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71.
This paper presents the concept of a Dielectric-lined Multiwave Cerenkov Generator(DMWCG) producing high power millimeter waves, which is investigated with a two and one half dimensional(
) electromagnetic relativistic Particle-in-Cell(PIC) simulation code. It is showed that the DMWCG can operate in a lower diode-voltage regime with much higher radiation efficiency as compared with the usual Multiwave Cerenkov Generator(MWCG). The simulation work indicates both the downshift of the wave frequency in the presence of the dielectric liner and the existence of the optima for the permittivity of the liner as well as for the magnitude of the guiding magnetic field. The required intensity of the guiding field is reduced with the introducing of the liner. The radiation is generated at the dominant frequency of 31.5GHz. The power level of 1.5GW is achieved, with radiation efficiency up to 15%. The features of parameter dependency are presented. And reasonable explanation is put forward. In addition, the enhanced propagation of the electron beam is studied in the presence of the dielectric liner. 相似文献
72.
A. Osiadacz 《国际流体数值方法杂志》1983,3(2):125-135
Finite difference methods for solving the linear model describing unsteady state flow in pipelines are considered in the present paper. These methods are compared with each other in order to determine the best one, which meets the criteria of accuracy and relatively small computation time. 相似文献
73.
Fractional low order moments have been reported as beneficial for sampling computations using the K distribution. However, it has been recently pointed out that this it not the case for the homodyned-K distribution for a tissue discrimination problem. In this paper we show that such an statement is not fully justified. To that end, we follow a standard pattern recognition procedure both to determine class separability measures and to classify data with several classifiers. We conclude that the optimum order of the moments is intimately linked to the specific statistical properties of the tissues to be discriminated. Some ideas on how to choose the optimum order are discussed. 相似文献
74.
Dikshitulu K. Kalluri Joo Hwa Lee Monzurul M. Ehsan 《International Journal of Infrared and Millimeter Waves》2003,24(3):349-365
This paper deals with the Finite Difference Time Domain (FDTD) simulation of interaction of an electromagnetic wave with a switched plasma slab. In formulating the simulation the well-known concepts of (a) total-field/scattered-field formulation (b) and PML lattice truncation are adapted to suit the simulation under consideration.FDTD is particularly well suited to handle the switched (time-varying) medium (including sudden switching) since the time varying parameters of the medium can be easily interpreted in the algorithm. The technique is applied to the difficult problem of interaction of an electromagnetic pulse source wave of frequency 0 and a gaussian envelope with a newly created plasma slab of time-varying and space varying electron density profile. The creation of a pulse of Wiggler magnetic field in the slab is illustrated. 相似文献
75.
Hagslätt H Jönsson B Nydén M Söderman O 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2003,161(2):138-147
Pulsed field gradient NMR diffusometry is a promising tool for investigating structures of porous material through determinations of dynamic displacements of molecules in porous systems. A problem with this approach is the lack of closed analytical expressions for echo-decays in anything but idealized pore geometries. We present here an approach based on calculating the appropriate diffusion propagator by means of finite element calculations. The suggested method is quite general, and can be applied to arbitrary porous systems. The protocol for the calculations is outlined and we show results from some different cases: diffusion in confined geometries and in systems that are spatially inhomogeneous with respect to concentration. 相似文献
76.
用Matlab软件对大气压均匀辉光放电等离子体(OAUGDP)激励器系统的电特性进行了仿真。在仿真模型中,等离子体放电被建模成一个电压控制的电流源:当加在气隙上的电压超过等离子体产生电压时,该受控电流源接通;电流源的输出电流和所加电压之间遵循幂律。建立了一个OAUGDP激励器系统中等离子体放电的电路模型。仿真结果与实际激励器系统的实验数据很吻合。仿真结果表明,在不同的运行条件下,放电电流与电压之间遵循不同的指数幂律,仿真放电电流波形也不同。 相似文献
77.
Demetre J. Economou 《Applied Surface Science》2007,253(16):6672-6680
Ion-ion plasmas can form in the late afterglow of pulsed discharges or downstream of continuous wave discharges in electronegative gases. In ion-ion plasmas, negative ions replace electrons as the negative charge carriers. In the absence of electrons, ion-ion plasmas behave quite differently compared to conventional electron-ion plasmas. Application of a radio frequency bias to a substrate immersed in an ion-ion plasma can be used to extract alternately positive and negative ions, thereby minimizing charging on device features during micro-device fabrication. Ion-ion plasmas are also important in negative ion sources, dusty plasmas, and the D-layer of the earth's atmosphere. 相似文献
78.
The paper tackles the problem of pricing, under interest-rate risk, a default-free sinking-fund bond which allows its issuer to recurrently retire part of the issue by (a) a lottery call at par, or (b) an open market repurchase. By directly modelling zero-coupon bonds as diffusions driven by a single-dimensional Brownian motion, a pricing formula is supplied for the sinking-fund bond based on a backward induction procedure which exploits, at each step, the martingale approach to the valuation of contingent-claims. With more than one sinking-fund date, however, the pricing formula is not in closed form, not even for simple parametrizations of the process for zerocoupon bonds, so that a numerical approach is needed. Since the computational complexity increases exponentially with the number of sinking-fund dates, arbitrage-based lower and upper bounds are provided for the sinking-fund bond price. The computation of these bounds is almost effortless when zero-coupon bonds are as described by Cox, Ingersoll and Ross. Numerical comparisons between the price of the sinking-fund bond obtained via Monte Carlo simulation and these lower and upper bounds are illustrated for different choices of parameters. 相似文献
79.
80.
Yang Li Jian Dong Ke Chen Wei Guo 《International Journal of Infrared and Millimeter Waves》2008,29(7):663-672
This paper presents a signal-level simulation model for simulating the process that antenna array of Aperture Synthesis Radiometer
(ASR) collecting thermal radiation and transforming thermal radiation signal into radio frequency (RF) signal. By using the
equivalent complex baseband signals to represent the practical thermal radiation and RF signals, simulation efficiency is
improved significantly. The statistic characteristics of simulation results are found to match the corresponding theoretical
analysis well. Results of an imaging simulation experiment show that this model can be employed in ASR system-level simulator
design. 相似文献