GPR clutter amplitude processing to detect shallow geological targets

The analysis of clutter in A-scans produced by energy randomly scattered in some specific geological structures, provides information about changes in the shallow sedimentary geology. The A-scans are composed by the coherent energy received from reflections on electromagnetic discontinuities and the incoherent waves from the scattering in small heterogeneities. The reflected waves are attenuated as consequence of absorption, geometrical spreading and losses due to reflections and scattering. Therefore, the amplitude of those waves diminishes and at certain two-way travel times becomes on the same magnitude as the background noise in the radargram, mainly produced by the scattering. The amplitude of the mean background noise is higher when the dispersion of the energy increases. Then, the mean amplitude measured in a properly selected time window is a measurement of the amount of the scattered energy and, therefore, a measurement of the increase of scatterers in the ground. This paper presents a simple processing that allows determining the Mean Amplitude of Incoherent Energy (MAEI) for each A-scan, which is represented in front of the position of the trace. This procedure is tested in a field study, in a city built on a sedimentary basin. The basin is crossed by a large number of hidden subterranean streams and paleochannels. The sedimentary structures due to alluvial deposits produce an amount of the random backscattering of the energy that is measured in a time window. The results are compared along the entire radar line, allowing the location of streams and paleochannels. Numerical models were also used in order to compare the synthetic traces with the field radargrams and to test the proposed processing methodology. The results underscore the amount of the MAEI over the streams and also the existence of a surrounding zone where the amplitude is increasing from the average value to the maximum obtained over the structure. Simulations show that this zone does not correspond to any particular geological change but is consequence of the path of the antenna that receives the scattered energy before arriving to the alluvial depositsPeer ReviewedPostprint (published version

Tectonic Development of Panama, Costa Rica, and the Colombian Andes: Constraints from Global Positioning System Geodetic Studies and Gravity

Global Positioning System (GPS) measurements suggest the existence of a rigid Panama- Costa Rica microplate that is moving northward relative to the stable Caribbean Plate. Northward motion of South America relative to the Caribbean plate is independently suggested by the April 1991 Costa Rica earthquake, active folding in the North Panama deformed belt, and a south-dipping Wadati-Benioff zone beneath Panama. Panama may also be continuing to collide eastward with the northern Andes. Rapid subduction is occurring at the Middle America (72mm/yr), Ecuador (70mm/yr), and Colombia (50mm/yr) trenches. The northern Andes are moving northeastward relative to stable South America. Preliminary GPS results also suggest Caribbean-North Andean convergence and an independent North Nazca plate. About 6 Ma the Panama-Choco island arc collided with the northwestern margin of South America, eventually forming a land bridge between the Americas; closed the Pacific-Caribbean seaway, changing ocean circulation patterns and perhaps the world\u27s climate; folded the East Panama deformed belt; and uplifted the Eastern Cordillera of Colombia. An interpretation of the paleo-Romeral suture in southern Colombia as a low-angle fault dipping to the west into the lower crust under the Cordillera Occidental is compatable with seismic velocity and gravity data. During the Late Cretaceous the Western Cordillera oceanic terrain was obducted eastward on the fault system over continental crust

On the thermodynamical limit of self-gravitating systems

It is shown that the diluted thermodynamical limit of a self-gravitating system proposed by de Vega and Sanchez suffers from the same problems as the usual thermodynamical limit and leads to divergent thermodynamical functions. This question is also discussed from the point of view of mean field theory.Comment: 11 pages. A typo corrected. Cosmetic changes in some equations. Version that appear in the journa

Silver Nanoparticles and PDMS Hybrid Nanostructure for Medical Applications

For many years, people have known about silver’s antibacterial qualities. Silver nanoparticles are widely used in consumer products, biomedical equipment, textile products and in other applications. Having a larger surface area to coat or spread over another surface, offers a greater contact area, therefore, increases antimicrobial properties. Also, these nanoparticles can be incorporated into polydimethylsiloxane (PDMS) implants as immobilized or occluded particles to improve their performance in the body. PDMS is commonly used for biomedical applications, including components for microfluidics, catheters, implants, valves, punctual plugs, orthopedics and micro gaskets. It can be manufactured easily in different forms such as fibers, fabrics, films, blocks and porous surfaces. The use of silver nanoparticles for their antimicrobial qualities improves PDMS biocompatibility, because it inhibits microbial growth, thereby making it more attractive for biomedical applications. The presence of metal nanoparticles also helps to reduce the hydrophobic nature of PDMS. This property of PDMS does not encourage cell adhesion, which is a very critical requirement for medical implants. Silver nanoparticles improve the silicone’s wettability. The exceptional properties of silver nanoparticles combined with the PDMS have made this hybrid nanostructure applicable to different medical uses

Phase structure of self-gravitating systems

The equilibrium properties of classical self-gravitating systems in the grand canonical ensemble are studied by using the correspondence with an euclidean field theory with infrared and ultraviolet cutoffs. It is shown that the system developes a first order phase transition between a low and a high density regime. In addition, due to the long range of the gravitational potential, the system is close to criticality within each phase, with the exponents of mean field theory. The coexistence of a sharp first order transition and critical behavior can explain both the presence of voids in large regions of the universe as well as the self-similar density correlations in terms of self-gravity alone.Comment: 12 pages, 1 figure. Some comments and references added. Version which appear in the journa

Plate Motions in the North Andean Region

Repeated geodetic measurements with the Global Positioning System (GPS) provide direct measurements of displacements due to plate motions and active crustal deformation in Central America and northern South America, an area of complex interaction of the Nazca, Cocos, Caribbean and South American plates. The displacement rates for the period 1988-1991, obtained from the results of the first three Central And South America (CASA) GPS campaigns, are in general agreement with the predictions of the NUVEL-1 plate motion model, but there are differences in detail between the observations and the model. The Nazca-North Andes convergence rate vector measured by GPS is different from the NUVEL-1 vector at 95% confidence. The difference implies that the North Andes are moving northward relative to South America. The measured convergence between the Caribbeanp late and the North Andes suggests that the southern margin of the Caribbean plate is located in the South Caribbean deformed belt. The April 1991 Costa Rica earthquake and the Cocos-Caribbean convergence rate determined by GPS suggest the possibility of significant ongoing deformation between Central America and the stable interior of the Caribbean plate. Our GPS results are consistent with deformation of the overriding plates at the convergent margins of Central and South America and confirm that active convergence is occurring around much of the southern margin of the Caribbean plate, from Colombia west to Costa Rica. Costa Rica and Panama are not part of the stable Caribbean plate. Instead, the South Caribbean deformed belt and the North Panama fold belt probably represent the southern margin of the Caribbean plate

Source–sink relationships during early crop development influence earliness of sugar accumulation in sugarcane

In subtropical environments where sugarcane (Saccharum spp.) crops are frequently limited by the duration of the growth cycle, earliness in maturity is a key genotypic trait. Using the concept of source–sink relationships, we hypothesised that earliness is controlled by the dynamics of tillering (DT), which define sink strength early in the growth cycle. Five modern commercial sugarcane genotypes with similar sucrose yields and varying degrees of earliness in ripening were grown in the field over three years and their DT, dynamics of sucrose accumulation (DS), and source–sink relationships over time were characterised. Canonical correlations and principal components analysis revealed that DT explained 68% of the total variance in DS. Early ripening genotypes exhibited the shortest thermal time to the end of tiller mortality (θTilmort), the lowest tiller survival and millable tiller number, and greatest sugar content at θTilmort (Sconc,Tilmort). The rate and duration of the sucrose accumulation phase did not explain the genotypic variation either in final sugar content or in earliness when considered in isolation without taking into account the effect of Sconc,Tilmort. In the set of genotypes examined, the variation in final sucrose yield was most explained by the variation in stalk number. We conclude that the dynamics of tiller appearance and senescence modified the early source–sink relationships and thus determined the differential sucrose contents around θTilmort and the earliness of maximal sugar accumulation. θTilmort, which was closely associated with the 14-leaf phenological stage, emerged as a candidate trait to screen for genotypic variation in early ripening, crop cycle duration, and yield.EEA FamailláFil: Saez, Julio Victor. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Famaillá; ArgentinaFil: Mariotti, Jorge. Universidad Nacional de Salta. Facultad de Ciencias Naturales. Cátedra de Mejoramiento Genético Vegetal; ArgentinaFil: Vega, Claudia R.C. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Manfredi. Área de Agronomía; Argentin