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Dynamic cortical connectivity alterations associated with Alzheimer's disease: An EEG and fNIRS integration study
摘要： Emerging evidence indicates that cognitive deficits in Alzheimer’s disease (AD) are associated with disruptions in brain network. Exploring alterations in the AD brain network is therefore of great importance for understanding and treating the disease. This study employs an integrative functional near-infrared spectroscopy (fNIRS) – electroencephalography (EEG) analysis approach to explore dynamic, regional alterations in the AD-linked brain network. FNIRS and EEG data were simultaneously recorded from 14 participants (8 healthy controls and 6 patients with mild AD) during a digit verbal span task (DVST). FNIRS-based spatial constraints were used as priors for EEG source localization. Graph-based indices were then calculated from the reconstructed EEG sources to assess regional differences between the groups. Results show that patients with mild AD revealed weaker and suppressed cortical connectivity in the high alpha band and in beta band to the orbitofrontal and parietal regions. AD-induced brain networks, compared to the networks of age-matched healthy controls, were mainly characterized by lower degree, clustering coefficient at the frontal pole and medial orbitofrontal across all frequency ranges. Additionally, the AD group also consistently showed higher index values for these graph-based indices at the superior temporal sulcus. These findings not only validate the feasibility of utilizing the proposed integrated EEG-fNIRS analysis to better understand the spatiotemporal dynamics of brain activity, but also contribute to the development of network-based approaches for understanding the mechanisms that underlie the progression of AD.
关键词： Alzheimer’s disease,Brain network,Functional near-infrared spectroscopy,Graph theory,EEG source imaging
更新于2025-09-09 09:28:46
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Advances in Raman spectroscopy and imaging techniques for quality and safety inspection of horticultural products
摘要： This paper gives an overview of Raman technology for inspecting quality and safety of horticultural products. Emphasis is put on introduction and demonstration of Raman spectroscopy and imaging techniques for practical uses to assess the horticultural products. Raman scattering principles are presented first, followed by introduction and comparison to Raman measurement techniques, such as backscattering Raman spectroscopy, transmission Raman spectroscopy, spatially offset Raman spectroscopy, Raman chemical imaging, surface-enhanced Raman spectroscopy, etc. Raman measurement instruments, including excitation sources, wavelength separation devices, detectors, commercial integrated and custom-developed systems, and system calibration methods, are discussed and compared. Raman data analysis methods, such as data preprocessing, spectral mixture analysis, and quantitative analysis, are presented with examples for analyzing Raman spectral and image data of selected horticultural products including tomato and carrot. Raman spectroscopy and imaging applications for quality and safety evaluation of the horticultural products are also reviewed.
关键词： Horticultural products,Raman spectroscopy,Quality,Lasers,Safety,Chemical imaging
更新于2025-09-09 09:28:46
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Replacement Orthogonal Wavelengths Selection as a new method for multivariate calibration in spectroscopy
摘要： Wavelength selection is a critical step in multivariate calibration. Variable selection methods are used to find the most relevant variables, leading to improved prediction accuracy, while simplifying both the built models and their interpretation. In addition, different spectrophotometer designs and measurement principles result in non-destructive technologies applied in many fields, such as agriculture, food chemistry and pharmaceutics. However, an on-chip or portable device does not allow acquiring data from a large number of wavelengths. Therefore, the most informative combination of a limited number of variables should be selected. The Replacement Orthogonal Wavelengths Selection (ROWS) method is described here as a new method. This algorithm aims at selecting as few wavelengths as possible, while keeping or improving the prediction performance of the model, compared to when no variable selection is applied. The ROWS is applied to several near infrared spectroscopic data sets leading to improved analytical figures of merits upon wavelength selection in comparison to a built PLS model using entire spectral range. The performance of the ROWS-MLR method was compared to the FCAM-PLS method. The resulting models are not significantly different from those of FCAM-PLS; however, it involves a significantly smaller amount of variables.
关键词： Replacement Method,ROWS-MLR,Orthogonalization,FCAM-PLS,Near-Infrared spectroscopy
更新于2025-09-09 09:28:46
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The theory of selective reflection for a Fabry–Perot interferometer
摘要： In this paper we revisit the theory of selective reflection from a dilute vapor cell. A self-consistent theory is developed for reflection spectrum for Fabry-Perot interferometer. Formulas for single and multiple reflections are obtained. We also obtain the effective refractive index for a single selective reflection. The results of the paper are in a good agreement with existing experimental results.
关键词： Reflection and refraction,Lineshapes, widths, and shifts,Laser spectroscopy,Interference
更新于2025-09-09 09:28:46
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Paper-based Versatile SERS Chip with Smartphone-based Raman Analyzer for Point of Care Application
摘要： With the advanced development of the miniaturized Raman spectroscopy, surface enhanced Raman spectroscopy (SERS) has extended its applications into the field of Point of Care Testing (POCT) and demonstrated its great significance in virtue non-invasive property and capability of fingerprint identification. In the SERS-based analysis and/or sensing system, the preparation of low cost, high-performance SERS substrate is critically important. In this manuscript, vacuum filtration is utilized to fabricate the silver nanoparticles (AgNPs) embedded nylon filter membrane (ANFM) as flexible paper-based SERS chips. By characterizing the typical analytes with the miniaturized smartphone-based Raman analyzer, the proposed SERS chips have successfully demonstrated good sensitivity, repeatability and stability. The lowest concentration as detected can approach 1 pmol for Rhodamine 6G (RH6G) and 10 pmol for both crystal violet (CV) and malachite green (MG), respectively. With the help of microporous structure of the membrane, the ANFM based SERS chips can implement the separation of small molecules from complex mixture and can achieve “purified” SERS signals of targeted molecules. Besides, with the function of anti-friction resistance and flexibility, the ANFM can serve as SERS papers to pre-concentrate the contaminates by multiple swapping and further enhance the SERS signals for point of care analysis. Therefore, we demonstrate multi-functions of the flexible ANFM based SERS chips, which provides a promising solution for the POCT analysis with SERS technique on account of its flexibility and low fabrication cost.
关键词： silver nanoparticles,SERS chips,nylon filter membrane,Point of Care Testing,smartphone-based Raman analyzer,Surface-enhanced Raman spectroscopy
更新于2025-09-09 09:28:46
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Probing the upper band gap of atomic rhenium disulfide layers
摘要： Here, we investigate the ultrafast carrier dynamics and electronic states of exfoliated ReS2 films using time-resolved second harmonic generation (TSHG) microscopy and density functional theory (DFT) calculations. The second harmonic generation (SHG) of layers with various thicknesses is probed using a 1.19-eV beam. Up to ~13 nm, a gradual increment is observed, followed by a decrease caused by bulk interferometric light absorption. The addition of a pump pulse tuned to the exciton band gap (1.57 eV) creates a decay-to-rise TSHG profile as a function of the probe delay. The power and thickness dependencies indicate that the electron–hole recombination is mediated by defects and surfaces. The two photon absorptions of 2.38 eV in the excited state that are induced by pumping from 1.57 to 1.72 eV are restricted because these transitions highly correlate with the forbidden d–d intrasubshell orbital transitions. However, the combined usage of a frequency-doubled pump (2.38 eV) with wavelength-variant SHG probes (2.60–2.82 eV) allows us to vividly monitor the variations in TSHG profiles from decay-to-rise to rise-to-decay, which imply the existence of an additional electron absorption state (s-orbital) at an approximate distance of 5.05 eV from the highest occupied molecular orbital states. This observation was critically examined by considering the allowance of each electronic transition and a small upper band gap (~0.5 eV) using modified DFT calculations.
关键词： density functional theory,ReS2,time-resolved spectroscopy,ultrafast carrier dynamics,second harmonic generation
更新于2025-09-09 09:28:46
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<i>Ab Initio</i> Prediction of Fluorescence Lifetimes Involving Solvent Environments by Means of COSMO and Vibrational Broadening
摘要： The fluorescence lifetime is a key property of fluorophores that can be utilized for microenvironment probing, analyte sensing, and multiplexing as well as barcoding applications. For the rational design of lifetime probes and barcodes, theoretical methods have been developed to enable the ab initio prediction of this parameter, which depends strongly on interactions with solvent molecules and other chemical species in the emitter′s immediate environment. In this work, we investigate how a conductor-like screening model (COSMO) can account for variations in fluorescence lifetimes that are caused by such fluorophore-solvent interactions. Therefore, we calculate vibrationally broadened fluorescence spectra using the nuclear ensemble method to obtain distorted molecular geometries to sample the electronic transitions with time-dependent density functional theory (TDDFT). The influence of the solvent on fluorescence lifetimes is accounted for with COSMO. For an example 4-hydroxythiazole fluorophore containing different heteroatoms and acidic and basic moieties in aprotic and protic solvents of varying polarity, this approach was compared to experimentally determined lifetimes in the same solvents. Our results demonstrate a good correlation between theoretically predicted and experimentally measured fluorescence lifetimes except for the polar solvents ethanol and acetonitrile that can specifically interact with the heteroatoms and the carboxylic acid of the thiazole derivative.
关键词： Fluorescence Lifetimes,Quantum Chemistry,Molecular Structure,TDDFT,Spectroscopy,Vibrational Broadening,COSMO
更新于2025-09-09 09:28:46
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Effect of Environmental Humidity in the Electrical Properties of Lead Halide Perovskites
摘要： In large quantities, water is detrimental to lead halide perovskite solar cells, mainly because of the decomposition of the perovskite layer. On the contrary, the presence of small quantities of water has been observed to play a key role in the crystallization of the perovskite and in the performance of the corresponding devices. However, it is still under debate the exact role of water during the operation of perovskite solar cells. In this paper, impedance spectroscopy is used to analyze the changes produced by environmental humidity in the electronic properties of methylammonium lead triiodide perovskite. Our results show that water absorbed from environmental humidity induces a huge increase in the capacitance of this material. This capacitance can reach values as large as the accumulation capacitance found in devices based in perovskite, which is the responsible of the characteristic large hysteresis observed between forward and reverse J-V curves. In parallel to this outstanding rise of the capacitance, water absorption produces a significant rise of the conductivity, in agreement with previous reports in the literature. Activation energy of 0.52 eV is found for electronic transport, a value in line with activation energy of ionic transport found in literature, what suggests ambipolar diffusion as the transport mechanism that links these two phenomena.
关键词： impedance spectroscopy,environmental humidity,electrical properties,lead halide perovskites,capacitance,conductivity
更新于2025-09-09 09:28:46
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Impact of Molecular Order on Polaron Formation in Conjugated Polymers
摘要： The nature of polaron formation has profound implications on the transport of charge carriers in conjugated polymers, but still remains poorly understood. Here we develop in situ electrochemical resonant Raman spectroscopy, a powerful structural probe that allows direct observation of polaron formation. We report that polaron formation in ordered poly(3-hexyl)thiophene (P3HT) polymer domains (crystalline phase) results in less pronounced changes in molecular conformation, indicating smaller lattice relaxation, compared to polarons generated in disordered polymer domains (amorphous phase) for which we observe large molecular conformational changes. These conformational changes are directly related to the effective conjugation length of the polymer. Furthermore, we elucidate how blending the P3HT polymer with phenyl C-61 butyric acid methyl ester (PCBM) affects polaron formation in the polymer. We find that blending disturbs polymer crystallinity, reducing the density of polarons that can form upon charge injection at the same potential, whilst the lost capacity is partly restored during post-deposition thermal annealing. Our study provides direct spectroscopic evidence for a lower degree of lattice reorganisation in crystalline (and therefore more planarised) polymers than in conformationally disordered polymers. This observation is consistent with higher charge carrier mobility and better device performance commonly found in crystalline polymer materials.
关键词： electrochemical resonant Raman spectroscopy,conjugated polymers,polaron formation,molecular order,PCBM,charge transport,P3HT
更新于2025-09-09 09:28:46
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Low-Energy Photoelectron Spectrum and Dissociative Photoionization of the Smallest Amides: Formamide and Acetamide
摘要： The threshold photoelectron spectrum and low-energy dissociative photoionization processes of formamide and acetamide were studied using photoelectron photoion coincidence spectroscopy and vacuum ultraviolet synchrotron radiation. Ab initio calculations and Franck–Condon simulations helped us assign the main vibrational progressions in the spectra and enabled the first conclusive assignment of the first electronically excited states. The adiabatic ionization energies to the ???+ and ???+ states of formamide (10.236 ± 0.004 eV and 10.643 ± 0.015 eV) and acetamide (9.734 ± 0.008 and 10.282 ± 0.020 eV) have been re-evaluated and spectroscopic transitions were assigned using a Franck–Condon approach. The cationic potential energy surface was explored to rationalize the observed fragmentation patterns and to construct a statistical model, which was fitted to the experimental breakdown diagram. Thermochemical thresholds were measured and calculated for H, CO, and NH2 loss from HCONH2+ as well as for CH3, NH2, CO, HCCO, and NH3 loss from CH3CONH2+. We present the first comprehensive, experimental and theoretical treatise of these fragmentation processes. The statistical model confirms fast internal conversion between the ???+ and ???+ states in formamide, as H-transfer in CO loss is shown to take place on the excited state surface. It also explains the five almost simultaneously opening dissociation channels in the acetamide cation quantitatively. The derived 0 K appearance energies have been confirmed by ab initio calculations and by comparison with state-of-the-art thermochemical data, and revise some of the previous results by more than ten times their stated uncertainty.
关键词： Dissociative Photoionization,Photoelectron Spectrum,Acetamide,Formamide,Quantum Chemistry,Spectroscopy,Molecular Structure
更新于2025-09-09 09:28:46