569 research outputs found

    ÂżDĂ“NDE DUERMEN LAS AVES? OBSERVACIONES DE AVES DESCANSANDO EN EL SOTOBOSQUE DE LAS TIERRAS BAJAS DE COSTA RICA

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    El uso del hábitat nocturno de las aves diurnas es poco conocido. Este estudio presenta observaciones de los sitios de descanso y comportamiento nocturnal de 18 especies de aves en el sotobosque de las tierras bajas de Costa Rica. Realizamos muestreos nocturnos en hábitats riparios y no-riparios en potreros, bosques secundarios y bosques maduros. Observamos un mayor número de aves posadas en hábitats riparios (67) que en hábitats no riparios (3). El sotobosque ripario es utilizado por un grupo diverso de especies de aves como dormidero. Nuestras observaciones resaltan la importancia de corredores riparios, especialmente en hábitats alterados por el ser humano como los potreros

    Impact of slowdown of Atlantic overturning circulation on heat and freshwater transports

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    Recent measurements of the strength of the Atlantic overturning circulation at 26°N show a 1 year drop and partial recovery amid a gradual weakening. To examine the extent and impact of the slowdown on basin wide heat and freshwater transports for 2004–2012, a box model that assimilates hydrographic and satellite observations is used to estimate heat transport and freshwater convergence as residuals of the heat and freshwater budgets. Using an independent transport estimate, convergences are converted to transports, which show a high level of spatial coherence. The similarity between Atlantic heat transport and the Agulhas Leakage suggests that it is the source of the surface heat transport anomalies. The freshwater budget in the North Atlantic is dominated by a decrease in freshwater flux. The increasing salinity during the slowdown supports modeling studies that show that heat, not freshwater, drives trends in the overturning circulation in a warming climate

    Impact of slowdown of Atlantic overturning circulation on heat and freshwater transports

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    Recent measurements of the strength of the Atlantic overturning circulation at 26°N show a 1 year drop and partial recovery amid a gradual weakening. To examine the extent and impact of the slowdown on basin wide heat and freshwater transports for 2004–2012, a box model that assimilates hydrographic and satellite observations is used to estimate heat transport and freshwater convergence as residuals of the heat and freshwater budgets. Using an independent transport estimate, convergences are converted to transports, which show a high level of spatial coherence. The similarity between Atlantic heat transport and the Agulhas Leakage suggests that it is the source of the surface heat transport anomalies. The freshwater budget in the North Atlantic is dominated by a decrease in freshwater flux. The increasing salinity during the slowdown supports modeling studies that show that heat, not freshwater, drives trends in the overturning circulation in a warming climate

    The extragalactic radio-source population at 95 GHz

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    We have used the Australia Telescope Compact Array (ATCA) at 95GHz to carry out continuum observations of 130 extragalactic radio sources selected from the Australia Telescope 20GHz (AT20G) survey. Over 90% of these sources are detected at 95 GHz, and we use a triple-correlation method to measure simultaneous 20 and 95 GHz flux densities. We show that the ATCA can measure 95GHz flux densities to ~10% accuracy in a few minutes for sources above ~50mJy. The median 20-95GHz spectral index does not vary significantly with flux density for extragalactic sources with S20>150 mJy. This allows us to estimate the extragalactic radio source counts at 95GHz by combining our observed 20-95GHz spectral-index distribution with the accurate 20GHz source counts measured in the AT20G survey. The resulting 95GHz source counts down to 80 mJy are significantly lower than those found by several previous studies. The main reason is that most radio sources with flat or rising spectra in the frequency range 5-20GHz show a spectral turnover between 20 and 95 GHz. As a result, there are fewer 95GHz sources (by almost a factor of two at 0.1 Jy) than would be predicted on the basis of extrapolation from the source populations seen in lower-frequency surveys. We also derive the predicted confusion noise in CMB surveys at 95GHz and find a value 20-30% lower than previous estimates. The 95GHz source population at the flux levels probed by this study is dominated by QSOs with a median redshift z~1. We find a correlation between optical magnitude and 95GHz flux density which suggests that many of the brightest 95 GHz sources are relativistically beamed, with both the optical and millimetre continuum significantly brightened by Doppler boosting.Comment: Replaced with final version (MNRAS, in press), 15 pages plus two landscape data table

    Advanced EFL learners' beliefs about language learning and teaching: a comparison between grammar, pronunciation, and vocabulary

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    This paper reports on the results of a study exploring learners’ beliefs on the learning and teaching of English grammar, pronunciation and vocabulary at tertiary level. While the importance of learners’ beliefs on the acquisition process is generally recognized, few studies have focussed on and compared learners’ views on different components of the language system. A questionnaire containing semantic scale and Likert scale items probing learners’ views on grammar, pronunciation and vocabulary was designed and completed by 117 native speakers of Dutch in Flanders, who were studying English at university. The analysis of the responses revealed that (i) vocabulary was considered to be different from grammar and pronunciation, both in the extent to which an incorrect use could lead to communication breakdown and with respect to the learners’ language learning strategies, (ii) learners believed in the feasibility of achieving a native-like proficiency in all three components, and (iii) in-class grammar, pronunciation and vocabulary exercises were considered to be useful, even at tertiary level. The results are discussed in light of pedagogical approaches to language teaching
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