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Although paper-based analysis is known for centuries, only during the last decade this simple substrate became an object of detailed microfluidic studies. In order to obtain optimum performance and separation of the analytes in a microfluidic channel, devices should be optimized, both in terms of architecture and paper properties. Enzyme immobilization methods can not only increase the storage stability but also have an impact on the flow in paper matrix, providing additional charges, and changing the porous structure of paper. Therefore it should be guaranteed that the method of choice will not obstruct the flux in the final device. Paper-based device proposed in this study was composed of a bioactive channel, Pt working electrode, pencil drawn pseudo-reference electrode, a buffer filled sponge providing the wicking solution and a stack of wicking pads to guarantee continuous flow. Based on our previous research we chose 4 methods of enzyme immobilization relying on different phenomena (adsorption, covalent linkage, layer-by-layer, capsules). Different channel architectures were also evaluated in order to achieve optimum time of the enzymatic reaction, separation of peaks and the time of measurement. Experimental results were compared with computer simulations. Final device could quantify glucose (2.0-10.0 mmol L−1) and uric acid (0.1-1.2 mmol L−1) in their clinical range with good repeatability. [ABSTRACT FROM AUTHOR]

For the past 15 years, pre-university students in many countries including the United States have encountered data analysis and probability as separate, mostly independent strands. Classroom-based research suggests, however, that some of the difficulties students have in learning basic skills in Exploratory Data Analysis stem from a lack of rudimentary ideas in probability. We describe a recent project that is developing materials to support middle-school students in coming to see the “data in chance” and the “chance in data.” Instruction focuses on four main ideas: model fit, distribution, signal-noise, and the Law of Large Numbers. Central to our approach is a new modeling and simulation capability that we are building into a future version of the data-analysis software TinkerPlots. We describe three classroom-tested probability investigations that employ an iterative model-fit process in which students evaluate successive theories by collecting and analyzing data. As distribution features become a focal point of students’ explorations, signal and noise components of data become visible as variation around an “expected” distribution in repeated samples. An important part of students’ learning experience, and one enhanced through visual aspects of TinkerPlots, is becoming able to see things in data they were previously unable to see.

The paper delves into the possibilities of computer modeling for manipulator systems within the Matlab program. The analysis is directed towards a two-link manipulator model. Within the framework of kinematic analysis, the paper confronts the solution to the inverse kinematics problem and subsequently navigates through the solution to the direct kinematics problem. The trajectory is modeled by a fifth-degree polynomial during the motion from a known initial position to the specified final position within defined working regions of the manipulator. The work encompasses graphical representation of the results. The manipulator's workspace is also delineated, considering angular constraints on both arms and illustrating the trajectories during operational movement. [ABSTRACT FROM AUTHOR]

Researchers have found that computer modeling fosters the learning of causal mechanisms in systems, an important crosscutting concept in science that many novice learners find challenging. Despite the research that highlights the role of teacher's instructional practices in enacting computer tools, few studies have considered teachers' use of computer modeling and its implications for student learning in classroom interactions, compared to interactions without computer tools. In this study, we examine (a) the impact of computer modeling on students' understanding of causal links in decomposition and (b) classroom interactions with use of computer modeling. We employed a quasi‐experimental design with eight middle school science classes that served predominately Latinx students. The random treatment was at the class level (computer modeling; n = 60, four classes) and control (paper modeling; n = 59, four classes). Analyses incorporated student preassessment and postassessment, classroom observations, and audio‐recorded modeling instruction. Results indicate that compared to paper modeling, computer modeling enriched systems thinking, particularly students' ability to provide causally coherent statements in explaining scientific ideas and evidence. Enactment of computer modeling may be associated with a shift in classroom interactions to include more invitation for students' elaboration of causal systems. We discuss aspects of computer modeling that may foster systems thinking, with implications for the future design of tools and curricula. [ABSTRACT FROM AUTHOR]

The paper overviews the results of computational studies of the molecular mechanisms underlying the adaptation of model cell membranes taking place during their interaction with proteins and peptides. We discuss changes in the structural and dynamic parameters of the water–lipid environment, the hydrophobic/hydrophilic organization of the lipid bilayer surface (the so-called "mosaicity"), etc. Taken together, these effects are called the "membrane response" (MR) and constitute the most important ability of the cell membranes to respond specifically and consistently to the incorporation of extraneous agents, primarily proteins and peptides, and their subsequent functioning. The results of the authors' long-term research in the field of molecular modeling of MR processes with various spatial and temporal characteristics are described, from the effects of binding of individual lipid molecules to proteins to changes in the integral macroscopic parameters of membranes. The bulk of the results were obtained using the "dynamic molecular portrait" approach developed by the authors. The biological role of the observed phenomena and potential ways of rationally designing artificial membrane systems with specified MR characteristics are discussed. This, in turn, is important for targeted changes in the activity profile of proteins and peptides exerting action on biomembranes, not least as promising pharmacological agents. [ABSTRACT FROM AUTHOR]

Plain-weave fabric is a kind of fiber preform which has been commonly used in resin transfer molding (RTM) to manufacture polymer composites. However, the edge area of plain-weave fabric is easy to shed yarns which will cause the uneven distribution of permeability between edge channel and center of mold in filling process of RTM. Meanwhile, the uneven distribution of permeability will cause the edge effect and seriously affect the final quality of composite materials. In this paper, a method to numerically calculate the permeability of edge channel which fully considers the edge area of plain-weave fabric is proposed. The experiment and simulation of edge effect in filling process are performed. The results show that the simulation of edge effect which applies the edge channel's permeability calculated by this method are in good agreement with the experimental results. The research in this paper is meaningful to improve the accuracy of edge effect simulation so as to provide a reference for the design of mold structure. [ABSTRACT FROM AUTHOR]

Road tunnels are equipped with various safety installations that enable the tunnel's autonomous response to fire in order to ensure conditions suitable for safe self-rescue and evacuation. A key role in this effort is played by the monitoring of the longitudinal airflow velocity and its regulation. This study contributes to validation of the Fire Dynamics Simulator (FDS 6) capabilities to model tunnel airflow generated by emergency ventilation. A previous study, in which an FDS 6 model of a real 900 m long motorway tunnel was developed and validated by a full-scale ventilation test, pointed to the relatively high inaccuracies of the average steady-state airflow velocity generated by ventilation measured by tunnel anemometers (13%, 17% and 14% for three ventilation modes). In this paper, it is shown that the application of a modified evaluation procedure and improving the representation of tunnel anemometers leads to the significant improvement of simulation results with inaccuracies of 5%, 1% and 3% for the considered ventilation modes. The observed inaccuracies are even comparable to the measurement accuracy of the tunnel anemometers. A further extension of the modeling of the steady-state airflow velocity generated by emergency ventilation measured by the used anemometers is also described. [ABSTRACT FROM AUTHOR]

Spacecraft are affected by cosmic plasma electrons, which cause the electrification of their dielectric materials. As a result, electrostatic discharges occur, leading to failures in the operation of onboard radio electronics, reducing the period of the active existence of the spacecraft. The use of composite polymer dielectrics with increased conductivity is a promising method for protecting against the effects of electrostatic discharges. This paper presents the results of modeling the characteristics of a broadband amplifier made on a printed circuit board using a highly conductive composite dielectric. Resistances are added to the model of the ongoing electrical processes that characterize current leakage from the circuit nodes to the zero conductor due to the decrease in the specific volume resistance of the printed circuit board's material. A computer simulation of a broadband amplifier and an experimental study of its performance in the operating frequency band of 0.5–70 MHz are carried out. It is shown that a change in the bandwidth and gain occurs only when the conductivity becomes higher than 6 × 10–4 Ohm–1 m–1. The results of an experimental study of a broadband amplifier show that the proposed model for accounting for the specific volume resistance of the printed circuit board material adequately describes its characteristics. The fact that even with a conductivity of 10–9 Ohm–1 m–1 electrostatic discharges are excluded indicates the possibility of protecting broadband amplifiers as part of the radio-electronic devices of spacecraft from electrification when using composite dielectrics of increased conductivity. [ABSTRACT FROM AUTHOR]

Cryptocurrencies have increasingly attracted the attention of several players interested in crypto assets. Their rapid growth and dynamic nature require robust methods for modeling their volatility. The Generalized Auto Regressive Conditional Heteroskedasticity (GARCH) model is a well-known mathematical tool for predicting volatility. Nonetheless, the Realized-GARCH model has been particularly under-explored in the literature involving cryptocurrency volatility. This study emphasizes an investigation on the performance of the Realized-GARCH against a range of GARCH-based models to predict the volatility of five prominent cryptocurrency assets. Our analyses have been performed in both in-sample and out-of-sample cases. The results indicate that while distinct GARCH models can produce satisfactory in-sample fits, the Realized-GARCH model outperforms its counterparts in out of-sample forecasting. This paper contributes to the existing literature, since it better reveals the predictability performance of Realized-GARCH model when compared to other GARCH-types analyzed when an out-of-sample case is considered. [ABSTRACT FROM AUTHOR]

This research paper uses a numerical modeling process to recreate the actual operating conditions of the water distribution system in the town of Kleosin, located on the border with Bialystok. The performed calculations allowed for the creation of a model for the functioning of the water supply network and for taking rational and optimal decisions affecting the effective operation of the entire system. The numerical modeling process is presented as a common tool to rationally and optimally manage the water distribution system. At the same time, numerous possibilities of computationally modeling and processing accurate real data were presented. The scope of the study included the network model analyzed in terms of the basic quality parameters that the network should meet, such as flow velocity, pressure, unit losses, water age, and operating conditions during simulated events, such as expansion or system failure, broken down into assumed time variants. As part of the paper, a situational variant was presented, which concerned the planned modernization in order to improve the functioning of the system by extending water distribution with new sections. The Epanet computer program distributed by US EPA was used in the research. [ABSTRACT FROM AUTHOR]

In some reversible deactivation radical polymerization (RDRP) processes retention of chain‐end functionality appears to be higher than expected based on the estimated rate constants of propagation and termination. In the recent paper, Ballard and Asua explained this observation using their concept of the probability density functions of the termination reactions, dependent on the initial diffusion stage of radicals being the nearest neighbors. Here, a new explanation of the observed phenomenon is proposed, alternative to their proposition. The presented hypothesis assumes interaction of growing radical with the RDRP deactivator, resulting in two types of radicals. [ABSTRACT FROM AUTHOR]

In the paper, based on the method of computer simulation, the process of charging a lithium-ion battery for an electric car from a wireless charger of the inductive-resonance type was investigated. It is shown that when modeling this process, it is necessary to take into account the simultaneous flow of two processes of different scales in time and interconnected - a short-term high-frequency process in the inverter of the charger with a characteristic time of 10-5 s and a long-term process of charging the battery with a characteristic time of 104 s. Direct numerical calculation of these two processes simultaneously requires significant computer resources. To solve this problem, a new approach is proposed and implemented in the Matlab/Simulink package, according to which, at the first stage, when calculating high-frequency processes in the inverter, there are modified Thevenin and Norton equivalents for a wireless charging device, taking into account the total internal losses in this device, and at in the second stage, the long-term battery charging process is calculated first in the mode of a constant current source, using the constructed Norton equivalent, and then in the mode of a constant voltage source, using the constructed Thevenin equivalent. This approach makes it possible to take into account interrelated and time-varying processes in the inverter and in the battery and to investigate the efficiency of wireless transmission of electrical energy from a stationary power source to a battery located on board an electric vehicle. According to the results of the calculations, it is shown that for the developed device, the integral efficiency of the entire battery charging process when the battery parameter increases from 20% to 95% is 86%. References 9, figures 8. [ABSTRACT FROM AUTHOR]

Ducted fans with thin‐shelled tubular structures are typically used in unmanned aerial vehicles. However, due to their thinness and heterogeneity, the ducts are prone to warpage deformation, which can adversely affect the aerodynamic characteristics of the fans. In this study, Moldflow software was used to analyze and reduce the warpage deformation of a duct made of 15 wt% glass fiber‐reinforced acrylonitrile butadiene styrene. First, a Taguchi experiment was performed to determine the main factors affecting the warpage: the mold surface temperature, melt temperature, injection pressure, and holding pressure. Subsequently, the response surface methodology (RSM) was employed to define a regression equation and response surface relating the dependent and independent variables, and a genetic algorithm (GA) was used for optimization. The maximum warpage was successfully reduced from 0.2217 to 0.0465 and 0.0578 mm through the RSM and GA analyzes, respectively, and the simulated results were validated by data collected using a COMET L3D system. Finally, the influence of the warpage of the ducted rear deflector on the aerodynamic performance was investigated by performing computational fluid dynamics analysis. The results indicated that curving the rear deflector has a beneficial effect on aerodynamic performance, as it increases velocity, but it also reduces the impact of the torque balance. This paper describes an innovative application method using a specific combination of analysis tools to address the problem of optimizing the design, modeling, and performance of ducted fans. This work can help predict manufacturing results and aerodynamic effectiveness at an early stage. [ABSTRACT FROM AUTHOR]

The paper is devoted to the study of dynamic growth of shear cracks in brittle materials with various degrees of inhomogeneity of the internal structure. The study was carried out by DEM modeling using an advanced model of fracture based on the principles of kinetic theory of strength and taking into account the finite time of local fracture. The complexity of the material internal structure was effectively taken into account by changing the key parameter of the model – the fracture incubation time. It is shown that an increase in the degree of inhomogeneity of the internal structure leads to a decrease in the crack propagation velocity according to a logarithmic law. The key result of the research is the assessment of the size of fracture process zone. It is shown that the size of fracture process zone is not constant, but changes during dynamic crack growth. The nature of its change, as well as the average value, depends on the degree of heterogeneity of the material structure. [ABSTRACT FROM AUTHOR]

In 1976 M.W. Mahaffy published a basic ice-sheet model which did not make the usual steady-state assumption of constant height and which allowed for time-varying ice accumulation rates. For this reason his model should be of interest to creation researchers, who can use it to model the rapid growth of post-Flood ice sheets. This paper provides a brief overview of the theory and assumptions behind Mahaffy's model and its solution. The model is used to simulate the rapid growth of a long but thin isothermal ice ridge. The results are then compared with the results from the Vardiman model. A suggested technique for using the Dansgaard-Johnsen and Mahaffy ice sheet models to estimate annual layer thicknesses near an ice divide is also presented. [ABSTRACT FROM AUTHOR]

This paper aims to improve the accuracy of the finite element analysis for the preform shape transformation according to the difference in the type of carbon fiber and friction force. The carbon fiber type (Toray T700, Zoltek), the fiber direction (0°/90°, ± 45°), and the frictional force were measured, which occurred between the fiber and the mold and between the fiber and the fiber. A comparative experiment was conducted through actual preform production by designating it as a variable for element analysis. The analysis was conducted according to the difference between the static friction coefficient and the dynamic friction coefficient in the molding analysis. Within the range of the Coulomb equation, the shear angle changing was compared with the actual preform shape to show similar results. [ABSTRACT FROM AUTHOR]

This paper focuses on antenna modeling using wire-grid and surface triangulation as two of the most commonly used MoM-based approaches in this field. A comprehensive overview is provided for each of them, including their history, applications, and limitations. The mathematical background of these approaches is briefly presented. Two working algorithms were developed and described in detail, along with their implementations using acceleration techniques. The wire-grid-based algorithm enables modeling of arbitrary antenna solid structures using their equivalent grid of wires according to a specific modeling recommendation proposed in earlier work. On the other hand, the surface triangulation-based algorithm enables calculation of antenna characteristics using a novel excitation source model. Additionally, a new mesh generator based on the combined use of the considered algorithms is developed. These algorithms were used to estimate the characteristics of several antenna types with different levels of complexity. The algorithms computational complexities were also obtained. The results obtained using these algorithms were compared with those obtained using the finite difference time domain numerical method, as well as those calculated analytically and measured. The analysis and comparisons were performed on the example of a rectangle spiral, a spiral, rounded bow-tie planar antennas, biconical, and horn antennas. Furthermore, the validity of the proposed algorithms is verified using the Monte Carlo methodology. [ABSTRACT FROM AUTHOR]

In this paper, a model for Cr (VI) removal and optimization was made using a novel aerogel material, chitosan-resole CS/R aerogel, where a freeze-drying and final thermal treatment was employed to fabricate the aerogel. This processing ensures a network structure and stability for the CS, despite the non-uniform ice growth promoted by this process. Morphological analysis indicated a successful aerogel elaboration process., FTIR spectroscopy corroborated the aerogel precursor's identity and ascertained chemical bonding after adsorption. Owing to the variability of formulations, the adsorption capacity was modeled and optimized using computational techniques. The response surface methodology (RSM), based on the Box–Behnken design using three levels, was used to calculate the best control parameters for the CS/R aerogel: the concentration at %vol (50–90%), the initial concentration of Cr (VI) (25–100 mg/L), and adsorption time (0.3–4 h). Analysis of variance (ANOVA) and 3D graphs reveal that the CS/R aerogel concentration and adsorption time are the main parameters that influence the initial concentration of CS/R aerogel metal-ion uptake. The developed model successfully describes the process with a correlation coefficient of R2 = 0.96 for the RSM. The model obtained was optimized to find the best material design proposal for Cr (VI) removal. Numerical optimization was used and showed superior Cr (VI) removal (94.4%) under conditions of a CS/R aerogel concentration of 87/13 %vol, with an initial concentration of Cr (VI) of 31 mg/L, and an adsorption time of 3.02 h. These results suggest that the proposed computational model can obtain an effective and viable model for CS material processing and for optimization of the uptake of this metal. [ABSTRACT FROM AUTHOR]

Non-conventional crystallization techniques have been developed in recent years. Non-conventional crystallization techniques use primary structural elements (for example, clusters) rather than atoms and molecules. Modern nanomaterial science is going through great changes as an entirely new approach of non-conventional growth mechanisms is emerging due to cluster coupling, catalyzing interest in cluster physics. The formation of fractal and percolation clusters has increased. We carried out step-by-step modeling and an experimental study of the formation of fractal and percolation clusters based on tin dioxide and silicon dioxide and formed by sol–gel technology. In this paper, the growth of fractal aggregates (clusters) from sol particles SnO2 and SiO2 based on the modified models of diffusion-limited and cluster–cluster aggregation is discussed. A percolation model using simulated fractal clusters of SnO2 and SiO2 particles is proposed. Experimental data on the sol–gel percolation structure of porous nanocomposites are presented. The modeling of SnO2 and SiO2 particles, which also consist of clusters (the next step in the hierarchy), is shown. We propose a generalized hierarchical three-dimensional percolation cluster model that allows calculating the surface area, knowing the experimental sizes of macropores and taking into account the micro- and mesopores (sizes less than a few nanometers). [ABSTRACT FROM AUTHOR]

The void defect is one common problem in liquid composite molding (LCM), which seriously affects the quality of the polymer composites. The prediction of void content has become a focus of research. However, the existing studies are based on isothermal conditions and the effect of non-isothermal conditions on void formation has been rarely studied yet. In this paper, based on the analysis of the micro-flow and meso-flow in the plain-weave fabric, a mathematical model to predict the void formation has been proposed. The change of resin viscosity, curing reaction, energy transfer and surface tension under non-isothermal conditions are fully considered, so the effect of non-isothermal conditions on void formation has been obtained. The void content has been measured experimentally. The results of the prediction model are in good agreement with the experimental results. This study can provide reference for the prediction of void content and distribution of composites in polymer industry. [ABSTRACT FROM AUTHOR]

In the present work a computational approach is applied to model and predict the results of X‐ray resonant magnetic reflectometry – a non‐destructive synchrotron‐based technique to probe chemical composition, crystallographic environment and magnetization in multilayer epitaxial heterostructures with nanoscale depth resolution. The discussed 2D mapping approach is a step forward with respect to conventional resonant X‐ray reflectometry and consists of collecting a fine step array of reflected intensity as a function of grazing angle and photon energy across the absorption edge of a particular chemical element. With the use of circularly polarized photons the method can be extended to magnetic systems to produce a map of dichroic reflectance directly related to the magnetization profile of the heterostructure. Studying the magnetic field dependence of dichroic reflectance maps can provide valuable information on the magnetization reversal of individual sublayers of a multilayer heterostructure. In the present paper modeling is performed for a bilayer system mimicking the behavior of a 30 nm ϵ‐Fe2O3 thin film that is known to exhibit a pronounced two‐component magnetic hysteresis. A technique to find optimal energy/angle combinations in order to sense magnetization of individual sublayers is proposed. Also discussed is the advantage of heavy‐element capping, which leads to a substantial increase of the dichroic intensity oscillation contrast in the pre‐edge region where the sensitivity to the magnetic behavior of the deeply buried interfaces is most pronounced. [ABSTRACT FROM AUTHOR]

Obtaining uniform hardening of the near-surface area to a given depth requires precise selection and control of laser radiation parameters, depending on the geometry of the part and its properties. Since laser irradiation is performed locally with step-by-step processing of the entire surface, the accumulated heat leads to an increase in the hardening depth and surface melting. In order to avoid uneven depths, it is necessary to vary the laser energy supply during processing to maintain stationary heating of the material. Experimental selection of technological parameters usually takes an excessive amount of time and material resources. This article presents a technique for the mathematical modeling of a high-carbon tool steel hardening process by calculating the temperature fields induced by laser radiation. The boundary of the hardening zone was determined as the isotherm of the corresponding austenitizing critical temperature in accordance with the heating rate. Experimental verification of the model was carried out on tool steels with carbon contents of 0.7 and 1.2%. The influence of the main processing technological parameters (radiation power, the laser spot diameter, and scanning speed) on the hardening zone size is shown. The paper also presents the use of the model for selection of the technological parameters of multi-track treatment to harden materials to a constant depth without surface melting. The effect of back tempering in overlapped regions is also considered. [ABSTRACT FROM AUTHOR]

This paper presents the construction of a computer model of crater formation during nanosecond laser evaporation of matter based on the example of monocrystalline silicon. The computer simulation is used to determine the dynamics of crater formation on the material surface exposed to nanosecond laser pulses. The diameter of the obtained crater and its depth were evaluated. The corresponding experiments on laser ablation of monocrystalline silicon were also carried out. Analysis of experimental data and simulation results showed that depending on the pulse duration and energy density of laser radiation the mechanism of material removal changes. Thus, the presence of the liquid phase in the ablation process seriously affects the crater depth and diameter for the entire range of energy densities from 0.4 to 104.0 J/cm2. It is shown that the computer model makes it possible to determine the volume of removed material due to evaporation and evaluate the effect of the liquid phase on crater characteristics. [ABSTRACT FROM AUTHOR]

S-acylation is a post-translational linkage of long chain fatty acids to cysteines, playing a key role in normal physiology and disease. In human cells, the reaction is catalyzed by a family of 23 membrane DHHC-acyltransferases (carrying an Asp-His-His-Cys catalytic motif) in two stages: (1) acyl-CoA-mediated autoacylation of the enzyme; and (2) further transfer of the acyl chain to a protein substrate. Despite the availability of a 3D-structure of human acyltransferase (hDHHC20), the molecular aspects of lipid selectivity of DHHC-acyltransferases remain unclear. In this paper, using molecular dynamics (MD) simulations, we studied membrane-bound hDHHC20 right before the acylation by C12-, C14-, C16-, C18-, and C20-CoA substrates. We found that: (1) regardless of the chain length, its terminal methyl group always reaches the "ceiling" of the enzyme's cavity; (2) only for C16, an optimal "reactivity" (assessed by a simple geometric criterion) permits the autoacylation; (3) in MD, some key interactions between an acyl-CoA and a protein differ from those in the reference crystal structure of the C16-CoA-hDHHS20 mutant complex (probably, because this structure corresponds to a non-native dimer). These features of specific recognition of full-size acyl-CoA substrates support our previous hypothesis of "geometric and physicochemical selectivity" derived for simplified acyl-CoA analogues. [ABSTRACT FROM AUTHOR]

In this study, the authors explored the issues of the Soderbergh electrolysis cell's increase in economic efficiency. This result was achieved by analyzing the temperature fields of the electrolysis cell in order to determine the overheating points. As a result, it led to the determination of the points of the hearth bottom's subsequent breakdown, causing the failure of the electrolysis cell. In this paper, the mathematical modeling of the temperature fields using a spatially distributed mathematical model and conducted experimental studies were carried out. The mathematical model also provides the opportunity to measure the temperature field in the hearth bottom (at the bottom) of the OA-300M electrolysis cell. The results of the given research can be used to solve the experimental determination of the hearth bottom internal defect problem. [ABSTRACT FROM AUTHOR]

In this paper, we construct a mathematical model for estimating the mass of water flooding the coastline of a basin. The models of the relief of the bottom of the basin and the relief of the flooding part of the coastline are constructed by stochastic methods. The simulation is based on empirical data of measurements of depths of the basin and the study of level lines on maps of the coastal zone. The equations of the surface relief of the coastal zone are constructed by using empirical data from maps with level lines. [ABSTRACT FROM AUTHOR]

During the last years, cryptocurrencies have been increasingly becoming a relevant subject of academic researchers and investors. This paper adopts a novel framework that combines a multivariate Generalized AutoRegressive Conditional Heteroskedasticity (GARCH) and Copula modeling in a two-stage approach to analyze the cryptocurrency volatility dynamics. By combining the aforementioned techniques, on top of showing that price movements in one cryptocurrency can significantly influence others, the use of copulas highlight how these effects can vary across different parts of distributions and thus for different types of events with respect to their extreme nature. The interconnectedness complexity should be taken into consideration when managing risk in portfolio and constructing relevant models. • Cryptocurrencies are characteristic by high levels of volatility. • This paper adopts a novel framework to analyze the cryptocurrency volatility. • The results show that large cryptoassets are highly interconnected. • Diversification in such setting is highly challenging. • Investor needs to explore more risky and less liquid avenues to manage their portfolio. [ABSTRACT FROM AUTHOR]

Hybrid systems for generating electricity from multiple sources are becoming an increasingly popular subject of analysis in science and industry. This paper presents a validated model of a hybrid ORC plant powered by solar and geothermal energy. A key challenge in optimizing the operating parameters over time was the variability of solar conditions, which was the main energy source of the system. The operation of the ORC plant is simulated using a complex model with Multiple Input Multiple Output (MIMO) variables, which is nonlinear. The input variables represent the system's operational parameters, while the output variables describe the plant's performance indicators. The main objective of this paper is to optimize the year-round performance of the ORC installation through different computational techniques. The first approach involves the application of the gradient-based optimization method that is known as sequential quadratic programming (SQP). With the use of SQP, two distinct simulation runs (SQP-N and SQP-Q/N) of the system are performed, each with a specific objective function to be optimized. The second approach is based on reinforcement learning principles and leverages the method known as Deep Deterministic Policy Gradient (DDPG) algorithm. The main advantage of DDPG over SQP is that DDPG does not require knowledge of the model. This improves the algorithm flexibility, making it well-adapted to fluctuating environmental conditions. Overall, three optimization runs (two using SQP, one using DDPG) have been performed, aiming at identifying the optimal year-round control strategy for the installation. The results revealed that under the control of DDPG, the hybrid system has produced the highest amount of electricity (4993.4 MWh), outperforming in this matter SQP-N and SQP-Q/N optimization variants by 16.83 % and 10.49%, respectively. • Thermodynamic model of a hybrid organic Rankine cycle (ORC) system is developed. • Three approaches for optimizing the annual operation of the ORC are presented. • An approach based on the Deep Deterministic Policy Gradient (DDPG) algorithm is proposed. • Application of the DDPG algorithm results in the best annual performance of the ORC. [ABSTRACT FROM AUTHOR]

This paper extends the observations presented in the previously published work on the afterhyperpolarization (AHP) duration changes in motoneurones (MNs) on the paretic (more affected) side of 11 post-stroke patients by the same analysis on the non-paretic (less-affected) side. The estimated AHP duration for patients’ MNs supplying more-affected muscles was significantly longer than control values and the elongation decreased with patient age and disorder duration. For MNs supplying less-affected muscles, dependency of AHP duration on age was closer to the control data, but the scatter was substantially bigger. However, the AHP duration estimate of less-affected MNs tended to be longer than that of controls in the short time elapsed since the stroke, and shorter than controls in the long time. Our results thus suggest that the spinal MNs on both sides respond to the cerebral stroke rapidly with prolongation of AHP duration, which tends to normalize with time, in line with functional recovery. This suggestion is in concert with the published research on post-stroke changes in brain hemispheres. To our knowledge, these dependencies have never been investigated before. Since the number of our data was limited, the observed trends should be verified in a larger sample of patients and such a verification could take into account the suggestions for data analysis that we provide in this paper. Our data are in line with the earlier published research on MN firing characteristics post-stroke and support the conclusion that the MUs of the muscles at the non-paretic side are also affected and cannot be considered a suitable control for the MUs on the paretic side. [ABSTRACT FROM AUTHOR]