EGRET Spectral Index and the Low-Energy Peak Position in the Spectral Energy Distribution of EGRET-Detected Blazars

In current theoretical models of the blazar subclass of active galaxies, the broadband emission consists of two components: a low-frequency synchrotron component with a peak in the IR to X-ray band, and a high-frequency inverse Compton component with a peak in the gamma-ray band. In such models, the gamma-ray spectral index should be correlated with the location of the low-energy peak, with flatter gamma-ray spectra expected for blazars with synchrotron peaks at higher photon energies and vice versa. Using the EGRET-detected blazars as a sample, we examine this correlation and possible uncertainties in its construction.Comment: 17 pages including 1 figure, accepted for publication in The Astrophysical Journa

Índice de sustentabilidade agroambiental para o perímetro irrigado Ayres de Souza.

Uma análise integrada do atual uso dos recursos naturais do Perímetro Irrigado de Ayres de Souza, localizado no Vale do Acaraú, Ceará, foi realizada através do desenvolvimento de um índice de sustentabilidade agroecológica. Os dados dessa pesquisa foram oriundos de questionários aplicados a 33 produtores agrícolas beneficiados pelo projeto de irrigação. Os indicadores de sustentabilidade foram estimados pelo emprego de análise fatorial, método da análise fatorial/análise de componentes principais. O índice de sustentabilidade estimado a partir dos indicadores selecionados registrou uma situação de sustentabilidade fragilizada ou de insustentabilidade reversível. As unidades produtivas apresentaram um porcentual de 60,6% com alguma sustentabilidade; e os demais 39,4% estão em condições de insustentabilidade. Os resultados também mostraram que os fatores dominantes do índice de sustentabilidade foram: nível da atividade agrícola praticada, agricultura familiar, condições atuais do sistema água-solo e infraestrutura,fontes alternativas de renda e experiência em tratos culturais

Mesoplastics and large microplastics along a use gradient on the Uruguay Atlantic coast: Types, sources, fates, and chemical loads

Plastic pollution is a global problem with great local and regional variability. Plastic litter reaches beaches directly and indirectly through different pathways, due to both terrestrial and marine pressures. In this study, we assess and characterize meso and microplastic pollution on four Uruguayan oceanic beaches along a gradient of tourist use within a complex regional coastal marine system. In Punta del Diablo we found a total mean density of 106 items m of different debris (pellets, fragments, and foams) with different polymeric compositions, and diverse persistent bioaccumulative and toxic chemicals (PAHs, PCBs, OCs, heavy metals). However, the trend of plastic debris densities along this gradient was not what was expected. Fabeiro, one of the sites furthest from the urban center, had the highest total mean density of plastics (292 items m) suggesting that marine influences (winds, currents, and beach orientation) have a preponderant role in the distribution of micro and mesoplastics. Meanwhile, the density in the urban site (Pueblo) was highest during summer (March, 201 items m), 200 times higher than the density observed in winter (July, 1 item m). Although this difference could be associated to the peak season (southern summer), the analysis of types of plastics (171 pellets m vs. 8 cigarette butts m) suggested a predominance of marine inputs. Seasonal changes in the configuration of the beaches due to natural geomorphological dynamics imply alternating states (Source or Sink of debris) that also affect the final density of plastics in the system. The relative importance of both sources is highly variable throughout the year and understanding them may directly improve beach management and stranded coastal plastic litter cleaning.With funding from the Spanish government through the "María de Maeztu Unit of Excellence" accreditation (MDM-2017-0737

The Search for Living Worlds and the Connection to Our Cosmic Origins

International audienceOne of the most exciting scientific challenges is to detect Earth-like planets in the habitable zones of other stars in the galaxy and search for evidence of life. The ability to observe and characterise dozens of potentially Earth-like planets now lies within the realm of possibility due to rapid advances in key space and imaging technologies. The associated challenge of directly imaging very faint planets in orbit around nearby very bright stars is now well understood, with the key instrumentation also being perfected and developed. Such advances will allow us to develop large transformative telescopes, covering a broad UV-optical-IR spectral range, which can carry out the detailed research programmes designed to answer the questions we wish to answer: Carry out high contrast imaging surveys of nearby stars to search for planets within their habitable zones. Characterise the planets detected to determine masses and radii from photometric measurements. Through spectroscopic studies of their atmospheres and surfaces, search for habitability indicators and for signs of an environment that has been modified by the presence of life. Active studies of potential missions have been underway for a number of years. The latest of these is the Large UV Optical IR space telescope (LUVOIR), one of four flagship mission studies commissioned by NASA in support of the 2020 US Decadal Survey. LUVOIR, if selected, will be of interest to a wide scientific community and will be the only telescope capable of searching for and characterizing a sufficient number of exoEarths to provide a meaningful answer to the question - Are we alone?. This paper is a submission to the European Space Agency Voyage 2050 call for white papers outlining the case for an ESA contribution to a Large UVOIR telescope

The Search for Living Worlds and the Connection to Our Cosmic Origins

International audienceOne of the most exciting scientific challenges is to detect Earth-like planets in the habitable zones of other stars in the galaxy and search for evidence of life. The ability to observe and characterise dozens of potentially Earth-like planets now lies within the realm of possibility due to rapid advances in key space and imaging technologies. The associated challenge of directly imaging very faint planets in orbit around nearby very bright stars is now well understood, with the key instrumentation also being perfected and developed. Such advances will allow us to develop large transformative telescopes, covering a broad UV-optical-IR spectral range, which can carry out the detailed research programmes designed to answer the questions we wish to answer: Carry out high contrast imaging surveys of nearby stars to search for planets within their habitable zones. Characterise the planets detected to determine masses and radii from photometric measurements. Through spectroscopic studies of their atmospheres and surfaces, search for habitability indicators and for signs of an environment that has been modified by the presence of life. Active studies of potential missions have been underway for a number of years. The latest of these is the Large UV Optical IR space telescope (LUVOIR), one of four flagship mission studies commissioned by NASA in support of the 2020 US Decadal Survey. LUVOIR, if selected, will be of interest to a wide scientific community and will be the only telescope capable of searching for and characterizing a sufficient number of exoEarths to provide a meaningful answer to the question - Are we alone?. This paper is a submission to the European Space Agency Voyage 2050 call for white papers outlining the case for an ESA contribution to a Large UVOIR telescope