Desarrollo e implementación de un sistema de detección de fallas de materiales basado en el método de golpeteo

Se desarrolla analíticamente e implementa en forma práctica un sistema de predicción de fallas de materiales compuestos. El procedimiento se enmarca en la categoría END (Ensayos No Destructivos) y debido a su portabilidad, es aplicable a materiales que forman parte de estructuras ya construidas. A partir del análisis de las señales obtenidas experimentalmente mediante el golpeteo con un martillo modal -construido ex profeso-, se determinan los parámetros característicos que permiten la evaluación del estado del material compuesto, su tipificación y una eventual cuantificación del daño. Un software específicamente diseñado administra y procesa las señales obtenidas en los ensayos, y permite mediante su interfaz gráfica la rápida interpretación de los resultados. El sistema fue probado en muestras de materiales con fallas típicas, demostrando su efectividad. El método constituye una herramienta sólida para la detección temprana de fallas y para la toma de medidas correctivas sobre estructuras en servicio.Sociedad Argentina de Informática e Investigación Operativ

Discovering the most elusive radio relic in the sky: Diffuse shock acceleration caught in the act?

The origin of radio relics is usually explained via diffusive shock acceleration (DSA) or re-acceleration of electrons at/from merger shocks in galaxy clusters. The case of acceleration is challenged by the low predicted efficiency of low Mach number merger shocks, unable to explain the power observed in most radio relics. In this letter, we present the discovery of a new giant radio relic around the galaxy cluster Abell 2249 ($z$ = 0.0838) using Low-Frequency Array (LOFAR). It is special since it has the lowest surface brightness of all known radio relics. We study its radio and X-ray properties combining LOFAR data with uGMRT, JVLA, and XMM. This object has a total power of $L-{1.4rm, GHz}=4.1pm 0.8 times 10{23}$ W Hz-1 and integrated spectral index α = 1.15 ± 0.23. We infer for this radio relic a lower bound on the magnetization of $Bge 0.4, mu$G, a shock Mach number of $mathcal {M}approx 3.79$, and a low acceleration efficiency consistent with DSA. This result suggests that a missing population of relics may become visible, thanks to the unprecedented sensitivity of the new generation of radio telescopes

Discovering the most elusive radio relic in the sky: Diffuse Shock Acceleration caught in the act?

The origin of radio relics is usually explained via diffusive shock acceleration (DSA) or re-acceleration of electrons at/from merger shocks in galaxy clusters. The case of acceleration is challenged by the low predicted efficiency of low-Mach number merger shocks, unable to explain the power observed in most radio relics. In this Letter we present the discovery of a new giant radio relic around the galaxy cluster Abell 2249 ($z=0.0838$) using LOFAR. It is special since it has the lowest surface brightness of all known radio relics. We study its radio and X-ray properties combinig LOFAR data with uGMRT, JVLA and XMM. This object has a total power of $L_{1.4\rm GHz}=4.1\pm 0.8 \times 10^{23}$ W Hz$^{-1}$ and integrated spectral index $\alpha = 1.15\pm 0.23$. We infer for this radio relic a lower bound on the magnetisation of $B\geq 0.4\, \mu$G, a shock Mach number of $\mathcal{M}\approx 3.79$, and a low acceleration efficiency consistent with DSA. This result suggests that a missing population of relics may become visible thanks to the unprecedented sensitivity of the new generation of radio telescopes.Comment: Letter, 5 pages, 4 figures, accepted for publication on MNRAS Letter

The coma cluster at low frequency array frequencies. I. Insights into particle acceleration mechanisms in the radio bridge

Radio synchrotron emission from the bridges of low-density gas connecting galaxy clusters and groups is a challenge for particle acceleration processes. In this work, we analyze the Coma radio bridge using new LOw Frequency ARray (LOFAR) observations at 144 MHz. LOFAR detects the bridge and its substructures with unprecedented sensitivity and resolution. We found that the radio emission peaks on the NGC 4839 group. Toward the halo, in front of the NGC 4839 group, the radio brightness decreases and streams of radio emission connect the NGC 4839 group to the radio relic. Using X-ray observations, we found that thermal and non-thermal plasma are moderately correlated with a sublinear scaling. We use archival radio data at 326 MHz to constrain the spectral index in the bridge, and quantify the distribution of particles and magnetic field at different frequencies. We found that the spectrum is steeper than −1.4 ± 0.2, and that the emission is clumpier at 326 MHz than at 144 MHz. Using cosmological simulations and a simplified approach to compute particle acceleration, we derive under which conditions turbulent acceleration of mildly relativistic electrons generate the radio emission in the bridge. Assuming that the initial energy ratio of the seed electrons is 3 · 10−4 with respect to the thermal gas, we are able to reproduce the observed luminosity. Our results suggest that the seed electrons released by radio galaxies in the bridge and the turbulence generated by the motion of gas and galaxies are essential to producing the radio emission

A 3.5 Mpc-long radio relic in the galaxy cluster ClG 0217+70

Mega-parsec scale radio sources in the form of halos and relics are often detected in dynamically disturbed galaxy clusters. Although they are associated with merger-induced turbulence and shocks, respectively, their formation is not fully understood. We aim to identify the mechanisms responsible for particle acceleration and magnetic field amplification in the halo and relics of the galaxy cluster ClG 0217+70. We observed ClG 0217+70 with LOFAR at 141 MHz and VLA at 1.5 GHz, and combine these observations with VLA 1.4 GHz archival data to study the morphological and spectral properties of the diffuse sources. We add Chandra archival data to examine the thermal and non-thermal properties of the halo. Our LOFAR and VLA data confirm the presence of a giant radio halo in the cluster centre and multiple relics in the outskirts. The radio and X-ray emission from the halo are correlated, implying a tight relation between the thermal and non-thermal components. The diffuse radio structure in the south east with a projected size of 3.5 Mpc is the most extended radio relic detected to date. The spectral index across the relic width steepens towards the cluster centre, suggesting the electron ageing in the post-shock regions. The shock Mach numbers for the relics derived from the spectral index map range between 2.0 and 3.2. However, the integrated spectral indices lead to increasingly high Mach numbers for the relics farther from the cluster centre. This discrepancy could be because the relation between injection and integrated spectra does not hold for distant shocks, suggesting that the cooling time for the radio-emitting electrons is longer than the crossing time of the shocks. The variations in the surface brightness of the relics and the low Mach numbers imply that the radio-emitting electrons are re-accelerated from fossil plasma that could originate in active galactic nuclei

Deep Low-frequency Radio Observations of A2256. I. the Filamentary Radio Relic

We present deep and high-fidelity images of the merging galaxy cluster A2256 at low frequencies using the upgraded Giant Metrewave Radio Telescope (uGMRT) and LOw-Frequency ARray (LOFAR). This cluster hosts one of the most prominent known relics with a remarkably spectacular network of filamentary substructures. The new uGMRT (300-850 MHz) and LOFAR (120-169 MHz) observations, combined with the archival Karl G. Jansky Very Large Array (VLA; 1-4 GHz) data, allowed us to carry out the first spatially resolved spectral analysis of the exceptional relic emission down to 6″ resolution over a broad range of frequencies. Our new sensitive radio images confirm the presence of complex filaments of magnetized relativistic plasma also at low frequencies. We find that the integrated spectrum of the relic is consistent with a single power law, without any sign of spectral steepening, at least below 3 GHz. Unlike previous claims, the relic shows an integrated spectral index of -1.07 ± 0.02 between 144 MHz and 3 GHz, which is consistent with the (quasi)stationary shock approximation. The spatially resolved spectral analysis suggests that the relic surface very likely traces the complex shock front, with a broad distribution of Mach numbers propagating through a turbulent and dynamically active intracluster medium. Our results show that the northern part of the relic is seen edge-on and the southern part close to face-on. We suggest that the complex filaments are regions where higher Mach numbers dominate the (re)acceleration of electrons that are responsible for the observed radio emission

The Coma cluster at Low Frequency ARray frequencies: I. Insights into particle acceleration mechanisms in the radio bridge

High Energy Astrophysic

Projection of participant recruitment to primary care research: a qualitative study.

BACKGROUND: Recruitment to clinical trials remains a challenge, particularly in primary care settings. Initial projections of participant recruitment need to be as accurate as possible in order to avoid the financial, clinical and ethical costs of trial extensions or failures. However, estimation of recruitment rates is challenging and often poorly executed, if attempted at all. We used qualitative methods to explore the experiences and views of researchers on the planning of recruitment in this setting. METHODS: Participants had registered accrual to a UK-based primary care research study between April 2009 and March 2012. We conducted nine interviews with chief investigators or study managers, using a semi-structured topic guide. Analysis was conducted using the framework approach. RESULTS: Three themes are presented: 1) the factors affecting recruitment rates, 2) the use of planning techniques, and 3) influences on poor estimation. 1) A large number of factors affecting recruitment rates were discussed, including those relating to the study protocol, the clinical setting and the research setting. Use of targeted mail-outs to invite apparently eligible individuals to participate was preferred in order to eliminate some of the uncertainty in the recruitment rate associated with opportunistic clinician referrals. 2) The importance of pilot work was stressed. We identified significant uncertainty as to how best to schedule trial timelines to maximise efficiency. 3) Several potential sources of bias involved in the estimation of recruitment rates were explored and framed as technological, psychological or political factors. CONCLUSIONS: We found a large number of factors that interviewees felt impact recruitment rates to primary care research and highlighted the complexity of realistic estimation. Suitable early planning of the recruitment process is essential, and there may be potential to improve the projection of trial timelines by reducing biases involved in the process. Further research is needed to develop formal approaches that would be suitable for use in this setting