Defect detection and characterisation in composite materials using active IR thermography coupled with SVD analysis and thermal quadrupole modeling

Abstract In t his s tudy, a ctive i nfrared t hermography is us ed t o det ect and c haracterize def ects i n c arbon/epoxy c omposite plates. Defects are polymeric discs inserted between plies at different depths of the sample. The thermal excitation consists in a f inite t ime s tep us ing h alogen l amps. The t ransient t hermal m odeling pr ovides a one-dimensional analytical s olution through thermal quadrupoles. Finally an inversion procedure is carried out to estimate modeling unknown parameters, especially the depth and thermal resistance of the defect

On the flow-level stability of data networks without congestion control: the case of linear networks and upstream trees

In this paper, flow models of networks without congestion control are considered. Users generate data transfers according to some Poisson processes and transmit corresponding packet at a fixed rate equal to their access rate until the entire document is received at the destination; some erasure codes are used to make the transmission robust to packet losses. We study the stability of the stochastic process representing the number of active flows in two particular cases: linear networks and upstream trees. For the case of linear networks, we notably use fluid limits and an interesting phenomenon of "time scale separation" occurs. Bounds on the stability region of linear networks are given. For the case of upstream trees, underlying monotonic properties are used. Finally, the asymptotic stability of those processes is analyzed when the access rate of the users decreases to 0. An appropriate scaling is introduced and used to prove that the stability region of those networks is asymptotically maximized

Chemical Cartography with APOGEE: Large-scale Mean Metallicity Maps of the Milky Way

We present Galactic mean metallicity maps derived from the first year of the SDSS-III APOGEE experiment. Mean abundances in different zones of Galactocentric radius (0 < R < 15 kpc) at a range of heights above the plane (0 < |z| < 3 kpc), are derived from a sample of nearly 20,000 stars with unprecedented coverage, including stars in the Galactic mid-plane at large distances. We also split the sample into subsamples of stars with low and high-[{\alpha}/M] abundance ratios. We assess possible biases in deriving the mean abundances, and find they are likely to be small except in the inner regions of the Galaxy. A negative radial gradient exists over much of the Galaxy; however, the gradient appears to flatten for R < 6 kpc, in particular near the Galactic mid-plane and for low-[{\alpha}/M] stars. At R > 6 kpc, the gradient flattens as one moves off of the plane, and is flatter at all heights for high-[{\alpha}/M] stars than for low-[{\alpha}/M] stars. Alternatively, these gradients can be described as vertical gradients that flatten at larger Galactocentric radius; these vertical gradients are similar for both low and high-[{\alpha}/M] populations. Stars with higher [{\alpha}/M] appear to have a flatter radial gradient than stars with lower [{\alpha}/M]. This could suggest that the metallicity gradient has grown steeper with time or, alternatively, that gradients are washed out over time by migration of stars.Comment: 16 pages, 12 figures, submitted to A

Noisy Kondo impurities

The anti-ferromagnetic coupling of a magnetic impurity carrying a spin with the conduction electrons spins of a host metal is the basic mechanism responsible for the increase of the resistance of an alloy such as Cu${}_{0.998}$Fe${}_{0.002}$ at low temperature, as originally suggested by Kondo . This coupling has emerged as a very generic property of localized electronic states coupled to a continuum . The possibility to design artificial controllable magnetic impurities in nanoscopic conductors has opened a path to study this many body phenomenon in unusual situations as compared to the initial one and, in particular, in out of equilibrium situations. So far, measurements have focused on the average current. Here, we report on \textit{current fluctuations} (noise) measurements in artificial Kondo impurities made in carbon nanotube devices. We find a striking enhancement of the current noise within the Kondo resonance, in contradiction with simple non-interacting theories. Our findings provide a test bench for one of the most important many-body theories of condensed matter in out of equilibrium situations and shed light on the noise properties of highly conductive molecular devices.Comment: minor differences with published versio

High-resolution radiation hybrid mapping in wheat: an essential tool for the construction of the wheat physical maps

ArtigoO poema épico da época moderna nasce na literatura portuguesa como oceânico logo a partir da sua gestação. Este estudo enquadra a sua génese num contexto europeu.Università di Roma, La Sapienz

The chemical characterisation of halo substructure in the Milky Way based on APOGEE

Galactic haloes in a $\Lambda$-Cold Dark Matter ($\Lambda$CDM) universe are predicted to host today a swarm of debris resulting from cannibalised dwarf galaxies that have been accreted via the process of hierarchical mass assembly. The chemo-dynamical information recorded in the Galactic stellar populations associated with such systems helps elucidate their nature, placing constraints on the mass assembly history of the Milky Way. Using data from the APOGEE and \textit{Gaia} surveys, we examine APOGEE targets belonging to the following substructures in the stellar halo: Heracles, \textit{Gaia}-Enceladus/Sausage (GES), Sagittarius dSph, the Helmi stream, Sequoia, Thamnos, Aleph, LMS-1, Arjuna, I'itoi, Nyx, Icarus, and Pontus. We examine the distributions of all substructures in chemical space, considering the abundances of elements sampling various nucleosynthetic pathways. Our main findings include: {\it i)} the chemical properties of GES, Heracles, the Helmi stream, Sequoia, Thamnos, LMS-1, Arjuna, and I'itoi match qualitatively those of dwarf satellites of the Milky Way, such as the Sagittarius dSph; {\it ii)} the abundance pattern of the recently discovered inner Galaxy substructure Heracles differs statistically from that of populations formed {\it in situ}. Heracles also differs chemically from all other substructures; {\it iii)} the abundance patterns of Sequoia (selected in various ways), Arjuna, LMS-1, and I'itoi are indistinguishable from that of GES, indicating a possible common origin; {\it iv)} the abundance patterns of the Helmi stream and Thamnos substructures are different from all other halo substructures; {\it v)} the chemical properties of Nyx and Aleph are very similar to those of disc stars, implying that these substructures likely have an \textit{in situ} origin.Comment: Submitted to MNRAS. 39 page

Submarine record of volcanic island construction and collapse in the Lesser Antilles arc: First scientific drilling of submarine volcanic island landslides by IODP Expedition 340

IODP Expedition 340 successfully drilled a series of sites offshore Montserrat, Martinique and Dominica in the Lesser Antilles from March to April 2012. These are among the few drill sites gathered around volcanic islands, and the first scientific drilling of large and likely tsunamigenic volcanic island-arc landslide deposits. These cores provide evidence and tests of previous hypotheses for the composition and origin of those deposits. Sites U1394, U1399, and U1400 that penetrated landslide deposits recovered exclusively seafloor-sediment, comprising mainly turbidites and hemipelagic deposits, and lacked debris avalanche deposits. This supports the concepts that i/ volcanic debris avalanches tend to stop at the slope break, and ii/ widespread and voluminous failures of pre-existing low-gradient seafloor sediment can be triggered by initial emplacement of material from the volcano. Offshore Martinique (U1399 and 1400), the landslide deposits comprised blocks of parallel strata that were tilted or micro-faulted, sometimes separated by intervals of homogenized sediment (intense shearing), while Site U1394 offshore Montserrat penetrated a flat-lying block of intact strata. The most likely mechanism for generating these large-scale seafloor-sediment failures appears to be propagation of a decollement from proximal areas loaded and incised by a volcanic debris avalanche. These results have implications for the magnitude of tsunami generation. Under some conditions, volcanic island landslide deposits comprised of mainly seafloor sediment will tend to form smaller magnitude tsunamis than equivalent volumes of subaerial block-rich mass flows rapidly entering water. Expedition 340 also successfully drilled sites to access the undisturbed record of eruption fallout layers intercalated with marine sediment which provide an outstanding high-resolution dataset to analyze eruption and landslides cycles, improve understanding of magmatic evolution as well as offshore sedimentation processes. This article is protected by copyright. All rights reserved