2,510 research outputs found

    A Polynomial-time Bicriteria Approximation Scheme for Planar Bisection

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    Given an undirected graph with edge costs and node weights, the minimum bisection problem asks for a partition of the nodes into two parts of equal weight such that the sum of edge costs between the parts is minimized. We give a polynomial time bicriteria approximation scheme for bisection on planar graphs. Specifically, let WW be the total weight of all nodes in a planar graph GG. For any constant Δ>0\varepsilon > 0, our algorithm outputs a bipartition of the nodes such that each part weighs at most W/2+ΔW/2 + \varepsilon and the total cost of edges crossing the partition is at most (1+Δ)(1+\varepsilon) times the total cost of the optimal bisection. The previously best known approximation for planar minimum bisection, even with unit node weights, was O(log⁥n)O(\log n). Our algorithm actually solves a more general problem where the input may include a target weight for the smaller side of the bipartition.Comment: To appear in STOC 201

    Fractional diffusion emulates a human mobility network during a simulated disease outbreak

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    From footpaths to flight routes, human mobility networks facilitate the spread of communicable diseases. Control and elimination efforts depend on characterizing these networks in terms of connections and flux rates of individuals between contact nodes. In some cases, transport can be parameterized with gravity-type models or approximated by a diffusive random walk. As a alternative, we have isolated intranational commercial air traffic as a case study for the utility of non-diffusive, heavy-tailed transport models. We implemented new stochastic simulations of a prototypical influenza-like infection, focusing on the dense, highly-connected United States air travel network. We show that mobility on this network can be described mainly by a power law, in agreement with previous studies. Remarkably, we find that the global evolution of an outbreak on this network is accurately reproduced by a two-parameter space-fractional diffusion equation, such that those parameters are determined by the air travel network.Comment: 26 pages, 4 figure

    Vehicle lead-acid battery state-of-charge meter

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    We describe a state-of-charge, or “residual-capacity” meter for lead-acid batteries that intelligently synthesizes coulometric and terminal-voltage methods in a new algorithm to provide reliable, continuous readout of remaining capacity. Novel electronic circuit design eliminates the need to install a shunt in the vehicle. The meter learns the characteristics of a battery to which it is attached, removing the need for setup, customisation, programming or calibration at time of installation or battery replacement. The meter can thus be installed by unqualified personnel. Initial measurements suggest the design to be robust and accurate

    A Feasibility Template for Small, Multi-Species Meat Processing Plants

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    This article describes a spreadsheet-based template designed to help livestock producers and others examine the feasibility of operating a small, multi-species meat processing plant. The template allows users to define plant size and capacity, including the breakdown of processing activities by species and additional revenue opportunities. The spreadsheet utilizes user-defined information on capital and operating costs to develop depreciation schedules, loan amortization schedules, 10-year profit/loss projections, cash flow projections, and various measure of return on investment. An imbedded user\u27s guide and a companion how to use video helps template users examine the financial feasibility of a meat plant venture

    Integration of a contaminant source land use regression model in the Bayesian Maximum Entropy spatiotemporal geostatistical estimation of groundwater tetrachloroethylene across North Carolina

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    The assessment of groundwater tetrachloroethylene (PCE or PERC) exposure across North Carolina is currently hindered due to limited statewide spatiotemporal contaminant maps. In this study we incorporate data from multiple sources to create estimation maps of groundwater PCE. A land use regression (LUR) mean trend model was developed as a function of exponentially decaying contribution from contaminant sources in North Carolina. This mean trend model was integrated in a Bayesian Maximum Entropy (BME) framework to produce informative space/time (S/T) maps. We compare our method with standard geostatistical methods (i.e. kriging and BME with constant mean trends) and find a 25 % reduction in cross-validation mean square error. Our results suggest that dry cleaning and hazardous waste generator sites influence groundwater at distances of 1 km and 800 m respectively. This work introduces a novel integrated LUR and BME approach which produces accurate visual representations of PCE exposure across North Carolina

    Experimental Phase-equilibrium Constraints on the Phonolite Magmatic System of Erebus Volcano, Antarctica

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    International audienceField observations and petrological studies have recently advanced understanding of the magmatic system of Erebus volcano, renowned for its sustained CO2-rich degassing, and long-lived phonolitic lava lake. However, this body of work has highlighted uncertainty in several key parameters, including the magma temperature, redox state and the depth of the reservoir presumed to maintain the lava lake. Here, we use experimentally determined phase equilibria to constrain these unknowns. The experiments ranged in temperature from 900 to 1025°C, in pressure from atmospheric to 300 MPa, in water content from 0 to 8 wt %, and in oxygen fugacity from NNO + 4 (where NNO is nickel-nickel oxide) to QFM - 2 (where QFM is quartz-fayalite-magnetite). The natural system was experimentally reproduced at 950 ± 25°C, a pressure below 200 MPa, redox conditions between QFM and QFM - 1, and remarkably low water contents of less than 0*5 wt %. These findings help in understanding petrological observations, including melt inclusion data, as well as the measured composition of gas emissions from the lava lake. Biotite and amphibole appear in the crystallization sequence at around 925°C, even under very dry conditions (biotite). Both biotite and amphibole are absent in the phonolites erupted over the last 20 kyr at Erebus. The constant abundance of anorthoclase observed in the erupted lavas and bombs indicates that the shallow magmatic system feeding the Erebus lava lake (below pressures of 200 MPa) has been thermally buffered at 950 ± 25°C over this time period, possibly reflecting steady-state connection with the deep feeding system rooted in the mantle. Combined with recent seismological data, our results suggest that if a large phonolitic reservoir exists, then it should lie in the depth range 4-7*5 km. The tight constraints on temperature and redox conditions will be valuable for future thermodynamical and rheological modelling

    Leaders Like Me

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    The Workshop Program at the University of Rochester infuses collaborative learning into a variety of introductory STEM and non-STEM courses through small, weekly, peer-led problem solving sessions called Workshops. Decades of data from these Workshops indicate that 1) African American, Black, Hispanic, and Latinx students are less likely to attend them than White and Asian students and 2) that every additional Workshop students attend improves their final course grades, even if they only miss a single Workshop out of the 13 or 14 that are offered each semester. To address this situation, the UR Workshop Program has partnered with the People Like Me project at Bucknell University. Before the start of the Fall 2018 semester, Workshop leaders were asked to respond to the People Like Me survey questions, and we crafted their responses into profiles. We then posted these profiles for students in the courses to view on a platform on which we could track those views at the individual student level. In this work-in-progress, we hope to answer the question: to what extent does viewing personal information about Workshop leaders affect students\u27 likelihood to attend Workshops
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