Non-negative matrix factorization for medical imaging

A non-negative matrix factorization approach to dimensionality reduction is proposed to aid classification of images. The original images can be stored as lower-dimensional columns of a matrix that hold degrees of belonging to feature components, so they can be used in the training phase of the classification at lower runtime and without loss in accuracy. The extracted features can be visually examined and images reconstructed with limited error. The proof of concept is performed on a benchmark of handwritten digits, followed by the application to histopathological colorectal cancer slides. Results are encouraging, though dealing with real-world medical data raises a number of issues.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tec

Hopfield networks: from optimization to adaptive control

This paper proposes an adaptative control algorithm, which is designed by adding a parametric identification method to a non-linear controller. The identification module is built upon the Hopfield neural network, resulting in an unconventional network with time-varying weights and biases. The convergence of the estimations of the parameters of a dynamical system was proved in previous work, as long as the system inputs can be freely manipulated to provide persistent excitation. Henceforth the behaviour of the closed-loop system, when the inputs result from the controller equations, is here analyzed in order to assess both the tracking performance of the full adaptive controller and the identification ability of the neural estimator. The algorithm is applied to an idealized robotic system with two joints, whose positions and velocities are required to follow, as closely as possible, a prescribed reference trajectory. The simulation results show a satisfactory control performance, since the demanded trajectory is almost accurately followed. The estimated values also converge to the correct parameters, as long as the controller provides sufficiently rich signals to the system. The results are similar to a conventional least-squares adaptive controller, with a much lower computational cost.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Formalization of Universal Algebra in Agda

In this work we present a novel formalization of universal algebra in Agda. We show that heterogeneous signatures can be elegantly modelled in type-theory using sets indexed by arities to represent operations. We prove elementary results of heterogeneous algebras, including the proof that the term algebra is initial and the proofs of the three isomorphism theorems. We further formalize equational theory and prove soundness and completeness. At the end, we define (derived) signature morphisms, from which we get the contravariant functor between algebras; moreover, we also proved that, under some restrictions, the translation of a theory induces a contra-variant functor between models.Fil: Gunther, Emmanuel. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Gadea, Alejandro Emilio. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Pagano, Miguel Maria. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentin

Magnetic phases in the one-dimensional Kondo chain on a metallic surface

We study the low-temperature properties of a one-dimensional spin-1/2 chain of magnetic impurities coupled to a (normal) metal environment by means of anisotropic Kondo exchange. In the case of easy-plane anisotropy, we obtain the phase diagram of this system at T=0. We show that the in-plane Kondo coupling destabilizes the Tomonaga-Luttinger phase of the spin-chain, and leads to two different phases: i) At strong Kondo coupling, the spins in the chain form Kondo singlets and become screened by the metallic environment, and ii) At weak and intermediate Kondo coupling, we find a novel dissipative phase characterized by diffusive gapless spin excitations. The two phases are separated by a quantum critical point of the Wilson-Fisher universality class with dynamical exponent $z\simeq2$.Comment: 15 pages, 3 figures. New version contains clarifications about the specific approximations. Accepted for publication in PR

Gamma-ray triangles: a possible signature of asymmetric dark matter in indirect searches

We introduce a new type of gamma-ray spectral feature, which we denominate gamma-ray triangle. This spectral feature arises in scenarios where dark matter self-annihilates via a chiral interaction into two Dirac fermions, which subsequently decay in flight into another fermion and a photon. The resulting photon spectrum resembles a sharp triangle and can be readily searched for in the gamma-ray sky. Using data from the Fermi-LAT and H.E.S.S. instruments, we find no evidence for such spectral feature and therefore set strong upper bounds on the corresponding annihilation cross section. A concrete realization of a scenario yielding gamma-ray triangles consists of an asymmetric dark matter model where the dark matter particle carries lepton number. We show explicitly that this class of models can lead to intense gamma-ray spectral features, potentially at the reach of upcoming gamma-ray telescopes, opening a new window to explore asymmetric dark matter through indirect searches.Comment: 11 pages, 6 figures. Published versio

Social Exclusion in Latin America: Introduction and Overview

This paper presents the results of an Inter-American Development Bank Research Network project on Social Exclusion in Latin American and the Caribbean. The object of this project is to document and analyze the extent and consequences of some specific types of social exclusion in Latin America. The project has concentrated on some particular forms of exclusion that are important for the determination of incomeand thus poverty and income inequalityand that are relatively amenable to quantitative analysis. The purposes of the project are also to shed some light on the mechanisms of social exclusion, and to provide some guidance for policies aimed at addressing them.

Movilidad intergeneracional en América Latina

(Disponible en idioma inglés únicamente) El elevado grado de desigualdad ha sido visto por mucho tiempo como uno de los principales problemas que encaran los países latinoamericanos. Para comprender mejor los factores determinantes de la desigualdad y ayudar a orientar el pensar sobre las opciones de políticas, conviene averiguar primero si la desigualdad obedece o no principalmente a una escasa capacidad de movilización intergeneracional, o si es impulsada por diferencias en características individuales que surgen independientemente del historial familiar. En este trabajo empleamos cinco encuestas de hogares con preguntas sobre las características socioeconómicas de los padres de adultos, y un conjunto de 112 encuestas estándar entre hogares, para analizar la transmisión intergeneracional de escolaridad y el estado ocupacional en América Latina y Estados Unidos. Hallamos que la movilidad intergeneracional es mucho mayor en EE. UU. que en América Latina, que hay diferencias considerables de movilidad dentro de América Latina y que la movilidad en América Latina se relaciona fuertemente con los niveles de escolaridad y los gastos en educación.

Qualitative archives and biographical research methods. An introduction to the FQS special issue

The use of archival materials as a point of departure when designing and launching social research takes for granted that a culture of archiving (for sharing and re-use) has rooted time ago in our complex societies. This mentality and research practice first flourished and is fairly well installed in the case of statistics, surveys and certain other primary or secondary documents. On the contrary, it is less frequent and certainly not a routine activity for qualitative data. Only some of the raw and elaborated materials gathered during qualitative research become part of an archive for further reanalysis. These can include the backstage practices and experiences of a project, raw materials such as field notes, audio and visual recordings, and other documents produced during the research process. This issue presents a colorful range of articles that deal with experiences, challenges and opportunities of archiving and re-using qualitative material, particularly under the umbrella of biographical and narrative research. It aims to raise awareness of the importance of archiving in qualitative social research and highlights some of the new methodological reflections and approaches that have been and that are being developed within the European landscape. We hope that the articles in this issue will help promote further communication and exchange among qualitative archival practitioners from different countries and with different sensitivities and conceptual horizons. © 2011 FQS