592 research outputs found
Quantum electrodynamic calculation of the hyperfine structure of 3He
The combined fine and hyperfine structure of the states in He is
calculated within the framework of nonrelativistic quantum electrodynamics. The
calculation accounts for the effects of order and increases the
accuracy of theoretical predictions by an order of magnitude. The results
obtained are in good agreement with recent spectroscopic measurements in
He.Comment: 13 pages, spelling and grammar correcte
The scaling properties of exchange and correlation holes of the valence shell of second row atoms
We study the exchange and correlation hole of the valence shell of second row
atoms using variational Monte Carlo techniques, especially correlated
estimates, and norm-conserving pseudopotentials. The well-known scaling of the
valence shell provides a tool to probe the behavior of exchange and correlation
as a functional of the density and thus test models of density functional
theory. The exchange hole shows an interesting competition between two scaling
forms -- one caused by self-interaction and another that is approximately
invariant under particle number, related to the known invariance of exchange
under uniform scaling to high density and constant particle number. The
correlation hole shows a scaling trend that is marked by the finite size of the
atom relative to the radius of the hole. Both trends are well captured in the
main by the Perdew-Burke-Ernzerhof generalized-gradient approximation model for
the exchange-correlation hole and energy.Comment: 18 pages, 8 figure
Observing the intrinsic linewidth of a quantum-cascade laser: beyond the Schawlow-Townes limit
A comprehensive investigation of the frequency-noise spectral density of a
free-running mid-infrared quantum-cascade laser is presented for the first
time. It provides direct evidence of the leveling of this noise down to a white
noise plateau, corresponding to an intrinsic linewidth of a few hundred Hz. The
experiment is in agreement with the most recent theory on the fundamental
mechanism of line broadening in quantum-cascade lasers, which provides a new
insight into the Schawlow-Townes formula and predicts a narrowing beyond the
limit set by the radiative lifetime of the upper level.Comment: 4 pages, 4 figure
Metallic Species In Ambient Air Particles. PM10
In the present work metallic species of particulate matter(PM10) present in an urban area of Gran Canaria Island were quantified. Experimental measurements were carried out from October 2004 to September 2005 with a total of 53 samples (4 or 5 per month). PM10 was collected in fiber filters using high volume samplers. The average concentration was 32,6 ± 19,6 μg/m3. PM10 was determined gravimetrically. Concentrations of metallic elements were analized by atomic emission spectrophotometry using an ICP-OES. Two categories of elements were found: “abundant” and “scarce”. The examined elements were characterized according to their origin from natural or anthropogenic emissions on the basis of enrichment factors. Factor analysis of elemental composition pattern was also used to identify possible pollution source-types
Metallic species in ambient air particles of Canary Islands. Soluble fraction in total suspended matter
En el presente trabajo se cuantifican las fracciones metalicas total y soluble de la materia en suspensión total (MST),en una zona urbana de Gran Canaria. Las medidas se realizaron entre octubre de 2004 y septiembre de 2005 sobre un total de 53 muestras (4 o 5 por mes). La materia en suspensión total se recogió en fíltros de fibra de vídrio usando muestreadores de alto volumen. La concentración media resulto ser 68,5 ・} 35,5 μg/m3 . La MST se determinó gravimétricamente. La materia soluble en agua se extrajo mediante sonicación. Las concentraciones de los elementos metálicos se determinaron por espectrometría de emisión atómica, usando un ICP-OES. Se encontraron dos categorias de elementos de acuerdo con sus niveles de concentración: “abundantes” y “escasos”. En la fracción soluble los “abundantes” fueron principalmente Na,Ca, K y Zn; entre los “escasos” predominan Cu y Ti. Se estableció la disponibilidad de todos los elementos solubles, encontrandose altos coeficientes para todos ellos y especialmente para el Mn(99,9%). A fin de identificar las fuentes para dichos elementos se uso el análisis factorial. Los resultados muestran que Al, Ca, Fe, Mg y K provienen de fuentes naturales, en tanto que Ni, Co, V, Mo, Pt, Zn, Cu, Sb y Cr son antropogénicos
Frequency metrology of helium around 1083 nm and determination of the nuclear charge radius
We measure the absolute frequency of seven out of the nine allowed
transitions between the 2{\it S} and 2{\it P} hyperfine manifolds in a
metastable He beam by using an optical frequency comb synthesizer-assisted
spectrometer. The relative uncertainty of our measurements ranges from to , which is, to our knowledge, the most precise
result for any optical He transition to date. The resulting {\it
P}-2{\it S} centroid frequency is kHz.
Comparing this value with the known result for the He centroid and
performing {\em ab initio} QED calculations of the He-He isotope shift,
we extract the difference of the squared nuclear charge radii of
He and He. Our result for fm disagrees by
about with the recent determination [R. van Rooij {\em et al.},
Science {\bf 333}, 196 (2011)].Comment: 4 pages, 3 figures, 3 table
Clasificación climática de los bosques de Abies pinsapo en el sur de España
Understanding the current distribution of vegetation and its interaction with climate regularity is important for predicting its future change. 35 weather stations with monthly resolutions have been reconstructed using GENPT software to study the pinsapo fir forest climate types. Ten climate variables have been used to describe the particular climate of A. pinsapo forests following the Climatic System of Allué (1990). A climate examination suggests that pinsapo fir forests might be established in a particular climate, which seems to be unique in the Iberian Peninsula, though the species also grows under other climates. A multivariable analysis has been done, providing five classes of pinsapo fir forests sharing some climate features: Atlantic, Mediterranean, warm, continental and cold. Results are biogeographically consistent and may help to explain plant biogeography in this region. Preservation efforts in pinsapo fir forests should be concentrated on the distribution areas with the highest risk of the climate change impact.Los estudios de distribución actual de la vegetación, en un contexto de cambio global, son un elemento importante para predecir los posibles cambios futuros. En este trabajo, a partir de 35 estaciones meteorológicas, se realizó la reconstrucción de los tipos climáticos para el pinsapo, utilizando 10 variables del Sistema Fitoclimatico de Allué (1990). Los resultados sugieren la existencia de un clima específico para la distribución del pinsapo, que parece ser único en la península ibérica, aunque la especie también esta presente en otros fitoclimas. A partir de un análisis multivariable se han identificado cinco clases fitoclimáticas con presencia de pinsapo: atlántico, mediterráneo, templado, continental y frío. Los resultados son biogeográficamente consistentes y pueden ayudar a explicar la biogeografía de su área de distribución. Los programas de conservación del pinsapo deberían utilizar información fitoclimática para definir las zonas prioritarias de protección frente a los posibles efectos del cambio climático
Distribución por tamaños de la materia particulada en Las Palmas de Gran Canaria
En este trabajo se presenta la distribución por tamaños de la materia particulada (MP)en la ciudad de Las Palmas de Gran Canaria. La experiencia se llevó a cabo entre junio de 2002 y marzo de 2003. A tal efecto se han utilizado captadores de alto volumen equipados con impactadores en cascada, que permiten una separación, en filtros de fibra de vidrio, de la materia recogida en seis fracciones de tamaño. Al final del muestreo se dispuso de 42 muestras válidas para el análisis. La materia particulada se determinó gravimétricamente. Se establecióla distribución de la concentración másica en función de los diámetros de corte. Se utilizan los diagramas de Lundgreen para establecer la distribución por tamaños y la evolución estacional e histórica. Se estudian las fracciones fina y gruesa del aerosol así como su evolución temporal e histórica
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