Loglinear model selection and human mobility

Methods for selecting loglinear models were among Steve Fienberg’s research interests since the start of his long and fruitful career. After we dwell upon the string of papers focusing on loglinear models that can be partly attributed to Steve’s contributions and influential ideas, we develop a new algorithm for selecting graphical loglinear models that is suitable for analyzing hyper-sparse contingency tables. We show how multi-way contingency tables can be used to represent patterns of human mobility. We analyze a dataset of geolocated tweets from South Africa that comprises 46 million latitude/longitude locations of 476,601 Twitter users that is summarized as a contingency table with 214 variables

Synthesis and Characterization of Gold Nanoparticles Functionalized with Electropolymerizable or Optically Switchable π-Conjugated Systems

International audienc

Fruit Rot Caused by Phytophthora sp. in Cold-Stored Pears in the Valley of Rio Negro and Neuquén, Argentina

Pear fruit conservation for long periods is associated with postharvest fungal diseases. In Argentina, the most important and widespread diseases are caused by Penicillium spp. and Botrytis cinerea, followed by Alternaria sp. and Cladosporium sp. and Athelia epiphylla. The last one can be important depending on the fruit-lot. This study reports the presence of one Oomycete, as the cause of pear fruit rot in postharvest. In 2010, during the first months of conservation of ‘Williams’, ‘Packham’s Triumph’ and ‘Red Bartlet’ pears, in cold storage, in the eastern area of Alto Valle of Río Negro, fruit decay was recorded with losses between 5 and 20%, according to fruit-lot. Symptoms of decay were studied and its ethiology was determined using conventional and molecular methods. Fruit started showing circular, light to dark brown areas with irregular and diffuse margins that spread rapidly. The decayed area remained firm. The lesion diameter increased and it extended to pulp tissue to reach fruit core with a hyperbolic shape, different from the spherical shape caused by Penicillium spp. or Botrytis sp. The pathogen was isolated in V8 agar selective medium from pears with symptoms. By morphologic characteristics (colony and sporangia) of isolates, its association with clade 6 of Phytophthora was determined. The identification of isolates was confirmed by direct sequencing of the ITS rDNA region using DC6 and ITS4 primers. The nucleotide sequence showed 100% of similarity (745/745 pb) with sequences available in GenBank and was identified as an undescribed species inside P. gonapodyides- P. megasperma Clade 6. This is the first report of a new Phytophthora in postharvest pears.La conservación del fruto de pera por períodos prolongados se asocia con enfermedades fúngicas poscosecha. En Argentina las enfermedades más importantes y extendidas son causadas por Penicillium spp. y Botrytis cinerea , seguida de Alternaria sp. y Cladosporium sp. y Athelia epiphylla . Este último puede ser importante dependiendo del lote de fruta. Este estudio reporta la presencia de un Oomiceto, como causante de la pudrición del fruto de pera en poscosecha. En 2010, durante los primeros meses de conservación de peras 'Williams', 'Packham's Triumph' y 'Red Bartlet', en cámaras frigoríficas, en la zona oriental del Alto Valle de Río Negro, se registró pudrición de frutos con pérdidas entre 5 y 20 %, según lote de fruto. Se estudiaron los síntomas de la descomposición y se determinó su etiología mediante métodos convencionales y moleculares. Los frutos comenzaron a mostrar áreas circulares, de color marrón claro a oscuro, con márgenes irregulares y difusos que se extendieron rápidamente. La zona deteriorada se mantuvo firme. El diámetro de la lesión aumentó y se extendió al tejido pulpar hasta llegar al corazón del fruto con forma hiperbólica, diferente a la forma esférica causada por Penicillium spp. o Botrytis sp. El patógeno se aisló en medio selectivo agar V8 de peras con síntomas. Por características morfológicas (colonia y esporangios) de los aislados se determinó su asociación con el clado 6 de Phytophthora . La identificación de los aislados se confirmó mediante secuenciación directa de la región ITS rDNA utilizando cebadores DC6 e ITS4. La secuencia de nucleótidos mostró 100% de similitud (745/745 pb) con secuencias disponibles en GenBank y fue identificada como una especie no descrita dentro de P. gonapodyides - P. megasperma Clado 6. Este es el primer reporte de una nueva Phytophthora en peras poscosecha.Fil: Dobra, Alicia Cristina. Universidad Nacional del Comahue. Facultad de Ciencias Agrarias; Argentina.Fil: Sosa, María Cristina. Universidad Nacional del Comahue. Facultad de Ciencias Agrarias; Argentina.Fil: Lutz, María Cecilia. Universidad Nacional del Comahue. Facultad de Ciencias Agrarias; Argentina.Fil: Rodriguez, Gustavo. Universidad Nacional del Comahue. Facultad de Ciencias Agrarias; Argentina

New strategies for sustainable fisheries management: A case study of Atlantic salmon

This briefing paper considers the alarming declines in fish stocks in recent years, and how holistic, integrated approaches can help manage fish stocks within biologically sustainable limits. Using Atlantic salmon as a case study, the authors highlight the challenges facing fisheries management and conservation, and the implications for policy and management

Parametric Polyhedra with at least kk Lattice Points: Their Semigroup Structure and the k-Frobenius Problem

Given an integral $d \times n$ matrix $A$, the well-studied affine semigroup \mbox{ Sg} (A)=\{ b : Ax=b, \ x \in {\mathbb Z}^n, x \geq 0\} can be stratified by the number of lattice points inside the parametric polyhedra $P_A(b)=\{x: Ax=b, x\geq0\}$. Such families of parametric polyhedra appear in many areas of combinatorics, convex geometry, algebra and number theory. The key themes of this paper are: (1) A structure theory that characterizes precisely the subset \mbox{ Sg}_{\geq k}(A) of all vectors b \in \mbox{ Sg}(A) such that $P_A(b) \cap {\mathbb Z}^n$ has at least $k$ solutions. We demonstrate that this set is finitely generated, it is a union of translated copies of a semigroup which can be computed explicitly via Hilbert bases computations. Related results can be derived for those right-hand-side vectors $b$ for which $P_A(b) \cap {\mathbb Z}^n$ has exactly $k$ solutions or fewer than $k$ solutions. (2) A computational complexity theory. We show that, when $n$, $k$ are fixed natural numbers, one can compute in polynomial time an encoding of \mbox{ Sg}_{\geq k}(A) as a multivariate generating function, using a short sum of rational functions. As a consequence, one can identify all right-hand-side vectors of bounded norm that have at least $k$ solutions. (3) Applications and computation for the $k$-Frobenius numbers. Using Generating functions we prove that for fixed $n,k$ the $k$-Frobenius number can be computed in polynomial time. This generalizes a well-known result for $k=1$ by R. Kannan. Using some adaptation of dynamic programming we show some practical computations of $k$-Frobenius numbers and their relatives