175 research outputs found

    First attempts of linking modelling, Postharvest behaviour and Melon Genetics

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    The onset of climacteric is associated with the end of melon fruit shelf-life. The aim of this research was to develop practical and applicable models of fruit ripening changes (hardness, moisture loss) also able to discriminate between climacteric and non-climacteric behaviour. The decrease in firmness was measured non-destructively by flat-plate compression; moisture loss was measured by weight loss. A set of 13-15 near-isogenic lines (NILs) derived from the climacteric line SC3-5 was used to verify the relationship among the climacteric behaviour and ripening related changes (weight loss, softening and color) during two consecutive seasons. The biological variance models for moisture loss and firmness followed a simple exponential behaviour that explained more than 90% of the total variance. Results of the analyses using these models could not be linked to properties of near-isogenic lines like climacteric behaviour, ethylene production or skin thickness. The results suggest that the phenotype is more important than genotype, when considering mean values. These results seem to suggest that relations may exist between the different processes and properties of NILs on an individual basis, not on mean values

    Water-exchange MRI detects subtle blood-brain barrier breakdown in Alzheimer's disease rats

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    Blood-brain barrier (BBB) breakdown has been hypothesized to play a key role in the onset and progression of Alzheimer's disease (AD). However, the question of whether AD itself contributes to loss of BBB integrity is still uncertain, as many in-vivo studies have failed to detect signs of AD-related BBB breakdown. We hypothesize AD-related BBB damage is subtle, and that these negative results arise from a lack of measurement sensitivity. With the aim of developing a more sensitive measure of BBB breakdown, we have designed a novel MRI scanning protocol to quantify the trans-BBB exchange of endogenous water. Using this method, we detect increased BBB water permeability in a rat model of AD that is associated with reduced expression of the tight junction protein occludin. BBB permeability to MRI contrast agent, assessed using dynamic contrast-enhanced (DCE)-MRI, did not differ between transgenic and wild-type animals and was uncorrelated with occludin expression. Our data supports the occurrence of AD-related BBB breakdown, and indicates that such BBB pathology is subtle and may be undetectable using existing ‚Äėtracer leakage‚Äô methods. Our validated water-exchange MRI method provides a new powerful tool with which to study BBB damage in-vivo

    Analysis of the modified optical properties and band structure of GaAs12xSbx-capped InAs/GaAs quantum dots

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    The origin of the modified optical properties of InAs/GaAs quantum dots (QD) capped with a thin GaAs1‚ąíxSbx layer is analyzed in terms of the band structure. To do so, the size, shape, and composition of the QDs and capping layer are determined through cross-sectional scanning tunnelling microscopy and used as input parameters in an 8‚ÄČ√ó‚ÄČ8‚ÄČk¬∑p model. As the Sb content is increased, there are two competing effects determining carrier confinement and the oscillator strength: the increased QD height and reduced strain on one side and the reduced QD-capping layer valence band offset on the other. Nevertheless, the observed evolution of the photoluminescence (PL) intensity with Sb cannot be explained in terms of the oscillator strength between ground states, which decreases dramatically for Sb‚ÄČ>‚ÄČ16%, where the band alignment becomes type II with the hole wavefunction localized outside the QD in the capping layer. Contrary to this behaviour, the PL intensity in the type II QDs is similar (at 15‚ÄČK) or even larger (at room temperature) than in the type I Sb-free reference QDs. This indicates that the PL efficiency is dominated by carrier dynamics, which is altered by the presence of the GaAsSb capping layer. In particular, the presence of Sb leads to an enhanced PL thermal stability. From the comparison between the activation energies for thermal quenching of the PL and the modelled band structure, the main carrier escape mechanisms are suggested. In standard GaAs-capped QDs, escape of both electrons and holes to the GaAs barrier is the main PL quenching mechanism. For small-moderate Sb (<16%) for which the type I band alignment is kept, electrons escape to the GaAs barrier and holes escape to the GaAsSb capping layer, where redistribution and retraping processes can take place. For Sb contents above 16% (type-II region), holes remain in the GaAsSb layer and the escape of electrons from the QD to the GaAs barrier is most likely the dominant PL quenching mechanism. This means that electrons and holes behave dynamically as uncorrelated pairs in both the type-I and type-II structures

    High efficient luminescence in type-II GaAsSb-capped InAs quantum dots upon annealing

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    The photoluminescence efficiency of GaAsSb-capped InAs/GaAs type II quantum dots (QDs) can be greatly enhanced by rapid thermal annealing while preserving long radiative lifetimes which are ‚ąľ20 times larger than in standard GaAs-capped InAs/GaAs QDs. Despite the reduced electron-hole wavefunction overlap, the type-II samples are more efficient than the type-I counterparts in terms of luminescence, showing a great potential for device applications. Strain-driven In-Ga intermixing during annealing is found to modify the QD shape and composition, while As-Sb exchange is inhibited, allowing to keep the type-II structure. Sb is only redistributed within the capping layer giving rise to a more homogeneous composition

    Analysis of the evolution of hake (Merluccius hubbsi and Merluccius australis) catch and effort by Spanish vessels operating in the Patagonian shelf area since the beginning of this industrial fishery

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    The hake fishery (Merluccius hubbsi and Merluccius australis) is one of the most important ones for Spanish vessels operating in the Southwest Atlantic. Both species are widely distributed along the Patagonian shelf, although M. australis occupies mainly more southern waters. This paper presents a historical review of fishery data on the Spanish fishing fleet operating in the SW Atlantic collected and collated during the EC Study Project 99/016 ‚ÄúData collection for stock assessment of two hakes (Merluccius hubbsi and M. australis) in International and Falkland waters of the SW Atlantic‚ÄĚ, in order to analyse the evolution of catch and effort in the hake fishery since 1983 to 2000. Data on landings and effort by Spanish vessels from 1983 onwards were utilised to study trends and shifts within the fishery. These data were provided by Asociaci√≥n Nacional de Armadores de Buques Congeladores de Pesca de Merluza (ANAMER), the most important Spanish ship-owners fishing association operating in distant fishing grounds. Catch and effort data collected by observer‚Äôs programmes carried out by Instituto Espa√Īol de Oceanograf√≠a (IEO) and the Falkland Islands Government Fisheries Department (FIGFD), as well as by observers provided by the project were used to estimate CPUE by area and season.The data included landings in kgs by commercial size category of hake (both species together) and effort made by vessels appertaining to ANAMER in number of fishing days and number of vessels by vessel size category. Conversion factors obtained by scientific observers onboard of these vessels were used to obtain the whole catch from landings. Total effort of the Spanish fleet was estimated from ANAMER logbooks, assuming a similar pattern for the whole fleet and taking into account the different ratio of ANAMER fleet compared to the total Spanish fleet. An increase of the catches and effort was observed from 1983 to a maximum in 1990 coinciding with the closure of Namibian fisheries. After that, catches and effort decreased corresponding to the development of the Greenland halibut fishery in the NW Atlantic, until its stabilisation from 1993. CPUE showed different patterns of fishing activity by area and season

    Effect of the AlAs capping layer thickness on the structure of InAs/GaAs QD

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    Recently, very thin AlAs capping layers (CLs) have been proposed as a useful tool to increase the performance of InAs/GaAs quantum dot (QDs) devices. However, the structure of QDs after AlAs deposition remains poorly understood and the mechanisms to explain it are often contradictory. In this work, the structural and compositional changes of InAs QDs using different AlAs CL thicknesses have been studied by state-of-the-art STEM-related techniques. First, the heights and In contents of InAs QDs progressively increase with the CL thickness, demonstrating that the AlAs capping produces a strong shielding effect against the decomposition of QDs. However, QD populations for CL thicknesses above 5 ML split into a bimodal distribution in which smaller lenticular QDs cohabit with bigger truncated pyramids. Second, the actual Al contents around the QDs are well below the nominal design, but increasing for thicker CLs. Its distribution is initially non-uniform, tending to accumulate on the flanks of the QDs to the detriment of the apex. Only for thicknesses above 2 ML the Al contents around the QDs start to be similar to those in the regions between the QDs, behaving as a continuous film without irregularities from 5 ML onwards. © 2021 The Author(s)The work has been co-financed by the Spanish National Research Agency (AEI projects MAT2016-77491-C2-2-R and PID2019-106088RB-C33), Regional Government of Andalusia (project FEDER-UCA18-108319) and the European Regional Development Fund (ERDF)

    First-Principles Studies of Hydrogenated Si(111)--7√ó\times7

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    The relaxed geometries and electronic properties of the hydrogenated phases of the Si(111)-7√ó\times7 surface are studied using first-principles molecular dynamics. A monohydride phase, with one H per dangling bond adsorbed on the bare surface is found to be energetically favorable. Another phase where 43 hydrogens saturate the dangling bonds created by the removal of the adatoms from the clean surface is found to be nearly equivalent energetically. Experimental STM and differential reflectance characteristics of the hydrogenated surfaces agree well with the calculated features.Comment: REVTEX manuscript with 3 postscript figures, all included in uu file. Also available at http://www.phy.ohiou.edu/~ulloa/ulloa.htm

    Growth interruption strategies for interface optimization in GaAsSb/GaAsN type-II superlattices

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    Recently, GaAsSb/GaAsN type II short-period superlattices (SLs) have been proposed as suitable structures to be implemented in the optimal design of monolithic multi-junction solar cells. However, due to strong surface Sb segregation, experimental Sb composition profiles differ greatly from the nominal square-wave design. In this work, the improvement of the interface quality of these SLs in terms of compositional abruptness and surface roughness has been evaluated by implementing different growth interruption times under Sb4/As4 (soaking) and As4 (desorption) overpressure conditions before and after the growth of GaAsSb layers, respectively. The com-bined effects of both processes enhance Sb distribution, achieving squarer compositional profiles with reduced surface roughness interfaces. It has been found that the improvement in compositional abruptness is quantita-tively much higher at the lower interface, during soaking, than at the upper interface during desorption. Conversely, a larger decrease in surface roughness is achieved at the upper interface than at the lower interface. Fitting of the Sb segregation profiles using the 3-layer kinetic fluid model has shown that the increase in Sb incorporation rate is due to the decrease in segregation energy, presumably to changes in the surface recon-struction of the floating layer at the surface

    Fiabilidad de la velocidad de ejecución en tres modalidades del ejercicio de press de banca: influencia del nivel de experiencia

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    Premio Congreso SIBB 2019El objetivo del estudio fue comparar la fiabilidad de la velocidad media propulsiva (VMP) entre tres variantes del ejercicio de press de banca (PB). Quince hombres con experiencia y 15 sin experiencia con el ejercicio de PB realizaron en orden aleatorizado tres variantes del ejercicio de PB en diferentes sesiones (s√≥lo-conc√©ntrico, exc√©ntrico-r√°pido y exc√©ntrico-controlado). La VMP se registr√≥ ante tres cargas (‚Čą 30%1RM, 50%1RM y 75%1RM) con un transductor lineal de velocidad. La fiabilidad fue siempre alta (coeficiente de variaci√≥n [CV] ‚ȧ 5,76%, coeficiente de correlaci√≥n intraclase [CCI] ‚Č• 0,74). La comparaci√≥n de los CV revel√≥ una mayor fiabilidad para las variantes s√≥lo-conc√©ntrico y exc√©ntrico-r√°pido en comparaci√≥n con la variante exc√©ntrico-controlado (CV ratio > 1,15), no existiendo diferencias significativas en fiabilidad entre las variantes s√≥lo-conc√©ntrico y exc√©ntrico-r√°pido (CV ratio < 1,15). No se observaron diferencias en fiabilidad entre los participantes con (CV ‚ȧ 5,76%; CCI ‚Č• 0,83) y sin experiencia (CV ‚ȧ 5,21%; CCI ‚Č• 0,74). Estos resultados apoyan el uso de las modalidades de PB s√≥lo-conc√©ntrico y exc√©ntrico-r√°pido para evaluar la fuerza de los miembros superiores a trav√©s de la medici√≥n de la velocidad de ejecuci√≥n en participantes con y sin ¬†experiencia con el ejercicio de PB.Award-winningPremio Congreso SIBB 2019Peer Reviewe

    Data collection for stock assessment of two Hakes (Merluccius Hubbsi and M. Australis) in international and Falkland Waters of the SW Atlantic

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    Study Project 99/016 ‚ÄúData collection for stock assessment of two hakes (Merluccius hubbsi and M. australis) in international and Falkland waters of the SW Atlantic‚ÄĚ ran from January 2000 to December 2001. The main objective of the project was the collection and collation of already existing and newly acquired fishery and biological data needed for preliminary assessment of two hake species occurring in the study area. In addition to this basic remit, additional objectives included the creation of a common database, study of spawning seasons and areas, discard pattern and length-frequency composition of target and non-target species, estimation of annual by-catch rates, analysis of trophic relationships, marine mammals by-catch and sightings, morphometric analysis for stock differentiation, and developing GIS applications for analysis of the data collected. Historical fishery and biological data series available from IEO and FIGFD (since 1988 and 1987 respectively) were provided to the project. New fishery and biological data were collected by scientific observers provided by IEO, ANAMER and FIGFD, and placed on board Spanish fishing vessels operating in the study area during the project period. Data on fishing activity included effort, catches and discards of target and non-target species on a haul-by-haul basis. Biological information (size, sex, maturity stage, etc) of target and non-target species was recorded on a daily basis. Data on landings and effort were provided by ANAMER to its subcontractor (MG OTERO) for processing and estimation of total catch and effort of the whole Spanish fishing fleet in the area; MG OTERO was also responsible for organisation of observers in collaboration with ANAMER staff in Vigo and Port Stanley. Ancillary data on location, time of fishing, depth, SST, SBT, sea roughness, wind, etc, was recorded on a haul-by-haul basis. This type of information was essential for development of GIS at AU to relate the species distribution to physical and environmental factors. Other information collected was about by-catches and sightings of small cetaceans and seabirds, and biological samples such as otoliths, stomachs and whole specimens of hakes for subsequent studies on growth (IEO, FIGFD), diet and morphometrics (AU). All the historical and new data collected during the project were collated and integrated into a common database designed by all participants and built at IEO. The information was used for preliminary assessment of two hake populations co-ordinated by RRAG during a workshop held in London in July 2001. All these data will be analysed and written up for future publications. Discard rates of target species were generally low in all areas and seasons with the highest discard rate for Notothen sp. (around 100% of the catch). Illex squid was found to be the major by-catch for hake fishery in the 46 S area. IEO observers reported data on incidental catches of marine mammals and sea birds since 1993 and the analysis of this information was made by AU. The observed mortality in the fishing gears comprised small numbers of black-browed albatross, gentoo penguin and the hourglass dolphin. The species most frequently sighted was the Peale‚Äôs dolphin, although this species did not appear in by-catches, followed by the hourglass dolphin. The project provided an opportunity to collect and integrate for the first time at European level the necessary fishery and biological data for the development of partial stock assessment for the future rational management of the fisheries in the area. Such management is needed for the sustainability of the commercial fisheries, the conservation of the onshore and offshore jobs and the supply of fish to the most important markets worldwide.EUROPEAN COMMISSION DIRECTORATE GENERAL FISHERIES ‚Äď DG XI
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