Gyrotactic phytoplankton in laminar and turbulent flows: a dynamical systems approach

Gyrotactic algae are bottom heavy, motile cells whose swimming direction is determined by a balance between a buoyancy torque directing them upwards and fluid velocity gradients. Gyrotaxis has, in recent years, become a paradigmatic model for phytoplankton motility in flows. The essential attractiveness of this peculiar form of motility is the availability of a mechanistic description which, despite its simplicity, revealed predictive, rich in phenomenology, easily complemented to include the effects of shape, feed-back on the fluid and stochasticity (e.g. in cell orientation). In this review we consider recent theoretical, numerical and experimental results to discuss how, depending on flow properties, gyrotaxis can produce inhomogeneous phytoplankton distributions on a wide range of scales, from millimeters to kilometers, in both laminar and turbulent flows. In particular, we focus on the phenomenon of gyrotactic trapping in nonlinear shear flows and in fractal clustering in turbulent flows. We shall demonstrate the usefulness of ideas and tools borrowed from dynamical systems theory in explaining and interpreting these phenomena

Do parties adjust their policy proposals to the political context? A study of election promises during the 2022 Italian general election

This paper investigates towards which policy issues Italian political parties oriented their commitments in the run-up to the 2022 parliamentary election. Do parties make more promises in salient domains? Or, do they prioritise those issues in which they enjoy ownership? To answer these questions, we created a novel dataset that contains 3,992 election pledges made by Italian political parties in the 2022 electoral campaign. By looking at the programmatic policies included in the campaign manifestos of the main political parties and coalitions during the last general election, we find that Italian parties seem to compete around the same issues. In particular, in 2022 a large share of election promises was devoted to economic and social matters. Although the Ukrainian war, the resulting energy crisis, and the implementation of EU-funded investments were the backdrop to the 2022 electoral campaign, Italian political parties do not seem to prioritize these issues

The disregarded weight of the ancestors: Honouring the complexities and cultural subtleties of islandscape

Starting from a comparison between the Belep Islands (Kanaky New Caledonia) and O’ahu (Hawai’i), this paper aims to contribute to the debates about islands and the Anthropocene, highlighting the relevance of the social and ecological responsibilities deriving from genealogical connections to the islands: ‘the weight of the ancestors’. Considering the implications of these kinds of responsibilities can help to understand human and non-human relational entanglements better so as to value the agentive role of other-than-human perspectives

Arsenic-bearing phases in South Andean volcanic ashes: Implications for As mobility in aquatic environments

Three samples of volcanic ashes collected after eruptions of the volcanos Hudson in 1991, Chaitén in 2008 and Puyehue in 2011 were analyzed in order to define the solid speciation of arsenic and the dynamics of its release to the aqueous phase. The bulk chemical and mineralogical characterization of the samples was performed by ICP/OES, DRX, and SEM/EDS analyses. The chemical composition of the near surface region (first 2-10. nm), along with the As and Fe solid speciation was performed by XPS. Batch experiments were conducted to evaluate the kinetics of the arsenic release under variable pH conditions. The integrated analysis of these data indicates that arsenic compounds are concentrated onto the ash surface in the form of As(III)-S and As(V)-O species. The As(III) species have been assigned to arsenian pyrite, while As(V)-O compounds have been assigned to adsorbed arsenate ions or Fe arsenate salts precipitated as thin coatings.Although the main As carrier in the studied volcanic ashes is Al-silicate glass, this phase is stable at the neutral pH that dominates the aqueous reservoirs of the area affected by ashfall. Thus, its contribution to the pool of dissolved arsenic is minor. Higher contributions are clearly associated with the more mobile As species that concentrate onto the surface of Al-silicate glass. This more available arsenic represents less than 6% of the total measured arsenic.Fil: Bia, Gonzalo Luis. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; ArgentinaFil: Borgnino Bianchi, Laura Carolina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; ArgentinaFil: Gaiero, Diego Marcelo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; ArgentinaFil: Garcia, Maria Gabriela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; Argentin

Scaling of Rayleigh-Taylor mixing in porous media

Pushing two fluids with different density one against the other causes the development of the Rayleigh-Taylor instability at their interface, which further evolves in a complex mixing layer. In porous media, this process is influenced by the viscous resistance experienced while flowing through the pores, which is described by the Darcy's law. Here, we investigate the mixing properties of the Darcy-Rayleigh-Taylor system in the limit of large P\'eclet number by means of direct numerical simulations in three and two dimensions. In the mixing zone, the balance between gravity and viscous forces results in a non-self-similar growth of elongated plumes, whose length increases linearly in time while their width follows a diffusive growth. The mass-transfer Nusselt number is found to increase linearly with the Darcy-Rayleigh number supporting a universal scaling in porous convection at high Ra numbers. Finally, we find that the mixing process displays important quantitative differences between two and three dimensions.Comment: 7 pages, 3 figure

Scale-dependent colocalization in a population of gyrotactic swimmers

We study the small scale clustering of gyrotactic swimmers transported by a turbulent flow, when the intrinsic variability of the swimming parameters within the population is considered. By means of extensive numerical simulations, we find that the variety of the population introduces a characteristic scale $R^*$ in its spatial distribution. At scales smaller than $R^*$ the swimmers are homogeneously distributed, while at larger scales an inhomogeneous distribution is observed with a fractal dimension close to what observed for a monodisperse population characterized by mean parameters. The scale $R^*$ depends on the dispersion of the population and it is found to scale linearly with the standard deviation both for a bimodal and for a Gaussian distribution. Our numerical results, which extend recent findings for a monodisperse population, indicate that in principle it is possible to observe small scale, fractal clustering in a laboratory experiment with gyrotactic cells.Comment: 6 pages, 6 figure

Comparison of measurements of the outer scale of turbulence by three different techniques

We have made simultaneous and nearly simultaneous measurements of L0, the outer scale of turbulence, at the Palomar Observatory by using three techniques: angle-of-arrival covariance measurements with the Generalized Seeing Monitor (GSM), differential-image-motion measurements with the adaptive-optics system on the Hale 5-m telescope, and fringe speed measurements with the Palomar Testbed Interferometer (PTI). The three techniques give consistent results, an outer scale of approximately 10-20 m, despite the fact that the spatial scales of the three instruments vary from 1 m for the GSM to 100 m for the PTI

Integration of the atmospheric fluctuations in a dual-field optical interferometer: the short exposure regime

Spatial phase-referencing in dual-field optical interferometry is reconsidered. Our analysis is based on the 2-sample variance of the differential phase between target and reference star. We show that averaging over time of the atmospheric effects depends on this 2-sample phase variance (Allan variance) rather than on the true variance. The proper expression for fringe smearing beyond the isoplanatic angle is derived. With simulations of atmospheric effects, based on a Paranal turbulence model, we show how the performances of a dual-field optical interferometer can be evaluated in a diagram 'separation angle' versus 'magnitude of faint object'. In this diagram, a domain with short exposure is found to be most useful for interferometry, with about the same magnitude limits in the H and K bands. With star counts from a Galaxy model, we evaluate the sky coverage for differential astrometry and detection of exoplanets, i.e. likelihood of faint reference stars in the vicinity of a bright target. With the 2mass survey, we evaluate sky coverage for phase-referencing, i.e. avaibility of a bright enough star for main delay tracking in the vicinity of any target direction.Comment: 9 pages, 8 figures, accepted for publication in A&

Identification of the As-bearing phases in fresh volcanic Andean ashes

The sources and dynamics of arsenic in fresh volcanic ashes collected during the eruptions of Hudson (1991) and Puyehue (2011) volcanos, have been studied. The chemical and mineralogical compositions of both volcanic ashes were analyzed by ICP/OES, XRD, and SEM-EDS. Batch experiments were conducted to evaluate the kinetics of the arsenic release under variable pH. Results indicate that the release is enhanced under both, acidic and alkaline conditions. Besides, the positive significant linear trend found between Fe and As concentrations in the leachates suggests that arsenopyrite or/and its alteration product scorodite is one important As-bearing phase present in the ash samples. This phase would be the main responsible of the As release under acidic conditions. At higher pH, two other mechanisms are involved: desorption from Fe(hydr)oxide coatings (at neutral to slightly alkaline conditions) and dissolution of both arsenopyrite and volcanic glass at pH higher than 9.Fil: Bia, Gonzalo Luis.Consejo Nacional de Investigaciones Científicas y Técnicas. Centro de Investigaciones en Ciencias de la Tierra; Argentina.Fil: Bia, Gonzalo Luis. Universidad Nacional de Córdoba; Argentina.Fil: Borgnino, Laura. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro de Investigaciones en Ciencias de la Tierra; Argentina.Fil: Borgnino, Laura. Universidad Nacional de Córdoba; Argentina.Fil: Gaiero, Diego M. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro de Investigaciones en Ciencias de la Tierra; Argentina.Fil: Gaiero, Diego M. Universidad Nacional de Córdoba; Argentina.Fil: García, Maria Gabriela. Universidad Nacional de Córdoba; Argentina.Fil: García, Maria Gabriela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro de Investigaciones en Ciencias de la Tierra; Argentina.Otras Ciencias Química