2,230 research outputs found
Parent, Child and Public Involvement in Child Health Research: Core value not just an optional extra
Non-equilibrium mean-field theories on scale-free networks
Many non-equilibrium processes on scale-free networks present anomalous
critical behavior that is not explained by standard mean-field theories. We
propose a systematic method to derive stochastic equations for mean-field order
parameters that implicitly account for the degree heterogeneity. The method is
used to correctly predict the dynamical critical behavior of some binary spin
models and reaction-diffusion processes. The validity of our non-equilibrium
theory is furtherly supported by showing its relation with the generalized
Landau theory of equilibrium critical phenomena on networks.Comment: 4 pages, no figures, major changes in the structure of the pape
Solution of the 2-star model of a network
The p-star model or exponential random graph is among the oldest and
best-known of network models. Here we give an analytic solution for the
particular case of the 2-star model, which is one of the most fundamental of
exponential random graphs. We derive expressions for a number of quantities of
interest in the model and show that the degenerate region of the parameter
space observed in computer simulations is a spontaneously symmetry broken phase
separated from the normal phase of the model by a conventional continuous phase
transition.Comment: 5 pages, 3 figure
Percolation in invariant Poisson graphs with i.i.d. degrees
Let each point of a homogeneous Poisson process in R^d independently be
equipped with a random number of stubs (half-edges) according to a given
probability distribution mu on the positive integers. We consider
translation-invariant schemes for perfectly matching the stubs to obtain a
simple graph with degree distribution mu. Leaving aside degenerate cases, we
prove that for any mu there exist schemes that give only finite components as
well as schemes that give infinite components. For a particular matching scheme
that is a natural extension of Gale-Shapley stable marriage, we give sufficient
conditions on mu for the absence and presence of infinite components
Dynamic ploidy changes drive fluconazole resistance in human cryptococcal meningitis.
BACKGROUND: Cryptococcal meningitis (CM) causes an estimated 180,000 deaths annually, predominantly in sub-Saharan Africa, where most patients receive fluconazole (FLC) monotherapy. While relapse after FLC monotherapy with resistant strains is frequently observed, the mechanisms and impact of emergence of FLC resistance in human CM are poorly understood. Heteroresistance (HetR) - a resistant subpopulation within a susceptible strain - is a recently described phenomenon in Cryptococcus neoformans (Cn) and Cryptococcus gattii (Cg), the significance of which has not previously been studied in humans. METHODS: A cohort of 20 patients with HIV-associated CM in Tanzania was prospectively observed during therapy with either FLC monotherapy or in combination with flucytosine (5FC). Total and resistant subpopulations of Cryptococcus spp. were quantified directly from patient cerebrospinal fluid (CSF). Stored isolates underwent whole genome sequencing and phenotypic characterization. RESULTS: Heteroresistance was detectable in Cryptococcus spp. in the CSF of all patients at baseline (i.e., prior to initiation of therapy). During FLC monotherapy, the proportion of resistant colonies in the CSF increased during the first 2 weeks of treatment. In contrast, no resistant subpopulation was detectable in CSF by day 14 in those receiving a combination of FLC and 5FC. Genomic analysis revealed high rates of aneuploidy in heteroresistant colonies as well as in relapse isolates, with chromosome 1 (Chr1) disomy predominating. This is apparently due to the presence on Chr1 of ERG11, which is the FLC drug target, and AFR1, which encodes a drug efflux pump. In vitro efflux levels positively correlated with the level of heteroresistance. CONCLUSION: Our findings demonstrate for what we believe is the first time the presence and emergence of aneuploidy-driven FLC heteroresistance in human CM, association of efflux levels with heteroresistance, and the successful suppression of heteroresistance with 5FC/FLC combination therapy. FUNDING: This work was supported by the Wellcome Trust Strategic Award for Medical Mycology and Fungal Immunology 097377/Z/11/Z and the Daniel Turnberg Travel Fellowship
The Donegal Mackerel Fishery
Irish Mackerel landings have increased dramatically, from less than 2,000 tonnes in 1970 to nearly 30,000 tonnes in 1978. The development of this fishery can be ensured only if a satisfactory management plan is drawn up. To provide the basis for such a plan a major investigation of the Donegal stocks was launched by the Department of Fisheries in 1978 and will continue for some years. At the same time the fishery scientists of other countries are studying other parts of the same mackerel stock and their results are discussed at an annual meeting in Copenhagen. These results are the basis for the total allowable catch imposed by the EEC
Statistical ensemble of scale-free random graphs
A thorough discussion of the statistical ensemble of scale-free connected
random tree graphs is presented. Methods borrowed from field theory are used to
define the ensemble and to study analytically its properties. The ensemble is
characterized by two global parameters, the fractal and the spectral
dimensions, which are explicitly calculated. It is discussed in detail how the
geometry of the graphs varies when the weights of the nodes are modified. The
stability of the scale-free regime is also considered: when it breaks down,
either a scale is spontaneously generated or else, a "singular" node appears
and the graphs become crumpled. A new computer algorithm to generate these
random graphs is proposed. Possible generalizations are also discussed. In
particular, more general ensembles are defined along the same lines and the
computer algorithm is extended to arbitrary (degenerate) scale-free random
graphs.Comment: 10 pages, 6 eps figures, 2-column revtex format, minor correction
The structure of typical clusters in large sparse random configurations
The initial purpose of this work is to provide a probabilistic explanation of
a recent result on a version of Smoluchowski's coagulation equations in which
the number of aggregations is limited. The latter models the deterministic
evolution of concentrations of particles in a medium where particles coalesce
pairwise as time passes and each particle can only perform a given number of
aggregations. Under appropriate assumptions, the concentrations of particles
converge as time tends to infinity to some measure which bears a striking
resemblance with the distribution of the total population of a Galton-Watson
process started from two ancestors. Roughly speaking, the configuration model
is a stochastic construction which aims at producing a typical graph on a set
of vertices with pre-described degrees. Specifically, one attaches to each
vertex a certain number of stubs, and then join pairwise the stubs uniformly at
random to create edges between vertices. In this work, we use the configuration
model as the stochastic counterpart of Smoluchowski's coagulation equations
with limited aggregations. We establish a hydrodynamical type limit theorem for
the empirical measure of the shapes of clusters in the configuration model when
the number of vertices tends to . The limit is given in terms of the
distribution of a Galton-Watson process started with two ancestors
Effect of jet exit vanes on flow pulsations in an open-jet wind tunnel
An investigation was conducted of various jet exit vane configurations in the open test section of the Langley 4- by 7-Meter Tunnel to determine their effectiveness in reducing flow pulsations. The data consist of the instantaneous velocity fluctuations measured with hot-wire anemometers located at the tunnel centerline, 39.5 ft (12.0) downstream of the jet exit. The data are presented in the form of measured root-mean-square turbulence levels in the test section and a time series analysis for the baseline jet exit configuration (without vanes) and forthe most effective vane configuration, which consisted of triangular vanes alternating into and out of the flow around the jet exit
Exact Solution for the Time Evolution of Network Rewiring Models
We consider the rewiring of a bipartite graph using a mixture of random and
preferential attachment. The full mean field equations for the degree
distribution and its generating function are given. The exact solution of these
equations for all finite parameter values at any time is found in terms of
standard functions. It is demonstrated that these solutions are an excellent
fit to numerical simulations of the model. We discuss the relationship between
our model and several others in the literature including examples of Urn,
Backgammon, and Balls-in-Boxes models, the Watts and Strogatz rewiring problem
and some models of zero range processes. Our model is also equivalent to those
used in various applications including cultural transmission, family name and
gene frequencies, glasses, and wealth distributions. Finally some Voter models
and an example of a Minority game also show features described by our model.Comment: This version contains a few footnotes not in published Phys.Rev.E
versio
- …