10,454 research outputs found
Learning users' interests by quality classification in market-based recommender systems
Recommender systems are widely used to cope with the problem of information overload and, to date, many recommendation methods have been developed. However, no one technique is best for all users in all situations. To combat this, we have previously developed a market-based recommender system that allows multiple agents (each representing a different recommendation method or system) to compete with one another to present their best recommendations to the user. In our system, the marketplace encourages good recommendations by rewarding the corresponding agents who supplied them according to the usersâ ratings of their suggestions. Moreover, we have theoretically shown how our system incentivises the agents to bid in a manner that ensures only the best recommendations are presented. To do this effectively in practice, however, each agent needs to be able to classify its recommendations into different internal quality levels, learn the usersâ interests for these different levels, and then adapt its bidding behaviour for the various levels accordingly. To this end, in this paper we develop a reinforcement learning and Boltzmann exploration strategy that the recommending agents can exploit for these tasks. We then demonstrate that this strategy does indeed help the agents to effectively obtain information about the usersâ interests which, in turn, speeds up the market convergence and enables the system to rapidly highlight the best recommendations
The effects of walking volume on blood pressure in hypertensive postmenopausal women
The American College of Sports Medicine and the Centers for Disease and Control and Prevention (ACSM-CDC) recommend that 30 minutes of accumulated moderate intensity activity, such as brisk walking, should be performed daily for the attainment of health benefits. However, the effectiveness of these recommendations remain untested, particularly for their efficacy in lowering blood pressure in hypertensive postmenopausal women. Therefore, postmenopausal women with borderline to mild hypertension were randomly assigned to either a 16 kilometer/week (low) walking group (N = 12), 32 kilometer/week walking (high) group (N = 12), or sedentary control group (N = 13). The low and high groups walked an average of 13 and 22 kilometers/week respectively, above their baseline walking activity for 12 weeks, while walking activity remained unchanged for the controls. There were no significant reductions in blood pressure with walking in either low or high group. No significant changes were observed in variables associated with blood pressure including body composition, insulin, glucose, insulin/glucose ratio, or caloric intake. Also, there were no changes in depression, hostility, aggression, or self-esteeem scores with walking. There were also no significant differences in submaximal heart rate or blood pressure, however, the respiratory exchange ratio was significantly reduced in the low and high groups (p \u3c 0.05), demonstrating a training adaptation. Women who responded favorably (decrease in systolic or diastolic blood pressure \u3e 10 mm Hg) to the walking were characterized by having a greater adherence rate to the walking program, higher baseline levels of blood pressure, and a larger reduction in body mass in comparison to non-responders. It was concluded that a 12 week program meeting or exceeding the ACSM-CDC physical activity recommendations was ineffective in lowering blood pressure in postmenopausal women with borderline to mild hypertension. However, the strong associations between exercise adherence and blood pressure reduction as well as between weight loss and blood pressure decline suggest that these factors are critical to blood pressure reduction in postmenopausal hypertensive women
The scenario of two-dimensional instabilities of the cylinder wake under EHD forcing: A linear stability analysis
We propose to study the stability properties of an air flow wake forced by a dielectric barrier discharge (DBD) actuator, which is a type of electrohydrodynamic (EHD) actuator. These actuators add momentum to the flow around a cylinder in regions close to the wall and, in our case, are symmetrically disposed near the boundary layer separation point.
Since the forcing frequencies, typical of DBD, are much higher than the natural shedding frequency of the flow, we will be considering the forcing actuation as stationary.
In the first part, the flow around a circular cylinder modified by EHD actuators will be experimentally studied by means of particle image velocimetry (PIV). In the second part, the EHD actuators have been numerically implemented as a boundary condition on the cylinder surface. Using this boundary condition, the computationally obtained base flow is then compared with the experimental one in order to relate the control parameters from both methodologies.
After validating the obtained agreement, we study the Hopf bifurcation that appears once the flow starts the vortex shedding through experimental and computational approaches. For the base flow derived from experimentally obtained snapshots, we monitor the evolution of the velocity amplitude oscillations. As to the computationally obtained base flow, its stability is analyzed by solving a global eigenvalue problem obtained from the linearized NavierâStokes equations. Finally, the critical parameters obtained from both approaches are compared
Alien Registration- Moreau, Lucienne L. (Sanford, York County)
https://digitalmaine.com/alien_docs/2620/thumbnail.jp
Extent of force indeterminacy in packings of frictional rigid disks
Static packings of frictional rigid particles are investigated by means of
discrete element simulations. We explore the ensemble of allowed force
realizations in the space of contact forces for a given packing structure. We
estimate the extent of force indeterminacy with different methods. The
indeterminacy exhibits a nonmonotonic dependence on the interparticle friction
coefficient. We verify directly that larger force-indeterminacy is accompanied
by a more robust behavior against local perturbations. We also investigate the
local indeterminacy of individual contact forces. The probability distribution
of local indeterminacy changes its shape depending on friction. We find that
local indeterminacy tends to be larger on force chains for intermediate
friction. This correlation disappears in the large friction limit.Comment: 5 pages, 6 figure
The post-Higgs MSSM scenario: Habemus MSSM?
We analyze the Minimal Supersymmetric extension of the Standard Model that we
have after the discovery of the Higgs boson at the LHC, the hMSSM (habemus
MSSM?), i.e. a model in which the lighter boson has a mass of approximately
125 GeV which, together with the non-observation of superparticles at the LHC,
indicates that the SUSY-breaking scale is rather high, TeV. We
first demonstrate that the value GeV fixes the dominant
radiative corrections that enter the MSSM Higgs boson masses, leading to a
Higgs sector that can be described, to a good approximation, by only two free
parameters. In a second step, we consider the direct supersymmetric radiative
corrections and show that, to a good approximation, the phenomenology of the
lighter Higgs state can be described by its mass and three couplings: those to
massive gauge bosons and to top and bottom quarks. We perform a fit of these
couplings using the latest LHC data on the production and decay rates of the
light boson and combine it with the limits from the negative search of the
heavier and states, taking into account the current
uncertainties.Comment: 1+12 pages, pdflatex, 7 figure
The forward-backward asymmetry of top quark production at the Tevatron in warped extra dimensional models
The CDF and D0 experiments have reported on the measurement of the
forward-backward asymmetry of top quark pair production at the Tevatron and the
result is that it is more than 2 standard deviations above the predicted value
in the Standard Model. This has to be added to the longstanding anomaly in the
forward-backward asymmetry for bottom quark production at LEP which is 3
standard deviations different from the Standard Model value. The discrepancy in
the bottom asymmetry can be accounted for by the contributions of Kaluza-Klein
excitations of electroweak gauge bosons at LEP in warped extra dimensional
models in which the fermions are localized differently along the extra
dimension so that the gauge interactions of heavy third generation fermions are
naturally different from that of light fermions. In this paper, we show that it
is more difficult to elaborate a model generating a significant top asymmetry
in a similar way -- through exchanges of Kaluza-Klein gluons at the Tevatron --
due to the indirect constraints originating from precision electroweak data.Comment: 4 pages, 1 figure, published versio
Stress-strain behavior and geometrical properties of packings of elongated particles
We present a numerical analysis of the effect of particle elongation on the
quasistatic behavior of sheared granular media by means of the Contact Dynamics
method. The particle shapes are rounded-cap rectangles characterized by their
elongation. The macroscopic and microstructural properties of several packings
subjected to biaxial compression are analyzed as a function of particle
elongation. We find that the shear strength is an increasing linear function of
elongation. Performing an additive decomposition of the stress tensor based on
a harmonic approximation of the angular dependence of branch vectors, contact
normals and forces, we show that the increasing mobilization of friction force
and the associated anisotropy are key effects of particle elongation. These
effects are correlated with partial nematic ordering of the particles which
tend to be oriented perpendicular to the major principal stress direction and
form side-to-side contacts. However, the force transmission is found to be
mainly guided by cap-to-side contacts, which represent the largest fraction of
contacts for the most elongated particles. Another interesting finding is that,
in contrast to shear strength, the solid fraction first increases with particle
elongation, but declines as the particles become more elongated. It is also
remarkable that the coordination number does not follow this trend so that the
packings of more elongated particles are looser but more strongly connected.Comment: Submited to Physical Review
Dynamic Provenance for SPARQL Update
While the Semantic Web currently can exhibit provenance information by using
the W3C PROV standards, there is a "missing link" in connecting PROV to storing
and querying for dynamic changes to RDF graphs using SPARQL. Solving this
problem would be required for such clear use-cases as the creation of version
control systems for RDF. While some provenance models and annotation techniques
for storing and querying provenance data originally developed with databases or
workflows in mind transfer readily to RDF and SPARQL, these techniques do not
readily adapt to describing changes in dynamic RDF datasets over time. In this
paper we explore how to adapt the dynamic copy-paste provenance model of
Buneman et al. [2] to RDF datasets that change over time in response to SPARQL
updates, how to represent the resulting provenance records themselves as RDF in
a manner compatible with W3C PROV, and how the provenance information can be
defined by reinterpreting SPARQL updates. The primary contribution of this
paper is a semantic framework that enables the semantics of SPARQL Update to be
used as the basis for a 'cut-and-paste' provenance model in a principled
manner.Comment: Pre-publication version of ISWC 2014 pape
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