Influence of fiber type and matrix composition on adhesive strength in fiber reinforced concrete

Introduction. The purpose of the article is to determine the influence of the steel fiber profile and the composition of the matrix on their adhesion in dispersed reinforced concrete.Materials and methods. Studies have been carried out using the test methods set out in national standards. To determine the characteristics of the adhesion strength of fibers with a matrix, an original technique developed at SPbGASU was used.Results. The degree of influence of the geometric shape of steel fibers – anchor and wave profile on the adhesion strength characteristic is determined. The adhesion strength of steel fiber with cement and concrete matrix was assessed (Cement: Sand = 1:1, Cement: Sand = 1:2 and Cement: Sand = 1:3). The influence of the volume fraction of the cement paste on the characteristic of the adhesion strength of the steel fiber with the matrix has been experimentally proven.Conclusions. The experimental data obtained confirm the effectiveness of dispersed reinforcement through the use of anchor fibers in combination with a rationally selected composition of the concrete matrix

Evaluation of dispersion reinforcement in concrete in terms of strength and crack resistance

Introduction. The purpose of the study was to evaluate the effectiveness of dispersed concrete reinforcement in terms of strength and crack resistance.Materials and methods. When conducting research, test methods were used, regulated by the provisions of national standards, equipment specially designed for this study was used.Results. The results of testing fiber-reinforced concretes made using low-modulus and high-modulus fibers are presented.Discussion and conclusions. As a result of the analysis of the data presented, it is shown that in order to assess the effectiveness and the correct choice of reinforcing fibers, it is not enough to characterise fiber-reinforced concrete only by tensile strength in bending. For a more accurate assessment, it is proposed to use crack resistance characteristics, for example, the critical stress intensity factor, or to supplement the description of the advantages of dispersed reinforcement with the features of the behavior of fiber-reinforced concrete under load

Синтез алгоритма векторной широтно-импульсной модуляции в девятифазном активном выпрямителе напряжения

The article is devoted to the problems of synthesis of multiphase electromechanic modules consisting of a multiphase electrical machine (m > 3) and a multiphase controlled converter. In the multi-phase design of the electric machine, it is possible to obtain a trapezoidal electromotive force and to increase the specific power conversion provided that the EMF and the current at the output of the m-phase generator are matched. The development of the vector pulse width modulation algorithm for the m-phase active voltage rectifier is considered, which will make it possible to match the shape and phase of the currents and voltages at the output of the m-phase generator in order to obtain the maximum active power of the module under study. The analysis of possible combinations of states of the keys of a nine-phase active rectifier is carried out. Each key state is assigned a base vector in a fixed coordinate system. It is noted that there are a number of combinations in which two or more different key states correspond to one base vector. The system of basic vectors is differentiated into its constituent levels, sectors and subsectors. In order to obtain any given voltage vector that does not coincide with the base vectors, the method of spacevector modulation is used. This method provides using 100 % DC link voltage as compared with sinusoidal pulse width modulation (86.6 %). The goal of space-vector modulation for a nine-phase active voltage rectifier is to implement the resultant spatial vector of the output voltage with a given average value within the modulation period. For this, the three vectors nearest to the given base vector must be found. To implement a given voltage vector, a sequence of sampling the base vectors in the modulation period is given, providing one commutation (commutation of two complementary keys) while passing from one basic vector to another to reduce switching losses. Analytic relationships of the weight coefficients for the generators of vectors are obtained, as well as the equations of the boundaries of the subsectors that form a diagram of combinations of states of the circuit. The sequence of the calculations presented in the paper is a technique for realizing the vector pulse-width modulation in nine-phase controlled electrical energy converters.Статья посвящена вопросам синтеза многофазных электромехатронных модулей, состоящих из многофазной электрической машины (m > 3) и многофазного управляемого преобразователя. При многофазном исполнении электрической машины существует возможность получения трапецеидальной электродвижущей силы и увеличения удельной преобразуемой мощности при условии согласования ЭДС и тока на выходе m-фазного генератора. Рассмотрен вопрос разработки алгоритма векторной широтно-импульсной модуляции для m-фазного активного выпрямителя напряжения, который позволит обеспечить согласование формы и фазы токов и напряжений на выходе m-фазного генератора с целью получения максимальной активной мощности исследуемого модуля. Проведен анализ возможных комбинаций состояний ключей девятифазного активного выпрямителя. Каждому состоянию ключей поставлены в соответствие базовые векторы в неподвижной системе координат. Установлено, что существует ряд комбинаций, при которых одному базовому вектору соответствуют два и более различных состояния ключей. Система базовых векторов продифференцирована на составляющие ее уровни, сектора и подсектора. Для получения любого заданного вектора напряжения, не совпадающего с базовыми векторами, применен метод пространственно-векторной модуляции. Он позволяет на 100 % использовать напряжение звена постоянного тока по сравнению с синусоидальной широтно-импульсной модуляцией (86,6 %). Цель пространственно-векторной модуляции для девятифазного активного выпрямителя напряжения состоит в реализации результирующего пространственного вектора выходного напряжения с заданным средним значением в пределах периода модуляции. Для этого должны быть найдены три ближайших к заданному базовых вектора. Для реализации заданного вектора напряжения задана последовательность перебора базовых векторов в периоде модуляции, обеспечивающая одну коммутацию (коммутация двух комплементарных ключей) при переходе от одного базового вектора к другому для уменьшения коммутационных потерь. Получены аналитические соотношения весовых коэффициентов для образующих векторов, а также уравнения границ подсекторов, образующих диаграмму комбинаций состояний схемы. Последовательность приведенных расчетов представляет собой методику реализации векторной широтно-импульсной модуляции в девятифазных управляемых преобразователях электрической энергии

Infectious Speciation Revisited: Impact of Symbiont-Depletion on Female Fitness and Mating Behavior of Drosophila paulistorum

The neotropical Drosophila paulistorum superspecies, consisting of at least six geographically overlapping but reproductively isolated semispecies, has been the object of extensive research since at least 1955, when it was initially trapped mid-evolution in flagrant statu nascendi. In this classic system females express strong premating isolation patterns against mates belonging to any other semispecies, and yet uncharacterized microbial reproductive tract symbionts were described triggering hybrid inviability and male sterility. Based on theoretical models and limited experimental data, prime candidates fostering symbiont-driven speciation in arthropods are intracellular bacteria belonging to the genus Wolbachia. They are maternally inherited symbionts of many arthropods capable of manipulating host reproductive biology for their own benefits. However, it is an ongoing debate as to whether or not reproductive symbionts are capable of driving host speciation in nature and if so, to what extent. Here we have reevaluated this classic case of infectious speciation by means of present day molecular approaches and artificial symbiont depletion experiments. We have isolated the α-proteobacteria Wolbachia as the maternally transmitted core endosymbionts of all D. paulistorum semispecies that have coevolved towards obligate mutualism with their respective native hosts. In hybrids, however, these mutualists transform into pathogens by overreplication causing embryonic inviability and male sterility. We show that experimental reduction in native Wolbachia titer causes alterations in sex ratio, fecundity, and mate discrimination. Our results indicate that formerly designated Mycoplasma-like organisms are most likely Wolbachia that have evolved by becoming essential mutualistic symbionts in their respective natural hosts; they have the potential to trigger pre- and postmating isolation. Furthermore, in light of our new findings, we revisit the concept of infectious speciation and discuss potential mechanisms that can restrict or promote symbiont-induced speciation at post- and prezygotic levels in nature and under artificial laboratory conditions

Influence of fiber type and matrix composition on adhesive strength in fiber reinforced concrete

Introduction. The purpose of the article is to determine the influence of the steel fiber profile and the composition of the matrix on their adhesion in dispersed reinforced concrete.Materials and methods. Studies have been carried out using the test methods set out in national standards. To determine the characteristics of the adhesion strength of fibers with a matrix, an original technique developed at SPbGASU was used.Results. The degree of influence of the geometric shape of steel fibers – anchor and wave profile on the adhesion strength characteristic is determined. The adhesion strength of steel fiber with cement and concrete matrix was assessed (Cement: Sand = 1:1, Cement: Sand = 1:2 and Cement: Sand = 1:3). The influence of the volume fraction of the cement paste on the characteristic of the adhesion strength of the steel fiber with the matrix has been experimentally proven.Conclusions. The experimental data obtained confirm the effectiveness of dispersed reinforcement through the use of anchor fibers in combination with a rationally selected composition of the concrete matrix.</jats:p

Synthesis of the Algorithm of the Vector Width-Pulse Modulation in a Nine-Phase Active Voltage Rectifier

The article is devoted to the problems of synthesis of multiphase electromechanic modules consisting of a multiphase electrical machine (m &gt; 3) and a multiphase controlled converter. In the multi-phase design of the electric machine, it is possible to obtain a trapezoidal electromotive force and to increase the specific power conversion provided that the EMF and the current at the output of the m-phase generator are matched. The development of the vector pulse width modulation algorithm for the m-phase active voltage rectifier is considered, which will make it possible to match the shape and phase of the currents and voltages at the output of the m-phase generator in order to obtain the maximum active power of the module under study. The analysis of possible combinations of states of the keys of a nine-phase active rectifier is carried out. Each key state is assigned a base vector in a fixed coordinate system. It is noted that there are a number of combinations in which two or more different key states correspond to one base vector. The system of basic vectors is differentiated into its constituent levels, sectors and subsectors. In order to obtain any given voltage vector that does not coincide with the base vectors, the method of spacevector modulation is used. This method provides using 100 % DC link voltage as compared with sinusoidal pulse width modulation (86.6 %). The goal of space-vector modulation for a nine-phase active voltage rectifier is to implement the resultant spatial vector of the output voltage with a given average value within the modulation period. For this, the three vectors nearest to the given base vector must be found. To implement a given voltage vector, a sequence of sampling the base vectors in the modulation period is given, providing one commutation (commutation of two complementary keys) while passing from one basic vector to another to reduce switching losses. Analytic relationships of the weight coefficients for the generators of vectors are obtained, as well as the equations of the boundaries of the subsectors that form a diagram of combinations of states of the circuit. The sequence of the calculations presented in the paper is a technique for realizing the vector pulse-width modulation in nine-phase controlled electrical energy converters