The Effect of the Semiconductive Screen on Space Charge Suppression in Cross-Linked Polyethylene

The space charge distributions of cross-linked polyethylene （XLPE） with Borouge＇s BorlinkTM semiconductive screen type LE0550 and LE0595 from a pulsed electro-acoustic method are obtained. The contact interface morphology at the semiconductive screen and the structure of XLPE near the interface are characterized. The dielectric spectrum and the conductivity current of XLPE with the different semiconduetive electrodes are com- pared. The semiconduetive screen changes the structure and the dielectric characteristic of XLPE near the contact interface, which may be the main reason for space charge suppression in XLPE with Borouge＇s type LEO550 semiconduetive screen.     

Critical Behavior of the Gaussian Model with Periodic Interactions on Diamond—Type Hierarchical Lattices in External Magnetic Fields

The Gaussian spin model with periodic interactions on the diamond-type hierarchical lattices is constructed by generalizing that with uniform interactions on translationally invariant lattices according to a class of substitution sequences.The Gaussian distribution constants and imposed external magnetic fields are also periodic depending on the periodic characteristic of the interaction onds.The critical behaviors of this generalized Gaussian model in external magnetic fields are studied by the exact renormalization-group approach and spin rescaling method.The critical points and all the critical exponents are obtained.The critical behaviors are found to be determined by the Gaussian distribution constants and the fractal dimensions of the lattices.When all the Gaussian distribution constants are the same,the dependence of the critical exponents on the dimensions of the lattices is the same as that of the Gaussian model with uniform interactions on translationally invariant lattices.     

Space-charge limiting current in spherical cathode diodes

The results of the investigation on the space-charge limiting current for a spherical-cathode diode in the nonrelativistic situation are presented in this paper,The results show that the current enhancement factor equals the square of E-field enhancement factor on the cathode surface,The generated space-charge limiting current is deduced.In the case of a pin-shaped-cathode diode,the space-charge limiting current is also obtained.Indicating that the current is independent of the geometric paramters of the diode.Analyses of the shielding effects and the conditions for generation of the uniform space-charge limiting beam show that ,for pin-arrayed cathodes,the distance between pins should be in the range from 1.2D to 1.5D.where D is the distance between the two electrodes.     

A three-dimensional time-dependent theory for helix traveling wave tubes in beam-wave interaction

This paper presents a three-dimensional time-dependent nonlinear theory of helix traveling wave tubes for beamwave interaction.The radio frequency electromagnetic fields are represented as the superposition of azimuthally symmetric waves in a vacuum sheath helix.Coupling impedance is introduced to the electromagnetic field equations’ stimulating sources,which makes the theory easier and more flexible to realize.The space charge fields are calculated by electron beam space-charge waves expressed as the superposition solutions of Helmholtz equations.The focusing forces due to either a solenoidal field or a periodic permanent magnetic field is also included.The dynamical equations of electrons are Lorentz equations associating with electromagnetic fields,focusing fields and space-charge fields.The numerically simulated results of a tube are presented.     

Two—phase flow in correlated pore—throat random porous media

We have constructed a porous media model in which there are percolation clusters with varying percolation probability P and correlated site-bonds. Taking into account both the pore and the throat geometry, the viscous fingering (VF) in porous media has been investigated by using the standard over-relaxed Gauss-Seidel scheme. The simulation results show that the VF structure varies with the correlation parameter ε, the viscosity ratio M and the percolation probability P. The smaller the correlation parameter ε, the greater the deviation of the normalized size distribution of the invaded throat N_inv(r) from the truncated Rayleigh distribution. For a larger viscosity ratio M, the VF pattern looks like a diffusion-limited-aggregation structure in percolation clusters. The fractal dimension D increases with the increase of the percolation probability P and the correlation parameter ε. The velocity distribution f(α) of VF in percolation clusters is of a parabola-like curve. The tail of the distribution (large α) is longer for a larger correlation parameter ε. For a smaller ε, the distribution is very sharp. The sweep efficiency E decreases along with the decrease of the correlation parameter ε and the increase of the network size L_nz. E has a minimum as L_nz increases up to the maximum no matter what the values of P, M and ε. The E～ L_nz curve has a frozen zone and an active zone. The geometry and the topology of the porous media have strong effects on the displacement processes and the structure of VF.     

Differential Cross Section and Polarization of Radiative Recombination

The formulae of photon angular distribution and polarization degree for radiative recombination are presented to include the contribution of multipoles and their correlations. A fully relativistic code is then developed to calculate the photon angular distribution and polarization. The calculated polarization degree and differential cross-sections agree well with that of Scofild＇s results within 10%. The effects of multipoles on polarization and angular distribution are investigated. The polarization and the angular distribution become asymmetric when the multipoles are accounted as the electron energy increases.     

Optical characteristic and gap states distribution of amorphous SnO2:（Zn,In） film

In this paper the fabrication technique of amorphous SnO 2:(Zn,In) film is presented.The transmittance and gap-states distribution of the film are given.The experimental results of gap-states distribution are compared with the calculated results by using the facts of short range order and lattice vacancy defect of the gap states theory.The distribution of gap state has been proved to be discontinuous due to the short-range order of amorphous structure.     

Monto Carlo simulation of the behaviour of electrons during electron—assisted chemical vapour deposition of diamond

The behaviour of electrons during electron-assisted chemical vapour deposition of diamond is investigated using Monte Carlo simulation. The electron energy distribution and velocity distribution are obtained over a wide range of reduced field E/N (the ratio of the electric field to gas molecule density) from 100 to 2000 in units of 1Td=10^-17Vcm². Their effects on the diamond growth are also discussed. The main results obtained are as follows. (1) The velocity profile is asymmetric for the component parallel to the field. The velocity distribution has a peak shift in the field direction. Most electrons possess non-zero velocity parallel to the substrate. (2) The number of atomic H is a function of E/N. (3) High-quality diamond can be obtained under the condition of E/N from 50 to 800Td due to sufficient atomic H and electron bombardment.     

Schottky Barrier Height Inhomogeneity of Ti／n—GaAs Contact Studied by the I—V—T Technique

The current-voltage characteristics of Ti/n-GaAs Schottky diodes measured over a temperature range of 78-299K have been interpreted on the basis of thermionic emission across an inhomogeneous Schottky contact.The experiment shows that the apparent barrier height (φap) increases from 0.437eV at 78K to 0.698eV at room temperature.the plot of φap versus 1/T does not exhibit a simple linear relationship over the whole temperature range,indicating that the barrier height distribution is more complicated than the frequently observed single Gaussian distribution.A new multi-Gaussian distribution model is developed.Our experimental results can be explained by a double Gaussian distribution of the barrier heights.The weight,the mean barrier height,and the standard deviation of the two Gaussian functions are 0.00001 and 0.99999,0.721 and 0.696,0.069 and 0.012eV,respectively.     

Numerical analysis of the mechanism of carrier transport in organic light—emitting devces

The mechanism of carrier transport in organic light-emitting devices is numerically studied,on the basis of trappedcharge-limited conduction with an exponential trap distribution.The spatial distributions of the electrical potential,field and carrier density in the organic layer are calculated and analysed.Most carriers are distributed near the two electrodes,only a few of them are distributed over the remaining part of the orgaic layer,The carriers are accumulated near the electrodes,and the remaining region is almost exhausted of carriers.When the characteristic energy of trap distribution is greater than 0.3eV.it leads to a reduction of current density.In order to improve the device efficiency,organic materials with minor traps and low characteristic energy should be chosen.The diffusion current is the dominant component near the injection electrode.whereas the drift current dominates the remaining region of the organic layer.     

Magnetization relaxation of uniaxial anisotropic ferromagnetic particles with linear reaction dynamics driven by DC/AC magnetic field

The response of uniaxial anisotropic ferromagnetic particles with linear reaction dynamics subjected to alternating current(AC) or direct current(DC) bias magnetic field is evaluated by the reaction–diffusion equation for the probability distribution function of the molecular concentration in the spherical coordinate system. The magnetization function and the probability distribution function of the magnetic particles in the reaction system are derived by using the Legendre polynomials and Laplace transform. We discuss the characteristics of magnetization and probability distribution of the magnetic particles with different anisotropic parameters driven by a DC and AC magnetic fields, respectively. It is shown that both the magnetization and the probability distribution decrease with time increasing due to the reaction process. The uniformity of the probability distribution and the amplitude of the magnetization are both affected by the anisotropic parameters.Meanwhile, the difference between the case with linear reaction dynamics and the non-reaction case is discussed.     

Level Statistics and Specific Heat of Metallic Nano—Particles

The thermodynamic properties of an ensemble of metallic nano-particles are affected by the level distribution and the level correlation between the discrete electronic energy levels.We numerically calculate the specific heat of metallic nano-particles in the canonical ensemble with an odd or even number of electrons by considering the effects of the level distribution and the level correlation.The behaviour of the specific heat at low and high temperatures,compared with the average nearest-neighbour level spacing,is also investigated.     

Approximate analytical expressions of apertured broadband beams in the far field

The approximate analytical expressions of the apertured broadband beams in the far field with Gaussian and Laguerre-Gaussian spatial modes are presented.For the radially polarized Laguerre-Gaussian beam,the result reveals that the electromagnetic field in the far field is transverse magnetic.The influences of bandwidth(Γ) and truncation parameter(C 0) on the transverse intensity distribution of the Gaussian beam and on the energy flux distribution of radially polarized Laguerre-Gaussian beam are analysed.     

The specular component of light scattering and the charac- terization of the height distribution for random surfaces

The relations between the specular reflection component of the intensity scattered by random surfaces and the height distributions of the surfaces are analyzed theoretically. In the extraction of the height distribution, both the phase and the amplitude of the specular wave are required. The measured specular intensity data versus the perpendicular component of the wave vector are used for the retrieval of the phase distribution of the specular wave, in which the Ger-chberg-Saxton iterative algorithm is employed, and the characterization of the height distribution of random surfaces is accomplished. In the experiment, two samples with Gaussian and quasi-two level height distributions, respectively, are practically measured and the results of the height probability density function obtained by light scattering method are in good accordance with those by atomic force microscopy. The method of this paper is of important significance for the characterizations and studies of random surfaces.     

A modal analysis for the acoustic radiation problems, Ⅱ. Examples

The acoustic radiation modes and the field distribution modes describe the radiation patterns of a complex vibrating surface and the field distribution patterns respectively. The physical meanings of the acoustic radiation modes and the field distribution modes are revealed by numerical method. For a sphere body, a spinning body and a rectangular body, the geometrical patterns of the acoustic radiation modes and the field distribution modes are given. The radiation mode 1 represents the radiation behavior of a monopole radiator, the radiation modes 2 through 4 represent the radiation behavior of dipole radiators respectively, and the radiation modes 5 through 9 represent the radiation behavior of quadrapole radiators respectively. The acoustic radiation modes and the field distribution modes introduce the multi-pole decomposition method into discussion of the acoustic radiation problems.     

Analysis and finite element simulation of electromagnetic heating in the nitride MOCVD reactor

Electromagnetic field distribution in the vertical metal organic chemical vapour deposition (MOCVD) reactor is simulated by using the finite element method (FEM). The effects of alternating current frequency, intensity, coil turn number and the distance between the coil turns on the distribution of the Joule heat are analysed separately, and their relations to the value of Joule heat are also investigated. The temperature distribution on the susceptor is also obtained. It is observed that the results of the simulation are in good agreement with previous measurements.     

Influence of intensity on the steady and transient state space—charge fields in photorefractive polymers

We have proven theoretically that there are sublinear,linear and superlinear relations between the response rates and total incident intensity for different cases of traps in photorefractive polymer materials.These relations were observed in inorganic photorefractive crystals many years ago.Also,the steady-state space-charge field is a function of the total incident intensity,which has also been found in inorganic photorefractive crystals.We have measured the relations of the steady-state diffraction efficiency and the response rate with respect to the total incident intensity in the photorefractive composite consisting of the polymer (N-vinylcarbazole) (PVK) doped with 4,4‘-n-pentylcyanobiphenyl (5CB) and C60.The results obtained show that the composite belongs to the case of low trap density.     

Non—equilibrium extrapolation method for velocity and pressure boundary conditions in the lattice Boltzmann method

In this paper, we propose a new approach to implementing boundary conditions in the lattice Boltzmann method (LBM). The basic idea is to decompose the distribution function at the boundary node into its equilibrium and non-equilibrium parts, and then to approximate the non-equilibrium part with a first-order extrapolation of the non-equilibrium part of the distribution at the neighbouring fluid node. Schemes for velocity and pressure boundary conditions are constructed based on this method. The resulting schemes are of second-order accuracy. Numerical tests show that the numerical solutions of the LBM together with the present boundary schemes are in excellent agreement with the analytical solutions. Second-order convergence is also verified from the results. It is also found that the numerical stability of the present schemes is much better than that of the original extrapolation schemes proposed by Chen et al. (1996 Phys. Fluids 8 2527).     

Fractional Fourier transform of Lorentz-Gauss vortex beams

An analytical expression for a Lorentz-Gauss vortex beam passing through a fractional Fourier transform (FRFT) system is derived. The influences of the order of the FRFT and the topological charge on the normalized intensity distribution, the phase distribution, and the orbital angular momentum density of a Lorentz-Gauss vortex beam in the FRFT plane are examined. The order of the FRFT controls the beam spot size, the orientation of the beam spot, the spiral direction of the phase distribution, the spatial orientation of the two peaks in the orbital angular momentum density distribution, and the magnitude of the orbital angular momentum density. The increase of the topological charge not only results in the dark-hollow region becoming large, but also brings about detail changes in the beam profile. The spatial orientation of the two peaks in the orbital angular momentum density distribution and the phase distribution also depend on the topological charge.     

Distribution Characteristics of Dirac Energy Levels in Non—Kerr Space—time

The distribution of Dirac energy levels in a non-Kerr black hole space-time is related to an arbitrary set of multiple monents determined by the parameters αn.A singular point appears on the event horizon of the black hole ,at which the Dirac energy levels have obvious distribution characteristics and are different from those in the space-time of the Kerr black hole.