ABSTRACT
We report the results of experimental and theoretical studies of monochromatic coherent terahertz radiation generated by a short relativistic electron bunch interacting with a metasurface. The metasurface consists of subwavelength metal elements arranged on a dielectric substrate. The constructed theory explains the experimental spectra of Smith-Purcell radiation and grating transition radiation with very high precision. The orientational distribution of transition radiation shows a fine structure, which, as we suppose, may be due to contribution of coupling between the metasurface's elements.
ABSTRACT
Smith-Purcell effect is well known as a source of monochromatic electromagnetic radiation. In this paper we present the generalized theory of Smith-Purcell radiation from periodic beams. The form-factors describing both coherent and incoherent regimes of radiation are calculated. The radiation characteristics are investigated in two practically important frequency ranges, THz and X-ray, for two modulation profiles, most frequently used in practice - a train of microbunches and a Gaussian-shaped one, characterized by sinusoidal modulation with an arbitrary modulation depth. On the base of the theory developed we show that a modulated electron beam consisting of a set of bunches makes it possible to improve significantly the spectral line monochromaticity of the light emitted, reaching values better than 1% for short gratings. We demonstrate as well that Smith-Purcell radiation can be used for non-destructive diagnostics of the depth of modulation for partially modulated beams. These findings not only open up a new way to manipulate the light emission using Smith-Purcell effect but also promise a profound impact for other radiation sources based on charged particle beams, such as undulator radiation in FELs, next-generation X-ray radiation source based on inverse Compton scattering, in a wide range from THz to X-rays.
ABSTRACT
Studied was the content of mercury in certain fish species from ocean and the Black Sea catch (mackerel, scad, and merluccius), sold on the home markets. The study of samples of merluccius revealed that the average level of mercury was 0.088 ppm, the deviations being from 0.036 ppm up to 0.16 ppm. In mackerel samples mercury averaged 0.075 ppm, with deviations of 0.04 ppm to 0.013 ppm. And in scad mercury was shown to vary from 0.03 ppm to 0.085, an average of 0.059 ppm. Mercury in the investigated species of fishes was considerably lower than the standards of the World Health Organization and the Food and Agriculture Organization and the maximum admissible tolerance in USA, Canada, and France.
Subject(s)
Fishes/metabolism , Mercury/analysis , Animals , Environmental Pollutants , Muscles/analysisABSTRACT
Established were the thin-layer chromatography conditions for the demonstration of the herbicide Zenkor as a pure substance and a preparation. Comparative experiments were carried out applying Thomson and Stanley's thin-layer chromatography conditions and the authors' personal ones. Most adequate proved to be the following conditions: sorbent-Kieselgel 60F 254 (Merck); solvent -- chloroform: 1,4-dioxan (9:1); developer -- ultraviolet light (authors' technique). Essential with this method is the preliminary (prior to apply the pure substances on the thin-layer chromatographic plaque) moving of the plaque in the indicated mobile phase (authors' technique). Under these thin-layer chromatography conditions work is made feasible and the method is fast and simple, achieving high sensitivity -- 0.5 mug Zenkor.
Subject(s)
Chromatography, Thin Layer/methods , Herbicides/analysis , Triazines , Bulgaria , Indicators and Reagents , Ultraviolet RaysABSTRACT
Developed was an atom-absorption method for determining microconcentrations of copper, lead, cadmium, and zink in milk originating from various regions of this country. The study was carried out by means of an atom-absorption spectrophotometer AA-5. Established were the optimal conditions for determining the trace elements reaching the following values of susceptibility: for copper--0.04; for lead--0.11; for cadmium--0.001; and for zinc--0.009 mg/cu.cm, with an allowance of 5%. The results obtained are discussed and statistically processed. Literature data are comparatively studied reflecting the amounts of these elements in milk as found in this country and abroad. Such data will be made use of in the elaboration of Bulgarian reference tables necessary for establishing various regimes and norms concerning the food products offered in children creches, hospitals, canteens, etc.
