Main Spectral Bands Research Articles

SPECTRAL-KINETIC CHARACTERISTICS OF CATHODOLUMINESCENCE OF LANTHANIDE NIOBATES (Y,Lu,Gd)NbO4:Bi3+

The study is devoted to the study of lanthanide niobates doped with bismuth ions, which are of interest as potential phosphors used in various fields of human activity, such as medicine, industry, and science. In this paper, an experimental study of the cathodoluminescence of niobates (Y,Lu,Gd)NbO4:Bi3+, namely, spectral characteristics with time resolution, as well as the kinetics of luminescence attenuation for the main spectral bands, is carried out. The temperature dependence of the cathodoluminescence attenuation time for the YNbO4 sample is presented.:Bi3+ measured in the temperature range of 5–295 K with an interval of 10 K. The study of the kinetics of luminescence attenuation made in this study showed that at least three pronounced components are observed in the kinetics of attenuation at low temperature. Of the three components, the main contribution to the light sum is made by a slow microsecond component with a decay time in the range of 2–9 microseconds. However, the nanosecond kinetics of intrinsic luminescence of samples in the ultraviolet region of the spectrum is of particular interest. The presence of several fast components indicates the complex structure of this glow associated with the superposition of the glow bands of autolocalized excitons. The data obtained are of both scientific and practical interest in the further development of functional materials.

Characterization of soil organic carbon at profile scale in two forest soils under pine and holm oak

Context It is essential to promote soil carbon sequestration as a means to mitigate climate change. Thus, it is fundamental to know the distribution of C in the soil at profile scale, the characteristics of humic substances as indicators of soil organic matter (SOM) turnover and their relationship with other soil properties. Aims Two forest ecosystems under pine and holm oak developed under a Meso-Mediterranean climate in Spain were used to characterize SOM through the complete sequence of layers of the soil profile. Methods General soil analysis, infrared spectroscopic analysis and soil color measurements were conducted for the characterization. Key results Humus form under oak was found to be Mull mesotrophic–Mull acid while humus under pine Moder oligotrophic. The infrared spectrum determined that oxidation of the humic acids was more complete in the deeper horizons. Relationships between intensities of the main spectral bands in both soils followed similar maximum and minimum sequence values. The total humic extract (THE) color measured by reflection was found inversely related to the THE color measured by transmission. In the same way, the color spectrum between 350 and 800 nm in the THE showed an inverse relation between hue/brightness and absorbance values. Conclusions Infrared analysis and color measurements provided evidence of a different level of stabilization of humic substances from each soil, and between the different horizons. Large spatial variability in soil organic carbon quantity and quality was observed. Implications Better understanding of carbon sequestration behavior in different soil ecosystems in its crucial role within the global carbon cycle

Estimation and Compensation of the Ionospheric Path Delay Phase in PALSAR-3 and NISAR-L Interferograms

Spatial and temporal variation in the free electron concentration in the ionosphere affects SAR interferograms, in particular at low radar frequencies. In this work, the identification, estimation, and compensation of ionospheric path delay phases in PALSAR-3 and NISAR-L interferograms are discussed. Both of these L-band sensors simultaneously acquire SAR data in a main spectral band and in an additional, spectrally separated, narrower second band to support the mitigation of ionospheric path delays. The methods presented permit separating the dispersive and the non-dispersive phase terms based on the double-difference interferogram between the two available spectral bands and the differential interferogram of the main band. The applicability of the proposed methods is demonstrated using PALSAR-3-like data that were simulated based on PALSAR-2 SM1 mode data.

BODIPY dyes for optical limiting applications on the nanosecond timescale.

Since 2017, the Institute for Nanotechnology Innovation at Rhodes University has studied the optical limiting properties of boron dipyrromethene (BODIPY) dyes with respect to high-intensity nanosecond timescale laser pulses. Concerns over the irresponsible use of laser pointers in the context of aviation safety have provided a need for materials that can readily transmit light under ambient conditions while rapidly attenuating intense incident laser pulses. The structural flexibility of the BODIPY chromophore facilitates the red shift of the main BODIPY spectral band that typically lies at ca. 500 nm to the red end of the visible and the near-infrared through the introduction of vinylene groups at the 3,5-positions or an aza-nitrogen atom. Research carried out in this context is described, and possible future directions are discussed.

Effect of different HITRAN databases on the calculation of radiative heat transfer of H2O and CO2 in a one-dimensional planar layer

The performance of HITRAN 2020 and 2016 databases on calculating radiative heat transfer of H2O and CO2 was evaluated in this study. The main spectral bands and lines contributing to the discrepancy in accuracy between the HITRAN 2020 and 2016 databases were determined. For the calculation of radiation of H2O, the HITRAN 2020 database showed higher accuracy than the HITRAN 2016 database in the isothermal/homogeneous cases. The maximum relative error of radiative heat flux of the HITRAN 2020 was reduced by 3.93%, due to the addition of 157, 165, 110 and 121 spectral lines in the 3425–3450 cm−1, 3600–3625 cm−1, 3950–3975 cm−1 and 4050–4075 cm−1 wavebands, respectively. Whereas, for the isothermal/homogeneous CO2, the difference of the average relative error in radiative source calculated by the HITRAN 2020 and 2016 databases was less than 0.1%. For the air and oxy-fuel combustion cases, the HITRAN 2020 showed a better performance than the HITRAN 2016 on predicting radiative heat transfer. The maximum relative error of radiative heat flux of the HITRAN 2020 was reduced by 4.32%. This was mainly ascribed to the increase in the number of the spectral lines of H2O in the HITRAN 2020 in the wavebands of 3425–3450 cm−1, 3600–3625 cm−1, 3950–3975 cm−1 and 4050–4075 cm−1 at high temperatures.

Features kept generative adversarial network data augmentation strategy for hyperspectral image classification

In recent years, significant breakthroughs have been achieved in hyperspectral image (HSI) processing using deep learning techniques, including classification, object detection, and anomaly detection. However, the practical application of deep learning in HSI processing is limited by challenges such as small-sample size and sample imbalance issues. To mitigate these limitations, we propose a novel data augmentation strategy called Feature-Preserving Generative Adversarial Network Data Augmentation (FPGANDA). What sets our data augmentation strategy apart from existing generative model-based approaches is that we preserve the main spectral bands of HSI data using a newly designed band selection method. Additionally, our proposed generative model generates synthetic spectral bands, which are combined with the real spectral bands using a mixture strategy to create augmented data. This approach ensures that the augmented data retain the main features of the original data while also incorporating diverse features from the generated data. We evaluate our method on three different HSI datasets, comparing it with state-of-the-art techniques. Experimental results demonstrate that our proposed method significantly improves classification performance in most scenes and exhibits remarkable compatibility.

Diiodinated Mono- and Dipyridylvinyl BODIPY Dyes: Photophysicochemical Properties, invitro Antibacterial Studies, Molecular Docking and Theoretical Calculations.

In this study, novel mono- and dipyridylvinyl boron dipyrromethene dyes are prepared to compare their photodynamic antimicrobial chemotherapy (PACT) activities against Staphylococcus aureus to the corresponding core dyes. Pyridylvinyl substitution at the 3- or 3,5-positions of a meso-4-bromophenylBODIPY core dye via a Knoevenagel reaction with an aromatic 2-bromopyridinecarboxaldehyde shifts the major BODIPY spectral band to longer wavelength. The extended π-conjugation red shifts the main spectral band into the 602-618 nm region in CHCl3 , THF, ethanol and DMSO after monopyridylvinyl substitution and to 685-704 nm after dipyridylvinyl substitution. An enhancement of the population of the T1 state through the incorporation of iodine atoms at the 2,6-positions results in moderately high singlet oxygen quantum yields in DMSO. The π-extended dyes were found to have significantly lower PACT activities than the diiodinated core dye.

FTIR-ATR for the identification of Psidium guajava plants infested with Meloidogyne enterolobii

The Meloidogyne enterolobii Yang and Eisenback nematode represents one of the most devastating pests in guava cultivation in Venezuela and the world. The diagnosis of this parasite requires specialized knowledge and very laborious procedures. The objective of this research was to identify the infrared spectra of guava plants, in the nursery phase, infested with M. enterolobii using Fourier-transform infrared spectroscopy coupled to attenuated total reflectance (FTIR-ATR). Leaves from healthy and infested plants were taken 60 days after nematode inoculation and analyzed in a FTIR-ATR spectrometer. The main spectral bands corresponding to the chemical compounds (lipids, proteins and carbohydrates) produced by plant metabolism as a result of nematode infestation were characterized. These results represent the starting point to determine the potential of this rapid and non-destructive technique for the early diagnosis of plants infested by the “guava root-knot nematode”.

Assessing Neural Oscillations during Erotic and Negative Emotional Pictures Viewing: An Event-Related Potential Study

The present study was designed to determine whether or not there are components of the ERPs that discriminate the erotic and negative pictures during affective picture processing. Participants viewed erotic, negative and neutral pictures form the International Affective Picture System (IAPS). Eighteen right-handed volunteer students from North-Eastern University participated in the experiment. Electrode from the frontal site (F3 and F4), C3 and C4 (central electrodes), P3 andP4 (parietal electrodes) and O1 and O2 (occipital electrodes) were averaged with the stimuli type and brain hemisphere. The change in spectral power of the brain signal and its main spectral bands of theta (3-7.5 Hz), Alpha (7.5-13 Hz) and Beta (13-25 Hz) were analyzed. Erotic stimuli showed ERP components deflected more negatively at the frontal electrode site than the negative picture stimuli during the time window of 200-300 ms whereas the negative valence stimuli processing reflected a positively twisted amplitude at the time window of 120-300 ms. The erotic and negative valence emotional picture stimuli show a significant difference in the spectral power of theta, alpha and beta frequency bands for the left vs. right hemisphere and frontal vs. occipital sites. Nonetheless, the time-frequency plots show us those emotionally valence visual stimuli triggered an increase of alpha band (7.5-13 Hz).

Theoretical modeling and experimental study of sodium oleate properties for wastewater cleaning with magnetic nanoparticles stabilized with oleate

We present some preliminary results regarding possible reducing of environment phenol contamination with nanotechnology involving. Magnetic nanoparticles stabilized in water dispersion with oleate were prepared for experimental testing of their interaction with wastewater samples containing phenol residues from industrial and sanitation sources. Magnetite with moderate level of cobalt doping was synthesized by co-precipitation method in the form of nanoparticles; further their surface was modified by the reaction with sodium oleate solution. Quantum chemical simulation of oleate structure recommended it for the interaction with water dipolar molecules as well as with metal cations at the nanocores surface. Transmission Electron Microscopy confirmed fine granulation of the prepared sample meaning significant total surface of nanoparticle sample. Phenol loaded water model was let to interact with magnetic nanoparticles in various reaction conditions. Phenol absorbance in the main spectral band showed the concentration diminution following magnetic nanoparticle action in the presence of ultraviolet radiation and hydrogen peroxide supply. Further experiments are planned for the better optimization of the phenol concentration decreasing in the large volumes of wastewater with adequate nanostructures, able to develop efficient interaction mechanisms with pollutant molecules.

Partition of Relative Maximum Region Band Based Image Compression

The proposed work presents a novel multispectral image compression method using Partition of Relative Maximum Region Band Algorithm (PRMSB). In the proposed method, 2D multispectral image is decorrelated in the first and second stage of intra and inter band correlation. From this process, the main spectral band component for analysis is selected. These components were given to Partition Band Selection Method, where the sequences of band components are extracted. In this approach, the spectral bands are treated dependently, so there will be 6 sequences as the number of bands. Relative Region Algorithm generate a spectral sub band wavelet transforms, performs better in terms of maximum estimation and compression efficiency. Throughout the experiments, the proposed work shows good performance with the surveyed methods.

Photo-switchable iron-terpyridine complexes functionalized with styrylbenzene unit

The manuscript deals with synthesis, characterization, photophysics, and reversible trans-cis photoisomerization behaviours of three homoleptic Fe(II)-terpyridine complexes, ([Fe(tpy-pvp-X)2]2+ where XH, Me, and NO2) covalently coupled with photo-active styrylbeneze moiety. The complexes underwent trans-trans to cis-cis isomerization upon the action of both visible and UV light with remarkable change in their absorption and emission spectral profiles. The isomerization studies were performed in four different solvents, viz. DCM, MeCN, MeOH and DMSO with both UV and visible light sources. The reversal from cis-cis to trans-trans isomerization also proceeds, albeit very slowly, on keeping and can be accelerated upon heating. The rate, rate constant and quantum yield of photoisomerization were determined in all the solvents. The rate and quantum yield of isomerization found to be much higher in presence of visible light source in all solvents than that of UV light. To better understand the electronic structures and correctly assign the experimental optical spectral bands, DFT and TD-DFT computational studied were also carried out in their trans-trans, trans-cis and cis-cis forms. Reasonably good correlation between the experimental and calculated bands could lead us to assign the main absorption spectral bands of the compounds.

NIR Absorbing AzaBODIPY Dyes for pH Sensing.

Two near-infrared (NIR) absorbing di(thien-2-nyl)-di(dimethylanilino)azaBODIPY dyes 2a and 2b were synthesized and characterized that differ depending on whether the dimethylaniline substituents are introduced at the 3,5- or 1,7-positions of the azaBODIPY core. The main spectral bands lie at 824 and 790 nm, respectively, in CH2Cl2. The effect of substituent position on the photophysical and pH sensing properties was analyzed through a comparison of the optical properties with the results of time-dependent density functional theory (TD-DFT) calculations. Protonation of the dimethylamino nitrogen atoms eliminates the intramolecular charge transfer properties of these compounds, and this results in a marked blue-shift of the main absorption bands to 696 and 730 nm, respectively, in CH2Cl2, and a fluorescence “turn-on” effect in the NIR region. The pH dependence studies reveal that the pKa values of the non-protonated 2a and 2b molecules are ca. 6.9 (±0.05) and 7.3 (±0.05), respectively, while that of the monoprotonated species for both dyes is ca. 1.4 (±0.05) making them potentially suitable for use as colorimetric pH indicators under highly acidic conditions.

Community detectability and structural balance dynamics in signed networks.

We investigate signed networks with community structure with respect to their spectra and their evolution under a dynamical model of structural balance, a prominent theory of signed social networks. The spectrum of the adjacency matrix generated by a stochastic block model with two equal-size communities shows detectability transitions in which the community structure becomes manifest when its signal eigenvalue appears outside the main spectral band. The spectrum also exhibits "sociality" transitions involving the homogeneous structure representing the average tie value. We derive expressions for the eigenvalues associated with the community and homogeneous structure as well as the transition boundaries, all in good agreement with numerical results. Using the stochastically generated networks as initial conditions for a simple model of structural balance dynamics yields three outcome regimes: two hostile factions that correspond with the initial communities, two hostile factions uncorrelated with those communities, and a single harmonious faction of all nodes. The detectability transition predicts the boundary between the assortative and mixed two-faction states and the sociality transition predicts that between the mixed and harmonious states. Our results may yield insight into the dynamics of cooperation and conflict among actors with distinct social identities.

Study of a discharge with a liquid cathode by the methods of high-speed visualization and emission spectroscopy

In this work the detailed structure of a direct current discharge with a liquid cathode was studied by high-speed imaging and emission spectroscopy. The movement of filaments into which the discharge channel is divided is studied. The processes of formation and destruction of filaments are investigated. Spectra were recorded at different distances from the liquids surface on the discharge axis. The dependences of the luminescence intensity of the main spectral lines and bands on the distance to the liquid surface at different discharge currents are found.

Optical Limiting and Femtosecond Pump-Probe Transient Absorbance Properties of a 3,5-distyrylBODIPY Dye.

The optical limiting (OL) properties of a 3,5-di-p-benzyloxystyrylBODIPY dye with an p-acetamidophenyl moiety at the meso-position have been investigated by using the open-aperture Z-scan technique at 532 nm with 10 ns laser pulses. There is a ca. 140 nm red shift of the main spectral band to 644 nm relative to the corresponding BODIPY core dye, due to the incorporation of p-benzyloxystyryl groups at the 3,5-positions. As a result, there is relatively weak absorbance across most of the visible region under ambient light conditions. Analysis of the observed reverse saturable absorbance (RSA) profiles demonstrates that the dye is potentially suitable for use in optical limiting applications as has been reported previously for other 3,5-distyrylBODIPY dyes. Time-resolved transient absorption spectroscopy and kinetic studies with femtosecond and nanosecond scale laser pulses provide the first direct spectral evidence that excited state absorption (ESA) from the S1 state is responsible for the observed OL properties.

Dithienosilole extended BODIPYs: Synthesis and spectroscopic properties

3,/3,5-Dithienosilole-vinyl-BODIPYs were readily synthesized through Knoevenagel condensation reactions. Spectroscopic properties of two dyes in various solvents were investigated. Dyes 1 and 2 show an absorption maxima at 620 and 738 nm with absorption coefficient of 60900 and 77900 [Formula: see text] cm[Formula: see text] in DCM, respectively. Significant red shifts of the main spectral bands are observed relative to that of the parent 1,3,5,7-tetramethyl-BODIPY. TD-DFT calculations reproduce the spectral shifts and experimental spectra.

An analysis of the photophysical and optical limiting properties of a novel 1,3,5-tristyrylBODIPY dye

The synthesis and characterization of a novel dibrominated 1,3,5-tristyrylBODIPY dye is reported, and its potential utility as a singlet oxygen photosensitizer and optical limiting material is assessed. The main spectral band lies in the therapeutic window, and there is a moderately high singlet oxygen quantum yield making the dye potentially suitable for use in biomedical applications and as an optical limiting dye at 532 nm. The optical limiting parameters are comparable to those reported previously for 3,5-distyrylBODIPYs, which suggests that mixtures of 3,5-distyryl and 1,3,5-tristyryl compounds that are formed in Knoevenagel condensation reactions could be used for this application. Theoretical calculations are used to assess the effect of 1,3,5-tristyryl substitution. A smaller red shift of the main spectral band is observed upon styrylation at the 1-position than is the case with the 3,5-positions due to there being smaller MO coefficients at this position, limiting the utility of this structural modification method for shifting the main BODIPY spectral band further into the therapeutic window.

Thieno[3,2-b]thiophene fused BODIPYs: synthesis, near-infrared luminescence and photosensitive properties.

The fusion of π-sufficient heteroaryl moieties has proven to be an effective strategy for achieving the red shift of the main spectral bands of BODIPY. In this paper, thieno[3,2-b]thiophene-fused BODIPY derivatives 1 and 2 have been designed and characterized by various spectroscopic methods, and their photosensitive properties have also been explored. Both dyes absorb in the near-infrared region with extremely high molar extinction coefficients, due to the extension of π-conjugation by fusion of the thieno[3,2-b]thiophene moiety. Their fluorescence quantum yields and singlet oxygen generation properties are significantly affected by iodine substitutions; dye 2 displays a moderate singlet oxygen generation value of 0.32, which makes it a potential NIR photosensitizer for photodynamic therapy of cancer in future research.

Polarization sensitivity error analysis and measurement of a greenhouse gas monitoring instrument.

Greenhouse gas monitoring instruments (GMI) are spatial heterodyne spectroscopy (SHS) sensors that monitor greenhouse gases (GHG) from space. Due to several kinds of polarization-sensitive optical elements in GMIs, to some extent, the instrument becomes a polarization-sensitive sensor. Its polarization sensitivity will reduce the radiometric accuracy and spectral inversion accuracy of GHG column concentration. Theoretical radiation response models for analyzing the polarization sensitivity of a GMI, which is mainly affected by a scanning mirror beam splitter and diffraction gratings, are presented in this paper. Based on these models and the polarization performance testing, the theoretical and experimental results of the main spectral band of a GMI, covering the wavelength range of 1.568-1.583μm for carbon dioxide (CO2) detection, have been given. The result shows that the linear polarization sensitivity is less than 0.65% and 1.32% in the nadir (45°, 0°) and in the oblique view direction (45±20°, ±31°), respectively, and that it meets the qualification requirement for an absolute radiometric calibration accuracy better than 5%. The absolute radiometric calibration accuracy directly affects the accuracy of GHG concentration retrieval.