Abstract. The article deals with issues of the thermal cracking resistance in massive concrete and reinforced concrete structures during the building period. The paper gives the calculation results of thermal stressed state in massive foundation slabs with different time organization of the thermal protection. It was found that the thermal crack resistance is fully guaranteed when the insulation is installed immediately after concrete has been placed or it has been placed with short delay. The delay can be allowed if the relative tensile strain of the concrete does not exceed the tensility limit. The acceptable delay ranges from 8 to 30% of time it takes to reach the maximum temperature in the concrete block. The surface insulation installation at the time of the temperature peak inevitably leads to the formation and development of cracks.

No abstract

АннотацияПредмет исследования. Рассмотрены метрики, позволяющие оценивать устойчивость графа и меры центральности, на основе расчета которых осуществляется перколяция ключевых элементов графа. Метод. При проведении эксперимента использовались методы расчета среднего расстояния пути вершинной связности, коэффициента кластеризации и эффективности графа, на основе теории графов. Для определения оптимальной метрики устойчивости сети применен метод главных компонент, основанный на положениях теории математической статистики. Основные результаты. В работе решались две научные задачи: основная и вспомогательная. Вспомогательная задача -обзор существующих метрик устойчивости сети, позволивший выбрать оптимальную. Выбор метрики осуществлялся при помощи метода главных компонент. В результате показано, что оптимальной является среднее расстояние пути. Решение вспомогательной задачи позволило выполнить анализ способов снижения устойчивости сетей на основе последовательного удаления ключевых элементов, что и является основной научной задачей исследования. После проведенного анализа установлено, что наилучшим образом для снижения устойчивости сети подходят узлы, важность которых выражена на основе измерения центральности по степени. Практическая значимость. Для оценивания устойчивости сетей разработан оригинальный комплексный двухкритериальный коэффициент. Анализ способов снижения устойчивости проводился путем измерения этого коэффициента для модельных и реальных сетей. Таким образом, предложенные способы апробированы, подтверждена их работоспособность и возможное применение в различных областях науки и техники: социологии, медицине, физике и радиотехнике.

The article deals with issues of the thermal cracking resistance in massive concrete and reinforced concrete structures during the building period. The paper lists the calculation results of the NPP reactor foundation mat thermal stressed state and thermal cracking resistance. The research also considers the concrete hardening temperature influence on its thermo-physical and deformation characteristics. The deformation criterion is used to calculate the concrete thermal cracking resistance. In addition, the paper focuses on the assignment of safe concrete pouring technological parameters in the winter period. Furthermore, the article estimates the necessity of the structure peripheral electric heating during the building period.

A new method is proposed for determining the relative transfer coefficients of the sensors in a standing-wave analyzer based on a multiprobe measurement line, which is used with loads whose parameters are known only subject to some error. The method is based on the exact solution of the long-line equations obtained by the maximum-likelihood method.Standing-wave analyzers based on multiprobe measurement lines are widely used to automate measurements on UHF circuit parameters [1--4]. The measurements involve analyzing the field distribution within the line, which is dependent on the load parameters (amplitude and phase of the reflection coefficient) and on the amplitude of the wave in the line. Then three probes are sufficient to give a system of nonlinear equations in terms of the unknowns. Additional probes are often used to extend the working frequency range [1][2][3].The UHF system in the line gives rise to a standing wave whose parameters are related to those of the generator and load. The following conditions are assumed:1) the line is free from loss; 2) the probes lie at exactly known distances from the load; 3) the probe reflection coefficients are negligibly small, i~e., the probes do not disrupt the field pattern; and 4) the detectors in the probes have ideal square-law characteristics.To provide low probe reflection coefficients, the outputs must work into attenuators that heavily attenuate the coupling between the probes and the field within the line (less than 30 dB). This is responsible for the low signal-noise ratio at the detector output, which represents serious interference for precision measurements. However, the signals at the detector inputs are weak (some microvolts), and the requirement of square-law characteristics is met. With these assumptions, the model for the line is represented by the system [3, 5] uj =ajU2[l+p 2 +2cos(tp-4/r, dj/)Q]+~j, j=I,N, (1) in which uj is the voltage amplitude at the output from probe j; ctj is the transfer coefficient for probe j; U 2 is the square of the amplitude of the standing wave; 9 and tp are the modulus and phase of the load's reflection coefficient; dj is the distance from the load connection to probe j; ~, is the wavelength in the line; ~/is the error in measuring the voltage at probe j; and N is the number of probes. The additive errors ~j are due primarily to the shot noise in the detectors and the thermal noise in the amplifiers in the data collection board, so they may be considered as independent normally distributed quantities having zero mathematical expectation and unknown variance ~2.The accuracy of such an analyzer is determined primarily by the errors: the noise in the detectors and amplifiers, errors in estimating the probe transfer coefficients (calibration errors), and error in determining the wavelength in the line. As a rule, the main source of error is the error in calibrating the probe relative transfer coefficients.Calibration Method Analysis. The relative transfer coefficients are usually found by calibrating the line with a...