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Gamma-ray bursts and optical brightness: insights from Swift satellite
Full text linkDuring the examination of optical properties of gamma-ray bursts (GRBs) measured during the life of the Neil Gehrels Swift Observatory satellite, significant discoveries were made. While the satellite measures gamma, X-ray, and optical data simultaneously, in many cases, only an upper limit is established in the optical domain. Hence, survival analysis, a.k.a. dependability modelling, was necessary, serving as a tool for studying samples where some cases are bound only by the upper limit, as mentioned earlier. This method is used to analyse datasets that may have upper or lower bounds rather than precise observations, but nevertheless contain relevant information. It was previously established that the duration, gamma fluence, and peak flux all have a substantial effect on the optical brightness distribution, probably due to the energy of the beam from the GRB’s central engine. However, after analysing more than 200 data points, we no longer see this association. This disagreement shows that the previously reported impact may not be as significant as previously derived, needing more research to better understand the underlying processes that determine the optical brightness in connection to gamma-ray properties
RESEARCH ON FLEXURAL CALCULATION THEORY OF REINFORCED CONCRETE T-BEAM STRENGTHENED BY STEEL WIRE MESH AND POLYURETHANE CEMENT (SWM-PUC) COMPOSITE
Full text linkIn order to solve the problem of poor bonding and easy peeling of reinforced concrete structure strengthened by steel wire mesh and polymer mortar (SWM-PM). In this paper, a steel wire mesh and polyurethane cement (SWM-PUC) composite strengthening technique is presented. The flexural properties of one unreinforced beam, two SWM-PM strengthened beams and four SWM-PUC composite strengthened beams were studied experimentally. The experimental results show that the SWM-PUC composite reinforcement layer can improve the load carrying capacity and rigidity of reinforced concrete beams and limit the unfolding cracks significantly. The SWM-PUC composite strengthened beams have pure bending damage and peeling damage between the strengthening layer and the concrete has not occurred. However, SWM-PM strengthened beams with the same SWM reinforcement ratio occurred with peeling damage between the reinforcement and the concrete. On basis of an experimental study, the theoretical formulas for cracking load, ultimate load, deflection and width of crack of SWM-PUC composite strengthened beams are proposed by the simplified stress-strain constitutive relation of the material and the theoretical formulas are deduced with the code. By contrasting the test results with the theoretical computation results, the accuracy of the experiment results and the reliability of the theoretical formulas were verified
Effect of variability of material properties on resistance of existing post-tensioned concrete bridge – case study
Full text linkThe study deals with the sensitivity analysis in determining the load-bearing capacity of existing bridges made of post-tensioned precast girders. Focusing on a specific road bridge, the effect of variations of important basic variables on load-bearing capacity is investigated. When assessing existing structures, values of some basic variables often need to be estimated due to the lack of background information (missing documentation, limited range of structural survey). The aim of this study is to identify basic variables with key influence on load-bearing capacity of the bridge. Numerical example is specifically focused on the mid-span cross-section of a simply supported KA-73 beam structure. It appears that corrosion is the key factor affecting reliability of the bridge at the Ultimate Limit State while prestressing loss is dominating the Servieability Limit State verification. Further research will be focused on reliability analysis of bridges based on the results of structural surveys
Cable optimization of extradosed bridges
Full text linkExtradosed bridges offer a competitive alternative to traditional systems used in spans ranging from 100 to 250 m. The trend in the world is the development of new materials and with it the design of thin structures, which is a challenging change for further development. Extradosed bridge is a relatively new type of construction (first in Odawara, Japan 1994), although there are many bridges of this type in the world, there are no strict design rules in terms of statics and even less in terms of dynamic behavior. To research this area closer, parametric analysis can be performed. Due to the complexity of this task and the non-linear coupling of the design parameters, it is necessary to approach it by an optimization method that, for predefined boundary conditions, optimizes the design response
Prestress load distribution modeling for containment digital twin model
Full text linkThis paper examines the prestress load distribution in the ducts of the prestressing tendons of a VVER-type nuclear reactor containment. It introduces a method for distributing the simplified linear load from the prestressing cable onto the surface area of the duct. Furthermore, a procedure for applying this calculation to a detailed numerical 3D model of a containment segment is described. This method can be implemented into computational software, such as OOFEM, to incorporate this more accurately defined load into a comprehensive stress analysis of the segment. Realistic definition of load distribution from prestressing tendons on the surface of the ducts is critical for identifying potential deviations from a uniform prestress distribution within the containment wall. This, in turn, facilitates assessments such as evaluating the extension of the structure’s service life
A study of the behavior of samples of high-performance concrete shells with filled core exposed to compression
Full text linkThe production of concrete has a huge impact on the environment, especially due to its emission of CO2. Nowadays, it is required to reduce CO2 emissions and at the same time reduce the consumption of non-renewable resources. One way to achieve these goals is through the usage of recycled aggregate. However, when these materials are used, there are significant changes in the properties of concrete, particularly a reduction of mechanical strength, modulus of elasticity, and durability. This article presents the possibility of using a thin shell made of high-performance concrete as core protection of a concrete sample with recycled aggregate to improve the abovementioned properties. Moreover, using high-performance concrete as the outer layer enables the potential of high-performance concrete to be exploited. The article describes the influence of different shell reinforcements on the failure of the samples under compressive stress. A shell layer without additional reinforcement was used for the reference samples. Other sets of samples contained dispersed reinforcement in the form of polypropylene or polyvinyl alcohol fibers. The last reinforcement was a technical textile – a laboratory-prepared composite grid made of carbon rovings. All samples were subjected to a compressive test and the failure mode of the samples was observed in particular
High-temperature oxidation of non-zirconium materials for ATF
Full text linkNon-zirconium materials, such as silicon carbide (SiC) and FeCrAl alloys, have attracted interest for developing Accident-Tolerant Fuel (ATF) cladding systems owing to their superior hightemperature oxidation resistance. SiC offers excellent thermal stability, high-temperature properties, irradiation tolerance, and low activation, while FeCrAl alloys provide outstanding oxidation resistance in steam and air through a stable alumina (Al2O3) layer. This study examines their oxidation behavior under simulated severe-accident conditions. Microstructural changes and mechanical integrity after exposure were analyzed using scanning electron microscopy (SEM) and ring compression tests (RCT). The analysis revealed material-specific strengths and limitations, emphasizing the role of temperature and oxidation environment
Impact of fecral oxide composition on severe accident progression in MELCOR
Full text linkExperimental studies have shown that the composition of the oxide layer forming on FeCrAl surface depends strongly on the temperature of the environment, with varying fractions of aluminum, chromium, and iron oxides forming under different conditions.In this work, multiple oxide compositions were incorporated into MELCOR simulations for evaluation of their impact on cladding degradation. The weight fractions of aluminum, chromium, and iron oxides were derived from published experimental data, serving as basis for modifications of the material model.Simulations of a representative Loss of Coolant Accident scenario show that these changes significantly affect cladding temperature evolution, oxidation progression, and hydrogen generation. These results highlight the need to account for environmentally dependent behavior when modeling advanced cladding materials in integral codes
Research on long-term strains for beams wrapped with self-compacted concrete
Full text linkMany objects built in the past do not meet the new construction standards and may be at risk from the action of special loads. Therefore there is a need for their structural elements to be reinforced by increasing the moment of inertia, and with this, there is a need to increase the cross-sectional dimensions.
The realization of reinforcing structural elements, particulary columns and beams, can be easily achieved by increasing their dimesions using self-compacting concrete, which benefits from its excellent workability properties as fresh concrete, enabling easy filling of formworks.
In this case, the reinforced elements of reinforced concrete structures will be subjected to a new process of strains, whether elastic or more importantly, they are also subjected to strains in the long-term process such as shrinkage strains and creep strains.
For the analysis of strains in structural elements reinforced with self-compacting concrete both at the moment of load action and in the long-term process of load action, an experiment was carried out for a period of two years.
During this experiment, the mechanical and deformable characteristics of elements (laboratory samples and beams) from normal concrete and from self-compacting concrete were analysed. The research of these characteristics was carried out both at the time t0=40 days, of the load action, and in the long-term process up to the time t∞=400 days
This paper presents the results obtained for shrinkage strains and creep strains during the analysis of beams made of ordinary concrete, self-compacting concrete, as well as repaired beams, whose core is made of ordinary concrete and after hardening, at the age of 40 days they are wrapped with a layer of self-compacting concrete on three sides of the beam. Results for the modulus of elasticity, compressive strength, breaking toughness, and water permeability results obtained from laboratory sample testing will also be provided.
Received: 29.4.2025
Received in revised form: 9.7.2025
Accepted: 7.8.2025
Influence of radiation energy losses in a numerical simulation of subsonic vacuum arc in the presence of an axial magnetic field
No full textWe present a three-dimensional (3D) Magneto Hydrodynamic Model (MHD) at two temperatures (electronic and ionic) of inter-electrodes plasma, simulated with Ansys Fluent coupled with specific developments in C language. The stationary model describes a subsonic arc in vacuum at 15 kA between copper contacts, submitted to an Axial Magnetic Field (AMF). Due to high temperatures, losses by radiation need to be considered. Even if departures from Local Thermal Equilibrium (LTE) exist, currently due to lack of appropriate data, net emission coefficient data calculated under LTE are used and attributed exclusively to electron energy equation. Two cases are investigated in this study, with or without considering the radiation in the electrons energy equation. The study highlights the importance of better characterizing radiative losses in order to improve the reliability of numerical models