Relaciones analíticas entre la salinidad y la temperatura para aguas de la termoclina superior en el margen oriental del giro subtropical del Atlántico Norte

[EN] We study the dependence of salinity on temperature in two by two degrees latitude-longitude boxes, for surface and upper-thermocline waters of the eastern North Atlantic subtropical gyre. The initial data set, from historical databases as well as from recent hydrographic cruises in the region, is carefully scrutinized to reject dubious measurements. We search for polynomial relations of variable degree between salinity and temperature, the optimal fit is selected as the polynomial with the lowest degree that satisfies several statistical criteria. An independent hydrographic cruise is used to confirm that the method performs substantially better than estimates from climatological data, and leads to relatively low deviations in geopotential anomaly and other derived quantities. An error propagation analysis using the Monte Carlo method shows equally good results[ES] En este estudio caracterizamos la dependencia de la salinidad con la temperatura en cajas de dos por dos grados de latitud y longitud para aguas superficiales y de la termoclina superior en el margen oriental del giro subtropical del Atlántico Norte. El conjunto inicial de datos, procedente de bases de datos históricos, así como los procedentes de recientes campañas hidrográficas en la región, son cuidadosamente analizados para eliminar las medidas de calidad dudosa. Se analizan varias relaciones polinómicas de grado variable para la salinidad en función de la temperatura, eligiendo como ajuste óptimo aquel polinomio de menor grado que satisface diversos criterios estadísticos. Se utiliza una campaña hidrográfica independiente para confirmar que el método da resultados substancialmente mejores que estimaciones a partir de datos climatológicos, y que produce desviaciones relativamente bajas en la anomalía geopotencial y en otras magnitudes derivadas. Un análisis de la propagación del error usando el Método de Montecarlo muestra resultados igualmente buenosWe are grateful to the Institut für Meereskunde and IFREMER for making their data sets available. The Spanish cruises that gathered some of the data analyzed here were carried out through projects from the Spanish government (program CYTMAR) and the European Union (program MAST). This work has been carried out with the support of the Spanish Government through project FRENTES (AMB95-0731) and the European Union through projects CANIGO (MAS3-CT96-0060) and OASIS (EVK3-CT-2002-00073). Part of this work was written while JLP was at the University of Wisconsin-Madison with funding from the Secretaría de Estado de Educación y Universidades of the Spanish governmentPeer reviewe

Relaciones analíticas entre la salinidad y la temperatura para aguas de la termoclina superio en el margen oriental del giro subtropical del Atlántico norte

We study the dependence of salinity on temperature in two by two degrees latitude-longitude boxes, for surface and upper-thermocline waters of the eastern North Atlantic subtropical gyre. The initial data set, from historical databases as well as from recent hydrographic cruises in the region, is carefully scrutinized to reject dubious measurements. We search for polynomial relations of variable degree between salinity and temperature, the optimal fit is selected as the polynomial with the lowest degree that satisfies several statistical criteria. An independent hydrographic cruise is used to confirm that the method performs substantially better than estimates from climatological data, and leads to relatively low deviations in geopotential anomaly and other derived quantities. An error propagation analysis using the Monte Carlo method shows equally good results.En este estudio caracterizamos la dependencia de la salinidad con la temperatura en cajas de dos por dos grados de latitud y longitud para aguas superficiales y de la termoclina superior en el margen oriental del giro subtropical del Atlántico Norte. El conjunto inicial de datos, procedente de bases de datos históricos, así como los procedentes de recientes campañas hidrográficas en la región, son cuidadosamente analizados para eliminar las medidas de calidad dudosa. Se analizan varias relaciones polinómicas de grado variable para la salinidad en función de la temperatura, eligiendo como ajuste óptimo aquel polinomio de menor grado que satisface diversos criterios estadísticos. Se utiliza una campaña hidrográfica independiente para confirmar que el método da resultados substancialmente mejores que estimaciones a partir de datos climatológicos, y que produce desviaciones relativamente bajas en la anomalía geopotencial y en otras magnitudes derivadas. Un análisis de la propagación del error usando el Método de Montecarlo muestra resultados igualmente buenos.

Assessment of the time resolution used to estimate the central solar receiver lifetime

This study assesses the impact of the time resolution and design day on the estimated lifetime of the molten-salt external tubular receiver of a solar power tower, one of the most damaged components of these facilities, considering operation under clear conditions. A global analysis is performed by first determining the heliostat field aiming strategy; the receiver operation limits are set to keep a low enough film temperature and to avoid the stress reset. The former prevents excessive corrosion rates of the tubes while the latter assures the global stress relaxation, which significantly reduces their damage during the receiver cyclic operation. Time steps of 60, 30, 15, 5 and 1 min are tested considering the spring equinox design day, as well as only solar noon conditions. The latter significantly underpredicts the receiver lifetime with respect to the 1-min case, being early discarded. The lifetime in the most damaged panel is underestimated over 18% and 16% using the 60- and 30-minute time steps, dropping to 2.57% using the 5-min time step at a reasonable computational cost. Finer resolutions enable more precise aiming strategy selection, decreasing the receiver peak fluxes. Lastly, a set of 8 representative days for the year, equally spaced in solar height, is more accurate than using the spring equinox alone, which results in an underestimate of the receiver lifetime that may be overly conservative. The summer solstice is the least-damaging day, with the lifetime decreasing as approaching the winter one, as long as the storage tank is filled.This research is partially funded by the scholarship "Ayudas para la formación del profesorado universitario" (FPU-02361) awarded by the Spanish Ministerio de Educación, Cultura y Deporte (MECD), the Spanish government under the project RTI2018-096664-B-C21 (MICINN/FEDER, UE) and the call "Programa de apoyo a la realización de proyectos interdisciplinares de I + D para jóvenes investigadores de la Universidad Carlos III de Madrid 2019-2020", under the projects RETOrenovable-CM-UC3M and ZEROGASPAIN-CM-UC3M, funded on the frame of the Convenio Plurianual Comunidad de Madrid- Universidad Carlos III de Madrid

Exergy analysis of solar central receivers

A high-resolution method to analyse the exergy of the SPT external tubular receivers is presented, examining the different heat transfer process involved individually. This sheds light on the role that each irreversibility source plays in the outcome, aiding in the receiver design and the facility location selection. The exergy efficiency is around 32% in the base configuration. Besides the exergy loss in the heliostat field, over 40%, it is found that the biggest exergy destruction cause are the radiation emissions and absorptions in the tube outer surface, around 17%. From the remaining ones, the greatest are the exergy destructed in the HTF and the one escaping to the ambient (over 4% each). Then, the exergy balance for a variety of strategies and ambient conditions is performed: optical properties of the tubes coating, peak and flat aiming strategies, DNI and ambient temperature. The heliostat field exergy loss rate only varies when changing the aiming. However, the emission and absorption losses and the ones in the HTF suffer the greater modifications with all the parameters studied. The impact of the optical properties degradation, 1% descent in the efficiency per 5% degradation, would advise repainting works in order to avoid greater exergy destruction. The surroundings temperature modification impacts considerably the exergy efficiency, showing the suitability of locations with low ambient temperature and a moderate DNI: descends of over 0.35% occur every 5 °C increase of the temperature for a fixed DNI.This research is partially funded by the scholarship "Ayudas para la formación del profesorado universitario"; (FPU-02361) awarded by the Spanish Ministerio de Educación, Cultura y Deporte (MECD), the fellowship"Ayuda a la investigación en energía y medio ambiente" of the Iberdrola España Foundation, the Spanish government under the project RTI2018-096664-B-C21 (MICINN/FEDER, UE) and the call "Programa de apoyo a la realización de proyectos interdisciplinares de I+D para jóvenes investigadores de la Universidad Carlos III de Madrid 2019-2020", under the frame of the Convenio Plurianual Comunidad de Madrid- Universidad Carlos III de Madrid

Material selection for solar central receiver tubes

The severe operation conditions and great capital investment of solar power tower central receivers motivate the lifetime analysis of a molten-salt external-cylindrical-tubular receiver, considering five alloy alternatives for its tubes manufacturing: Haynes 230, alloy 316H, Inconel 625, 740H and 800H. An analytical low-computational cost methodology is employed, considering the temperature dependence of tube material properties, elastic-plastic stresses/strains and stress relaxation. Thus, creep and fatigue experimental data available in the literature for these alloys are compiled in this work, providing the coefficients required for the methodology followed. A great alloys operation limitation is the film temperature to avoid corrosion issues; the most permissive are H230, 740H and 800H (650 °C), followed by Inconel 625 (630 °C) and 316H (600 °C). This, and the twice the yield strength, is regarded to set the heliostat field aiming strategy as equatorial as possible for each alloy, resulting in great power production divergences: 24% and 65% less for 625 and alloy 316H receivers with respect to the 740H receiver. Then, the lifetime analysis for a clear design day operation, representative of the receiver during ideal operation, is performed. The stress relaxation regard becomes critical for the accurate damage prediction; alloys 316H and 800H show stress reset during operation, not benefitting from a global stress relaxation. Thus, 800H exhibits a poor endurance. For the clear-day assumption, 740H shows the best lifetime and costs/power performance; the levelized cost of alloy of H230, 625 and alloy 316H is 0.01, 0.09 and over 0.25, respectively, with respect to 740H.This research is partially funded by the scholarship "Ayudas para la formación del profesorado universitario" [grant number FPU-02361] awarded by the Spanish Ministerio de Educación, Cultura y Deporte (MECD), the Spanish government under the project RTI2018-096664-B-C21 (MICINN/FEDER, UE) and the call "Programa de apoyo a la realización de proyectos interdisciplinares de I+D para jóvenes investigadores de la Universidad Carlos III de Madrid 2019-2020", under the projects RETOrenovable-CM-UC3M [grant number 2020/00034/001] and ZEROGASPAIN-CM-UC3M [grant number 2020/00033/001], funded on the frame of the Convenio Plurianual Comunidad de Madrid- Universidad Carlos III de Madrid

Tourism consumption and social inequality in Spain

El artículo reexamina la relación entre consumo turístico y desigualdad social en el marco de la sociedad española, actualizando la perspectiva sociológica sobre este tema a partir de una encuesta realizada en origen a población adulta. El consumo turístico es operacionalizado mediante una tipología que permite examinar críticamente las tesis de la universalización y la diferenciación del consumo turístico, mediante análisis de segmentación (CHAID) que permiten reflejar las interacciones entre las múltiples dimensiones de la estructura social, identificando grupos privilegiados y excluidos del consumo turístico. Los resultados del estudio muestran que el consumo turístico en España se encuentra altamente polarizado, con un grupo relativamente reducido de personas que realizan muchos viajes (20%), aproximadamente un tercio de la población con una participación media en el turismo y más de un 40% de la población excluida del consumo turístico, ya sea por motivos económicos (28%) o por otros motivos (14%). En cuanto a los factores que influyen en el consumo turístico, los resultados del estudio muestran que los tradicionalmente asociados a la estructura y la desigualdad social (relación con la actividad económica, clase social) son los que más influyen en la participación en el turismo.The paper examines the relationship between tourism consumption and social inequality within the Spanish Society, updating the sociological perspective on this issue through a survey to general population. The participation in tourism is operationalized in a typology that facilitates critical examination of the thesis that tourism is currently both differentiated and generalized. The segmentation (CHAID) analysis permits to reflect the interactions between the manifold dimensions of social structure, identifying privileged and excluded groups in their relations with tourism consumption. Study results show that tourism consumption in Spain is highly polarized, with a relatively small group of people traveling a lot (20%), about one third of the population with an average participation in tourism and over 40% of the population excluded from tourism consumption, either for economic reasons (28%) or other reasons (14%). As for the factors affecting tourism consumption, the study results show that those traditionally associated with social structure and social inequality (economic activity, social class) are the most influential factors in tourism participation

Thermodynamic and economic assessment of a new generation of subcritical and supercritical solar power towers

The feasibility of using more efficient Rankine power blocks in solar power towers (SPTs) with molten salt as the heat transfer fluid has been studied as a method for increasing the global efficiency of these power plants. The temperature and pressure of the main steam and the reheating pressure affect the temperature of the molten salt in the receiver; for temperature increase decreasing the receiver efficiency and increasing the power block efficiency. Therefore, a detailed study of these SPTs has been conducted to determine whether the proposed changes increase the global efficiency of the SPTs. A total of eight different subcritical and supercritical SPTs have been investigated. To set the most important cost of the SPT, the same heliostat field has been used. The receiver geometry has been optimised for each SPT to maximise the heliostat-receiver efficiency, fulfilling the material limitations. It has been observed that the pressure at the inlet of the turbine increases the SPT efficiency even more than the temperature. However, special attention has to be paid to the reheating pressure, which is the most influential factor on the SPT efficiency. A high reheating pressure considerably decreases the SPT efficiency. Therefore, the best efficiencies have been obtained for the supercritical SPTs with a low reheating pressure and high temperature. It is closely followed by subcritical SPTs at high pressure and temperature. The investment cost of the different SPTs also increases with the pressure and the temperature of the PB, with subcritical SPTs being less expensive than supercritical SPTs. However, the cost increase is balanced by the increase in the efficiency. The same cost per kWe is found in subcritical SPTs working at 16 MPa and in supercritical SPTs with low reheating pressure

Comparison of the shear bond strength of brackets between two adhesive systems (SEP and MIP Transbond) at 60 minutes and 24 hours

AbstractThe purpose of this study was to compare the resistance when debonding the braces of the enamel after 60 minutes and 24 hours of its fixation with two different adhesive systems. 60 bicuspids where divided into 4 groups of 15 samples each one and were treated with self-etching adhesive SEP Transbond Plus 3M Unitek (group 3 and 4) and conventional adhesive Transbond MIP 3M Unitek (group 1 and 2). The samples were submitted to tangential forces with the universal machine Instron with speed load shedding 1.0mm/min to obtain the resistance when debonding. After doing the statically analysis ANOVA showed that there are not significant statically difference at the debonding forces between Transbond MIP at 24 hours (mean=6.8, SD=2.9) and SEP Transbond at 24 hours (mean=6.1, SD=2.8) (t=0.73 p=0.46). There is no statistically significant difference between Transbond MIP at 60 minutes (mean=6.01 SD=5.2) and SEP Transbond Plus at 60 minutes (mean=7.35, SD=5.1) (t=-.71 p=0.48). It was seen lees than the middle of the remnant adhesive in most of the sample

Reproductive biology of Polioptila lembeyei (Aves: Polioptilidae) in the Siboney-Juticí Ecological Reserve, Santiago de Cuba, Cuba

Se estudió la biología reproductiva de Polioptila lembeyei en la Reserva Ecológica Siboney-Juticí, Santiago de Cuba, Cuba durante los años 2006 y 2007 en seis formaciones vegetales. Se describieron aspectos de su reproducción en términos de cronología reproductiva, tamaño de puesta, duración del período de incubación, permanencia de los polluelos en el nido, morfometría de nidos y huevos, y caracterización del sitio de nidificación en cuanto a la altura de los nidos y especie y altura de las plantas utilizadas como sitio de nidificación. Se localizaron 89 nidos durante las dos temporadas reproductivas, 43 en el año 2006 y 46 en el 2007. El período reproductivo se extendió desde finales de marzo hasta julio, abarcando 129 días en el año 2006 y 122 días durante el año 2007. Las nidadas tuvieron una duración de 36–56 días (construcción 8,6 ± 2,8 días, puesta 8,6 ± 2,7 días, incubación de 14,0 ± 1,2 días y permanencia de los pichones en el nido 14,5 ± 1,0 días). De los 45 nidos examinados el tamaño de puesta modal fue de tres huevos (88,9 %), encontrándose también nidadas de dos (6,7 %) y cuatro huevos (4,4 %). De 38 nidos con huevos para ambas temporadas, 15 nidos produjeron pichones (32 pichones en el 2006 y 20 pichones en el 2007) y solo tres nidos durante el 2006 (37,5 %) lograron producir volantones, los cuales salieron con éxito del nido. La planta más utilizada como sitio de nidificación fue Acacia macracantha (80 % de los nidos detectados), aunque también se hallaron nidos en otras ocho especies de plantas. Las alturas de ubicación del nido fue de 2,7 ± 1,5 m (n = 82; rango 0,3–6,4 m) y la distancia del nido al dosel de la planta utilizada como sustrato fue de 1,1 ± 0,9 m (n = 80; rango 0,1–5,4 m).The reproductive biology of Polioptila lembeyei was studied in six vegetation types during the years 2006 and 2007 in the Siboney-Juticí Ecological Reserve, Santiago de Cuba, Cuba. Breeding aspects including reproductive chronology, clutch size, incubation length, nestling period, egg and nest morphometrics, and aspects of the nesting site (nest height, plant species, and plant height) were described. Eighty-nine nests were found during both reproductive seasons, 43 in 2006 and 46 in 2007. The reproductive period occurred from late March to July for 129 days in 2006 and 122 days in 2007. The length of the nesting period was 36–56 days (nest construction 8.6 ± 2.8 days, laying 8.6 ± 2.7 days, incubation 14.0 ± 1.2 days, and nestling period 14.5 ± 1.0 days). Of the 45 nests examined, modal clutch size was three eggs (88.9 %), although nests with two (6.7 %) and four eggs (4.4 %) also occurred. Of 38 clutches in both seasons, 15 of them produced chicks (32 chicks in the 2006 and 20 chicks in the 2007) and only three nests in the 2006 season (37.5 %) produced fledglings. Acacia macracantha was the plant species most used as nesting substrate (80 % of detected nests) although nests were also found in eight other plant species. Nest heights were 2,7 ± 1,5 m (n = 82; range 0.3–6.4 m) and the distance from nest to the canopy of the substrate plant was 1.1 ± 0.9 m (n = 80; range 0.1–5.4 m)

Diapycnal Nutrient Fluxes in the Cape Ghir upwelling region

European Geosciences Union General Assembly 22-27 April 2012, Vienna, Austria.-- 1 pageAn oceanographic survey was carried out from 18 to 29 October 2010 in the Canary Basin (PROMECA project). Near Cape Ghir, in the Northwest Africa coastal upwelling, 17 CTD casts were made to obtain continuous records of conductivity and temperature with depth, and to collect waters samples for nutrients analyses. Additionally, free-fall turbulence profiles were obtained at each station. 14 Expandable bathythermographs (XBTs) were deployed between stations to increase the grid resolution of the temperature field. Velocity data were acquired with a vessel-mounted Acoustic Doppler Current Profiler (ADCP) with a vertical bin size of 8 m. Water samples for nutrients: nitrate + nitrite (N+N), phosphates and silicates, were collected from 12 depths (down to 2000 m or the maximum depth), with 12-l Niskin bottles mounted on the rosettes sampler. The first results show low to moderate concentrations of nutrients offshore, with average values in the upper 150 m of 2.45 ± 1.98, 0.37 ± 0.18 and 1.47 ± 0.94 μM for N+N, phosphate and silicate, respectively. However, for stations near the Cape Ghir upwelling filament or influenced by this feature, a significant increase in the concentration of nutrients (up to 10 µM of N+N at 200 m) was observed. We have estimated and compared the diapycnal nutrient flux in the region by using two different approaches. First, we used the dissipation rates of turbulent kinetic energy and thermal variance estimated from microstructure data acquired from turbulence profilers, and applied a model based on the dissipation ratio. This way we obtain net turbulence diffusivities in regions where there is an interaction of processes of double diffusion and turbulence induced by vertical shear of the flow. The second approach is based on obtaining diapycnal diffusivities with parameterizations of the gradient Richardson number and density ratioPeer Reviewe