Numerical stability of nonorthogonal FDTD methods

In this paper, a sufficient test for the numerical stability of generalized grid finite-difference time-domain (FDTD) schemes is presented. It is shown that the projection operators of such schemes must be symmetric positive definite. Without this property, such schemes can exhibit late-time instabilities. The origin and the characteristics of these late-time instabilities are also uncovered. Based on this study, nonorthogonal grid FDTD schemes (NFDTD) and the generalized Yee (GY) methods are proposed that are numerically stable in the late time for quadrilateral prism elements, allowing these methods to be extended to problems requiring very long-time simulations. The study of numerical stability that is presented is very general and can be applied to most solutions of Maxwell's equations based on explicit time-domain schemes     

Isopropylbenzene catabolic pathway in Pseudomonas putida RE204: nucleotide sequence analysis of the ipb operon and neighboring DNA from pRE4

Middle cerebral artery occlusion (MCAo) leads to brain cell death. However, quantitation of injured brain cells and inflammatory cells after MCAo has not been determined in the rat. Transient (2 h) MCAo was therefore induced in male Wistar rats by means of an intraluminal monofilament. Immunohistochemical and histochemical procedures performed at 46 h after MCAo were used to identify specific cellular populations in ischemic and control rats (n = 11). In the ischemic core of the lesion, approximately 24.7% of cells disappeared. Forty-four point eight percent of parenchymal cells consisted of intact (13.0%) or reversibly injured swollen (7.6%) and scalloped/shrunken dark (24.2%) cells. The percentage of irreversibly damaged cells was 55.2%, and included 49.9% necrotic cells (10.5% red and 39.4% ghost) and 5.4% apoptotic cells. In the inner boundary zone of the lesion, 15.9% of cells disappeared. Viable cells constituted 62.0% of all remaining cells. Neutrophils and macrophages were localized to this area. In the outer boundary zone of the lesion, 9.0% of cells disappeared. Viable cells constituted 91.6% of all remaining cells. The ratio of apoptotic to necrotic cells was 1:9, 1:6, 1:13 in the ischemic core, inner and outer boundary zones, respectively. Our data suggest the presence of three zones within the ischemic lesion: the core, and inner and outer boundaries. At 46 h after 2 h of MCAo the ischemic lesion is highly heterogeneous containing relatively large percentages of morphologically intact cells, suggesting the possibility of an extended window of therapeutic opportunity.     

The efficient implementation of the surface impedance boundarycondition in general curvilinear coordinates

This paper discusses the efficient incorporation of skin-effect losses into the nonorthogonal finite-difference time-domain technique. A survey of previous work is presented and it is shown that the exponential approximations used by previous methods may lead to considerable error when good conductors are modeled using a fine time discretization. Subsequently, an improved exponential approximation is given and applied to various curved conducting waveguide surfaces using the nonorthogonal finite-difference time-domain technique     

Analysis of the electromagnetic scattering by thick gratings usinga combined FEM/MM solution

The problem of diffraction by a thick, conducting grating situated in an inhomogeneous dielectric slab is investigated using the generalized network formulation. This formulation combines the method of moments and the finite-element method, permitting the treatment of periodic elements of arbitrary cross section and inhomogeneous profiles. Solutions are presented for both transverse electric (TE) and transverse magnetic (TM) polarizations. Transmission gratings composed of rectangular conductors filled with dielectric materials of arbitrary profiles are studied     

Perfectly matched layer media with CFS for an unconditionallystable ADI-FDTD method

A perfectly matched layer (PML) medium with complex frequency shifted (CFS) constitutive parameters is introduced for the three-dimensional alternating direction implicit (ADI) formulation of the finite-difference time-domain (FDTD) method. The absorbing boundary is implemented using the convolutional PML (CPML) approach. It is demonstrated that the resulting ADI-CPML scheme is unconditionally stable. The effectiveness of the absorbing medium as a function of the time step is also demonstrated. The proposed method has the advantage that it allows the application of the ADI method to low-frequency analysis     

An anisotropic perfectly matched layer-absorbing medium for thetruncation of FDTD lattices

A perfectly matched layer (PML) absorbing material composed of a uniaxial anisotropic material is presented for the truncation of finite-difference time-domain (FDTD) lattices. It is shown that the uniaxial PML material formulation is mathematically equivalent to the perfectly matched layer method published by Berenger (see J. Computat. Phys., Oct. 1994). However, unlike Berenger's technique, the uniaxial PML absorbing medium presented in this paper is based on a Maxwellian formulation. Numerical examples demonstrate that the FDTD implementation of the uniaxial PML medium is stable, equal in effectiveness as compared to Berenger's PML medium, while being more computationally efficient     

The coming age of telecommunications in psychological research and practice.

Rapid and far-reaching technological advances are revolutionizing the ways in which people relate, communicate, and live their daily lives. Technologies that were hardly used a few years ago, such as the Internet, e-mail, and video teleconferencing, are becoming familiar methods for modern communication. Telecommunications will continue to evolve quickly, spawning telehealth applications for research and the provision of clinical care in communities, university settings, clinics, and medical facilities. The impact on psychology will be significant. This article examines the application of developing technologies as they relate to psychology and discusses implications for professional research and practice. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A combined FEM/MoM approach to analyze the plane wave diffractionby arbitrary gratings

The diffraction of TE- and TM-polarized plane waves by planar gratings is numerically analyzed using a combined finite-element-method/method-of-moments (FEM/MoM) algorithm based on the generalized network formulation. The interior region, treated using the FEM, is truncated to a single unit cell with the introduction of an exact periodic boundary condition, which is enforced as a natural boundary condition. Using the FEM to compute the fields within the periodic structure allows gratings of arbitrary cross section and material composition to be efficiently modeled     

Electromagnetic transmission through inhomogeneously filled slotsin a thick conducting plane-arbitrary incidence

The penetration of an arbitrarily incident electromagnetic wave through a slot filled with inhomogeneous material in a thick conducting plane is analyzed. The solution is obtained via a combined finite-element method/method of moments algorithm based on the generalized network formulation. The discretization of the generalized network formulation is performed via the method of moments. The finite-element method is then used to compute the fields within the inhomogeneous interior cavity region, leading to the construction of the interior aperture admittance matrix. It is shown that with the use of entire domain basis functions, the construction of the aperture admittance matrices is computationally efficient. Furthermore, this method is attractive since it preserves the sparsity of the finite-element method matrix, reducing computational memory requirements. Some examples of the penetration of inhomogeneously filled slots of various cross sections are presented     

Effect of a finite ground plane on radiated emissions from acircular loop antenna

A thin-wire circular loop antenna located above a perfectly conducting square plate is analyzed by a physical optics (PO) method. The electric field integral equation (EFIE) is solved using the method of moments to compute the current on the loop in the presence of an infinite ground plane whereby the edge effects of the plate on the loop current are neglected. The current distribution on the loop is obtained from a full-wave Fourier series analysis which requires no matrix inversion. We then use physical optics to compute the current induced on the plate in terms of the incident magnetic-field intensity. Our aim is to compare the PO solution with results obtained from a mixed wire-patch MOM code and explore its accuracy as a function of plate size and loop height. The benefits are considerable reduction in analytical and computational efforts and much less CPU time