Applied Spectroscopy最新文献

A technique for quenching-independent, two-photon absorption laser-induced fluorescence (TALIF) measurements of atomic nitrogen in high-enthalpy facilities is presented. The technique relies on high-laser intensity, which results in the photoionization rate dominating other depopulation channels for the induced excited state. The photoionization-dominated technique is applied here to study the distribution of atomic nitrogen in the vicinity of an ablating graphite sample in a plasma plume. Three different plasma conditions are investigated: a 17 MJ/kg air plasma delivering 145 W/cm² to the graphite surface, an 18 MJ/kg air plasma delivering 195 W/cm², and a 24 MJ/kg nitrogen plasma delivering 85 W/cm². The number density of atomic nitrogen is measured along the stagnation streamline of the flow on the graphite sample in each case. The highest number densities are observed in the nitrogen plume, as would be expected given the pure nitrogen composition and high enthalpy. The 195 W/cm² air condition has the second-highest atomic nitrogen distribution, followed by the 145 W/cm² air condition. This technique may provide a valuable method for studying atomic nitrogen, an important species to air/carbon gas-surface interaction at hypersonic-relevant conditions, in high-enthalpy facilities.

We present the first implementation of complex-valued classical least squares (CLS) regression in spectroscopy. Although the results indicate that complex-valued CLS does not outperform methods that utilize only the more suitable part of the complex refractive index spectra, it includes an error detection feature that enables a self-correction mechanism. This mechanism decreases the mean absolute error (MAE) to approximately 26% relative to using only the mid-infrared (MIR) absorption index (k) spectra for CLS, and to about 46% relative to using only the MIR refractive index (n) spectra of benzene-toluene mixtures. For benzene-cyclohexane mixtures, the MAE was reduced to approximately 75% relative to the k spectra and 58% relative to the n spectra. In contrast, for benzene-carbon tetrachloride (CCl₄) mixtures, i.e., a system that exhibits particularly large deviations from Beer's law, no improvement over the n spectra was observed; the n-based MAE was 81% relative to the k spectra. These percentages may further vary based on the complexity of the system, the spectral regions selected for CLS and the corresponding deviations from Beer's approximation.

This study assessed the feasibility of using portable infrared and handheld Raman devices for the rapid screening of alcohol-based gel hand sanitizers to detect potential adulteration or misbranding. Alcohol potency was estimated by analyzing the concentration-dependent hydrogen bond-induced peak shifting characteristic of alcohol-water mixtures. Specifically, alcohol concentration in water (v/v%) was plotted as a function of the ratio of two characteristic peak positions affected by this shifting, yielding linear responses between 30%-100% for infrared spectroscopy and 40%-100% for Raman spectroscopy. Calibration equations derived from these curves were applied to estimate alcohol concentration, resulting in average errors (± standard deviations) of 1.6% (1.2%) for infrared spectroscopy and 2.4% (1.7%) for Raman spectroscopy, compared to gas chromatography with flame ionization detection (GC-FID). A total of 24 products were analyzed using this screening workflow, with results used to prioritize samples for further analysis via official compendial methods. All 21 samples identified as violative or presumptively violative by the rapid screening devices were confirmed as violative using GC-FID, while all three samples classified as presumptively non-violative were confirmed as non-violative. This method may be suitable for field deployment at locations such as mail facilities, points of entry, and express courier hubs, where expedited screening of these products is beneficial. Its implementation could enhance regulatory enforcement efforts and support consumer safety by identifying non-compliant products more efficiently.

Currently, there is increasing interest in identifying the mechanistic characteristics of the α-synuclein amyloid protein aggregation during its early stages. The initiation of amyloid protein incubation was investigated by applying the concepts of hydrophobic hydration in the early-formed protein aggregates and the light transport in the protein samples by using near-infrared light. These are unexplored concepts in amyloid protein aggregation research. Early-formed protein aggregates develop solvent-exposed hydrophobic residue segments, and intramolecular and intermolecular interactions can be identified by hydrophobic hydration, while consecutive intramolecular interactions can cancel this effect. In the light transport within protein samples, at low protein concentrations, the early-formed protein aggregates achieve stability, whereas at higher concentrations, such as those found in neuronal synapses (∼50  µM), the early-formed aggregates continue to develop.

Given fungi's critical role in public health and their impact during pandemics such as COVID-19, precise identification and classification are essential. Additionally, fungi hold significant value in medical and economic applications. For this work, fungi were isolated from various fruit. The fungi were initially identified based on their morphological characteristics using microscopic techniques. To achieve a comprehensive characterization, the eight fungal species were analyzed using rapid and cost-effective spectroscopic techniques, including attenuated total reflectance Fourier transform infrared spectroscopy (ATR FT-IR), Raman spectroscopy (RS), and ultraviolet-visible spectroscopy (UV-Vis). Fungal samples were used in the powder form, generating distinct spectral fingerprints in the biochemical region specific to components such as proteins, lipids, polysaccharides, carbohydrates, and nucleic acids. Results demonstrated the efficacy of these spectroscopic approaches for rapid and accurate identification, enabling discrimination between fungal species and reliable classification at the genus level. The results showed the species were identified as Aspergillus parasiticus, Phytophthora spp., Chaetomium globosum, Penicillium digitatum, Penicillium sp., Penicillium italicum, Rhizoctonia solani, and Myrothecium roridum. This highlights the potential of these techniques as efficient tools for fungi identification.

This study proposes a method to remove background pixels from near-infrared hyperspectral images based on the pixel-wise standard deviation of reflectance method (px-wise SD method). This method calculates the standard deviation (SD) of reflectance in each pixel, namely each spectrum, and determines a threshold to distinguish between background and object pixels from the resulting histogram of the px-wise SD. The method effectiveness is evaluated using hyperspectral images of a leaf-like pastry with a hole placed on either a low-reflectance sheet or white paper. On white paper, the px-wise SD of reflectance exhibits a trimodal histogram with two prominent peaks and one small peak between them. The prominent peak with a lower SD corresponds to the white paper pixels, whereas the other peak with a higher SD is associated with the surface and edge pixels of the pastry. The small peak represents the pixels of the hole. The background and object pixels can be effectively separated by setting a threshold between this small peak and the prominent peak for the pastry pixels. Moreover, the mean spectrum calculated using only object pixels remains consistent, regardless of the type of background material. Conversely, the mean spectrum calculated using all pixels is distorted due to the spectral inclusion of the background material.

Some attenuated total reflection (ATR) correction formalisms share the drawback that they can only be applied to materials with relatively low oscillator strength, as they rely on one or another form of the low absorption assumption. In this contribution, we present an iterative formalism that does not suffer from this limitation and can be applied not only to attenuated total reflection spectra but also to spectra acquired under internal reflection conditions at subcritical incidence angles. Its accuracy is primarily limited near the critical angle and Brewster's angle. The formalism is based on the perpendicular component of the wavevector and Fresnel's equations, and it is fully compatible with wave optics. Its application is straightforward, and a corresponding program is available via the Supplemental Material.

We describe a radioisotope-excited energy dispersive X-ray fluorescence spectrometric facility for the elemental analysis of minerals containing the rare earth elements (REEs) by the use of the K-line X-rays. Two ²⁴¹Am sources are used in purpose-designed holders that fit a high-resolution solid-state germanium detector. The system is capable of exciting all the light actinides up to element 69, Tm. The analysis through the well-separated K-lines allows an easy identification of lanthanide elements with advantages over traditional L-line detection particularly in mineral samples with high Fe concentration, enabling the recognition of most lanthanide elements at values close to 10 ppm. We report the achieved elemental sensitivity obtained with a set of pure element standards and spectra of mineral concentrates derived from a REEcontaining Venezuelan Laterite.

Sensing with undetected photons has enabled new, unconventional approaches to Fourier transform infrared spectroscopy (FT-IR). Leveraging properties of non-degenerate entangled photon pairs, mid-infrared (mid-IR) information can be accessed in the near-infrared (near-IR) spectral domain to perform mid-IR spectroscopy with silicon-based detection schemes. Here, we address practical aspects of vibrational spectroscopy with undetected photons using a quantum FT-IR (QFT-IR) implementation. The system operates in the spectral range from around 3000 cm^-1 to 2380 cm^-1 (detection at around 12 500 cm^-1) and possesses only 68 pW of mid-IR probing power for spectroscopic measurements with a power-dependence of the signal-to-noise ratio of 1.5 × 10⁵ mW^-1/2. We evaluate the system's short- and long-term stability and experimentally compare it to a commercial FT-IR instrument using Allan-Werle plots to benchmark our QFT-IR implementation's overall performance and stability. In addition, comparative qualitative spectroscopic measurements of polymer thin films are performed using the QFT-IR spectrometer and a commercial FT-IR with identical resolution and integration times. Our results show under which conditions QFT-IR can practically be competitive or potentially outperform conventional FT-IR technology.