Improving elevation resolution in phased-array inspections for NDT

The Phased Array Ultrasonic Technique (PAUT) offers great advantages over the conventional ultrasound technique (UT), particularly because of beam focusing, beam steering and electronic scanning capabilities. However, the 2D images obtained have usually low resolution in the direction perpendicular to the array elements, which limits the inspection quality of large components by mechanical scanning. This paper describes a novel approach to improve image quality in these situations, by combining three ultrasonic techniques: Phased Array with dynamic depth focusing in reception, Synthetic Aperture Focusing Technique (SAFT) and Phase Coherence Imaging (PCI). To be applied with conventional NDT arrays (1D and non-focused in elevation) a special mask to produce a wide beam in the movement direction was designed and analysed by simulation and experimentally. Then, the imaging algorithm is presented and validated by the inspection of test samples. The obtained images quality is comparable to that obtained with an equivalent matrix array, but using conventional NDT arrays and equipments, and implemented in real time.Fil: Brizuela, Jose David. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Camacho, J.. Consejo Superior de Investigaciones Científicas; EspañaFil: Cosarinsky, Guillermo Gerardo. Comisión Nacional de Energía Atómica; ArgentinaFil: Iriarte, Juan Manuel. Comisión Nacional de Energía Atómica; ArgentinaFil: Cruza, Jorge F.. Consejo Superior de Investigaciones Científicas; Españ

Radioactive Probes of the Supernova-Contaminated Solar Nebula: Evidence that the Sun was Born in a Cluster

We construct a simple model for radioisotopic enrichment of the protosolar nebula by injection from a nearby supernova, based on the inverse square law for ejecta dispersion. We find that the presolar radioisotopes abundances (i.e., in solar masses) demand a nearby supernova: its distance can be no larger than 66 times the size of the protosolar nebula, at a 90% confidence level, assuming 1 solar mass of protosolar material. The relevant size of the nebula depends on its state of evolution at the time of radioactivity injection. In one scenario, a collection of low-mass stars, including our sun, formed in a group or cluster with an intermediate- to high-mass star that ended its life as a supernova while our sun was still a protostar, a starless core, or perhaps a diffuse cloud. Using recent observations of protostars to estimate the size of the protosolar nebula constrains the distance of the supernova at 0.02 to 1.6 pc. The supernova distance limit is consistent with the scales of low-mass stars formation around one or more massive stars, but it is closer than expected were the sun formed in an isolated, solitary state. Consequently, if any presolar radioactivities originated via supernova injection, we must conclude that our sun was a member of such a group or cluster that has since dispersed, and thus that solar system formation should be understood in this context. In addition, we show that the timescale from explosion to the creation of small bodies was on the order of 1.8 Myr (formal 90% confidence range of 0 to 2.2 Myr), and thus the temporal choreography from supernova ejecta to meteorites is important. Finally, we can not distinguish between progenitor masses from 15 to 25 solar masses in the nucleosynthesis models; however, the 20 solar mass model is somewhat preferred.Comment: ApJ accepted, 19 pages, 3 figure

Non-destructive evaluation techniques for pressure vessels made of composite material

Los recipientes fabricados en materiales compuestos COPVs (Composite Overwrapped Pressure Vessels) son extensamente aplicados en la industria aeroespacial para contener líquidos a alta presión debido a sus elevadas propiedades mecánicas, además de ser un componente muy liviano. Consisten en una delgada estructura metálica (contenedor o liner) recubierta por un compuesto plástico, reforzado con fibras estructurales de carbono. Un aspecto importante en el marco del desarrollo de estos componentes, es el aseguramiento de la calidad de los recipientes una vez completado el proceso de fabricación. Este trabajo aborda la inspección de un COPV de forma cilíndrica de 100 litros de capacidad con liner de aluminio. Para ello se emplean dos técnicas de ensayos no destructivos: ultrasonido acoplado en aire y shearografía. Ambas técnicas fueron adaptadas específicamente para este tipo de recipiente y montadas sobre un escáner experimental que proporciona soporte y repetitividad a los ensayos, garantizando resultados cualitativos en la inspección de estos componentes. Los resultados que se obtuvieron con las dos técnicas se comparan y se observa un acuerdo entre ellos en lo que concierne a la calidad del proceso de fabricación del componente. A partir de los ensayos efectuados y de sus resultados se realizaron aportes y recomendaciones para una posible mejora del proceso de fabricaciónComposite Overwrapped Pressure Vessels (COPV) are extensively applied in the aerospace industry to contain high pressure liquids due to their elevated mechanical properties as well as being a lightweight component. They consist of a thin metallic structure (liner) wrapped by a plastic compound, reinforced with structural carbon fibers. An important aspect in the development of COPVs is the quality assurance once the manufacturing process has been completed. This work aims to the inspection of a cylindrical-aluminum-liner COPV of 100 liters of capacity. For this purpose, two non-destructive testing techniques were applied: aircoupled ultrasound and shearography. Both techniques were specifically adapted to the COPV geometry and mounted on an experimental scanner that provides support and repetitiveness to the tests. This mechanical arrangement guarantees qualitative results in the COPVs inspection. The obtained results with both techniques were compared and they show good agreement regarding the quality of the manufacturing process. Based on the tests carried out and their results, contributions and recommendations were made for a possible improvement of the manufacturing process.Fil: Romero Rosero, Christian Rodrigo. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Gerencia de Ende (CAC); ArgentinaFil: Cosarinsky, Guillermo Gerardo. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Gerencia de Ende (CAC); ArgentinaFil: Iriarte, Juan Manuel. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Gerencia de Ende (CAC); ArgentinaFil: Brizuela, Jose David. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica; ArgentinaFil: Poodts, Exequiel. Kohlenia; ArgentinaFil: Ruiz Gale, María Fernanda. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Gerencia de Ende (CAC); Argentin

An oxygen isotope study of Wark–Lovering rims on type A CAIs in primitive carbonaceous chondrites

Calcium–aluminium-rich Inclusions(CAIs) and the thin Wark–Lovering (WL) rims of minerals surrounding them offer a record of the nature of changing conditions during the earliest stages of Solar System formation. Considerable heterogeneity in the gas composition in the immediate vicinity of the proto-Sun had previously been inferred from oxygen isotopic variations in the WL rim of a CAI from Allende (Simon et al., 2011). However, high precision and high spatial resolution oxygen isotope measurements presented in this study show that WL rim and pristine core minerals of individual CAIs from meteorites that had experienced only low degrees of alteration or low grade metamorphism (one from Léoville (reduced CV3), two in QUE 99177 (CR3.0) and two in ALHA 77307 (CO3.0)) are uniformly 16O-rich. This indicates that the previously observed variations are the result of secondary processes, most likely on the asteroid parent body, and that there were no temporal or spatial variations in oxygen isotopic composition during CAI and WL rim formation. Such homogeneity across three groups of carbonaceous chondrites lends further support for a common origin for the CAIs in all chondrites. 16O-poor oxygen reservoirs such as those associated with chondrule formation, were probably generated by UV photo-dissociation involving self-shielding mechanisms and must have occurred elsewhere in outer regions of the solar accretion disk

Using Long-Term Volunteer Records to Examine Dormouse (Muscardinusavellanarius) Nestbox Selection.

Within ecology, there are unanswered questions about species-habitat interactions, which could potentially be resolved by a pragmatic analysis of a long-term volunteer-collected dataset. Here, we analysed 18 years of volunteer-collected data from a UK dormouse nestbox monitoring programme to determine the influence of habitat variables on nestbox choice by common dormice (Muscardinusavellanarius). We measured a range of habitat variables in a coppiced woodland in Gloucestershire, UK, and analysed these in relation to dormouse nestbox occupancy records (by dormice, other small mammals, and birds) collected by volunteers. While some characteristics of the woodland had changed over 18 years, simple transformation of the data and interpretation of the results indicated that the dataset was informative. Using stepwise regressions, multiple environmental and ecological factors were found to determine nestbox selection. Distance from the edge of the wood was the most influential (this did not change over 18 years), with boxes in the woodland interior being selected preferentially. There was a significant negative relationship with the presence of ferns (indicative of damp shady conditions). The presence of oak (a long-lived species), and the clumped structural complexity of the canopy were also important factors in the final model. There was no evidence of competition between dormice and birds or other mammals. The results provide greater understanding of artificial dormouse nest-site requirements and indicate that, in terms of habitat selection, long-term volunteer-collected datasets contribute usefully to understanding the requirements of species with an important conservation status

Desarrollo de un modelo que explique la formación de los precios spot del gas natural en la cuenca neuquina

Esta tesis solo está en formato papel por lo que se debe consultar en la propia Biblioteca Di Tella. La consulta se hace solo bajo reserva escribiendo a [email protected] tesis no tiene permisos por parte del autor para ser reproducida, por lo que no se puede fotocopiar, ni fotografiar ni reproducir con ningún medio. Si eres el autor de la tesis y quieres dar tu autorización para la reproducción, puedes ponerte en contacto con [email protected]

Plane Wave Imaging through Interfaces

Plane Wave Imaging (PWI) has been recently proposed for fast ultrasound inspections in the Non-Destructive-Testing (NDT) field. By using a single (or a reduced number) of plane wave emissions and parallel beamforming in reception, frame rates of hundreds to thousands of images per second can be achieved without significant image quality losses with regard to the Total Focusing Method (TFM) or Phased Array (PA). This work addresses the problem of applying PWI in the presence of arbitrarily shaped interfaces, which is a common problem in NDT. First, the mathematical formulation for generating a plane wave inside a component of arbitrary geometry is given, and the characteristics of the resultant acoustic field are analyzed by simulation, showing plane wavefronts with non-uniform amplitude. Then, an imaging strategy is proposed, accounting for this amplitude effect. Finally, the proposed method is experimentally validated, and its application limits are discussed

Micromorfología de nidos de termitas de la República Argentina

La presente contribución representa el primer estudio micromorfológico de nidos de termitas neotropicales. Incluye un análisis comparativo de la micromorfología de termiteros de diferentes especies, del nido y suelo circundante, y de los diferentes sectores del nido. Asimismo, se comparan rasgos micromorfológicos que han sido descriptos en nidos de especies de África y Australia con los observados en especies de Argentina, y se describen rasgos nuevos. Las descripciones micromorfológicas incluyen diferentes tipos de pellets, microestructuras, análisis de granulometría, frecuencia, selección de tamaño y distribución de los componentes minerales gruesos, rasgos compuestos de materia orgánica fina de origen fecal (material cementante de granos minerales y pellets, revestimientos de galerías e intercalaciones lineales en la masa basal), fábricas de birrefringencia del material fino, microagregación de arcillas, incrustraciones lenticulares cuarzo-arcillosas, relación de distribución de materiales finos y gruesos, presencia de restos vegetales y fragmentos cuticulares de termitas. Los nidos de termitas presentan una gran diversidad micromorfológica, sin embargo no se pudo hallar una relación directa entre la sistemática y la micromorfología de los nidos debido a que existe una notable variación intraespecífica de rasgos micromorfológicos en nidos localizados en diferentes tipos de suelo. En los nidos de Cornitermes cumulans, que presentan una arquitectura compleja, cada sector exhibe una micromorfología particular, relacionada con la función que cumple. La muralla presenta una densa estructura masiva o agrietada, relacionada con la protección mecánica y el aislamiento ambiental del nido. La región media exhibe una estructura pelicular muy porosa o esponjosa, que probablemente favorecería la termorregulación del nido. El sector hipógeo presenta una estructura masiva, de granos compactados o comentados, probablemente relacionada con el soporte del nido y el aislamiento del suelo. El habitáculo posee una estructura laminar de cartón estercoral, material muy higroscópico, adecuado para conservar la alta humedad necesaria para el desarrollo de las larvas. Asimismo, este tipo de nidos presenta una paulatina variación micromorfológica en las sucesivas etapas de madurez. En los nidos inmaduros, el montículo entero exhibe una microestructura densa, mientras que en los maduros, la muralla y la región hipógea presenta una estructura muy compacta que contrasta con la estructura porosa que posee la región media. Las termitas que construyen nidos epígeos e hipógeos modifican considerablemente la micromorfología del suelo. En molisoles arenosos, con una microestructura suelta de microagregados entre granos, granular y de bloques subangulares pequeños, los nidos de Cornitermes cumulans presentan una estructura de granos cementados en la muralla y en la región hipógea, estructura pelicular en la región media y estructura laminar en el habitáculo. En suelos de similares características, los nidos de Termes saltans poseen una estructura compacta y compleja, que alterna estructuras laminar y migajosa, y los nidos de Cortaritermes fulviceps presentan una densa estructura de granos cementados. En ultisoles arenosos con estructura esponjosa, los nidos de Cornitermes cumulans exhiben estructuras agrietada y masiva en la muralla, una estructura compleja donde se alteman estructuras esponjosa, masiva y de granos compactados en la región media, estructura laminar en el habitáculo y estructura de granos compactados en el sector hipógeo. En molisoles y entisoles franco-limosos, con estructura masiva, los nidos de Cortaritermes fulviceps presentan respectivamente estructura lenticular y compleja con estructuras masiva y esponjosa alternadas. En molisoles franco-arcillosos con una estructura débil de granos y microagregados de materia orgánica sueltos, los nidos de Cortaritermes fulviceps exhiben estructuras migajosa y masiva alternadas. En entisoles franco-limosos con estructura masiva, los nidos de Nasutitermes poseen estructura lenticular y agrietada en el sector epígeo e hipógeo respectivamente. La micromorfologia de nidos epígeos de hormigas neotropicales es analizada y comparada con la de nidos epígeos de termitas de la misma región. A diferencia de los termiteros, los hormigueros carecen totalmente de rasgos compuestos de materia orgánica fina de origen fecal y de microagregación de arcillas en los pellets. La micromorfología de termiteros actuales es una valiosa herramienta para la correcta identificación de termiteros fósiles. A modo de ejemplo, se compara la micromorfologia de los termiteros actuales con icnofósiles de diferentes formaciones y edades de Argentina y Uruguay, los cuales han sido atribuidos a posibles termiteros fósiles. La presencia de microagregados ultrafinos, intercalaciones de pigmento orgánico y distribución porfirica de materiales finos y gruesos de la masa basal son positivas evidencias micromorfológicas para el reconocimiento de los icnofósiles como posibles construcciones termíticas.This contribution is the first study on Micromorphology of nests of Neotropical termites. It includes a comparative analysis of the micromorphology of nests of different species, of nests and their surrounding soil, and of different sectors of the nest. Micromorphological features, that have been observed in termite nests of African and Australian species, are compared with those observed in Argentinean species, and new features are also described. Micromorphological descriptions include presence of pellets, different types of microstructure, an analysis of the granulometry, frequency, sorting and distribution of coarse mineral componentes, fine organic features of fecal origin (cementing material of pellets and coarse grains, gallery coatings and linear intercalations in the groundmass), birefringence fabrics of fine material, clay microaggregation, lenticular clayey-quartzose crusts, porphyric distribution of coarse and fine components, and presence of plant remains and cuticle fragments of termites. A great micromorphological diversity occurs among nests of different termite species. However, a direct relation between termite systematic and micromorphology of its nests couldn’t be found because of the wide intraspecific variation of micromorphological features shown at different kinds of soils. In big and complex nests of Cornitermes cumulans, each region shows a particular micromorphology, which probably reflects its function in the nest. Dense massive or crack structures are present in peripheral walls, providing mechanical protection and environmental isolation, porous spongy or pellicular structures in the middle region probably enhance the thermoregulation of the nest, compact grain or massive intergrain cemented structures are present at the hipogeus region, probably related with soil isolation and weight support, hive has a platy stercoral carton structure, a very higroscopic material that keeps the high humidity level that larvae need. In addition, these complex nests show gradual micromorphological changes in its consecutive maturity stages: inmature nests show a dense structure in the whole mound, whereas mature ones show a porous structure in the middle region and a dense structure in the peripheral wall and hipogeous region. Termites with epigean and hipogean nests modify considerably the soil micromorphology. In sandy molisols with a loose intergrain microaggregate, granular and subangular blocky structures, nests of cornitermes cumulans show intergrain cemented structure at the peripheral wall of the mound and hipogeous region, pellicular structure at the middle region and platy structure in the hive. In similar soils, nests of Termes saltans have a compact complex structure with alternate platy and crumb structures, and nests of Cortaritermes fulviceps have intergrain cemented structure. In sandy ultisols with spongy structure, nests of Cornitermes cumulans show crack and massive structure in the peripheral wall of the mound, a complex structure at the middle region with alternate spongy, massive and compact grain structures, a platy structure at the hive and a compact grain structure at the hipogeous region. In silt-loamy molisols and entisols with an homogeneous massive structure, nests of Cortaritermes fulviceps have a lenticular structure and complex structure with alternate massive and spongy structures respectively. In clay-loamy molisols, with a very loose structure of single grains and organic microaggregates, the nests of Cortaritermes fulviceps have a complex structure with alternate crumb and massive structures. In silt-loamy entisols with a massive structure, the nests of Nasutitermes have lenticular and crack structure at the epigeous and hipogeous region respectively. The micromorphology of some epigean nests of Neotropical ants is analyzed and compared with those of termites. Ant nests differ from termite ones because ant nests don’t show any organic feature of fecal origin and their pellets don’t show clay microaggregation. The micromorphology of present-day termite nests may be a very useful tool for the correct identification of possible fossil termite nests. To test this, the micromorphology of present-day termite nests is compared with icnofossils of different formations and ages of Argentina and Uruguay, which have been attributed to termites. Micromorphological features like ultrafine microaggregates, intercalations of organic pigment and porphyric distribution of fine and coarse materials are positive evidences that suggest these ichnofossils might have arisen in termite constructions.Fil:Cosarinsky, Marcela Irene. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina