41 research outputs found
The cosmic gravitational wave background in a cyclic universe
Inflation predicts a primordial gravitational wave spectrum that is slightly
``red,'' i.e., nearly scale-invariant with slowly increasing power at longer
wavelengths. In this paper, we compute both the amplitude and spectral form of
the primordial tensor spectrum predicted by cyclic/ekpyrotic models. The
spectrum is blue and exponentially suppressed compared to inflation on long
wavelengths. The strongest observational constraint emerges from the
requirement that the energy density in gravitational waves should not exceed
around 10 per cent of the energy density at the time of nucleosynthesis.Comment: 4 pages, 3 figuer
An estimate of the flavour singlet contributions to the hyperfine splitting in charmonium
We explore the splitting between flavour singlet and non-singlet mesons in
charmonium. This has implications for the hyperfine splitting in charmonium
Application of heavy-quark effective theory to lattice QCD: III. Radiative corrections to heavy-heavy currents
We apply heavy-quark effective theory (HQET) to separate long- and
short-distance effects of heavy quarks in lattice gauge theory. In this paper
we focus on flavor-changing currents that mediate transitions from one heavy
flavor to another. We stress differences in the formalism for heavy-light
currents, which are discussed in a companion paper, showing how HQET provides a
systematic matching procedure. We obtain one-loop results for the matching
factors of lattice currents, needed for heavy-quark phenomenology, such as the
calculation of zero-recoil form factors for the semileptonic decays . Results for the Brodsky-Lepage-Mackenzie scale are also
given.Comment: 35 pages, 17 figures. Program LatHQ2QCD to compute matching one-loop
coefficients available at http://theory.fnal.gov/people/kronfeld/LatHQ2QCD
Ultra-High Energy Neutrino Fluxes and Their Constraints
Applying our recently developed propagation code we review extragalactic
neutrino fluxes above 10^{14} eV in various scenarios and how they are
constrained by current data. We specifically identify scenarios in which the
cosmogenic neutrino flux, produced by pion production of ultra high energy
cosmic rays outside their sources, is considerably higher than the
"Waxman-Bahcall bound". This is easy to achieve for sources with hard injection
spectra and luminosities that were higher in the past. Such fluxes would
significantly increase the chances to detect ultra-high energy neutrinos with
experiments currently under construction or in the proposal stage.Comment: 11 pages, 15 figures, version published in Phys.Rev.
Cloning, expression and characterization of SeM protein of Streptococcus equi subsp. equi and evaluation of its use as antigen in an indirect ELISA
Fluoreto nas ĂĄguas subterrĂąneas dos aqĂŒĂferos TubarĂŁo e Cristalino, regiĂŁo de Salto-Indaiatuba (SP)
Electrochemical studies of hexafluorotungstate(V) and tungsten oxide tetrafluoride in acetonitrile
High oxidation state fluorides can be studied electrochemically in the conventional solvent acetonitrile. Alkali metal hexafluorotungstates(V) are substantially soluble in acetonitrile and have been studied by cyclic voltammetry using vacuum line techniques for solution manipulation. [WF6]â is oxidised to WF6 at +0.81 V vs SCE and is not reduced over a wide potential range. WOF4 in acetonitrile is reduced at â1.1 V vs. SCE. Electrogenerated WF6 is slowly hydrolysed to WOF4 in acetonitrile
The 2dF-SDSS LRG and QSO survey: the QSO luminosity function at 0.4 \lt z \lt 2.6
We present the QSO luminosity function of the completed 2dF-SDSS LRG and QSO
(2SLAQ) survey, based on QSOs photometrically selected from Sloan Digital Sky
Survey imaging data and then observed spectroscopically using the 2dF
instrument on the Anglo-Australian Telescope. We analyse 10637 QSOs in the
redshift range 0.4<z<2.6 to a g-band flux limit of 21.85 (extinction corrected)
and an absolute continuum magnitude of Mg(z=2)<-21.5. This sample covers an
area of 191.9 deg^2.
The binned QSO luminosity function agrees with that of the brighter SDSS main
QSO sample, but extends ~2.5 mags fainter, clearly showing the flattening of
the luminosity function towards faint absolute magnitudes. 2SLAQ finds an
excess of QSOs compared to the 2dF QSO Redshift Survey at g>20.0, as found
previously by Richards et al. (2005). The luminosity function is consistent
with other previous, much smaller, samples produced to the depth of 2SLAQ.
By combining the 2SLAQ and SDSS QSO samples we produce a QSO luminosity
function with an unprecedented combination of precision and dynamic range. With
this we are able to accurately constrain both the bright and faint ends of the
QSO LF. While the overall trends seen in the evolution of the QSO LF appear
similar to pure luminosity evolution, the data show very significant departures
from such a model. Most notably we see clear evidence that the number density
of faint QSOs peaks at lower redshift than bright QSOs: QSOs with Mg>-23 have
space densities which peak at z2. By fitting
simple luminosity function models in narrow Mg intervals we find that this
downsizing is significant at the 99.98 per cent level (abridged).Comment: 20 pages, 18 figures. Accepted for publication in MNRAS. The data on
which this paper is based can be accessed at http://www.2slaq.info
Off-Field Behavior of Athletes and Team Identification: Using Social Identity Theory and Balance Theory to Explain Fan Reactions
Coexistence of a sulphate-reducing Desulfovibrio species and the dehalorespiring Desulfitobacterium frappieri TCE1 in defined chemostat cultures grown with various combinations of sulphate and tetrachloroethene
A two-member co-culture consisting of the dehalorespiring Desulfitobacterium frappieri TCE1 and the sulphate-reducing Desulfovibrio sp. strain SULF1 was obtained via anaerobic enrichment from soil contaminated with tetrachloroethene (PCE), In this co-culture, PCE dechlorination to cis-dichloroethene was due to the activity of the dehalorespiring bacterium only. Chemostat experiments with lactate as the primary electron donor for both strains along with varying sulphate and PCE concentrations showed that the sulphate-reducing strain outnumbered the dehalogenating strain at relatively high ratios of sulphate/PCE. Stable co-cultures with both organisms present at similar cell densities were observed when both electron accepters were supplied in the reservoir medium in nearly equimolar amounts. In the presence of low sulphate/PCE ratios, the Desulfitobacterium sp. became the numerically dominant strain within the chemostat co-culture, Surprisingly, in the absence of sulphate, strain SULF1 did not disappear completely from the co-culture despite the fact that there was no electron acceptor provided with the medium to be used by this sulphate reducer. Therefore, we propose a syntrophic association between the sulphate-reducing and the dehalorespiring bacteria via interspecies hydrogen transfer. The sulphate reducer was able to sustain growth in the chemostat co-culture by fermenting lactate and using the dehalogenating bacterium as a 'biological electron acceptor'. This is the first report describing growth of a sulphate-reducing bacterium in a defined two-member continuous culture by syntrophically coupling the electron and hydrogen transfer to a dehalorespiring bacterium