3,801 research outputs found
Dynamical Encoding by Networks of Competing Neuron Groups: Winnerless Competition
Following studies of olfactory processing in insects and fish, we investigate neural networks whose dynamics in phase space is represented by orbits near the heteroclinic connections between saddle regions (fixed points or limit cycles). These networks encode input information as trajectories along the heteroclinic connections. If there are N neurons in the network, the capacity is approximately e(N-1)!, i.e., much larger than that of most traditional network structures. We show that a small winnerless competition network composed of FitzHugh-Nagumo spiking neurons efficiently transforms input information into a spatiotemporal output
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Aryl Hydrocarbon Receptor-Dependent inductions of omega-3 and omega-6 polyunsaturated fatty acid metabolism act inversely on tumor progression.
The Western diet contains a high ratio of omega-6 (Ï6) to omega-3 (Ï3) polyunsaturated fatty acids (PUFA). The prototypical aryl hydrocarbon receptor (AHR) ligand, 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD), induces CYP1 family enzymes, which can metabolize PUFA to epoxides. Mice fed Ï3-rich or Ï6-rich diets were treated with TCDD and injected subcutaneously with AHR-competent Hepa1-GFP hepatoma cells or AHR-deficient LLC lung cancer cells. TCDD reduced the growth rates of the resulting tumors in Ï3-fed mice and inhibited their metastasis to the liver and/or lung, but had the opposite effects in mice fed Ï6 PUFA. These responses were likely attributable to the corresponding PUFA epoxides generated in tumor cells and/or host, since many depended upon co-administration of a soluble epoxide hydrolase (EPHX2) inhibitor in males, and/or were associated with increases in epoxide levels in tumors and sites of metastasis. Equivalent effects occurred in females in the absence of EPHX2 inhibition, probably because this sex expressed reduced levels of EPHX2. The responses elicited by TCDD were associated with effects on tumor vascularity, tumor cell proliferation and/or apoptosis. Thus environmental AHR agonists, and potentially also endogenous, nutritional, and microbiome-derived agonists, may reduce or enhance cancer progression depending on the composition of dietary PUFA, particularly in females
Contact tracing and epidemics control in social networks
A generalization of the standard susceptible-infectious-removed (SIR)
stochastic model for epidemics in sparse random networks is introduced which
incorporates contact tracing in addition to random screening. We propose a
deterministic mean-field description which yields quantitative agreement with
stochastic simulations on random graphs. We also analyze the role of contact
tracing in epidemics control in small-world networks and show that its
effectiveness grows as the rewiring probability is reduced.Comment: 4 pages, 4 figures, submitted to PR
Free Form of the Foldy-Wouthuysen Transformation in External Electromagnetic Fields
We derive the exact Foldy-Wouthuysen transformation for Dirac fermions in a
time independent external electromagnetic field in the basis of the Ritus
eigenfunctions, namely the eigenfunctions of the operator , with . In this basis, the transformation
acquires a free form involving the dynamical quantum numbers induced by the
field.Comment: 8 pages. Accepted in J. Phys. A: Math. and Theo. (Fast Track
Communication
Vibration-induced granular segregation: a phenomenon driven by three mechanisms
The segregation of large spheres in a granular bed under vertical vibrations
is studied. In our experiments we systematically measure rise times as a
function of density, diameter and depth; for two different sinusoidal
excitations. The measurements reveal that: at low frequencies, inertia and
convection are the only mechanisms behind segregation. Inertia (convection)
dominates when the relative density is greater (less) than one. At high
frequencies, where convection is suppressed, fluidization of the granular bed
causes either buoyancy or sinkage and segregation occurs.Comment: 4 pages. 3 figures, revtex4, to appear in PRL (in press
Entanglement and alpha entropies for a massive scalar field in two dimensions
We find the analytic expression of the trace of powers of the reduced density
matrix on an interval of length L, for a massive boson field in 1+1 dimensions.
This is given exactly (except for a non universal factor) in terms of a finite
sum of solutions of non linear differential equations of the Painlev\'e V type.
Our method is a generalization of one introduced by Myers and is based on the
explicit calculation of quantities related to the Green function on a plane,
where boundary conditions are imposed on a finite cut. It is shown that the
associated partition function is related to correlators of exponential
operators in the Sine-Gordon model in agreement with a result by Delfino et al.
We also compute the short and long distance leading terms of the entanglement
entropy. We find that the bosonic entropic c-function interpolates between the
Dirac and Majorana fermion ones given in a previous paper. Finally, we study
some universal terms for the entanglement entropy in arbitrary dimensions
which, in the case of free fields, can be expressed in terms of the two
dimensional entropy functions.Comment: 13 pages, 2 figure
Mirror matter admixtures and isospin breaking in the \Delta I=1/2 rule in \Omega^- two body non-leptonic decays
We discuss a description of \Omega^- two body non-leptonic decays based on
possible, albeit tiny, admixtures of mirror matter in ordinary hadrons. The
\Delta I=1/2 rule enhancement is obtained as a result of isospin symmetry and,
more importantly, the rather large observed deviations from this rule result
from small isospin breaking. This analysis lends support to the possibility
that the enhancement phenomenon observed in low energy weak interactions may be
systematically described by mirror matter admixtures in ordinary hadrons.Comment: Changed conten
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