Caracterización dinámica de un martillo de impacto para análisis modal

El siguiente estudio se centra en la caracterización dinámica de un martillo de impacto instrumentalizado, del cual no se tiene carta de calibración por lo que se desconoce la frecuencia propia máxima que se puede determinar en los sistemas de estudio. Dicha caracterización se hace después de diseñar y fabricar puntas de impacto de diferentes materiales (acero, plástico y goma) conociendo que la frecuencia máxima de excitación del martillo dependerá de la dureza de la punta con la que se impacte. En dicha frecuencia también tiene influencia la masa, por lo que se estudiará también la influencia de una masa añadida (contramasa). Como resultado de los ensayos realizados, se presentará la carta de calibración del martillo para las diferentes opciones de impacto con el fin de su empleo industrial. Se validarán estos resultados en los ensayos realizados en una viga biapoyada a la que se le determinará su comportamiento modal de forma teórica mediante un modelo matemático y experimentalmente haciendo uso del martillo.The following study focuses on the dynamic characterization of an instrumented impact hammer, whose highest natural frequency determinable by study systems is unknown due to the absence of a calibration chart. Said characterization is made after designing and producing impact tips out of different materials (steel, plastic and rubber) knowing that the hammer's highest excitation frequency will depend on the hardness of the tip which it impacts with. Mass also affects said frequency, therefore the influence of an added mass (countermass) will also be analyzed. As a result of the performed tests, the hammer's calibration chart will be presented for the different impact options with the aim of its industrial use. These results will be validated by the tests carried out on a bi-supported beam whose modal behaviour will be determined theoretically through a matemathical model and experimentally through the use of the hammer.Universidad de Sevilla. Grado en Ingeniería de las Tecnologías Industriale

Análisis del efecto de la rodadura en fretting

El presente trabajo versa sobre el estudio generalizado de un problema de contacto en el que intervienen tanto rodadura como fuerzas tangenciales oscilantes. Para ello, se ha partido de un modelo en deformación bidimensional plano-cilindro en el que se simulan diferentes relaciones de carga tangencial y rodadura. El objetivo es evaluar las tensiones que se producen en la zona del contacto, con la intención de proyectar un estudio posterior de fretting, problema de fatiga tan presente en la ingeniería actual. Dicho estudio desborda los contenidos que se tratan en este trabajo, por lo que no serán abarcados con tanta profundidad.The present work deals with the generalized study of a contact problem in which both rolling and oscillating tangential forces intervene. To do this, we have started from a plane-cylinder twodimensional deformation model in which different relationships of rolling and tangential load are simulated. The objective is to evaluate the stresses that occur in the contact area, with the intention of projecting a later study of fretting, a fatigue problem so present in current engineering. Said study goes beyond the contents that are dealt with in this work, so it will not be covered in such depth.Universidad de Sevilla. Máster en Ingeniería Industria

Natural and anthropic pollution episodes during the Late Holocene evolution of the Tinto River estuary (SW Spain)

This paper investigates the paleoenvironmental evolution of a core extracted in the middle sector of the Tinto River estuary, SW Spain, one of the most polluted areas in the world due to mining over thousands of years (>4 kyr BP) and recent industrial discharges. This evolution includes alluvial sands (>6.4 cal kyr BP), bioclastic sands and silts deposited in subtidal and intertidal channels during and after the Holocene transgression maximum (6.4-4.3 cal kyr BP), the sedimentation of clayey-sandy silts in low and high marshes during the last 2.4 kyr BP and a final anthropic filling. Three sharp peaks of pollution have been detected, representing a) a natural origin during the Holocene transgression; b) the impact of the first mining activities (~4.5 cal kyr BP); and c) the effect of industrial discharge and a new period of mining activity throughout the 19th and 20th centuries. Foraminifera, ostracods and molluscs disappeared during these last two peaks

Geodivulgar: Geología y Sociedad

Depto. de Geodinámica, Estratigrafía y PaleontologíaDepto. de Química InorgánicaDepto. de Didáctica de las Ciencias Experimentales , Sociales y MatemáticasFac. de Ciencias GeológicasFac. de Ciencias QuímicasFac. de EducaciónFALSEsubmitte

Apixaban compared with warfarin in patients with atrial fibrillation and previous stroke or transient ischaemic attack: A subgroup analysis of the ARISTOTLE trial

Background: In the ARISTOTLE trial, the rate of stroke or systemic embolism was reduced by apixaban compared with warfarin in patients with atrial fibrillation (AF). Patients with AF and previous stroke or transient ischaemic attack (TIA) have a high risk of stroke. We therefore aimed to assess the efficacy and safety of apixaban compared with warfarin in prespecified subgroups of patients with and without previous stroke or TIA. Methods: Between Dec 19, 2006, and April 2, 2010, patients were enrolled in the ARISTOTLE trial at 1034 clinical sites in 39 countries. 18 201 patients with AF or atrial flutter were randomly assigned to receive apixaban 5 mg twice daily or warfarin (target international normalised ratio 2·0-3·0). The median duration of follow-up was 1·8 years (IQR 1·4-2·3). The primary efficacy outcome was stroke or systemic embolism, analysed by intention to treat. The primary safety outcome was major bleeding in the on-treatment population. All participants, investigators, and sponsors were masked to treatment assignments. In this subgroup analysis, we estimated event rates and used Cox models to compare outcomes in patients with and without previous stroke or TIA. The ARISTOTLE trial is registered with ClinicalTrials.gov, number NTC00412984. Findings: Of the trial population, 3436 (19%) had a previous stroke or TIA. In the subgroup of patients with previous stroke or TIA, the rate of stroke or systemic embolism was 2·46 per 100 patient-years of follow-up in the apixaban group and 3·24 in the warfarin group (hazard ratio [HR] 0·76, 95% CI 0·56 to 1·03); in the subgroup of patients without previous stroke or TIA, the rate of stroke or systemic embolism was 1·01 per 100 patient-years of follow-up with apixaban and 1·23 with warfarin (HR 0·82, 95% CI 0·65 to 1·03; p for interaction=0·71). The absolute reduction in the rate of stroke and systemic embolism with apixaban versus warfarin was 0·77 per 100 patient-years of follow-up (95% CI -0·08 to 1·63) in patients with and 0·22 (-0·03 to 0·47) in those without previous stroke or TIA. The difference in major bleeding with apixaban compared with warfarin was 1·07 per 100 patient-years (95% CI 0·09-2·04) in patients with and 0·93 (0·54-1·32) in those without previous stroke or TIA. Interpretation: The effects of apixaban versus warfarin were consistent in patients with AF with and without previous stroke or TIA. Owing to the higher risk of these outcomes in patients with previous stroke or TIA, the absolute benefits of apixaban might be greater in this population. Funding: Bristol-Myers Squibb and Pfizer. © 2012 Elsevier Ltd

Apixaban versus warfarin in patients with atrial fibrillation

BACKGROUND: Vitamin K antagonists are highly effective in preventing stroke in patients with atrial fibrillation but have several limitations. Apixaban is a novel oral direct factor Xa inhibitor that has been shown to reduce the risk of stroke in a similar population in comparison with aspirin. METHODS: In this randomized, double-blind trial, we compared apixaban (at a dose of 5 mg twice daily) with warfarin (target international normalized ratio, 2.0 to 3.0) in 18,201 patients with atrial fibrillation and at least one additional risk factor for stroke. The primary outcome was ischemic or hemorrhagic stroke or systemic embolism. The trial was designed to test for noninferiority, with key secondary objectives of testing for superiority with respect to the primary outcome and to the rates of major bleeding and death from any cause. RESULTS: The median duration of follow-up was 1.8 years. The rate of the primary outcome was 1.27% per year in the apixaban group, as compared with 1.60% per year in the warfarin group (hazard ratio with apixaban, 0.79; 95% confidence interval [CI], 0.66 to 0.95; P<0.001 for noninferiority; P = 0.01 for superiority). The rate of major bleeding was 2.13% per year in the apixaban group, as compared with 3.09% per year in the warfarin group (hazard ratio, 0.69; 95% CI, 0.60 to 0.80; P<0.001), and the rates of death from any cause were 3.52% and 3.94%, respectively (hazard ratio, 0.89; 95% CI, 0.80 to 0.99; P = 0.047). The rate of hemorrhagic stroke was 0.24% per year in the apixaban group, as compared with 0.47% per year in the warfarin group (hazard ratio, 0.51; 95% CI, 0.35 to 0.75; P<0.001), and the rate of ischemic or uncertain type of stroke was 0.97% per year in the apixaban group and 1.05% per year in the warfarin group (hazard ratio, 0.92; 95% CI, 0.74 to 1.13; P = 0.42). CONCLUSIONS: In patients with atrial fibrillation, apixaban was superior to warfarin in preventing stroke or systemic embolism, caused less bleeding, and resulted in lower mortality. Copyright © 2011 Massachusetts Medical Society. All rights reserved