First-passage times in complex scale-invariant media.

How long does it take a random walker to reach a given target point? This quantity, known as a first-passage time (FPT), has led to a growing number of theoretical investigations over the past decade. The importance of FPTs originates from the crucial role played by first encounter properties in various real situations, including transport in disordered media, neuron firing dynamics, spreading of diseases or target search processes. Most methods of determining FPT properties in confining domains have been limited to effectively one-dimensional geometries, or to higher spatial dimensions only in homogeneous media. Here we develop a general theory that allows accurate evaluation of the mean FPT in complex media. Our analytical approach provides a universal scaling dependence of the mean FPT on both the volume of the confining domain and the source-target distance. The analysis is applicable to a broad range of stochastic processes characterized by length-scale-invariant properties. Our theoretical predictions are confirmed by numerical simulations for several representative models of disordered media, fractals, anomalous diffusion and scale-free networks.

Probing microscopic origins of confined subdiffusion by first-passage observables.

Subdiffusive motion of tracer particles in complex crowded environments, such as biological cells, has been shown to be widespread. This deviation from Brownian motion is usually characterized by a sublinear time dependence of the mean square displacement (MSD). However, subdiffusive behavior can stem from different microscopic scenarios that cannot be identified solely by the MSD data. In this article we present a theoretical framework that permits the analytical calculation of first-passage observables (mean first-passage times, splitting probabilities, and occupation times distributions) in disordered media in any dimensions. This analysis is applied to two representative microscopic models of subdiffusion: continuous-time random walks with heavy tailed waiting times and diffusion on fractals. Our results show that first-passage observables provide tools to unambiguously discriminate between the two possible microscopic scenarios of subdiffusion. Moreover, we suggest experiments based on first-passage observables that could help in determining the origin of subdiffusion in complex media, such as living cells, and discuss the implications of anomalous transport to reaction kinetics in cells.

Recommendations for the evaluation and management of the anticipated and non-anticipated difficult airway of the Societat Catalana d'Anestesiologia, Reanimació i Terapèutica del Dolor, based on the adaptation of clinical practice guidelines and expert consensus. / Recomendaciones para la evaluación y manejo de la vía aérea difícil prevista y no prevista de la Societat Catalana d'Anestesiologia, Reanimació i Terapèutica del Dolor, basadas en la adaptación de guías de práctica clínica y consenso de expertos.

The Airway Division of the Catalan Society of Anaesthesiology, Intensive Care and Pain Management (SCARTD) presents its latest guidelines for the evaluation and management of the difficult airway. This update includes the technical advances and changes observed in clinical practice since publication of the first edition of the guidelines in 2008. The recommendations were defined by a consensus of experts from the 19 participating hospitals, and were adapted from 5 recently published international guidelines following an in-depth analysis and systematic comparison of their recommendations. The final document was sent to the members of SCARTD for evaluation, and was reviewed by 11 independent experts. The recommendations, therefore, are supported by the latest scientific evidence and endorsed by professionals in the field. This edition develops the definition of the difficult airway, including all airway management techniques, and places emphasis on evaluating and classifying the airway into 3 categories according to the anticipated degree of difficulty and additional safety considerations in order to plan the management strategy. Pre-management planning, in terms of preparing patients and resources and optimising communication and interaction between all professionals involved, plays a pivotal role in all the scenarios addressed. The guidelines reflect the increased presence of video laryngoscopes and second-generation devices in our setting, and promotes their routine use in intubation and their prompt use in cases of unanticipated difficult airway. They also address the increased use of ultrasound imaging as an aid to evaluation and decision-making. New scenarios have also been included, such as the risk of bronchoaspiration and difficult extubation Finally, the document outlines the training and continuing professional development programmes required to guarantee effective and safe implementation of the guidelines.

Occupation times of random walks in confined geometries: from random trap model to diffusion-limited reactions.

We consider a random walk in confined geometry, starting from a site and eventually reaching a target site. We calculate analytically the distribution of the occupation time on a third site, before reaching the target site. The obtained distribution is exact and completely explicit in the case or parallelepipedic confining domains. We discuss implications of these results in two different fields: The mean first passage time for the random trap model is computed in dimensions greater than 1 and is shown to display a nontrivial dependence with the source and target positions. The probability of reaction with a given imperfect center before being trapped by another one is also explicitly calculated, revealing a complex dependence both in geometrical and chemical parameters.

Close or connected: distance and connectivity effects on transport in networks.

We develop an analytical approach that provides the dependence of the mean first-passage time (MFPT) for random walks on complex networks both on the target connectivity and on the source-target distance. Our approach puts forward two strongly different behaviors depending on the type-compact or non compact-of the random walk. In the case of non compact exploration, we show that the MFPT scales linearly with the inverse connectivity of the target and is largely independent of the starting point. On the contrary, in the compact case, the MFPT is controlled by the source-target distance, and we find that unexpectedly the target connectivity becomes irrelevant for remote targets.

Global mean first-passage times of random walks on complex networks.

We present a general framework, applicable to a broad class of random walks on complex networks, which provides a rigorous lower bound for the mean first-passage time of a random walker to a target site averaged over its starting position, the so-called global mean first-passage time (GMFPT). This bound is simply expressed in terms of the equilibrium distribution at the target and implies a minimal scaling of the GMFPT with the network size. We show that this minimal scaling, which can be arbitrarily slow, is realized under the simple condition that the random walk is transient at the target site and independently of the small-world, scale-free, or fractal properties of the network. Last, we put forward that the GMFPT to a specific target is not a representative property of the network since the target averaged GMFPT satisfies much more restrictive bounds.

Zero constant formula for first-passage observables in bounded domains.

In this Letter, we develop an analytical approach which provides an explicit determination of mean first-passage times (MFPTs) for random walks in bounded domains for a wide class of transport processes. In particular, we derive for the first time explicit expressions of MFPTs for emblematic models of transport in complex media, such as diffusion on deterministic and random fractals. This approach relies on a scale-invariance hypothesis and a large volume expansion of the MFPT, which actually proves to be very accurate even for small system sizes as shown by numerical simulations. This explicit determination of MFPTs can be straightforwardly generalized to further useful first-passage observables such as occupation times and splitting probabilities.

Modificación de las reservas orgánicas secundaria a sugerencias alimentarias en alumnos de la Licenciatura en Nutrición de la UBA / Changes in organic reserves following food suggestions in students of nutrition (bachelor) from the university of Bs. As

Introducción: La valoración del estado nutricional como indicador de salud, permite la identificación de grupos de riesgo, ya sea por déficit o exceso de la reservas, aceptándose que dichos factores aumentan la morbimortalidad por enfermedades asociadas. Esta realidad no es ajena a la población universitaria. En Estados Unidos, el sobrepeso y la obesidad resultan frecuentes, asociados a una historia familiar de obesidad, mientras que en nuestro ámbito el sobrepeso y la obesidad no superan el 12%. Una investigación realizada en la carrera de Licenciatura en Nutrición de la Universidad de Buenos Aires en el año 2005 evidenció una alta incidencia de reservas proteicas disminuidas (31%). Objetivo: Valorar las modificaciones logradas en las reservas orgánicas secundarias a sugerencias alimentarias. Material y Métodos: Del total de alumnos valorados (n=120), fueron seleccionados aquellos con reserva proteica (RP) disminuida (n=60) y con reserva calórica (RC) aumentada (n=14). Para la valoración de dichas reservas se aplicó el Método de Fraccionamiento Antropométrico propuesto por Drinkwater y Ross. Se procedió a sugerir una terapia nutricional para la corrección de la alteración encontrada. Al año se valoraron ambas reservas nuevamente. Los resultados mostraron diferencias significativas (p=0.0155; α=0.05) entre la primera medición de RP (2.00 ± 0.12) y la siguiente (2.05 ± 0.19). En relación a la RC se observaron diferencias significativas (p=0.030; α=0.05) entre la primera medición (1.83 ± 0.40) y la siguiente (1.61 ± 0.44). Conclusiones: La incidencia de sobrepeso y obesidad fue de 11.6%. Luego de las sugerencias alimentarias el 64.2% disminuyó dicha reserva, obteniendo un diagnóstico de normalidad. Sin embargo, cabe señalar la alta incidencia de alumnos que presentaron RP disminuidas (50% del total medido). De ellos, agravaron la desnutrición el 30% en el período de estudio, a pesar de las pautas alimentarias sugeridas.

Informe especial: Coberturas de vacunación en residentes de la CABA en contexto Covid-19: 2 de octubre de 2020 / Special report: Vaccination coverage in CABA residents in context of Covid19

La vacunación es considerada una actividad esencial durante la pandemia de COVID-19 y se han desarrollado diferentes estrategias para el sostenimiento de la vacunación en el contexto actual, facilitar el acceso a través de la adaptación y reorganización de los servicios de salud, el no requerimiento de permisos de circulación para la vacunación, vacunación en instituciones fuera de salud, así como la elaboración de recomendaciones para realizar la vacunación de manera segura protegiendo tanto al vacunador como la persona a vacunar, entre otros. Con el objetivo de realizar la medición del impacto en las actividades de vacunación, se realiza el análisis comparativo de las vacunas aplicadas durante el primer semestre de los años 2018-2020, con la información recibida en el nivel central del Programa de Inmunizaciones. Se excluye del presente análisis la información referida a la vacuna antigripal ya que tiene una modalidad diferente de aplicación. (AU)

El fraccionamiento antropométrico en estudios poblacionales / Anthropometric fractioning in populational studies

Este estudio fue realizado con el objeto de determinar las posibilidades operativas del método de fraccionamiento en comparación con la antropometría clásica como es el peso, la talla, circunferencia muscular del brazo, pliegue tricipital y BMI a nivel poblacional