Grain size characterization of Ti-6Al-4V titanium alloy based on laser ultrasonic random forest regression.

In this paper, a random forest regression (RFR) rain size characterization method based on a laser ultrasound technique is investigated to predict the grain size of titanium alloy (Ti-6Al-4V). The longitudinal wave velocity of the ultrasound signal and the attenuation coefficient at different frequencies are used as the input and the grain size is used as the output. An RFR algorithm was used to develop a grain size prediction model.

The effect of copper grain size on laser ultrasonic backscattered signal.

Grain size has an essential influence on the serviceability of metallic materials. In this paper, a noncontact laser ultrasonic testing platform is built to study the effect of copper grain size on the laser ultrasonic backscattered signal. According to the correlation between grain size and ultrasonic wavelength, the ultrasonic scattering by copper grains in the experiment contains not only Rayleigh scattering but also the transition region from Rayleigh scattering to stochastic scattering.

Nonlinear resonance decomposition for weak signal detection.

This paper attempts to investigate the behaviors of coupling stochastic resonance (CSR) subject to α-stable noise and a periodic signal by using the residence-time ratio. Then, a nonlinear resonance decomposition is designed to successfully enhance and detect weak unknown multi-frequency signals embedded in strong α-stable noise by decomposing the noisy signal into a series of useful resonant components and a residue, where the residence-time ratio, instead of the output signal-to-noise ratio and other objective functions depending on the prior knowledge of the signals to be detected, can optimize the CSR to enhance weak unknown signals. Finally, the nonlinear resonance decomposition is used to process the raw vibration signal of rotating machinery.

Analysis for angular dispersions of surface acoustic wave velocities in BCC crystals.

Based on the propagation theory of acoustic waves in anisotropic media, the angular dispersion curves of SAW velocities propagated in some unusual oriented, such as (016)- and (331)-oriented, Body-Centered Cubic (BCC) single crystals are simulated using an optimized numerical method. Meanwhile, the angular dispersion curves of SAW velocities propagated in these unusual oriented BCC single crystals are measured by Impulsive Stimulated Scattering (ISS) laser ultrasonic method, which show that the measurement results are in good agreement with those of the simulations. By the optimized numerical method, the relationships between the temperature and the dispersion curves of SAW velocity propagated in these single crystals are also simulated.

Weld quality inspection of small-diameter thin-walled pipes by a laser ultrasonic method.

Defect inspection of small-diameter thin-walled pipes is a difficult problem in the field of nondestructive testing. In this paper, a new detection method based on laser ultrasonics and guided circumferential wave technology is proposed and used to inspect the defects in pipes. First, a theoretical model based on the theory of acoustic propagation in solids is proposed for the small-diameter thin-walled pipes.

Rapid measurement of the fourth-order texture coefficient by laser ultrasonic surface acoustic waves based on a neural network expert system.

In anisotropic materials, texture components and orientation density directly affect the surface acoustic waves' (SAW) velocity dispersion and SAW velocity variation. In this paper, a texture feature recognition and analysis system for a neural network is constructed based on the corresponding characteristics of texture components and orientation density and SAW velocity dispersion and variation by combining laser ultrasound technology with the partial texture analysis method, which is used for the identification and analysis of texture type and feature. At the same time, based on the relationship between surface wave velocity and the fourth-order texture coefficient, an expert system for accurate prediction of the fourth-order texture coefficient is constructed.

Texture in steel plates revealed by laser ultrasonic surface acoustic waves velocity dispersion analysis.

A photoacoustic, laser ultrasonics based approach in an Impulsive Stimulated Scattering (ISS) implementation was used to investigate the texture in polycrystalline metal plates. The angular dependence of the 'polycrystalline' surface acoustic wave (SAW) velocity measured along regions containing many grains was experimentally determined and compared with simulated results that were based on the angular dependence of the 'single grain' SAW velocity within single grains and the grain orientation distribution. The polycrystalline SAW velocities turn out to vary with texture.

[Antigenicity and physicochemical properties of two human NR1a polypeptides related to activation of NMDA receptor].

Objective: To investigate the distribution of antigenic sites in two human NR1a polypeptides related to activation of N-methyl-D-aspartate receptor (NMDAR) and their physicochemical properties.

Methods: The amino acid sequences of two polypeptides, P1, a region containing 151 amino acid residues preceding the first transmembrane domain of the human NR1a, and P2 with 144 residues following the third transmembrane domain, were obtained from protein database by GOLDKEY software (4.0 version).