129,107 research outputs found
The dissipation of the system and the atom in two-photon Jaynes-Cummings model with degenerate atomic levels
The method of perturbative expansion of master equation is employed to study
the dissipative properties of system and of atom in the two-photon
Jaynes-Cummings model (JCM) with degenerate atomic levels. The numerical
results show that the degeneracy of atomic levels prolongs the period of
entanglement between the atom and the field. The asymptotic value of atomic
linear entropy is apparently increased by the degeneration. The amplitude of
local entanglement and disentanglement is suppressed. The better the initial
coherence property of the degenerate atom, the larger the coherence loss.Comment: 11 pages, 4 figure
Corrections to scaling in the dynamic approach to the phase transition with quenched disorder
With dynamic Monte Carlo simulations, we investigate the continuous phase
transition in the three-dimensional three-state random-bond Potts model. We
propose a useful technique to deal with the strong corrections to the dynamic
scaling form. The critical point, static exponents and , and
dynamic exponent are accurately determined. Particularly, the results
support that the exponent satisfies the lower bound .Comment: 10 pages, 6 figures, 2 table
Fluctuation-Driven Vortex Fractionalization in Topologically Ordered Superfluids of Cold Atoms
We have studied spin structures of fluctuation-driven fractionalized vortices
and topological spin order in 2D nematic superfluids of cold sodium atoms. Our
Monte Carlo simulations suggest a softened pi-spin disclination structure in a
half-quantum vortex when spin correlations are short ranged; in addition,
calculations indicate that a unique non-local topological spin order emerges
simultaneously as cold atoms become a superfluid below a critical temperature.
We have also estimated fluctuation-dependent critical frequencies for
half-quantum vortex nucleation in rotating optical traps and discussed probing
these excitations in experiments.Comment: 5 pages, 2 figures; revised version accepted by Europhysics Letter
Dynamic effect of overhangs and islands at the depinning transition in two-dimensional magnets
With the Monte Carlo methods, we systematically investigate the short-time
dynamics of domain-wall motion in the two-dimensional random-field Ising model
with a driving field ?DRFIM?. We accurately determine the depinning transition
field and critical exponents. Through two different definitions of the domain
interface, we examine the dynamics of overhangs and islands. At the depinning
transition, the dynamic effect of overhangs and islands reaches maximum. We
argue that this should be an important mechanism leading the DRFIM model to a
different universality class from the Edwards-Wilkinson equation with quenched
disorderComment: 9 pages, 6 figure
Development of a hybrid multi-scale simulation approach for spray processes
This paper presents a multi-scale approach coupling a Eulerian interface-tracking method and a Lagrangian particle-tracking method to simulate liquid atomisation processes. This method aims to represent the complete spray atomisation process including the primary break-up process and the secondary break-up process, paving the way for high-fidelity simulations of spray atomisation in the dense spray zone and spray combustion in the dilute spray zone. The Eulerian method is based on the coupled level-set and volume-of-fluid method for interface tracking, which can accurately simulate the primary break-up process. For the coupling approach, the Eulerian method describes only large droplet and ligament structures, while small-scale droplet structures are removed from the resolved Eulerian description and transformed into Lagrangian point-source spherical droplets. The Lagrangian method is thus used to track smaller droplets. In this study, two-dimensional simulations of liquid jet atomisation are performed. We analysed Lagrangian droplet formation and motion using the multi-scale approach. The results indicate that the coupling method successfully achieves multi-scale simulations and accurately models droplet motion after the Eulerian–Lagrangian transition. Finally, the reverse Lagrangian–Eulerian transition is also considered to cope with interactions between Eulerian droplets and Lagrangian droplets.This work was supported by the Engineering and Physical Sciences Research Council of the UK (grant number EP/L000199/1)
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All-optical non-volatile tuning of an AMZI-coupled ring resonator with GST phase-change material
We present a Ge2Sb2Te5 (GST)-integrated ring resonator with the tuning enabled by an all-optical phase change of GST using a sequence of optical pulses. The tuning is non-volatile and repeatable, with no static power consumption due to the “self-holding” feature of the GST phase-change material. The 2 μm long GST can be partially crystallized by controlling the number of pulses, increasing the tuning freedom. The coupling between the ring resonator and the bus waveguide is based on an asymmetric Mach–Zehnder interferometer. The coupling strength is wavelength-dependent, so that an optimal wavelength can be selected for the probe light to get more than 20 dB transmission contrast between the amorphous and crystalline GST states
Cutout reinforcements for shear loaded laminate and sandwich composite panels
This paper presents the numerical and experimental studies of shear loaded
laminated and sandwich carbon/epoxy composite panels with cutouts and
reinforcements aiming at reducing the cutout stress concentration and increasing
the buckling stability of the panels. The effect of different cutout sizes and
the design and materials of cutout reinforcements on the stress and buckling
behaviour of the panels are evaluated. For the sandwich panels with a range of
cutout size and a constant weight, an optimal ratio of the core to the face
thickness has been studied for the maximum buckling stability. The finite
element method and an analytical method are employed to perform parametric
studies. In both constant stress and constant displacement shear loading
conditions, the results are in very good agreement with those obtained from
experiment for selected cutout reinforcement cases. Conclusions are drawn on the
cutout reinforcement design and improvement of stress concentration and buckling
behaviour of shear loaded laminated and sandwich composite panels with cutouts
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Enhanced forward stimulated Brillouin scattering in silicon photonic slot waveguide Bragg grating
We study the forward stimulated Brillouin scattering process in a suspended silicon slot waveguide Bragg grating. Full-vectorial formalism is applied to analyze the interplay of electrostriction and radiation pressure. We show that radiation pressure is the dominant factor in the proposed waveguide. The Brillouin gain strongly depends on the structural parameters and the maximum value in the order of 106 W−1 m−1 is obtained in the slow light regime, which is more than two orders larger than that of the stand-alone strip and slot waveguides
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