8,792 research outputs found

    Good Edge, Bad Edge: How Network Structure Affects a Group’s Ability to Coordinate

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    Coordination is a core concern in social science. Problems as diverse as deciding where to go to dinner, what price to charge for a good or service, which political candidate to support or what regulatory policy to adopt all contain coordination as a core element. Most coordination problems arise among actors connected in a network, and these connections can both improve and impede a group’s ability to achieve coordination. To model how links influence coordination we distinguish between “constraining edges” that make coordination harder by reducing the number of equilibrium outcomes, and “redundant edges” that make coordination easier by merely increasing communication without affecting the number of equilibria. We show experimentally that the addition of constraining edges reduces coordination, while redundant edges improve subjects’ ability to solve a coordination problem

    Accurate Realizations of the Ionized Gas in Galaxy Clusters: Calibrating Feedback

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    Using the full, three-dimensional potential of galaxy cluster halos (drawn from an N-body simulation of the current, most favored cosmology), the distribution of the X-ray emitting gas is found by assuming a polytropic equation of state and hydrostatic equilibrium, with constraints from conservation of energy and pressure balance at the cluster boundary. The resulting properties of the gas for these simulated redshift zero clusters (the temperature distribution, mass-temperature and luminosity-temperature relations, and the gas fraction) are compared with observations in the X-ray of nearby clusters. The observed properties are reproduced only under the assumption that substantial energy injection from non-gravitational sources has occurred. Our model does not specify the source, but star formation and AGN may be capable of providing this energy, which amounts to 3 to 5 x10^{-5} of the rest mass in stars (assuming ten percent of the gas initially in the cluster forms stars). With the method described here it is possible to generate realistic X-ray and Sunyaev-Zel'dovich cluster maps and catalogs from N-body simulations, with the distributions of internal halo properties (and their trends with mass, location, and time) taken into account.Comment: Matches ApJ published version; 30 pages, 7 figure

    Dispersive magnetic excitations in the S=1 antiferromagnet Ba3_3Mn2_2O8_8

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    We present powder inelastic neutron scattering measurements of the S=1 dimerized antiferromagnet Ba3_3Mn2_2O8_8. The T=1.4T=1.4 K magnetic spectrum exhibits a spin-gap of Δ1.0\Delta \approx 1.0 meV and a dispersive spectrum with a bandwidth of approximately 1.5 meV. Comparison to coupled dimer models describe the dispersion and scattering intensity accurately and determine the exchange constants in Ba3_3Mn2_2O8_8. The wave vector dependent scattering intensity confirms the proposed S=1 dimer bond. Temperature dependent measurements of the magnetic excitations indicate the presence of both singlet-triplet and thermally activated triplet-quintet excitations.Comment: 8 pages, 8 figures, Submitted to Physical Review B, Resubmited versio

    Beyond the random phase approximation in the Singwi-Sj\"olander theory of the half-filled Landau level

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    We study the ν=1/2\nu=1/2 Chern-Simons system and consider a self-consistent field theory of the Singwi-Sj\"olander type which goes beyond the random phase approximation (RPA). By considering the Heisenberg equation of motion for the longitudinal momentum operator, we are able to show that the zero-frequency density-density response function vanishes linearly in long wavelength limit independent of any approximation. From this analysis, we derive a consistency condition for a decoupling of the equal time density-density and density-momentum correlation functions. By using the Heisenberg equation of motion of the Wigner distribution function with a decoupling of the correlation functions which respects this consistency condition, we calculate the response functions of the ν=1/2\nu=1/2 system. In our scheme, we get a density-density response function which vanishes linearly in the Coulomb case for zero-frequency in the long wavelength limit. Furthermore, we derive the compressibility, and the Landau energy as well as the Coulomb energy. These energies are in better agreement to numerical and exact results, respectively, than the energies calculated in the RPA.Comment: 9 Revtex pages, 4 eps figures, typos correcte

    Prediction of a surface state and a related surface insulator-metal transition for the (100) surface of stochiometric EuO

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    We calculate the temperature and layer-dependent electronic structure of a 20-layer EuO(100)-film using a combination of first-principles and model calculation based on the ferromagnetic Kondo-lattice model. The results suggest the existence of a EuO(100) surface state which can lead to a surface insulator-metal transition.Comment: 9 pages, 5 figures, Phys. Rev. Lett. (in press

    Performance measures in three rounds of the English bowel cancer screening pilot

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    OBJECTIVES: To compare performance measures across all three rounds of the English bowel cancer screening faecal occult blood test pilot and their relation to social deprivation and ethnicity. METHODS: In each round in three primary care trusts, data for a restricted population of over 48 500 aged 60–69 years were analysed. Individual-based data included postcode linked to area-based data on the Index of Multiple Deprivation (IMD) 2004, and ethnicity. Outcomes were the rates of screening and colonoscopy uptake, positivity and detection of neoplasia (adenomas or bowel cancer) and bowel cancer, and the positive predictive values (PPVs) of a positive test for neoplasia and bowel cancer. Sensitivity was calculated by the proportional incidence method using data on interval cancers identified from cancer registrations. RESULTS: The overall uptake rate was 61.8%, 57.0% and 58.7% in the first, second and third rounds, respectively. Although the PPV for cancer decreased over the course of the three rounds (10.9% in the 1st round, 6.5% in 3rd round), the PPV for all neoplasia remained relatively constant (42.6% in 1st round, 36.9% in 3rd round). Deprivation and non-white ethnic background (principally Indian subcontinent in the pilot region) were associated with low screening and colonoscopy uptake rates, and this changed little over the three screening rounds. Uptake was lower in men, although differences in uptake between men and women decreased over time. Non-participation in previous rounds was a strong predictor of low uptake. CONCLUSIONS: Performance measures are commensurate with expectations in a screening programme reaching its third round of screening, but a substantial ongoing effort is needed, particularly to address the effects of deprivation and ethnicity in relation to uptake
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