Biomedical subjects

Ning Xiang

Publications and source records attributed to Ning Xiang.

8 recordsLinked to original sources

PubMed2006

A specialized fast cross-correlation for acoustical measurements using coded sequences.

In acoustics applications, binary maximal-length sequences and related sequences are increasingly used for acoustics system identification tasks. A number of coded sequences, such as binary maximal-length related sequences and ternary sequences possess two-valued or pulselike autocorrelation functions. It is this correlation property that is exploited in most of acoustical applications. However, the length of some of these sequences is not directly suitable for FFT-based cross-correlation algorithms. This paper explores using standard FFTs to calculate the cross-correlation between two periodic finite-length sequences of equal length, where the lengths of the sequences are not a power of 2. We apply our specialized correlation algorithm to analyze data collected in a room-acoustic environment to simultaneously obtain impulse responses between multiple sources and multiple receivers.

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PubMed2006

Evaluation of decay times in coupled spaces: an efficient search algorithm within the Bayesian framework.

This paper discusses an efficient method for evaluating multiple decay times within the Bayesian framework. Previous works [N. Xiang and P. M. Goggans, J. Acoust. Soc. Am. 110, 1415-1424 (2001); 113, 2685-2697 (2003); N. Xiang, P. M. Goggans, T. Jasa, and M. Kleiner, 117, 3707-3715 (2005)] have applied the Bayesian inference to cope with demanding tasks in estimating multiple decay times from Schroeder decay functions measured or calculated in acoustically coupled spaces. Since then a number of recent works call for efficient estimation methods within the Bayesian framework. An efficient analysis is of practical significance for better understanding and modeling the sound energy decay process in acoustically coupled spaces or even in single spaces for reverberation time estimation. This paper will first formulate the Bayesian posterior probability distribution function (PPDF) in a matrix form to reduce the dimensionality as applied to the decay time evaluation. Based on existence of only global extremes of PPDFs as observed from extensive experimental data, this paper describes a dedicated search algorithm for an efficient estimation of decay times.

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PubMed2005

Simultaneous acoustic channel measurement via maximal-length-related sequences.

A wide variety of acoustic systems has multiple sources and receivers. This paper proposes a technique for making acoustic measurements simultaneously for multiple sources. The proposed technique features a collection of excitation signals of the maximum-length sequence (MLS) and MLS-related classes. Each signal in the set has a pulse-like autocorrelation function, and the cross-correlation functions between arbitrary pairs of signals drawn from the set have peak values that are significantly lower than the peak magnitude of the autocorrelation functions. The proposed method is particularly valuable when characterization of multisource, multireceiver system must be accomplished in a limited time period. Both simulation and experimental results are presented that demonstrate the feasibility and fidelity of the proposed techniques in characterizing acoustic systems.

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PubMed2005

Evaluation of decay times in coupled spaces: reliability analysis of Bayeisan decay time estimation.

This paper discusses quantitative tools to evaluate the reliability of "decay time estimates" and inter-relationships between multiple decay times for estimates made within a Bayesian framework. Previous works [Xiang and Goggans, J. Acoust. Soc. Am. 110, 1415-1424 (2001); 113, 2685-2697 (2003)] have applied Bayesian framework to cope with the demanding tasks in estimating multiple decay times from Schroeder decay functions measured in acoustically coupled spaces. A parametric model of Schroeder decay function [Xiang, J. Acoust. Soc. Am. 98, 2112-2121 (1995)] has been used for the Bayesian model-based analysis. The relevance of this work is that architectural acousticians need to know how well determined are the estimated decay times calculated within Bayesian framework using Schroeder decay function data. This paper will first address the estimation of global variance of the residual errors between the Schroeder function data and its model. Moreover, this paper discusses how the "landscape" shape of the posterior probability density function over the decay parameter space influences the individual decay time estimates, their associated variances, and their inter-relationships. This paper uses experimental results from measured room impulse responses in real halls to describe a model-based sampling method for an efficient estimation of decay times, and their individual variances. These parameters along with decay times are relevant decay parameters for evaluation and understanding of acoustically coupled spaces.

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PubMed2004

Mode-locked ytterbium fiber lasers.

A compact fiber laser is demonstrated with use of a Gires-Tournois compensator and a short length (2-4 cm-long) of highly doped ytterbium (Yb) fiber providing net anomalous group-velocity dispersion. With use of a novel semiconductor saturable absorber mirror based on GaInNAs structure, self-started 1.5-ps-pulse mode-locked operation was obtained at 1023 nm with a repetition rate of 95 MHz. A mode-locked Yb-doped fiber laser was developed without the use of any dispersion compensation technique. Overall group-velocity dispersion was minimized by using a short length of highly doped Yb fiber in a compact amplifying loop cavity. Self-started mode-locked operation was obtained in 980-1030-nm wavelength range with a fundamental repetition rate of 140 MHz.

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PubMed2003

An experimental study on antipersonnel landmine detection using acoustic-to-seismic coupling.

An acoustic-to-seismic system to detect buried antipersonnel mines exploits airborne acoustic waves penetrating the surface of the ground. Acoustic waves radiating from a sound source above the ground excite Biot type I and II compressional waves in the porous soil. The type I wave and type II waves refract toward the normal and cause air and soil particle motion. If a landmine is buried below the surface of the insonified area, these waves are scattered or reflected by the target, resulting in distinct changes to the acoustically coupled ground motion. A scanning laser Doppler vibrometer measures the motion of the ground surface. In the past, this technique has been employed with remarkable success in locating antitank mines during blind field tests [Sabatier and Xiang, IEEE Trans. Geosci. Remote Sens. 39, 1146-1154 (2001)]. The humanitarian demining mission requires an ability to locate antipersonnel mines, requiring a surmounting of additional challenges due to a plethora of shapes and smaller sizes. This paper describes an experimental study on the methods used to locate antipersonnel landmines in recent field measurements.

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PubMed2003

Reciprocal maximum-length sequence pairs for acoustical dual source measurements.

In this paper we propose and demonstrate a method to obtain simultaneous dual source-receiver impulse responses in acoustical systems using binary maximum-length sequences (MLS). A binary MLS and its reversed-order sequence form a reciprocal MLS pair. Their correlation property includes a two-valued "pulse-like" autocorrelation function and a relatively smaller-valued cross-correlation function. This unique property, along with other number-theory properties, makes the reciprocal MLS pair suitable for simultaneous dual source cross-correlation measurements. In the measurement of a dual source system, each of the reciprocal MLS pairs simultaneously excite one of two separate sources, one or several receiver signals cross-correlate in turn with each of the MLS pairs, resulting in impulse responses associated with two separate sources. The proposed method is particularly valuable for system identification tasks with multiple sound/vibration sources and receivers that have to be accomplished in a limited time period. A fast algorithm called a fast MLS transform is exploited for the cross-correlation. In this paper we propose a fast MLS transform pair for the reciprocal MLS pairs. Its efficiency lies in the requirement of one single permutation matrix for a pair of two fast MLS transforms. Its feasibility and usefulness in the acoustical measurements are demonstrated using experimental results.

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PubMed2003

Evaluation of decay times in coupled spaces: Bayesian decay model selection.

This paper applies Bayesian probability theory to determination of the decay times in coupled spaces. A previous paper [N. Xiang and P. M. Goggans, J. Acoust. Soc. Am. 110, 1415-1424 (2001)] discussed determination of the decay times in coupled spaces from Schroeder's decay functions using Bayesian parameter estimation. To this end, the previous paper described the extension of an existing decay model [N. Xiang, I. Acoust. Soc. Am. 98, 2112-2121 (1995)] to incorporate one or more decay modes for use with Bayesian inference. Bayesian decay time estimation will obtain reasonable results only when it employs an appropriate decay model with the correct number of decay modes. However, in architectural acoustics practice, the number of decay modes may not be known when evaluating Schroeder's decay functions. The present paper continues the endeavor of the previous paper to apply Bayesian probability inference for comparison and selection of an appropriate decay model based upon measured data. Following a summary of Bayesian model comparison and selection, it discusses selection of a decay model in terms of experimentally measured Schroeder's decay functions. The present paper, along with the Bayesian decay time estimation described previously, suggests that Bayesian probability inference presents a suitable approach to the evaluation of decay times in coupled spaces.

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