Derrick Allen

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We asked the question "is the visual field temporally homogeneous when the well known spatial inhomogeneity is taken into account?" Our results show that the visual field exhibits inhomogeneity for stimuli of low spatial frequency for which the spatial inhomogeneity is minimal. This inhomogeneity takes the form of a reduction in sensitivity for stimuli of(More)
Determining the effectiveness of in situ immobilization for P-amended, Pb-contaminated soils has typically relied on non-spectroscopic methods. However in recent years, these methods have come under scrutiny due to technical and unforeseen error issues. In this study, we analyzed 18 soil samples via X-ray diffraction (XRD), selective sequential extraction(More)
In this study, a comparison of laboratory batch and column experiments on metal release profile from a mineral processing waste (MPW) is presented. Batch (equilibrium) and column (dynamic) leaching tests were conducted on ground MPW at different liquid-solid ratios (LS) to determine the mechanisms controlling metal release. Additionally, the effect of pH on(More)
This paper presents the effect of pH and redox potential on the potential mobility of arsenic (As) from a contaminated mineral processing waste. The selected waste contained about 0.47 g kg(-1) of As and 66.2 g kg(-1) of iron (Fe). The characteristic of the waste was identified by acid digestion, X-ray diffraction and sequential extraction procedures. Less(More)
Evaluation of metal leaching using a single leach test such as the Toxicity Characteristic Leaching Procedure (TCLP) is often questionable. The pH, redox potential (E(h)), particle size and contact time are critical variables in controlling metal stability, not accounted for in the TCLP. This paper compares the leaching behavior of metals in mineral(More)
PURPOSE To describe clinical outcomes of endovascular interventions in the setting of thrombosis or dysfunction of anterior chest wall ("necklace") arteriovenous (AV) hemodialysis grafts. MATERIALS AND METHODS Eight percutaneous interventions (balloon angioplasty, pharmacologic thrombolysis, and mechanical thrombectomy) were performed in five patients(More)
A visual examination of the GLIMPSE images has revealed 322 partial and closed rings that we propose represent partially or fully enclosed threedimensional bubbles. We argue that the bubbles are primarily formed by hot young stars in massive star formation regions. We have found an average of about 1.5 bubbles per square degree. About 25% of the bubbles(More)
A thermodynaic model is presented for predicting the thermomechanical response, including temperature change, in a uniaxial bar composed of a thermoviscoplastic metallic medium. The model is constructed using the concept of internal state variables, and it is shown that this general framework is capable of encompassing several constitutive models currently(More)
Introduction: Cassini ISS imaged the surface of Io in eclipse by Jupiter in late 2000 and early 2001 and obtained multiple-filter images over timescales of hours. Images like these have been used to study the temperature and variability of the numerous hotspots on the surface [1, 2, 3]. For example, Pele was found to be an active lava lake with most likely(More)