Scalar Resonances in Axially Symmetric Spacetimes

We study properties of resonant solutions to the scalar wave equation in several axially symmetric spacetimes. We prove that non-axial resonant modes do not exist neither in the Lanczos dust cylinder, the $(2+1)$ extreme BTZ spacetime nor in a class of simple rotating wormhole solutions. Moreover, we find unstable solutions to the wave equation in the Lanczos dust cylinder and in the $r^2 <0$ region of the extreme $(2+1)$ BTZ spacetime, two solutions that possess closed timelike curves. Similarities with previous results obtained for the Kerr spacetime are explored.Comment: International Journal of Modern Physics D, in pres

Characteristics of a multicolor dye laser

An experimental investigation on the possibility of obtaining tunable, multiple wavelength output in mixture of dyes pumped by a nitrogen laser has been carried out. A great number of binary dye mixtures have been tested. Simultaneous two wavelength operation is generally possible provided the gain profiles of both dyes are neither strongly overlapped nor too widely separated. Three color emission is feasible in many mixtures, but the possible combinations are limited. A simple scheme for multiple, simultaneous wavelength tuning is presented

Spectroscopic analysis of the transverse excited C3Πu–B3Πg(0–0) UV laser band of N2 at room temperature: comments

Recently Petit et al.published a paper devoted to a high-resolution spectroscopy study of the 0-0 laser band in the Second Positive System of molecular nitrogen and explaining the optical gain formation on its different branches.All the results by Petit et al. are equivalent to those previously published by Massone et al.and are in accordance with theoretical predictions reported by Tocho et al.Summarizing, we would comment as follows

Instabilities of naked singularities and black hole interiors in general relativity

Metrics representing black holes in General Relativity may exhibit naked singularities for certain values of their parameters. This is the case for super-extremal (J2 \u3e M \u3e 0) Kerr and super-extremal (|Q| \u3e M \u3e 0) Reissner-Nördstrom spacetimes, and also for the negative mass Schwarzschild spacetime. We review our recent work where we show that these nakedly singular spacetimes are unstable under linear gravitational perturbations, a result that supports the cosmic censorship conjecture, and also that the inner stationary region beyond the inner horizon of a Kerr black hole (J2 \u3c M) is linearly unstable. © 2009 World Scientific Publishing Company

Enhancement of photoacoustic detection of inhomogeneities in polymers

We report a series of experiments on laser pulsed photoacoustic excitationin turbid polymer samples addressed to evaluate the sound speed in the samples and the presence of inhomogeneities in the bulk. We describe a system which allows the direct measurement of the speed of the detected waves by engraving the surface of the piece under study with a fiduciary pattern of black lines. We also describe how this pattern helps to enhance the sensitivity for the detection of an inhomogeneity in the bulk. These two facts are useful for studies in soft matter systems including, perhaps, biological samples. We have performed an experimental analysis on Grilon(R) samples in different situations and we show the limitations of the method.Comment: 8 pages, 7 figure

A Xenon Ion Pumped Open Dye Stream Laser

A pulsed xenon ion laser with an output power of 1 kW over the blue-green lines was used to pump an open dye stream laser. An efficiency of the order of 40 percent was determined in broadband mode operation. The bandwidth in this case was 48 nm (from 582 to 630 nm)

Enhancement of photoacoustic detection of inhomogeneities in polymers

We report a series of experiments on laser pulsed photoacoustic excitation in turbid polymer samples addressed to evaluate the sound speed in the samples and the presence of inhomogeneities in the bulk. We describe a system which allows the direct measurement of the speed of the detected waves by engraving the surface of the piece under study with a fiduciary pattern of black lines. We also describe how this pattern helps to enhance the sensitivity for the detection of an inhomogeneity in the bulk. These two facts are useful for studies in soft matter systems including, perhaps, biological samples. We have performed an experimental analysis on Grilon®samples in different situations and we show the limitations of the method.Facultad de Ingenierí

Alineación empleando un sistema óptico de enfoque y un láser.

Se describe un m&eacute;todo de alineaci&oacute;n empleando un l&aacute;ser de He-Ne ($latex \lambda$= 632,8 nm, P = 2 mW) acoplado a un sistema telesc&oacute;pico que permite enfocar el haz luminoso hasta obtener puntos &#39;brillant&iacute;simos de di&aacute;metros mucho menores que 50 &mu;m. Se analiza su aplicaci&oacute;n a la deter&middot; minaci&oacute;n de rectas, planos y relaciones entre ellos (paralelismo, perpendicularidad, etc.). Se detalla su utilizaci&oacute;n en dos casos concretos: a) Verificaci&oacute;n de la alineaci&oacute;n del cig&uuml;e&ntilde;al del motor principal de un buque frigor&iacute;fico surto en el puerto de Buenos Aires (Argentina), y b) Verificaci&oacute;n de la colinealidad entre los ejes de dos cojinetes de un tubo de tim&oacute;n de un barco en construcci&oacute;n en el Astillero R&iacute;o Santiago (Argentina)