-mBJ potential. Formation energy of each doped structure is calculated to examine the stability and feasibility of the synthesis. Incorporating Te into BaTiO3 efficiently reduces the electronic band gap and the level of band gap reduction can be controlled by varying the amount of dopant. Hence, the absorption ability is improved in the visible light. Our findings suggest that all the doped structures are significantly absorbent and productive with an optical absorption that exceeds 105 cm-1 in the visible range. In addition, BaTiO3 revealed a smaller dielectric constant at zero frequency compared to Te doped-BTO: 8.3%, while the optical energy gap is reduced from 3.692 eV to 1.619 eV by growing Te concentration. Then, optical conductivity and Urbach's parameters are predicted. The transport properties are assessed as a function of temperature. It is found that the electrical conductivity is considerably enhanced with increase properties such as Seebeck coefficient and figure of merit are also investigated. Our theoretical results can be useful for thermoelectric and visible light photoelectrical device applications.

cond-mat.mtrl-sci↗
arXiv2020

Rare-earth effect on the physical properties of Na$_{0.5}$Bi$_{0.5}$TiO$_3$ system: A Density Functional Theory investigation

Na$_{0.5}$(Bi$_3$/4RE$_{1/4}$)$_{0.5}$TiO$_3$ (RENBT, RE = Nd, Gd, Dy, and Ho) compounds were investigated in the framework of first-principles calculations using the full potential linearized augmented plane wave (FP-LAPW) method based on the spin-polarized density functional theory implemented in the WIEN2k code. Combined charge density distribution and Ti K-edge x-ray absorption spectra revealed that the RENBT compositions with high polarization values were accompanied by a higher TiO$_6$ distortion, DyNBT, and NdNBT compounds. The effect of the rare-earth elements on the polarization were confirmed experimentally with the collection of the hysteresis loops. The investigation of the electronic properties of the compounds highlighted the emergence of a magnetization owing to the 4f orbital effect of the rare-earth elements. Besides, the investigation of the chemical ordering showed a short-range chemical ordering for the pure composition and an increased A-site disorder for dysprosium doped NBT system. The increased disorder may speak for increased relaxor properties in the RE doped compositions.

cond-mat.mtrl-sci↗
arXiv2020

Erythrocyte-erythrocyte aggregation dynamics under shear flow

Red blood cells (RBCs) -- erythrocytes -- suspended in plasma tend to aggregate and form rouleaux. During aggregation the first stage consists in the formation of RBC doublets [Blood cells, molecules, and diseases 25, 339 (1999)]. While aggregates are normally dissociated by moderate flow stresses, under some pathological conditions the aggregation becomes irreversible, which leads to high blood viscosity and vessel occlusion. We perform here two-dimensional simulations to study the doublet dynamics under shear flow in different conditions and its impact on rheology. We sum up our results on the dynamics of doublet in a rich phase diagram in the parameter space (flow strength, adhesion energy) showing four different types of doublet configurations and dynamics. We find that membrane tank-treading plays an important role in doublet disaggregation, in agreement with experiments on RBCs. A remarkable feature found here is that when a single cell performs tumbling (by increasing vesicle internal viscosity) the doublet formed due to adhesion (even very weak) remains stable even under a very strong shear rate. It is seen in this regime that an increase of shear rate induces an adaptation of the doublet conformation allowing the aggregate to resist cell-cell detachment. We show that the normalized effective viscosity of doublet suspension increases significantly with the adhesion energy, a fact which should affect blood perfusion in microcirculation.

physics.bio-ph↗
arXiv2020

Electrical and structural properties of pure and dysprosium doped $Na_{0.5}Bi_{0.5}TiO_{3}$ system: DFT and Monte Carlo simulation

The chemical ordering, electrical, optical, and magnetic properties of $Na_{0.5}Bi_{0.5}TiO_{3}$ (NBT) and 25$\%$ dysprosium doped NBT (DyNBT) were investigated in the framework of first-principles calculations using the full potential linearized augmented plane wave (FP-LAPW) method based on spin-polarized density functional theory implemented in the WIEN2k code. We demonstrated that NBT structure is stable in the 001 A-site configuration, while DyNBT presents an A-site disorder perceived by the minimal energy difference between the different A-site configurations. A significant magnetic moment of $5μB$ emerges in DyNBT system, while NBT is known to be non-magnetic. Dysprosium in NBT matrix seems to form an ionic bonding with oxygen atoms whereas Bi-O forms covalent bonding which is responsible for the decrease of the polarization value from 42.3 $μC/cm^{2}$ for NBT to 22.08 $μC/cm^{2}$ for the doped compound. In the second part, the transition temperature and the hysteresis loops of $Na_{0.5}(Bi_{1-x}Dy_{x})_{0.5}TiO_{3}$ system x = 0 - $25\%$ were investigated using the Monte Carlo simulation. We observed a decrease in the transition temperature as a function of dysprosium introduction. We pointed out from the hysteresis loops, an apparent decrease of the coercive field together with the remanent polarization as a function of doping and also as a function of temperature. Our proposed model was seen to approach the values of experimental studies.

cond-mat.mtrl-sci↗
arXiv2018

Vesicle dynamics in confined steady and harmonically modulated Poiseuille flows

We present a numerical study of the time-dependent motion of a two-dimensional vesicle in a channel under an imposed flow. In a Poiseuille flow the shape of the vesicle depends on the flow strength, the mechanical properties of the membrane, and the width of the channel as reported in the past. This study is focused on the centered snaking (CSn) shape, where the vesicle shows an oscillatory motion like a swimmer flagella even though the flow is stationary. We quantify this behavior by the amplitude and frequency of the oscillations of the vesicle's center of mass. We observe regions in parameter space, where the CSn coexists with the parachute or the unconfined slipper. The influence of an amplitude modulation of the imposed flow on the dynamics and shape of the snaking vesicle is also investigated. For large modulation amplitudes transitions to static shapes are observed. A smaller modulation amplitude induces a modulation in amplitude and frequency of the center of mass of the snaking vesicle. In a certain parameter range we find that the center of mass oscillates with a constant envelope indicating the presence of at least two stable states.

physics.bio-ph↗
arXiv2018

Predicting optimal hematocrit in silico

Optimal hematocrit $H_o$ maximizes oxygen transport. In healthy humans, the average hematocrit $H$ is in the range of 40-45$\%$, but it can significantly change in blood pathologies such as severe anemia (low $H$) and polycythemia (high $H$). Whether the hematocrit level in humans corresponds to the optimal one is a long standing physiological question. Here, using numerical simulations with the Lattice Boltzmann method and two mechanical models of the red blood cell (RBC) we predict the optimal hematocrit, and explore how altering the mechanical properties of RBCs affects $H_o$. We develop a simplified analytical theory that accounts for results obtained from numerical simulations and provides insight into the physical mechanisms determining $H_o$. Our numerical and analytical models can easily be modified to incorporate a wide range of mechanical properties of RBCs as well as other soft particles thereby providing means for the rational design of blood substitutes. Our work lays the foundations for systematic theoretical study of the optimal hematocrit and its link with pathological RBCs associated with various diseases (e.g. sickle cell anemia, diabetes mellitus, malaria, elliptocytosis).

cond-mat.soft↗
arXiv2015

Toric Geometry and String Theory Descriptions of Qudit Systems

In this paper, we propose a new way to approach qudit systems using toric geometry and related topics including the local mirror symmetry used in the string theory compactification. We refer to such systems as (n,d) quantum systems where $n$ and $d$ denote the number of the qudits and the basis states respectively. Concretely, we first relate the (n,d) quantum systems to the holomorphic sections of line bundles on n dimensional projective spaces CP^{n} with degree n(d-1). These sections are in one-to-one correspondence with d^n integral points on a n-dimensional simplex. Then, we explore the local mirror map in the toric geometry language to establish a linkage between the (n,d) quantum systems and type II D-branes placed at singularities of local Calabi-Yau manifolds. (1,d) and (2,d) are analyzed in some details and are found to be related to the mirror of the ALE space with the A_{d-1} singularity and a generalized conifold respectively.

hep-th↗
arXiv2006

The Effect Of On-Ramp And Off-Ramp On The One Dimensional Road With Open Boundaries

The effect of one on-ramp (entry) and one off-ramp (exit) is investigated numerically in one dimensional-cellular automaton traffic flow model, with open boundary conditions, using parallel dynamics. Our aim in this paper is to study how the injecting rates $α$ and $α_{0}$ and the extracting rates $β$ and $β_{0}$ acts on the density and flux of cars in one dimensional road. The priority of occupation at entry site $i_{1}$ (moving at exit site $i_{2}$) is attributed to the particle which entered (absorbed) in the chain. Phase diagrams in ($β_{0},α_{0}$), and ($β,α_{0}$) plans are established. For $α=0.1$, they show three different topologies in the flow behaviour. The first one correspond to the presence of four regions, by varying $α_{0}$; namely low density phase (LDP), intermediate density phase (IDP), plateau current phase (PCP) and high density phase (HDP). In the second topology the interdmediate density phase disappears. The third topology presents only two regions; i.e. low and high density phases. For small values of $α$, the (IDP) and (PCP) disappears, respectively, by increasing $β$. When increasing $α$, the forth topology, corresponding to one phase (HDP), appears for low values of $β$ and $β_{0}$

physics.soc-ph↗
arXiv2006

Multicritical Behaviours in One-Dimensional Traffic Flow

The effect of the on-ramp and off-ramp positions $i_1$ and $i_2$, respectively, on the one dimensional-cellular automaton traffic flow behaviour, is investigated numerically. The on-ramp and off-ramp rates at $i_1$ and $i_2$ are $α_0$ and $β_0$, respectively. However, in the open boundary conditions, with injecting and extracting rates $α$ and $β$ and using parallel dynamics, several phases occur, depending on the position of $i_1$ by respect to $i_2$. Namely, low density phase (LDP), intermediate density phase (IDP), plateau current phase (PCP) and high density phase (HDP). Furthermore, critical, tricritical and multicritical behaviours take place in the $(i_1,α_0)$ phase diagrams.

cond-mat.other↗
arXiv2004

Phase diagrams of a Spin-1 Ising Superlattice

The three-dimensional spin-1 Ising superlattice consisting of two different ferromagnetic materials with two different crystal fields $Δ_1$ and $Δ_2$ is considered in the mean field approximation. The phase diagrams are considered in the (t,$d_2$) plane for different ranges of variation of $d_1$ (t=T/J, $d_1$/J and $d_2$/J are the reduced temperature and crystal fields respectively). The phase diagrams exhibit a variety of multicritical points and reentrant and double reentrant behaviours. They are found to depend qualitatively and/or quantitatively on the thicknesses of the materials in a supercell. This has direct consequences on the nature of the magnetic states of superlattices with different thicknesses.

cond-mat.stat-mech↗
arXiv2004

The Effect of absorbing sites on the one-dimensional cellular automaton traffic flow with open boundaries

The effect of the absorbing sites with an absorbing rate $β_{0}$, in both one absorbing site (one way out) and two absorbing sites (two ways out) in a road, on the traffic flow phase transition is investigated using numerical simulations in the one-dimensional cellular automaton traffic flow model with open boundaries using parallel dynamics.In the case of one way out, there exist a critical position of the way out $ i_{c1}$ below which the current is constant for $β_{0}$$<$$β_{0c2}$ and decreases when increasing $β_{0}$ for $β_{0}$$>$$β_{0c2}$. When the way out is located at a position greater than $ i_{c2}$, the current increases with $β_{0}$ for $β_{0}$$<$$β_{0c1}$ and becomes constant for any value of $β_{0}$ greater than $β_{0c1}$. While, when the way out is located at any position between $ i_{c1}$ and $ i_{c2}$ ($ i_{c1}$$<$$ i_{c2}$), the current increases, for $β_{0}$$<$$β_{0c1}$, with $β_{0}$ and becomes constant for $β_{0c1}$$<$$β_{0}$$<$$β_{0c2}$ and decreases with $β_{0}$ for $β_{0}$$>$$β_{0c2}$. In the later case the density undergoes two successive first order transitions; from high density to maximal current phase at $β_{0}$$=$$β_{0c1}$ and from intermediate density to the low one at $β_{0}$$=$$β_{0c2}$. In the case of two ways out located respectively at the positions $ i_{1}$ and $ i_{2}$, the two successive transitions occur only when the distance $i_{2}$-$i_{1}$ separating the two ways is smaller than a critical distance $d_{c}$. Phase diagrams in the ($α,β_{0}$), ($β,β_{0}$) and ($i_{1},β_{0}$) planes are established. It is found that the transitions between Free traffic, Congested traffic and maximal current phase are first order.

cond-mat.stat-mech↗
arXiv2003

Phase Diagrams of the Spin-1 Blume-Capel Film With an Alternating Crystal Field

The spin-1 ferromagnetic Blume-Capel film with an alternating crystal field $Δ=Δ_1$ on the odd layers and $Δ=Δ_2$ on the even ones is considered in the mean field approximation. The ground state phase diagrams in the ($d_1,d_2$) plane ($d_1=Δ_1/J$ and $d_2=Δ_2/J$) are determined analytically; the number of their phases depends on the parity of the number of layers of the film. At finite temperature, fifteen types of topology, depending on the range of variation of $d_1$, are found in the (t,$d_2$) plane for an even number of layers, but only fourteen for an odd number of layers. The phase diagrams exhibit a variety of multicritical points. In particular, a tricritical point C appears in the paramagnetic-ferromagnetic line of transition, but only for values of $d_1$ larger than a threshold value $d_{trc}^{(2)} ={8 \ln 2 \over 3}$ which is but the tricritical crystal field (in the mean field approximation) of the spin-1 Blume-Capel model on a square lattice. Moreover, lines of transition presenting the reentrant and double reentrant behaviors may also take place.

cond-mat↗