Analysis Of Spectra Research Articles

Fabrication of highly stable and durable wood materials by modification of polyacrylamide (PAM)-glyoxal (GLY)

Facile and efficient protection strategies to improve wood dimensional stability and resistance to mold and termite are urgently needed in the architectural constructional materials market. In this study, polyacrylamide (PAM)-glyoxal (GLY) system impregnation and thermal curing were used to modify Scots pine wood. The results showed that the average anti-swelling efficacy (ASE) of 160-AGE, 160-AGEP, and 200-AGE modified wood was 36.09 %, 26.67 % and 19.00 % in volume, respectively. Compared with the untreated wood, the modified wood exhibited better mold resistance. Furthermore, the modified wood samples show higher termite mortality and lower mass losses, indicating good termite resistance. Among them, the anti-mold efficacy in 200-AGE was 91.10 %, and the termite resistance rating in 160-AGE was 9.2. The modulus of elasticity (MOE) of the modified wood sample was 16–25 % higher than that of the untreated wood. Obtained by infrared spectrum and electron microscope analysis, the acrylamide polymer penetrates into the wood cell cavities and forms polyacrylamide, which is crosslinked to wood cell wall -OH by glyoxal. This study can prove that the polyacrylamide-glyoxal system modifier has great potential as a modifier to improve the mold resistance and dimensional stability of wood.

Solvents and their influence on electronic properties in IEFPCM solvation model, anticancer activity, and docking studies on (E)-2-((4-chlorobenzylidene) amino)phenol

The Schiff base (E)-2-((4-chlorobenzylidene)amino)phenol (4CL2AM) has been synthesized from 4-chlorobenzaldehyde and 2-aminophenol. Spectroscopic techniques like FTIR, Raman, UV, fluorescence, and NMR were used to characterize the synthesized compound. The experimental data well matched with the DFT method (B3LYP/cc-pVDZ basis set). The frontier molecular orbital (FMO), molecular electrostatic potential (MEP), and electronic spectra (UV–visible) analysis were conducted on three different solvents such as gas, DMSO, and water. The frontier molecular orbital (FMO) analysis calculated the HOMO-LUMO energy gap as 4.0109 eV, 4.0406 eV, and 4.0411 eV for the gas phase, DMSO, and water respectively. Molecular electrostatic potential (MEP), localized orbital locator (LOL), and electron localize function (ELF) analysis revealed positions of localized and delocalized orbitals as well as electrophilic and nucleophilic attack sites. The natural bond orbital analysis (NBO) predicted highest stabilization energy was 33.37 kcal/mol. The locations of the covalent and non-covalent interactions were investigated by density overlaps region indicator (DORI), interaction region indicator (IRI), and noncovalent interaction (NCI) analysis. Drug likeness and ADME analysis were investigated. In vitro, anticancer activity studies revealed against MCF-7 breast cancer cell lines. In the molecular docking study, the predicted lowest binding energy is −5.77 kcal/mol for the 6NLV-4CL2AM system.

The Evolution of Vector Network Analyzers to Provide Precision Vector Spectrum Analysis for 6G Applications: VNA Evolves for 6G EVM Signals

The Evolution of Vector Network Analyzers to Provide Precision Vector Spectrum Analysis for 6G Applications: VNA Evolves for 6G EVM Signals

Revitalizing temperature records: A novel framework towards continuous data reconstruction using univariate and multivariate imputation techniques

Data gaps are a recurring challenge in climate research, hindering effective time series analysis and modeling. This study proposes a novel two-step data imputation framework to address temperature time series with a long continuous gap surrounded by predictor stations with sporadic missingness. The method leverages iterative gap-filling Singular Spectrum Analysis (SSA) for the small sporadic gaps, followed by multivariate techniques like Inverse Distance Weightage (IDW), Kriging, Spatial Regression Test (SRT), Point Estimation method of Biased Sentinel Hospital-based Area Disease Estimation (P-BSHADE), Random Forest (RF), Support Vector Machines (SVM), and MissForest (MF) for the longer gap. Once the sporadic gaps are effectively addressed with SSA, the method carefully applies multivariate techniques to impute the long continuous gap. Prioritizing accuracy, comprehensive cross-validation with class-based statistical indicators are employed to minimize any potential biases introduced by the imputation process. The study shows the effectiveness of SSA in filling small sporadic gaps using an optimal window length (M ≈ 365 days) and eigentriple grouping (ET = 30). Notably, for maximum temperature, P-BSHADE and SVM achieve an impressive accuracy (e.g., Legates's Coefficient of Efficiency (LCE), 0.75–0.44, Combined Performance Index (CPI), 6.3 % ~ 19.1 %) attributed to their ability to capture spatial and/or temporal heterogeneity. While SRT and P-BSHADE offers acceptable performance for minimum temperature (e.g., LCE, 0.51–0.27, CPI, 0.7 % ~ 23.7 %), the study also uncovers a complex interplay between missing data, predictor stations, and autocorrelation affecting imputation accuracy. This suggests that the reduced performance of certain techniques likely stems from the decline in spatial and spatiotemporal autocorrelation between the target station and its predictors. Overall, this study presents a promising framework for handling complex missing data scenarios often encountered in climate time series analysis, paving the way for more robust and reliable analysis and modeling.

Targeted Regulation of Osteoblasts and Osteoclasts in Osteosarcoma Patients by CSF3R Receptor Inhibition of Osteolysis Caused by Tumor Inflammation Based on Transcriptional Spectrum Analysis and Drug Library Screening.

Osteosarcoma (OS) is a common primary malignant bone tumor that mainly occurs in children and adolescents. The use of IL-8 inhibitor compounds has been reported in patents, which can be used to treat and/or prevent osteosarcoma, but the pathogenesis of osteosarcoma remains to be investigated. At present, osteoblasts and osteoclasts play an important role in the occurrence and development of OS. However, the relationship between osteoblasts and osteoclasts in the specific participation mechanism and inflammatory response of OS patients has not been further studied. The transcriptome, clinical data, and other data related to OS were downloaded from the GEO database to analyze them with 200 known inflammatory response genes. We set the screening conditions as p < 0.05 and | log2FC| > 0.50, screened the differentially expressed genes (DEGs) related to OS, tested the correlation coefficient between the OS INF gene and clinical risk, and analyzed the survival prognosis. We further enriched and analyzed the DEGs and inflammatory response genes of OS with GO/KEGG to explore the potential biological function and signal pathway mechanism of OS inflammatory response genes. Moreover, the virtual screening of drug sensitivity of OS based on the FDA drug library was also carried out to explore potential therapeutic drugs targeted to regulate OS osteogenesis and osteoclast inflammation, and finally, the molecular dynamics simulation verification of OS core protein and potential drugs was carried out to explore the binding stability and mechanism between potential drugs and core protein. Through differential analysis of GSE39058, GSE36001, GSE87624, and three other data sets closely related to OS osteoblasts and osteoclasts, we found that there was one upregulated gene (CADM1) and one down-regulated gene (PHF15) related to OS. In addition, GSEA enrichment analysis of the DEGs of OS showed that it was mainly involved in the progress of OS through biological functions, such as oxidative photosynthesis, acute junction, and epithelial-mesenchymal transition. The enrichment analysis of OS DEGs revealed that they mainly affect the occurrence and progress of OS by participating in the regulation of the actin skeleton, PI3K Akt signal pathway, complement and coagulation cascade. According to the expression of CSF3R in OS patients, a risk coefficient model and a diagnostic model were established. It was found that the more significant the difference in the CSF3R gene in OS patients, the greater the risk coefficient of disease (p < 0.05). The AUC under the curve of the CSF3R gene was greater than 0.65, which had a good diagnostic significance for OS. The above results showed that the prognosis risk gene CSF3R related to OS inflammation was closely related to the survival status of OS patients. Finally, through the virtual screening of the ZINC drug library and molecular dynamics simulation, it was found that the docking model formed by the core protein CSF3R and the compounds, Leucovorin and Methotrexate, were the most stable, which revealed that the compounds Leucovorin and Methotrexate might play a role in the treatment of OS by combining with the inflammatory response related factor CSF3R of OS. CSF3R participates in the occurrence and development of OS bone destruction by regulating the inflammatory response of osteoblasts and osteoclasts and can affect the survival prognosis of OS patients.

Technical feasibility of automated blur detection in digital mammography using convolutional neural network

Abstract Background The presence of a blurred area, depending on its localization, in a mammogram can limit diagnostic accuracy. The goal of this study was to develop a model for automatic detection of blur in diagnostically relevant locations in digital mammography. Methods A retrospective dataset consisting of 152 examinations acquired with mammography machines from three different vendors was utilized. The blurred areas were contoured by expert breast radiologists. Normalized Wiener spectra (nWS) were extracted in a sliding window manner from each mammogram. These spectra served as input for a convolutional neural network (CNN) generating the probability of the spectra originating from a blurred region. The resulting blur probability mask, upon thresholding, facilitated the classification of a mammogram as either blurred or sharp. Ground truth for the test set was defined by the consensus of two radiologists. Results A significant correlation between the view (p &lt; 0.001), as well as between the laterality and the presence of blur (p = 0.004) was identified. The developed model AUROC of 0.808 (95% confidence interval 0.794–0.821) aligned with the consensus in 78% (67–83%) of mammograms classified as blurred. For mammograms classified by consensus as sharp, the model achieved agreement in 75% (67–83%) of them. Conclusion A model for blur detection was developed and assessed. The results indicate that a robust approach to blur detection, based on feature extraction in frequency space, tailored to radiologist expertise regarding clinical relevance, could eliminate the subjectivity associated with the visual assessment. Relevance statement This blur detection model, if implemented in clinical practice, could provide instantaneous feedback to technicians, allowing for prompt mammogram retakes and ensuring that only high-quality mammograms are sent for screening and diagnostic tasks. Key Points Blurring in mammography limits radiologist interpretation and diagnostic accuracy. This objective blur detection tool ensures image quality, and reduces retakes and unnecessary exposures. Wiener spectrum analysis and CNN enabled automated blur detection in mammography. Graphical Abstract

Forecasting Gate-Front Water Levels Using a Coupled GRU–TCN–Transformer Model and Permutation Entropy Algorithm

Water level forecasting has significant impacts on transportation, agriculture, and flood control measures. Accurate water level values can enhance the safety and efficiency of water conservancy hub operation scheduling, reduce flood risks, and are essential for ensuring sustainable regional development. Addressing the nonlinearity and non-stationarity characteristics of gate-front water level sequences, this paper introduces a gate-front water level forecasting method based on a GRU–TCN–Transformer coupled model and permutation entropy (PE) algorithm. Firstly, an analysis method combining Singular Spectrum Analysis (SSA) and Complete Ensemble Empirical Mode Decomposition with Adaptive Noise (CEEMDAN) is used to separate the original water level data into different frequency modal components. The PE algorithm subsequently divides each modal component into sequences of high and low frequencies. The GRU model is applied to predict the high-frequency sequence part, while the TCN–Transformer combination model is used for the low-frequency sequence part. The forecasting from both models are combined to obtain the final water level forecasting value. Multiple evaluation metrics are used to assess the forecasting performance. The findings indicate that the combined GRU–TCN–Transformer model achieves a Mean Absolute Error (MAE) of 0.0154, a Root Mean Square Error (RMSE) of 0.0205, and a Coefficient of Determination (R2) of 0.8076. These metrics indicate that the model outperforms machine learning Support Vector Machine (SVM) models, GRU models, Transformer models, and TCN–Transformer combination models in forecasting performance. The forecasting results have high credibility. This model provides a new reference for improving the accuracy of gate-front water level forecasting and offers significant insights for water resource management and flood prevention, demonstrating promising application prospects.

Evaluating Pressure‐dependent Discharge Behavior of Foil Versus In situ Plated Lithium Metal Anodes in Solid‐State Batteries

AbstractAnode‐free manufacturing of solid‐state batteries (SSBs) shows promise to maximize energy density by eliminating excess lithium (Li) and simplifying battery production. However, high reversibility during discharge (stripping of Li) is necessary for long‐lifetime SSBs with a limited Li reservoir. Further, the plastic flow of Li changes depending on the Li thickness, leading to possible differences in discharge performance under stack pressure. This work investigates the pressure‐dependent discharge performance of anode‐free manufactured SSBs with in situ plated Li and compares the performance to that of conventional thick Li foil cells. Distinct stripping behavior is observed at low pressures (0–1 MPa), where Li diffusivity and initial interfacial contact may control accessible capacity, compared to high pressures (3–10 MPa) where mechanical deformation of Li likely governs stripping behavior. Analysis of impedance spectra collected during stripping shows that additional stack pressure delays the formation of deep, as opposed to lateral, voids in the Li anode. These results provide insights to guide the transition from thick Li foil anodes to anode‐free manufactured SSBs.

Tissue-Specific Effects of Aging on Repeat-Mediated Mutation Hotspots In Vivo

Aging constitutes complex and dynamic alterations in molecular and physiological processes and is associated with numerous disorders, in part due to increased genetic instability. The aging population is projected to double by 2050, underscoring the urgent need to better understand the relationships between aging and age-related disorders. Repetitive DNA elements are intrinsic sources of genetic instability and have been found to co-localize with mutation hotspots in human cancer genomes. In this study, we explored the relationship between aging and DNA repeat-mediated genetic instability in vivo using an H-DNA-forming mirror-repeat sequence from the cancer-associated human c-MYC gene. Utilizing a unique mutation-reporter mouse model, we observed tissue-specific effects of aging on H-DNA-induced genetic instability, with mutation frequencies increasing in spleen tissues and remaining unchanged in testis tissues. Analysis of the mutation spectra revealed large deletion mutations as the primary contributor to increasing H-DNA-induced mutations, supported by increased cleavage activity of H-DNA structures in aged spleen tissues. Our findings demonstrate that aging has distinct tissue-specific effects on repeat-mediated, cancer-associated mutations, providing insights into the complex relationship between aging and cancer.

A multi-faceted view of the X-ray spectral variability in Seyfert galaxy Ark 120

Abstract Utilizing a range of techniques including multi-band light curves, softness ratio analysis, structure functions, rms spectra, cross-correlation functions, and ratios of spectra from different intervals, we present a comprehensive study of the complex X-ray spectral variability in Seyfert 1 galaxy Ark 120, through re-analyzing its six XMM-Newton observations taken between 2003 and 2014. We find a clear ``softer-when-brighter" trend in the 2--10 keV power-law component over long timescales, with this trend being timescale dependent, as it is much weaker on shorter timescales, similar to that previously detected in NGC 4051. Notably, a rare ``harder-when-brighter" trend is observed during one exposure, indicating dynamic changes in the spectral variability behavior of the power-law component. This exceptional exposure, with the spectral variability indeed marked by a power-law pivoting at an unusually low energy of $\sim$ 2 keV, suggests intricate variations in the thermal Comptonization processes within the corona. Furthermore, when the data below 2 keV are included, we identify that the soft excess component adds significant complexity to the spectral variability, such as evidenced by a transition from ``harder-when-brighter” to ``softer-when-brighter” during another single exposure.Such extra complexity arises because the variability of the soft excess sometimes follows and sometimes does not follow the changes in the power-law component.Our findings underscore the necessity of applying multiple analytic techniques to fully capture the multifaceted spectral variability of AGNs.

A search for H i absorption in distant star-forming galaxies with ASKAP-FLASH - I. Selection and analysis of the radio sample

Abstract We present and discuss two catalogues of UV-selected (NUV &amp;lt;22.8 mag) galaxies that lie within a 200 deg2 area of sky covered by the ASKAP FLASH survey and have an impact parameter of less than 20 arcsec to a FLASH radio continuum source. These catalogues are designed to enable a future search for 21 cm H i absorption in and around star-forming galaxies at redshift 0.4 &amp;lt; z &amp;lt; 1. We outline the production of this UV-bright dataset, which has optical spectroscopy from the WiggleZ and SDSS surveys and a median redshift of ∼0.6. Analysis of the optical spectra, using multiple diagnostic diagrams, shows that galaxies with an impact parameter of less than 5 arcsec are likely to be physically associated with the radio source and are five times more likely to be an AGN than objects without a radio match. Conversely, objects with impact factors between 5 and 20 arcsec are largely (&amp;gt; 80 percent) star-forming and resemble the overall WiggleZ population. The (g − i) colour evolution with redshift is consistent with a history of active star-formation, but the radio-associated objects are typically redder and have colours similar to high-excitation radio galaxies. The redshift distribution of the two catalogues matches the overall distribution for WiggleZ galaxies, despite their otherwise rare radio properties. These catalogues can be expanded in future as new radio data become available, and a forthcoming paper will present the H i absorption results.

Spectral analysis of Ultra-Luminous X-ray pulsars with models of X-ray pulsars

Abstract A fraction of the Ultra Luminous X-ray (ULX) sources are known to be accreting neutron stars as they show coherent X-ray pulsations with pulse periods ranging from ∼1 − 30 seconds. While initially thought to host intermediate-mass black holes, ULXs have since been recognized as a diverse class of objects, including ULX pulsars. These pulsars require models specifically tailored to account for their unique accretion physics, distinct from those used for Galactic black hole binaries. The X-ray spectra of all Galactic accreting X-ray pulsars (including sources in the Magellanic Clouds) are dominated by a high energy cut-off power-law and some of the sources show a soft excess, some emission lines, cyclotron absorption features, etc. In this work, we undertake a comprehensive analysis of the broadband X-ray spectra of five ULX pulsars using simultaneous XMM-Newton and NuSTAR observations and show that their X-ray spectra can be effectively described by spectral models, similar to those used for the local accretion-powered X-ray pulsars. A soft excess is detected in all the sources which is also consistent with the local X-ray pulsars that have low absorption column density. We have marginal detection or low upper limit on the presence of the iron K-alpha emission line from these sources, which is a key difference of the ULX pulsars with the local accreting X-ray pulsars. We discuss the implication of this on the nature of the binary companion and the accretion mechanism in the ULX pulsars.

Influence of Soil Plugging on Dynamic Soil Response During Simulated Pipe Pile Driving Model Test in Sands

The squeezing effect and strike-induced vibration generated by pile driving pose a threat to adjacent structures. To mitigate the squeezing effect, open-ended pipe piles were implemented. However, this type of pile brings a degree of soil-plugging effect, particularly in sandy soil, which complicates the squeezing effect and the dynamic responses of the pile during pile driving. In this study, model experiments were conducted using both open-ended piles and open-ended piles with different fixed-length soil plugs to investigate the squeezing effect and dynamic responses of the piles. Moreover, spectrum analysis was performed to explore the patterns of vibration waves in the open-ended pipe pile during the striking process. For open-ended pipe piles, acceleration fluctuations were detectable solely when the pile reached the sensor depth and at the end of the pile driving process, which revealed that the hammering energy was mainly consumed by pile settlement and the formation of the soil plug. When the formation of the soil plug was completed, the majority of the energy was converted into propagating vibration, resulting in the emergence of another crest of acceleration. The spectrum analysis revealed that the maximum amplitude occurred when the penetration depth was equal to half of the pile length.

Optimized detection modality for radio-frequency sensing with a double-resonance alignment magnetometer

In this work, we present a comprehensive and comparative analysis of two detection modalities, i.e., polarization rotation and absorption measurement of light, for a double-resonance alignment magnetometer (DRAM). We derive algebraic expressions for magnetometry signals based on the description of multipole moments. Experiments are carried out using a room-temperature paraffin-coated cesium-vapor cell and measuring either the polarization rotation or absorption of the transmitted laser light. A detailed experimental analysis of the resonance spectra is performed to validate the theoretical findings for various input parameters. The results signify the use of a single isotropic relaxation rate, thus simplifying the data analysis for optimization of the DRAM. The sensitivity measurements are performed and reveal that the polarization-rotation detection mode yields larger signals and better sensitivity than absorption measurement of light. Published by the American Physical Society 2024

Broad Instantaneous Bandwidth Microwave Spectrum Analyzer with a Microfabricated Atomic Vapor Cell

We report on broad instantaneous bandwidth microwave spectrum analysis with hot Rb87 atoms in a microfabricated vapor cell in a large magnetic field gradient. The sensor is a MEMS atomic vapor cell filled with isotopically pure Rb87 and N2 buffer gas to localize the motion of the atoms. The microwave signals of interest are coupled through a coplanar waveguide to the cell, inducing spin-flip transitions between optically pumped ground states of the atoms. A static magnetic field with large gradient maps the frequency spectrum of the input microwave signals to a position-dependent spin-flip pattern on absorption images of the cell recorded with a laser beam onto a camera. In our proof-of-principle experiment, we demonstrate a microwave spectrum analyzer that has ≈1 GHz instantaneous bandwidth centered around 13 GHz, 3 MHz frequency resolution, 2 kHz refresh rate, and a −23 dBm single-tone microwave power detection limit in 1 s measurement time. A theoretical model is constructed to simulate the image signals by considering the processes of optical pumping, microwave interaction, diffusion of Rb87 atoms, and laser absorption. We expect to reach more than 25 GHz instantaneous bandwidth in an optimized setup, limited by the applied magnetic field gradient. Our demonstration offers a practical alternative to conventional microwave spectrum analyzers based on electronic heterodyne detection. Published by the American Physical Society 2024

Synthesis of the cis‐ and trans‐3‐Fluoro Analogues of Febrifugine and Halofuginone

AbstractThe novel synthesis of racemic cis‐ and trans‐3‐fluorofebrifugine and halofuginone is described. This straight‐forward seven‐step process relies on an electrophilic fluorination‐allylation sequence that generates a mixture of N‐Cbz protected, diastereomeric 2‐allyl‐3‐fluoropiperidines. On separation, a Wacker oxidation‐methyl functionalisation sequence enabled introduction of the required quinazolinone portion. Finally, removal of the N‐Cbz protecting group lead to isolation of the 3‐fluorofebrifugine dihydrobromide analogues that are of potentially pharmacological use. Analysis of the NMR spectra for each stereoisomer provides information concerning the preferred conformers of the different diastereomers. Evidence indicates that the cis‐diastereomer favours a conformation where the F‐atom occupies an axial orientation. In contrast, for its trans‐stereoisomeric counterpart, the 2‐substituent overrides any F‐atom effect and it preferentially occupies a conformer where both substituents occupy equatorial positions. Finally, interconversion between the cis‐ and trans‐diastereomers was studied. In DMSO‐d6 and as their free‐bases, isomerisation of each diastereomer gave a common 65 : 35 ratio of trans‐ to cis‐3‐fluorofebrifugine. Determination of the reaction rate constants for the isomerisation process at different temperatures enabled calculation of the activation energy barriers, for each process, using an Arrhenius plot. The activation energy barrier for the isomerisation of the trans‐isomer was 94.3±4.9 kJ mol−1, whereas for the cis‐isomer it was 84.5±3.9 kJ mol−1.

A Novel Neural Network Architecture Dedicated for LIBS Spectrum Analysis With Its Application to Steel Pipe Classification

Abstract As a non-destructive rapid composition analysis method, Laser-induced breakdown spectroscopy (LIBS) has received widespread attention in recent years. However, its application in the steel industry has not achieved an effective breakthrough in its detection accuracy due to the existence of matrix effect. This paper introduces a neural network model for LIBS spectral line analysis, which can automatically construct the features and analyze the correlation between them, and this model has been applied in the steel sample classification of seamless steel pipe with good results.

Cc¯ and bb¯ suppression in the glasma

This study investigates the evolution and dissociation dynamics of cc¯ and bb¯ pairs within the preequilibrium, gluon-dominated stage of high energy nuclear collisions. An attractive potential made of a perturbative Coulomb-like term and of a confining term is used to simulate the attractive strong force in the pairs. Besides, we implement the interaction of the pairs with the evolving glasma fields by virtue of the Wong equations. The interaction with the classical color fields dominates the dynamics, causing an increase in pair separation and subsequent dissociation. The observed finite probability of dissociation for these states reveals the intricate interplay between quantum chromodynamics (QCD) dynamics and the suppression of cc¯ and bb¯ states during the preequilibrium stage. The research highlights differences between cc¯ and bb¯ pairs, revealing the role of quark flavor in the dissociation process. Dissociation spectra analysis indicates a peak shift toward higher momentum, reflecting a slight energy gain by the pairs. This investigation provides valuable insights into the complex dynamics of cc¯ and bb¯ pairs in the glasma, which may help in better interpretation of experimental results on further integration with subsequent phases of the created matter. Published by the American Physical Society 2024

The Analysis of Vibrational Spectra: Past, Present and Future.

Vibrational spectroscopy can be said to have started with the seminal work of Coblentz in the 1900s, who recorded the first recognisable infrared spectra. Today, vibrational spectroscopy is ubiquitous and there are many ways to measure a vibrational spectrum. But this is usually only the first step, almost always there is a need to assign the resulting spectra: "what property of the system results in a feature at this energy"? How this question has been answered has changed over the last century, as our understanding of the fundamental physics of matter has evolved. In this Perspective, I will present my view of how the analysis of vibrational spectra has evolved over time. The article is divided into three sections: past, present and future. The "past" section consists of a very brief history of vibrational spectroscopy. The "present" is centered around ab initio studies, particularly with density functional theory (DFT) and I will describe how this has become almost routine. For the "future", I will extrapolate current trends and also speculate as to what might come next.

Comprehensive Analysis of Optical Resonances and Sensing Performance in Metasurfaces of Silicon Nanogap Unit

Metasurfaces composed of silicon nanogap units have a variety of optical resonances, including bound states in the continuum (BIC). We show comprehensive numerical results on metasurfaces of Si-nanogap units, analyze the optical resonances, and clarify optically prominent resonances as well as symmetry-forbidding resonances that are the BIC, based on the numerical analyses of optical spectra and resonant electromagnetic field distributions. Introducing asymmetry in the unit cell, the BIC become optically allowed, being identified as magnetic dipole, electric quadrupole, and magnetic quadrupole resonances. Moreover, the optical resonances are examined in terms of refractive index sensing performance. A pair of the resonances associated with electric field localization at the nanogap was found to be sensitive to the refractive index in contact with the metasurfaces. Consequently, the gap mode resonances are shown to be suitable for a wide range of refractive index sensing over 1.0–2.0.