39,714 research outputs found
Hydrometallurgy of the delta sulfide ores, second stage report
This report contains results of the Fluidized-Bed Leaching (FBL) initially adapted to improve Leaching-Flotation processing of Delta ores in sulfate solution. The research carried out in the continuous laboratory installation show, however, that the new, 3-phase (solid-liquid-gaseous) reactor also performs satisfactorily in other leaching systems. A new process of pyritic matrix destruction for precious metals recovery in the FBL reactor, and a new process for recovery of zinc and other metals in a chloride system are proposed on the basis of laboratory results.Submitted to:
Nerco Minerals Compan
Horrocks Correspondence on a Quadric Surface
We extend the Horrocks correspondence between vector bundles and cohomology
modules on the projective plane to the product of two projective lines. We
introduce a set of invariants for a vector bundle on the product of two
projective lines, which includes the first cohomology module of the bundle, and
prove that there is a one to one correspondence between these sets of
invariants and isomorphism classes of vector bundles without line bundle
summands.Comment: 19 page
Horrocks Correspondence on ACM Varieties
We describe a vector bundle \sE on a smooth -dimensional ACM variety in
terms of its cohomological invariants H^i_*(\sE), , and
certain graded modules of "socle elements" built from \sE. In this way we
give a generalization of the Horrocks correspondence. We prove existence
theorems where we construct vector bundles from these invariants and uniqueness
theorems where we show that these data determine a bundle up to isomorphisms.
The cases of the quadric hypersurface in and the Veronese
surface in are considered in more detail.Comment: 18 pages, not figure
Taxonomy and clustering in collaborative systems: the case of the on-line encyclopedia Wikipedia
In this paper we investigate the nature and structure of the relation between
imposed classifications and real clustering in a particular case of a
scale-free network given by the on-line encyclopedia Wikipedia. We find a
statistical similarity in the distributions of community sizes both by using
the top-down approach of the categories division present in the archive and in
the bottom-up procedure of community detection given by an algorithm based on
the spectral properties of the graph. Regardless the statistically similar
behaviour the two methods provide a rather different division of the articles,
thereby signaling that the nature and presence of power laws is a general
feature for these systems and cannot be used as a benchmark to evaluate the
suitability of a clustering method.Comment: 5 pages, 3 figures, epl2 styl
Hydrometallurgy of the delta sulfide ores, first stage report
This report presents the results of hydrometallurgical research carried out from September 16, 1985 to June 30, 1986 on metals recovery from complex sulfide ores from the Delta deposit near Tok, Alaska. The leaching characteristics performed for 6 different ore samples indicate that the most valuable components form the following order: Zn > Au > Pb > Ag > Cu > So. Further study demonstrates that direct leaching of the ore is effective both in chloride as well
as in sulfate oxidizing solutions coupled with separating of leached solid components by flotation. Three variants of the ore processing with ferric chloride or fenic sulfate leaching are analyzed: one flowsheet with direct ore leaching in ferric chloride solution followed by leaching-flotation step, with subsequent zinc separation in a solvent extraction step and electrolysis in chloride solution; and two flowsheets of direct ore leaching with ferric sulfate solution followed by a leaching-flotation step, with zinc sulfate electrolysis and other metals recovery in chloride leaching sreps. In two last flowsheets silver is recovered during the chloride leaching steps and gold h m flotation products during the cyanide leaching. Preliminary economic and technical evaluation is presented. The engineering study on apparatus for the fast leaching- flotation processing and on better accumulation of gold and silver in one semi-product are concluded for the next year of research
Absence of ferromagnetism in Mn- and Co-doped ZnO
Following the theoretical predictions of ferromagnetism in Mn- and Co-doped
ZnO, several workers reported ferromagnetism in thin films as well as in bulk
samples of these materials. While some observe room-temperature ferromagnetism,
others find magnetization at low temperatures. Some of the reports, however,
cast considerable doubt on the magnetism of Mn- and Co-doped ZnO. In order to
conclusively establish the properties of Mn- and Co-doped ZnO, samples with 6
percent and 2 percent dopant concentrations, have been prepared by the
low-temperature decomposition of acetate solid solutions. The samples have been
characterized by x-ray diffraction, EDAX and spectroscopic methods to ensure
that the dopants are substitutional. All the Mn- and Co-doped ZnO samples
(prepared at 400 deg C and 500 deg C) fail to show ferromagnetism. Instead,
their magnetic properties are best described by a Curie-Weiss type behavior. It
appears unlikely that these materials would be useful for spintronics, unless
additional carriers are introduced by some means.Comment: 23 pages, 9 figures. submitted to J. Mater. Chem 200
Neutrino processes with power law dispersion relations
We compute various processes involving neutrinos in the initial and/or final
state and we assume that neutrinos have energy momentum relation with a general
power law correction due to Lorentz invariance violation.
We find that for the bounds on from direct time of flight
measurement are much more stringent than from constraining the neutrino
Cerenkov decay process.Comment: 13 pages, 1 figure, Title change, replacement matches version
accepted in Phys. Rev.
Cryostatless high temperature supercurrent bearings for rocket engine turbopumps
The rocket engine systems examined include SSME, ALS, and CTV systems. The liquid hydrogen turbopumps in the SSME and ALS vehicle systems are identified as potentially attractive candidates for development of Supercurrent Bearings since the temperatures around the bearings is about 30 K, which is considerably lower than the 95 K transition temperatures of HTS materials. At these temperatures, the current HTS materials are shown to be capable of developing significantly higher current densities. This higher current density capability makes the development of supercurrent bearings for rocket engines an attractive proposition. These supercurrent bearings are also shown to offer significant advantages over conventional bearings used in rocket engines. They can increase the life and reliability over rolling element bearings because of noncontact operation. They offer lower power loss over conventional fluid film bearings. Compared to conventional magnetic bearings, they can reduce the weight of controllers significantly, and require lower power because of the use of persistent currents. In addition, four technology areas that require further attention have been identified. These are: Supercurrent Bearing Conceptual Design Verification; HTS Magnet Fabrication and Testing; Cryosensors and Controller Development; and Rocket Engine Environmental Compatibility Testing
Evaluation of mixed energy partial arcs for volumetric modulated arc therapy for prostate cancer
An analysis method for multi-component airfoils in separated flow
The multi-component airfoil program (Langley-MCARF) for attached flow is modified to accept the free vortex sheet separation-flow model program (Analytical Methods, Inc.-CLMAX). The viscous effects are incorporated into the calculation by representing the boundary layer displacement thickness with an appropriate source distribution. The separation flow model incorporated into MCARF was applied to single component airfoils. Calculated pressure distributions for angles of attack up to the stall are in close agreement with experimental measurements. Even at higher angles of attack beyond the stall, correct trends of separation, decrease in lift coefficients, and increase in pitching moment coefficients are predicted
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