Journal of Applied Spectroscopy最新文献

Surface-enhanced Raman spectroscopy (SERS) was used to study electrode processes at the interface between Al and an ionic liquid. This method has great promise for studying electrochemical processes, since it allows one to determine the composition of the electrolyte in a thin near-electrode layer during electrode polarization. It was demonstrated that aluminum has SERS-activity in a chloroaluminate ionic liquid based on Et₃NHCl. It was shown using in situ SERS that the intensity of peaks associated with the ({text{AlCl}}_{4}^{-}) ion increased and the intensity of peaks associated with Al₂({text{Cl}}_{7}^{-}) ion decreased upon increasing the cathodic polarization. The reverse process was observed during anodic polarization of the electrode, i.e., the content of ({text{AlCl}}_{4}^{-}) ions decreased and the concentration of Al₂({text{Cl}}_{7}^{-}) increased. The concentrations of chloroaluminate anions in the near-electrode layer did not change at cathodic overpotentials above the overpotential of reaching the limiting current and at anodic overpotentials above the passivation overpotential. The obtained dependences of the relative intensities of ({text{AlCl}}_{4}^{-}) and Al₂({text{Cl}}_{7}^{-}) peaks on the electrode overpotential correlated with the stationary polarization curves. It was experimentally proved that passivation of an aluminum electrode during anodic dissolution was caused by the formation of aluminum chloride on the electrode surface.

Up-conversion luminescence (UCL) spectra of fluorophosphate glasses doped with the pair of rare-earth ions (REIs) ytterbium (4%) and thulium (0.1%) excited by radiation of a diode laser operating in steady-state mode at wavelength 975 nm are studied. Each of the observed UCL bands is a result of manifestation of several up-conversion processes (UCPs) corresponding to luminescence of thulium ions from different excited states. These UCPs are characterized by different degrees of effective nonlinearity (EN). The effect of pump power on UCL spectra formed by UCPs with different ENs is studied. The possibility of separation of spectra corresponding to individual UCPs from the total experimentally measured UCL spectrum of fluorophosphate glass doped with the pair of REIs ytterbium (4%) and thulium (0.1%) is demonstrated. The separation is based on the calculation of the EN based on the dependences of the UCL on the excitation power.

The electromagnetically induced transparency (EIT) resonance on the ³⁹K D₁ line was studied in a potassium microcell with a vapor column thickness of L = 30 μm. The experimentally obtained width of the EIT resonance was 60 times narrower than the Doppler width of the potassium atom. The EIT resonance split into three spectrally narrow components in an external longitudinal magnetic field. Theoretical curves calculated using the Rabi–Breit formula were in good agreement with the experimental results.

Regularities of formation of the spatial-energy profile (SEP) of the visibility zone (VZ) of active-pulse vision systems (APVS) have been numerically studied, taking into account the ratio of the cross sections of the observation object A_ob and the laser illumination beam A_las in the plane of the object location. For this, the concepts of the boundary distance S_bd, at which A_ob = A_las and the multiplier w = A_ob/A_las, which is added to the well-known equation for the recorded APVS signal, are introduced. Taking into account the finite length of the VZ, the following cases can be distinguished. If S_bd ≥ S_end (end point of the VZ) within the VZ w =1. Previously known studies were performed for this case. When S_start (starting point of the VZ) ≤ S_bd < S_end within the VZ, there may first be a range of distances with a maximum value w₁ = 1, after which there is a range with a factor decreasing to a certain minimum value w₂ < 1. Finally, when S_bd < S_start within the limits of the VZ, w₁(S_del1) < 1 and w₂(S_del2) < 1 (in this case, w₂ is always less than w₁, and the delay distance S_del1 < S_del2). Taking into account the multiplier w < 1 leads, in the corresponding range, to a change in the shape of the SEP, maximum signal values, and other characteristics implemented within the visibility zone. A generalizing parameter that in practice characterizes the infl uence of the range of distances, where w < 1, is the maximum operating range (MOR) of the system S_MOR. For the parameters used in the calculations, taking into account the indicated influence led to a decrease in the S_MOR by 2.9–5.0 times. The main mechanisms for the influence of the relative position of S_bd and the VZ on the characteristics of MOR are given. The main results of numerical modeling are confirmed experimentally.

The carbon levels in low-alloy steel samples were measured using laser-induced breakdown spectroscopy (LIBS) and a random forest (RF) method. When employing the RF method, the root-mean-square error of cross-validation (RMSECV) criterion was first used to select the spectral range of the spectral variables for RF model input, to prevent over-fitting of the RF model when only a few relevant variables are accompanied by many other variables. Second, the out-of-bag (OOB) error criterion was used to optimize the numbers of decision trees (n_tree) and characteristic variables (m_try) in the RF model, which optimizes the RF structure. The availability of a large amount of relevant spectral information, coupled with the remarkable regression capacity of RF, greatly improved the carbon analytical accuracy. The results showed that the root-mean-square error of prediction (RMSEP) was 0.034 wt.% for the calibration curve method and 0.023 wt.% for the RF method; the reduction afforded by the latter method was 32.4%. Thus, the RF method improved the carbon analytical accuracy for low-alloy steels.

Terahertz (THz) single-pixel imaging has received major research attention because of the lack of a suitable high-resolution array detector for THz imaging applications. Improving both imaging speed and quality has become a research hotspot for this field in recent years. In this study, a terahertz single-pixel imaging system with Hadamard spatial encoding was constructed by using optically induced semiconductor materials to perform THz wave modulation. Sparse coding was added to the system’s reconstruction algorithm to enhance imaging quality. Numerous image patches were then collected from a natural image set to train an overcomplete dictionary and each patch in the measured image was reconstructed through sparse representation. To validate the effectiveness of the proposed algorithm, the reconstruction performances of different algorithms were compared under various conditions (i.e., with sampling rates varying from 5 to 100% and with noise levels within a signal-to-noise ratio range of 10–50 dB). The proposed algorithm, in combination with sparse representation of an overcomplete dictionary, showed a higher peak signal-to-noise ratio and a lower mean square error than both the inverse Hadamard transform (IHT) and TVAL3 algorithms. Finally, THz imaging experiments were performed to validate the algorithm’s reconstruction performance at sub-Nyquist sampling rates. The experimental and simulation results coincided closely, thus indicating that the use of the proposed algorithm enhances the signal-to-noise ratio of the reconstructed image, reduces its mean square error, and retains greater image detail. The proposed algorithm was demonstrated to be the preferred choice for THz single-pixel imaging applications.

Ivacaftor is a selective small molecule potentiator Transmembrane Conductance Regulator protein used for the treatment of cystic fibrosis. This report describes the validation of simple, rapid, sensitive and cost-effective zeroorder and first-order derivative spectrophotometric methods for the estimation of ivacaftor in bulk and in its marketed formulation. Preliminary spectrophotometric analysis of the drug was carried out in methanol and a total of 21 parametric variations were considered. Three selected method variants employing absorbance (zero-order), peak-peak- to-peak (first-order), and peak-to-zero (second order) techniques were assessed for their stability indicating potential in stress degraded solutions of the drug. The developed method was validated with respect to parameters including linearity, accuracy, precision, robustness, and solution stability. Excellent linearity was observed in the concentration range of 5.0–30.0 μg/mL with a correlation coefficient of 0.99 and above for the selected method variants. The limits of assay detection values ranged from 0.90–1.06 μg/mL, and quantitation limits ranged from 2.72–3.22 μg/mL for the proposed method variants. The proposed methods were used to quantify the drug in its marketed tablet formulation, and good recoveries ranging from 95.98 to 98.81% were obtained.

Laser-induced breakdown spectroscopy (LIBS) technology faces the challenge of redundant or irrelevant features when dealing with high-dimensional data of steel. To enhance the accuracy and interpretability of multivariate classification, this study introduces an innovative hybrid feature selection (FS) method that skillfully combines the filtering characteristics of the select percentile (SP) algorithm with the embedded advantages of the elastic net (EN) algorithm. Under this framework, the support vector machine (SVM) algorithm was applied for classification, demonstrating outstanding performance with an accuracy, precision, and F1 score of 0.9888, 0.9895, and 0.9889 on the test set, respectively. To address the ‘black box’ nature of the SVM algorithm, this paper further introduces the local interpretable model-agnostic explanations (LIME) method. LIME allows for the visualization of the importance of each variable, thereby enhancing the interpretability and credibility of the model. Overall, the model and methods proposed in this study show significant effectiveness in eliminating redundant or irrelevant features and in precise classification, effectively solving most of the challenges faced by LIBS in steel classification issues.

A procedure based on dispersive liquid-liquid microextraction (DLLME) for cadmium (Cd) quantification in an Iraqi environmental matrix by flame atomic absorption spectroscopy (FAAS) was applied in this work. A case study approach was chosen to obtain further in-depth information on the Cd levels and to evaluate the effectiveness of N-salicylideneaniline (SAN) as a complexing agent for preconcentration and extraction of Cd. Univariate strategy was utilized for achieving the optimum extraction conditions: 75.0 μL of carbon tetrachloride as the extraction solvent, 10 mL of a sample solution adjusted the pH at 8.50 containing 0.8% (w/v) SAN, and 1400 μL of methanol as the dispersive solvent, within 30 s complexation time. The estimated limits of detection (LOD) and quantification (LOQ) under optimum conditions were 0.26 and 0.87 μg/L, respectively. Enrichment factors were obtained in two manners, found to be 24.4 and 44.3. To evaluate the accuracy of the method, known amounts of analytes were spiked and compared with the results achieved using microwave digestion/graphite furnace atomic absorption spectrometer (MWD/GF-AAS) for solid samples, and direct graphite furnace atomic absorption spectrometer (GF-AAS) for water samples. Procedure was applied for analyzing eight environmental samples, the Cd levels for water samples ranged from 3.01 to 7.33 μg/L with a relative standard deviation (4.1–10.4 RSD%), while the concentration for the solid sample (Mentha piperita) was 2.71 μg/g (RSD% = 7.4). DLLME/FAAS proposed procedure is eff ective, simple, and has the benefi t of minimizing the organic solvent consumption, by a few microliters, which results in little waste.

Five types of plastics were classified based on NIR optical density spectra using multivariate cluster analysis in principal component space. An accuracy above 0.96 was obtained by ranking spectral variables by decreasing variance of measured optical density. Changes in polycarbonate VIS-NIR spectra during thermal degradation were modeled using a partial least squares method with searching combination moving windows of optimal width. A quantitative calibration of an aging time up to 11.5 years was obtained with a root mean square error of the estimate around 19 days and a residual predictive deviation of more than 45.