794 research outputs found
A Learning Automata Based Solution to Service Selection in Stochastic Environments
With the abundance of services available in today’s world, identifying those of high quality is becoming increasingly difficult. Reputation systems can offer generic recommendations by aggregating user provided opinions about service quality, however, are prone to ballot stuffing and badmouthing . In general, unfair ratings may degrade the trustworthiness of reputation systems, and changes in service quality over time render previous ratings unreliable. In this paper, we provide a novel solution to the above problems based on Learning Automata (LA), which can learn the optimal action when operating in unknown stochastic environments. Furthermore, they combine rapid and accurate convergence with low computational complexity. In additional to its computational simplicity, unlike most reported approaches, our scheme does not require prior knowledge of the degree of any of the above mentioned problems with reputation systems. Instead, it gradually learns which users provide fair ratings, and which users provide unfair ratings, even when users unintentionally make mistakes. Comprehensive empirical results show that our LA based scheme efficiently handles any degree of unfair ratings (as long as ratings are binary). Furthermore, if the quality of services and/or the trustworthiness of users change, our scheme is able to robustly track such changes over time. Finally, the scheme is ideal for decentralized processing. Accordingly, we believe that our LA based scheme forms a promising basis for improving the performance of reputation systems in general
Improving Time and Position Resolution of RPC detectors using Time Over Threshold Information
INO-ICAL is a proposed underground particle physics experiment to study the
neutrino oscillation parameters by detecting neutrinos produced in the
atmospheric air showers. Iron CALorimeter (ICAL) is to have 151 layers of iron
stacked vertically, with active detector elements in between the iron layers.
The iron layers will be magnetized to enable the measurement of momentum and
charge of the (or ) produced by (or )
interactions. Resistive Plate Chambers (RPCs) have been chosen as the active
detector elements due to their large area coverage, uncompromised sensitivity,
consistent performance for decades, as well as cost effectiveness. The major
factors that decide the physics potential of the ICAL experiment are
efficiency, position resolution and time resolution of the large area RPCs. A
prototype detector called miniICAL (with 11 iron layers) was commissioned to
understand the engineering challenges in building the large scale magnet and
its ancillary systems, and also to study the performance of the RPC detectors
and readout electronics developed by the INO collaboration. As part of the
performance study of the RPC detectors, an attempt is made to improve the
position and time resolution of them. Even a small improvement in the position
and time resolution will help to improve the measurements of momentum and
directionality of the neutrinos in ICAL. The Time-over-Threshold (ToT) of the
RPC pulses (signals) is recorded by the readout electronics. ToT is a measure
of the pulse width and consequently the amplitude. This information is used to
improve the time and position resolution of the RPCs and consequently INO
physics potential
Electromagnetic transition from the 4 to 2 resonance in Be measured via the radiative capture in He+He
An earlier measurement on the 4 to 2 radiative transition in Be
provided the first electromagnetic signature of its dumbbell-like shape.
However, the large uncertainty in the measured cross section does not allow a
stringent test of nuclear structure models. The present paper reports a more
elaborate and precise measurement for this transition, via the radiative
capture in the He+He reaction, improving the accuracy by about a factor
of three. The {\it ab initio} calculations of the radiative transition strength
with improved three-nucleon forces are also presented. The experimental results
are compared with the predictions of the alpha cluster model and {\it ab
initio} calculations.Comment: 5 pages and 7 figures, Submitted to Physical Review Letter
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