Theoretical Computer Modeling Research Articles

Theoretical analysis and computational modeling of nonlinear fractional-order victim-two predators model

The victim-predator model has been investigated in several papers in the literature since it is considered one of the very important models. The relation between predator and victim is an important aspect of ecology. The principal object of this research is to propose a new Caputo fractional one victim-two predators model with variable parameters. In addition, we study its stability and prove the existence and uniqueness of its solution. We calculate its approximate solution using Laplace transform coupled with the Adomian Decomposition Method (ADM) in two cases. Also, in order to complete the study of the proposed paradigm, we simulate and show its fractional dynamics plus the effect of changing certain parameters on its fractional dynamics against various fractional orders.

Modeling of centrifugal deployment of three-section minisatellite boom

The aim of the article is to model the processes of centrifugal deployment of a three-section boom and preliminary analyze the feasibility of this deployment method for an Earth remote sensing (ERS) minisatellite (MS). During the research, methods of theoretical mechanics, multibody dynamics, control theory, and computer modeling were used. Centrifugal deployment of multi-section booms have been successfully used on spin stabilized satellites, but not on ERS satellites, which have other features of operation and require additional studies. The main part of the MS is a platform to which a transformable antenna is attached by means of a transformable boom. Before deployment, the stowed boom and antenna are attached to the MS platform. The boom sections are connected by joints with one rotational degree of freedom and deployed sequentially due to centrifugal forces when the MS rotates in the required direction. Each of the boom joints has a locking mechanism that latches when a predetermined deploy angle is reached. To model the processes of the boom deployment, the MS is presented as a system of connected bodies, where the platform and the stowed antenna are absolutely rigid bodies, and the boom consists of three flexible beams of a tubular cross-section. The differential equations of the MS dynamics during the deployment are obtained using the Lagrangian formalism, which are supplemented by algebraic equations describing the constraints from the joints. The scenarios of the boom deployment with a constant control torque and a constant angular velocity of the MS are considered. These scenarios are simulated, and estimates of the control actions needed to ensure full deployment of the boom and the stabilization of the MS after latching of the joints are calculated. Dependences of variations of the loads on the boom structure during deployment are obtained. The simulation results allow us to conclude that it is feasible to implement the method of the boom centrifugal deployment for the MS, which can perform fast rotations about the three axes of the body reference frame. Implementation of this method allows designers to reduce mass of the MS because it does not require any servo drives in the boom deployment system.

Modes of wide-aperture acousto-optic diffraction in a uniaxial birefringent crystal

Acousto-optic (AO) anisotropic interaction in uniaxial birefringent crystals is a widespread and versatile approach to tunable spectral filtration of light. Its principal constraints are limited values of spectral and angular bandwidth restricting the light transmission and imaging performance of AO filters. A way to overcome these drawbacks is simultaneous Bragg diffraction of two or more light beams. In this paper, we discuss and compare the main features of four available modes of anisotropic wide-aperture AO interactions in uniaxial birefringent crystals. We calculate the angular aperture, spectral resolution and other parameters and estimate the spectral image quality features related to each one. Theoretical consideration and computational modeling are carried out for tellurium dioxide (TeO2)—the main AO crystal. Derived results are important for the development of AO imaging devices, particularly multi-channel AO tunable filters.

Electrodeposition mechanism of chromium nanoparticle coatings: Modeling and experimental validation

In this paper the deposition and surface growth of chromium nanoparticles (CrNPs) coatings on a commercial steel substrate by electrodeposition at a constant current, is presented; both theoretically through a theoretical-computational model applying a modified Schrödinger equation, energy potentials and electrochemistry and phitosynthesis of Cr Nanoparticles . For the simulation process, the finite element method (FEM) was used considering the equation of electric potential and electroneutrality with and without the inclusion of a quantum leap. The theoretical results are in accordance with the experimental results, considering a three-level multifactorial experiment design with current, voltage and ion concentration as factors and the formation and growth of the coatings as a response function. The results obtained indicate the presence of electro-diffusion at the substrate-coating interface. The developed model has the predictive ability of 97 ± 2 % for the electrochemical deposition of CrNPs on a steel substrate.

Metal‐Organic‐Framework‐Based Single‐Atomic Catalysts for Energy Conversion and Storage: Principles, Advances, and Theoretical Understandings

AbstractIn recent years, the development of alternative energy‐saving, efficient, and clean catalysts for various electrochemical reactions has attracted increasing research attention. Among the various types of catalysts, single‐atom catalysts (SACs) have unique properties. However, individual atoms are prone to agglomeration due to their high surface energy, which poses a major challenge to the development of SACs. Metal‐organic frameworks (MOFs) have the advantages of high porosity and specific surface area, and MOF materials can be ideal carriers for single atoms, which can be anchored from a monoatomic dispersion of metal atoms by simple pyrolysis. Moreover, single atoms derived from MOF materials have high structural order, allowing them to be modeled using theoretical computational models to enable a deeper understanding of the mechanisms of SACs. SAC synthesis methods and applications in various fields are reviewed. Finally, the catalytic processes of SACs in the context of theoretical calculations are reviewed.

From three-dimensional tessellations to lightweight filling materials for additively manufactured structures: Concept, simulation, and testing

To improve the structural efficiency and reduce costs, most additively manufactured parts are printed as thin shells filled with a lightweight cellular material. The filling material reacts to secondary stresses and provides distributed support for the load-carrying outer shell. In a recent publication, the authors have proposed a two-step method to design lightweight filling metamaterials that are intrinsically strong and stiff. Conceptually, the space is first divided into repetitive volumes according to known three-dimensional tessellation schemes. The tessellation is then replaced by a kinematically rigid wireframe with beams along the edges and across the faces of the native volumes. Elaborating on that idea, the present paper pursues three objectives: (a) show the variety of material designs that derive from the tessellation-wireframe approach; (b) characterize the materials through finite element analyses on full-scale models and compare them with former predictions based on scaling and homogenization techniques; (c) validate the numerical results against experimental tests on a selection of prototype structures. Good correlation is revealed between theoretical predictions, computational models, and experimental data.

Scholte Wave Dispersion Modeling and Subsequent Application in Seabed Shear-Wave Velocity Profile Inversion

Recent studies have illustrated that the Multichannel Analysis of Surface Waves (MASW) method is an effective geoacoustic parameter inversion tool. This particular tool employs the dispersion property of broadband Scholte-type surface wave signals, which propagate along the interface between the sea water and seafloor. It is of critical importance to establish the theoretical Scholte wave dispersion curve computation model. In this typical study, the stiffness matrix method is introduced to compute the phase speed of the Scholte wave in a layered ocean environment with an elastic bottom. By computing the phase velocity in environments with a typical complexly varying seabed, it is observed that the coupling phenomenon occurs among Scholte waves corresponding to the fundamental mode and the first higher-order mode for the model with a low shear-velocity layer. Afterwards, few differences are highlighted, which should be taken into consideration while applying the MASW method in the seabed. Finally, based on the ingeniously developed nonlinear Bayesian inversion theory, the seafloor shear wave velocity profile in the southern Yellow Sea of China is inverted by employing multi-order Scholte wave dispersion curves. These inversion results illustrate that the shear wave speed is below 700 m/s in the upper layers of bottom sediments. Due to the alternation of argillaceous layers and sandy layers in the experimental area, there are several low-shear-wave-velocity layers in the inversion profile.

Interrogating theoretical models of neural computation with emergent property inference.

A cornerstone of theoretical neuroscience is the circuit model: a system of equations that captures a hypothesized neural mechanism. Such models are valuable when they give rise to an experimentally observed phenomenon -- whether behavioral or a pattern of neural activity -- and thus can offer insights into neural computation. The operation of these circuits, like all models, critically depends on the choice of model parameters. A key step is then to identify the model parameters consistent with observed phenomena: to solve the inverse problem. In this work, we present a novel technique, emergent property inference (EPI), that brings the modern probabilistic modeling toolkit to theoretical neuroscience. When theorizing circuit models, theoreticians predominantly focus on reproducing computational properties rather than a particular dataset. Our method uses deep neural networks to learn parameter distributions with these computational properties. This methodology is introduced through a motivational example of parameter inference in the stomatogastric ganglion. EPI is then shown to allow precise control over the behavior of inferred parameters and to scale in parameter dimension better than alternative techniques. In the remainder of this work, we present novel theoretical findings in models of primary visual cortex and superior colliculus, which were gained through the examination of complex parametric structure captured by EPI. Beyond its scientific contribution, this work illustrates the variety of analyses possible once deep learning is harnessed towards solving theoretical inverse problems.

Influence of geometric parameters of screw nozzles of a twin screw extrusion press on the oil output

The relevance of the study is due to the search for rational geometric parameters of screw nozzles and the identification of the influence of the compression ratio of twin screw extrusion presses on the oil compression process. An important criterion in this paper is the indicator of the value of oil yield to obtain economic profit. From the analysis of optimisation methods in similar studies, the following variable geometric parameters of screw nozzles were selected for twin screw extruders: axial pitch, channel width between turns, rig width of the turn, and nozzle length. Two sets of experimental working bodies with modified geometric parameters were manufactured based on theoretical calculations and computer modelling to improve the working bodies of the EK 75/1200 twin screw extrusion press. Their theoretical compression ratio is determined, which is 5.50 and 4.33, respectively. It is also defined for the basic set of working bodies, which was recommended by the manufacturer, which was 4.69. It is established that the general nature of changes in the free volume along the length of the screw shaft is accompanied by an uneven decrease from 40 to 80% toward the press cake output. From the reviewed scientific literature, it was identified that the nature of changes in the free volume of turns along the length of the screw shaft characterises the correctness of its design. However, after analysing the results of the work performed, it was determined that the selection of rational geometric parameters of the working bodies should be considered in conjunction with other structural parameters, which will further intensify the oil compression process. It is experimentally confirmed that the oil yield depends on the degree of compression due to the geometric parameters of the screw nozzles. The oil yield increased by 0.9% when using a set of working bodies of set 1 when compared with the basic set of working bodies from the manufacturer’s factory (set 2) in terms of volume of processed raw materials per unit will bring additional profit. It was determined that with the production volume of 50 tons of oil with an improved set of working bodies (set 1), the economic effect amounted to UAH 19,250

Influence of spatial welding on the accuracy of working dimensions of drilling chisels of cutting-erasing type

The article considers the problem of PDC drill bit quality provided during manufacturing. Schemes of welded joint making are theoretically substantiated based on theoretical research, computer modelling and experimental tests for L-shaped details like PDC drill bit blades. The recommendations to provide welded joints for L-shaped details are developed. Based on the elastic-plastic analysis, means to reduce thermal longitudinal and transverse internal deformations caused by a heat source moving along the weld are theoretically substantiated. Simulation models have been developed to assess the influence of welding thermal action and residual deformations on accuracy of drill bit external diameter for different schemes of welding. Based on the developed models, it is shown that the thermal welding deformations of spatial curved welds are significant, and relate mainly to the blades rather than the body (i.e. less massive parts); there are bends, turns and skews of the blades. Finite-element simulation of the bit body – welded blades stress-strain state was performed sequentially in the environment ANSYS (academic license) – Transient Thermal (determination of heat load) and Static Structural (determination of deformations and stresses). It is established that the smallest deformations of the blade are observed for the welding scheme, which envisages making the weld from the point of cylindrical and ellipse surface pairing. The results obtained by simulations were confirmed by experimental data and this made possible substitution for a rational scheme of drill bit body – blade based on the method of reverse deformation, to ensure the accuracy of the product as a whole. Recommendations for weld joint making for spatial curved welds of complex products with requirements to their accuracy allow increasing the accuracy of the technology by minimizing the thermal load and residual thermal deformation of the joints.

Spatiospectral transformation of noncollimated light beams diffracted by ultrasound in birefringent crystals

Spatiospectral structure of wave phase matching in birefringent crystals has a strong dependence on the geometry of the acousto-optic interaction and incident light spectrum. This dependence defines details of light beam profile transformation. It is especially important for imaging applications related to a large angular aperture and a wide spectral bandwidth of the incident light. In this paper, we demonstrate accurate three-dimensional plotting of a light transmission pattern without small birefringence approximation. The rather complicated shape of the phase-matching locus in the spatiospectral domain inevitably leads to residual spatially nonuniform chromatic aberrations in the spectral image. Theoretical consideration and computational modeling are confirmed by the experiments on Bragg diffraction in paratellurite crystal. The results are especially important for the development of acousto-optical imaging devices and laser beam shaping technologies.

SIMULATION OF AN ELECTROMYOGRAPHIC SIGNAL CONVERTER FOR ADAPTIVE ELECTRICAL STIMULATION TASKS

The subject matter of the article is an electromyographic signal transducer, which are an integral part of devices for adaptive electrical stimulation of muscle structures based on reverse electromyographic communication. The goal of the work is to study the features, obtaining the corresponding theoretical relationships and computer modeling of a differential biopotential converter, providing amplification of the useful component and suppression of harmful interference, the spectra of which intersect. The following tasks were solved in the article: determining the effect of electrode width and electrode spacing on crosstalk; formation of the electrode-skin model and the input circuit of the transducer, obtaining theoretical relations for calculating the rejection coefficient, construction of the transducer circuit and its computer simulation. The following methods were used – methods of mathematical modeling of processes and technical devices; methods of analysis, structural and parametric synthesis of nonlinear electronic circuits; methods of machine design. The following results were obtained – a biopotential amplifier circuit with tracking feedback on power supply is proposed; modeling of dynamic processes by means of the Multisim program was carried out; on the basis of the constructed model of the electrode-skin input circuit and the obtained analytical relationships, the rejection coefficient of the input circuit of the equivalent circuit is calculated; the requirements for the signal registration module are formulated. Conclusions: The considered version of the electromyographic signal converter circuit based on tracking communication on power supply, effectively rejects 50 Hz common mode noise. On the basis of the constructed equivalent model of the input circuit of the amplifier, the theoretical relation for calculating the rejection coefficient of such amplifiers. The circuit is simulated in the Multisim program, the results confirmed the correctness of its functioning. The requirements for the interelectrode distance and the thickness of the electrodes themselves are also formulated. The results obtained can be used to design complexes for adaptive electrical stimulation.

Timely determination of static stability margins in power supply systems equipped with distributed generation installations

The article aims to develop a methodology to ensure timely determination of the margins of static aperiodic stability in power supply systems, at the nodal points of which distributed generation units are installed. The authors used mathematical methods and algorithms based on the application of limiting regime equations. Transitional processes were analysed for various points in the space of controlled mode parameters according to the simulation modelling in Matlab using the Simulink and SimPowerSystems packages. On the basis of the obtained results, an effective technique for analysing stability margins in electrical networks with distributed generation units was implemented. This method is applicable in design problems, as well as in operational and emergency control. The conducted theoretical analysis and computer modelling showed the effectiveness of the proposed methodology for calculating stability margins; the nondegeneracy of the Jacobi matrix of limiting regime equations at the solution point ensures the guaranteed reliability of the results. It was shown that an alternative approach to solving the problem of timely determination of aperiodic stability margins can be implemented on the basis of limiting regime equation with increased nonlinearity. Dynamic modelling of an electrical network with distributed generation units confirmed the correctness of determining the stability margins calculated using limiting regime equations. The developed technique can be recommended for practical use in the design of power supply systems or in operational control of synchronous generators. In particular, the presented methodology can be used to implement a multi-agent emergency control system for distributed generation installations located in generalpurpose distribution electrical networks.

Ordering, phase behavior, and correlations of semiflexible polymers in confinement.

Semiflexible polymers are ubiquitous in biological systems, e.g., as building blocks of the cytoskeleton, and they also play an important role in various materials due to their ability to form liquid-crystalline order. These rigid macromolecules are characterized by numerous (hierarchical) length-scales that define their static and dynamic properties. Confinement can promote uniform order, e.g., through capillary nematization in narrow slits, but it can also introduce long-ranged disruptions of the nematic ordering field through (unavoidable) topological defects in spherical containers. This Perspective concentrates on the theoretical description and computational modeling of such confined systems, with the focus on spherical containers that play an important role in the injection/ejection of double-stranded DNA from viral capsids and the fabrication of nematic droplets. Basic principles and recent developments are reviewed, followed by a discussion of open questions and potential directions for future research in this field.

Theoretical Characterization of the Reduction Potentials of Nucleic Acids in Solution.

Here, we present the theoretical–computational modeling of the oxidation properties of four DNA nucleosides and nucleotides and a set of dinucleotides in solutions. Our estimates of the vertical ionization energies and reduction potentials, close to the corresponding experimental data, show that an accurate calculation of the molecular electronic properties in solutions requires a proper treatment of the effect of the environment. In particular, we found that the effect of the environment is to stabilize the oxidized state of the nucleobases resulting in a remarkable reduction—up to 6.6 eV—of the energy with respect to the gas phase. Our estimates of the aqueous and gas-phase vertical ionization energies, in good agreement with photoelectron spectroscopy experiments, also show that the effect on the reduction potential of the phosphate group and of the additional nucleotide in dinucleotides is rather limited.

Протонпроводящая керамика на основе гафната и церата бария, легированных оксидами циркония, иттрия и иттербия для электролитов топливных элементов

Nanopowders of the compositions BaHf1 – xYbxO3 – δ (x = 0.04; 0.08; 0.10) and BaCe0.9 – xZrxY0.1O3 – δ (x = 0; 0.5; 0.6; 0.7 and 0.8) were synthesized by the combined crystallization and nitric acid salts using the citrate-nitrate method. Those nanopowders were used to produce ceramic materials with a cubic crystal structure of the perovskite type, with a grain size of ~ 20 – 70 nm. The study of electrophysical properties revealed that they have a proton type of conductivity in the temperature range of 500 – 700 °C; σ = 10–2 – 10–5 Cm/cm. Type and mechanism of electrical conductivity of ceramics of the composition BaHf1 – xYbxO3 – δ (x = 0.04; 0.08; 0.10) have been studied both experimentally and using theoretical calculations-by computer modeling using the electron density functional method; the results are in good agreement. The research shows the prospects of using the obtained ceramic materials as proton-conducting electrolytes of solid-oxide fuel cells.

Relative control of an underactuated spacecraft using reinforcement learning

The aim of the article is to approximate optimal relative control of an underactuated spacecraft using reinforcement learning and to study the influence of various factors on the quality of such a solution. In the course of this study, methods of theoretical mechanics, control theory, stability theory, machine learning, and computer modeling were used. The problem of in-plane spacecraft relative control using only control actions applied tangentially to the orbit is considered. This approach makes it possible to reduce the propellant consumption of reactive actuators and to simplify the architecture of the control system. However, in some cases, methods of the classical control theory do not allow one to obtain acceptable results. In this regard, the possibility of solving this problem by reinforcement learning methods has been investigated, which allows designers to find control algorithms close to optimal ones as a result of interactions of the control system with the plant using a reinforcement signal characterizing the quality of control actions. The well-known quadratic criterion is used as a reinforcement signal, which makes it possible to take into account both the accuracy requirements and the control costs. A search for control actions based on reinforcement learning is made using the policy iteration algorithm. This algorithm is implemented using the actor–critic architecture. Various representations of the actor for control law implementation and the critic for obtaining value function estimates using neural network approximators are considered. It is shown that the optimal control approximation accuracy depends on a number of features, namely, an appropriate structure of the approximators, the neural network parameter updating method, and the learning algorithm parameters. The investigated approach makes it possible to solve the considered class of control problems for controllers of different structures. Moreover, the approach allows the control system to refine its control algorithms during the spacecraft operation.

Computational Simulations of Nanomechanical Resonators for Understanding their Frequency Dynamics and Sensing Performances

Nanomechanical resonators have received the attention due to their ability to perform as a high-frequency device and/or a (bio)sensor that exhibits the unprecedented detection limit even down to a single-molecule or atomic resolution. For effective design of nanomechanical resonators, it is necessary to quantitatively understand the dynamic behavior of nanomechanical resonators based on theoretical models and/or computational models. In this article, we address the current state-of-arts in the theoretical modeling and/or computational modeling of nanomechanical resonators for characterizing their dynamic behavior and their sensing performances. In particular, we present the different types of models at multiple length scales ranging from continuum models to coarse-grained and atomistic models for characterizing the dynamics and sensing performances of nanomechanical resonators. In addition, we discuss the role of finite size effect, nonlinear dynamics, and stiffness effect in the dynamic behavior and/or sensing performances of nanomechanical resonators. Our article sheds light on the theoretical/computational models, which are able to predict and characterize the dynamics and sensing performances of nanomechanical resonators for effective design of them acting as an actuator and/or a sensor.

Reconstruction of the Parameters of the Lower Midlatitude Ionosphere in M- and X-Class Solar Flares

The paper presents the results of the reconstruction of the effective height h' and the slope of the profile β of the electron concentration in the D layer of the ionosphere during X-ray flares of M- and X-classes at the midlatitudes. The reconstruction was carried out with data from measurements at the observatory of the Institute of Geospheres Dynamics of the Russian Academy of Sciences at the Mikhnevo observatory of amplitudes and the phases of signals from VLF transmitters GQD (19.6 kHz) and GBZ (22.1 kHz) that propagate along one mid-latitude path. Based on the calculations, the empirical dependencies of the parameters h' and β on the flare energy according to the X-ray flux measurements on the GOES satellite are in the range 0.05–0.4 nm. Criteria are proposed for the selection of solar flares for the verification of theoretical computational models.

Where the eyes wander: The relationship between mind wandering and fixation allocation to visually salient and semantically informative static scene content.

Vision is crucial for many everyday activities, but the mind is not always focused on what the eyes see. Mind wandering occurs frequently and is associated with attenuated visual and cognitive processing of external information. Corresponding changes in gaze behavior—namely, fewer, longer, and more dispersed fixations—suggest a shift in how the visual system samples external information. Using three computational models of visual salience and two innovative approaches for measuring semantic informativeness, the current work assessed whether these changes reflect how the visual system prioritizes visually salient and semantically informative scene content, two major determinants in most theoretical frameworks and computational models of gaze control. Findings showed that, in a static scene viewing task, fixations were allocated to scene content that was more visually salient 10 seconds prior to probe-caught, self-reported mind wandering compared to self-reported attentive viewing. The relationship between mind wandering and semantic content was more equivocal, with weaker evidence that fixations are more likely to fall on locally informative scene regions. This indicates that the visual system is still able to discriminate visually salient and semantically informative scene content during mind wandering and may fixate on such information more frequently than during attentive viewing. Theoretical implications are discussed in light of these findings.