An electrostatic model of the cutoff probe

Although a circuit model of the previously developed cutoff probe for plasma diagnostics elucidates the basic physics and contributes to the development of the cutoff probe, a theoretical validation of the circuit model has yet to be accomplished. For theoretical validation, this paper proposes a one-dimensional electrostatic model, or 1dESM, of the cutoff probe, which is based on electrostatic field analysis in a finite two-wire approximation. The transmission spectrum S₂₁ calculated by the 1dESM shows a good agreement with that from a three-dimensional full electromagnetic wave simulation for various electron densities and pressures. Based on the 1dESM, the formation mechanism of the S₂₁ of the cutoff probe was analyzed. Theoretical validation of the circuit model was then achieved by comparing the circuit model with the 1dESM. This paper is believed to contribute to a better understanding of the cutoff probe and to the development of cutoff probe models.     

Optimization of an 8-Channel Loop-Array Coil for a 7 T MRI System with the Guidance of a Co-Simulation Approach

Minimizing coupling between coil elements is technically challenging in designing large-sized, volume-type phased-array coils for human head imaging at ultrahigh fields, e.g., 7 T. As a widely used decoupling method, the capacitive decoupling method has shown excellent performance for loop array. However, building a multi-channel loop array with capacitive decoupling method is laborious that tuning frequency and matching of one coil element will affect adjacent elements and even next adjacent elements. In this study, we made an 8-channel loop-array transmit/receive radio-frequency coil on a 7 T magnetic resonance imaging system with the guidance of frequency domain three-dimensional electromagnetic and radio-frequency circuit co-simulation. The position of decoupling capacitors was investigated and values of all capacitors were predicted from co-simulation. The co-simulation approach cost about 2 days and the error of the predicted and practical capacitance was <5 %. To demonstrate the accuracy of simulation, we evaluated the simulated and measured S-parameter matrixes and B ₁ ⁺ profiles in a birdcage-like excitation mode on a cylindrical water phantom. In addition, B ₁ ⁺ maps and images of human head were shown with the fabricated coil. To demonstrate the parallel imaging performance of this coil array, GRE images using GRAPPA acceleration with the reduction factor R of 1, 2, 3, and 4 were acquired.     

Calculation of structure factors for a simple model of adsorption on a surface by real-space renormalization-group method

The structure factor S(q) of a simple model describing adsorption on a two-dimensional surface is computed by real-space renormalization-group technique for T ? T_c. The method used is based on first-order cumulant expansion implemented with an ad hoc recursion relation for the coupling constants. The model is equivalent to an antiferromagnetic Ising model in an external field.     

Crystal field interpretation of the magnetic properties of UX2 compounds (X = P,As, Sb,Bi)

Based on the crystal field model and molecular field approximation, an interpretation of the magnetic properties of uranium dipnictide series is given. In this phenomenological approach a simple, 2-parameter crystal field model is adquate to explain the available magnetic data (in particular μ_ord'T_ord' and S_m) along the UX₂ series, including the anomaly in the induced ordered moments of UP₂ and UAS₂.     

An equivalent circuit model of a novel photodetector

An equivalent circuit model of a novel photodetector (PD) is proposed in this article. We use this model to describe the relation between the bias voltage and current (I–V), also the bias voltage and capacitance(C–V) of this kind of novel PD. The circuit model could optimize the structure of the circuit and could be linked with the readout circuit. According to the comparison between the simulation result and the experimental result by circuit testing, we could find they are in good agreement, which proving the correctness of the equivalent circuit model. The signification of this equivalent circuit model is to design an optimal readout circuit (ROIC) for the novel PD.     

Consistent cluster model description of the electromagnetic properties of lithium and beryllium nuclei

We calculate the electromagnetic properties of lithium and beryllium nuclei within a resonating group model using bare charges and g-factors. For ⁶Li we give results for reduced transition strengths and explain the tiny quadrupole moment. For ⁷Li and ⁷Be we compute electromagnetic moments and transitions between bound states. Furthermore we reproduce the existing data on the radiative captures ³He(α, γ)⁷Be and ³H(α, γ)⁷Li. In the ⁷Li case the calculations indicate an increase of the astrophysical S- factor for decreasing energy which might have astrophysical consequences. We show that closed channels do not influence results on the astrophysical S-factor at low energy. Finally we demonstrate that the polarisability of ⁷Li originates from the virtual break-up at low energies. In this case, the ⁶Li + n channels contribute appreciably.     

Modal series solution for an epidemic model

In this article, we generalize a recently proposed method to obtain an exact general solution for the classical Susceptible, Infected, Recovered and Susceptible (SIRS) epidemic mathematical model. This generalization is based upon the nonlinear coupling of two frequencies in an infinite modal series solution. It is shown that these series provide a nonstandard approach in order to obtain an accurate analytical solution for the classical SIRS epidemic model. Numerical results of the SIRS epidemic model for real and complex frequencies are included in order to test the validity and reliability of the method. This method could be applied to a wide class of models in physics, chemistry or engineering.     

A comprehensive equivalent circuit model for the study of thermal and spectral characteristics in laser diodes

An improved electrical equivalent model for multimode laser diode incorporating thermal effects and spectral behavior is developed from the multi mode rate equations. The temperature dependent optical power, wavelength shift, spectral widths are determined in the dc sweep simulations. The output power, frequency chirp and temperature rise are evaluated under pulse modulation conditions. Further, the laser diode bandwidth dependence on temperature is also evaluated. Analysis is carried out in the temperature range of 283–343 K, by simulating the equivalent circuit, using PSpice circuit simulator.     

Hydrogen damage in AISI 304 stainless steel studied by Doppler broadening

Hydrogen damage of AISI 304 stainless steel has been systemically investigated by measuring Doppler broadening of positron annihilation. Defect profiles of the S-parameter, the low-momentum annihilation fraction as a function of positron incident energy up to 30 keV (i.e. ∼1 μm depth) have been analyzed. Experimental results show that hydrogen damage between the surface and the bulk has a significant variation with depth, and strongly depends on the condition of hydrogen-charging, i.e. current density and charging time. It has been suggested that the increase in S-parameter near the surface after hydrogen-charging mainly comes from the formation of voids; however the increase in S-parameter in the bulk after hydrogen-charging mainly comes from the production of structural defects (dislocations). Defect densities induced due to hydrogen-charging in some cases (e.g. dislocation density in the bulk) are estimated based on the simple two-state trapping model.     

A unitary isobar model for pion photo- and electroproduction on the proton up to 1 GeV

A new operator for pion photo- and electroproduction has been developed for nuclear applications at photon equivalent energies up to 1 GeV. The model contains Born terms, vector mesons and nucleon resonances (P₃₃(1232), P₁₁(1440), D₁₃(1520), S₁₁(1535), F₁₅(1680), and D₃₃(1700)). The resonance contributions are included taking into account unitarity to provide the correct phases of the pion photoproduction multipoles. The Q² dependence of electromagnetic resonance vertices is described with appropriate form factors in the electromagnetic helicity amplitudes. Within this model we have obtained good agreement with the experimental data for pion photo- and electroproduction on the nucleon for both differential cross sections and polarization observables. The model can be used as a starting point to predict and analyze forthcoming data.     

The external demagnetizing factor and the static characteristic loop

In this paper a proposal is put forward for the calculation of the shearing factor N_S linked to the well known, demagnetization coefficient N_D, from the data of a sheared saturation loop, obtained by a non-toroidal, open circuit hysteresis measurement. Following that, the paper illustrates the way to recover the real static loop data from an open circuit, measured data. The proposal is based on the hyperbolic model. The proposed method was illustrated on the tests carried out on two closed and open toroidal samples, mimicking the demagnetization effect of the open circuit VSM measurement, made of NO Fe–Si electrical steel sheets. These test results, presented here, agree very well with the calculated results, based on the hyperbolic modeling.     

The nonextensive parameter for nonequilibrium electron gas in an electromagnetic field

The nonextensive parameter for nonequilibrium electron gas of the plasma in an electromagnetic field is studied. We exactly obtained an expression of the q$q$-parameter based on Boltzmann kinetic theories for plasmas, where Coulombian interactions and Lorentz forces play dominant roles. We show that the q$q$-parameter different from unity is related by an equation to temperature gradient, electric field strength, magnetic induction as well as overall bulk velocity of the gas. The effect of the magnetic field on the q$q$-parameter depends on the overall bulk velocity. Thus the q$q$-parameter for the electron gas in an electromagnetic field represents the nonequilibrium nature or nonisothermal configurations of the plasma with electromagnetic interactions.     

Positron beam studies on polyaniline and Ag-coated polyaniline

The effect of doping of the polyaniline emeraldine base (PEB), with Ni as well as Ni over layer coating has been investigated using variable low energy positron beam. Depth-resolved Doppler S-parameter measurements have been performed on undoped, Ni-doped polyaniline (PANI), and Ag (40 nm) film deposited PANI samples. Significant variation in S-parameter is observed for undoped and Ni-doped PANI. The size of the free volume hole has shifted to lower values upon doping with Ni as compared to that of undoped PANI, which is consistent with the conductivity measurements. For Ag-coated PANI systems, the S vs. E_p curves show distinct changes at the surface and interior regions. These results are discussed in the light of changes in free volume hole size distribution.     

An analytical model for coplanar waveguide on silicon-on-insulator substrate with conformal mapping technique

In this paper, the authors present an analytical model for coplanar waveguide on silicon-on-insulator substrate. The four-element topological network and the conformal mapping technique are used to analyse the capacitance and the conductance of the sandwich substrate. The validity of the model is verified by the full-wave method and the experimental data. It is found that the inductance, the resistance, the capacitance and the conductance from the analytical model show they are in good agreement with the corresponding values extracted from experimental S-parameter until 10 GHz.     

A k-band broadband monolithic distributed frequency multiplier based on nonlinear transmission line

A fabrication technology of GaAs planar Schottky varactor diode (PSVD) is successfully developed and used to design and manufacture GaAs-based monolithic frequency multiplication based on 23-section nonlinear transmission lines (NLTLs) consisting of a coplanar waveguide transmission line and periodically distributed PSVDs. The throughout design and optimization procedure of 23-section monolithic NLTLs for frequency multiplication in the k-band range is based on a large signal equivalent model of PSVD extracted from small-signal S-parameter measurements. This paper reports that the distributed SPVD exhibits a capacitance ratio of 5.4, a normalized capacitance of 0.86 fF/μm2 and a breakdown voltage in excess of 22 V. The integrated 23-section NLTLs fed by 20-dBm input power demonstrates a 26-GHz peak second harmonic output power of 14-dBm with 25.3% conversion efficiency in the second harmonic output frequency range of 6 GHz-26 GHz.     

Slow positron beam study of corrosion-related defects in pure iron

Corrosion-related defects of pure iron were investigated by measuring Doppler broadening energy spectra (DBES) of positron annihilation and positron annihilation lifetime (PAL). Defect profiles of the S-parameter from DBES as a function of positron incident energy up to 30 keV (i.e. ∼1 μm depth) were analyzed. The DBES data show that S-parameter increases as a function of positron incident energy (mean depth) after corrosion, and the increase in the S-parameter is larger near the surface than in the bulk due to corrosion. Furthermore, information on defect size from PAL data as a function of positron incident energy up to 10 keV (i.e. ∼0.2 μm depth) was analyzed. In the two-state trapping model, the lifetime τ₂ = 500 ps is ascribed to annihilation of positrons in voids with a size of the order of nanometer. τ₁, which decreases with depth from the surface to the bulk, is ascribed to the annihilation of positrons in dislocations and three-dimensional vacancy clusters. The corroded samples show a significant increase in τ₁ and the intensity I₂, and near the surface the corroded iron introduces both voids and large-size three-dimensional vacancy clusters. The size of vacancy clusters decreases with depth.     

Magnetizations of a nanoparticle described by the transverse Ising model

The characteristic influences of size S, exchange interaction and transverse field on the longitudinal and transverse magnetizations of a ferroelectric small particle described by the transverse Ising model are investigated by the use of the standard mean-field theory. In particular, the longitudinal magnetization of a nanoparticle is strongly affected by the surface situations. The effective exponent β_eff of the longitudinal magnetization is also studied. We find some characteristic phenomena of β_eff, depending on the values of S and the ratios of the physical parameters. In relation of recent investigations, the thermal variations of longitudinal and transverse magnetizations in the nanoparticle, consisting of a ferromagnetic core with size S=3 surrounded by a ferromagnetic surface shell with an antiferromagnetic inter-shell coupling, are examined and some typical ferrimagnetic behaviors are found in them. In relation to these phenomena, the effects of surface dilution on the magnetizations are investigated and some novel features are found in the system with size S=3 surrounded by such a ferromagnetic diluted surface shell.     

Computer Aided Analysis of Nonlinear Distortion for Laser Diode under Intensity Modulation

1.IntroductionNonlineardistortionisanimportantindextoappreciateasubcarriermultiplexing(SCs)lightwavetransmissionsystem.Itconsistsofthedistortionoflaserdiode(LD)module,distortionoffiber--optictransmissionsystemandthatofreceiversystem,amongwhichLD'shasagreatinfluenceonsystem'scharacteristicsbecauseitisanonlineardeviceinitself.LDnonlineardistortioncomesfromP--Icharacreristicsandinteractionbetweenphotonsandelectrons.WhenLDworksatlineararea,theformercanbeneglectedandthelatteristhemain,whichisd…     

基于二极管精确电路模型的183GHz分谐波混频器设计

针对亚毫米波混频二极管管对电路模型不够精确的问题,采用场路结合协同分析,将进出二极管的频率信号分类处理,建立了一种应用于亚毫米波分谐波混频器电路的反向并联二极管对精确电路模型。基于获取的管对精确电路模型,建立了全局性的分谐波混频器电路的集总元件等效电路模型,设计并实现了一款183GHz分谐波混频器。测试结果表明混频器在本振频率为92GHz、功率为2mW,射频频率176~192GHz范围内,双边带变频损耗小于6.8dB,等效噪声温度小于800K,在182GHz测得最小双边带变频损耗为4.9dB,与仿真数据吻合较好。