8 research outputs found
Comments on Noncommutative Sigma Models
We review the derivation of a noncommutative version of the nonlinear sigma
model on \CPn and it's soliton solutions for finite emphasizing the
similarities it bears to the GMS scalar field theory. It is also shown that
unlike the scalar theory, some care needs to be taken in defining the
topological charge of BPS solitons of the theory due to nonvanishing surface
terms in the energy functional. Finally it is shown that, like its commutative
analogue, the noncommutative \CPn-model also exhibits a non-BPS sector.
Unlike the commutative case however, there are some surprises in the
noncommutative case that merit further study.Comment: 22 pages, 4 figures, LaTeX (JHEP3), Minor changes, Discussion
expanded and references adde
Approximate Analytical Solutions of the Baby Skyrme Model.
In present paper we show that many properties of the baby skyrmions, which
have been determined numerically, can be understood in terms of an analytic
approximation. In particular, we show that this approximation captures
properties of the multiskyrmion solutions (derived numerically) such as their
stability towards decay into various channels, and that it is more accurate for
the "new baby Skyrme model" which describes anisotropic physical systems in
terms of multiskyrmion fields with axial symmetry. Some universal
characteristics of configurations of this kind are demonstrated, which do not
depend on their topological number.Comment: 12 pages, no figures; submitted to JET
Cherry stones as precursor of activated carbons for supercapacitors
5 pages, 4 figures, 3 tables.-- Available online Oct 31, 2008.It is shown that cherry stones-wastes can be recycled as activated carbons for electrode material in supercapacitors. KOH-activation of this precursor at 800â900°C is an efficient process to obtain carbons with large specific surface areas (1100â1300 m2 gâ1), average pore sizes around 0.9â1.3 nm, which makes them accessible to electrolyte ions, and conductivities between 1 and 2 S cmâ1. These features lead to capacitances at low current density as high as 230 F gâ1 in 2 M H2SO4 aqueous electrolyte and 120 F gâ1 in the aprotic medium 1 M (C2H5)4NBF4/acetonitrile. Furthermore, high performance is also achieved at high current densities, which means that this type of materials competes well with commercial carbons used at present in supercapacitors.Financial support from the Ministerio de EducaciĂłn y Ciencia (project BQU2002-03600) of Spain is gratefully acknowledged. The authors wish to thank NORIT and ARKEMA-CECA for the gift of carbons Super DLC-30 and SC-10, respectively.Peer reviewe
The longest path problem is polynomial on cocomparability graphs
The longest path problem is the problem of finding a path of maximum length in a graph. As a generalization of the Hamiltonian path problem, it is NP-complete on general graphs and, in fact, on every class of graphs that the Hamiltonian path problem is NP-complete. Polynomial solutions for the longest path problem have recently been proposed for weighted trees, ptolemaic graphs, bipartite permutation graphs, interval graphs, and some small classes of graphs. Although the Hamiltonian path problem on cocomparability graphs was proved to be polynomial almost two decades ago [9], the complexity status of the longest path problem on cocomparability graphs has remained open until now; actually, the complexity status of the problem has remained open even on the smaller class of permutation graphs. In this paper, we present a polynomial-time algorithm for solving the longest path problem on the class of cocomparability graphs. Our result resolves the open question for the complexity of the problem on such graphs, and since cocomparability graphs form a superclass of both interval and permutation graphs, extends the polynomial solution of the longest path problem on interval graphs [18] and provides polynomial solution to the class of permutation graphs