Collective optimization over average quantities

This paper addresses the design of algorithms for the collective optimization of a cost function defined over average quantities in the presence of limited communication. We argue that several meaningful collective optimization problems can be formulated in this way. As an application of the proposed approach, we propose a novel algorithm that achieves synchronization or balancing in phase models of coupled oscillators under mild connectedness assumptions on the (possibly time-varying and unidirectional) communication graphs. © 2006 IEEE.

A canonical normal SBLI flow relevant to external compression inlets

The normal shock wave / boundary layer interaction (normal SBLI) is important to the operation and performance of a supersonic inlet, and the normal SBLI is particularly prominent in external compression inlets. To improve our understanding of such interactions, it is helpful to make use of fundamental flows which capture the main elements of inlets, without resorting to the level of complexity and system integration associated with full-geometry inlets. In this paper, several fundamental fiow-fleld configurations have been considered as possible test cases to represent the normal SBLI aspects found in typical external compression inlets, and it was found that the spillage-diffuser more closely retains the basic flow features of an external compression inlet than the other configurations. In particular, this flow-fleld allows the normal shock Mach number as well as the amount and rate of subsonic diffusion to be all held approximately constant mid independent of the application of flow control. In addition, a survey of several external compression inlets was conducted to quantify the flow and geometric parameters of the spillage-diffuser relevant to actual inlets. The results indicated that such a flow may be especially relevant if the terminal Mach number is about 1.3 to 1.4, the confinement parameter is around 10%, the width around twice or three times the height, and with the area expansion just downstream of the shock on the conservative side of the stall limit for incompressible diffusers. © 2013 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.

Canonical normal shock wave/boundary-layer interaction flows relevant to external compression inlets

The normal shock wave/boundary-layer interaction is important to the operation and performance of a supersonic inlet, and the normal shock wave/boundary-layer interaction is particularly prominent in external compression inlets. To improve understanding of such interactions, it is helpful to make use of fundamental flows that capture the main elements of inlets, without resorting to the level of complexity and system integration associated with full-geometry inlets. In this paper, several fundamental flowfield configurations have been considered as possible test cases to represent the normal shock wave/boundary-layer interaction aspects found in typical external compression inlets, and it was found that the spillage diffuser more closely retains the basic flow features of an external compression inlet than the other configurations. In particular, this flowfield allows the normal shock Mach number as well as the amount and rate of subsonic diffusion to all be held approximately constant and independent of the application of flow control. In addition, a survey of several external compression inlets was conducted to quantify the flow and geometric parameters of the spillage diffuser relevant to actual inlets. The results indicated that such a flow may be especially relevant if the terminal Mach number is about 1.3 to 1.4, the confinement parameter is around 10%, and the width is around twice or three times the height. In addition, the area expansion downstream of the shock should be limited to the conservative side of incipient stall based on incompressible diffusers. Copyright © 2013 by the authors.

Average corotation of line segments near a point and vortex identification

An easy-to-interpret kinematic quantity measuring the average corotation of material line segments near a point is introduced and applied to vortex identification. At a given point, the vector of average corotation of line segments is defined as the average of the instantaneous local rigid-body rotation over "all planar cross sections" passing through the examined point. The vortex-identification method based on average corotation is a one-parameter, region-type local method sensitive to the axial stretching rate as well as to the inner configuration of the velocity gradient tensor. The method is derived from a well-defined interpretation of the local flow kinematics to determine the "plane of swirling" and is also applicable to compressible and variable-density flows. Practical application to direct numerical simulation datasets includes a hairpin vortex of boundary-layer transition, the reconnection process of two Burgers vortices, a flow around an inclined flat plate, and a flow around a revolving insect wing. The results agree well with some popular local methods and perform better in regions of strong shearing. Copyright © 2013 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.

High average power and short pulse duration continuous wave mode-locked Nd : GdVO4 laser with a semiconductor absorber mirror

Passive mode locking of a solid-state Nd:GdVO4 laser is demonstrated. The laser is mode locked by use of a semiconductor absorber mirror (SAM). A low Nd3+ doped Nd:GdVO4 crystal is used to mitigate the thermal lens effect of the laser crystal at a high pump power. The maximum average output power is up to 6.5 W, and the pulse duration is as short as 6.2 ps. The optic-to-optic conversion efficiency is 32.5% and the repetition rate is about 110 MHz.

High-average-power and high-conversion-efficiency continuous wave mode-locked Nd : YVO4 laser with a semiconductor absorber mirror

A high-power continuous wave (cw) mode-locked Nd:YVO4 solid-state laser was demonstrated by use of a semiconductor absorber mirror (SAM). The maximum average output power was 8.1 W and the optic-to-optic conversion efficiency was about 41 %. At the maximum incident pump power, the pulse width was about 8.6 ps and the repetition rate was 130 MHz. Experimental results indicated that this absorber was suitable for high power mode-locked solid-state lasers. (C) 2006 Elsevier Ltd. All rights reserved.

Dynamics of quantum dissipation systems interacting with fermion and boson grand canonical bath ensembles: Hierarchical equations of motion approach

A hierarchical equations of motion formalism for a quantum dissipation system in a grand canonical bath ensemble surrounding is constructed on the basis of the calculus-on-path-integral algorithm, together with the parametrization of arbitrary non-Markovian bath that satisfies fluctuation-dissipation theorem. The influence functionals for both the fermion or boson bath interaction are found to be of the same path integral expression as the canonical bath, assuming they all satisfy the Gaussian statistics. However, the equation of motion formalism is different due to the fluctuation-dissipation theories that are distinct and used explicitly. The implications of the present work to quantum transport through molecular wires and electron transfer in complex molecular systems are discussed. (c) 2007 American Institute of Physics.

A differential recursive scheme for suppression of Peak to average power ratio for OFDM

A differential recursive scheme for suppression of Peak to average power ratio (PAPR) for Orthogonal frequency division multiplexing (OFDM) signal is proposed in this thesis. The pseudo-randomized modulating vector for the subcarrier series is differentially phase-encoded between successive components in frequency domain first, and recursion manipulates several samples of Inverse fast Fourier transformation (IFFT) output in time domain. Theoretical analysis and experimental result exhibit advantage of differential recursive scheme over direct output scheme in PAPR suppression. And the overall block diagram of the scheme is also given.

Realization of GaAs/AlGaAs quantum-cascade lasers with high average optical power

Quasi-continuous-wave operation of GaAs/AlGaAs quantum-cascade lasers with high average optical power is demonstrated. Double X-ray diffraction has been used to investigate the quality of the epitaxial material. The compositional gradients and the interface quality are controlled effectively. The corrected average power of per facet about 17 mW and temperature tuning coefficient of the gain peak about 0.91 nm/K from 83 K to 140 K is achieved in pulse operation. Best value of threshold current density is less than 3.0 kA/cm(2) at 83 K. (C) 2005 Elsevier Ltd. All rights reserved.

An automatic step adjustment method for average power analysis technique used in fiber amplifiers

An automatic step adjustment (ASA) method for average power analysis (APA) technique used in fiber amplifiers is proposed in this paper for the first time. In comparison with the traditional APA technique, the proposed method has suggested two unique merits such as a higher order accuracy and an ASA mechanism, so that it can significantly shorten the computing time and improve the solution accuracy. A test example demonstrates that, by comparing to the APA technique, the proposed method increases the computing speed by more than a hundredfold under the same errors. By computing the model equations of erbium-doped fiber amplifiers, the numerical results show that our method can improve the solution accuracy by over two orders of magnitude at the same amplifying section number. The proposed method has the capacity to rapidly and effectively compute the model equations of fiber Raman amplifiers and semiconductor lasers. (c) 2006 Optical Society of America