A phylogenetic comparative analysis on the evolution of sequential hermaphroditism in seabreams (Teleostei : Sparidae)

The Sparids are an ideal group of fish in which to study the evolution of sexual systems since they exhibit a great sexual diversity, from gonochorism (separate sexes) to protandrous (male-first) and protogynous (female-first) sequential hermaphroditism (sex-change). According to the size-advantage model (SAM), selection should favour sex change when the second sex achieves greater reproductive success at a larger body size than the first sex. Using phylogenetic comparative methods and a sample of 68 sparid species, we show that protogyny and protandry evolve from gonochorism but evolutionary transitions between these two forms of sequential hermaphroditism are unlikely to happen. Using male gonadosomatic index (GSI) as a measure of investment in gametes and proxy for sperm competition, we find that, while gonochoristic and protogynous species support the predictions of SAM, protandrous species do not, as they exhibit higher GSI values than expected even after considering mating systems and spawning modes. We suggest that small males of protandrous species have to invest disproportionally more in sperm production than predicted not only when spawning in aggregations with high levels of sperm competition, but also when spawning in pairs due to the need to fertilize highly fecund females, much larger than themselves. We propose that this compensatory mechanism, together with Bateman’s principles in sequential hermaphrodites, should be formally incorporated in the SAM

Competition, efficiency and collective behavior in the "El Farol" bar model

The El Farol bar model, proposed to study the dynamics of competition of agents in a variety of contexts (W. B. Arthur, Amer. Econ. Assoc. Pap. and Proc. 84, 406 (1994)) is studied. We characterize in detail the three regions of the phase diagram (efficient, inefficient and better than random) of the simplest version of the model (D. Challet and Y.-C. Zhang, Physica A, 246, 407 (1997)). The efficient region is shown to have a rich structure, which is investigated in some detail. Changes in the payoff function enhance further the tendency of the model towards a wasteful distribution of resources.Comment: 7 pages Latex, 7 Postscript figures; changed reference, acknowledgments included. Accepted for publication in Europen Physics Journal

Cáculo del riesgo de ingición a partir de imágenes AVHRR (NOAA)

El riesgo de incendio forestal puede resumirse en dos factores principales: el riesgo de ignición y la probabilidad de que el fuego se expanda y acabe produciendo un incendio forestal. El riesgo de ignición puede ser debido a diferentes causas: factor humano y el estado de la vegetación. La probabilidad de expansión es principalmente debido a: condiciones meteorológicas, situación geográfica, características de la vegetación y facilidad de extinción. El principal objetivo del presente trabajo es la obtención de un índice de riesgo de ignición debido al estado de la vegetación. Para cumplir dicho objetivo se ha elaborado una serie temporal de 8 años de imágenes AVHRR (NOAA). A partir de las imágenes diarias se ha calculado el índice de vegetación NDVI, promedios mensuales y también promedios del mismo mes para los distintos años. A partir de la comparación del NDVI mensual del año en curso con el promedio de la serie de temporal para el mes correspondiente se detectan las zonas con diferencias importantes de estado de la vegetación. Las zonas con NDVI promedio más bajos para el año en curso respecto a la serie temporal, son zonas con riesgo de ignición más elevado que el resto de zonas.The risk of forest fires can be summarized in two main factors: the risk of ignition and the probability of fire spreading and causing a forest fires. The risk of ignition may be due to different causes: human factor and the state of vegetation. The probability of expansion is mainly due to: weather, geography, vegetation characteristics and ease of extinction. The main aim of this study is to obtain an index of risk of ignition due to the state of vegetation. To meet this objective a series of 8 years of images AVHRR (NOAA) has been developed. From daily images we have calculated vegetation index NDVI, monthly averages and averages of the same month for different years. From the comparison of monthly NDVI for current month with the average time series for the corresponding month, in order to detect areas with significant differences in the state of the vegetation. Areas with lower average NDVI for the current year with respect to the time series, are areas with higher fire risks than other areas

Active Control of Fan Noise-Feasibility Study. Volume 2: Canceling Noise Source-Design of an Acoustic Plate Radiator Using Piezoceramic Actuators

The feasibility of using acoustic plate radiators powered by piezoceramic thin sheets as canceling sources for active control of aircraft engine fan noise is demonstrated. Analytical and numerical models of actuated beams and plates are developed and validated. An optimization study is performed to identify the optimum combination of design parameters that maximizes the plate volume velocity for a given resonance frequency. Fifteen plates with various plate and actuator sizes, thicknesses, and bonding layers were fabricated and tested using results from the optimization study. A maximum equivalent piston displacement of 0.39 mm was achieved with the optimized plate samples tested with only one actuator powered, corresponding to a plate deflection at the center of over 1 millimeter. This is very close to the deflection required for a full size engine application and represents a 160-fold improvement over previous work. Experimental results further show that performance is limited by the critical stress of the piezoceramic actuator and bonding layer rather than by the maximum moment available from the actuator. Design enhancements are described in detail that will lead to a flight-worthy acoustic plate radiator by minimizing actuator tensile stresses and reducing nonlinear effects. Finally, several adaptive tuning methods designed to increase the bandwidth of acoustic plate radiators are analyzed including passive, active, and semi-active approaches. The back chamber pressurization and volume variation methods are investigated experimentally and shown to be simple and effective ways to obtain substantial control over the resonance frequency of a plate radiator. This study shows that piezoceramic-based plate radiators can be a viable acoustic source for active control of aircraft engine fan noise

Investigation of methods to produce a uniform cloud of fuel particles in a flame tube

The combustion of a uniform, quiescent cloud of 30-micron fuel particles in a flame tube was proposed as a space-based, low-gravity experiment. The subject is the normal- and low-gravity testing of several methods to produce such a cloud, including telescoping propeller fans, air pumps, axial and quadrature acoustical speakers, and combinations of these devices. When operated in steady state, none of the methods produced an acceptably uniform cloud (+ or - 5 percent of the mean concentration), and voids in the cloud were clearly visible. In some cases, severe particle agglomeration was observed; however, these clusters could be broken apart by a short acoustic burst from an axially in-line speaker. Analyses and experiments reported elsewhere suggest that transient, acoustic mixing methods can enhance cloud uniformity while minimizing particle agglomeration