Fundamental Solutions for the Klein-Gordon Equation in de Sitter Spacetime

In this article we construct the fundamental solutions for the Klein-Gordon equation in de Sitter spacetime. We use these fundamental solutions to represent solutions of the Cauchy problem and to prove $L^p-L^q$ estimates for the solutions of the equation with and without a source term

A cytogenetic follow-up of some highly irradiated victims of the Chernobyl accident

Altres ajuts: The authors wish to thank INTAS (research grant no. 97-1152) for financial support for this workA follo w-up of 10 highly irradiated men, mostly reactor crew, from the Chernobyl accident is described. Their pre-accident medical conditions and relevant medical status approximately 10-13 y later are listed. A comparison is made between estimates of their average whole-body penetrating radiation doses derived from several biological parameters. First estimates were based on their presenting severity of prodromal sickness, early changes in blood cell counts and dicentric chromosome aberrations in lymphocytes. In three cases ESR measurements on tooth enamel were also made. Retrospective dosimetry using FISH translocations was attempted 10-13 y later. This showed good agreement for those patients with the lower earlier dose estimates, up to about 3 Gy. For the others, extending up to about 12 Gy, the translocations indicated lower values, suggesting that in these cases translocations had somewhat declined. Repeated chromosomal examinations during the follow-up period showed an expected decline in dicentric frequencies. The pattern of decline was bi-phasic with a more rapid first phase, with a half-life of ∼4 months followed by a slower decline with half-lives around 2-4 y. The rapid phase persisted for a longer time in those patients who had received the highest doses. 10-13 y later dicentric levels were still above normal background, but well below the translocation frequencies

Multifunctional light beam control device by stimuli-responsive liquid crystal micro-grating structures

There is an increasing need to control light phase with tailored precision via simple means in both fundamental science and industry. One of the best candidates to achieve this goal are electro-optical materials. In this work, a novel technique to modulate the spatial phase profile of a propagating light beam by means of liquid crystals (LC), electro-optically addressed by indium-tin oxide (ITO) grating microstructures, is proposed and experimentally demonstrated. A planar LC cell is assembled between two perpendicularly placed ITO gratings based on microstructured electrodes. By properly selecting only four voltage sources, we modulate the LC-induced phase profile such that non-diffractive Bessel beams, laser stretching, beam steering, and 2D tunable diffraction gratings are generated. In such a way, the proposed LC-tunable component performs as an all-in-one device with unprecedented characteristics and multiple functionalities. The operation voltages are very low and the aperture is large. Moreover, the device operates with a very simple voltage control scheme and it is lightweight and compact. Apart from the demonstrated functionalities, the proposed technique could open further venues of research in optical phase spatial modulation formats based on electro-optical materials.This work was supported by the Comunidad de Madrid and FEDER Program (S2018/NMT-4326), the Ministerio de Economía y Competitividad of Spain (TEC2016-77242-C3-1-R and TEC2016-76021-C2-2-R), the FEDER/Ministerio de Ciencia, Innovación y Universidades and Agencia Estatal de Investigación (RTC2017-6321-1, PID2019-109072RB-C31 and PID2019-107270RB-C21). The authors also acknowledge the support by the Ministry of National Defense of Poland (GBMON/13-995/2018/WAT), Military University of Technology (Grant no. 23-895)

Grammatical and lexical meaning of a preposition in Spanish language

The article analyzes the linguistic approaches to the question of studying the grammatical and lexical content of a preposition. The article seeks to clarify what is meant by the lexical meaning of a preposition, and what refers to the grammatical one. By analyzing the provisions the article proves that the lexical and grammatical meaning of a preposition must be studied complexly, without being separated from each other

Polarization-Dependent Photoinduced Surface Microgratings In Amorphous Chalcogenide Glasses

Recently, the chalcogenide glasses (ChG) have attracted much attention in the field of optical communication and integrated optics. High transparency in the infrared spectral region, low phonon energy, high nonlinear properties, and high photosensitivity at near band-gap (Eg 2.35 eV, a 1-2 x iO cm1 at 5 14 nm) are important characteristics of these glasses. In particular, the photosensitive effects, among them photodarkening and giant photoexpansion (2-5%) [1], have been extensively studied and several holographic elements, such as microlenses, diffraction and Bragg gratings, and channel waveguides have been realized in fiber, bulk, and thin film forms of these materials [2-4]. In this work, we report for the first time to our knowledge, the observation and study of the strong polarization dependent photoinduced surface relief gratings in As2S3 thin films. A model to describe the observed phenomena is also presented. © 2000 SPIE