107 research outputs found
Optical Properties of Graphene Nanoflakes: Shape Matters
In recent years there has been significant debate on whether the edge type of
graphene nanoflakes (GNF) or graphene quantum dots (GQD) are relevant for their
electronic structure, thermal stability and optical properties. Using computer
simulations, we have proven that there is a fundamental difference in the
calculated absorption spectra between samples of the same shape, similar size
but different edge type, namely, armchair or zigzag edges. These can be
explained by the presence of electronic structures near the Fermi level which
are localized on the edges. These features are also evident from the dependence
of band gap on the GNF size, which shows three very distinct trends for
different shapes and edge geometries.Comment: 8 pages, 9 figures. Submitted to The Journal of Chemical Physic
Stability of moving solitons in trans-polyacetylene in an electric field
In this work we study the dynamics and stability of charged solitons in
trans-polyacetylene (tPA), and revisit the issue of the stability of these
non-linear excitations under the effect of an external electric field applied
parallel to the polymer. Using the formalism of the Su-Schrieffer-Heeger (SSH)
model, we solve the coupled dynamical equations for electrons and classical
nuclei at the mean-field level and in the regime of low external electric field
, where the dynamics of the moving soliton is adiabatic. Analyzing
observable quantities in real space and frequency space, we identify the
microscopic mechanisms triggering the dynamical instabilities of the soliton.
In addition, we put forward the definition of a proper quantitative measure of
its stability, an issue which to the best of our knowledge has remained an open
question. Besides its intrinsic interest from the fundamental point of view,
our work might be relevant for the design of novel organic electronic devices
based on soliton-mediated transport.Comment: 14 pages, 9 figures, 1 appendi
Diagnóstico de la evolución de los procesos de gestión del espacio público en la ciudad de Armenia Quindío del año 2010 a 2014
Trabajo de investigaciónEn el año 2010 comenzó a regir en el municipio de Armenia Quindío el primer plan de ordenamiento territorial de segunda generación en todo el ámbito nacional. Transcurridos 4 años se hace necesario diagnosticar los resultados obtenidos con la adopción de este instrumento de gestión de espacio público, mucho más cuando en el año 2010 el documento Conpes 3718, estableció que los estándares de este componente urbano en el municipio se encontraba por debajo de la media nacional. Considerando que a finales del año 2009, fue aprobado el plan de ordenamiento territorial (acuerdo 019 de 01 de diciembre de 2009), el cual concibe el espacio público como un elemento estructural del sistema urbano y además se encuentra articulado con las políticas nacionales, tal y como lo estipula su artículo 44 el cual establece como estrategia: “incrementar los estándares de área libre por habitante”, ya transcurridos 4 años se considera necesario diagnosticar los resultados obtenidos con la adopción de este modelo de gestión del espacio público, en relación con lo anterior se formuló la siguiente pregunta de investigación: ¿cómo han evolucionado los procesos de gestión del espacio público en la ciudad de Armenia Quindío del año 2010 a 2014? Pregunta que conllevó a analizar tres aspectos de vital importancia: obras de infraestructura ejecutadas a la fecha, instrumentos de gestión del espacio público adoptados y percepción ciudadana. En éste diagnóstico la información requerida para el desarrollo de sus objetivos, se obtuvo del análisis de documentos técnicos y legales de la alcaldía de Armenia como fuente primaria de información y como fuente secundaria se empleó la encuesta de percepción ciudadana e inspecciones técnicas del área de estudio, mecanismos que permitieron recolectar información puntual de los objetivos específicos. La información recolectada fue procesada y analizada por el grupo de trabajo.EspecializaciónEspecialista en Gerencia de Obras Civile
Magneto-mechanical interplay in spin-polarized point contacts
We investigate the interplay between magnetic and structural dynamics in
ferromagnetic atomic point contacts. In particular, we look at the effect of
the atomic relaxation on the energy barrier for magnetic domain wall migration
and, reversely, at the effect of the magnetic state on the mechanical forces
and structural relaxation. We observe changes of the barrier height due to the
atomic relaxation up to 200%, suggesting a very strong coupling between the
structural and the magnetic degrees of freedom. The reverse interplay is weak,
i.e. the magnetic state has little effect on the structural relaxation at
equilibrium or under non-equilibrium, current-carrying conditions.Comment: 5 pages, 4 figure
Optimizing Credit Limit Adjustments Under Adversarial Goals Using Reinforcement Learning
Reinforcement learning has been explored for many problems, from video games
with deterministic environments to portfolio and operations management in which
scenarios are stochastic; however, there have been few attempts to test these
methods in banking problems. In this study, we sought to find and automatize an
optimal credit card limit adjustment policy by employing reinforcement learning
techniques. In particular, because of the historical data available, we
considered two possible actions per customer, namely increasing or maintaining
an individual's current credit limit. To find this policy, we first formulated
this decision-making question as an optimization problem in which the expected
profit was maximized; therefore, we balanced two adversarial goals: maximizing
the portfolio's revenue and minimizing the portfolio's provisions. Second,
given the particularities of our problem, we used an offline learning strategy
to simulate the impact of the action based on historical data from a super-app
(i.e., a mobile application that offers various services from goods deliveries
to financial products) in Latin America to train our reinforcement learning
agent. Our results show that a Double Q-learning agent with optimized
hyperparameters can outperform other strategies and generate a non-trivial
optimal policy reflecting the complex nature of this decision. Our research not
only establishes a conceptual structure for applying reinforcement learning
framework to credit limit adjustment, presenting an objective technique to make
these decisions primarily based on data-driven methods rather than relying only
on expert-driven systems but also provides insights into the effect of
alternative data usage for determining these modifications.Comment: 29 pages, 16 figure
Power flow control using a DC-DC MMC for HVdc grid connected wind power plants
This paper proposes the use of a transformer-less
DC-DC Modular Multilevel Converter (MMC) topology, based
on cascaded H-bridge converters, for power flow control in High
Voltage Direct Current (HVDC) grids used to connect off-shore
wind power plants to on-shore grids. An energy based approach
is used to regulate the DC voltage of H-bridge modules. Results
for the operation of the DC-DC MMC supplying energy to a DC
network and controlling the power flow in a HVDC system are
presented.The support of Fondecyt grant 1151325,
CONICYT/FONDAP/15110019, the Spanish Ministry of Economy Grant DPI2014-53245-R, University La Frontera
grant DIUFRO09-0037 and Universitat Jaume I grants
P1ā1B2013-51 and E-2014-24 is kindly acknowledged
A modelling study highlights the power of detecting and isolating asymptomatic or very mildly affected individuals for COVID-19 epidemic management
Background: Mathematical modelling of infectious diseases is a powerful tool for the design of management policies and a fundamental part of the arsenal currently deployed to deal with the COVID-19 pandemic. Methods: We present a compartmental model for the disease where symptomatic and asymptomatic individuals move separately. We introduced healthcare burden parameters allowing to infer possible containment and suppression strategies. In addition, the model was scaled up to describe different interconnected areas, giving the possibility to trigger regionalized measures. It was specially adjusted to Mendoza-Argentina’s parameters, but is easily adaptable for elsewhere. Results: Overall, the simulations we carried out were notably more effective when mitigation measures were not relaxed in between the suppressive actions. Since asymptomatics or very mildly affected patients are the vast majority, we studied the impact of detecting and isolating them. The removal of asymptomatics from the infectious pool remarkably lowered the effective reproduction number, healthcare burden and overall fatality. Furthermore, different suppression triggers regarding ICU occupancy were attempted. The best scenario was found to be the combination of ICU occupancy triggers (on: 50%, off: 30%) with the detection and isolation of asymptomatic individuals. In the ideal assumption that 45% of the asymptomatics could be detected and isolated, there would be no need for complete lockdown, and Mendoza’s healthcare system would not collapse. Conclusions: Our model and its analysis inform that the detection and isolation of all infected individuals, without leaving aside the asymptomatic group is the key to surpass this pandemic.Fil: Mayorga, Lía. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto de Histología y Embriología de Mendoza Dr. Mario H. Burgos. Universidad Nacional de Cuyo. Facultad de Ciencias Médicas. Instituto de Histología y Embriología de Mendoza Dr. Mario H. Burgos; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química Biológica de la Facultad de Ciencias Exactas y Naturales. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química Biológica de la Facultad de Ciencias Exactas y Naturales; ArgentinaFil: García Samartino, Clara. Universidad Nacional de Cuyo. Facultad de Odontologia; ArgentinaFil: Flores, Gabriel. No especifíca;Fil: Masuelli, Sofía. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto de Histología y Embriología de Mendoza Dr. Mario H. Burgos. Universidad Nacional de Cuyo. Facultad de Ciencias Médicas. Instituto de Histología y Embriología de Mendoza Dr. Mario H. Burgos; ArgentinaFil: Sanchez Sanchez, Maria Victoria. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto de Medicina y Biología Experimental de Cuyo; ArgentinaFil: Mayorga, Luis Segundo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto de Histología y Embriología de Mendoza Dr. Mario H. Burgos. Universidad Nacional de Cuyo. Facultad de Ciencias Médicas. Instituto de Histología y Embriología de Mendoza Dr. Mario H. Burgos; ArgentinaFil: Sánchez, Cristián G.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Interdisciplinario de Ciencias Básicas. - Universidad Nacional de Cuyo. Instituto Interdisciplinario de Ciencias Básicas; Argentin
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