443 research outputs found
Spin polarons in triangular antiferromagnets
The motion of a single hole in a 2D triangular antiferromagnet is
investigated using the t-J model. The one-hole states are described by strings
of spin deviations around the hole. Using projection technique the one-hole
spectral function is calculated. For large J/t we find low-lying
quasiparticle-like bands which are well separated from an incoherent background
by a gap of order J. However, for small J/t this gap vanishes and the spectrum
becomes broad over an energy range of several t. The results are compared with
SCBA calculations and numerical data.Comment: 4 pages, 6 figs, to be publish in PR
Linear response within the projection-based renormalization method: Many-body corrections beyond the random phase approximation
The explicit evaluation of linear response coefficients for interacting
many-particle systems still poses a considerable challenge to theoreticians. In
this work we use a novel many-particle renormalization technique, the so-called
projector-based renormalization method, to show how such coefficients can
systematically be evaluated. To demonstrate the prospects and power of our
approach we consider the dynamical wave-vector dependent spin susceptibility of
the two-dimensional Hubbard model and also determine the subsequent magnetic
phase diagram close to half-filling. We show that the superior treatment of
(Coulomb) correlation and fluctuation effects within the projector-based
renormalization method significantly improves the standard random phase
approximation results.Comment: 17 pages, 7 figures, revised versio
Role of carbon dioxide and ion transport in the formation of sub-embryonic fluid by the blastoderm of the Japanese quail
1. The explanted blastoderm of the Japanese quail was used to explore the role of ions and carbon dioxide in determining the rate of sub-embryonic fluid (SEF) production between 54 and 72 h of incubation.
2. Amiloride, an inhibitor of Na+/H+ exchange, at concentrations of 10-3 to 10-6 M substantially decreased the rate of SEF production when added to the albumen culture medium. N-ethylmaleimide, an inhibitor of V type H+ ATPase, also decreased this rate but only to a small extent at the highest dose applied, 10-3 M. Both inhibitors had no effect on SEF production when added to the SEF. 3. The inhibitors of cellular bicarbonate and chloride exchange, 4-acetamido-4-'isothiocyano-2, 2-'disulphonic acid (SITS) and 4,4'diisothiocyanostilbene-2,2-'disulphonic acid (DIDS), had no effect upon SEF production.
4. Ouabain, an inhibitor of Na+/K+ ATPase, decreased SEF production substantially at all concentrations added to the SEF (10-3 to 10-6 M). Three sulphonamide inhibitors of carbonic anhydrase, acetazolamide, ethoxzolamide and benzolamide, decreased SEF production when added to the SEF at concentrations of 10-3 to 10-6 M. Benzolamide was by far the most potent. Neither ouabain nor the sulphonamides altered SEF production when added to the albumen culture medium.
5. Using a cobalt precipitation method, carbonic anhydrase activity was localised to the endodermal cells of the area vasculosa. The carbonic anhydrase activity was primarily associated with the lateral plasma membranes, which together with the potent inhibitory effect of benzolamide, suggests the carbonic anhydrase of these cells is the membrane-associated form, CA IV.
6. The changes in SEF composition produced by inhibitors were consistent with the production of SEF by local osmotic gradients.
7. It is concluded that a Na+/K+ ATPase is located on the basolateral membranes of the endodermal cells of the area vasculosa , and that a sodium ion/hydrogen ion exchanger is located on their apical surfaces. Protons for this exchanger would be provided by the hydration of CO2 catalysed by the membrane-associated carbonic anhydrase. Furthermore, it is proposed that the prime function of the endodermal cells of the area vasculosa is the production of SEF
Minimalistic Neutrino Mass Model
We consider the simplest model which solves the solar and atmospheric
neutrino puzzles, in the sense that it contains the smallest amount of beyond
the Standard Model ingredients. The solar neutrino data is accounted for by
Planck-mass effects while the atmospheric neutrino anomaly is due to the
existence of a single right-handed neutrino at an intermediate mass scale
between 10^9 GeV and 10^14 GeV. Even though the neutrino mixing angles are not
exactly predicted, they can be naturally large, which agrees well with the
current experimental situation. Furthermore, the amount of lepton asymmetry
produced in the early universe by the decay of the right-handed neutrino is
very predictive and may be enough to explain the current baryon-to-photon ratio
if the right-handed neutrinos are produced out of thermal equilibrium. One
definitive test for the model is the search for anomalous seasonal effects at
Borexino.Comment: 19 pages, 3 figures, references added, results unchange
Search for direct production of charginos and neutralinos in events with three leptons and missing transverse momentum in âs = 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 fbâ1 of protonâproton 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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