Cost of dynamical quark simulations: O(a) improved Wilson fermions

I report on cost estimates and algorithmic performance in simulations using 2 flavours of non-perturbatively O(a) improved Wilson quarks together with the Wilson plaquette action.Comment: Contribution to Lattice2001 (panel discussion), 2 pages, 2 figure

The three-loop beta-fuction of QCD with the clover action

We calculate, to 3 loops in perturbation theory, the bare $\beta$-function of QCD, formulated on the lattice with the clover fermionic action. The dependence of our result on the number of colors $N$, the number of fermionic flavors $N_f$, as well as the clover parameter $c_{SW}$, is shown explicitly. A direct outcome of our calculation is the two-loop relation between the bare coupling constant $g_0$ and the one renormalized in the MS-bar scheme. Further, we can immediately derive the three-loop correction to the relation between the lattice $\Lambda$-parameter and $g_0$, which is important in checks of asymptotic scaling. For typical values of $c_{SW}$, this correction is found to be very pronounced.Comment: 14 pages, 2 eps figure

Swift observations of the 2006 outburst of the recurrent nova RS Ophiuchi: III. X-ray spectral modelling

Following the Swift X-ray observations of the 2006 outburst of the recurrent nova RS Ophiuchi, we developed hydrodynamical models of mass ejection from which the forward shock velocities were used to estimate the ejecta mass and velocity. In order to further constrain our model parameters, here we present synthetic X-ray spectra from our hydrodynamical calculations which we compare to the Swift data. An extensive set of simulations was carried out to find a model which best fits the spectra up to 100 days after outburst. We find a good fit at high energies but require additional absorption to match the low energy emission. We estimate the ejecta mass to be in the range (2-5) x 10^{-7} solar masses and the ejection velocity to be greater than 6000 km/s (and probably closer to 10,000 km/s). We also find that estimates of shock velocity derived from gas temperatures via standard model fits to the X-ray spectra are much lower than the true shock velocities.Comment: 13 pages, 5 figures, Accepted for publication in Ap

Kramers-Kronig, Bode, and the meaning of zero

The implications of causality, as captured by the Kramers-Kronig relations between the real and imaginary parts of a linear response function, are familiar parts of the physics curriculum. In 1937, Bode derived a similar relation between the magnitude (response gain) and phase. Although the Kramers-Kronig relations are an equality, Bode's relation is effectively an inequality. This perhaps-surprising difference is explained using elementary examples and ultimately traces back to delays in the flow of information within the system formed by the physical object and measurement apparatus.Comment: 8 pages; American Journal of Physics, to appea

Spin-polarized surface states close to adatoms on Cu(111)

We present a theoretical study of surface states close to 3d transition metal adatoms (Cr, Mn, Fe, Co, Ni and Cu) on a Cu(111) surface in terms of an embedding technique using the fully relativistic Korringa-Kohn-Rostoker method. For each of the adatoms we found resonances in the s-like states to be attributed to a localization of the surface states in the presence of an impurity. We studied the change of the s-like densities of states in the vicinity of the surface state band-edge due to scattering effects mediated via the adatom's d-orbitals. The obtained results show that a magnetic impurity causes spin-polarization of the surface states. In particular, the long-range oscillations of the spin-polarized s-like density of states around an Fe adatom are demonstrated.Comment: 5 pages, 5 figures, submitted to PR

Monopole Current Dynamics and Color Confinement

Color confinement can be understood by the dual Higgs theory, where monopole condensation leads to the exclusion of the electric flux from the QCD vacuum. We study the role of the monopole for color confinement by investigating the monopole current system. When the self-energy of the monopole current is small enough, long and complicated monopole world-lines appear, which is a signal of monopole condensation. In the dense monopole system, the Wilson loop obeys the area-law, and the string tension and the monopole density have similar behavior as the function of the self-energy, which seems that monopole condensation leads to color confinement. On the long-distance physics, the monopole current system almost reproduces essential features of confinement properties in lattice QCD. In the short-distance physics, however, the monopole-current theory would become nonlocal and complicated due to the monopole size effect. This monopole size would provide a critical scale of QCD in terms of the dual Higgs mechanism.Comment: 6 pages LaTeX, 5 figures, uses espcrc1.sty, Talk presented at International Conference on Quark Lepton Nuclear Physics, Osaka, May. 199

Determination of the Her-2/neu gene amplification status in cytologic breast cancer specimens using automated silver-enhanced in-situ hybridization (SISH)

Silver-enhanced in-situ hybridization (SISH) is an emerging tool for the determination of the Her-2/neu amplification status in breast cancer. SISH is technically comparable to fluorescence in-situ hybridization (FISH) but does not require a fluorescence microscope for its interpretation. Although recent studies on histologic evaluations of SISH are promising, we aimed to evaluate its performance on 71 cytologic breast cancer specimens with the new combined Her-2/Chr17 probe. Her-2/neu status as routinely determined by FISH was available for all patients. We found SISH signals in cytologic cell blocks and smear specimens easy to evaluate in most cases. Small numbers of tumor cells and difficulties in identifying tumor cells in lymphocyte-rich backgrounds were limiting factors. Her-2/neu status, as determined by Her-2/Chr17 SISH, was basically identical to the results of the corresponding FISH. The discrepancies were mainly owing to the heterogeneity of Her-2/neu amplification in the tumor tissue. Interobserver agreement for the SISH evaluation was high (kappa value: 0.972). We conclude that Her-2/Chr17 SISH is a useful and accurate method for the evaluation of the Her-2/neu gene amplification status in cytologic breast cancer specimens, particularly in metastatic breast cancer lesions. The advantages of signal permanency and bright-field microscopic result interpretation make this technique an attractive alternative to the current FISH-based gold standard

Chandra detection of extended X-ray emission from the recurrent nova RS Ophiuchi

Radio, infrared, and optical observations of the 2006 eruption of the symbiotic recurrent nova RS Ophiuchi (RS Oph) showed that the explosion produced non-spherical ejecta. Some of this ejected material was in the form of bipolar jets to the east and west of the central source. Here we describe Xray observations taken with the Chandra X-ray Observatory one and a half years after the beginning of the outburst that reveal narrow, extended structure with a position angle of approximately 300 degrees (east of north). Although the orientation of the extended feature in the X-ray image is consistent with the readout direction of the CCD detector, extensive testing suggests that the feature is not an artifact. Assuming it is not an instrumental effect, the extended X-ray structure shows hot plasma stretching more than 1,900 AU from the central binary (taking a distance of 1.6 kpc). The X-ray emission is elongated in the northwest direction - in line with the extended infrared emission and some minor features in the published radio image. It is less consistent with the orientation of the radio jets and the main bipolar optical structure. Most of the photons in the extended X-ray structure have energies of less than 0.8 keV. If the extended X-ray feature was produced when the nova explosion occurred, then its 1".2 length as of 2007 August implies that it expanded at an average rate of more than 2 mas/d, which corresponds to a flow speed of greater than 6,000 km/s (d/1.6 kpc) in the plane of the sky. This expansion rate is similar to the earliest measured expansion rates for the radio jets.Comment: accepted in Ap