423 research outputs found
Experiences of teaching UML within the information systems curriculum
The Unified Modelling Language (UML) has been a standard modelling language for the development of software intensive systems since 2000. As a consequence, the information systems (IS) curriculum, at the Cavendish School of Computer Science, University of Westminster in London, had UML teaching incorporated two years ago. We have encouraged the introduction to and use of UML in modules that replaced traditional approaches to IS development. In this paper we report on experiences of using UML within the two modules of our undergraduate curriculum, delivered by the IS department. The first module is taught in the second year, i.e. at level 5, and delivers requirements analysis with UML. The second module uses the UML for modelling and designing distributed business applications and is taught in the final year, at level 6. In both modules it is assumed that an introduction to modelling in IS, with the syntax and semantics of a selection of UML modelling elements and diagrams, has been done earlier. We single out some problems and give a rationale for changes in the next academic yea
Asteroids Observed by The Sloan Digital Sky Survey
We announce the first public release of the SDSS Moving Object Catalog, with
SDSS observations for 58,117 asteroids. The catalog lists astrometric and
photometric data for moving objects observed prior to Dec 15, 2001, and also
includes orbital elements for 10,592 previously known objects. We analyze the
correlation between the orbital parameters and optical colors for the known
objects, and confirm that asteroid dynamical families, defined as clusters in
orbital parameter space, also strongly segregate in color space. Their
distinctive optical colors indicate that the variations in chemical composition
within a family are much smaller than the compositional differences between
families, and strongly support earlier suggestions that asteroids belonging to
a particular family have a common origin.Comment: 6 pages, 1 color figure, to be presented at "Astronomical Telescopes
& Instrumentation", SPIE 200
Supporting quality indicators in the UK national health service
Quality indicators for performance
management of the UK National Health Service
have been introduced for general practitioners
(GPs) in order to monitor if they are meeting
their performance targets. Such requirements
impose significant load to GPs’ everyday
operations and any type of software solution that
stores relevant information and addresses
performance indicators can help GPs to justify
their fundholding. In this paper we report on a
way of incorporating the semantics of a set of
quality indicators in a database schema that can
fit any GPs' practice. We concentrate on
indicators that posed problems when creating the
database and we provide a discussion that
justifies our design decisions
A ring as a model of the main belt in planetary ephemerides
We assess the ability of a solid ring to model a global perturbation induced
by several thousands of main-belt asteroids. The ring is first studied in an
analytical framework that provides an estimate of all the ring's parameters
excepting mass. In the second part, numerically estimated perturbations on the
Earth-Mars, Earth-Venus, and Earth-Mercury distances induced by various subsets
of the main-belt population are compared with perturbations induced by a ring.
To account for large uncertainties in the asteroid masses, we obtain results
from Monte Carlo experiments based on asteroid masses randomly generated
according to available data and the statistical asteroid model. The radius of
the ring is analytically estimated at 2.8 AU. A systematic comparison of the
ring with subsets of the main belt shows that, after removing the 300 most
perturbing asteroids, the total main-belt perturbation of the Earth-Mars
distance reaches on average 246 m on the 1969-2010 time interval. A ring with
appropriate mass is able to reduce this effect to 38 m. We show that, by
removing from the main belt ~240 asteroids that are not necessarily the most
perturbing ones, the corresponding total perturbation reaches on average 472 m,
but the ring is able to reduce it down to a few meters, thus accounting for
more than 99% of the total effect.Comment: 18 pages, accepted in A&
Kappa-deformed Snyder spacetime
We present Lie-algebraic deformations of Minkowski space with undeformed
Poincare algebra. These deformations interpolate between Snyder and
kappa-Minkowski space. We find realizations of noncommutative coordinates in
terms of commutative coordinates and derivatives. Deformed Leibniz rule, the
coproduct structure and star product are found. Special cases, particularly
Snyder and kappa-Minkowski in Maggiore-type realizations are discussed. Our
construction leads to a new class of deformed special relativity theories.Comment: 12 pages, no figures, LaTeX2e class file, accepted for publication in
Modern Physics Letters
Evolution of Giant Planets in Eccentric Disks
We investigate the interaction between a giant planet and a viscous
circumstellar disk by means of high-resolution, two-dimensional hydrodynamical
simulations. We consider planet masses that range from 1 to 3 Jupiter masses
(Mjup) and initial orbital eccentricities that range from 0 to 0.4. We find
that a planet can cause eccentricity growth in a disk region adjacent to the
planet's orbit, even if the planet's orbit is circular. Disk-planet
interactions lead to growth in a planet's orbital eccentricity. The orbital
eccentricities of a 2 Mjup and a 3 Mjup planet increase from 0 to 0.11 within
about 3000 orbits. Over a similar time period, the orbital eccentricity of a 1
Mjup planet grows from 0 to 0.02. For a case of a 1 Mjup planet with an initial
eccentricity of 0.01, the orbital eccentricity grows to 0.09 over 4000 orbits.
Radial migration is directed inwards, but slows considerably as a planet's
orbit becomes eccentric. If a planet's orbital eccentricity becomes
sufficiently large, e > ~0.2, migration can reverse and so be directed
outwards. The accretion rate towards a planet depends on both the disk and the
planet orbital eccentricity and is pulsed over the orbital period. Planet mass
growth rates increase with planet orbital eccentricity. For e~0.2 the mass
growth rate of a planet increases by approximately 30% above the value for e=0.
For e > ~0.1, most of the accretion within the planet's Roche lobe occurs when
the planet is near the apocenter. Similar accretion modulation occurs for flow
at the inner disk boundary which represents accretion toward the star.Comment: 20 pages 16 figures, 3 tables. To appear in The Astrophysical Journal
vol.652 (December 1, 2006 issue
Computations of drop collision and coalescence
Computations of drops collision and coalescence are presented. The computations are made possible by a recently developed finite difference/front tracking technique that allows direct solutions of the Navier-Stokes equations for a multi-fluid system with complex, unsteady internal boundaries. This method has been used to examine the boundaries between the various collision modes for drops of equal size and two examples, one of a 'reflective' collision and another of a 'grazing' collision is shown. From drops of unequal size, coalescence can result in considerable mixing between the fluid from the small and the large drop. This problem is discussed and one example showed. In many cases it is necessary to account also for heat transfer along with the fluid mechanics. We show two preliminary results where we are using extensions of the method to simulate such a problem. One example shows pattern formation among many drops moving due to thermal migration, the other shows unstable evolution of a solidification front
Color-Induced Displacement double stars in SDSS
We report the first successful application of the astrometric color-induced
displacement technique (CID, the displacement of the photocenter between
different bandpasses due to a varying contribution of differently colored
components to the total light), originally proposed by Wielen (1996) for
discovering unresolved binary stars. Using the Sloan Digital Sky Survey (SDSS)
Data Release 1 with 2.5 million stars brighter than 21m in the u and g bands,
we select 419 candidate binary stars with CID greater than 0.5 arcsec. The SDSS
colors of the majority of these candidates are consistent with binary systems
including a white dwarf and any main sequence star with spectral type later
than ~K7. The astrometric CID method discussed here is complementary to the
photometric selection of binary stars in SDSS discussed by Smolcic et al.
(2004), but there is considerable overlap (15%) between the two samples of
selected candidates. This overlap testifies both to the physical soundness of
both methods, as well as to the astrometric and photometric quality of SDSS
data.Comment: submitted to A&A, 13 pages, 6 figure
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