2,853 research outputs found
Smallest eigenvalues of Hankel matrices for exponential weights
AbstractWe obtain the rate of decay of the smallest eigenvalue of the Hankel matrices â«Itj+kW2(t)dtj,k=0n for a general class of even exponential weights W2=exp(â2Q) on an interval I. More precise asymptotics for more special weights have been obtained by many authors
Superradiant and Aharonov-Bohm effect for the quantum ring exciton
The Aharonov-Bohm and superradiant effect on the redaitive decay rate of an
exciton in a quantum ring is studied. With the increasing of ring radius, the
exciton decay rate is enhanced by superradiance, while the amplitude of AB
oscillation is decreased. The competition between these two effects is shown
explicitly and may be observable in time-resolved exeriments.Comment: 4 pages, 2 figures, to appear in Solid State Communications (2004
UAV Maneuvering Target Tracking in Uncertain Environments based on Deep Reinforcement Learning and Meta-learning
This paper combines Deep Reinforcement Learning (DRL) with Meta-learning and proposes a novel approach, named Meta Twin Delayed Deep Deterministic policy gradient (Meta-TD3), to realize the control of Unmanned Aerial Vehicle (UAV), allowing a UAV to quickly track a target in an environment where the motion of a target is uncertain. This approach can be applied to a variety of scenarios, such as wildlife protection, emergency aid, and remote sensing. We consider multi-tasks experience replay buffer to provide data for multi-tasks learning of DRL algorithm, and we combine Meta-learning to develop a multi-task reinforcement learning update method to ensure the generalization capability of reinforcement learning. Compared with the state-of-the-art algorithms, Deep Deterministic Policy Gradient (DDPG) and Twin Delayed Deep Deterministic policy gradient (TD3), experimental results show that the Meta-TD3 algorithm has achieved a great improvement in terms of both convergence value and convergence rate. In a UAV target tracking problem, Meta-TD3 only requires a few steps to train to enable a UAV to adapt quickly to a new target movement mode more and maintain a better tracking effectiveness
Impact of Subleading Corrections on Hadronic B Decays
We study the subleading corrections originating from the 3-parton (q\bar q g)
Fock states of final-state mesons in B decays. The corrections could give
significant contributions to decays involving an \omega or \eta^{(\prime)} in
the final states. Our results indicate the similarity of \omega K and \omega
\pi^- rates, of order 5\times 10^{-6}, consistent with the recent measurements.
We obtain a_2(B\to J/\psi K)\approx 0.27+0.05i, in good agreement with data.
Without resorting to the unknown singlet annihilation effects, 3-parton Fock
state contributions can enhance the branching ratios of K\eta' to the level
above 50\times 10^{-6}.Comment: 5 pages, 5 figures, revtex4; some typos corrected, a new figure and a
reference added, more explanations for the calculation provided, to appear in
Phys. Rev.
Orientations of two coupled molecules
Orientation states of two coupled polar molecules controlled by laser pulses
are studied theoretically. By varying the period of a series of periodically
applied laser pulse, transition from regular to chaotic behavior may occur.
Schmidt decomposition is used to measure the degree of entanglement. It is
found that the entanglement can be enhanced by increasing the strength of laser
pulse.Comment: 4 pages, 4 figures, to appear in Chem. Phys. Lett.(2004
Dynamic Analysis of a Rotating Shaft Subject to the Double Cutting Force and Time-varying Mass Effects of the Rod
AbstractThis paper investigates the dynamic behaviors of a rotating shaft subjected to the double cutting force and time-varying mass effects. The Timoshenko beam theory is used to model the rotating shaft, and the general boundary condition is assumed as the clamped-hinged supports. This system is used to simulate the manufacture process of the double turret CNC lathes, and the mass of the rod which is reduced gradually in cutting process. The system equations of motion are derived based on the global assumed mode method, and the dynamic responses of the system are obtained by Runge-Kutta numerical method. The transformation matrix is derived to make the equation of motion completing the boundary geometric constraints. The numerical results compare the dynamic response in different moving speeds and skew angles of the cutting forces with/without the time-varying mass effects. Additionally, this paper compares the response with single cutting force and double force. The results show that the double moving force system can reduce not only the machining time but also the amplitude of shaft vibration
Propagation inhibition and wave localization in a 2D random liquid medium
Acoustic propagation and scattering in water containing many parallel
air-filled cylinders is studied. Two situations are considered and compared:
(1) wave propagating through the array of cylinders, imitating a traditional
experimental setup, and (2) wave transmitted from a source located inside the
ensemble. We show that waves can be blocked from propagation by disorders in
the first scenario, but the inhibition does not necessarily imply wave
localization. Furthermore, the results reveal the phenomenon of wave
localization in a range of frequencies.Comment: Typos in Fiures are correcte
Implications of Recent Measurements of Hadronic Charmless B Decays
Implications of recent CLEO measurements of hadronic charmless B decays are
discussed. (i) Employing the Bauer-Stech-Wirbel (BSW) model for form factors as
a benchmark, the data indicate that the form factor
is smaller than that predicted by the BSW model, whereas the
data of imply that the form factors are greater than the BSW model's values. (ii) The tree-dominated
modes imply that the effective
number of colors N_c(LL) for (V-A)(V-A) operators is preferred to be smaller,
while the current limit on shows that N_c(LR)>3. The data of and clearly indicate that . (iii) In
order to understand the observed suppression of and
non-suppression of modes, both being governed by the form factor
, the unitarity angle is preferred to be greater than
. By contrast, the new measurement of no
longer strongly favors . (iv) The observed pattern K^-\pi^+\sim
\ov K^0\pi^-\sim {2\over 3}K^-\pi^0 is consistent with the theoretical
expectation: The constructive interference between electroweak and QCD penguin
diagrams in the mode explains why {\cal B}(B^-\to K^-\pi^0)>{1\over
2}{\cal B}(\ov B^0\to K^-\pi^+). (v) The observation \nc(LL)<3<\nc(LR) and
our preference for \nc(LL)\sim 2 and \nc(LR)\sim 6 are justified by a
recent perturbative QCD calculation of hadronic rare B decays in the heavy
quark limit.Comment: 21 pages; CLEO measurements of several charmless B decay modes are
updated. Discussion of the unitarity angle gamma in the \rho\pi mode is
revise
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