Computational Modeling Methods Research Articles

A Computational Multiscale Modeling Method for Nanosilver-Sintered Joints with Stochastically Distributed Voids

A high power density is required in wide band gap power semiconductor packaging, which has led to the popularity of sintered nanosilver as an interconnecting material. However, affected by stochastically distributed voids in its microstructure, this material in practice exhibits instability leading to reduced reliability. In this paper, a computational multiscale modeling method is proposed to simulate the influence of micro-voids on macro-properties, providing an efficient tool to analyze the aforementioned problem. At the micro-scale, the three-parameter Weibull distribution of the equivalent Young’s modulus and the normal distribution of the equivalent Poisson’s ratio are captured by Monte Carlo-based finite element simulation on the reconstructed stochastic representative elements, where the density and distribution morphology of micro-voids are taken into consideration. At the macro-scale, the effect of the microscopic voids is transferred through a random sampling process to construct the multiscale model. The effectiveness and validity of the proposed method are verified through experimental case studies involving the modeling of nanosilver-sintered joints sintered at temperatures of 275°C and 300°C. In addition, the effects of the sintering temperature on the dispersion of the micro-voids, the distribution fluctuation of the constitutive parameters, and the mechanical properties are also discussed based on numerical and experimental results.Graphical

Change in the melting temperature baric dependence during the transition from macro to nanocrystal

In this work we present new analytical (i.e., without computer modeling) method for calculating the dependence of the nanocrystal melting temperature both on pressure and on the size (number of atoms N) and surface shape of the nanocrystal. This method is based on the paired Mie–Lennard-Jones interatomic interaction potential, and takes into account the dependence of both the state equation and other lattice properties on the size and shape of the nanocrystal. For the first time, the dependences of the melting temperature on the pressure P, size N, and shape f of the nanocrystal were obtained. Calculations have been performed for gold, platinum and iron. It is shown that at any pressure, the melting point Tm(P, N, f) decreases both with an isomorphic-isobaric (f, P – const) decrease in the number of N atoms, and with an isomeric-isobaric (N, P – const) deviation of the nanocrystal shape from the energy-optimal shape. It is shown that the value of the baric derivative of the melting temperature Tm′(P) for a nanocrystal at low pressures is greater, and at high pressures less than the Tm′(P) value for a macrocrystal. At this, the dependence of the Tm′(P) function on the nanocrystal size is insignificant, i.e., at constant N-f-arguments, the baric dependences Tm(P, ∞) and Tm(P, N, f) are practically parallel. It is indicated how this method can be applied for experimental evaluation of the pressure under which a nanocrystal is located in a refractory matrix.

Improvement of the methodology for calculating the expected drilling speed with PDC chisels

Purpose. Determination of the dependence of the depth of penetration of the PDC cutter into the bottom hole rock, taking into account its geometric parameters and spatial placement in relation to the destroyed array. Methodology. The tasks were solved by a comprehensive research method, including analysis and generalization of literary and patent sources, conducting theoretical research, which consists in solving the theoretical problem of the impact of a superhard circular cutter on an elastically fragile mountain range, using computer and mathematical modeling methods. Findings. A simplified expression has been obtained that allows taking into account the features of the PDC cutter with sufficient accuracy for engineering calculations when determining the depth of its penetration into the bottom hole rock. A method is proposed for calculating the depth of fracture in one revolution of a diamond carbide cutter PDC into the rock of the bottom of the well. The patterns of destruction by the proposed diamond-hard-alloy PDC chisel of a rock mass at the bottom of the well from the parameters of the drilling regime and the hardness of the drilled rocks have been established. Originality. For the first time, the dependence has been obtained of the influence of the geometric parameters of the shape of a single diamond-carbide PDC cutter and its spatial placement in the body of the bit matrix on the magnitude of the technological parameters of drilling a well, and their effect on the nature of the destruction of the array PDC cutter. Practical value. A technique for determining the depth of penetration of a single PDC cutter is proposed, the use of which will allow predicting the mechanical speed, depending on the geological and technical conditions of drilling wells. And taking into account the abrasive properties of rocks, it is possible to reduce the wear of the bits, and therefore the amount of necessary rock-crushing tools for the entire volume of drilling operations during the construction of the well.

Advantages of using CONCRETE CANVAS materials in railway track construction

Purpose. Justification of the feasibility of using new types of drainage materials, such as Concrete Canvas (CC), under the upper structure of the railway permanent way. Methodology. The tasks were solved by a complex research method, including analysis and generalization of literary and patent sources, analytical, experimental studies, using computer and mathematical modeling methods. Tests were conducted with and without the CC layer in a multi-level shear box. After the shear test, the specimens were also tested for load-bearing capa­city (E2, according to the Hungarian standard) and particle breakage. The contact surface between the bottom of the ballast and the CC was measured using a precision 3D laser scanner (GOM ATOS) and visualized graphically using AutoCAD software. Findings. Experimental testing of the vertical load during connection and analysis compared with the test results of geocomposite/geogrid structures, internal shear resistance, and other parameters proved the structure’s higher load-bearing capacity with the CC layer. Based on the results, the Concrete Canvas structure provides higher reinforcement than the average geogrid type. Originality. The advantages of using new Concrete Canvas materials in the structure of a railway track have been demonstrated for the first time to provide greater internal shear resistance than the average for geogrids. Practical value. These results may provide primary data for using Concrete Canvas in railway tracks and superstructures in the future.

ПОВЫШЕНИЕ ВЗРЫВОПОЖАРНОЙ БЕЗОПАСНОСТИ ПРОИЗВОДСТВЕННЫХ ПОМЕЩЕНИЙ С ВЫДЕЛЕНИЕМ ОРГАНИЧЕСКИХ ПЫЛЕЙ

The stability of the work of enterprises of dust-forming areas of industry critically depends on the ability of enterprises to ensure the required level of explosion and fire safety of production, which increases the relevance of improving the traditional methods used, as well as the introduction of new and additional explosion prevention measures.
 In the article, using mathematical and computer modeling methods, the main factors and patterns of the formation of an explosive dust situation in ventilated industrial premises with the release of combustible dust are investigated. On this basis, the possibility of using permanent general exchange ventilation to reduce the likelihood of the formation of explosive situations and prevent the occurrence of explosions and fires in dusty industrial premises is shown.

Improving Transportation Management Systems (TMSs) Based on the Concept of Digital Twins of an Organization

Transportation process reliability is a competitive advantage in the market of cargo delivery services. Transportation customers are interested in shipping cargoes within agreed timeframes and ensuring their safety. These are the two main parameters of transportation process reliability, compliance with which depends on a number of factors. In particular, changes in the external environment where road transportation companies operate inevitably affect the transportation process stability. The purpose of this study is to develop an approach to road transportation reliability and risk mitigation based on the digital twin concept. The variability of business processes is usually the reason for deviations from the transportation terms agreed with the customer. These deviations can be interpreted as failures in delivering cargoes. A prerequisite for ensuring smooth cargo transportation by a road transportation company is the reduction of deviations in the performance of its business processes. The article proposes methods of computer modeling and creating a digital twin of a company reflecting the reference business processes for transportation. As a result, various deviations from the reference digital model that business processes exhibit when there are changes in the external environment can be promptly identified and corrected.

Разработка программного комплекса для испытания цифровых измерительных трансформаторов на вибростенде

The presented work examines a software package for monitoring the condition of a hydraulic servo drive with hydrostatic guides as part of a diagnostic vibration stand for digital transformers. The service life of digital instrument transformers is 25 years, and the calibration interval is 8 years. To achieve such high performance characteristics, it is necessary to conduct a large number of tests for such products. One such test is the vibration test. The uniqueness of the hydraulic drive used in the diagnostic vibration stand lies in its long service life under operational loads (up to 100 million cycles). This reliability is achieved with special hydrostatic guides in the hydraulic drive design and requires special software. The architecture of the software complex for the vibration stand has been created. To test the functionality of the package, simulation modeling of the operation of the components of the software package was performed. Aim. Based on the analysis of the functioning of technological equipment and options for implementing control software, develop the architecture of a software package for implementing a system for condition monitoring of a servo hydraulic drive with hydrostatic guides as part of a diagnostic vibration stand for digital transformers. Materials and methods. The stated scientific problems were solved using methods of system analysis, computer, mathematical and simulation modeling of the interaction of the software complex with the components of the servo hydraulic drive with hydrostatic guides. Results. The main practical result of the research is the development of the architecture of a software package for testing digital instrument transformers on a vibration stand. It is proposed to use cross-platform solutions when implementing the complex software and rely on modern experience in using freely distributed software. Conclusion. The developed architecture of the software package is focused on ensuring the automated operation of servo hydraulic drives, allows you to configure all the necessary equipment parameters, monitor the condition of the equipment using digital data transfer protocols, centrally save and replicate hydraulic drive settings for specific operating conditions on the enterprises. Analysis of implementation options showed that the use of a SCADA system simplifies the process of developing standard projects for dispatch control and data collection and condition monitoring, but at the same time, it has increased complexity at the stage of deployment and operation. The functionality of none of the widespread and reliable SCADA systems covers all the requirements for this project. This particularly applies to USB connectivity and high frequency signal processing required by design requirements. In addition, when using universal SCADA systems, the end user must purchase a license for the RunTime SCADA component.

Calculation of a heat exchanger using heat pipes in the exhaust air heat recovery system

Objective. The purpose of the work is to develop practical recommendations for the design and manufacture of a heat exchanger using heat pipes, which could find widespread use in heating, ventilation and air conditioning systems at facilities for various purposes. Method. The research is based on methods of thermodynamic analysis, full-scale and computational modeling of processes and objects of refrigeration and cryogenic technology, air conditioning and life support systems. Result. The implementation of the practical recommendations studied in the work on the use and design of heat exchangers using heat pipes in ventilation, heating and air conditioning systems will provide significant savings in energy spent on heating and/or cooling the air supplied to the room served by the HVAC system. To reduce heat loss in a building, it is rational to maintain air balance and compensate for the exhaust air with an organized influx of outside air, to heat which the heat of the removed exhaust air is utilized. Conclusion. Compared to a heat exchanger based on a glycol recuperator, a regenerator using heat pipes is less energy-intensive, requires virtually no maintenance, and is also more energy efficient due to the absence of a pumping device that requires electricity in the design. At the same time, the ability to completely separate the supply and exhaust ventilation flows of the regenerator on heat pipes is preserved, which is extremely in demand in medical institutions, due to the need to comply with strict sanitary standards.

A computational mechanical constitutive modeling method based on thermally-activated microstructural evolution and strengthening mechanisms

A mechanical constitutive relationship is the basis for the design and application of structural materials, and the establishment of a mechanical constitutive relationship generally relies on experimental data. Herein a computational mechanical constitutive modeling method is proposed, in which all required parameters possess unambiguous physical interpretations and/or can be obtained from accurate numerical simulations. With the inclusion of interaction between dislocations and crystal defects, the dislocation density and grain size evolution with strain for polycrystalline metallic materials are mathematically modeled, and the corresponding contribution to strength is analyzed, further a computational mechanical constitutive relationship can be obtained. Its effectiveness is verified by comparing it with experimental stress-strain relationships for Cu, Al-Mg, and Cu-W alloys. This method might be a powerful tool for the design of structural materials with desirable mechanical properties.

Mathematical and computational modeling of membrane distillation technology: A data-driven review

Membrane distillation (MD) technology is increasingly gaining attention as an environmentally sustainable water treatment method of emerging interest. During last three decades there has been wide efforts to model and improve the performance of this technology. In this study we examine both the mathematical and computational modeling methods used in MD with a data-driven method. To gather the dataset, a broad range of terms related with theoretical modeling of MD were searched in the Scopus database. The collection consists of 526 documents including 116 journals, 14,291 references used by authors, 1252 involved authors and 29.47 % international co-authorship rate. The overall pattern of publications is found to increase over time indicating the enhancing interest on theoretical modeling of MD process. Journal of Membrane Science and Desalination are the top two journals publishing theoretical modeling of MD, with 105 and 100 articles, respectively. Dr. Ghaffour N. contributed with the highest number of articles, 24; and Dr. Khayet M. has the highest articles fractionalized value with 7.08. The dataset was categorized first into mathematical and computational modeling, then into the used mass transport approaches through membrane hydrophobic pores. Recently, in MD field computational modeling has been considered more than mathematical modeling. The combined Knudsen diffusion/ordinary molecular diffusion model is the dominant mass transport approach considered in MD mathematical modeling with 117 articles. On the other hand, computational fluid dynamics is the most used computational method with 114 articles.

STUDY OF THE POTENTIAL FOR MODIFYING THE DESIGN OF A TURBINE STIRRER BLADE TO REDUCE THE EFFECT OF SHEAR STRESSES ON MICROORGANISMS IN CULTIVATION PROCESSES

Stirring in bioreactors is an important element for the efficient cultivation of cell cultures in biotechnological production. But high-speed stirrers can create high level of shear stresses that negatively affect microorganisms. Therefore, it is important to develop the design of new stirring devices to minimize the negative impact of shear stresses on cells during cultivation. The purpose of this study is to analyze the effect of the designs of turbine stirring devices, proposed by authors, on the parameters of the stirring process during the cultivation of cell cultures by methods of computer modeling. The computer modeling was performed in ANSYS for the process of liquid stirring in a bioreactor. Two new designs of turbine stirrers have been proposed. The idea of the new design is to divide the working blade into two, i.e. to create a cutout in the blade. In the first case, the cutout is a rectangle, in the second - a parallelogram. To compare the efficiency of the proposed designs, we also modeled the stirring with a classical turbine 6-blade stirrer. Based on the modeling results, were obtained contours of the velocity distribution, turbulent kinetic energy, shear strain rate, velocity vectors, and ISO-surfaces forming the core of the rotation vortex. It was found that the presence of cutouts in the turbine stirrer does not lead to a decrease in the velocity of the main flows and redistribution of motion vectors, but significantly reduces the value of turbulent kinetic energy from and shear strain rate. The maximum value of turbulent kinetic energy for the classical stirrer is 2.489 m2/s2, while for the stirrers with cutouts it barely reaches 1.245 m2/s2. The shear stresses decrease by 10 % from 19.63·10-3 Pa for the classical design to 17.67·10-3 Pa for the stirrer with parallelogram-shaped cutouts. The further development of this study will be to analyze the influence of the geometric parameters of the stirrer with parallelogram-shaped cutouts on the qualitative indicators of stirring. The results obtained in this work can be used by engineers and technologists to design bioreactors with reduced values of shear stresses.

Post-Translational Modifications in Tau and Their Roles in Alzheimer's Pathology.

Microtubule-Associated Protein Tau (also known as tau) has been shown to accumulate into paired helical filaments and neurofibrillary tangles, which are known hallmarks of Alzheimer's disease (AD) pathology. Decades of research have shown that tau protein undergoes extensive post-translational modifications (PTMs), which can alter the protein's structure, function, and dynamics and impact the various properties such as solubility, aggregation, localization, and homeostasis. There is a vast amount of information describing the impact and role of different PTMs in AD pathology and neuroprotection. However, the complex interplay between these PTMs remains elusive. Therefore, in this review, we aim to comprehend the key post-translational modifications occurring in tau and summarize potential connections to clarify their impact on the physiology and pathophysiology of tau. Further, we describe how different computational modeling methods have helped in understanding the impact of PTMs on the structure and functions of the tau protein. Finally, we highlight the tau PTM-related therapeutics strategies that are explored for the development of AD therapy.

Experimental Digital Twins with Socio-Economic Artificial Environments of Forecast and Analytical Simulation Models

The technological development of Russia in recent years has been moving at an active pace due to external challenges that dictate the need to search for internal resources and poses serious challenges to the scientific community in terms of developing research potential and creating software and technological sovereignty, especially emphasizing the importance of the IT industry and long-term forecasting. Nanotechnology, which incorporates the concepts of IT, is a supra-industry technology, that is, it is the basis for achieving progress in any area of human activity. Without the use of information technology, it will be extremely difficult to achieve outstanding achievements in a dynamically changing world. There is an emerging interest in new computer modeling methods that make it possible to create experimental digital twins in the form of simulation models and can partially compensate for the incompleteness of information. Having modeled the necessary processes, it is possible to make management decisions on the construction of facilities, simulate socio-economic processes, and formulate a 10-year forecast about the demographic situation of the country. The applied modeling tools discussed in the article demonstrate the usefulness of such management tools with developed functional elements in information and analytical management structures. Soon, this trend will increase and those countries that will take leading positions in this direction will be able to create ultra-effective forecasting and analytical scenarios with various levels of detail. By using all the functionality of simulation modeling, it is possible to create truly applied instrumental complexes with a potential basis for the implementation of such solutions in the structures of systems of distributed situational centers for the future development of technological sovereignty and the introduction of fundamentally new methods of strategic forecasting in the Russian Federation.

Effect of the Microorganisms Dynamics on the Base Subsidence of the Solid Household Waste Storage During Consolidation

The effect of the dynamics of the development of the microorganism biomass on the subsidence of the surface of the mass of the porous medium at the base of the storage of solid household waste was studied using mathematical and computer modeling methods. The repository of solid household waste is considered a source of the spread of organic pollutants that contribute to the development of the biomass of microorganisms. The subsidence model is considered from the theory of filtration consolidation of porous media. For this purpose, a corresponding boundary value problem in the domain with a free-moving boundary is formed. The classical equation of filtration consolidation is modified for the case of variable porosity due to biomass change. The finite element method allowed for solving the resulting mathematical model numerically in the form of a boundary value problem for the system of parabolic equations in the variable domain. Based on the developed algorithms, a software package for numerical experiments was created where the effect of microorganisms on the subsidence dynamics of a porous medium was investigated. Numerical experiments on a model example showed that the presence of microorganisms in soil pores slows the dissipation of excess pressure. However, this does not lead to a slowdown in subsidence but, on the contrary, to a particular increase of up to 18 % compared to the case of neglecting bioprocesses. From the point of view of the physics of the processes, this is explained by the increase in biomass, which leads to an increase in pressure, thus increasing the volume of filtered pore fluid and, hence, increasing subsidence.

Problems and prospects of functional nutrition in Russia: industry and social aspect

In recent years, great importance has been attached to the preservation and strengthening of public health, the role of disease prevention and the formation of a healthy lifestyle, including the formation of a culture of healthy nutrition of the population. Prolonged improper, irrational nutrition is a factor of increased risk of developing diseases: oncological diseases, alimentary risk factors of which are the presence of carcinogenic additives in food products; diseases of the cardiovascular system; obesity; disorders of the gastrointestinal tract due to the low content of dietary fiber in food; osteoporosis is a change in the composition of bones due to the loss of calcium. The analysis of the nutrition structure of the Russian population indicates significant deviations from the recommendations on rational norms of food consumption that meet modern requirements of a healthy diet. In this paper, a matrix method of developing a formula for a fermented milk product with a high protein content is considered by enriching yogurt with vegetable components: hemp flour, jerusalem artichoke syrup and agave syrup. Using the obtained recipes, samples of fermented milk products were prepared and tasting was carried out. According to the organoleptic results, the expediency of using the matrix method of computer modeling in the development of formulations of fermented milk products is confirmed. The resulting yogurts can be recommended for use by people with diabetes and those who lead a healthy lifestyle, because the protein content in the samples has been increased to 3.7% and the introduction of sugar is excluded.

Computer-Aided Prediction of the Interactions of Viral Proteases with Antiviral Drugs: Antiviral Potential of Broad-Spectrum Drugs.

Human society is facing the threat of various viruses. Proteases are promising targets for the treatment of viral infections. In this study, we collected and profiled 170 protease sequences from 125 viruses that infect humans. Approximately 73 of them are viral 3-chymotrypsin-like proteases (3CLpro), and 11 are pepsin-like aspartic proteases (PAPs). Their sequences, structures, and substrate characteristics were carefully analyzed to identify their conserved nature for proposing a pan-3CLpro or pan-PAPs inhibitor design strategy. To achieve this, we used computational prediction and modeling methods to predict the binding complex structures for those 73 3CLpro with 4 protease inhibitors of SARS-CoV-2 and 11 protease inhibitors of HCV. Similarly, the complex structures for the 11 viral PAPs with 9 protease inhibitors of HIV were also obtained. The binding affinities between these compounds and proteins were also evaluated to assess their pan-protease inhibition via MM-GBSA. Based on the drugs targeting viral 3CLpro and PAPs, repositioning of the active compounds identified several potential uses for these drug molecules. As a result, Compounds 1-2, modified based on the structures of Ray1216 and Asunaprevir, indicate potential inhibition of DENV protease according to our computational simulation results. These studies offer ideas and insights for future research in the design of broad-spectrum antiviral drugs.

PyRates-A code-generation tool for modeling dynamical systems in biology and beyond.

The mathematical study of real-world dynamical systems relies on models composed of differential equations. Numerical methods for solving and analyzing differential equation systems are essential when complex biological problems have to be studied, such as the spreading of a virus, the evolution of competing species in an ecosystem, or the dynamics of neurons in the brain. Here we present PyRates, a Python-based software for modeling and analyzing differential equation systems via numerical methods. PyRates is specifically designed to account for the inherent complexity of biological systems. It provides a new language for defining models that mirrors the modular organization of real-world dynamical systems and thus simplifies the implementation of complex networks of interacting dynamic entities. Furthermore, PyRates provides extensive support for the various forms of interaction delays that can be observed in biological systems. The core of PyRates is a versatile code-generation system that translates user-defined models into "backend" implementations in various languages, including Python, Fortran, Matlab, and Julia. This allows users to apply a wide range of analysis methods for dynamical systems, eliminating the need for manual translation between code bases. PyRates may also be used as a model definition interface for the creation of custom dynamical systems tools. To demonstrate this, we developed two extensions of PyRates for common analyses of dynamic models of biological systems: PyCoBi for bifurcation analysis and RectiPy for parameter fitting. We demonstrate in a series of example models how PyRates can be used in combination with PyCoBi and RectiPy for model analysis and fitting. Together, these tools offer a versatile framework for applying computational modeling and numerical analysis methods to dynamical systems in biology and beyond.

INFORMATION MODELING OF CONCRETE: CURRENT STATUS AND DEVELOPMENT PROSPECT S

The publication relates to the problems of digitalization of building materials science. The relevance of developing a digital model of concrete for solving optimization problems of design and synthesis of its structure, clarifying methods for calculating building structures, and improving the technology of their production is shown. The evolution of information modeling of concrete is analyzed in the context of the stages of development of system-building materials science and technology.
 A review of the main modern methods of computer modeling of concrete structure in domestic and foreign scientific research is provided. It is noted that these methods do not take into account the complexity of the structure of concrete. In the article, concrete is presented as a conglomerate composite with a hierarchically organized structure with dimensions from 10-10 to 10-1 m. It has a minimum of 5-6 scale levels and three types of substructure design. Substructures differ in their scale, genesis and mechanics of manifestation of properties. The first type of substructure is characteristic of the macro-, meso- and micro-scale levels. It is accepted in the form of a two-component “construction” of a spatially continuous matrix and discrete inclusions deterministically and stochastically distributed in it. The second type refers to the submicro-, ultra-micro- and nanoscale levels. It is believed to be in the form of a “microscale spatial structure” of new formations of a cementing substance from consolidated individual crystalline differences. The third type corresponds to the atomic-molecular structure of new formations of the cementing substance.
 The characteristics of each type of substructure are given according to: the scale of the components; features of formation; mechanics of properties manifestation; design criteria; means of synthesis. An assumption is made about the specificity of modeling each of the three types of concrete substructures and their integration into a single digital model. The task is to develop an information platform for such a model. The platform should include: a theoretical knowledge base; empirical data base; database of analytical, numerical and statistical models; algorithms for designing and synthesizing structures; optimization criteria and boundary conditions; terms of reference for computer modeling of concrete.

Bursting activity in the reduced mean-field model of neuron-glial interaction

The study of neural activity synchronization in the brain is a central focus of modern neurobiology and neurodynamics. In a healthy brain, cognitive functions necessitate the accurate integration of neural activity at specific spatiotemporal scales. Some neurological and psychiatric disorders exhibit observable variations in patterns of synchronous population activity. One of the most significant and compelling synchronous population activity patterns is the bursting activity that participates in various informational and physiological processes, including epilepsy. Several mathematical models have been proposed to explain the mechanisms of formation of the bursting activity. The most intriguing and scientifically sound models enable incorporation of astrocytic modulation of neural activity [1]. In this paper, we present a novel phenomenological model for accurately replicating the bursting neural population activity. Our model builds upon the Tsodyks-Markram [2] model and incorporates vital aspects of neuron-glial interaction through a tripartite synapse. The presented model is a simplified version of the previously proposed model [3]. During astrocyte activity (which lasts seconds), we can set the probability of neurotransmitter release, u, which is determined in fractions of a second. This enables the proposed model to be written in the following manner: r=–E+α ln(1+exp((Ju(Y)xE+I0)/α)), =(1–x)/τD–u(Y)xE, =–y/τY+βσy(X). Here, E(t) represents the average neuronal activity of the excitatory population, while x(t) denotes the quantity of available neurotransmitter. Additionally, y(t) describes the concentration of gliotransmitters, which are released as a result of biochemical reactions during neuron-astrocyte interactions. The function describes the alteration in the likelihood of neurotransmitter release when gliotransmitters are present u(y)=u0+(∆u0)/(1+exp(–50(y–ythr)). Here u0 represents the probability of neurotransmitter release without astrocytic influence; ∆u0 indicates the change in the probability of neurotransmitter release caused by the interaction of the gliotransmitter with the presynaptic terminal, and ythr represents the threshold value that determines the change in the probability of neurotransmitter release due to the effect of a gliotransmitter. The function describes the influence of neurotransmitter on the concentration of the gliotransmitter σy(x)=1/(1+exp(–20(x–xthr)), where xthr is the astrocyte activation threshold. Note that the proposed model does not account for synaptic depression’s mechanism. Therefore, various dynamical regimes’ formation in the model is solely controlled by astrocytic dynamics. In the study, control parameters I0 and u0 were selected while the remaining parameters were held constant. Specifically, τ=0.013, τD=0.08, α=1.58, J=3.07. Changes in the concentration of neurotransmitters and gliotransmitters were characterized by parameters ∆u0=0.305, τν=3.3, β=0.3, xxthr=0.75, ythr=0.4. The research was conducted using computer modeling and numerical methods in nonlinear dynamics. The proposed model exhibits a diverse range of population activity patterns, such as spiking and bursting regular and chaotic activity. Chaotic dynamics zones are identified in the control parameter plane. An account is given of the mechanisms behind the emergence of these activity patterns through bifurcation analysis. It is shown that the occurrence of chaotic activity in the system can be associated both with the cascade of period doubling bifurcations and with the further development of chaos, as a result of which a homoclinic attractor appears in the system according to the Shilnikov scenario. It was also shown that multistability is observed in the system in a certain range of parameters. Note that the emergence of multistability and bursting activity in the model is independent of the intricacy of neuron and glial cell dynamics. These dynamics are instead influenced by the feedback loop between the presynaptic neuron and the glial cell. The effects of neuron-like dynamics and neural-glial interaction demonstrated are generally applicable, without specifying particular characteristics of neural-glial interaction, network architecture, or single-cell neuron dynamics. It should be noted that our proposed model solely concerns the potentiation of synaptic transmission by astrocytes. In summary, the proposed phenomenological model for population activity can replicate various patterns of neuron activity found in a wide range of dynamic memory and information processing studies. This research can potentially lead to the development of new, effective treatment methods for neurological diseases that involve neuron-glial interaction. Another potential application for these results is in the development of an optimized live chip that has preset functions. This requires a deeper understanding of rhythmogenesis in neural networks and brain function.

A matched-pair case control study identifying hemodynamic predictors of cerebral aneurysm growth using computational fluid dynamics.

Introduction: Initiation and progression of cerebral aneurysms is known to be driven by complex interactions between biological and hemodynamic factors, but the hemodynamic mechanism which drives aneurysm growth is unclear. We employed robust modeling and computational methods, including temporal and spatial convergence studies, to study hemodynamic characteristics of cerebral aneurysms and identify differences in these characteristics between growing and stable aneurysms. Methods: Eleven pairs of growing and non-growing cerebral aneurysms, matched in both size and location, were modeled from MRA and CTA images, then simulated using computational fluid dynamics (CFD). Key hemodynamic characteristics, including wall shear stress (WSS), oscillatory shear index (OSI), and portion of the aneurysm under low shear, were evaluated. Statistical analysis was then performed using paired Wilcoxon rank sum tests. Results: The portion of the aneurysm dome under 70% of the parent artery mean wall shear stress was higher in growing aneurysms than in stable aneurysms and had the highest significance among the tested metrics (p = 0.08). Other metrics of area under low shear had similar levels of significance. Discussion: These results align with previously observed hemodynamic trends in cerebral aneurysms, indicating a promising direction for future study of low shear area and aneurysm growth. We also found that mesh resolution significantly affected simulated WSS in cerebral aneurysms. This establishes that robust computational modeling methods are necessary for high fidelity results. Together, this work demonstrates that complex hemodynamics are at play within cerebral aneurysms, and robust modeling and simulation methods are needed to further study this topic.