Reprint of: Flow filtering and the physical sources of aerodynamic sound

The physical sources of sound are expressed in terms of the non-radiating part of the flow. The non-radiating part of the flow can be obtained from convolution filtering, as we demonstrate numerically by using an axi-symmetric jet satisfying the Navier-Stokes equations. Based on the frequency spectrum of the source, we show that the sound sources exhibit more physical behaviour than sound sources based on acoustic analogies. To validate the sources of sound, one needs to let them radiate within the non-radiating flow field. However, our results suggest that the traditional Euler operator linearized about the time-averaged part of the flow should be sufficient to compute the sound field. © 2010 Published by Elsevier Ltd.

Ballasted CNT structures for use as electron sources

The aim of this paper is to describe the growth and optimization of ballasted carbon nanotube (CNT) and CNT/Zinc Oxide nanostructures to produce novel electron sources for use in lighting and x-ray applications. © 2010 ITE and SID.

Comment on "Acoustic chaos in a duct with two separate sound sources" [J. Acoust. Soc. Am. 110, 120-126 (2001)] (L)

In a paper published in this journal in 2001 by Dong [W. G. Dong, X. Y. Huang, and Q. L. Wo, J. Acoust. Soc. Am. 110, 120-126 (2001)] it was claimed that acoustic chaos was obtained experimentally by the nonlinear interaction of two acoustic waves in a duct. In this comment a simple experimental setup and an analytical model is used to show that the dynamics of such systems corresponds to a quasiperiodic motion, and not to a chaotic one. © 2008 Acoustical Society of America.

Spread transform watermarking for video sources

Spread Transform (ST) is a quantization watermarking algorithm in which vectors of the wavelet coefficients of a host work are quantized, using one of two dithered quantizers, to embed hidden information bits; Loo had some success in applying such a scheme to still images. We extend ST to the video watermarking problem. Visibility considerations require that each spreading vector refer to corresponding pixels in each of several frames, that is, a multi-frame embedding approach. Use of the hierarchical complex wavelet transform (CWT) for a visual mask reduces computation and improves robustness to jitter and valumetric scaling. We present a method of recovering temporal synchronization at the detector, and give initial results demonstrating the robustness and capacity of the scheme.

Uncooled DWDM transmission system using tunable laser sources with anti-mode-hop control protocol

We propose an uncooled DWDM system where errors from uncontrolled laser mode-hopping are avoided by using a control protocol based on monitoring SMSR. We describe a proof-of-principle demonstration of a novel uncooled 50GHz DWDM system. © 2011 IEEE.

The silent base flow and the sound sources in a laminar jet.

An algorithm to compute the silent base flow sources of sound in a jet is introduced. The algorithm is based on spatiotemporal filtering of the flow field and is applicable to multifrequency sources. It is applied to an axisymmetric laminar jet and the resulting sources are validated successfully. The sources are compared to those obtained from two classical acoustic analogies, based on quiescent and time-averaged base flows. The comparison demonstrates how the silent base flow sources shed light on the sound generation process. It is shown that the dominant source mechanism in the axisymmetric laminar jet is "shear-noise," which is a linear mechanism. The algorithm presented here could be applied to fully turbulent flows to understand the aerodynamic noise-generation mechanism.

Data Analysis on Complicated Construction Data Sources: Vision, Research, and Recent Developments

Compared with construction data sources that are usually stored and analyzed in spreadsheets and single data tables, data sources with more complicated structures, such as text documents, site images, web pages, and project schedules have been less intensively studied due to additional challenges in data preparation, representation, and analysis. In this paper, our definition and vision for advanced data analysis addressing such challenges are presented, together with related research results from previous work, as well as our recent developments of data analysis on text-based, image-based, web-based, and network-based construction sources. It is shown in this paper that particular data preparation, representation, and analysis operations should be identified, and integrated with careful problem investigations and scientific validation measures in order to provide general frameworks in support of information search and knowledge discovery from such information-abundant data sources.