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Search Results: 1 - 10 of 318204 matches for " Lee J. McEwan "
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Monodromy of plane curves and quasi-ordinary surfaces
Gary Kennedy,Lee J. McEwan
Mathematics , 2009,
Abstract: We develop recursive formulas for the horizontal and vertical monodromies of a quasi-ordinary surface. These are monodromies associated to the Milnor fiber of a slice transverse to a component of the singular locus. In the course of working out these recursions, we have discovered what appears to be a new way to express the monodromy associated to the Milnor fibration of a singular plane curve.
Canonical Resolution of a Quasi-ordinary Surface Singularity
Chunsheng Ban,Lee J. McEwan
Mathematics , 1998,
Abstract: We describe the embedded resolution of a quasi-ordinary surface singularity (V,p) which results from applying the canonical resolution of Bierstone-Milman to (V,p). We show that this process depends solely on the characteristic pairs of (V,p), as predicted by Lipman. We describe the process explicitly enough that a resolution graph for (V,p) could in principle be obtained by computer using only the characteristic pairs.
The Embedded Resolution of f(x,y)+z^2: (C^3,0) -> (C,0)
Chunsheng Ban,Lee J. McEwan,András Némethi
Mathematics , 1999,
Abstract: The goal of this paper is the presentation of an ``embedded resolution'' of ({f(x,y)+z^2=0},0) \subset (C^3,0) using the method of Jung.
The Lingering Effects of an Artificial Blind Spot
Michael J. Morgan, William McEwan, Joshua Solomon
PLOS ONE , 2007, DOI: 10.1371/journal.pone.0000256
Abstract: Background When steady fixation is maintained on the centre of a large patch of texture, holes in the periphery of the texture rapidly fade from awareness, producing artificial scotomata (i.e., invisible areas of reduced vision, like the natural ‘blind spot’). There has been considerable controversy about whether this apparent ‘filling in’ depends on a low-level or high-level visual process. Evidence for an active process is that when the texture around the scotomata is suddenly removed, phantasms of the texture appear within the previous scotomata. Methodology To see if these phantasms were equivalent to real low-level signals, we measured contrast discrimination for real dynamic texture patches presented on top of the phantasms. Principal Findings Phantasm intensity varied with adapting contrast. Contrast discrimination depended on both (real) pedestal contrast and phantasm intensity, in a manner indicative of a common sensory threshold. The phantasms showed inter-ocular transfer, proving that their effects are cortical rather than retinal. Conclusions We show that this effect is consistent with a tonic spreading of the adapting texture into the scotomata, coupled with some overall loss of sensitivity. Our results support the view that ‘filling in’ happens at an early stage of visual processing, quite possibly in primary visual cortex (V1).
The Impact of Point Mutations in the Human Androgen Receptor: Classification of Mutations on the Basis of Transcriptional Activity
Colin W. Hay, Iain J. McEwan
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0032514
Abstract: Androgen receptor mediated signaling drives prostate cancer cell growth and survival. Mutations within the receptor occur infrequently in prostate cancer prior to hormonal therapy but become prevalent in incurable androgen independent and metastatic tumors. Despite the determining role played by the androgen receptor in all stages of prostate cancer progression, there is a conspicuous dearth of comparable data on the consequences of mutations. In order to remedy this omission, we have combined an expansive study of forty five mutations which are predominantly associated with high Gleason scores and metastatic tumors, and span the entire length of the receptor, with a literature review of the mutations under investigation. We report the discovery of a novel prevalent class of androgen receptor mutation that possesses loss of function at low levels of androgen yet transforms to a gain of function at physiological levels. Importantly, mutations introducing constitutive gain of function are uncommon, with the majority of mutations leading to either loss of function or no significant change from wild-type activity. Therefore, the widely accepted supposition that androgen receptor mutations in prostate cancer result in gain of function is appealing, but mistaken. In addition, the transcriptional outcome of some mutations is dependent upon the androgen receptor responsive element. We discuss the consequences of these findings and the role of androgen receptor mutations for prostate cancer progression and current treatment options.
Scintigraphic imaging of focal hypoxic tissue: development and clinical applications of 123I-IAZA
Wiebe, Leonard I.;McEwan, Alexander J. B.;
Brazilian Archives of Biology and Technology , 2002, DOI: 10.1590/S1516-89132002000500010
Abstract: affected tissues in a number of diseases, including cancer, stroke, cardiac infarction and diabetes, develop focal tissue hypoxia during their progression. the presence of hypoxic tissue may make the disease refractory to therapy, as in the case of solid tumor therapy using low let ionizing radiation. in other pathologies, the detection of viable but hypoxic tissues may serve as a prodromal indicator of developing disease (e.g. diabetes),or as a prognostic indicator for management of the disease (e.g. stroke). over the past two decades, a number of hypoxia radioimaging agents have been developed and tested clinically. of these, 18f-fmiso and 123i-iaza are the most widely used radiotracers for pet and spect/planar imaging, respectively. iaza and fmiso are a 2-nitroimidazoles that chemically bind to subcellular components of viable hypoxic tissues. they sensitize hypoxic tumour to the killing effects of ionizing radiation via mechanisms that mimic the radiosensitizing effects of oxygen, and are therefore called oxygen mimetics. the oxygen mimetic effect is attributable in large part to the covalent binding of reductively-activated nitroimidazole intermediates to critical cellular macromolecules. nitroimidazoles labelled with gamma-emitting radionuclides (e.g. 18f-fmiso and 123i-iaza) have been used as scintigraphic markers of tumour hypoxia, based on the need to identify radioresistant hypoxic tumour cells as part of the radiotherapy planning process. broader interest in non-invasive, imaging-based identification of focal hypoxia in a number of diseases has extended hypoxia studies to include peripheral vascular disease associated with diabetes, rheumatoid arthritis, stroke, myocardial ischaemia, brain trauma and oxidative stress. in this review, the current status of hypoxia-selective studies with 123i-iaza , an experimental diagnostic radiopharmaceutical, is reviewed with respect to its pre-clinical development and clinical applications.
Scintigraphic imaging of focal hypoxic tissue: development and clinical applications of 123I-IAZA
Wiebe Leonard I.,McEwan Alexander J. B.
Brazilian Archives of Biology and Technology , 2002,
Abstract: Affected tissues in a number of diseases, including cancer, stroke, cardiac infarction and diabetes, develop focal tissue hypoxia during their progression. The presence of hypoxic tissue may make the disease refractory to therapy, as in the case of solid tumor therapy using low LET ionizing radiation. In other pathologies, the detection of viable but hypoxic tissues may serve as a prodromal indicator of developing disease (e.g. diabetes),or as a prognostic indicator for management of the disease (e.g. stroke). Over the past two decades, a number of hypoxia radioimaging agents have been developed and tested clinically. Of these, 18F-Fmiso and 123I-IAZA are the most widely used radiotracers for PET and SPECT/planar imaging, respectively. IAZA and Fmiso are a 2-nitroimidazoles that chemically bind to subcellular components of viable hypoxic tissues. They sensitize hypoxic tumour to the killing effects of ionizing radiation via mechanisms that mimic the radiosensitizing effects of oxygen, and are therefore called oxygen mimetics. The oxygen mimetic effect is attributable in large part to the covalent binding of reductively-activated nitroimidazole intermediates to critical cellular macromolecules. Nitroimidazoles labelled with gamma-emitting radionuclides (e.g. 18F-Fmiso and 123I-IAZA) have been used as scintigraphic markers of tumour hypoxia, based on the need to identify radioresistant hypoxic tumour cells as part of the radiotherapy planning process. Broader interest in non-invasive, imaging-based identification of focal hypoxia in a number of diseases has extended hypoxia studies to include peripheral vascular disease associated with diabetes, rheumatoid arthritis, stroke, myocardial ischaemia, brain trauma and oxidative stress. In this review, the current status of hypoxia-selective studies with 123I-IAZA , an experimental diagnostic radiopharmaceutical, is reviewed with respect to its pre-clinical development and clinical applications.
Modelling of an Oesophageal Electrode for Cardiac Function Tomography
J. Nasehi Tehrani,C. Jin,A. L. McEwan
Computational and Mathematical Methods in Medicine , 2012, DOI: 10.1155/2012/585786
Abstract: There is a need in critical care units for continuous cardiopulmonary monitoring techniques. ECG gated electrical impedance tomography is able to localize the impedance variations occurring during the cardiac cycle. This method is a safe, inexpensive and potentially fast technique for cardiac output imaging but the spatial resolution is presently low, particularly for central locations such as the heart. Many parameters including noise deteriorate the reconstruction result. One of the main obstacles in cardiac imaging at the heart location is the high impedance of lungs and muscles on the dorsal and posterior side of body. In this study we are investigating improvements of the measurement and initial conductivity estimation of the internal electrode by modelling an internal electrode inside the esophagus. We consider 16 electrodes connected around a cylindrical mesh. With the random noise level set near 0.05% of the signal we evaluated the Graz consensus reconstruction algorithm for electrical impedance tomography. The modelling and simulation results showed that the quality of the target in reconstructed images was improved by up to 5 times for amplitude response, position error, resolution, shape deformation and ringing effects with perturbations located in cardiac related positions when using an internal electrode.
DICHOTOMOUS INDIUM-111 LABELED LEUKOCYTE SCAN FINDINGS WHILE EVALUATING OSTEOMYELITIS IN A FAILED MANDIBULAR GRAFT
Jack R McEwan,Simin Dadparvar,Walter J Slizofski
Iranian Journal of Nuclear Medicine , 1997,
Abstract: Markedly elevated111 In labeled leukocyte activity suggestive of acute osteomyelitis was observed in a region of a composite mandibular allograft that was photon deficient on 99mTc MDP bone scintigraphy. This finding was later confirmed by surgical pathology. The patient was treated with intravenous antibiotics and returned two months later with persistent bone infection. The foHow-up three phase bone and 111In labeled leukocyte scans were performed. The photopenic region noted in the previous bone scan demonstrated a mild interval increase in activity, while the 111In labeled leukocyte activity was essentially normal. Additional imaging of the composite allograft was then performed using 67Ga-citrate at 24 and 48 hours post injection. These images revealed focal areas of increased Gallium activity in the photopenic region of the graft exhibiting normal mIn leukocyte activity. The tissue culture comfirmed underlying chronic osteomyelitis. We conclude that normal uptake on niIn labeled leukocyte and photon deficient regions on 99mTc bone scintigraphy do not necessarily exclude the presence of chronic osteomyelitis. In the management of patients who have been on prolonged antibiotic therapy with persistent infection, 67Ga scintigraphy is warranted.
Saxl and Boll
Dorothea McEwan
Journal of Art Historiography , 2011,
Abstract: We know of Aby Warburg being Fritz Saxl’s mentor. What is less known is that Saxl had a second mentor, equally important for his research development, Franz Boll, the celebrated classical philologist. The article charts Boll’s involvement in Saxl’s research activities upon leaving university.
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