Centaurus A as a source of extragalactic cosmic rays with arrival energies well beyond the GZK cutoff

The ultra-high energy cosmic rays recently detected by several air shower experiments could have an extragalactic origin. In this case, the nearest active galaxy Centaurus A might be the source of the most energetic particles ever detected on Earth. We have used recent radio observations in order to estimate the arrival energy of the protons accelerated by strong shock fronts in the outer parts of this southern radio source. We expect detections coresponding to particles with energies up to 2.2 × 10²¹ eV and an arrival direction of (l ≈ 310°, b ≈ 20°) in galactic coordinates. The future Southern Hemisphere Pierre Auger Observatory might provide a decisive test for extragalactic models of the origin of the ultra-high energy cosmic rays.     

A note on Einstein-Maxwell solutions and vacuum to electrovac solutions transforms

We discuss a direct construction of solitonic solutions in the Einstein-Maxwell system and analyze the connection of these with vacuum to electrovac transforms of the usual Belinskii-Zakharov vacuum solutions in the static and Einstein-Rosen waves cases.It should be noted that the construction of Belinskii is the same as the one that appears in the Kaluza-Klein ansatz, although in his case there is no direct interpretation to the scalarg ₅₅ fieldSupported by a CONICET fellowship.     

Neutrino transport with isoenergetic and neutrino-electron scattering

Solution to steady-state, bigroup neutrino transport with isoenergetic and neutrino-electron scattering have been obtained for idealized conditions representative of the outer core or envelope of a star whose inner core is undergoing gravitational collapse. The solutions are presented in a form suitable for comparison with other numerical schemes. The incident neutrino distribution was chosen to be nonequilibrium, and the solutions clearly show the tendency of the neutrinos to equilibrate via neutrino-electron scattering as they propagate through the material. Care is taken to compare solutions obtained by two completely different techniques to ensure that the solutions presented here are accurate and error free. The solutions are compared with those obtained by a simple diffusion scheme, and by a flux limited diffusion scheme. The solutions given by the latter agree well with the solutions derived here, except when the neutrino angular distribution becomes oblate.     

Active region flare rates and 8.6 mm brightness temperatures

The relationship between the flaring rates and 8.6 mm brightness temperatures of active regions has been analyzed. We find that as the 8.6 mm brightness temperature of an active region increases, a larger proportion of the energy released by the region in the form of flares is contained in progressively larger flares. At all temperatures subflares are the most frequent event. At intermediate and high temperatures about 10% of the events are flares of importance 1 or larger with flares of importance 2 or larger contributing an increasing fraction of these events as the brightness temperature increases.     

Impulsive phase of flares in soft X-ray emission

Observations using the Bent Crystal Spectrometer instrument on the Solar Maximum Mission show that turbulence and blue-shifted motions are characteristic of the soft X-ray plasma during the impulsive phase of flares, and are coincident with the hard X-ray bursts observed by the Hard X-ray Burst Spectrometer. A method for analysing the Ca xix and Fe xxv spectra characteristic of the impulsive phase is presented. Non-thermal widths and blue-shifted components in the spectral lines of Ca xix and Fe xxv indicate the presence of turbulent velocities exceeding 100 km s^-1 and upward motions of 300–400 km s^-1.The April 10, May 9, and June 29, 1980 flares are studied. Detailed study of the geometry of the region, inferred from the Flat Crystal Spectrometer measurements and the image of the flare detected by the Hard X-ray Imaging Spectrometer, shows that the April 10 flare has two separated footpoints bright in hard X-rays. Plasma heated to temperatures greater than 10⁷ K rises from the footpoints. During the three minutes in which the evaporation process occurs an energy of 3.7 × 10³⁰ ergs is deposited in the loop. At the end of the evaporation process, the total energy observed in the loop reaches its maximum value of 3 × 10³⁰ ergs. This is consistent with the above figures, allowing for loss by radiation and conduction. Thus the energy input due to the blue-shifted plasma flowing into the flaring loop through the footpoints can account for the thermal and turbulent energy accumulated in this region during the impulsive phase.On leave from Torino University, Italy.     

The Late Neoproterozoic granitoid magmatism of the Pelotas Batholith, southern Brazil

Geological mapping, petrography, geochemistry, and isotope studies enable the division of the Pelotas Batholith into six granitic suites: Pinheiro Machado (PMS), Erval (ES), Viamão (VS), Encruzilhada do Sul (ESS), Cordilheira (CS), and Dom Feliciano (DFS). The rocks of the PMS show a large compositional range (granite through granodiorite to tonalite), and the suite is considered pre- to syncollisional. Other suites show restricted compositional variations (granite to granodiorite) and are late to postcollisional. In general, the suites are metaluminous to slightly peraluminous (PMS, ES, and VS) or peraluminous (CS) or have alkaline tendencies (ESS and DFS). The magmatic evolution corresponds to high-K calc-alkaline to alkaline magmatism. The suites are enriched in K, Rb, and REE compared with rocks of typical calc-alkaline series. Initial ⁸⁷Sr/⁸⁶Sr ratios vary from 0.705 to 0.716, except in the CS, where they attain values of 0.732–0.740. Sm–Nd T_DM model ages vary between 0.98 and 2.0 Ga, with initial ε_Nd values ranging from −0.3 to −10. U–Pb zircon dates of samples from PMS, VS, and ESS suggest an age between 0.63 and 0.59 Ga for magmatism. Rb–Sr dates of samples of alkaline granites from DFS present ages between 0.57 and 0.55 Ga. The main tectonic controls of the magmatism of the Pelotas Batholith are high-dip sinistral shear zones.     

The current tectonic motion of the Northern Andes along the Algeciras Fault System in SW Colombia

Riedel, synthetic and antithetic type faults, principal displacement zones (PDZ), pull-apart basins (such as lazy-S shaped releasing bend, extensive and rhomboidal shaped and releasing sidestep basins) and minor folds located oblique to the main trace of the Algeciras Fault System (AFS) are interpreted from Landsat TM 5 images and geological mapping. These tectonic features are affecting Quaternary deposits and are related to major historical earthquakes and recent registered seismic events, indicating neotectonic activity of the structure.The AFS is classified as a right lateral wrench complex structure, with an important vertical component in which sedimentary cover and basement rocks are involved. In addition, the system represents a simple shear caused by the oblique convergence between the Nazca Plate and the northern Andes. The transpressive boundary in SW Colombia was previously located along the Eastern Frontal Fault System. However, this paper shows that the AFS constitutes the actual boundary of the current transpressive regime along the Northern Andes, which begins at the Gulf of Guayaquil in Ecuador and continues into Colombia and Venezuela.     

A high-resolution satellite-derived sea surface temperature climatology for the western North Atlantic Ocean

Long-term and high-resolution (∼1.2 km) satellite-derived sea surface temperature (SST) fields of a monthly mean time series for the 1985–1999 period, and a daily climatology have been calculated for the North West Atlantic Ocean. The SST fields extend from 78°W to 41°W in longitude, and 30°N to 56°N in latitude, encompassing the region off Cape Hatteras, North Carolina, to the southern Labrador Sea. The monthly mean time series, consists of 180 cloud-masked monthly mean SST fields, derived from a full-resolution NOAA/NASA Pathfinder SST data set for the 1985–1999 period. The satellite-derived monthly mean SST fields, as compared with in situ monthly mean near-surface ocean temperatures from buoys located in the western North Atlantic, yield an overall RMS difference of 1.15 °C. The daily climatology, which consists of 365 fields, was derived by applying a least-squares harmonic regression technique on the monthly mean SST time series for the full study period. The monthly mean and daily climatological SST fields will be useful for studying inter-annual variability related to climate variability of SST over the study domain.     

Estimation or simulation? That is the question

The issue of smoothing in kriging has been addressed either by estimation or simulation. The solution via estimation calls for postprocessing kriging estimates in order to correct the smoothing effect. Stochastic simulation provides equiprobable images presenting no smoothing and reproducing the covariance model. Consequently, these images reproduce both the sample histogram and the sample semivariogram. However, there is still a problem, which is the lack of local accuracy of simulated images. In this paper, a postprocessing algorithm for correcting the smoothing effect of ordinary kriging estimates is compared with sequential Gaussian simulation realizations. Based on samples drawn from exhaustive data sets, the postprocessing algorithm is shown to be superior to any individual simulation realization yet, at the expense of providing one deterministic estimate of the random function.