2,888 research outputs found
On the strange quark mass with improved staggered quarks
We present results on the sum of the masses of light and strange quark using
improved staggered quarks. Our calculation uses 2+1 flavours of dynamical
quarks. The effects of the dynamical quarks are clearly visible.Comment: Lattice2002(spectrum) Latex 3 pages, 2 figure
Tunable Conductivity and Conduction Mechanism in a UV light activated electronic conductor
A tunable conductivity has been achieved by controllable substitution of a
novel UV light activated electronic conductor. The transparent conducting oxide
system H-doped Ca12-xMgxAl14O33 (x = 0; 0.1; 0.3; 0.5; 0.8; 1.0) presents a
conductivity that is strongly dependent on the substitution level and
temperature. Four-point dc-conductivity decreases with x from 0.26 S/cm (x = 0)
to 0.106 S/cm (x = 1) at room temperature. At each composition the conductivity
increases (reversibly with temperature) until a decomposition temperature is
reached; above this value, the conductivity drops dramatically due to hydrogen
recombination and loss. The observed conductivity behavior is consistent with
the predictions of our first principles density functional calculations for the
Mg-substituted system with x=0, 1 and 2. The Seebeck coefficient is essentially
composition- and temperature-independent, the later suggesting the existence of
an activated mobility associated with small polaron conduction. The optical gap
measured remains constant near 2.6 eV while transparency increases with the
substitution level, concomitant with a decrease in carrier content.Comment: Submitted for publicatio
Optical extinction efficiency measurements on fine and accumulation mode aerosol using single particle cavity ring-down spectroscopy
We report a new single aerosol particle approach using cavity ringdown spectroscopy to accurately determine optical extinction cross sections at multiple wavelengths.</p
First determination of the strange and light quark masses from full lattice QCD
We compute the strange quark mass and the average of the and
quark masses using full lattice QCD with three dynamical quarks
combined with experimental values for the pion and kaon masses. The simulations
have degenerate and quarks with masses as low as
, and two different values of the lattice spacing. The bare lattice
quark masses obtained are converted to the \msbar scheme using perturbation
theory at . Our results are: m_s^\msbar(2 GeV) = 76(0)(3)(7)(0)
MeV, \hat m^\msbar(2 GeV) = 2.8(0)(1)(3)(0) MeV and =
27.4(1)(4)(0)(1), where the errors are from statistics, simulation,
perturbation theory, and electromagnetic effects, respectively.Comment: 5 pages, revtex, 2 figures. v2: New ms/hat(m) discussion and
reference, v3: slight change in discussion of referenc
Point interactions in one dimension and holonomic quantum fields
We introduce and study a family of quantum fields, associated to
delta-interactions in one dimension. These fields are analogous to holonomic
quantum fields of M. Sato, T. Miwa and M. Jimbo. Corresponding field operators
belong to an infinite-dimensional representation of the group SL(2,\Rb) in
the Fock space of ordinary harmonic oscillator. We compute form factors of such
fields and their correlation functions, which are related to the determinants
of Schroedinger operators with a finite number of point interactions. It is
also shown that these determinants coincide with tau functions, obtained
through the trivialization of the -bundle over a Grassmannian
associated to a family of Schroedinger operators.Comment: 17 page
Bright galaxies at Hubble's redshift detection frontier: Preliminary results and design from the redshift z~9-10 BoRG pure-parallel HST survey
We present the first results and design from the redshift z~9-10 Brightest of
the Reionizing Galaxies {\it Hubble Space Telescope} survey BoRG[z9-10], aimed
at searching for intrinsically luminous unlensed galaxies during the first 700
Myr after the Big Bang. BoRG[z9-10] is the continuation of a multi-year
pure-parallel near-IR and optical imaging campaign with the Wide Field Camera
3. The ongoing survey uses five filters, optimized for detecting the most
distant objects and offering continuous wavelength coverage from
{\lambda}=0.35{\mu}m to {\lambda}=1.7{\mu}m. We analyze the initial ~130
arcmin of area over 28 independent lines of sight (~25% of the total
planned) to search for z>7 galaxies using a combination of Lyman break and
photometric redshift selections. From an effective comoving volume of (5-25)
Mpc for magnitudes brighter than in the
-band respectively, we find five galaxy candidates at z~8.3-10
detected at high confidence (S/N>8), including a source at z~8.4 with mAB=24.5
(S/N~22), which, if confirmed, would be the brightest galaxy identified at such
early times (z>8). In addition, BoRG[z9-10] data yield four galaxies with . These new Lyman break galaxies with m are
ideal targets for follow-up observations from ground and space based
observatories to help investigate the complex interplay between dark matter
growth, galaxy assembly, and reionization.Comment: Accepted for publication on ApJ. 21 pages, 11 figures, 4 table
Organic chemistry of NH<sub>3</sub> and HCN induced by an atmospheric abnormal glow discharge in N<sub>2</sub>-CH<sub>4</sub> mixtures
The formation of the chemical products produced in an atmospheric glow discharge fed by a N2-CH4 gas mixture has been studied using Fourier Transform InfraRed (FTIR) and Optical Emission Spectrometry (OES). The measurements were carried out in a flowing regime at ambient temperature and pressure with CH4 concentrations ranging from 0.5% to 2%. In the recorded emission spectra the lines of the second positive system CN system and the first negative system of N2 were found to be the most intensive but atomic Hα, HÎČ, and C (247 nm) lines were also observed. FTIR-measurements revealed HCN
and NH3 to be the major products of the plasma with traces of C2H2. These same molecules have been detected in Titan's atmosphere and the present experiments may provide some novel insights into the
chemical and physical mechanisms prevalent in Titan's atmosphere with these smaller species believed to be the precursors of heavier organic species in Titan's atmosphere and on its surface
Metabolic Roles of Uncultivated Bacterioplankton Lineages in the Northern Gulf of Mexico "Dead Zone".
This is the final version of the article. Available from American Society for Microbiology via the DOI in this record.Marine regions that have seasonal to long-term low dissolved oxygen (DO) concentrations, sometimes called "dead zones," are increasing in number and severity around the globe with deleterious effects on ecology and economics. One of the largest of these coastal dead zones occurs on the continental shelf of the northern Gulf of Mexico (nGOM), which results from eutrophication-enhanced bacterioplankton respiration and strong seasonal stratification. Previous research in this dead zone revealed the presence of multiple cosmopolitan bacterioplankton lineages that have eluded cultivation, and thus their metabolic roles in this ecosystem remain unknown. We used a coupled shotgun metagenomic and metatranscriptomic approach to determine the metabolic potential of Marine Group II Euryarchaeota, SAR406, and SAR202. We recovered multiple high-quality, nearly complete genomes from all three groups as well as candidate phyla usually associated with anoxic environments-Parcubacteria (OD1) and Peregrinibacteria Two additional groups with putative assignments to ACD39 and PAUC34f supplement the metabolic contributions by uncultivated taxa. Our results indicate active metabolism in all groups, including prevalent aerobic respiration, with concurrent expression of genes for nitrate reduction in SAR406 and SAR202, and dissimilatory nitrite reduction to ammonia and sulfur reduction by SAR406. We also report a variety of active heterotrophic carbon processing mechanisms, including degradation of complex carbohydrate compounds by SAR406, SAR202, ACD39, and PAUC34f. Together, these data help constrain the metabolic contributions from uncultivated groups in the nGOM during periods of low DO and suggest roles for these organisms in the breakdown of complex organic matter.IMPORTANCE Dead zones receive their name primarily from the reduction of eukaryotic macrobiota (demersal fish, shrimp, etc.) that are also key coastal fisheries. Excess nutrients contributed from anthropogenic activity such as fertilizer runoff result in algal blooms and therefore ample new carbon for aerobic microbial metabolism. Combined with strong stratification, microbial respiration reduces oxygen in shelf bottom waters to levels unfit for many animals (termed hypoxia). The nGOM shelf remains one of the largest eutrophication-driven hypoxic zones in the world, yet despite its potential as a model study system, the microbial metabolisms underlying and resulting from this phenomenon-many of which occur in bacterioplankton from poorly understood lineages-have received only preliminary study. Our work details the metabolic potential and gene expression activity for uncultivated lineages across several low DO sites in the nGOM, improving our understanding of the active biogeochemical cycling mediated by these "microbial dark matter" taxa during hypoxia
High-Precision Lattice QCD Confronts Experiment
We argue that high-precision lattice QCD is now possible, for the first time,
because of a new improved staggered quark discretization. We compare a wide
variety of nonperturbative calculations in QCD with experiment, and find
agreement to within statistical and systematic errors of 3% or less. We also
present a new determination of alpha_msbar(Mz); we obtain 0.121(3). We discuss
the implications of this breakthrough for phenomenology and, in particular, for
heavy-quark physics.Comment: 2 figures, revte
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