7,189 research outputs found
A novel evolutionary formulation of the maximum independent set problem
We introduce a novel evolutionary formulation of the problem of finding a
maximum independent set of a graph. The new formulation is based on the
relationship that exists between a graph's independence number and its acyclic
orientations. It views such orientations as individuals and evolves them with
the aid of evolutionary operators that are very heavily based on the structure
of the graph and its acyclic orientations. The resulting heuristic has been
tested on some of the Second DIMACS Implementation Challenge benchmark graphs,
and has been found to be competitive when compared to several of the other
heuristics that have also been tested on those graphs
Topics in Born-Infeld Electrodynamics
Classical version of Born-Infeld electrodynamics is recalled and its most
important properties discussed. Then we analyze possible abelian and
non-abelian generalizations of this theory, and show how certain soliton-like
configurations can be obtained. The relationship with the Standard Model of
electroweak interactions is also mentioned.Comment: (One new reference added). 15 pages, LaTeX. To be published in the
Proceedings of XXXVII Karpacz Winter School edited in the Proceedings Series
of American Mathematical Society, editors J. Lukierski and J. Rembielinsk
Mass Generation from Lie Algebra Extensions
Applied to the electroweak interactions, the theory of Lie algebra extensions
suggests a mechanism by which the boson masses are generated without resource
to spontaneous symmetry breaking. It starts from a gauge theory without any
additional scalar field. All the couplings predicted by the Weinberg-Salam
theory are present, and a few others which are nevertheless consistent within
the model.Comment: 11 pages; revtex; title and PACS have been changed; comments included
in the manuscrip
Crossover of thermal to shot noise in chaotic cavities
We study the crossover between thermal and shot-noise power in a chaotic
quantum dot in the presence of non-ideal contacts at finite temperature. The
result explicitly demonstrates that the temperature affect the
suppression-amplification effect present in the main quantum noise. In
particular, the weak localization contribution to the noise has an anomalous
thermal behavior when one let the barriers vary, indicating the presence of a
critical point related to specific value of the tunneling barriers. We also
show how to get to the opaque limit of the quantum dot at finite temperature.Comment: 6 pages, 5 figures. To be published in Europhysics Letter
Bioremediation of trace organic compounds found in precious metals refineries wastewaters: A review of potential options
Platinum group metal (PGM) refining processes produce large quantities of wastewater, which is contaminated with the compounds that make up the solvents/extractants mixtures used in the process. These compounds often include solvesso, β-hydroxyxime, amines, amides and methyl isobutyl ketone. A process to clean up PGM refinery wastewaters so that they could be re-used in the refining process would greatly contribute to continual water storage problems and to cost reduction for the industry. Based on the concept that organic compounds that are produced biologically can be destroyed biologically, the use of biological processes for the treatment of organic compounds in other types of waste stream has been favoured in recent years, owing to their low cost and environmental acceptability. This review examines the available biotechnologies and their effectiveness for treating compounds likely to be contained in precious metal extraction process wastewaters. The processes examined include: biofilters, fluidized bed reactors, trickle-bed bioreactors, bioscrubbers, two-phase partitioning bioreactors, membrane bioreactors and activated sludge. Although all processes examined showed adequate to excellent removal of organic compounds from various gaseous and fewer liquid waste streams, there was a variation in their effectiveness. Variations in performance of laboratory-scale biological processes are probably due to the inherent change in the microbial population composition due to selection pressure, environmental conditions and the time allowed for adaptation to the organic compounds. However, if these factors are disregarded, it can be established that activated sludge and membrane bioreactors are the most promising processes for use in the treatment of PGM refinery wastewaters
On the Potential of the Excluded Volume and Auto-Correlation as Neuromorphometric Descriptors
This work investigates at what degree two neuromorphometric measurements,
namely the autocorrelation and the excluded volume of a neuronal cell can
influence the characterization and classification of such a type of cells.
While the autocorrelation function presents good potential for quantifying the
dendrite-dendrite connectivity of cells in mosaic tilings, the excluded volume,
i.e. the amount of the surround space which is geometrically not accessible to
an axon or dendrite, provides a complementary characterization of the cell
connectivity. The potential of such approaches is illustrated with respect to
real neuronal cells.Comment: 15 pages, 6 figure
The ground state properties of the spin-1/2 transverse Ising chain with periodically varying bonds and fields
Using continued fractions we study the ground state properties of the
spin-1/2 Ising chain in a transverse field with periodically varying
interaction strengths and external fields. We consider in detail the chain
having the period of modulation of interactions equals 2 and compare the
results obtained with those corresponding to the spin-1/2 isotropic XY chain in
a transverse field. In contrast to the behaviour of the transverse XY chain,
the transverse Ising chain does not exhibit a step-like magnetization vs. field
dependence caused by the alternation of bonds, its susceptibility exhibits a
logarithmic singularity at the field determined by interaction strengths, and
it is stable with respect to spin-Peierls dimerization.Comment: 11 pages, latex, 4 figure
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