24 research outputs found
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 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 region of the extreme 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 IngenierÃ
Alineación empleando un sistema óptico de enfoque y un láser.
Se describe un método de alineación empleando un láser de He-Ne (= 632,8 nm, P = 2 mW) acoplado a un sistema telescópico que permite enfocar el haz luminoso hasta obtener puntos 'brillantísimos de diámetros mucho menores que 50 μm. Se analiza su aplicación a la deter· minación de rectas, planos y relaciones entre ellos (paralelismo, perpendicularidad, etc.). Se detalla su utilización en dos casos concretos: a) Verificación de la alineación del cigüeñal del motor principal de un buque frigorífico surto en el puerto de Buenos Aires (Argentina), y b) Verificación de la colinealidad entre los ejes de dos cojinetes de un tubo de timón de un barco en construcción en el Astillero Río Santiago (Argentina)