The Comprehensive Retrieval Method of Electromagnetic Parameters Using the Scattering Parameters of Metamaterials for Two Choices of Time-Dependent Factors

The electromagnetic parameters (permittivity and permeability) method,retrieved from the reflection and transmission coefficients of a slab,is presented.Improvements over existing methods,including the determination of the permittivity,permeability and impedance of the slab,are expressed as explicit functions of the S parameters for both the time-dependent factors,e^(iwt) and e^(-iwt) (ω is the angular frequency of the incident electromagnetic wave),and the proper selection of the sign of impedance and the real part of the refractive index.Moreover,based on the retrieving method,the calculations of the electromagnetic parameters of the conventional-material teflon slab standard sample through the experimental data of the S parameters are performed,which confirm the validity of the technique for the retrieval of electromagnetic parameters.

Micro-Nanometer Parasitic Crystal Growth and Photoluminescence Property of Unique Screw-Cone Like Zn_(2)GeO_(4)-ZnO by Combustion Oxidization

screw-cone-like Zn_(2)GeO_(4)-ZnO particles with a base diameter of approximately 400 nm and a height of 400–800 nm or so were successfully synthesised by combustion oxidation of zinc and germanium powder at 960℃.No catalyst or carrier gases were used.XRD and SEM analyses reveal that Zn_(2)GeO_(4) and ZnO grew to parasitic crystals evenly in interaction with each other.EDS images exhibit the homogeneity of the distribution of Ge and Zn.The formation mechanism is discussed and attributed to the unique growth process of the screw-cone-like Zn_(2)GeO_(4)-ZnO particles and its vapour-solid(VS)growth mechanism.In addition,the Zn_(2)GeO_(4)-ZnO particles could tune the energy level structure of nano-tetrapod ZnO,which leads to the emission peak redshift from 376 nm to 435 nm and enhances the light emission intensity in the visible light region.

Polarization Mechanism of Oxygen Vacancy and Its Influence on Dielectric Properties in ZnO

We report on the mechanism of the dielectric properties of oxygen vacancy in ZnO,using ab initio numerical simulations of oxygen vacancy on the band structure and dielectric properties,to develop photoelectric material applications.It is revealed that the appearance of oxygen vacancies leads to wider energy band gap,obvious blue shift and increase in the peak of dielectric function as compared to the intrinsic ZnO simulation.We explain these unusual phenomena and analyze the dielectric changes with the mechanism of polarization in the semiconductors.It is shown that the main mechanism of influencing dielectric properties is the electron displacement polarization.The result may be helpful for development of photoelectric materials.

Microwave Absorption Properties of Ni-Foped SiC Powders in the 2-18 GHz Frequency Range

Ni-doped SiC powder with improved dielectric and microwave absorption properties was prepared by selfpropagating high-temperature synthesis(SHS).The XRD analysis of the asynthesized powders suggests that Ni is accommodated in the sites of Si in the lattice of SiC,which shrinks in the presence of Ni.The experimental results show an improvement in the dielectric properties of the Ni-doped SiC powder in the frequency range of 2-18 GHz.The bandwidth of the reflection loss below-10 dB is broadened from 3.04(for pure SiC)to 4.56 GHz(for Ni-doped SiC),as well as the maximum reflection loss of produced powders from 13.34 to 22.57dB,indicating that Ni-doped SiC could be used as an effective microwave absorption material.

Dynamic Mechanical Behavior and Failure Mechanism of Polymer Composites Embedded with Tetraneedle-Shaped ZnO Whiskers

Quasi-static and dynamic mechanical properties of glass-fiber reinforced polymer composites embedded with and without tetraneedle-shaped ZnO whiskers(T-ZnOw)in two loading directions are investigated by a split Hopkinson pressure bar.The stress-strain curves,ultimate strength,failure strain and elastic modulus are obtained and the failure mechanism of the composites is investigated by a high-speed camera and a scanning electron microscope.Strain rate effects on the mechanical behavior are discussed and the corresponding models are derived by fitting the experimental data.The experimental results show that the composites with T-ZnOw under dynamic loading have multiple failure modes and better mechanical properties.Finally,the strengthening and toughening mechanisms of T-ZnOw are analyzed.It is shown that T-ZnOw can improve mechanical properties of the composites,and can make the composites have some new features.The present results provide a reliable basis for advanced composite design and manufacture,and have broad applications in the field of aerospace.

High-Temperature Permittivity and Data-Mining of Silicon Dioxide at GHz Band

The high-temperature permittivity of quartz fibre-reinforced silicon dioxide (SiO2/SiO2 ) nano-composites is studied on the basis of the multi-scale theoretical model.We obtain the permittivity of the SiO2/SiO2 at high temperature,which is dependent on the temperature by data-mining.The result shows that the permittivity and loss tangent obtained by data-mining are well consistent with the measured ones.The high-temperature permittivity can be well predicted for SiO2/SiO2 by the as-proposed model and the data-mining method.

Electrical Properties of Lead Zirconate Titanate Thick Film Containing Micro-and Nano-Crystalline Particles

We report the ferroelectric,dielectric and piezoelectric properties of a dense and crack-free lead zirconate titanate (Pb(Zro.52 Tio.48)O3,PZT) thick film containing micro- and nano-crystalline particles. The results show that these electrical properties are dependent strongly on the annealing temperature and film thickness. For the different-annealing-temperature and different-thickness films,the higher-annealing-temperature thicker ones show the larger remnant polarization and smaller coercive field. The dielectric results show that relative dielectric constant achieves the largest value at annealing temperature of 700℃,and increases with the increasing film thickness.For the piezoelectric properties,the longitudinal piezoelectric coefficient increases linearly with the film thickness increasing and the 4-μm-thick PZT film shows the largest value of about 200.65 pC/N.Therefore,the PZT thick films present good electric properties and enlarged potential in MEMS applications.

Different Roles of a Boron Substitute for Carbon and Silicon in β-SiC

The first-principles numerical simulation is employed-to calculate the effect of replacement of carbon and silicon with boron on the electronic structure and optical properties of β-SiC.Mulliken analysis shows that the B impurity bond lengths shrink in the case of Bsi,while they expand with reference to Bc.In addition,Bsi contains C-C,Si-Si and B-Si bonds.The calculated results show that the two systems of Bc and Bsi apply different dispersion.Bc is in accordance with the Lorentz dispersion theory while Bsi follows the Drude dispersion theory.Theoretic analysis and quantitative calculation are used for conductivity spectra in the infrared region.

First Principle Study of the Electronic Properties of 3C-SiC Doped with Different Amounts of Ni

The electronic properties of 3C-SiC doped with different contents of Ni are investigated by using first-principles calculations.It is observed that the non-filled impurity energy levels in the band-gap region increase with increasing Ni content,which subsequently results in an enhancement of electrical conductivity of 3C-SiC.This enhancement in conductivity is verified by the conductivity spectrum in which new peaks appear in the middleinfrared region,visible region,and middle-ultraviolet region.It is further observed that the width and intensity of these newly appeared peaks increase with the increase of Ni content.The electronic density of states exhibits the peaks crossing the Fermi level,which favors the electronic transitions and proves Ni-doped 3C-SiC to be a half-metallic semiconductor.Through the analysis of electron density difference and Mulliken overlap population,it is found that the covalent bonds are formed between Ni and near-by C atoms.These features confirm that the Ni-doped 3C-SiC semiconductor is a promising material for device applications in modern day electronics.

Enhanced Ferromagnetism and Microwave Dielectric Properties of Bi0.95Y0.05FeO3 Nanocrystals

Bi_(0.95)_(0.05)FeO_(3)nanocrystals are synthesized by a hydrothermal method,and are crystallized in a rhombohedrally distorted perovskite BiFeO_(3)structure in the R3c space,with compressive lattice distortion induced by the Y substitution at Bi sites from XRD study Compared with BiFeO_(3)gained under similar conditions,the magnetic properties are greatly enhanced,with saturate magnetization of 2.3emu/g at room temperature.Microwave dielectric properties of Bi0.95 Y0.05FeO_(3)nanocrystals are investigated in the range of 2-18 GHz.The Y substitution results in the increase of permeability and decrease of permittivity which are attributed to the enhanced spin relaxation of domain wall motion and the weakened electron-relaxation caused by decreasing Fe^(2+),respectively.The changes for microwave dielectric response could lead to the excellent microwave absorption due to the improvement of the impedance match between BiFeO_(3)and air.

Electronic Non-Resonant Tunneling through Diaminoacenes:A First-Principles Investigation

The electron transport through diaminoacenes sandwiched between two Au electrodes is simulated by using a first-principles analysis.The nonlinear current-voltage characteristic is observed.Effects of the ring number and positions of amine groups on equilibrium transport properties are found.For 1,4 series,the greater the number of the rings,the stronger the transmission spectrum near the Fermi energy.For 2,6 series,the larger the number of the rings,the weaker the transmission spectrum near the Fermi energy.This is helpful for understanding the recently reported results on conductance measurements using amines.

MWCNTs/SiO2 Composite System:Carrier Transmission,Twin-Percolation and Dielectric Properties

We synthesize composite systems of multi-wall carbon nanotubes(MWCNTs)/SiO_(2) by using the sol−gel method.The dielectric properties of the systems with different-concentration MWCNTs are studied.In our MWCNTs/SiO_(2) inorganic systems,the twin−percolation phenomenon exists when the concentrations of MWCNTs are 5–10%and 15–20%.The permittivity and conductivity have jumping changes.The twin−percolation phenomenon is attributed to the special transfer mechanism of MWCNTs in the system,determined by hopping and migrating electrons.Variations of dielectric properties and conductance of the MWCNTs/SiO_(2) systems are conformed to the percolation theory.The special percolation phenomenon and electric properties of MWCNTs/SiO_(2) can help us comprehend the conductivity mechanism of the MWCNTs/SiO2 systems effectively,and promote the development of a high performance function composite system.

Dynamic Tensile Behavior and Fracture Mechanism of Polymer Composites Embedded with Tetraneedle-Shaped ZnO Nanowhiskers

Dynamic tensile properties of glass-fiber polymer composites embedded with ZnO nanowhiskers are investigated by a split Hopkinson tensile bar. The stress-strain curves, ultimate strength, failure strain and elastic modulus are obtained and the failure mechanism of the composites is investigated by the macroscopic and microscopic observation of fractured specimens. The strain rate effect on the mechanical behavior is discussed and a constitutive model is derived by simulating the experimental data. The experimental results show that the materials have an obvious non-linear constitutive relation and strain rate strengthening effect. The composites with ZnO nanowhiskers under dynamic loading have various failure modes and better mechanical properties.

Airline Overbooking

This article deals with an optimal booking service system. According to the optimization object economic effects, we build an objective function with constraint conditions. Based on this function we prove the model so as to get it more conform to the common situation producer can im-prove the model so as to get it more conform to the common situation.