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Search Results: 1 - 10 of 601679 matches for " R. A. McKinney "
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Numerical simulations of super-critical black hole accretion flows in general relativity
A. Sadowski,R. Narayan,J. C. McKinney,A. Tchekhovskoy
Physics , 2013, DOI: 10.1093/mnras/stt2479
Abstract: A new general relativistic radiation magnetohydrodynamical code KORAL, is described, which employs the M1 scheme to close the radiation moment equations. The code has been successfully verified against a number of tests. Axisymmetric simulations of super-critical magnetized accretion on a non-rotating black hole (a=0.0) and a spinning black hole (a=0.9) are presented. The accretion rates in the two models are \dot M = 100-200 \dot M_Edd. These first general relativistic simulations of super-critical black hole accretion are potentially relevant to tidal disruption events and hyper-accreting supermassive black holes in the early universe. Both simulated models are optically and geometrically thick, and have funnels through which energy escapes in the form of relativistic gas, Poynting flux and radiative flux. The jet is significantly more powerful in the a=0.9 run. The net energy outflow rate in the two runs correspond to efficiencies of 5% (a=0) and 33% (a=0.9), as measured with respect to the mass accretion rate at the black hole. These efficiencies agree well with those measured in previous simulations of non-radiative geometrically thick disks. Furthermore, in the a=0.9 run, the outflow power appears to originate in the spinning black hole, suggesting that the associated physics is again similar in non-radiative and super-critical accretion flows. While the two simulations are efficient in terms of total energy outflow, both runs are radiatively inefficient. Their luminosities are only \sim 1-10 L_Edd, which corresponds to a radiative efficiency \sim 0.1%. Interestingly, most of the radiative luminosity emerges through the funnels, which subtend a very small solid angle. Therefore, measured in terms of a local radiative flux, the emitted radiation is highly super-Eddington.
Tissue-Specific Expressed Antibody Variable Gene Repertoires
Bryan S. Briney, Jordan R. Willis, Jessica A. Finn, Brett A. McKinney, James E. Crowe
PLOS ONE , 2014, DOI: 10.1371/journal.pone.0100839
Abstract: Recent developments in genetic technologies allow deep analysis of the sequence diversity of immune repertoires, but little work has been reported on the architecture of immune repertoires in mucosal tissues. Antibodies are the key to prevention of infections at the mucosal surface, but it is currently unclear whether the B cell repertoire at mucosal surfaces reflects the dominant antibodies found in the systemic compartment or whether mucosal tissues harbor unique repertoires. We examined the expressed antibody variable gene repertoires from 10 different human tissues using RNA samples derived from a large number of individuals. The results revealed that mucosal tissues such as stomach, intestine and lung possess unique antibody gene repertoires that differed substantially from those found in lymphoid tissues or peripheral blood. Mutation frequency analysis of mucosal tissue repertoires revealed that they were highly mutated, with little evidence for the presence of na?ve B cells, in contrast to blood. Mucosal tissue repertoires possessed longer heavy chain complementarity determining region 3 loops than lymphoid tissue repertoires. We also noted a large increase in frequency of both insertions and deletions in the small intestine antibody repertoire. These data suggest that mucosal immune repertoires are distinct in many ways from the systemic compartment.
Letrozole Potentiates Mitochondrial and Dendritic Spine Impairments Induced by β Amyloid
P. K.-Y. Chang,S. Boridy,R. A. McKinney,D. Maysinger
Journal of Aging Research , 2013, DOI: 10.1155/2013/538979
Abstract: Reduced estrogens, either through aging or postsurgery breast cancer treatment with the oral nonsteroidal aromatase inhibitor letrozole, are linked with declined cognitive abilities. However, a direct link between letrozole and neuronal deficits induced by pathogenic insults associated with aging such as beta amyloid ( ) has not been established. The objective of this study was to determine if letrozole aggravates synaptic deficits concurrent with insult. We examined the effects of letrozole and oligomeric treatment in dissociated and organotypic hippocampal slice cultures. Changes in glial cell morphology, neuronal mitochondria, and synaptic structures upon letrozole treatment were monitored by confocal microscopy, as they were shown to be affected by oligomers. Oligomeric or letrozole alone caused decreases in mitochondrial volume, dendritic spine density, synaptophysin (synaptic marker), and the postsynaptic protein, synaptopodin. Here, we demonstrated that mitochondrial and synaptic structural deficits were exacerbated when letrozole therapy was combined with treatment. Our novel findings suggest that letrozole may increase neuronal susceptibility to pathological insults, such as oligomeric in Alzheimer’s disease (AD). These changes in dendritic spine number, synaptic protein expression, and mitochondrial morphology may, in part, explain the increased prevalence of cognitive decline associated with aromatase inhibitor use. 1. Introduction Currently, aromatase inhibitors, leading to reduction of estradiol synthesis from testosterone, have been favoured in the treatment of breast cancer of postmenopausal women [1]. Letrozole is one such oral nonsteroidal aromatase inhibitor which prevents the aromatase from producing estrogens by competitive, reversible binding to the heme of its cytochrome P450 unit [2, 3]. Patients receiving letrozole have shown deficits in learning and memory [4]. However, it is still unclear if these functional impairments occur because of neurosteroid deficits and if they become exacerbated in the presence of an additional insult associated with aging, such as an excess of soluble, conformationally altered . Such forms of can interact with synapses and cause pronounced degenerative changes, an observation made in brain tissue from postmortem Alzheimer’s disease (AD) patients and animal models [5]. It has been well documented in AD that there are changes in neuronal and glial morphologies such as dendritic spine atrophy and increased glial growth [5, 6]. In contrast to these negative effects caused by , it is well established that
Seasonal habitat use of whale sharks in the northern Gulf of Mexico, USA 2003 - 2013
Jennifer A McKinney,Eric R Hoffmayer,Jim S Franks,Jill M Hendon,William B Driggers
PeerJ , 2015, DOI: 10.7287/peerj.preprints.93v1
Abstract: Background: Reports of whale sharks (Rhincodon typus) in the northern Gulf of Mexico (GOM) date back to the 1930s. In 2003, the Northern Gulf of Mexico Whale Shark Research Program was established and began making directed efforts to document the regional occurrence, seasonal distribution and habitat preferences of whale sharks. Methods: Whale shark sightings data (WSS: 1989 – present; n=644) and tagging geoposition data (TD: 2009-2012; n=450) were used in seasonal kernel density (KD) analyses to delineate home range (95%) and core habitat (50%) use areas in the northern GOM. Kernel density estimation of distribution is a statistically robust manner of handling data sources with differing sampling designs (anecdotal vs. directed). Habitat use patterns from the two datasets were used to identify critical use areas. Results: In the study area, whale shark home range was 276,000 km2 (WSS) to 369,000 km2 (TD) in size, with 52,000 km2 (WSS) to 62,000 km2 (TD) being core habitat. Whale shark habitat use varied seasonally, with the largest home range occurring during summer (WSS: 213,000 km2) and fall (TD: 221,000 km2). Tag data revealed more winter habitat (75,000 km2) than the sightings dataset (41,000 km2), which was shifted further offshore to slope waters. Significant use patterns occurred along the continental shelf-edge, encompassing shelf-edge banks south of Louisiana, and near the mouth of the Mississippi River. Conclusions: The combination of sightings data and satellite tagging data represents an effective methodology for assessing seasonality of occurrence, distribution, and habitat use of whale sharks. Shelf-edge bank habitats were most commonly used by whale sharks in the region. Satellite tagging data provided additional evidence of connectivity between multiple jurisdictions, which lends support for international management of the species.
On The Number of Edge-3-Colourings of A Snipped Snark
Scott A. McKinney
Mathematics , 2013,
Abstract: For a given snark G and edge e of G, we can form a cubic graph G_e using an operation we call "edge subtraction". The number of 3-edge-colourings of G_e is 18 * \psi(G,e) for some nonnegative integer \psi(G,e). Given snarks G_1 and G_2, we can form a new snark G using techniques given by Isaacs and Kochol. In this note we give relationships between \psi(G_1,e_1), \psi(G_2,e_2), and \psi(G,e) for particular edges e_1, e_2, and e, in G_1, G_2, and G (respectively). As a consequence, if g,h,i,j,k,l are each a nonnegative integer, then there exists a cyclically 5-edge-connected snark G with an edge e such that \psi(G,e)=5^g * 7^h, and a cyclically 4-edge-connected snark G_0 with an edge e_0 such that \psi(G_0,e_0)=2^i * 3^j * 5^k * 7^l.
Prolonged QT Syndrome and Seizure Secondary to Alkaline Earth Metal Deficiency: A Case Report
A. McKinney,B. C. Keegan
Case Reports in Medicine , 2011, DOI: 10.1155/2011/863029
Abstract: Introduction. Alkaline earth metal deficiency is recognized as a cause of both seizure and long QT syndrome. Their deficiency can have significant repercussions on the function of cells, tissues, and organs of the body. An understanding of the role of electrolytes allows an appreciation of the significance of depleted levels on cell function. Case Report. A 65-year-old lady was admitted with symptoms of chest discomfort, vomiting, increased stoma output, and dizziness. Two days following admission she suffered a tonic-clonic seizure. ECG review demonstrated a prolonged QTc interval, raising the possibility of an underlying Torsades de Pointes as the precipitant. This was attributed to electrolyte disturbance arising as a result of multiple aetiologies. Discussion. This paper highlights the multisystem effects of electrolyte disturbance, with emphasis upon its role in precipitating cardiac arrhythmia and neurological symptoms.
Intracranial Vertebrobasilar Artery Dissection Associated with Postpartum Angiopathy
James S. McKinney,Steven R. Messé,Bryan A. Pukenas,Sudhakar R. Satti,John B. Weigele,Robert W. Hurst,Joshua M. Levine,Scott E. Kasner,Lauren H. Sansing
Stroke Research and Treatment , 2010, DOI: 10.4061/2010/320627
Abstract: Background. Cervicocephalic arterial dissection (CCAD) is rare in the postpartum period. To our knowledge this is the first reported case of postpartum angiopathy (PPA) presenting with ischemic stroke due to intracranial arterial dissection. Case. A 41-year-old woman presented with blurred vision, headache, and generalized seizures 5 days after delivering twins. She was treated with magnesium for eclampsia. MRI identified multiple posterior circulation infarcts. Angiography identified a complex dissection extending from both intradural vertebral arteries, through the basilar artery, and into both posterior cerebral arteries. Multiple segments of arterial dilatation and narrowing consistent with PPA were present. Xenon enhanced CT (Xe-CT) showed reduced regional cerebral blood flow that is improved with elevation in blood pressure. Conclusion. Intracranial vertebrobasilar dissection causing stroke is a rare complication of pregnancy. Eclampsia and PPA may play a role in its pathogenesis. Blood pressure management may be tailored using quantitative blood flow studies, such as Xe-CT. 1. Case Report A 41-year-old pregnant woman with no other past medical history presented to a community hospital with pre-eclampsia at 36-week gestation. She had a systolic blood pressure (SBP) of 160?mmHg with proteinuria but no neurologic signs or symptoms. Twins were delivered by emergent Cesarean section under spinal anesthesia without apparent complications. She was discharged home on hospital day 5. The following day she developed a severe headache, blurred vision, and SBP > 160?mmHg. She had a generalized tonic-clonic seizure in the emergency department. She was orotracheally intubated for airway protection, treated with magnesium sulfate, levetiracetam, and labetalol. She had no further clinical seizures. A noncontrast CT of the head was normal. After extubation the following day, she became lethargic, and her mental status rapidly declined. MRI of the brain showed several areas of acute infarction in the posterior circulation. She was transferred to our neurological intensive care unit (NeuroICU) for further evaluation on the third day of hospitalization. On presentation to our facility, she was lethargic and opened her eyes only to repeated tactile stimulation. She was oriented to name, could follow simple commands, and was severely dysarthric with incomprehensible speech. She had a right homonymous hemianopia, disconjugate gaze, and was quadriparetic. She was treated with a magnesium infusion, intravenous levetiracetam, aspirin 325?mg daily, and a nicardipine
The First Synchrotron Infrared Beamlines at the ALS: Spectromicroscopy and Fast Timing
Michael C. Martin,Wayne R. McKinney
Physics , 1999,
Abstract: Two recently commissioned infrared beamlines on the 1.4 bending magnet port at the Advanced Light Source, LBNL, are described. Using a synchrotron as an IR source provides three primary advantages: increased brightness, very fast light pulses, and enhanced far-IR flux. The considerable brightness advantage manifests itself most beneficially when performing spectroscopy on a microscopic length scale. Beamline (BL) 1.4.3 is a dedicated FTIR spectromicroscopy beamline, where a diffraction-limited spot size using the synchrotron source is utilized. BL 1.4.2 consists of a vacuum FTIR bench with a wide spectral range and step-scan capability. This BL makes use of the pulsed nature of the synchrotron light as well as the far-IR flux. Fast timing is demonstrated by observing the pulses from the electron bunch storage pattern at the ALS. Results from several experiments from both IR beamlines will be presented as an overview of the IR research currently being done at the ALS.
Grammatical Immune System Evolution for Reverse Engineering Nonlinear Dynamic Bayesian Models
B.A. McKinney,D. Tian
Cancer Informatics , 2008,
Abstract: An artificial immune system algorithm is introduced in which nonlinear dynamic models are evolved to t time series of interacting biomolecules. This grammar-based machine learning method learns the structure and parameters of the underlying dynamic model. In silico immunogenetic mechanisms for the generation of model-structure diversity are implemented with the aid of a grammar, which also enforces semantic constraints of the evolved models. The grammar acts as a DNA repair polymerase that can identify recombination and hypermutation signals in the antibody (model) genome. These signals contain information interpretable by the grammar to maintain model context. Grammatical Immune System Evolution (GISE) is applied to a nonlinear system identification problem in which a generalized (nonlinear) dynamic Bayesian model is evolved to t biologically motivated artificial time-series data. From experimental data, we use GISE to infer an improved kinetic model for the oxidative metabolism of 17β-estradiol (E2), the parent hormone of the estrogen metabolism pathway.
Magnetic Reconnection with Radiative Cooling. I. Optically-Thin Regime
Dmitri A. Uzdensky,Jonathan C. McKinney
Physics , 2010, DOI: 10.1063/1.3571602
Abstract: Magnetic reconnection, a fundamental plasma process associated with a rapid dissipation of magnetic energy, is believed to power many disruptive phenomena in laboratory plasma devices, the Earth magnetosphere, and the solar corona. Traditional reconnection research, geared towards these rather tenuous environments, has justifiably ignored the effects of radiation on the reconnection process. However, in many reconnecting systems in high-energy astrophysics (e.g., accretion-disk coronae, relativistic jets, magnetar flares) and, potentially, in powerful laser plasma and z-pinch experiments, the energy density is so high that radiation, in particular radiative cooling, may start to play an important role. This observation motivates the development of a theory of high-energy-density radiative magnetic reconnection. As a first step towards this goal, we present in this paper a simple Sweet--Parker-like theory of non-relativistic resistive-MHD reconnection with strong radiative cooling. First, we show how, in the absence of a guide magnetic field, intense cooling leads to a strong compression of the plasma in the reconnection layer, resulting in a higher reconnection rate. The compression ratio and the layer temperature are determined by the balance between ohmic heating and radiative cooling. The lower temperature in the radiatively-cooled layer leads to a higher Spitzer resistivity and hence to an extra enhancement of the reconnection rate. We then apply our general theory to several specific astrophysically important radiative processes (bremsstrahlung, cyclotron, and inverse-Compton) in the optically thin regime, for both the zero- and strong-guide-field cases. We derive specific expressions for key reconnection parameters, including the reconnection rate. We also discuss the limitations and conditions for applicability of our theory.
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