Exchange Energy Research Articles

Magnetic Skyrmions Under Confinement

We present a variational treatment of confined magnetic skyrmions in a minimal micromagnetic model of ultrathin ferromagnetic films with interfacial Dzylashinksii-Moriya interaction (DMI) in competition with the exchange energy, with a possible addition of perpendicular magnetic anisotropy. Under Dirichlet boundary conditions that are motivated by the asymptotic treatment of the stray field energy in the thin film limit we prove existence of topologically non-trivial energy minimizers that concentrate on points in the domain as the DMI strength parameter tends to zero. Furthermore, we derive the leading order non-trivial term in the Γ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\Gamma $$\\end{document}-expansion of the energy in the limit of vanishing DMI strength that allows us to completely characterize the limiting magnetization profiles and interpret them as particle-like states whose radius and position are determined by minimizing a renormalized energy functional. In particular, we show that in our setting the skyrmions are strongly repelled from the domain boundaries, which imparts them with stability that is highly desirable for applications. We provide explicit calculations of the renormalized energy for a number of basic domain geometries.

Exchange energies and density functionals for systems of fermions of arbitrary spin

Exchange energies and density functionals for systems of fermions of arbitrary spin

Role of 4d electrons in room temperature ferromagnetism, and thermoelectric properties of Sr2CrXO6 (X = Nb, Mo) for spintronic applications

The spintronic is an emerging technology which controls the properties of multifactional devices with spin of electrons. In present manuscript, Wien2k and Boltz Trap codes are used to explore electronic, magnetic, and thermoelectric characteristics of Sr2CrXO6 (X = Nb, Mo) double perovskites (DPs). The evaluation of energies released in paramagnetic (PM), antiferromagnetic (AFM), and ferromagnetic (FM) states assure the stability of FM states. Both the negative formation energy and the tolerance factor confirm structural and thermodynamic stability in FM states. The 100 % spin polarization was confirmed by both integer values of magnetic moment (MM) and the spin polarization factor. The values of exchange energy, double exchange model, hybridization of p-d states, and exchange constants are calculated to explore the nature of ferromagnetism and spin functionality. The effect of thermoelectric parameters on spin of electrons and thermoelectric performance are elaborated by thermal to electrical conductivity ratio, Seebeck coefficient and power factor.

Social media and optimization of the promotion of Lake Toba tourism destinations in Indonesia

Tourism is one of the largest contributors to Indonesia's foreign exchange earnings, surpassing taxation, energy, and gas. This study seeks to investigate the use of social media to optimize the promotion of Lake Toba as a tourist destination, which has been impacted by the COVID-19 pandemic. Using interview techniques and live field observations, it was discovered that social media, particularly the Instagram platform, play a significant role in promoting Lake Toba tourism. The Department of Culture and Tourism of the North Sumatra Province uses landscape photography as its primary promotion method, which has proved to be more effective and interesting than conventional methods such as the distribution of brochures or the use of manuals. The capture procedure and techniques for landscape photography were carried out by professional photographers in collaboration with the Department of Culture and Tourism of the North Sumatra Province. In addition to providing information, tourism_sumut's Instagram account functions as a platform to raise public awareness about Lake Toba tourism and as a promotional medium for North Sumatra's tourist attractions on an international scale. Department of Culture and Tourism of the North Sumatra Province collaborates with travel agencies and local communities to disseminate Lake Toba tourism information.

Social media and optimization of the promotion of Lake Toba tourism destinations in Indonesia

Tourism is one of the largest contributors to Indonesia's foreign exchange earnings, surpassing taxation, energy, and gas. This study seeks to investigate the use of social media to optimize the promotion of Lake Toba as a tourist destination, which has been impacted by the COVID-19 pandemic. Using interview techniques and live field observations, it was discovered that social media, particularly the Instagram platform, play a significant role in promoting Lake Toba tourism. The Department of Culture and Tourism of the North Sumatra Province uses landscape photography as its primary promotion method, which has proved to be more effective and interesting than conventional methods such as the distribution of brochures or the use of manuals. The capture procedure and techniques for landscape photography were carried out by professional photographers in collaboration with the Department of Culture and Tourism of the North Sumatra Province. In addition to providing information, tourism_sumut's Instagram account functions as a platform to raise public awareness about Lake Toba tourism and as a promotional medium for North Sumatra's tourist attractions on an international scale. Department of Culture and Tourism of the North Sumatra Province collaborates with travel agencies and local communities to disseminate Lake Toba tourism information.

Assisted heat transfer enhancement in non-Newtonian dielectric fluids based on ion conduction phenomena

Electric field-assisted technologies show prospects for heat removal in electronic cooling scenarios with electro-thermo-convection phenomena. The coupled multiphysics field model is built using the finite volume method, and two configurations (depending upon the orientation of the electric field and gravity) are investigated for different shear-thinning properties and polymer elasticities. The results demonstrate a remarkable impact on the heat exchange efficiency, energy budget, plume morphology, and force distribution features. Two key partitions (buoyancy or Coulomb force-dominated regions) can be divided by Rayleigh number Ra ≤ 103 and electric Reynolds number ReE ≤ 1.57. A heat transfer boost of 13.9 times and 5.0 times was obtained in the two arrangements vs no electric reinforcement. The shear-thinning shows a noticeable positive contribution, and the heat transfer efficiency can be modulated by polymer elasticity within a wide parameter range. A detailed evaluation of the interfacial forces reveals the nonmonotonic curves of fluid convection and energy inputs.

Kinetic Energy Exchanges between a Two-Dimensional Front and Internal Waves

Abstract Fronts and near-inertial waves (NIWs) are energetic motions in the upper ocean that have been shown to interact and provide a route for kinetic energy (KE) dissipation of balanced oceanic flows. In this paper, we study these KE exchanges using an idealized model consisting of a two-dimensional geostrophically balanced front undergoing strain-induced semigeostrophic frontogenesis and internal wave (IW) vertical modes. The front–IW KE exchanges are quantified separately during two frontogenetic stages: an exponential sharpening stage that is characterized by a low Rossby number and is driven by the imposed strain (i.e., mesoscale frontogenesis), followed by a superexponential sharpening stage that is characterized by an Rossby number and is driven by the convergence of the secondary circulation (i.e., submesoscale frontogenesis). It is demonstrated that high-frequency IWs quickly escape the frontal zone and are very efficient at extracting KE from the imposed geostrophic strain field through the deformation shear production (DSP). Part of the extracted KE is then converted to wave potential energy. On the contrary, NIWs remain locked to the frontal zone and readily exchange energy with the ageostrophic frontal circulation. During the exponential stage, NIWs extract KE from the geostrophic strain through DSP and transfer it to the frontal secondary circulation via the ageostrophic shear production (AGSP) mechanism. During the superexponential stage, a newly identified mechanism, convergence production (CP), plays an important role in the NIW KE budget. The CP transfers KE from the convergent ageostrophic secondary circulation to the NIWs and largely cancels out the KE loss due to the AGSP. This CP may explain previous findings of KE transfer enhancement from balanced motions to IWs in frontal regions of realistic ocean models. We provide analytical estimates for the aforementioned energy exchange mechanisms that match well the numerical results. This highlights that the strength of the exchanges strongly depends on the frontal Rossby and Richardson numbers. Significance Statement Fronts with large horizontal density and velocity gradients are ubiquitous in the upper ocean. They are generated by a process known as frontogenesis, which is often initialized by straining motions of mesoscale balanced circulations. Here we examine the energy exchanges between fronts and internal waves in an idealized configuration, aiming to elucidate the mechanisms that can drain energy from oceanic balanced circulations. We identify a new mechanism for energy transfers from the frontal circulation to near-inertial internal waves called convergence production. This mechanism is especially effective during the later stages of frontogenesis when the convergent ageostrophic secondary circulation that develops is strong.

Key Transmission Section Search Based on Graph Theory and PMU Data for Vulnerable Line Identification in Power System

Failure of vulnerable lines in the power system often results in tidal shifts, and triggering chain failures and their corresponding transmission sections are concentrated manifestations of the weak links in the power system. It is very important to identify the vulnerable lines and search the transmission section to prevent the chain faults as well as to analyze the stability of the power system. Aiming at the problems of inaccurate search of vulnerable lines, difficulties adapting to the complex and changing power system as well as wrong selection and omission of transmission section search in the existing references, this paper proposes an algorithm for searching vulnerable lines and their key transmission sections based on the graph theory and PMU (phasor measurement unit) data. First, the method combines with the graph theory and PMU data to construct the grid topology map. Second, the comprehensive indicators for screening vulnerable lines are proposed by fully considering the network topology and line capacity, which combines with power exchange efficiency and energy fluctuation probability. Third, the distance matrix in the Floyd algorithm is transformed into a unit group that can store more elements, which reduces the traversal times of the algorithm and improves computational efficiency. The fast localization of transmission cross sections associated with vulnerable lines is realized. Finally, the critical transmission cross sections are screened according to the line outage distribution factor and line safety margin. The IEEE 39-bus system is selected for simulation experiments, and the simulation results show that the key transmission section search method proposed in this paper can better adapt to the variable power grid and is faster and more accurate than the other common method.

Lead-free silver-indium based halide double perovskites for energy harvesting applications

Herein, density functional theory (DFT) is utilized to analyze physical characteristics of two novel halide double perovskites (HDPs) Na2AgInBr6 and K2AgInBr6. Exchange and correlation energies were estimated via employing generalized gradient approximation (GGA) along with modified Becke-Johnson (mBJ) potential. Geometry optimization predicted nonmagnetic ground state for both HDPs with cubic structure having Fm3m space group. Computed formation enthalpies (ΔHf) and tolerance factors (τG) revealed the thermodynamically stability of both compounds in cubic phase. Na2AgInBr6 is regarded as brittle while K2AgInBr6 is ductile in nature. Na2AgInBr6 exhibited a band gap (Eg) of 1.39 eV while K2AgInBr6 has a Eg of 1.41 eV. Density of states analysis reveals that 4d of Ag- and 4p of Br states are majorly contributing in the higher valence band while In-5s and 4p of Br states are present in lower conduction band and all these states define the semiconductive nature of these systems. Both HDPs are optically active in visible light region suggesting the suitability for solar cell applications. Thermoelectric efficiency is also computed in terms of figure of merit (ZT(e)) whose values for both compounds are 0.7. Based on these outcomes, both HDPs can be considered as highly suitable candidates for energy harvesting applications.

Multicomponent solutions: Combining rules for multisolute osmotic virial coefficients.

This paper presents an exploration of a specific type of a generalized multicomponent solution model, which appears to be first given by Saulov in the current explicit form. The assumptions of the underlying theory and a brief derivation of the main equation have been provided preliminarily for completeness and notational consistency. The resulting formulae for the Gibbs free energy of mixing and the chemical potentials are multivariate polynomials with physically meaningful coefficients and the mole fractions of the components as variables. With one additional assumption about the relative magnitudes of the solvent-solute and solute-solute interaction exchange energies, combining rules were obtained that express the mixed coefficients of the polynomial in terms of its pure coefficients. This was done by exploiting the mathematical structure of the asymmetric form of the solvent chemical potential equation. The combining rules allow one to calculate the thermodynamic properties of the solvent with multiple solutes from binary mixture data only (i.e., each solute with the solvent), and hence, are of practical importance. Furthermore, a connection was established between the osmotic virial coefficients derived in this work and the original osmotic virial coefficients of Hill found by employing a different procedure, illustrating the equivalency of what appears to be two different theories. A validation of the combining rules derived here has been provided in a separate paper where they were successfully used to predict the freezing points of ternary salt solutions of water.

Rare earth based MgPm2X4 (X = S, Se) spinel chalcogenides for spintronic and thermoelectric applications

In current report, the structural, magnetic, and thermoelectric properties of RE doped MgPm2X4 (X = S, Se) spinels were investigated. The energy difference in ferromagnetic and antiferromagnetic states reveals the stability of MgPm2(S/Se)4 in the ferromagnetic states. The computation of enthalpy of formation also ascertains thermodynamic stability of crystal structure. Spin-dependent band structure and density of states analysis reveal ferromagnetic semiconducting character showing different electronic behavior in both spin channels. The room temperature ferromagnetism, spin polarization and Curie temperature are estimated from exchange energies analysis. In addition, exchange constants (N0α and N0β), exchange energy Δx(pd), crystal field energy, and double exchange mechanism were studied to explore the magnetic response. Likewise, the electrical conductivity, thermal conductivity, Seebeck co-efficient, and power factor show effect on electrons spin and their potential for thermoelectric devices.

Study of curie temperaure, spin polarization, ferromagnetism and transport behavior of Ba2CrXO6 (X = Ta, W, Re, Os) for spintronic

The double perovskites (DPs) have become emerging aspirant for spintronic technology because of their stable, and multifunctional properties. Here in present article, the role 5d-electrons of Ta, W, Re, and Os in ferromagnetism, and thermoelectric behavior has been illustrated briefly. The ideal values of tolerance factor, formation energy and phonons dispersions are reported for structural, thermodynamic, and lattice dynamic stabilities. The higher Curie temperature and spin polarization has been addressed by Heisenberg model and spin density calculations. The ferromagnetism has been explained by the metallic and insulating channels of spin up and spin down configuration through hybridization, exchange energies, and exchange constants. The shifting of magnetic moments from Cr and X sites to Ba, O and interstitial sites ensures the exchange coupling due to spin of electrons rather than clustering. Furthermore, thermoelectric effect on the spin degree of electrons and transport characteristics are calculated by BoltzTraP code.

Computational Modeling of Gold Nanoparticle Interacting with Molecules of Pharmaceutical Interest in Water.

We derived a theory of biomolecule binding to the surface of Aun clusters and of the Au plane based on the hard soft acid base (HSAB) principle and the free electron metallic surface model. With the use of quantum mechanical calculations, the chemical potential (μ) and the chemical hardness (η) of the biomolecules are estimated. The effect of the gold is introduced via the empirical value of the gold chemical potential (-5.77 eV) as well as by using the expression (modified here) for the chemical hardness (η). The effect of an aqueous environment is introduced by means of the ligand molecular geometry influenced by the PCM field. This theory allows for a fast and low-cost estimation of binding biomolecules to the AuNPs surface. The predicted binding of thiolated genistein and abiraterone to the gold surface is about 20 kcal/mol. The model of the exchange reaction between these biomolecules and citrates on the Au surface corresponds well with the experimental observations for thiolated abiraterone. Moreover, using a model of the place exchange of linear mercaptohydrocarbons on 12-mercaptododecane acid methyl ester bound to the Au surface, the present results reflect the known relation between exchange energy and the size of the reagents.

Determination of thermodynamic properties and phase transition temperatures of phenylbenzoate-based calamitic liquid crystals by inverse gas chromatography method

ABSTRACT In this study, Phenylbenzoate-based calamitic liquid crystals (LCs) were synthesized and characterized, and then the thermodynamic properties and phase transition temperatures were investigated by inverse gas chromatography (IGC) at infinite dilution. The phase transition temperatures of the LCs were determined in the range of 40–170°C by the IGC method. Finally, in the thermodynamic equilibrium region (the range of 160–200°C), Flory-Huggins theory and the equation of state theory with the LC-solvent interaction parameters, the effective exchange energy parameters, the weight fraction activity coefficient, and also the partial molar heat of mixing at infinite dilution of solvent, the molar heat of vaporization of solvent, and the partial molar heat of sorption of solvent were calculated.

Agrophysical properties of soil depending on crops of grass field crop root summary

Relevance. The agrophysical state of the soil is essential for the successful development of agricultural production. The purpose of the study is to study the influence of grass-field crop rotation on the agrophysical, biological properties of soil fertility and crop productivity in the forest-steppe zone of North Ossetia — Alania.Methodology. The studies were carried out in 2020–2022 in the field stationary crop rotation of the in the conditions of the forest-steppe zone of the North Ossetia — Alania . The soil of the experimental plot is represented by leached chernozems on pebbles. Bookmarking experiments, phenological observations, statistical processing of the data obtained was carried out according to generally accepted methods.Results. It was found that at the beginning of the growing season, the lumpy fraction under crop rotation varied from 13.34 to 49.45%, in the macrostructure — from 48.42 to 81.77%, for an aggregate 0.25 mm thick — from 1.77 up to 7.99%. By the end of the growing season, the proportion of dusty fraction under winter wheat decreased from 8.01 to 1.09%. The structural coefficient varied from 2.22% (corn) to 2.49% (oats + clover). Studies have shown that the studied soil has a good structure, since it contains from 46.0 to 66.2% of water-stable aggregates. On crops of oats + clover (average (0–30 cm) soil layer), the soil density was 0.95 g/cm3 at the beginning of the growing season, 1.19 g/cm3 — during the period of intensive growth, 1.22 g/cm3 — in the end of the growing season. This trend is manifested in all crop rotation crops. It should be noted that grass links are more productive, where the collection of fodder units (16.37 t/ha) exceeds the indicators of the tilled link by 1.98 t/ha. In general, the exchange energy of the grass-field link of the crop rotation turned out to be 2.17 GJ/ha more than the tilled one and amounted to 13.43 GJ/ha.

Fostering mica exfoliation through biaxial straining strategy with monovalent cation substitution

Efficiently exfoliating mica for 2D applications remains a challenge, partly due to a lack of comprehensive design principles based on atomistic modelling of its solid mechanics. In this investigation, we employed a threefold approach: (1) Biaxial straining principles were utilized to compute electron–electron, electron–phonon, and phonon–phonon interactions at crack tips, (2) first-principles calculations were employed to explore the intrinsic relationship between muscovite mica's crystalline structure, electronic properties, ion exchange energy, and exfoliation energy, particularly in the context of various interlayer cations, and (3) experiments were conducted to corroborate the theoretical forecasts. Our findings reveal a compelling correlation between the unit cell size and the ionic radius of the interlayer cation, a phonon-dependent parameter, whereas the bandgap energy, an electron-dominant parameter, remains relatively unaffected. The electron–phonon interactions, characterized by the dihedral angle and size of the hexagonal tetrahedral ring, are influenced by the properties of the interlayer cation, crucially governing ion exchange and exfoliation energy. Significantly, mica featuring H+ interlayer cations demonstrates substantial biaxial strains, aligning with the lowest exfoliation energy, thereby facilitating efficient exfoliation. Our experimental endeavors validate that Li+ intercalation prompts a reduction in number of layers in resulted nanosheets, observed in the order of Li+ nanosheets < Na+ nanosheets < K+ nanosheets. Notably, Li+ intercalation enhances mica's exfoliation into thinner nanosheets. We propose a strategic biaxial straining approach: either replacing the interlayer cation with the smallest cation (H+) or employing larger cations within the boundaries of ion exchange. These outcomes contribute valuable insights into mica's exfoliation mechanisms and furnish a comprehensive guideline for proficiently exfoliating layer-structured materials.

Energy exchange in the body of broilers when introducing Quercus cortex extract and chlortetracycline into the diet

Feed antibiotics are widely used in the diet of poultry as growth stimulants, to maintain health and increase productivity. However, their use carries some risks, which leads to a reduction in the use of antibiotics in diets. Therefore, the search for an alternative that can minimize the negative effect of antibacterial substances is a global task. Plants containing phytochemical compounds are of great interest in the search. One of such phytobiotics is oak bark (Quercus cortex), some of its components act as agents of alternative antibacterial strategies (blocking of the Quorum Sensing signaling system (QS)). However, studies on the effects of Quercus cortex are few. It is interesting to study the additional effects of this phytobiotic in combination with other biologically active substances (probiotics, enzymes and antibiotics in small doses). Based on this, the purpose of this work was to evaluate the effect of Quercus cortex extract and Biovit 200 feed antibiotic based on 20% chlortetracycline on energy metabolism in broiler chickens. The study was conducted using generally accepted methods of analyzing metabolic processes in the body of a bird. The calculation of net and exchange energies, energy protein ratio, coefficient of productive use of exchange energy, gross energy was made. The results obtained allow us to conclude that the inclusion of Quercus cortex extract at a dosage of 0,2 ml/kg both independently and in combination with Biovit 200 at a dosage of 0,63 g/kg w.m./ day contributed to a reduction in the amount of energy loss with excrement with an increase in the KPI of OE and the compliance indicator, which shows a more rational use of energy for the process of tissue synthesis in the body of birds of I and III groups.

SIRT1 induction in the skeletal muscle of male mice partially attenuates changes to whole-body metabolism in response to androgen deprivation

In males, androgens regulate whole body metabolism. The components in androgen target organs contributing to whole-body metabolic function remain ill defined. Sirtuin1 (SIRT1) protein levels are lower in the limb muscle of male mice subjected to androgen deprivation. Because SIRT1 can influence whole-body metabolism, the purpose was to assess whether muscle specific SIRT1 induction attenuated changes to whole-body metabolism in response to androgen deprivation. Physically mature male mice containing an inducible muscle specific SIRT1 transgene (SIRT1) were subjected to a sham or castration surgery and compared to sham and castrated male mice where the SIRT1 transgene was not induced (WT). The respiratory exchange ratio (RER), energy expenditure, and carbohydrate and fat oxidation rates were determined using metabolic cages. Castration lowered RER in WT mice and the lower RER coincided with lower energy expenditure, lower carbohydrate oxidation rates, and higher fat oxidation rates. SIRT1 induction attenuated the castration-induced changes to RER and fat oxidation rates. Changes to energy expenditure and glucose oxidation rates were not affected by SIRT1. Decreases in muscle SIRT1 protein in males may partially contribute to the dysregulation of whole-body metabolism in response to androgen deprivation.

Exploiting the (-C-H···C-) Interaction to Design Cage-Functionalized Organic Superbases and Hyperbases: A Computational Study.

A set of carbon center-based P-ylidesubstituting bases have been exploited computationally with pentacyclo[5.4.0.02,6.03,10.05.9]undecane (PCU) and pentacyclo [6.4.0.02,7.03,11.06,10] dodecane (PCD) scaffolds using the B3LYP-D3/6-311+G(d,p) level of theory. The proton affinities calculated in the gas phase are in the range of superbases and hyperbases. The Atomsin-Molecules and Natural Bond Orbital calculations reveal that the -C-H···C- interaction plays a substantial role in improving the basicity, and tuning the -C-H···C- interaction can enhance the basicity of such systems. The free activation energy for proton exchange for PCD and PCU scaffolds substituted with P-ylide is substantially low. The computed results reveal the strength and nature of such - C-H···C- interactions compared to the -N-H···N- hydrogen bonds. The isodesmic reactions suggest that the superbasicity achieved using these frameworks arises from a combination of several factors, such as the ring strain of the bases in their unprotonated form, steric repulsion, and the intramolecular -C-H···C- interaction.

Real-Time Hierarchical MPC Applied to an MMC in Grid-Forming Mode: Implementation and Validation in Power Hardware-in-The-Loop

Modular Multilevel Converters (MMC) are now expected to fulfill AC and DC grid stability functions while at the same time they must ensure their own operation. In this paper, we propose a new MIMO control structure to coordinate the AC/DC power exchange and MMC internal energy control using a hierarchical MPC. This controller is tested on an AC/DC system where the MMC works in grid-forming mode on the AC side and controls the DC-grid voltage at the same time. This MPC solution is implemented in a real-time controller to operate a physical mockup of a 6kVA MMC which contains 60 submodules and interfaces a 400V DC grid and a 120V (line-to-ground) AC grid. The MPC solution shows similar tracking performance with the state-of-the-art dual PI control solution based on two PI controllers working in parallel, and exhibits a better disturbance rejection capacity than this dual PI.