Classificació paleoecològica de les formes dels rudistes -una eina per a l'anàlisi paleoambiental

Els rudistes com a suspensívors epibentònics sèssils sols podien adaptar-se a les pressions ambientals per mitjà del creixement de la closca. Per això, les closques dels rudistes mostren una sèrie de formes, les característiques bàsiques de les quals estan en estreta relació amb el caràcter de l'hàbitat que ocupaven. Skelton & Gili (en premsa) classifiquen les closques dels rudistes en tres morfotipus ecològics generals, basats en els paradigmes definits per Skelton (1979a). En aquest treball exposem els trets principals d'aquesta classificació, fent ressaltar les seves implicacions paleoecològiques. Elevadors (elevators): tot el marge de creixement de la valva fixa estava involucrat en el creixement cap amunt. L'índex d'elevació, E, que comprèn la mitjana entre la màxima (α) i la mínima (β) inclinació de la paret externa del marge de creixement de la valva fixa, s'aproximava a 90°. E podia variar, pero el límit inferior per al creixement normal és per definició E=45°. Aconseguien l'estabilització per la implantació passiva de la valva fixa en el sediment, eventualment reforçada per la fixació lateral en els veïns. Ocupaven substrats tous, generalment fangosos, amb acumulació neta positiva. Els rudistes elevadors estaven, doncs, restringits a ambients d'energia baixa a moderada, rarament subjectes a torrents tractius. Adherents (clingers): una part del marge de creixement de la valva fixa creixia directament sobre el substrat, cimentant-se, si era dur, (adherents fixos) o adaptant-se a la seva superfície (adherents friccionals). Com que (β tendia aixi a 0°, E havia de ser per definició 0.75. Ocupaven substrats des de relativament estables a durs amb sedimentació neta de negligible a positiva, però amb fluxos de sediment solament ocasionals. La majoria dels rudistes adherents podien afrontar entrades de sediment intermitents fent crèixer cap amunt, escalonadament, la superfície de creixement basal. Les condicions de corrent associades podien implicar la inhibició freqüent o regular de deposició, però els torrents tractius eren rars. Ajaçats (recumbents): la clau d'aquest morfotipus era també l'estabilització, generant amb els marges Mures de les valves sobre el substrat una base ampla per a la closca. E era així, una altra vegada < 45°. Però a diferència de l'adherent, l'àrea de contacte amb el substrat (inestable), A, tenia poca importància per a 1'estabilització. Els rudistes ajaçats extremaven els diàmetres efectius del contorn de la base de la closca (és a dir A') de manera que aquesta adquiria una forma arquejada o estrellada que resistia la boleiada i soscavació dels corrents. En consequència, A/A' era menor que 1, i per definició havia de ser < 0.75. Ocupaven sorres calcàries mòbils, amb removiments de sediment freqüents i sedimentació positiva neta negigible

Dietary lipid level affects growth performance and nutrient utilisation of Senegalese sole (Solea senegalensis) juveniles

Over the last few years, several aspects of Senegalese sole (Solea senegalensis) culture have been developed and optimised but the dietary lipid level for optimal growth has never been determined. Hence, five isonitrogenous diets (56 % dietary protein) with increasing dietary lipid levels (4, 8, 12, 16 and 20 % DM) were fed to satiation to triplicate groups of twenty fish (mean initial weight 10 g). Fifteen tanks were randomly assigned one of the five diets. Feed was distributed using automatic feeders, and fish were fed over a 16-week period. At the end of the experiment the fish fed on diets containing the two lowest dietary lipid levels (4 and 8 %) showed a 3-fold body-weight increase with a significantly higher daily growth index than fish fed higher lipid levels (1-2 v. 0-8). Moreover, these fish displayed a significantly lower dry feed intake (12g/kg per d) and feed conversion ratio (1-0) compared with fish fed higher lipids levels (16-19 g/kg per d; feed conversion ratio 2-0). Low dietary lipid levels (< 12 %) significantly improved nutrient retention and gain and hence growth, without major effects on whole-body composition. Despite the slight alteration in n-3 PUFA muscle content in the fish fed low-fat-diets, this fish fed low dietary lipid still remains a rich n-3 PUFA product and generally maintained its nutritional value. These results evidenced a low lipid tolerance of Senegalese sole juveniles and suggest a maximal dietary inclusion level of 8 % lipids for both optimal growth and nutrient utilisation without compromising flesh quality.IDEIA; European fund FEDERinfo:eu-repo/semantics/publishedVersio

Viscous fingering in liquid crystals: Anisotropy and morphological transitions

We show that a minimal model for viscous fingering with a nematic liquid crystal in which anisotropy is considered to enter through two different viscosities in two perpendicular directions can be mapped to a two-fold anisotropy in the surface tension. We numerically integrate the dynamics of the resulting problem with the phase-field approach to find and characterize a transition between tip-splitting and side-branching as a function of both anisotropy and dimensionless surface tension. This anisotropy dependence could explain the experimentally observed (reentrant) transition as temperature and applied pressure are varied. Our observations are also consistent with previous experimental evidence in viscous fingering within an etched cell and simulations of solidification.Comment: 12 pages, 3 figures. Submitted to PR

A central place foraging seabird flies at right angles to the wind to jointly optimize locomotor and olfactory search efficiency

To increase the probability of detecting odour plumes, and so increase prey capture success, when winds are stable central place foraging seabirds should fly crosswind to maximize the round-trip distance covered. At present, however, there is no empirical evidence of this theoretical prediction. Here, using an extensive GPS tracking dataset, we investigate, for the first time, the foraging movements of Bulwer's petrels (Bulweria bulwerii) in the persistent North Atlantic trade winds. To test the hypotheses that, in stable winds, petrels use crosswind to maximize both the distance covered and the probability of detecting olfactory cues, we combine state-space models, generalized additive models and Gaussian plume models. Bulwer's petrels had the highest degree of selectivity for crosswinds documented to date, often leading to systematic zig-zag flights. Crosswinds maximized both the distance travelled and the probability of detecting odour plumes integrated across the round-trip (rather than at any given point along the route, which would result in energetically costly return flight). This evidence suggests that petrels plan round-trip flights at departure, integrating expected costs of homeward journeys. Our findings, which are probably true for other seabirds in similar settings, further highlight the critical role of wind in seabird foraging ecology.info:eu-repo/semantics/acceptedVersio

A phase-field model of Hele-Shaw flows in the high viscosity contrast regime

A one-sided phase-field model is proposed to study the dynamics of unstable interfaces of Hele-Shaw flows in the high viscosity contrast regime. The corresponding macroscopic equations are obtained by means of an asymptotic expansion from the phase-field model. Numerical integrations of the phase-field model in a rectangular Hele-Shaw cell reproduce finger competition with the final evolution to a steady state finger the width of which goes to one half of the channel width as the velocity increases

Phase-field model for Hele-Shaw flows with arbitrary viscosity contrast. II. Numerical study

We implement a phase-field simulation of the dynamics of two fluids with arbitrary viscosity contrast in a rectangular Hele-Shaw cell. We demonstrate the use of this technique in different situations including the linear regime, the stationary Saffman-Taylor fingers and the multifinger competition dynamics, for different viscosity contrasts. The method is quantitatively tested against analytical predictions and other numerical results. A detailed analysis of convergence to the sharp interface limit is performed for the linear dispersion results. We show that the method may be a useful alternative to more traditional methods.Comment: 13 pages in revtex, 5 PostScript figures. changes: 1 reference added, figs. 4 and 5 rearrange

Phase-field model for Hele-Shaw flows with arbitrary viscosity contrast. I. Theoretical approach

We present a phase-field model for the dynamics of the interface between two inmiscible fluids with arbitrary viscosity contrast in a rectangular Hele-Shaw cell. With asymptotic matching techniques we check the model to yield the right Hele-Shaw equations in the sharp-interface limit and compute the corrections to these equations to first order in the interface thickness. We also compute the effect of such corrections on the linear dispersion relation of the planar interface. We discuss in detail the conditions on the interface thickness to control the accuracy and convergence of the phase-field model to the limiting Hele-Shaw dynamics. In particular, the convergence appears to be slower for high viscosity contrasts.Comment: 17 pages in revtex. changes: 1 reference adde