Applied Spectroscopy最新文献

Discrete frequency infrared (IR) imaging is an exciting experimental technique that has shown promise in various applications in biomedical science. This technique often involves acquiring IR absorptive images at specific frequencies of interest that enable pathologically relevant chemical contrast. However, certain applications, such as tracking the spatial variations in protein secondary structure of tissue specimens, necessary for the characterization of neurodegenerative diseases, require deeper analysis of spectral data. In such cases, the conventional analytical approach involves band fitting the hyperspectral data to extract the relative populations of different structures through their fitted areas under the curve (AUC). While Gaussian spectral fitting for one spectrum is viable, expanding that to an image with millions of pixels, as often applicable for tissue specimens, becomes a computationally expensive process. Alternatives like principal component analysis (PCA) are less structurally interpretable and incompatible with sparsely sampled data. Furthermore, this detracts from the key advantages of discrete frequency imaging by necessitating the acquisition of more finely sampled spectral data that is optimal for curve fitting, resulting in significantly longer data acquisition times, larger datasets, and additional computational overhead. In this work, we demonstrate that a simple two-step regressive neural network model can be utilized to mitigate these challenges and employ discrete frequency imaging for retrieving the results from band fitting without significant loss of fidelity. Our model reduces the data acquisition time nearly six-fold by requiring only seven wavenumbers to accurately interpolate spectral information at a higher resolution and subsequently using the upscaled spectra to accurately predict the component AUCs, which is more than 3000 times faster than spectral fitting. Our approach thus drastically cuts down the data acquisition and analysis time and predicts key differences in protein structure that can be vital towards broadening potential applications of discrete frequency imaging.

When injection-molded polyoxymethylene is heat-treated below its melting point, it shows increased polarized reflection along the injection direction, as confirmed through micro-infrared spectroscopy. A characteristic dip or step-like structure appears around 940 cm^-1. Previously, the origin of this structure was unclear. However, we have found that it can be explained by refining the calculation model to account for the relative permittivity perpendicular to the sample surface.

The dynamic spectroscopic method, as a noninvasive blood component measurement method, currently uses spectrometers as the main measurement instrument. However, spectrometers have limited accuracy in measuring light intensity at each wavelength, which restricts the measurement accuracy of the dynamic spectrum method. In this paper, a combination of a multispectral camera and a spectrometer is utilized for the first time to measure spectral photoplethysmography (PPG) signals. Both the high amplitude resolution and high accuracy of the multispectral camera in terms of sampling values and the advantage of the spectrometer in terms of the number of wavelengths are exploited. According to the experimental data, this method effectively improves the measurement results. In particular, when measuring for hemoglobin, the mean absolute percentage error (MAPE) decreased by 25.3% and 22.9%, respectively compared with a single spectrometer and a multispectral camera. For platelet measurements, the MAPE decreased by 28.9% and 22.8%, respectively. For total bilirubin measurements, the MAPE decreased by 14.5 and 26.3%, respectively. It demonstrates that the noninvasive blood component measurement method of a combined multispectral camera and spectrometer can effectively reduce the interference of non-target components and improve measurement accuracy.

In X-ray fluorescence spectroscopy, specific elements, particularly neighboring elements, interfere with each other. A wavelength-dispersive optical system based on double-curved crystal (DCC) with multiple faces was designed. A Johann-type graphite curved crystal was used to focus the monochromatic excitation light, and a logarithmic spiral graphite curved crystal was used to collect the target fluorescence (Cl, 2.62  keV). The experimental results show that the wavelength dispersion device based on the DCC technology has a Cl detection limit of 0.18 part per million (ppm) when used for oil products. In the detection of a 1  ppm standard sample, the detection range of the device was 0.38  ppm, demonstrating good stability. Based on the fluorescence spectroscopy and detection results, the DCC technology could completely eliminate the influence of a high S concentration on Cl detection.

The single parameter detection of temperature (H₂O) is no longer sufficient for the absorption combustion diagnosis. There is a huge demand for simultaneous computed tomography (CT) diagnosis of multi-parameters. This paper studied CO and NO, two representative combustion products based on tunable diode laser absorption spectroscopy (TDLAS) and ultraviolet absorption spectroscopy (UVAS). Different from the research on low detection limits, the absorbance needs to be corrected in high-temperature and high-pressure conditions due to the equipment performance of the CT system. A high-temperature and high-pressure chamber system was applied for the basic absorbance experiment. The corrected absorbance databases of 2325.2/2326.8  nm for CO, and 215/226  nm band for NO were established. The corrected absorbance databases were first compared with the HITRAN and ExoMol databases. The accuracy of the corrected databases was also analyzed by standard gas with 1D detection in the high-temperature and high-pressure chamber and two-dimensional (2D) reconstruction in a customed CT cell. The maximum CO mean relative error (MRE) of the 2D results is 2.75% while the maximum NO MRE is 4.99%. This study provides a basis for research on the CO and NO distribution in high-temperature and high-pressure combustion fields.

The correlation filter (CF) technique is introduced as a versatile tool for data pretreatment to selectively attenuate interfering or overlapping signals of congested spectra. This technique leverages two-dimensional correlation spectroscopy (2D-COS) to create a filter multiplier that effectively addresses limitations inherent in traditional null-space projection (NSP) methods based on least-squares subtraction. We apply CF to the analysis of a model solution mixture system undergoing spontaneous evaporation, where volatile solvent concentrations change concurrently but at only slightly different rates. Despite the similarity of these parallel processes, CF successfully separates the overlapped dynamics of individual components by attenuating dominant signal contributions. CF also enables streamlined 2D codistribution spectroscopy (2D-CDS) analysis to determine the sequential order of component appearance. Multiple layers of CF can be applied to isolate individual component dynamics. Heterocomponent 2D correlation can then recover lost information by recombining CF-treated spectra. CF is applicable to two-trace two-dimensional (2T2D) correlation for comparative spectral analysis of a pair of spectra. CF treatment is expected to be a useful tool beyond 2D-COS applicable to many areas of spectral analyses, including the environmental and interfacial studies.

We evaluated the application of Fourier transform infrared (FT-IR) microspectroscopy in the mid-IR region (1500-550 cm^-1) in reflectance mode as a semi-automated tool to quantify common heavy minerals (HM) found in natural sediments and sedimentary rocks. An in-house database of IR spectra for the main HM was acquired. Then, automated HM identification using FT-IR spectroscopy was tested on synthetic mixtures with known HM proportions. HM fractionation during sampling and mounting in epoxy is evaluated by testing several sample preparations techniques. Overall, HM are properly determined using FT-IR microspectroscopy. Most of the HM are found in proportions comparable to those documented in the synthetic mixtures. Main drawbacks to this method include: (i) the mid-IR region does not give access to the absorption bands of some HM, such as fluorite, pyrite, and cassiterite, compared to other methods such as Raman microspectroscopy, (ii) the failure to discriminate titanium dioxide (TiO₂) polymorphs, and (iii) large spectral variations in some mineral groups such as amphiboles. Beyond these limitations, mid-FT-IR microspectroscopy in reflectance mode can be used to accurately determine HM proportions and could be simpler, faster, and/or cheaper when compared to other methods such as optical microscopy or scanning electron microscopy.

Raman microscopes are widely used in various fields and their spectral resolutions differ greatly depending on the system and optical components. Thus, it is important to evaluate the spectral resolution of Raman systems under measurement conditions. Although calcite is a crystal with a trigonal structure and its narrow peak at ∼1086 cm^-1 has been used to evaluate the spectral resolution of Raman spectrometers, the peak width of calcite itself (∼1.3 cm^-1 at full width half-maximum [FWHM]) is not negligible under high spectral resolution conditions. Because the calcite peak at ∼1086 cm^-1 originates from symmetric stretching, which is a common vibration mode for carbonate salts, we examined strontium carbonate (SrCO₃), barium carbonate (BaCO₃), and lead carbonate (PbCO₃) reagents to find a material having a narrower peak width than calcite. SrCO₃, BaCO₃, and PbCO₃ peaks originating from symmetric stretching were observed at 1072, 1059, and 1054 cm^-1, respectively, and their peak widths at FWHM (0.67, 0.92, and 1.09 cm^-1, respectively) were narrower than that of calcite (1.36 cm^-1). The narrow peak width of SrCO₃ was strongly dependent on its purity, probably due to its high structural regularity, and the change in the peak width (FWHM) was only 0.12 cm^-1 between 5 °C and 45 °C. Thus, we concluded that the high-purity SrCO₃ peak at 1072 cm^-1 was the narrowest peak of Raman scattering light under ambient conditions and is suitable for evaluating high spectral resolution for Raman spectrometers.

Deep eutectic solvents (DESs) exhibit dynamic heterogeneity, where the intricate and dynamic hydrogen bonding within the DES mediates dynamic spatial variation in the DES local environment. The Type III DES composed of choline chloride and glycerol (ChCl:Gly) exhibits this effect prominently, and we report on the observed local organization and its dependence on system composition using the time-resolved reorientation dynamics of three illustrative chromophores of different polarities: perylene (neutral, nonpolar), oxazine 725 (cation, polar) and rose bengal (dianion, polar). Our findings demonstrate that the environments sensed by all three chromophores are markedly different than that predicted by the bulk viscosity of the DES, and that these local environments exhibit remarkably little change as the mole ratio of the DES constituents is varied. Taken collectively, these data provide clear evidence of short-range organization that bears very little resemblance to the longer-range structural organization that determines DES bulk properties.

An absorption imaging technique was described for visualizing molybdenum pentachloride (MoCl₅) flow during an atomic layer deposition/pulsed chemical vapor deposition process. The imaging system was composed of a telecentric lens and a commercial 7.1 megapixels (MP) complementary metal oxide semiconductor (CMOS) camera. The light source was a fiber-coupled light emitting diode operating at a peak emission wavelength of 443  nm. Flow images of MoCl₅ vapor entrained in a carrier gas were recorded at approximately 93 frames per second in a research-grade vapor deposition chamber. The utility of this technique was illustrated by comparing the MoCl₅ flow patterns for two precursor injection conditions, conditions consisting of different argon carrier gas flow rate and chamber pressure. For a low flow rate and chamber pressure, the flow images showed a gradual expansion of the MoCl₅ concentration front through the field of view with a relatively short MoCl₅ residence time. These flow patterns result in a relatively uniform precursor concentration front impinging on the wafer surface with the precursor being efficiently exhausted from the chamber, making these conditions desirable for thin film deposition in this chamber. For a high carrier gas flow rate and elevated chamber pressure, the flow images showed a high gas velocity jet impinging on the wafer chuck surface and the formation of gas recirculation zones, resulting in a relatively long residence time. These flow conditions would make it difficult to reproducibly deposit uniform thin films in this chamber. This comparison demonstrated the utility of this technique for qualitative characterization of precursor flow fields with minimal data processing. However, the two-dimensional data obtained from this technique can also provide the basis for training and validating computational fluid dynamics models. Furthermore, the addition of duplicate optical systems would provide the basis for determining the three-dimensional precursor distribution through tomographic analysis.