Design of a thin wide-band absorber based on metamaterials and resistance frequency selective surface
Three kinds of absorbers, based on square metal patch structure(SMP) metamaterials, resistance frequency selective surface (RFSS), and the combined SMP with RFSS structures, are designed, respectively. The absorptivities of these absorbers are simulated and analyzed by FDTD method. The simulation results indicate that in a frequency range of 2–30 GHz, SMP absorber can achieve stronger multi-bands absorption by the proper design of geometrical parameters of unit cell; RFSS absorber can achieve stronger high-frequency broadband absorption by the proper design of the square resistance of unit cell. However, the bandwidth of stronger absorption is limited; the absorption of the composite absorber combined with SMP and RFSS structure is greater than 90% in a frequency range of 3–25 GHz, which has a characteristic of better impedance matching to the free space in a wide frequency range.
Design of a low-frequency broadband metamaterial absorber based on resistance frequency selective surface
A low-frequency broadband, polarization-insensitive and wide-angle metamaterial absorber is presented, which is based on resistance frequency selective surface (RFSS). The unit cell of this absorber consists of cave cross planar metamaterial (CCPM), RFSS, dielectric substrate and metal backboard. The simulated results based on FDTD method indicate that with the absorptions of compared to the individual CCPM absorber and RFSS absorber, the absorption of the composite structure absorber of CCPM and RFSS is enhanced greatly, and it is greater than 80% and the absorption peak is over 98% in the whole frequency range of 1–5 GHz. The simulated absorptions under the conditons of different polarization and incident angles indicate that this composite structure absorber has polarization-insensitive and wide-angle absorption.
The study of asymmetric energy transmission based on the nonlinear supratransmission
In this paper, the phenomenon of the asymmetric energy transmission is numerically investigated in the forbidden band of the electrical transmission line formed by two nonlinear segments which are identical in structure but different in inductor parameter. By considering the driving voltage at the frequency within the forbidden bands of both segments, the carrier of the asymmetric energy flux is the nonlinear wave beyond the band, instead of the linear wave in the passband, and the mechanism is closly related to the nonlinear supratransmission. To further understand this phenomenon in electrical transmission line, we also study the correlations between the energy intensity and the circuit parameters. Finally, we investigate the dependency of the voltage threshold on the driving frequency in physical experiment, and the result is qualitatively identical with that calculated by using equation.
Electromagnetic coupling and shielding effectiveness of apertured rectangular cavity under plane wave illumination
Ray ellipse method of analyzing the power and polarization state of partially polarized light
The electric and magnetic polarization singularities of Gaussian vortex beam in the free-space propagation
Using the Fresnel vector diffraction integral and taking the Gaussian vortex beam as an example, the analytical expressions for the electric and magnetic components of Gaussian vortex beam propagating in the free-space are derived, and used to study the variations of electric and magnetic polarization singularities in free space. It is found that there exist two-dimensional (2D) and three-dimensional (3D) electric and magnetic polarization singularities in the free-space, which do not coincide in general. By varying waist width ratio, amplitude ratio, and propagation distance, the motion of polarization singularities takes place. In the 2D and the 3D electric and magnetic fields, the V-point may appear under a certain condition.
Focal depth research of digital holographic reconstructed image
Generation and control of electromagnetically induced double photonic band-gaps
By using the technique of electromagnetically induced transparency and solving density matrix equations for atoms and transfer matrix equations of fields, we study the steady optical properties of a four-level system of cold atoms driven by a traveling-wave field and a standing-wave field. It is found that a nearly perfect structure of double photonic band-gap can be generated with specific parameters. In particular, the reflectivity inside each photonic band-gap is homogeneous over 95%. It is convenient to modulate the positions and widths of both photonic band-gaps by changing intensities and frequencies of the driving fields. The double photonic band-gaps can be used to achieve all-optical routing and switching and therefore may have applications in all-optical information networks.
Precise frequency control of an Er-doped fiber comb
Study on characteristics of acoustic modes via stimulated Brillouin scattering in photonic crystal fiber
Discrete soliton interaction in quasi one-dimensional optically induced photonic lattice
Research on one-dimensional function photonic crystals
Ultrahigh-Q small-V photonic crystal nanobeam cavities based on parabolic-shaped width and taper holes
Properties of photonic quantum well structures containing left-handed materials
Viscosity coefficient in granular medium
Sectorial oscillation of acoustically levitated viscous drops
The sectorial oscillation of acoustically levitated viscous drops is investigated by applying a series of aqueous glycerol solutions (viscosity μ = 0.94–75.65 mPa·s). It is found that there exists a critical viscosity μc for a definite mode of sectorial oscillation, and that mode can be excited only when μ < μc. The critical viscosities for the l = 2–9th mode sectorial oscillation are experimentally determined with a modulation amplitude to the acoustic field reaching η = 0.23. It is found that ln μc decreases approximately linearly with l. Analysis based on the parametric resonance theory indicates that in order to excite the sectorial oscillation, the equatorial radius of the drop must be perturbed overs a threshold hc, which is proportional to the viscosity μ and increases with l. Therefore, the sectorial oscillations can hardly be excited to those drops with high viscosity and large oscillation modes. Both the amplitude and resonant modulating frequency width decrease with the enlargement of viscosity. No obvious effect of viscosity is found on the eigenfrequency of sectorial oscillation.
Research on a cylindrical cloak with active acoustic metamaterial layers
Study of bone fatigue evaluation with ultrasonic guide waves based on elastic modulus
Experimental study and improvement of frequency lowering algorithm in Chinese digital hearing aids
Effects of Ge profile in base region on thermal characteristics of SiGe HBTs
As is well known, the base Ge composition can improve the DC characteristics, frequency characteristics and noise characteristics of SiGe HBTs. However, the reports about the effects of Ge profile on HBTs thermal characteristics are rare. In this paper, by use of SILVACO simulator, the effects of different Ge gradients on thermal and electrical characteristics of SiGe HBT are investigated. It is found that under the same total Ge amount condition, as Ge gradient increases, the fT of device increases significantly, the uniformity of temperature distribution becomes better, the influences of temperature on the β and fT are weakened, but the gain β becomes smaller. For the device with uniform Ge composition, the β is high, but the influence of temperature on the β is enormous, the uniformity of temperature distribution is poor. Based on these results, in order to make a tradeoff among thermal, gain and frequency characteristics, a novel Ge composition structure with the combination of the uniform and graded Ge composition is proposed. The results show that the novel Ge composition structure SiGe HBT has good performances lower peak temperature, better uniform temperature profile, smaller variabilities of β and fT with temperature, sufficient high β and fT compared with the uniform Ge composition device. These new results provide valuable reference for the device thermal design, and are supplemental to the research and application of SiGe HBTs.
Study on ultra fast nonequilibrium heat transfers in nano metal films by femtosecond laser pump and probe method
The reduction in size and the increase in speed of microelectronic device make the probability of nonequilibrium electron-phonon phenomena become greater, leading to the increase of thermal resistance in the device. The measurement of electron-phonon coupling factor in material resistance increasingly becomes important for accurate thermal treatment. The femtosecond laser pump and probe method is used for studing the nonequilibrium heat transfer in nano metal films with different thicknesses. Exploring parabolic two-step model (PTS) to fit the experimental data. During the fitting process, we considered the proportional relationship between the changes of electron temperature and phonon temperature, which affects the reflectivity. By studying the different thicknesses of Ni and Al films electron-phonon coupling factors, we find that the electron-phonon coupling factor does not change with film thickness. In addition, the experimental result verifies that the reflectivity of probe laser is affected by electron temperature and phonon temperature at the same time. Through the data analysis, we also get the influence coefficients of electron temperature and phonon temperature on reflectivity.
Experimental and theoretical investigations of the effect of “Brazil Nut” segregation in vibrating granular matters
Low speed water-entry of cylindrical projectile
Experimental studies of the water-entry of cylinder bodies are conducted using high-speed camera to capture the splashes over the water surface and the subsurface cavity shapes during water entry and the cavity-running phase. Cavity evolution is discussed on single 140° conical cylinder body such as formation, development, and pinch-off of vertical and oblique entry. The dependence of the pinch-off type on the entry velocity is discussed for various entry speeds. The phenomena of two-body water entry in series and side-by-side are discussed in the end of this paper, and the data show that the spatial distance between the two bodies has a great influence on the development and the stability of the cavity and the dynamics of both bodies themselves.
Research on simultaneous reconstruction of the temperature distribution of a 3D participating medium and its boundary
In-situ and nonintrusive 3D temperature measurement is very important for combustion diagnosis and controlling of pollutants. The temperature reconstruction technique based on radiation inverse analysis has received intensive attention. In order to reduce the computation cost and take boundary temperature into consideration, a discrete method is presented for 3D temperature distribution determination for an absorbing, emitting and scattering combustion medium and its boundary by using the emission image measured by four CCD cameras. First the radiative source term is retrieved through the discrete transfer method. Then, the temperature is inferred from the blackbody intensity obtained by subtracting the media scattering and boundary reflecting contribution from the source term by the discrete ordinate approximation. The least squares minimum residual algorithm is improved to solve the ill-posed reconstruction equations. The performance of the proposed method is examined by numerical test. The effects of measurement noise and radiative properties on the reconstruction accuracy are investigated. The results show that the method proposed in this paper is capable of reproducing the temperature of the medium and its boundary accurately, even with noise. The reconstruction time cost is reduced significantly compared with those of other methods.
Elecrohydrodynamical characteristics of liquid film motor driven by a square-wave electrophoresis electric field
Liquid film motor as a novel experimental device will play an important role in basic research and technology applications. In-depth theoretical studies on its electro-hydrodynamics (EHD) motions under various conditions are of great significance. In current paper, the dynamical characteristics of the liquid film motor driven by a square-wave electrophoresis electric field perpendicular to a uniform constant external electric field are investigated. Space-time dependence of the film's rotation linear velocity is derived analytically. The theoretical results indicate that a symmetrical reciprocating rotation in the film gradually converts to a vibration as the frequency of the electrophoresis electric field increases. This not only helps us understand the physical origin of the vibration of the liquid film motor, but also provides a new option to design a liquid film mixer in the application.
A small-angle X-ray scattering study of micro-defects in thermally treated HMX
The defects in HMX, induced by thermal expansion, phase transition and chemical decomposition, have large effects on the performance of HMX. In this work, the defects of HMX samples under heat treatment are characterized by small angle X-ray scattering (SAXS) and atomic force microscopy. A large number of pores with an average size of 10 nm are found during the β-δ phase transition of HMX (180 ℃), and the pores increase in size and decrease in number with time increasing. A new population of small pores with sizes of 5–8 nm are produced in HMX during the thermal decompositions (190 ℃ and 200 ℃). The size and the number of the small pores increase with temperature increasing.
Research on the influences of point defects on the thermal conductivity of carbon nanotube by simulation with orthogonal array testing strategy
In the preparation process of carbon nanotubes, various point defects inevitably come into being in the lattice structures. The defects strongly affect the thermal transport properties of carbon nanotubes. Thermal conduction in carbon nanotube is simulated by using nonequilibrium molecular dynamics method with reactive bond order (REBO) potential. Thermal conductivities of carbon nanotubes with and without defects are calculated for comparison. An orthogonal array testing strategy is employed. In the calculation it greatly saves the experimental effort and identifies the degrees of influence of such structural factors as defect type, tube length, tube radius, etc. on thermal conductivity of tube. The effects of three types of point defects: vacancy, doping and adsorption are primarily studied, and the ambient temperature factor is also analyzed. Simulation results show that the thermal conductivity of carbon nanotubes with defects decreases significantly due to point defects compared with that of perfect carbon nanotubes. The defect type has the first greatest influence on the decrease of thermal conductivity, and hvae the second third greatest infuluences respeetively the radius and the length of carbon nanotubes. The degrees of influence of the above types of point defect are in the order of vacancy>doping>adsorption. Different types of point defects have different effects on tubes at different ambient temperatures.
Simulation study on thermodynamic, dynamic and structural transition mechanisms during the formation of Ca70Mg30 metallic glass
The rapid quenching process of Ca70Mg30 alloy is simulated by using the molecular dynamics method. During the liquid-glass transition process, the thermodynamic, dynamic and structural transition mechanisms are investigated deeply, and the relations between glass transition temperatures determined by different methods are discussed. It is found that both the simulated structural factor of Ca70Mg30 metallic glass and glass transition temperature are consistent with the experimental results, and the icosahedral local configuration plays a critical role in the formation of Ca70Mg30 metallic glass. The dynamic property of supercooled liquid gradually deviates from the Arrhenius law and satisfies the MCT power law due to the cage effect formed by neighbor atoms. It is also found that the structural glass transition temperature is close to the dynamic one, and they are higher than the calorimetric glass transition temperature. The relationship between them and the ideal dynamic glass transition temperature satisfies the Odagaki relation.
Vibrational dynamics of water confined in mesoporous silica under low temperature
The Raman vibrational spectra of water inside mesoporous silicate are measured in a temperature range of 100 ≤ T ≤ 303 K. It is found that the Raman spectrum of confined water becomes more different from that of bulk water with the decrease of water content in pores. For samples with high water content in pore, the main peak position of the Raman spectrum of water changes abruptly in a narrow temperature range. However, when water content decreases down to 20%, the red shift of the main peak of the Raman spectrum is continuous with temperature decreasing. At the same time, its temperature-dependence is the same as that of bulk amorphous ice.
Geometric structures and nitrogen adsorption properties of BaO adlayer on Ru(0001) surface
First principles calculations are performed to study the geometric structures and the nitrogen adsorption properties of BaO adlayer on Ru(0001) surface. It is suggested that BaO adlayer is more stable on Ru(0001) surface at low coverage. A configuration is observed in surface phase at low coverage. In this structure oxygen is adsorbed on the hcp site of one p(1× 1) cell, and barium is adsorbed close to the top site of the same p(1× 1) cell. Bond length of oxygen and ruthenium is calculated to be 0.209 nm, longer than the EXAFS experimental value about 0.018 nm. Nitrogen prefers to be adsorbed on the sites close to barium. Nitrogen adsorption energies at those sites are calculated to be in a range from 0.70 to 0.87 eV, which are bigger than those at the sites close to oxygen. Adsorption sites near barium atoms have more activities to weaken nitrogen. The lowest N-N stretching vibrational frequency on the sites is about 1946 cm-1, less than the highest frequency on sites around oxygen (about 130 cm- 1). Bond strengths of nitrogen on Ru(0001) /BaO surface are between those on clean Ru(0001) and Ru(0001) /Ba surface. The adsorption properties of sites around BaO layer are determined by chemical characteristic of barium and oxygen. Electron transfer from barium to ruthenium enhances the hybridization between ruthenium and nitrogen by reducing and increasing the occupation of σ* and π* orbitals respectively.
Modification of zigzag graphene nanoribbons by patterning vacancies
The transport properties of zigzag graphene nanoribbons (ZGNRs) with different patterns of vacancies are investigated by using the density functional theory and nonequilibrium Green's function (NEGF) formalism. It is found that the transport properties vary with lattice type vacancy. For two vacancies, A-B type vacancies have the most significant influence on the conductance of ZGNRs, while A-A type vacancies have the most slightly influence on the conductance. More importantly, the pattern of vacancies has enormous influence on electron transport around the Femi energy. As hexagon carbons are removed, the ZGNRs will be modified, changing from metallic to semiconducting. This lays the theoretical foundation for tuning the electron properties of ZGNRs by patterning vacancies.
First-principles study of FeAl(B2) microalloyed with La, Ac, Sc and Y
Quasiparticle band structure calculation for SiC using self-consistent GW method
Quasiparticle band structures of 3C-SiC and 2H-SiC were calculated using ab initio many body perturbation theory with GW approximation. Quasiparticle energies along high symmetry lines in the first Brillouin zone were evaluated using quasiparitcle self-consistent GW (QPscGW) method and the Maximally-localized Wannier Function interpolation. Both 3C-SiC and 2H-SiC have an indirect band gap with valence band maximum locating at Γ point. The conduction band maximum of 3C-SiC is at X point. As a comparison, band gaps of 3C-SiC calculated by DFT-LDA, one-shot G0W0 and QPscGW are 1.30 eV, 2.23 eV and 2.88 eV respectively. The conduction band minimum of 2H-SiC locates at K point with a band gap of 2.12 eV, 3.12 eV and 3.75 eV predicted by DFT-LDA, one-shot G0W0 and QPscGW respectively. Lattice parameters calculated by DFT-LDA were used in this work. The QPscGW calculations are based on pseudopotential method, predicting slightly larger bandgaps for both 3C-SiC and 2H-SiC comparing with experiments.
The model of valence-band dispersion for strained Ge/Si1-xGex
Based on the k·p theory, the valence-band dispersion model for biaxial strained Ge/Si1-xGex is derived by taking strained Hamiltonian perturbation into account. The model can be used to calculate the valence band structure and hole effective mass along arbitrarily k wavevector direction in strained Ge grown on arbitrarily oriented relaxed Si1-xGex virtual substrate. The MATLAB simulation results of the model show that by comparison with relaxed Ge, the more anisotropy of the hole effective mass occurs in strained Si1-xGex and the hole effective mass of the top valence band decreases with the increase of Ge fraction. The results can supply valuable references to the conduction channel design related to stress and orientation in the Si-based strained Ge MOS devices and integrated circuits.
Synthesis and characteristic research of nanoparticles KY3F10: Yb, RE (RE=Er, Ho, Tm) by thermal decomposition
Organic dyes and quantum dots possess the defects: wide emission spectrum and the poor photothermal stability and cytotoxicity, which restricts their applications in biological studies. Lanthanide-doped upconversion fluorescent materials in which there exists neither "autofluorescence" nor "light bleaching" phenomenon, has high sensitivity and good long-term stability, which are conducive to in vivo detection. KY3F10: Yb, RE(RE=Er, Ho, Tm) nanocrystals are synthesized by the thermal decomposition method and oleic acid as surface coating agent. The effects of the oleic acid content on morphology and particle size are studied. Optimal ratio of oleic acid to octadecene is 3:1 for the preparation of spherical monodisperse nanocrystals. Strong yellow green, green and blue emissions from the prepared samples are observed at 980 nm laser excitation. These results show that KY3F10: Yb, RE (RE=Er, Ho, Tm) nanoparticles as biological probes have excellent features in multiple fluorescent markers.
Large-deviation analysis for counting statistics in double-dot Aharonov-Bohm interferometer
The effect of electrostatic discharge on the I-V and low frequency noise characterization of Schottky barrier diodes
Based on the analysis of thermal electron emission, the model of the carrier mobility fluctuation and the white noise theory, the effect of electrostatic discharge (ESD) on the I-V and low frequency noise of Schottky barrier diode (SBD) is discussed in this paper. The different Human Body Model(HBM) ESD injected times with the same voltage peaks are applied to the cathode and anode separately. It is found that the diode subjected to the cathode stress shows greater degradation than subjected to the anode stress, and the magnitude of noise shows significant change. With the increase of ESD injected times, the forward characteristic has no change, while reverse current almost increases at each time. The magnitudes of forward and reverse 1/f noise increase all the time. In view of the relationship between defects and damage, and the noise sensibility, the low frequency noise can serve as a tool for researching the sensitivity to the electrostatic discharge damage of SBD.
Investigation of the nonlinear response mechanism of photovoltaic HgCdTe detector irradiated by CW band-in laser
The effect of ITO annealing on electrical characteristic of GaN based LED
The effects of magnetization methods with additional permanent magnet on the magnetic field distribution and levitation force of single domain GdBCO bulk superconductor
The effects of magnetization methods with additional permanent magnet on the magnetic field distribution and the levitation force of single domain GdBCO bulk superconductor are investigated with a cubic permanent magnet in their coaxial configuration in zero field cooled state at liquid nitrogen temperature in three different ways. It is found that when the N pole of the cubic permanent magnet, for the levitation force measurement, is placed above the GdBCO bulk superconductor and in the downward direction, the maximal levitation force can be improved to 31.8 N, and that when the N pole of the additional cubic permanent magnet points to upward and sticks to the bottom of the GdBCO bulk, the maximal levitation force is increased up to about 222% of the levitation force of 14.3 N for the system without additional permanent magnet. The maximal levitation force can be improved to 21.6 N (or reduced to 8.6 N), when the GdBCO bulk superconductor is closely placed below and magnetized by the additional cubic permanent magnet with N pole in the upward (or downward) direction, and the additional permanent magnet is removed away after the magnetization, the maximal levitation force is about 151% (or 60%) of 14.3 N for the system without the additional permanent magnet. The results indicate that the levitation force of high temperature bulk superconductors can be effectively improved by introducing additional permanent magnet based on the scientific and reasonable designing of the system configurations, which is very important for the practical design and application of superconducting magnetic levitation system.
Phonon softening and superconductivity of β-pyrochlore oxide superconductors AOs2O6 (A=K, Rb)
Using the first-principles calculational method based on the density functional theory, we study the structural instabilities, phonon softenings, and their relation to the superconductivities of two β-pyrochlore oxide superconductors AOs2O6(A=K, Rb). It is found that there are structural instabilities of alkali ions along the 〈111〉 direction in the two β-pyrochlore oxide superconductors AOs2O6(A=K, Rb), especially in KOs2O6. Meanwhile, a comparison of the phonon frequency at zone-center between KOs2O6 and RbOs2O6 shows that the frequency of KOs2O6 is lower in general than that of RbOs2O6, leading to the stronger electron-phonon coupling. We conclude that K atom located in a large oxygen cage has an unusual large atomic displacement parameter and strong activity, thereby resulting in strong phonon softening. This is the foundamental cause for stronger electron-phonon coupling and higher superconducting transition temperature of KOs2O6. These are of significance for explaining the superconductivities in β-pyrochlore oxide superconductors AOs2O6(A=K, Rb).
Influence of annealing ambience on the magnetic properties of doped ZnO films
Effects of Fe doping on the crystal structures and photoluminescences of ZnO: Ni thin films prepared by sol-gel method
Zn0.95-xNi0.05FexO (x=0, 0.005, 0.01, 0.03, 0.05) thin films are fabricated on the glass substrates by the sol-gel method. The surface morphologies and crystal structures of the films are investigated using scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results reveal that preferential orientations are all along the (002) direction in all films. the qualities of ZnO: Ni films for low or high Fe concentration become worse, the crystal grain sizes of ZnO: Ni film are reduced, but moderate Fe doping seems to improve the film quality. XPS results reveal that Ni elements exist as Ni2+, and Fe elements exist as Fe2+ and Fe3+. Strong ultraviolet emission peaks, blue double emission peaks and green emission peaks are observed in the photoluminescence spectra of all samples at room temperature. It is found that the PL intensities of (Ni, Fe) co-doped ZnO films could be well modulated by Fe doping. In combination with other reports, we think that the ultraviolet emission peaks are due to exciton recombination; while the blue double peaks are caused by transition of electrons from the zinc interstitial to the top of the valence band or from the oxygen vacancy to the zinc vacancy. However, the green peak is highly dependent on oxygen vacancy and zinc vacancy formed by doping.
Fabrication and magnetic properties of Co70Cu30 alloy nanowire arrays with high coercivity
CoCu solid solution alloy nanowire arrays which exhibit the face-centered cubic structure with strong  orientation along the nanowire axes are fabricated for first time in the anodic aluminum oxide template by electrodeposition. The proportion of Co ingredient in CoCu alloy nanowire arrays is up to 70%. Transmission electron microscopy revealts that the nanowire arrays are uniform and continuous and have a large aspect ratio of about 300. The magnetic hysteresis loop demonstrates that the Co70Cu30 alloy nanowire arrays have a large coercivity of about 2438 Oe and relatively large squareness of about 0.76 parallel to nanowire arrays which greatly exceeds the value previousely reported. Good magnetic properties are achieved due mainly to the larger proportion of Co ingredient than that in the normal CoCu alloy nanowire arrays and the large shape anisotropy. The results of magnetic measurement and the calculations from formula demonstrate that the symmetric fanning mechanism of sphere chains model could be employed to explain the magnetization reversal process which is related to the structure of the Co70Cu30 nanowire arrays.
Effect of adjustable bias voltage on magnetoelectric properties of magnetostrictive/piezoelectric laminated transducer structure
The magnetoelectric properties of PZT5/Terfenol-D/PZT8 laminated transducer structure are analyzed and detected for adjusting the bias voltage across PZT5. A control method of one-order resonant frequency for a magnetostrictive/piezoelectric laminated magnetoelectric transducer structure is proposed. The resonant frequency and the prestrain of the magnetoelectric laminated structure can be adjusted by changing the bias voltage across PZT5. The relationships between the control voltage, the strain, the Young's modulus, the resonant frequencies and the resonant magnetoelectric coefficient are analyzed. Theoretical analyses show that the resonant frequency of the laminated structure is almost a linear function of the applied dc bias voltage at a small strain. The magnetoelectric coefficient is hardly related to the control voltage. The experimental results verify the theoretical analyses. For a control voltage of –170 V to +170 V, the resonant frequency can be linearly adjusted. The adjusted maximum of the resonant frequency is 1 kHz. The ratio of the adjusted value to the bias control voltage is 2.94 Hz/V. For a bias magnetic field from 0 Oe to 225 Oe, the resonant frequency is almost unrelated to the bias magnetic field. The magnetoelectric voltage coefficient changes with the bias magnetic field. A maximum magnetoelectric voltage coefficient of 1.65 V/Oe is obtained at a bias magnetic field of >178 Oe.
Application of high-k dielectrics in novel semiconductor devices
As the feature size of MOSFET scales beyond 45 nm, SiO2 as gate dielectric fails to meet the performance requirement because of the high gate oxide leakage current. It is necessary to replace SiO2 with high-k materials. However, high-k materials as gate dielectric have some limitations and are not expectedly compatible with the conventional structure, inducing new challenges such as bad interfacial quality, increased threshold voltage, mobility degradation, etc. In this paper we review the problems encountered in the introduction of high-k gate dielectric into planar devices and the solutions in terms of material, device structure and process integration. Some novel applications of high-k materials in new devices and the future trend are also reviewed.
Theoretical and experimental investigation of W doped ZnO
The properties of high valence difference W doped ZnO films (WZO) are investigated by means of plane wave pseudo-potential method based on the density-functional theory (DFT) and pulsed DC magnetron sputtering technique. The theoretical result shows after incorporation of W the Fermi level enters into the conduction band, showing that a typical n-type metallic characteristic and the optical band gap Eg* increase significantly. The carriers originate from the orbits of W 5d, O 2p and Zn 3d. Moreover, the increase of the lattice constant is due to the longer bond length of W-O and lattice distortion. The experimental results demonstrate that the deposited WZO film grows preferentially in the (002) crystallographic direction but the lattice constant increases. The resistivity decreases from 1.35× 10-2 Ω·cm to 1.55× 10-3 Ω·cm and the optical bandgap extends from 3.27 eV to 3.48 eV compared with those of ZnO. The average transmittance is over 83 % in a wavelength range from 400 to 1100 nm. The experimental results are in good agreement with the theoretical results, showing that the WZO thin film has a great potential application as transparent conductive oxide.
Solvothermal recrystallized synthesis of one-dimensional CdS nanorods self-assembled from nanoparticles
Two different solvothermal synthesis routines are used to fabricate CdS nanocrystals with different morphologies and sizes. Anhydrous ethylenediamine (en) is chosen as solvent, CdCl2. 2.5H2O and thiourea (H2NCSH2N) as the cadmium source and sulfur source respectively in the first method. CdS Nanocrystals are prepared at different reaction temperatures (160 ℃-220 ℃) and the influence of the reaction temperature on the growth of CdS nanocrystals is discussed. In the other routine, anhydrous ethylenediamine (en) is also chosen as solvent. The synthesized products at 160 ℃ are recrystallized under 200 ℃ for 2-8 h. The influence of the recrystallisation time on the growth of CdS Nanocrystal is discussed. The in-situ analysis of effect of the growth time on the growth of CdS nanocrystals is performed. The phase, morphology and crystallographic structure of CdS nanocrystals are investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) respectively. The results show that both products exhibit pure hexagonal structures, the morphology of the product is nanoparticles at the temperatures below 160 ℃, when the temperature is rasied to higher than 160 ℃, the products are CdS nanorods. Meanwhile, the morphologies of the recrystallisation products under 200 ℃ for different times are found to convert from nanoparticles into nanorods gradually. The nanorods are composed of zero-dimensional particles through self-assembly process which could be demonstrated by field emission scanning electron microscopy (HRTEM) analysis. Finally, the factors that influence the morphology changes of CdS nanocrystals and the mechanism of the growth of nanorods are discussed.
Influence of surface fluorination temperature on space charge accumulation in polyethylene
Improving the light-soaking stability of a-Si: H/μc-Si: H tandem solar cells
High-speed and high-power uni-traveling-carrier photodetector
The preparation and performance analysis of GaN-based high-voltage DC light emitting diode
Numerical study of spectrum-control in dual-wavelength LED with doped quantum well barriers of different doping concentration
Dual-wavelength LEDs with doped quantum well barriers of different doping concentrations are numerically investigated by using the APSYS simulation software. The carrier concentrations, radiative recombination rates, energy band diagrams and spectra are investigated at different doping types and different doping concentrations. The results show that through adjusting the doping concentration of the quantum well barrier a suitable spectrum can be obtained, which will satisfy the need of application. And the effect of spectrum-control in dual-wavelength LED is due to the blocking effect of electrons and holes by doped quantum well barriers.
Optimization of quantum dot solar cells based on structures of GaAs/InAs-GaAs/ZnSe
Based on the structures of GaAs/InAs-GaAs/ZnSe P-i-N quantum dot solar cells, according to the optical principle and diffusion theory, mathematic model describing the relationship between photogenerated electron current density and thickness of layer is proposed, and the effect of the quantum dot layer on the characteristics of solar cell is analyzed quantitatively for improving the power conversion efficiency of quantum dot solar cells. Simulations show that the optimal thicknesses of P(GaAs) and N(ZnSe) are 1541 nm and 78 nm respectively when the i layer thickness is 3000 nm, and the power conversion efficiency of solar cell is 20.1% at a single wavelength; At the same time, the volume of quantum dot and the temperature affect I-V property of quantum dot solar cell, and the value of open voltage reduces with the increase of the volume of quantum dot and temperature, so that the power conversion efficiency will be reduced.
Simulation of reflection spectrum of FBG with uniaxial anisotropic crystal cladding
A method of constructing infinite sequence soliton-like solutions of nonlinear evolution equations
The auxiliary equation method is used to construct the finite new exact solutions of nonlinear evolution equations. To search for infinite sequence soliton-like exact solutions of nonlinear evolution equations, characteristics of constructivity and mechanization of auxiliary equation method are analyzed and summarized. Therefore, the quasi-Bäcklund transformation between new solutions of a kind of auxiliary equation with Riccati equation is presented, then (2+1)-dimensional modified dispersive water-wave system is taken as an applicable example to find infinite sequence soliton-like new exact solutions by choosing two kinds of formal solutions of nonlinear evolution equations with the help of symbolic computation system Mathematica, where included are the infinite sequence smooth soliton-like solutions, compact soliton solutions and peak soliton-like solutions.
The stability of solitay wave solution to a modified Kadomtsev-Petviashvili equation
The influence of the disorderded substrate potential on static friction force
Stochastic resonance in FHN neural system driven by non-Gaussian noise
Stochastic resonance in an over-damped linear oscillator driven by multiplicative quadratic noise
For an over-damped linear oscillator driven by multiplicative quadratic noise and periodic modulated noise, the exact analytical expressions of the first two moments, the amplitude and variance of the system steady-state response are obtained. We find that this system has richer dynamic behaviors than the traditional linear systems driven by linear noise; when the coefficients of the quadratic noise satisfy certain conditions, both the amplitude and the variance of the system steady-state response present stochastic resonance.
Control of fast-scale bifurcation in single-phase SPWM inverter and its stability analysis
H bridge inverter is a basic nonlinear topology in power electronic circuits. However it is prone to the generation of fast-scale instability phenomenon due to the variation of some parameters in the operation process, which can be eliminated with the slope compensation simply and effectively. Experience plays the leading role and common engineering design is lacking in necessary design criteria. Accrording to the bifurcation control theory of nonlinear system, in this paper we analyze the implementation of slope compensation on H bridge inverter under peak current mode control in detail, thereby obtaining the accurate amplitude requirements of the compensated slope signal and realize the optimization. The results of the analysis are consistent with those of simulation experiment, and the inverter circuit under appropriate slope compensation can operate in stable regime especially with the performances being enhanced remarkably. The research method is also applicable for the stability analysis of other power electronic circuits.
The normalized KLD coefficient and its application in detection of correlation and synchronization from multivariable series
The KLD coefficient and the normalized KLD coefficient are proposed to characterize the correlation of multivariable series in order to overcome the intrinsic limitations of the KLD dimension density. Using the uncorrelated or perfectly correlated multivariable series, the upper and the lower bound functions of the KLD dimension density, and furthermore the upper and the lower bounds of the KLD coefficient are analytically deduced. Then, the normalized KLD coefficient is proposed in the paper. The analyses and numerical simulations prove that the changes of correlation of multivariable series can lead to linear variation of the normalized KLD coefficient. The simulations also prove that the normalized KLD coefficient can detect the changes of correlation sensitively, even if these are induced by only two channels of multivariable series. Furthermore, the normalized KLD coefficient can be used to analyze the nonstationary time series. The simulation results of coupled map lattice prove that the normalized KLD coefficient can also be used for the nonlinear system analysis.
Amplitude spiral wave in coupled complex Ginzburg-Landau equation
A novel amplitude spiral wave in coupled complex Ginzburg-Landau equation (CGLE) system is proposed. The stability conditions and the relevant factors are investigated via numerical simulations. On the tip of an amplitude spiral wave there exist no topological defect, which is different from the commonly observed phase spiral wave, and in its amplitude part (instead of phase part) there is a spiral structure. In this research, the stability of amplitude spiral wave is studied by considering the different initial patterns in the case of the system parameter mismatches.
Application of FuzzyEn algorithm to the analysis of complexity of chaotic sequence
To analyze the complexity of chaotic sequence correctly, complexity of systems, including typical discrete chaotic systems and continuous chaotic systems, are investigated based on the FuzzyEn algorithm. Compared with ApEn, SampEn and Intensive statistical complexity algorithm, the FuzzyEn algorithm is an effective measure algorithm for analyzing chaotic sequence complexity, and it has low sensitivity to and slight dependences on phase space dimension (m), similar tolerance (r) and sequence length (N), better robustness and measure value continuities. Results of the complexities of chaotic systems show that the complexity of continuous chaotic systems are much smaller than those of the discrete chaotic systems. However, having been disturbed by high complex discrete chaotic pseudo-random sequences or classical m-series, the pseudo-random sequences of continuous chaotic systems increase their complexities significantly. Our result provides a theoretical basis for the application of chaotic sequences to the field of cryptography and secure communication.
Research of Chaotic encryption system based on FPGA technology
Simulation of pedestrian evacuation with asymmetrical pedestrian layout
Simulation of pedestrian evacuation from a room with multi-exit and asymmetrical pedestrian layout is presented based on an improved dynamic parameter model in this paper. The computation and the count-area of imaginary distance are improved based on the "Max-Min" evacuation path selection of actual and imaginary distance in order to reduce evacuation imbalance caused by the asymmetry of pedestrian layout. An imbalance coefficient is introduced to describe the asymmetry of pedestrian layout. The effects of pedestrian layout asymmetry on the evacuation time are analyzed respectively from fixed and unfixed pedestrian initialization site. The simulation results of the improved and original models are compared and analyzed, and the improved model can effectively reduce evacuation imbalance. Simulation results show that under normal evacuation condition with considerring reasonable pedestrian and jam around exits, evacuation time is hardly affected by pedestrian and exit layout and depends mainly on cognition coefficient, total width of exits and pedestrian initialization amount.
Structures and melting behaviors of ultrathin platinum nanowires
Molecular dynamics simulation on friction process of silicon-doped diamond-like carbon films
Maximum correlation at the transition to the saturation regime of nonsequential double ionization
Investigations of vibrational levels and dissociation energies of diatomic systems using a variational algebraic method
A theoretical study on double differential cross sections for (e, 2e) process of hydrogen
Shock timing experiment based on imaging velocity interferometer system for any reflector
The effects of local density of states on surface plasmon polaritons
3D simulation optimization and design of multicusp ion source
In this paper, a permanent magnet of multicusp ion source is calculated in theory, using the "binary collision" model to deal with coulomb collision between electrons. Collision between electrons and hydrogen species is treated with the "null-collision" model. Therefore, the three-dimensional PIC-MCC simulation algorithm is developed. Two optimization design models of multicusp ion source, ET-60U, are simulated by the software. Also, the spatial distribution characteristics and the relevant issues of the volume negative hydrogen ion production rate of the two kinds of ion sources are explored. Finally, The basic idea about the design of the negative hydrogen ion source is proposed. indicating that appropriately regulating the magnetic field distribution of the multicusp ion source can produce uniform ion beam, and that appropriately adjusting the size of the extraction magnetic field and the ion source structure can obtain both the ion beam spatial uniformity and the high production rate.
Laser-driven reservoir target for quasi-isentropic compression in aluminum
The quasi-isentropic compression of material with high strain rate can be obtained by the ramp wave loading of plasma jet produced by laser-driven reservoir target. The quasi-isentropic compression experiments of aluminum are carried out on the high power laser facility of SG-III prototype. The smooth and continuous speed history of free surface of specimen is recorded with a line-imaging velocity interferometer (VISAR). The peak pressure (>60 GPa), the rise time of the load (～ 10 ns) and the strain (～ 108 s-1) are derived by the back-integrating method, and the reverberation of compression wave at the rear surface of the sample is observed.
Dynamical identification of a heavy “sauna” weather event in northern China in 2009
A "sauna" weather event in northern China in July 2009 is numerically simulated and diagnostically analyzed. The atmospheric circulation characteristics, the horizontal and vertical distributions of temperatures and moistures, and the distribution of potential vorticities are studied. It is found that anticyclone dominates the upper troposphere during the "sauna" weather event. In the horizontal chart, the relative humidity in the lower troposphere is large. From the vertical sections, descending airflow dominates the moist and warm sectors at the middle and lower levels. There are clear humidity gradient, evident vertical gradient of temperature, and slanting distribution of potential vorticity. The "sauna" weather event occurs in the generally high-temperature environment of summertime, so it is difficult to dynamically identify and diagnose the "sauna" weather depending on some single factor, e.g., temperature or moisture. According to the high-temperature, large-moisture, and strong-potential vorticity characteristics during the "sauna" weather in northern China, a moist thermal potential vorticity parameter MTPV, may be expressed as ▽ q · (▽ θ × ▽ Q), where q is the sum of water vapor and all hydrometeors including cloud water, rain water, cloud ice, snow and graupel; θ is potential temperature; Q is potential vorticity) which is appropriate for "sauna" weather, is introduced. Then it is used to dynamically diagnose "sauna" weather event. And it is simplified by calculation analysis in case study. It is found that the MTPV anomaly is accompanied by the "sauna" weather process. Although high temperature, large moisture and strong slanting potential vorticity development present in the "sauna" weather process in northern China in July 2009, their coverages for these single variables are larger than our target region of this "sauna" weather event. While for the MTPV and its simplified form combining these variables, their anomalies maintain in the lower troposphere around Beijing and its peripheral areas in northern China, viewing from either zonal or meridional section. Therefore, both MTPV and its simplified form can better dynamically identify this high-temperature and high-humidity "sauna" weather event.
The analysis of the influence of globe SST anomalies on 500 hPa temperature field based on Bayesian
In this paper, we break down sea surface temperature(SST) anomaly field by using the empirical orthogonal function (EOF) to obtain a rebuilding space made up of different patterns which are orthogonal to each other, then we unfold 500 hPa temperature field in this space. Furthermore, with the method of Bayesian analysis, we define the impact index of different patterns on 500 hPa air temperature field and research the variation characteristic of index with the change of spatial pattern of SST. It is found that SST field has a great effect on 500 hPa temperature field between April to June. Besides, after the abrupt climate change, different patterns of SST have different effects on temperature field.
A differentiable thresholding function and an adaptive threshold selection technique for pulsar signal denoising
Because of the extremely low signal-to-noise ratio of pulsar signals, it is difficult to suppress noise while preserving details by the traditional denoise methods. Therefore, a wavelet domain pulsar signal denoising method based on a differentiable thresholding function and an adaptive threshold selection technique is presented. The signal-to-noise ratio(SNR), the root mean square error(RMSE), the relative error of the peak value (REPV) and the error of the peak position (EPP) are used to evaluate the performance of the proposed denoising method. Experimental results show that the proposed method can remove the pulsar signal noise and keep the useful information effectively. At the same time, it can achieve a higher PSNR, a lower RMSE, a lower REPV and a lower EPP than the soft thresholding and hard thresholding methods.