Three-dimensional organization of electrical turbulence in the heart

Three-dimensional organization of electrical turbulence that is induced via the phenomenon of spiral breakup is studied in a computer model of the heart, which includes realistic ventricular geometries and cardiac anisotropy. We find filaments of rotors during the turbulence and study their number and length as a function of the heart size. We perform a dimensional analysis of turbulence

Phototaxis during the slug stage of Dictyostelium discoideum: a model study

During the slug stage, the cellular slime mould Dictyostelium discoideum moves towards light sources. We have modelled this phototactic behaviour using a hybrid cellular automata/partial differential equation model. In our model, individual amoebae are not able to measure the direction from which the light comes, and differences in light intensity do not lead to differentiation in motion velocity among the amoebae. Nevertheless, the whole slug orientates itself towards the light. This behaviour is mediated by a modification of the cyclic AMP (cAMP) waves. As an explanation for phototaxis we propose the following mechanism, which is basically characterized by four processes: (i) light is focused on the distal side of the slug as a result of the so-called `lens-e¡ect'; (ii) differences in luminous intensity cause differences in NH3 concentration; (iii) NH3 alters the excitability of the cell, and thereby the shape of the cAMP wave; and (iv) chemotaxis towards cAMP causes the slug to turn.We show that this mechanism can account for a number of other behaviours that have been observed in experiments, such as bidirec- tional phototaxis and the cancellation of bidirectionality by a decrease in the light intensity or the addition of charcoal to the medium

Superplastic Deformation Behavior of High-Temperature Titanium Alloys VT8 and Ti6242S

Superplastic forming (SPF) is an effective process that allows for forming the sheet metal parts of complex configuration. Superplastic deformation behavior of conventional sheets of a high temperature titanium alloys VT8 и Ti6242S was studied by constant strain rate tests in a temperature range of 850–950 ∘C. The research identified the optimum superplastic temperature of studied alloys in a constant strain rate of 3 × 10−4 s −1 with elongation above 150 %.     Keywords: superplasticity, titanium alloys, stress, elongation

Pressure effect on magnetic susceptibility and exchange interactions in GdMx (x = 1, 2, 3, 5) systems

Effect of pressure on electronic structure and magnetic properties of GdMx (x = 1, 2, 3, 5) systems is studied experimentally and theoretically. By employing the ab initio electronic structure calculations, the magnetic susceptibilities, saturation moments, exchange parameters, magnetic ordering temperature and their pressure derivatives are evaluated and appeared to be consistent with available experimental data. The obtained results are expected to promote further advance in the theory of magnetic ordering in rare-earth systems

Elimination of spiral waves in cardiac tissue by multiple electrical shocks

We study numerically the elimination of a spiral wave in cardiac tissue by application of multiple shocks of external current. To account for the effect of shocks we apply a recently developed theory for the interaction of the external current with cardiac tissue. We compare two possible feedback algorithms for timing of the shocks: a "local" feedback algorithm (using an external electrode placed directly on the tissue) and a "global" feedback algorithm (using the electrocardiogram). Our main results are: application of the external current causes a parametric resonant drift similar to that reported in previous model computations; the ratio of the threshold of elimination of the spiral wave by multiple shocks to the threshold of conventional single shock defibrillation in our model for cardiac tissue is about 0.5, while earlier, less realistic models predicted the value about 0.2; we show that an important factor for successful defibrillation is the location of the feedback electrode and the best results are achieved if the feedback electrode or the ECG lead is located at the boundary (or edge) of the cardiac tissue; the "local" and the "global" feedback algorithms show similar efficiency

Spatial Pattern Formation During Aggregation of the Slime Mould Dictyostelium discoideum

Stream formation and spiral wave behaviour during the aggregation of Dictyostelium discoideum (Dd) are studied in a model based on the Martiel-Goldbeter equations for cAMP relay, combined with chemotactic motion of Dd cells. The results show that stream formation occurs if the turnover rate of intracellular cAMP is increased. This increase in the turnover rate of cAMP[in] leads to a dependence of the speed of the cAMP wave on the cell density. We propose that this dependence of wave speed on cell density is the underlying mechanism for stream formation. Besides stream formation, increasing the turnover rate of cAMP[in] also results in a spiral wave period that decreases during aggregation, a phenomenon that is commonly observed in situ. Furthermore, the dependence of wave speed on cell density is measured empirically[ The speed of the cAMP wave is found to decrease as the wave travels from high to low cell density. This indicates that in situ, wave speed does depend on cell density

Assessment of possible cable car accidents by employee competencies using neural networks

Rope transport has received quite a lot of development in the field of passenger and cargo transportation. In some cases (for example, in ski resorts), it is indispensable. To prevent emergency situations, a sufficiently large number of standards and rules for safe operation and maintenance have been developed. However, emergencies do occur. One of the reasons is the insufficient professional training of rope transport workers, who must know and possess the skills to apply the provisions of regulatory documentation, as well as properly perform their professional duties. This article is devoted to the scientific problem of probabilistic assessment of the possibility of various emergency situations on cable transport, depending on the level of mastery of professional competencies and their constituent knowledge, skills and abilities. To solve this problem, a technology based on neural network training has been applied. As an example, specialists in the professional standard «Specialist in the organization of safe operation of passenger cable cars and funiculars» are considered

Control of ropes during the operation of machines with rope traction

The methods of rope control during the operation of lifting structures, elevators, freight and passenger cable cars, funiculars and other machines with cable traction are considered. It is indicated that the main indicator of the technical condition of ropes is the appearance, development and interaction of defects that reduce the strength of ropes, contribute to their destruction and, accordingly, an emergency situation. The analysis of existing methods of rope control is carried out, the designs of flaw detectors are described, with the help of which the technical condition of ropes can be assessed during operation. It is established that one of the promising methods of control of steel ropes is optical based on machine vision and artificial intelligence technologies

Algorithmization of the problem of videoscopic evaluation of the steel ropes state

The paper considers the problem of monitoring the technical state of steel ropes used in industrial and civil installations, such as elevators, cable cars, lifts, etc. To date, the assessment of the state of steel ropes and the safety of their operation is carried out mainly through visual-instrumental control, which is long in time and subject to the influence of the human factor, which determines the relevance of the task of automating this process using computer technology and artificial intelligence methods in order to improve the quality of the assessment, reducing the check interval, detecting defects in steel ropes at an early stage. The article proposes two approaches to the algorithmizing of the problem of videoscopic control of the state of steel ropes using computer vision technologies, based on software modeling of the logic of visual analysis and machine learning methods, such as deep learning artificial neural networks. The authors have developed algorithms for automatic detection of the main types of defects in images of the surface of steel ropes: increase/decrease in diameter, deformation in the form of rope, breaks in the outer wires, thermal and electric damage. The paper presents the results of preliminary testing of the developed algorithms and programs, the composition and methods for determining the main indicators for evaluating their effectiveness are proposed

Pressure effect on magnetic properties of gadolinium in paramagnetic state

In this report we are mostly focused on refinement of the experimental dependence of the magnetic transition temperature TC on pressure under pure hydrostatic (gaseous) conditions. Unlike previously used methods, we employed a new procedure, based on the measurement of pressure effect on the dc magnetic susceptibility of Gd in the paramagnetic state at temperatures above TC. The dc paramagnetic susceptibility of Gd was measured in the temperature range of 295−365 K and under hydrostatic pressure up to 0.16 GPa, yielding values of the paramagnetic Curie temperature Θ and its pressure derivative. Also we explored a possibility to describe pressure effects on magnetism of Gd within simple mean-field approaches, which are based on ab initio electronic structure calculations. Based on the results of electronic structure calculations within the density functional theory, the experimental behavior of Θ under pressure was described in the framework of mean-field like approach.Проведены измерения парамагнитной восприимчивости Gd в интервале температур 295−365 K в условиях гидростатического сжатия до 0.16 GPa, что позволило получить значения парамагнитной температуры Кюри Θ и ее производной по давлению. Основываясь на результатах расчетов электронной структуры с использованием теории функционала плотности, было исследовано поведение Θ под давлением в рамках теории среднего поля. С этой целью были вычислены эффективная восприимчивость зонных d-электронов и соответствующие обменные интегралы как функции параметров решетки.Було виміряно парамагнітну сприйнятливість Gd в інтервалі температур 295−365 K в умовах гідростатичного тиску до 0.16 GPa, що дозволило отримати значення парамагнітної температури Кюрі Θ та її похідної за тиском. На основі результатів розрахунків електронної структури з використанням теорії функціонала густини було досліджено поведінку Θ під тиском у рамках теорії середнього поля. З цією метою були обчислені ефективна сприйнятливість зонних d-станів і відповідні обмінні інтеграли як функції параметрів ґратки