Mode-matching analysis of a shielded rectangular dielectric-rod waveguide

Rectangular cross-section dielectric waveguides are widely used at millimeter wavelengths. In addition, shielded dielectric resonators having a square cross-section are often used as filter elements, however there is almost no information available on the effect of the shield. Rectangular or square dielectric waveguide is notoriously difficult to analyze, because of the singular behaviour of the fields at the corners. Most published analyses are for materials with a low dielectric constant, and do not include the effects of a shield. This paper describes a numerically efficient mode matching method for the analysis of shielded dielectric rod waveguide, which is applicable to both low and high dielectric constant materials. The effect of the shield on the propagation behaviour is studied. The shield dimensions may be selected such that the shield has a negligible effect, so that results can be compared with free space data. The results are verified by comparison with several sets of published data, and have been confirmed by measurement for a nominal 'e' r of 37.4

Joining of thirty three percent by weight random glass fibre reinforced polystyrene using variable frequency microwave

[Abstract]: This paper extends the range of applications for Variable Frequency Microwave (VFM) (2 – 18 GHz) facilities to joining thirty three percent by weight glass fibre reinforced polystyrene composite [PS/GF (33%)]. With a given power level, the composite was exposed to various exposure times to microwave irradiation. The primer or coupling agent used was 5-minute two-part adhesive containing 100% liquid epoxy and 8% amine, i.e. Araldite, which was more readily microwave reactive than the composite itself. Bond strengths of the joints were lap shear tested and results were compared with those obtained using fixed frequency (2.45 GHz) microwave processing. The VFMF was operated under software control, which provided automatic data logging facilities. The maximum lap shear bond strength of joint was 430 N/cm2 using variable frequency microwave facility while that obtained by fixed frequency microwave configuration was only 331 N/cm2. The former is nearly 30% stronger than the latter

Permittivity measurement of thermoplastic composites at elevated temperature

[Abstract]: The material properties of greatest importance in microwave processing of a dielectric are the complex relative permittivity Epsilon = Epsilon' - jEpsilon'', and the loss tangent, tan Delta = Epsilon'/Epsilon''. This paper describes two convenient laboratory based methods to obtain Epsilon', Epsilon'' and hence tan Delta of fibre-reinforced thermoplastic (FRTP) composites. One method employs a microwave network analyser in conjunction with a waveguide transmission technique, chosen because it provides the widest possible frequency range with high accuracy. The values of the dielectric constant and dielectric loss of glass fibre reinforced (33%) low density polyethylene, LDPE/GF (33%), polystyrene, PS/GF (33%), and Nylon 66/GF (33%), were obtained. Results are compared with those obtained by another method using a high-temperature dielectric probe

Surface-wave propagation on a grounded dielectric slab covered by a high-permittivity material

A grounded dielectric slab covered by a higher permittivity material would not normally be expected to support surface waves. This conclusion must be modified when the covering material is sufficiently lossy. Assuming a thin slab, approximate analysis shows that the fundamental TM0 surface wave is able to propagate if the cover loss is high enough. A numerical analysis has verified these conclusions. propagation of higher order TM and TE modes is found to be possible above cutoff frequencies, which reduce as cover loss is increased. These results are of significance when printed circuit transmission lines such as microstrip or slotline are used as contact sensors, e.g., for moist materials

Incompatible sets of gradients and metastability

We give a mathematical analysis of a concept of metastability induced by incompatibility. The physical setting is a single parent phase, just about to undergo transformation to a product phase of lower energy density. Under certain conditions of incompatibility of the energy wells of this energy density, we show that the parent phase is metastable in a strong sense, namely it is a local minimizer of the free energy in an $L^1$ neighbourhood of its deformation. The reason behind this result is that, due to the incompatibility of the energy wells, a small nucleus of the product phase is necessarily accompanied by a stressed transition layer whose energetic cost exceeds the energy lowering capacity of the nucleus. We define and characterize incompatible sets of matrices, in terms of which the transition layer estimate at the heart of the proof of metastability is expressed. Finally we discuss connections with experiment and place this concept of metastability in the wider context of recent theoretical and experimental research on metastability and hysteresis.Comment: Archive for Rational Mechanics and Analysis, to appea

Metamorphosis of plasma turbulence-shear flow dynamics through a transcritical bifurcation

The structural properties of an economical model for a confined plasma turbulence governor are investigated through bifurcation and stability analyses. A close relationship is demonstrated between the underlying bifurcation framework of the model and typical behavior associated with low- to high-confinement transitions such as shear flow stabilization of turbulence and oscillatory collective action. In particular, the analysis evinces two types of discontinuous transition that are qualitatively distinct. One involves classical hysteresis, governed by viscous dissipation. The other is intrinsically oscillatory and non-hysteretic, and thus provides a model for the so-called dithering transitions that are frequently observed. This metamorphosis, or transformation, of the system dynamics is an important late side-effect of symmetry-breaking, which manifests as an unusual non-symmetric transcritical bifurcation induced by a significant shear flow drive.Comment: 17 pages, revtex text, 9 figures comprised of 16 postscript files. Submitted to Phys. Rev.

Andrew Melville, sacred chronology and world history: the Carmina Danielis 9 and the Antichristus

The accepted view of the ecclesiastical reformer Andrew Melville (1545–1622) as the dynamic leader of the Presbyterian movement in Jacobean Scotland has been severely eroded in recent years, with particular criticism of the actual importance of his contribution to the Kirk and to Scottish higher education. While this reductionism has been necessary, it has resulted in an inversion of the overwhelmingly positive traditional image of Melville, and does not give us a rounded assessment of his life and works. This article attempts to partially redress this balance by looking at a neglected aspect of Melville's Latin writings, which showcase his talents as a humanist intellectual and biblical commentator. It focuses on two long poems that are both commentaries and paraphrases of Daniel and Revelation: the Carmina Danielis and the Antichristus. Through these poems, we see how Melville engaged with two problems exercising reformed theologians across Europe: the dating of key biblical events and the historicised meaning of prophecies within these texts. We also find evidence that Melville read widely among both contemporary and ancient commentators on both these issues

Approaches for advancing scientific understanding of macrosystems

The emergence of macrosystems ecology (MSE), which focuses on regional- to continental-scale ecological patterns and processes, builds upon a history of long-term and broad-scale studies in ecology. Scientists face the difficulty of integrating the many elements that make up macrosystems, which consist of hierarchical processes at interacting spatial and temporal scales. Researchers must also identify the most relevant scales and variables to be considered, the required data resources, and the appropriate study design to provide the proper inferences. The large volumes of multi-thematic data often associated with macrosystem studies typically require validation, standardization, and assimilation. Finally, analytical approaches need to describe how cross-scale and hierarchical dynamics and interactions relate to macroscale phenomena. Here, we elaborate on some key methodological challenges of MSE research and discuss existing and novel approaches to meet them

High Energy Hadron-Nucleus Cross Sections and Their Extrapolation to Cosmic Ray Energies

Old models of the scattering of composite systems based on the Glauber model of multiple diffraction are applied to hadron-nucleus scattering. We obtain an excellent fit with only two free parameters to the highest energy hadron-nucleus data available. Because of the quality of the fit and the simplicity of the model it is argued that it should continue to be reliable up to the highest cosmic ray energies. Logarithmic extrapolations of proton-proton and proton-antiproton data are used to calculate the proton-air cross sections at very high energy. Finally, it is observed that if the exponential behavior of the proton-antiproton diffraction peak continues into the few TeV energy range it will violate partial wave unitarity. We propose a simple modification that will guarantee unitarity throughout the cosmic ray energy region.Comment: 8 pages, 9 postscript figures. This manuscript replaces a partial manuscript incorrectly submitte

Burrowing owls, Pulex irritans and plague

Western burrowing owls (Athene cunicularia hypugaea) are small, ground-dwelling owls ofwestern North America that frequent prairie dog (Cynomys spp.) towns and other grasslands.As they rely on rodent prey and occupy burrows once or concurrently inhabited by fossorialmammals, the owls often harbor fleas. We examined the potential role of fleas found onburrowing owls in plague dynamics by evaluating prevalence of Yersinia pestis in fleas and inowl blood. During 2012-2013 fleas and blood were collected from burrowing owls in portionsof five states with endemic plague: Idaho, Oregon, Washington, Colorado, and South Dakota.Fleas were enumerated, taxonomically identified, pooled by nest and assayed for Y. pestis usingculturing and molecular (PCR) approaches. Owl blood underwent serological analysis for plagueantibodies and nested PCR for detection of Y. pestis. Of \u3e4750 fleas collected from owls, Pulexirritans, a known plague vector in portions of its range, comprised more than 99.4%. However,diagnostic tests for Y. pestis of flea pools (culturing and PCR) and owl blood (PCR and serology)were negative. Thus, despite that fleas were prevalent on burrowing owls, and the potentialfor a relationship with burrowing owls as a phoretic host of infected fleas exists, we found noevidence of Y. pestis in sampled fleas or in owls that harbored them. We suggest that studiessimilar to those reported here during plague epizootics will be especially useful for confirmingthese results