Results 1 - 10 of 3542
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[en] Discusses conclusions reached by A E Dubinov and D A Mytareva in their paper 'Invisible cloaking of material bodies using the wave flow method' (Usp. Fiz. Nauk 180 475 (2010) [Phys. Usp. 53 455 (2010)]) on whether the perfect optical cloaking of material objects is possible. (letters to the editors)
[en] Replies are made to comments in N N Rozanov's letter to the editors ''Can even monochromatic radiation ensure ideal invisibility?'' (see Usp. Fiz. Nauk 181 787 (2011) [Phys. Usp. 54 763 (2011)]) concerning our paper ''Invisible cloaking of material bodies using the wave flow method'' (Usp. Fiz. Nauk 180 475 (2010) [Phys. Usp. 53 455 (2010)]). Examples are given of spatial configurations that enable the creation of singularity-free cloaking materials. Some emerging cloaking ideas are discussed. (letters to the editors)
[en] Biological spectral weighting functions (BSWF) play a key role in calculating the increase of biologically effective solar ultraviolet-B radiation (UV-BBE) due to ozone reduction, assessing current latitudinal gradients of UV-BBE. and comparing solar UV-BBE with that from lamps and filters in plant experiments. Plant UV action spectra (usually determined with monochromatic radiation in the laboratory with exposure periods on the order of hours) are often used as BSWF. The realism of such spectra for plants growing day after day in polychromatic solar radiation in the field is questionable. We tested the widely used generalized plant action spectrum since preliminary data from an action spectrum being developed with monochromatic radiation for a cultivated oat variety indicate reasonable agreement with the generalized spectrum. These tests involved exposing plants to polychromatic radiation either from a high-pressure xenon arc lamp in growth chambers or in the field under solar radiation with supplemental UV-B lamps. Different broad-spectrum combinations were achieved by truncating the spectrum at successively longer UV wavelengths with various filters. In the growth chamber experiments, the generalized plant spectrum appeared to predict plant growth responses at short (<310nm) wavelengths but not at longer wavelengths. The field experiment reinforced these conclusions, showing (in addition to the expected direct UV-B effects) both direct UV-A effects and UV-A mitigation of UV-B effects. (author)
[en] I consider a landscape containing three vacua and study the topology of global spacelike slices in eternal inflation. A discrete toy model, which generalizes the well-studied Mandelbrot model, reveals a rich phase structure. Novel phases include monochromatic tubular phases, which contain crossing curves of only one vacuum, and a democratic tubular phase, which contains crossing curves of all three types of vacua. I discuss the generalization to realistic landscapes consisting of many vacua. Generically, the system ends up in a grainy phase, which contains no crossing curves or surfaces and consists of packed regions of different vacua. Other topological phases arise on the scale of several generations of nucleations.
[en] Here, synchrotrons can provide almost perfectly unidirectional and monochromatic x-rays. Such x-rays reflect from ideal crystals only over a minute part of the angular range that must be searched for the reflection. Spoiling the incoming x-rays' directionality with sandpaper makes it easier to find the reflection.
[en] When a person observes an object, illuminated incoherently by a quasi-monochromatic source, through a grating, he will see more than one image. Angular positions of these images are derived in terms of wavelength, period of the grating, separation between the object and the grating, and position of the object relative to the observer. In a special case, when the object is another grating, the condition of coincidence of its multiple images is investigated. The relation derived is, to some extent, similar to that seen in the Lau effect. As a secondary outcome, it is shown that the sum of the squared modulus of the odd Fourier series coefficients for a binary grating function is equal to that of the even coefficients. (paper)
[en] Backlighting is a powerful technique to observe the flow of cold and dense material in highenergy- density-plasma experiments. High-performance, direct-drive cryogenic deuterium-tritium (DT) implosions are a challenging backlighting configuration because of the low opacity of the DT shell, the high shell velocity, the small size of the stagnating shell, and the very bright selfemission of the hot core.
[en] In this article we provide experimental evidence of an interference phenomenon that, to the best of our knowledge, has so far not been observed with either matter or light. In a nanometer-sized version of Feynman's famous two-slit 'thought' experiment with single electrons, we managed to observe that the width of a quasi-monochromatic line oscillates with the detection angle. Furthermore, we find that it occurs in counterphase with the line intensity. We discuss the underlying mechanism that produces this unexpected result.