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Effect of fibers on self-healing properties of microbial mineralized cement mortars
Full text linkIn this study, we selected cement mortar as the research object, used the expanded perlite (EP) which adsorbed bacteria as the self-healing agent, and mixed basalt fibers to improve the properties. The effects of different dosages and sizes of self-healing agent and basalt fibers on the mechanical properties and self-healing properties of cement mortar were investigated by compressive strength, SEM, EDS, XRD, and optical microscopy tests. The results of the study showed that the bacteria were able to survive in cement mortar using expanded perlite as a carrier and induced the generation of calcium carbonate precipitates to fill the cracks. The dosage of the healing agent is proportional to the amount of healing products generated, which can significantly improve the self-healing performance of cracks in mortar. Fibers can bond the material, play the role of bridging, and become the adsorption carrier of bacterial metabolic precipitates, which is beneficial to the dense bonding of the products. The addition of appropriate amount of basalt fiber can simultaneously improve the self-healing properties and compressive strength of mortar. The simultaneous addition of healing agent and basalt fiber can realize the complementary advantages. By adding a small amount of healing agent and a moderate amount of fiber, not only can achieve 100% self-healing performance, but also improve the compressive strength of mortar. This study provides useful theoretical guidance for the design, preparation, and application of concrete
R WAVE PEAK TIMES DISPLAYED IN BODY SURFACE ISOCHRONE MAPS OF YOUNG ADULT MEN
Full text linkIn standard 12-lead electrocardiography, the peak time or intrinsicoid deflection is defined as the activation time of the ventricular muscle lying under the exploratory electrode. It serves as an easy measurable parameter used in the diagnosis of cardiac diseases related to disturbed or delayed ventricular activation. The aim of this study was to analyse the R wave peak isochrone maps in young adult volunteers using the time normalisation of the QRS complex. Body surface isochrone maps of the peak time were constructed and analysed in 13 healthy young men. It was found to start always on the anterior chest surface and mainly in its upper half. After spreading downward and leftward, it mostly ended mainly in the back chest, mainly in its upper half, and around the right shoulder. This agrees with previously published results of mean maps, also in older subjects without known cardiovascular diseases obtained from different mapping lead systems. The R wave peak times obtained from our maps also agreed with known intrinsicoid deflections for the standard leads V5 and V6, published previously. To conclude, the R wave peak isochrone maps allow simple visualisation of activation sequence, which will differ in cardiac diseases related to disturbed or delayed ventricular activation, like ventricular hypertrophy, myocardial infarction or bundle branch blocks
Dirac fermion in a time-dependent spherical box
Full text linkWe consider a Dirac particle in a spherical box with a time-dependent radius. Analytical and numerical solutions of the time-dependent Dirac equation with time-dependent boundary (Dirichlet) conditions are obtained. Using the obtained solutions, physically observable characteristics of the dynamical confinement, such as the average kinetic energy (as a function of time) and average quantum force acting on the particle by the moving wall, are calculated. The trembling motion is analysed by computing the average coordinate of the Dirac particle as a function of time. The absence of the geometric phase is shown by direct calculation
Prestressed textile reinforced concrete with carbon composite reinforcement
Full text linkThe article deals with the potential of prestressed textile concrete. The prestressing principle, which is nowadays commonly used part of construction, is combined with the developing technology of textile concrete which is concrete reinforced with non-metallic reinforcement. In this case the carbon reinforcement is used because it shows the best mechanical parameters in comparison with glass or basalt reinforcement. The paper presents the advantages of using prestressed textile carbon composite reinforcement of textile reinforced concrete and at the same time deals with problems related to it, such as the correct choice of impregnation using epoxy resin and the technological method of introducing prestress into the sample. The article focuses on comparison between 3 types of epoxy resin, specifically Sikafloor 156, LH 300 and EPOREZIT EPOVILL-A. The results are presented on experimental samples tested in four-point bending test
Experimental analysis of physical properties of lightweight gypsum plasterboard
Full text linkThis article presents an experimental analysis of a newly developed gypsum plasterboard for dry construction. The new board has a density that is 40 kgm−3 lower than existing boards and was created with an emphasis on conserving resources and reducing the energy consumption required for its production. Because gypsum is the most energy-intensive raw material, the research team focused on minimizing its content. As a result, the new board uses 12 % of mass less gypsum, which translates into an approximately 6 % reduction in CO2 emissions from the annual production process. Crucially, this was achieved while meeting the relevant standard requirements for mechanical, thermal-technical, and fire performance, and maintaining the board’s “sustainable” user properties. The article details the experimental analysis conducted on key mechanical and thermal-technical parameters of the board
Study on Mechanical Response Law of Shield Assembly Tunnel with Complex Section During Construction
Full text linkTo clarify the stress and deformation behavior of complex section assembly tunnel with mushroom shape, the mechanical behavior variation law of assembly tunnel in different construction stages were explored through intelligent monitoring. The longitudinal and cross-sectional distribution characteristics of the mechanical behavior of the assembly tunnel and the deformation control effect of the support on the surrounding rock were analyzed based on numerical simulation. Through comparative analysis, the applicability of different excavation methods in this project is explored. By comparing with theoretical methods, the bearing characteristics of the assembly tunnel were discussed, and the engineering suggestions were given. The results show that the excavation of the lower section has little effect on the arch of the mushroom head and has a continuous impact on the side wall. The arch support of mushroom head can enhance the restraint ability of lower section support to surrounding rock deformation. The initial support deformation and the bolt axial force of the mushroom head gradually decrease from the position near the centroid to both sides. In the corner of the wall, the support appears to deviate from the tunnel, where the bolt is compressed. The contact stress of mushroom head increases first, then decreases and then increases from the position near the centroid to both sides. The stress in the transition area between the arch and the straight wall on both sides increases locally, and the stress concentration occurs at the corner of the wall. The deformation of the initial support and the bolt axial force on both sides of the lower section increase first and then decrease from top to bottom, while the law of the contact stress is opposite. For the combined support of flat arch and vertical straight wall, more attention should be paid to the stress and deformation characteristics of arch foot and side wall in engineering.
Received: 13.06.2024
Received in revised form: 13.06.2025
Accepted: 24.11.202
Research on seismic resistance of cable-stayed arch bridge
No full textBridges are prone to damage during earthquakes, with large-scale or complex structural systems being particularly sensitive to seismic impacts. Taking the bridge that integrates a cable-stayed bridge with a backless slanted tower and a lower-supported irregular arch bridge as the background, this paper establishes a spatial analysis model for Xiangfeng River Bridge using the finite element software Midas Civil. Based on the concept of structural vibration control design, the concept of time-history response influence factors is introduced to conduct a time-history response parameter analysis of the structure. The study investigates the effects of wind brace arrangement, concrete elastic modulus, length of arch rib concrete sections, and the inclination angle of the pylon on the seismic performance of the bridge. It further compares and analyzes structural vibration control and damping, conducts structural seismic checks, and performs elasto-plastic time-history response analysis at the consolidated positions of the tower, beam, and pier by defining elasto-plastic materials and fiber hinges. The research results indicate that the sensitivity of the overall seismic performance of the structure to different parameters follows the order from strongest to weakest as: pylon inclination angle > length of arch rib concrete sections > concrete elastic modulus > wind brace arrangement. “K”-shaped wind braces are more conducive to structural seismic resistance compared to parallel wind braces, and omitting wind braces will significantly impact the seismic performance of the structure. Increasing the short length of the arch rib concrete sections affects the structural spatial mass distribution and reduces the overall lateral stability of the structure.
Received: 26.06.2025
Received in revised form: 10.09.2025
Accepted: 24.11.202
Arc conductance decay as a performance indicator for thermal interruption in CO2/O2 mixture
Full text linkArc conductance decay is a well-established performance indicator for thermal interruption in SF6, with a narrow range of known limit values. It is also shown that conductance decay can also serve as a performance indicator in CO2-based mixtures, although different limit values for successful thermal interruption apply. In this publication, values of arc conductance 200 ns before current zero are presented for a large number of experiments performed in CO2/O2 90/10 mixture under short line fault-like conditions. These measurements are used to establish limit values for the CO2/O2 mixture, and to investigate the pressure dependence of conductance decay
Magnetohydrodynamic modeling of direct current arc interruption in a low-voltage switch
Full text linkThis paper proposes a magnetohydrodynamic arc model for direct current arc interruption simulation in a low-voltage switch with a contact bridge design. Arc voltage and current for the interruption of an initial current and voltage in the 800 V and 800 A range are compared and differences discussed between the simulation and an experiment. The arc is successfully quenched in the simulation, but discrepancies between simulation and experiment may be attributable to erosion modeling
Study of the behavior of an electric arc during the passage of an 8/20 µs impulse current and a follow current in a spark gap
Full text linkThe technologies of spark gaps involve two distinct types of current: an impulse current that simulates a lightning strike and a follow current resulting from the persistence of the arc after the impulse. This study shows the behavior of the electric arc with 8/20 µs impulse current followed by a 200 A follow current, using both experiments and numerical tools. The geometry includes a pre-chamber, a main chamber (without separators), and an open outlet. We developed a three-dimensional (3D) numerical model to simulate the arc movement. This model is based on the assumption of local thermodynamic equilibrium (LTE) and operates under unsteady conditions. In our experiments, we use high-speed camera recordings and electrical measurements. A good agreement is observed between the numerical model and the experimental measurements, both in terms of arc shape and arc voltage values