301 research outputs found

    Activation Energy of Hydrogen Adsorption on Pt(111) in Alkaline Media: An Impedance Spectroscopy Study at Variable Temperatures

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    The hydrogen evolution reaction is one of the most studied processes in electrochemistry, and platinum is by far the best catalyst for this reaction. Despite the importance of this reaction on platinum, detailed and accurate kinetic measurements of the steps that lead to the main reaction are still lacking, particularly because of the fast rate of the reaction. Hydrogen adsorption on Pt(111) has been taken as a benchmark system in a large number of computational studies, but reliable experimental data to compare with the computational studies is very scarce. To gain further knowledge on this matter, a temperature study of the hydrogen adsorption reaction has been carried out to obtain kinetic information for this process on Pt(111) in alkaline solution. This was achieved by measuring electrochemical impedance spectra and cyclic voltammograms in the range of 278 ≤ T ≤ 318 (K) to obtain the corresponding surface coverage by adsorbed species and the faradaic charge transfer resistance. From this data, the standard rate constant has been extracted with a kinetic model assuming a Frumkin-type isotherm, resulting in values of 2.60 × 10–7 ≤ k0 ≤ 1.68 × 10–6 (s–1). The Arrehnius plot gives an activation energy of 32 kJ mol–1. Comparisons are made with values calculated by computational methods and reported values for the overall HER, giving a reference frame to support future studies on hydrogen catalysis.This work was financially supported by the MINECO (Spain) project no. CTQ2016-76221-P. L.E.B. thanks the Generalitat Valenciana for funding from the Santiago Grisolia Program (no. GRISOLIAP/2017/181)

    Pyrolysis of polyethylene in the presence and absence of clay catalysts

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    La actividad catalítica en la pirólisis del PE de materiales arcillosos como bentonita y zeolita fue estudiada. Los resultados obtenidos muestran que estos catalizadores tienen propiedades catalíticas sufcientes para producir una disminución de la temperatura de descomposición del PE logrando mejores resultados con la zeolita. La cinética de la degradación térmica del PE fue determinada y se encontró que la energía de activación de la degradación térmica catalítica es menor que la energía de activación de la degradación térmica.Abstract: The catalytic efect of clay materials such as bentonite and zeolite in the pyrolysis of PE was studied. The results show that these catalysts have catalytic properties that produce a decrease in decomposition temperature of PE achieving beter results with the zeolite. The kinetics of thermal degradation of PE was determined and was found that the activation energy of catalytic thermal degradation is less than the activation energy for thermal degradation

    Valor del índice de resistencia arterial medido por Doppler en la función del injerto renal a mediano y largo plazos

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    Objective: To evaluate the association between the value of the arterial resistance index (RI) measured by Doppler at the month after transplantation, and the loss of graft. Secondary outcomes of loss greater than or equal to 50% of renal function, eath with functioning graft, biopsy findings (inflammation, hyalinosis, rejection, interstitial fibrosis - tubular atrophy, IFTA) are reported. Methods: A cohort study of 66 patients, who underwent renal transplantation at San José Hospital of Bogotá between October 2007 and April 2011. The RI of the hilar artery was measured by Doppler ultrasound at the month post-transplant. Most patients had follow-up until the second year. We describe the cumulative incidence of renal graft loss, loss greater than or equal to 50% of the glomerular filtration rate. At the second year after transplantation, rejection, IFTA, hyalinosis and documented inflammation were reported in protocol biopsies. Association analysis was performed on the histological outcomes. Results: only 2 cases of renal graft loss were reported, belonging to the group with normal RI (3.8%). At 3 years of follow-up, 5 patients had lost more than 50% of GFR compared to baseline, 4 occurred in patients with RI <0.8, 2 of them (3.7%) ocurred in the first year and only one patient with RI> 0.8 ocurred at 3 years. The median GFR at 3 years of follow-up in both groups is greater than 60 ml / min. In the first year of follow-up 22 (47%) patients with normal RI had IFTA, and 7 (54%) with RI> 0.8 had IFTA. Hyalinosis was reported for 23% with RI> 0.8 and 25.5% with RI <0.8. Conclusion: the outcome of the grafts depends not only on RI, but also on factors such as cold ischemia, induction and maintenance immunosuppressive treatment, degree of incompatibility between donor and recipient. Histopathological changes such as IFTA, inflammation, hyalinosis, were observed in both groups, suggesting that there are other factors stronger than the RI, which correlates with the occurrence of these findings.Objetivo: evaluar la asociación entre el valor del índice de resistencia arterial (IR) medido por doppler al mes postrasplante y la pérdida de injerto. Se reportan los desenlaces secundarios de pérdida mayor o igual al 50% de la función renal, muerte con injerto funcionante, hallazgos de la biopsia (inflamación, hialinosis, rechazo, fibrosis intersticial - atrofia tubular, IFTA, por sus siglas en inglés). Métodos: se realizó un estudio de cohorte de 66 pacientes, que recibieron trasplante renal, del Hospital San José de Bogotá, entre octubre de 2007 y abril de 2011; se midió el IR de la arteria hilar por ecografía doppler al mes postrasplante. La mayoría de los pacientes fueron seguidos hasta el segundo año. Se describe la incidencia acumulada de pérdida del injerto renal, pérdida mayor o igual al 50% de la tasa filtración glomerular; al segundo año postrasplante se reporta el rechazo, IFTA, hialinosis e inflamación documentada en las biopsias de protocolo. Se realizó análisis de asociación en los desenlaces histológicos. Resultados: solo se reportaron 2 casos de pérdida del injerto renal, pertenecientes al grupo con IR normal (3.8%). A los 3 años de seguimiento 5 pacientes habían perdido más del 50% de la TFG respecto a la basal, 4 ocurrieron en los pacientes con IR <0.8, 2 de ellos (3.7%) fueron al primer año y solo un paciente con IR >0.8 a los 3 años. La mediana de la TFG a los 3 años de seguimiento en ambos grupos es mayor de 60 ml/ min. En el primer año de seguimiento 22 (47%) pacientes con IR normal presentaron IFTA y 7 (54%) con IR >0.8 presentaron IFTA; la hialinosis con un 23% para IR >0.8 y 25.5% para IR <0.8. Conclusión: los desenlaces de los injertos no solo dependen del IR, hay otros factores que pueden influir como es el tiempo de isquemia fría, esquema de tratamiento inmunosupresor de inducción y mantenimiento, grado de incompatibilidades entre donante, receptor. Cambios histopatológicos como IFTA, inflamación, hialinosis, se observaron en cualquiera de los 2 grupos, lo que sugiere que hay otros factores más fuertes que el IR, que se correlaciona con la aparición de estos hallazgos

    Medical Students’ Perception Towards the COVID-19 Pandemic in Mexico: Distance Learning, Assisting Hospitals, and Vaccination

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    Background: Mexico has been one of the most affected countries by the COVID-19 pandemic. Its health workers are playing a substantial role, but they are suffering from a high mortality rate, which highlights the need of vaccinating them before any other population. Medical interns have reduced their practices, some continue to assist clinical rotations without the protective equipment, and they are not being considered for vaccination. We wanted to determine the attitude of medical students and interns towards distance learning, assisting hospitals, and vaccination. Methods: We conducted a paired survey of a cohort of medical students who were evaluated twice, in June 2020 and in December 2020, using an online survey (32-online questions) to assess their perception of the pandemic. Results: We collected the response of 384 students in the summer period and 331 in the winter period; the majority were women from non-clinical semesters, and the median age of response was 21 years old (IQR 19 – 22). We found that the percentage of acceptance for vaccination was 95.6% in the summer and 93.7% in the winter, a remarkable acceptance in both periods. The percentage of students who manifested having someone close to them with symptoms suggestive of COVID-19 was 38.5% in the summer, showing an increase to 77.6% in the winter. Conclusion: We observed that medical students had a positive attitude towards vaccination and that the probable COVID-19 cases among them have increased in just a few months

    Primer registro de la cojolita (Penelope purpurascens) en el estado de Guanajuato, México

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    -Aquí se informa sobre el registro de la cojolita en la Reserva de Biosfera Sierra Gorda de Guanajuato, el cual es el registro más central para esa latitud y el primero para el estado. Esta especie fue registrada fotográfícamente en un bosque de encino. La presencia de esta especie enfatiza la necesidad de continuar realizando inventarios biológicos en esta Reserva de la Biosfer

    Correlation between obesity and severity of distal radius fractures

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    Introduction: The incidence of obesity has increased significantly worldwide. Our hypothesis was that patients with obesity have a more severe distal radius fracture and we realized a study to evaluate this correlation between obesity and severity of distal radius fractures caused by low-energy injuries. Materials and methods: A total of 114 patients with distal radius fracture were examined in
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