Statistical Properties of Interacting Bose Gases in Quasi-2D Harmonic Traps

The analytical probability distribution of the quasi-2D (and purely 2D) ideal and interacting Bose gas are investigated by using a canonical ensemble approach. Using the analytical probability distribution of the condensate, the statistical properties such as the mean occupation number and particle number fluctuations of the condensate are calculated. Researches show that there is a continuous crossover of the statistical properties from a quasi-2D to a purely 2D ideal or interacting gases. Different from the case of a 3D Bose gas, the interaction between atoms changes in a deep way the nature of the particle number fluctuations.Comment: RevTex, 10pages, 4 figures, E-mail: [email protected]

Consensus analysis of multiagent networks via aggregated and pinning approaches

This is the post-print version of of the Article - Copyright @ 2011 IEEEIn this paper, the consensus problem of multiagent nonlinear directed networks (MNDNs) is discussed in the case that a MNDN does not have a spanning tree to reach the consensus of all nodes. By using the Lie algebra theory, a linear node-and-node pinning method is proposed to achieve a consensus of a MNDN for all nonlinear functions satisfying a given set of conditions. Based on some optimal algorithms, large-size networks are aggregated to small-size ones. Then, by applying the principle minor theory to the small-size networks, a sufficient condition is given to reduce the number of controlled nodes. Finally, simulation results are given to illustrate the effectiveness of the developed criteria.This work was jointly supported by CityU under a research grant (7002355) and GRF funding (CityU 101109)

Heat transfer from the stagnation area of a heated cylinder at Re(D) = 140,000 affected by free-stream turbulence

This is the post-print version of the final paper published in International Journal of Heat and Mass Transfer. The published article is available from the link below. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. Copyright @ 2011 Elsevier B.V.The effect of free-stream grid-turbulence on the flow around and heat transfer from the stagnation region of a circular cylinder was studied using direct numerical simulations (DNS). Simulations with and without free-stream fluctuations were carried out at a Reynolds number of Re(D) = 140,000 (based on the inflow velocity and the cylinder diameter D), which is in the higher subcritical range. A splitter plate was introduced behind the cylinder to counteract the formation of a vortex street. To resolve the flow up to 746.5 million grid points were employed. Compared to the fully laminar simulation, the addition of Tu = 30% grid turbulence at the inflow plane was found to lead to an increase in heat transfer at the stagnation line of the cylinder of 66%. A very good agreement was obtained with the correlations of Dullenkopf and Mayle [K. Dullenkopf, R. Mayle, The effects of incident turbulence and moving wakes on laminar heat transfer in gas turbines, ASME J. Turbomach. 116 (1994) 23–28; K. Dullenkopf, R. Mayle, An account of free-stream-turbulence length scale on laminar heat transfer, ASME J. Turbomach. 117 (1995) 401–406].The German Research Foundatio

Single-input and single-output (SISO) controller reduction based on the L1L_1-norm

This paper proposes a new method to solve the controller-reduction problem based on the $L_1$-norm. This method uses a reduced-order closed-loop system to deduce reduced-order controllers. The problem of obtaining the required lower-order closed-loop system was formulated as an $L_1$-norm optimization, and the conditions were provided for guaranteeing the internal stability and the existence of lower-order controllers from the obtained reduced-order closed-loop system. In addition, the particle swarm optimization and sequence linear programming were adopted to solve the resultant $L_1$-norm optimization. Two numerical examples demonstrated the effectiveness of the proposed method

Entanglement fidelity and measurement of entanglement preserving in quantum processes

The entanglement fidelity provides a measure of how well the entanglement between two subsystems is preserved in a quantum process. By using a simple model we show that in some cases this quantity in its original definition fails in the measurement of the entanglement preserving. On the contrary, the modified entanglement fidelity, obtained by using a proper local unitary transformation on a subsystem, is shown to exhibit the behavior similar to that of the concurrence in the quantum evolution.Comment: 4 pages, 2 figures. v2: repaired a severe oversight, removed an incorrect claim, added references; v3: version accepted for publication in Phys. Rev.

Zitterbewegung by Quantum Field Theory Considerations

The validity of the work by Lamata et al [Phys. Rev. Lett. 98, 253005 (2007)] can be further shown by quantum field theory considerations.Comment: 5 pages, no figure, to be published in Physical Review