6 research outputs found
Evolving trends in the management of acute appendicitis during COVID-19 waves. The ACIE appy II study
Background: In 2020, ACIE Appy study showed that COVID-19 pandemic heavily affected the management of patients with acute appendicitis (AA) worldwide, with an increased rate of non-operative management (NOM) strategies and a trend toward open surgery due to concern of virus transmission by laparoscopy and controversial recommendations on this issue. The aim of this study was to survey again the same group of surgeons to assess if any difference in management attitudes of AA had occurred in the later stages of the outbreak.
Methods: From August 15 to September 30, 2021, an online questionnaire was sent to all 709 participants of the ACIE Appy study. The questionnaire included questions on personal protective equipment (PPE), local policies and screening for SARS-CoV-2 infection, NOM, surgical approach and disease presentations in 2021. The results were compared with the results from the previous study.
Results: A total of 476 answers were collected (response rate 67.1%). Screening policies were significatively improved with most patients screened regardless of symptoms (89.5% vs. 37.4%) with PCR and antigenic test as the preferred test (74.1% vs. 26.3%). More patients tested positive before surgery and commercial systems were the preferred ones to filter smoke plumes during laparoscopy. Laparoscopic appendicectomy was the first option in the treatment of AA, with a declined use of NOM.
Conclusion: Management of AA has improved in the last waves of pandemic. Increased evidence regarding SARS-COV-2 infection along with a timely healthcare systems response has been translated into tailored attitudes and a better care for patients with AA worldwide
Object kinetic Monte Carlo simulations of irradiated tungsten for nuclear fusion reactors
El wolframio es considerado como el principal candidato para revestimientos de materiales expuestos a plasmas, tanto para materiales de primera pared en el caso de reactores de fusión por confinamiento inercial como para recubrimiento de ciertas partes del divertor en el caso de reactores de fusión por confinamiento magnético. Esto es debido a sus propiedades, tales como alto punto de fusión, alta conductividad térmica, bajo coeficiente de erosión y baja retención de tritio. Sin embargo, además de los altos requerimientos termomecánicos, el wolframio tendrá que soportar la irradiación iónica de helio e hidrógeno entre otros, la cual puede dar lugar a efectos perjudiciales de origen atómico, tales como el agrietamiento, exfoliación o hinchamiento. Todavía se necesitan muchos esfuerzos para desarrollar un material basado en tungsteno que sea capaz de soportar las condiciones realistas de irradiación en las futuras plantas de fusión nuclear, en particular, los pulsos de alta intensidad que se espera tengan lugar. El modelo multiescala secuencial se muestra como una buena metodología para el estudio de la irradiación de helio o hidrógeno en wolframio, ya que ayuda a comprender los procesos clave de los efectos físicos que se observan experimentalmente. En el modelo multiescala secuencial, los resultados de un determinado paso son los datos de entrada del siguiente. Gracias al uso combinado de la teoría de la densidad del funcional (DFT), la dinámica molecular (MD), la aproximación de colisiones binarias (BCA) y el Monte Carlo cinético de objetos (OKMC), el modelo multiescala cubre un amplio espectro en las escalas temporal y espacial, desde ~nm y ~ps hasta μm y horas o incluso días. El estudio que se presenta en esta tesis está basado principalmente en simulaciones con OKMC de irradiación de helio o hidrógeno en wolframio, utilizado como material de revestimientos de materiales expuestos a plasmas. El estudio cubre diferentes aspectos de la irradiación iónica: la naturaleza de los iones (helio o hidrógeno) y el flujo (bien continuo o pulsado) en wolframio tanto con baja como con alta densidad de bordes de grano (wolframio monocristalino o nanocristalino respectivamente). Dado que la metodología OKMC necesita como datos de entrada tanto la energía de unión como la energía de migración, estos parámetros se obtuvieron gracias a cálculos de DFT. Como resultado, se presenta una completa parametrización tanto para irradiación de hidrógeno como de helio en wolframio. Las cascadas de daño producidas en el wolframio debido a la irradiación iónica son también datos de entrada para los códigos de computación de OKMC. Con el objetivo de determinar si las cascadas obtenidas con BCA son realistas o no, se ha realizado una comparación con unas cascadas obtenidas con MD. Aunque la técnica MD tiene en cuenta tanto la evolución de la temperatura como la migración, aglomeración y recombinación de defectos, el tiempo de computación requerido y las limitaciones temporales y espaciales de simulación hacen que sea muy atractivo el uso de un método mucho más rápido como el BCA. Los resultados obtenidos muestran que, en el caso de irradiación con iones ligeros (los cuales producen PKAs de baja energía), las cascadas obtenidas con BCA son suficientemente adecuadas para ser utilizadas en un posterior cálculo con OKMC. El código de computación de OKMC utilizado en esta tesis fue un código abierto recientemente desarrollado, el código MMonCa. Por ese motivo, se hizo una validación previa del código para el caso de irradiación iónica en wolframio y se obtuvieron resultados similares a aquellos obtenidos con otros códigos y que habían sido encontrados en la literatura. Por un lado, el flujo iónico que llegará al wolframio en fusión por confinamiento inercial es pulsado por naturaleza. Por otro lado, en fusión por confinamiento magnético, los efectos más nocivos provienen de las pulsos iónicos debidos a los llamados modos localizados de borde (ELMs). Sin embargo, muchos estudios experimentales se llevan a cabo en instalaciones de irradiación convencionales, que operan en modo continuo. La comparativa entre ambos modos de irradiación muestra que en el caso de irradiación pulsada de helio hay más retención de He, los átomos de He están retenidos en aglomerados de He-V con un menor número de vacantes y que esos aglomerados de He-V se localizan en un volumen mucho menor. Por ello, se espera una peor respuesta del wolframio ante irradiación pulsada de He. El efecto del flujo ha de ser tenido en cuenta cuando se estudie el wolframio para revestimientos de materiales expuestos a plasmas. Con el objetivo de mitigar los efectos perjudiciales de la irradiación de helio, se están investigando nuevos materiales basados en el uso de wolframio nanoestructurado (NW). En el caso de irradiación con helio, las simulaciones de OKMC mostraron que el helio está atrapado en aglomerados de He-V mayores y con menor relación He/V que en el caso de wolframio monocristalino (MW). Es más, con el aumento de la fluencia, aumenta la diferencia de la energía de tensión elástica total. En el caso de irradiación con hidrógeno, se reprodujeron mediante simulaciones OKMC experimentos a diferentes condiciones de irradiación (sólo irradiación de hidrógeno e irradiación de C e H, tanto simultánea como secuencial) tanto en MW como en NW. Los resultados mostraron que, de nuevo, la densidad de bordes de grano tiene un claro efecto en la aniquilación entre vacantes y átomos intersticiales de W. Más aún, de la comparativa entre los experimentos y las simulaciones en el caso de NW, se infirió que los bordes de grano actúan como caminos preferenciales para la difusión de hidrógeno. Los estudios tanto de helio como de hidrógeno en MW y NW mostraron que el NW se comporta de un modo diferente al MW con respecto a la irradiación iónica y que una mejor respuesta se espera en el caso de NW. Por último, se ha estudiado la irradiación de helio en condiciones que tendrán lugar en los futuros reactores de fusión por confinamiento magnético. Con estas condiciones de irradiación, una nanoestructura muy poco densa (el llamado fuzz) se ha observado experimentalmente, pero únicamente dentro de una ventana de temperaturas definida (desde 900 hasta 2000 K). Gracias a un nuevo modelo implementado en MMonCa, este efecto pudo ser estudiado. Los resultados mostraron que el proceso es dominado por el atrapamiento y emisión de los átomos de He en las vacantes. A bajas temperaturas, el He es atrapado en aglomerados de He-V muy estables. A temperaturas intermedias, estos aglomerados atrapan y emiten átomos de He, que dan lugar finalmente a mayores aglomerados de He-V, que son los que provocan el crecimiento del fuzz. Para terminar, a alta temperatura, el He es emitido de los aglomerados de He-V que se forman, terminando en una falta de retención de He y, por consiguiente, una falta de formación de fuzz. ABSTRACT Tungsten is considered the main candidate for plasma facing material applications, for both the first-wall in inertial confinement fusion reactors and divertor regions in magnetic confinement fusion reactors. This is due to its properties such as high melting point, high thermal conductivity, low sputtering coefficient and low tritium retention. However, in addition to the high thermomechanical requirements, tungsten will have to deal with ion irradiation, helium and hydrogen among others, which results in detrimental effects of atomistic origin such as cracking, exfoliation or blistering. Many efforts are still needed to develop a tungsten-based material capable of dealing with realistic irradiation conditions in future power plants, in particular, the expected intense ion pulses. Sequential multiscale modelling is a powerful methodology to study helium or hydrogen irradiation in tungsten, since it helps to understand the driving processes of the physical effects observed experimentally. In the sequential multiscale modelling, the results of one step are the input data for the next one. Thanks to the combined used of density functional theory (DFT), molecular dynamics (MD), binary collision approximation (BCA) and object kinetic Monte Carlo (OKMC), the multiscale modelling covers a wide range of spatial and temporal scales, from ~nm and ~ps to μm and hours or even days. In this thesis, a study mainly based on OKMC simulations of helium or hydrogen irradiation in tungsten as a plasma facing material is presented. The study covers different aspects of ion irradiation: ion nature (helium or hydrogen) and flux (continuous or pulsed modes) on tungsten with low or high grain boundary density (monocrystalline or nanocrystalline, respectively). Since OKMC makes use of binding and migration energies as input data, these parameters were obtained from density functional theory calculations. As a result, a complete parameterization of hydrogen or helium irradiation in tungsten is presented. Damage cascades generated in tungsten due to ion irradiation are also input for OKMC codes. In order to determine whether BCA damage cascades are realistic or not, a comparison with cascades obtained by means of MD was done. Although MD takes into account temperature evolution and defect migration, clustering and recombination, the computational time needed and the limited spatial and temporal accessible ranges makes attractive the use of a fast method such as BCA. The results showed that, for light ion irradiation (which generates low energy PKAs), BCA cascades are accurate enough to be used as input for the OKMC calculations. The OKMC code used in this thesis was a newly developed open-source code, the MMonCa code. Thus, a previous validation of the code for ion irradiation in tungsten was done, obtaining similar results than those from other codes found in the literature. On the one hand, the ion flux that will reach tungsten in inertial fusion confinement is pulsed by the nature. On the other hand, in magnetic confinement fusion, the most detrimental effects stem from ion pulses due to so called edge localized modes (ELMs). However, many experimental studies use conventional irradiation facilities that operate in continuous mode. The comparison between both modes of irradiation showed that in the case of pulsed helium irradiation, there is more He retention, He atoms are retained in He-V clusters with a lower number of vacancies and that these He-V clusters are located in a much smaller volume. Thus, a worse response of tungsten under pulsed He irradiation is expected. The flux effect should be taken in account when studying tungsten for plasma facing material purposes. In order to mitigate the deleterious effects under helium irradiation, new approaches based on the use of nanostructured tungsten (NW) are being investigated. In the case of helium irradiation, OKMC simulations showed that helium is trapped in larger He-V clusters with lower He/V ration in the case of NW, as a result of the influence of GBs on the annihilation process between vacancies and self-interstitial atoms (SIAs). Thus, these He-V clusters are less pressurized than the equivalent ones in monocrystalline tungsten (MW). Moreover, the higher the fluence, the higher the difference of the total elastic strain energy. In the case of hydrogen irradiation, experiments with different irradiation conditions (single H irradiation and C and H simultaneously and sequentially irradiated) were reproduced with OKMC simulations in both MW and NW. The results showed that, again, the grain boundary density has a clear effect on the annihilation between vacancies and SIAs. Furthermore, from the comparison between experiments and simulations in the case of NW, it was inferred that GBs act as preferential paths for H diffusion. Both helium and hydrogen studies on MW and NW showed that NW behaves in a different way as compared to MW regarding ion irradiation and that a better response is expected in the case of NW. Finally, helium irradiation in conditions that will take place in magnetic fusion confinement reactors was studied. At these irradiation conditions, an underdense nanostructure (so called “fuzz”) has been observed experimentally, but only in a defined temperature window (from 900 to 2000 K). Thanks to a new model implemented in MMonCa, this effect could be studied. The results showed that the process is driven by the trapping/detrapping of He atoms in vacancies. At low temperatures, He is trapped in very stable He-V clusters. At intermediate temperatures, these clusters trap and emit He atoms, leading to larger He-V clusters which promote fuzz growth. Finally, at high temperature, He is detrapped from the formed He-V clusters, leading to no He atom retention and thus, no fuzz formation
MMonCa: An Object Kinetic Monte Carlo simulator for damage irradiation evolution and defect diffusion
In this work, we introduce the Object Kinetic Monte Carlo (OKMC) simulator MMonCa and simulate the defect evolution in three different materials. We start by explaining the theory of OKMC and showing some details of how such theory is implemented by creating generic structures and algorithms in the objects that we want to simulate. Then we successfully reproduce simulated results for defect evolution in iron, silicon and tungsten using our simulator and compare with available experimental data and similar simulations. The comparisons validate MMonCa showing that it is powerful and flexible enough to be customized and used to study the damage evolution of defects in a wide range of solid materials.I. M.-B. wants to acknowledge funding of the project MASTIC (PCIG09-GA-2011-293783) by the Marie Curie Actions Grant FP7-PEOPLE-2011-CIG program. This work contributes to the Joint Programme of Nuclear Materials of the European Energy Research Alliance
Evolving trends in the management of acute appendicitis during COVID-19 waves. The ACIE appy II study (vol 46, pg 2021, 2022)
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Global attitudes in the management of acute appendicitis during COVID-19 pandemic: ACIE Appy Study
Background: Surgical strategies are being adapted to face the COVID-19 pandemic. Recommendations on the management of acute appendicitis have been based on expert opinion, but very little evidence is available. This study addressed that dearth with a snapshot of worldwide approaches to appendicitis.
Methods: The Association of Italian Surgeons in Europe designed an online survey to assess the current attitude of surgeons globally regarding the management of patients with acute appendicitis during the pandemic. Questions were divided into baseline information, hospital organization and screening, personal protective equipment, management and surgical approach, and patient presentation before versus during the pandemic.
Results: Of 744 answers, 709 (from 66 countries) were complete and were included in the analysis. Most hospitals were treating both patients with and those without COVID. There was variation in screening indications and modality used, with chest X-ray plus molecular testing (PCR) being the commonest (19\ub78 per cent). Conservative management of complicated and uncomplicated appendicitis was used by 6\ub76 and 2\ub74 per cent respectively before, but 23\ub77 and 5\ub73 per cent, during the pandemic (both P < 0\ub7001). One-third changed their approach from laparoscopic to open surgery owing to the popular (but evidence-lacking) advice from expert groups during the initial phase of the pandemic. No agreement on how to filter surgical smoke plume during laparoscopy was identified. There was an overall reduction in the number of patients admitted with appendicitis and one-third felt that patients who did present had more severe appendicitis than they usually observe.
Conclusion: Conservative management of mild appendicitis has been possible during the pandemic. The fact that some surgeons switched to open appendicectomy may reflect the poor guidelines that emanated in the early phase of SARS-CoV-2