Calculation Of Spectra Research Articles

Analysis of Possible Interference Effects Minimization in IEEE 802.11ax Network by Partial Allocation of Resource Units

Statement of the problem: one of the main tasks in IEEE 802.11 networks planning is adjacent channel interference mitigation. The purpose of the work is to synthesize a model and analyze the possibility of adjacent channel effects minimization by partial allocation of OFDMA resource units allocation. Methods used: mathematical analysis methods and spectrum modeling. Novelty: in contrast to the existing approaches, quantative estimations of data rate gain has been calculated and a corresponding step-by-step method has been proposed. Result: in this paper an analysis of partial allocation of resourve units within IEEE 802.11ax channel has been carried out. A model of the adjacent channel interference has been proposed, where signal to noise ratio is estimated via spectrum calculation of target and interferer signals. The model parameters range is estimated which corresponds to the gain of total multi user data rate gain in comparison to full target channel resource units utilization. Theoretical and practical relevance: method may be used to additional increase of total data rate in multi user channel operation mode in case of IEEE 802.11 networks interference presence.

Discovery of antifungal secondary metabolites from an intestinal fungus Fusarium sp.

Intestinal fungi, which are important parts of the gut microbiota, have the ability to produce specialized metabolites that significantly contribute to maintaining the balance of the gut microbiota and promoting the health of the host organism. In the present study, two new glycosides, including fusintespyrone A (1) and cerevisterolside A (4), as well as ten known compounds were isolated from the intestinal fungus Fusarium sp. LE06. The structures of the new compounds were elucidated by a combination of spectroscopic methods, such as mass spectrometry (MS) and nuclear magnetic resonance (NMR), along with chemical reactions and calculations of NMR and ECD spectra. Compounds 1-3 showed significant growth inhibition against Aspergillus fumigatus, Fusarium oxysporum, and Verticillium dahliae with MIC values in the range of 1.56-6.25 μg ml-1.

Scaling Exponents of Time Series Data: A Machine Learning Approach.

In this study, we present a novel approach to estimating the Hurst exponent of time series data using a variety of machine learning algorithms. The Hurst exponent is a crucial parameter in characterizing long-range dependence in time series, and traditional methods such as Rescaled Range (R/S) analysis and Detrended Fluctuation Analysis (DFA) have been widely used for its estimation. However, these methods have certain limitations, which we sought to address by modifying the R/S approach to distinguish between fractional Lévy and fractional Brownian motion, and by demonstrating the inadequacy of DFA and similar methods for data that resembles fractional Lévy motion. This inspired us to utilize machine learning techniques to improve the estimation process. In an unprecedented step, we train various machine learning models, including LightGBM, MLP, and AdaBoost, on synthetic data generated from random walks, namely fractional Brownian motion and fractional Lévy motion, where the ground truth Hurst exponent is known. This means that we can initialize and create these stochastic processes with a scaling Hurst/scaling exponent, which is then used as the ground truth for training. Furthermore, we perform the continuous estimation of the scaling exponent directly from the time series, without resorting to the calculation of the power spectrum or other sophisticated preprocessing steps, as done in past approaches. Our experiments reveal that the machine learning-based estimators outperform traditional R/S analysis and DFA methods in estimating the Hurst exponent, particularly for data akin to fractional Lévy motion. Validating our approach on real-world financial data, we observe a divergence between the estimated Hurst/scaling exponents and results reported in the literature. Nevertheless, the confirmation provided by known ground truths reinforces the superiority of our approach in terms of accuracy. This work highlights the potential of machine learning algorithms for accurately estimating the Hurst exponent, paving new paths for time series analysis. By marrying traditional finance methods with the capabilities of machine learning, our study provides a novel contribution towards the future of time series data analysis.

Thermoelectric Power and Hall Effect in Correlated Metals and Doped Mott–Hubbard Insulators: DMFT Approximation

We present comparative theoretical investigation of thermoelectric power and Hall effect in the Hubbard model for correlated metal and Mott insulator (considered as prototype cuprate superconductor) for different concentrations of current carriers. Analysis is performed within standard DMFT approximation. For Mott insulator we consider the typical case of partial filling of the lower Hubbard band (hole doping). We calculate the dependence of thermopower on doping level and determine the critical concentration of carriers corresponding to sign change of thermopower. An anomalous dependence of thermopower on temperature is obtained significantly different from linear temperature dependence typical for the usual metals. The role of disorder scattering is analyzed on qualitative level. The comparison with similar studies of the Hall effect shows, that breaking of electron-hole symmetry leads to the appearance of the relatively large interval of band-fillings (close to the half-filling) where thermopower and Hall effects have different signs. We propose a certain scheme allowing to determine the number of carriers from ARPES data and perform semi-quantitative estimate of both thermopower and Hall coefficient using the usual DFT calculations of electronic spectrum.

Exploring the fluorescence action spectrum of photosynthesis

The mathematical study of the fluorescence action spectrum of photosynthesis was performed. The calculation of typical spectra for photosynthesis was done for the red and blue frequencies. The transition of the action spectrum of photosynthesis from wavelengths to the frequency scale was completed. A numerical method based on the use of the inverse Fourier transform approach was used to obtain a relaxation curve for the impulse (time) characteristic of fluorescence. It turned out that the radius vector of the module of impulse response in polar coordinates makes one half-turn or half of the period of light oscillations in time. It was established that the optical medium of a plant during the relaxation time has a negative space charge of electrons, inverse properties and properties of the coherent radiation. The condition of neutrality of the material environment is not met. It was found that the ratio of the variable chlorophyll fluorescence for red and blue light has almost the same value. An analysis of the dependence of the quality factor of the chlorophyll spectrum on frequency shows that the fluorescence energy loss in blue light significantly exceeds the energy loss in red light. The proposed method can be used for express analysis of the intensity of photosynthesis. It was also concluded that plants can emit ultra-wideband signals. The relaxation time of chlorophyll fluorescence is shorter than the relaxation time of electronic polarization in atoms (molecules). As a result, a population inversion is created in the optical medium of chlorophyll - there are more atoms in the upper energy level than in the lower level. Due to this, stimulated emission and amplification of light of the radiative recombination occur. In this case, the emission of fluorescence light becomes coherent. All these properties of plants are considered for the first time and have not been described either in domestic or in foreign articles.

Global comparison between experimentally measured isomeric yield ratios and nuclear model calculations

The level density steers transition probabilities between different states in the decay and de-excitation of excited nuclei. Reliable level density modelling is, therefore, key in describing, e.g., de-excitation of fission fragments, with implications on neutron and gamma-rays multiplicities, and also manifested in the population of isomeric states. We test six currently used level density models and the spin distribution in the level density by comparing calculations with measured isomeric yield ratios. The model calculations are performed with the TALYS code and experimental data for nuclear reactions populating spin isomers are retrieved from the EXFOR database. On average, calculations are in agreement with measured data. However, we find that the population of the high-spin state in an isomeric pair is clearly favoured in all of the six studied level density models. Further studies are then performed on the three used phenomenological level density models, to investigate the significance of their effect. We find that a significant reduction of the spin width distribution improves the agreement between calculated and experimentally observed isomeric yield ratios. This result is independent of the incident particle in the nuclear reaction. The needed reduction of the spin width distribution to comply with empirical data has, e.g., implications for studies in angular momentum generation in fission using isomeric yield rations, calculations of anti-neutrino spectra from nuclear reactors, as well as neutron and gamma-ray multiplicities in nuclear reactor calculations.

Vibrational Spectra of Highly Anharmonic Water Clusters: Molecular Dynamics and Harmonic Analysis Revisited with Constrained Nuclear-Electronic Orbital Methods.

Vibrational spectroscopy is widely used to gain insights into structural and dynamic properties of chemical, biological, and materials systems. Thus, an efficient and accurate method to simulate vibrational spectra is desired. In this paper, we justify and employ a microcanonical molecular simulation scheme to calculate the vibrational spectra of three challenging water clusters: the neutral water dimer (H4O2), the protonated water trimer (H7O3+), and the protonated water tetramer (H9O4+). We find that with the accurate description of quantum nuclear delocalization effects through the constrained nuclear-electronic orbital framework, including vibrational mode coupling effects through molecular dynamics simulations can additionally improve the vibrational spectrum calculations. In contrast, without the quantum nuclear delocalization picture, conventional ab initio molecular dynamics may even lead to less accurate results than harmonic analysis.

Positron spectroscopy of γ-flashes in the earth atmoshear

The registration of the fast thermonuclear transformation in Earth’s atmosphere is considered. One of them is γ-flashes from thunder lightning. The atmospheric chemical composition and bound conditions in the thunder lightning plasma tubes were associated with thermonuclear transformation. Nuclear reaction channel cross-sections were selected for the calculation of the γ-ray spectra. It was found that under existing conditions the γ-spectrum is formed due to the formation of unstable proton-excess nuclei with their further decay. It has been shown that electron-atom collisions are important and only initiate the formation of proton and fully ionized He (after sufficient acceleration, we call them α-particles) current flows. In this case, protons and α-particles initiate nuclear transformation after collisions with atmospheric He, C, N, O, and Ne atoms. The time scale of γ-fluorescence is estimated and related to observation with traditional γ-ray detectors. Separately calculated contribution of pollution admixture from dust into γ-spectra.

First Simulations for the EuAPS Betatron Radiation Source: A Dedicated Radiation Calculation Code

X-ray production through betatron radiation emission from electron bunches is a valuable resource for several research fields. The EuAPS (EuPRAXIA Advanced Photon Sources) project, within the framework of EuPRAXIA, aims to provide 1–10 keV photons (X-rays), developing a compact plasma-based system designed to exploit self-injection processes that occur in the highly nonlinear laser-plasma interaction (LWFA) to drive electron betatron oscillations. Since the emitted radiation spectrum, intensity, angular divergence, and possible coherence strongly depend on the properties of the self-injected beam, accurate preliminary simulations of the process are necessary to evaluate the optimal diagnostic device specifications and to provide an initial estimate of the source’s performance. A dedicated tool for these tasks has been developed; electron trajectories from particle-in-cell (PIC) simulations are currently undergoing numerical analysis through the calculation of retarded fields and spectra for various plasma and laser parameter combinations. The implemented forward approach evaluation of the fields could allow for the integration of the presented scheme into already existing PIC codes. The spectrum calculation is thus performed in detector time, giving a linear complex exponential phase; this feature allows for a semi-analitical Fourier transform evaluation. The code structure and some trajectories analysis results are presented.

First-principles calculation of Si–C–N structures with metallicity and high hardness

Stable hard and conductive ceramics under ambient conditions are vital for many industrial applications. However, maintaining high hardness while achieving semiconducting-metallic transition in Si3N4 materials is greatly challenging both experimentally and theoretically. Herein, two hexagonal Si–C–N structures, denoted SiC6N7-1 and SiC6N7-2, were constructed using α-Si3N4 as a matrix model. Calculations of elastic constants and phonon spectra showed stable structures under ambient pressure. Both SiC6N7-1 and SiC6N7-2 can possibly be synthesized at the pressures attainable by large-volume press technology. Compared to a-Si3N4, both Si–C–N ternary compounds achieved a semiconductive-metallic transition owing to the elemental substitution. Property calculations showed conductive Si–C–N compounds with high hardness values of 52 GPa for SiC6N7-1 and 31 GPa for SiC6N7-2. Therefore, the introduction of C atoms tuned the intrinsic properties of both structures, achieving high hardness along with good electrical conductivity. Overall, these findings look promising for future design and synthesis paths of novel conductive ceramics with prospective applications.

Electron interaction with point defects in CdSe0.35Te0.65: joining of ab initio approach with short-range principle

This study examines the problem of influence of point defects on transport phenomena in CdSexTe1-x (x=0.35) crystals. For the first time, the calculation of the electronic spectrum, wave function and potential energy of the electron in CdSe0.35Te0.65 samples at a prearranged temperature was carried out. Using the supercell method, the types of point defects were established, as well as the temperature dependence of their ionization energies in the studied temperature range. The temperature dependences of the deformation constants of the optical and acoustic scattering potentials were detected and also calculated the dependences on temperature of electron scattering constants on different crystal point defects. Temperature dependences of the mobility and Hall factor of electrons were found based on the scattering models on the short-range potential.

Umbrella-like Helical Structure of α-Synuclein at the Air-Water Interface Observed with Experimental and Theoretical Sum Frequency Generation Spectroscopy.

The misfolding of α-synuclein (αS) into amyloid aggregates is catalyzed by hydrophobic surfaces and associated with severe brain disorders, such as Parkinson's disease. Despite the important role of interfaces, the three-dimensional structure of αS at the interfaces is still not clear. We report interface-specific sum frequency generation (SFG) experiments of monomeric αS binding to the air-water interface, a model system for the important hydrophobic surfaces. We combine the SFG spectra with calculations of theoretical spectra based on molecular dynamics simulations to show that αS, which is an intrinsically disordered protein in solution, folds into a defined, mostly helical secondary structure at the air-water interface. The binding pose resembles an umbrella shape, where the C-terminus protrudes into the water phase, while the N-terminus and the NAC region span the canopy at the interface. In this binding pose, αS is prone to aggregate, which could explain the catalytic effect of hydrophobic interfaces and air bubbles on αS fibrillation.

The bain and orthorhombic paths of the bcc–fcc transformation in a bcc metal

The energy of the Bain and orthorhombic paths in niobium and the instability of phonons during uniaxial deformation along <001> are studied with the application of the ab initio method. The orthorhombic transformation path is refined with regard to its symmetry. The calculation of the phonon spectrum in the entire irreducible Brillouin zone depending on deformation makes it possible to find the softest branches of the phonon spectrum responsible for the loss of stability of the structure. The nature of the loss of stability is revealed, and the strain at which stability is lost both in tension and compression is evaluated. Possible mechanisms determining the stability of the structure and theoretical strength of niobium are discussed. The results obtained can relate to experimental situations when small defect-free regions are deformed, for example, in nanostructured materials, when surface layers are modified by modern methods of plastic deformation, and during nanoindentation.

Insight into synergistic corrosion inhibition of sodium benzoate and sodium silicate on LZ91 magnesium alloy: Experimental and theoretical calculations

The synergistic inhibition effect of sodium benzoate (SB) and sodium silicate (SS) on LZ91 magnesium alloy in 3.5 wt.% NaCl solution was investigated by electrochemical testing, In situ microscopic observation, Fourier transform infrared spectrum and theoretical calculations. The combined electrochemical test and in-situ microscopic observation results demonstrated that the highest inhibition efficiency was 92.3 % at the concentration of 0.1 M SB and 0.015 M SS, while the compound inhibitors displayed excellent synergistic corrosion inhibition even after 48 h of immersion. Sodium benzoate is mainly absorbed on the surface of LZ91 alloy, whereas sodium silicate is preferentially adsorbed on the local corrosion. Theoretical calculations indicated that silicate enhances the spontaneous adsorption of benzoate onto the surface of MgO. The adsorption energy significantly increased from -16.4 to -35.5 kJ/mol, transforming the adsorption of SB on the MgO surface from weak physical adsorption to stronger physical-chemical adsorption. Finally, the corrosion mechanism of LZ91 alloy in 3.5 wt.% NaCl solution with and without 0.1 M SB and 0.015 M SS was discussed. In view of the high corrosion resistance of compound inhibitors, this research may have potential applications for protecting transportation pipelines against corrosion.

Development of sweeping detector phase contrast imaging in Large Helical Device

Phase contrast imaging (PCI) has been used for the turbulence profile measurement in Large Helical Devices; however, it does not have sufficient spatial resolution owing to the small number of two-dimensional (2D) detector elements. Therefore, in this study, we limited the measurement target to steady-state plasmas and conduct a pseudo multichanneling of a 2D detector array by sweeping using a one-dimensional detector. This new system is called SD-PCI. SD-PCI needs two detectors, one is one-dimensional detector and the other is single channel detector. By selecting suitable detector and imaging magnification for target turbulence or device characteristics, SD-PCI demonstrates the potential capability and enhancements. The wavenumber spectra comparison from the correlation calculations of the simultaneous measurement of the actual plasma with conventional 2D-PCI and proposed SD-PCI shows that SD-PCI is as effective as 2D-PCI in spectral broadening. The simplicity of the proposed system is expected to be applicable to various devices. In this paper, the SD-PCI system was explained along with the initial results of the 2D wavenumber spectrum calculation, which was necessary for obtaining turbulence profile.

Band structure optimization of superconducting photonic crystals based on transmission spectrum calculation

The design of photonic crystals using novel materials is of great significance for the construction of high-performance, next-generation photonic crystal devices. We propose a universal Band structure-Transmission optimization-Band structure method based on moving asymptotic (MMA) method, which can be widely applied to photonic crystal structures. In this paper, we use the method to optimize the band structure of high temperature superconducting photonic crystal, and obtain a wider photonic bandgap and better band flatness in a specific frequency band. This method avoids the disadvantages of traditional scanning methods such as low efficiency and high resource consumption, allows multi-parameter optimization, and improves the accuracy and effectiveness of band modulation based on the iterative process of numerical calculation. The study provides some insights for the design of novel wide-bandgap optical devices.

Optical properties of charged defects in monolayer MoS2

We present theoretical calculations of the optical spectrum of monolayer MoS2 with a charged defect. In particular, we solve the Bethe–Salpeter equation based on an atomistic tight-binding model of the MoS2 electronic structure which allows calculations for large supercells. The defect is modelled as a point charge whose potential is screened by the MoS2 electrons. We find that the defect gives rise to new peaks in the optical spectrum approximately 100–200 meV below the first free exciton peak. These peaks arise from transitions involving in-gap bound states induced by the charged defect. Our findings are in good agreement with experimental measurements.

Improved Huygens’ Principle for Metamaterial

In this paper, we propose a new method based on Huygens’ principle for calculations of transmission spectra with weak coupling and we call this method an improved Huygens’ principle. The original Huygens’ principle for metamaterial can only deal with transmission spectra without coupling between metamaterial structures. Our improved Huygens’ principle can give the approximate calculations of transmission spectra while considering coupling by employing the original Huygens’ principle. We demonstrate our method by employing full-wave simulations and experimental results.

Cu3 BiS3 : Two-Dimensional Coordination Induces Out-of-Plane Phonon Scattering Enabling Ultralow Thermal Conductivity.

The discovery of compounds with low thermal conductivity and the understanding of their microscopic mechanisms are of great challenges and scientific significance. Herein, we report a unique ternary sulfide compound, Cu3 BiS3 , in which all Cu atoms are coordinated within a two-dimensional [CuS3 ] triangle plane. This local coordination leads to efficient out-of-plane phonon scattering and an ultralow thermal conductivity. Through DFT phonon spectrum calculations and analyses, we reveal that the lowest vibration frequency decreases from 2 THz for high-dimensional [CuS4 ] tetrahedral coordinated Cu atoms in CuBiS2 (CN=4, with an average Cu-S bond length of 2.328 Å) to 1.5 THz for low-dimensional [CuS3 ] triangular coordinated Cu atoms in Cu3 BiS3 (CN=3, with a shorter Cu-S bond length of 2.285 Å). This is due to the out-of-plane thermal vibration of the Cu atoms in the latter. Consequently,Cu3 BiS3 exhibits one of the lowest values of κlat (0.32 W/m K) among its peer, with a 36 % reduction compared to CuBiS2 (0.50 W/m K). This groundbreaking discovery highlights the significant role of 2D local coordination in reducing thermal conductivity through characteristic out-of-plane phonon scattering, while also contributing to a large Grüneisen parameter (2.06) in Cu3 BiS3 .

Cu3BiS3: Two‐Dimensional Coordination Induces Out‐of‐Plane Phonon Scattering Enabling Ultralow Thermal Conductivity

AbstractThe discovery of compounds with low thermal conductivity and the understanding of their microscopic mechanisms are of great challenges and scientific significance. Herein, we report a unique ternary sulfide compound, Cu3BiS3, in which all Cu atoms are coordinated within a two‐dimensional [CuS3] triangle plane. This local coordination leads to efficient out‐of‐plane phonon scattering and an ultralow thermal conductivity. Through DFT phonon spectrum calculations and analyses, we reveal that the lowest vibration frequency decreases from 2 THz for high‐dimensional [CuS4] tetrahedral coordinated Cu atoms in CuBiS2 (CN=4, with an average Cu−S bond length of 2.328 Å) to 1.5 THz for low‐dimensional [CuS3] triangular coordinated Cu atoms in Cu3BiS3 (CN=3, with a shorter Cu−S bond length of 2.285 Å). This is due to the out‐of‐plane thermal vibration of the Cu atoms in the latter. Consequently,Cu3BiS3 exhibits one of the lowest values of κlat (0.32 W/m K) among its peer, with a 36 % reduction compared to CuBiS2 (0.50 W/m K). This groundbreaking discovery highlights the significant role of 2D local coordination in reducing thermal conductivity through characteristic out‐of‐plane phonon scattering, while also contributing to a large Grüneisen parameter (2.06) in Cu3BiS3.