Two-Dimensional Hydrodynamics of Pre-Core Collapse: Oxygen Shell Burning

By direct hydrodynamic simulation, using the Piecewise Parabolic Method (PPM) code PROMETHEUS, we study the properties of a convective oxygen burning shell in a SN 1987A progenitor star prior to collapse. The convection is too heterogeneous and dynamic to be well approximated by one-dimensional diffusion-like algorithms which have previously been used for this epoch. Qualitatively new phenomena are seen. The simulations are two-dimensional, with good resolution in radius and angle, and use a large (90-degree) slice centered at the equator. The microphysics and the initial model were carefully treated. Many of the qualitative features of previous multi-dimensional simulations of convection are seen, including large kinetic and acoustic energy fluxes, which are not accounted for by mixing length theory. Small but significant amounts of carbon-12 are mixed non-uniformly into the oxygen burning convection zone, resulting in hot spots of nuclear energy production which are more than an order of magnitude more energetic than the oxygen flame itself. Density perturbations (up to 8%) occur at the `edges' of the convective zone and are the result of gravity waves generated by interaction of penetrating flows into the stable region. Perturbations of temperature and electron fraction at the base of the convective zone are of sufficient magnitude to create angular inhomogeneities in explosive nucleosynthesis products, and need to be included in quantitative estimates of yields. Combined with the plume-like velocity structure arising from convection, the perturbations will contribute to the mixing of nickel-56 throughout supernovae envelopes. Runs of different resolution, and angular extent, were performed to test the robustness of theseComment: For mpeg movies of these simulations, see http://www.astrophysics.arizona.edu/movies.html Submitted to the Astrophysical Journa

Performance of a deterministic source of entangled photonic qubits

We study the possible limitations and sources of decoherence in the scheme for the deterministic generation of polarization-entangled photons, recently proposed by Gheri et al. [K. M. Gheri et al., Phys. Rev. A 58, R2627 (1998)], based on an appropriately driven single atom trapped within an optical cavity. We consider in particular the effects of laser intensity fluctuations, photon losses, and atomic motion.Comment: 10 pages, 6 figure

Thrombolytic therapy: Adjuvant mechanical intervention for acute myocardial infarction

Following successful pharmacologic thrombolysis, early coronary angiography frequently shows a tight residual stenosis in the infarct-related artery at the site of recent occlusion. Approaches to the management of the residual stenosis have undergone a gradual evolution from an aggressive strategy of immediate balloon dilation to a more conservative approach. Randomized, controlled trials have indicated that immediate percutaneous transluminal coronary angioplasty (PTCA) to associated with no greater recovery in regional or global left ventricular function, and a tendency toward an increased incidence of complications, including the need for emergency coronary artery surgery and blood ransfusion. The role of immediate rescue PTCA for failed thrombolysis has not been as rigorously investigated, but selected patients, including those with evidence of ongoing myocardial ischemia or homodynamic instability, may benefit from this approach. A major source of current controversy is the value of routine coronary anglography after uncomplicated myocardial infarction. Two carefully conducted trials have indicated that a conservative strategy of clinically indicated, predischarge cardiac catheterization may be associated with an increased need for readmission and late, elective cardiac catheterization when compared wtth a more invasive strategy of routine coronary angiography, but that the conservative approach is not associated wtth an increased incidence of death or reinfarction. Provision was not made in these studies, however, for evaluating the positive economic and psychologic impact of early coronary angiography, early hospital discharge, and early return to work of patients wtth a favorable postinfarction prognosis. It is concluded that early mechanical revascularization following thrombolysis should be considered for ongoing myocardial ischemia, but should otherwise be deferred pending the results of predischarge functional studies. For most patients, routine coronary angtography to likely to remain an important diagnostic tool and an integral component of the management of the convalescent phase of acute myocardial infarction.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/30246/1/0000641.pd

Implantable devices in the coronary artery from metal to genes

Preliminary data from nonrandomized clinical trials suggest that, in selected subgroups of patients, the implantation of endovascular stents may improve the initial results of coronary dilatation, may successfully treat arterial dissection and abrupt closure, and may reduce the incidence of recurrent stenosis. The widespread use of stents remains limited, however, by the need for intensive anticoagulation to prevent arterial thrombosis. The development of sustained-release drug delivery systems and gene-transfer technology may enable local delivery of antithrombotic and antiproliferative therapies that would greatly increase the safety and applicability of these devices.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/29147/1/0000189.pd

Facilitated advancement of the Palmaz-Schatz stent delivery system with the use of an adjacent 0.018′ stiff wire

The 5.0 French Palmaz-Schatz stent delivery system is a relatively bulky, stiff system which can be advanced only over a 0.014′ wire. Although crossing failure is rare, advancement of the delivery system through tortuous, rigid vessels may be unsuccessful. We report on four consecutive cases in which the initial advancement of the Palmaz-Schatz stent delivery system was unsuccessful due to vessel tortuosity or vessel angulation. The use of a 0.018′ stiff wirer adjacent to the Palmaz-Schatz delivery system, to “straighten” the vessels and to give additional guide catheter support, allowed for the successful advancement and delivery of coronary stents in all four cases. © 1996 Wiley-Liss, Inc.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/38223/1/24_ftp.pd

Atherectomy of the left main coronary artery with percutaneous cardiopulmonary bypass support

Left main (LM) coronary artery stenoses have conventionally been precluded from percutaneous coronary angioplasty because of the prohibitive risk of irreversible hemodynamic collapse after acute closure of the artery, and a relatively high risk of late sudden death.1 When protected by left anterior descending and circumflex coronary artery by-pass grafts, angioplasty of the LM coronary artery can be safely performed but is limited by a rate of recurrent stenosis in excess of 50%.2 Coronary atherectomy has recently been advocated as an alternative procedure because of preliminary data suggesting a lower incidence of acute closure and restenosis after peripheral atherectomy.3 A percutaneous cardiopulmonary support system has also been reported to reduce the hazards of high risk conventional angioplasty including angioplasty of the LM coronary artery.4 We report the successful combined use of percutaneous cardiopulmonary bypass and LM coronary atherectomy in a patient incompletely protected by aortocoronary bypass grafts.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/27864/1/0000277.pd

Nebulized heparin in burn patients with inhalation trauma : safety and feasibility

Background: Pulmonary hypercoagulopathy is intrinsic to inhalation trauma. Nebulized heparin could theoretically be beneficial in patients with inhalation injury, but current data are conflicting. We aimed to investigate the safety, feasibility, and effectiveness of nebulized heparin. Methods: International multicenter, double-blind, placebo-controlled randomized clinical trial in specialized burn care centers. Adult patients with inhalation trauma received nebulizations of unfractionated heparin (25,000 international unit (IU), 5 mL) or placebo (0.9% NaCl, 5 mL) every four hours for 14 days or until extubation. The primary outcome was the number of ventilator-free days at day 28 post-admission. Here, we report on the secondary outcomes related to safety and feasibility. Results: The study was prematurely stopped after inclusion of 13 patients (heparin N = 7, placebo N = 6) due to low recruitment and high costs associated with the trial medication. Therefore, no analyses on effectiveness were performed. In the heparin group, serious respiratory problems occurred due to saturation of the expiratory filter following nebulizations. In total, 129 out of 427 scheduled nebulizations were withheld in the heparin group (in 3 patients) and 45 out of 299 scheduled nebulizations were withheld in the placebo group (in 2 patients). Blood-stained sputum or expected increased bleeding risks were the most frequent reasons to withhold nebulizations. Conclusion: In this prematurely stopped trial, we encountered important safety and feasibility issues related to frequent heparin nebulizations in burn patients with inhalation trauma. This should be taken into account when heparin nebulizations are considered in these patients