48,602 research outputs found
Natural waters in Amazonia. III. Ammonium molybdate-reactive silica
Natural waters of the Amazonian Tertiary formations along the Manaus-Itacoatjara Road were studied with respect to variations in average seasonal and yearly soluble silica content. In general the variations are small and concentrations very low, for all input fractions, i. e., rainfall, stemflow, and throughfall [about 90 percent of the total (470 analyses) lower than 1.0 mg/l]. While 90 percent of total ground water analyses (excluding well IV 3) have soluble silica concentrations lower than 1.5 mg/l, high rain forest stream waters are slightly higher (90 percent of all values lower than 2.0 mg/l). The Rio Negro waters show 90 percent of the total samples analyzed between 2.0 mg/l and 3.0 mg/l soluble silica
Ferromagnetism and temperature-dependent Electronic Structure of hcp Gadolinium
We use a combination of a many-body model analysis with an ab initio band
structure calculation to derive the temperature dependent electronic
quasiparticle structure of the rare-earth metal Gadolinium. As a local-moment
system Gd is properly represented by the ferromagnetic (multiband)
Kondo-lattice model (s-f (d-f) model). The single-particle part of the
model-Hamiltonian is taken from an augmented spherical wave (ASW) band
calculation. The proposed method avoids the double counting of relevant
interactions by exploiting an exact limiting case of the model and takes into
account the correct symmetry of atomic orbitals. The a priori only weakly
correlated 5d conduction bands get via interband exchange coupling to the
localized 4f levels a distinct temperature dependence which explains by a
Rudermann-Kittel-Kasuya-Yosida (RKKY) -type mechanism the ferromagnetism of Gd.
We get a self-consistently derived Curie temperature of 294.1 K and a
T=0-moment of 7.71 , surprisingly close to the experimental
values. The striking induced temperature-dependence of the 5d conduction bands
explains respective photoemission data. The only parameter of the theory
(interband exchange coupling J) is uniquely fixed by the band calculation.Comment: 12 pages, 9 figure
A rotating cylinder in an asymptotically locally anti-de Sitter background
A family of exact solutions is presented which represents a rigidly rotating
cylinder of dust in a background with a negative cosmological constant. The
interior of the infinite cylinder is described by the Godel solution. An exact
solution for the exterior solution is found which depends both on the rotation
of the interior and on its radius. For values of these parameters less than a
certain limit, the exterior solution is shown to be locally isomorphic to the
Linet-Tian solution. For values larger than another limit, it is shown that the
exterior solution extends into a region which contains closed timelike curves.
At large distances from the source, the space-time is shown to be asymptotic
locally to anti-de Sitter space.Comment: To appear in Classical and Quantum Gravit
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