118,871 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
Electrokinetic iron pan generation in unconsolidated sediments: implications for contaminated land remediation and soil engineering
No full textElectrokinetic remediation is an emerging technology that has generated considerable interest as a technique for the in situ remediation of clay-rich soils and sediments. Despite promising experimental results, however, at present there is no standardised universal electrokinetic soil/sediment remediation approach. Many of the current technologies are technically complex and energy intensive, and geared towards the removal of 90% or more of specific contaminants, under very specific field or laboratory-based conditions. However, in the real environment a low-tech, low-energy contaminant reduction/containment technique may be more appropriate and realistic. Such a technique, FIRS (Ferric Iron Remediation and Stabilisation), is discussed here. The FIRS technique involves the application of a low magnitude (typically less than 0.2 V/cm) direct electric potential between two or more sacrificial, Fe-rich, electrodes emplaced in, or either side of, a contaminated soil or sediment. The electric potential is used to generate a strong pH (and Eh) gradient within the soil column (pH 2–13), and force the precipitation of an Fe-rich barrier or “pan” in the soil between the electrodes. Geochemical and geotechnical data for FIRS-treated sediments from the Ravenglass estuary, Cumbria, UK indicate that the technique can significantly reduce contaminant concentration in treated soil, by remobilisation of contaminants and concentration on, or around, the Fe-rich barrier. Arsenic, in particular, seems highly amenable to the FIRS treatment, due to its solubility under the high pH conditions generated near to the cathode, and its marked geochemical affinity with the freshly precipitated Fe oxides and oxyhydroxides in the Fe barrier. Geotechnical tests indicate that the Fe barrier produced by the technique is practically impervious (permeability = 10?9 m/s or less), and has moderate mechanical strength (UCS ?11 N/mm2). Notably, a large increase in shear strength in the treated soil near to the anode electrode (due to Fe cementation and/or dewatering) is also observed, without significant loss of porosity. The data indicate that the FIRS technique shows considerable promise as an in situ method for contaminated land remediation and soil water containment, and for improving the mechanical properties of soils (contaminated or otherwise) for civil engineering purposes
A fossil, serpentinization-related hydrothermal vent, Ocean Drilling Program Leg 173, Site 1068 (Iberia Abyssal Plain): some aspects of mineral and fluid chemistry
No full textUnimarc : What next ?
No full textIntervention audio en anglais de Alan Hopkinson, Chair of the PUC, Middlesex University évoquant le comité permanent Unimarc, l\u27histoire de l\u27Unimarc et son développement actuel
Unimarc : What Next ? - Diaporama
No full textDiaporama de l\u27intervention de Alan Hopkinson, représentant du Comité permanent Unimarc à l\u27occasion de la 3e Rencontre internationale des utilisateurs d\u27Unimarc
The nature of a serpentinite-hosted detachement fault underlying the Cretaceous proto-Atlantic: evidence from the Iberia non-volcanic rifted margin
No full textOBTENCIÓN 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
Experiences of health changes and reasons for delay in seeking care: a UK study of the months prior to the diagnosis of lung cancer
No full textThe problem of ‘delay’ in diagnosing cancer as a result of late presentation by individuals who have symptoms, or through doctor or hospital system failures, are currently the subject of close attention as part of broader initiatives to reduce deaths from cancer. However, in lung cancer there has been a generally held view that ‘late’ diagnosis is inevitable because of the biomedical difficulties in detecting the disease at an early stage. Data about events recalled prior to diagnosis from an interview study with 22 individuals recently diagnosed with operable (early stage) and inoperable (late stage) lung cancer are reported. Findings reveal that individuals, regardless of their disease stage, or their social background failed to recognise symptoms that they experienced over many months prior to their eventual diagnosis as serious and warranting medical attention. Symptoms, even when severe, were instead attributed to everyday causes and were not interpreted as indicative of ill-health. There was a reluctance to seek help for symptoms among some because they were unsure whether what they were experiencing was normal or not, and in one case because as a smoker, the individual felt ‘unworthy’ of medical care. This study suggests that previous assumptions that focus on individual or psychological factors in the processes of delay in cancer diagnosis need revisiting and the broader social influences that may affect the timing of diagnosis among people with lung cancer should be considered
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
Electrokinetic generation of reactive iron-rich barriers in wet sediments: implications for contaminated land management
No full textHere we describe preliminary research into the in situ electrokinetic generation of continuous iron-rich precipitates to act as sub-surface barriers for the containment of contaminated sites. This is achieved using sacrificial iron electrodes emplaced either side of a soil/sediment mass to introduce iron into the system, and their dissolution and re-precipitation under the influence of an applied (DC) electric field. Continuous vertical and horizontal iron-rich bands (up to 2 cm thick) have been generated over a timescale of 300–500 h, at voltages of <5 V with an electrode separation of between 15 and 30 cm. The thickness of the iron-rich band increases as the applied voltage is increased. Geotechnical tests in sand indicate that the iron-rich band produced is practically impervious (coefficient of permeability of 10?9 ms?1 or less), and has significant mechanical strength (unconfined compressive strength of 10.8 N mm?2). By monitoring the current, the integrity of the iron-rich band may be assessed, and by continued application of current, the barrier may ‘self heal’. The iron-rich barrier is composed of amorphous iron, goethite, lepidocrocite, maghemite and native iron
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