791 research outputs found
Lefschetz fibrations over the disc
We provide a complete set of moves relating any two Lefschetz fibrations over the disc having as their total space the same four-dimensional 2-handlebody up to 2-equivalence. As a consequence, we also obtain moves relating diffeomorphic three-dimensional open books, providing a different approach to an analogous previous result by Harer
Postoperative peri-axillary seroma following axillary artery cannulation for surgical treatment of acute type A aortic dissection
The arterial cannulation site for optimal tissue perfusion and cerebral protection during cardiopulmonary bypass (CPB) for surgical treatment of acute type A aortic dissection remains controversial. Right axillary artery cannulation confers significant advantages, because it provides antegrade arterial perfusion during cardiopulmonary bypass, and allows continuous antegrade cerebral perfusion during hypothermic circulatory arrest, thereby minimizing global cerebral ischemia. However, right axillary artery cannulation has been associated with serious complications, including problems with systemic perfusion during cardiopulmonary bypass, problems with postoperative patency of the artery due to stenosis, thrombosis or dissection, and brachial plexus injury. We herein present the case of a 36-year-old Caucasian man with known Marfan syndrome and acute type A aortic dissection, who had direct right axillary artery cannulation for surgery of the ascending aorta. Postoperatively, the patient developed an axillary perigraft seroma. As this complication has, not, to our knowledge, been reported before in cardiothoracic surgery, we describe this unusual complication and discuss conservative and surgical treatment options
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Recommendations for probabilistic seismic hazard analysis: Guidance on uncertainty and use of experts
Probabilistic Seismic Hazard Analysis (PSHA) is a methodology that estimates the likelihood that various levels of earthquake-caused ground motion will be exceeded at a given location in a given future time period. Due to large uncertainties in all the geosciences data and in their modeling, multiple model interpretations are often possible. This leads to disagreement among experts, which in the past has led to disagreement on the selection of ground motion for design at a given site. In order to review the present state-of-the-art and improve on the overall stability of the PSHA process, the U.S. Nuclear Regulatory Commission (NRC), the U.S. Department of Energy (DOE), and the Electric Power Research Institute (EPRI) co-sponsored a project to provide methodological guidance on how to perform a PSHA. The project has been carried out by a seven-member Senior Seismic Hazard Analysis Committee (SSHAC) supported by a large number other experts. The SSHAC reviewed past studies, including the Lawrence Livermore National Laboratory and the EPRI landmark PSHA studies of the 1980`s and examined ways to improve on the present state-of-the-art. The Committee`s most important conclusion is that differences in PSHA results are due to procedural rather than technical differences. Thus, in addition to providing a detailed documentation on state-of-the-art elements of a PSHA, this report provides a series of procedural recommendations. The role of experts is analyzed in detail. Two entities are formally defined-the Technical Integrator (TI) and the Technical Facilitator Integrator (TFI)--to account for the various levels of complexity in the technical issues and different levels of efforts needed in a given study
A test of Local Realism with entangled kaon pairs and without inequalities
We propose the use of entangled pairs of neutral kaons, considered as a
promising tool to close the well known loopholes affecting generic Bell's
inequality tests, in a specific Hardy-type experiment. Hardy's contradiction
without inequalities between Local Realism and Quantum Mechanics can be
translated into a feasible experiment by requiring ideal detection efficiencies
for only one of the observables to be alternatively measured. Neutral kaons are
near to fulfil this requirement and therefore to close the efficiency loophole.Comment: 4 RevTeX page
Finite-size scaling of the helicity modulus of the two-dimensional O(3) model
Using Monte Carlo methods, we compute the finite-size scaling function of the
helicity modulus of the two-dimensional O(3) model and compare it to
the low temperature expansion prediction. From this, we estimate the range of
validity for the leading terms of the low temperature expansion of the
finite-size scaling function and for the low temperature expansion of the
correlation length. Our results strongly suggest that a Kosterlitz-Thouless
transition at a temperature is extremely unlikely in this model.Comment: 4 pages, 3 Postscript figures, to appear in Phys. Rev. B Jan. 1997 as
a Brief Repor
Exploring the conformational dynamics of alanine dipeptide in solution subjected to an external electric field: A nonequilibrium molecular dynamics simulation
In this paper, we investigate the conformational dynamics of alanine
dipeptide under an external electric field by nonequilibrium molecular dynamics
simulation. We consider the case of a constant and of an oscillatory field. In
this context we propose a procedure to implement the temperature control, which
removes the irrelevant thermal effects of the field. For the constant field
different time-scales are identified in the conformational, dipole moment, and
orientational dynamics. Moreover, we prove that the solvent structure only
marginally changes when the external field is switched on. In the case of
oscillatory field, the conformational changes are shown to be as strong as in
the previous case, and non-trivial nonequilibrium circular paths in the
conformation space are revealed by calculating the integrated net probability
fluxes.Comment: 23 pages, 12 figure
Percolation properties of the 2D Heisenberg model
We analyze the percolation properties of certain clusters defined on
configurations of the 2--dimensional Heisenberg model. We find that, given any
direction \vec{n} in O(3) space, the spins almost perpendicular to \vec{n} form
a percolating cluster. This result gives indications of how the model can avoid
a previously conjectured Kosterlitz-Thouless phase transition at finite
temperature T.Comment: 4 pages, 3 eps figures. Revised version (more clear abstract, some
new references
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