1,163 research outputs found
Evidence for pronounced quark loop effects in QCD
We have measured the hadron spectrum in lattice QCD, using staggered
fermions, for 0 (the quenched approximation), 2 and 4 light degenerate
dynamical quarks. In addition to earlier results involving extrapolations in
valence quark masses for fixed dynamical mass, we also report results where we
extrapolate in the dynamical mass for 4 flavors. We see a marked difference in
the hadron spectrum for 2 and 4 flavors; the hadron spectrum is nearly parity
doubled for 4 flavors, indicating smaller effects of chiral symmetry breaking.
This pronounced effect in the hadron spectrum cannot be removed by a simple
change in scale as the number of light quark flavors is changed. Further
simulations at larger volume are needed to rule out finite volume effects.Comment: 5 pages, 4 figures. Presented at Lattice QCD on Parallel Computers,
Tsukuba, Japan, march 199
Efficient Classification for Metric Data
Recent advances in large-margin classification of data residing in general
metric spaces (rather than Hilbert spaces) enable classification under various
natural metrics, such as string edit and earthmover distance. A general
framework developed for this purpose by von Luxburg and Bousquet [JMLR, 2004]
left open the questions of computational efficiency and of providing direct
bounds on generalization error.
We design a new algorithm for classification in general metric spaces, whose
runtime and accuracy depend on the doubling dimension of the data points, and
can thus achieve superior classification performance in many common scenarios.
The algorithmic core of our approach is an approximate (rather than exact)
solution to the classical problems of Lipschitz extension and of Nearest
Neighbor Search. The algorithm's generalization performance is guaranteed via
the fat-shattering dimension of Lipschitz classifiers, and we present
experimental evidence of its superiority to some common kernel methods. As a
by-product, we offer a new perspective on the nearest neighbor classifier,
which yields significantly sharper risk asymptotics than the classic analysis
of Cover and Hart [IEEE Trans. Info. Theory, 1967].Comment: This is the full version of an extended abstract that appeared in
Proceedings of the 23rd COLT, 201
Global Trade Impacts: Addressing the Health, Social and Environmental Consequences of Moving International Freight Through Our Communities
Examines freight transportation industry trends; the impact of global trade on workers, the environment, and health in both exporting and importing countries; and organizing strategies and policy innovations for minimizing the damage and ensuring health
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