Simple potential–density pairs for flat rings

Potential–density pairs representing flat-ring structures in terms of elementary functions are presented. Structures representing one or several concentric flat rings, and discs surrounded by concentric flat rings are examined. The stability of concentric circular orbits of particles moving on a flat-ring structure is analyzed for radial perturbations.     

Unsteady thermoelastic analysis of a circular disk with a hot central core and subjected to adiabatic conditions

The unsteady thermoelastic analysis of a cooling circular disk or cylinder which is originally at uniform temperature is a classical problem of the theory of thermal stresses. More recent studies consider the case of composite structural configurations. The present paper deals with a situation which, apparently, has not been previously considered: unsteady thermal stresses caused by the presence of a hot, central nucleus. The temperature field is obtained in terms of a Fourier–Bessel expansion and then, radial and tangential stresses are evaluated analytically. The problem is of basic interest in mechanical and naval engineering systems.     

Differential piscivory of the native Percichthys trucha and exotic salmonids upon the native forage fish Galaxias maculatus in Patagonian Andean lakes

The present paper analyses predation patterns, of Percichthys trucha and salmonid fish upon Galaxias maculatus in five lakes of northern Patagonia with differing community and environmental characteristics. Tank experiments were performed to evaluate relative efficiency of native and exotic predators of G. maculatus under treatments with and without cover (aquatic vegetation). Important differences were found between predators with regards to distribution and consumption of G. maculatus. Salmonids are more efficient than P. trucha in consuming G. maculatus in deep environments with scarcely vegetation; in contrast to native species they frequently use the pelagic environment. Although pelagic habitat might have served in the past as a refuge from native predators in the past, G maculatus now experiences intense predation in the pelagic zone by exotic salmonids. It is suggested that the widespread distribution of G. maculatus in Patagonian lakes may have facilitated the success of salmonids throughout Patagonia.     

Breeding cycle of the red squat lobster Pleuroncodes monodon H. Milne Edwards, 1837 (Decapoda,Muninidae) from deepwater Pacific of Costa Rica

Reproduction and larval development of the red squat lobster Pleuroncodes monodon is strongly linked to temperature changes provoked by upwelling along the Chilean coast. Here, we propose the hypothesis that both the breeding cycle and the spatial distribution of egg‐bearing females of P. monodon in Costa Rica are related to decreasing water temperatures during seasonal coastal upwelling. To describe the breeding cycle, squat lobsters were collected between February 2007 and January 2008 from the Central Pacific coast of Costa Rica. The presence of egg‐bearing females in other areas of the Costa Rican coast was studied from samples collected during two latitudinal research cruises (August 2008: rainy season; May 2009: dry season). Our results revealed that P. monodon has a marked seasonal breeding period (from November to March), which is associated with decreasing water surface temperatures registered during coastal upwelling events. All females with embryos close to hatching were found in areas surrounding the Gulf of Nicoya, when upwelling events have been reported. The near absence of egg‐bearing females in zones where upwelling does not occur suggests the existence of a strong correlation between upwelling events and the breeding cycle of P. monodon. Our information should be considered when developing management measures for the sustainable use of this potential fishery resource in the Pacific coast of Central America.     

Steerable wavelet analysis of CMB structures alignment

This paper reviews the application of a novel methodology for analysing the isotropy of the universe by probing the alignment of local structures in the CMB. The strength of the proposed methodology relies on the steerable wavelet filtering of the CMB signal. One the one hand, the filter steerability renders the computation of the local orientation of the CMB features affordable in terms of computation time. On the other hand, the scale-space nature of the wavelet filtering allows to explore the alignment of the local structures at different scales, probing possible different phenomena. We present the WMAP first-year data analysis recently performed by the same authors (Wiaux et al.), where an extremely significant anisotropy was found. In particular, a preferred plane was detected, having a normal direction with a northern end position at (θ, ) = (34°, 331°), close to the northern end of the CMB dipole axis. In addition, a most preferred direction was found in that plane, with a northern end direction at (θ, ) = (71°, 91°), very close to the north ecliptic pole. This result synthesised for the first time previously reported anomalies identified in the direction of the dipole and the ecliptic poles axes. In a forthcoming paper (Vielva et al.), we have extended our analysis to the study of individual frequency maps finding first indications for discarding foregrounds as the origin of the anomaly. We have also tested that the preferred orientations are defined by structures homogeneously distributed in the sky, rather than from localised regions. We have also analysed the WMAP 3-year data, finding the same anomaly pattern, although at a slightly lower significance level.     

The 1877–1878 El Niño episode: associated impacts in South America

At times when attention on climate issues is strongly focused on the assessment of potential impacts of future climate change due to the intensification of the planetary greenhouse effect, it is perhaps pertinent to look back and explore the consequences of past climate variability. In this article we examine a large disruption in global climate that occurred during 1877–1878, when human influence was negligible. The mechanisms explaining this global disturbance are not well established, but there is considerable evidence that the major El Niño episode that started by the end of 1876 and peaked during the 1877–1878 boreal winter contributed significantly to it. The associated regional climate anomalies were extremely destructive, particularly in the Northern Hemisphere, where starvation due to intense droughts in Asia, South-East Asia and Africa took the lives of more than 20 million people. In South America regional precipitation anomalies were typical of El Niño events, with rainfall deficit and droughts in the northern portion of the continent as well as in northeast Brazil and the highlands of the central Andes (Altiplano). In contrast, anomalously intense rainfall and flooding episodes were reported for the coastal areas of southern Ecuador and Northern Perú, as well as along the extratropical West coast of the continent (central Chile, 30° S–40° S), and in the Paraná basin in the southeast region. By far the most devastating impacts in terms of suffering and loss of life occurred in the semiarid region of northeast Brazil where several hundreds of thousands of people died from starvation and diseases during the drought that started in 1877.