High-Resolution Keck Adaptive Optics Imaging of Violent Volcanic Activity on Io

Io, the innermost Galilean satellite of Jupiter, is a fascinating world. Data taken by Voyager and Galileo instruments have established that it is by far the most volcanic body in the Solar System and suggest that the nature of this volcanism could radically differ from volcanism on Earth. We report on near-IR observations taken in February 2001 from the Earth-based 10-m W. M. Keck II telescope using its adaptive optics system. After application of an appropriate deconvolution technique (MISTRAL), the resolution, ∼100 km on Io's disk, compares well with the best Galileo/NIMS resolution for global imaging and allows us for the first time to investigate the very nature of individual eruptions. On 19 February, we detected two volcanoes, Amirani and Tvashtar, with temperatures differing from the Galileo observations. On 20 February, we noticed a slight brightening near the Surt volcano. Two days later it had turned into an extremely bright volcanic outburst. The hot spot temperatures (>1400 K) are consistent with a basaltic eruption and, being lower limits, do not exclude an ultramafic eruption. These outburst data have been fitted with a silicate-cooling model, which indicates that this is a highly vigorous eruption with a highly dynamic emplacement mechanism, akin to fire-fountaining. Its integrated thermal output was close to the total estimated output of Io, making this the largest ionian thermal outburst yet witnessed.     

Relationships between the AE, ap and Dst indices near solar minimum (1974) and at solar maximum (1979)

Three-hourly average values of the Dst, AE and ap geomagnetic activity indices have been studied for 1 years duration near the solar minimum (1974) and also at the solar maximum (1979). In 1979 seven intense geomagnetic storms (Dst < –100 nT) occurred, whereas in 1974 only three were reported. This study reveals: (1) the yearly average of AE is greater in 1974 than in 1979, whereas the inverse seems to be true for the yearly average of Dst, when a higher number of intense storms is present. These averages indicate the kind of activity occurring on the sun as shown in earlier work. (2) The seasonal variation of Dst is higher than that of ap and is almost negligible in AE. (3) The correlation coefficient of ap × AE is in general the highest, as the magnetometers that monitor both indices are close, and is surpassed only by the ap × Dst correlation during geomagnetic storms, when the influence of the ring current is dominant. The correlation of ap × Dst also shows a seasonal variability. (4) For the first time a study of correlation between ap and a linear combination of AE and Dst has also been made. We found higher correlation coefficients in this case as compared to those between ap × Dst and ap ×xs AE.     

Geological,geophysical and geochemical structure of a fault zone developed in granitic rocks: Implications for fault zone modeling in 3-D

The structure of a fault zone developed in granitic rocks can be established on the basis of the spatial variability of geological, geophysical and geochemical parameters. In the North Fault of the Mina Ratones area (SW Iberian Massif, Spain), fault rocks along two studied traverses (SR-2 and SR-3 boreholes) exhibit systematic changes in mineralogy, geochemistry, fabrics and microstructures that are related to brittle deformation and alteration of granite to form cataclasite and subsequent gouge. The spatial distribution and intensity of these changes suggest a North Fault morphology that is consistent with the fault-core/damage-zone model proposed by Chester et al. (1993) to describe a fault zone architecture. North Fault damage zone thickness can be defined by the development of mechanically related mesoscopic faults and joints, that produce a Fracture Index (FI)>10. High FI values are spatially correlated with relative low seismic velocity zones (V_P<5 km/s and V_S<2.5 km/s in the well-logs), more probably related to a high concentration of fractures and geochemical alteration produced by meteoric water-granite interaction along fault surfaces. This correlation is the base of a geostatistical model proposed in the final part of this study to image the fault zone architecture of a granitic massif.     

Participatory slum upgrading as a disjunctive process in Recife,Brazil: Urban coproduction and the absent ground of the city

This article engages with the coproduction of urban space by focusing on a slum upgrading project in Recife, Brazil. It argues that the urban situation is essentially inconsistent, unpredictable and unstable. It documents the history of urban planning in Recife, paying special attention to the coexistence of two different planning traditions, one aimed at what city planners call the informal city, which is participatory, bottom up and democratic, yet susceptible to be corrupted by political clientelism, and another aimed at the formal city, which is ‘strategic’, top down, technocratic and neoliberal. It argues that the informal/formal binary operates as a disjunctive synthesis that separates social actors rather than connecting them and provides the coordinates within which processes of coproduction take place. The disjunctive synthesis renders possible all sorts of fantastic imaginations that both disavow and reveal the missing ground of the city. Community leaders play a central role in the coproduction of urban space and function as the symptom of this absent ground. The article concludes that participatory urban development interventions aiming to curtail the role of community leaders end up as veritable tyrannies of participation, which should be seen as evidence of the disjointed character of planning rather than as forms of effective governmentality.     

Isotropic and anisotropic pointing models

This paper describes an alternative approach for generating pointing models for telescopes equipped with serial kinematics, esp. equatorial or alt-az mounts. Our model construction does not exploit any assumption for the underlying physical constraints of the mount, however, one can assign various effects to the respective components of the equations. In order to recover the pointing model parameters, classical linear least squares fitting procedures can be applied. This parameterization also lacks any kind of parametric singularity. We demonstrate the efficiency of this type of model on real measurements with meter-class telescopes where the results provide a root mean square accuracy of 1.5?2 arcseconds.     

Light curve and O−C diagram analysis of RZ Cassiopeiae

The aim of the present paper is to analyze the light variation as well as the period changes of the eclipsing binary RZ Cas. New photometric elements are computed using the frequency-domain method. The possibility of the light-time effect and the apsidal motion is discussed.     

New geological model of the Lagoa Real uraniferous albitites from Bahia (Brazil)

New evidence supported by petrography (including mineral chemistry), lithogeochemistry, U-Pb geochronology by Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS), and physicochemical study of fluid and melt inclusions by LA-ICP-MS and microthermometry, point to an orogenic setting of Lagoa Real (Bahia-Brazil) involving uraniferous mineralization. Unlike the previous models in which uraniferous albitites represent Na-metasomatised 1.75 Ga anorogenic granitic rocks, it is understood here that they correspond to metamorphosed sodium-rich and quartz-free 1.9 Ga late-orogenic syenitic rocks (Na-metasyenites). These syenitic rocks are rich not only in albite, but also in U-rich titanite (source of uranium). The interpretation of geochemical data points to a petrogenetic connection between alkali-diorite (local amphibolite protolith) and sodic syenite by fractional crystallization through a transalkaline series. This magmatic differentiation occurred either before or during shear processes, which in turn led to albitite and amphibolite formation. The metamorphic reactions, which include intense recrystallization of magmatic minerals, led uraninite to precipitate at 1.87 Ga under Oxidation/Reduction control. A second population of uraninites was also generated by the reactivation of shear zones during the 0.6 Ga Brasiliano Orogeny. The geotectonic implications include the importance of the Orosirian event in the Paramirim Block during paleoproterozoic S?o Francisco Craton edification and the influence of the Brasiliano event in the Paramirim Block during the West-Gondwana assembly processes. The regional microcline-gneiss, whose protolith is a 2.0 Ga syn-collisional potassic granite, represents the albitite host rock. The microcilne-gneiss has no petrogenetic association to the syenite (albitite protolith) in magmatic evolutionary terms.     

Stability analysis of a two-inlet bay system

The stability analysis for a double-inlet bay system is applied to an inlet system resembling Big Marco Pass and Capri Pass on the lower west coast of Florida. Since the opening of Capri Pass in 1967, the length of Big Marco Pass has increased from 2000 m in 1967 to 3000 m in 1988 and the cross-sectional area has decreased from 1200 m² in 1967 to 1000 m² in 1988. Since 1967, the cross-sectional area of Capri Pass has steadily increased and in 1988 was 700 m². Tides off the inlets are of the mixed type with a diurnal range of 1 m. The gross littoral transport rate in the vicinity of the inlets is estimated at 150,000 m³ yr⁻¹.For each inlet the maximum tidal velocities are calculated as a function of the gorge cross-sectional areas using a lumped-parameter model to describe the hydrodynamics of the flow. In the model it is assumed that the bay level fluctuates uniformly and the bay surface area remains constant. The velocities are used to calculate the tidal maximum of the bottom shear stress in each inlet as a function of the cross-sectional areas of the two inlets (=closure surface). Values of the equilibrium shear stress are derived from an empirical relationship between cross-sectional area and tidal prism for stable inlets along the west coast of Florida. Closure surfaces and equilibrium stress values are calculated for values of friction factors ranging from F=4×10⁻³ to F=6×10⁻³. Using the closure surfaces and equilibrium stress values, the equilibrium flow curve for each inlet is determined. The equilibrium flow curve represents the locus of the combination of cross-sectional areas for which the actual bottom shear stress in the inlet equals the equilibrium shear stress.Based on the equilibrium flow curves and the known values of the cross-sectional areas of the two inlets in 1988, it is expected that, ultimately, Big Marco Pass will close and Capri Pass will remain as the sole inlet with a cross-sectional area of 1250 m² and a maximum tidal velocity pertaining to a diurnal tide of 0.85 m s⁻¹.