24 research outputs found
Adaptive-network models of swarm dynamics
We propose a simple adaptive-network model describing recent swarming
experiments. Exploiting an analogy with human decision making, we capture the
dynamics of the model by a low-dimensional system of equations permitting
analytical investigation. We find that the model reproduces several
characteristic features of swarms, including spontaneous symmetry breaking,
noise- and density-driven order-disorder transitions that can be of first or
second order, and intermittency. Reproducing these experimental observations
using a non-spatial model suggests that spatial geometry may have a lesser
impact on collective motion than previously thought.Comment: 8 pages, 3 figure
Coordination, Differentiation and Fairness in a population of cooperating agents
In a recent paper, we analyzed the self-assembly of a complex cooperation
network. The network was shown to approach a state where every agent invests
the same amount of resources. Nevertheless, highly-connected agents arise that
extract extraordinarily high payoffs while contributing comparably little to
any of their cooperations. Here, we investigate a variant of the model, in
which highly-connected agents have access to additional resources. We study
analytically and numerically whether these resources are invested in existing
collaborations, leading to a fairer load distribution, or in establishing new
collaborations, leading to an even less fair distribution of loads and payoffs.Comment: 10 pages, 3 figure
Meso-scale obstructions to stability of 1D center manifolds for networks of coupled differential equations with symmetric Jacobian
A linear system , , , with , has a one-dimensional center
manifold . If a differential equation
has a one-dimensional center manifold at an equilibrium
then is tangential to with and for stability of
it is necessary that has no spectrum in , i.e.\ if
is symmetric, it has to be negative semi-definite.
We establish a graph theoretical approach to characterize semi-definiteness.
Using spanning trees for the graph corresponding to , we formulate
meso-scale conditions with certain principal minors of which are necessary
for semi-definiteness. We illustrate these results by the example of the
Kuramoto model of coupled oscillators
Patterns of cooperation: fairness and coordination in networks of interacting agents
We study the self-assembly of a complex network of collaborations among
self-interested agents. The agents can maintain different levels of cooperation
with different partners. Further, they continuously, selectively, and
independently adapt the amount of resources allocated to each of their
collaborations in order to maximize the obtained payoff. We show analytically
that the system approaches a state in which the agents make identical
investments, and links produce identical benefits. Despite this high degree of
social coordination some agents manage to secure privileged topological
positions in the network enabling them to extract high payoffs. Our analytical
investigations provide a rationale for the emergence of unidirectional
non-reciprocal collaborations and different responses to the withdrawal of a
partner from an interaction that have been reported in the psychological
literature.Comment: 20 pages, 8 figure
Acquisition and Evolution of Plant Pathogenesis–Associated Gene Clusters and Candidate Determinants of Tissue-Specificity in Xanthomonas
is a large genus of plant-associated and plant-pathogenic bacteria. Collectively, members cause diseases on over 392 plant species. Individually, they exhibit marked host- and tissue-specificity. The determinants of this specificity are unknown. lineage. genome and indicate that differentiation with respect to host- and tissue-specificity involved not major modifications or wholesale exchange of clusters, but subtle changes in a small number of genes or in non-coding sequences, and/or differences outside the clusters, potentially among regulatory targets or secretory substrates
Finishing the euchromatic sequence of the human genome
The sequence of the human genome encodes the genetic instructions for human physiology, as well as rich information about human evolution. In 2001, the International Human Genome Sequencing Consortium reported a draft sequence of the euchromatic portion of the human genome. Since then, the international collaboration has worked to convert this draft into a genome sequence with high accuracy and nearly complete coverage. Here, we report the result of this finishing process. The current genome sequence (Build 35) contains 2.85 billion nucleotides interrupted by only 341 gaps. It covers ∼99% of the euchromatic genome and is accurate to an error rate of ∼1 event per 100,000 bases. Many of the remaining euchromatic gaps are associated with segmental duplications and will require focused work with new methods. The near-complete sequence, the first for a vertebrate, greatly improves the precision of biological analyses of the human genome including studies of gene number, birth and death. Notably, the human enome seems to encode only 20,000-25,000 protein-coding genes. The genome sequence reported here should serve as a firm foundation for biomedical research in the decades ahead
Safety and efficacy of fluoxetine on functional outcome after acute stroke (AFFINITY): a randomised, double-blind, placebo-controlled trial
Background
Trials of fluoxetine for recovery after stroke report conflicting results. The Assessment oF FluoxetINe In sTroke recoverY (AFFINITY) trial aimed to show if daily oral fluoxetine for 6 months after stroke improves functional outcome in an ethnically diverse population.
Methods
AFFINITY was a randomised, parallel-group, double-blind, placebo-controlled trial done in 43 hospital stroke units in Australia (n=29), New Zealand (four), and Vietnam (ten). Eligible patients were adults (aged ≥18 years) with a clinical diagnosis of acute stroke in the previous 2–15 days, brain imaging consistent with ischaemic or haemorrhagic stroke, and a persisting neurological deficit that produced a modified Rankin Scale (mRS) score of 1 or more. Patients were randomly assigned 1:1 via a web-based system using a minimisation algorithm to once daily, oral fluoxetine 20 mg capsules or matching placebo for 6 months. Patients, carers, investigators, and outcome assessors were masked to the treatment allocation. The primary outcome was functional status, measured by the mRS, at 6 months. The primary analysis was an ordinal logistic regression of the mRS at 6 months, adjusted for minimisation variables. Primary and safety analyses were done according to the patient's treatment allocation. The trial is registered with the Australian New Zealand Clinical Trials Registry, ACTRN12611000774921.
Findings
Between Jan 11, 2013, and June 30, 2019, 1280 patients were recruited in Australia (n=532), New Zealand (n=42), and Vietnam (n=706), of whom 642 were randomly assigned to fluoxetine and 638 were randomly assigned to placebo. Mean duration of trial treatment was 167 days (SD 48·1). At 6 months, mRS data were available in 624 (97%) patients in the fluoxetine group and 632 (99%) in the placebo group. The distribution of mRS categories was similar in the fluoxetine and placebo groups (adjusted common odds ratio 0·94, 95% CI 0·76–1·15; p=0·53). Compared with patients in the placebo group, patients in the fluoxetine group had more falls (20 [3%] vs seven [1%]; p=0·018), bone fractures (19 [3%] vs six [1%]; p=0·014), and epileptic seizures (ten [2%] vs two [<1%]; p=0·038) at 6 months.
Interpretation
Oral fluoxetine 20 mg daily for 6 months after acute stroke did not improve functional outcome and increased the risk of falls, bone fractures, and epileptic seizures. These results do not support the use of fluoxetine to improve functional outcome after stroke