1,197 research outputs found
Two-dimensional anisotropic Heisenberg antiferromagnet in a field
The classical, square lattice, uniaxially anisotropic Heisenberg
antiferromagnet in a magnetic field parallel to the easy axis is studied using
Monte Carlo techniques. The model displays a long-range ordered
antiferromagnetic, an algebraically ordered spin-flop, and a paramagnetic
phase. The simulations indicate that a narrow disordered phase intervenes
between the ordered phases down to quite low temperatures. Results are compared
to previous, partially conflicting findings on related classical models as well
as the quantum variant with spin S=1/2.Comment: 8 pages, 9 figure
Phase diagrams of a classical two-dimensional Heisenberg antiferromagnet with single-ion anisotropy
A classical variant of the two-dimensional anisotropic Heisenberg model
reproducing inelastic neutron scattering experiments on La_5 Ca_9 Cu_24 O_41
[M. Matsuda et al., Phys.Rev. B 68, 060406(R) (2003)] is analysed using mostly
Monte Carlo techniques. Phase diagrams with external fields parallel and
perpendicular to the easy axis of the anisotropic interactions are determined,
including antiferromagnetic and spin-flop phases. Mobile spinless defects, or
holes, are found to form stripes which bunch, debunch and break up at a phase
transition. A parallel field can lead to a spin-flop phase.Comment: 9 pages, 9 figures; final version as accepted by Phys. Rev. B (Fig. 5
replaced, added remarks in Secs. I, III, and V
Study on ash deposition under oxyfuel combustion of coal/biomass blends
Combustion in an Oâ‚‚/COâ‚‚mixture (oxyfuel) has been recognized as a promising technology for COâ‚‚capture as it produces a high COâ‚‚concentration flue gas. Furthermore, biofuels in general contribute to COâ‚‚reduction in comparison with fossil fuels as they are considered COâ‚‚neutral. Ash formation and deposition (surface fouling) behavior of coal/biomass blends under Oâ‚‚/COâ‚‚combustion conditions is still not extensively studied. Aim of this work is the comparative study of ash formation and deposition of selected coal/biomass blends under oxyfuel and air conditions in a lab scale pulverized coal combustor (drop tube). The fuels used were Russian and South African coals and their blends with Shea meal (cocoa). A horizontal deposition probe, equipped with thermocouples and heat transfer sensors for on line data acquisition, was placed at a fixed distance from the burner in order to simulate the ash deposition on heat transfer surfaces (e.g. water or steam tubes). Furthermore, a cascade impactor (staged filter) was used to obtain size distributed ash samples including the submicron range at the reactor exit. The deposition ratio and propensity measured for the various experimental conditions were higher in all oxyfuel cases. The SEM/EDS and ICP analyses of the deposit and cascade impactor ash samples indicate K interactions with the alumina silicates and to a smaller extend with Cl, which was all released in the gas phase, in both the oxyfuel and air combustion samples. Sulfur was depleted in both the air or oxyfuel ash deposits. S and K enrichment was detected in the fine ash stages, slightly increased under air combustion conditions. Chemical equilibrium calculations were carried out to facilitate the interpretation of the measured data; the results indicate that temperature dependence and fuels/blends ash composition are the major factors affecting gaseous compounds and ash composition rather than the combustion environment, which seems to affect the fine ash (submicron) ash composition, and the ash deposition mechanismsThe research work reported in this paper was partly carried out with the financial support from the RFCS contract number RFCRCT- 2006-00010. The very fine work done by Peter Heere in carrying out the experiments is highly acknowledgedPublicad
The chemical potential of the electron gas on a one dimensional lattice
The chemical potential of the electron gas on a one-dimensional lattice is
determined within the discrete Hubbard model. The result will have applications
in studies of transport properties of quasi one-dimensional organic conductors
such as the Bechgaard salts.Comment: 4 pages,plain TeX,presented at the 9 National Congress of Yugoslav
Physicists,held in May 1995.,and published in the proceedings.The author can
be contacted at: [email protected]
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