2,769 research outputs found
A Study of Finite Temperature Gauge Theory in (2+1) Dimensions
We determine the critical couplings and the critical exponents of the finite
temperature transition in SU(2) and SU(3) pure gauge theory in (2+1)
dimensions. We also measure Wilson loops at on a wide range of
values using APE smearing to improve the signal. We extract the string tension
from a fit to large distances, including a string fluctuation term.
With these two entities we calculate .Comment: Talk presented at LATTICE96(finite temperature), not espcrc2 style: 7
pages, 4 ps figures, 22 k
Asymptotic Behavior of the Correlator for Polyakov Loops
The asymptotic behavior of the correlator for Polyakov loop operators
separated by a large distance is determined for high temperature QCD. It is
dominated by nonperturbative effects related to the exchange of magnetostatic
gluons. To analyze the asymptotic behavior, the problem is formulated in terms
of the effective field theory of QCD in 3 space dimensions. The Polyakov loop
operator is expanded in terms of local gauge-invariant operators constructed
out of the magnetostatic gauge field, with coefficients that can be calculated
using resummed perturbation theory. The asymptotic behavior of the correlator
is , where is the mass of the lowest-lying glueball in
-dimensional QCD. This result implies that existing lattice calculations
of the Polyakov loop correlator at the highest temperatures available do not
probe the true asymptotic region in .Comment: 10 pages, NUHEP-TH-94-2
Fiber-optic probe for noninvasive real-time determination of tissue optical properties at multiple wavelengths
We present a compact, fast, and versatile fiber-optic probe system for real-time determination of tissue optical properties from spatially resolved continuous-wave diffuse reflectance measurements. The system collects one set of reflectance data from six source-detector distances at four arbitrary wavelengths with a maximum overall sampling rate of 100 Hz. Multivariate calibration techniques based on two-dimensional polynomial fitting are employed to extract and display the absorption and reduced scattering coefficients in real-time mode. The four wavelengths of the current configuration are 660, 785, 805, and 974 nm, respectively. Cross-validation tests on a 6 x 7 calibration matrix of Intralipid-dye phantoms showed that the mean prediction error at, e.g., 785 nm was 2.8% for the absorption coefficient and 1.3% for the reduced scattering coefficient. The errors are relative to the range of the optical properties of the phantoms at 785 nm, which were 0-0.3/cm for the absorption coefficient and 6-16/cm for the reduced scattering coefficient. Finally, we also present and discuss results from preliminary skin tissue measurements. (C) 2001 Optical Society of Americ
The equation of state for two flavor QCD at N_t=6
We calculate the two flavor equation of state for QCD on lattices with
lattice spacing a=(6T)^{-1} and find that cutoff effects are substantially
reduced compared to an earlier study using a=(4T)^{-1}. However, it is likely
that significant cutoff effects remain. We fit the lattice data to expected
forms of the free energy density for a second order phase transition at
zero-quark-mass, which allows us to extrapolate the equation of state to m_q=0
and to extract the speed of sound. We find that the equation of state depends
weakly on the quark mass for small quark mass.Comment: 24 pages, latex, 11 postscipt figure
The instanton liquid in QCD at zero and finite temperature
In this paper we study the statistical mechanics of the instanton liquid in
QCD. After introducing the partition function as well as the gauge field and
quark induced interactions between instantons we describe a method to calculate
the free energy of the instanton system. We use this method to determine the
equilibrium density and the equation of state from numerical simulations of the
instanton ensemble in QCD for various numbers of flavors. We find that there is
a critical number of flavors above which chiral symmetry is restored in the
groundstate. In the physical case of two light and one intermediate mass flavor
the system undergoes a chiral phase transition at MeV. We show
that the mechanism for this transition is a rearrangement of the instanton
liquid, going from a disordered, random, phase at low temperatures to a
strongly correlated, molecular, phase at high temperature. We also study the
behavior of mesonic susceptibilities near the phase transition.Comment: 50 pages, revtex, 16 figures, uuencode
Rapidly rotating Bose-Einstein condensates in anharmonic potentials
Rapidly rotating Bose-Einstein condensates confined in anharmonic traps can
exhibit a rich variety of vortex phases, including a vortex lattice, a vortex
lattice with a hole, and a giant vortex. Using an augmented Thomas-Fermi
variational approach to determine the ground state of the condensate in the
rotating frame -- valid for sufficiently strongly interacting condensates -- we
determine the transitions between these three phases for a
quadratic-plus-quartic confining potential. Combining the present results with
previous numerical simulations of small rotating condensates in such anharmonic
potentials, we delineate the general structure of the zero temperature phase
diagram.Comment: 5 pages, 5 figure
Vortex oscillations in confined Bose-Einstein condensate interacting with 1D optical lattice
We study Bose-Einstein condensate of atomic Boson gases trapped in a
composite potential of a harmonic potential and an optical lattice potential.
We found a series of collective excitations that induces localized vortex
oscillations with a characteristic wavelength. The oscillations might be
observed experimentally when radial confinement is tight. We present the
excitation spectra of the vortex oscillation modes and propose a way to
experimentally excite the modes.Comment: 5 pages, 7 figures. Title, abstract and references are update
Testing improved actions for dynamical Kogut-Susskind quarks
We extend tests of "Naik" and "fat link" improvements of the Kogut-Susskind
quark action to full QCD simulations, and verify that the improvements
previously demonstrated in the quenched approximation apply also to dynamical
quark simulations. We extend the study of flavor symmetry improvement to the
complete set of pions, and find that the nonlocal pions are significantly
heavier than the local non-Goldstone pion. These results can be used to
estimate the lattice spacing necessary for realistic simulations with this
action.Comment: 16 pages, LaTeX, PostScript figures include
The Thermodynamics of Quarks and Gluons
This is an introduction to the study of strongly interacting matter. We
survey its different possible states and discuss the transition from hadronic
matter to a plasma of deconfined quarks and gluons. Following this, we
summarize the results provided by lattice QCD finite temperature and density,
and then investigate the nature of the deconfinement transition. Finally we
give a schematic overview of possible ways to study the properties of the
quark-gluon plasma.Comment: 19 pages, 21 figures; lecture given at the QGP Winter School,
Jaipur/India, Feb.1-3, 2008; to appear in Springer Lecture Notes in Physic
Direct and Inverse Solutions for Thermal-and Stress-Transients and the Analytical Determination of Boundary Conditions Using Remote Temperature or Strain Data
From an analytical standpoint, a majority of calculations use known boundary conditions (temperature or flux) and the so-called direct route to determine internal temperatures, strains, and/or stresses. For such problems where the thermal boundary condition is known a priori, the analytical procedure and solutions are tractable for the linear case where the thermophysical properties are independent of temperature. On the other hand, the inverse route where the boundary conditions must be determined from remotely determined temperature and/or flux data is much more difficult mathematically, as well as inherently sensitive to data errors (i.e., ill-posed). When solutions are available, they are often restricted to a harsh, albeit unrealistic step change in temperature or flux and/or are only valid for relatively short time frames before temperature changes occur at the far boundary. While the two approaches may seem to be at odds with each other, a generalized direct solution based on polynomial temperature or strain-histories can also be used to determine unknown boundary conditions via least-squares determination of coefficients. Once the inverse problem (and unknown boundary condition) is solved via these coefficients, the resulting polynomial can then be used with the generalized direct solution to determine the thermal-and stress-states as a function of time and position. When used for both thick slabs and tubes, excellent agreement was seen for various test cases. In fact, the derived solutions appear to be well suited for many thermal scenarios, provided the analysis is restricted to the time interval used to determine the polynomial and the thermophysical properties that do not vary with temperature. Since temperature dependent properties can certainly be an issue that affects accuracy in these types of calculations, some recent analytical procedures for both direct and inverse solutions are also discussed
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