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3. Prediction and research of dynamic recrystallization evolution in hadfield steel turnout coresHongchao Ji, Yupeng Zeng, Xiaomin Huang, Changzhe Song, Mingming Wang, Jingsheng Li, 2025, original scientific article Keywords: dynamic recrystallization, turnout core, forging, numerical simulation, constitutive model
Published in DiRROS: 24.04.2025; Views: 170; Downloads: 102
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5. Some experience in numerical modelling of unsaturated slope instabilitiesJosif Josifovski, Stanislav Lenart, 2016, published scientific conference contribution Abstract: In the past couple years, the region of South-East Europe is subjected to gust rainfall events activating many landslides which cause significant material and human losses. To revaluate the existing risk maps and set new standards some old case histories are revaluated. This paper presents two case histories of landslide instabilities subjected to excess climatic perturbations, gust rainfall, namely the «Stanjevci» cut-slope near the railway line in North-East of Slovenia; and the «Ramina» a natural landslide in urban area near the city of Veles in Central Macedonia. They are briefly described later to be analysed using coupled thermo-mechanical calculations. They are subjected to specific short and gusting rainfall considered as possible trigger. Hence, van Genuchten's hydraulic model is used in combination with elastoplastic material models. The results are summarized with critical comments regarding the mathematical formulation used to describe atmospheric-soil interaction and the influence of different aspects on the accuracy is discussed briefly.
Keywords: numerical, unsaturated soil, slope stability analysis, climate effect
Published in DiRROS: 04.03.2025; Views: 221; Downloads: 125
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6. Monotonicity properties of weighted geometric symmetrizationsKatarina Bogdanović, Aljoša Peperko, 2024, original scientific article Abstract: We prove new monotonicity properties for spectral radius, essential spectral radius, operator norm, Hausdorff measure of non-compactness and numerical radius of products and sums of weighted geometric symmetrizations of positive kernel operators on $L^2$. To our knowledge, several proved properties are new even in the finite dimensional case.
Keywords: mathematics, weighted Hadamard-Schur geometric mean, Hadamard-Schur product, spectral radius, operator norm, Hausdorff measure of non-compactness, numerical radius, non-negative matrices, positive kernel operators
Published in DiRROS: 31.01.2025; Views: 268; Downloads: 141
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7. Is the order of learning numerals universal? : evidence from eight countries and six languagesLee Copping, Peter Tymms, Gabriela Aleksic, Tiago Bartholo, Sarah J. Howie, Mariane Koslinski Campelo, Christine Merrell, Maša Vidmar, Helen R. Wildy, 2024, original scientific article Abstract: Cramman et al. (2018) proposed that numerical symbol identification may constitute a universally predictive measure of early mathematical development. While a broad pathway to learning number symbols is unsurprising, lack of systematic variation in acquisition order relative to factors such as teaching, age, country, progression stage, is. This study evidences unidimensionality of measurement of the order of ability clusters of numbers, showing that variations are minor across eight countries and, importantly, six instructional languages. This invariance suggests early symbol identification could represent a universal measurement which could a) instructionally inform teaching and learning of classroom mathematics, b) work predictively as an educational research tool and c) offer a foundation for valid international comparisons of the mathematical development of children. Tentatively, this study suggests numerical symbol identification may be a universal measure to assess mathematical cognition in early years education that is unaffected by language of instruction, gender, time of assessment and country.
Keywords: education, financial relationship, numeracy mathematical development, numerical symbol, learning numerals, international comparison
Published in DiRROS: 27.01.2025; Views: 286; Downloads: 160
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8. On the thermal stability of multilayer optics for use with high X-ray intensitiesMargarita Zakharova, Zlatko Rek, Božidar Šarler, Saša Bajt, 2024, original scientific article Abstract: High-intensity X-ray free electron laser (XFEL) beams require optics made of materials with minimal radiation absorption, high diffraction efficiency, and high radiation hardness. Multilayer Laue lenses (MLLs) are diffraction-based X-ray optics that can focus XFEL beams, as already demonstrated with tungsten carbide/silicon carbide (WC/SiC)-based MLLs. However, high atomic number materials such as tungsten strongly absorb X-rays, resulting in high heat loads. Numerical simulations predict much lower heat loads in MLLs consisting of low atomic number Z materials, although such MLLs have narrower rocking curve widths. In this paper, we first screen various multilayer candidates and then focus on Mo2C/SiC multilayer due to its high diffraction efficiency. According to numerical simulations, the maximum temperature in this multilayer should remain below 300°C if the MLL made out of this multilayer is exposed to an XFEL beam of 17.5 keV photon energy, 1 mJ energy per pulse and 10 kHz pulse repetition rate. To understand the thermal stability of the Mo2C/SiC multilayer, we performed a study on the multilayers of three different periods (1.5, 5, and 12 nm) and different Mo2C to SiC ratios. We monitored their periods, crystallinity, and stress as a function of annealing temperature for two different heating rates. The results presented in this paper indicate that Mo2C/SiC-based MLLs are viable for focusing XFEL beams without being damaged under these conditions.
Keywords: x-ray optics, multilayer Laue lens, thermal stability, numerical simulation
Published in DiRROS: 20.12.2024; Views: 376; Downloads: 179
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9. Experimental investigation on the effect of natural fire exposure on the post-fire behavior of reinforced concrete beams using electric radiant panelBalša Jovanović, Robby Caspeele, Edwin Reynders, Geert Lombaert, Florian Put, Andrea Lucherini, Ruben Van Coile, 2024, original scientific article Abstract: In this study, the effects of natural fire exposure on the post-fire behavior of concrete beams are investigated. The study is based on laboratory tests where three reinforced concrete beams were subjected to fire exposure using an electric radiant panel. This panel enables a precise application of radiative heat exposure closely mimicking natural fire exposure in a safe manner. During the test, the deflections, deformations and temperature changes are measured for all three concrete beams. Additionally, finite element modeling (FEM) is applied to supplement these tests, demonstrating the performance of existing structural fire engineering calculation tools in evaluating the burnout performance of concrete beams. The results of the tests show that the electric radiant panel provide a novel approach for fire simulation which is effective in replicating natural fire conditions, by applying the heat flux as specified in the Eurocode Parametric Fire Curve in a highly controlled manner. The uniformity of the temperature field measured inside the beams and the consistent deformations observed during the heat exposure across all three tests underscores the accuracy of the fire simulation. Furthermore, post-fire assessments reveal that while the exposed beams suffered some reduction in load-bearing capacity, they retained a significant portion of their original strength that was consistent across all three beams. The numerical simulations conducted in this study demonstrate a high level of accuracy in predicting the behavior of the concrete beams during fire exposure. These simulations effectively mirrored the experimental results, validating that they are a valuable tool for assessing concrete structures' performance in fire scenarios.
Keywords: concrete beam, fire testing, numerical modeling, radiant panel
Published in DiRROS: 28.11.2024; Views: 395; Downloads: 145
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10. Analysis of eigenvalue condition numbers for a class of randomized numerical methods for singular matrix pencilsDaniel Kressner, Bor Plestenjak, 2024, original scientific article Abstract: The numerical solution of the generalized eigenvalue problem for a singular matrix pencil is challenging due to the discontinuity of its eigenvalues. Classically, such problems are addressed by first extracting the regular part through the staircase form and then applying a standard solver, such as the QZ algorithm, to that regular part. Recently, several novel approaches have been proposed to transform the singular pencil into a regular pencil by relatively simple randomized modifications. In this work, we analyze three such methods by Hochstenbach, Mehl, and Plestenjak that modify, project, or augment the pencil using random matrices. All three methods rely on the normal rank and do not alter the finite eigenvalues of the original pencil. We show that the eigenvalue condition numbers of the transformed pencils are unlikely to be much larger than the ▫$\delta$▫-weak eigenvalue condition numbers, introduced by Lotz and Noferini, of the original pencil. This not only indicates favorable numerical stability but also reconfirms that these condition numbers are a reliable criterion for detecting simple finite eigenvalues. We also provide evidence that, from a numerical stability perspective, the use of complex instead of real random matrices is preferable even for real singular matrix pencils and real eigenvalues. As a side result, we provide sharp left tail bounds for a product of two independent random variables distributed with the generalized beta distribution of the first kind or Kumaraswamy distribution.
Keywords: singular pencil, singular generalized eigenvalue problem, eigenvalue condition number, randomized numerical method, random matrices
Published in DiRROS: 26.08.2024; Views: 519; Downloads: 236
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