795 research outputs found

    Slow epidemic extinction in populations with heterogeneous infection rates

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    We explore how heterogeneity in the intensity of interactions between people affects epidemic spreading. For that, we study the susceptible-infected-susceptible model on a complex network, where a link connecting individuals ii and jj is endowed with an infection rate βij=λwij\beta_{ij} = \lambda w_{ij} proportional to the intensity of their contact wijw_{ij}, with a distribution P(wij)P(w_{ij}) taken from face-to-face experiments analyzed in Cattuto et  al.et\;al. (PLoS ONE 5, e11596, 2010). We find an extremely slow decay of the fraction of infected individuals, for a wide range of the control parameter λ\lambda. Using a distribution of width aa we identify two large regions in the aλa-\lambda space with anomalous behaviors, which are reminiscent of rare region effects (Griffiths phases) found in models with quenched disorder. We show that the slow approach to extinction is caused by isolated small groups of highly interacting individuals, which keep epidemic alive for very long times. A mean-field approximation and a percolation approach capture with very good accuracy the absorbing-active transition line for weak (small aa) and strong (large aa) disorder, respectively

    The Mainstreaming of US Games Journalism

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    Single Electron Transistors

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    Contains description of one research project and a list of publications.Joint Services Electronics Program Contract DAAL03-92-C-0001National Science Foundation Grant ECS 88-13250National Science Foundation Grant ECS 92-0342

    Is there a link between urinary microbiota and bladder cancer?

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    Magnetic Field Dependence of the Level Spacing of a Small Electron Droplet

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    The temperature dependence of conductance resonances is used to measure the evolution with the magnetic field of the average level spacing Δϵ\Delta\epsilon of a droplet containing 30\sim 30 electrons created by lateral confinement of a two-dimensional electron gas in GaAs. Δϵ\Delta\epsilon becomes very small (<30μ< 30\mueV) near two critical magnetic fields at which the symmetry of the droplet changes and these decreases of Δϵ\Delta\epsilon are predicted by Hartree-Fock (HF) for charge excitations. Between the two critical fields, however, the largest measured Δϵ=100μ\Delta\epsilon= 100\mueV is an order of magnitude smaller than predicted by HF but comparable to the Zeeman splitting at this field, which suggests that the spin degrees of freedom are important. PACS: 73.20.Dx, 73.20.MfComment: 11 pages of text in RevTeX, 4 figures in Postscript (files in the form of uuencoded compressed tar file

    Single Wall Nanotubes: Atomic Like Behaviour and Microscopic Approach

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    Recent experiments about the low temperature behaviour of a Single Wall Carbon Nanotube (SWCNT) showed typical Coulomb Blockade (CB) peaks in the zero bias conductance and allowed us to investigate the energy levels of interacting electrons. Other experiments confirmed the theoretical prediction about the crucial role which the long range nature of the Coulomb interaction plays in the correlated electronic transport through a SWCNT with two intramolecular tunneling barriers. In order to investigate the effects on low dimensional electron systems due to the range of electron electron repulsion, we introduce a model for the interaction which interpolates well between short and long range regimes. Our results could be compared with experimental data obtained in SWCNTs and with those obtained for an ideal vertical Quantum Dot (QD). For a better understanding of some experimental results we also discuss how defects and doping can break some symmetries of the bandstructure of a SWCNT.Comment: 8 pages, 4 figure

    Risk factors for otitis media and carriage of multiple strains of Haemophilus influenzae and Streptococcus pneumoniae.

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    We studied genetic diversity in Streptococcus pneumoniae and Haemophilus influenzae in throat culture isolates from 38 children attending two day-care centers in Michigan. Culture specimens were collected weekly; 184 S. pneumoniae and 418 H. influenzae were isolated from the cultures. Pulsed-field gel electrophoresis identified 29 patterns among the S. pneumoniae isolates and 87 among the H. influenzae isolates. Of the cultures, 5% contained multiple genetic types of S. pneumoniae, and 43% contained multiple types of H. influenzae. Carriage of multiple H. influenzae isolates, which was associated with exposure to smoking, history of allergies, and age 36 to 47 months, may increase risk for otitis media in children
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