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Search Results: 1 - 10 of 226711 matches for " Alexander L Coon "
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Treatment of mechanically-induced vasospasm of the carotid artery in a primate using intra-arterial verapamil: a technical case report
Alexander L Coon, Geoffrey P Colby, William J Mack, Lei Feng, Philip Meyers, E Sander Connolly
BMC Cardiovascular Disorders , 2004, DOI: 10.1186/1471-2261-4-11
Abstract: As part of a study assessing the placement feasibility and safety of a catheter capable of delivering intra-arterial cerebroprotective therapy, a female 16 kg baboon prophylaxed with intravenous nitroglycerin underwent transfemoral CCA catheterization with a metallic 6-Fr catheter without signs of acute spasm. The protocol dictated that the catheter remain in the CCA for 12 hours. Upon completion of the protocol, arteriography revealed a marked decrease in CCA size (mean cross-sectional area reduction = 31.6 ± 1.9%) localized along the catheter length. Intra-arterial verapamil (2 mg/2cc) was injected and arteriography was performed 10 minutes later. Image analysis at 6 points along the CCA revealed a 21.0 ± 1.7% mean increase in vessel diameter along the length of the catheter corresponding to a 46.7 ± 4.0% mean increase in cross-sectional area. Mean systemic blood pressure did not deviate more than 10 mm Hg during the procedure.Intraluminal CCBs like verapamil may constitute an effective endovascular treatment for mechanically-induced vasospasm in medium to large-sized vessels such as the CCA.Rapid advancements in endovascular technology and techniques allow for treatment of an ever-increasing range of neurovascular diseases. Despite improvements in the safety and efficacy of these procedures, complications such as vasospasm, stroke, and perforation still occur [1]. Vasospasm, or contraction of smooth muscle fibers in the wall of a vessel, is a commonly recognized adverse event that may complicate an endovascular procedure by limiting distal blood flow.Vasospasm complicates many disease states, particularly those affecting small vessels. Recently, treatment of small-vessel vasospasm has proven amenable to pharmacological intervention. For example, in the treatment of cerebral artery spasm, intravenous nitrates [2], intravenous calcium channel blockers (CCBs) [3], and intra-arterial papaverine [4] and CCBs [5] have been shown to prevent or mitigate this small artery
Femoral access in 100 consecutive subarachnoid hemorrhage patients: the "craniotomy" of endovascular neurosurgery
Alexandra R Paul, Geoffrey P Colby, Martin G Radvany, Judy Huang, Rafael J Tamargo, Alexander L Coon
BMC Research Notes , 2010, DOI: 10.1186/1756-0500-3-285
Abstract: The records of a prospective single-center aneurysm database were reviewed to identify 100 consecutive SAH patients. Using an oblique femoral arteriogram, the presence of significant atherosclerosis, iliac tortuosity, and the CFA bifurcation were assessed. The CFA bifurcation was graded according to its position with respect to the femoral head: below (grade 1), lower half (grade 2), and above the upper half (grade 3).We found a CFA bifurcation grade 1 in 50 patients (50%, mean age 51.2 years), grade 2 in 40 patients (40%, mean age 55.5 years), and grade 3 in 10 patients (10%, mean age 58.2 years). Whereas 30 of 90 patients with CFA grades I or II were male (33%), only 10% with grade 3 were male (1 of 10, p = 0.12). Mean age for significant atherosclerosis was 65.5 +/- 2.6 years versus 50.9 +/- 1.6 years (p < 0.001) without, and iliac tortuosity was 64.9 +/- 2.4 years versus 50.3 +/- 1.6 years (p < 0.001) without.Although a requisite element of endovascular treatment in SAH patients, femoral access can be complicated by a high common femoral artery bifurcation and the presence of atherosclerotic disease and/or iliac artery tortuosity. In this study, we found a grade 3 (above the femoral head) CFA bifurcation in 10% patients, with 90% of these patients being female. We also found the presence of atherosclerotic disease and iliac tortuosity to be significantly more likely in patients older than 65 years of age.Femoral access is a fundamental element of catheter-based cerebral angiography and neurointerventional procedures. The femoral artery is most commonly used for arterial access. The common femoral artery (CFA) is the continuation of the external iliac artery from the level of the inguinal ligament to its bifurcation into the profunda femoris (deep femoral artery) and the superficial femoral artery. The CFA is considered to be the safest site for arterial puncture however there is little published data relating the CFA and its bifurcation to the landmarks typicall
JNK2 Promotes Endothelial Cell Alignment under Flow
Cornelia Hahn, Chong Wang, A. Wayne Orr, Brian G. Coon, Martin Alexander Schwartz
PLOS ONE , 2011, DOI: 10.1371/journal.pone.0024338
Abstract: Endothelial cells in straight, unbranched segments of arteries elongate and align in the direction of flow, a feature which is highly correlated with reduced atherosclerosis in these regions. The mitogen-activated protein kinase c-Jun N-terminal kinase (JNK) is activated by flow and is linked to inflammatory gene expression and apoptosis. We previously showed that JNK activation by flow is mediated by integrins and is observed in cells plated on fibronectin but not on collagen or basement membrane proteins. We now show thatJNK2 activation in response to laminar shear stress is biphasic, with an early peak and a later peak. Activated JNK localizes to focal adhesions at the ends of actin stress fibers, correlates with integrin activation and requires integrin binding to the extracellular matrix. Reducing JNK2 activation by siRNA inhibits alignment in response to shear stress. Cells on collagen, where JNK activity is low, align slowly. These data show that an inflammatory pathway facilitates adaptation to laminar flow, thereby revealing an unexpected connection between adaptation and inflammatory pathways.
On Diffusive Confining a Galvanic Crystallization out of Molten Salts  [PDF]
Alexander L. Shimkevich
Journal of Crystallization Process and Technology (JCPT) , 2012, DOI: 10.4236/jcpt.2012.24021
Abstract: The electron-energy band structure of electric Double Layer (DL) between a molten salt and metal electrode (an anode or cathode) is studied for the electrodepositing crystallization process when the width of DL metal part is less than the one in the molten salt. It is shown that just the molten-salt part of the double layer confines a rate of electrodepositing process. The reason of this is a neutralization of depositing ions into the molten-salt near the electrode and hence their diffusively confined motion in a density gradient field. It is important to minimize the electrodepositing potential for effective component crystallization out of the molten salt and its exchange process including selective extracting of salt components by their crystallization on electrodes of galvanic circuit. It is shown that this can be carried out by means of fine and controllable variation of reduction-oxidation (RedOx) potential of the non-stoichiometric salts. A possible application of a potentiometer for monitoring and managing the salt composition is considered. For this, one uses precise methods of electric-motion-force and coulometer titration by solid electrolyte(for example, M+–β ”–Al2O3) of the basic salt metal (M) as a reduction agent in the molten-salt solution.
Charge-Symmetry Breaking and the Two-Pion-Exchange Two-Nucleon Interaction
J. L. Friar,U. van Kolck,G. L. Payne,S. A. Coon
Physics , 2003, DOI: 10.1103/PhysRevC.68.024003
Abstract: Charge-symmetry breaking in the nucleon-nucleon force is investigated within an effective field theory, using a classification of isospin-violating interactions based on power-counting arguments. The relevant charge-symmetry-breaking interactions corresponding to the first two orders in the power counting are discussed, including their effects on the 3He-3H binding-energy difference. The static charge-symmetry-breaking potential linear in the nucleon-mass difference is constructed using chiral perturbation theory. Explicit formulae in momentum and configuration spaces are presented. The present work completes previously obtained results.
Nucleon polarization in three-body models of polarized \bbox{^6}Li
N. W. Schellingerhout,L. P. Kok,S. A. Coon,R. M. Adam
Physics , 1993, DOI: 10.1103/PhysRevC.52.439
Abstract: Just as $^3\roarrow{\rm He}$ can be approximately characterized as a polarized neutron target, polarized \Li6D has been advocated as a good {\em isoscalar} nuclear target for the extraction of the polarized gluon content of the nucleon. The original argument rests upon a presumed ``alpha + deuteron'' picture of \Li6, with the polarization of the nucleus carried by the polarization of the deuteron. We have calculated the polarization of the constituents of \Li6 as a three-body bound state of $\alpha + n + p$ interacting with local potentials fitted to the scattering data. It is necessary to include partial waves up to $j=17/2$ (75 channels, or, when including the $T=1$ state, 150 channels) in the Faddeev equations before the energy eigenvalue converges. The longitudinal formfactors are then described well by the wave function. Various combinations of $\alpha$N and NN strong and Coulomb potentials yield a straight line in the charge radius {\em vs.} energy plane which, unlike those of previous calculations, passes through the experimental datum. We find for all cases a polarization of the valence neutron in excess of 90\%. This may make polarized \Li6D an attractive target for many nuclear physics purposes, since its neutrons are effectively 45\% polarized.
Spin-Flip Scattering at Quantum Hall Transition  [PDF]
Victor Kagalovsky, Alexander L. Chudnovskiy
Journal of Modern Physics (JMP) , 2011, DOI: 10.4236/jmp.2011.29117
Abstract: We formulate a generalized Chalker-Coddington network model that describes the effect of nuclear spins on the two-dimensional electron gas in the quantum Hall regime. We find exact analytical expression for spin-dependent transmission coefficients of a charged particle through a saddle point potential in a perpendicular magnetic field. Spin-flip scattering creates a metallic state in a finite range around the critical energy of quantum Hall transition. As a result we find that the usual insulating phases with Hall conductance σxy=0,1,2 are separated by novel metallic phases.
Infrared and ultraviolet cutoffs in variational calculations with a harmonic oscillator basis
Sidney A Coon
Physics , 2013,
Abstract: I abstract from a recent publication [1] the motivations for, analysis in and conclusions of a study of the ultraviolet and infrared momentum regulators induced by the necessary truncation of the model spaces formed by a variational trial wave function. This trial function is built systematically from a complete set of many-body basis states based upon three-dimensional harmonic oscillator (HO) functions. Each model space is defined by a truncation of the expansion characterized by a counting number (N) and by the intrinsic scale ($\hbar\omega$) of the HO basis. Extending both the uv cutoff to infinity and the ir cutoff to zero is prescribed for a converged calculation. In [1] we established practical procedures which utilize these regulators to obtain the extrapolated result from sequences of calculations with model spaces. Finally, I update this subject by mentioning recent work on our extrapolation prescriptions which have appeared since the submission of [1]. The numerical example chosen for this contribution consists of calculations of the ground state energy of the triton with the "bare" and "soft" Idaho N3LO nucleon-nucleon (NN) interaction.
Chiral Symmetry and Low Energy Pion-Nucleon Scattering
Sidney A. Coon
Physics , 1999, DOI: 10.1023/A:1022868110424
Abstract: In these lectures, I examine the effect of the meson factory $\pi$N data on the current algebra/PCAC program which describes chiral symmetry breaking in this system. After historical remarks on the current algebra/PCAC versus chiral Lagrangians approaches to chiral symmetry, and description of the need for $\pi$N amplitudes with virtual (off-mass-shell) pions in nuclear force models and other nuclear physics problems, I begin with kinematics and isospin aspects of the invariant amplitudes. A detailed introduction to the hadronic vector and axial-vector currents and the hypothesis of partially conserved axial-vector currents (PCAC) follows. I review and test against contemporary data the PCAC predictions of the Goldberger-Treiman relation, and the Adler consistency condition for a $\pi$N amplitude. Then comes a detailed description of the current algebra Ward-Takahashi identities in the chiral limit and a brief account of the on-shell current algebra Ward-Takahashi identities. The latter identities form the basis of so-called current algebra models of $\pi$N scattering. I then test these models against the contemporary empirical $\pi$N amplitudes extrapolated into the subthreshold region via dispersion relations. The scale and the t dependence of the "sigma term" is determined by the recent data.
The u-d quark mass difference and nuclear charge symmetry breaking
Sidney A. Coon
Physics , 2000, DOI: 10.1016/S0375-9474(01)00826-0
Abstract: The group theoretical analysis of the Coleman-Glashow tadpole picture of "meson-mixing" is quantitatively reproduced by the u-d constituent quark mass difference in quantum loop calculations of the self-energies of mesons. This demonstration that the Coleman-Glashow scales can be directly calculated from the constituent $u - d$ quark mass difference finishes the link between charge symmetry breaking in low energy nuclear physics and the $u - d$ quark mass difference in particle physics.
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