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Soil nutrients are an important component of soil fertility, and having accurate and timely soil nutrients information is conducive to scientifically guided agricultural fertilization and improved crop yields. Traditional soil nutrient measurement methods are accurate but time-consuming and costly. Visible near-infrared (vis-NIR) and mid-infrared (MIR) as techniques of spectroscopy measurements are cheap, fast, and non-destructive, and, after training, have been used separately to predict soil nutrients. They can give complementary information, so using them separately may not be optimal. This study investigated whether the fusion of vis-NIR and MIR spectra would improve the prediction of six soil nutrients: total nitrogen (TN), total phosphorus (TP), total potassium (TK), alkali-hydrolyzable nitrogen (AN), available phosphorus (AP) and available potassium (AK). The sample set was 501 tillage (0 ∼ 20 cm) soil samples from Guizhou Province (China). Three different sensor fusion techniques were compared: (1) direct fusion of spectra (low-level fusion; SF1); (2) fusion of spectral features selected by the least absolute shrinkage and selection operator (LASSO) algorithm (middle-level fusion; SF2); and (3) fusion using the Granger-Ramanathan averaging (GRA) method of the separate vis-NIR and MIR results (high-level fusion; SF3). Prediction models were built using partial least squares regression (PLSR) and support vector machine (SVM), and evaluated using leave-one-out cross-validation (LOOCV), coefficient of determination (R2), and ratio of performance to interquartile (RPIQ), defined as Rcv2 and RPIQCV. All three sensor fusion methods were more accurate than single-sensor methods in predicting TN, TK and AN (0.60 ≤ Rcv2 ≤ 0.92, 1.86 ≤ RPIQCV ≤ 5.08), but were less accurate for TP, AP and AK (Rcv2 ≤ 0.34, RPIQCV ≤ 1.55). Compared to the best prediction using each single sensor model, low-level fusion improved the prediction of TN and AN; middle-level fusion improved the prediction of TN, TP, AN, AP and AK; and high-level fusion improved the prediction of all soil nutrients. Moreover, the SF2-PLSR model provided the best prediction for TN (Rcv2 = 0.83, RPIQCV = 3.18), the SF2-SVM model for AN (Rcv2 = 0.67, RPIQCV = 2.06), and the SF3-PLSR model for TK (Rcv2 = 0.92, RPIQCV = 5.08). The SF2 and SF3 methods are recommended to predict TN and AN, and MIR spectra are recommended to predict TK (Rcv2 = 0.92, RPIQCV = 5.02) since using only a single sensor is cost-effective. The SF2 and SF3 methods improved the prediction accuracy of AP and AK, but the prediction accuracy was still low. This study only covered one area with its set of soil landscapes, and only used well-established modelling methods. The results can motivate research on new spectra techniques and advanced modelling methods, as well as transferability to other soil landscapes.

The second-generation Chinese polar-orbit meteorological satellite Fengyun-3D carries the MEdium-Resolution Spectral Imager (MERSI-II). MERSI-II has 19 solar channels and 6 middle and thermal infrared channels and can provide daily global coverage observation at daytime and nighttime. Land surface temperature (LST) products have a wide range of application requirements. Unfortunately, there is no official LST product of MERSI-II yet. This article proposed a temperature-emissivity separation algorithm to estimate LST and emissivity from two mid-infrared (MIR) and two thermal infrared (TIR) nighttime MERSI-II images. The sensitive analysis and ground validation show the following. First, the algorithm can theoretically retrieve LST with an error of less than 0.7 K, emissivity with errors of about 0.025 for MIR channel and 0.01 for TIR channel, respectively. Second, the nighttime LST retrieval error was approximately 2.19 K, and the bias was approximately 0.60 K among 6 SURFRAD sites and 2 PKULSTNet sites. The retrieved emissivity was cross-validated using MODIS emissivity product over a desert area and its difference was obtained as 0.01 and 0.016 for two TIR channels. Finally, the TES algorithm was applied to obtain LST and emissivity images over North China Plain as an example, and the nighttime LST and land surface emissivity (LSE) were obtained well. As a result, this study shows that the proposed TES algorithm provides an effective way to get LST and LSE image from FY-3D/ MERSI-II nighttime observation, which will improve their applications in different fields.

This paper introduces the ProSpecTool, a MATLAB toolbox for automated selection of preprocessing methods for obtaining optimal PLS regression models in vibrational spectroscopy. Trial-and-error approaches for preprocessing can be time-consuming, and the success of the process relies on the experience of analysts. The ProSpecTool addresses this challenge by using objective criteria analogous to expert judgment to filter and iterate preprocessing methods based on raw data properties. The toolbox quantifies noise, identifies multiplicative and additive scatter-effects, and selects preprocessing algorithms to correct them. Results demonstrate that the ProSpecTool can produce models that resemble those proposed by experienced analysts based on trial-and-error in terms of performance and robustness, making it a valuable exploratory tool for vibrational spectroscopy practitioners. [Display omitted] • Preprocessing automation for vibrational spectroscopy with objective criteria. • Quantifies noise and scatter-effects, then selecting algorithms for removing them. • Optimal models outperform analyst proposals in robustness and performance. • Surpasses trial-and-error and other software for faster, effective preprocessing. [ABSTRACT FROM AUTHOR]

Summary: Leaf optical properties impact leaf energy balance and thus leaf temperature. The effect of leaf development on mid‐infrared (MIR) reflectance, and hence thermal emissivity, has not been investigated in detail.We measured a suite of morphological characteristics, as well as directional‐hemispherical reflectance from ultraviolet to thermal infrared wavelengths (250 nm to 20 µm) of leaves from five temperate deciduous tree species over the 8 wk following spring leaf emergence.By contrast to reflectance at shorter wavelengths, the shape and magnitude of MIR reflectance spectra changed markedly with development. MIR spectral differences among species became more pronounced and unique as leaves matured. Comparison of reflectance spectra of intact vs dried and ground leaves points to cuticular development – and not internal structural or biochemical changes – as the main driving factor. Accompanying the observed spectral changes was a drop in thermal emissivity from about 0.99 to 0.95 over the 8 wk following leaf emergence.Emissivity changes were not large enough to substantially influence leaf temperature, but they could potentially lead to a bias in radiometrically measured temperatures of up to 3 K. Our results also pointed to the potential for using MIR spectroscopy to better understand species‐level differences in cuticular development and composition. [ABSTRACT FROM AUTHOR]

• Soil TN, TK, and AN were all better predicted. • High-level fusion method improves prediction accuracy for all soil nutrients. • Both SF2 and SF3 methods are recommended for improving TN and AN prediction accuracy. • MIR spectra are more recommendable for predicting TK content. Soil nutrients are an important component of soil fertility, and having accurate and timely soil nutrients information is conducive to scientifically guided agricultural fertilization and improved crop yields. Traditional soil nutrient measurement methods are accurate but time-consuming and costly. Visible near-infrared (vis-NIR) and mid-infrared (MIR) as techniques of spectroscopy measurements are cheap, fast, and non-destructive, and, after training, have been used separately to predict soil nutrients. They can give complementary information, so using them separately may not be optimal. This study investigated whether the fusion of vis-NIR and MIR spectra would improve the prediction of six soil nutrients: total nitrogen (TN), total phosphorus (TP), total potassium (TK), alkali-hydrolyzable nitrogen (AN), available phosphorus (AP) and available potassium (AK). The sample set was 501 tillage (0 ∼ 20 cm) soil samples from Guizhou Province (China). Three different sensor fusion techniques were compared: (1) direct fusion of spectra (low-level fusion; SF1); (2) fusion of spectral features selected by the least absolute shrinkage and selection operator (LASSO) algorithm (middle-level fusion; SF2); and (3) fusion using the Granger-Ramanathan averaging (GRA) method of the separate vis-NIR and MIR results (high-level fusion; SF3). Prediction models were built using partial least squares regression (PLSR) and support vector machine (SVM), and evaluated using leave-one-out cross-validation (LOOCV), coefficient of determination (R2), and ratio of performance to interquartile (RPIQ), defined as R c v 2 and R P I Q C V . All three sensor fusion methods were more accurate than single-sensor methods in predicting TN, TK and AN (0.60 ≤ R c v 2 ≤ 0.92, 1.86 ≤ R P I Q C V ≤ 5.08), but were less accurate for TP, AP and AK (R c v 2 ≤ 0.34, R P I Q C V ≤ 1.55). Compared to the best prediction using each single sensor model, low-level fusion improved the prediction of TN and AN; middle-level fusion improved the prediction of TN, TP, AN, AP and AK; and high-level fusion improved the prediction of all soil nutrients. Moreover, the SF2-PLSR model provided the best prediction for TN (R c v 2 = 0.83, R P I Q C V = 3.18), the SF2-SVM model for AN (R c v 2 = 0.67, R P I Q C V = 2.06), and the SF3-PLSR model for TK (R c v 2 = 0.92, R P I Q C V = 5.08). The SF2 and SF3 methods are recommended to predict TN and AN, and MIR spectra are recommended to predict TK (R c v 2 = 0.92, R P I Q C V = 5.02) since using only a single sensor is cost-effective. The SF2 and SF3 methods improved the prediction accuracy of AP and AK, but the prediction accuracy was still low. This study only covered one area with its set of soil landscapes, and only used well-established modelling methods. The results can motivate research on new spectra techniques and advanced modelling methods, as well as transferability to other soil landscapes. [ABSTRACT FROM AUTHOR]

A robust and reliable method for fabricating porous anodic alumina (PAA)-based distributed Bragg reflectors (DBRs), operating in mid-infrared (MIR) spectral region, is presented. The method relies on application of high (UH) and low (UL) voltage pulse sequence repeated in cycles. PAA-based DBR consists of alternating high-(dH) and low-porosity (dL) layers translated directly into periodically varied refractive index. Two anodization modes were used: time- and charge density-controlled mode. The former generated dH + dL pairs with non-uniform thickness (∆d) and effective refractive index (∆neff). It is supposed, that owing to a compensation effect between the ∆d and ∆neff, the photonic stopbands (PSBs) were symmetrical and intensive (transmittance close to zero). Under the charge density-controlled mode dH + dL pairs of uniform thickness were formed. However, the remaining ∆neff provided an asymmetrical broadening of PSBs. Furthermore, it is demonstrated that the spectral position of the PSBs can be precisely tuned in the 3500–5500 nm range by changing duration of voltage pulses, the amount of charge passing under subsequent UH and UL pulses, and by pore broadening after the electrochemical synthesis. The material can be considered to be used as one-dimensional transparent photonic crystal heat mirrors for solar thermal applications.

Remote sensing of atmospheric hydrogen fluoride (HF) is challenging because it has weak absorption signatures in the atmosphere and is surrounded by strong absorption lines from interfering gases. In this study, we first present a multi-year time series of HF total columns over Hefei, China by using high-resolution ground-based Fourier transform infrared (FTIR) spectrometry. Both near-infrared (NIR) and mid-infrared (MIR) solar spectra suites, which are recorded following the requirements of Total Carbon Column Observing Network (TCCON) and Network for the Detection of Atmospheric Composition Change (NDACC), respectively, are used to retrieve total column of HF (THF) and column-averaged dry-air mole fractions of HF (XHF). The NIR and MIR observations are generally in good agreement with a correlation coefficient (R) of 0.87, but the NIR observations are found to be (6.90 ± 1.07 (1σ)) pptv, which is lower than the MIR observations. By correcting this bias, the combination of NIR and MIR observations discloses that the XHF over Hefei showed a maximum monthly mean value of (64.05 ± 3.93) pptv in March and a minimum monthly mean value of (45.15 ± 2.93) pptv in September. The observed XHF time series from 2015 to 2020 showed a negative trend of (−0.38 ± 0.22) % per year. The variability of XHF is inversely correlated with the tropopause height, indicating that the variability of tropopause height is a key factor that drives the seasonal cycle of HF in the stratosphere. This study can enhance the understanding of ground-based high-resolution remote sensing techniques for atmospheric HF and its evolution in the stratosphere and contribute to forming new reliable remote sensing data for research on climate change.

In this work, the influence of various electrochemical parameters on the production of porous anodic alumina (PAA)-based DBRs (distributed Bragg reflector) during high-temperature-pulse-anodization was studied. It was observed that lowering the temperature from 30 to 27 °C brings about radical changes in the optical performance of the DBRs. The multilayered PAA fabricated at 27 °C did not show optical characteristics typical for DBR. The DBR performance was further tuned at 30 °C. The current recovery (iamax) after application of subsequent UH pulses started to stabilize upon decreasing high (UH) and low (UL) voltage pulses, which was reflected in a smaller difference between initial and final thickness of alternating dH and dL segments (formed under UH and UL, respectively) and a better DBR performance. Shortening UH pulse duration resulted in a progressive shift of photonic stopbands (PSBs) towards the blue part of the spectrum while keeping intensive and symmetric PSBs in the NIR-MIR range. Despite the obvious improvement of the DBR performance by modulation of electrochemical parameters, the problem regarding full control over the homogeneous formation of dH+dL pairs remains. Solving this problem will certainly lead to the production of affordable and efficient PAA-based photonic crystals with tunable photonic properties in the NIR-MIR region.

The applicability of near-infrared (NIR) and mid-infrared (MIR) spectroscopy combined with chemometrics was explored in this study to develop rapid, low-cost and non-destructive spectroscopic methods for classification and quantification of aflatoxins in brown rice. A total of 132 brown rice samples within the aflatoxin concentration range of 0–2435.8 μg/kg were prepared by artificially inoculated with A. flavus and A. parasiticus strains of fungus. For the classification of samples at varying levels of aflatoxin B1, the linear discriminant analysis model obtained correct classification rate of 96.9 and 90.6% for NIR and MIR spectroscopy, respectively. For the simultaneous determination of aflatoxins B1, B2, G1, G2 and the total aflatoxins, partial least squares regression also showed good predictive accuracy for both NIR (rv = 0.936–0.973, RPD = 2.5–4.0) and MIR spectroscopy (rv = 0.922–0.970, RPD = 2.5–4.0). The overall results indicated that the two spectroscopic techniques offered the feasibility to be used as alternative tools for rapid detection of various aflatoxin contaminations in grain. [ABSTRACT FROM AUTHOR]

In recent years, the Fourier transform infrared spectroscopy (FT-IR) was used to assess the diet, digestibility or nutritional values of food items of ruminants. However, it has never been used to analyse the diet of grouse species. Commonly used methods have so far been direct observations of birds and microscopical analyses of droppings. The sample preparation and comparison of microscopical analyses is a highly time-consuming procedure. The comparison is based on morphological structures of epidermal cells, like the shape of cells, stomata or trichomes. In contrast, the sample preparation for the FT-IR and the subsequent measuring is simple and quickly done. We investigated the diet of Black Grouse ( Tetrao tetrix L.) in two study areas with infrared spectroscopic methods comparing summer and winter droppings' content with plant reference material. The study areas are located in the provinces of Salzburg and Upper Austria, Austria. In our study, samples were measured in the mid- and near-infrared range. We tried to determine the dominating content of faecal samples at species, genera or family level or at least to assign samples to one of four main plants groups (i.e. woody plants, heathers, herbs and grasses). Our results showed a dominance of Larix decidua within the group of woody plants in both areas and, within the group of heathers, a dominance of Calluna vulgaris and Rhododendron hirsutum in one study area. Partially, our results are in marked contrast to other studies conducted in the Alps, as Vaccinium myrtillus was not detected in the samples. For further methodological studies, faecal sampling over larger areas, larger samples of plant reference material (including seeds and other parts of plants at different seasons), taking more samples per dropping and synchronous comparisons of microscopic analyses as well as FT-IR spectroscopy, are recommended. [ABSTRACT FROM AUTHOR]

Compared with thermal infrared (8-14\;\upmu\rmm) spectrum, mid-infrared (MIR) spectrum is less sensitive to land surface emissivity (LSE) for estimating land surface temperature (LST). This work addressed the retrieval of LST from two adjacent MIR (3-5\;\upmu\rmm) night-time airborne hyperspectral imager (AHS) simulated data with a split-window method, which can be expressed as a linear combination of the brightness temperature measured in two adjacent MIR channels with coefficients depending on LSE, view zenith angle (VZA), and water vapor content (WVC). Meanwhile, the LST retrieval accuracy for various channel combination was investigated and it was noted that the AHS channels 66 (3.5 - 4.25\;\upmu\rmm) and 68 (4.25 - 5.0\;\upmu\rmm) were the optimal channels for LST retrieval with a root-mean-square error (RMSE) less than 0.4 K for dry atmosphere and less than 0.5 K for wet atmosphere. Finally, the sensitivity analysis in terms of the instrumental noise, the uncertainties of LSE, and WVC were performed. It is worth noting that the combination of CH66 and CH68 performed well, and the LST retrieval errors were less than 0.5, 0.2, and 0.3 K caused by an noise equivalent delta temperature (\rmNE\Delta \rmT) of 0.33 K, WVC error of 20%, and LSE error of 0.01, respectively. [ABSTRACT FROM PUBLISHER]

The principal energy band gaps [E(), E(L), and E(X)] of the pentanary alloyare calculated over the entire composition space(x,y,andz)using the universal tight-binding method based onbasis functions. As the compositionsx,y,andzincrease,increases rapidly and approachesE(X)orE(L). A direct-to-indirect transition occurs in the high-composition range ofbecause of eitherE(X)orE(L). It is found that the direct band-gap energy ranges from 0.18 to 1.98 eV. The independent composition effects ofx, y,andzin the band gaps are investigated and compared with experimental data, and the results are in good agreement. In addition, the energy band gaps of the alloythat were lattice matched on InAs and GaSb are found to be in the mid-infrared spectral range, which ranges from 0.35 to 0.57 eV (3.50–2.17 m) and 0.32 to 0.54 eV (3.88–2.29 m), respectively. [ABSTRACT FROM AUTHOR]

In this paper, an optical-based device for online black powder detection in gas pipelines is proposed. The device uses different optical wavelengths within the infrared (IR) range and applies chemometric algorithms to quantify the actual amount of black powder. Hence, three methods based on near-infrared (NIR), mid-infrared (MIR), and Raman spectroscopy are used to acquire various spectra. The principal component regression (PCR) and the partial least square regression (PLSR) algorithms are then applied to assess the capability of each of the three methods when black powder is subject to different environmental conditions that may occur in real-life fields. The experimental results indicated that the mean squared error of prediction for the PLSR is 0.0008731, 0.0001983, and 5.04e-5 for NIR, MIR, and Raman, respectively, while for the PCR it is 0.0009065, 0.0002068, and 5.099e-5. Also, the coefficient of determination (R^2) for the PLSR was 0.9744, 0.9753, and 0.998199 for NIR, MIR, and Raman, respectively, while for the PCR it was 0.9743, 0.9744, and 0.998165. In addition, both PCR and PLSR completed the analysis very fast (in tens or hundreds of microseconds), however, PLSR accomplished the prediction analysis faster than PCR which serves as an advantage for online monitoring especially when multiprobes are used for the monitoring. Hence, while both PLSR and PCR perform equally well, the PLSR is even more robust since it can compensate for systematic and human errors more than PCR. The predictions from all three techniques (NIR, MIR, and Raman spectroscopy) were similarly good and no specific technique was superior to the others. [ABSTRACT FROM PUBLISHER]

A non conventional source or receiver of THz and above THz electromagnetic radiation is proposed. Specifically, electron or hole oscillations in DNA dimers (two interacting DNA base-pairs or monomers) are predicted, with frequency in the range [ABSTRACT FROM AUTHOR]

Highlights: [•] Two Harpagophytum species are used interchangeably to treat inflammation and are resolved by spectral methods here. [•] Chemical congruency and bio-equivalence of the two species have not been proven. [•] Multivariate analysis models for species authentication were developed. [•] The two developed models had good statistics with R 2 X values of 0.86 and 0.99 for MIR and SWIR data, respectively. [Copyright &y& Elsevier]

Laboratory spectral libraries of well-characterized natural samples are necessary for accurate interpretation of remote sensing spectral data. Tephra deposits, the result of explosive volcanic eruptions, are potentially found on all differentiated terrestrial bodies and are important chronologic and compositional marker beds on Earth. Here we present a visible/near-infrared (VNIR, 0.35–2.5 μm) and mid-infrared (MIR, 3.5–25 μm) spectral library composed of nineteen natural tephra samples from ten volcanic sources that span a range of compositions and components. The bulk, glass, and mineral phase compositions of each sample are measured and spectra from multiple size fractions of each sample were collected. The library can be found via the Terrestrial Analog portal (DOI: https://doi.org/10.5066/P9O54M4Q). • Library of visible-near-infrared and mid-infrared spectra of tephra samples. • Tephra span wide-range of terrestrial compositions, including alkaline endmembers. • Tephra compositions and phase assemblages were characterized. [ABSTRACT FROM AUTHOR]

Abstract: Chemometrical models for determination of milk fatty acids (FA) are typically developed using spectral data from a single spectroscopy technique, e.g., mid-infrared spectroscopy in milk control. Such models perform poorly in determining minor components and are highly dependent on the spectral data source and on the type of matrix. In milk fat, the unsuccessful determination of minor (fatty acids lower than 1.0g/100g in total fat) FA is often the result of: (1) the molecular structure similarity between the minor and the major FA within the milk fat matrix (thus the chemical signature specific to individual fatty acids has restricted specificity), and (2) the low signal intensity (detection limit) for specific vibrational modes. To overcome these limitations, data from different types of spectroscopy techniques, which brings additional chemical information in relation to the variation of the FA, could be included in the regression models to improve quantification. Here, Fourier transform (FT) Raman spectra were concatenated with attenuated total reflectance FT infrared (ATR/FTIR) spectra. The new combinatorial models showed up to 25% decrease in the root mean squared error of cross-validation (RMSECV) values, accompanied with a higher R cv 2 for most individual FA or sums of FA groups, as compared to regression models based on Raman only or ATR/FTIR only spectra. In addition, improved models included less PLS components indicating an increased robustness. Interpretation of the most contributing regression coefficients indicated the value of newly combined spectral regions as carriers of specific chemical information. Although requiring additional spectroscopy instrumentation and prolonged acquisition time, this new combinatorial approach can be automated and is sufficient for semi-routine determination of the milk FA profile. [Copyright &y& Elsevier]

Abstract: A mid-infrared (MIR) CH4 sensor was experimentally demonstrated by employing an asymmetric ellipsoid multi-pass gas-cell. Novel theory and formulas were proposed for optimizing the gas-cell structure, and both hardware and algorithm were designed to determine the accurate characteristics by reducing effect of reference voltage-fluctuation of analog-to-digital converter (ADC). The CH4 sensor was fabricated and experiments were carried out to obtain its performance. The absolute detection error is less than 5%. The minimum detection level (MDL) and the detection sensitivity are determined to be about 5 and 6–7ppm, respectively, under the low concentration of less than 1000ppm. The response time is measured to be within the range of 5–6s, and the Allan variation plot shows that the system possesses acceptable stability over long term operation. Compared to our two previous reported detection devices with symmetric ellipsoid gas-cell and without reducing voltage-fluctuation, this sensor exhibits enhanced performances including higher detection sensitivity, lower MDL and shorter response time. [Copyright &y& Elsevier]

Temperature and emissivity separation (TES) algorithms designed to work with mid-infrared (MIR) hyperspectral data are extremely limited. Two TES algorithms originally designed for long-wave infrared hyperspectral data, specifically, the iterative spectrally smooth (ISS) algorithm and the stepwise refining algorithm, are extended into MIR and renamed the extended iterative spectrally smooth (EISS) and extended stepwise refining algorithms (ESR), respectively. Numerical experiments are first conducted to evaluate their feasibility. The results of the numerical experiments indicate that the accuracy of the ESR algorithm is higher than that of the EISS algorithm. Moreover, the ESR algorithm is more robust than the EISS algorithm under sunlit conditions. Their accuracy is then validated with in situ measurements. Finally, the emissivity root mean square errors (RMSEs) of the EISS and ESR algorithms are compared with the data derived with the ISS algorithm using in situ measurements. Results show that the average emissivity RMSEs of 0.03 in 2000–2200 \cm^-1 and of 0.03–0.30 in 2400–3000 \cm^-1 for nighttime, and 0.02 in 2000–2200 \cm^-1 and 0.03 in 2500–3000 \cm^-1 for daytime, can be obtained from ground-based MIR hyperspectral data using the ESR algorithm. [ABSTRACT FROM AUTHOR]

Abstract: Thermally induced conformational changes that occur in high-density polyethylene (HDPE) crystal were studied by mid-infrared (MIR) spectroscopy. Spectral changes of four conformational “defect mode” bands in 1390–1280cm−1 region were observed during the heating up to the melt. The spectra were analyzed by generalized two-dimensional (2D) correlation technique to elucidate correlations in their responses against temperature. Among the conformational defect bands, two bands at 1368 and 1308cm−1 have traditionally been assigned to non-planar conformers of gtg′ (kink) and gtg. However, the present study shows the intensity increment of the band at 1368cm−1 happens at a lower temperature than that of the band at 1308cm−1. This finding is in favor of the assignment proposed by Cates et al., in which the 1368cm−1 band is assigned to the gtg conformation excluding the involvement of kink. The spectral correlation among the band at 1368 (gtg), 1353 (double-gauche, gg′), and 1341cm−1 (end-gauche, eg) has also been studied by 2D correlation analysis. As a result, it was found that the formation of gg′ and eg sequences mostly proceeds at a temperature range higher than 115°C. The formation of gtg conformer sequence measured by the band at 1368cm−1 apparently proceeds in two steps: the first at a temperature around 70°C and the later one occurring at a temperature very close to T m. The results of this study make correlation relationships clear in the temperature dependency of MIR bands due to conformational disorder sequences. [Copyright &y& Elsevier]

[Display omitted] • Anharmonicity in MIR spectra of CHCl 3 , CDCl 3 , CHBr 3 and CDBr 3. • Contributions from MIR and NIR ranges to the vibrational intensity. • Fermi resonances in MIR and Raman spectra of CHCl 3 , CDCl 3 , CHBr 3 and CDBr 3. • Spectral parameters of the fundamentals and the overtone/combination bands. This work provides new quantitative information on vibrational spectra of liquid CHCl 3 , CDCl 3 , CHBr 3 and CDBr 3. Deconvolution of the mid-infrared (MIR), near-infrared (NIR) and Raman spectra permitted for determination of the parameters of fundamentals, overtones and combination bands. Simultaneously, the anharmonic vibrational spectra were calculated by MP2 and B3LYP methods. Using these data, for the first time, we estimated the experimental and theoretical contributions from the anharmonic vibrations (overtones and combination bands) to MIR spectra of all studied compounds. For chloroforms and CHBr 3 these vibrations contribute to less than 5.5% (experimental) and 8% (theoretical) of MIR intensity. Only for CDBr 3 this contribution is much higher (21% and 24%) due to strong Fermi resonance (FR) between ν 4 and ν 3 + ν 5 vibrations. Besides, we estimated the contributions from the MIR and NIR ranges to the total vibrational intensity. As expected, the contributions from NIR range are small (<2.5%) for all studied samples. It is of note that the theoretical contributions from MIR and NIR regions are very close to the experimental ones. It results from accurate theoretical prediction of the intensities of the fundamental bands. On the other hand, the intensities of the overtones and combination bands are predicted less satisfactory, what is clearly seen in NIR spectra. The MIR spectra of all compounds reveal the presence of FR. The FR resonances increase the intensity of the non-fundamental transitions, for CDBr 3 this increase is significant. Interestingly, Raman spectra of both chloroforms were also influenced by FR. As a result, the spectra of CHCl 3 and CDCl 3 develop two intense binary combinations of a total contribution ≈12%. Our results reveal that the overtones and combination bands are significantly weaker as compared with the fundamental bands. Some departures from this trend result from FR. We did not observe any correlation between the intensities of the fundamentals and the corresponding overtones and combination bands. The bands due to the first overtones are broader as compared with the fundamental bands, but we did not observe any regular relationship. Surprisingly, the more regular trend was observed for the second overtone of the ν 1 band, which is four times broader than the corresponding fundamental band. [ABSTRACT FROM AUTHOR]

A robust and reliable method for fabricating porous anodic alumina (PAA)-based distributed Bragg reflectors (DBRs), operating in mid-infrared (MIR) spectral region, is presented. The method relies on application of high (UH) and low (UL) voltage pulse sequence repeated in cycles. PAA-based DBR consists of alternating high-(dH) and low-porosity (dL) layers translated directly into periodically varied refractive index. Two anodization modes were used: time- and charge density-controlled mode. The former generated dH + dL pairs with non-uniform thickness (∆d) and effective refractive index (∆neff). It is supposed, that owing to a compensation effect between the ∆d and ∆neff, the photonic stopbands (PSBs) were symmetrical and intensive (transmittance close to zero). Under the charge density-controlled mode dH + dL pairs of uniform thickness were formed. However, the remaining ∆neff provided an asymmetrical broadening of PSBs. Furthermore, it is demonstrated that the spectral position of the PSBs can be precisely tuned in the 3500–5500 nm range by changing duration of voltage pulses, the amount of charge passing under subsequent UH and UL pulses, and by pore broadening after the electrochemical synthesis. The material can be considered to be used as one-dimensional transparent photonic crystal heat mirrors for solar thermal applications. [ABSTRACT FROM AUTHOR]

This work presents new experimental and theoretical insights on vibrational spectra of CH 3 I and CD 3 I in the liquid phase. For the first time, we provided the contributions from different vibrational modes to mid-infrared (MIR) and near-infrared (NIR) spectra and estimated the extent of anharmonicity in the MIR region. Direct comparison of the intensities from ATR-IR and NIR transmission spectra was possible due to normalization of ATR-IR spectra. As a reference for normalization, we applied the area of the ν s (CH 3)/ν s (CD 3) band recorded in transmission mode. Our results show that the corresponding vibrational modes of CH 3 I and CD 3 I have similar contributions to the total intensity (MIR + NIR), however, these contributions are distributed in a different way between MIR and NIR regions. As expected, most of intensity in MIR spectra originates from the fundamental transitions (>90%). The fundamental bands together with the first overtones and the binary combinations contribute to more than 99% of MIR intensity for both compounds. Therefore, reliable reconstruction of MIR spectra can be achieved by considering only these vibrational modes. On the other hand, accurate simulation of NIR spectra requires including the higher-order transitions. In the case of CD 3 I, the fourth-order transitions contribute to 12.7% of NIR intensity. The contributions from NIR region are significantly smaller than those from MIR range and were estimated to be 6.7% for CH 3 I and 2.3% for CD 3 I. The theoretical calculations provide a reasonable estimation of the total contribution from the fundamental bands. Yet, the calculated contributions from the anharmonic transitions are different from those obtained from the experimental data. MIR spectra of CH 3 I and CD 3 I reveal an unexpected increase in the intensity of some overtones and combination bands indicating the presence of Fermi resonances. These resonances are responsible for differences in contributions from the first overtones and binary combinations between CH 3 I and CD 3 I. [ABSTRACT FROM AUTHOR]

Remote sensing of atmospheric hydrogen fluoride (HF) is challenging because it has weak absorption signatures in the atmosphere and is surrounded by strong absorption lines from interfering gases. In this study, we first present a multi-year time series of HF total columns over Hefei, China by using high-resolution ground-based Fourier transform infrared (FTIR) spectrometry. Both near-infrared (NIR) and mid-infrared (MIR) solar spectra suites, which are recorded following the requirements of Total Carbon Column Observing Network (TCCON) and Network for the Detection of Atmospheric Composition Change (NDACC), respectively, are used to retrieve total column of HF (THF) and column-averaged dry-air mole fractions of HF (XHF). The NIR and MIR observations are generally in good agreement with a correlation coefficient (R) of 0.87, but the NIR observations are found to be (6.90 ± 1.07 (1σ)) pptv, which is lower than the MIR observations. By correcting this bias, the combination of NIR and MIR observations discloses that the XHF over Hefei showed a maximum monthly mean value of (64.05 ± 3.93) pptv in March and a minimum monthly mean value of (45.15 ± 2.93) pptv in September. The observed XHF time series from 2015 to 2020 showed a negative trend of (−0.38 ± 0.22) % per year. The variability of XHF is inversely correlated with the tropopause height, indicating that the variability of tropopause height is a key factor that drives the seasonal cycle of HF in the stratosphere. This study can enhance the understanding of ground-based high-resolution remote sensing techniques for atmospheric HF and its evolution in the stratosphere and contribute to forming new reliable remote sensing data for research on climate change. [ABSTRACT FROM AUTHOR]

In this work, the influence of various electrochemical parameters on the production of porous anodic alumina (PAA)-based DBRs (distributed Bragg reflector) during high-temperature-pulse-anodization was studied. It was observed that lowering the temperature from 30 to 27 °C brings about radical changes in the optical performance of the DBRs. The multilayered PAA fabricated at 27 °C did not show optical characteristics typical for DBR. The DBR performance was further tuned at 30 °C. The current recovery (iamax) after application of subsequent UH pulses started to stabilize upon decreasing high (UH) and low (UL) voltage pulses, which was reflected in a smaller difference between initial and final thickness of alternating dH and dL segments (formed under UH and UL, respectively) and a better DBR performance. Shortening UH pulse duration resulted in a progressive shift of photonic stopbands (PSBs) towards the blue part of the spectrum while keeping intensive and symmetric PSBs in the NIR-MIR range. Despite the obvious improvement of the DBR performance by modulation of electrochemical parameters, the problem regarding full control over the homogeneous formation of dH+dL pairs remains. Solving this problem will certainly lead to the production of affordable and efficient PAA-based photonic crystals with tunable photonic properties in the NIR-MIR region. [ABSTRACT FROM AUTHOR]

We design, fabricate, and study GaSb-based bipolar cascade vertical-cavity surface emitting lasers (VCSELs) for laser emission of around 2.3 \mum. An electrically coupled two-stage design shows high-temperature continuous wave (CW) operation and an approximately one-order-of-magnitude increase of CW output power at 30^\circC as compared with single-stage VCSELs. [ABSTRACT FROM PUBLISHER]