ANALISI DELLO STATO TENSIONALE IN RESINE EPOSSIDICHE SOTTOPOSTE AD INVECCHIAMENTO IDROTERMICO MEDIANTE TECNICA FOTOELASTICA

In questo lavoro si è analizzato lo stato tensionale che nasce in sistemi epossidici DGEBA quando sono sottoposti ad invecchiamento idro-termico, tramite la tecnica fotoelastica a trasmissione, basata sul metodo a variazione di fase di Compensazione di Tardy. I provini, monitorati ad intervalli di tempo regolari durante i processi di assorbimento e desorbimento di acqua, sono stati osservati al polariscopio circolare. La tecnica ha permesso di analizzare, sia qualitativamente, sia quantitativamente, lo stato tensionale indotto dal non uniforme “swelling” durante l’intero processo di invecchiamento. Inoltre, lo studio ha analizzato anche provini criccati di tipo Single Edge Notched Bending; l’analisi fotoelastica ha evidenziato come all’apice della cricca si crea un sistema di frange fotoelastiche peculiari, influenzato dalla presenza della singolarit

Water diffusion and swelling stresses in highly crosslinked epoxy matrices

The present work investigates the swelling induced stresses arising in two epoxy systems during water uptake. The analysed systems are two epoxy resin based on DGEBA monomer and DGEBF monomer respectively, both fully cured by DDS amine. The systems achieve different cross-link density degrees, and are characterised by high glass transition temperatures ranging between 200 and 230 °C. Both epoxies have been conditioned in deionized water baths at two different temperatures (50 °C and 80 °C). A desorption process at room temperature in a dry airborne environment was performed after saturation. Dynamic Mechanical Thermal Analysis, carried out at the various stages of hydrothermal conditioning, has allowed to characterise the modifications occurring in the network structures during aging. Photoelastic Stress Analysis is adopted to monitor the evolution of stresses on rectangular beam samples during absorption and desorption of water. Correlation of water uptake, dynamic mechanical behaviour and transitory stress fields, has allowed to make some assumptions about the influence of the epoxy network on the swelling behaviour

Determinação e análise estatística da composição de gases produzidos num piloto de recuperação avançada de petróleo

The oil industry in Colombia has the challenge of exploiting deposits with heavy and extra-heavy oil. For this reason, Enhanced Oil Recovery methods (EOR) have been implemented in the country, looking for high production rates. Air injection is one of the EOR methods that allows to achieve high production rates. The Air Injection Pilot (PIAR) at Chichimene (Meta) is a pioneer in the world for implementing this method in a reserve of extra heavy oil (API <10) in a high depth. The monitoring of the physicochemical properties of the fluids generated during this process helps to ensure the correct operational functioning of the pilot. In this work, the gas composition from 16 wells located in the pilot area was determined by gas chromatography (GC). Methane was found mainly (68.5 ± 7.1), followed by CO2 (11.4 ± 5.6) and N2 (6.7 ± 4.2). The composition of the gases was dissimilar throughout the area, so Principal Component Analysis (PCA) and Cluster Analysis (CA) were made to assess the similarities between the gases of the wells. As a result, the wells were organized into three groups by similarity: a group with the highest methane levels (75.8%); the second group with N2 (11.9%); and a third group with the highest CO2 values (20.1%), consisting of three wells. These groups were plotted on a map and it was noted that they are in defined areas within the pilot.La industria petrolera en Colombia tiene el desafío de la explotación de yacimientos con crudo pesado y extrapesado. Por este motivo, en el país se han implementado métodos de recobro mejorado (EOR) que suelen tener altos índices de producción. La inyección de aire es uno de los métodos de recobro mejorado que permite alcanzar altos índices de producción. La planta Piloto de Inyección de Aire para Recobro (PIAR), ubicada en Chichimene (Meta), es pionera en el mundo por implementar este método en una reserva de crudo extrapesado (API<10) de alta profundidad. El monitoreo de las propiedades fisicoquímicas de los fluidos generados durante este proceso contribuye a asegurar el correcto funcionamiento operativo del piloto. En este trabajo se determinó por cromatografía de gases (GC) la composición de los gases de producción de 16 pozos ubicados en el área del piloto. Se encontró principalmente metano (68.5±7.1), CO2 (11.4±5.6) y N2 (6.7±4.2). La composición de los gases fue disímil en toda el área, por lo que se hicieron análisis multivariados Análisis de Componentes Principales (ACP) y Análisis de Conglomerados (AC) para evaluar las similitudes entre los gases de los pozos. Como resultado, los pozos fueron organizados en tres grupos por similitud: un grupo con los niveles más altos de metano (75.8%); el segundo grupo con N2 (11.9%) y un tercer grupo con los valores más altos de CO2 (20.1%), conformado por tres pozos. Estos grupos fueron graficados en un mapa y se observó que se encuentran en áreas muy definidas dentro del piloto.A indústria petroleira em Colômbia tem o desafio da exploração de depósitos com petróleo pesado e extrapesado. Por este motivo, no país tem sido implementados métodos de recuperação avançada de petróleo (EOR) os quais apresentam altos índices de produção. A injeção de ar é um dos métodos de recuperação que permite alcançar altos índices de produção. A planta piloto de injeção de ar para recobro (PIAR) no campo Chichimene (Meta) é pioneira no mundo por implementar este método numa reserva de petróleo extrapesado (API <10) de alta profundidade. O monitoramento das propriedades físico-químicas dos fluidos gerados durante este processo contribui no asseguramento do correto funcionamento operativo do piloto. Neste trabalho determinou-se por cromatografia de gases (GC) a composição dos gases de produção de 16 poços localizados na área do piloto. Encontrou-se principalmente metano (68,5 ± 7,1), CO2 (11,4 ± 5,6) e N2 (6,7 ± 4,2). A composição dos gases foi variável em toda a área, por tanto foram feitos análise multivariados análise de componentes principais (ACP) e análise de conglomerados (AC) para avaliar as semelhanças entre os gases dos poços. Como resultado os poços se organizaram em 3 grupos por similaridade: um grupo com os níveis mais altos de metano (75.8%); o segundo grupo com N2 (11,9%); e um terceiro grupo com os valores mais altos de CO2 (20,1%), conformado por três poços. Estes grupos foram plotados em um mapa e observou-se que se encontram em áreas bem definidas dentro do piloto

Fracture Toughness of Hydrothermally Aged Epoxy Systems with Different Crosslink Density

The present work investigates the fracture toughness behaviour of Single Edge Notched Bending (SENB) samples of epoxy systems subject to water uptake aging. Two epoxy systems with a significantly different Glass Transition Temperature, Tg, are in particular considered: a typical commercial non-aeronautical grade resin matrix for composite applications, reaching aTgof 90°C, and a DGEBA+DDS epoxy system achieving a Tg of 230°C.The materials have been conditioned by hydrothermal aging in a thermal bath at the temperature of 50°C. TransmissionPhotoelastic Stress Analysisis carried outon SENB samples during water aging, monitoring the presence and evolution of swelling stresses. The KIC Fracture toughness is measured and correlated with the internal stress field, with the water diffusion kinetics evaluated by gravimetric tests, and with the data from DMTA analyses. Results have highlighted significant differences in the fracture behaviour ofthe two epoxy systems

Where Brain, Body and World Collide

The production cross section of electrons from semileptonic decays of beauty hadrons was measured at mid-rapidity (|y| < 0.8) in the transverse momentum range 1 < pt < 8 Gev/c with the ALICE experiment at the CERN LHC in pp collisions at a center of mass energy sqrt{s} = 7 TeV using an integrated luminosity of 2.2 nb^{-1}. Electrons from beauty hadron decays were selected based on the displacement of the decay vertex from the collision vertex. A perturbative QCD calculation agrees with the measurement within uncertainties. The data were extrapolated to the full phase space to determine the total cross section for the production of beauty quark-antiquark pairs

European Multicenter Study of ET-COVID-19

International audienceBackground and Purpose: Acute ischemic stroke and large vessel occlusion can be concurrent with the coronavirus disease 2019 (COVID-19) infection. Outcomes after mechanical thrombectomy (MT) for large vessel occlusion in patients with COVID-19 are substantially unknown. Our aim was to study early outcomes after MT in patients with COVID-19. Methods: Multicenter, European, cohort study involving 34 stroke centers in France, Italy, Spain, and Belgium. Data were collected between March 1, 2020 and May 5, 2020. Consecutive laboratory-confirmed COVID-19 cases with large vessel occlusion, who were treated with MT, were included. Primary investigated outcome: 30-day mortality. Secondary outcomes: early neurological improvement (National Institutes of Health Stroke Scale improvement ≥8 points or 24 hours National Institutes of Health Stroke Scale 0–1), successful reperfusion (modified Thrombolysis in Cerebral Infarction grade ≥2b), and symptomatic intracranial hemorrhage. Results: We evaluated 93 patients with COVID-19 with large vessel occlusion who underwent MT (median age, 71 years [interquartile range, 59–79]; 63 men [67.7%]). Median pretreatment National Institutes of Health Stroke Scale and Alberta Stroke Program Early CT Score were 17 (interquartile range, 11–21) and 8 (interquartile range, 7–9), respectively. Anterior circulation acute ischemic stroke represented 93.5% of cases. The rate modified Thrombolysis in Cerebral Infarction 2b to 3 was 79.6% (74 patients [95% CI, 71.3–87.8]). Thirty-day mortality was 29% (27 patients [95% CI, 20–39.4]). Early neurological improvement was 19.5% (17 patients [95% CI, 11.8–29.5]), and symptomatic intracranial hemorrhage was 5.4% (5 patients [95% CI, 1.7–12.1]). Patients who died at 30 days exhibited significantly lower lymphocyte count, higher levels of aspartate, and LDH (lactate dehydrogenase). After adjustment for age, initial National Institutes of Health Stroke Scale, Alberta Stroke Program Early CT Score, and successful reperfusion, these biological markers remained associated with increased odds of 30-day mortality (adjusted odds ratio of 2.70 [95% CI, 1.21–5.98] per SD-log decrease in lymphocyte count, 2.66 [95% CI, 1.22–5.77] per SD-log increase in aspartate, and 4.30 [95% CI, 1.43–12.91] per SD-log increase in LDH). Conclusions: The 29% rate of 30-day mortality after MT among patients with COVID-19 is not negligible. Abnormalities of lymphocyte count, LDH and aspartate may depict a patient’s profiles with poorer outcomes after MT. Registration: URL: https://www.clinicaltrials.gov . Unique identifier: NCT04406090

Charge correlations using the balance function in Pb?Pb collisions at ?sNN = 2.76 TeV

In high-energy heavy-ion collisions, the correlations between the emitted particles can be used as a probe to gain insight into the charge creation mechanisms. In this article, we report the first results of such studies using the electric charge balance function in the relative pseudorapidity \Delta\eta and azimuthal angle \Delta\phi in Pb-Pb collisions at sqrt{s_{NN}} = 2.76 TeV with the ALICE detector at the Large Hadron Collider. The width of the balance function decreases with growing centrality (i.e. for more central collisions) in both projections. This centrality dependence is not reproduced by HIJING, while AMPT, a model which incorporates strings and parton rescattering, exhibits qualitative agreement with the measured correlations in \Delta\phi but fails to describe the correlations in \Delta\eta. A thermal blast wave model incorporating local charge conservation and tuned to describe the p_T spectra and v_2 measurements reported by ALICE, is used to fit the centrality dependence of the width of the balance function and to extract the average separation of balancing charges at freeze-out. The comparison of our results with measurements at lower energies reveals an ordering with sqrt{s_{NN}}: the balance functions become narrower with increasing energy for all centralities. This is consistent with the effect of larger radial flow at the LHC energies but also with the late stage creation scenario of balancing charges. However, the relative decrease of the balance function widths in \Delta\eta and \Delta\phi with centrality from the highest SPS to the LHC energy exhibits only small differences. This observation cannot be interpreted solely within the framework where the majority of the charge is produced at a later stage in the evolution of the heavy-ion collision