516 research outputs found
Uniqueness of Ground States for Short-Range Spin Glasses in the Half-Plane
We consider the Edwards-Anderson Ising spin glass model on the half-plane with zero external field and a wide range of choices, including
mean zero Gaussian, for the common distribution of the collection J of i.i.d.
nearest neighbor couplings. The infinite-volume joint distribution
of couplings J and ground state pairs with periodic
(respectively, free) boundary conditions in the horizontal (respectively,
vertical) coordinate is shown to exist without need for subsequence limits. Our
main result is that for almost every J, the conditional distribution
is supported on a single ground state pair.Comment: 20 pages, 3 figure
Magnetospheric convection electric field dynamics and stormtime particle energization: Case study of the magnetic storm of 4 May 1998
It is shown that narrow channels of high electric field are an effective mechanism for injecting plasma into the inner magnetosphere. Analytical expressions for the electric field cannot produce these channels of intense plasma flow, and thus, result in less entry and adiabatic energization of the plasma sheet into near-Earth space. For the ions, omission of these channels leads to an underprediction of the strength of the stormtime ring current and therefore, an underestimation of the geoeffectiveness of the storm event. For the electrons, omission of these channels leads to the inability to create a seed population of 10-100 keV electrons deep in the inner magnetosphere. These electrons can eventually be accelerated into MeV radiation belt particles. To examine this, the 1-7 May 1998 magnetic storm is studied with a plasma transport model by using three different convection electric field models: Volland-Stern, Weimer, and AMIE. It is found that the AMIE model can produce particle fluxes that are several orders of magnitude higher in the <i>L</i> = 2 – 4 range of the inner magnetosphere, even for a similar total cross-tail potential difference. <br><br><b>Key words.</b> Space plasma physics (charged particle motion and acceleration) – Magnetospheric physics (electric fields, storms and substorms
Trades in complex Hadamard matrices
A trade in a complex Hadamard matrix is a set of entries which can be changed
to obtain a different complex Hadamard matrix. We show that in a real Hadamard
matrix of order all trades contain at least entries. We call a trade
rectangular if it consists of a submatrix that can be multiplied by some scalar
to obtain another complex Hadamard matrix. We give a
characterisation of rectangular trades in complex Hadamard matrices of order
and show that they all contain at least entries. We conjecture that all
trades in complex Hadamard matrices contain at least entries.Comment: 9 pages, no figure
Towards an Iterative Algorithm for the Optimal Boundary Coverage of a 3D Environment
This paper presents a new optimal algorithm for locating a set of sensors in 3D able to see the boundaries of a polyhedral environment. Our approach is iterative and is based on a lower bound on the sensors' number and on a restriction of the original problem requiring each face to be observed in its entirety by at least one sensor. The lower bound allows evaluating the quality of the solution obtained at each step, and halting the algorithm if the solution is satisfactory. The algorithm asymptotically converges to the optimal solution of the unrestricted problem if the faces are subdivided into smaller part
Properties of Random Graphs with Hidden Color
We investigate in some detail a recently suggested general class of ensembles
of sparse undirected random graphs based on a hidden stub-coloring, with or
without the restriction to nondegenerate graphs. The calculability of local and
global structural properties of graphs from the resulting ensembles is
demonstrated. Cluster size statistics are derived with generating function
techniques, yielding a well-defined percolation threshold. Explicit rules are
derived for the enumeration of small subgraphs. Duality and redundancy is
discussed, and subclasses corresponding to commonly studied models are
identified.Comment: 14 pages, LaTeX, no figure
Ecological model of extinctions
We present numerical results based on a simplified ecological system in
evolution, showing features of extinction similar to that claimed for the
biosystem on Earth. In the model each species consists of a population in
interaction with the others, that reproduces and evolves in time. Each species
is simultaneously a predator and a prey in a food chain. Mutations that change
the interactions are supposed to occur randomly at a low rate. Extinctions of
populations result naturally from the predator-prey dynamics. The model is not
pinned in a fitness variable, and natural selection arises from the dynamics.Comment: 16 pages (LaTeX type, RevTeX style), including 6 figures in gif
format. To be published in Phys. Rev. E (prob. Dic. 96
A General Formalism for Inhomogeneous Random Graphs
We present and investigate an extension of the classical random graph to a
general class of inhomogeneous random graph models, where vertices come in
different types, and the probability of realizing an edge depends on the types
of its terminal vertices. This approach provides a general framework for the
analysis of a large class of models. The generic phase structure is derived
using generating function techniques, and relations to other classes of models
are pointed out.Comment: 7 pages, no figures. To appear in Phys. Rev.
Bloggers Behavior and Emergent Communities in Blog Space
Interactions between users in cyberspace may lead to phenomena different from
those observed in common social networks. Here we analyse large data sets about
users and Blogs which they write and comment, mapped onto a bipartite graph. In
such enlarged Blog space we trace user activity over time, which results in
robust temporal patterns of user--Blog behavior and the emergence of
communities. With the spectral methods applied to the projection on weighted
user network we detect clusters of users related to their common interests and
habits. Our results suggest that different mechanisms may play the role in the
case of very popular Blogs. Our analysis makes a suitable basis for theoretical
modeling of the evolution of cyber communities and for practical study of the
data, in particular for an efficient search of interesting Blog clusters and
further retrieval of their contents by text analysis
Line Graphs of Weighted Networks for Overlapping Communities
In this paper, we develop the idea to partition the edges of a weighted graph
in order to uncover overlapping communities of its nodes. Our approach is based
on the construction of different types of weighted line graphs, i.e. graphs
whose nodes are the links of the original graph, that encapsulate differently
the relations between the edges. Weighted line graphs are argued to provide an
alternative, valuable representation of the system's topology, and are shown to
have important applications in community detection, as the usual node partition
of a line graph naturally leads to an edge partition of the original graph.
This identification allows us to use traditional partitioning methods in order
to address the long-standing problem of the detection of overlapping
communities. We apply it to the analysis of different social and geographical
networks.Comment: 8 Pages. New title and text revisions to emphasise differences from
earlier paper
Book Reviews
Review of New Perspectives in Archeology, by Sally R. Binford and Lewis R. Binford, eds.; The Archaeology of Ancient China, by Kwang-chih Chang; Prehistoric Animals and Their Hunters, by I. W. Cornwall; Contes Malgaches en Dialecte Sakalava: Textes, Traduction, Grammaire et Lexique, by Otto Chr. Dahl; An Ethnographic Bibliography of New Guinea; Archaeology on the Island of Mo'orea, French Polynesia, by Roger C. Green, Kaye Green, Roy Rappaport, Ann Rappaport, and Janet Davidson; Polynesian Culture History: Essays in Honor of Kenneth P. Emory, by Genevieve A. Highland, et al.; Computer Analysis of Chronological Seriation, by Frank Hole and Mary Shaw; Prehistoric Japanese Arts: Jomon Pottery, by J. Edward Kidder and Teruya Esaka; A Selected and Annotated Bibliography of Korean Anthropology, by Eugene I. Knez and Chang-Su Swanson; Die Religionen der Sudsee und Australiens, by Hans Nevermann, Ernest A. Worms, and Helmut Petri; Geschichte und Sozialordnung der Sherpa, by Michael Oppitz; The Vermilion Bird: T'ang Images of the South, by Edward H. Schafer; Fijian Material Culture: A Study of Cultural Context, Function, and Change, by Alan Richard Tippett
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