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Monte Carlo Calculations for Liquid He at Negative Pressure
A Quadratic Diffusion Monte Carlo method has been used to obtain the equation
of state of liquid He including the negative pressure region down to the
spinodal point. The atomic interaction used is a renewed version (HFD-B(HE)) of
the Aziz potential, which reproduces quite accurately the features of the
experimental equation of state. The spinodal pressure has been calculated and
the behavior of the sound velociy around the spinodal density has been
analyzed.Comment: 10 pages, RevTex 3.0, with 4 PostScript figures include
Exact particle and kinetic energy densities for one-dimensional confined gases of non-interacting fermions
We propose a new method for the evaluation of the particle density and
kinetic pressure profiles in inhomogeneous one-dimensional systems of
non-interacting fermions, and apply it to harmonically confined systems of up
to N=1000 fermions. The method invokes a Green's function operator in
coordinate space, which is handled by techniques originally developed for the
calculation of the density of single-particle states from Green's functions in
the energy domain. In contrast to the Thomas-Fermi (local density)
approximation, the exact profiles under harmonic confinement show negative
local pressure in the tails and a prominent shell structure which may become
accessible to observation in magnetically trapped gases of fermionic alkali
atoms.Comment: 8 pages, 3 figures, accepted for publication in Phys. Rev. Let
New Cardiovascular Indices Based on a Nonlinear Spectral Analysis of Arterial Blood Pressure Waveforms
A new method for analyzing arterial blood pressure is presented in this
report. The technique is based on the scattering transform and consists in
solving the spectral problem associated to a one-dimensional Schr\"odinger
operator with a potential depending linearly upon the pressure. This potential
is then expressed with the discrete spectrum which includes negative
eigenvalues and corresponds to the interacting components of an N-soliton. The
approach is similar to a nonlinear Fourier transform where the solitons play
the role of sine and cosine components. The method provides new cardiovascular
indices that seem to contain relevant physiological information. We first show
how to use this approach to decompose the arterial blood pressure pulse into
elementary waves and to reconstruct it or to separate its systolic and
diastolic phases. Then we analyse the parameters computed from this technique
in two physiological conditions, the head-up 60 degrees tilt test and the
isometric handgrip test, widely used for studying short term cardiovascular
control. Promising results are obtained
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