Position Of Maximum Research Articles

A Modified Oxazolone Dye Dedicated to Spectroscopy and Optoelectronics

Here we present a newly synthesized bifunctional organic chromophore with appealing spectroscopic and nonlinear optical features. The positions of absorption and emission maxima of the dye vary with increasing solvent polarity and exhibit positive solvatochromism. The determined change in the dipole moment upon excitation based on the Bilot and Kawski theory is 5.94 D, which corresponds to the intermolecular displacement of a charge equal to 1.24 Å. An investigated organic-based system represents a significant, repeatable, and stable over time optical signal modulation in the manner of the refractive index value. Its magnitude is varied both by optical pumping intensity as well as by external frequency modulation, which indicates that such system is an alluring and alternative core unit for optoelectronic devices and complex networks. Then, the same active system, due to the nonresonant mechanism of higher harmonics of light inducement, can provide second and third harmonic signals. According to the introduced laser line spatial modifications (parallel or perpendicular polarization directions), it is resulted in output SHG signal with magnitude varied about 100%. Its magnitude is noticeably small; however, to construct sensitive optical sensors or infrared indicators, such feature may guarantee satisfying circumstances.

On-demand measurement of higher topological charges using Hadamard-coded apertures with a DMD

The diffraction of an orbital angular momentum (OAM) beam behind slits and polygon apertures has enabled the measurement of light’s topological charge (TC). In this work, we present a simple technique to measure higher TCs using Hadamard-coded apertures programmed in a digital micromirror device (DMD). Apart from pattern recognition, a common approach in relating the topological properties of the beam with its diffraction, we demonstrate that we can determine TCs from m=±1 to ±10 using the position of diffracted intensity centroid R. We show thru experiments and simulations that indeed the centroids of the diffracted beams move depending on the magnitude and the sign of the TC, and the order N of the Hadamard aperture. Based on our results, distinguishing the TC of a beam is easier when |m|>5. Lastly, we infer the source of the movement of the centroid using simple interference of three points derived from a Hadamard N = 2. By tracing the position of the zeroth-order maxima in the interference, we relate the maximum intensity position with the intensity centroid position in the diffraction. Our technique is crucial for determining higher-order modes whose TC are difficult to determine with the currently available methods.

An Experimental and Theoretical Study of the Optical Properties of (C2H7N4O)2BiCl5 for an Optoelectronic Application

This study explores the electronic properties of (C2H7N4O)2BiCl5 using the density functional theory (DFT) method, which was compared with the experimental data. The band structure of the compound indicated that it is a direct semiconductor with a band gap energy of 3.54 eV, which was comparable with the value (3.20 eV) obtained experimentally from the UV–vis spectroscopy. The density of state study showed that the conduction band was formed mainly by Bi 6p, C 2p, and N 2p states, while the valence band was formed mainly by Cl 2p, O 2p, and N 2p states. Hirshfeld surface analysis and enrichment ratio (E) were further used to investigate and quantify the intermolecular interactions within the compound. These studies established that the most important role in the stability of the structure of this crystalline material was provided by hydrogen bonding and π–π stacking interactions. The crystalline morphology of the compound was determined using BFDH simulation, based on the single-crystal structure result. Furthermore, Fourier transform infrared spectroscopy (FTIR) was used to study the vibrational modes of carbamoyl-ganidinium cations. The charge transfer process within the anionic chains of [BiCl5]∝, studied using photoluminescence spectroscopy, resulted in a broad emission band with two positions of maxima centered at 336 and 358 nm. This work offers a good understanding of the optical, structural, as well as the electrical properties of (C2H7N4O)2BiCl5, which are necessary in its applications in areas such as multifunctional magnetic, optoelectronic, and photonic systems.

Programmable particles patterning by multifrequency excitation radiation force of acoustic resonance modes

Acoustic radiation force has been extensively investigated to trap and spatially manipulate particles into various patterns. Existing acoustical methods for particles manipulation are developed by designing the acoustic structures or modulating the transducers arrays. These patterns and trajectories manipulation of particles have been limited to nodal lines by the prefabricated acoustic structures. Additionally, the acoustic potential field is limited by the wavelength due to the excitation of narrow frequency band, which is only suitable for local trapping and translation of particles. It is challenging to accomplish various programmable particles patterning by acoustic radiation force. In this work, we theoretically and numerically investigate the mechanisms for multifrequency excitation radiation force of acoustic resonance modes. The acoustic potential field can be programmed to arbitrary functional distributions by simultaneously exciting multiple resonance modes. Thus, we propose the programmable algorithm for arbitrary acoustic radiation potential, particles are trapped at the minima, forming a wide variety of patterns. Further, the selective manipulation of particles is realized by the programmable localized maximum of the acoustic radiation potential. Finally, the temporally modulated patterns of particles are achieved through modulating the positions of the localized maximum of acoustic radiation potential. This work paves the way for manipulation of arbitrary functional acoustic potential field, thereby opening up the realm of programmable particles patterning.

Gearbox Fault Diagnosis Based on Improved Variational Mode Extraction.

Gearboxes are widely used in drive systems of rotating machinery. The health status of gearboxes considerably influences the normal and reliable operation of rotating machinery. When a gearbox experiences tooth failure, a vibration signal with impulse features is excited. However, these impulse features tend to be relatively weak and difficult to extract. To solve this problem, a novel approach for gearbox fault feature extraction and fault diagnosis based on improved variational mode extraction (VME) is proposed. Since the initial value of the desired mode center frequency and the value of the penalty parameter in VME must be assigned, a short-time Fourier transform (STFT) was performed, and a new index, the standard deviation of differential values of envelope maxima positions (SDE), is proposed. The feasibility and effectiveness of the proposed approach was verified by a simulation signal and two datasets associated with a gearbox test bench. The results demonstrate that the VME-based approach outperforms the variational mode decomposition (VMD) approach.

Imaging of a High-Power Millimeter Wave Beam Using a Millimeter Wave-Induced Gas Breakdown Initiated by a Metal-Dielectric Screen

A semiquantitative technique for imaging of high-power millimeter wave (MMW) beam using visible light from the plasma of an MMW-induced gas breakdown, which was initiated by a metal-dielectric (MD) screen, is discussed. The design of the gas breakdown sensor for imaging of the wave beam is presented. A plane MD screen was placed in a shallow airtight chamber with a transparent window of a thin mylar film. The chamber was filled with gas at a near atmospheric pressure. An MMW-induced breakdown in air, nitrogen, helium, and krypton, initiated by an MD screen, has been experimentally studied. In the experiments, a high-power 250-GHz pulsed gyrotron served as the source of MMWs. In a chamber filled with noble gases, bulk plasma was formed at an MMW intensity above the gas breakdown threshold. A single-pulse wave beam was imaged using a profile of the flux density of light from the breakdown plasma in helium and krypton. It was shown that using the presented technique, one can determine the position of the intensity maxima and the beam profile of an MMW beam in the range from one to two threshold intensities of an MMW-induced gas breakdown initiated by an MD screen.

Electrical Conductivity and Dielectric Relaxation in Ag1−xLixNbO3

The broadband electrical properties of Ag1−xLixNbO3 (ALNx) ceramics (x ≤ 0.1) together with AgNbO3 (AN) crystals were studied over a wide temperature interval of 20–800 K. For ALNx with x ≤ 0.05, a very diffused ferroelectric phase transition was observed. The position of the dielectric permittivity maximum in this phase transition is strongly frequency-dependent and is described well by the Vogel–Fulcher law. The freezing temperature decreases when the lithium concentration increases. Below the ferroelectric phase transition temperature, the dielectric dispersion is mainly caused by ferroelectric domain dynamics. Moreover, for ALN3 and ALN5 ceramics at very low temperatures (below 100 K), behavior typical of dipolar glasses is observed. At higher temperatures (above 650 K for ALN5), electrical conductivity effects become important. The DC conductivity increases with temperature according to the Arhenius law and the activation energy is highest in the antiferroelectric phase. Moreover, the activation energy is strongly dependent on the lithium concentration and it is greatest when x = 0.02.

Band Gap Control and Properties of Indium–Zinc Oxynitride Thin Films Grown by Molecular Beam Epitaxy

The material system of II–III oxynitride semiconductors has opened new prospects in solar energy harvesting and photocatalysis in recent years due to a tunable band gap and favorable band edge positions with respect to important redox levels. A promising member of this family is In–Zn–O–N (IZNO), as its band gap can be tailored to lower values compared to its better studied cousin Ga–Zn–O–N. We study IZNO thin films grown on sapphire substrates by molecular beam epitaxy (MBE) and investigate their structural, surface morphology, optical absorption, and photoemission characteristics. We investigate the influence of the constituting elements in the alloy on the position of valence band maxima, conduction band minima, and the structural properties. Through precise variation of the composition, samples with a band gap range between 1.0 and 2.6 eV have been deposited and analyzed. Based on our results, Zn and N have been identified to lower the energy of valence and conduction band edges with respect to the vacuum level, while In and O have the opposite effect. Structural characterization reveals that the samples are polycrystalline with grain sizes of about 30 nm, comprising a mixture of cubic and hexagonal crystal phases with distinct short-range disorder. While in the ternary compounds In–O–N and Zn–O–N metal–oxide bonds are dominant, we elucidate the formation of metal–oxynitride bonds in IZNO. Electrical and optical measurements reveal charge carrier concentrations of 1018–1020 cm–3 and absorption coefficients of 105 cm–1 above about 2 eV excitation energy, accompanied by pronounced free carrier absorption found in samples in the upper carrier concentration range in the infrared energy region. Typical Urbach energies are 80–220 meV, with no clear correlation with the elemental composition. By introducing MBE growth for IZNO, we overcome the limitations typically inflicted by the fabrication methods on stoichiometric InN:ZnO solid solutions and provide unprecedented access to new compounds in this material class.

Lanthanide Complexes with 4,4′‐Bis(2‐sulfonatostyryl)‐biphenyl: Crystal Structures and Luminescence Properties

AbstractA series of new tris(pyrazolyl)borate (Tp−) and tris(2‐pyridylpyrazolyl)borate (TpPy−) Eu3+, Gd3+, Tb3+ and Dy3+ complexes with the dianionic ligand 4,4′‐bis(2‐sulfonatostyryl)biphenyl (Ssp2−, a widely used fluorescent whitener) were synthesized and their luminescence properties were studied. The Gd3+, Tb3+ and Dy3+ compounds possess only ligand‐centered emission, arising from the Ssp2− ligand, with quantum yields of up to 60 %. While the emission centers in these complexes are similar, the positions of the luminescence maxima, the emission quantum yields, and the lifetimes change in the order [(Tp2Ln)2Ssp]<[(TpPyLnSsp)2]<[Ln2Ssp3]n. Among the complexes studied, Eu3+‐centered emission was observed for only [(Tp2Eu)2Ssp]. In this compound, Tp− plays the role of an antenna ligand for Eu3+‐radiation, though the quantum yield is only 5 %.

The Method for Evaluating Cross-Shore Migration of Sand Bar under the Influence of Nonlinear Waves Transformation

Sand bar migration on the gently sloping sandy bottom in the coastal zone as a result of nonlinear wave transformation and corresponding sediment transport is discussed. Wave transformation on the intermediate depth causes periodic exchange of energy in space between the first and the second wave harmonics, accompanied by changes in the wave profile asymmetry. This leads to the occurrence of periodical fluctuations in the wave-induced sediment transport. It is shown that the position of the second nonlinear wave harmonic maximum determines location of the divergence point of sediment transport on the inclined bottom profile, where it changes direction from the onshore to the offshore. Such sediment transport pattern leads to formation of an underwater sand bar. A method is proposed to predict the position of the bar on an underwater slope after a storm based on calculation of the position of the maximum amplitude of the second nonlinear harmonic. The method is validated on the base of field measurements and ERA 5 reanalysis wave data.

FEATURES OF MECHANICALLY STIMULATED CHANGES IN THE ELECTRICAL CONDUCTIVITY OF P-Si CRYSTALS AFTER THE ACTION OF A MAGNETIC FIELD

The research investigated mechanically stimulated changes in resistance ( R/R 0 = f(σ) ) of p -type conductivity single-crystal silicon samples that underwent long-term (~ 600 days) magnetic treatment. The permanent magnetic field induction was В = 0.354 Т . It was established that the action of the magnetic field leads to the appearance of a characteristic maximum on the curves R/R 0 = f(σ) at the initial stage of uniaxial elastic deformation. A similar effect was observed after small doses of X-irradiation ( D = 312 Gy ). It was found that the position and magnitude of the characteristic maximum on the R/R 0 = f(σ) curves significantly depend on the time that has passed since the previous cycle of deformation (compression-decompression). In particular, it is shown that the characteristic maximum is not observed if this time does not exceed 20 hours. It was also found that with an increase in time (which has passed since the previous deformation cycle), the value of the maximum increases, and its position shifts towards higher mechanical stresses σ . At the same time, the amount of residual resistance at the beginning of the next deformation cycle also decreases. So, it can be seen that the relaxation processes, which are accompanied by a change in the value of the residual resistance of the crystal, do not have a clear time periodicity, but there is a clear tendency to its increase in value. The change of the defective background in the crystal under the action of the load and the magnetic field affects the concentration and mobility of the charge carriers, which are related to the electrical conductivity of the semiconductor. A characteristic feature of dislocations in silicon crystals is the presence around them of areas with an increased concentration of point defects (Cottrell clouds). It has been confirmed that the long-term effect of a constant magnetic field on experimental p -Si crystals leads to the disintegration of defects, such as hydrogen-containing and oxygen-containing complexes (Si–O–Si, Si–H 2 , O–Si–O, Si–O–C, Si –CH 3 , H–OH, H 2 O, Si–OH, etc.). As a result of such decay, the formed hydrogen can migrate in the elastic stress fields of the near-surface layer, passivating the acceptor bonds. This, accordingly, leads to a decrease in the surface electrical conductivity of the experimental samples. Key words : silicon, magnetic field, dislocations, uniaxial elastic deformation.

Разработка методики количественного определения суммы флавоноидов в полыни метельчатой траве

Plants of the genus Artemisia have a rich complex of biologically active compounds, among which essential oils, sesquiterpene lactones, flavonoids, and acetylenic compounds predominate. Particular attention is drawn to Artemisia scoparia Waldst. et Kit. Due to a wide range of therapeutic activity, wormwood paniculata is used as a choleretic, hepatoprotective, antimicrobial, anti-inflammatory agent. Flavonoids are one of the leading groups of biologically active compounds (BAS) in water and water-alcohol extracts from the aerial part of Artemisia scoparia. These compounds have powerful hepatoprotective, choleretic, anti-inflammatory, antiviral effects. Objective: development of a method for quantitative determination of the amount of flavonoids in the herb Artemisia scoparia. Materials and methods. The object of the study was Artemisia scoparia herb, collected in the flowering phase in the Nikitsky Botanical Garden in 2016-2020. Quantitative determination of the amount of flavonoids in raw materials was carried out by UV spectroscopy. Results. It has been established that the differential spectrum of the complex compound of the studied extract with aluminum chloride does not differ in terms of the position of the light absorption maximum (410 nm) from the differential spectrum of the complex of rutin with aluminum ions. The content of total flavonoids in terms of rutin in Artemisia scoparia herb was 1.95% ± 0.05. Conclusion. A method has been developed for the quantitative determination of the amount of flavonoids in the raw material of Artemisia scoparia by UV spectrophotometry in terms of rutin.

Comparative study of the MeV ion channeling implantation induced damage in 6H-SiC by the iterative procedure and phenomenological CSIM computer code

Due to its unique material properties, such as extreme hardness and radiation resistance, silicon carbide has been used as an important construction material for environments with extreme conditions, like those present in nuclear reactors. As such, it is constantly exposed to energetic particles (e.g., neutrons) and consequently subjected to gradual crystal lattice degradation. In this article, the 6H-SiC crystal damage has been simulated by the implantation of 4 MeV C3+ ions in the (0001) axial direction of a single 6H-SiC crystal to the ion fluences of 1.359 1015 cm-2, 6.740 1015 cm-2, and 2.02 1016 cm-2. These implanted samples were subsequently analyzed by Rutherford and elastic backscattering spectrometry in the channeling orientation (RBS/C & EBS/C) by the usage of 1 MeV protons. Obtained spectra were analyzed by channeling simulation phenomenological computer code (CSIM) to obtain quantitative crystal damage depth profiles. The difference between the positions of damage profile maxima obtained by CSIM code and one simulated with stopping and range of ions in matter (SRIM), a Monte Carlo based computer code focused on ion implantation simulation in random crystal direction only, is about 10%. Therefore, due to small profile depth shifts, the usage of the iterative procedure for calculating crystal damage depth profiles is proposed. It was shown that profiles obtained by iterative procedure show very good agreement with the ones obtained with CSIM code. Additionally, with the introduction of channeling to random energy loss ratio the energy to depth profile scale conversion, the agreement with CSIM profiles becomes excellent.

The effect of Landau-Zener transitions on the ac-susceptibility

A model spin system S=1 with a strongly anisotropic g-factor is considered. Numerical calculations of the response of the system to an alternating magnetic field of low frequency are carried out. The influence of Landau--Zener transitions on the response of the system when it passes through the vicinity of the levels anti-crossing is studied. The ac-susceptibility is calculated and the effect of such transitions on the position of the ac-susceptibility maximum is analyzed. Keywords: level anti-crossing, quantum tunneling of magnetization, Landau--Zener transitions, ac-susceptibility, relaxation of magnetization.

Photoexcitation of oxazine 4 dye in aqueous solution: TD-DFT study

The vibronic absorption spectra of oxazine 4 (OX4) dye in an aqueous solution using 40 hybrid functionals, the 6–31++G(d,p) basis set, and the SMD solvent model were calculated. It turned out that the X3LYP functional provided the best agreement with the experiment in the positions of the main maximum and the short-wavelength shoulder. Our calculations showed that this shoulder is vibronic and is not caused by a separate electronic transition. At the same time, the shoulder intensity in the calculated spectrum turned out to be lower than in the experimental one. Various parameters of the OX4 cation in the ground and excited states (IR spectra, atomic charges, dipole moments, and transition moment) were calculated. Maps of the distribution of electron density and electrostatic potential have been built. The influence of four strong hydrogen bonds of the dye with water molecules on the absorption spectrum was analyzed. It has been shown that these bonds were strengthened upon OX4 excitation. It was found that explicit assignment of water molecules strongly bound to the dye leads to a redshift of the spectrum as a whole, but does not change its shape. Photoexcitation of the dye leads to a noticeable polarization of only one of the four considered water molecules (associated with the endocyclic nitrogen atom in the central ring of the chromophore, the electron density on which increases the most).

PECULIAR PROPERTIES OF ELECTROMAGNETIC RADIATION 
 PROPAGATION IN PHOTONIC CRYSTALLINE 
 METAL-DIELECTRIC SYSTEMS BASED ON OPALS

The article studies the propagation of electromagnetic waves in metal-dielectric systems based on opals. We revealed anomalous transmission and absorption of light by hybrid plasmon- photonic layered heterostructures associated with the excitation of surface plasmon polaritons propagating along the metal-dielectric interface. The position of maxima in the reflection spectra of nanocomposites, obtained by filling the opal matrix with metal by the electrothermodiffusion method, is explained by the Bragg diffraction, and the asymmetric form of the spectral curves is attributed to the Fano resonance.

Study of Atomic Oxygen Airglow Intensities and Air Temperature near Mesopause Obtained by Ground-Based and Satellite Instruments above Baikal Natural Territory

The research studied the comparison of the night air temperatures and the atomic oxygen airglow intensities at the mesopause obtained with satellite and ground-based instruments. Satellite data used in this study were obtained with the SABER limb-scanning radiometer operating aboard the TIMED satellite. Data of ground-based monitoring were obtained using the KEO Scientific “Arinae” Fabry–Pérot interferometer adapted for aeronomic research. Since an interferometer detects parameters of the 557.7 nm line for the entire emission layer, it is not quite appropriate to perform a direct comparison between the upper atmospheric temperature obtained from ground-based observations and that from a satellite at a particular height. To compare temperatures correctly, the effective temperature must be calculated based on satellite data. The effective temperature is a height-averaged temperature profile with the weight factors equal to the 557.7 nm line intensity at relevant heights. The height profile of intensity of this natural green airglow of the upper atmosphere is calculated from the height profile of atomic oxygen concentration. Data on chemical composition and air temperature at the mesopause from SABER were used to calculate the profiles. The night intensity of the 557.7 nm emission obtained from satellite data in this way was in good accordance with the results of ground-based observations, but the temperatures were different. The reason for temperature discrepancy was assumed to lie in the incorrect position of the intensity maximum of the reconstructed emission layer. According to our calculations based on SABER data, the intensity peak was observed at the height of 94–95 km. By shifting it relative to the SABER temperature height profile, we re-calculated the effective temperatures and compared them with the interferometer data. The best coincidence between seasonal temperature variations obtained using the proposed method was achieved when the maximum of the reconstructed 557.7 nm intensity height profile was shifted to 97 km, but it could not eliminate minor local differences in temperature behavior.

Temperature-induced orbital polarizations and tunable charge dynamics in layered double perovskite thin films

The realization of lead-free all-inorganic perovskites in emergent materials requires an in-depth understanding of strongly correlated systems toward optoelectronics or spintronics applications. Herein, we report the electronic and optical variation of the <111>-oriented layered double perovskites (LDP) family with the formula of Cs4MIIBi2Br12 thin films (where MII: Cu, Mn, Pb, or Sr). The element and shell-specific orbital polarization based on soft X-ray linear dichroism spectroscopy probes the Cs M4,5- and Mn L2,3- edges of Cs4MnBi2Br12 thin films as a function of temperature. A strong reversal orbital polarization at the respective edges at 150 K indicates a thermally induced orbital-selective rearrangement at low temperature. In addition, the valence band analysis indicates different orbital admixtures of Br 4p and MIId states, corroborated by the density functional theory calculations. In terms of the transient charge dynamics, we observe the photoluminescence peak maxima position trend line is shifted toward a longer wavelength. In addition, the longest average lifetime is recorded for Cs4CuBi2Br12 at 27.40 ± 1 μs. As the LDP structural integrity is lead-free, therefore, these all-inorganic perovskites hold promising potentials as sustainable and green materials for photophysics applications.

Environment-sensitive fluorogens based on a GFP chromophore structural motif

In this paper, we present a new series of arylidene-imidazolones with a structural motif of Green Fluorescent Protein chromophore with a pronounced solvent-dependent FQY variation. The identified structure-activity patterns made possible creation of a series of fluorogenic dyes with various positions of spectral maxima and Stokes shift. The developed dyes are cell-permeable and can be used for selective staining of the endoplasmic reticullum in living eukaryotic cells.

Vibronic absorption spectra and excited states of acridine red dye in aqueous solution: TD-DFT/DFT study

Abstract The vibronic absorption spectra of acridine red (AR) xanthene dye in an aqueous solution using 40 hybrid functionals, the 6-31++G(d,p) basis set, and the IEFPCM solvent model were calculated. It turned out that the O3LYP functional provided the best agreement with the experiment in the positions of the main maximum and the short-wavelength subband (shoulder). The calculations showed that this shoulder is vibronic. At the same time, the shoulder intensity in the calculated spectrum turned out to be lower than in the experimental one. Apparently, insignificant dimerization, which occurs even at low concentrations of the dye in solution, contributes to the shoulder of the experimental absorption spectrum. Various parameters of the AR cation in the ground and excited states (IR spectra, atomic charges, dipole moments, and transition moment) were calculated. Maps of the distribution of electron density and electrostatic potential have been built. The influence of the strong hydrogen bonds of the dye with three water molecules on the absorption spectrum was analyzed. It has been shown that these bonds are strengthened upon AR excitation. The strengthening of two hydrogen bonds with water upon excitation leads to a lowering of the potential energy surface of the excited state, which causes a decrease in the excitation energy (i.e., an increase in the wavelength of the absorbed photon) as compared to a purely implicit specification of the water environment. Therefore, explicit assignment of waters strongly bound to the dye leads to spectrum redshift.