81,654 research outputs found
Disk-Halo Interaction - I. Three-Dimensional Evolution of the Galactic Disk
The results of a three-dimensional model for disk-halo interaction are
presented here. The model considers explicitly the input of energy and mass by
isolated a nd correlated supernovae in the disk. Once disrupted by the
explosions, the disk never returns to its initial state. Instead it approaches
a state where a thin HI disk is formed in the Galactic plane overlayed by thick
HI and HII gas disk w ith scale heights of 500 pc and of 1 to 1.5 kpc,
respectively. The upper parts o f the thick HII disk (the diffuse ionized
medium) act as a disk-halo interface a nd its formation and stability are
directly correlated to the supernova rate per unit area in the simulated disk.Comment: 19 pages, 18 figures; to appear in Monthly Notices of Royal
Astronomical Societ
Lisa Blas: Meet Me at the Mason Dixon
The Schmucker Art Gallery at Gettysburg College is extremely pleased to mount the remarkable series of paintings, photographs, and mixed-media installation by contemporary artist Lisa Blas entitled Meet Me at the Mason Dixon. This exhibition is an official part of Gettysburg area’s 150th Commemoration of the American Civil War as well as Gettysburg College’s Kick-Off event for this significant anniversary. Gettysburg provides an especially appropriate backdrop for the exhibition, as the artist took the history of this “hallowed ground” and its current resonances as the subject of her work. Blas traveled the Gettysburg National Military Park, as well as to the Antietam National Battlefield, the Smithsonian Institution, the National Archives and the Museum of the Confederacy in Richmond, Virginia, among many other sites, to investigate how national identity and cultural myths are shaped in response to this momentous period of American history.
The title of this exhibition, Meet Me at the Mason Dixon, invokes an encounter at a historical boundary line known for centuries of conflict. The Mason-Dixon Line originally was intended to solve a British colonial dispute. Later, it divided the northern from the southern United States based on the legality of slavery, and as such, symbolizes the massive fracturing of the country during the American Civil War. To contemporary artist Lisa Blas, however, the Mason-Dixon emblematizes the tensions implicit in the concept of historical memory. How are traumas witnessed and remembered? What becomes codified as history, and what other narratives are thereby repressed? What age-old divisions haunt us in the present? Blas comprehends such questions as open-ended, visualizing the past as fundamentally, and persistently, conflicted. [excerpt]https://cupola.gettysburg.edu/artcatalogs/1006/thumbnail.jp
Traffic Sign Recognition System
The research group CAOS at the Computing Department of the Carlos III University of Madrid, Spain, offers an efficient recognition system for traffic signs using a set of classifiers. This system can be used as part of an active security system in cars. The fact that the system is based on a set of classifiers facilitates a distributed implementation, resulting in cheaper hardware and an improvement in fault-tolerance.Contrato Programa de Comercialización e Internacionalización. Sistema Regional de Investigación Científica e Innovación Tecnológica. (Comunidad de Madrid; Universidad Carlos III de Madrid
From graphs to tensegrity structures: Geometric and symbolic approaches
A form-finding problem for tensegrity structures is studied; given an
abstract graph, we show an algorithm to provide a necessary condition for it to
be the underlying graph of a tensegrity in (typically )
with vertices in general position. Furthermore, for a certain class of graphs
our algorithm allows to obtain necessary and sufficient conditions on the
relative position of the vertices in order to underlie a tensegrity, for what
we propose both a geometric and a symbolic approach.Comment: 17 pages, 8 figures; final versio
A zero-thickness mortar/ interface formulation with application to fracture mechanics
A zero-thickness mortar/interface element formulation is briefly described and demonstrated. This element may be considered as an extension of traditional zero-thickness interface element, in order to represent material interfaces located in between subdomains with non-matching FE meshes. In the context of small strain analysis, these elements may be equipped with the same type of constitutive laws as traditional interface elements. Therefore, if friction or fracture-mechanics-based laws are adopted, mortar/interface elements may be used to represent frictional sliding or cracking following the lines (surfaces) along which they have been pre-inserted. Two basic verification examples of this type are presented, showing that the model can correctly represent uniform states of stress and deformation when connecting unmatched mesh subdomains
Non-relativistic free-free emission due to distribution of electrons - Radiative cooling and thermally averaged and total Gaunt factors
Tracking the thermal evolution of plasmas, characterized by an
n-distribution, using numerical simulations, requires the determination of the
emission spectra and of the radiative losses due to free-free emission from the
correspond- ing temperature averaged and total Gaunt factors. Detailed
calculations of the latter are presented, associated to n-distributed electrons
with the parameter n ranging from 1 (corresponding to the Maxwell-Boltzmann
distribu- tion) to 100. The temperature averaged and total Gaunt factors, with
decreasing n tend to those obtained with the Maxwell-Boltzmann distribution.
Radiative losses due to free-free emission in a plasma evolving under
collisional ionization equilibrium conditions and composed by H, He, C, N, O,
Ne, Mg, Si, S, and Fe ions, are presented. These losses decrease with the
decrease in the parameter n reaching a minimum when n = 1, and, thus converging
to the losses of a thermal plasma.
Tables of the thermal averaged and total Gaunt factors calculated for n
distributions and a wide range electron and photon energies are presented.Comment: Accepted for publication in ApJS. 70 pages, 7 figures and 11 table
The Evolution of the Large-scale ISM: Bubbles, Superbubbles and Non-Equilibrium Ionization
The ISM, powered by SNe, is turbulent and permeated by a magnetic field (with
a mean and a turbulent component). It constitutes a frothy medium that is
mostly out of equilibrium and is ram pressure dominated on most of the
temperature ranges, except for T 1E6 K, where magnetic and
thermal pressures dominate, respectively. Such lack of equilibrium is also
imposed by the feedback of the radiative processes into the ISM flow. Many
models of the ISM or isolated phenomena, such as bubbles, superbubbles, clouds
evolution, etc., take for granted that the flow is in the so-called collisional
ionization equilibrium (CIE). However, recombination time scales of most of the
ions below 1E6 K are longer than the cooling time scale. This implies that the
recombination lags behind and the plasma is overionized while it cools. As a
consequence cooling deviates from CIE. This has severe implications on the
evolution of the ISM flow and its ionization structure. Here, besides reviewing
several models of the ISM, including bubbles and superbubbles, the validity of
the CIE approximation is discussed, and a presentation of recent developments
in modeling the ISM by taking into account the time-dependent ionization
structure of the flow in a full-blown numerical 3D high resolution simulation
is presented.Comment: 15 pages, 6 figures with 15 panels. Invited review for "The Dynamic
ISM: A celebration of the Canadian Galactic Plane Survey" conference;
Naramata BC, Canada June 6-10, 2010. To be published in the ASP Conference
Serie
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