The risk of upper respiratory infections (URIs) is increased in people who are under heavy physical stress, including recreational and competitive swimmers. Additional treatment options are needed, especially in the younger age group. The aim of this study was to determine whether 1 g/day vitamin C supplementation affects the rate, length, or severity of URIs in adolescent swimmers. We carried out a randomized, double-blind, placebo-controlled trial during three winter months, among 39 competitive young swimmers (mean age 13.8 ± 1.6 years) in Jerusalem, Israel. Vitamin C had no effect on the incidence of URIs (rate ratio = 1.01; 95% confidence interval (CI) = 0.70-1.46). The duration of respiratory infections was 22% shorter in vitamin C group, but the difference was not statistically significant. However, we found a significant interaction between vitamin C effect and sex, so that vitamin C shortened the duration of infections in male swimmers by 47% (95% CI: -80% to -14%), but had no effect on female swimmers (difference in duration: +17%; 95% CI: -38% to +71%). The effect of vitamin C on the severity of URIs was also different between male and female swimmers, so that vitamin C was beneficial for males, but not for females. Our study indicates that vitamin C does not affect the rate of respiratory infections in competitive swimmers. Nevertheless, we found that vitamin C decreased the duration and severity of respiratory infections in male swimmers, but not in females. This finding warrants further research.

We present a new and optimal design approach for obtaining maximal confinement of the field in radial Bragg cavities and lasers for TM polarization. The presented approach outperforms substantially the previously employed periodic and semi-periodic design schemes of such lasers. We show that in order to obtain maximal confinement, it is essential to consider the complete reflection properties (amplitude and phase) of the propagating radial waves at the interfaces between Bragg layers. When these properties are taken into account, we find that it is necessary to introduce a wider ("half-wavelength") layer at a specific radius in the "quarter-wavelength" radial Bragg stack. It is shown that this radius corresponds to the cylindrical equivalent of Brewster's angle. The confinement and field profile are calculated numerically by means of transfer matrix method.

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Single-mode lasing from broad area radial Bragg lasers is demonstrated experimentally. Numerical analysis as well as experimental characterization reveals surprising property of high mode discrimination at large angular modal numbers.Circular optical resonators are a key-component for numerous applications such as optical communication systems, spectroscopy, and for research in non-linear optics and cavity quantum electrodynamics. In addition, they play a key role in various sensing applications, ranging from rotation sensing, to biomedical and chemical sensing.For many of these applications, active resonators (i.e. lasers) are employed, primarily due to their superior signal to