20,316 research outputs found
Dynamics of opinion formation in a small-world network
The dynamical process of opinion formation within a model using a local
majority opinion updating rule is studied numerically in networks with the
small-world geometrical property. The network is one in which shortcuts are
added to randomly chosen pairs of nodes in an underlying regular lattice. The
presence of a small number of shortcuts is found to shorten the time to reach a
consensus significantly. The effects of having shortcuts in a lattice of fixed
spatial dimension are shown to be analogous to that of increasing the spatial
dimension in regular lattices. The shortening of the consensus time is shown to
be related to the shortening of the mean shortest path as shortcuts are added.
Results can also be translated into that of the dynamics of a spin system in a
small-world network.Comment: 10 pages, 5 figure
Identity and Search in Social Networks
Social networks have the surprising property of being "searchable": Ordinary
people are capable of directing messages through their network of acquaintances
to reach a specific but distant target person in only a few steps. We present a
model that offers an explanation of social network searchability in terms of
recognizable personal identities: sets of characteristics measured along a
number of social dimensions. Our model defines a class of searchable networks
and a method for searching them that may be applicable to many network search
problems, including the location of data files in peer-to-peer networks, pages
on the World Wide Web, and information in distributed databases.Comment: 4 page, 3 figures, revte
Depression Earlier on in Life Predicts Frailty at 50 Years: Evidence from the 1958 British Birth Cohort Study
Frailty and depression in older ages have a bidirectional relationship, sharing some symptoms and characteristics. Most evidence for this has come from cross-sectional studies, or longitudinal studies with limited follow-up periods. We used data from the National Child Development Study (1958 Birth Cohort) to investigate the relationship between depression and early-onset frailty using a life course perspective. The primary outcome was frailty based on a 30-item inventory of physical health conditions, activities of daily living and cognitive function at 50 years. The main exposure was depression (based on a nine-item Malaise score ≥ 4) measured at 23, 33 and 42 years. We investigated this relationship using multiple logistic regression models adjusted for socio-demographic factors, early life circumstances and health behaviours. In fully adjusted models, when modelled separately, depression at each timepoint was associated with around twice the odds of frailty. An accumulated depression score showed increases in the odds of frailty with each unit increase (once: OR 1.92, 95%CI 1.65, 2.23; twice OR 2.33, 95%CI 1.85, 2.94; thrice: OR 2.95, 95%CI 2.11, 4.11). The public health significance of this finding is that it shows the potential to reduce the physical burden of disease later in life by paying attention to mental health at younger ages
Scale-free networks with tunable degree distribution exponents
We propose and study a model of scale-free growing networks that gives a
degree distribution dominated by a power-law behavior with a model-dependent,
hence tunable, exponent. The model represents a hybrid of the growing networks
based on popularity-driven and fitness-driven preferential attachments. As the
network grows, a newly added node establishes new links to existing nodes
with a probability based on popularity of the existing nodes and a
probability based on fitness of the existing nodes. An explicit form of
the degree distribution is derived within a mean field approach. For
reasonably large , , where the
function is dominated by the behavior of for small
values of and becomes -independent as , and is a
model-dependent exponent. The degree distribution and the exponent
are found to be in good agreement with results obtained by extensive numerical
simulations.Comment: 12 pages, 2 figures, submitted to PR
Finite size effects in perturbed boundary conformal field theories
We discuss the finite-size properties of a simple integrable quantum field
theory in 1+1 dimensions with non-trivial boundary conditions. Novel
off-critical identities between cylinder partition functions of models with
differing boundary conditions are derived.Comment: 7 pages, 11 figures, JHEP proceedings style. Uses epsfig, amssymb.
Talk given at the conference `Nonperturbative Quantum Effects 2000', Pari
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Digital measurement of lightning impulse parameters using curving fitting algorithms
This paper describes the application of curve fitting algorithms to aid the evaluation of lightning impulse parameters. A number of popular curve fitting algorithms have been evaluated and compared. Investigations using the genetic algorithm and other optimisation methods for the purpose of curve fitting have also been carried out and will be described
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Today's problems with the evaluation methods of full lightning impulse parameters as described in IEC 60060-1
In this paper the present problems with the evaluation methods for lightning impulse parameters, as defined in IEC 60060-1, are described. Also the current practice of evaluation in many laboratories world-wide, that is obtained by a questionnaire, is presented. Some of the work performed up the present time and the initial conclusions are reported, then some recommendations are made for future work
Pre-Big Bang Scenario on Self-T-Dual Bouncing Branes
We consider a new class of 5-dimensional dilatonic actions which are
invariant under T-duality transformations along three compact coordinates,
provided that an appropriate potential is chosen. We show that the invariance
remains when we add a boundary term corresponding to a moving 3-brane, and we
study the effects of the T-duality symmetry on the brane cosmological
equations. We find that T-duality transformations in the bulk induce scale
factor duality on the brane, together with a change of sign of the pressure of
the brane cosmological matter. However, in a remarkable analogy with the
Pre-Big Bang scenario, the cosmological equations are unchanged. Finally, we
propose a model where the dual phases are connected through a scattering of the
brane induced by an effective potential. We show how this model can realise a
smooth, non-singular transition between a pre-Big Bang superinflationary
Universe and a post-Big Bang accelerating Universe.Comment: 18 pages, minor typos corrected, Sec. 2 expanded with more details on
the self-T-dual background, Sec.4 and 5 revised accordingly. Version to
appear on JCA
A new possibility for light-quark Dark Matter
Despite many decades of study the physical origin of "dark matter" in the Universe remains elusive. In this letter we calculate the properties of a completely new dark matter candidate - Bose-Einstein condensates formed from a recently discovered bosonic particle in the light-quark sector, the hexaquark. In this first study, we show stable Bose-Einstein condensates could form in the primordial early universe, with a production rate sufficiently large that they are a plausible new candidate for dark matter. Some possible astronomical signatures of such dark matter are also presented
The Number of Incipient Spanning Clusters in Two-Dimensional Percolation
Using methods of conformal field theory, we conjecture an exact form for the
probability that n distinct clusters span a large rectangle or open cylinder of
aspect ratio k, in the limit when k is large.Comment: 9 pages, LaTeX, 1 eps figure. Additional references and comparison
with existing numerical results include
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