The Role of Center Vortices in QCD

Center vortices are unambiguously identified after Laplacian Center Gauge fixing and their influence on confinement and chiral symmetry breaking is investigated on a sample of SU(2) configurations at zero and finite temperature.Comment: LaTeX, 4 pages, 3 figures, espcrc1.sty. Talk at PANIC '99, Uppsala, Sweden, June 9

Computational methods for higher real K-theory with applications to tmf

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mathematics, 2006.Includes bibliographical references (p. 67-69).We begin by present a new Hopf algebra which can be used to compute the tmf homology of a space or spectrum at the prime 3. Generalizing work of Mahowald and Davis, we use this Hopf algebra to compute the tmf homology of the classifying space of the symmetric group on three elements. We also discuss the E3 Tate spectrum of tmf at the prime 3. We then build on work of Hopkins and his collaborators, first computing the Adams-Novikov zero line of the homotopy of the spectrum eo4 at 5 and then generalizing the Hopf algebra for tmf to a family of Hopf algebras, one for each spectrum eop_l at p. Using these, and using a K(p - 1)-local version, we further generalize the Davis-Mahowald result, computing the eop_1 homology of the cofiber of the transfer map [...]. We conclude by computing the initial computations needed to understand the homotopy groups of the Hopkins-Miller real K-theory spectra for heights large than p- 1 at p. The basic computations are supplemented with conjectures as to the collapse of the spectral sequences used herein to compute the homotopy.by Michael Anthony Hill.Ph.D

High-pressure study of X-ray diffuse scattering in ferroelectric perovskites

We present a high-pressure x-ray diffuse scattering study of the ABO$_3$ ferroelectric perovskites BaTiO_3 and KNbO_3. The well-known diffuse lines are observed in all the phases studied. In KNbO_3, we show that the lines are present up to 21.8 GPa, with constant width and a slightly decreasing intensity. At variance, the intensity of the diffuse lines observed in the cubic phase of BaTiO_3 linearly decreases to zero at $\sim 11$ GPa. These results are discussed with respect to x-ray absorption measurements, which leads to the conclusion that the diffuse lines are only observed when the B atom is off the center of the oxygen tetrahedron. The role of such disorder on the ferroelectric instability of perovskites is discussed.Comment: 4 pages, Accepted in PR

Naval air defense threat assessment: Cognitive factors and model

This paper reports the results of an investigation into the cognitive aspects of threat assessment. Threat assessment is the process of evaluating aircraft that are flying in the vicinity of one’s ship and determining how much of a threat they represent to one’s own ship and to the larger battle group. Data were collected from experienced U.S. Navy air defense officers as they interacted with a realistic scenario. Participants assigned threat and priority levels to selected aircraft, and described the factors and rationale that they used to arrive at their decisions. Twenty-two factors (e.g., Altitude, Speed, IFF) were identified. Participants consistently used different, but overlapping, subsets of factors, called profiles: A schema that lists the factors to be considered for a particular type of track, and the expected range of values that any given factor can take on. The participants appeared to sequentially evaluate the factors, and set threat levels that were inversely related to the fit between data and expectations. Aircraft that matched expectations were assigned lower threat levels than aircraft that did not match expectations. Threat Levels were biased by the Geopolitical Situation. A model was proposed that embodied the major findings in the data. This research was supported by the Office of Naval Research. Special thanks to Dr. Sue Hutchins at the Naval Postgraduat

Coulomb Energy, Vortices, and Confinement

We estimate the Coulomb energy of static quarks from a Monte Carlo calculation of the correlator of timelike link variables in Coulomb gauge. We find, in agreement with Cucchieri and Zwanziger, that this energy grows linearly with distance at large quark separations. The corresponding string tension, however, is several times greater than the accepted asymptotic string tension, indicating that a state containing only static sources, with no constituent gluons, is not the lowest energy flux tube state. The Coulomb energy is also measured on thermalized lattices with center vortices removed by the de Forcrand-D'Elia procedure. We find that when vortices are removed, the Coulomb string tension vanishes.Comment: 8 pages, 4 EPS figures, RevTeX4; reference adde

Instantons and <A2><A^2> Condensate

We argue that the $$condensate found in the Landau gauge on lattices, when an Operator Product Expansion of Green functions is performed, might be explained by instantons. We use cooling to estimate the instanton contribution and extrapolate back the result to the thermalised configuration. The resulting$$ is similar to $$.Comment: 6 pages, 1 fig., 1 tab., RevTeX to be use

Balancing the robustness and predictive performance of biomarkers.

Recent studies have highlighted the importance of assessing the robustness of putative biomarkers identified from experimental data. This has given rise to the concept of stable biomarkers, which are ones that are consistently identified regardless of small perturbations to the data. Since stability is not by itself a useful objective, we present a number of strategies that combine assessments of stability and predictive performance in order to identify biomarkers that are both robust and diagnostically useful. Moreover, by wrapping these strategies around logistic regression classifiers regularized by the elastic net penalty, we are able to assess the effects of correlations between biomarkers upon their perceived stability. We use a synthetic example to illustrate the properties of our proposed strategies. In this example, we find that: (i) assessments of stability can help to reduce the number of false-positive biomarkers, although potentially at the cost of missing some true positives; (ii) combining assessments of stability with assessments of predictive performance can improve the true positive rate; and (iii) correlations between biomarkers can have adverse effects on their stability and hence must be carefully taken into account when undertaking biomarker discovery. We then apply our strategies in a proteomics context to identify a number of robust candidate biomarkers for the human disease HTLV1-associated myelopathy/tropical spastic paraparesis (HAM/TSP)

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OEHHA also acknowledges the following contributors