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Improvement of sintering,nonlinear electrical,and dielectric properties of ZnO-based varistors doped with TiO2

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Chinese Physics B 2016年第6期25卷 575-580页

作者： Osama A Desouky K e Rady Bilbis Higher Institute of engineering (BHIe) Bilbis Sharqia Egypt engineering Basic Sciences Department Faculty of engineering Menoufia University Shebin EI-Kom Egypt

The effects of TiO2 on sintering and nonlinear electrical properties of（98.5-x）ZnO–0.5MnO2–0.5Co2O3-0.5Bi2O3–xTiO2（x = 0.3,0.5,0.7,0.9 mol%） ceramic varistors prepared by the ceramic technique are investigated in this *** optimum sintering temperature of the prepared samples is deduced by determining the firing shrinkage and water absorption *** optimum sintering temperature is found to be 1200℃,at which each of the samples shows a maximum firing shrinkage and minimum water *** minimum water absorption appears in a sample of x = 0.9 mol%.Higher sintering temperature and longer sintering time give rise to a reduction in bulk density due to the increased amount of porosity between the large grains of ZnO resulting from the rapid grain growth induced by the liquid phase *** crystal size of ZnO decreases with increasing TiO2 *** addition of TiO2 improves the nonlinear coefficient and attains its maximum value at x = 0.7 mol% of TiO2,further addition negatively affects it.A decrease in capacitance consequently in the dielectric constant is recorded with increasing the frequency in a range of 30 kHz–200 *** temperature and composition dependences of the dielectric constant and AC conductivity are also *** increase of temperature raises the dielectric constant because it increases ionic response to the field at any particular frequency.

关键词： ZnO varistors water absorption nonlinear electrical properties dielectric constant

Destructive Interactions between Pore Forming Agents and Matrix Phase during the Fabrication Process of Porous BiFeO_3 Ceramics

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Journal of Materials Science & Technology 2015年第8期31卷 798-805页

作者： e.Mostafavi A.Ataie School of Metallurgy and Materials engineering College of EngineeringUniversity of Tehran

Porous bismuth ferrite ceramics were synthesized by sacrificial pore former method. A mixture of BiFeO3 and 20 wt% of various pore formers including high density polyethylene, polyethylene glycol, polyvinyl alcohol, urea and graphite was intensively milled for 10 h in a planetary ball mill, uniaxially cold pressed and then subjected to the multi-stage heat treatment. The results revealed that urea and polyvinyl alcohol are appropriate candidates for maintaining the strength of the final porous structure. Density and porosity measurements showed that by employing 20 wt% of high density polyethylene and graphite, a porous sample with a maximum porosity of nearly 40% could be obtained. Mercury porosimetry results showed that using urea as a pore former gives porous bismuth ferrite with a mean pore diameter of 7μm, uniform pore distribution as well as interconnected pores. Moreover, reactions between BiFeO3 matrix phase and thermal decomposition products of pore formers can lead to degradation of the BiFeO3 phase in the final porous samples. Analysis of X-ray diffraction patterns illustrated that in the samples pro- cessed with graphite, high density polyethylene and polyvinyl alcohol as pore former, BiFeO3 matrix phase partially or completely decomposed to intermediate phases of Bi2Fe4O9 and Bi25FeO40. Using of urea did not damage the matrix phase and porous BiFeO3 within the original perovskite structure could be prepared. Furthermore, thermodynamic investigation was carried out for prediction of possible in- teractions between matrix phase and pore former at elevated temperatures.

关键词： Multiferroic Bismuth ferrite Porous ceramics Sacrificial pore former Porosity Phase composition

electronic,optical,and mechanical properties of BN,AlN,and InN with zinc-blende structure under pressure

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Chinese Physics B 2017年第8期26卷 320-327页

作者： A R Degheidy e B elkenany Department of Physics Faculty of ScienceMansoura UniversityP.O.Box 35516MansouraEgypt

In this work, the electronic, optical, and mechanical properties of BN, AlN, and InN under the action of pressure are calculated. For each of these compounds, the energy band structure, band gaps（e^L_g, e~Γ_g, e^X_g）, refractive index（n）,dielectric constants（ε_∞, ε_0）, elastic constants（C_11, C_12, C_44）, and relevant parameters such as bulk（B_u）, shear（S_h）, and Young＇s（Y_0） moduli are studied, and other important parameters such as bond-stretching（α）, bond-bending（β） force constant, internal-strain parameter（ζ）, effective charges（e~＊_T, Z~＊）, anisotropy factor（I_s）, Poisson＇s ratio（P_o）, Cauchy ratio（C_a）, the ductility index（μ_D）, and linear compressibility（C0_） are also calculated. The effects of pressure on all studied properties are investigated. Our results are in good agreement with the available experimental and theoretical data for BN,AlN, and InN.

关键词： electronic properties optical properties mechanical properties BN A1N InN

Schrodinger equation for an Open System

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Chinese Physics Letters 2002年第9期19卷 1238-1243页

作者：毕桥 H.e.Ruda ComplexityScienceCenter YangzhouUniversityYangzhou225002 energeniusCentreforAdvancednanotechnology UniversityofTorontoTorontoM5S3E4Canada

We present a Schr?dinger (Liouville) type of equation for a quantum open system. It has a correlated part, and various master equations may be its special cases. It also has significant applications for constructing decoherence-free subspace for quantum computation. It is related to the original Schrodinger (Liouville) equation for the total system through a non-unitary similarity transformation. It is unnecessary for its correlated part to be self-adjoint, so there is a complex spectrum for the corresponding Hamiltonian (Liouvillian), which enables the time evolution of states to be asymmetric. This shows just the correlation to produce evolution of world.

关键词： Liouville equation

Heavy metals partitioning in the sediments of Izmir Inner Bay

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Journal of environmental Sciences 2008年第4期20卷 413-418页

作者： GUVeN Duyusen e AKINCI Gorkem Dokuz eylul University Faculty of Engineering Department of Environmental EngineeringKaynaklar Campus35160BucalzmirTurkey.

Izmir Bay is known to be polluted by high concentrations of heavy metals and organic pollutants. Sediment samples taken from 7 different stations in Izmir Inner Bay were analyzed for their total organic matter content and, Cu, Cr, Pb and Zn. In addition, the chemical distribution of the metals were determined by means of the BCR （Community Bureau of Reference） extraction Procedure （developed by european Commission for Standards, Measurement and Testing） which allows the determination of metals bound as four fractions; exchangeable and acid soluble, reducible （bound to iron-manganese oxides）, oxidizable （bound to organics） and residual. The results show that Izmir Inner Bay contains sediments with high metal concentrations. According to the chemical distribution of metals, Cr and Cu tend to accumulate mostly on the organic fraction of the sediment. Pb is mostly found in the reducible fraction where Zn is mobile in the sediment, and it is distributed evenly on each fraction.

关键词： heavy metal pollution Izmir Inner Bay sediment sequential extraction

Dynamics of air transport networks：A review from a complex systems perspective

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Chinese Journal of Aeronautics 2017年第2期30卷 469-478页

作者： Luis e.C.Rocha Department of Public Health Sciences Karolinska Institutet Stockholm 17177 Sweden Department of Mathematics University of Namur 5000 Belgium

Air transport systems are highly dynamic at temporal scales from minutes to *** dynamic behavior not only characterizes the evolution of the system but also affect the system＇s *** the evolutionary mechanisms is thus fundamental in order to better design optimal air transport networks that benefits companies,passengers and the *** this review,we briefly present and discuss the state-of-the-art on time-evolving air transport *** distinguish the structural analysis of sequences of network snapshots,ideal for long-term network evolution（*** evolution）,and temporal paths,preferred for short-term dynamics（*** evolution）.We emphasize that most previous research focused on the first modeling approach（***-term） whereas only a few studies look at high-resolution temporal *** conclude the review highlighting that much research remains to be done,both to apply already available methods and to develop new measures for temporal paths on air transport *** particular,we identify that the study of delays,network resilience and optimization of resources（aircraft and crew） are critical topics.

关键词： Air transport Airport network Complex network Dynamic network Temporal network

First-principles study of the structural,elastic,electronic,optical,and vibrational properties of intermetallic Pd_2Ga

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Chinese Physics B 2012年第3期21卷 341-348页

作者： Yildirim A Koc H Deligoz e Department of Physics Siirt University Department of Physics Aksaray University

The structural, elastic, electronic, optical, and vibrational properties of the orthorhombic Pd2Ga compound are investigated using the norm-conserving pseudopotentials within the local density approximation in the frame of density functional theory. The calculated lattice parameters have been compared with the experimental values and found to be in good agreement with these results. The second-order elastic constants and the other relevant quantities, such as the Young＇s modulus, shear modulus, Poisson＇s ratio, anisotropy factor, sound velocity, and Debye temperature, have been calculated. It is shown that this compound is mechanically stable after analysing the calculated elastic constants. Furthermore, the real and imaginary parts of the dielectric function and the optical constants, such as the optical dielectric constant and the effective number of electrons per unit cell, are calculated and presented. The phonon dispersion curves are derived using the direct method. The present results demonstrate that this compound is dynamically stable.

关键词： Pd2Ga vibrational properties optical properties elastic constants

Development of Powerful RF Plasma Sources for Present and Future NBI Systems

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Plasma Science and Technology 2004年第1期6卷 2135-2140页

作者： e.Speth NBI-Team Max-Planck-Institut fiir Plasmaphysik 85748 Garching Germany EURATOM-AssociationMax-Planck-Institut fiir Plasmaphysik 85748 Garching Germany EURATOM-Association

This paper deals with the topic of RF plasma sources and their application inhigh-power neutral beam heating systems for nuclear fusion devices. RF sources represent aninteresting alternative to the conventional arc discharge sources. Due to the absence of hotfilaments they exhibit an inherent simplicity both in mechanical and electrical aspects andconsequently offer advantages in terms of cost savings, gain in availability and reliability andreduced maintenance. This renders the RF plasma source attractive for any long pulse (> 10 sec) NBIsystem and in particular for the ITeR NBI system. The latter, however, requires that the RF plasmasource is also capable of delivering negative rather than positive hydrogen ions. In the first partof the paper the types, characteristics and operation experience of RF plasma sources for positiveions in operation are described. The second part is devoted to the development for ITeR NBI: thebasic requirements, physics and technology issues and the present status are discussed.

关键词： neutral beam injection negative ions RF plasma source

Superplasticity-like creep behavior of coarse grained ternary Al alloys

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Transactions of Nonferrous Metals Society of China 2010年第4期20卷 564-571页

作者：乔军 e.M.TALeFF College of Materials Science and engineering University of Science and Technology Liaoning Department of Mechanical engineering University of Texas at Austin

enhanced tensile ductilities in coarse grained Al-Mg-Zn and Al-Mg-Fe materials were *** materials were Al-2Mg-5Zn,Al-3Mg-5Zn,Al-4Mg-5Zn,Al-3Mg-0.11Fe,Al-3Mg-0.27Fe,and *** elongation-to-failure tests were conducted at constant cross-head speed and constant temperatures from 300 to 450℃.Strain rate change tests were conducted at a constant temperature from 300 to 450℃and in strain-rate range from 4.31×10-5to 1.97×*** results show that over 100%ductilities are consistently achieved in these *** superplasticity-like behavior is rate-controlled by solute-drag *** ternary Zn and Fe additions do not have an adverse effect on solute-drag creep and ductility,they increase stress exponent and its sensitivity to Mg content during solute-drag creep.

关键词： Al-Mg alloys superplasticity solute-drag creep tensile ductility strain-rate sensitivity