3,135 research outputs found
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
Quantum railroads and directed localization at the juncture of quantum Hall systems
The integer quantum Hall effect (QHE) and one-dimensional Anderson
localization (AL) are limiting special cases of a more general phenomenon,
directed localization (DL), predicted to occur in disordered one-dimensional
wave guides called "quantum railroads" (QRR). Here we explain the surprising
results of recent measurements by Kang et al. [Nature 403, 59 (2000)] of
electron transfer between edges of two-dimensional electron systems and
identify experimental evidence of QRR's in the general, but until now entirely
theoretical, DL regime that unifies the QHE and AL. We propose direct
experimental tests of our theory.Comment: 11 pages revtex + 3 jpeg figures, to appear in Phys. Rev.
Super Yang-Mills on the lattice with domain wall fermions
The dynamical N=1, SU(2) Super Yang-Mills theory is studied on the lattice
using a new lattice fermion regulator, domain wall fermions. This formulation
even at non-zero lattice spacing does not require fine-tuning, has improved
chiral properties and can produce topological zero-mode phenomena. Numerical
simulations of the full theory on lattices with the topology of a torus
indicate the formation of a gluino condensate which is sustained at the chiral
limit. The condensate is non-zero even for small volume and small supersymmetry
breaking mass where zero mode effects due to gauge fields with fractional
topological charge appear to play a role.Comment: LaTeX, 35 pages, 11 eps figures. A few changes in sec. 5.3, figure 11
added. To appear in Phys. Rev.
A Shock-Induced Pair of Superbubbles in the High-Redshift Powerful Radio Galaxy MRC 0406-244
We present new optical spectroscopy of the high-redshift powerful radio
galaxy MRC 0406244 at redshift of 2.429. We find that the two extensions
toward NW and SE probed in the rest-frame ultraviolet image are heated mainly
by the nonthermal continuum of the active galactic nucleus. However, each
extension shows a shell-like morphology, suggesting that they are a pair of
superbubbles induced by the superwind activity rather than by the interaction
between the radio jet and the ambient gas clouds. If this is the case, the
intense starburst responsible for the formation of superbubbles could occur
yr ago. On the other hand, the age of the radio jets may
be of the order of yr, being much shorter than the starburst age.
Therefore, the two events, i.e., the starburst and the radio-jet activities,
are independent phenomena. However, their directions of the expanding motions
could be governed by the rotational motion of the gaseous component in the host
galaxy. This idea appears to explain the alignment effect of MRC 0406244.Comment: 4 pages (emulateapj.sty), Fig. 1 (jpeg) + Fig.2 (eps). Accepted for
publications in ApJ (Letters
Binary Blue Metal-Poor Stars: Evidence for AGB Mass Transfer
We present new abundance analyses of six blue metal-poor (BMP) stars with
very low iron abundances ([Fe/H] < -2), based on new high resolution echelle
spectra. Three are spectroscopic binaries and three have constant radial
velocities. The chemical compositions of these two groups are very different,
as the binary BMP stars have large enhancements of carbon and neutron-capture
elements that are products of s-process nucleosynthesis. One star, CS
29497-030, has an extreme enhancement of lead, [Pb/Fe] = +3.7, the largest
abundance in any star yet discovered. It probably also has an oxygen
overabundance compared to the other BMP stars of our sample. The binary BMP
stars must have attained their status via mass transfer during the asymptotic
giant branch (AGB) evolutions of their companion stars, which are now unseen
and most likely are compact objects. We have not found any examples of AGB mass
transfer among BMP binaries with [Fe/H] > -2.Comment: 34 pages, 9 figures, 7 tables; To appear in the Astrophysical Journa
The Absolute Magnitude of RRc Variables From Statistical Parallax
We present the first definitive measurement of the absolute magnitude of RR
Lyrae c-type variable stars (RRc) determined purely from statistical parallax.
We use a sample of 247 RRc selected from the All Sky Automated Survey (ASAS)
for which high-quality light curves, photometry and proper motions are
available. We obtain high-resolution echelle spectra for these objects to
determine radial velocities and abundances as part of the Carnegie RR Lyrae
Survey (CARRS). We find that M_(V,RRc) = 0.52 +/- 0.11 at a mean metallicity of
[Fe/H] = -1.59. This is to be compared with previous estimates for RRab stars
(M_(V,RRab) = 0.75 +/- 0.13 and the only direct measurement of an RRc absolute
magnitude (RZ Cephei, M_(V, RRc) = 0.27 +/- 0.17). We find the bulk velocity of
the halo to be (W_pi, W_theta, W_z) = (10.9,34.9,7.2) km/s in the radial,
rotational and vertical directions with dispersions (sigma_(W_pi),
sigma_(W_theta), sigma_(W_z)) = (154.7, 103.6, 93.8) km/s. For the disk, we
find (W_pi, W_theta, W_z) = (8.5, 213.2, -22.1) km/s with dispersions
(sigma_(W_pi), sigma_(W_theta), sigma_(W_z)) = (63.5, 49.6, 51.3) km/s.
Finally, we suggest that UCAC2 proper motion errors may be overestimated by
about 25%Comment: Submitted to ApJ. 11 pages including 6 figure
Intersecting branes and a standard model realization in matrix models
We consider intersecting brane solutions of the type IIB matrix model. It is
shown that fermionic zero-modes arise on such backgrounds, localized at the
brane intersections. They lead to chiral fermions in four dimensions under
certain conditions. Such configurations reproduce many of the welcome features
in similar string-theoretic constructions. Therefore they can be used to
construct semi-realistic particle physics models in the framework of Yang-Mills
matrix models. In particular, we present a brane configuration which realizes
the correct chiral spectrum of the standard model in the matrix model.
Furthermore, the stability of intersecting branes is discussed by analyzing the
1-loop effective action. It is shown that intersecting branes may form a bound
state for certain flux configurations. The four-dimensional geometry of the
branes is generic, and determined by the (emergent) gravity sector of the
matrix model.Comment: 35 pages. V2: discussion on SUSY added V3: improved discussion of the
Higgs secto
Sirolimus-Eluting Versus Paclitaxel-Eluting Stent Implantation for the Percutaneous Treatment of Left Main Coronary Artery Disease A Combined RESEARCH and T-SEARCH Long-Term Analysis
ObjectivesThe purpose of this study was to investigate the long-term clinical and angiographic profile of sirolimus-eluting stent (SES) versus paclitaxel-eluting stent (PES) in patients undergoing percutaneous intervention for left main (LM) coronary disease.BackgroundThe long-term clinical and angiographic impact of SES as opposed to PES implantation in this subset of patients is unknown.MethodsFrom April 2002 to March 2004, 110 patients underwent percutaneous intervention for LM stenosis at our institution; 55 patients were treated with SES and 55 with PES. The two groups were well balanced for all baseline characteristics.ResultsAt a median follow-up of 660 days (range 428 to 885), the cumulative incidence of major adverse cardiovascular events was similar (25% in the SES group vs. 29%, in the PES group; hazard ratio 0.88 [95% confidence interval 0.43 to 1.82]; p = 0.74), reflecting similarities in both the composite death/myocardial infarction (16% in the SES group and 18% in the PES group) and target vessel revascularization (9% in the SES group and 11% in the PES group). Angiographic in-stent late loss (mm), evaluated in 73% of the SES group and in 77% of the PES group, was 0.32 ± 74 in the main and 0.36 ± 0.59 in the side branch in the SES group vs. 0.46 ± 0.57 (p = 0.36) and 0.52 ± 0.42 (p = 0.41) in the PES group, respectively.ConclusionsIn consecutive patients undergoing percutaneous LM intervention, PES may perform closely to SES both in terms of angiographic and long-term clinical outcome
Measurement of the cross-section and charge asymmetry of bosons produced in proton-proton collisions at TeV with the ATLAS detector
This paper presents measurements of the and cross-sections and the associated charge asymmetry as a
function of the absolute pseudorapidity of the decay muon. The data were
collected in proton--proton collisions at a centre-of-mass energy of 8 TeV with
the ATLAS experiment at the LHC and correspond to a total integrated luminosity
of 20.2~\mbox{fb^{-1}}. The precision of the cross-section measurements
varies between 0.8% to 1.5% as a function of the pseudorapidity, excluding the
1.9% uncertainty on the integrated luminosity. The charge asymmetry is measured
with an uncertainty between 0.002 and 0.003. The results are compared with
predictions based on next-to-next-to-leading-order calculations with various
parton distribution functions and have the sensitivity to discriminate between
them.Comment: 38 pages in total, author list starting page 22, 5 figures, 4 tables,
submitted to EPJC. All figures including auxiliary figures are available at
https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/STDM-2017-13
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