15,410 research outputs found
Resolving Non-Determinism in Choreographies
Resolving non-deterministic choices of choreographies is a crucial task. We introduce a novel notion of realisability for choreographies –called whole-spectrum implementation– that rules out deterministic implementations of roles that, no matter which context they are placed in, will never follow one of the branches of a non-deterministic choice. We show that, under some conditions, it is decidable whether an implementation is whole-spectrum. As a case study, we analyse the POP protocol under the lens of whole-spectrum implementation
Modelling the hepatitis B vaccination programme in prisons
A vaccination programme offering hepatitis B (HBV) vaccine at reception into prison has been introduced into selected prisons in England and Wales. Over the coming years it is anticipated this vaccination programme will be extended. A model has been developed to assess the potential impact of the programme on the vaccination coverage of prisoners, ex-prisoners, and injecting drug users (IDUs). Under a range of coverage scenarios, the model predicts the change over time in the vaccination status of new entrants to prison, current prisoners and IDUs in the community. The model predicts that at baseline in 2012 57% of the IDU population will be vaccinated with up to 72% being vaccinated depending on the vaccination scenario implemented. These results are sensitive to the size of the IDU population in England and Wales and the average time served by an IDU during each prison visit. IDUs that do not receive HBV vaccine in the community are at increased risk from HBV infection. The HBV vaccination programme in prisons is an effective way of vaccinating this hard-to-reach population although vaccination coverage on prison reception must be increased to achieve this
Vlasov moment flows and geodesics on the Jacobi group
By using the moment algebra of the Vlasov kinetic equation, we characterize
the integrable Bloch-Iserles system on symmetric matrices
(arXiv:math-ph/0512093) as a geodesic flow on the Jacobi group. We analyze the
corresponding Lie-Poisson structure by presenting a momentum map, which both
untangles the bracket structure and produces particle-type solutions that are
inherited from the Vlasov-like interpretation. Moreover, we show how the Vlasov
moments associated to Bloch-Iserles dynamics correspond to particular subgroup
inclusions into a group central extension (first discovered in
arXiv:math/0410100), which in turn underlies Vlasov kinetic theory. In the most
general case of Bloch-Iserles dynamics, a generalization of the Jacobi group
also emerges naturally.Comment: 45 page
On-sky observations with an achromatic hybrid phase knife coronagraph in the visible
CONTEXT: The four-quadrant phase mask stellar coronagraph, introduced by D.
Rouan et al., is capable of achieving very high dynamical range imaging and was
studied in the context of the direct detection of extra-solar planets.
Achromatic four-quadrant phase mask is currently being developed for broadband
IR applications. AIMS: We report on laboratory and on-sky tests of a prototype
coronagraph in the visible. This prototype, the achromatic hybrid phase knife
coronagraph, was derived from the four-quadrant phase mask principle. METHODS:
The instrumental setup implementing the coronagraph itself was designed to
record the pre- and post-coronagraphic images simultaneously so that an
efficient real-time image selection procedure can be performed. We describe the
coronagraph and the associated tools that enable robust and repeatable
observations. We present an algorithm of image selection that has been tested
against the real on-sky data of the binary star HD80081 (* 38 Lyn). RESULTS
Although the observing conditions were poor, the efficiency of the proposed
method is proven. From this experiment, we derive procedures that can apply to
future focal instruments associating adaptive optics and coronagraphy,
targeting high dynamic range imaging in astronomy, such as detecting
extra-solar planets
Surface wave generation and propagation on metallic subwavelength structures measured by far-field interferometry
Transmission spectra of metallic films or membranes perforated by arrays of
subwavelength slits or holes have been widely interpreted as resonance
absorption by surface plasmon polaritons (SPPs). Alternative interpretations
involving evanescent waves diffracted on the surface have also been proposed.
These two approaches lead to divergent predictions for some surface wave
properties. Using far-field interferometry, we have carried out a series of
measurements on elementary one-dimensional (1-D) subwavelength structures with
the aim of testing key properties of the surface waves and comparing them to
predictions of these two points of view
Deformation of grain boundaries in polar ice
The ice microstructure (grain boundaries) is a key feature used to study ice
evolution and to investigate past climatic changes. We studied a deep ice core,
in Dome Concordia, Antarctica, which records past mechanical deformations. We
measured a "texture tensor" which characterizes the pattern geometry and
reveals local heterogeneities of deformation along the core. These results
question key assumptions of the current models used for dating
Production of a high-density state-selected metastable neon beam
We have developed a high-density source of metastable neon and have selectively quenched both metastable species using a standing-wave dye laser. The source is compact, stable, and produces an average intensity of 3.6 x 1014 sr -1 s -1 and a density on target of 7.7 x 106 cm-3
Secondary schooling and rural youth transitions in Lesotho and Zimbabwe
Based on case studies centred on two rural secondary schools in Lesotho and Zimbabwe, this paper examines the gendered impacts of schooling on young people’s transitions to adulthood. School attendance is shown, first, to disrupt the conventional pathways to adulthood: young people attending school may leave home sooner than they otherwise would, and take responsibility for their day-to-day survival, while marriage and childbearing are often delayed. More significantly, secondary schooling reflects, and contributes to, a growing sense that adulthood itself is not fixed. An alternative version of adulthood is promoted through schools in which formal sector employment is central. Yet while young people are encouraged to opt for, and work towards, this goal, only a minority are able to obtain paid employment. The apparent possibility of determining one’s own lifecourse serves to cast the majority of young people as failures in their transitions to adulthood
Production of a high-density state-selected metastable neon beam
We have developed a high-density source of metastable neon and have selectively quenched both metastable species using a standing-wave dye laser. The source is compact, stable, and produces an average intensity of 3.6 x 1014 sr -1 s -1 and a density on target of 7.7 x 106 cm-3
Un-reduction
This paper provides a full geometric development of a new technique called
un-reduction, for dealing with dynamics and optimal control problems posed on
spaces that are unwieldy for numerical implementation. The technique, which was
originally concieved for an application to image dynamics, uses Lagrangian
reduction by symmetry in reverse. A deeper understanding of un-reduction leads
to new developments in image matching which serve to illustrate the
mathematical power of the technique.Comment: 25 pages, revised versio
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