235 research outputs found
An Architecture of an Intelligent Tutoring System to Support Distance Learning
This paper outlines a design framework of an intelligent tutoring system (ITS). ITS focuses on a newer and more comprehensive distance learning (DL) process as compared to the established traditional DL programs practiced today. The DL model presented in this paper (CHARLIE) is a high level software based tutorial that has the ability to encompass a wide variety of current DL technologies in a single DL session. CHARLIE's architecture has four components: Control Component (responsible for the interaction between software agents and the operating system); Instructional Component (concerned with the instructional aspects of an ITS session); Text Analysis Component (analyzes the partial syntax and partial semantics of the text in the session); Student Modeling Component (analyzes a student's progress and determines the best model for learning during a session). Each component is serviced by a set of software agents to accomplish its mission. Three additional entities in CHARLIE are two separate databases and an explanation facility. Six agents have been implemented in CHARLIE to create a DL course in C++ programming. Much of CHARLIE remains to be completed which opens many areas for research
Temporally resolved second-order photon correlations of exciton-polariton Bose-Einstein condensate formation
Second-order time correlation measurements with a temporal resolution better
than 3 ps were performed on a CdTe microcavity where spontaneous Bose-Einstein
condensation is observed. After the laser pulse, the nonresonantly excited
thermal polariton population relaxes into a coherent polariton condensate.
Photon statistics of the light emitted by the microcavity evidences a clear
phase transition from the thermal state to a coherent state, which occurs
within 3.2 ps after the onset of stimulated scattering. Following this very
fast transition, we show that the emission possesses a very high coherence that
persists for more than 100 ps after the build-up of the condensate.Comment: 4 pages, 3 figure
Periodic squeezing in a polariton Josephson junction
The use of a Kerr nonlinearity to generate squeezed light is a well-known way
to surpass the quantum noise limit along a given field quadrature.
Nevertheless, in the most common regime of weak nonlinearity, a single Kerr
resonator is unable to provide the proper interrelation between the field
amplitude and squeezing required to induce a sizable deviation from Poissonian
statistics. We demonstrate experimentally that weakly coupled bosonic modes
allow exploration of the interplay between squeezing and displacement, which
can give rise to strong deviations from the Poissonian statistics. In
particular, we report on the periodic bunching in a Josephson junction formed
by two coupled exciton-polariton modes. Quantum modeling traces the bunching
back to the presence of quadrature squeezing. Our results, linking the light
statistics to squeezing, are a precursor to the study of nonclassical features
in semiconductor microcavities and other weakly nonlinear bosonic systems.Comment: 6 pages, 4 figure
Anderson localisation in steady states of microcavity polaritons
We present an experimental signature of the Anderson localisation of
microcavity polaritons, and provide a systematic study of the dependence on
disorder strength. We reveal a controllable degree of localisation, as
characterised by the inverse-participation ratio, by tuning the positional
disorder of arrays of interacting mesas. This constitutes the realisation of
disorder-induced localisation in a driven-dissipative system. In addition to
being an ideal candidate for investigating localisation in this regime,
microcavity polaritons hold promise for low-power, ultra-small devices and
their localisation could be used as a resource in quantum memory and quantum
information processing.Comment: 7 pages, 3 figure
Dephasing effects on coherent exciton-polaritons and the breakdown of the strong coupling regime
International audienceUsing femtosecond pump-probe spectroscopy, we identify excitation-induced dephasing as a major mechanism responsible for the breakdown of the strong coupling between excitons and photons in a semiconductor microcavity. The effects of dephasing are observed on the transmitted probe-pulse spectrum as a density-dependent broadening of the exciton-polariton resonances and the emergence of a third resonance at high excitation density. A striking asymmetry in the energy shift between the upper and the lower polaritons is also evidenced. Using the excitonic Bloch equations, we quantify the respective contributions to the energy shift of many-body effects associated with Coulomb fermion exchange and photon assisted exchange processes and the contribution to collisional broadening
Transverse momentum and centrality dependence of dihadron correlations in Au+Au collisions at sqrt(s_NN)=200 GeV: Jet-quenching and the response of partonic matter
Azimuthal angle \Delta\phi correlations are presented for charged hadrons
from dijets for 0.4 < p_T < 10 GeV/c in Au+Au collisions at sqrt(s_NN) = 200
GeV. With increasing p_T, the away-side distribution evolves from a broad to a
concave shape, then to a convex shape. Comparisons to p+p data suggest that the
away-side can be divided into a partially suppressed "head" region centered at
Delta\phi ~ \pi, and an enhanced "shoulder" region centered at Delta\phi ~ \pi
+/- 1.1. The p_T spectrum for the "head" region softens toward central
collisions, consistent with the onset of jet quenching. The spectral slope for
the "shoulder" region is independent of centrality and trigger p_T, which
offers constraints on energy transport mechanisms and suggests that the
"shoulder" region contains the medium response to energetic jets.Comment: 420 authors from 58 institutions, 6 pages, 4 figures. Submitted to
Physical Review Letters. Plain text data tables for the points plotted in
figures for this and previous PHENIX publications are (or will be) publicly
available at http://www.phenix.bnl.gov/papers.htm
Transverse momentum dependence of J/psi polarization at midrapidity in p+p collisions at sqrt(s)=200 GeV
We report the measurement of the transverse momentum dependence of inclusive
J/psi polarization in p+p collisions at sqrt(s)=200 GeV performed by the PHENIX
Experiment at RHIC. The polarization is studied in the helicity,
Gottfried-Jackson, and Collins-Soper frames for p_T < 5 GeV/c and |y| < 0.35.
The J/psi polarization in the helicity and Gottfried-Jackson frames is
consistent with zero for all transverse momenta, with a slight (1.8 sigma)
trend towards longitudinal polarization for transverse momenta above 2 GeV/c.
No conclusion is allowed due to the limited acceptance in the Collins-Soper
frame and the uncertainties of the current data. The results are compared to
observations for other collision systems and center of mass energies and to
different quarkonia production models.Comment: 384 authors from 62 institutions, 11 pages, 9 figures, 2 tables. v2
is expanded version submitted to Physical Review D. Plain text data tables
for the points plotted in figures are available at
http://www.phenix.bnl.gov/papers.htm
Azimuthal anisotropy of neutral pion production in Au+Au collisions at sqrt(s_NN) = 200 GeV: Path-length dependence of jet quenching and the role of initial geometry
We have measured the azimuthal anisotropy of pi0's for 1 < pT < 18 GeV/c for
Au+Au collisions at sqrt s_NN = 200 GeV. The observed anisotropy shows a
gradual decrease in 3 < pT < 7 - 10 GeV/c, but remains positive beyond 10
GeV/c. The magnitude of this anisotropy is under-predicted, up to at least 10
GeV/c, by current perturbative QCD (pQCD) energy-loss model calculations. An
estimate of the increase in anisotropy expected from initial-geometry
modification due to gluon saturation effects and initial-geometry fluctuations
is insufficient to account for this discrepancy. Calculations which implement a
path length dependence steeper than what is implied by current pQCD energy-loss
models, show reasonable agreement with the data.Comment: 384 authors, 6 pages text, 3 figures. Submitted to Phys. Rev. Lett.
Plain text data tables for the points plotted in figures for this and
previous PHENIX publications are (or will be) publicly available at
http://www.phenix.bnl.gov/papers.htm
Particle-species dependent modification of jet-induced correlations in Au+Au collisions at sqrt(s_NN) = 200 GeV
We report PHENIX measurements of the correlation of a trigger hadron at
intermediate transverse momentum (2.5<p_{T,trig}<4 GeV/c), with associated
mesons or baryons at lower p_{T,assoc}, in Au+Au collisions at sqrt(s_NN) = 200
GeV. The jet correlations for both baryons and mesons show similar shape
alterations as a function of centrality, characteristic of strong modification
of the away-side jet. The ratio of jet-associated baryons to mesons for this
jet increases with centrality and p_{T,assoc} and, in the most central
collisions, reaches a value similar to that for inclusive measurements. This
trend is incompatible with in-vacuum fragmentation, but could be due to
jet-like contributions from correlated soft partons which recombine upon
hadronization.Comment: 344 authors, 4 pages text, RevTeX, 4 figures. Submitted to Physical
Review Letters. Plain text data tables for the points plotted in figures for
this and previous PHENIX publications are (or will be) publicly available at
http://www.phenix.bnl.gov/papers.htm
High p_T Direct Photon and pi^0 Triggered Azimuthal Jet Correlations in sqrt(s)=200 GeV p+p Collisions
Correlations of charged hadrons of 1 < pT < 10 GeV/c with high pT direct
photons and pi^ 0 mesons in the range 5 <pT < 15 GeV/c are used to study jet
fragmentation in the photon+jet and di-jet channels, respectively. The
magnitude of the partonic transverse momentum, kT, is obtained by comparing to
a model incorporating a Gaussian kT smearing. The sensitivity of the associated
charged hadron spectra to the underlying fragmentation function is tested and
the data are compared to calculations using recent global fit results. The
shape of the direct photon-associated hadron spectrum as well as its charge
asymmetry are found to be consistent with a sample dominated by quark-gluon
Compton scattering. No significant evidence of fragmentation photon correlated
production is observed within experimental uncertainties.Comment: 431 authors, 18 pages, 18 figures, 4 tables, RevTeX-4. Submitted to
Physical Review D. Plain text data tables for the points plotted in figures
for this and previous PHENIX publications are (or will be) publicly available
at http://www.phenix.bnl.gov/papers.htm
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