845 research outputs found
Probing the QCD Equation of State
We propose a novel quasiparticle interpretation of the equation of state of
deconfined QCD at finite temperature. Using appropriate thermal masses, we
introduce a phenomenological parametrisation of the onset of confinement in the
vicinity of the phase transition. Lattice results of bulk thermodynamic
quantities are well reproduced, the extension to small quark chemical potential
is also successful. We then apply the model to dilepton production and charm
suppression in ultrarelativistic heavy-ion collisions.Comment: 6 pages, 8 figures. Invited talk presented by R. A. Schneider at the
XVI International Conference on Particles and Nuclei (PANIC02), Osaka, Japan,
September 30 - October 4, 200
Diversity and taxonomy of Chaetomium and chaetomium-like fungi from indoor environments
During a study of indoor fungi, 145 isolates belonging to Chaetomiaceae were cultured from air, swab and dust samples from 19 countries. Based on the phylogenetic analyses of DNA-directed RNA polymerase II second largest subunit (rpb2), ÎČ-tubulin (tub2), ITS and 28S large subunit (LSU) nrDNA sequences, together with morphological comparisons with related genera and species, 30 indoor taxa are recognised, of which 22 represent known species, seven are described as new, and one remains to be identified to species level. In our collection, 69 % of the indoor isolates with six species cluster with members of the Chaetomium globosum species complex, representing Chaetomium sensu stricto. The other indoor species fall into nine lineages that are separated from each other with several known chaetomiaceous genera occurring among them. No generic names are available for five of those lineages, and the following new genera are introduced here: Amesia with three indoor species, Arcopilus with one indoor species, Collariella with four indoor species, Dichotomopilus with seven indoor species and Ovatospora with two indoor species. The generic concept of Botryotrichum is expanded to include Emilmuelleria and the chaetomium-like species B. muromum (= Ch. murorum) in which two indoor species are included. The generic concept of Subramaniula is expanded to include several chaetomium-like taxa as well as one indoor species. Humicola is recognised as a distinct genus including two indoor taxa. According to this study, Ch. globosum is the most abundant Chaetomiaceae indoor species (74/145), followed by Ch. cochliodes (17/145), Ch. elatum (6/145) and B. piluliferum (5/145). The morphological diversity of indoor Chaetomiaceae as well as the morphological characteristics of the new genera are described and illustrated. This taxonomic study redefines the generic concept of Chaetomium and provides new insight into the phylogenetic relationships among different genera within Chaetomiaceae
Mineralogy and geochemistry of reservoir and non-reservoir chalk from the Norwegian continental shelf
A first and detailed study of the geochemistry and mineralogy characterizing the North Sea reservoir and non-reservoir chalk is provided in this work. The study is based on 185 cores from exploration and development wells in the North Sea. The cores related to reservoir development have different flooding status â unflooded or waterflooded at various temperatures â and are directly sampled from the Ekofisk field. Optical petrography shows a micritic carbonate matrix, with grains represented by various microfossils such as foraminifers and sponge spicules. Scanning electron microscopy (SEM) reveals post-depositional calcite precipitation and cementation. Dolomite is found only in the reservoir samples, but it is discussed as a diagenetic feature, unrelated to the hydrocarbon content or EOR exposure. The non-carbonate minerals observed with BSE-SEM and XRD include mostly quartz but also smectite, illite, kaolinite, mica, and pyrite. The abundance of clastic input varies, and there is a clear decrease in porosity stratigraphically downwards, with stronger cementation and higher compaction. ÎŽ13C reflects primary trends for Upper Cretaceous stages while ÎŽ18O in all samples is lower than the secular global isotopic values for this period. However, the ÎŽ18O values are not sufficiently low to imply a strong diagenetic overprint, but rather suggest the influence of a secondary fluid. This fluid cannot be a hydrocarbon-rich one, nor EOR fluids, as non-reservoir samples, as well as flooded and unflooded reservoir samples show very similar stable isotope values.publishedVersio
Suppression of inhomogeneous broadening in rf spectroscopy of optically trapped atoms
We present a novel method for reducing the inhomogeneous frequency broadening
in the hyperfine splitting of the ground state of optically trapped atoms. This
reduction is achieved by the addition of a weak light field, spatially
mode-matched with the trapping field and whose frequency is tuned in-between
the two hyperfine levels. We experimentally demonstrate the new scheme with Rb
85 atoms, and report a 50-fold narrowing of the rf spectrum
White Light Interferometry for Quantitative Surface Characterization in Ion Sputtering Experiments
White light interferometry (WLI) can be used to obtain surface morphology
information on dimensional scale of millimeters with lateral resolution as good
as ~1 {\mu}m and depth resolution down to 1 nm. By performing true
three-dimensional imaging of sample surfaces, the WLI technique enables
accurate quantitative characterization of the geometry of surface features and
compares favorably to scanning electron and atomic force microscopies by
avoiding some of their drawbacks. In this paper, results of using the WLI
imaging technique to characterize the products of ion sputtering experiments
are reported. With a few figures, several example applications of the WLI
method are illustrated when used for (i) sputtering yield measurements and
time-to-depth conversion, (ii) optimizing ion beam current density profiles,
the shapes of sputtered craters, and multiple ion beam superposition and (iii)
quantitative characterization of surfaces processed with ions. In particular,
for sputter depth profiling experiments of 25Mg, 44Ca and 53Cr ion implants in
Si (implantation energy of 1 keV per nucleon), the depth calibration of the
measured depth profile curves determined by the WLI method appeared to be
self-consistent with TRIM simulations for such projectile-matrix systems. In
addition, high depth resolution of the WLI method is demonstrated for a case of
a Genesis solar wind Si collector surface processed by gas cluster ion beam: a
12.5 nm layer was removed from the processed surface, while the transition
length between the processed and untreated areas was 150 {\mu}m.Comment: Applied Surface Science, accepted: 7 pages and 8 figure
The High Energy Telescope for STEREO
The IMPACT investigation for the STEREO Mission includes a complement of Solar Energetic Particle instruments on each of the two STEREO spacecraft. Of these instruments, the High Energy Telescopes (HETs) provide the highest energy measurements. This paper describes the HETs in detail, including the scientific objectives, the sensors, the overall mechanical and electrical design, and the on-board software. The HETs are designed to measure the abundances and energy spectra of electrons, protons, He, and heavier nuclei up to Fe in interplanetary space. For protons and He that stop in the HET, the kinetic energy range corresponds to âŒ13 to 40 MeV/n. Protons that do not stop in the telescope (referred to as penetrating protons) are measured up to âŒ100 MeV/n, as are penetrating He. For stopping He, the individual isotopes 3He and 4He can be distinguished. Stopping electrons are measured in the energy range âŒ0.7â6 MeV
Gaussian Tunneling Model of c-Axis Twist Josephson Junctions
We calculate the critical current density for c-axis Josephson
tunneling between identical high temperature superconductors twisted an angle
about the c-axis. We model the tunneling matrix element squared as a
Gaussian in the change of wavevector q parallel to the junction, . The
obtained for the s- and extended-s-wave order parameters (OP's) are consistent
with the BiSrCaCuO data of Li {\it et al.}, but only
for strongly incoherent tunneling, . A -wave OP
is always inconsistent with the data. In addition, we show that the apparent
conventional sum rule violation observed by Basov et al. might be
understandable in terms of incoherent c-axis tunneling, provided that the OP is
not -wave.Comment: 6 pages, 6 figure
On the thermal sunset diagram for scalar field theories
We study the so-called `` sunset diagram'', which is one of two-loop
self-energy diagrams, for scalar field theories at finite temperature.
For this purpose, we first find the complete expression of the bubble
diagram, the one-loop subdiagram of the sunset diagram, for arbitrary momentum.
We calculate the temperature independent part and dependent part of the
sunset diagram separately. For the former, we obtain the discontinuous part
first and the finite continuous part next using a twice-subtracted dispersion
relation. For the latter, we express it as a one-dimensional integral in terms
of the bubble diagram.
We also study the structure of the discontinuous part of the sunset diagram.
Physical processes, which are responsible for it, are identified. Processes due
to the scattering with particles in the heat bath exist only at finite
temperature and generate discontinuity for arbitrary momentum, which is a
remarkable feature of the two-loop diagrams at finite temperature.
As an application of our result, we study the effect of the diagram on the
spectral function of the sigma meson at finite temperature in the linear sigma
model, which was obtained at one-loop order previously. At high temperature
where the decay is forbidden, sigma acquires a finite width
of the order of while within the one-loop calculation its width
vanishes. At low temperature, the spectrum does not deviate much from that at
one-loop order. Possible consequences with including other two-loop diagrams
are discussed.Comment: 30 page
Quasi-Particle Description of Strongly Interacting Matter: Towards a Foundation
We confront our quasi-particle model for the equation of state of strongly
interacting matter with recent first-principle QCD calculations. In particular,
we test its applicability at finite baryon densities by comparing with Taylor
expansion coefficients of the pressure for two quark flavours. We outline a
chain of approximations starting from the Phi-functional approach to QCD which
motivates the quasi-particle picture.Comment: Aug 2006. 6 pp. Invited Talk given at Hot Quarks 2006, Villasimius,
Sardinia, Italy, 15-20 May 200
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