Configurational lattice dynamics: The phase diagram of Rh − Pd

Free energies of Rh-Pd alloys as functions of both temperature and composition are calculated using quasiharmonic lattice dynamics. The free energy of the disordered solid is determined from an ensemble of a large number of randomly generated configurations. Both configurational and vibrational contributions to the entropy and enthalpy of mixing are taken into account. We study the convergence with the number of random configurations, and analyze the validity of the zero static internal stress approximation ZSISA, where only external strains are relaxed fully dynamically while internal stresses are relaxed in the static approximation. It is shown that the use of ZSISA allows an accurate calculation of free energies in a fraction of the time needed to carry out fully dynamic optimizations. From the values of free energies as functions of composition and temperature the phase diagram of Rh-Pd alloys is calculated, showing a good agreement with Monte Carlo simulations as well as with experiment. It is also shown that although free energies of mixing appear to be linear functions of temperature to a good approximation, the explicit expressions given by the configurational lattice dynamics method show that both enthalpies and entropies of mixing change appreciably with temperature.Fil: Cienfuegos, Clarisa. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de la Patagonia "San Juan Bosco"; ArgentinaFil: Isoardi, E. P.. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Química Inorgánica, Analítica y Química Física; ArgentinaFil: Barrera, Gustavo Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de la Patagonia "San Juan Bosco"; Argentin

The stoichiometry of P2X2/6 receptor heteromers depends on relative subunit expression levels

Fast synaptic transmission involves the operation of ionotropic receptors, which are often composed of at least two types of subunit. We have developed a method, based on atomic force microscopy imaging to determine the stoichiometry and subunit arrangement within ionotropic receptors. We showed recently that the P2X(2) receptor for ATP is expressed as a trimer but that the P2X(6) subunit is unable to oligomerize. In this study we addressed the subunit stoichiometry of heteromers containing both P2X(2) and P2X(6) subunits. We transfected tsA 201 cells with both P2X(2) and P2X(6) subunits, bearing different epitope tags. We manipulated the transfection conditions so that either P2X(2) or P2X(6) was the predominant subunit expressed. By atomic force microscopy imaging of isolated receptors decorated with antiepitope antibodies, we demonstrate that when expression of the P2X(2) subunit predominates, the receptors contain primarily 2 x P2X(2) subunits and 1 x P2X(6) subunit. In contrast, when the P2X(6) subunit predominates, the subunit stoichiometry of the receptors is reversed. Our results show that the composition of P2X receptor heteromers is plastic and dependent on the relative subunit expression levels. We suggest that this property of receptor assembly might introduce an additional layer of subtlety into P2X receptor signaling

Dipolar interactions among magnetite nanoparticles for magnetic hyperthermia: a rate-equation approach

Rate equations are used to study the dynamic magnetic properties of interacting magnetite nanoparticles viewed as double well systems (DWS) subjected to a driving field in the radio-frequency range. Dipole-dipole interaction among particles is modeled by inserting an ad-hoc term in the energy barrier to simulate the dependence of the interaction on both the interparticle distance and degree of dipole collinearity. The effective magnetic power released by an assembly of interacting nanoparticles dispersed in a diamagnetic host is shown to be a complex function of nanoparticle diameter, mean particle interdistance and frequency. Dipolar interaction markedly modifies the way a host material is heated by an assembly of embedded nanoparticles in magnetic hyperthermia treatments. Nanoparticle fraction and strength of the interaction can dramatically influence the amplitude and shape of the heating curves of the host material; the heating ability of interacting nanoparticles is shown to be either improved or reduced by their concentration in the host material. A frequency-dependent cut-off length of dipolar interactions is determined and explained. Particle polydispersity entailing a distribution of particle sizes brings about non-trivial effects on the heating curves depending on the strength of dipolar interaction

Specific loss power of magnetic nanoparticles: A machine learning approach

A machine learning approach has been applied to the prediction of magnetic hysteresis properties (coercive field, magnetic remanence, and hysteresis loop area) of magnetic nanoparticles for hyperthermia applications. Trained on a dataset compiled from numerical simulations, a neural network and a random forest were used to predict power losses of nanoparticles as a function of their intrinsic properties (saturation, anisotropy, and size) and mutual magnetic interactions, as well as of application conditions (temperature, frequency, and applied field magnitude), for values of the parameters not represented in the database. The predictive ability of the studied machine learning approaches can provide a valuable tool toward the application of magnetic hyperthermia as a precision medicine therapy tailored to the patient's needs. (C) 2022 Author(s)

Entropy-driven cutoff phenomena

In this paper we present, in the context of Diaconis' paradigm, a general method to detect the cutoff phenomenon. We use this method to prove cutoff in a variety of models, some already known and others not yet appeared in literature, including a chain which is non-reversible w.r.t. its stationary measure. All the given examples clearly indicate that a drift towards the opportune quantiles of the stationary measure could be held responsible for this phenomenon. In the case of birth- and-death chains this mechanism is fairly well understood; our work is an effort to generalize this picture to more general systems, such as systems having stationary measure spread over the whole state space or systems in which the study of the cutoff may not be reduced to a one-dimensional problem. In those situations the drift may be looked for by means of a suitable partitioning of the state space into classes; using a statistical mechanics language it is then possible to set up a kind of energy-entropy competition between the weight and the size of the classes. Under the lens of this partitioning one can focus the mentioned drift and prove cutoff with relative ease.Comment: 40 pages, 1 figur

A new functional for improving cell area distribution

In this work we present a new area functional that help us improve the cell area distribution in structured grids over plane irregular regions, which avoids very small and very large cell areas as much as possible. We present some results and an implementation of this functional in a preliminary version of the latest UNAMalla system

Assessment of the splitting-tensile strength of ZP-306 steel fiber reinforced concrete

El concreto reforzado con fibras de acero (CRFA) es un material con gran potencial de uso en viviendas de concreto de baja altura, ya que la capacidad de resistencia de los muros está controlada por la resistencia a tensión diagonal. El artículo presenta los resultados de un estudio experimental para caracterizar la resistencia a tensión por compresión diametral del CRFA que es elaborado con fibra ZP-306 y con concretos locales. El programa experimental incluyó el ensayo de 52 especímenes en forma de cilindros. En el estudio se discuten los modelos de predicción disponibles y se realiza un análisis estadístico para comparar los resultados calculados con los datos medidos. Con base en las tendencias de los resultados experimentales, se proponen ecuaciones para estimar los parámetros que describen la envolvente del comportamiento esfuerzo-deformación del CRFA sometido a esfuerzos de compresión diametral. Las ecuaciones se han desarrollado en un formato versátil para ser incluidas en un reglamento de diseño. Abstract Steel fibers reinforced concrete (SFRC) is a material with great potential to be used in low-rise concrete housing because the strength capacity of the walls is controlled by diagonal tension strength. The paper shows the results of an experimental study intended to characterize splitting-tensile strength of SFRC made of both ZP-306 fiber and local concrete. The experimental program included the tests of 52 cylindrical-shaped specimens. The study discusses the available predictive models and shows a statistical analysis to compare the predicted results with measured data. Based on trends of the experimental results, equations to estimate the parameters describing the backbone of the stress-strain behavior of SFRC under splitting-tensile strength are proposed. The equations have been developed in a versatile format to be included in a design code

Area metropolitana e citta' diffusa: potenzialita' e limiti di un modello urbano

Recenti proposte parlamentari porpongono di mettere fine ad una discussione sulla città e/o area metropolitana di Roma, confermandone: • una dimensione d’area vasta coincidente con quella della provincia; • la sussidiarietà e la sostenibilità come principi ispiratori ed ordinatori dell’azione di governo del territorio; • le funzioni unitarie e complementari di livello territoriale (programmazione degli interventi per Roma Capitale, le opere di interesse statale, il patrimonio pubblico e privato nazionale ed internazionale, la valorizzazione e la gestione del sistema culturale, ambientale e del turismo, la ricerca e la formazione universitaria, le attività fieristico-congressuali-espositive, l’industria innovativa legata all’ICS); collocando la questione della scelta metropolitana per Roma ad un livello europeo, eppure intermedio tra la scala politica propria della città-capitale e i compiti di programmazione e gestione che il nostro ordinamento costituzionale attribuisce alle province (per l’Europa, le NUT 3). Rispetto a questo obiettivo, Roma non appare in posizione soddisfacente nella mappatura europea delle aree/città capitali metropolitane. Anche se, la spinta al policentrismo impressa dall’Unione potrebbe trovare già una base di corrispondenze nell’organizzazione – soprattutto spontanea - del territorio e dell’economia romana (non solo della Città). Se per un verso, dunque, c’è da augurarsi che attraverso un più stretto recepimento delle indicazioni europee (Cfr. strutture già cooperative su base policentrica), l’area vasta romana, cioè la provincia, diventi nel prossimo periodo 2007-2013 molto più visibile; la mancanza di strumenti appropriati al raggiungimento di questo obiettivo rappresenta un freno alla piena realizzazione di una metropoli diversa dalla semplice somma di progetti ed impostazioni negoziati “dall’alto”, di portata nazionale e regionale, che escludono, ad una lettura “fisica e formale” del territorio, la domanda di integrazione “dal basso”, cioè il riconoscimento, anche economico, delle forme insediative coese riconoscibili romane. In tal senso Roma e la sua provincia rappresentano il livello ideale per una lettura della programmazione territoriale europea, ma anche il livello sussidiario della mediazione tra una visione metropoitana globale e una locale, somma di insediamenti continui, diffusi o nucleari isolati (perirubanizzazione mista ad insediamento puntuale), attualmente privi di orientamento alla governance; lontani cioè da quell’insieme di regole con cui si attua la programmazione spaziale e fisica richiesta dall’Unione, entro cui ogni NUT offre il proprio contributo alla creazione di uno spazio integrato, anche attraverso scelte sussidiarie di metropolitanizzazione (cfr. Territorial Agenda 2007)