18,111 research outputs found
NS Branes in Type I Theory
We consider novel nonperturbative effects of type I theories compactified on
singular ALE spaces obtained by adding NS branes. Such effects include a
description of small instantons at singularities.Comment: 6 pages, Harvmac.tex, updated referenc
Calculation of Nonperturbative Terms in Open String Models
Nonperturbative corrections in type II string theory corresponding to Riemann
surfaces with one boundary are calculated in several noncompact geometries of
desingularized orbifolds. One of these models has a complicated phase structure
which is explored. A general condition for integrality of the numerical
invariants is discussed
Construct, Merge, Solve and Adapt: Application to the repetition-free longest common subsequence problem
In this paper we present the application of a recently proposed, general, algorithm for combinatorial optimization to the repetition-free longest common subsequence problem. The applied algorithm, which is labelled Construct, Merge, Solve & Adapt, generates sub-instances based on merging the solution components found in randomly constructed solutions. These sub-instances are subsequently solved by means of an exact solver. Moreover, the considered sub-instances are dynamically changing due to adding new solution components at each iteration, and removing existing solution components on the basis of indicators about their usefulness. The results of applying this algorithm to the repetition-free longest common subsequence problem show that the algorithm generally outperforms competing approaches from the literature. Moreover, they show that the algorithm is competitive with CPLEX for small and medium size problem instances, whereas it outperforms CPLEX for larger problem instances.Peer ReviewedPostprint (author's final draft
The Ionizing Stars of the Galactic Ultra-Compact HII Region G45.45+0.06
Using the NIFS near-infrared integral-field spectrograph behind the facility
adaptive optics module, ALTAIR, on Gemini North, we have identified several
massive O-type stars that are responsible for the ionization of the Galactic
Ultra-Compact HII region G45.45+0.06. The sources ``m'' and ``n'' from the
imaging study of Feldt et a. 1998 are classified as hot, massive O-type stars
based on their K-band spectra. Other bright point sources show red and/or
nebular spectra and one appears to have cool star features that we suggest are
due to a young, low-mass pre-main sequence component. Still two other embedded
sources (``k'' and ``o'' from Feldt et al.) exhibit CO bandhead emission that
may arise in circumstellar disks which are possibly still accreting. Finally,
nebular lines previously identified only in higher excitation planetary nebulae
and associated with KrIII and SeIV ions are detected in G45.45+0.06.Comment: Latex, 28 pages, 10 figure
Towards an analytical theory for charged hard spheres
Ion mixtures require an exclusion core to avoid collapse. The Debye Hueckel
theory, where ions are point charges, is accurate only in the limit of infinite
dilution. The MSA is the embedding of hard cores into DH, is valid for higher
densities. In the MSA the properties of any ionic mixture can be represented by
a single screening parameter . For equal ionic size restricted model is
obtained from the Debye parameter . This one parameter representation
(BIMSA) is valid for complex and associating systems, such as the general
n-polyelectrolytes. The BIMSA is the only theory that satisfies the infinite
dilution limit of the DH theory for any chain length. The contact pair
distribution function of hard ions mixture is a functional of and a
small mean field parameter. This yields good agreement with the Monte Carlo
(Bresme et al. Phys. Rev. E {\textbf 51} 289 (1995)) .Comment: 6 pages, 1 figur
A Continuation Method for Nash Equilibria in Structured Games
Structured game representations have recently attracted interest as models
for multi-agent artificial intelligence scenarios, with rational behavior most
commonly characterized by Nash equilibria. This paper presents efficient, exact
algorithms for computing Nash equilibria in structured game representations,
including both graphical games and multi-agent influence diagrams (MAIDs). The
algorithms are derived from a continuation method for normal-form and
extensive-form games due to Govindan and Wilson; they follow a trajectory
through a space of perturbed games and their equilibria, exploiting game
structure through fast computation of the Jacobian of the payoff function. They
are theoretically guaranteed to find at least one equilibrium of the game, and
may find more. Our approach provides the first efficient algorithm for
computing exact equilibria in graphical games with arbitrary topology, and the
first algorithm to exploit fine-grained structural properties of MAIDs.
Experimental results are presented demonstrating the effectiveness of the
algorithms and comparing them to predecessors. The running time of the
graphical game algorithm is similar to, and often better than, the running time
of previous approximate algorithms. The algorithm for MAIDs can effectively
solve games that are much larger than those solvable by previous methods
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