14,622 research outputs found
Neutron star matter in the quark-meson coupling model in strong magnetic fields
The effects of strong magnetic fields on neutron star matter are investigated
in the quark-meson coupling (QMC) model. The QMC model describes a nuclear
many-body system as nonoverlapping MIT bags in which quarks interact through
self-consistent exchange of scalar and vector mesons in the mean-field
approximation. The results of the QMC model are compared with those obtained in
a relativistic mean-field (RMF) model. It is found that quantitative
differences exist between the QMC and RMF models, while qualitative trends of
the magnetic field effects on the equation of state and composition of neutron
star matter are very similar.Comment: 16 pages, 4 figure
Evaluating tag-based information access in image collections
The availability of social tags has greatly enhanced access to information. Tag clouds have emerged as a new "social" way to find and visualize information, providing both one-click access to information and a snapshot of the "aboutness" of a tagged collection. A range of research projects explored and compared different tag artifacts for information access ranging from regular tag clouds to tag hierarchies. At the same time, there is a lack of user studies that compare the effectiveness of different types of tag-based browsing interfaces from the users point of view. This paper contributes to the research on tag-based information access by presenting a controlled user study that compared three types of tag-based interfaces on two recognized types of search tasks - lookup and exploratory search. Our results demonstrate that tag-based browsing interfaces significantly outperform traditional search interfaces in both performance and user satisfaction. At the same time, the differences between the two types of tag-based browsing interfaces explored in our study are not as clear. Copyright 2012 ACM
Neutral top-pion and the rare top decays
We study the rare top decays in the
framework of topcolor-assisted technicolor() models. We find that the
neutral top-pion can produce significant contributions to these
processes via the flavor changing couplings and
. For the mass and
the parameter , the branching ratio (t can
reach . Taking into account the constraints of the present
experimental limit of the process on the free parameters of
models, we find that the value of ()() is in the range of
1.8.Comment: To be published in Phys.
Multi-Atomic Mirror for Perfect Reflection of Single Photons in A Wide Band of Frequency
A resonant two level atom doped in one dimensional waveguide behaves as a
mirror, but this single-atom "mirror" can only reflect single photon perfectly
at a specific frequency. For a one dimensional coupled-resonator waveguide, we
propose to extend the perfect reflection region from a specific frequency to a
wide band by placing many atoms individually in the resonators in a finite
coordinate region of the waveguide. Such a doped resonator array promises us to
control the propagation of a practical photon wave packet with certain momentum
distribution instead of a single photon, which is ideally represented by a
plane wave with specific momentum. The studies based on the discrete-coordinate
scattering theory display that such hybrid structure indeed provides a
near-perfect reflection for single photon in a wide band. We also calculated
photon group velocity distribution, which shows that the perfect reflection
with wide band exactly corresponds to the stopping light region.Comment: 8 pages, 10 figure
Probing Topcolor-Assisted Technicolor from Like-sign Top Pair Production at LHC
The topcolor-assisted technicolor (TC2) theory predicts tree-level
flavor-changing neutral-current (FCNC) top quark Yukawa couplings with
top-pions. Such FCNC interactions will induce like-sign top quark pair
productions at CERN Large Hadron Collider (LHC). While these rare productions
are far below the observable level in the Standard Model and other popular new
physics models such as the Minimal Supersymmetric Model, we find that in a
sound part of parameter space the TC2 model can enhance the production cross
sections to several tens of fb and thus may be observable at the LHC due to
rather low backgrounds. Searching for these productions at the LHC will serve
as an excellent probe for the TC2 model.Comment: 10 pages, 6 fig
Inherent Mach-Zehnder interference with "which-way" detection for single particle scattering in one dimension
We study the coherent transport of single photon in a one-dimensional
coupled-resonator-array, "non-locally" coupled to a two-level system. Since its
inherent structure is a Mach-Zehnder interferometer, we explain the destructive
interference phenomenon of the transmission spectrums according to the effect
of which-way detection. The quantum realization of the present model is a
nano-electromechanical resonator arrays with two nearest resonators coupled to
a single spin via their attached magnetic tips. Its classical simulation is a
waveguide of coupled defected cavity array with double couplings to a side
defected cavity.Comment: 5 papges, 4 figure
Production and decay of the neutral top-pion in high energy colliders
We study the production and decay of the neutral top-pion
predicted by topcolor-assisted technicolor(TC2) theory. Our results show that,
except the dominant decay modes , and , the
can also decay into and modes. It can
be significantly produced at high energy collider(LC) experiments
via the processes and . We further calculate the production cross sections of the
processes and . We find that the signatures of the neutral top-pion
can be detected via these processes.Comment: Latex file, 13 Pages, 6 eps figures. to be published in Phys.Rev.
A Raman study of the Charge-Density-Wave State in AMoO (A = K,Rb)
We report a comparative Raman spectroscopic study of the
quasi-one-dimensional charge-density-wave systems \ab (A = K, Rb). The
temperature and polarization dependent experiments reveal charge-coupled
vibrational Raman features. The strongly temperature-dependent collective
amplitudon mode in both materials differ by about 3 cm, thus revealing the role
of alkali atom. We discus the observed vibrational features in terms of
charge-density-wave ground state accompanied by change in the crystal symmetry.
A frequency-kink in some modes seen in \bb between T = 80 K and 100 K supports
the first-order lock-in transition, unlike \rb. The unusually sharp Raman
lines(limited by the instrumental response) at very low temperatures and their
temperature evolution suggests that the decay of the low energy phonons is
strongly influenced by the presence of the temperature dependent charge density
wave gap.Comment: 13 pages, 7 figure
Reactive direction control for a mobile robot: A locust-like control of escape direction emerges when a bilateral pair of model locust visual neurons are integrated
Locusts possess a bilateral pair of uniquely identifiable visual neurons that respond vigorously to
the image of an approaching object. These neurons are called the lobula giant movement
detectors (LGMDs). The locust LGMDs have been extensively studied and this has lead to the
development of an LGMD model for use as an artificial collision detector in robotic applications.
To date, robots have been equipped with only a single, central artificial LGMD sensor, and this
triggers a non-directional stop or rotation when a potentially colliding object is detected. Clearly,
for a robot to behave autonomously, it must react differently to stimuli approaching from
different directions. In this study, we implement a bilateral pair of LGMD models in Khepera
robots equipped with normal and panoramic cameras. We integrate the responses of these LGMD
models using methodologies inspired by research on escape direction control in cockroaches.
Using ‘randomised winner-take-all’ or ‘steering wheel’ algorithms for LGMD model integration,
the khepera robots could escape an approaching threat in real time and with a similar
distribution of escape directions as real locusts. We also found that by optimising these
algorithms, we could use them to integrate the left and right DCMD responses of real jumping
locusts offline and reproduce the actual escape directions that the locusts took in a particular
trial. Our results significantly advance the development of an artificial collision detection and
evasion system based on the locust LGMD by allowing it reactive control over robot behaviour.
The success of this approach may also indicate some important areas to be pursued in future
biological research
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