A hybrid finite element method for near bodies of revolution (EM scattering)

A genetic formulation for a hybrid finite element solution for three-dimensional electromagnetic scattering is given using the equivalent current approach. The major computational tasks involved in monostatic scattering calculations are analyzed and compared as a function of the method of implementing the near-field radiation condition, i.e. method of moments, model expansion, and body of revolution (BOR). A method utilizing a BOR formulation that addresses these computational issues is given. This BOR implementation utilizes Hermite cubic basis functions and a variable number of modes per basis function in order to achieve the greatest efficiency. The combined field integral equation formulation is used to eliminate nonphysical resonance of the mesh boundary. Examples are given showing the efficiency and accuracy of this BOR code by itself, and as part of this hybrid finite-element method.<>     

Continuous potential Maxwell solutions on nodal-based finiteelements

A nodal-based finite-element approach for computing electric fields in heterogeneous media is presented. The primary calculation is formulated in terms of continuous potentials, so that no special care is required on element assembly at dielectric interfaces. The resulting Galerkin weak-form matrices exhibit the special Helmholtz structure, which guarantees the absence of parasitic solutions in driven problems with physically well-posed boundary conditions. The enhanced sparsity of the Helmholtz form mitigates the extra coupling effort associated with introduction of a fourth degree of freedom relative to direct E solution. E can be extracted from the computed potentials as a postprocessing step either at nodal positions or element centroids. Solutions obtained with this approach for several benchmark and practical problems are shown to be parasite-free and essentially indistinguishable from previously reported direct E computations     

Accurate solutions of Maxwell's equations around PEC corners andhighly curved surfaces using nodal finite elements

A method is presented for computing accurate solutions of Maxwell's equations in the presence of perfect electrical conductors (PECs) with sharp corners and highly curved surfaces using conventional nodal finite elements and a scalar/vector (S/V) potential formulation. This technique approximates the PEC with an impedance boundary condition (IBC) where the impedance is small. Critically, it couples both potentials through this boundary condition, rather than setting the scalar potential to zero. This permits cancellation of the tangential components of the vector potential, resulting in an accurate normal electric field. The cause for the inaccuracies that nodal methods experience In the presence of sharp PEC corners or highly curved PEC surfaces is elucidated. It is then shown how the inclusion of the scalar potential cures these deficiencies permitting accurate solutions. Spectral analysis of the resulting finite element matrices are shown validating the boundary conditions used. Examples are presented comparing a benchmark solution, conventional PEC and IBC boundary conditions, and the new S/V potential IBC on a PEC wedge and PEC ellipse. In both cases the new S/V IBC produces superior results     

A hybrid finite element method for 3-D scattering using nodal andedge elements

A hybrid finite element method for three-dimensional scattering is presented and numerical examples shown. This approach, which couples finite element discretization with the method of moments, is particularly well suited for monostatic radar cross section calculations. The method is based on a scalar and vector potential formulation of Maxwell's equations, the use of nodal elements, and a highly efficient body of revolution implementation of the method of moments. Combined nodal and edge elements are employed to accurately model fields around corners and edges. A curvature-based sampling criterion is derived and shown to ensure accurate answers for highly curved scatterers. Numerical results and Cray computer timings are compared with published results for an edge element code using radiation boundary conditions     

Study of tungsten oxide and sulfate interactions on doubly-doped zirconia aerogels

A zirconia aerogel, prepared by a sol-gel route followed by supercritical drying, was doped with both tungstate and sulfate by sequential incipient wetness impregnations. The role of the dopants and activation temperature on the physical and chemical properties was studied. The materials were characterized by nitrogen adsorption, X-ray diffraction, n-butane isomerization, Raman and infrared spectroscopy. Tungstate and sulfate were catalytically active over non-overlapping ranges of activation temperature and thus offered no synergistic catalytic effects. The effects of the two dopants on each other appeared to be primarily physical. This revised version was published online in July 2006 with corrections to the Cover Date.     

Preparation and characterization of zirconia-phosphate aerogels

Zirconia-phosphate aerogels were prepared by two methods: a one-step sol-gel synthesis followed by supercritical drying and an incipient wetness impregnation synthesis of a calcined zirconia aerogel. These samples were characterized by nitrogen adsorption, X-ray diffraction, infrared spectroscopy, and 1-butene isomerization. We identified both the conditions when zirconia-phosphate aerogels possess Bronsted acid sites, and the phosphate species responsible for their generation.     

Odortypes: their origin and composition

Odors that distinguish one individual from another member of the species and are determined by polymorphic genes are called odortypes. Odortypes and their considerable societal significance have been studied intimately only in mice and mainly with respect to the genes of the major histocompatibility complex. Further understanding and the matter of human relevance have been hampered by the apparent restriction of odortype expression to urine. The present finding that odorants comprising prerenal odortypes are already present in blood, albeit in masked form, affords the basis of a comprehensive view of odortypes. Accordingly, major histocompatibility complex and other polymorphic genes of antiquity are seen inter alia as agents of normal variation, which entails quantitative variation in output of odorant metabolites. Relatively few such normal variations should suffice for a vast range of compound odors whose specificity is determined by combinative assortment of the same set of individual volatile compounds.     

Applications of potentials to finite element modeling of Maxwell'sequations

A scalar and vector potential formulation for Maxwell's equations at low frequency is presented which is suitable for discretization with conventional node-based finite elements. The formulation is based on the Lorentz gauge and results in coupled Helmholtz equations for the potentials. With a proper combination of boundary conditions, the solutions are free of spurious modes for the nonresonant cases of interest. Examples are presented for cases of electromagnetic borehole sonde modeling and hyperthermia treatment planning     

GMSolid: Interactive Modeling for Design and Analysis of Solids

In GMSolid, designers can work directly with primitives to build complex solids. This and GMSolid's friendliness, flexibility, and 3-D feel make it superior to wireframe CAD tools.     

Fetal H-2 odortypes are evident in the urine of pregnant female mice

PURPOSE: Patients with insulin-dependent diabetes mellitus (IDDM) are especially susceptible to microangiopathic complications such as nephropathy, retinopathy, and neuropathy. Microangiopathic changes are also the most important findings in histopathologic studies of the inner ear and central nervous systems in diabetic subjects. No previous studies have measured acoustic-reflex latencies (ARL) or amplitudes (ARA) in patients with IDDM. ARL and ARA reflect the function of the acoustic-reflex arch. Furthermore, possible changes in the tympanic membrane, ossicular chain, and stapedius muscle may affect the shape of acoustic-reflex. SUBJECTS AND METHODS: Acoustic-reflex thresholds, latencies, and amplitudes were studied in 53 patients with IDDM and 42 randomly selected nondiabetic control subjects, aged between 20 and 40 years, using the Madsen Model ZO 73 Impedance Bridge (Madsen Electronics, Copenhagen, Denmark). Subjects with an abnormal tympanic membrane, conductive hearing loss, and known cause for hearing impairment eg, noise damage, were excluded from the study. RESULTS: There were no differences between control and diabetic subjects in the contralateral acoustic-reflex thresholds. In contrast, patients with IDDM had longer ARLs and decreased ARAs compared with those of control subjects. ARA amplitude had linear correlation with the amplitude of tympanogram, whereas ARL had no linear correlation with auditory brainstem latencies in the same study subjects. Acoustic-reflex responses in insulin-dependent diabetic patients were not associated with the duration of diabetes, metabolic control, microangiopathy, or neuropathy. CONCLUSIONS: Prolonged ARLs and decreased ARAs in patients with insulin-dependent diabetes are probably caused more by the stiff middle ear system than disturbances in the brainstem.