4,763 research outputs found
Spectroscopy of Globular Clusters in the Sculptor Group Galaxies NGC 253 and NGC 55
We have obtained spectra for 103 published globular cluster candidates in the
Sculptor Group galaxies NGC 253 and NGC 55. On the basis of radial velocities
and digitized plate images, 14 globular clusters are identified in NGC 253 and
one probable globular cluster is identified in NGC 55. The majority of the
objects in the sample appear to be background galaxies. We have obtained and
analysed COSMOS plate scans of NGC 253 and NGC 55 and use these along with the
spectroscopically identified clusters to define new samples of globular cluster
candidates in the two galaxies which should have reduced contamination.Comment: 11 pages, 9 postscript figures, accepted for publication in MNRA
The Atacama Large Millimeter/submillimeter Array: Overview & status
The Atacama Large Millimeter/submillimeter Array (ALMA) is an international
radio telescope under construction in the Atacama Desert of northern Chile.
ALMA will be situated on a high-altitude site at 5000 m elevation which
provides excellent atmospheric transmission over the instrument wavelength
range of 0.3 to 3 mm. ALMA will be comprised of two key observing components:
an array of up to sixty-four 12-m diameter antennas arranged in a multiple
configurations ranging in size from 0.15 to ~14 km, and a set of four 12-m and
twelve 7-m antennas operating in closely-packed configurations ~50m in diameter
(known as the Atacama Compact Array, or ACA), providing both interferometric
and total-power astronomical information. High-sensitivity dual-polarization 8
GHz-bandwidth spectral-line and continuum measurements between all antennas
will be available from two flexible digital correlators
Scheduling aircraft landings - the static case
This is the publisher version of the article, obtained from the link below.In this paper, we consider the problem of scheduling aircraft (plane) landings at an airport. This problem is one of deciding a landing time for each plane such that each plane lands within a predetermined time window and that separation criteria between the landing of a plane and the landing of all successive planes are respected. We present a mixed-integer zero–one formulation of the problem for the single runway case and extend it to the multiple runway case. We strengthen the linear programming relaxations of these formulations by introducing additional constraints. Throughout, we discuss how our formulations can be used to model a number of issues (choice of objective function, precedence restrictions, restricting the number of landings in a given time period, runway workload balancing) commonly encountered in practice. The problem is solved optimally using linear programming-based tree search. We also present an effective heuristic algorithm for the problem. Computational results for both the heuristic and the optimal algorithm are presented for a number of test problems involving up to 50 planes and four runways.J.E.Beasley. would like to acknowledge the financial support of the Commonwealth Scientific and Industrial Research Organization, Australia
Preparation and properties of amorphous MgB/MgO superstructures: A new model disordered superconductor
In this paper we introduce a novel method for fabricating MgB/MgO
multilayers and demonstrate the potential for using them as a new model for
disordered superconductors. In this approach we control the annealing of the
MgB to yield an interesting new class of disordered (amorphous)
superconductors with relatively high transition temperatures. The multilayers
appear to exhibit quasi-two-dimensional superconductivity with controlled
anisotropy. We discuss the properties of the multilayers as the thickness of
the components of the bilayers vary.Comment: 7 pages, 8 figure
On F-theory Quiver Models and Kac-Moody Algebras
We discuss quiver gauge models with bi-fundamental and fundamental matter
obtained from F-theory compactified on ALE spaces over a four dimensional base
space. We focus on the base geometry which consists of intersecting F0=CP1xCP1
Hirzebruch complex surfaces arranged as Dynkin graphs classified by three kinds
of Kac-Moody (KM) algebras: ordinary, i.e finite dimensional, affine and
indefinite, in particular hyperbolic. We interpret the equations defining these
three classes of generalized Lie algebras as the anomaly cancelation condition
of the corresponding N =1 F-theory quivers in four dimensions. We analyze in
some detail hyperbolic geometries obtained from the affine A base geometry by
adding a node, and we find that it can be used to incorporate fundamental
fields to a product of SU-type gauge groups and fields.Comment: 13 pages; new equations added in section 3, one reference added and
typos correcte
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