46,220 research outputs found
Implementation of viscoelastic Hopkinson bars
No full textIncludes bibliographical references (p. 107-112).The properties of soft, viscoelastic materials at high strain rates are important in furthering our understanding of their role during blast or impact events. Testing these soft or low impedance materials using metallic bars in a split Hopkinson pressure bar setup, poor signal to noise ratios and impedance mismatching occur. One solution is to use polymeric Hopkinson bars. In this dissertation, Polycarbonate, Polymethyl Methacrylate and Nylon are considered for use as Hopkinson bars. Conventional Hopkinson bar analysis cannot be used on the polymeric bars due to the viscoelastic nature of the bar material. As stress waves propagate along the length of the bars, viscoelastic effects result in dispersion and attenuation. The main topic of this dissertation is to account for this viscoelastic material effect
The hydrothermal plumbing of a serpentinite-hosted detachment: evidence from the West Iberia non-volcanic rifted continental margin
No full textThis study documents the critical role of structurally-induced fluid flow during the evolution of the footwall succession to a major low-angle normal (detachment) fault, drilled by the Ocean Drilling Program leg 173, Site 1068 beneath the Southern Iberia Abyssal Plain. The fault zone comprises (carbonate-altered, rodingitized, and albitized) metabasite-rich sedimentary breccias and serpentinized mantle peridotites. The brittle infrastructure of the detachment consists of mineralized high dilation breccias, and meshes of mineralized extensional and shear veins, that root into
chlorite and serpentine cataclasite, and gouge. The fault rocks are underlain by cohesive serpentinite that shows kernel textures, indicative of volume expansion accompanying serpentinization of peridotite. The texture is disrupted and offset by small-scale fractures and faults. The distribution of serpentine polytypes, carbonates, Fe^Ni alloys, sulfides, oxides, and other silicate phases, varies across the fault zone in patterns consistent with mineralization, and replacement, from solutions derived from two end member components: seawater, and CH4-bearing calciumhydroxide
enriched hydrothermal solutions. The latter form when heated seawater reacts with peridotite to form serpentinite at low water to rock ratios. Serpentine mineral chemistries indicate that fracture-controlled serpentinite recrystallization and replacement occurred at various fO2, aSiO2 and Ca2þ conditions. In places this also involved mild prograde thermal events. The serpentinite also hosts tochilinite-valleriite group minerals and aragonite, both are interpreted as indicators of sea water incursions into the upper reaches of the detachment. To account for the evidence of coeval hydrothermal mineralization and displacements across the detachment we relate hydrothermal discharge to the buffering of high pore fluid pressures by fault slip. Localized sources of high fluid pressures at depth are attributed to serpentinization of peridotite around the fault that promotes changes to solution mass density, exothermic reactions and swelling pressures. Sealing of the fault between the serpentinization front and the top of the detachment results from hydrothermal mineralization, alteration, and serpentine gouges. Hydrothermal discharges from the detachment accompanying shear failure allow for variable mixing between the hydrothermal solutions and seawater, and post-slip convective draw down of seawater into the detachment. It is suggested that the latter may have been limited in duration by ongoing mineralization leading to the restoration of the fault seal. Concomitant serpentinization around the detachment at depth provides scope for cyclic hydrothermal discharges and fault slip
Psychosocial implications of living 5 years or more following a cancer diagnosis: a systematic review of the research evidence
No full textMortality associated with cancer remains high, but more people are surviving cancer. Some people experience long-term problems associated with cancer and its treatment, and there is a need to know how to support them. This systematic literature review explores primary research for psychosocial implications of long-term survival (>or=5 years) following a cancer diagnosis and interventions designed to address psychosocial problems in the long term. A systematic search of BIDS, BNI, Cancer.gov, CINAHL, Medline, PsychINFO and Web of Science was conducted to identify research publications from 1960 to 2006. Papers were selected on the basis of pre-defined criteria and rated by three independent coders. Forty-three studies met the eligibility criteria. These indicated that most people experience few problems five or more years after their diagnosis of cancer. However, 20-30% of survivors consistently reported problems associated with cancer and its treatment including physical problems, poorer quality of life, psychological distress, sexual problems, problems with social relationships and financial concerns. Not all cancer types are represented in this review. Only two intervention studies met the eligibility criteria. Research is needed to establish appropriate interventions to support those experiencing problems in the long term to enhance well-being
OBTENCIÓN DE CURVAS Ɛ-T DE ALUMINIO PLEGADO MEDIANTE UN SISTEMA BARRA DE HOPKINSON (OBTAINING CURVES Ɛ-T OF FOLDED ALUMINUM BY MEANS OF A HOPKINSON BAR SYSTEM)
No full textUn Sistema Barra de Hopkinson fue utilizado para medir altas tazas de deformación a compresión de aluminio plegado. Para ello se seleccionó un material adecuado para las barras del Sistema de Hopkinson que fuera cercano a la impedancia del material a estudiar. Se realizó la instrumentación de la barra mediante galgas extensométricas con un arreglo de puente completo de Wheatstone y un adquisidor de datos. Las gráficas obtenidas de deformación (Ɛ) en función del tiempo (t) muestran un comportamiento típico de materiales de baja impedancia, tal como es reportado en la literatura. La configuración lograda para el Sistema Barra de Hopkinson permitirá obtener la respuesta dinámica de deformación de materiales suaves o de baja impedancia, así como caracterizar las propiedades mecánicas de los mismos.Palabra(s) Clave: Aluminio plegado, Barra de Hopkinson, Materiales suaves. AbstractA Hopkinson Bar System was used to measure high rates of compression deformation of folded aluminum. For this, a suitable material was selected for the bars of the Hopkinson System that was close to the impedance of the material to be studied. The instrumentation of the bar was performed by strain gauges with a complete Wheatstone bridge arrangement and a data acquisition. The graphs obtained from deformation (Ɛ) as a function of time (t) show a typical behavior of low impedance materials, as reported in the literature. The configuration achieved for the Hopkinson Bar System will allow to obtain the dynamic deformation response of soft or low impedance materials, as well as to characterize the mechanical properties of them.Keywords: Folded aluminum, Hopkinson Bar, Soft materials
Endothelial failure and rejection in recipients of corneas from the same donor
No full textObjectiveTo determine whether patients who receive corneas from the same donor have similar risks of endothelial failure and rejection.Methods and AnalysisPatients with Fuchs endothelial dystrophy (FED) and pseudophakic bullous keratopathy (PBK) who received their first corneal transplant between 1999 and 2016 were analysed. Patients receiving corneas from donors who donated both corneas for the same indication were defined as ‘paired’. Gray’s test was used to compare the cumulative incidence of endothelial failure and rejection within 5 years post-transplant for ‘paired’ and ‘unpaired’ groups. Cox regression models were fitted to determine whether there was an association between recorded donor characteristics (endothelial cell density (ECD), age and sex and endothelial graft failure and rejection.Results10 838 patients were analysed of whom 1536 (14%) were paired. The unpaired group comprised 1837 (69%) recipients of single corneal donors and 7465 (69%) donors who donated both corneas for another indication. ECD was lower for unpaired single cornea donors (p<0.01). There was no significant difference in endothelial graft failure or rejection between paired and unpaired groups for FED (p=0.37, p=0.99) or PBK (p=0.88, p=0.28) nor for donor ECD, age, sex and paired donation after adjusting for transplant factors (across all models p>0.16 for ECD, p>0.32 for donor age, p>0.14 for sex match and p>0.17 for the donor effect).ConclusionThe absence of a significant difference in graft outcome for corneal transplants for FED and PBK between paired and unpaired donors may reflect a homogeneous donor pool in the UK.</jats:sec
Erratum to: Effect of moderate red wine intake on cardiac prognosis after recent acute myocardial infarction of subjects with Type 2 diabetes mellitus (Diabetic Medicine, (2006), 23, 9, (974-981), 10.1111/j.1464-5491.2006.01886.x)
No full textIn an article by Marfella et al, the author name C. Saron is incorrect and should be listed as C. Sardu. Therefore the correct author list is: R. Marfella, F. Cacciapuoti, M. Siniscalchi, F. C. Sasso, F. Marchese, F. Cinone, E. Musacchio, M. A. Marfella, L. Ruggiero, G. Chiorazzo, D. Liberti, G. Chiorazzo, G. F. Nicoletti, C. Sardu, F. D'Andrea, C. Ammendola, M. Verza and L. Coppola.In an article by Marfella et al, the author name C. Saron is incorrect and should be listed as C. Sardu. Therefore the correct author list is: R. Marfella, F. Cacciapuoti, M. Siniscalchi, F. C. Sasso, F. Marchese, F. Cinone, E. Musacchio, M. A. Marfella, L. Ruggiero, G. Chiorazzo, D. Liberti, G. Chiorazzo, G. F. Nicoletti, C. Sardu, F. D'Andrea, C. Ammendola, M. Verza and L. Coppola
CONSTRUCCIÓN DE UNA BARRA DE HOPKINSON PARA PRUEBAS DINÁMICAS EN MATERIALES PLEXOPLEGADOS
No full textRecientemente los materiales ligeros capaces de absorber energía se han estudiado como una alternativa innovadora para diferentes aplicaciones en el transporte o en el diseño de sistemas de absorción de impactos; las espumas de aluminio y las hojas de aluminio plegado ofrecen un campo de estudio muy amplio para las aplicaciones ya mencionadas, por lo que es importante el diseño y construcción de un dispositivo capaz de determinar el comportamiento de estos materiales ante una carga de compresión aplicada a altas velocidades. El ensayo de compresión utilizando un dispositivo de barra de Hopkinson es una opción que puede aportar la información deseada.En este artículo se muestra el proceso de construcción de este dispositivo, en el cual se consideran propiedades del material de ensayo como la impedancia acústica, cuya importancia es significativa para la selección de las barras que realizan la compresión durante el ensayo. Palabra(s) Clave(s): Aluminio plexoplegado, barra de Hopkinson, impedancia acústica, tasa de deformación
Boreal ecosystem changes due to permafrost thaw across the discontinuous to sporadic permafrost zone
No full textThis PhD thesis developed a framework to model, quantify, and improve understanding of spatially explicit changes in short-to-tall-stature vegetation structure in the southern Taiga of northwestern Canada. This region is still changing due to the retreat of the Laurentide Ice Sheet since the last glacial maximum (~22.1 cal ka BP). In addition, climate change has caused rapid ecosystem changes, for example due to permafrost thaw, with implications to carbon sink strength and wildland fire susceptibility, amongst others. Regional allometric equations for shrubs and short-stature trees were developed to estimate aboveground biomass (AGB) and live aboveground plant carbon stocks using 1D, 2D, and 3D field measurements. Spatially coincident bi-temporal airborne lidar data were used to develop a single AGB model applicable across changing relationships between lidar point clouds and AGB magnitudes as ecosystems change form, ecosystem boundaries expand and recede, and airborne lidar technologies evolve. By fusing field data with bi-temporal airborne lidar data, the study quantified and analyzed changes in vegetation structure and aboveground plant carbon stocks. By employing geospatial statistical analysis and machine learning the underlying important drivers of these changes were identified.
Key findings of this thesis were the following: (1) the developed framework has improved understanding of the magnitudes and directions of short-to-tall-stature vegetation structural changes over the past decade (2010 to 2019); (2) increases in the growth and abundance of short-stature vegetation were substantial across the study region and need to be integrated into carbon accounting frameworks with extension to unmanaged forest and peatland ecosystems. Overall, the established framework could aid in the modelling of wildland fire fuel dynamics and fire behavior also in peatlands, which could reduce community risk to fire in this region.This project was funded in part by NSERC Discovery Grants to L. Chasmer [Grant number: (2017-04492)] and C. Hopkinson [Grant number: (2017-04362)], a University of Lethbridge start up grant to L. Chasmer, the NSERC Canada Wildfire Network (Chasmer) [Grant number: RES0049086], a CFI grant for field survey equipment to C. Hopkinson [Grant number: (32436)], and a grant to purchase the Titan lidar system through Western Economic Diversification Canada [Grant number: (000015316)]
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