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The absorption of neutrons in nano-${\mathrm{\text{Si}}}_3{\mathrm{\text{N}}}_4$ particles at different energies has been studied by computer modeling. The investigation was carried out separately for the silicon and nitrogen atoms that contain ${\mathrm{\text{Si}}}_3{\mathrm{\text{N}}}_4$ nanoparticles. Since the effective cross-section of absorption in different types of isotopes of silicon and nitrogen atoms is different, the modeling was performed separately for each stable isotope. Simultaneously, the effective cross-section spectra of neutrons for silicon and nitrogen atoms were studied.

The dissipation of the excitation wavefronts is a specific mechanism of propagation failure if the sharp gradient of the transmembrane voltage at the wavefront smears out and spread of voltage becomes diffusive, as the main excitation current becomes inactivated. This is produced by the normal kinetics of the ionic currents underlying the action potential. Here we demonstrate that the dissipation of the excitation wavefront can cause arrhythmia as well as lead to its self-termination. We use Courtemanche et al. model of human atrial action potential to demonstrate how reentry creates dynamic electrophysiologic inhomogeneity of the tissue. Local dissipation of the excitation front causes wave breaks and instantaneous displacement of the tip of the reentry, and the same mechanism can lead to elimination of all wavelets, as the inhomogeneity creates conditions for simultaneous dissipation of their excitation fronts.

Genetic and drug-induced abnormalities of cardiac repolarization have been linked to fatal arrhythmias. These arrhythmias result from a complex interaction of the remaining currents during excitation and repolarization. In this review, we examine recent advancement in investigations of genetic heart diseases and mechanisms of arrhythmia generation. We also present our simulation of repolarization during rapid pacing for different levels of block of the rapid delayed rectifier current, I_Kr, and pharmacological interventions using the Luo–Rudy model. Control simulations showed the development of alternans at a basic cycle length (BCL) of 131 ms. Two levels of I_Kr block were simulated corresponding to type 2 of familial long QT syndrome, LQT2. At 100% I_Kr block, the threshold BCL for the appearance of alternans increased to 145 ms and for shorter cycle lengths showed increasingly complex patterns of periodic and chaotic behavior. We examined the potential of other currents to correct this complex behavior. Improvement of the threshold for bifurcation as a function of BCL was achieved by: (1) 100% block of a nonspecific Ca²⁺-activated current; (2) 15% block of L-type Ca²⁺ current; (3) 20% increase of Na⁺/K⁺ pump current; (4) 50% increase of SERCA2 pump activity. Conversely, increased L-type Ca²⁺ current, decreased Na⁺/K⁺ pump current, or decreased SERCA2 pump activity increased the threshold BCL. Modification of several other currents had little effect. Alternans and chaotic activity develop at fast pacing rates in model guinea pig ventricular myocytes through a sequence of bifurcations. We elucidated mechanisms that modify the development of alternans which may provide novel targets for treatment of patients with LQT2.

A set of parametric equations of an algebraic curve or surface is called normal, if all the points of the curve or the surface can be given by the parametric equations. In this paper, we present a method to decide whether a set of parametric equations is normal. In addition, we give some simple criteria for a set of parametric equations to be normal. As an application, we present a method to find normal parametric equations for conics. We also present a new method to find parametric equations for conicoids, and if the parametric equations found are not normal, the missing points can also be given.

Quantifying differences in joint loading for coxa vara and coxa valga is important for understanding what constitutes a pathological deformity. Prior free-body analyses for varus and valgus femora suggest that the loading direction in single-leg stance becomes more vertical for coxa valga and more horizontal for coxa vara. The objectives of this study were: 1) to apply a density-based load estimation technique to varus and valgus femora; 2) to infer potential differences in femoral loading for varus and valgus femora from the density; and 3) to compare the results with previous studies of femoral loading for single-leg stance. Representative valgus, normal, and varus femora from male cadavers were scanned in the plane of the femoral neck using computed tomography. A two-dimensional finite element model, including the density data from the CT scans, was constructed for each femur. A density-based bone load estimation method was used to determine the dominant loading pattern, and an average load direction was calculated. The average load direction varied consistently from more vertical for coxa valga to more horizontal for coxa vara. The results indicate that the differences in loading directions reduce the risk of epiphyseal slip or neck fracture in coxa vara and increase the tendency for subluxation or dislocation in coxa valga. Agreement between relative load angles from the density-based load estimation and free-body analyses confirms that internal femoral density is adapted to applied loads regardless of external femoral geometry.

Early afterdepolarizations (EADs) in cardiac myocytes have been reported to be associated with a series of cardiac arrhythmias. The generation of EADs has a high correlation with the excitation period, leading to repolarization dispersion over the cardiac tissue. However, the mechanism of EAD rate dependence has not been thoroughly revealed. In this study, the simulation approach was used to investigate the mechanism underlying EAD rate dependence. The results indicated that the gating variable of the delayed rectifier potassium current ($x$-gate) and the intracellular sodium ion concentration ([Na${}^{+}$]${}_i)$ were key factors contributing to EAD rate dependence. Also, different mathematical models showed different types of EAD rate dependence, which needs to be considered in the future simulation research related to EADs.

There is a need for more individualized treatment of critically ill patients receiving mechanical ventilation (MV). Therefore, this research aims to create a preliminary multi-scale computational modeling framework for MV in critically ill COVID-19 patients as a step toward studying region-specific and overall lung dynamics in these patients. This goal was accomplished by developing proof-of-concept image-based computer models providing insight into airflow redistribution and volume and pressure gradients on a lobe-specific basis. Our in silico multi-scale MV models simulated redistribution of ventilation for up to 20% of air volume from severely damaged lung lobes to the lobes less affected by COVID-19, hence potentially revealing a risk factor of MV-induced volutrauma due to heterogeneity of lung damage distribution in COVID-19. This study lays the foundation for future COVID-19 patient-specific lung models for individualized simulation of MV.

Intelligence — algorithmic method of modeling of microkinetics for biotechnological processes (BTP) is considered. The generalized mathematical model of microkinetics of biotechnological processes received on the basis of the system approach is given. The question of regularization of a task of parametrical identification is considered.

The results of investigation of the distribution of electrical and magnetic properties over the cross-section are presented for Cu${}_{98}$Be₂/Fe${}_{20}$Co₆Ni${}_{74}$ composite wire of the “highly conductive core-magnetically soft coating” type, obtained by electrolytic deposition of the FeCoNi layer. Studies performed by the magneto-impedance tomography (MIT) made it possible to determine the specific electrical conductivity of the materials of the core and coating. It was established that the electrodeposited coating had a magnetic structure that was inhomogeneous over the thickness.

Theoretical approach was developed for description of clathrate hydrates stability area at low and modestly high temperatures on molecular level. The approach permits to account for interactions between guest molecules and dependence of unit cell structure upon guest's sort, temperature and pressure. Non-ideality of the gas phase was accounted using Van-der-Waals equation of state. Within this approach, methane hydrate calculations have been performed both for low temperature and low pressure region (in equilibrium with ice Ih) and for modestly high temperatures and pressures (in equilibrium with liquid pure water). Calculations show the notable dependence of hydrates thermodynamic properties upon the guest-guest interactions. For methane hydrates, the guest-guest interaction energy can reach 10% of the guest-host value. The results of calculations are in good agreement with available experimental data. This method is applicable for accurate prediction of clathrate hydrate stability in a wide range of P–T conditions.

A successful manufacturing industry can make a significant contribution to the prosperity of a nation. For companies to consistently realize success in manufacturing, they must have an effective manufacturing strategy. An effective manufacturing strategy is realized through a formal planning process which takes proper account of all relevant factors. This chapter provides a uniquely broad view in developing a manufacturing strategy.