Thermodynamics with 3 and 2+1 Flavors of Improved Staggered Quarks

We present preliminary results from exploring the phase diagram of finite temperature QCD with three degenerate flavors and with two light flavors and the mass of the third held approximately at the strange quark mass. We use an order $\alpha_s^2 a^2, a^4$ Symanzik improved gauge action and an order $\alpha_s a^2, a^4$ improved staggered quark action. The improved staggered action leads to a dispersion relation with diminished lattice artifacts, and hence better thermodynamic properties. It decreases the flavor symmetry breaking of staggered quarks substantially, and we estimate that at the transition temperature for an $N_t=8$ to $N_t=10$ lattice {\em all} pions will be lighter than the lightest kaon. Preliminary results on lattices with $N_t=4$, 6 and 8 are presented.Comment: 3 pages, 6 figures, contribution to Lattice2001(hightemp) August 19--24, 2001, Berlin, German

A long-term strategic plan for development of solar thermal electric technology

Solar thermal electric (STE) technologies--parabolic troughs, power towers, and dish/engine systems--can convert sunlight into electricity efficiently and with minimum effect on the environment. These technologies currently range from developmental to early commercial stages of maturity. This paper summarizes the results of a recent strategic planning effort conducted by the US department of Energy (DOE) to develop a long-term strategy for the development of STE technologies. The planning team led by DOE included representatives from the solar thermal industry, domestic utilities, state energy offices, and Sun{center_dot}Lab (the cooperative Sandia National laboratories/National Renewable Energy Laboratory partnership that supports the STE Program) as well as project developers. The plan was aimed at identifying specific activities necessary to achieve the DOE vision of 20 gigawatts of installed STE capability by the year 2020. The planning team developed five strategies that both build on the strengths of, and opportunities for, STE technology and address weaknesses and threats. These strategies are to: support future commercial opportunities for STE technologies; demonstrate improved performance and reliability of STE components and systems; reduce STE energy costs; develop advanced STE systems and applications; and address nontechnical barriers and champion STE power. The details of each of these strategies are discussed

Subsumer-First: Steering Symbolic Reachability Analysis

Abstract. Symbolic reachability analysis provides a basis for the veri-fication of software systems by offering algorithmic support for the ex-ploration of the program state space when searching for proofs or coun-terexamples. The choice of exploration strategy employed by the anal-ysis has direct impact on its success, whereas the ability to find short counterexamples quickly and—as a complementary task—to efficiently perform the exhaustive state space traversal are of utmost importance for the majority of verification efforts. Existing exploration strategies can optimize only one of these objectives which leads to a sub-optimal reach-ability analysis, e.g., breadth-first search may sacrifice the exploration ef-ficiency and chaotic iteration can miss minimal counterexamples. In this paper we present subsumer-first, a new approach for steering symbolic reachability analysis that targets both minimal counterexample discovery and efficiency of exhaustive exploration. Our approach leverages the re-sult of fixpoint checks performed during symbolic reachability analysis to bias the exploration strategy towards its objectives, and does not require any additional computation. We demonstrate how the subsumer-first ap-proach can be applied to improve efficiency of software verification tools based on predicate abstraction. Our experimental evaluation indicates the practical usefulness of the approach: we observe significant efficiency improvements (median value 40%) on difficult verification benchmarks from the transportation domain.

Quark Loop Effects with an Improved Staggered Action

We have been studying effects of dynamical quarks on various hadronic observables, using our recently formulated improvement for staggered fermions. To illustrate improvement, we show that the light hadron spectrum in the quenched approximation gives remarkably good scaling. We highlight three new results: (1) We find no apparent quark loop effects in the Edinburgh plot with 2+1 flavors of dynamical quarks at a = 0.14 fm. (2) We show that dynamical quarks modify the shape of the heavy quark potential. (3) We present results hinting at meson decay effects in light hadron spectroscopy.Comment: 5 pages, 7 figures, Lattice 2000 (Spectrum

Photoproduction of mesons off nuclei

Recent results for the photoproduction of mesons off nuclei are reviewed. These experiments have been performed for two major lines of research related to the properties of the strong interaction. The investigation of nucleon resonances requires light nuclei as targets for the extraction of the isospin composition of the electromagnetic excitations. This is done with quasi-free meson photoproduction off the bound neutron and supplemented with the measurement of coherent photoproduction reactions, serving as spin and/or isospin filters. Furthermore, photoproduction from light and heavy nuclei is a very efficient tool for the study of the interactions of mesons with nuclear matter and the in-medium properties of hadrons. Experiments are currently rapidly developing due to the combination of high quality tagged (and polarized) photon beams with state-of-the-art 4pi detectors and polarized targets

Surface charging and electrostatic dust acceleration at the nucleus of comet 67P during periods of low activity

We have investigated through simulation the electrostatic charging of the nucleus of Comet 67 P/Churyumov-Gerasimenko during periods of weak outgassing activity. Specifically, we have modeled the surface potential and electric field at the surface of the nucleus during the initial Rosetta rendezvous at 3.5 AU and the release of the Philae lander at 3 AU. We have also investigated the possibility of dust acceleration and ejection above the nucleus due to electrostatic forces. Finally, we discuss these modeling results in the context of possible observations by instruments on both the Rosetta orbiter and the Philae lander

Heavy quarkonium: progress, puzzles, and opportunities

A golden age for heavy quarkonium physics dawned a decade ago, initiated by the confluence of exciting advances in quantum chromodynamics (QCD) and an explosion of related experimental activity. The early years of this period were chronicled in the Quarkonium Working Group (QWG) CERN Yellow Report (YR) in 2004, which presented a comprehensive review of the status of the field at that time and provided specific recommendations for further progress. However, the broad spectrum of subsequent breakthroughs, surprises, and continuing puzzles could only be partially anticipated. Since the release of the YR, the BESII program concluded only to give birth to BESIII; the $B$-factories and CLEO-c flourished; quarkonium production and polarization measurements at HERA and the Tevatron matured; and heavy-ion collisions at RHIC have opened a window on the deconfinement regime. All these experiments leave legacies of quality, precision, and unsolved mysteries for quarkonium physics, and therefore beg for continuing investigations. The plethora of newly-found quarkonium-like states unleashed a flood of theoretical investigations into new forms of matter such as quark-gluon hybrids, mesonic molecules, and tetraquarks. Measurements of the spectroscopy, decays, production, and in-medium behavior of c\bar{c}, b\bar{b}, and b\bar{c} bound states have been shown to validate some theoretical approaches to QCD and highlight lack of quantitative success for others. The intriguing details of quarkonium suppression in heavy-ion collisions that have emerged from RHIC have elevated the importance of separating hot- and cold-nuclear-matter effects in quark-gluon plasma studies. This review systematically addresses all these matters and concludes by prioritizing directions for ongoing and future efforts.Comment: 182 pages, 112 figures. Editors: N. Brambilla, S. Eidelman, B. K. Heltsley, R. Vogt. Section Coordinators: G. T. Bodwin, E. Eichten, A. D. Frawley, A. B. Meyer, R. E. Mitchell, V. Papadimitriou, P. Petreczky, A. A. Petrov, P. Robbe, A. Vair

Avaliação da embebição e do desenvolvimento inicial das estruturas embrionárias de sementes de milho submetidas a diferentes potenciais hídricos

Substrates with water potentials between O and -12atm, were used to evaluate the behavior of corn seeds during the germination process. Water deficiency treatments were compared with the control (adequate available water) using seeds with and without fungicide treatment. The analysis and the interpretation of the results permitted to conclude that the absorption of water, the emergency and the initial development of the embryonic structures are interdependent and vary with the water deficit. For these cases the reduction of water potential promotes difficulties in the evolution of the processes. The presence of fungicide treatment may not influence quantitatively the processes occurring in the beginning of the germination.Empregando substratos com potenciais hídricos variáveis entre 0 e -12atm, o presente trabalho objetivou avaliar o comportamento das sementes de milho postas a germinar. As situações de deficiência hídrica foram diretamente comparadas à testemunha (plena disponibilidade de água), usando sementes com e sem tratamento fungicida. A análise e a interpretação dos resultados permitiram concluir que a absorção de água, a emergência e o desenvolvimento inicial das estruturas embrionárias são interdependentes e reagem no mesmo sentido ao déficit hídrico; para esses casos, a redução do potencial hídrico promove dificuldades na evolução dos processos. Paralelamente, a presença de tratamento fungicida pode não influenciar, quantitativamente, os fenômenos envolvidos no início da germinação