501,530 research outputs found
Complex Dynamics of Correlated Electrons in Molecular Double Ionization by an Ultrashort Intense Laser Pulse
With a semiclassical quasi-static model we achieve an insight into the
complex dynamics of two correlated electrons under the combined influence of a
two-center Coulomb potential and an intense laser field. The model calculation
is able to reproduce experimental data of nitrogen molecules for a wide range
of laser intensities from tunnelling to over-the-barrier regime, and predicts a
significant alignment effect on the ratio of double over single ion yield. The
classical trajectory analysis allows to unveil sub-cycle molecular double
ionization dynamics.Comment: 5 pages, 5 figures. to appear in Phys. Rev. Lett.(2007
Roll waves in mud
The stability of a viscoplastic fluid film falling down an inclined plane is explored, with the aim of determining the critical Reynolds number for the onset of roll waves. The HerschelâBulkley constitutive law is adopted and the fluid is assumed two-dimensional and incompressible. The linear stability problem is described for an equilibrium in the form of a uniform sheet flow, when perturbed by introducing an infinitesimal stress perturbation. This flow is stable for very high Reynolds numbers because the rigid plug riding atop the fluid layer cannot be deformed and the free surface remains flat. If the flow is perturbed by allowing arbitrarily small strain rates, on the other hand, the plug is immediately replaced by a weakly yielded âpseudo-plugâ that can deform and reshape the free surface. This situation is modelled by lubrication theory at zero Reynolds number, and it is shown how the fluid exhibits free-surface instabilities at order-one Reynolds numbers. Simpler models based on vertical averages of the fluid equations are evaluated, and one particular model is identified that correctly predicts the onset of instability. That model is used to describe nonlinear roll waves
High-order harmonic generation from diatomic molecules with large internuclear distance: The effect of two-center interference
In the present paper, we investigate the high-order harmonic generation (HHG)
from diatomic molecules with large internuclear distance using a strong field
approximation (SFA) model. We find that the hump and dip structure emerges in
the plateau region of the harmonic spectrum, and the location of this striking
structure is sensitive to the laser intensity. Our model analysis reveals that
two-center interference as well as the interference between different
recombination electron trajectories are responsible for the unusual enhanced or
suppressed harmonic yield at a certain order, and these interference effects
are greatly influenced by the laser parameters such as intensity.Comment: 5 pages,4 figure
A Numerical Study of Improved Quark Actions on Anisotropic Lattices
Tadpole improved Wilson quark actions with clover terms on anisotropic
lattices are studied numerically.
Using asymmetric lattice volumes, the pseudo-scalar meson dispersion
relations are measured for 8 lowest lattice momentum modes with quark mass
values ranging from the strange to the charm quark with various values of the
gauge coupling and 3 different values of the bare speed of light
parameter . These results can be utilized to extrapolate or interpolate to
obtain the optimal value for the bare speed of light parameter
at a given gauge coupling for all bare quark mass values . In particular,
the optimal values of at the physical strange and charm quark mass are
given for various gauge couplings.
The lattice action with these optimized parameters can then be used to study
physical properties of hadrons involving either light or heavy quarks.Comment: 22 pages, 7 figures, 2 tables. Analysis greatly modified compared
with previous versio
Synchronization of coupled neutral-type neural networks with jumping-mode-dependent discrete and unbounded distributed delays
This is the post-print version of the Article. The official published version can be accessed from the links below - Copyright @ 2013 IEEE.In this paper, the synchronization problem is studied for an array of N identical delayed neutral-type neural networks with Markovian jumping parameters. The coupled networks involve both the mode-dependent discrete-time delays and the mode-dependent unbounded distributed time delays. All the network parameters including the coupling matrix are also dependent on the Markovian jumping mode. By introducing novel Lyapunov-Krasovskii functionals and using some analytical techniques, sufficient conditions are derived to guarantee that the coupled networks are asymptotically synchronized in mean square. The derived sufficient conditions are closely related with the discrete-time delays, the distributed time delays, the mode transition probability, and the coupling structure of the networks. The obtained criteria are given in terms of matrix inequalities that can be efficiently solved by employing the semidefinite program method. Numerical simulations are presented to further demonstrate the effectiveness of the proposed approach.This work was supported in part by the Royal Society of the U.K., the National Natural Science Foundation of China under Grants 61074129, 61174136 and 61134009, and the Natural Science Foundation of Jiangsu Province of China under Grants BK2010313 and BK2011598
Observational Test of Coronal Magnetic Field Models I. Comparison with Potential Field Model
Recent advances have made it possible to obtain two-dimensional line-of-sight
magnetic field maps of the solar corona from spectropolarimetric observations
of the Fe XIII 1075 nm forbidden coronal emission line. Together with the
linear polarization measurements that map the azimuthal direction of the
coronal magnetic field, these coronal vector magnetograms now allow for direct
observational testing of theoretical coronal magnetic field models. This paper
presents a study testing the validity of potential-field coronal magnetic field
models. We constructed a theoretical coronal magnetic field model of active
region AR 10582 observed by the SOLARC coronagraph in 2004 by a global
potential field extrapolation of the synoptic map of Carrington Rotation 2014.
Synthesized linear and circular polarization maps from thin layers of the
coronal magnetic field model above the active region along the line of sight
are compared with the observed maps. We found that reasonable agreement occurs
from layers located just above the sunspot of AR 10582, near the plane of the
sky. This result provides the first observational evidence that potential field
extrapolation can yield a reasonable approximation of the magnetic field
configuration of the solar corona for simple and stable active regions.Comment: 25 pages, 11 figures. ApJ in pres
Robust synchronization of an array of coupled stochastic discrete-time delayed neural networks
Copyright [2008] IEEE. This material is posted here with permission of the IEEE. Such permission of the IEEE does not in any way imply IEEE endorsement of any of Brunel University's products or services. Internal or personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution must be obtained from the IEEE by writing to [email protected]. By choosing to view this document, you agree to all provisions of the copyright laws protecting it.This paper is concerned with the robust synchronization problem for an array of coupled stochastic discrete-time neural networks with time-varying delay. The individual neural network is subject to parameter uncertainty, stochastic disturbance, and time-varying delay, where the norm-bounded parameter uncertainties exist in both the state and weight matrices, the stochastic disturbance is in the form of a scalar Wiener process, and the time delay enters into the activation function. For the array of coupled neural networks, the constant coupling and delayed coupling are simultaneously considered. We aim to establish easy-to-verify conditions under which the addressed neural networks are synchronized. By using the Kronecker product as an effective tool, a linear matrix inequality (LMI) approach is developed to derive several sufficient criteria ensuring the coupled delayed neural networks to be globally, robustly, exponentially synchronized in the mean square. The LMI-based conditions obtained are dependent not only on the lower bound but also on the upper bound of the time-varying delay, and can be solved efficiently via the Matlab LMI Toolbox. Two numerical examples are given to demonstrate the usefulness of the proposed synchronization scheme
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