Adaptive Aggregation Based Domain Decomposition Multigrid for the Lattice Wilson Dirac Operator

In lattice QCD computations a substantial amount of work is spent in solving discretized versions of the Dirac equation. Conventional Krylov solvers show critical slowing down for large system sizes and physically interesting parameter regions. We present a domain decomposition adaptive algebraic multigrid method used as a precondtioner to solve the "clover improved" Wilson discretization of the Dirac equation. This approach combines and improves two approaches, namely domain decomposition and adaptive algebraic multigrid, that have been used seperately in lattice QCD before. We show in extensive numerical test conducted with a parallel production code implementation that considerable speed-up over conventional Krylov subspace methods, domain decomposition methods and other hierarchical approaches for realistic system sizes can be achieved.Comment: Additional comparison to method of arXiv:1011.2775 and to mixed-precision odd-even preconditioned BiCGStab. Results of numerical experiments changed slightly due to more systematic use of odd-even preconditionin

Aggregation-based Multilevel Methods for Lattice QCD

In Lattice QCD computations a substantial amount of work is spent in solving the Dirac equation. In the recent past it has been observed that conventional Krylov solvers tend to critically slow down for large lattices and small quark masses. We present a Schwarz alternating procedure (SAP) multilevel method as a solver for the Clover improved Wilson discretization of the Dirac equation. This approach combines two components (SAP and algebraic multigrid) that have separately been used in lattice QCD before. In combination with a bootstrap setup procedure we show that considerable speed-up over conventional Krylov subspace methods for realistic configurations can be achieved.Comment: Talk presented at the XXIX International Symposium on Lattice Field Theory, July 10-16, 2011, Lake Tahoe, Californi

Crosspolarization with imperfect infrared polarizers

The analysis of vibrational bands is a core application of infrared (IR) spectroscopy. Polarization-dependent measurements enable the study of anisotropic materials. However, imperfect IR polarizers exhibit polarizer leakage, which causes pronounced bandshape and baseline distortions for samples with weak optical anisotropy. Based on the 4 × 4 Mueller-matrix formalism, we propose a polarimetric measurement scheme for handling imperfect polarizers and source prepolarization that delivers correct co- and crosspolarized transmission and reflection IR spectra. The scheme is applied to a weakly anisotropic polypropylene sheet, resolving crosspolarized signatures as small as 5⋅10−5. We determine the polymer's direction-dependent complex refractive index in the vibrational fingerprint range

The retreat of the state from entrepreneurial activities: an extended survey

There is a huge body of literature in the social sciences that deals with the privatization of public enterprises in developed OECD countries after World War II. In the first part of this article, we present and critically examine empirical findings of comparative inquiries on the factors influencing cross-national differences in privatization efforts across the OECD world. Although these empirical studies provide valuable and interesting evidence, it turns out that these studies are incomplete insofar, as they mostly focus just on one dimension of privatization: the monetary or ‘material’ aspect typically measured with privatization proceeds raised by governments. Against this background, in the second part of this paper we point out that there are also formal privatization (i.e., ‘privatizing’ the legal form of a public enterprise) and functional privatization (i.e., contracting out public service production). Moreover it is emphasized that privatization does not automatically imply a retreat of the state from entrepreneurial activities. From there we plead for taking into account the development of regulatory policies and public subsidies to private enterprises over time as well, in order to get a more comprehensive picture of the development of the entrepreneurial state in the OECD world. Therefore, for each of these dimensions of entrepreneurial activity the current ‘state of the art’ regarding theory and empirics is surveyed and enriched by own empirical data. -- Dieser Aufsatz zieht eine Zwischenbilanz des Rückzugs des Staates aus unternehmerischen Tätigkeiten in der OECD-Welt seit 1980. Der Beitrag präsentiert einen kritischen Überblick über empirische Studien zu den Bestimmungsfaktoren der nationalen Unterschiede in den Bereichen Privatisierung, Subventionszahlungen und Regulierung. Es wird gezeigt, dass erhebliche Forschungslücken bestehen; abschließend werden Wege für die künftige Forschung skizziert, um zu einem umfassenderen Bild der Entwicklung des unternehmerisch tätigen Staates zu gelangen.

FEI Titan 80-300 TEM

The FEI Titan 80-300 TEM is a high-resolution transmission electron microscope equipped with a field emission gun and a corrector for the spherical aberration (CS) of the imaging lens system. The instrument is designed for the investigation of a wide range of solid state phenomena taking place on the atomic scale, which requires true atomic resolution capabilities. Under optimum optical settings of the image CS-corrector (CEOS CETCOR) the point-resolution is extended up to the information limit of well below 100 pm with 200 keV and 300 keV electrons. A special piezo-stage design allows ultra-precise positioning of the specimen in all 3 dimensions. Digital images are acquired with a Gatan 2k x 2k slow-scan charged coupled device camera

Measurement of the full excitation spectrum of the 7Li(p,{\gamma}){\alpha}{\alpha} reaction at 441 keV

A current challenge for ab initio calculations is systems that contain large continuum contributions such as 8Be. We report on new measurements of radiative decay widths in this nucleus that test recent Green's function Monte Carlo calculations. Traditionally, {\gamma} ray detectors have been utilized to measure the high energy photons from the 7Li(p, {\gamma}){\alpha}{\alpha} reaction. However, due to the complicated response function of these detectors it has not yet been possible to extract the full {\gamma} ray spectrum from this reaction. Here we present an alternative measurement using large area Silicon detectors to detect the two {\alpha} particles, which provides a practically background free spectrum and retains good energy resolution. The resulting spectrum is analyzed using a many-level multi channel R-matrix parametrization. Improved values for the radiative widths are extracted from the R-matrix fit. We find evidence for significant non-resonant continuum contributions and tentative evidence for a broad 0+ resonance at 12 MeV.Comment: Accepted version. Fixed Fig. 5 ordinate label