Threshold of microvascular occlusion: injury size defines the thrombosis scenario

Damage to the blood vessel triggers formation of a hemostatic plug, which is meant to prevent bleeding, yet the same phenomenon may result in a total blockade of a blood vessel by a thrombus, causing severe medical conditions. Here, we show that the physical interplay between platelet adhesion and hemodynamics in a microchannel manifests in a critical threshold behavior of a growing thrombus. Depending on the size of injury, two distinct dynamic pathways of thrombosis were found: the formation of a nonocclusive plug, if injury length does not exceed the critical value, and the total occlusion of the vessel by the thrombus otherwise. We develop a mathematical model that demonstrates that switching between these regimes occurs as a result of a saddle-node bifurcation. Our study reveals the mechanism of self-regulation of thrombosis in blood microvessels and explains experimentally observed distinctions between thrombi of different physical etiology. This also can be useful for the design of platelet-aggregation-inspired engineering solutions.Comment: 7 pages, 5 figures + Supplementary informatio

Blood flow controls coagulation onset via the positive feedback of factor VII activation by factor Xa

<p>Abstract</p> <p>Background</p> <p>Blood coagulation is a complex network of biochemical reactions, which is peculiar in that it is time- and space-dependent, and has to function in the presence of rapid flow. Recent experimental reports suggest that flow plays a significant role in its regulation. The objective of this study was to use systems biology techniques to investigate this regulation and to identify mechanisms creating a flow-dependent switch in the coagulation onset.</p> <p>Results</p> <p>Using a detailed mechanism-driven model of tissue factor (TF)-initiated thrombus formation in a two-dimensional channel we demonstrate that blood flow can regulate clotting onset in the model in a threshold-like manner, in agreement with existing experimental evidence. Sensitivity analysis reveals that this is achieved due to a combination of the positive feedback of TF-bound factor VII activation by activated factor X (Xa) and effective removal of factor Xa by flow from the activating patch depriving the feedback of "ignition". The level of this trigger (i.e. coagulation sensitivity to flow) is controlled by the activity of tissue factor pathway inhibitor.</p> <p>Conclusions</p> <p>This mechanism explains the difference between red and white thrombi observed <it>in vivo </it>at different shear rates. It can be speculated that this is a special switch protecting vascular system from uncontrolled formation and spreading of active coagulation factors in vessels with rapidly flowing blood.</p

Continuous Modeling of Arterial Platelet Thrombus Formation Using a Spatial Adsorption Equation

In this study, we considered a continuous model of platelet thrombus growth in an arteriole. A special model describing the adhesion of platelets in terms of their concentration was derived. The applications of the derived model are not restricted to only describing arterial platelet thrombus formation; the model can also be applied to other similar adhesion processes. The model reproduces an auto-wave solution in the one-dimensional case; in the two-dimensional case, in which the surrounding flow is taken into account, the typical torch- like thrombus is reproduced. The thrombus shape and the growth velocity are determined by the model parameters. We demonstrate that the model captures the main properties of the thrombus growth behavior and provides us a better understanding of which mechanisms are important in the mechanical nature of the arterial thrombus growth

Simulation of the Electrical-Technical Complex of the Power Transmission Line of DC in the MATLAB Program Environment

Одним из основных направлений развития электроэнергетических систем является внедрение устройств и технологий на базе силовых полупроводниковых ключей (HVDC (High Voltage Direct Current) технологий), в частности вставок постоянного тока на базе преобразователя источника напряжения (VSC). VSC-HVDC используются для решения таких задач, как соединение несинхронных электрических сетей различных частот, передача электроэнергии, повышение локальной и системной управляемости электроэнергетической системы, повышение пропускной способности элементов сети, содержащих «слабые» связи. Благодаря высокой степени управляемости преобразователей источника напряжения (VSC) в основном рассматривается работа HVDC. Однако внедрение и эксплуатация VSC-HVDC определяют необходимость в проведении широкого спектра анализа и исследований, которые можно провести только с помощью математического моделирования. Поэтому целью работы является: анализ поведения системы передачи HVDC на основе VSC с использованием различных режимов управления путем моделирования в программной среде MATLAB. One of the main directions of the development of electric power systems is the introduction of devices and technologies based on high-power semiconductor switches (HVDC (High Voltage Direct Current) technologies; one of the elements of this technology is direct current link on the basis of voltage source converter (VSC). VSC-HVDC are used for tasks such as connecting asynchronous power grids for various frequencies, transmission of electricity, improve local and systemic handling of electric power system, increasing the capacity of network elements that contains a “weak” connection. Due to the high degree of controllability of voltage source converters (VSCs), it is mainly addressed in the recent literature on HVDC operation. However, the implementation and operation of VSC-HVDC determines the need for a wide range of analysis and research that can only be done with the help of mathematical modeling. therefore, the purpose of the work is: to analyze the behavior of the HVDC transmission system based on VSC using various control modes by modeling in the MATLAB software environmen

MODEL OF GEOMEDIA CONTAINING DEFECTS: COLLECTIVE EFFECTS OF DEFECTS EVOLUTION DURING FORMATION OF POTENTIAL EARTHQUAKE FOCI

This paper describes the statistical thermo-dynamical evolution of an ensemble of defects in the geomedium in the field of externally applied stresses. The authors introduce ‘tensor structural’ variables associated with two specific types of defects, fractures and localized shear faults (Fig. 1). Based on the procedure for averaging of the structural variables by statistical ensembles of defects, a self-consistency equation is developed; it determines the dependence of the macroscopic tensor of defects-induced strain on values of external stresses, the original pattern and interaction of defects. In the dimensionless case, the equation contains only the parameter of structural scaling, i.e. the ratio of specific structural scales, including the size of defects and an average distance between the defects.The self-consistency equation yields three typical responds of the geomedium containing defects to the increasing external stress (Fig. 2). The responses are determined from values of the structural scaling parameter. The concept of non-equilibrium free energy for a medium containing defects, given similar to the Ginzburg-Landau decomposition, allowed to construct evolutionary equations for the introduced parameters of order (deformation due to defects, and the structural scaling parameter) and to explore their solutions (Fig. 3).It is shown that the first response corresponds to stable quasi-plastic deformation of the geomedium, which occurs in regularly located areas characterized by the absence of collective orientation effects. Reducing the structural scaling parameter leads to the second response characterized by the occurrence of an area of meta-stability in the behavior of the medium containing defects, when, at a certain critical stress, the orientation transition takes place in the ensemble of interacting defects, which is accompanied by an abrupt increase of deformation (Fig. 2). Under the given observation/averaging scale, this transition is manifested by localized cataclastic deformation (i.e. a set of weak earthquakes), which migrates in space at a velocity several orders of magnitude lower than the speed of sound, as a ‘slow’ deformation wave (Fig. 3). Further reduction of the structural scaling parameter leads to degeneracy of the orientation meta-stability and formation of localized dissipative defect structures in the medium. Once the critical stress is reached, such structures develop in the blow-up regime, i.e. the mode of avalanche-unstable growth of defects in the localized area that is shrinking eventually. At the scale of observation, this process is manifested as brittle fracturing that causes formation of a deformation zone, which size is proportional to the scale of observation, and corresponds to occurrence of a strong earthquake.On the basis of the proposed model showing the behavior of the geomedium containing defects in the field of external stresses, it is possible to describe main ways of stress relaxation in the rock massives – brittle large-scale destruction and cataclastic deformation as consequences of the collective behavior of defects, which is determined by the structural scaling parameter.Results of this study may prove useful for estimation of critical stresses and assessment of the geomedium status in seismically active regions and be viewed as model representations of the physical hypothesis about the uniform nature of deve­lopment of discontinuities/defects in a wide range of spatial scales

Control Strategies of the Electrical Complex of High-Voltage Electricity Transmission Lines of the Direct Current

В настоящее время спрос на энергию растет высокими темпами, и возникают проблемы, стоящие перед интеграцией электрической сети, в первую очередь с передачей энергии на большие расстояния. Описанная выше проблема может быть решена с использованием систем передачи HVDC. Основные преимущества этих систем связаны с более низкими потерями при передаче, а также меньшими затратами по сравнению с традиционными системами передачи HVAC. По ряду причин технология преобразования напряжения (преобразователь источника напряжения – VSC) с использованием широтно-импульсной модуляции (ШИМ) системы передачи постоянного тока высокого напряжения (VSC- HVDC) имеет ряд потенциальных преимуществ по сравнению с системой передачи постоянного тока с использованием преобразователей с линейной коммутацией (LCC-HVDC), в частности, упрощается реализация многотерминальных систем передачи постоянного тока HVDC, появляется возможность быстродействующего и независимого регулирования активной и реактивной мощности, возможность двунаправленной передачи мощности при сохранении неизменной полярности напряжения постоянного тока. Благодаря высокой степени управляемости преобразователей источника напряжения (VSC) в основном рассматривается в недавней литературе работа HVDC. В прошлом было проведено много исследований и разработок в области передачи VSC-HVDC, особенно в аспектах ее управления. Однако в большинстве случаев для описания операционных характеристик различных предлагаемых стратегий управления использовались только качественные методы. Поэтому цель исследовательской работы в этой статье – заполнение некоторых пробелов, таких как исследование различных стратегий управления терминалами VSC-HVDC для использования в сетях постоянного токаCurrently, the demand for energy is growing at a high rate, and there are problems facing the integration of the electrical network, primarily with the transmission of energy over long distances. The problem described above can be solved using HVDC transmission systems. The main advantages of these transmission systems are associated with lower transmission losses as well as lower costs compared to traditional HVAC transmission systems. For a number of reasons, voltage conversion technology (Voltage Source Converter – VSC) using Pulse Width Modulation (PWM) high voltage direct current (VSC-HVDC) transmission system has a number of potential advantages over a DC transmission system using line commutated converters. (LCC-HVDC), in particular, the implementation of multi-terminal HVDC DC transmission systems is simplified, it becomes possible to quickly and independently control active and reactive power, the possibility of bidirectional power transmission while maintaining the same DC voltage polarity. Due to the high degree of controllability of voltage source converters (VSC), it is mainly dealt with in the recent literature on HVDC operation. Much research and development has been done in the past in the field of VSC-HVDC transmission, especially in its control aspects. However, in most cases, only qualitative methods have been used to describe the operational characteristics of the various proposed management strategies. Therefore, the purpose of the research work in this article is to fill in some of the gaps, such as investigating different control strategies for VSC-HVDC terminals for use in DC network

Effective Targeted Chemoprophylaxis of Recurrent Liver Echinococcosis with Haplotype CYP1A2F1*A/A: a Clinical Case

Background. One of the main long­term quality criteria for treatment and prevention of echinococcosis is postoperative relapse, which rate varies widely within 3–54% between medical facilities. The genetic traits of recurrent liver echinococcosis comprise an important subject of research into its etiopathogenetic factors for  an effective prognosis of cyst relapse and treatment personalisation.Materials and methods. Bashkir State Medical University (Ufa, Russia) provided facilities to study targeted  chemoprophylaxis efficacy in a case of relapsed liver echinococcosis with haplotype CYP1A2F1*A/A (AA) and the  UM phenotype of ultrarapid albendazole sulfoxide­to­albendazole sulfone metaboliser.Results and discussion. The clinical case presented illustrates the rationale behind personalised  chemoprevention of recurrent echinococcosis with albendazole based on genotyping data. Genotyping allows  detection of an ultrafast metaboliser haplotype in blood implicating a rapid degradation of administered albendazole, reduced antiparasitic impact of drug therapy and more feasible relapse, in contrast with a normal metaboliser phenotype.Conclusion. A successful secondary prevention of relapsed echinococcosis suggests the efficacy of personalising  albendazole­based chemoprophylaxis of recurrent echinococcosis with genotyping data

Power Flow Control in Multi-Terminal Electrical Complexes, Taking Into Account the Effect of Dc Line Resistance

Потери из-за снижения напряжения в линии постоянного тока оказывают значительное влияние на точное управление потоком мощности в многотерминальных системах ПИН-ВППТ с использованием управления напряжением на шинах постоянного тока. Когда управление напряжением на шинах постоянного тока используется в многотерминальных системах ПИН- ВППТ, из-за неравных напряжений на шинах постоянного тока снижения напряжения в линии постоянного тока возникают большие отклонения потока мощности. Потери мощности в линии постоянного тока и в преобразователях также вызывают отклонения потока мощности в сети постоянного тока от желаемого значения. Для точного управления потоком мощности в сети постоянного тока необходимо устранить отклонения мощности, возникающие из-за каждого из этих факторов. При моделировании пятитерминальной системы ПИН-ВППТ в Matlab/ Simulink показано, как добиться точного управления потоком мощности в системе с учетом снижения напряжения постоянного тока и потерь мощности в линии постоянного тока (учет потерь мощности преобразователя выходит за рамки данной статьи)Losses due to voltage drop in the DC line have a significant impact on the accurate control of power flow in multi-terminal VSC-HVDCs using DC voltage droop control. When DC voltage droop controls are used in multi-terminal VSC-HVDC, due to unequal DC bus voltages, voltage drops in the DC link cause large power flow variations in the DC grid. Power losses in the DC link and converter power losses also cause deviations in the power flow in the DC network. To accurately control the power flow in a DC network, it is necessary to eliminate the power deviations that occur due to each of these factors. Modeling a five-terminal VSC-HVDC system in Matlab/Simulink shows how to achieve precise power flow control in a multi-terminal VSC-HVDC, taking into account the reduction of DC voltage and power losses in the DC line (accounting for converter power losses is beyond the scope of this article

Influence of DC Line Resistance on Power Balance Distribution in Multi-Terminal Electrical Complexes

В этой статье обсуждается влияние сопротивления линии постоянного тока на распределение баланса мощности системы постоянного тока МППТ при стабилизации напряжения постоянного тока. Сопротивление линии постоянного тока в многотерминальной системе MППТ приводит к изменениям напряжения на шине постоянного тока при изменении потока мощности в системе. Это, в свою очередь, влияет на распределение мгновенного баланса мощности в системе МППТ при управлении с целью стабилизации напряжения постоянного тока. Значения коэффициента усиления напряжения постоянного тока определяют степень влияния снижения напряжения постоянного тока на распределение баланса мощности в системе постоянного тока. В данной статье получена математическая модель для оценки распределения баланса мощности с учетом влияния сопротивления постоянного тока. Система МППТ с пятью терминалами ПИН-ВППТ была смоделирована в программном пакете Matlab/Simulink для демонстрации влияния сопротивления линии постоянного тока на распределение баланса мощности, а также для проверки предложенной математической модели, которая оценивает распределение баланса мощностиThis article discusses the impact of direct current resistance on the distribution of the power of the DC power system of the MPPT when stabilizing direct current voltage. The resistance of the DC line in the multi-terminal MTDC system leads to changes in the voltage on the direct current with a change in power flow in the system. This, in turn, affects the distribution of instant power balance in the MTDC system during control in order to stabilize direct current voltage. The values of the direct current voltage reinforcement values determine the degree of influence of a reduction in direct current on the distribution of power balance in the DC system. In this article, a mathematical model was obtained to assess the distribution of power balance, taking into account the effect of direct current resistance. The MTDC system with five VSC-HVDC terminals was modeled in the Matlab/Simulink software package to demonstrate the impact of direct current resistance on the distribution of power balance, as well as to check the proposed mathematical model, which evaluates the distribution of power balanc