Dependence Of Parameters Research Articles

Thermal and magnetoelastic properties of the van der Waals ferromagnet Fe3−δGeTe2 : Anisotropic spontaneous magnetostriction and ferromagnetic magnon excitations

By determining the lattice parameters as a function of temperature of the hexagonal van der Waals ferromagnet Fe2.92(1)Ge1.02(3)Te2 we obtain the temperature dependence of the spontaneous in-plane magnetostriction in the ferromagnetic and the linear thermal expansion coefficients in the paramagnetic state. The spontaneous magnetostriction is clearly seen in the temperature dependence of the in-plane lattice parameter a(T), but less well pronounced perpendicular to the planes along c. Below TC the spontaneous magnetostriction follows a power law M(T)3/2 of the magnetization and leads to an expansion of the hexagonal layers. Extrapolating to T→ 0 K we obtain a spontaneous in-plane saturation magnetostriction of λsp,a(T→0)≈−220×10−6. In the paramagnetic state the linear thermal expansion coefficients amount to 13.9(1)×10−6K−1 and to 23.2(2)×10−6K−1 for the in-plane and out-of-plane direction, respectively, indicating a linear volume thermal expansion coefficient of 50.8(4)×10−6K−1 which we use to estimate the volume thermal expansion contribution to the heat capacity determined at constant pressure. A Sommerfeld-type linear term in the low-temperature heat capacities can be quantitatively ascribed to two-dimensional (2D) ferromagnetic magnon excitations. Published by the American Physical Society 2024

MODELING OF SPATIAL-TEMPORAL VARIATIONS OF PHYSICAL PROCESS PARAMETERS IN THE IONOSPHERIC PLASMA OVER UKRAINE DURING THE MAXIMUM PHASE OF THE 24-TH SOLAR ACTIVITY CYCLE (2012—2015)

The object of research is physical processes occurring in the ionospheric plasma. The subject of research: spatial-temporal variations of the main parameters of the ionospheric plasma, which were obtained using incoherent scatter radar. Research methods include the ground-based radiophysical method of incoherent scatter of radio waves, statistical analysis of observation results, and semi-empirical modeling of parameters of dynamic and thermal processes. Modeling and analysis of spatial-temporal variations of the dynamic and thermal processes parameters in the ionosphere during the maximum phase of the 24th solar activity cycle (2012—2015) have been performed using experimental data obtained by the Kharkiv incoherent scatter radar. For the periods of the equinoxes and solstices, diurnal dependences of process parameters in the ionospheric plasma at altitudes from 210 to 450 km were constructed. The values of plasma transfer velocity due to ambipolar diffusion, the density of the full plasma flux, and the flux of charged particles due to ambipolar diffusion were determined. The values of the energy supplied to the electron gas, the density of the heat flux transferred by electrons from the plasmasphere to the ionosphere, as well as the velocity of the equivalent neutral wind and the meridional component of the neutral wind velocity, were calculated. It was established that for the considered periods, the effects of space weather variations and geomagnetic activity were significantly manifested in variations of the plasma flux density due to ambipolar diffusion, the density of the full plasma flux, as well as the energy supplied to electrons per unit time. Quantitative and qualitative characteristics of these parameters were typical but changed significantly (by 2…3 times) in some cases, even with a slight increase in geomagnetic activity.

Deviation from the prediction of the Maier-Saupe theory of mixtures of charged discotic Gay-Berne and Lennard-Jones particles

ABSTRACT We report an analysis of the orientational order and orientational distribution functions of mixtures of discotic charged Gay-Berne (GB) and Lennard-Jones (LJ) particles as models of ionic liquid crystals and colloidal suspensions. We have studied three different stoichiometries (GB:LJ of 1:2, 1:1 and 2:1), with the opposite charges on the two particles selected to guarantee electroneutrality. We have found that for relatively low values of the scaled charge the dependence of the fourth-rank orientational order parameter, <P 4>, on the second-rank orientational order parameter, <P 2>, is in very good agreement with the prediction of the Maier-Saupe theory. In contrast, for relatively high values of the charge a deviation is observed which is in opposite directions for mixtures with an excess for GB particles and mixtures with an excess of LJ particles.

Insight into the Structural and Dynamical Processes of Peptides by Means of Vibrational and Ultrasonic Relaxation Spectroscopies, Molecular Docking, and Density Functional Theory Calculations

We report a detailed investigation of the vibrational modes, structure, and dynamics of glutathione (GSH) solutions using ultrasonic relaxation spectroscopy, FT-IR vibrational spectroscopy, and electronic absorption measurements. The experimental data were analyzed using density functional theory (DFT) and molecular docking calculations. Three distinct Debye-type relaxation processes can be observed in the acoustic spectra, which are assigned to conformational changes between GSH conformers, the self-association of GSH, and protonation processes. The standard volume changes for each process were estimated both experimentally and theoretically, revealing a close resemblance among them. The higher the effect of the relaxation process in the structure, the greater the induced volume changes. From the temperature dependence of specific acoustic parameters, the thermodynamic characteristics of each process were determined. The experimental FT-IR spectra were compared with the corresponding theoretically predicted vibrational spectra, revealing that the GSH dimers and extended conformers dominate the structure of GSH solutions in the high-concentration region. The absorption spectra in the ultraviolet region confirmed the gradual aggregation mechanism that takes place in the aqueous GSH solutions. The results of the present study were discussed and analyzed in the framework of the current phenomenological status of the field.

FDTD-based computational model applied to assess the influence of the frequency dependence of soil parameters on the lightning response of grounding electrodes for typical parameters of first and subsequent return stroke currents

This paper considers an evaluation of the influence of the frequency-dependence of soil parameters on the lightning response of horizontal grounding electrodes by means of the finite-difference time domain (FDTD) electromagnetic model. The FDTD simulations assumed the soil modeled as a multipole Debye medium and the response of grounding electrodes due to lightning return stroke currents with typical front time parameters of negative first and subsequent strokes was assessed. The results in terms of the ground potential rise (GPR) and grounding impulse impedance (ZP), were compared to those provided by the application of the Hybrid Electromagnetic Model (HEM), a frequency domain model widely applied for lightning related problems, and revealed the top quality of the modeled approach in FDTD. The largest percentage variations of the calculated impulse impedance compared to HEM were around 6 % and 10 % for first and subsequent stroke currents, respectively.

Optimized convergence of stochastic gradient descent by weighted averaging

Under mild assumptions stochastic gradient methods asymptotically achieve an optimal rate of convergence if the arithmetic mean of all iterates is returned as an approximate optimal solution. However, in the absence of stochastic noise, the arithmetic mean of all iterates converges considerably slower to the optimal solution than the iterates themselves. And also in the presence of noise, when a termination of the stochastic gradient method after a finite number of steps is considered, the arithmetic mean is not necessarily the best possible approximation to the unknown optimal solution. This paper aims at identifying optimal strategies in a particularly simple case, the minimization of a strongly convex function with i. i. d. noise terms and termination after a finite number of steps. Explicit formulas for the stochastic error and the optimality error are derived in dependence of certain parameters of the SGD method. The aim was to choose parameters such that both stochastic error and optimality error are reduced compared to arithmetic averaging. This aim could not be achieved; however, by allowing a slight increase of the stochastic error it was possible to select the parameters such that a significant reduction of the optimality error could be achieved. This reduction of the optimality error has a strong effect on the approximate solution generated by the stochastic gradient method in case that only a moderate number of iterations is used or when the initial error is large. The numerical examples confirm the theoretical results and suggest that a generalization to non-quadratic objective functions may be possible.

Research of nonstationary dynamic models of the organizational and technological process of railway transport technical vehicles repair

The problems of analytical and computer research of dynamic models of repair and operation of technical vehicles used in railway transport are among the urgent problems related to ensuring safety and stability of traffic, with the development of digital twins and the improvement of monitoring and diagnostic systems. The analysis of models described by various types of multidimensional nonlinear differential equations requires the use of modern methods of dynamical systems theory, numerical optimization and computer algebra. The purpose of the article is to conduct a qualitative and numerical analysis of mathematical models of organizational and technological processes (OTP) in railway transport, as well as the synthesis of new controlled OTP models. Nonstationary generalizations of a two-dimensional dynamic model describing the repair process of railway transport equipment are proposed. Various cases of using constant and time-dependent parameters are considered. The case of linear and exponential dependences of parameters on time is studied. For the studied models, trajectories are obtained taking into account the variation of constant parameters and taking into account the choice of parametric dependencies, a comparative analysis of the results is presented. The formulation of the problem of optimal control of the number of repaired and repaired railway wagons is proposed. Promising methods for solving this problem using numerical optimization methods, including those inspired by nature, are described. The results can be used in the tasks of constructing and analyzing mathematical models of dynamic systems, in the tasks of numerical modeling of transport systems and technological processes, in the tasks of optimizing the number of vehicles and improving the transportation process, as well as in the tasks of creating digital counterparts in the transport industry.

Sagittal Profi le of the Spine in Patients after Lumbar Stabilisation Surgeries

Spine stabilization surgery is nowadays one of the most common spinal surgical procedures. Spinopelvic alignment is considered to be an important factor impacting the patients' preoperative diffi culties as well as the outcome of surgery. In our study, the outcomes of stabilization surgeries in patients with lumbar spine disorders were evaluated - especially in those with stenosis and spondylolisthesis, in whom the importance of sagittal parameters were assessed with respect to the patients' clinical outcomes and diffi culties. The study included 50 patients with lumbar spine disorders who had undergone a spine stabilization surgery for a degenerative disease - lumbar spinal stenosis, spondylolisthesis between 2015 and 2017. Spino-pelvic radiological parameters and clinical parameters were evaluated using the nonparametric Kruskal-Wallis, Mann-Whitney, and Wilcoxon tests. In 38 of 50 patients, who at the end of the follow-up period did not have the PI-LL (pelvic incidence-lumbar lordosis) mismatch, i.e. PI-LL was ≤10°, a statistically signifi cant difference in pelvic tilt (p=0.049) and sagittal vertical axis (p<0.001) was reported, which was not the case in the remaining patients of the study population. Claudication and OSWESTRY (ODI) showed no statistically signifi cant difference. We have also compared the differences in the number of fused vertebrae and type of stabilization. A signifi cant change was seen in the claudication parameter at 12 and 24 months after surgery (p=0.007, p=0.005), with better outcomes achieved by 360° lumbar fusion compared to posterior lumbar fusion. The improvement of VAS and ODI scores in both the groups over time (from 6.1 to 3.6 or from 6.3 to 3.5 in VAS and from 62 to 32, or from 62 to 30 in ODI) was also statistically signifi cant (p<0.001 in both groups), while when comparing the groups against each other it was statistically insignifi cant. The authors confi rmed signifi cant improvement in the studied clinical parameters in all groups of patients (VAS, ODI, claudication), which is consistent with the results of recently published papers. The authors also established the correlation between different radiological parameters in the studied groups. The results do not confi rm the importance of the length or type of instrumentation for the clinical outcomes. This is consistent with the fi ndings of other published manuscripts. The authors failed to confi rm a signifi cant change in clinical parameters in dependence on the matching relationship between the pelvic incidence and lumbar lordosis. Proper spinopelvic balance in patients after spinal surgery is a very important indicator of postoperative development and condition, but our cohort showed no statistically signifi cant difference in the clinical outcomes of patients whose postoperative sagittal parameters were unsatisfactory. sagittal profi le, spine stabilization, pelvic tilt, pelvic incidence, sagittal vertical axis, SVA.

Electron effective mass in GaN revisited: New insights from terahertz and mid-infrared optical Hall effect

Electron effective mass is a fundamental material parameter defining the free charge carrier transport properties, but it is very challenging to be experimentally determined at high temperatures relevant to device operation. In this work, we obtain the electron effective mass parameters in a Si-doped GaN bulk substrate and epitaxial layers from terahertz (THz) and mid-infrared (MIR) optical Hall effect (OHE) measurements in the temperature range of 38–340 K. The OHE data are analyzed using the well-accepted Drude model to account for the free charge carrier contributions. A strong temperature dependence of the electron effective mass parameter in both bulk and epitaxial GaN with values ranging from (0.18 ± 0.02) m0 to (0.34 ± 0.01) m0 at a low temperature (38 K) and room temperature, respectively, is obtained from the THz OHE analysis. The observed effective mass enhancement with temperature is evaluated and discussed in view of conduction band nonparabolicity, polaron effect, strain, and deviations from the classical Drude behavior. On the other hand, the electron effective mass parameter determined by MIR OHE is found to be temperature independent with a value of (0.200 ± 0.002) m0. A possible explanation for the different findings from THz OHE and MIR OHE is proposed.

Unveiling non-flat profiles within magnetic islands in tokamaks

The presence of non-flat profiles on magnetic island is studied for the first time through gyrokinetic simulations alongside a simplified Lagrangian model. We have identified that inside a magnetic island, the non-flatness of density and temperature profiles is controlled by a dimensionless parameter α≡w*ŝϵ/qρ*, which is a function of normalized island width w*=w/a0, magnetic shear ŝ, inverse aspect ratio ϵ=a0/R, safety factor q, and normalized gyroradius ρ*=ρ/a0. The gyroradius ρ* dependence of the control parameter α leads to a species-selective transition of profiles from flat to concave only for electrons having high α∼O(1). The finding elucidates that electron profiles tend to increasingly deviate from the flat state for a larger magnetic island, in contrast to the conventional wisdom.

Dependence of Growth Parameters of Atomic Chains on Changes in the Substrate Temperature

Dependence of Growth Parameters of Atomic Chains on Changes in the Substrate Temperature

Digital Twin of the Photoelectric Converter of the Power Transmission System over Optical Fiber

The photovoltaic converter (PVC) is a key device in a power-over-fiber system (PoFS). The aim of the work is to create a digital twin (DT) to predict the behaviour of PVC based on their specification data, which is the first step towards creating a universal DT of the entire PoFS. The paper considers the theoretical principles of operation of PVC using the zone theory of solids. A relationship has been established between the theoretical parameters and specification data of real converters. A five-element equivalent circuit of a PVC has been created and a DT in MATLAB Simulink has been developed on its basis. The dependences of the main parameters of the DT on the optical power at the converter input are calculated. Experiments were carried out on an installation with PVC of the YCH-H6424-15-FC-A brand. The optical powers at which all characteristics of the solar cell coincide with an accuracy of 2% are determined. The discrepancy between the calculated and experimental characteristics with increasing optical power is explained by the fact that the current transfer coefficient decreases at high current strength. This phenomenon is substantiated by the zone theory, but is not taken into account in the DT.

Dependence of Drillability Parameters on Engineering Properties of Selected Rocks from Pakistan

Dependence of Drillability Parameters on Engineering Properties of Selected Rocks from Pakistan

Remnant loop quantum black holes

Polymer models inspired by Loop Quantum Gravity (LQG) have been used to describe non-singular quantum black holes with spherical symmetry, with the classical singularity replaced by a transition from a black hole to a white hole. A recent model, with a single polymerisation parameter, leads to a symmetric transition with same mass for the black and white phases, and to an asymptotically flat exterior metric. The radius of the transition surface is, however, not fixed, increasing with the mass. Following similar procedures, in a previous paper we have fixed that radius by identifying the minimal area on the transition surface with the area gap of LQG. This allowed to find a dependence of the polimarisation parameter on the black hole mass, with the former increasing as the latter decreases. It also permitted to extend the model to Planck scale black holes, with quantum fluctuations remaining small at the horizon. In the present letter we extend this analysis to charged black holes, showing that the Cauchy horizon lies beyond of the transition surface. We also show the existence of limiting states with zero surface gravity, the lightest one with Q = 0 and m=2/4 , and the heaviest with Q=m=2/2 . Using our solutions to approximate quasi-steady horizons, we show that Hawking evaporation leads asymptotically to these extremal states, leaving remnant black holes of Planck size.

New and robust gravitational-waveform model for high-mass-ratio binary neutron star systems with dynamical tidal effects

For the analysis of gravitational-wave signals, fast and accurate gravitational-waveform models are required. These enable us to obtain information on the system properties from compact binary mergers. In this article, we introduce the model, which contains a closed-form expression that describes tidal effects, focusing on the description of binary neutron star systems. The model improves upon previous versions by employing a larger set of numerical-relativity data for its calibration, by including high-mass ratio systems covering also a wider range of equations of state. It also takes into account dynamical tidal effects and the known post-Newtonian mass-ratio dependence of individual calibration parameters. We implemented the model in the publicly available uite software library by augmenting different binary black hole waveform models (, , and ). We test the validity of by comparing it with numerical-relativity waveforms, as well as other tidal models. Finally, we perform parameter estimation for GW170817 and GW190425 with the new tidal approximant and find overall consistent results with respect to previous studies. Published by the American Physical Society 2024

Temperature Dependence of Membrane Permeability Parameters for Five Cell Types Using Nonideal Thermodynamic Assumptions to Mathematically Model Cryopreservation Protocols.

Cryopreservation is the process of preserving biological matter at subzero temperatures for long-term storage. During cryopreservation, cells are susceptible to various injuries that can be mitigated by controlling the cooling and warming profiles and cryoprotective agent (CPA) addition and removal procedures. Mathematical modeling of the changing cell volume at different temperatures can greatly reduce the experiments needed to optimize cryopreservation protocols. Such mathematical modeling requires as inputs the cell membrane permeabilities to water and CPA and the osmotically inactive fraction of the cell. Since the intra- and extracellular solutions are generally thermodynamically nonideal, our group has been incorporating the osmotic virial equation to model the solution thermodynamics that underlie the cell volume change equations, adding the second and third osmotic virial coefficients of the grouped intracellular solute to the cell osmotic parameters that must be measured. In our previous work, we reported methods to obtain cell osmotic parameters at room temperature by fitting experimental cell volume kinetic data with equations that incorporated nonideal solution thermodynamics assumptions. Since the relevant cell volume excursions occur at different temperatures, the temperature dependence of the osmotic parameters plays an important role. In this work, we present a new two-part fitting method to obtain five cell-type-specific parameters (water permeability, dimethyl sulfoxide permeability, osmotically inactive fraction, and the second and third osmotic virial coefficients of the intracellular solution) from experimental measurements of equilibrium cell volume and cell volume as a function of time at room temperature and 0 °C for five cell types, namely, human umbilical vein endothelial cells (HUVECs), H9c2 rat myoblasts, porcine corneal endothelial cells (PCECs), the Jurkat T-lymphocyte cell line, and human cerebral microvascular endothelial cells (hCMECs/D3 cell line). The fitting method in this work is based on both equilibrium and kinetic cell volume data, enabling us to solve some technical challenges and expand our previously reported measurement technique to 0 °C. Finally, we use the measured parameters to model the cell volume changes for a HUVEC cryopreservation protocol to demonstrate the impact of the nonideal thermodynamic assumptions on predicting the changing cell volume during freezing and thawing.

Time behavior of hubble parameter by torsion

Consequences of the consistent exact solution of Einstein–Cartan equation on the time dependence of Hubble parameter are discussed. The torsion leads to a space and time-dependent expansion parameter which results into nontrivial windows of Hubble parameter between diverging behavior. Only one window shows a period of decreasing followed by increasing time dependence. Provided a known cosmological constant and the present values of Hubble and deceleration parameter this changing time can be given in the past as well as the ending time of the windows or universe. The comparison with the present experimental data allows to determine all parameters of the model. Large-scale spatial periodic structures appear. From the metric with torsion outside matter, it is seen that torsion can feign dark matter.

Characteristics of turboexpander unit used to prepare natural gas for transportation

Before being supplied to the transportation pipeline, natural gas must be cleaned from various impurities, with the specified parameters at the inlet to the transportation system — such as composition, mass or volumetric flow rate, pressure, and temperature — to be ensured. To this effect, a gas preparation system is designed, which includes various heat exchange units, cleaning and separation devices, as well as a turboexpander unit (TEU) consisting of a turbine and a coupled compressor.During the operation of this system, the gas parameters are constantly changing due to variations in external and operating conditions, such as the parameters of the ambient air, the gas pressure and flow rate at the wellhead, the composition and the amount of impurities.The gas preparation system therefore almost never operates in the designed conditions, which means that its proper operation requires the knowledge of its characteristics, i.e., the dependencies of the system parameters on external and operational conditions. Besides, the knowledge of the characteristics enables to control the system by affecting its various parameters.The characteristics of the gas preparation system are determined by the characteristics of all of its elements, including the characteristics of the TEU as one of its most important elements.The characteristics of the TEU enable to assess the impact of external conditions on its operating conditions and thus optimize the system's operation during its design stage. They also allow the determination of the parameters for regulating the TEU conditions.A methodology for calculating the TEU characteristics is proposed, an example of the calculation is provided, and analysis of the obtained results is presented.

The effect of elevated temperature on LCF damage growth in 2024AA – Experiment and modeling

This paper presents the results of experimental low-cycle fatigue (LCF) tests conducted on EN-AW 2024 alloy in T3511 temper at 100 °C, 200 °C and 300 °C. The material's basic fatigue characteristics were determined, such as fatigue life curve and cyclic strain curve. Both the hysteresis loop and nature of fracture surfaces obtained in macro- and microscopic observations (scanning electron microscope, SEM) were accounted for. The results of tests at elevated temperature were compared with results obtained at room temperature in the authors’ previous papers. Based on the results of experimental tests, an analytical model of fatigue damage growth was proposed. In this model, it was assumed that damage accumulation mainly depends on the current normal stress and increment of plastic strain. Dependencies of the model's parameters with respect to temperature were determined, and the model was validated experimentally. Good concurrency of the numerical simulations with the experimental results was obtained.

First principal calculations for understanding physical properties and possible applications of vacancy ordered double perovskite Cs2ZrI6 (CZI)

First principal calculations are performed to understand structural, elastic, electronic, thermoelectric, thermodynamic and optical properties of inorganic vacancy ordered double perovskite, the Cs2ZrI6 (CZI). Calculated lattice constant of the rock-salt structured CZI shows closeness to that reported in the Materials Project Database. It exhibits mechanical stability, elastic anisotropy, brittleness, dominating ionic bonding, predominant stretching in chemical bonds, fair thermal stability and high melting temperature. It is an indirect band-gap (Γ-X) semiconductor with a band-gap of 2.267eV, which would be suitable for fabricating low-cost tandem solar cells. Calculated thermoelectric properties predicted holes as the majority charge carriers and also shows its thermoelectric efficiency in the higher temperature region. Though, calculated specific heat at constant volume in the very low temperature region obeys the Debye's T3 law, it reaches the Dulong-Petit limit in the very high temperature region. The temperature and pressure dependence of some other thermodynamic parameters are also calculated in the present study. In terms of real and imaginary part of the dielectric function as well as some other auxiliary parameters, we have investigated the optical properties of the CZI and found its high optical absorbance capability in the far UV to extreme UV region of solar spectra.