4,077 research outputs found
Solid-solid phase transition in hard ellipsoids
We present a computer simulation study of the crystalline phases of hard
ellipsoids of revolution. A previous study [Phys. Rev. E, \textbf{75}, 020402
(2007)] showed that for aspect ratios the previously suggested
stretched-fcc phase [Mol. Phys., \textbf{55}, 1171 (1985)] is unstable with
respect to a simple monoclinic phase with two ellipsoids of different
orientations per unit cell (SM2). In order to study the stability of these
crystalline phases at different aspect ratios and as a function of density we
have calculated their free energies by thermodynamic integration. The
integration path was sampled by an expanded ensemble method in which the
weights were adjusted by the Wang-Landau algorithm.
We show that for aspect ratios the SM2 structure is more stable
than the stretched-fcc structure for all densities above solid-nematic
coexistence. Between and our calculations reveal a
solid-solid phase transition
Einstein-Yang-Mills-Chern-Simons solutions in D=2n+1 dimensions
We investigate finite energy solutions of the
Einstein--Yang-Mills--Chern-Simons system in odd spacetime dimensions, D=2n+1,
with n>1. Our configurations are static and spherically symmetric, approaching
at infinity a Minkowski spacetime background. In contrast with the Abelian
case, the contribution of the Chern-Simons term is nontrivial already in the
static, spherically symmetric limit. Both globally regular, particle-like
solutions and black holes are constructed numerically for several values of D.
These solutions carry a nonzero electric charge and have finite mass. For
globally regular solutions, the value of the electric charge is fixed by the
Chern-Simons coupling constant. The black holes can be thought as non-linear
superpositions of Reissner-Nordstrom and non-Abelian configurations. A
systematic discussion of the solutions is given for D=5, in which case the
Reissner-Nordstrom black hole becomes unstable and develops non-Abelian hair.
We show that some of these non-Abelian configurations are stable under linear,
spherically symmetric perturbations. A detailed discussion of an exact D=5
solution describing extremal black holes and solitons is also provided.Comment: 34 pages, 14 figures; v2: misprints corrected and references adde
ShotgunWSD: An unsupervised algorithm for global word sense disambiguation inspired by DNA sequencing
In this paper, we present a novel unsupervised algorithm for word sense
disambiguation (WSD) at the document level. Our algorithm is inspired by a
widely-used approach in the field of genetics for whole genome sequencing,
known as the Shotgun sequencing technique. The proposed WSD algorithm is based
on three main steps. First, a brute-force WSD algorithm is applied to short
context windows (up to 10 words) selected from the document in order to
generate a short list of likely sense configurations for each window. In the
second step, these local sense configurations are assembled into longer
composite configurations based on suffix and prefix matching. The resulted
configurations are ranked by their length, and the sense of each word is chosen
based on a voting scheme that considers only the top k configurations in which
the word appears. We compare our algorithm with other state-of-the-art
unsupervised WSD algorithms and demonstrate better performance, sometimes by a
very large margin. We also show that our algorithm can yield better performance
than the Most Common Sense (MCS) baseline on one data set. Moreover, our
algorithm has a very small number of parameters, is robust to parameter tuning,
and, unlike other bio-inspired methods, it gives a deterministic solution (it
does not involve random choices).Comment: In Proceedings of EACL 201
Total order in opportunistic networks
Opportunistic network applications are usually assumed to work only with unordered immutable messages, like photos, videos, or music files, while applications that depend on ordered or mutable messages, like chat or shared contents editing applications, are ignored. In this paper, we examine how total ordering can be achieved in an opportunistic network. By leveraging on existing dissemination and causal order algorithms, we propose a commutative replicated data type algorithm on the basis of Logoot for achieving total order without using tombstones in opportunistic networks where message delivery is not guaranteed by the routing layer. Our algorithm is designed to use the nature of the opportunistic network to reduce the metadata size compared to the original Logoot, and even to achieve in some cases higher hit rates compared to the dissemination algorithms when no order is enforced. Finally, we present the results of the experiments for the new algorithm by using an opportunistic network emulator, mobility traces, and Wikipedia pages.Peer ReviewedPostprint (author's final draft
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