Rippling and a phase-transforming mesoscopic model for multiwalled carbon nanotubes

We propose to model thick multiwalled carbon nanotubes as beams with non-convex curvature energy. Such models develop stressed phase mixtures composed of smoothly bent sections and rippled sections. This model is motivated by experimental observations and large-scale atomistic-based simulations. The model is analyzed, validated against large-scale simulations, and exercised in examples of interest. It is shown that modelling MWCNTs as linear elastic beams can result in poor approximations that overestimate the elastic restoring force considerably, particularly for thick tubes. In contrast, the proposed model produces very accurate predictions both of the restoring force and of the phase pattern. The size effect in the bending response of MWCNTs is also discussed.Peer ReviewedPostprint (author’s final draft

Phase-field modeling and simulation of fracture in brittle materials with strongly anisotropic surface energy

Crack propagation in brittle materials with anisotropic surface energy is important in applications involving single crystals, extruded polymers, or geological and organic materials. Furthermore, when this anisotropy is strong, the phenomenology of crack propagation becomes very rich, with forbidden crack propagation directions or complex sawtooth crack patterns. This problem interrogates fundamental issues in fracture mechanics, including the principles behind the selection of crack direction. Here, we propose a variational phase-field model for strongly anisotropic fracture, which resorts to the extended Cahn-Hilliard framework proposed in the context of crystal growth. Previous phase-field models for anisotropic fracture were formulated in a framework only allowing for weak anisotropy. We implement numerically our higher-order phase-field model with smooth local maximum entropy approximants in a direct Galerkin method. The numerical results exhibit all the features of strongly anisotropic fracture and reproduce strikingly well recent experimental observations.Peer ReviewedPostprint (author’s final draft

Dvadeset godina Konvencije UN-a

Gosti urednici Irene Balaguer i Peter Moss predstavljaju broj 17 koji se tematski bavi pravima djece

Fracture toughening and toughness asymmetry induced by flexoelectricity

Cracks generate the largest strain gradients that any material can withstand. Flexoelectricity (coupling between strain gradient and polarization) must therefore play an important role in fracture physics. Here we use a self-consistent continuum model to evidence two consequences of flexoelectricity in fracture: the resistance to fracture increases as structural size decreases, and it becomes asymmetric with respect to the sign of polarization. The latter phenomenon manifests itself in a range of intermediate sizes where piezo- and flexoelectricity compete. In BaTiO3 at room temperature, this range spans from 0.1 to 50 nm, a typical thickness range for epitaxial ferroelectric thin films.Fil: Abdollahi, Amir. Universidad Politécnica de Catalunya; EspañaFil: Peco Regales, Christian. Universidad Politécnica de Catalunya; EspañaFil: Millán, Raúl Daniel. Universidad Politécnica de Catalunya; España. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Arroyo Balaguer, Marino. Universidad Politécnica de Catalunya; EspañaFil: Catalan, Gustau. Institut Catalá de Recerca I Estudis Avançats; España. Institut Catala de Nanociéncia i Nanotecnologia; EspañaFil: Arias, Irene. Universidad Politécnica de Catalunya; España. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

Is elective surgery during the COVID-19 pandemic safe? A multi-center prospective study in a high incidence area

Elective surgery; COVID-19 pandemicCirugía electiva; Pandemia de COVID-19Cirurgia electiva; Pandèmia de COVID-19Objective: The aim of this study was to describe the evolution of patients admitted for elective orthopaedic surgery during the immediate post-COVID-19 peak of the pandemic. Methods: This is a multi-center, observational study conducted in 8 high complexity hospitals of Catalonia, one of the highest COVID-19 incidence areas in Spain. We included patients ≥18 years of age undergoing elective surgery (total knee or hip arthroplasty, knee or hip revision arthroplasty, shoulder or knee arthroscopy, hand or wrist surgery, forefoot surgery, or hardware removal) after the COVID-19 peak (between May 5th and June 30th, 2020). The main exclusion criterion was a positive result for SARS-CoV-2 PCR within the 7 days before the surgery. The primary outcomes were postoperative complications within 60 days (+/-30) or hospital readmission due to a COVID-19 infection. Following the recommendations of the International Consensus Group (ICM), elective surgeries were re-started when the nationwide lockdown was lifted. Before the surgery, patients were contacted by phone to rule out any exposure to confirmed COVID-19 cases, a reverse transcription-polymerase chain reaction (PCR) assay was performed in all patients 48-72 hours before hospital admission, and they were asked to maintain home confinement until the day of the surgery. Results: 675 patients were included: 189 patients in the arthroplasty group (28%) and 486 in the ambulatory surgery group (72%). Mean [SD] age was 57.6 [15.3] years. The mean Charlson Comorbidity Index score was 2.21 (SD = 2.01, Min = 0, Max = 13). A total of 84 patients (12.75%) obtained an American Society of Anesthesiologists (ASA) score ≥ 3, showing no association between the ASA score and the risk of developing COVID-19 symptoms at follow-up (χ 2 (4) = 0.77, P = 0.94). The mean occupation rate of hospital beds for COVID-19 patients was 13% and the mean occupation rate of critical care beds for COVID-19 patients was 27% at the time of re-introducing elective surgeries. These were important rates to consider to decide when to reintroduce elective surgeries after lockdown. Surgical time, time of ischemia and intra-operative bleeding were not related with a higher risk of developing COVID-19 post-operatively (χ 2 (1) = 0.00, P = 0.98); (χ 2 (2) = 2.05, P = 0.36); (χ 2 (2) = 0.37, P = 0.83). Only 2 patients (0.3 %) presented with a suspected COVID-19 infection at follow-up. None of them presented with pneumonia or required confirmation by a reverse transcription PCR assay. Hospital re-admission was not needed for these patients. Conclusion: The risk of developing COVID-19 during the immediate post-COVID-19 peak in a region with a high incidence of COVID-19 has not been proved. These data suggest that elective orthopaedic surgeries can be resumed when assertive and strict protocols are followed

Fokus na Utjecaj Lorisa Malaguzzija

Prošlo je 20 godina od smrti Lorisa Malaguzzija, čovjeka čije je djelovanje duboko promijenilo kulturu djetinjstva. Njegova misao imala je osobit utjecaj na odgoj i obrazovanje Reggio Emilie, no lokalni utjecaj se brzo proširio i na odgojno-obrazovnu praksu drugih zemalja. Prikupili smo svjedočanstva o njegovu izvornom doprinosu iz različitih europskih zemalja

Imaginarios sobre la violencia escolar, asimetrías de poder e interseccionalidad en la serie Merlí

Violences in the school environment, an increasingly widespread phenomenon, are based on inequality and the abuse of power, and can be analyzed through the imaginaries of fictional narratives. In this work we carry out a qualitative-quantitative content analysis of the three seasons of the series Merlí (2015-2018), we explore the types of school violence represented and their link with the coordinates of power relations and inequality. 57 situations of school violence were identified, distributed in 80 % of the episodes, mostly related to psychological violence between teachers and students and to the inequality of hierarchies. The imaginaries of school violences in the series is linked to a representation of violences as an individual and monofocal problem, leaving out the complexity of intersectional elements and the structural dynamics of power that develops in the school.Las violencias en el ámbito escolar, un fenómeno cada vez más extendido, están basadas en la desigualdad y el abuso de poder, y pueden analizarse a través de los imaginarios de las narrativas de ficción. En este trabajo realizamos un análisis de contenido cuali-cuantitativo de las tres temporadas de la serie Merlí (2015-2018) y exploramos los tipos de violencia escolar representados y su vinculación con las coordenadas de las relaciones de poder y desigualdad. Se identificaron 57 situaciones de violencia escolar distribuidas en el 80 % de los episodios, en su mayoría relacionadas con la violencia psicológica entre docentes y estudiantes y con la desigualdad de jerarquías. Los imaginarios de la violencia escolar en la serie se vinculan con una representación de la violencia enfocada como un problema individual y monofocal, dejando por fuera la complejidad de los elementos interseccionales y la dinámica estructural de poder que se desarrolla en el dispositivo escolar