Distribució batimètrica dels peixos litorals de substract rocós a l'illa de Cabrera

La ictiofauna que es troba sobre fons rocosos litorals de l'illa de Cabrera ha estat estudiada, mitjançant la tècnica de comptatges visuals, en transsectes fixos de 50 x 5 m, situats a -6, -30 i -45 m de fondària. En total han estat observades 46 espècies, pertanyents a 19 famílies, entre les quals dominen clarament els làbrids i els espàrids. La fondària és el principal factor que determina les diferències qualitatives i quantitatives observades al llarg de l'estudi. El segon factor sembla ser degut a la diferència en l'heterogeneïtat del substrat, i a l'existència a absència d'algues frondoses. En fondària hom observa una certa disminució del nombre d'espècies de làbrids i espàrids. L'ampli marge de fondàries estudiades i l'extrema polarització de les mostres en les comunitats bentòniques de Cabrera permet definir dues associacions de peixos litorals: una de superficial, carateritzada sobretot per Symphodus roissali, Symphodus ocellatus, Thalassoma pavo, i Parablennius rouxij i una de fonda, caracteritzada, entre d'altres per Anthias anthias, Labrus bimaculatus, Symphodus melanocercus i Gobius vittatus. Amb tot, més que una zonació en sentit estricte, hom postula l'existència d'un continuum, on les diferències quantitatives són gairebé tan importants com les qualitatives, i on unes espècies succeeixen les altres de forma gradual. En un treball subsidiari, hom estudia amb més detall la distribució en fondària de dues espècies simpàtriques, Serranus cabrilla i Serranus scriba, entre les quals es produeix, més que una competència per l'espai, un cas de compartimentació espacial. Les pautes de distribució en fondària d'aquestes dues espècies poden ser paradigmàtiques del que ocorre en molts altres casos.The coastal fish fauna from Cabrera island rocky bottoms has been studied by visual censuses along 50 x 5 m strip transects sitted at -6, -30 and -45 m depth. 46 fish species have been recorded, belonging to 19 families dominated by Labridae (11 species) and Sparidae (9 species). Depth is the main environmental factor affecting qualitative and quantitative fish distribution, being bottom heterogenity (hole size and presence or absence of frondose algae) the second one. A decrease of Labridae and Sparidae species has been found with depth. Two rocky fish assemblages have been distinguished attending to their depth distribution ranks: a shallow one, characterized by Symphodus roissali, Symphodus ocellatus, Thalassoma pavo and Parablennius rouxij and a deep one, characterized mainly by Anthias anthias, Labrus bimaculatus, Symphodus melanocercus and Gobius vittatus. However, there is a continuum change of species with depth instead of critical discontinuities between the two fish assemblages. Depth patterns of two sympatric species (Serranus cabrilla and Serranus scribal has been studied as an example of this continuos depth fish distribution

On the Torelli problem and Jacobian Nullwerte in genus three

We give a closed formula for recovering a non-hyperelliptic genus three curve from its period matrix, and derive some identities between Jacobian Nullwerte in dimension three

Design and FDM/FFF Implementation of a Compact Omnidirectional Wheel for a Mobile Robot and Assessment of ABS and PLA Printing Materials

This paper proposes the design and 3D printing of a compact omnidirectional wheel optimized to create a small series of three-wheeled omnidirectional mobile robots. The omnidirectional wheel proposed is based on the use of free-rotating passive wheels aligned transversally to the center of the main wheel and with a constant separation gap. This paper compares a three inner-passive wheels design based on mass-produced parts and 3D printed elements. The inner passive wheel that better combines weight, cost, and friction is implemented with a metallic ball bearing fitted inside a 3D printed U-grooved ring that holds a soft toric joint. The proposed design has been implemented using acrylonitrile butadiene styrene (ABS) and tough polylactic acid (PLA) as 3D printing materials in order to empirically compare the deformation of the weakest parts of the mechanical design. The conclusion is that the most critical parts of the omnidirectional wheel are less prone to deformation and show better mechanical properties if they are printed horizontally (with the axes that hold the passive wheels oriented parallel to the build surface), with an infill density of 100% and using tough PLA rather than ABS as a 3D printing material

Square-free OM computation of global integral bases

© 2022 Mathematical Sciences PublishersFor a prime p, the OM algorithm finds the p-adic factorization of an irreducible polynomial f¿Z[x]¿¿Z[¿] in polynomial time. This may be applied to construct p-integral bases in the number field K defined by f. In this paper, we adapt the OM techniques to work with a positive integer N instead of p. As an application, we obtain an algorithm to compute global integral bases in K, which does not require a previous factorization of the discriminant of f.Partially supported by grants MTM2015-66180-R and MTM2016-75980-P from the Spanish MECPeer ReviewedPostprint (author's final draft

Superradiance and subradiance in a gas of two-level atoms

Cooperative effects describe atomic ensembles with exchange of photonic excitations, such as dipole-dipole interactions. As a particular example, superradiance arises from spontaneous emission when this exchange leads to constructive interference of the emitted photons. Here, we introduce an integrated method for studying cooperative radiation in many-body systems. This method, which allows to study extended systems with arbitrarily large number of particles can be formulated by an effective, nonlinear, two-atom master equation that describes the dynamics using a closed form which treats single- and many-body terms on an equal footing. We apply this method to a homogeneous gas of initially inverted two-level atoms, and demonstrate the appearance of both superradiance and subradiance, identifying a many-body coherence term as the source of these cooperative effects. We describe the many-body induced broadening - which is analytically found to scale with the optical depth of the system - and light shifts, and distinguish spontaneous effects from induced ones. In addition, we theoretically predict the time-dependence of subradiance, and the phase change of the radiated field during the cooperative decay.Comment: 30 pages, 11 figure