152 research outputs found

    Envejecimiento hidrotérmico en nanocompuestos epoxi/organoarcilla

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    Las dispersiones de organoarcillas como refuerzo en nanocompuestos de matriz polimérica han sido ampliamente estudiadas como una vía en la mejora de las propiedades (mecánicas, térmicas, de barrera frente a gases y disolventes e inflamabilidad). Una ventaja añadida es que se consigue una mejora de propiedades con la adición de una pequeña cantidad de refuerzo. En este trabajo se han preparado nanocompuestos basados en una matriz epoxi tipo DGEBA reforzada con dos organoarcillas, C30B e I.30E. Con el fin de mejorar la interfase matriz-refuerzo, también se han preparado nanocompuestos en los que las organoarcillas han sido previamente funcionalizadas a través del anclaje a la superficie de las mismas de un agente silano que contiene grupos reactivos con la matriz. Se ha realizado el estudio de la absorción de agua de estos nanocompuestos a temperatura constante hasta alcanzar el equilibrio de hinchamiento, determinando gravimétricamente la cantidad de agua absorbida en función del tiempo. El análisis de los resultados mediante el modelo de Fick y Langmuir nos ha permitido obtener los valores de los coeficientes de difusión (D). Los nanocompuestos han sido caracterizados mediante Difracción de Rayos X (DRX) y Calorimetría Diferencial de Barrido (DSC). Los valores de D obtenidos por el modelo de Fick son menores que los hallados a través del modelo de Langmuir, el cual se ajusta mejor a los valores experimentales. Como resultado y de acuerdo con la bibliografía, se ha observado que la presencia de las organoarcillas disminuyen el valor de D debido al camino tortuoso que ha de seguir el agua a través del nanocompuesto. Sin embargo, la presencia de grupos silano no mejora los resultados obtenidos del coeficiente de difusión para los nanocompuestos epoxi/organoarcilla

    Influence of different organoclays on the curing, morphology, and dynamic mechanical properties of an epoxy adhesive

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    The thermal, mechanical, and adhesive properties of nanoclay-modified adhesives were investigated. Two organically modified montmorillonites: Cloisite 93A (C93A) and Nanomer I.30E (I.30E) were used as reinforcement of an epoxy adhesive. C93A and I.30E are modified with tertiary and primary alkyl ammonium cations, respectively. The aim was to study the influence of the organoclays on the curing, and on the mechanical and adhesive properties of the nanocomposites. A specific goal was to compare their behavior with that of Cloisite30B/epoxy and Cloisite15A/ epoxy nanocomposites that we have previously studied. Both C30B and C15A are modified with quaternary alkyl ammonium cations. Differential scanning calorimetry results showed that the clays accelerate the curing reaction, an effect that is related to the chemical structure of the ammonium cations. The three Cloisite/nanocomposites showed intercalated clay structures,the interlayer distance was independent of the clay content. The I.30E/epoxy nanocomposites presented exfoliated structure due to the catalytic effect of the organic modifier. Clay-epoxy nanocompo-sites showed lower glass transition temperature (Tg) and higher values of storage modulus than neat epoxy thermoset, with no significant differences between exfoliated or intercalated nanocom-posites. The shear strength of aluminum joints using clay/epoxy adhesives was lower than with the neat epoxy adhesive. The wáter aging was less damaging for joints with I.30E/epoxy adhesive

    Validación a largo plazo de datos de nivel 3 de tierra de SMOS con medidas de ELBARA-II en la Valencia Anchor Station

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    Revista oficial de la Asociación Española de Teledetección[EN] The Soil Moisture and Ocean Salinity (SMOS) mission was launched on 2nd November 2009 with the objective of providing global estimations of soil moisture and sea salinity. The main activity of the Valencia Anchor Station (VAS) is currently to assist in a long-term validation of SMOS land products. This study focus on a level 3 SMOS data validation with in situ measurements carried out in the period 2010-2012 over the VAS. ELBARA-II radiometer is placed in the VAS area, observing a vineyard field considered as representative of a major proportion of an area of 50×50 km, enough to cover a SMOS footprint. Brightness temperatures (TB) acquired by ELBARA-II have been compared to those observed by SMOS at the same dates and time. They were also used for the L-MEB model inversion to retrieve soil moisture (SM), which later on have been compared to those provided by SMOS as level 3 data. A good correlation between both TB datasets was found, improving year by year, mainly due to the decrease of precipitations in the analyzed period and the mitigation of radio frequency interferences at L-band. The larger homogeneity of the radiometer footprint as compared to SMOS explains the higher variability of its TB. Periods of more intense precipitation (spring and autumn) also presented higher SM, which corroborates the consistency of SM retrieved from ELBARA-II’s observations. However, the results show that SMOS level 3 data underestimate SM as compared to ELBARA-II’s, probably due to the influence of the small soil fraction which is not cultivated in vineyards. SMOS estimations in descending orbit (6 pm) had better quality (higher correlation, lower RMSE and bias) than the ones in ascending orbit (6 am, when there is a higher soil moisture). Guardar / Salir Siguiente >[ES] La misión de SMOS (Soil Moisture and Ocean Salinity) se lanzó el 2 de Noviembre de 2009 con el objetivo de proporcionar datos de humedad del suelo y salinidad del mar. La principal actividad de la conocida como Valencia Anchor Station(VAS) es asistir en la validación a largo plazo de productos de suelo de SMOS. El presente estudio se centra en una validación de datos de nivel 3 de SMOS en la VAS con medidas in situ tomadas en el periodo 2010-2012. El radiómetro ELBARA-II está situado dentro de los confines de la VAS, observando un campo de viñedos que se con-sidera representativo de una gran proporción de un área de 50×50 km, suficiente para cubrir un footprint de SMOS. Las temperaturas de brillo (TB) adquiridas por ELBARA-II se compararon con las observadas por SMOS en las mismas fechas y horas. También se utilizó la inversión del modelo L-MEB con el fin de obtener humedades de suelo (SM) que, posteriormente, se compararon con datos de nivel 3 de SMOS. Se ha encontrado una buena correlación entre ambas series de TB, con mejoras año tras año, achacable fundamentalmente a la disminución de precipitaciones en el perio-do objeto de estudio y a la mitigación de las interferencias por radiofrecuencia en banda L. La mayor homogeneidad del footprintdel radiómetro ELBARA-II frente al de SMOS explica la mayor variabilidad de sus TB. Los periodos de preci-pitación más intensa (primavera y otoño) también son de mayor SM, lo que corrobora la consistencia de los resultados de SM simulados a través de las observaciones del radiómetro. Sin embargo, se debe resaltar una subestimación por parte de SMOS de los valores de SM respecto a los obtenidos por ELBARA-II, presumiblemente debido a la influencia que la pequeña fracción de suelo no destinado al cultivo de la vid tiene sobre SMOS. Las estimaciones por parte de SMOS en órbita descendente (6 p.m.) resultaron de mayor calidad (mayor correlación y menores RMSE y bias) que en órbita ascendente (6 a.m., momento de mayor humedad de suelo).This work is carried out within the framework of the project MIDAS-7/UVEG Productos y Aplicaciones Avanzados de SMOS y Futuras Misiones (Parte UVEG) from the Spanish Research Programme on Space, Spanish Ministry for Economy and Competitiveness.Fernandez-Moran, R.; Wigneron, JP.; López-Baeza, E.; Miernecki, M.; Salgado-Hernanz, P.; Coll, M.; Kerr, YH.... (2015). Towards a long-term dataset of ELBARA-II measurements assisting SMOS level-3 land product and algorithm validation at the Valencia Anchor Station. Revista de Teledetección. (43):55-62. doi:10.4995/raet.2015.2297.SWORD55624

    Two-loop two-point functions with masses: asymptotic expansions and Taylor series, in any dimension

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    In all mass cases needed for quark and gluon self-energies, the two-loop master diagram is expanded at large and small q2q^2, in dd dimensions, using identities derived from integration by parts. Expansions are given, in terms of hypergeometric series, for all gluon diagrams and for all but one of the quark diagrams; expansions of the latter are obtained from differential equations. Pad\'{e} approximants to truncations of the expansions are shown to be of great utility. As an application, we obtain the two-loop photon self-energy, for all dd, and achieve highly accelerated convergence of its expansions in powers of q2/m2q^2/m^2 or m2/q2m^2/q^2, for d=4d=4.Comment: 25 pages, OUT--4102--43, BI--TP/92--5

    Cost-effectiveness of exercise referral schemes enhanced by self-management strategies to battle sedentary behaviour in older adults: Protocol for an economic evaluation alongside the SITLESS three-armed pragmatic randomised controlled trial

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    Introduction: Promoting physical activity (PA) and reducing sedentary behaviour (SB) may exert beneficial effects on the older adult population, improving behavioural, functional, health and psychosocial outcomes in addition to reducing health, social care and personal costs. This paper describes the planned economic evaluation of SITLESS, a multicountry three-armed pragmatic randomised controlled trial (RCT) which aims to assess the short-term and long-term effectiveness and cost-effectiveness of a complex intervention on SB and PA in community-dwelling older adults, based on exercise referral schemes enhanced by a group intervention providing self-management strategies to encourage lifestyle change. Methods and analysis: A within-trial economic evaluation and long-term model from both a National Health Service/personal social services perspective and a broader societal perspective will be undertaken alongside the SITLESS multinational RCT. Healthcare costs (hospitalisations, accident and emergency visits, appointment with health professionals) and social care costs (eg, community care) will be included in the economic evaluation. For the cost-utility analysis, quality-adjusted life-years will be measured using the EQ-5D-5L and capability well-being measured using the ICEpop CAPability measure for Older people (ICECAP-O) questionnaire. Other effectiveness outcomes (health related, behavioural, functional) will be incorporated into a cost-effectiveness analysis and cost-consequence analysis. The multinational nature of this RCT implies a hierarchical structure of the data and unobserved heterogeneity between clusters that needs to be adequately modelled with appropriate statistical and econometric techniques. In addition, a long-term population health economic model will be developed and will synthesise and extrapolate within-trial data with additional data extracted from the literature linking PA and SB outcomes with longer term health states. Methods guidance for population health economic evaluation will be adopted including the use of a long-time horizon, 1.5% discount rate for costs and benefits, cost consequence analysis framework and a multisector perspective. Ethics and dissemination: The study design was approved by the ethics and research committee of each intervention site: the Ethics and Research Committee of Ramon Llull University (reference number: 1314001P) (Fundació Blanquerna, Spain), the Regional Committees on Health Research Ethics for Southern Denmark (reference number: S-20150186) (University of Southern Denmark, Denmark), Office for Research Ethics Committees in Northern Ireland (ORECNI reference number: 16/NI/0185) (Queen’s University of Belfast) and the Ethical Review Board of Ulm University (reference number: 354/15) (Ulm, Germany). Participation is voluntary and all participants will be asked to sign informed consent before the start of the study. This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement number 634 270. This article reflects only the authors' view and the Commission is not responsible for any use that may be made of the information it contains. The findings of the study will be disseminated to different target groups (academia, policymakers, end users) through different means following the national ethical guidelines and the dissemination regulation of the Horizon 2020 funding agency. Use of the EuroQol was registered with the EuroQol Group in 2016. Use of the ICECAP-O was registered with the University of Birmingham in March 2017. Trial registration number: NCT02629666; Pre-results

    Additional value of screening for minor genes and copy number variants in hypertrophic cardiomyopathy

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    Introduction: Hypertrophic cardiomyopathy (HCM) is the most prevalent inherited heart disease. Next-generation sequencing (NGS) is the preferred genetic test, but the diagnostic value of screening for minor and candidate genes, and the role of copy number variants (CNVs) deserves further evaluation. Methods: Three hundred and eighty-seven consecutive unrelated patients with HCM were screened for genetic variants in the 5 most frequent genes (MYBPC3, MYH7, TNNT2, TNNI3 and TPM1) using Sanger sequencing (N = 84) or NGS (N = 303). In the NGS cohort we analyzed 20 additional minor or candidate genes, and applied a proprietary bioinformatics algorithm for detecting CNVs. Additionally, the rate and classification of TTN variants in HCM were compared with 427 patients without structural heart disease. Results: The percentage of patients with pathogenic/likely pathogenic (P/LP) variants in the main genes was 33.3%, without significant differences between the Sanger sequencing and NGS cohorts. The screening for 20 additional genes revealed LP variants in ACTC1, MYL2, MYL3, TNNC1, GLA and PRKAG2 in 12 patients. This approach resulted in more inconclusive tests (36.0% vs. 9.6%, p<0.001), mostly due to variants of unknown significance (VUS) in TTN. The detection rate of rare variants in TTN was not significantly different to that found in the group of patients without structural heart disease. In the NGS cohort, 4 patients (1.3%) had pathogenic CNVs: 2 deletions in MYBPC3 and 2 deletions involving the complete coding region of PLN. Conclusions: A small percentage of HCM cases without point mutations in the 5 main genes are explained by P/LP variants in minor or candidate genes and CNVs. Screening for variants in TTN in HCM patients drastically increases the number of inconclusive tests, and shows a rate of VUS that is similar to patients without structural heart disease, suggesting that this gene should not be analyzed for clinical purposes in HCM

    Limit cycles in uniform isochronous centers of discontinuous differential systems with four zones

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    We apply the averaging theory of first order for discontinuous differential systems to study the bifurcation of limit cycles from the periodic orbits of the uniform isochronous center of the differential systems ẋ = -y+x, y = x + xy, and ẋ = -y + xy, y = x + xy, when they are perturbed inside the class of all discontinuous quadratic and cubic polynomials differential systems with four zones separately by the axes of coordinates, respectively. Using averaging theory of first order the maximum number of limit cycles that we can obtain is twice the maximum number of limit cycles obtained in a previous work for discontinuous quadratic differential systems perturbing the same uniform isochronous quadratic center at origin perturbed with two zones separately by a straight line, and 5 more limit cycles than those achieved in a prior result for discontinuous cubic differential systems with the same uniform isochronous cubic center at the origin perturbed with two zones separately by a straight line. Comparing our results with those obtained perturbing the mentioned centers by the continuous quadratic and cubic differential systems we obtain 8 and 9 more limit cycles respectively
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