603 research outputs found
Confinement and chiral symmetry breaking via a domainlike mean field
Singular gauge fields in the partition function for QCD can lead to a
domain-like picture for the QCD vacuum by virtue of constraints on quantum
fluctuations at the singularities. With a simple model of hyperspherical
domains with interiors of constant field strength we show that the main
features of gluon condensation and an area law for static quarks can be
realised.The Dirac operator in such a background is exactly soluble. Chirality
properties of the solutions show agreement with recent lattice results.Comment: Contribution to the proceedings of the Workshop on Lattice Hadron
Physics, July 9-18 2001, Cairns, Austalia. 5 pages. Elsevier 2 column style
file include
Bioaugmentation of UASB reactors with immobilized Sulfurospirillum barnesii for simultaneous selenate and nitrate removal
Whole-cell immobilization of selenate-respiring Sulfurospirillum barnesii in polyacrylamide gels was investigated to allow the treatment of selenate contaminated (790¿µg Se¿×¿L-1) synthetic wastewater with a high molar excess of nitrate (1,500 times) and sulfate (200 times). Gel-immobilized S. barnesii cells were used to inoculate a mesophilic (30°C) bioreactor fed with lactate as electron donor at an organic loading rate of 5 g chemical oxygen demand (COD)¿×¿L-1 day-1. Selenate was reduced efficiently (>97%) in the nitrate and sulfate fed bioreactor, and a minimal effluent concentration of 39¿µg Se¿×¿L-1 was obtained. Scanning electron microscopy with energy dispersive X-ray (SEM–EDX) analysis revealed spherical bioprecipitates of =2¿µm diameter mostly on the gel surface, consisting of selenium with a minor contribution of sulfur. To validate the bioaugmentation success under microbial competition, gel cubes with immobilized S. barnesii cells were added to an Upflow Anaerobic Sludge Bed (UASB) reactor, resulting in earlier selenate (24 hydraulic retention times (HRTs)) and sulfate (44 HRTs) removal and higher nitrate/nitrite removal efficiencies compared to a non-bioaugmented control reactor. S. barnesii was efficiently immobilized inside the UASB bioreactors as the selenate-reducing activity was maintained during long-term operation (58 days), and molecular analysis showed that S. barnesii was present in both the sludge bed and the effluent. This demonstrates that gel immobilization of specialized bacterial strains can supersede wash-out and out-competition of newly introduced strains in continuous bioaugmented systems. Eventually, proliferation of a selenium-respiring specialist occurred in the non-bioaugmented control reactor, resulting in simultaneous nitrate and selenate removal during a later phase of operatio
Quantum Electrodynamics in the Light-Front Weyl Gauge
We examine QED(3+1) quantised in the `front form' with finite `volume'
regularisation, namely in Discretised Light-Cone Quantisation. Instead of the
light-cone or Coulomb gauges, we impose the light-front Weyl gauge . The
Dirac method is used to arrive at the quantum commutation relations for the
independent variables. We apply `quantum mechanical gauge fixing' to implement
Gau{\ss}' law, and derive the physical Hamiltonian in terms of unconstrained
variables. As in the instant form, this Hamiltonian is invariant under global
residual gauge transformations, namely displacements. On the light-cone the
symmetry manifests itself quite differently.Comment: LaTeX file, 30 pages (A4 size), no figures. Submitted to Physical
review D. January 18, 1996. Originally posted, erroneously, with missing
`Weyl' in title. Otherwise, paper is identica
Towards Solving QCD - The Transverse Zero Modes in Light-Cone Quantization
We formulate QCD in (d+1) dimensions using Dirac's front form with periodic
boundary conditions, that is, within Discretized Light-Cone Quantization. The
formalism is worked out in detail for SU(2) pure glue theory in (2+1)
dimensions which is approximated by restriction to the lowest {\it transverse}
momentum gluons. The dimensionally-reduced theory turns out to be SU(2) gauge
theory coupled to adjoint scalar matter in (1+1) dimensions. The scalar field
is the remnant of the transverse gluon. This field has modes of both non-zero
and zero {\it longitudinal} momentum. We categorize the types of zero modes
that occur into three classes, dynamical, topological, and constrained, each
well known in separate contexts. The equation for the constrained mode is
explicitly worked out. The Gauss law is rather simply resolved to extract
physical, namely color singlet states. The topological gauge mode is treated
according to two alternative scenarios related to the In the one, a spectrum is
found consistent with pure SU(2) gluons in (1+1) dimensions. In the other, the
gauge mode excitations are estimated and their role in the spectrum with
genuine Fock excitations is explored. A color singlet state is given which
satisfies Gauss' law. Its invariant mass is estimated and discussed in the
physical limit.Comment: LaTex document, 26 pages, one figure (obtainable by contacting
authors). To appear in Physical. Review
Mass Spectra of Supersymmetric Yang-Mills Theories in 1+1 Dimensions
Physical mass spectra of supersymmetric Yang-Mills theories in 1+1 dimensions
are evaluated in the light-cone gauge with a compact spatial dimension. The
supercharges are constructed and the infrared regularization is unambiguously
prescribed for supercharges, instead of the light-cone Hamiltonian. This
provides a manifestly supersymmetric infrared regularization for the
discretized light-cone approach. By an exact diagonalization of the supercharge
matrix between up to several hundred color singlet bound states, we find a
rapidly increasing density of states as mass increases.Comment: LaTeX file, 32 page, 7 eps figure
Emergence of Skyrme crystal in Gross-Neveu and 't Hooft models at finite density
We study two-dimensional, large field theoretic models (Gross-Neveu
model, 't Hooft model) at finite baryon density near the chiral limit. The same
mechanism which leads to massless baryons in these models induces a breakdown
of translational invariance at any finite density. In the chiral limit baryonic
matter is characterized by a spatially varying chiral angle with a wave number
depending only on the density. For small bare quark masses a sine-Gordon kink
chain is obtained which may be regarded as simplest realization of the Skyrme
crystal for nuclear matter. Characteristic differences between confining and
non-confining models are pointed out.Comment: 27 pages, 11 figures, added reference, corrected sig
The position of graptolites within Lower Palaeozoic planktic ecosystems.
An integrated approach has been used to assess the palaeoecology of graptolites both as a discrete group and also as a part of the biota present within Ordovician and Silurian planktic realms. Study of the functional morphology of graptolites and comparisons with recent ecological analogues demonstrates that graptolites most probably filled a variety of niches as primary consumers, with modes of life related to the colony morphotype. Graptolite coloniality was extremely ordered, lacking any close morphological analogues in Recent faunas. To obtain maximum functional efficiency, graptolites would have needed varying degrees of coordinated automobility. A change in lifestyle related to ontogenetic changes was prevalent within many graptolite groups. Differing lifestyle was reflected by differing reproductive strategies, with synrhabdosomes most likely being a method for rapid asexual reproduction. Direct evidence in the form of graptolithophage 'coprolitic' bodies, as well as indirect evidence in the form of probable defensive adaptations, indicate that graptolites comprised a food item for a variety of predators. Graptolites were also hosts to a variety of parasitic organisms and provided an important nutrient source for scavenging organisms
Search for direct production of charginos and neutralinos in events with three leptons and missing transverse momentum in √s = 7 TeV pp collisions with the ATLAS detector
A search for the direct production of charginos and neutralinos in final states with three electrons or muons and missing transverse momentum is presented. The analysis is based on 4.7 fb−1 of proton–proton collision data delivered by the Large Hadron Collider and recorded with the ATLAS detector. Observations are consistent with Standard Model expectations in three signal regions that are either depleted or enriched in Z-boson decays. Upper limits at 95% confidence level are set in R-parity conserving phenomenological minimal supersymmetric models and in simplified models, significantly extending previous results
Jet size dependence of single jet suppression in lead-lead collisions at sqrt(s(NN)) = 2.76 TeV with the ATLAS detector at the LHC
Measurements of inclusive jet suppression in heavy ion collisions at the LHC
provide direct sensitivity to the physics of jet quenching. In a sample of
lead-lead collisions at sqrt(s) = 2.76 TeV corresponding to an integrated
luminosity of approximately 7 inverse microbarns, ATLAS has measured jets with
a calorimeter over the pseudorapidity interval |eta| < 2.1 and over the
transverse momentum range 38 < pT < 210 GeV. Jets were reconstructed using the
anti-kt algorithm with values for the distance parameter that determines the
nominal jet radius of R = 0.2, 0.3, 0.4 and 0.5. The centrality dependence of
the jet yield is characterized by the jet "central-to-peripheral ratio," Rcp.
Jet production is found to be suppressed by approximately a factor of two in
the 10% most central collisions relative to peripheral collisions. Rcp varies
smoothly with centrality as characterized by the number of participating
nucleons. The observed suppression is only weakly dependent on jet radius and
transverse momentum. These results provide the first direct measurement of
inclusive jet suppression in heavy ion collisions and complement previous
measurements of dijet transverse energy imbalance at the LHC.Comment: 15 pages plus author list (30 pages total), 8 figures, 2 tables,
submitted to Physics Letters B. All figures including auxiliary figures are
available at
http://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/HION-2011-02
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