Elastic scattering of electrons by water: An ab initio study

In this work we devise a theoretical and computational method to compute the elastic scattering of electrons from a non-spherical potential, such as in the case of molecules and molecular aggregates. Its main feature is represented by the ability of calculating accurate wave functions for continuum states of polycentric systems via the solution of the Lippmann-Schwinger equation, including both the correlation effects and multi-scattering interference terms, typically neglected in widely used approaches, such as the Mott theory. Within this framework, we calculate the purely elastic scattering matrix elements. As a test case, we apply our scheme to the modelling of electron-water elastic scattering. The Dirac-Hartree-Fock self-consistent field method is used to determine the non-spherical molecular potential projected on a functional space spanned by Gaussian basis set. By adding a number of multi-centric radially-arranged s-type Gaussian functions, whose exponents are system-dependent and optimized to reproduce the properties of the continuum electron wave function in different energy regions, we are able to achieve unprecedented access to the description of the low energy range of the spectrum (0.001 < E < 10 eV) up to keV, finding a good agreement with experimental data and previous theoretical results. To show the potential of our approach, we also compute the total elastic scattering cross section of electrons impinging on clusters of water molecules and zundel cation. Our method can be extended to deal with inelastic scattering events and heavy-charged particle

Aplicación de indicadores cuali-cuantitativos para evaluar un programa de admisión a la educación superior

Las altas tasas de deserción observadas en los primeros años de la educación superior, podrían tener su origen en buena medida en dificultades de estudio generadas por insuficiencias en los conocimientos y capacidades adquiridas en las instancias educativas anteriores. Esto ha llevado a que buena parte de las instituciones implementen programas de admisión que, a través de cursos de nivelación, pretenden facilitar la inserción de los alumnos en la etapa universitaria. Sin embargo, si la proporción de alumnos ingresantes que no logran superarlos convenientemente es alta, dichos programas pueden llegar a entenderse como un obstáculo para el acceso a la educación superior. Las causas del mal desempeño de los ingresantes pueden ser diversas y no debe descartarse que entre ellas se encuentre un mal diseño de los cursos de nivelación. Los indicadores que en este trabajo se aplicarán intentarán por un lado cuantificar los resultados del programa a través del desempeño de los alumnos en el mismo, y por otro analizar cualitativamente, a través de la opinión de los alumnos, en que medida los cursos implementados cumplen con los objetivos del programa

Una nueva datación radiocarbónica en la Argentina y la primera para la arqueología de la provincia del Chaco

Entre otros imperativos, uno ineludible para el arqueólogo es determinar la cronología de sus hallazgos y entre los recursos que dispone, el fechaje por el método del carbono 14 ha resultado un auxiliar de extraordinaria jerarquía y su aplicación trascendente ha marcado un jalón inicial de nuevos logros, cada vez más ajustados. Ello no implica aceptar que los problemas cronológicos de la arqueología tengan en la datación radio carbónica su panacea para resolverlos, pero es indudable que, correctamente manejado y cohesionado con otros tipos de informaciones, propias y emergentes de la tarea arqueológica, sus resultados sean en algunos casos significativamente aproximados y en otros cercanos a lo que podríamos calificar de sorprendentes. Su aplicación, que en nuestro país se inicia alrededor del año 1952, debida en gran parte a la iniciativa del doctor Alberto Rex González, destacado investigador en esta ardua y difícil disciplina como es la arqueología y quien ha realizado y propiciado numerosos fechados radio-carbónicos, mostró una nueva realidad para la Prehistoria Argentina y muchos de los esquemas culturales clásicos debieron ser substancialmente modificados. Al pensar y evaluar que este recurso geocronológico no es infalible pero sí que debe ser utilizado en las investigaciones arqueológicas, consideramos impostergable fechar material exhumado de las Ruinas de Km. 75, sitio ubicado en la Provincia del Chaco, Argentina, tareas en estado de investigación, iniciadas concretamente a mediados de 1967, a cargo de la Sección Antropología, bajo nuestra dirección, del Instituto de Historia de la Facultad de Humanidades de la Universidad Nacional del Nordeste. Consecuentemente, requerimos al doctor Harold W. Krueger, Director Técnico del Geochron Laboratories de USA, uno de los institutos privados de mayor prestigio, especializado en estas mediciones radiométricas, la datación de una muestra consistente en pedazos de carbón vegetal, exhumada del yacimiento aludido. La responsabilidad y seriedad científica del instituto requerido para procesar el análisis, el hecho de contener la muestra la substancia más adecuada, por su alto contenido de carbón, para este tipo de trabajo y haberse arbitrado todos los recaudos exigidos para la extracción y envío del material anticipaban, según nuestra opinión, un resultado probablemente útil para la hipótesis de trabajo que supone que las Ruinas de Km. 75 son los vestigios dejados por la ciudad de Concepción del Bermejo, fundada por Alonso de Vera y Aragón en el año 1585 y abandonada entre 1631-32. Esta ciudad, tuvo un breve tiempo de vida, pero su localización en el sitio significaría un aporte extraordinario, jerárquico y trascendente para la historia en el período hispánico en la Argentina y más aún, para el área del nordeste, poco conocido y trajinado, en este tipo particular de investigaciones. Breve advertencia la que antecede que nos permitirá introducirnos en la motivación esencial de esta noticia, cuyo objetivo consiste en: difundir el resultado del fechaje; ensayar un intento interpretativo de la edad radiocarbónica, sin olvidar sus limitaciones; manejar su utilización junto a otras evidencias, en cuanto pueda servir a la identificación histórica de las Ruinas de Km. 75 y apreciar el valor computativo de este fechado para la Arqueologia Argentina y Regional.Facultad de Humanidades y Ciencias de la Educació

Symmetry-Breaking Phase Transition without Peierls Mechanism in Conducting Monoatomic Chains

The one-dimensional (1D) model system Au/Ge(001), consisting of linear chains of single atoms on a surface, is scrutinized for lattice instabilities predicted in the Peierls paradigm. By scanning tunneling microscopy and electron diffraction we reveal a second-order phase transition at 585 K. It leads to charge ordering with transversal and vertical displacements and complex interchain correlations. However, the structural phase transition is not accompanied by the electronic signatures of a charge density wave, thus precluding a Peierls instability as origin. Instead, this symmetry-breaking transition exhibits three-dimensional critical behavior. This reflects a dichotomy between the decoupled 1D electron system and the structural elements that interact via the substrate. Such substrate-mediated coupling between the wires thus appears to have been underestimated also in related chain systems.Comment: 5 pages, 4 figures, accepted at Physical Review Letters 09/201

High-performance versatile setup for simultaneous Brillouin-Raman micro-spectroscopy

This is the author accepted manuscript. The final version is available from American Physical Society via the DOI in this record.Brillouin and Raman scattering spectroscopy are established techniques for the nondestructive contactless and label-free readout of mechanical, chemical and structural properties of condensed matter. Brillouin-Raman investigations currently require separate measurements and a site-matched approach to obtain complementary information from a sample. Here we demonstrate a new concept of fully scanning multimodal micro-spectroscopy for simultaneous detection of Brillouin and Raman light scattering in an exceptionally wide spectral range, from fractions of GHz to hundreds of THz. It yields an unprecedented 150 dB contrast, which is especially important for the analysis of opaque or turbid media such as biomedical samples, and spatial resolution on a sub-cellular scale. We report the first applications of this new multimodal method to a range of systems, from a single cell to the fast reaction kinetics of a curing process, and the mechano-chemical mapping of highly scattering biological samples.S. Corezzi acknowledges financial support from MIUR-PRIN (Project No. 2012J8X57P). S. Caponi acknowledges support from PAT (Provincia Autonoma di Trento) (GP/PAT/2012) “Grandi Progetti 2012” Project “MaDEleNA.” P. S., A. M., M. P. acknowledge financial support from Centro Nazionale Trapianti (Project: “Studio di cellule per uso clinico umano, con particolare riferimento a modelli cellulari (liposomi) e linee cellulari in interazione con crioconservanti e con materiali biocompatibili”). L. C. and S. Caponi acknowledge financial support from Consiglio Nazionale delle Ricerche-Istituto Officina dei Materiali. F. P. acnowledges support from the UK Engineering and Physical Sciences Research Council (Grant No. EP/M028739/1 (F. P.)). The authors acknowledge Jacopo Scarponi for valuable help in setting up the hardware and software system for simultaneous Raman and BLS measurements

Monte Carlo simulations of measured electron energy-loss spectra of diamond and graphite: Role of dielectric-response models

N.M.P. is supported by the European Research Council PoC 2015 ”Silkene” No. 693670, by the European Commission H2020 under the Graphene Flagship Core 1 No. 696656 (WP14 ”Polymer Nanocomposites”) and under the FET Proactive ”Neurofibres” No. 732344. M.D., G.G., and S.T acknowledge funding from the Graphene Flagship (WP14 “Polymer composites”, no. 696656). This work used the ARCHER UK National Supercomputing Service (http://www.archer.ac.uk). Access to computing and storage facilities owned by parties and projects contributing to the National Grid Infrastructure MetaCentrum provided under the programme ”Projects of Large Research, Development, and Innovations Infrastructures” (CESNET LM2015042), is greatly appreciated (https://www.metacentrum.cz/en/). Furthermore, we acknowledge FBK for providing unlimited access to the KORE computing facility

Anisotropic Approach for Simulating Electron Transport in Layered Materials: Computational and Experimental Study of Highly Oriented Pyrolitic Graphite

In this work, we propose a theoretical and computational model for taking into account the anisotropic structure of Highly Oriented Pyrolitic Graphite (HOPG) in the Monte Carlo simulations of charge transport. In particular, the dielectric characteristics, such as the inelastic mean free path and energy losses, are treated by linearly combining the contributions to these observables along the two main orthogonal directions identifying the layered crystalline structure of HOPG (along the layer plane and perpendicular to it). Energy losses are evaluated from ab initio calculations of the dielectric function of the system along these two perpendicular directions. Monte Carlo simulated spectra, obtained with our anisotropic approach, are compared with acquired experimental data of Reflection Electron Energy Loss and Secondary Electron spectra, showing a good agreement. These findings validate the idea of the importance of considering properly-weighted inter-planar and intra-planar interactions in the simulation of electron transport in layered materials

A novel combined experimental and multiscale theoretical approach to unravel the structure of SiC/SiOx core/shell nanowires for their optimal design

In this work we propose a realistic model of nanometer-thick SiC/SiOxcore/shell nanowires (NWs) using a combined first-principles and experimental approach. SiC/SiOxcore/shell NWs were first synthesised by a low-cost carbothermal method and their chemical-physical experimental analysis was accomplished by recording X-ray absorption near-edge spectra. In particular, the K-edge absorption lineshapes of C, O, and Si are used to validate our computational model of the SiC/SiOxcore/shell NW architectures, obtained by a multiscale approach, including molecular dynamics, tight-binding and density functional simulations. Moreover, we present ab initio calculations of the electronic structure of hydrogenated SiC and SiC/SiOxcore/shell NWs, studying the modification induced by several different substitutional defects and impurities into both the surface and the interfacial region between the SiC core and the SiOxshell. We find that on the one hand the electron quantum confinement results in a broadening of the band gap, while hydroxyl surface terminations decrease it. This computational investigation shows that our model of SiC/SiOxcore/shell NWs is capable to deliver an accurate interpretation of the recorded X-ray absorption near-edge spectra and proves to be a valuable tool towards the optimal design and application of these nanosystems in actual devices

Effect of DMSO on the mechanical and structural properties of model and biological membranes

This is the final version. Available from Elsevier via the DOI in this recordDimethyl sulfoxide (DMSO) is widely used in a number of biological and biotechnological applications, mainly because of its effects on the cell plasma membrane, but the molecular origins of this action are yet to be fully clarified. In this work, we used two- and three-component synthetic membranes (liposomes) and the plasma membrane of human erythrocytes to investigate the effect of DMSO when added to the membrane-solvating environment. Fourier transform infrared spectroscopy and thermal fluctuation spectroscopy revealed significant differences in the response of the two types of liposome systems to DMSO in terms of the bilayer thermotropic behavior, available free volume of the bilayer, its excess surface area, and bending elasticity. DMSO also alters the mechanical properties of the erythrocyte membrane in a concentration-dependent manner and is capable of increasing membrane permeability to ATP at even relatively low concentrations (3% v/v and above). Taken in its entirety, these results show that DMSO is likely to have a differential effect on heterogeneous biological membranes, depending on their local composition and structure, and could affect membrane-hosted biological functions.Engineering and Physical Sciences Research Council (EPSRC

Insight into Elderly ALS Patients in the Emilia Romagna Region: Epidemiological and Clinical Features of Late-Onset ALS in a Prospective, Population-Based Study

Few studies have focused on elderly (>80 years) amyotrophic lateral sclerosis (ALS) patients, who represent a fragile subgroup generally not included in clinical trials and often neglected because they are more difficult to diagnose and manage. We analyzed the clinical and genetic features of very late-onset ALS patients through a prospective, population-based study in the Emilia Romagna Region of Italy. From 2009 to 2019, 222 (13.76%) out of 1613 patients in incident cases were over 80 years old at diagnosis, with a female predominance (F:M = 1.18). Elderly ALS patients represented 12.02% of patients before 2015 and 15.91% from 2015 onwards (p = 0.024). This group presented with bulbar onset in 38.29% of cases and had worse clinical conditions at diagnosis compared to younger patients, with a lower average BMI (23.12 vs. 24.57 Kg/m2), a higher progression rate (1.43 vs. 0.95 points/month), and a shorter length of survival (a median of 20.77 vs. 36 months). For this subgroup, genetic analyses have seldom been carried out (25% vs. 39.11%) and are generally negative. Finally, elderly patients underwent less frequent nutritional- and respiratory-supporting procedures, and multidisciplinary teams were less involved at follow-up, except for specialist palliative care. The genotypic and phenotypic features of elderly ALS patients could help identify the different environmental and genetic risk factors that determine the age at which disease onset occurs. Since multidisciplinary management can improve a patient’s prognosis, it should be more extensively applied to this fragile group of patients