Search

Aim. To analyze various strategies aimed at mitigating complications of the portal hypertension syndrome at the Minsk Scientific and Practical Center for Surgery, Transplantology, and Hematology.Material and methods. Patients who had undergone different types of treatment were retrospectively observed: shunt surgery to form portacaval anastomoses, transjugular portosystemic shunt placement, and liver transplantation. The following parameters were analyzed: incidence of complications, hospital mortality rate, survival rate, and perioperative indicators.Results. Since 1980, 131 shunt surgeries have been performed at the Center, while 880 liver transplantations and 232 transjugular portosystemic shunt placement procedures have been performed since 2008. Among 68 patients with compensated cirrhosis who had undergone shunt placement, no hospital mortality rate was reported, whereas in patients with Child-Pugh B cirrhosis and Child–Pugh C cirrhosis, it reached 19.5% and 87.5%, respectively. Following TIPS, the overall case mortality rate amounted to 9.9% (following TIPS prior to transplantation – 8.2%, following TIPS used as the final treatment – 12.8%). After liver transplantation, in-hospital mortality rate reached 7.7%.Conclusion. Over 50 years, the strategy for managing portal hypertension has undergone significant changes due to the establishment of institutions providing a complete cycle of all treatment measures for such patients. Patients suffering from the complications of the portal hypertension syndrome tend to receive the most effective treatment in hospitals having experience in rational conservative therapy, endovascular procedures, and transplantation.

A novel two-cylinder single-stage piston hybrid power machine with liquid movement effectuated by vacuum on the suction side is described. The presented results of an experimental study on the cooling efficiency of the cylinder-piston group and the effect of compressor cooling on the feed rate show that the temperature of the valve plate decreases by 10–12 K, while that of the cylinder walls decreases by 7–8 K. Based on the analysis of the working processes of a reciprocating compressor, the effect of cooling on the feed rate was found to be ambiguous, leading both to its possible increase and reduction; this was confirmed as a result of experimental studies.

Recent judicial practice regarding the interpretation of the ‘controlled group’ in order to apply exceptions from prohibition on cartel agreements is controversial. Taking advantage of the uncertainty that has arisen, many participants in cartel cases make attempts (and sometimes successfully) to prove that in fact the conspiracy took place within a controlled group, and, therefore, was permissible. In this article we will consider the most common arguments used by business entities in cases of cartels and evaluate the possibility of their application in modern conditions.

The present article considers operating processes occurring in a positive displacement two-stage piston hybrid energy-generating machine having a gas cap. The conducted numerical experiment revealed the physical picture of viscous fluid flow, as well as the features associated with implementing a mathematical model of these operating processes. It was found that a change in any of the independent parameters leads to a corresponding change in the amount of fluid entering the second-stage working chamber of the machine, the maximum and minimum fluid levels, the liquid piston stroke, clearance space volume, as well as the amount of fluid ejected into the compressor discharge line. The presented ranking of the obtained results shows that the discharge pressure of compressible gas has the greatest influence on the operating processes.

The paper proposes a method for calculating the kinematic parameters (acceleration, speed, and displacement) and inertial losses of a liquid piston head in the profiled working chamber of the second stage of a piston hybrid energy-generating machine (PHEM). The working chamber is formed by two rotating truncated cones. Using a continuity equation of fluid flow in the machine, a general expression is obtained for determining the acceleration of the surface layer of the liquid piston when changing the geometry of the working chamber. The solution is reduced to an analytical form. The numerical experiment made it possible to evaluate the effect of changing the geometry of the working chamber on the kinematic parameters of the liquid piston and inertial head losses in the working chamber of the second stage of the PHEM.

Введение. Одна из главнейших проблем современной трансплантологии – иммунологическая дисфункция трансплантата, частота развития которой достигает 40%. Пункционная биопсия в 2,2% случаев сопряжена с развитием осложнений и может привести к летальному исходу. Цель исследования – разработка методики неинвазивной диагностики отторжения трансплантата печени в отдаленном периоде после операции с использованием терминально-дифференцированных эффекторных CD8+Т-лимфоцитов. Материал и методы. Проведено пилотное одноцентровое обсервационное ретроспективное случай-контроль исследование, включающее 45 реципиентов после ортотопической трансплантации печени. По клиническому течению послеоперационного периода пациенты стратифицировались на 2 группы в зависимости от наличия эпизодов отторжения в трансплантате. Все пациенты после трансплантации получали иммуносупрессивную терапию. Иммунофенотипы реципиентов определялись методом проточной цитофлоуметрии. Всем пациентам была выполнена пункционная биопсия трансплантата. Результаты. Результаты исследования биоптатов трансплантатов печени показали, что 14 пациентов (31%) из 45 имели морфологические признаки отторжения. У пациентов с отторжением был достоверно более высокий уровень абсолютного количества СD8+ Тemra-клеток, что составило 0,23 (0,14; 0,38) ×109/л по сравнению с пациентами без отторжения – 0,09 (0,034; 0,16)×109/л (р=0,034). Результаты ROC- анализа показали, что наиболее оптимальный порог отсечения уровня СD8+ Тemra-лимфоцитов при диагностике иммунологической дисфункции трансплантата печени в отдаленном периоде составил 0,1882×109/л, чувствительность и специфичность при данном пороге отсечения составила 73,33 (95% ДИ: 44,9-92,0) и 96,55 (95% ДИ: 82,2-99,4,) соответственно. Выводы. Увеличение абсолютной численности терминально-дифференцированных эффекторных CD8+ Т-лимфоцитов является диагностическим критерием у пациентов с иммунологической дисфункцией трансплантата в позднем посттрансплантационном периоде. Высокая чувствительность и специфичность порога отсечения абсолютного количества CD8+ Тemra-лимфоцитов у пациентов после трансплантации печени и достоверная разница между количеством клеток у пациентов с нормальным послеоперационным течением, имеющих иммунологическую дисфункцию трансплантата, позволяет рассматривать субпопуляцию Т-лимфоцитов как прогностический биомаркер отторжения в позднем посттрансплантационном периоде. Корреляция этого показателя с результатами морфологического исследования делает его альтернативным и, главное, безопасным неинвазивным способом ранней диагностики отторжения.

This paper examines the use of various types of cooling liquids in a two-cylinder single-stage piston hybrid power machine with fluid flow due to vacuum at suction. Liquids with various basic thermal properties were used as working fluids: distilled water, antifreeze, and transmission oil. Specific heat capacities and dynamic viscosities of these liquids differed from 2 to 10 times. The experimental studies showed that the greatest cooling effect on the cylinder-piston group was observed when using distilled water, and the least — when using transmission oil. The average surface temperature of the working chamber when cooled with water was minimal in the range of 330–340 K. The average surface temperature of the working chamber when cooled with transmission oil was maximum and ranged from 345 to 355 K, i. e. it was about 15 K higher than when cooled with water. The average surface temperature of the working chamber when cooled with antifreeze occupied an intermediate position between the average temperatures of the working chamber when cooled with water and that with transmission oil and was in the range of 335–345 K, i. e. about 5 K higher than when cooled with water.

This article presents a method for calculating the dynamics of fluid motion in a two-stage hybrid energy machine with a gas cap. The developed method is based on the Bernoulli energy conservation equation, taking the linear hydraulic resistances, local hydraulic resistances, and inertial forces into account. The expressions for the current coordinate values of the liquid levels and pressures in the gas cap apply to the second stage compressor section and the first stage pump section. The developed method of calculation can be used for the analysis of working processes in compressor machines based on the principle of the liquid piston.

Techniques of determining the velocities of a piston for performing isothermal and polytropic processes of compression in the absence of leakage in the second stage of the compressor section of a hybrid power machine are considered. The laws of variation of the velocities of the piston over time (relative to the crank angle) and their average value are determined. A comparison of the instantaneous and average velocities of the piston for performing isothermal and polytropic processes of compression to the instantaneous and average velocities of a piston possessing a crank drive is performed. It is shown that the isothermal process of compression is not practically realizable with the use of a crank drive, while the polytropic process of compression may be realized with index of polytropy 1.15–1.2 and higher.

Different methods of profiling the working cavity of the second stage of a volumetric hybrid piston power machine are considered. Profiling of the working chamber in order to achieve a constant velocity of the liquid piston and attain the maximal magnitude of the heat-exchange surface, as well as profiling of the surface of a working chamber consisting of a cone and cylinder are performed. Computational formulas in analytic form are obtained in order to create a profiled surface that satisfies the first two conditions. For the third condition criteria for estimating the efficiency relative to the maximal magnitude of the heat-exchange surface and relative to the deviation of the velocity of the liquid piston from some constant velocity of the liquid in the working chamber are developed. As a result of a numerical experiment forms of the working chamber that satisfy the first two conditions are established and it is proved that a conical surface is best for a working chamber consisting of a cone and cylinder.

A prototype of a crossheadless hybrid piston power machine is developed based on a basic diagram protected by a patent for an invention. An experimental investigation of the crossheadless machine as well as of a crosshead hybrid piston power machines with a smooth, respectively, multistep groove seal is carried out. It is experimentally demonstrated that the surface temperature of the valve plate and the temperature of the intake gas developed by the new crossheadless hybrid piston power machine is, correspondingly, 10–15 K and 6–8 K lower than the comparable temperatures of a crosshead hybrid piston power machine with smooth, respectively, multistep slot seal. Improved cooling of the compressible gas makes it possible to increase the volume efficiency of the compressor section and its indicated efficiency.

An analysis of the processes involved in heating of the liquid present above a piston in the working cavity of the compressor section of a positive-displacement hybrid power machine is given. On the basis of the general fundamental laws of conservation of energy and mass a thermodynamic calculation of the parameters of a two-phase, two-component open thermodynamic system with deformation and thermal interaction of phases is carried out. The influence of deformation work, external heat exchange, and direct-contact heat transfer on the variation of the temperature of the liquid is determined.

Piston hybrid power machines combining the functions of a compressor and a pump in one unit have become widespread, with a new class of machines that do not have a crosshead currently under development. A prototype of such a machine was designed and manufactured based on the new concept of a crossheadless piston hybrid power machine. A plan for conducting a series of experimental studies was developed. The experimental studies confirmed the feasibility of the prototype in the entire range of independent operating parameters (discharge pressure in the compressor section, discharge pressure in the pump section, the number of revolutions of the crankshaft). The effect of operating parameters on the instantaneous and integral characteristics of the compressor and the pump sections of the crossheadless piston hybrid power machine was also assessed through the experimental studies.

A generalized approach to the analysis of feed unevenness in positive displacement pumps is considered. A procedure for calculating the working processes in chambers of constant or variable volume in a discharge line as well as a nonstationary one-dimensional gas flow in a discharge pipe is developed. Boundary conditions are defined. Nonstationary one-dimensional flow is calculated by the method of “characteristics.” By means of a numerical experiment, variations in the pressure in the working chambers and along the length of the pipe as a function of the turning angle of the shaft are established. On the basis of pressure fluctuation in a discharge pipe, it is proved that the feed unevenness significantly exceeds the magnitude of the feed unevenness determined when the pressure fluctuation is not taken into account.

Currently, one of the main ways to improve the efficiency of piston compressors and volumetric pumps is to combine them into a single unit, called a piston hybrid energy machine. Recently, a new class of crossheadless piston hybrid energy positive displacement machines has appeared. In this work, a comparison of mass-dimensional indicators of experimental crosshead and crossheadless hybrid energy machines is performed. The analysis of the results shows that the crossheadless machine has significantly smaller masses of moving parts performing reciprocating motion (almost 3 times) and a smaller maximal overall size (almost 1.5 times) in comparison to the crosshead machine. The specific mass-dimensional indicators of the two machines are comparable.

A mathematical model of the working processes in positive-displacement machines designed to compress two-phase, two-component working fluids is developed on the basis of the general laws of conservation of energy, mass, volume and motion. A mathematical model of the working processes of a hybrid piston power machine where there is a layer of liquid above the piston in the compressor section is given. Two open thermodynamic systems (gas and droplet liquid) in the presence of deformation and thermal interactions are considered.

The operation of a bulk-action hybrid piston power unit is described by a mathematical model based on the laws of energy, mass, and momentum conservation and the equation of state. The influence of the pressure in the pump and compressor sections, the gap in the compressor section, and the eccentricity on the relation between the opposing liquid flow rates through the piston seal and on the thickness of the liquid layer above the piston is analyzed.

The experimental dependencies of the quantity of liquid in the discharge line of the compressor section on the discharge pressures of the compressor and pump sections of a piston hybrid energy-generating machine having stepped slot seal are presented and analyzed. The dependencies of the characteristics of the studied machine on the slot seal gap sizes obtained in the numerical study are presented and analyzed.

Compression of the working fluid in bulk-action pumps (such as piston, gear-driven, and plate-type pumps) under the action of deformation, mass transfer, and heating is considered. A method of calculating the compression is developed, for each factor and for the combination of deformation and mass transfer. The effectiveness of compression is analyzed for each case.

This article considers the development and research of a new design of crosshead-free piston hybrid power machine. After verification of a system of simplifying assumptions based on the fundamental laws of energy, mass, and motion conservation, as well as using the equation of state, mathematical models of the work processes of the compressor section, pump section, and liquid flow in a groove seal have been developed. In accordance with the patent for the invention, a prototype of a crosshead-free piston hybrid power machine (PHPM) was developed, it was equipped with the necessary measuring equipment and a stand for studying the prototype. Using the developed mathematical model, the physical picture of the ongoing work processes in the compressor and pump sections is considered, taking into account their interaction through a groove seal. Using the developed plan, a set of experimental studies was carried out with the main operational parameters of the crosshead-free PHPM: operating processes, temperature of the cylinder–piston group and integral parameters (supply coefficient of the compressor section, volumetric efficiency of the pump section, etc.). As a result of numerical and experimental studies, it was determined that this PHPM design has better cooling of the compressor section (decrease in temperature of the valve plate is from 10 to 15 K, decrease in temperature of intake air is from 6 to 8 K, as well as there is increase in compressor and pump section efficiency up to 5%).

The operation of a new stepped piston seal used in a hybrid piston power machine is described. The hydropneumatic design of the test bench is provided. A mathematical description of the working processes that occur in the seal is presented. Results of theoretical and experimental studies and an analysis of the influence of the angular spin rate of the crankshaft on the working processes and operational properties of a hybrid piston power machine are presented.