22,127 research outputs found
Long period variables and mass loss in the globular clusters NGC 362 and NGC 2808
The pulsation periods of long period variables (LPVs) depend on their mass
and helium abundance as well as on their luminosity and metal abundance.
Comparison of the observed periods of LPVs in globular clusters with models is
capable of revealing the amount of mass lost on the giant branch and the helium
abundance.} {We aim to determine the amount of mass loss that has occurred on
the giant branches of the low metallicity globular clusters NGC 362 and NGC
2808. We also aim to see if the LPVs in NGC 2808 can tell us about helium
abundance variations in this cluster.} We have used optical monitoring of NGC
362 and NGC 2808 to determine periods for the LPVs in these clusters. We have
made linear pulsation models for the pulsating stars in these clusters taking
into account variations in mass and helium abundance. Reliable periods have
been determined for 11 LPVs in NGC 362 and 15 LPVs in NGC 2808. Comparison of
the observed variables with models in the logP - K diagram shows that mass loss
of ~0.15-0.2 Msun is required on the first giant branch in these clusters, in
agreement with estimates from other methods. In NGC 2808, there is evidence
that a high helium abundance of Y~0.4 is required to explain the periods of
several of the LPVs. It would be interesting to determine periods for LPVs in
other Galactic globular clusters where a helium abundance variation is
suspected to see if the completely independent test for a high helium abundance
provided by the LPVs can confirm the high helium abundance estimates.Comment: 13 pages, 12 figures, accepted for publication in Astronomy &
Astrophysic
Coset Constructions of Logarithmic (1,p)-Models
One of the best understood families of logarithmic conformal field theories
is that consisting of the (1,p) models (p = 2, 3, ...) of central charge
c_{1,p} = 1 - 6 (p-1)^2 / p. This family includes the theories corresponding to
the singlet algebras M(p) and the triplet algebras W(p), as well as the
ubiquitous symplectic fermions theory. In this work, these algebras are
realized through a coset construction.
The W^(2)_n algebra of level k was introduced by Feigin and Semikhatov as a
(conjectured) quantum hamiltonian reduction of affine sl(n)_k, generalising the
Bershadsky-Polyakov algebra W^(2)_3. Inspired by work of Adamovic for p=3,
vertex algebras B_p are constructed as subalgebras of the kernel of certain
screening charges acting on a rank 2 lattice vertex algebra of indefinite
signature. It is shown that for p <= 5, the algebra B_p is a homomorphic image
of W^(2)_{p-1} at level -(p-1)^2 / p and that the known part of the operator
product algebra of the latter algebra is consistent with this holding for p>5
as well. The triplet algebra W(p) is then realised as a coset inside the full
kernel of the screening operator, while the singlet algebra M(p) is similarly
realised inside B_p. As an application, and to illustrate these results, the
coset character decompositions are explicitly worked out for p=2 and 3.Comment: 22 pages, v2: clarified our definition of Feigin-Semikhatov algebras
and added ref
Learning computing heritage through gaming – whilst teaching digital development through history
This paper analyses the potential of computer games and interactive projects within the learning programmes for cultural heritage institutions through our experiences working in partnership between higher education and a museum. Gamification is cited as a key disruptive technology for the business and enterprise community, and developments in games technology are also driving the expansion of digital media into all different screen spaces, and various platforms. Our research aims to take these as beneficial indicators for pedagogic development, using gaming to support knowledge transfer related to a museum setting, and using the museum as a key scenario for our students to support the practice of game development. Thus gamification is applied as both a topic and a methodology for educational purposes
Emission from Very Small Grains and PAH Molecules in Monte Carlo Radiation Transfer Codes: Application to the Edge-On Disk of Gomez's Hamburger
We have modeled optical to far infrared images, photometry, and spectroscopy
of the object known as Gomez's Hamburger. We reproduce the images and spectrum
with an edge-on disk of mass 0.3M_sun and radius 1600AU, surrounding an A0 III
star at a distance of 280pc. Our mass estimate is in excellent agreement with
recent CO observations. However, our distance determination is more than an
order of magnitude smaller than previous analyses which inaccurately
interpreted the optical spectrum. To accurately model the infrared spectrum we
have extended our Monte Carlo radiation transfer codes to include emission from
polycyclic aromatic hydrocarbon (PAH) molecules and very small grains (VSG). We
do this using pre-computed PAH/VSG emissivity files for a wide range of values
of the mean intensity of the exciting radiation field. When Monte Carlo energy
packets are absorbed by PAHs/VSGs we reprocess them to other wavelengths by
sampling from the emissivity files, thus simulating the absorption and
re-emission process without reproducing lengthy computations of statistical
equilibrium, excitation and de-excitation in the complex many level molecules.
Using emissivity lookup tables in our Monte Carlo codes gives the flexibility
to use the latest grain physics calculations of PAH/VSG emissivity and opacity
that are being continually updated in the light of higher resolution infrared
spectra. We find our approach gives a good representation of the observed PAH
spectrum from the disk of Gomez's Hamburger. Our models also indicate the
PAHs/VSGs in the disk have a larger scaleheight than larger radiative
equilibrium grains, providing evidence for dust coagulation and settling to the
midplane.Comment: ApJ accepte
Unitary and non-unitary minimal models
The unitary superconformal minimal models have a long history in
string theory and mathematical physics, while their non-unitary (and
logarithmic) cousins have recently attracted interest from mathematicians.
Here, we give an efficient and uniform analysis of all these models as an
application of a type of Schur-Weyl duality, as it pertains to the well-known
Kazama-Suzuki coset construction. The results include straightforward
classifications of the irreducible modules, branching rules, (super)characters
and (Grothendieck) fusion rules.Comment: 32 page
Industrial change in the north east region and the implications for further education departments of electrical and electronic engineering
The research study examines a number of recent developments in the electrical/electronics industry in terms of new skill requirements of the workforce and in-service training provision for both employees in industry and teaching staff in the providing colleges of further education in the North East Region. Many of the major changes which are taking place in the Region's industries are due mainly to the introduction or planned introduction of new microelectronic/computerised technology. Therefore, it is imperative that the relevant manpower planning which takes place in industry is supported by recent and relevant further education and training of its employees so that an adequate supply of sufficiently-skilled personnel is made available in order that companies can take advantage of high technology in their manufacturing processes. Data was collected, using structured interview questionnaires, from samples of managers employed in local industry and teachers in further education departments of electrical/electronic engineering. The results were later analysed using computer standard non-parametric statistics. Much of the data obtained from the survey shows that, although further training and retraining of staff was often necessary with the introduction of new computerised equipment into a company, very little reliance was actually placed on further education. Many of the in- service training needs were provided by equipment manufacturers, external agencies, and in-company programmes. Staff development in a number of the sampled colleges did no always place sufficient emphasis on regular retraining/updating of the teachers' subject area. Therefore, as a consequence, many FE teachers had not attended any recent subject-specific in-service training courses and often had to rely on text-books and other sources for information on new subject and curricular developments. Although most of the sampled managers were aware of the lack of close liaison between their industry and colleges of further education, many recognised the need to further their own involvement in local education and contribute to the content and organisation of college course curricula. In education, a disproportionately large percentage of those teachers interviewed had little or no contact with local firms, even at a superficial level of involvement e.g. an industrial visit, and many had never consulted with industry nor discussed any issues involving the courses offered by their department. The absence of any structured links between the two samples has inevitably helped to exacerbate many existing problems, and in a number of cases has, unfortunately, resulted in a complete lack of co-operation and co-ordination in terms of course planning and design
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