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Molybdenum (IV) sulfide is widely employed in electronic device applications. Recognized as one of the most efficacious methods for fabricating high-quality molybdenum (IV) sulfide, the chemical vapor deposition (CVD) method's application necessitates the development of a straightforward, swift and nondestructive characterization tool. Thus, this paper presents a rapid and reliable differential reflectance spectroscopy (DRS) instrumentation, grounded on the optical microscope, capable of characterizing two-dimensional materials prepared by CVD. This universal nondestructive identification tool facilitates the investigation of two-dimensional materials on both opaque and transparent substrates. MoS2 samples prepared by CVD were characterized on SiO2/Si and sapphire substrate. The results indicate that the exciton absorption peak can be accurately identified, validating the instrumentation's utility for material detection and monolayer identification. The characterization results, corroborated by the Raman spectra with a wavenumber difference of approximately 20 cm−1 and the triangular appearance of the optical image, affirm the application of this instrumentation. Ultimately, the DRS instrumentation provides a swift and nondestructive route to characterize physical properties such as bandgap and optical properties for two-dimensional materials. [ABSTRACT FROM AUTHOR]

In nonlinear ultrasonic damage detection, the appropriate Lamb wave mode to accurately characterise the nonlinearity attributed to the material damage should be selected important. However, an effective mode is more difficult to select practically as impacted by the dispersion and multi-mode characteristic of the Lamb wave. In this study, based on the dispersion curve of Lamb waves, the modes meeting the second harmonics and third harmonics phase velocity matching were given, and the nonlinear cumulative effects exerted by different modes on fatigue cracks were compared. In addition, an investigation was conducted on the amplitude change of the second and third harmonics signal of the identical fatigue damage. The results show that the harmonic amplitude decreases with the increase of the fatigue crack length. The third harmonics under the two modes are more sensitive to fatigue damage than the second harmonics. Moreover, the amplitude of the third harmonic excited by S1 mode exceeds that of the other mode. As the fatigue crack length increases, the relative second- and third-order nonlinear coefficients generated by S1 mode have approximately the same trend, first increasing and then decreasing. The results reveal that the third harmonic under S1 mode could more effectively characterise fatigue damage. [ABSTRACT FROM AUTHOR]

Near infrared spectroscopy (NIRS) combined with a partial least squares (PLS) algorithm was utilized as a rapid alternative analytical method for estimating the four main oxides in cement raw meal samples. An algorithm, known as cross-validation-absolute-deviation-F-test (CVADF), was proposed to eliminate the outliers existed in the calibration set. 5, 6, 2 and 2 out of 76 samples were identified as outliers for CaO, SiO2, Al2O3 and Fe2O3, respectively. The correlation coefficient of prediction (Rp) increased from 0.7773, 0.7877, 0.8894 and 0.6357 to 0.9075, 0.8572, 0.9038 and 0.6400, while the root mean square error of prediction (RMSEP) decreased from 0.2493, 0.2331, 0.0832 and 0.0449 to 0.1664, 0.1949, 0.0779 and 0.0447, respectively, indicating that the outliers are accurately identified and that the prediction performance of the PLS models established by the remaining samples was significantly improved. Some common outlier elimination methods, leverage diagnostic (LD), Euclidean distance diagnostic (EDD), Mahalanobis distance diagnostic (MDD) and principal component scores diagnostic (PCSD) were used for comparison. The results show that the proposed method is very promising with good results for the prediction capability. [ABSTRACT FROM AUTHOR]

A rapid and accurate method is presented to determine CaCO3, SiO2, Fe2O3, and Al2O3 in cement raw meal using near-infrared (NIR) spectroscopy. Multiplicative scatter correction (MSC) was employed to eliminate the scattering signal and partial least squares (PLS) regression was used to build the analysis model. The results demonstrated good performance by this approach for the determination of CaCO3, SiO2, Fe2O3, and Al2O3. NIR spectroscopy exhibits the feasibility to characterize the quality of cement raw meal. Compared with prompt gamma neutron activation analysis (PGNAA) and X-ray fluorescence (XRF), this method is more efficient and safer. [ABSTRACT FROM AUTHOR]

An optical fibre Fabry–Perot interferometer (FPI) sensor for relative humidity (RH) measurement is proposed. The FPI is formed by splicing a short section of hollow-core photonic crystal fibre(HCPCF) to single mode fibre and covering a chitosan film at the end of HCPCF. The refractive index of chitosan and film thickness will change with ambient RH, leading to the change in the reflected interference spectrum of FPI. RH response of the FPI sensor is analysed theoretically and demonstrated experimentally. It shows nonlinear response to RH values from 35 to 95%RH. The interference fringe shifts to shorter wavelength as RH increases with a maximum sensitivity of 0.28 nm/%RH at high RH level. And the fringe contrast also decreases as RH increases with an available maximum sensitivity of 0.5 dB/%RH. The sensor shows good stability and fast response time less than 1 min. With its advantages of compact structure, good performance, simple and safe fabrication, the proposed optical fibre FPI sensor has great potential for RH sensing. [ABSTRACT FROM PUBLISHER]

Acoustic emission location is important for finding the structural crack and ensuring the structural safety. In this paper, an acoustic emission location method by using fiber Bragg grating (FBG) sensors and particle swarm optimization (PSO) algorithm were investigated. Four FBG sensors were used to form a sensing network to detect the acoustic emission signals. According to the signals, the quadrilateral array location equations were established. By analyzing the acoustic emission signal propagation characteristics, the solution of location equations was converted to an optimization problem. Thus, acoustic emission location can be achieved by using an improved PSO algorithm, which was realized by using the information fusion of multiple standards PSO, to solve the optimization problem. Finally, acoustic emission location system was established and verified on an aluminum alloy plate. The experimental results showed that the average location error was 0.010 m. This paper provided a reliable method for aluminum alloy structural acoustic emission location. [ABSTRACT FROM PUBLISHER]

A fiber Bragg grating (FBG) sensors-based impact localization system on composite structure and a novel localization algorithm independent of wave velocity were proposed. Six FBG sensors constitute two isosceles right triangle FBG arrays. Impact signals were detected by a high-speed FBG interrogation system. Morlet wavelet transform was employed to extract time differences of impact signals. The straight lines equations, which are through impact source and FBG sensors of right-angled vertices of FBG arrays, can be obtained by the time differences. The coordinate of impact source is the intersection of straight lines. Testing experiments were carried out on composite plate within 400 mm × 400 mm monitor area. The experimental results showed that the maximum and average errors were 20.92 and 8.67 mm, respectively. This article provides a simple and stable impact source localization system independent of wave velocity. [ABSTRACT FROM AUTHOR]

An intelligent acoustic emission (AE) source localization technique by using fiber Bragg grating (FBG) sensors was investigated. Four FBGs sensing network was established for detecting the AE signal. And power intensity demodulation method was initialized employing narrow-band tunable laser. The intelligent AE source localization method was proposed based on wavelet transform, cross-correlation analysis, and least squares support vector machines (LS-SVM). LS-SVM modal’s input is signal time difference and output is AE source position. The location experiments were carried out on a 500 mm × 500 mm × 2 mm aluminum alloy plate. The results showed that the AE source position abscissa and ordinate localization errors are all less than 10 mm. The maximum and average localization errors are 8.65 and 6.78 mm, respectively. The research results provided a novel method for AE source localization by using FBG sensors. [ABSTRACT FROM AUTHOR]

The effects of external optical feedback mainly introduced by Rayleigh backscattering (RB) in long lead fiber, reflection of fiber end facet, and the fusion splices on the stability of asymmetric distributed feedback fiber laser (DFB-FL) have been investigated. Theoretical analysis based on the compound cavity model is presented, and the critical lengthLp,cof lead fiber is obtained to evaluate the tolerance of DFB-FL to RB. Analysis and experimental results show that RB is the main factor causing the instability. The critical length for the shorter end of our asymmetric DFB-FL is measured to be about 170?m. To isolate the laser from the effect of RB, we propose a method using isolator and WDMs, which is experimentally proved to be an efficient way. [ABSTRACT FROM AUTHOR]