3,752 research outputs found
Photo-desorption of H2O:CO:NH3 circumstellar ice analogs: Gas-phase enrichment
We study the photo-desorption occurring in HO:CO:NH ice mixtures
irradiated with monochromatic (550 and 900 eV) and broad band (250--1250 eV)
soft X-rays generated at the National Synchrotron Radiation Research Center
(Hsinchu, Taiwan). We detect many masses photo-desorbing, from atomic hydrogen
(m/z = 1) to complex species with m/z = 69 (e.g., CHNO, CHO,
CHN), supporting the enrichment of the gas phase.
At low number of absorbed photons, substrate-mediated exciton-promoted
desorption dominates the photo-desorption yield inducing the release of weakly
bound (to the surface of the ice) species; as the number of weakly bound
species declines, the photo-desorption yield decrease about one order of
magnitude, until porosity effects, reducing the surface/volume ratio, produce a
further drop of the yield.
We derive an upper limit to the CO photo-desorption yield, that in our
experiments varies from 1.4 to 0.007 molecule photon in the range ~absorbed photons cm. We apply these findings to a
protoplanetary disk model irradiated by a central T~Tauri star
Perceptual basis of evolving Western musical styles
The brain processes temporal statistics to predict future events and to categorize perceptual objects. These statistics, called expectan- cies, are found in music perception, and they span a variety of different features and time scales. Specifically, there is evidence that music perception involves strong expectancies regarding the distri- bution of a melodic interval, namely, the distance between two consecutive notes within the context of another. The recent availability of a large Western music dataset, consisting of the historical record condensed as melodic interval counts, has opened new possibilities for data-driven analysis of musical perception. In this context, we present an analytical approach that, based on cognitive theories of music expectation and machine learning techniques, recovers a set of factors that accurately identifies historical trends and stylistic transitions between the Baroque, Classical, Romantic, and Post-Romantic periods. We also offer a plausible musicological and cognitive interpretation of these factors, allowing us to propose them as data-driven principles of melodic expectation.Facultad de Bellas Arte
Absence of mutagenicity and antimutagenicity of the extract obtained from the flowers of "ipĂȘ roxo" Tabebuia impetiginosa (Mart. ex DC.) Standl
A Tabebuia impetiginosa, conhecida popularmente como ipĂȘ-roxo, Ă© uma planta nativa das florestas tropicais chuvosas da AmĂ©rica do Sul e Central. Componentes quĂmicos obtidos da casca tĂȘm mostrado efeito terapĂȘutico, como antiinflamatĂłrio, antifĂșngico e antibacteriano. PorĂ©m, pela falta de dados na literatura, pouco se sabe sobre os efeitos do extrato das flores. Assim, o objetivo do presente trabalho foi avaliar o potencial mutagĂȘnico e antimutagĂȘnico do extrato obtido das flores da T. impetiginosa, em trĂȘs diferentes concentraçÔes (100, 300 e 500 mg kg-1 p.c.) pelo teste do micronĂșcleo. Para o teste de mutagenicidade, a doxorrubicina (DXR, 90 mg kg-1 p.c.) foi utilizada como indutor de danos no DNA e para o teste de antimutagenicidade, os tratamentos com o extrato foram realizados simultaneamente com este agente quĂmico. O sangue perifĂ©rico dos animais foi coletado 24 horas apĂłs os tratamentos. A comparação da frequĂȘncia de eritrĂłcitos policromĂĄticos (PCEs) em 400 eritrĂłcitos/animal entre os diferentes grupos nĂŁo demonstrou qualquer citotoxicidade do extrato. Em relação Ă s frequĂȘncias de micronĂșcleos em PCEs (PCEMNs), nĂŁo foram observadas diferenças significativas entre os grupos tratados com as diferentes concentraçÔes de extrato e o controle negativo. Da mesma forma, todos os grupos de animais que receberam os tratamentos simultĂąneo do extrato (100, 300 ou 500 mg kg-1 p.c.) com a DXR, apresentaram valores de PCEMNs muito prĂłximos quando comparados com os dados observados no grupo de animais que recebeu somente a DXR. Esses resultados apresentados indicam ausĂȘncia de efeito mutagĂȘnico e antimutagĂȘnico do extrato obtido das flores da T. impetiginosa em sistema teste in vivo.T. impetiginosa, known as "ipĂȘ-roxo", is a plant native to tropical rain forests of Central and South Americas. Chemical compounds obtained from its bark have shown anti-inflammatory, antifungal and antibacterial therapeutic effect. However, due to the lack of data in the literature, little is known about the effects of its flower extract. Thus, the aim of this study was to evaluate the mutagenic and antimutagenic potential of the extract obtained from T. impetiginosa flowers at three different concentrations (100, 300 and 500 mg kg-1 p.c.) by the micronucleus test. For the mutagenicity test, doxorubicin (DXR, 90 mg kg-1 p.c.) was used as DNA-damage inducer, while for the antimutagenicity test, treatments with the extract were performed simultaneously with this chemical agent. The peripheral blood of animals was collected 24 hours after the treatments. The frequency of polychromatic erythrocytes (PCEs) in 400 erythrocytes/animal was compared among the different groups and showed no extract cytotoxicity. As regards the frequency of micronuclei in PCEs (PCEMNs), there were no significant differences between the groups treated with different concentrations of extract and the negative control. Similarly, all groups of animals that received the simultaneous extract treatments (100, 300 or 500 mg kg-1 p.c.) with DXR showed very similar values of PCEMNs when compared with the data observed for the group of animals that received DXR alone. These results indicate no mutagenic and antimutagenic effect of the extract obtained from T. impetiginosa flowers in the testing system in vivo.Conselho Nacional de Desenvolvimento Cientifico e TecnolĂłgico (CNPq
A reappraisal of the genus Megacaryon (Boraginaceae, Lithospermeae) based on molecular, morphological, and karyological evidence
Perceptual basis of evolving Western musical styles
The brain processes temporal statistics to predict future events and to categorize perceptual objects. These statistics, called expectan- cies, are found in music perception, and they span a variety of different features and time scales. Specifically, there is evidence that music perception involves strong expectancies regarding the distri- bution of a melodic interval, namely, the distance between two consecutive notes within the context of another. The recent availability of a large Western music dataset, consisting of the historical record condensed as melodic interval counts, has opened new possibilities for data-driven analysis of musical perception. In this context, we present an analytical approach that, based on cognitive theories of music expectation and machine learning techniques, recovers a set of factors that accurately identifies historical trends and stylistic transitions between the Baroque, Classical, Romantic, and Post-Romantic periods. We also offer a plausible musicological and cognitive interpretation of these factors, allowing us to propose them as data-driven principles of melodic expectation.Facultad de Bellas Arte
Hydrological balance of the Boura dam (Burkina Faso)
In developing countries, where many basins are ungauged or poorly gauged, small reservoirs could be used as hydrometric stations for estimating runoff of small watersheds upstream of the dams. Thus, hydrological monitoring of dam is essential in water resources management by predicting where there may be shortages or surplus water
Optical spin injection and spin lifetime in Ge heterostructures
We demonstrate optical orientation in Ge/SiGe quantum wells and study their
spin properties. The ultrafast electron transfer from the center of the
Brillouin zone to its edge allows us to achieve high spin-polarization
efficiencies and to resolve the spin dynamics of holes and electrons. The
circular polarization degree of the direct-gap photoluminescence exceeds the
theoretical bulk limit, yielding ~37% and ~85% for transitions with heavy and
light holes states, respectively. The spin lifetime of holes at the top of the
valence band is found to be ~0.5 ps and it is governed by transitions between
heavy and light hole states. Electrons at the bottom of the conduction band, on
the other hand, have a spin lifetime that exceeds 5 ns below 150 K. Theoretical
analysis of the electrons spin relaxation indicates that phonon-induced
intervalley scattering dictates the spin lifetime.Comment: 5 pages, 3 figure
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