A new procedure of point-matching method for calculating theabsorption and scattering of lossy dielectric objects

A method of numerically calculating the electromagnetic scattering and absorption by dielectric objects of high aspect ratios and composite geometrics has been developed. The solution procedure is based on expanding the scattered and internal fields in terms of multiple spherical vector wave functions, using point-matching to satisfy the boundary conditions and the least-square method to solve the resulting system of equations. The unique feature of this technique is that it utilizes multiple spherical expansions to describe the fields both inside and outside the object. The various parameters used to examine the convergence of the solution are discussed; they include the number of subdomain expansions interior and exterior to the object, the number of terms in each expansion and the advantages of the least-square method of solution. The new method was found suitable for making calculations for objects with aspect ratios as high as nine, and even for objects with composite geometries, including a capped cylinder and an object that consists of a spherical and a prolate spheroidal section. Numerical results were compared with results based on volume integral equations and method of moments, and excellent agreement was found     

Absorption Characteristics of Prolate Spheroidal Models Exposed to the Near Fields of Electrically Small Apertures

Irradiation of prolate spheroidal models of biological models by the near fields of electrically small apertures is analyzed. The solution procedure involves the replacement of the aperture source by an equivalent configuration of electric and magnetic dipoles. The specific absorption rate (SAR) induced in the irradiated object is then calculated using the extended boundary condition method (EBCM). Numerical results are presented for the exposure case where the incident electric field at the spheroid location is parallel to the major axis of the model. This polarization is associated with the maximum low-frequency absorption in biological models and, hence, is the most important polarization case in microwave dosimetry.     

A method for LEFM analysis of RPV during SBLOCA

A somewhat simplified two-dimensional linear elastic fracture mechanics (LEFM) model of the beltline of a reactor pressure vessel is presented. The fracture mechanics model used tends to be conservative in the sense that it ignores possible beneficial effects of warm prestressing and cladding.

For LEFM studies that require a large number of analyses on the same geometry but with different loads and material toughnesses, the superposition principle is an accurate and simple method to determine the stress intensity factor K₁, provided that K₁ due to a unit load (called K* in this paper), acting on an arbitrary point on the crack surface is known. The details of the superposition principle and the procedure used for determining K* have been presented.

Once these K* are determined for a specific geometry, then the determination of K₁ for the same geometry can be made accurately and in a manner that permits parametric studies involving thousands of individual analyses. It is believed that the error in the K₁ values so determined is less than 3·5%.

An example of the use of the simplified model for a parametric analysis is also presented.     

Accuracy of Digital Image Correlation for Measuring Deformations in Transparent Media

Experimental models to measure spatial deformation patterns within a soil mass are typically limited by the fact that soil sensors do not provide a continuous image of the measured continuum. Additionally, soil sensors exhibit static and dynamic characteristics that are different from those of the surrounding soils and therefore can change the response of the measured continuum. The fundamental premise of this research is that transparent synthetic soil surrogates can be used to overcome these difficulties using digital image correlation (DIC). A system consisting of a laser source and a line-generating lens was used to optically slice the transparent synthetic soil models. A digital camera was used to capture images of the slices before and after deformation. This paper presents a new technique for quantifying spatial deformation throughout transparent synthetic soil models using DIC. The accuracy of the DIC technique was evaluated based on a scheme of predefined digital movement of synthetic soil images. Finally, a model consisting of a strip footing on a synthetic transparent soil is presented. The spatial deformations in the model are evaluated using the proposed DIC methodology and compared with the result of finite-element analysis.     

Black tea and mammary gland carcinogenesis by 7,12-dimethylbenz[a]anthracene in rats fed control or high fat diets

Epidemiological studies suggest that tea may reduce cancer risk, and in laboratory rodents, chemopreventive effects of tea or purified extracts of tea have been demonstrated in lung, gastrointestinal tract and skin. There is some evidence of chemoprevention by tea in the mammary gland, but the data are not conclusive. In order to evaluate more fully the possible influence of black tea on 7,12-dimethylbenz[a]anthracene (DMBA)-induced mammary gland tumors in the female S-D (Sprague-Dawley) rat, three large studies were performed: experiment 1, tumorigenesis in rats fed AIN-76A diet and given 25 mg/kg DMBA and 1.25 or 2.5% whole tea extract or water to drink; experiment 2, tumorigenesis in rats given 15 mg/kg DMBA and the same diet and fluids as in experiment 1; experiment 3, tumorigenesis in rats fed control or HF (high fat, corn oil) diet and given 15 mg/kg DMBA and 2% tea or water to drink. Tea was given throughout the experiment; DMBA was given by gastric gavage at 8 weeks of age. There was no consistent effect of tea on tumorigenesis in rats fed AIN-76A diet; there was, however, evidence in experiment 3 of a reduction of tumorigenesis by tea in rats fed the HF diet. In experiment 3, rats fed the HF diet and given water showed the expected increase in tumor burden (number and weight) compared with rats fed control diet. However, rats fed the HF diet and given 2% tea showed no increase in tumor burden; their tumor burden was significantly lower than in rats fed the HF diet and given water (P < 0.01) and was not different from rats fed control diet and given water or tea. In addition, in experiment 3, the number of malignant tumors per tumor-bearing rat was increased by the HF diet in water-drinking rats (P < 0.01) but not in tea-drinking rats. Therefore, it appears that tea partially blocked the promotion of DMBA-induced mammary tumorigenesis by the HF diet.     

Performance optimization of Stirling engines

The search for an engine cycle with high efficiency, multi-sources of energy and less pollution has led to reconsideration of the Stirling cycle. Several engine prototypes were designed but their performances remain relatively weak when compared with other types of combustion engines. In order to increase their performances and analyze their operations, a numerical simulation model taking into account thermal losses has been developed and used, in this paper, to optimize the engine performance. This model has been tested using the experimental data obtained from the General Motor GPU-3 Stirling engine prototype. A good correlation between experimental data and model prediction has been found. The model has also been used to investigate the influence of geometrical and physical parameters on the Stirling engine performance and to determine the optimal parameters for an acceptable operational gas pressure.     

Design and performance optimization of GPU-3 Stirling engines

To increase the performance of Stirling engines and analyze their operations, a second-order Stirling model, which includes thermal losses, has been developed and used to optimize the performance and design parameters of the engine. This model has been tested using the experimental data obtained from the General Motor GPU-3 Stirling engine prototype. The model has also been used to investigate the effect of the geometrical and physical parameters on Stirling engine performance and to determine the optimal parameters for acceptable operational gas pressure. When the optimal design parameters are introduced in the model, the engine efficiency increases from 39% to 51%; the engine power is enhanced by approximately 20%, whereas the engine average pressure increases slightly.     

Propagation-prediction and site-planning software for wireless communication systems

Propagation-prediction and site-planning software for wireless communication networks has been developed. The software has a user-friendly graphical user interface (GUI), and provides calculations for large-scale and small-scale propagation parameters, including path loss (or received power) and delay profiles. Angles of arrival/departure, which are useful for the design of wireless systems employing multiple antennas, are also provided in the simulation. Some of the main features of the software include the use of a computationally efficient ray-tracing approach for simulating propagation in wireless environments, and the fact that users can upload AutoCAD .dxf files for indoor or outdoor environments. Both a single-building floor plan or an entire city layout can be simulated, and the user is provided with the ability to assign wall geometries and electrical parameters. User-defined realistic antenna radiation patterns for both the transmitting and receiving antennas are incorporated in the simulation. Broadband as well as polarization-dependent simulations are also included in the software.     

FDTD analysis of high frequency electronic interconnection effects

A full-wave analysis of coupled high-frequency interconnect discontinuities is presented using the finite-difference time-domain (FDTD) method. The electromagnetic effects of two via holes on microstrip lines in close proximity to one another are examined and equivalent circuits are presented. The effects of two adjacent lines with bond wires, used, for example, to connect a die to the leadframe of an integrated circuit (IC) package are also analyzed. Frequency domain results are presented by using the discrete Fourier transform of the time-domain results. Guidelines regarding the effective use of the FDTD code including the use a priori calculated electric field distribution in the excitation plane, and the use of a weighted ϵ_r,eff to minimize reflections at the absorbing boundaries are described. The obtained FDTD results and the developed equivalent circuit models show the importance of radiation effects at frequencies beyond 20-30 GHz, the possibilities of reducing the inductive effect of bond wires by using two parallel bond wires instead of one, and the importance of including mutual inductance elements in the equivalent circuit model to account for the crosstalk between parallel vias across a ground plane     

The stability test for symmetric alpha-stable distributions

Symmetric alpha-stable distributions are a popular statistical model for heavy-tailed phenomena encountered in communications, radar, biomedicine, and econometrics. The use of the symmetric alpha stable model is often supported by empirical evidence, where qualitative criteria are used to judge the fit, leading to subjective decisions. Objective decisions can only be made through quantitative statistical tests. Here, a goodness-of-fit hypothesis test for symmetric alpha-stable distributions is developed based on their unique stability property. Critical values for the test are found using both asymptotic theory and from bootstrap estimates. Experiments show that the stability test, using bootstrap estimates of the critical values, is better able to discriminate between symmetric alpha stable distributions and other heavy-tailed distributions than classical tests such as the Kolmogorov-Smirnov test.