246 research outputs found
Solution of the Percus-Yevick equation for hard discs
We solve the Percus-Yevick equation in two dimensions by reducing it to a set
of simple integral equations. We numerically obtain both the pair correlation
function and the equation of state for a hard disc fluid and find good
agreement with available Monte-Carlo calculations. The present method of
resolution may be generalized to any even dimension.Comment: 9 pages, 3 figure
The spectrum of large powers of the Laplacian in bounded domains
We present exact results for the spectrum of the Nth power of the Laplacian
in a bounded domain. We begin with the one dimensional case and show that the
whole spectrum can be obtained in the limit of large N. We also show that it is
a useful numerical approach valid for any N. Finally, we discuss implications
of this work and present its possible extensions for non integer N and for 3D
Laplacian problems.Comment: 13 pages, 2 figure
Finite-distance singularities in the tearing of thin sheets
We investigate the interaction between two cracks propagating in a thin
sheet. Two different experimental geometries allow us to tear sheets by
imposing an out-of-plane shear loading. We find that two tears converge along
self-similar paths and annihilate each other. These finite-distance
singularities display geometry-dependent similarity exponents, which we
retrieve using scaling arguments based on a balance between the stretching and
the bending of the sheet close to the tips of the cracks.Comment: 4 pages, 4 figure
Scale calculus and the Schrodinger equation
We introduce the scale calculus, which generalizes the classical differential
calculus to non differentiable functions. The new derivative is called the
scale difference operator. We also introduce the notions of fractal functions,
minimal resolution, and quantum representation of a non differentiable
function. We then define a scale quantization procedure for classical
Lagrangian systems inspired by the Scale relativity theory developped by
Nottale. We prove that the scale quantization of Newtionian mechanics is a non
linear Schrodinger equation. Under some specific assumptions, we obtain the
classical linear Schrodinger equation.Comment: 49 page
Solution of the Percus-Yevick equation for hard hyperspheres in even dimensions
We solve the Percus-Yevick equation in even dimensions by reducing it to a
set of simple integro-differential equations. This work generalizes an approach
we developed previously for hard discs. We numerically obtain both the pair
correlation function and the virial coefficients for a fluid of hyper-spheres
in dimensions and 8, and find good agreement with available exact
results and Monte-Carlo simulations. This paper confirms the alternating
character of the virial series for , and provides the first evidence
for an alternating character for . Moreover, we show that this sign
alternation is due to the existence of a branch point on the negative real
axis. It is this branch point that determines the radius of convergence of the
virial series, whose value we determine explicitly for . Our results
complement, and are consistent with, a recent study in odd dimensions [R.D.
Rohrmann et al., J. Chem. Phys. 129, 014510 (2008)].Comment: Accepted for publication in J. Chem. Phys. (11 pages, 6 figures
Continuum field description of crack propagation
We develop continuum field model for crack propagation in brittle amorphous
solids. The model is represented by equations for elastic displacements
combined with the order parameter equation which accounts for the dynamics of
defects. This model captures all important phenomenology of crack propagation:
crack initiation, propagation, dynamic fracture instability, sound emission,
crack branching and fragmentation.Comment: 4 pages, 5 figures, submitted to Phys. Rev. Lett. Additional
information can be obtained from http://gershwin.msd.anl.gov/theor
Feasibility of low-dose coronary CT angiography: first experience with prospective ECG-gating
AIMS: To determine the feasibility of prospective electrocardiogram (ECG)-gating to achieve low-dose computed tomography coronary angiography (CTCA). METHODS AND RESULTS: Forty-one consecutive patients with suspected (n = 35) or known coronary artery disease (n = 6) underwent 64-slice CTCA using prospective ECG-gating. Individual radiation dose exposure was estimated from the dose-length product. Two independent readers semi-quantitatively assessed the overall image quality on a five-point scale and measured vessel attenuation in each coronary segment. One patient was excluded for atrial fibrillation. Mean effective radiation dose was 2.1 +/- 0.6 mSv (range, 1.1-3.0 mSv). Image quality was inversely related to heart rate (HR) (57.3 +/- 6.2, range 39-66 b.p.m.; r = 0.58, P 63 b.p.m. (P < 0.001). CONCLUSION: This first experience documents the feasibility of prospective ECG-gating for CTCA with diagnostic image quality at a low radiation dose (1.1-3.0 mSv), favouring HR <63 b.p.
Feasibility of low-dose coronary CT angiography: first experience with prospective ECG-gating
AIMS: To determine the feasibility of prospective electrocardiogram (ECG)-gating to achieve low-dose computed tomography coronary angiography (CTCA). METHODS AND RESULTS: Forty-one consecutive patients with suspected (n = 35) or known coronary artery disease (n = 6) underwent 64-slice CTCA using prospective ECG-gating. Individual radiation dose exposure was estimated from the dose-length product. Two independent readers semi-quantitatively assessed the overall image quality on a five-point scale and measured vessel attenuation in each coronary segment. One patient was excluded for atrial fibrillation. Mean effective radiation dose was 2.1 +/- 0.6 mSv (range, 1.1-3.0 mSv). Image quality was inversely related to heart rate (HR) (57.3 +/- 6.2, range 39-66 b.p.m.; r = 0.58, P 63 b.p.m. (P < 0.001). CONCLUSION: This first experience documents the feasibility of prospective ECG-gating for CTCA with diagnostic image quality at a low radiation dose (1.1-3.0 mSv), favouring HR <63 b.p.
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