236 research outputs found
Ultrasound-induced acoustophoretic motion of microparticles in three dimensions
We derive analytical expressions for the three-dimensional (3D)
acoustophoretic motion of spherical microparticles in rectangular
microchannels. The motion is generated by the acoustic radiation force and the
acoustic streaming-induced drag force. In contrast to the classical theory of
Rayleigh streaming in shallow, infinite, parallel-plate channels, our theory
does include the effect of the microchannel side walls. The resulting
predictions agree well with numerics and experimental measurements of the
acoustophoretic motion of polystyrene spheres with nominal diameters of 0.537
um and 5.33 um. The 3D particle motion was recorded using astigmatism particle
tracking velocimetry under controlled thermal and acoustic conditions in a
long, straight, rectangular microchannel actuated in one of its transverse
standing ultrasound-wave resonance modes with one or two half-wavelengths. The
acoustic energy density is calibrated in situ based on measurements of the
radiation dominated motion of large 5-um-diam particles, allowing for
quantitative comparison between theoretical predictions and measurements of the
streaming induced motion of small 0.5-um-diam particles.Comment: 13 pages, 8 figures, Revtex 4.
Dynamical QCD thermodynamics with domain wall fermions
We present results from numerical simulations of full, two flavor QCD
thermodynamics at N_t=4 with domain wall fermions. For the first time a
numerical simulation of the full QCD phase transition displays a low
temperature phase with spontaneous chiral symmetry breaking but intact flavor
symmetry and a high temperature phase with the full SU(2) x SU(2) chiral flavor
symmetry.Comment: LATTICE98(hightemp
Quenched QCD with domain wall fermions
We report on simulations of quenched QCD using domain wall fermions, where we
focus on basic questions about the formalism and its ability to produce
expected low energy hadronic physics for light quarks. The work reported here
is on quenched lattices at and 5.85, using values
for the length of the fifth dimension between 10 and 48. We report results for
parameter choices which lead to the desired number of flavors, a study of
undamped modes in the extra dimension and hadron masses.Comment: Contribution to Lattice '98. Presented by R. Mawhinney. 3 pages, 3
figure
The domain wall fermion chiral condensate in quenched QCD
We examine the chiral limit of domain wall fermions in quenched QCD. One
expects that in a quenched simulation, exact fermion zero modes will give a
divergent, 1/m behavior in the chiral condensate for sufficiently small valence
quark masses. Unlike other fermion formulations, domain wall fermions clearly
demonstrate this behavior.Comment: LATTICE98(spectrum), G. R. Fleming presented talk, 5 pages, 3
figures, corrected typos in printed versio
Small eigenvalues of the staggered Dirac operator in the adjoint representation and Random Matrix Theory
The low-lying spectrum of the Dirac operator is predicted to be universal,
within three classes, depending on symmetry properties specified according to
random matrix theory. The three universal classes are the orthogonal, unitary
and symplectic ensemble. Lattice gauge theory with staggered fermions has
verified two of the cases so far, unitary and symplectic, with staggered
fermions in the fundamental representation of SU(3) and SU(2). We verify the
missing case here, namely orthogonal, with staggered fermions in the adjoint
representation of SU(N_c), N_c=2, 3.Comment: 3 pages, revtex, 2 postscript figure
The finite temperature QCD phase transition with domain wall fermions
The domain wall formulation of lattice fermions is expected to support
accurate chiral symmetry, even at finite lattice spacing. Here we attempt to
use this new fermion formulation to simulate two-flavor, finite temperature QCD
near the chiral phase transition. In this initial study, a variety of quark
masses, domain wall heights and domain wall separations are explored using an
8^3 x 4 lattice. Both the expectation value of the Wilson line and the chiral
condensate show the temperature dependence expected for the QCD phase
transition. Further, the desired chiral properties are seen for the chiral
condensate, suggesting that the domain wall fermion formulation may be an
effective approach for the numerical study of QCD at finite temperature.Comment: 44 pages, 15 figure
Status of the QCDSP project
We describe the completed 8,192-node, 0.4Tflops machine at Columbia as well
as the 12,288-node, 0.6Tflops machine assembled at the RIKEN Brookhaven
Research Center. Present performance as well as our experience in commissioning
these large machines is presented. We outline our on-going physics program and
explain how the configuration of the machine is varied to support a wide range
of lattice QCD problems, requiring a variety of machine sizes. Finally a brief
discussion is given of future prospects for large-scale lattice QCD machines.Comment: LATTICE98(machines), 3 pages, 1 picture, 1 figur
Domain wall fermion zero modes on classical topological backgrounds
The domain wall approach to lattice fermions employs an additional dimension,
in which gauge fields are merely replicated, to separate the chiral components
of a Dirac fermion. It is known that in the limit of infinite separation in
this new dimension, domain wall fermions have exact zero modes, even for gauge
fields which are not smooth. We explore the effects of finite extent in the
fifth dimension on the zero modes for both smooth and non-smooth topological
configurations and find that a fifth dimension of around ten sites is
sufficient to clearly show zero mode effects. This small value for the extent
of the fifth dimension indicates the practical utility of this technique for
numerical simulations of QCD.Comment: Updated fig. 3-7, small changes in sect. 3, added fig. 8, added more
reference
Domain Wall Fermions in Quenched Lattice QCD
We study the chiral properties and the validity of perturbation theory for
domain wall fermions in quenched lattice QCD at beta=6.0. The explicit chiral
symmetry breaking term in the axial Ward-Takahashi identity is found to be very
small already at Ns=10, where Ns is the size of the fifth dimension, and its
behavior seems consistent with an exponential decay in Ns within the limited
range of Ns we explore. From the fact that the critical quark mass, at which
the pion mass vanishes as in the case of the ordinary Wilson-type fermion,
exists at finite Ns, we point out that this may be a signal of the parity
broken phase and investigate the possible existence of such a phase in this
model at finite Ns. The rho and pi meson decay constants obtained from the
four-dimensional local currents with the one-loop renormalization factor show a
good agreement with those obtained from the conserved currents
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