Coherent Radiation from Extensive Air Showers in the Ultra-High Frequency Band

Using detailed Monte Carlo simulations we have characterized the features of the radio emission of inclined air showers in the Ultra-High Frequency band (300 MHz - 3 GHz). The Fourier-spectrum of the radiation is shown to have a sizable intensity well into the GHz frequency range. The emission is mainly due to transverse currents induced by the geomagnetic field and to the excess charge produced by the Askaryan effect. At these frequencies only a significantly reduced volume of the shower around the axis contributes coherently to the signal observed on the ground. The size of the coherently emitting volume depends on frequency, shower geometry and observer position, and is interpreted in terms of the relative time delays. At ground level, the maximum emission at high frequencies is concentrated in an elliptical ring-like region around the intersection of a Cherenkov cone with its vertex at shower maximum and the ground. The frequency spectrum of inclined showers when observed at positions that view shower maximum in the Cherenkov direction, is shown to be in broad agreement with the pulses detected by the Antarctic Impulsive Transient Antenna (ANITA) experiment, making the interpretation that they are due to Ultra-High Energy Cosmic Ray atmospheric showers consistent with our simulations. These results are also of great importance for experiments aiming to detect molecular bremsstrahlung radiation in the GHz range as they present an important background for its detection.Comment: 8 pages, 8 figure

Ultra high frequency geomagnetic radiation from extensive air showers

Using the ZHAireS Monte Carlo code, we show that the Fourier-spectrum of the radio emission of inclined airshowers can have a sizable intensity up to the GHz frequency range. At these frequencies only a signi¿cantly reducedvolume of the shower around the axis contributes coherently to the signal observed on the ground, which is mainly due to thegeomagnetic and charge excess mechanisms. At ground level, the maximum emission at high frequencies is concentrated in aring-like elliptical region defined by the intersection with the ground of a Cherenkov cone with its vertex at shower maximum.The frequency-spectrum of inclined showers, when observed at positions close to the ring-like maximum emission region, isin broad agreement with the pulses detected by the ANITA experiment, making the interpretation that they are due to ultra-high energy cosmic ray atmospheric showers consistent with our simulations. These results are also relevant for ground-basedradio experiments aiming at detecting molecular bremsstrahlung radiation in the GHz range - an entirelly different emissionmechanism which is not included in ZHAireS simulations - since they present an important background for such experiments.Fil: Alvarez Muñiz, Jaime. Universidad de Santiago de Compostela; EspañaFil: Carvalho, Washington R., Jr.. Universidad de Santiago de Compostela; EspañaFil: Romero Wolf, Andrés. California Institute of Technology; Estados UnidosFil: Tueros, Matias Jorge. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Instituto Argentino de Radioastronomía. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto Argentino de Radioastronomía; Argentina. Universidad de Santiago de Compostela; EspañaFil: Zas, Enrique. Universidad de Santiago de Compostela; España5th International Workshop on Acoustic and Radio EeV Neutrino detection ActivitiesErlangenAlemaniaErlangen Centre for Astroparticle Physic

Coherent Cherenkov radio pulses from hadronic showers up to EeV energies

The Cherenkov radio pulse emitted by hadronic showers of energies in the EeV range in ice is calculated for the first time using full three dimensional simulations of both shower development and the coherent radio pulse emitted as the excess charge develops in the shower. A Monte Carlo, ZHA ire S, has been developed for this purpose combining the high energy hadronic interaction capabilities of AIRES, and the dense media propagation capabilities of TIERRAS, with the precise low energy tracking and specific algorithms developed to calculate the radio emission in ZHS. A thinning technique is implemented to allow the simulation of radio pulses induced by showers up to 10 EeV in ice. The code is validated comparing the results for electromagnetic and hadronic showers to those obtained with GEANT4 and ZHS codes. The contribution to the pulse of other shower particles in addition to electrons and positrons, mainly protons, pions and muons, is found to be below 3% for 10 PeV and above proton induced showers. The characteristics of hadronic showers and the corresponding Cherenkov frequency spectra are compared with those from purely electromagnetic showers. The dependence of the spectra on shower energy and high-energy hadronic model is addressed and parameterizations for the radio emission in hadronic showers in ice are given for practical applications.Facultad de Ciencias Exacta

Os conhecimentos ecológicos dos pescadores Xikrin-Mẽbêngôkre, Terra Indígena Trincheira Bacajá, Pará, Brasil

The ecological knowledge of the Xikrin-Mẽbêngôkre and its praxis in aquatic environments of Indigenous Trincheira Bacajá (ILTB) are relevant to improving the use of fisheries resources. The fish were aquatic resources most cited as a supply of food needs of Xikrin. Fishermen consider switching this seasonal cycle creates different etnohabitats conducive to a spatiotemporal ichthyodiversity associated with subsistence and commercial fishing. The experts were able to identify the types of landforms associated with Basin of Bacajá river, facilitating orientation in the ways and paths traversed during fishing trips. It is noteworthy that in the description of the occurrence and distribution of fish in the ethnohabitats ILTB there are important specifics beyond the seasonal periods, such as those related to fishing intrinsic and inherent to fish (size, weight, eating behavior and ethno-ecological aspects). The details in the categorization of aquatic ethnohabitats and biodiversity associated with these sites highlights the relationship of Xikrin with their area of usage as well as the agreed divisions of space between the villages, which must be kept, not only for survival and strengthening communities, but also the intrinsic value of belonging and being Xikrin.Os conhecimentos ecológicos dos pescadores Xikrin-Mẽbêngôkre e sua práxis nos ambientes aquáticos da TITB foram estudados visando obter informações relacionadas à percepção local sobre a dinâmica espaço-temporal dos peixes no rio Bacajá. Os dados foram obtidos por meio de entrevistas; observações diretas e excursões guiadas. Os peixes foram os recursos aquáticos mais citados como suprimento das necessidades alimentares dos Xikrin. Os pescadores consideram que a alternância entre o ciclo sazonal cria diferentes etnohabitats propícios a uma ictiodiversidade espaço-temporal, associada à pesca de subsistência e comercial. Destaca-se que na descrição de ocorrência e de distribuição dos peixes nos etnohabitats da TITB há especificidades importantes além dos períodos sazonais, tais como aqueles relacionados intrínsecos à pesca e os inerentes aos peixes (tamanho, peso, comportamento alimentar e aspectos ecológicos). O detalhamento na categorização dos etnohabitats aquáticos e na biodiversidade associado a estes locais ressalta a existência de uma ampla relação dos Xikrin com sua área de uso, bem como as acordadas divisões do espaço entre as aldeias, que devem ser mantidos, não apenas para sobrevivência e fortalecimento das comunidades, mas também pelo próprio valor intrínseco de pertencimento e ser Xikrin

Distributional and reproductive aspects of the bigeye thresher shark (Alopias superciliosus) in the Atlantic ocean

Captura asociada a la pesquería de palangre de superficie dirigida a pez espadaThe bigeye thresher shark, Alopias supercilious is sometimes caught as bycatch in pelagic longline fisheries targeting tunas and swordfish in the Atlantic Ocean. As part of an ongoing cooperative program for fisheries and biological data collection, fishery observer data from various fishing nations and projects were compiled and analyzed. Those data sets include information on geographic location of the observations, as well as size, sex and in some cases maturity stage. A total of 4371 bigeye threshers were recorded throughout the Atlantic Ocean between 1992 and 2013, with the sizes ranging from 70 to 305 cm FL (fork length). Considerable variability was observed in the catchat- size, with particular emphasis on the tropical region where the mean sizes tended to be smaller than in the other regions. The expected distribution of juvenile and adult specimens also showed considerable variability, and the sex-ratios varied between regions and size classes. Maturity ogives were fitted to data from 642 specimens, with the median sizes at maturity estimated at 208.6 cm FL (corresponding to 349.1 cm TL) for females and 159.2 cm FL (corresponding to 269.8 cm TL) for males. In addition, a segmented regression model (SRM) was used for males, and two breakpoints (Bk1: 122.5cm FL, Bk2: 173.3cm FL) estimated, identifying transitions between the three different maturity stages for male sharks (immature, maturing and mature). Only a few pregnant females were recorded, always with the presence of two embryos (one per uterus), and were distributed predominantly in the tropical northeast Atlantic closer the African continent, and in the southwest region, with those regions possibly serving as nursery areas for this species. These reproductive parameters, and especially the estimated median sizes at maturity and low fecundity, highlight the vulnerability of this species, reinforcing that the bigeye thresher tends to mature at a larger size than the other species of the Alopiidae family. The biological and distributional patterns presented can help managers adopt more informed and efficient conservation measures for this species.En prensa0,000

Analyzing collaborative learning processes automatically

In this article we describe the emerging area of text classification research focused on the problem of collaborative learning process analysis both from a broad perspective and more specifically in terms of a publicly available tool set called TagHelper tools. Analyzing the variety of pedagogically valuable facets of learners’ interactions is a time consuming and effortful process. Improving automated analyses of such highly valued processes of collaborative learning by adapting and applying recent text classification technologies would make it a less arduous task to obtain insights from corpus data. This endeavor also holds the potential for enabling substantially improved on-line instruction both by providing teachers and facilitators with reports about the groups they are moderating and by triggering context sensitive collaborative learning support on an as-needed basis. In this article, we report on an interdisciplinary research project, which has been investigating the effectiveness of applying text classification technology to a large CSCL corpus that has been analyzed by human coders using a theory-based multidimensional coding scheme. We report promising results and include an in-depth discussion of important issues such as reliability, validity, and efficiency that should be considered when deciding on the appropriateness of adopting a new technology such as TagHelper tools. One major technical contribution of this work is a demonstration that an important piece of the work towards making text classification technology effective for this purpose is designing and building linguistic pattern detectors, otherwise known as features, that can be extracted reliably from texts and that have high predictive power for the categories of discourse actions that the CSCL community is interested in