The derived category of quasi-coherent sheaves and axiomatic stable homotopy

We prove in this paper that for a quasi-compact and semi-separated (non necessarily noetherian) scheme X, the derived category of quasi-coherent sheaves over X, D(A_qc(X)), is a stable homotopy category in the sense of Hovey, Palmieri and Strickland, answering a question posed by Strickland. Moreover we show that it is unital and algebraic. We also prove that for a noetherian semi-separated formal scheme X, its derived category of sheaves of modules with quasi-coherent torsion homologies D_qct(X) is a stable homotopy category. It is algebraic but if the formal scheme is not a usual scheme, it is not unital, therefore its abstract nature differs essentially from that of the derived category of a usual scheme.Comment: v2: 31 pages, some improvements in exposition; v3 updated bibliography, to appear Adv. Mat

On the existence of a compact generator on the derived category of a noetherian formal scheme

In this paper, we prove that for a noetherian formal scheme X, its derived category of sheaves of modules with quasi-coherent torsion homologies D_qct(X) is generated by a single compact object. In an appendix we prove that the category of compact objects in D_qct(X) is skeletally small.Comment: 13 page

Assessing controls on the displacement of tracers in gravel-bed rivers

Particle travel length is one of the main dimensions of bedload and strongly influences river morpho-dynamics, particularly when exploring the interactions between sediment transport and channel morphology. This process has been traditionally studied by using tagged stones that allow tracking the movement experienced by individual grains during transport episodes. In this paper, we relate measured particle travel lengths to flow metrics and river channel parameters. First, we link the event-based bedload volumes to the active-layer dimensions, and the product between the average bedload rates and the duration of competent flows. We then hypothesize that travel length depends on channel width, surface grain-size, particle size, bed structure, flow strength, and duration of competent flow. The results from this approach are, subsequently, tested with a set of tracer observations from eight rivers that were available in the literature. The relationship between travel length and flow metrics was found to be statistically strong and has the potential to allow us to quantitatively assess the one-day dynamics of particles moving along streambeds. We also analyzed the influence of channel morphology and bed structure and identified morphological signatures for particle transport in gravel-bed rivers.The present work has been possible thanks to the financial support provided by the grant ACB17-44, co-funded by the post-doctoral ‘Clarín’ program-FICYT (Government of the Principality of Asturias) and the Marie Curie Co-Fund. This research was partly undertaken through the MorphPeak (CGL2016-78874-R) project funded by the Spanish Ministry of Economy and Competiveness and the European Regional Development Fund Scheme. Authors acknowledge the support from the Economy and Knowledge Department of the Catalan Government through the Consolidated Research Group ‘Fluvial Dynamics Research Group’ -RIUS (2017 SGR 459), as well as support from the project RIVERCHANGES-CGL2015-68824-R (MINECO/FEDER, UE)

The Ribbed Stone Vaults of Galicia: Identifying Some Solutions

El artículo presenta los distintos grupos de soluciones de bóvedas pétreas nervadas sobre cuatro apoyos que existen en Galicia, representándolas gráficamente a la misma escala. Complementariamente se incluye también un pequeño grupo de bóvedas sobre ocho apoyos. Para clasificar los ejemplos se ha empleado un sistema basado en los rasgos constructivos de las bóvedas, que tiene en cuenta el número de apoyos de éstas y los distintos tipos de nervios presentes. Este criterio sistemático permite apreciar tanto soluciones que tradicionalmente han pasado desapercibidas como las dimensiones con las éstas que han sido construidas[Abstract]This article presents the different groups of solutions of ribbed stone vaults on four supports that exist in Galicia and it plots them at the same scale. A small group of vaults on eight supports is also included. In order to classify the samples, a system based on the constructive features of the vaults has been used, taking into account their number of supports and the different types of nerves. The systematic approach used allows determining both the dimensions with which the different types of vaults were built as well as the solutions traditionally overlooke

Erratic overdispersion of three molecular clocks: GPDH, SOD, and XDH

The neutrality theory predicts that the rate of neutral molecular evolution is constant over time, and thus that there is a molecular clock for timing evolutionary events. It has been observed that the variance of the rate of evolution is generally larger than expected according to the neutrality theory, which has raised the question of how reliable the molecular clock is or, indeed, whether there is a molecular clock at all. We have carried out an extensive investigation of three proteins, glycerol-3-phosphate dehydrogenase (GPDH), superoxide dismutase (SOD), and xanthine dehydrogenase (XDH). We have observed that (i) the three proteins evolve erratically through time and across lineages and (ii) the erratic patterns of acceleration and deceleration differ from locus to locus, so that one locus may evolve faster in one than another lineage, whereas the opposite may be the case for another locus. The observations are inconsistent with the predictions made by various subsidiary hypotheses proposed to account for the overdispersion of the molecular clock.F.R.-T. has received support from the Spanish Council for Scientific Research (Contrato Temporal de Investigación) and Grant AGL2000- 1073 from the Ministerio de Ciencia y Tecnología to A. Ballester. Research was supported by National Institutes of Health Grant GM42397 (to F.J.A.).Peer Reviewe

Enjarjes y plementos en las bóvedas pétreas gallegas

El texto analiza y clasifica los enjarjes y la plementería de las distintas soluciones de bóvedas pétreas nervadas sobre cuatro apoyos que existen en Galicia. En trabajos anteriores se han levantado y clasificado estas bóvedas, analizado su proporción e investigado sus formas de trazado. Siendo el trabajo que se presenta un nuevo paso dentro del estudio sistemático iniciado años atrás. El arranque de una bóveda es un punto crítico que aúna las dificultades geométricas y constructivas (replanteo y labra) con una notabilísima capacidad plástica a la que contribuye la solución de apoyo sobre columnas o voladas a partir de ménsulas, capitel-ménsula o ‘cul de lampe’ o directamente desde el muro. Tras analizar una serie de casos-tipo escogidos de entre el conjunto de bóvedas levantadas, se bosqueja, con el apoyo de las fuentes bibliográficas, una clasificación descriptiva que sistematiza la catalogación de estos elementos. Dicha clasificación es abierta, permitiendo la incorporación de nuevos criterios en función del grado descriptivo deseado. La segunda parte de la exposición versa sobre el estudio de la plementería. Se estudia el tipo de piezas pétreas empleadas, su acabado –existencia de revestimientos, presencia o no de talla-y su disposición en relación a las nervaduras de la bóveda. Ello obliga a introducir en el estudio el número y tipo de nervios que presentan las bóvedas, las proporciones de éstas y su tamaño

A Grid Portal for an Undergraduate Parallel Programming Course

[Abstract] This paper describes an experience of designing and implementing a portal to support transparent remote access to supercomputing facilities to students enrolled in an undergraduate parallel programming course. As these facilities are heterogeneous, are located at different sites, and belong to different institutions, grid computing technologies have been used to overcome these issues. The result is a grid portal based on a modular and easily extensible software architecture that provides a uniform and user-friendly interface for students to work on their programming laboratory assignments.Universidade da Coruña; UDC-TIC03-057Xunta de Galicia; PGIDIT02TIC00103CTXunta de Galicia; PGIDIT04TIC105004PREuropean Commission; IST-2001-3224

Perverse coherent t-structures through torsion theories

Bezrukavnikov (later together with Arinkin) recovered the work of Deligne defining perverse $t$-structures for the derived category of coherent sheaves on a projective variety. In this text we prove that these $t$-structures can be obtained through tilting torsion theories as in the work of Happel, Reiten and Smal\o. This approach proves to be slightly more general as it allows us to define, in the quasi-coherent setting, similar perverse $t$-structures for certain noncommutative projective planes.Comment: New revised version with important correction