6,171 research outputs found
Lattice QCD Production on Commodity Clusters at Fermilab
We describe the construction and results to date of Fermilab's three
Myrinet-networked lattice QCD production clusters (an 80-node dual Pentium III
cluster, a 48-node dual Xeon cluster, and a 128-node dual Xeon cluster). We
examine a number of aspects of performance of the MILC lattice QCD code running
on these clusters.Comment: Talk from the 2003 Computing in High Energy and Nuclear Physics
(CHEP03), La Jolla, Ca, USA, March 2003, 6 pages, LaTeX, 8 eps figures. PSN
TUIT00
New measure of electron correlation
We propose to quantify the "correlation" inherent in a many-electron (or
many-fermion) wavefunction by comparing it to the unique uncorrelated state
that has the same single-particle density operator as it does.Comment: Final version to appear in PR
Exceptional type-I superconductivity of the layered silver oxide AgPbO
We report zero-resistivity transition and the details of magnetic transition
of a layered silver oxide AgPbO single crystal, which make
definitive evidence of superconductivity in this compound. In the AC
susceptibility of a mono-crystal, we observed large supercooling, as well as
positive peaks in the real part of the susceptibility indicating the
reversibility of magnetic process. These observations reveal that
AgPbO is probably the first oxide that shows type-I
superconductivity. Evaluation of the superconducting parameters not only gives
confirming evidence of type-I superconductivity, but also indicates that it is
a dirty-limit superconductor. We also analyze supercooling to determine the
upper limit of the Ginzburg-Landau parameter.Comment: v2: PACS numbers are adde
Pressure and non-linear susceptibilities in QCD at finite chemical potentials
When the free energy density of QCD is expanded in a series in the chemical
potential, mu, the Taylor coefficients are the non-linear quark number
susceptibilities. We show that these depend on the prescription for putting
chemical potential on the lattice, making all extrapolations in chemical
potential prescription dependent at finite lattice spacing. To put bounds on
the prescription dependence, we investigate the magnitude of the non-linear
susceptibilities over a range of temperature, T, in QCD with two degenerate
flavours of light dynamical quarks at lattice spacing 1/4T. The prescription
dependence is removed in quenched QCD through a continuum extrapolation, and
the dependence of the pressure, P, on mu is obtained.Comment: 15 pages, 2 figures. Data on chi_uuuu added, discussion enhance
The Traveling Salesman Problem: Low-Dimensionality Implies a Polynomial Time Approximation Scheme
The Traveling Salesman Problem (TSP) is among the most famous NP-hard
optimization problems. We design for this problem a randomized polynomial-time
algorithm that computes a (1+eps)-approximation to the optimal tour, for any
fixed eps>0, in TSP instances that form an arbitrary metric space with bounded
intrinsic dimension.
The celebrated results of Arora (A-98) and Mitchell (M-99) prove that the
above result holds in the special case of TSP in a fixed-dimensional Euclidean
space. Thus, our algorithm demonstrates that the algorithmic tractability of
metric TSP depends on the dimensionality of the space and not on its specific
geometry. This result resolves a problem that has been open since the
quasi-polynomial time algorithm of Talwar (T-04)
Potential model calculations and predictions for heavy quarkonium
We investigate the spectroscopy and decays of the charmonium and upsilon
systems in a potential model consisting of a relativistic kinetic energy term,
a linear confining term including its scalar and vector relativistic
corrections and the complete perturbative one-loop quantum chromodynamic short
distance potential. The masses and wave functions of the various states are
obtained using a variational technique, which allows us to compare the results
for both perturbative and nonperturbative treatments of the potential. As well
as comparing the mass spectra, radiative widths and leptonic widths with the
available data, we include a discussion of the errors on the parameters
contained in the potential, the effect of mixing on the leptonic widths, the
Lorentz nature of the confining potential and the possible
interpretation of recently discovered charmonium-like states.Comment: Physical Review published versio
Baryon Density Correlations in High Temperature Hadronic Matter
As part of an ongoing effort to characterize the high temperature phase of
QCD, in a numerical simulation using the staggered fermion scheme, we measure
the quark baryon density in the vicinity of a fixed test quark at high
temperature and compare it with similar measurements at low temperature and at
the crossover temperature. We find an extremely weak correlation at high
temperature, suggesting that small color singlet clusters are unimportant in
the thermal ensemble. We also find that at the total induced
quark number shows a surprisingly large component attributable to baryonic
screening. A companion simulation of a simple flux tube model produces similar
results and also suggests a plausible phenomenological scenario: As the
crossover temperature is approached from below, baryonic states proliferate.
Above the crossover temperature the mean size of color singlet clusters grows
explosively, resulting in an effective electrostatic deconfinement.Comment: 26 pp, RevTeX, 12 postscript figures, combined in a single shell
archive file. (Also available in 13 postscript files by anonymous ftp from
einstein.physics.utah.edu, /pub/milc/paper.sh.Z.
Laboratory And Astronomical Detection Of The Negative Molecular Ion C3N-
The negative molecular ion C3N- has been detected at millimeter wavelengths in a low-pressure laboratory discharge, and then with frequencies derived from the laboratory data in the molecular envelope of IRC+10216. Spectroscopic constants derived from laboratory measurements of 12 transitions between 97 and 378 GHz allow the rotational spectrum to be calculated well into the submillimeter-wave band to 0.03 km s(-1) or better in equivalent radial velocity. Four transitions of C3N- were detected in IRC+10216 with the IRAM 30 m telescope at precisely the frequencies calculated from the laboratory measurements. The column density of C3N- is 0.5% that of C3N, or approximately 20 times greater than that of C4H- relative to C4H. The C3N- abundance in IRC+10216 is compared with a chemical model calculation by Petrie & Herbst. An upper limit in TMC-1 for C3N- relative to C3N (< 0.8%) and a limit for C4H- relative to C4H (< 0.004%) that is 5 times lower than that found in IRC+10216, were obtained from observations with the NRAO 100 m Green Bank Telescope (GBT). The fairly high concentration ofNRFKorean government MEST 2012R1A1A1014646, 2012M4A2026720Southeast Physics Network (SEP-Net)Science and Technology Facilities Council ST/F002858/1, ST/I000976/1Swedish Research Council 2009-4088U.S. NSF AST-0708176, AST-1009799NASA NNX07AH09G, NNG04G177G, NNX11AE09GChandra grant SAO TM8-9009XBiochemistr
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