Relationship between drying rates and mechanical properties in refractory concretes

The effect of drying rates on compressive strength was investigated in two aluminosilicate refractory concretes with different water content, which were cured at room temperature and dried at 3 heating rates (30, 40 and 50°C/h) up to 260ºC with different holding times. The results show that the lightweight refractory concrete developed better mechanical resistance with 48% of water content and heating rate of 40ºC/h, while for dense refractory concrete the best conditions were 12% of water content with heating rates of 30ºC/h, both during 2 hours of holding time. Se investigó el efecto de las velocidades de secado sobre la resistencia a la compresión en dos concretos refractarios silicoaluminosos con diferente contenido de agua, los cuales se curaron a temperatura ambiente y se secaron a 3 velocidades de calentamiento (30, 40 y 50°C/h) hasta 260°C con diferentes tiempos de permanencia. Los resultados muestran que el concreto refractario aislante desarrolló mejor resistencia con 48% de agua y velocidad de calentamiento de 40ºC/h, mientras que para el concreto refractario denso las mejores condiciones fueron 12% de agua y velocidad de calentamiento de 30ºC/h, ambos durante 2 horas de permanencia.&nbsp

Relationwship between drying rates and mechanical properties in refractory concretes

Se investigó el efecto de las velocidades de secado sobre la resistencia a la compresión en dos concretos refractarios silicoaluminosos con diferente contenido de agua, los cuales se curaron a temperatura ambiente y se secaron a 3 velocidades de calentamiento (30, 40 y 50°C/h) hasta 260°C con diferentes tiempos de permanencia. Los resultados muestran que el concreto refractario aislante desarrolló mejor resistencia con 48% de agua y velocidad de calentamiento de 40ºC/h, mientras que para el concreto refractario denso las mejores condiciones fueron 12% de agua y velocidad de calentamiento de 30ºC/h, ambos durante 2 horas de permanencia

Desarrollo de un refractario de MgO dopado con η-Al2O3

Se estudia el efecto de las nanopartículas de α-Al2O3 (hasta 5 % en peso) sobre las propiedades físicas, mecánicas y térmicas, así como sobre la evolución microestructural de un refractario de magnesia densa. Se utilizan temperaturas de sinterización a 1300°C, 1500°C y 1600°C. Las propiedades físicas de interés fueron la densidad y la porosidad aparentes, que se evaluaron mediante el método de Arquímedes. Las propiedades térmicas se examinaron mediante calorimetría diferencial de barrido. El comportamiento mecánico se estudió mediante pruebas de resistencia a la trituración en frío y micro dureza. Finalmente, la microestructura y las características cualitativas mineralógicas se estudiaron mediante microscopía electrónica de barrido y difracción de rayos X, respectivamente. El aumento de la temperatura de sinterización dio como resultado una densidad mejorada y una porosidad aparente reducida. Sin embargo, a medida que aumentaba el contenido de nanopartículas de α-Al2O3, la densidad y la micro dureza disminuían. Las observaciones microestructurales mostraron que la presencia de nanopartículas de α-Al2O3 en la matriz de magnesia indujo la formación de espinela de magnesio-aluminato (MgAl2O4), que mejoró la resistencia mecánica más significativamente a 1500°C

Measurement of the cosmic ray spectrum above 4×10184{\times}10^{18} eV using inclined events detected with the Pierre Auger Observatory

A measurement of the cosmic-ray spectrum for energies exceeding $4{\times}10^{18}$ eV is presented, which is based on the analysis of showers with zenith angles greater than $60^{\circ}$ detected with the Pierre Auger Observatory between 1 January 2004 and 31 December 2013. The measured spectrum confirms a flux suppression at the highest energies. Above $5.3{\times}10^{18}$ eV, the "ankle", the flux can be described by a power law $E^{-\gamma}$ with index $\gamma=2.70 \pm 0.02 \,\text{(stat)} \pm 0.1\,\text{(sys)}$ followed by a smooth suppression region. For the energy ($E_\text{s}$) at which the spectral flux has fallen to one-half of its extrapolated value in the absence of suppression, we find $E_\text{s}=(5.12\pm0.25\,\text{(stat)}^{+1.0}_{-1.2}\,\text{(sys)}){\times}10^{19}$ eV.Comment: Replaced with published version. Added journal reference and DO

Energy Estimation of Cosmic Rays with the Engineering Radio Array of the Pierre Auger Observatory

The Auger Engineering Radio Array (AERA) is part of the Pierre Auger Observatory and is used to detect the radio emission of cosmic-ray air showers. These observations are compared to the data of the surface detector stations of the Observatory, which provide well-calibrated information on the cosmic-ray energies and arrival directions. The response of the radio stations in the 30 to 80 MHz regime has been thoroughly calibrated to enable the reconstruction of the incoming electric field. For the latter, the energy deposit per area is determined from the radio pulses at each observer position and is interpolated using a two-dimensional function that takes into account signal asymmetries due to interference between the geomagnetic and charge-excess emission components. The spatial integral over the signal distribution gives a direct measurement of the energy transferred from the primary cosmic ray into radio emission in the AERA frequency range. We measure 15.8 MeV of radiation energy for a 1 EeV air shower arriving perpendicularly to the geomagnetic field. This radiation energy -- corrected for geometrical effects -- is used as a cosmic-ray energy estimator. Performing an absolute energy calibration against the surface-detector information, we observe that this radio-energy estimator scales quadratically with the cosmic-ray energy as expected for coherent emission. We find an energy resolution of the radio reconstruction of 22% for the data set and 17% for a high-quality subset containing only events with at least five radio stations with signal.Comment: Replaced with published version. Added journal reference and DO

Measurement of the Radiation Energy in the Radio Signal of Extensive Air Showers as a Universal Estimator of Cosmic-Ray Energy

We measure the energy emitted by extensive air showers in the form of radio emission in the frequency range from 30 to 80 MHz. Exploiting the accurate energy scale of the Pierre Auger Observatory, we obtain a radiation energy of 15.8 \pm 0.7 (stat) \pm 6.7 (sys) MeV for cosmic rays with an energy of 1 EeV arriving perpendicularly to a geomagnetic field of 0.24 G, scaling quadratically with the cosmic-ray energy. A comparison with predictions from state-of-the-art first-principle calculations shows agreement with our measurement. The radiation energy provides direct access to the calorimetric energy in the electromagnetic cascade of extensive air showers. Comparison with our result thus allows the direct calibration of any cosmic-ray radio detector against the well-established energy scale of the Pierre Auger Observatory.Comment: Replaced with published version. Added journal reference and DOI. Supplemental material in the ancillary file

Supporting Spartina: Interdisciplinary perspective shows Spartina as a distinct solid genus

In 2014 a DNA-based phylogenetic study confirming the paraphyly of the grass subtribe Sporobolinae proposed the creation of a large monophyletic genus Sporobolus, including (among others) species previously included in the genera Spartina, Calamovilfa, and Sporobolus. Spartina species have contributed substantially (and continue contributing) to our knowledge in multiple disciplines, including ecology, evolutionary biology, molecular biology, biogeography, experimental ecology, environmental management, restoration ecology, history, economics, and sociology. There is no rationale so compelling to subsume the name Spartina as a subgenus that could rival the striking, global iconic history and use of the name Spartina for over 200 years. We do not agree with the arguments underlying the proposal to change Spartina to Sporobolus. We understand the importance of taxonomy and of formalized nomenclature and hope that by opening this debate we will encourage positive feedback that will strengthen taxonomic decisions with an interdisciplinary perspective. We consider the strongly distinct, monophyletic clade Spartina should simply and efficiently be treated as the genus Spartina