7,438 research outputs found
Control of a lane-drop bottleneck through variable speed limits
In this study, we formulate the VSL control problem for the traffic system in
a zone upstream to a lane-drop bottleneck based on two traffic flow models: the
Lighthill-Whitham-Richards (LWR) model, which is an infinite-dimensional
partial differential equation, and the link queue model, which is a
finite-dimensional ordinary differential equation. In both models, the
discharging flow-rate is determined by a recently developed model of capacity
drop, and the upstream in-flux is regulated by the speed limit in the VSL zone.
Since the link queue model approximates the LWR model and is much simpler, we
first analyze the control problem and develop effective VSL strategies based on
the former. First for an open-loop control system with a constant speed limit,
we prove that a constant speed limit can introduce an uncongested equilibrium
state, in addition to a congested one with capacity drop, but the congested
equilibrium state is always exponentially stable. Then we apply a feedback
proportional-integral (PI) controller to form a closed-loop control system, in
which the congested equilibrium state and, therefore, capacity drop can be
removed by the I-controller. Both analytical and numerical results show that,
with appropriately chosen controller parameters, the closed-loop control system
is stable, effect, and robust. Finally, we show that the VSL strategies based
on I- and PI-controllers are also stable, effective, and robust for the LWR
model. Since the properties of the control system are transferable between the
two models, we establish a dual approach for studying the control problems of
nonlinear traffic flow systems. We also confirm that the VSL strategy is
effective only if capacity drop occurs. The obtained method and insights can be
useful for future studies on other traffic control methods and implementations
of VSL strategies.Comment: 31 pages, 14 figure
Tailoring Accelerating Beams in Phase Space
An appropriate design of wavefront will enable light fields propagating along
arbitrary trajectories thus forming accelerating beams in free space. Previous
ways of designing such accelerating beams mainly rely on caustic methods, which
start from diffraction integrals and only deal with two-dimensional fields.
Here we introduce a new perspective to construct accelerating beams in phase
space by designing the corresponding Wigner distribution function (WDF). We
find such a WDF-based method is capable of providing both the initial field
distribution and the angular spectrum in need by projecting the WDF into the
real space and the Fourier space respectively. Moreover, this approach applies
to the construction of both two- and three-dimensional fields, greatly
generalizing previous caustic methods. It may therefore open up a new route to
construct highly-tailored accelerating beams and facilitate applications
ranging from particle manipulation and trapping to optical routing as well as
material processing.Comment: 8 pages, 6 figure
Asymmetries and Violation in Charmed Baryon Decays into Neutral Kaons
We study the asymmetries and violations in charm-baryon
decays with neutral kaons in the final state. The asymmetry can
be used to search for two-body doubly Cabibbo-suppressed amplitudes of
charm-baryon decays, with the one in as a promising
observable. Besides, it is studied for a new -violation effect in these
processes, induced by the interference between the Cabibbo-favored and doubly
Cabibbo-suppressed amplitudes with the neutral kaon mixing. Once the new
CP-violation effect is determined by experiments, the direct asymmetry in
neutral kaon modes can then be extracted and used to search for new physics.
The numerical results based on symmetry will be tested by the
experiments in the future.Comment: 15 pages, 3 tables. Version published in JHE
KCRC-LCD: Discriminative Kernel Collaborative Representation with Locality Constrained Dictionary for Visual Categorization
We consider the image classification problem via kernel collaborative
representation classification with locality constrained dictionary (KCRC-LCD).
Specifically, we propose a kernel collaborative representation classification
(KCRC) approach in which kernel method is used to improve the discrimination
ability of collaborative representation classification (CRC). We then measure
the similarities between the query and atoms in the global dictionary in order
to construct a locality constrained dictionary (LCD) for KCRC. In addition, we
discuss several similarity measure approaches in LCD and further present a
simple yet effective unified similarity measure whose superiority is validated
in experiments. There are several appealing aspects associated with LCD. First,
LCD can be nicely incorporated under the framework of KCRC. The LCD similarity
measure can be kernelized under KCRC, which theoretically links CRC and LCD
under the kernel method. Second, KCRC-LCD becomes more scalable to both the
training set size and the feature dimension. Example shows that KCRC is able to
perfectly classify data with certain distribution, while conventional CRC fails
completely. Comprehensive experiments on many public datasets also show that
KCRC-LCD is a robust discriminative classifier with both excellent performance
and good scalability, being comparable or outperforming many other
state-of-the-art approaches
in a supersymmetric theory with an explicit R-parity violation
We studied the process in a
violating supersymmetric Model with the effects from both B- and L-violating
interactions. The calculation shows that it is possible to detect a
violating signal at the Next Linear Collider. Information about the B-violating
interaction in this model could be obtained under very clean background, if we
take the present upper bounds for the parameters in the supersymmetric interactions. Even if we can not detect a signal of in the
experiment, we may get more stringent constraints on the heavy-flavor
couplings.Comment: 16 pages, 6 figure
Does unemployment have asymmetric effects on suicide rates? Evidence from the United States: 1928β2013
This study applied the recently developed asymmetric causality
test and asymmetric generalised impulse-response method to
demonstrate the dynamic relationship between unemployment and
suicide rates in the U.S. over the period of 1928β2013. The results
suggest that there exist asymmetric effects of unemployment
on suicide rates. An economic recession (in terms of an increase
in unemployment rate) is more likely to increase the suicide rate
among an old age group (55β64 years old) than among other age
groups, while an economic expansion (in terms of a decrease in
unemployment rate) is more likely to reduce the suicide rate of young
(15β24 and 25β34 years old) and middle age groups (35β44 and 45β
54 years old) than their counterpart. Therefore, policy implications
generated from our results include the following: that intervention
to prevent suicidal behaviour should be directed more towards the
older age group during economic recession and that we may expect
that an economic expansion may not result in a great reduction of
suicide rates for the old age (55β64 years) group
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