2,072,592 research outputs found
Sound absorption by clamped poroelastic plates
Measurements and predictions have been made of the absorption coefficient and the surface acoustic impedance of poroelastic plates clamped in a large impedance tube and separated from the rigid termination by an air gap. The measured and predicted absorption coefficient and surface impedance spectra exhibit low frequency peaks. The peak frequencies observed in the absorption coefficient are close to those predicted and measured in the deflection spectra of the clamped poroelastic plates. The influences of the rigidity of the clamping conditions and the width of the air gap have been investigated. Both influences are found to be important. Increasing the rigidity of clamping reduces the low frequency absorption peaks compared with those measured for simply supported plates or plates in an intermediate clamping condition. Results for a closed cell foam plate and for two open cell foam plates made from recycled materials are presented. For identical clamping conditions and width of air gap, the results for the different materials differ as a consequence mainly of their different elasticity, thickness, and cell structure
Scaling regimes and critical dimensions in the Kardar-Parisi-Zhang problem
We study the scaling regimes for the Kardar-Parisi-Zhang equation with noise
correlator R(q) ~ (1 + w q^{-2 \rho}) in Fourier space, as a function of \rho
and the spatial dimension d. By means of a stochastic Cole-Hopf transformation,
the critical and correction-to-scaling exponents at the roughening transition
are determined to all orders in a (d - d_c) expansion. We also argue that there
is a intriguing possibility that the rough phases above and below the lower
critical dimension d_c = 2 (1 + \rho) are genuinely different which could lead
to a re-interpretation of results in the literature.Comment: Latex, 7 pages, eps files for two figures as well as Europhys. Lett.
style files included; slightly expanded reincarnatio
Relativistic Equation of State for Core-Collapse Supernova Simulations
We construct the equation of state (EOS) of dense matter covering a wide
range of temperature, proton fraction, and density for the use of core-collapse
supernova simulations. The study is based on the relativistic mean-field (RMF)
theory, which can provide an excellent description of nuclear matter and finite
nuclei. The Thomas--Fermi approximation in combination with assumed nucleon
distribution functions and a free energy minimization is adopted to describe
the non-uniform matter, which is composed of a lattice of heavy nuclei. We
treat the uniform matter and non-uniform matter consistently using the same RMF
theory. We present two sets of EOS tables, namely EOS2 and EOS3. EOS2 is an
update of our earlier work published in 1998 (EOS1), where only the nucleon
degree of freedom is taken into account. EOS3 includes additional contributions
from hyperons. The effect of hyperons on the EOS is
negligible in the low-temperature and low-density region, whereas it tends to
soften the EOS at high density. In comparison with EOS1, EOS2 and EOS3 have an
improved design of ranges and grids, which covers the temperature range
-- MeV with the logarithmic grid spacing (92 points including T=0), the proton fraction
range --0.65 with the linear grid spacing (66
points), and the density range --
with the logarithmic grid spacing (110 points).Comment: 43 pages, 10 figure
Supercriticality to subcriticality in dynamo transitions
Evidence from numerical simulations suggest that the nature of dynamo
transition changes from supercritical to subcritical as the magnetic Prandtl
number is decreased. To explore this interesting crossover we first use direct
numerical simulations to investigate the hysteresis zone of a subcritical
Taylor-Green dynamo. We establish that a well defined boundary exists in this
hysteresis region which separates dynamo states from the purely hydrodynamic
solution. We then propose simple dynamo models which show similar crossover
from supercritical to subcritical dynamo transition as a function of the
magnetic Prandtl number. Our models show that the change in the nature of
dynamo transition is connected to the stabilizing or de-stabilizing influence
of governing non-linearities.Comment: Version 3 note: Found a sign-error in an equation which propagated
further. Section 4 and Fig. 3,4,5 are updated in Version 3 (final form
Relativistic Equation of State of Nuclear Matter for Supernova Explosion
We construct the equation of state (EOS) of nuclear matter at finite
temperature and density with various proton fractions within the relativistic
mean field (RMF) theory for the use in the supernova simulations. The
Thomas-Fermi approximation is adopted to describe the non-uniform matter where
we consider nucleus, alpha-particle, proton and neutron in equilibrium. We
treat the uniform matter and non-uniform matter consistently using the RMF
theory. We tabulate the outcome as the pressure, free energy, entropy etc, with
enough mesh points in wide ranges of the temperature, proton fraction, and
baryon mass density.Comment: 22 pages, LaTeX, 9 ps-figures, Submitted to Prog.Theor.Phy
The Steady-State Transport of Oxygen through Hemoglobin Solutions
The steady-state transport of oxygen through hemoglobin solutions was studied to identify the mechanism of the diffusion augmentation observed at low oxygen tensions. A novel technique employing a platinum-silver oxygen electrode was developed to measure the effective diffusion coefficient of oxygen in steady-state transport. The measurements were made over a wider range of hemoglobin and oxygen concentrations than previously reported. Values of the Brownian motion diffusion coefficient of oxygen in hemoglobin solution were obtained as well as measurements of facilitated transport at low oxygen tensions. Transport rates up to ten times greater than ordinary diffusion rates were found. Predictions of oxygen flux were made assuming that the oxyhemoglobin transport coefficient was equal to the Brownian motion diffusivity which was measured in a separate set of experiments. The close correlation between prediction and experiment indicates that the diffusion of oxyhemoglobin is the mechanism by which steady-state oxygen transport is facilitated
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