Charge localization in multiply charged clusters and their electrical properties: Some insights into electrospray droplets

The surface composition of charged Lennard-Jones clusters A$_N^{n+}$, composed of N particles (55 \leq N \leq 1169) among which n are positively charged with charge q, thus having a net total charge Q = nq, is investigated by Monte Carlo with Parallel Tempering simulations. At finite temperature, the surface sites of these charged clusters are found to be preferentially occupied by charged particles carrying large charges, due to Coulombic repulsions, but the full occupancy of surface sites is rarely achieved for clusters below the stability limit defined in this work. Large clusters (N = 1169) follow the same trends, with a smaller propensity for positive particles to occupy the cluster surface at non-zero temperature. We show that these charged clusters rather behave as electrical spherical conductors for the smaller sizes (N \leq 147) but as spheres uniformly charged in their volume for the larger sizes (N = 1169).Comment: 10 pages and 4 figure

Enhancement of electron spin lifetime in GaAs crystals: the benefits of dichotomous noise

The electron spin relaxation process in n-type GaAs crystals driven by a fluctuating electric field is investigated. Two different sources of fluctuations are considered: (i) a symmetric dichotomous noise and (ii) a Gaussian correlated noise. Monte Carlo numerical simulations show, in both cases, an enhancement of the spin relaxation time by increasing the amplitude of the external noise. Moreover, we find that the electron spin lifetime versus the noise correlation time: (i) increases up to a plateau in the case of dichotomous random fluctuations, and (ii) shows a nonmonotonic behaviour with a maximum in the case of bulks subjected to a Gaussian correlated noise.Comment: 6 pages, 3 figure

A Bayesian hidden Markov model for assessing the hot hand phenomenon in basketball shooting performance

Sports data analytics is a relevant topic in applied statistics that has been growing in importance in recent years. In basketball, a player or team has a hot hand when their performance during a match is better than expected or they are on a streak of making consecutive shots. This phenomenon has generated a great deal of controversy with detractors claiming its non-existence while other authors indicate its evidence. In this work, we present a Bayesian longitudinal hidden Markov model that analyses the hot hand phenomenon in consecutive basketball shots, each of which can be either missed or made. Two possible states (cold or hot) are assumed in the hidden Markov chains of events, and the probability of success for each throw is modelled by considering both the corresponding hidden state and the distance to the basket. This model is applied to a real data set, the Miami Heat team in the season 2005-2006 of the USA National Basketball Association. We show that this model is a powerful tool for assessing the overall performance of a team during a match or a season, and, in particular, for quantifying the magnitude of the team streaks in probabilistic terms

Quasi-classical simulations of resonance Raman spectra based on path integral linearization

Based on a linearization approximation coupled with path integral formalism, we propose a method derived from the propagation of quasi-classical trajectories to simulate resonance Raman spectra. This method is based on a ground state sampling followed by an ensemble of trajectories on the mean surface between the ground and excited states. The method was tested on three models and compared to quantum mechanics solution based on a sum-over-states approach: harmonic and anharmonic oscillators and the HOCl molecule (hypochlorous acid). The method proposed is able to correctly characterize resonance Raman scattering and enhancement, including the description of overtones and combination bands. The absorption spectrum is obtained at the same time and the vibrational fine structure can be reproduced for long excited state relaxation times. The method can be applied also to dissociating excited states (as is the case for HOCl)

La Educación Física escolar : Tres experiencias, encuentros y desencuentros

El presente trabajo es el resultado de los informes finales para la Cátedra de Práctica IV en el Instituto Provincial de Educación Física de Córdoba, realizados en los años 2008-2009. La misma proponía "estructurar las prácticas como un proyecto de investigación acción participante", definida como una "auto-objetivación, que lleva a modificar y a transformar las prácticas instituidas y naturalizadas. El objetivo es mirar las propias estrategias, los abordajes curriculares, el sujeto que aprende, haciendo un esfuerzo de distanciamiento y desnaturalización de lo que nos parece cotidiano y normal... el trabajo es un ir y venir de la teoría a la realidad y de la realidad a la teoría...el resultado esperado de la investigación es obtener cambios cualitativos en las prácticas educativas de los agentes educativos". En este congreso decidimos contar las experiencias que nos generó investigar nuestra propia práctica, la cual nos permitió descubrir cosas ignoradas en nosotras: el accionar y el discurso no coincidían con las intenciones y pensamientos sobre ella. De esta forma la propuesta se transformó en un desafío: por un lado la pretensión de poder comprender y problematizar qué EF queremos para la escuela y la necesidad de facilitarle aprendizajes a los estudiantes, por el otro. Surgieron errores, equivocaciones, afloraron intentos de cambios en el patio y con ello la oportunidad de volver a fallar y seguir intentando, nacieron más y más dudas, y con ellas la posibilidad de continuar aprendiend

On the formation of propylene oxide from propylene in space: gas-phase reactions

In the present article, we have investigated the possibility of forming propylene oxide (PO) from propylene (PE) by bi-molecular reactions. Propylene oxide is the first chiral molecule observed in the interstellar medium, and studying the thermodynamics and kinetics of formation can suggest possible synthetic routes. We have focused our attention on gas-phase reactions, and the presence of an environment is discussed in particular for the possibility of forming it by association reactions. In particular, we have considered radical and ion–molecule reactions. Results show that the main gas-phase route to PO formation is represented by ion–molecule reactions which turn out to be compatible with astrophysical conditions, notably: PE + O + and PE+HO2+. Their final product is not PO, but its ionized variant PO + that can be neutralized by electron capture. The only thermodynamically and kinetically allowed reaction which can directly lead to neutral PO is a collision of PE with a singlet-excited OH + but two competing reactions (leading to PE + and PO +) are thermodynamically favored and thus more plausible in space

Studying the Experience of Care Through Latent Class Analysis: An Application to Italian Neonatal Intensive Care Units

Though many data on the experience of care of patients and caregivers are collected, they are rarely used to improve the quality of health care delivery. One of the main causes is the widespread struggle in interpreting and enhancing these data, requiring the introduction of new techniques to extract intelligible, meaningful, and actionable information. This research explores the potentiality of the latent class analysis (LCA) statistical model in studying experience data. A cross-sectional survey was administered to 482 parents of infants hospitalized in several Italian neonatal intensive care units. Through a 3-step LCA, four subgroups of parents with specific experience profiles, sociodemographic characteristics, and levels of satisfaction were identified. These were composed of parents who reported (1) a positive experience (36%), (2) problematic communication with unit staff (30%), (3) limited access to the unit and poor participation in their baby's care (26%), and (4) a negative experience (8%). Through its explorative segmentation, LCA can provide valuable information to design quality improvement interventions tailored to the specific needs and concerns of each subgroup

Doping dependence of spin dynamics of drifting electrons in GaAs bulks

We study the effect of the impurity density on lifetimes and relaxation lengths of electron spins in the presence of a static electric field in an n-type GaAs bulk. The transport of electrons and the spin dynamics are simulated by using a semiclassical Monte Carlo approach, which takes into account the intravalley scattering mechanisms of warm electrons in the semiconductor material. Spin relaxation is considered through the D’yakonov–Perel mechanism, which is the dominant mechanism in III–V semiconductors. The evolution of spin polarization is analyzed by computing lifetimes and depolarization lengths as a function of the doping density in the range 10^{13} - 5*10^{16} cm^{-3}, for different values of the amplitude of the static electric field (0.1 - 1.0 kV/cm). We find an increase of the electron spin lifetime as a function of the doping density, more evident for lattice temperatures lower than 150 K. Moreover, at very low intensities of the driving field, the spin depolarization length shows a nonmonotonic behaviour with the density. At the room temperature, spin lifetimes and depolarization lengths are nearly independent on the doping density. The underlying physics is analyzed