Optical absorption of divalent metal tungstates: Correlation between the band-gap energy and the cation ionic radius

We have carried out optical-absorption and reflectance measurements at room temperature in single crystals of AWO4 tungstates (A = Ba, Ca, Cd, Cu, Pb, Sr, and Zn). From the experimental results their band-gap energy has been determined to be 5.26 eV (BaWO4), 5.08 eV (SrWO4), 4.94 eV (CaWO4), 4.15 eV (CdWO4), 3.9-4.4 eV (ZnWO4), 3.8-4.2 eV (PbWO4), and 2.3 eV (CuWO4). The results are discussed in terms of the electronic structure of the studied tungstates. It has been found that those compounds where only the s electron states of the A2+ cation hybridize with the O 2p and W 5d states (e.g BaWO4) have larger band-gap energies than those where also p, d, and f states of the A2+ cation contribute to the top of the valence band and the bottom of the conduction band (e.g. PbWO4). The results are of importance in view of the large discrepancies existent in prevoiusly published data.Comment: 16 pages, 3 figures, 1 tabl

An Introduction to Space-Time Exterior Calculus

The basic concepts of exterior calculus for space-time multivectors are presented: interior and exterior products, interior and exterior derivatives, oriented integrals over hypersurfaces, circulation and flux of multivector fields. Two Stokes theorems relating the exterior and interior derivatives with circulation and flux respectively are derived. As an application, it is shown how the exterior-calculus space-time formulation of the electromagnetic Maxwell equations and Lorentz force recovers the standard vector-calculus formulations, in both differential and integral forms.Comment: 19 pages, 5 figure

Development and experimental validation of an overlay mortar with biocide activity

Biodeterioration of concrete by microorganism colonisation may be a problem in several structures, especially in irrigation and hydroelectric canals. The main problem in such structures is the proliferation of algae and cyanobacteria that affect the performance of the structure, increase the maintenance costs and affects its durability. A research was conducted to develop a novel cement-based material with biocide activity that can be used as an overlay mortar in existing structures, such as canals and pipes. With this aim, ten commercial biocides were evaluated in a laboratory campaign to assess the effectiveness of the compounds against the microbial colonisation of concrete. Both mono- and multicomponent formulations were designed from the commercial products, to increase their antimicrobial effect obtaining a set of biocide formulations. The formulations were submitted to a flowchart process to determine their influence on the physical properties of the concrete, evaluate the release of the actives, and their antimicrobial efficiency both before and after accelerated aging processes. During the campaign, some formulations were observed to diminish the strength of the concrete. Such behaviour was normally due to the interaction of the active with the cement hydration process. Other formulations showed a high release of active from the concrete in water, compromising the durability of the treatment. In general, monocomponent formulations did not succeed to fulfill all the requirements, thus multicomponent formulations were analysed. One studied multicomponent formulation presented particularly good results in all properties analysed. This product did not significantly change the properties of concrete and the release of active in water from the concrete was low, while the antimicrobial effects were long lasting.Peer ReviewedPostprint (author's final draft

Estudio topológico del ADN nucleosomal y su paradoja del número de enlace

[spa] El empaquetamiento del ADN en fibras de cromatina implica una gran cantidad de deformaciones geométricas de la doble hélice (enrollamiento y superenrollamiento del ADN) y la formación de una jerarquía de asas o dominios de distinto tamaño. Este empaquetamiento conlleva severas restricciones topológicas, las cuales juegan un papel determinante en los procesos metabólicos del ADN. Sin embargo, la arquitectura fina de la cromatina en 3D/4D, así como la trayectoria espacial y la topología de las cadenas de ADN a través de cada elemento individual de la cromatina, permanecen como aspectos enigmáticos y poco explorados. Ello es debido tanto a limitaciones metodológicas como a su dificultad conceptual, que hacen de la topología del ADN un área de estudio casi desconocida para gran parte de la comunidad científica. En los años 80, diversos estudios experimentales establecieron que la unidad estructural de la cromatina, el nucleosoma, estabilizaba una diferencia del número de enlace (∆Lk) igual a -1.0/por nucleosoma. Este valor, sin embargo, suponía una incongruencia respecto al valor teórico estimado a partir de otros estudios estructurales de los nucleosomas, que concluían que el valor ∆Lk debería ser > -1.0 y cercano a -2. Esta incongruencia generó la llamada “Paradoja del número de enlace del ADN nucleosomal”, que ha estado vigente hasta la actualidad. En esta tesis se ha realizado un minucioso análisis de la topología del ADN nucleosomal para determinar con precisión el valor ∆Lk. Los resultados presentados demuestran que los nucleosomas estabilizan un valor medio de ∆Lk = -1.26. Este valor, junto a las correcciones de los valores teóricos derivados de los estudios estructurales previos, soluciona la paradoja del número de enlace del ADN nucleosomal. La aproximación metodológica, utilizando pequeños minicromosomas circulares para el análisis topológico de elementos de la cromatina in vivo, hace del presente trabajo una apuesta novedosa y original en el campo de la topología.[eng] Packaging of DNA molecules into chromatin imposes severe geometrical deformations and topological constraints in the double helix (DNA wrapping, looping and supercoiling). These restrictions play an important role in the regulation of genome activities. Whereas the 3D/4D architecture of chromatin is being uncovered down to Kb resolution, the local path and the topology of the DNA strands constrained by individual chromatin elements remains elusive due to methodological limitations and conceptual complexity. In the ‘80s, it was established that the structural unit of chromatin, the nucleosome, constrains on average about one negative DNA supercoil (i.e. a DNA linking number difference, ∆Lk, of -1/ per nucleosome). However, this ∆Lk value was inconsistent with the theoretical value estimated from structural studies (∆Lk ≈ -2). This incongruence between the theoretical and the experimental value produced the so-called “linking number paradox”. In this thesis, we developed an approach to analyze the topology of DNA constrained by individual chromatin elements in vivo, so we could accurately determine the ∆Lk value stabilized by individual nucleosomes. Our result indicates that nucleosomes stabilize an average value of ∆Lk = -1.26. This value balances the twist (∆Tw ≈ +0.2) and writhe (∆Wr ≈ -1.5) deformations of nucleosomal DNA in terms of the equation ∆Lk = ∆Tw + ∆Wr. Our finding could solve the long standing “linking number paradox” of nucleosomal DNA

Importance Sampling for Coded-Modulation Error Probability Estimation

This paper proposes an efficient simulation method based on importance sampling to estimate the random-coding error probability of coded modulation. The technique is valid for complex-valued modulations over Gaussian channels, channels with memory, and naturally extends to fading channels. The simulation method is built on two nested importance samplers to respectively estimate the pairwise error probability and generate the channel input and output. The effect of the respective number of samples on the overall bias and variance of the estimate of the error probability is characterized. For a memoryless channel, the estimator is shown to be consistent and with a small variance, growing with the square root of the code length, rather than the exponential growth of a standard Monte Carlo estimator.This work has been funded in part by the European Research Council under ERC grant agreement 725411, and by the Spanish Ministry of Economy and Competitiveness under grant TEC2016-78434-C3-1-R

Rotación laboral en las empresas privadas de colombia

En el presente documento se habla mediante un estudio investigativo acerca de la rotación laboral en empresas privadas en Colombia en las que se reflejan diferentes elementos que se consideran importantes y que afectan directa o indirectamente en la notable desvinculación de la fuerza laboral en Colombia. En el país, existe una alta tasa de ocupación, de acuerdo a la revista “El nuevo siglo” bajo el artículo publicado “Rotación laboral en el país es alta “ publicado en 2018, se afirma que desde el año 2013 al 2017 la desvinculación laboral tuvo un incremento que llega hasta el 140 % en el 2017 lo que genera efectos como asignación de presupuesto para el reemplazo del colaborador, perjudica la imagen de la compañía, impacta la productividad en el área donde se encuentra el cargo y se dificulta constantemente la generación de experticia en los procesos de la organización.This document discusses through an investigative study about job rotation in Colombian companies, which reflects different elements that are considered important and that directly or indirectly affect the notable disengagement from the labor force in Colombia. In the country, there is a high employment rate, in the last 5 years, this turnover rate has been increasing, which generates instability for companies in different sectors of the economy, as well as evident costs generated by replacement in the different positions abandoned; However, as this factor has increased, the different means by which it seeks to stabilize the motivation of the worker to continue with their relationship have also diversified, such as variable salary, better working conditions and opportunities to climb within it

Multi-Class Cost-Constrained Random Coding for Correlated Sources over the Multiple-Access Channel.

This paper studies a generalized version of multi-class cost-constrained random-coding ensemble with multiple auxiliary costs for the transmission of N correlated sources over an N-user multiple-access channel. For each user, the set of messages is partitioned into classes and codebooks are generated according to a distribution depending on the class index of the source message and under the constraint that the codewords satisfy a set of cost functions. Proper choices of the cost functions recover different coding schemes including message-dependent and message-independent versions of independent and identically distributed, independent conditionally distributed, constant-composition and conditional constant composition ensembles. The transmissibility region of the scheme is related to the Cover-El Gamal-Salehi region. A related family of correlated-source Gallager source exponent functions is also studied. The achievable exponents are compared for correlated and independent sources, both numerically and analytically

Public housing policies: impacts and limitations of ProCreAr Program

Este artículo reflexiona sobre los impactos y las limitaciones del Programa de Crédito Argentino del Bicentenario para la Vivienda Única Familiar (ProCreAr), política pública contracíclica que buscó combinar la dinamización de la economía y la generación de empleo con el acceso a la vivienda por parte de los sectores medios. La ausencia de una política clara en la producción y la regulación del suelo urbano explica la existencia de desacoples entre las dimensiones macroeconómicas y territoriales del programa, que se expresan no sólo en el déficit de suelo urbano al momento de su implementación sino también en los efectos urbanos de la propia implementación. Asimismo, más allá de estas tendencias generales, el artículo muestra el impacto diferencial del programa dependiendo de la estructura urbana y de las articulaciones políticas en el momento de su implementación.We analyze the impacts and limitations of the Argentine Bicentennial Credit Program for Single Family Housing (ProCreAr), a countercyclical public policy that sought to combine the revitalization of the economy and the generation of employment with access to housing by the middle sectors. The absence of a clear policy in the production and regulation of urban land explains the existence of decoupling between the macroeconomic and territorial dimensions of the program, which are expressed not only in the deficit of urban land at the time of its implementation but also in the effects of the implementation itself. The challenges and potentialities that habitat - as a multidimensional reality -have for the social and productive development of the country are discussed. As well as the place that science and technology could take in those processes.Fil: Segura, Ramiro. Universidad Nacional de San Martín. Instituto de Altos Estudios Sociales; Argentina. Universidad Nacional de La Plata. Facultad de Trabajo Social. Laboratorio de Estudios en Cultura y Sociedad; ArgentinaFil: Cosacov Martinez, Natalia. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Sociales. Instituto de Investigaciones "Gino Germani"; Argentin

Explainable Hopfield Neural Networks Using an Automatic Video-Generation System

Hopfield Neural Networks (HNNs) are recurrent neural networks used to implement associative memory. They can be applied to pattern recognition, optimization, or image segmentation. However, sometimes it is not easy to provide the users with good explanations about the results obtained with them due to mainly the large number of changes in the state of neurons (and their weights) produced during a problem of machine learning. There are currently limited techniques to visualize, verbalize, or abstract HNNs. This paper outlines how we can construct automatic video-generation systems to explain its execution. This work constitutes a novel approach to obtain explainable artificial intelligence systems in general and HNNs in particular building on the theory of data-to-text systems and software visualization approaches. We present a complete methodology to build these kinds of systems. Software architecture is also designed, implemented, and tested. Technical details about the implementation are also detailed and explained. We apply our approach to creating a complete explainer video about the execution of HNNs on a small recognition problem. Finally, several aspects of the videos generated are evaluated (quality, content, motivation and design/presentation).University of the Bio-Bio. Vicerrectoria de Investigacion. Facultad de Ciencias Empresariales. Departamento de Sistemas de Informacion