Analysis of the EM scattering from arbitrary open-ended waveguide cavities using axial Gaussian Beam tracking

The electromagnetic (EM) scattering from a planar termination located inside relatively arbitrarily shaped open-ended waveguide cavities with smoothly curved interior walls is analyzed using a Gaussian Beam (GB) expansion of the incident plane wave fields in the open end. The cavities under consideration may contain perfectly-conducting interior walls with or without a thin layer of material coating, or the walls may be characterized by an impedance boundary condition. In the present approach, the GB's are tracked only to the termination of the waveguide cavity via beam reflections from interior waveguide cavity walls. The Gaussian beams are tracked approximately only along their beam axes; this approximation which remains valid for relatively well focussed beams assumes that an incident GB gives rise to a reflected GB with parameters related to the incident beam and the radius of curvature of the wall. It is found that this approximation breaks down for GB's which come close to grazing a convex surface and when the width of the incident beam is comparable to the radius of curvature of the surface. The expansion of the fields at the open end depend on the incidence angle only through the expansion coefficients, so the GB's need to be tracked through the waveguide cavity only once for a wide range of incidence angles. At the termination, the sum of all the GB's are integrated using a result developed from a generalized reciprocity principle, to give the fields scattered from the interior of the cavity. The rim edge at the open end of the cavity is assumed to be sharp and the external scattering from the rim is added separately using Geometrical Theory of Diffraction. The results based on the present approach are compared with solutions based on the hybrid asymptotic modal method. The agreement is found to be very good for cavities made up of planar surfaces, and also for cavities with curved surfaces which are not too long with respect to their width

A hybrid asymptotic-modal analysis of the EM scattering by an open-ended S-shaped rectangular waveguide cavity

The electromagnetic fields (EM) backscatter from a 3-dimensional perfectly conducting S-shaped open-ended cavity with a planar interior termination is analyzed when it is illuminated by an external plane wave. The analysis is based on a self-consistent multiple scattering method which accounts for the multiple wave interactions between the open end and the interior termination. The scattering matrices which described the reflection and transmission coefficients of the waveguide modes reflected and transmitted at each junction between the different waveguide sections, as well at the scattering from the edges at the open end are found via asymptotic high frequency methods such as the geometrical and physical theories of diffraction used in conjunction with the equivalent current method. The numerical results for an S-shaped inlet cavity are compared with the backscatter from a straight inlet cavity; the backscattered patterns are different because the curvature of an S-shaped inlet cavity redistributes the energy reflected from the interior termination in a way that is different from a straight inlet cavity

Inferring muscle functional roles of the ostrich pelvic limb during walking and running using computer optimization

Owing to their cursorial background, ostriches (Struthio camelus) walk and run with high metabolic economy, can reach very fast running speeds and quickly execute cutting manoeuvres. These capabilities are believed to be a result of their ability to coordinate muscles to take advantage of specialized passive limb structures. This study aimed to infer the functional roles of ostrich pelvic limb muscles during gait. Existing gait data were combined with a newly developed musculoskeletal model to generate simulations of ostrich walking and running that predict muscle excitations, force and mechanical work. Consistent with previous avian electromyography studies, predicted excitation patterns showed that individual muscles tended to be excited primarily during only stance or swing. Work and force estimates show that ostrich gaits are partially hip-driven with the bi-articular hip–knee muscles driving stance mechanics. Conversely, the knee extensors acted as brakes, absorbing energy. The digital extensors generated large amounts of both negative and positive mechanical work, with increased magnitudes during running, providing further evidence that ostriches make extensive use of tendinous elastic energy storage to improve economy. The simulations also highlight the need to carefully consider non-muscular soft tissues that may play a role in ostrich gait

Electromagnetic properties of material coated surfaces

The electromagnetic properties of material coated conducting surfaces were investigated. The coating geometries consist of uniform layers over a planar surface, irregularly shaped formations near edges and randomly positioned, electrically small, irregularly shaped formations over a surface. Techniques to measure the scattered field and constitutive parameters from these geometries were studied. The significance of the scattered field from these geometries warrants further study

Primary productivity in the Gerlache and Bransfield Straits of Antarctica

Distribution of the standing crop of phytoplankton and primary productivity in the Gerlache and Bransfield straits was studied during February and March 1965 aboard the Argentine Navy Icebreaker GENERAL SAN MARTIN. Relatively high standing-crop values, expressed in chlorophyll a per square meter, were exhibited in the euphotic zone, with ranges of 86-209 mg/m2 in the Gerlache Strait area and 20-209 mg/m2 in the Bransfield Strait area. Primary productivity was also high in both areas, but not commensurate with what might be expected for the standing crop in Gerlache Strait...

An Examination of Confirmatory Factor Analytic Models of the Spiritual Well-Being Scale

The Spiritual Well-Being Scale (SWBS) is a commonly used overall measure of perceived spiritual quality of life. The SWBS has been demonstrated as a valid and reliable measure, however questions and concerns exist regarding its construct validity. Further, a paucity of empirical literature exists examining the construct of spiritual well-being within the counseling profession. Using data from a study with 415 master’s level counseling students, the authors examined goodness-of-fit for the SWBS of one, two, three, and five-factor models identified in the literature. Results indicated no model yielded good fit. Implications and future research are discussed

High-frequency asymptotic methods for analyzing the EM scattering by open-ended waveguide cavities

Four high-frequency methods are described for analyzing the electromagnetic (EM) scattering by electrically large open-ended cavities. They are: (1) a hybrid combination of waveguide modal analysis and high-frequency asymptotics, (2) geometrical optics (GO) ray shooting, (3) Gaussian beam (GB) shooting, and (4) the generalized ray expansion (GRE) method. The hybrid modal method gives very accurate results but is limited to cavities which are made up of sections of uniform waveguides for which the modal fields are known. The GO ray shooting method can be applied to much more arbitrary cavity geometries and can handle absorber treated interior walls, but it generally only predicts the major trends of the RCS pattern and not the details. Also, a very large number of rays need to be tracked for each new incidence angle. Like the GO ray shooting method, the GB shooting method can handle more arbitrary cavities, but it is much more efficient and generally more accurate than the GO method because it includes the fields diffracted by the rim at the open end which enter the cavity. However, due to beam divergence effects the GB method is limited to cavities which are not very long compared to their width. The GRE method overcomes the length-to-width limitation of the GB method by replacing the GB's with GO ray tubes which are launched in the same manner as the GB's to include the interior rim diffracted field. This method gives good accuracy and is generally more efficient than the GO method, but a large number of ray tubes needs to be tracked

A preferred vision for administering elementary schools : a reflective essay

Education in today\u27s society has transformed almost completely and has changed dramatically. The techniques and curricula have shifted as students have change. The family unit is different now because of socio-economic problems, divorce, and single parent homes. Many values and beliefs taught in the past at home are now taught and learned in the schools. With both parents working in many families, quality time with children diminishes and is sometimes nonexistent. This quality time is where children learn morals, manners, and social interactions. Currently, children come to school without these appropriate social skills and it is up to the school to carry the burden of teaching these skills. Teachers are considered to be positive role models and by their demonstration of these skills in the classroom, children can learn to model these behaviors. According to Barth (1990), research suggests that students who experience pressure to obey will develop character and skills necessary to succeed throughout life. As society has changed, so has the student population. Schools have a difficult time keeping up with all the changes and pressures occurring in society. Students have changed dramatically as social entities have been the driving force of young people. These social vices are numerous. Drugs, alcohol, gang related crimes, sexual relations, and fatal sexually transmitted diseases have been 2 catalysts as to why children have matured very quickly. Recreational media like television and movies have made these children more informed about such social issues. Another driving force in a child\u27s life is peer pressure. Belonging to a peer group is vitally important for shaping identity and values. Children also seem to learn an abundant amount of knowledge, both helpful and detrimental, about society and life in general from their peer group. These social vices are just one of the modifiers that have changed education as a career and made it a great challenge. Since students are more of a challenge the school system needs to modify its\u27 processes so it can better serve the needs of all types of students. The standard paradigms of schools have remained constant in an inconsistent society. Barth (1990) indicates that if schools are to transform and improve, then educators need to be risk-takers, and input new and unusual ideas into the school system. By taking creative risks, the paradigms of schools will be able to shift so that our educational system can better educate the children of today

60 GHz indoor propagation studies for wireless communications based on a ray-tracing method

This paper demonstrates a ray-tracing method for modeling indoor propagation channels at 60 GHz. A validation of the ray-tracing model with our in-house measurement is also presented. Based on the validated model, the multipath channel parameter such as root mean square (RMS) delay spread and the fading statistics at millimeter wave frequencies are easily extracted. As such, the proposed ray-tracing method can provide vital information pertaining to the fading condition in a site-specific indoor environment