427 research outputs found
On-chip integrated amplifiers and lasers utilizing rare-earth-ion activation
This contribution reviews our recent results on rare-earth-ion-doped integrated amplifiers and lasers. We have concentrated our efforts on complex-doped polymers, amorphous Al2O3, and crystalline potassium double tungstates
Measurement of correlation between transmission and scattering during wound healing in hen corneas
Producción CientíficaThe aim of this work is to provide experimental data for corneal transparency and scattering to help create
a more complete model of corneal transparency. The scattered light in 96 healing hen corneas was measured
for three wavelengths by a scatterometer constructed in the Optics Laboratory (The University of Valladolid,
Spain). With the help of mirrors and beamsplitters, the light from the three lasers is directed toward the cell
containing the sample to be measured. The measured scattered light varies between six orders of magnitude.
Corneal transmissivity, mean cosine of a scattering angle, and angular distribution of scattered light were all
computed. The total transmitted light remained practically constant over a wide range of light values
transmitted in a forward direction (direct transmissivity). The value of the mean cosine of the scattering
direction is very close to the unit (g40:98), even in corneas with high opacities. The behavior of g indicates
that even damaged corneas evidence extremely small scattering, compared to other biological tissues.
The transmission reduction of each cornea is related to an increase in scattered light. In all cases, scattered
light is concentrated at very small angles. This behavior is acceptable in corneas that are healthy or which
evidence small lesions, but remains in corneas that are severely injured
Relación entre las concentraciones de polen aéreo de Artemisia, Chenopodiaceae, Plantago y Taraxacum y la prevalencia de polinosis en estudiantes universitarios de León
XV lnternational A.P.L.E. Symposium of Palynolog
Fabrication, operation, and applications of efficient dielectric waveguide lasers
This paper reviews our recent results on rare-earth-ion-doped integrated lasers. We have concentrated our efforts on crystalline potassium double tungstates and amorphous aluminum oxide. In the former material class we have demonstrated channel waveguide lasers based on Yb3+ doping, operating near 1 µm wavelength with slope efficiencies exceeding 70% and output powers up to 418 mW, as well as a record-low quantum defect of 0.7%. When activating with Tm3+, we have achieved lasers operating near 2 µm wavelength with a slope efficiency of 70% and 300 mW output power, which are currently tested for trace-gas sensing of NH3 and CO2. In Al2O3 layers on silicon wafers, when doped with Er3+, we have demonstrated a distributed-feedback channel waveguide laser at 1.5 µm wavelength with a free-running line width of 1.7 kHz. Yb3+ doping has resulted in distributed-feedback and distributed-Bragg-reflector channel waveguide lasers with 67% slope efficiency and up to 55 mW output power. Dual-wavelength lasers have been demonstrated with this approach and a stable microwave signal at 15 GHz has been generated via heterodyne detection, which has then been used as a simple read-out for intra-laser-cavity optical sensing of nanoparticles in these lasers
High Energy Cosmic Rays from Neutrinos
We discuss recent models in which neutrinos, which are assumed to have mass
in the eV range, originate the highest energy cosmic rays by interaction with
the enhanced density in the galactic halo of the relic cosmic neutrino
background. We make an analytical calculation of the required neutrino fluxes
to show that the parameter space for these models is constrained by horizontal
air shower searches and by the total number of background neutrinos, so that
only models which have fairly unnatural halo sizes and enhanced densities are
allowed.Comment: 14 pages, 3 ps figures. To appear in Phys. Rev.
Ultra-High Energy Cosmic Rays from Neutrino Emitting Acceleration Sources?
We demonstrate by numerical flux calculations that neutrino beams producing
the observed highest energy cosmic rays by weak interactions with the relic
neutrino background require a non-uniform distribution of sources. Such sources
have to accelerate protons at least up to 10^{23} eV, have to be opaque to
their primary protons, and should emit the secondary photons unavoidably
produced together with the neutrinos only in the sub-MeV region to avoid
conflict with the diffuse gamma-ray background measured by the EGRET
experiment. Even if such a source class exists, the resulting large
uncertainties in the parameters involved in this scenario does currently not
allow to extract any meaningful information on absolute neutrino masses.Comment: 6 pages, 4 figures, RevTeX styl
Evaluation of "Pampa-Corte" simulation model in different beef cattle fattening systems in Spain
One-year study of airborne sugar compounds: cross-interpretation with other chemical species and meteorological conditions
The daily evolution of seventeen sugar compounds (seven saccharides, seven alcohol-saccharides and three anhydrosaccharides) in atmospheric aerosol samples collected between 9 March 2016 and 14 March 2017 was studied in León (Spain). The main links between the concentration of sugar compounds and various chemical species, pollen, fungal spores and meteorological conditions were investigated. The results showed that, in spring, when high levels of metabolic activity of the plants occur and temperatures increase, glucose, sucrose, 2-methyl-erithritol, mannitol, arabitol and inositol, are significantly correlated with airborne pollen concentrations. Between spring and autumn, Alternaria air concentrations are significantly correlated with temperatures, arabitol and sorbitol + adonitol concentrations. Furthermore, during rainy days, Alternaria is also correlated with mannitol. In autumn, lower temperatures cause an increase in the concentrations of levoglucosan, mannosan and galactosan, probably due to the increased use of domestic heating devices. These anhydrosugars and arabinose, fructose and glucose, are significantly correlated with K, NO3−, EC, OC, Cu, Zn, Se, Pb, V and Ni, while mannosan also correlates with As, showing that these anhydrosaccharides can be emitted from different anthropogenic sources. Precipitation causes an increase in glucose and sucrose concentrations, due to the break of pollen particles that produce hundreds of fine size particles. Besides, precipitation causes an increase in arabitol concentrations, due to the release and growth of fungi.publishe
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