13,581 research outputs found

    Numerical modeling of the interstellar medium in galactic disks

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    We have been developing detailed hydrodynamic models of the global interstellar medium in the hope of understanding the mass and volume occupied by various phases, as well as their structure and kinematics. In our model, the gas is modeled by one fluid while representative Pop 1 stars are modeled by a second fluid. The two fluids are coupled in that the gas forms into stars at a rate given by a Schmidt law while stellar mass loss returns matter into the gas phase (on a time scale of 100 Myr). Also, the stars heat the gas through stellar winds and the gas cools through optically thin radiation. The time behavior of these two fluids is studied in two spatial dimensions with the Eulerian finite difference numerical hydrodynamic code Zen. The two spatial dimensions are along the plane of a disk (x, total length of 2 kpc) and perpendicular to the disk (z, total height of +/- 15 kpc) and a galactic gravitational field in the z direction, typical of that at the solar circle, is imposed upon the simulation; self-gravity and rotation are absent. For the boundary conditions, outflow is permitted at the top and bottom of the grid (z = +/- 15 kpc) while periodic boundary conditions are imposed upon left and right sides of the grid. As initial conditions, we assumed a gaseous distribution like that seen for the H1 by earlier researchers, although the results are insensitive to the initial conditions. We have run simulations in which the heating due to stars, parameterized as a stellar wind velocity, a, is varied from low (a = 150 km/s), to intermediate (a = 300 km/s), to high (a = 600 km/s). Since the intermediate case is roughly equivalent to the Galactic energy injection rate from supernovae, this summary will concentrate on results from this simulation

    Hot Spots on the Fermi Surface of Bi2212: Stripes versus Superstructure

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    In a recent paper Saini et al. have reported evidence for a pseudogap around (pi,0) at room temperature in the optimally doped superconductor Bi2212. This result is in contradiction with previous ARPES measurements. Furthermore they observed at certain points on the Fermi surface hot spots of high spectral intensity which they relate to the existence of stripes in the CuO planes. They also claim to have identified a new electronic band along Gamma-M1 whose one dimensional character provides further evidence for stripes. We demonstrate in this Comment that all the measured features can be simply understood by correctly considering the superstructure (umklapp) and shadow bands which occur in Bi2212.Comment: 1 page, revtex, 1 encapsulated postscript figure (color

    Honey bee colony losses

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    Buffalo Clover

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    Two clovers native to Kentucky, buffalo clover (Trifolium reflexum) and running buffalo clover (T. stoloniferum) recently have been re-discovered. These clovers were common in Kentucky until about 1850. Their names are derived from the fact that they occurred mostly along buffalo trails through woods. Historical records indicate that buffalo clover occurred on drier and less fertile soils of the former Big Barren Region and the Shawnee Hills, whereas running buffalo clover was widespread on moist, fertile soils in the Bluegrass Region. Both are now extremely rare in Kentucky. At present buffalo clover has been found in Mammoth Cave National Park, and running buffalo clover in Boone, Bourbon and Fayette Counties. Running buffalo clover has been designated as a federally endangered species

    Implementing a Business Process Management System Using ADEPT: A Real-World Case Study

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    This article describes how the agent-based design of ADEPT (advanced decision environment for processed tasks) and implementation philosophy was used to prototype a business process management system for a real-world application. The application illustrated is based on the British Telecom (BT) business process of providing a quote to a customer for installing a network to deliver a specified type of telecommunication service. Particular emphasis is placed upon the techniques developed for specifying services, allowing heterogeneous information models to interoperate, allowing rich and flexible interagent negotiation to occur, and on the issues related to interfacing agent-based systems and humans. This article builds upon the companion article (Applied Artificial Intelligence Vol.14, no 2, pgs. 145-189) that provides details of the rationale and design of the ADEPT technology deployed in this application

    Stress-State Adaptation Of Human Femur Increases Its Effective Fracture Toughness

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    Faktor-faktor Yang Mempengaruhi Tingkat Pengangguran Di Daerah Istimewa YOGYAKARTA (DIY) Tahun 1985-2011

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    This study aims to identify and analyze the efect of economic growth, real minimum wages, infation and the economic crisis in Indonesia in 1998 on the unemployment rate in the Special Region of Yogyakarta (DIY) in the 1985-2011 period. The data used are secondary data obtained from the Central Bureau of Statistics published in the various editions. Te analytical tool used to answer the problem formulation is the regression analysis using partial adjustment models (PAM). The analysis and hypothesis testing show that the economic growth, infation rate and the period of economic crisis in Indonesia in 1998 have a signifcant efect on the unemployment rate in the province, while the real minimum wage has no efect on the unemployment rate in the province
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