2,294 research outputs found
Lifetime Measurement of the 6s Level of Rubidium
We present a lifetime measurements of the 6s level of rubidium. We use a
time-correlated single-photon counting technique on two different samples of
rubidium atoms. A vapor cell with variable rubidium density and a sample of
atoms confined and cooled in a magneto-optical trap. The 5P_{1/2} level serves
as the resonant intermediate step for the two step excitation to the 6s level.
We detect the decay of the 6s level through the cascade fluorescence of the
5P_{3/2} level at 780 nm. The two samples have different systematic effects,
but we obtain consistent results that averaged give a lifetime of 45.57 +- 0.17
ns.Comment: 10 pages, 9 figure
Lifetime Measurement of the 8s Level in Francium
We measure the lifetime of the 8s level on a magneto-optically trapped sample
of ^{210}Fr atoms with time-correlated single-photon counting. The 7P_{1/2}
state serves as the resonant intermediate level for two-photon excitation of
the 8s level completed with a 1300 nm laser. Analysis of the fluorescence decay
through the the 7P_{3/2} level gives 53.30 +- 0.44 ns for the 8s level
lifetime.Comment: 4 pages, 4 figure
Características sedimentológicas y paleogeográficas del fan-delta albiense de la Formación Monte Grande y sus relaciones con el Flysh Negro (Arminza-Górliz, Vizcaya)
La Fm. Monte Grande (Albiense inferior-medio, Vizcaya) posee más de 500 m de conglomerados, areniscas, lutitas y calizas urgonianas, sedimentadas en un «fan-delta» retrogradante. Importantes disconformidades limitando la unidad sugieren dos variaciones relativas bruscas del nivel del mar
Preliminary studies for anapole moment measurements in rubidium and francium
Preparations for the anapole measurement in Fr indicate the possibility of
performing a similar measurement in a chain of Rb. The sensitivity analysis
based on a single nucleon model shows the potential for placing strong limits
on the nucleon weak interaction parameters. There are values of the magnetic
fields at much lower values than found before that are insensitive to first
order changes in the field. The anapole moment effect in Rb corresponds to an
equivalent electric field that is eighty times smaller than Fr, but the
stability of the isotopes and the current performance of the dipole trap in the
apparatus, presented here, are encouraging for pursuing the measurment.Comment: 16 pages, 6 figures. Accepted for publication in the J. Phys.
Taxonomic identification of Amazonian tree crowns from aerial photography
Question: To what extent can aerial photography be used for taxonomic identification of Amazonian tree crowns?
Objective: To investigate whether a combination of dichotomous keys and a web-based interface is a suitable approach to identify tree crowns.
Location: The fieldwork was conducted at Tiputini Biodiversity Station located in the Amazon, eastern Ecuador.
Methods: High-resolution imagery was taken from an airplane flying at a low altitude (600 m) above the ground. Imagery of the observable upper layer of the tree crowns was used for the analysis. Dichotomous identification keys for different types of crowns were produced and tested. The identification keys were designed to be web-based interactive, using Google Earth as the main online platform. The taxa analysed were Iriartea, Astrocaryum, Inga, Parkia, Cecropia, Pourouma, Guarea, Otoba, Lauraceae and Pouteria.
Results: This paper demonstrates that a combination of photo-imagery, dichotomous keys and a web-based interface can be useful for the taxonomic identification of Amazonian trees based on their crown characteristics. The keys tested with an overall identification accuracy of over 50% for five of the ten taxa with three of them showing accuracy greater than 70% (Iriartea, Astrocaryum and Cecropia).
Conclusions: The application of dichotomous keys and a web-based interface provides a new methodological approach for taxonomic identification of various Amazonian tree crowns. Overall, the study showed that crowns with a medium-rough texture are less reliably identified than crowns with smoother or well-defined surfaces
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