Complete spectra of the Dirac operator and their relation to confinement

We compute complete spectra of the staggered lattice Dirac operator for quenched SU(3) gauge configurations below and above the critical temperature. The confined and the deconfined phase are characterized by a different response of the Dirac eigenvalues to a change of the fermionic boundary conditions. We analyze the role of the eigenvalues in recently developed spectral sums representing the Polyakov loop. We show that the Polyakov loop gets its main contributions from the UV end of the spectrum.Comment: Typo fixed, to appear in Physics Letters

Domain decomposition improvement of quark propagator estimation

Applying domain decomposition to the lattice Dirac operator and the associated quark propagator, we arrive at expressions which, with the proper insertion of random sources therein, can provide improvement to the estimation of the propagator. Schemes are presented for both open and closed (or loop) propagators. In the end, our technique for improving open contributions is similar to the ``maximal variance reduction'' approach of Michael and Peisa, but contains the advantage, especially for improved actions, of dealing directly with the Dirac operator. Using these improved open propagators for the Chirally Improved operator, we present preliminary results for the static-light meson spectrum. The improvement of closed propagators is modest: on some configurations there are signs of significant noise reduction of disconnected correlators; on others, the improvement amounts to a smoothening of the same correlators.Comment: 19 pages, 8 figures, version to appear in Computer Physics Communication

Masses of excited baryons from chirally improved quenched lattice QCD

Whereas ground state spectroscopy for quenched QCD is well understood, it is still a challenge to obtain results for excited hadron states. In our study we present results from a new approach for determining spatially optimized operators for lattice spectroscopy of excited hadrons. In order to be able to approach physical quark masses we work with the chirally improved Dirac operator, i.e., approximate Ginsparg-Wilson fermions. Since these are computationally expensive we restrict ourselves to a few quark sources. We use Jacobi smeared quark sources with different widths and combine them to construct hadron operators with different spatial wave functions. This allows us to identify the Roper state and other excited baryons, also in the strange sector.Comment: Contribution to BARYONS 2004, Palaiseau, France, October 25 - 29, 2004; 4 pages, 1 figure, Style espcrc

Endogenous RGS proteins enhance acute desensitization of GABAB receptor-activated GIRK currents in HEK-293T cells

The coupling of GABAB receptors to G-protein-gated inwardly rectifying potassium (GIRK) channels constitutes an important inhibitory pathway in the brain. Here, we examined the mechanism underlying desensitization of agonist-evoked currents carried by homomeric GIRK2 channels expressed in HEK-293T cells. The canonical GABAB receptor agonist baclofen produced GIRK2 currents that decayed by 57.3±1.4% after 60s of stimulation, and then deactivated rapidly (time constant of 3.90±0.21s) upon removal of agonist. Surface labeling studies revealed that GABAB receptors, in contrast to µ opioid receptors (MOR), did not internalize with a sustained stimulation for 10 min, excluding receptor redistribution as the primary mechanism for desensitization. Furthermore, heterologous desensitization was observed between GABAB receptors and MOR, implicating downstream proteins, such G-proteins or the GIRK channel. To investigate the G-protein turnover cycle, the non-hydrolyzable GTP analogue (GTPγS) was included in the intracellular solution and found to attenuate desensitization to 38.3±2.0%. The extent of desensitization was also reduced (45.3±1.3%) by coexpressing a mutant form of the Gαq G-protein subunit that has been designed to sequester endogenous RGS proteins. Finally, reconstitution of GABAB receptors with Gαo G-proteins rendered insensitive to RGS resulted in significantly less desensitization (28.5±3.2%). Taken together, our results demonstrate that endogenous levels of RGS proteins effectively enhance GABAB receptor-dependent desensitization of GIRK current

The influence of annealings on structure and microhardness of Fe-Mo-V-Nb-C steel processed by high-pressure torsion

The influence of high-pressure torsion on microstructure, microhardness and thermal stability of lowcarbon steel Fe-0,1Mo-0,6Mn-0,8Cr-0,2Ni-0,3Si-0,2Cu-0,1V-0,06Nb-0,09C, (wt.%) was investigated. It was shown that ultrafine-grained structure formed by high-pressure torsion possesses a high microhardness (H[mu]=7,0 GPa) and high thermal stability up to the temperature of 400°С