2,117 research outputs found

    Estudio de la inhomogeneidad elástica en vidrios metalicos en la mesoescala

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    Metallic glasses are amorphous solids produced by rapid cooling, with disordered atomic structure and lacking long-range order. This structural disorder makes them to show mechanical properties different from those observed in a crystalline solid. Metallic glasses are ideally isotropic, but they can become anisotropic during the manufacturing process or as a result of non-homogeneous plastic deformation, creep, etc. Experimental studies showed remnant anisotropy in amorphous PdSiCuP under a homogeneous deformation regime at temperatures close to the glass transition (Tg). In this thesis we studied the remnant anisotropy induced by shear in two amorphous systems by using molecular dynamics simulation. The Cu13Ni34Pd53 system was chosen to approach the PdCuSiP compositions, while the Zr46Cu46Al8 system is an excellent metallic glass former. Amorphous systems were obtained by fast cooling from the liquid and subsequent thermal annealing. Both systems were then sheared in the [100] direction at a deformation speed of 10^10 s^(-1), and returned to its original form at the same speed. Shearing simulations were performed in isothermal-isobaric conditions at different temperatures. The resulting states were examined using the directional pair distribution function (d-PDF), calculated from the distribution function of interatomic distances in planes perpendicular to the selected axis. Remnant anisotropy was detected in both systems after a deformation-recovery cycle. Cu13Ni34Pd53 displays remnant anisotropy below the glass transition at 0 and 300 K after the shear process, and again at 700 K after the full deformation-recovery cycle. The intensity of anisotropy in the d-PDF of Zr46Cu46Al8 is lower than in Cu13Ni34Pd53, possibly due to the different atomic radii. However, it is found in all the studied temperature range, with decreasing intensity with temperature. Anisotropy is concentrated in the [110] planes and [1(-1)0], corresponding to the planes of maximum and minimum shear respectively. This result indicates that remnant anisotropy is highly directional and can go unnoticed if not searched for. It also states that the shear process is essentially symmetrical with respect to the plane [110]. The shear and recovery process induces the creation of free volume, falling into the category of rejuvenation processes discussed in the literature. Counterintuitively, the process of free volume creation is accompanied by a reduction of the distance of the first maximum of the pair distribution function g (r), indicating a decrease of the most likely distance (mode) between first neighbors. However, this decrease in mode is accompanied by an increase of the width of the first peak, increasing the standard deviation of the distribution of distances between first neighbors. This explains the apparent contradiction between the increase in the volume and reduction of the most probable distance between first neighbors. Simultaneously, the second coordination sphere is more homogenous after the deformation and recovery process. As a result, medium range order is increased. The discrepancy between the results obtained between Cu13Ni34Pd53 and Zr46Cu46Al8 may be due to the fact that the potential used in the simulations of Zr46Cu46Al8 is more representative of the behavior of metallic glasses. As a result, we hypothesize that the presence of remnant anisotropy after mechanical deformation could be a general feature in metallic glasses. The computational cost of this study was very high, since it was necessary to simulate million-atom systems to avoid that results were dependent on the size of the simulation box.Los vidrios metálicos son sólidos amorfos producidos por enfriamiento rápido, con estructura atómica desordenada y sin orden de largo alcance. Este desorden estructural les proporciona propiedades mecánicas diferentes de las observadas en un sólido cristalino. Idealmente los vidrios metálicos son isotrópicos pero pueden convertirse en anisotrópicos durante el proceso de fabricación o como consecuencia de una deformación plástica no homogénea, fluencia, etc. Estudios experimentales mostraron anisotropía remanente en PdSiCuP amorfo bajo un régimen de deformación homogéneo a temperaturas cercanas a la transición vítrea (Tg). En esta tesis estudiamos la anisotropía remanente inducida por cizalla en dos sistemas amorfos mediante simulación por dinámica molecular. El sistema Cu13Ni34Pd53 se eligió intentando aproximarse a las composiciones PdCuSiP. Por otra parte, el sistema Zr46Cu46Al8 es un excelente formador de vidrios metálicos. Tras la obtención del sistema amorfo por enfriamiento rápido y equilibrado térmico ambos modelos fueron sometidos a deformación por cizalladura en la dirección [100], a una velocidad de deformación de 10^10 s^(-1), y retornados a su forma original con la misma velocidad, en condiciones isotérmicas-isobáricas a diferentes temperaturas. Los estados obtenidos fueron examinados utilizando la función de distribución par direccional (dPDF), calculada a partir de la distribución de distancias interatómicas en los planos perpendiculares al eje escogido. En ambos sistemas se detectó anisotropía remanente después de un ciclo deformación- recuperación. En Cu13Ni34Pd53 se observa anisotropía remanente por debajo de la transición vítrea en 0 y 300 K al final del proceso de cizalla, y nuevamente en el estado deformado a 700 K. En Zr46Cu46Al8, la intensidad de la anisotropía determinada en las d-PDF es menor que en Cu13Ni34Pd53, posiblemente debido a los radios atómicos, pero se observa en todo el rango de temperaturas estudiadas con intensidad decreciente con la temperatura. La anisotropía se concentra en los planos [110] y [1(-1)0], correspondientes a los planos de máxima y mínima cizalla respectivamente. Este resultado indica que la anisotropía remanente es altamente direccional y puede pasar desapercibida si no se busca específicamente. Asimismo, se observa que el proceso de cizalla es esencialmente simétrico con respecto al plano [1(-1)0]. El proceso de cizalla y recuperación induce la creación de volumen libre, entrando dentro de la categoría de los procesos de rejuvenecimiento analizados en la literatura. Contraintuitivamente, el proceso de creación de volumen libre va acompañando de una reducción de la distancia del primer máximo de la función de distribución de pares g(r), indicando una disminución de la distancia más probable (moda) entre primeros vecinos. Sin embargo, esta disminución de la moda va acompañada de un aumento de la anchura del primer pico, aumentando la desviación estándard de la distribución de distancias entre primeros vecinos. Esto explica la aparente contradicción entre el aumento del volumen y la reducción de la distancia más probable entre primeros vecinos. Simultáneamente, la segunda esfera de coordinación es más homogénea después del proceso de deformación y recuperación. En consecuencia, se produce un aumento del orden a media distancia. La discrepancia entre los resultados obtenidos entre Cu13Ni34Pd53 y Zr46Cu46Al8 puede deberse a que el potencial en Zr46Cu46Al8 es más representativo del comportamiento de los vidrios metálicos. Consecuentemente, la presencia de anisotropía remanente después de deformación mecánica podría ser una característica general en los vidrios metálicos. El coste computacional de este estudio ha sido muy alto, puesto que ha sido necesario simular sistemas con muchos átomos para evitar que los resultados obtenidos fuesen dependientes del tamaño de la caja de simulación utilizadasPostprint (published version

    Estudio de la inhomogeneidad elástica en vidrios metalicos en la mesoescala

    Get PDF
    Metallic glasses are amorphous solids produced by rapid cooling, with disordered atomic structure and lacking long-range order. This structural disorder makes them to show mechanical properties different from those observed in a crystalline solid. Metallic glasses are ideally isotropic, but they can become anisotropic during the manufacturing process or as a result of non-homogeneous plastic deformation, creep, etc. Experimental studies showed remnant anisotropy in amorphous PdSiCuP under a homogeneous deformation regime at temperatures close to the glass transition (Tg). In this thesis we studied the remnant anisotropy induced by shear in two amorphous systems by using molecular dynamics simulation. The Cu13Ni34Pd53 system was chosen to approach the PdCuSiP compositions, while the Zr46Cu46Al8 system is an excellent metallic glass former. Amorphous systems were obtained by fast cooling from the liquid and subsequent thermal annealing. Both systems were then sheared in the [100] direction at a deformation speed of 10^10 s^(-1), and returned to its original form at the same speed. Shearing simulations were performed in isothermal-isobaric conditions at different temperatures. The resulting states were examined using the directional pair distribution function (d-PDF), calculated from the distribution function of interatomic distances in planes perpendicular to the selected axis. Remnant anisotropy was detected in both systems after a deformation-recovery cycle. Cu13Ni34Pd53 displays remnant anisotropy below the glass transition at 0 and 300 K after the shear process, and again at 700 K after the full deformation-recovery cycle. The intensity of anisotropy in the d-PDF of Zr46Cu46Al8 is lower than in Cu13Ni34Pd53, possibly due to the different atomic radii. However, it is found in all the studied temperature range, with decreasing intensity with temperature. Anisotropy is concentrated in the [110] planes and [1(-1)0], corresponding to the planes of maximum and minimum shear respectively. This result indicates that remnant anisotropy is highly directional and can go unnoticed if not searched for. It also states that the shear process is essentially symmetrical with respect to the plane [110]. The shear and recovery process induces the creation of free volume, falling into the category of rejuvenation processes discussed in the literature. Counterintuitively, the process of free volume creation is accompanied by a reduction of the distance of the first maximum of the pair distribution function g (r), indicating a decrease of the most likely distance (mode) between first neighbors. However, this decrease in mode is accompanied by an increase of the width of the first peak, increasing the standard deviation of the distribution of distances between first neighbors. This explains the apparent contradiction between the increase in the volume and reduction of the most probable distance between first neighbors. Simultaneously, the second coordination sphere is more homogenous after the deformation and recovery process. As a result, medium range order is increased. The discrepancy between the results obtained between Cu13Ni34Pd53 and Zr46Cu46Al8 may be due to the fact that the potential used in the simulations of Zr46Cu46Al8 is more representative of the behavior of metallic glasses. As a result, we hypothesize that the presence of remnant anisotropy after mechanical deformation could be a general feature in metallic glasses. The computational cost of this study was very high, since it was necessary to simulate million-atom systems to avoid that results were dependent on the size of the simulation box.Los vidrios metálicos son sólidos amorfos producidos por enfriamiento rápido, con estructura atómica desordenada y sin orden de largo alcance. Este desorden estructural les proporciona propiedades mecánicas diferentes de las observadas en un sólido cristalino. Idealmente los vidrios metálicos son isotrópicos pero pueden convertirse en anisotrópicos durante el proceso de fabricación o como consecuencia de una deformación plástica no homogénea, fluencia, etc. Estudios experimentales mostraron anisotropía remanente en PdSiCuP amorfo bajo un régimen de deformación homogéneo a temperaturas cercanas a la transición vítrea (Tg). En esta tesis estudiamos la anisotropía remanente inducida por cizalla en dos sistemas amorfos mediante simulación por dinámica molecular. El sistema Cu13Ni34Pd53 se eligió intentando aproximarse a las composiciones PdCuSiP. Por otra parte, el sistema Zr46Cu46Al8 es un excelente formador de vidrios metálicos. Tras la obtención del sistema amorfo por enfriamiento rápido y equilibrado térmico ambos modelos fueron sometidos a deformación por cizalladura en la dirección [100], a una velocidad de deformación de 10^10 s^(-1), y retornados a su forma original con la misma velocidad, en condiciones isotérmicas-isobáricas a diferentes temperaturas. Los estados obtenidos fueron examinados utilizando la función de distribución par direccional (dPDF), calculada a partir de la distribución de distancias interatómicas en los planos perpendiculares al eje escogido. En ambos sistemas se detectó anisotropía remanente después de un ciclo deformación- recuperación. En Cu13Ni34Pd53 se observa anisotropía remanente por debajo de la transición vítrea en 0 y 300 K al final del proceso de cizalla, y nuevamente en el estado deformado a 700 K. En Zr46Cu46Al8, la intensidad de la anisotropía determinada en las d-PDF es menor que en Cu13Ni34Pd53, posiblemente debido a los radios atómicos, pero se observa en todo el rango de temperaturas estudiadas con intensidad decreciente con la temperatura. La anisotropía se concentra en los planos [110] y [1(-1)0], correspondientes a los planos de máxima y mínima cizalla respectivamente. Este resultado indica que la anisotropía remanente es altamente direccional y puede pasar desapercibida si no se busca específicamente. Asimismo, se observa que el proceso de cizalla es esencialmente simétrico con respecto al plano [1(-1)0]. El proceso de cizalla y recuperación induce la creación de volumen libre, entrando dentro de la categoría de los procesos de rejuvenecimiento analizados en la literatura. Contraintuitivamente, el proceso de creación de volumen libre va acompañando de una reducción de la distancia del primer máximo de la función de distribución de pares g(r), indicando una disminución de la distancia más probable (moda) entre primeros vecinos. Sin embargo, esta disminución de la moda va acompañada de un aumento de la anchura del primer pico, aumentando la desviación estándard de la distribución de distancias entre primeros vecinos. Esto explica la aparente contradicción entre el aumento del volumen y la reducción de la distancia más probable entre primeros vecinos. Simultáneamente, la segunda esfera de coordinación es más homogénea después del proceso de deformación y recuperación. En consecuencia, se produce un aumento del orden a media distancia. La discrepancia entre los resultados obtenidos entre Cu13Ni34Pd53 y Zr46Cu46Al8 puede deberse a que el potencial en Zr46Cu46Al8 es más representativo del comportamiento de los vidrios metálicos. Consecuentemente, la presencia de anisotropía remanente después de deformación mecánica podría ser una característica general en los vidrios metálicos. El coste computacional de este estudio ha sido muy alto, puesto que ha sido necesario simular sistemas con muchos átomos para evitar que los resultados obtenidos fuesen dependientes del tamaño de la caja de simulación utilizada

    Plastic deformation induced anisotropy in metallic glasses: A molecular dynamics study

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    The atomic structure of a Cu13Ni34Pd53 metallic glass was studied by molecular dynamics simulation at different temperatures along a shear deformation cycle. A simulation box of 1 million atoms was deformed in the x axis and then the original orthogonal shape was recovered. Directional pair distribution functions were computed in the coordinate planes and some significant directions along the shear deformation cycle. No anisotropy was found in the initial state, while post-deformation anisotropy was revealed by significant differences of the partial pair distribution functions. The analysis of atomic environments concluded that the remnant anisotropy remains constrained into the shear plane. Low temperature samples showed remnant anisotropy after the full shear sample, while close to the glass transition the anisotropy induced by the initial shear process is removed by the subsequent recovery process.Peer ReviewedPostprint (published version

    Study of medium range reordering by plastic deformation in Cu46Zr46Al8

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    The influence of shear in the atomic structure of ternary Cu46Zr46Al8 metallic glass was studied at different temperatures by molecular dynamics (MD) simulation. At temperatures above and below the glass transition temperature the system was subjected to a shear deformation cycle; the shear deformation was carried in the [100] direction and then the original geometry was recovered. The system was analyzed in three states: initial state (before deformation), deformed state (sheared) and final state (recovery). The different states obtained by the atomistic simulations were examined by computing the directional pair distribution functions (dPDF) in the coordinate planes. The results showed by dPDFs of the planes perpendicular to the coordinate axis are apparently isotropic. However, the dPDF disengage when computed perpendicular to rotated axis. This reveals that the anisotropy introduced during the deformation cycles appears in directions [110] and [1?0], tilted 45° with respect to the direction of the applied shear. To analyze the subtle structural change we systematically computed the positions and widths of the dPDF peaks on the rotated directions, thence allowing us to describe in detail the different signatures of anisotropy induced by deformation in the metallic glasses.Peer ReviewedPostprint (published version

    Treatment with tocilizumab or corticosteroids for COVID-19 patients with hyperinflammatory state: a multicentre cohort study (SAM-COVID-19)

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    Objectives: The objective of this study was to estimate the association between tocilizumab or corticosteroids and the risk of intubation or death in patients with coronavirus disease 19 (COVID-19) with a hyperinflammatory state according to clinical and laboratory parameters. Methods: A cohort study was performed in 60 Spanish hospitals including 778 patients with COVID-19 and clinical and laboratory data indicative of a hyperinflammatory state. Treatment was mainly with tocilizumab, an intermediate-high dose of corticosteroids (IHDC), a pulse dose of corticosteroids (PDC), combination therapy, or no treatment. Primary outcome was intubation or death; follow-up was 21 days. Propensity score-adjusted estimations using Cox regression (logistic regression if needed) were calculated. Propensity scores were used as confounders, matching variables and for the inverse probability of treatment weights (IPTWs). Results: In all, 88, 117, 78 and 151 patients treated with tocilizumab, IHDC, PDC, and combination therapy, respectively, were compared with 344 untreated patients. The primary endpoint occurred in 10 (11.4%), 27 (23.1%), 12 (15.4%), 40 (25.6%) and 69 (21.1%), respectively. The IPTW-based hazard ratios (odds ratio for combination therapy) for the primary endpoint were 0.32 (95%CI 0.22-0.47; p < 0.001) for tocilizumab, 0.82 (0.71-1.30; p 0.82) for IHDC, 0.61 (0.43-0.86; p 0.006) for PDC, and 1.17 (0.86-1.58; p 0.30) for combination therapy. Other applications of the propensity score provided similar results, but were not significant for PDC. Tocilizumab was also associated with lower hazard of death alone in IPTW analysis (0.07; 0.02-0.17; p < 0.001). Conclusions: Tocilizumab might be useful in COVID-19 patients with a hyperinflammatory state and should be prioritized for randomized trials in this situatio

    Clonal chromosomal mosaicism and loss of chromosome Y in elderly men increase vulnerability for SARS-CoV-2

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    The pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2, COVID-19) had an estimated overall case fatality ratio of 1.38% (pre-vaccination), being 53% higher in males and increasing exponentially with age. Among 9578 individuals diagnosed with COVID-19 in the SCOURGE study, we found 133 cases (1.42%) with detectable clonal mosaicism for chromosome alterations (mCA) and 226 males (5.08%) with acquired loss of chromosome Y (LOY). Individuals with clonal mosaic events (mCA and/or LOY) showed a 54% increase in the risk of COVID-19 lethality. LOY is associated with transcriptomic biomarkers of immune dysfunction, pro-coagulation activity and cardiovascular risk. Interferon-induced genes involved in the initial immune response to SARS-CoV-2 are also down-regulated in LOY. Thus, mCA and LOY underlie at least part of the sex-biased severity and mortality of COVID-19 in aging patients. Given its potential therapeutic and prognostic relevance, evaluation of clonal mosaicism should be implemented as biomarker of COVID-19 severity in elderly people. Among 9578 individuals diagnosed with COVID-19 in the SCOURGE study, individuals with clonal mosaic events (clonal mosaicism for chromosome alterations and/or loss of chromosome Y) showed an increased risk of COVID-19 lethality

    Penilaian Kinerja Keuangan Koperasi di Kabupaten Pelalawan

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    This paper describe development and financial performance of cooperative in District Pelalawan among 2007 - 2008. Studies on primary and secondary cooperative in 12 sub-districts. Method in this stady use performance measuring of productivity, efficiency, growth, liquidity, and solvability of cooperative. Productivity of cooperative in Pelalawan was highly but efficiency still low. Profit and income were highly, even liquidity of cooperative very high, and solvability was good

    Optimasi Portofolio Resiko Menggunakan Model Markowitz MVO Dikaitkan dengan Keterbatasan Manusia dalam Memprediksi Masa Depan dalam Perspektif Al-Qur`an

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    Risk portfolio on modern finance has become increasingly technical, requiring the use of sophisticated mathematical tools in both research and practice. Since companies cannot insure themselves completely against risk, as human incompetence in predicting the future precisely that written in Al-Quran surah Luqman verse 34, they have to manage it to yield an optimal portfolio. The objective here is to minimize the variance among all portfolios, or alternatively, to maximize expected return among all portfolios that has at least a certain expected return. Furthermore, this study focuses on optimizing risk portfolio so called Markowitz MVO (Mean-Variance Optimization). Some theoretical frameworks for analysis are arithmetic mean, geometric mean, variance, covariance, linear programming, and quadratic programming. Moreover, finding a minimum variance portfolio produces a convex quadratic programming, that is minimizing the objective function ðð¥with constraintsð ð 𥠥 ðandð´ð¥ = ð. The outcome of this research is the solution of optimal risk portofolio in some investments that could be finished smoothly using MATLAB R2007b software together with its graphic analysis

    Juxtaposing BTE and ATE – on the role of the European insurance industry in funding civil litigation

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    One of the ways in which legal services are financed, and indeed shaped, is through private insurance arrangement. Two contrasting types of legal expenses insurance contracts (LEI) seem to dominate in Europe: before the event (BTE) and after the event (ATE) legal expenses insurance. Notwithstanding institutional differences between different legal systems, BTE and ATE insurance arrangements may be instrumental if government policy is geared towards strengthening a market-oriented system of financing access to justice for individuals and business. At the same time, emphasizing the role of a private industry as a keeper of the gates to justice raises issues of accountability and transparency, not readily reconcilable with demands of competition. Moreover, multiple actors (clients, lawyers, courts, insurers) are involved, causing behavioural dynamics which are not easily predicted or influenced. Against this background, this paper looks into BTE and ATE arrangements by analysing the particularities of BTE and ATE arrangements currently available in some European jurisdictions and by painting a picture of their respective markets and legal contexts. This allows for some reflection on the performance of BTE and ATE providers as both financiers and keepers. Two issues emerge from the analysis that are worthy of some further reflection. Firstly, there is the problematic long-term sustainability of some ATE products. Secondly, the challenges faced by policymakers that would like to nudge consumers into voluntarily taking out BTE LEI

    Search for stop and higgsino production using diphoton Higgs boson decays

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    Results are presented of a search for a "natural" supersymmetry scenario with gauge mediated symmetry breaking. It is assumed that only the supersymmetric partners of the top-quark (stop) and the Higgs boson (higgsino) are accessible. Events are examined in which there are two photons forming a Higgs boson candidate, and at least two b-quark jets. In 19.7 inverse femtobarns of proton-proton collision data at sqrt(s) = 8 TeV, recorded in the CMS experiment, no evidence of a signal is found and lower limits at the 95% confidence level are set, excluding the stop mass below 360 to 410 GeV, depending on the higgsino mass
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