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Hydrogen storage of mgi-xmxH2 （m--Ti, V, studied using first-principles calculations re）

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Chinese Physics B 2012年第9期21卷 477-483页

作者： m.Bhihi m.Lakhal H.Labrim A. Benyoussefa A.EI Kenz O.mounkachi E.K.Hlil Laboratoire de magnetisme et de Physique des Hautes Energies associe au CNRST (URAC 12) Departement de PhysiqueB.P. 1014 Faculte des Sciences Universite Mohammed V-Agdal Rabat Morocco National Centre for Energy Sciences and Nuclear Techniques ONESTEN Morocco Institute of Nanomaterials and Nanotechnologies MACslR Rabat Morocco Hassan II Academy of Science and Technology Rabat Morocco Institut N6el CNRS-UJF 38042 Grenoble Cedex 9 France

In this work, the hydrogen storage properties of the mg-based hydrides, i.e., mgl-xmxH2 （m=Ti, V, Fe, 0≤ x ≤ 0.1）, are studied using the Korringa-Kohn-Rostoker （KKR） calculation with the coherent potential approximation （CPA） . In particular, the nature and concentrations of the alloying elements and their effects are studied. moreover, the material＇s stability and hydrogen storage thermodynamic properties are discussed. In particular, we find that the stability and the temperature of desorption decrease without significantly affecting the storage capacities.

关键词： first-principles calculation formation energy electronic structure hydrogen storage

Numerical method for simulating rarefaction shocks in the approximation of phase-flip hydrodynamics

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Applied mathematics and mechanics(English Edition) 2021年第6期42卷 871-884页

作者： m.m.BASKO Keldysh Institute of Applied mathematics Russian Academy of SciencesMiusskaya Square 4Moscow 125047Russia

A finite-difference algorithm is proposed for numerical modeling of hydrodynamic flows with rarefaction shocks, in which the fluid undergoes a jump-like liquid-gas phase transition. This new type of flow discontinuity, unexplored so far in computational fluid dynamics, arises in the approximation of phase-flip(PF) hydrodynamics, where a highly dynamic fluid is allowed to reach the innermost limit of metastability at the spinodal, upon which an instantaneous relaxation to the full phase equilibrium(EQ) is assumed. A new element in the proposed method is artificial kinetics of the phase transition, represented by an artificial relaxation term in the energy equation for a "hidden"component of the internal energy, temporarily withdrawn from the fluid at the moment of the PF transition. When combined with an appropriate variant of artificial viscosity in the Lagrangian framework, the latter ensures convergence to exact discontinuous solutions, which is demonstrated with several test cases.

关键词： fluid dynamics with phase transitions two-phase flow rarefaction shock Lagrangian scheme artificial viscosity artificial kinetics

Comparative study of mo2Ga2C with superconducting mAX phase mo2GaC： First-principles calculations

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Chinese Physics B 2017年第3期26卷 297-302页

作者： m A Ali m R Khatun NJahan m m Hossain Department of Physics Chittagong University of Engineering and Technology Chittagong 4349 Bangladesh Department of Physics University of Rajshahi Rajshahi 6205 Bangladesh

The structural, electronic, optical and thermodynamic properties of mo2Ga2C are investigated using density func- tional theory （DFT） within the generalized gradient approximation （GGA）. The optimized crystal structure is obtained and the lattice parameters are compared with available experimental data. The electronic density of states （DOS） is calculated and analyzed. The metallic behavior for the compound is confirmed and the value of DOS at Fermi level is 4.2 states per unit cell per eV. Technologically important optical parameters （e.g., dielectric function, refractive index, absorption coefficient, photo conductivity, reflectivity, and loss function） are calculated for the first time. The study of dielectric constant （ε1） indicates the Drude-like behavior. The absorption and conductivity spectra suggest that the compound is metallic. The reflectance spectrum shows that this compound has the potential to be used as a solar reflector. The thermodynamic properties such as the temperature and pressure dependent bulk modulus, Debye temperature, specific heats, and thermal expansion coefficient of mo2Ga2C mAX phase are derived from the quasi-harmonic Debye model with phononic effect also for the first time. Analysis of Tc expression using available parameter values （DOS, Debye temperature, atomic mass, etc.） suggests that the compound is less likely to be superconductor.

关键词： first-principles calculations density of states (DOS) optical properties thermodynamic properties

Cost-effective integrated strategy for the fabrication of hard-magnet barium hexaferrite powders from low-grade barite ore

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International Journal of minerals,metallurgy and materials 2016年第9期23卷 991-1000页

作者： m.m.S.Sanad m.m.Rashad Central metallurgical R & D Institute

Ultrafine barium hexaferrite（BaFe12O19） powders were synthesized from the metallurgical extracts of low-grade Egyptian barite ore via a co-precipitation route. Hydrometallurgical treatment of barite ore was systematically studied to achieve the maximum dissolution efficiency of Fe（～99.7%） under the optimum conditions. The hexaferrite precursors were obtained by the co-precipitation of BaS produced by the reduction of barite ore with carbon at 1273 K and then dissolved in diluted HCl and FeCl3 solution at pH 10 using NaOH as a base; the product was then annealed at 1273 K in an open atmosphere. The effect of Fe^3＋/Ba^2＋ molar ratio and the addition of hydrogen peroxide（H2O2） on the phase structure, crystallite size, morphology, and magnetic properties were investigated by X-ray diffraction, scanning electron microscopy, and vibrating sample magnetometry. Single-phase BaFe（12）O（19） powder was obtained at an Fe^3＋/Ba^2＋ molar ratio of 8.00. The formed powders exhibited a hexagonal platelet-like structure. Good maximum magnetization（48.3 A×m^2×kg^–1） was achieved in the material prepared at an Fe^3＋/Ba^2＋ molar ratio of 8.0 in the presence of 5% H2O2 as an oxidizer and at 1273 K because of the formation of a uniform, hexagonal-shaped structure.

关键词： chemical process barite ore treatment characterization magnetic properties ferrites

Effect of substitution group on dielectric properties of 4H-pyrano [3,2-c] quinoline derivatives thin films

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Chinese Physics B 2016年第7期25卷 440-449页

作者： H m Zeyada F m El-Taweel m m El-Nahass m m El-Shabaan Department of Physics Faculty of Science Damietta University Department of Chemistry Faculty of Science Damietta University Department of Physics Faculty of Education Ain Shams University

The AC electrical conductivity and dielectrical properties of 2-amino-6-ethyl-5-oxo-4-（3-phenoxyphenyl）-5,6-dihydro-4H-pyrano[3, 2-c]quinoline-3-carbonitrile（Ph-HPQ） and 2-amino-4-（2-chlorophenyl）-6-ethyl-5-oxo-5,6-dihydro-4H-pyrano [3, 2-c] quinoline-3-carbonitrile（Ch-HPQ） thin films were determined in the frequency range of 0.5 k Hz–5 mHz and the temperature range of 290–443 K. The AC electrical conduction of both compounds in thin film form is governed by the correlated barrier hopping（CBH） mechanism. Some parameters such as the barrier height, the maximum barrier height, the density of charges, and the hopping distance were determined as functions of temperature and frequency. The phenoxyphenyl group has a greater influence on those parameters than the chlorophenyl group. The AC activation energies were determined at different frequencies and temperatures. The dielectric behaviors of Ph-HPQ and Ch-HPQ were investigated using the impedance spectroscopy technique. The impedance data are presented in Nyquist diagrams for different temperatures. The Ch-HPQ films have higher impedance than the Ph-HPQ films. The real dielectric constant and dielectric loss show a remarkable dependence on the frequency and temperature. The Ph-HPQ has higher dielectric constants than the Ch-HPQ.

关键词： thin films quinoline derivatives dielectrical properties correlated barrier hopping

Plasma ignition threshold disparity between silver nanoparticle-based target and bulk silver target at different laser wavelengths

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Plasma Science and Technology 2019年第1期21卷 63-71页

作者： A m EL SHERBINI m m HAGRASS m R m RIZK E A EL-BADAWY Laboratory of Laser and New materials Faculty of Science Cairo University Faculty of Engineering Electrical Engineering Department Alexandria University

Plasma ignition threshold of nanoparticle-based and bulk silver targets was measured in air. The plasma was initiated by a Nd:YAG laser at wavelengths of 355, 532, and 1064 nm. The plasma ignition was monitored utilizing the prominent Ag I line at 546.5 nm. Lower ignition thresholds of the nanoparticle-based silver target were estimated at 0.4?±?0.02, 0.34?±?0.04, and 0.27?±?0.035 J cm^(-2) coupled with the different laser wavelengths, respectively. In contrast, the bulk silver target plasma exhibited an order of magnitude higher ignition threshold. A three orders of magnitude enhanced emission intensity from the nano-based target over the bulk target was achieved at lower levels of laser irradiation. A reduction of the thermal diffusion length of the nanosilver was assumed in order to theoretically predict this reduction in the plasma threshold. In addition, the effect of self-reversal on the resonance lines was taken into consideration.

关键词： NELIBS enhancement nanosilver laser plasma threshold

Hunting down the ohmic contact of organic field-effect transistor

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Chinese Physics B 2019年第11期28卷 382-387页

作者： m micjan m Novota P Telek m Donoval m Weis Institute of Electronics and Photonics Slovak University of Technology

We report properties of contact resistances observed on pentacene organic field-effect transistors(OFET) with four different source/drain electrodes, namely, copper(Cu), gold(Au), silver(Ag), and germanium(Ge). The metals were selected to provide a wide range of energy barriers for charge injection, from blocking contact to smooth injection. All OFETs exhibited strong voltage dependence of the contact resistance, even for devices with smooth injection, which is in strong disagreement with the definition of ohmic contacts. A comparison with current crowding, resistive network, Fowler–Nordheim tunneling, and electric field enhanced thermionic injection(Schottky emission) pointed to importance of local electric fields and/or electrostatic field charges.

关键词： organic field-effect transistors contact resistance charge injection

Performance of m-QAm, m-DPSK and m-PSK with mRC diversity in a Nakagami-m fading channel

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Journal of Central South University 2014年第4期21卷 1347-1352页

作者： Alam S.m.Shamsul Alam Choi GoangSeog Department of Information and Communication Engineering Chosun University

The nature of a wireless communication channel is very unpredictable. To design a good communication link, it is required to know the statistical model of the channel accurately. The average symbol error probability(ASER) was analyzed for different modulation schemes. A unified analytical framework was presented to obtain closed-form solutions for calculating the ASER of m-ary differential phase-shift keying(m-DPSK), coherent m-ary phase-shift keying(m-PSK), and quadrature amplitude modulation(QAm) over single or multiple Nakagami-m fading channels. moreover, the ASER was estimated and evaluated by using the maximal ratio-combining(mRC) diversity technique. Simulation results show that an error rate of the fading channel typically depends on Nakagami parameters(m), space diversity(N), and symbol rate(m). A comparison between m-PSK, m-DPSK, and m-QAm modulation schemes was shown, and the results prove that m-ary QAm(m-QAm) demonstrates better performance compared to m-DPSK and m-PSK under all fading and non-fading conditions.

关键词： m-ary differential phase-shift keying(m-DPSK) m-ary phase shift keying(m-PSK) Nakagami-m fading channel probability density function(PDF) symbol error rate(SER) m-ary quadrature amplitude modulation(m-QAm)

Effect of Bohm quantum potential in the propagation of ion–acoustic waves in degenerate plasmas

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Chinese Physics B 2016年第10期25卷 222-229页

作者： m m Hasan m A Hossen A Rafat A A mamun Department of Physics Jahangirnagar University

A theoretical investigation has been carried out on the propagation of the ion–acoustic(IA) waves in a relativistic degenerate plasma containing relativistic degenerate electron and positron fluids in the presence of inertial non-relativistic light ion fluid. The Korteweg-de Vries(K-dV), modified K-dV(m K-dV), and mixed m K-dV(mm K-dV) equations are derived by adopting the reductive perturbation method. In order to analyze the basic features(phase speed, amplitude, width,etc.) of the IA solitary waves(SWs), the SWs solutions of the K-dV, m K-dV, and mm K-d V are numerically analyzed. It is found that the degenerate pressure, inclusion of the new phenomena like the Fermi temperatures and quantum mechanical effects(arising due to the quantum diffraction) of both electrons and positrons, number densities, etc., of the plasma species remarkably change the basic characteristics of the IA SWs which are found to be formed either with positive or negative potential. The implication of our results in explaining different nonlinear phenomena in astrophysical compact objects, e.g.,white dwarfs, neutron stars, etc., and laboratory plasmas like intense laser–solid matter interaction experiments, etc., are mentioned.

关键词： Bohm quantum potential degenerate relativistic plasma electron and positron quantum effect