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Evaluation of Machine Learning Approaches to Predict Soil Organic Matter and pH Using vis-NIR Spectra
摘要： Soil organic matter (SOM) and pH are essential soil fertility indictors of paddy soil in the middle-lower Yangtze Plain. Rapid, non-destructive and accurate determination of SOM and pH is vital to preventing soil degradation caused by inappropriate land management practices. Visible-near infrared (vis-NIR) spectroscopy with multivariate calibration can be used to effectively estimate soil properties. In this study, 523 soil samples were collected from paddy ?elds in the Yangtze Plain, China. Four machine learning approaches—partial least squares regression (PLSR), least squares-support vector machines (LS-SVM), extreme learning machines (ELM) and the Cubist regression model (Cubist)—were used to compare the prediction accuracy based on vis-NIR full bands and bands reduced using the genetic algorithm (GA). The coef?cient of determination (R2), root mean square error (RMSE), and ratio of performance to inter-quartile distance (RPIQ) were used to assess the prediction accuracy. The ELM with GA reduced bands was the best model for SOM (SOM: R2 = 0.81, RMSE = 5.17, RPIQ = 2.87) and pH (R2 = 0.76, RMSE = 0.43, RPIQ = 2.15). The performance of the LS-SVM for pH prediction did not differ signi?cantly between the model with GA (R2 = 0.75, RMSE = 0.44, RPIQ = 2.08) and without GA (R2 = 0.74, RMSE = 0.45, RPIQ = 2.07). Although a slight increase was observed when ELM were used for prediction of SOM and pH using reduced bands (SOM: R2 = 0.81, RMSE = 5.17, RPIQ = 2.87; pH: R2 = 0.76, RMSE = 0.43, RPIQ = 2.15) compared with full bands (R2 = 0.81, RMSE = 5.18, RPIQ = 2.83; pH: R2 = 0.76, RMSE = 0.45, RPIQ = 2.07), the number of wavelengths was greatly reduced (SOM: 201 to 44; pH: 201 to 32). Thus, the ELM coupled with reduced bands by GA is recommended for prediction of properties of paddy soil (SOM and pH) in the middle-lower Yangtze Plain.
关键词： soil organic matter,paddy soil,vis-NIR spectra,pH,machine learning approaches
更新于2025-09-19 17:15:36
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Raman spectra of the GFP-like fluorescent proteins
摘要： The objective of the study was to elucidate optical characteristics of the chromophore structures of fluorescent proteins. Raman spectra of commonly used GFP-like fluorescent proteins (FPs) with diverse emission wavelengths (green, yellow, cyan and red), including the enhanced homogenous FPs EGFP, EYFP, and ECFP (from jellyfish) as well as mNeptune (from sea anemone) were measured. High-quality Raman spectra were obtained and many marker bands for the chromophore of the FPs were identified via assignment of Raman spectra bands. We report the presence of a positive linear correlation between the Raman band shift of C5=C6 and the excitation energy of FPs, demonstrated by plotting absorption maxima (cm-1) against the position of the Raman band C5=C6 in EGFP, ECFP, EYFP, the anionic chromophore and the neutral chromophore. This study revealed new Raman features in the chromophores of the observed FPs, and may contribute to a deeper understanding of the optical properties of FPs.
关键词： Chromophore,Fluorescent protein,Raman spectra
更新于2025-09-19 17:15:36
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Deep Learning Spectroscopy: Neural Networks for Molecular Excitation Spectra
摘要： Deep learning methods for the prediction of molecular excitation spectra are presented. For the example of the electronic density of states of 132k organic molecules, three different neural network architectures: multilayer perceptron (MLP), convolutional neural network (CNN), and deep tensor neural network (DTNN) are trained and assessed. The inputs for the neural networks are the coordinates and charges of the constituent atoms of each molecule. Already, the MLP is able to learn spectra, but the root mean square error (RMSE) is still as high as 0.3 eV. The learning quality improves significantly for the CNN (RMSE = 0.23 eV) and reaches its best performance for the DTNN (RMSE = 0.19 eV). Both CNN and DTNN capture even small nuances in the spectral shape. In a showcase application of this method, the structures of 10k previously unseen organic molecules are scanned and instant spectra predictions are obtained to identify molecules for potential applications.
关键词： artificial intelligence,excitation spectra,organic molecules,DFT calculations,neural networks
更新于2025-09-19 17:15:36
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Preparation, structural and functional properties of PbTiO3-δ ceramics
摘要： In the present study, oxygen deficient PbTiO3-d ceramics were prepared by solid state-reaction method. The formation of the pure perovskite phase with tetragonal structure was confirmed for the 800°C/2h calcined sample by using X-ray diffraction analysis at room temperature. Energy dispersive X-ray spectroscopy analyses confirm the creation of oxygen vacancies in the system for charge compensations, as demonstrated by the percentage of O atoms of ~53%. The complex impedance data reveals important contributions of the oxygen vacancies to the total dielectric response that are homogeneous distributed within the sample. The room temperature magnetic properties show a weak ferromagnetic character in all the samples that might be attributed to the oxygen vacancies defects and to surface effects.
关键词： oxygen vacancies,EDX spectra,magnetic properties,ceramics,dielectric properties
更新于2025-09-19 17:15:36
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Optical Properties and Model of the Electronic and Spatial Structure of Hypercrosslinked Polystyrene
摘要： A number of hypercrosslinked polystyrene networks are studied. The networks are obtained via additional crosslinking of granules of styrene copolymer with 0.5% divinylbenzene (0.3–0.5 mm) and micro-granules with 1% divinylbenzene (3.5 μm) using monochlorodimethyl ether to densities of crosslinking from 60 to 500%. It is found that as the degree of crosslinking grows, the absorption in the electronic spectrum of the polymer extends to the visible region, and the granules change color (toward as dark as black); this phenomenon is much less expressed for microgranules and milled materials. For a consistent explanation of these two observations, assumptions are made about the appearance and increase in the contrast of density fluctuations of a tracery hypercrosslinked network and light scattering on such micro-inhomogeneities in the volume of particles of the compared series of polymers.
关键词： hypercrosslinked polystyrene,network structure,electronic spectra,degree of crosslinking
更新于2025-09-19 17:15:36
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Effects of near-field electromagnetic coupling in dimers of nanoparticles with a silver core and a J-aggregate dye shell
摘要： We report a theoretical study of the plasmon – exciton coupling effect on the absorption spectra of pairs of closely spaced double-layer hybrid nanoparticles consisting of a metallic core and a J-aggregate dye shell. The effect of frequency conversion of plasmonic lines due to the near-field interaction between plasmons and Frenkel excitons of the organic shell is demonstrated. The effect leads to the appearance of additional spectral lines in the long-wavelength part of the spectrum of the system of hybrid particles. The shapes and the relative intensities of the additional lines exactly reproduce the specific features of the original spectrum of plasmonic absorption bands in uncoated metallic nanoparticles. The discovered phenomenon can be used to design new types of high-sensitivity nanosensors, based on plasmon – exciton effects and principles of near-field optics.
关键词： near-field electromagnetic coupling,nanophotonics,Frenkel excitons,dimers of metalorganic nanoparticles,plasmon – exciton interaction,molecular J-aggregates,localised plasmons,absorption spectra
更新于2025-09-19 17:15:36
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Photosensitive Tin Sulfur Dioxide Complexes with Unexpected Bonding Modes
摘要： Infrared spectra of the matrix isolated Sn(η2-O2S), Sn(η2-OSO), Sn(η2-O2S)(η1-OSO), Sn(η2-O2S)2, OSn2(η2-SO) and Sn(μ2-O2)SnS molecules were observed following laser-ablated Sn atoms reactions with SO2 during condensation in solid argon. The assignments for the major vibrational modes were confirmed by appropriate S18O2 and 34SO2 isotopic shifts, and density functional vibrational frequency calculations (B3LYP and BPW91). Interestingly, the mononuclear complexes are interconvertible; that is, irradiation induces the isomerization of Sn(η2-O2S) and Sn(η2-O2S)(η1-OSO) to Sn(η2-OSO) and Sn(η2-O2S)2, respectively, and vice versa on annealing. However, there is no evidence of isomerization reaction in between the binuclear molecules OSn2(η2-SO) and Sn(μ2-O2)SnS. Bonding in these products is discussed, and the electronic structures change associated with different bonding types are revealed which is crucial for the observed photochemical reactions.
关键词： Quantum chemical calculation,Matrix-isolation,Reactive intermediate,Infrared spectra,Reaction mechanism
更新于2025-09-19 17:15:36
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Crystallization and spectroscopic characterizations of binary SrO-B2O3 glasses doped with LiF, NaF, CaF2, or TiO2
摘要： Glasses based on the basic chemical composition of binary strontium borate (SrO 50-B2O350 mol%) together with samples containing dopant (2%) with one of the fluorides (LiF, NaF, CaF2) or TiO2 have been synthesized through the routinely melting and annealing technique. Collective structural, optical, and thermal properties have been measured for the prepared glasses. X-ray diffraction and SEM measurements were carried out for their corresponding glass-ceramics which were synthesized by controlled thermal heat treatment with two-step regime. FT infrared absorption spectra reveal composite vibrational modes in the mid-range 400–1600 cm?1 which are related to the co-presence of both triangular and tetrahedral borate building units in their particular different wavenumber sites. The low dopant level did not make any distinct variations in the IR spectra. X-ray diffraction patterns elucidate the formed crystal phases after crystallization mainly strontium metaborate and other related borate phase and the LiF shows no distinct variation while NaF2 and CaF2 induce the formation of additional crystalline Na-containing or Ca-containing phases besides the formation of NaF or fluorite (CaF2). TiO2 acts as a nucleating agent and also separate as rutile. The crystallization behavior has been correlated with the assumption of the tendency of SrO to induce phase separation in the host binary borate glass and controlled heat treatment initiates the separation of strontium metaborate crystalline phase in the base binary SrO-B2O3 in accordance with its composition and the role of dopants is found to be varying with the type of dopant. The measured thermal expansion parameters of the prepared glasses reveal variations in their values for transformation and softening temperatures depending on the type of added dopant. The changes in the thermal expansion coefficients in the different parts of the thermal curves are related to the ability of the network to absorb lattice expansion through bending of the bonds. The uniform observed ultraviolet absorption bands are related to traces of iron (Fe3+) ions present as impurities.
关键词： LiF,CaF2,NaF,Thermal expansion,FTIR optical spectra,SrO.B2O3 glass,Glass-ceramics,TiO2
更新于2025-09-19 17:15:36
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Coordination Polymeric Ensemble of Silver with Nitrate and 4-(Aminomethyl)benzoate: Synthesis, Crystal Structure, and Luminescence Properties
摘要： Prismatic crystals of Ag3(4-Amba)2(NO3)2 (I) and Ag(4-AmbaH)NO3 (II) are isolated from the reaction mixture of aqueous solutions of 4-aminomethylbenzoic acid (4-AmbaH) and AgNO3 at Т ≈ 70°C. The crystal structure of compound I (СIF file CCDC no. 1851513) and the luminescence properties of compounds I and II are studied. The structure of compound I contains two crystallographically nonequivalent silver atoms Ag(1) and Ag(2) with the octahedral coordination mode (with allowance for Ag···Ag contacts) with different compositions of the internal spheres of the central atoms. Owing to the contacts, the silver atoms are joined into in?nite cluster ribbons (Ag···Ag 3.06?3.27 ?). The carboxylate group of the 4-Amba anion exhibits the bridging properties and binds the silver atoms of both types. The Ag(2) atoms also contact with the oxygen atom of the NO3– ion and coordinate the NH2 group of 4-Amba. The photoluminescence spectra of compounds I and II are of the same type and show the presence of two groups of emission bands with centers at 484 and 543 nm shifted to the red range of the spectrum relative to the band of 4-AmbaH.
关键词： polynuclear silver compounds,X-ray diffraction analysis,luminescence spectra
更新于2025-09-19 17:15:36
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On the photo-activation of the S <sub/>0</sub> ?→?S <sub/>1</sub> transition in polyenes
摘要： The evidence provided in this work allows us to conclude that the electronic transition S0 → S1 either for the diphenylhexatriene molecule or for the diphenyloctatetraene molecule is dipole allowed and induced by one‐photon absorption. Consequently, the model to explain the photophysics of these polyenes does not need the existence of an underlying 21Ag excited electronic state, to the converse of what Hudson and Kohler proposed, that the transition S0 → S1 must be induced by two‐photon absorption.
关键词： two‐photon absorption,excitation spectra,photophysics of polyenes
更新于2025-09-19 17:15:36