FP-LAPW Study of the EFG at Impurity Sites in Oxides: Cd in Rutile TiO2

We report here first-principles determination of the electric-field gradient (EFG) tensor at the Cd impurity located at cation sites in rutile TiO2. As far as we know, these represent the first ab initio calculations at impurity sites with the FP-LAPW method in oxide systems. We used super-cells to simulate the diluted impurity in the crystal. The free-relaxation process performed in our study shows that the changes in distances of the oxygen nearest-neighbours to the impurity are not isotropic as was supposed in a previous study within the muffin-tin approximation. Our prediction for the EFG component of major absolute value agrees well with the experiment and is opposite in sign and direction if isotropic relaxations are assumed. Our value of the asymmetry parameter η also compares very well with the experimental value.Facultad de Ciencias Exacta

FP-LAPW Study of the EFG at Impurity Sites in Oxides: Cd in Rutile TiO2

We report here first-principles determination of the electric-field gradient (EFG) tensor at the Cd impurity located at cation sites in rutile TiO2. As far as we know, these represent the first ab initio calculations at impurity sites with the FP-LAPW method in oxide systems. We used super-cells to simulate the diluted impurity in the crystal. The free-relaxation process performed in our study shows that the changes in distances of the oxygen nearest-neighbours to the impurity are not isotropic as was supposed in a previous study within the muffin-tin approximation. Our prediction for the EFG component of major absolute value agrees well with the experiment and is opposite in sign and direction if isotropic relaxations are assumed. Our value of the asymmetry parameter η also compares very well with the experimental value.Facultad de Ciencias Exacta

Non-mandatory immunization and its potential impact on pertussis epidemiology

En este trabajo, se analizan cuantitativamente las consecuenciasa corto plazo que tendría sobre coqueluche la sanción delProyecto de Ley de Consentimiento Informado en Materiade Vacunación presentado en Argentina, en 2017, el cualcontempla la no obligatoriedad de la aplicación de las vacunasdel Calendario Nacional a los menores de edad. Se utilizaun modelo matemático para la transmisión de pertusis,desarrollado previamente en nuestro grupo. Se considera quela sola presentación del proyecto provoca una disminución enlas coberturas por generar desconfianza sobre los beneficiosdel programa de vacunación. Asumiendo 5 % anual dereducción de las coberturas durante 4 años a partir de 2018,en el siguiente brote, los casos graves en menores del año seincrementarían en más del 100 % respecto del último brote, yse estiman 101 fallecidos. Con una reducción del 10 % anualpor 4 años, el siguiente brote superaría al previo en más del200 %, con 163 decesos.Fil: Bergero, Paula Elena. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; ArgentinaFil: Fabricius, Gabriel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; ArgentinaFil: Hozbor, Daniela Flavia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Biotecnología y Biología Molecular. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Biotecnología y Biología Molecular; Argentin

SIR model on a dynamical network and the endemic state of an infectious disease

In this work we performed a numerical study of an epidemic model that mimics the endemic state of whooping cough in the pre-vaccine era. We considered a stochastic SIR model on dynamical networks that involve local and global contacts among individuals and analysed the influence of the network properties on the characterization of the quasi-stationary state. We computed probability density functions (PDF) for infected fraction of individuals and found that they are well fitted by gamma functions, excepted the tails of the distributions that are q-exponentials. We also computed the fluctuation power spectra of infective time series for different networks. We found that network effects can be partially absorbed by rescaling the rate of infective contacts of the model. An explicit relation between the effective transmission rate of the disease and the correlation of susceptible individuals with their infective nearest neighbours was obtained. This relation quantifies the known screening of infective individuals observed in these networks. We finally discuss the goodness and limitations of the SIR model with homogeneous mixing and parameters taken from epidemiological data to describe the dynamic behaviour observed in the networks studied.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

SIR model with local and global infective contacts: A deterministic approach and applications

An epidemic model with births and deaths is considered on a two-dimensional L × L lattice. Each individual can have global infective contacts according to the standard susceptible–infected–recovered (SIR) model rules or local infective contacts with their nearest neighbors. We propose a deterministic approach to this model and, for the parameters corresponding to pertussis and rubella in the prevaccine era, verify that there is a close agreement with the stochastic simulations when epidemic spread or endemic stationarity is considered. We also find that our approach captures the characteristic features of the dynamic behavior of the system after a sudden decrease in global contacts that may arise as a consequence of health care measures. By using the deterministic approach, we are able to characterize the exponential growth of the epidemic behavior and analyze the stability of the system at the stationary values. Since the deterministic approximation captures the essential features of the disease transmission dynamics of the stochastic model, it provides a useful tool for performing systematic studies as a function of the model parameters. We give an example of this potentiality by analyzing the likelihood of the endemic state to become extinct when the weight of the global contacts is drastically reduced.Facultad de Ciencias ExactasInstituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

Assessment of pertussis vaccination strategies using a mathematical model of disease transmission

La tos convulsa o coqueluche es una enfermedad respiratoria inmunoprevenible que ha resurgido en las últimas décadas. La mayor morbimortalidad se registra en los lactantes, aunque también se detectan casos en adolescentes y adultos. La situación epidemiológica de la enfermedad ha obligado a revisar e implementar nuevas estrategias para mejorar su control. Sin embargo, muchas de estas estrategias aún no cuentan con un sustento experimental que permita su universalización. En este contexto, los modelos matemáticos de transmisión de enfermedades resultan herramientas útiles en la toma de decisiones. En este trabajo se evaluó, mediante un modelo matemático para coqueluche, el impacto que tendrían distintas medidas de control en la población más vulnerable (0 a 1 año). En particular, se analizó el impacto de la inclusión de un refuerzo a los 11 años, el efecto de la mejora en las coberturas de las dosis primarias y la disminución del retraso en la aplicación de estas. También se estimó el efecto de la vacunación a embarazadas. Los resultados muestran que la inclusión de un refuerzo a los 11 años disminuye un 3% la incidencia en los menores de 1 año. Por su parte, la aplicación de las dosis primarias a tiempo calendario (sin retrasos) la reduce un 16%. Al aumentar la cobertura del 80% al 95%, la incidencia en la población vulnerable se reduce signifcativamente (38%). Cuando el porcentaje de las embarazadas inmunizadas alcanza el 50%, la reducción de los casos más graves en los infantes superaría el 43% (0 - 2 meses).Fil: Pesco, Pablo Sebastián. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; ArgentinaFil: Bergero, Paula Elena. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; ArgentinaFil: Fabricius, Gabriel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; ArgentinaFil: Hozbor, Daniela Flavia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico La Plata. Instituto de Biotecnología y Biología Molecular; Argentin

Immunity acquired by a minority active fraction of the population could explain COVID-19 spread in Greater Buenos Aires (June-November 2020)

The coronavirus disease 2019 (COVID-19) pandemic had an uneven development in different countries. In Argentina, the pandemic began in March 2020 and, during the first 3 months, the vast majority of cases were concentrated in a densely populated region that includes the city of Buenos Aires (country capital) and the Greater Buenos Aires (GBA) area that surrounds it. This work focuses on the spread of COVID-19 between June and November 2020 in GBA. Within this period of time there was no vaccine, basically only the early wild strain of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) was present, and the official restriction and distancing measures in this region remained more or less constant. Under these particular conditions, the incidences show a sharp rise from June 2020 and begin to decrease towards the end of August until the end of November 2020. In this work we study, through mathematical modelling and available epidemiological information, the spread of COVID-19 in this region and period of time. We show that a coherent explanation of the evolution of incidences can be obtained assuming that only a minority fraction of the population got involved in the spread process, so that the incidences decreased as this group of people was becoming immune. The observed evolution of the incidences could then be a consequence at the population level of lasting immunity conferred by SARS-CoV-2.Fil: Fabricius, Gabriel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; ArgentinaFil: Borzi, Rodolfo Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Física de Líquidos y Sistemas Biológicos. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Física de Líquidos y Sistemas Biológicos; ArgentinaFil: Caminos, José María. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Física de Líquidos y Sistemas Biológicos. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Física de Líquidos y Sistemas Biológicos; ArgentinaFil: Grigera, Tomas Sebastian. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Física de Líquidos y Sistemas Biológicos. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Física de Líquidos y Sistemas Biológicos; Argentin

Distance between inherent structures and the influence of saddles on approaching the mode coupling transition in a simple glass former

We analyze through molecular dynamics simulations of a Lennard-Jones (LJ) binary mixture the statistics of the distances between inherent structures sampled at temperatures above the mode coupling transition temperature TMCT. After equilibrating at T>TMCT we take equilibrated configurations and randomly perturb the coordinates of a given number of particles. After that we find the nearby inherent structures (IS) of both the original and perturbed configurations and evaluate the distance between them. This distance presents an inflection point at Tli approximately 1 with a strong decrease below this temperature which goes to a small but nonzero value on approaching TMCT. In the low-temperature region we study the statistics of events which give zero distance, i.e., dominated by minima, and find evidence that the number of saddles decreases exponentially near TMCT. This implies that saddles continue to exist even at TMCT. As at TMCT the diffusivity goes to zero, our results imply that there are saddles associated with nondiffusive events at TMCT.Departamento de Físic