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Adsorption study of the charge distribution features of highly charged smectites

The study examines the results of assessing the charge density distribution of smectite layers from the bentonite province of the Republic. Kazakhstan (Taganskoye and Dinosaurovoye fields) by alkylammonium method. The method is based on the study of the interaction of a homologous series of fatty amines with the surface of smectites. Organic cations form monomolecular and bimolecular adsorption layers on the basal surfaces. This allows the analysis of the dependence of the position of the diffraction maximum in the small-angle region on the bounding area of the organic cation and to obtain the charge density distribution over the smectite layers. The results obtained for the studied samples show a similar composition of montmorillonite: in all cases, smectites were characterized by a significant charge density with a different proportion of highly charged layers (cation exchange capacity – 120-130 mEq/100 g). The obtained data on charge distribution were compared with some adsorption and colloid-chemical characteristics of smectites, including the values of their cation exchange capacities. At the same time, such technological parameters as the effective viscosity of aqueous dispersions, despite the close charge distribution, differed significantly and showed a sharp dependence on the proportion of sodium cations in the exchange complex.

Time evolution of the defect states at the surface of MoS2

MoS2 has generated significant attention due to its unique electronic properties and versatile applications. Being a van der Waals material, MoS2 is expected to exhibit an inert surface due to lack of dangling bond. However, our photoemission study finds MoS2 to be highly sensitive toward residual gases. The position of the valence band maximum (VBM) shifts even in a vacuum of 10−10 Torr. We find this to be due to CO adsorption causing unintentional electron doping. The time evolution of the position of VBM is exponential, and it reaches two different saturation points, depending on whether the sample is exposed to ultraviolet (UV) radiation or not. Our XPS (x-ray photoemission spectroscopy) study shows no time-dependent escape of sulfur, which was in a previous study attributed to a VBM shift. The VBM shift can be reversed by annealing, sputtering, and UV light, which desorb CO gases. The study shows that the MoS2 surface is easily doped, which offers the possibility of using it as a sensor but in many other applications could diminish device performance and needs to be considered.

Relative Strength of Polycation Adsorption on Oxide Surfaces.

Polyelectrolyte adsorption onto surfaces is widely employed in water treatment and mining. However, little is known of the relative interaction strengths between surfaces and polymer. This fundamental property is assumed to be dominated by electrostatics, i.e., attractive interactions between opposite charges, which are set by the overall ionic strength ("salt concentration") of the solution, and charge densities of the surface and the polymer. A common, counterintuitive finding is a range of salt concentrations over which the amount of adsorbed polyelectrolyte increases as electrostatic interactions are tempered by the addition of salt. After an adsorption maximum, higher salt concentrations then produce the expected gradual desorption of polyelectrolyte. In this work, the salt response of the adsorption of the same narrow molecular weight distribution polycation, poly(N-methyl-4-vinylpyridinium), PM4VP, to a variety of surfaces was explored. Oxide powders for adsorption included Al2O3, SiO2, Fe2O3, Fe3O4, TiO2, ZnO, and CuO. Planar surfaces included silicon wafers, mica, calcium carbonate, and CaF2 single crystals. The PM4VP was radiolabeled with 14C so that sensitive, submonolayer amounts could be detected. The position of the peak maximum, or the lack of a peak, in response to added salt was used to rank the electrostatic component of the interaction. The importance of charge regulation, a shift in the surface pKa in response to solution species, was highlighted as a mechanism for adsorption on the "wrong" side of the isoelectric point and also as a factor contributing to the difficulty of reaching the totally desorbed state even at the highest salt concentrations.

Expert System for Fourier Transform Infrared Spectra Recognition Based on a Convolutional Neural Network With Multiclass Classification.

Fourier transform infrared spectroscopy (FT-IR) is a widely used spectroscopic method for routine analysis of substances and compounds. Spectral interpretation of spectra is a labor-intensive process that provides important information about functional groups or bonds present in compounds and complex substances. In this paper, based on deep learning methods of convolutional neural networks, models were developed to determine the presence of 17 classes of functional groups or 72 classes of coupling oscillations in the FT-IR spectra. Using web scanning, the spectra of 14 361 FT-IR spectra of organic molecules were obtained. Several different variants of model architectures with different sizes of feature maps have been tested. Based on the Shapley additive explanations (SHAP) and gradient-weighted class activation mapping (GradCAM) methods, visualization tools have been developed for visualizing and highlighting the areas of absorption bands manifestation for corresponding functional groups or bonds in the spectrum. To determine 17 and 72 classes, the F1-weighted metric, which is the harmonic mean of the class' precision and class' recall weighted by class' fraction, reached 93 and 88%, respectively, when using data on the position of absorption maxima in the spectrum as an additional source layer. The resulting model can be used to facilitate the routine analysis of spectra for all areas such as organic chemistry, materials science, and biology, as well as to facilitate the preparation of the obtained experimental data for publication.

Compositional effects on structural, electronic, elastic, piezoelectric and dielectric properties of GaInN alloys: a first-principles study.

We conduct a comprehensive theoretical analysis of wurtzite GaxIn1-xN ternary alloys, focusing on their structural, electronic, elastic, piezoelectric, and dielectric properties through rigorous first-principles calculations. Our investigation systematically explores the influence of varying Ga composition (x = 0%, 25%, 50%, 75%, 100%) on the alloy properties. Remarkably, we observe a distinctive non-linear correlation between the band gap and Ga concentration, attributable to unique slopes in the absolute positions of the valence band maximum and conduction band minimum with respect to Ga concentration. Our effective band structure analysis reveals the meticulous preservation of Bloch characters near band extrema, minimizing charge carrier scattering. Furthermore, we scrutinize deviations from linear Vegard-like dependence in elastic, piezoelectric, and dielectric constants. Additionally, our calculations encompass various optical properties, including absorption coefficient, reflectivity, refractive index, energy loss function, and extinction coefficient. We analyze their trends with photon energy, providing valuable insights into the optical behavior of GaxIn1-xN alloys. Our results, in excellent agreement with available experimental data, significantly contribute to a deeper understanding of the alloys' electronic properties. This study offers valuable insights that may illuminate potential applications of GaxIn1-xN alloys in diverse technological fields.

Automatic and adaptive picking of surface-wave dispersion curves for near-surface application

Multichannel analysis of surface waves (MASW) is a widely used non-invasive method to reveal the S-velocity structure in near-surface applications. Automatic and adaptive picking of surface wave dispersion curves is crucial for the later surface wave analysis. The traditional way to acquire the dispersion curves is to identify the local extremum energy in phase-velocity images and manually pick the dispersion curve by following peaks at different frequencies. However, the large number of interactive works in extensive surveys could be more efficient, time-consuming, and prone to human error. In this work, we developed an automatic adaptive picking of dispersion curves (AAPDC) strategy, which automatically searches the surface-wave dispersion curve based on the position of the local energy maxima in the dispersion spectrum. This method is straightforward and efficient and requires only a few or no additional parameters to obtain a stable result. The typical synthetic model tests show that the automatic picking agrees with the theoretical dispersion curves. In addition, the proposed AAPDC method is used to land geophone data and DAS data. The final S-velocity tomograms have a good agreement with the geological and other geophysics results, which demonstrate that the AAPDC method could accurately and adaptive extract fundamental dispersion curves from the complex dispersion spectrum.

Polarization distribution of transverse ULF waves according to Van Allen Probe A data: whether toroidal and poloidal waves exist separately in the magnetosphere?

Ultralow-frequency (ULF) waves play an important role in energy transfer within Earth's magnetosphere due to intensive interaction with the surrounding plasma. Previous works have assumed that these waves are strictly divided by polarization into toroidal, when the magnetic field oscillates in the azimuthal direction, and poloidal, when it oscillates in the radial direction. The former are azimuthally large-scale and are excited by external sources, whereas the latter are small-scale and are generated by internal plasma instabilities. Observations show, however, that waves of mixed polarization often occur, and the nature of this mixing has not been explained. In this paper, we carry out a statistical study and show that the polarization of transverse waves has a normal distribution, and the maximum corresponds to oscillations of the toroidal and poloidal components with the same amplitude. At the same time, the spatial distributions of toroidal and poloidal waves are clearly different, but only lead to a small shift in the position of the distribution maximum. This result suggests that in order to compare the theory with ULF wave observations it is necessary to take into account the processes of polarization change, which can affect wave-particle interactions in the magnetosphere.

Dissipative light bullets in a doped and weakly nonlocal optical fiber

The letter introduces an extended (3+1)-dimensional [(3+1)D] nonlocal cubic complex Ginzburg-Landau equation describing the dynamics of dissipative light bullets in optical fiber amplifiers under the interplay between dopants and a spatially nonlocal nonlinear response. The model equation includes the effects of fiber dispersion, linear gain, nonlinear loss, fiber nonlinearity, atomic detuning, linear and nonlinear diffractive transverse effects, and nonlocal nonlinear response. A system of coupled ordinary differential equations for the amplitude, temporal, and spatial pulse widths and position of the pulse maximum, unequal wavefront curvatures, chirp parameters, and phase shift is derived using the variational technique. A stability criterion is established, where a domain of dissipative parameters for stable steady-state solutions is found. Direct integration of the proposed nonlocal evolution equation is performed, which allows us to investigate the evolution of the Gaussian beam along a doped nonlocal optical fiber, showing stable self-organized dissipative spatiotemporal light bullets.

Распределение поляризации поперечных УНЧ-волн по данным Van Allen Probe A: существуют ли раздельно тороидальные и полоидальные волны в магнитосфере?

Ultralow-frequency (ULF) waves play an important role in energy transfer within Earth's magnetosphere due to intensive interaction with the surrounding plasma. Previous works have assumed that these waves are strictly divided by polarization into toroidal, when the magnetic field oscillates in the azimuthal direction, and poloidal, when it oscillates in the radial direction. The former are azimuthally large-scale and are excited by external sources, whereas the latter are small-scale and are generated by internal plasma instabilities. Observations show, however, that waves of mixed polarization often occur, and the nature of this mixing has not been explained. In this paper, we carry out a statistical study and show that the polarization of transverse waves has a normal distribution, and the maximum corresponds to oscillations of the toroidal and poloidal components with the same amplitude. At the same time, the spatial distributions of toroidal and poloidal waves are clearly different, but only lead to a small shift in the position of the distribution maximum. This result suggests that in order to compare the theory with ULF wave observations it is necessary to take into account the processes of polarization change, which can affect wave-particle interactions in the magnetosphere.

Hierarchy of hydrogen bonding among constitutional isomers of hexanol

The strength and thermal stability of the hydrogen bonding influence the bulk properties of associating liquids, such as higher alcohols. Temperature-induced decay of the hydrogen bonds translates into uncommon trends in the heat capacity of the liquid, frequently exhibiting vast plateaus or distinct maxima. Experimental isobaric heat capacities of sixteen aliphatic hexanols in their liquid phase, resulting from Tian-Calvet calorimetry in the temperature range of 260–340 K, are presented. This temperature range is extended to 380 K with a power-compensation DSC for thirteen compounds. Among the studied compounds, a maximum on the temperature dependence of the heat capacity is explicitly observed below 380 K for six species. Upon derivation of residual heat capacities, this maximum gets amplified and can be recognized for 13 species (below 400 K). Molecular dynamics simulations of pure samples of all hexanol isomers are performed to interpret the observed trends. The hydrogen-bonding hierarchy is established computationally in terms of structural and energetic descriptors of bulk liquids. The strength of the hydrogen bonds is directly related to the extent of steric hindrance imposed on the hydroxyl moieties by the side alkyl chains in the bulk liquid. The hexanol isomers predicted computationally to form the weakest hydrogen bonds in the liquid match those, for which the non-monotonous trends of the heat capacities were observed. The position of the heat capacity maximum is sensitive to a subtle variation of the hydrogen bonding strength and shifts to higher temperatures upon strengthening of the hydrogen bonding for less branched and primary hexanol isomers.

Hybrid Bio-Nanocomposites by Integrating Nanoscale Au in Butterfly Scales Colored by Photonic Nanoarchitectures

Plasmonic metallic nanoparticles, like Au, can be used to tune the optical properties of photonic nanoarchitectures occurring in butterfly wing scales possessing structural color. The effect of the nanoscale Au depends on the location and the amount deposited in the chitin-based photonic nanoarchitecture. The following three types of Au introduction methods were compared regarding the structural and optical properties of the resulting hybrid bio-nanocomposites: (i) growth of Au nanoparticles inside the nanopores of butterfly wing scales by a light-induced in situ chemical reduction of HAuCl4 in aqueous solution containing sodium citrate, as a new procedure we have developed, (ii) drop-drying of the aqueous Au sol formed during procedure (i) in the bulk liquid phase, and (iii) physical vapor deposition of Au thin film onto the butterfly wing. We investigated all three methods at two different Au concentrations on the wings of laboratory-bred blue-colored male Polyommatus icarus butterflies and characterized the optical properties of the resulting hybrid bio-nanocomposites. We found that the drop-drying and the in situ growth produced comparable redshift in the spectral position of the reflectance maximum associated with the chitin-based photonic nanoarchitecture in the wing scales, while the 5 nm or 15 nm thick Au layers vacuum deposited onto the butterfly wing behaved like an optical filter, without inducing spectral shift. The in situ growth in the photonic nanoarchitecture under intense illumination produced uniform Au nanoparticles located in the pores of the biological template, which is more advantageous for further applications. An additional benefit of this method is that the Au nanoparticles do not aggregate on drying, like in the case of drop-drying of preformed Au nanoparticles from the citrate-stabilized sol.

Numerical Simulation of Taylor—Couette—Poiseuille Flow at Re = 10,000

A fully developed turbulent flow in a concentric annulus, Re =10,000, ri/ro=0.5, with an inner rotating cylinder in the velocity range N=Uω/Ub=0÷4, is studied via a large-eddy simulation. Also, for comparison, simulations by steady-state, unstatiounary RANS k-ω SST (URANS), and Elliptic Blending Model (EBM) were made. The main focus of this study is on the effect of high rotation on the mean flow, turbulence statistics, and vortex structure. Distribution of the tangential velocity and the Reynolds stress tensor change their behaviour at N>0.5∼1. With rotation increases, the production of tangential fluctuation becomes dominant over axial ones and the position of turbulent kinetic energy maximum shifts towards the wall into the buffer zone. URANS and EBM approaches show good agreement with LES in mean flow, turbulent statistics, and integral parameters. The difference in pressure loss prediction between LES and URANS does not exceed 20%, but the average difference is about 11%. The EBM approach underestimates pressure losses up to 9% and on average not more than 5%. Vortex structures are described well by URANS.

Numerical investigation on the effect of hydrogen share in NH3/H2 blends in a turbulent lean-premixed swirl burner

Climate change and the energy crisis urge the transition from fossil to renewable fuels. Ammonia and hydrogen are the most versatile carbon-free chemical energy carriers. Hydrogen-diluted ammonia combustion can drastically lower the emission of nitrogen oxides. The present paper focuses on the numerical analysis of ammonia/hydrogen combustion in a lean-premixed swirl burner, highlighting the effect of hydrogen share and equivalence ratio. The hydrogen share notably influences the axial position of the heat release maximum due to the higher reactivity, while it marginally influences the global velocity field. Unburned ammonia was observed at lean condition and low hydrogen concentration. At ultra-lean conditions, nitrogen oxide emission increases with hydrogen content, while a maximum can be reached by increasing the equivalence ratio. The values are compared to experimental data from the literature. Dinitrogen oxide emission decreases with both hydrogen concentration and equivalence ratio. Non-reacting flow field was validated by Particle Image Velocimetry measurements.

SYNTHESIS AND STUDY OF NANO-SIZED COMPLEX OF Fe(III) WITH ETHYLENEDIAMINEDISUCCINIC ACID

In this work, the FeEDDSNP nanocomplex was synthesized by dissolution peptization of a freshly precipitated sol of iron hydroxide Fe(OH)3 in an aqueous solution of the racemic form of Н4EDDS. The complex was characterized by electron absorption spectroscopy and IR spect­roscopy. It was shown that the structure of the nanocomplex is identical to the structure of the FeEDDS complex obtained using a two-stage technology. The position of the absorption maxima of iron nanoparticles practically does not change depending on the sto­rage time at room temperature, which indicates the stability of the synthesized nanocomplex. The nano­dispersed FeEDDSNP complex is more soluble in water (275 g/l) compared to the FeEDDS complex obtained by the classical method (150 g/l), which greatly facilitates its use as a biologically active compound. To determine the stability of the system depending on the pH, the electrokinetic potential was measured to select the optimal pH of the medium and concentrations to obtain stable dispersed systems. It is shown that at low pH (1.5–4.0) there is a drop in the electrokinetic potential, and when the pH increases, the

МОДЕЛЮВАННЯ ПЛАЗМОННИХ ВЛАСТИВОСТЕЙ ЧАСТИНОК МОНОСУЛЬФІДУ МІДІ В БЛИЖНЬОМУ ІЧ ДІАПАЗОНІ

This paper is devoted to the theoretical study of the extinction spectra of copper monosulfide particles under conditions of localized surface plasmon resonance. The study was conducted for plasmonic copper monosulfide particles of spherical and ellipsoidal shapes of variable size in media with different values of the refractive index. The simulation results reveal that increasing the radius of CuS nanoparticles leads to a significant enhancement in the amplitude of the plasmon peak and a shift of the peak towards longer wavelengths. It was investigated how the positions of the extinction peaks on the spectral scale and their amplitudes change when the particles deviate from the spherical shape. Simulations were performed for spherical and elongated ellipsoidal particles with fixed cross-sectional radius and variable length. Specifically, we varied the length of the major axis while keeping the lengths of the minor axes constant. It is shown that the deviation from the sphericity of the particles will affect both the position of the extinction maximum on the spectral scale and the shape of the spectral curve. An increase in the ratio of the ellipsoid semi-axes lengths leads to a significant increase in the amplitude of the extinction peak and its shift to the long-wavelength region. Besides, the position of the plasmonic peak on the spectral scale is influenced not only by the geometric parameters of the particles such as size and shape but also by the dielectric properties of the surrounding medium, including its refractive index. We assess the impact of changing the refractive index of the surrounding medium on the shape, amplitude, and position of the extinction maxima of CuS nanoparticles. It is showed that increasing the refractive index of the surrounding medium leads to a significant shift of the plasmon resonance peak into the long-wavelength region of the spectrum an increase in the peak width, and a decrease in its amplitude. Thus, ellipsoid copper monosulfide particles show improved surface plasmon characteristics compared to spherical ones and can be effectively used in the near-infrared spectral region.

INFLUENCE OF CERIUM CONCENTRATION AND SINTERING ATMOSPHERE ON THE PHASE COMPOSITION AND LUMINESCENT PROPERTIES OF Y2.98-хCeхAl5.02О12 CERAMICS

The phase composition and spectral-luminescent properties of ceramic samples obtained from oxide compositions with the general formula Y2.98-хCeхAl5.02О12 (x = 0.05, 0.10, 0.20, 0.30, 0.45, 0.60 formula units (f.u.)) were investigated. It was found that the phase composition of the ceramic powders depended significantly on the concentration of cerium and the calcination atmosphere. The maximum concentration of cerium cations in the garnet lattice was determined to be approximately 0.1 f.u. when calcined in air, and approximately 0.16 f.u. when calcined in the argon – hydrogen atmosphere. The photoluminescence of the ceramic samples was studied when excited by a laser with a wavelength of 445 nm. It was observed that ceramic samples sintered in argon and hydrogen had a higher luminescence intensity compared to samples synthesized in a vacuum. The possibility of shifting the wavelength of the maximum luminescence intensity from 546 nm to 570 nm by changing the cationic composition and sintering conditions of the ceramics was demonstrated. Additionally, the negative effect of oxidative annealing of ceramic samples on the intensity and position of luminescence maxima in Y2.98-хCeхAl5.02О12 oxide compositions heavily doped with cerium was shown.

Raman study of photoinduced crystallization of SnS2 in As2S3:Sn glasses

Raman spectra of synthesised As2S3:Sn samples with up to 2.7 at% Sn recorded at a moderate excitation power density (Pexc=4 kW/cm2) show their amorphous character. Raman measurements performed at a higher Pexc (40 kW/cm2) result in the local heating of the sample surface by up to 150 K, as estimated from the shift of the frequency positions of the As2S3 Raman maxima. For samples with Sn content above 2 at% a pronounced narrow peak at 311 cm–1 emerges as an evidence for SnS2 crystallites formed on the sample surface under above-bandgap illumination during the measurement. The higher-Pexc (40 kW/cm2) illumination results in a formation of a pit on the sample surface due to the material transfer and in a rapid decrease of the glass viscosity, enhancing the diffusion of atoms and facilitating their aggregation in SnS2 crystallites. This effect of mostly nonthermal nature is responsible for the SnS2-related feature observed in the Raman spectra upon illumination at Pexc= 40 kW/cm2. For As2S3 doped with 3 at% Sn the SnS2-related feature near 314 cm–1 is observed in the Raman spectra even under excitation at much lower Pexc, down to 0.4 kW/cm2. As follows from X-ray diffraction data, no crystalline SnS2 phase is present in this sample before the measurement, it appears upon illumination even at the low Pexc values.

Synthesis of new efficient fluorophores of thieno[2,3-<i>b</i>]pyridine series

The reaction of 4-amino-6-aryl-2-halopyridine-3,5-dicarbonitriles with thioglycolic acid ethyl ester was used to synthesize a series of new efficient fluorophores of thieno[2,3- b ]pyridine series. The long-wavelength absorption bands of DMSO solutions of the prepared compounds are at the boundary of the UV and visible regions of the spectrum (λabs 375-388 nm) and show an ambiguous influence of the substituent electronic effect, that was explained by quantum chemical calculations. The emission maxima are in the yellow-green region (λem 490- 510 nm) and they are blue-shifted in the presence of electron donor groups with slightly increasing intensity (Φem 37.8-60.6%). It was found that the nitro group presence causes a complete photoluminescence quenching both in solution and in the solid state. In addition, the position of the emission maximum (λem 473-505 nm) and its intensity (Φem 3.6-72.7%) strongly depend on the polarity and the basic properties of the medium, that was established using the Catalan empirical model.

Single-photon ionization of aligned H with near-ionization-threshold photon energy

We study single-photon ionization of aligned H in a high-frequency low-intensity laser field. We focus on the cases where the laser frequency is near to or somewhat larger than the ionization potential of the target. The calculated photoelectron momentum distribution through numerical solution of time-dependent Schrödinger equation shows clear interference patterns. However, different from the cases of photon energy far larger than the ionization potential usually explored in experiments, the positions of interference maxima and minima for the present cases can not be explained by the interference of the electronic wave with the observed momentum between these two atomic centers of the molecule. By developing a theory model applicable for ionization of molecules in high-frequency laser field, we show that the Coulomb potential plays an important role in the momentum component of the emitting electronic wave near the nuclei, resulting in a remarkable shift of the interference pattern. A simple expression with Coulomb-modified momentum is obtained to predict the interference extrema, which gives suggestions for probing the structure and electron dynamics of the aligned molecule in single-photon ionization with lower photon energy.

Anomalous bluish-green light emitting features of europium doped barium aluminate (BaAl2O4:Eu2+) phosphor

Eu doped barium aluminate is an important material for light emitting devices. Here we report structural, optical absorption and emission features of 1–5 % Eu doped barium aluminate phosphor and explore its ‘anomalous’ emission feature. The structural analysis suggests that the undoped sample has a mixture of BaAl2O4 and BaAl12O19. On the other hand, the samples doped with Eu have a mixture of BaAl2O4, Ba(Al2O4) and BaAl12O19 phases. Among these, the major phase in all the samples was BaAl2O4. The undoped sample shows a high absorption peak at around 209 nm followed by three weak intensity peaks apparent at around 250, 288 and 338 nm. In contrast, all the doped samples show three maxima at around 209, 266 and 340 nm. The position and intensity of these absorption maxima are found to vary with the Eu concentration. The optical bandgap of the undoped sample is estimated to be 5.05 eV and it is found to reduce to 4.68 eV after doping of Eu at 5 %. All the samples produce common PL emission peaks centred at ∼405, 428 and 456 nm due to potential oxygen vacancies. The doped samples show additional peaks at around 485, 518 and 657 nm due to Eu2+ and Eu3+ ions. In particular, the sample doped with 2 % of Eu produces a strong anomalous emission band of Eu2+ ion in the bluish-green region. Our study reveals that the broadband bluish-green emission of Eu2+ ions can be achieved when the barium aluminate crystal is doped by 2 % of Eu. When the host is doped by Eu at >2 % or <2 %, the emission band associated with oxygen vacancies dominates over the Eu2+ emission.