324,844 research outputs found
Spontaneous and Superfluid Chiral Edge States in Exciton-Polariton Condensates
We present a scheme of interaction-induced topological bandstructures based
on the spin anisotropy of exciton-polaritons in semiconductor microcavities. We
predict theoretically that this scheme allows the engineering of topological
gaps, without requiring a magnetic field or strong spin-orbit interaction
(transverse electric-transverse magnetic splitting). Under non-resonant
pumping, we find that an initially topologically trivial system undergoes a
topological transition upon the spontaneous breaking of phase symmetry
associated with polariton condensation. Under resonant coherent pumping, we
find that it is also possible to engineer a topological dispersion that is
linear in wavevector -- a property associated with polariton superfluidity.Comment: 6 pages, 4 figure
A generalized approach to construct benchmark problems for dynamic optimization
Copyright @ Springer-Verlag Berlin Heidelberg 2008.There has been a growing interest in studying evolutionary algorithms in dynamic environments in recent years due to its importance in real applications. However, different dynamic test problems have been used to test and compare the performance of algorithms. This paper proposes a generalized dynamic benchmark generator (GDBG) that can be instantiated into the binary space, real space and combinatorial space. This generator can present a set of different properties to test algorithms by tuning some control parameters. Some experiments are carried out on the real space to study the performance of the generator.This work was supported by the Engineering and Physical Sciences Research Council (EPSRC) of UK under Grant EP/E060722/1
On-Line Portfolio Selection with Moving Average Reversion
On-line portfolio selection has attracted increasing interests in machine
learning and AI communities recently. Empirical evidences show that stock's
high and low prices are temporary and stock price relatives are likely to
follow the mean reversion phenomenon. While the existing mean reversion
strategies are shown to achieve good empirical performance on many real
datasets, they often make the single-period mean reversion assumption, which is
not always satisfied in some real datasets, leading to poor performance when
the assumption does not hold. To overcome the limitation, this article proposes
a multiple-period mean reversion, or so-called Moving Average Reversion (MAR),
and a new on-line portfolio selection strategy named "On-Line Moving Average
Reversion" (OLMAR), which exploits MAR by applying powerful online learning
techniques. From our empirical results, we found that OLMAR can overcome the
drawback of existing mean reversion algorithms and achieve significantly better
results, especially on the datasets where the existing mean reversion
algorithms failed. In addition to superior trading performance, OLMAR also runs
extremely fast, further supporting its practical applicability to a wide range
of applications.Comment: ICML201
On the (non)rigidity of the Frobenius Endomorphism over Gorenstein Rings
It is well-known that for a large class of local rings of positive
characteristic, including complete intersection rings, the Frobenius
endomorphism can be used as a test for finite projective dimension. In this
paper, we exploit this property to study the structure of such rings. One of
our results states that the Picard group of the punctured spectrum of such a
ring cannot have -torsion. When is a local complete intersection,
this recovers (with a purely local algebra proof) an analogous statement for
complete intersections in projective spaces first given in SGA and also a
special case of a conjecture by Gabber. Our method also leads to many simply
constructed examples where rigidity for the Frobenius endomorphism does not
hold, even when the rings are Gorenstein with isolated singularity. This is in
stark contrast to the situation for complete intersection rings. Also, a
related length criterion for modules of finite length and finite projective
dimension is discussed towards the end.Comment: Minor changes in Example 2.2 and Theorem 2.9. Conjecture 1.2 was
added
Chiral field theory of glueball
A chiral field theory of glueball is presented. By adding a
glueball field to a successful Lagrangian of chiral field theory of
pseudoscalar, vector, and axial-vector mesons, the Lagrangian of this theory is
constructed. The couplings between the pseodoscalar glueball field and mesons
are via U(1) anomaly revealed. Qualitative study of the physical processes of
the glueball of is presented. The theoretical
predictions can be used to identify the glueball.Comment: 29 page
Type I planet migration in nearly laminar disks - long term behavior
We carry out 2-D high resolution numerical simulations of type I planet
migration with different disk viscosities. We find that the planet migration is
strongly dependent on disk viscosities. Two kinds of density wave damping
mechanisms are discussed. Accordingly, the angular momentum transport can be
either viscosity dominated or shock dominated, depending on the disk
viscosities. The long term migration behavior is different as well. Influences
of the Rossby vortex instability on planet migration are also discussed. In
addition, we investigate very weak shock generation in inviscid disks by small
mass planets and compare the results with prior analytic results.Comment: Accepted for publication in Ap
Method and apparatus for positioning a robotic end effector
A robotic end effector and operation protocol for a reliable grasp of a target object irrespective of the target's contours is disclosed. A robotic hand includes a plurality of jointed fingers, one of which, like a thumb, is in opposed relation to the other. Each finger is comprised of at least two jointed sections, and provided with reflective proximity sensors, one on the inner surface of each finger section. Each proximity sensor comprises a transmitter of a beam of radiant energy and means for receiving reflections of the transmitted energy when reflected by a target object and for generating electrical signals responsive thereto. On the fingers opposed to the thumb, the proximity sensors on the outermost finger sections are aligned in an outer sensor array and the sensors on the intermediate finger sections and sensors on the innermost finger sections are similarly arranged to form an intermediate sensor array and an inner sensor array, respectively. The invention includes a computer system with software and/or circuitry for a protocol comprising the steps in sequence of: (1) approach axis alignment to maximize the number of outer layer sensors which detect the target; (2) non-contact contour following the target by the robot fingers to minimize target escape potential; and (3) closing to rigidize the target including dynamically re-adjusting the end effector finger alignment to compensate for target motion. A signal conditioning circuit and gain adjustment means are included to maintain the dynamic range of low power reflection signals
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