335 research outputs found
Actors that Unify Threads and Events
There is an impedance mismatch between message-passing concurrency and virtual machines, such as the JVM. VMs usually map their threads to heavyweight OS processes. Without a lightweight process abstraction, users are often forced to write parts of concurrent applications in an event-driven style which obscures control flow, and increases the burden on the programmer. In this paper we show how thread-based and event-based programming can be unified under a single actor abstraction. Using advanced abstraction mechanisms of the Scala programming language, we implemented our approach on unmodified JVMs. Our programming model integrates well with the threading model of the underlying VM
Three-body recombination rates near a Feshbach resonance within a two-channel contact interaction model
We calculate the three-body recombination rate into a shallow dimer in a gas
of cold bosonic atoms near a Feshbach resonance using a two-channel contact
interaction model. The two-channel model naturally describes the variation of
the scattering length through the Feshbach resonance and has a finite effective
range. We confront the theory with the available experimental data and show
that the two-channel model is able to quantitatively describe the existing
data. The finite effective range leads to a reduction of the scaling factor
between the recombination minima from the universal value of 22.7. The
reduction is larger for larger effective ranges or, correspondingly, for
narrower Feshbach resonances.Comment: 9 pages, 7 figure
Persistent currents in a Bose-Einstein condensate in the presence of disorder
We examine bosonic atoms that are confined in a toroidal,
quasi-one-dimensional trap, subjected to a random potential. The resulting
inhomogeneous atomic density is smoothened for sufficiently strong, repulsive
interatomic interactions. Statistical analysis of our simulations show that the
gas supports persistent currents, which become more fragile due to the
disorder.Comment: 5 pages, RevTex, 3 figures, revised version, to appear in JLT
Unstable particles in matter at a finite temperature: the rho and omega mesons
Unstable particles (such as the vector mesons) have an important role to play
in low mass dilepton production resulting from heavy ion collisions and this
has been a subject of several investigations. Yet subtleties, such as the
implications of the generalization of the Breit-Wigner formula for nonzero
temperature and density, e.g. the question of collisional broadening, the role
of Bose enhancement, etc., the possibility of the kinematic opening (or
closing) of decay channels due to environmental effects, the problem of double
counting through resonant and direct contributions, are often given
insufficient emphasis. The present study attempts to point out these features
using the rho and omega mesons as illustrative examples. The difference between
the two versions of the Vector Meson Dominance Model in the present context is
also presented. Effects of non-zero temperature and density, through vector
meson masses and decay widths, on dilepton spectra are studied, for
concreteness within the framework of a Walecka-type model, though most of the
basic issues highlighted apply to other scenarios as well.Comment: text and figures modifie
Supersymmetry breaking in two dimensions: the lattice N=1 Wess-Zumino model
We study dynamical supersymmetry breaking by non perturbative lattice
techniques in a class of two-dimensional N=1 Wess-Zumino models. We work in the
Hamiltonian formalism and analyze the phase diagram by analytical
strong-coupling expansions and explicit numerical simulations with Green
Function Monte Carlo methods.Comment: 53 pages, 17 figures, revtex
Efimov Trimers near the Zero-crossing of a Feshbach Resonance
Near a Feshbach resonance, the two-body scattering length can assume any
value. When it approaches zero, the next-order term given by the effective
range is known to diverge. We consider the question of whether this divergence
(and the vanishing of the scattering length) is accompanied by an anomalous
solution of the three-boson Schr\"odinger equation similar to the one found at
infinite scattering length by Efimov. Within a simple zero-range model, we find
no such solutions, and conclude that higher-order terms do not support Efimov
physics.Comment: 8 pages, no figures, final versio
Tune in to your emotions: a robust personalized affective music player
The emotional power of music is exploited in a personalized affective music player (AMP) that selects music for mood enhancement. A biosignal approach is used to measure listeners’ personal emotional reactions to their own music as input for affective user models. Regression and kernel density estimation are applied to model the physiological changes the music elicits. Using these models, personalized music selections based on an affective goal state can be made. The AMP was validated in real-world trials over the course of several weeks. Results show that our models can cope with noisy situations and handle large inter-individual differences in the music domain. The AMP augments music listening where its techniques enable automated affect guidance. Our approach provides valuable insights for affective computing and user modeling, for which the AMP is a suitable carrier application
Harmonising data on the correlates of physical activity and sedentary behaviour in young people: Methods and lessons learnt from the international Children's Accelerometry database (ICAD).
BACKGROUND: Large, heterogeneous datasets are required to enhance understanding of the multi-level influences on children's physical activity and sedentary behaviour. One route to achieving this is through the pooling and co-analysis of data from multiple studies. Where this approach is used, transparency of the methodology for data collation and harmonisation is essential to enable appropriate analysis and interpretation of the derived data. In this paper, we describe the acquisition, management and harmonisation of non-accelerometer data in a project to expand the International Children's Accelerometry Database (ICAD). METHOD: Following a consultation process, ICAD partners were requested to share accelerometer data and information on selected behavioural, social, environmental and health-related constructs. All data were collated into a single repository for cataloguing and harmonisation. Harmonised variables were derived iteratively, with input from the ICAD investigators and a panel of invited experts. Extensive documentation, describing the source data and harmonisation procedure, was prepared and made available through the ICAD website. RESULTS: Work to expand ICAD has increased the number of studies with longitudinal accelerometer data, and expanded the breadth of behavioural, social and environmental characteristics that can be used as exposure variables. A set of core harmonised variables, including parent education, ethnicity, school travel mode/duration and car ownership, were derived for use by the research community. Guidance documents and facilities to enable the creation of new harmonised variables were also devised and made available to ICAD users. An expanded ICAD database was made available in May 2017. CONCLUSION: The project to expand ICAD further demonstrates the feasibility of pooling data on physical activity, sedentary behaviour and potential determinants from multiple studies. Key to this process is the rigorous conduct and reporting of retrospective data harmonisation, which is essential to the appropriate analysis and interpretation of derived data. These documents, made available through the ICAD website, may also serve as a guide to others undertaking similar projects
Analysis of LIGO data for gravitational waves from binary neutron stars
We report on a search for gravitational waves from coalescing compact binary
systems in the Milky Way and the Magellanic Clouds. The analysis uses data
taken by two of the three LIGO interferometers during the first LIGO science
run and illustrates a method of setting upper limits on inspiral event rates
using interferometer data. The analysis pipeline is described with particular
attention to data selection and coincidence between the two interferometers. We
establish an observational upper limit of 1.7 \times 10^{2}M_\odot$.Comment: 17 pages, 9 figure
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