Geologia

El ritmo y la magnitud de los esfuerzos dedicados a la exploración minera obedecen a tres factores principales. El primero, constituido por las circunstancias externas, que incluyen la oferta-demanda e inventarios del metal, precios actuales y previsibles, aspectos políticos, cambios en los incentivos legales y tributarios y, crecientemente, aspectos ambientales y de "aceptabilidad social" de la minería. El segundo se refiere a la aparición de nuevas herramientas de exploración, como las distintas formas de la prospección geofísica, la prospección geoquímica, la espectrometría infrarroja de la alteración hidrotermal, los métodos instrumentales de análisis geoquímico por multielementos y, desde luego, los avances en la tecnología y economía de los sondajes. El tercer factor, tema del presente artículo, es el surgimiento de nuevas ideas de exploración, concretadas en torno a modelos de yacimientos, que incluyen su contexto geológico, expresión geofísica, geoquímica y mineralógica, y expectativas de magnitud, leyes y asociaciones de metales valiosos presentes.

Resumen-Este ar tícu lo presenta un estado del arte sobre la ada ptación de la in for mación con respect o al con tenido y al despliegue en el dispositivo de acceso. Dicho estado del arte fue el origen de un modelo de adaptación denominado IAM (acrónimo en inglés de Modelo de Adaptación Integrado). Tal modelo permite representar las car acterísticas del usuario, de su dispositivo de acceso y del contexto en el que se desenvuelve la interacción del usuario con el sistema. Para definir cada uno de sus componentes se hizo un estudio de trabajos relacionados en los que se presenta un análisis de diver sas car acter ísticas que se consider an en el momento de adaptar la información. En dicho análisis se resaltan cier tas car acter ísticas como por ejemplo, la localización (en el caso del contexto) o las preferencias (en el caso de un perfil de usuar io). Finalmente se presenta una breve descr ipción de los componentes de IAM.

Sustained administration of opioid antagonists to rodents results in an enhanced antinociceptive response to agonists. We investigated the changes in spinal μ-opioid receptor signalling underlying this phenomenon. Rats received naltrexone (120 μg/h; 7 days) via osmotic minipumps. The antinociceptive response to the μ-agonist sufentanil was tested 24 h after naltrexone withdrawal. In spinal cord samples, we determined the interaction of μ-receptors with Gα proteins (agonist-stimulated [35S]GTPγS binding and immunoprecipitation of [35S]GTPγS-labelled Gα subunits) as well as μ-opioid receptor-dependent inhibition of the adenylyl cyclase (AC) activity. Chronic naltrexone treatment augmented DAMGO-stimulated [35S]GTPγS binding, potentiated the inhibitory effect of DAMGO on the AC/cAMP pathway, and increased the inverse agonist effect of naltrexone on cAMP accumulation. In control rats, the inhibitory effect of DAMGO on cAMP production was antagonized by pertussis toxin (PTX) whereas, after chronic naltrexone, the effect became resistant to the toxin, suggesting a coupling of μ-receptors to PTX-insensitive Gαz subunits. Immunoprecipitation assays confirmed the transduction switch from Gαi/o to Gαz proteins. The consequence was an enhancement of the antinociceptive response to sufentanil that, in consonance with the neurochemical data, was prevented by Gαz-antisense oligodeoxyribonucleotides but not by PTX. Such changes in opioid receptor signalling can be a double-edged sword. On the one hand, they may have potential applicability to the optimisation of the analgesic effects of opioid drugs for the control of pain. On the other hand, they represent an important homeostatic dysregulation of the endogenous opioid system that might account for undesirable effects in patients chronically treated with opioid antagonists.This article is part of a Special Issue entitled ‘Post-Traumatic Stress Disorder’.► Chronic treatment with opioid antagonists increases agonist-mediated antinociception. ► We examine spinal cord changes in μ-opioid receptor signalling underlying this effect. ► Opioid receptor coupling to G-proteins and inhibition of cAMP pathway are enhanced. ► μ-opioid receptors experience a transduction shift from Gαi/o to Gαz proteins. ► The inverse agonist effect of naltrexone on cAMP accumulation is enhanced.

OF DISSERTATION CONTROLS ON MIDDLE TO LATE ORDOVICIAN SYNOROGENIC DEPOSITION IN THE SOUTHEASTERN CORNER OF LAURENTIA Middle and Upper Ordovician strata in the southernmost Appalachians document initial collision along the southeastern margin of Laurentia during the Blountian orogeny, an early phase of the Taconic orogeny. Coeval drowning and exposure of different parts of the former platform and variations in stratal architecture have been attributed to tectonic and depositional loading along the collisional margin. Stratigraphic correlations, using a bentonite-graptoliteconodont time framework, a palinspastic map, and a map of subsurface basement structures, suggest that basement-fault reactivation, flexural subsidence, and eustasy variously controlled uplift, subsidence, and deposition at different sites within the peripheral foreland basin. This dissertation documents how pre-existing structures in the continental margin and interior affected subsidence, deposition, diagenesis, and composition of foreland strata, and deformation in tectonic loads. Stratigraphic correlations document an early episode of basementfault inversion in the distal foreland, and heterogeneous subsidence and provenance patterns in the middle and proximal foreland. Abrupt variations in depth of erosion of passive-margin strata and in thickness of distal foreland deposits coincide with the boundaries of the intraplate Birmingham graben. Inversion of the former graben increased the magnitude of erosion on inverted upthrown blocks; increased tectonic subsidence in adjacent blocks; supplied chert and quartz detritus to shallow-marine carbonate depocenters; and facilitated influx of meteoric water to aquifers in shallow-marine limestones. Tectonic subsidence of middle and proximal foreland deposits reflects local irregularities in the foreland subsidence and different rates of migration of the flexural wave along strike. Differential subsidence between embayments and promontories may have caused reactivation of transverse basement faults. Relief produced by reactivation of transverse basement faults and flexural normal reactivation of basement faults may provide sources for local conglomerates interbedded with deep-water shales. Differences in orogenicbelt deformation are reflected in provenance analyses that suggest exposure of dominantly feldspar-bearing basement rocks in the orogenic belt adjacent to the promontory and exposure of basement rocks and sedimentary cover in the orogenic belt adjacent to the embayment. Results of this study reveal the importance of considering the effects of pre-existing structures in the interpretation of along-and across-strike variations of foreland strata. Therefore, geodynamic modeling of the Blountian foreland basin needs to consider along-strike variations in the geometry of tectonic loads and reactivation of different basement structures.

- The aim of this article is to explore the recent social and economic evolution of a rural region that was formerly one of the poorest in Chile but has been transformed by a productive specialisation in table grapes for export markets. The region is that of the Upper Limari in ...