24 research outputs found
Study of infrared scintillations in gaseous and liquid argon - Part II: light yield and possible applications
We present here a comprehensive study of the light yield of primary and
secondary scintillations produced in gaseous and liquid Ar in the near infrared
(NIR) and visible region, at cryogenic temperatures. The measurements were
performed using Geiger-mode avalanche photodiodes (GAPDs) and pulsed X-ray
irradiation. The primary scintillation yield of the fast emission component in
gaseous Ar was found to be independent of temperature in the range of 87-160 K;
it amounted to 17000+/-3000 photon/MeV in the NIR in the range of 690-1000 nm.
In liquid Ar at 87 K, the primary scintillation yield of the fast component was
considerably reduced, amounting to 510+/-90 photon/MeV, in the range of
400-1000 nm. Proportional NIR scintillations (electroluminescence) in gaseous
Ar were also observed; their amplification parameter at 160 K was measured to
be 13 photons per drifting electron per kV. No proportional scintillations were
observed in liquid Ar up to the electric fields of 30 kV/cm. The applications
of NIR scintillations in dark matter search and coherent neutrino-nucleus
scattering experiments and in ion beam radiotherapy are considered.Comment: 20 pages, 11 figures. Submitted to JINS
Mechanisms of community assembly explaining beta-diversity patterns across biogeographic regions
Avaliação da orientação molecular de moldados de polipropileno utilizando figuras de pólo obtidas por difração de raios X
Plant functional and taxonomic diversity in European grasslands along climatic gradients
Aim: European grassland communities are highly diverse, but patterns and drivers of their continental-scale diversity remain elusive. This study analyses taxonomic and functional richness in European grasslands along continental-scale temperature and precipitation gradients.
Location: Europe.
Methods: We quantified functional and taxonomic richness of 55,748 vegetation plots. Six plant traits, related to resource acquisition and conservation, were analysed to describe plant community functional composition. Using a null-model approach we derived functional richness effect sizes that indicate higher or lower diversity than expected given the taxonomic richness. We assessed the variation in absolute functional and taxonomic richness and in functional richness effect sizes along gradients of minimum temperature, temperature range, annual precipitation, and precipitation seasonality using a multiple general additive modelling approach.
Results: Functional and taxonomic richness was high at intermediate minimum temperatures and wide temperature ranges. Functional and taxonomic richness was low in correspondence with low minimum temperatures or narrow temperature ranges. Functional richness increased and taxonomic richness decreased at higher minimum temperatures and wide annual temperature ranges. Both functional and taxonomic richness decreased with increasing precipitation seasonality and showed a small increase at intermediate annual precipitation. Overall, effect sizes of functional richness were small. However, effect sizes indicated trait divergence at extremely low minimum temperatures and at low annual precipitation with extreme precipitation seasonality.
Conclusions: Functional and taxonomic richness of European grassland communities vary considerably over temperature and precipitation gradients. Overall, they follow similar patterns over the climate gradients, except at high minimum temperatures and wide temperature ranges, where functional richness increases and taxonomic richness decreases. This contrasting pattern may trigger new ideas for studies that target specific hypotheses focused on community assembly processes. And though effect sizes were small, they indicate that it may be important to consider climate seasonality in plant diversity studies