Full-Wave Modal Analysis of Slow-Wave Periodic Structures Loaded With Elliptical Waveguides

In this paper, a novel full-wave method for the modal characterization of periodic structures loaded with elliptical waveguides is presented. This method relies on an integral equation formulation solved via the method of moments, which finally leads to the solution of a standard eigenvalue problem. The required modal spectrum of elliptical waveguides is determined through the boundary integral-resonant mode expansion technique. For validation purposes, the proposed analysis method is first successfully applied to periodic waveguide structures already considered in the technical literature. Then, our new algorithm is used to compute the related Brillouin diagrams and the interaction impedance of new periodic structures loaded with elliptical waveguides. Not only the main interacting mode (such as the $TM_{01}$ mode) is studied, but higher-order Floquet modes are also considered. These results have potential applications as slow-wave structures for high-power microwave devices and possibly filtering structures at millimeter-wave frequencies.      

Flavin mononucleotide-binding domain of the flavoprotein component of the sulfite reductase from Escherichia coli

The flavoprotein component (SiR-FP) of the sulfite reductase from Escherichia coli is an octamer containing one FAD and one FMN as cofactors per polypeptide chain. We have constructed an expression vector containing the DNA fragment encoding for the FMN-binding domain of SiR-FP. The overexpressed protein (SiR-FP23) was purified as a partially flavin-depleted polymer. It could incorporate FMN exclusively upon flavin reconstitution to reach a maximum flavin content of 1.2 per polypeptide chain. Moreover, the protein could stabilize a neutral air-stable semiquinone radical over a wide range of pHs. During photoreduction, the flavin radical accumulated first, followed by the fully reduced state. The redox potentials, determined at room temperature [E'1 (FMNH./FMN) = -130 +/- 10 mV and E'2 (FMNH2/FMNH.) = -335 +/- 10 mV], were very close to those previously reported for Salmonella typhimurium SiR-FP [Ostrowski, J., Barber, M. J., Rueger, D. C., Miller, B. E., Siegel, L. M., & Kredich, N. M. (1989) J. Biol. Chem. 264, 15796-15808]. Both the radical and fully reduced forms of SiR-FP23 were able to transfer their electrons to cytochrome c quantitatively. Altogether, the results presented herein demonstrate that the N-terminal end of E. coli SiR-FP forms the FMN-binding domain. It folds independently, thus retaining the chemical properties of the bound FMN, and provides a good model of the FAD-depleted form of native SiR-FP. Moreover, the FMN prosthetic group in SiR-FP23 and native SiR-FP is compared to that of cytochrome P450 reductase and bacterial cytochrome P450, which also contain one FAD and one FMN per polypeptide chain.     

Influence of intestinal resection and type of diet on the digestive and metabolic utilization of fats in rats

The effects of the quality of dietary fat, and the influence of ursodeoxycholic acid, an exogenous bile acid, on the digestive and metabolic utilization of fat were studied in rats in which 50% of the distal small intestine was resected. The fat content of the diets was quantitatively equivalent (4%), and differed only in the type of fat: olive oil (diet A) or 1/3 medium chain triglycerides (MCT), 1/3 sunflower oil and 1/3 olive oil (diet B). The removal of 50% of the distal small intestine led to a highly significant decline in the digestive utilization of fat (ADC) in animals given diet A. Rats fed diet B showed an increase in ADC to values approaching those seen in control animals. The addition of ursodeoxycholic acid to diet B failed to cause a further rise in the ADC of fat. After intestinal resection, serum levels of triglycerides and cholesterol fell more markedly in animals given diet A than in the diet B group, while the addition of ursodeoxycholic acid to diet B led to no further change. Serum lipid levels showed no significant influence of intestinal resection, but did accurately reflect the differences in fat composition between the two types of diet tested.     

Full-wave analysis of dielectric frequency-selective surfaces using a vectorial modal method

A novel vectorial modal method is presented for studying guidance and scattering of frequency-selective structures based on lossy all-dielectric multilayered waveguide gratings for both TE and TM polarizations. The wave equation for the transverse magnetic field is written in terms of a linear differential operator satisfying an eigenvalue equation. The definition of an auxiliary problem whose eigenvectors satisfy an orthogonality relationship allows for a matrix representation of the eigenvalue equation. Our proposed technique has been applied to the study of lossy all-dielectric periodic guiding media with periodicity in one dimension. This method yields the propagation constants and field distributions in such media. The reflection and transmission coefficients of a single layer under a plane-wave excitation can be obtained by imposing the boundary conditions. Study of the scattering parameters of the whole multilayered structure is accomplished by the cascade connection of components as characterized by their scattering parameters. Results obtained with this method for the propagation characteristics of a one-dimensional periodic dielectric medium are compared with those presented by other authors, and results for the scattering of several dielectric frequency-selective surfaces (DFSS) are compared with both theoretical and experimental results presented in the literature, finding a very good agreement. A symmetrical band-stop filter with a single waveguide grating is also demonstrated theoretically.     

The flavoprotein component of the Escherichia coli sulfite reductase can act as a cytochrome P450c17 reductase

Melatonin is proposed to be oncostatic in mammary tissue, and one mechanism by which this hormone may elicit its possible oncostatic effect is as an oxygen radical scavenger. Therefore, we examined melatonin's abilities to act as an oxygen radical scavenger at physiological or pharmacological concentrations. Hydrogen peroxide at 400 microM killed 97% of treated MCF7 cells within 8 h, and following melatonin at 10(-5) and 10(-4) M concentrations only 76 and 64% of cells, respectively, were killed by hydrogen peroxide. However, melatonin at lower concentrations (10(-7) M) did not protect MCF7 cells. Moreover, pretreatment with melatonin (10(-5) or 10(-7) M) prior to hydrogen peroxide stress offered no further efficacy, and pretreatment with melatonin followed by the withdrawal of melatonin eliminated its protective effect from hydrogen peroxide toxicity. These findings indicate that melatonin acts directly as an antioxidant and does not stimulate antioxidant defenses in MCF7 cells that protect against hydrogen peroxide. Glutathione levels were examined to substantiate this hypothesis and were not altered by melatonin treatment. In conclusion, melatonin is an excellent oxygen radical scavenger at pharmacological concentrations, but not at physiological concentrations. Thus, loss of melatonin is unlikely to be important in oxidative scavenger mechanisms in human mammary cells.     

Influence of dietary fat on nutritive utilization of protein in intestinally resected rats

The effects of different types of dietary fat on the digestive and metabolic utilization of protein were studied in rats with 50% resection of the distal small intestine and in sham-operated controls one month after surgery. The digestive utilization of protein was not significantly affected in intact animals when olive oil was replaced by butter as the dietary source of fat. In resected rats given either type of diet the apparent digestibility coefficient of protein declined significantly in comparison to intact controls. Intestinal resection decreased the retention of nitrogen significantly in rats given olive oil. The replacement of 2/3 of the dietary supply of olive oil with 1/3 medium chain triglycerides and 1/3 sunflower seed oil improved the metabolic utilization of protein in comparison to resected rats fed olive oil or butter as the only source of dietary fat. However, the addition of ursodeoxycholic acid to the diet containing equal parts of olive oil, medium chain triglycerides and sunflower seed oil failed to improve the metabolic utilization of protein in comparison to that seen in rats given olive oil only. Serum concentrations of total protein, urea and creatinine, albeit with slight changes in the first, remained within normal limits. Despite the lower retention of nitrogen in resected rats, these animals maintained homeostasis without resorting to muscular protein.     

Influence of medium chain triglycerides and vitamin D3 on digestive and metabolic utilization of protein in rats with intestinal resection

The effects of different types of diet and resecting 50% of the distal small intestine on the digestive and metabolic utilization of protein were studied in resected rats and sham-operated controls. Nutritional parameters were analyzed at 1 and 3 months postsurgery. Intestinal resection led to a deterioration in digestive utilization of protein, which improved with time (3 months postsurgery). A qualitative change in the dietary fat source from 100% olive oil to equal parts of medium chain triglycerides, sunflower seed oil and olive oil and this same diet supplemented with vitamin D3 favoured digestive utilization of protein as recorded 1 month after surgery. However, the beneficial effects were maintained at 3 months only in resected rats given dietary fat in the form of 100% olive oil.     

Bioavailable mercury cycling in polar snowpacks

Polar regions are subject to contamination by mercury (Hg) transported from lower latitudes, severely impacting human and animal health. Atmospheric Mercury Depletion Events (AMDEs) are an episodic process by which Hg is transferred from the atmospheric reservoir to arctic snowpacks. The fate of Hg deposited during these events is the subject of numerous studies, but its speciation remains unclear, especially in terms of environmentally relevant forms such as bioavailable mercury (BioHg). Here, using a bacterial mer-lux biosensor, we report the fraction of newly deposited Hg at the surface and at the bottom of the snowpack that is bioavailable. Snow samples were collected over a two-month arctic field campaign in 2008. In surface snow, BioHg is related to atmospheric Hg deposition and snow fall events were shown to contribute to higher proportions of BioHg than AMDEs. Based on our data, AMDEs represent a potential source of 20 t.y(-1) of BioHg, while wet and dry deposition pathways may provide 135-225 t.y(-1) of BioHg to Arctic surfaces.