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    Machinability of extruded H13 tool steel: Effect of cutting parameters on cutting forces, surface roughness, microstructure, and residual stresses
    (Elsevier, 2024-05-19) Kolomý, Štěpán; Malý, Martin; Sedlák, Josef; Zouhar, Jan; Slaný, Martin; Hrabec, Pavel; Kouřil, Karel
    The production of H13 tool steel (TS) by material extrusion (MEX) is a promising method in various applications, but as-built surface roughness does not comply with the quality requirements. Hence, this study investigated the effects of cutting parameters on tool wear, cutting forces, surface quality, microhardness, structure, and residual stresses when machining H13 TS produced by MEX. Dry machining (DM) proved advantageous in certain indicators such as tool wear and cutting forces in comparison to the flood cooling (FC). The lowest surface roughness (0.08 mu m) was achieved at the cutting speed of 80 m/min, feed per tooth of 0.005 mm, and FC which corresponded to a 41 % decrease compared to DM under same conditions. Surface microhardness increased by 20 % after machining, decreasing with distance from the surface. The highest compressive residual stresses were observed under FC, while the DM resulted in a 78.2 % decrease in residual stresses due to a partial annealing effect caused by higher surface temperature. Overall, DM exhibited great potential for achieving high-quality surfaces with a favorable structure and residual stresses. This studys novelty and robustness lie in its significant contribution to practical industrial applications, such as mold and core production.
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    A novel geometric method based on conformal geometric algebra applied to the resection problem in two and three dimensions
    (SPRINGER, 2024-06-02) Ventura Gil, Jorge; Martinez, Fernando; Manzano-Agugliaro, Francisco; Návrat, Aleš; Hrdina, Jaroslav; Eid, Ahmad H; Montoya, Francisco G.
    This paper introduces a novel method for solving the resection problem in two and three dimensions based on conformal geometric algebra (CGA). Advantage is taken because of the characteristics of CGA, which enables the representation of points, lines, planes, and volumes in a unified mathematical framework and offers a more intuitive and geometric understanding of the problem, in contrast to existing purely algebraic methods. Several numerical examples are presented to demonstrate the efficacy of the proposed method and to compare its validity with established techniques in the field. Numerical simulations indicate that our vector geometric algebra implementation is faster than the best-known algorithms to date, suggesting that the proposed GA-based methods can provide a more efficient and comprehensible solution to the two- and three-dimensional resection problem, paving the way for further applications and advances in geodesy research. Furthermore, the method's emphasis on graphical and geometric representation makes it particularly suitable for educational purposes, allowing the reader to grasp the concepts and principles of resection more effectively. The proposed method has potential applications in a wide range of other fields, including surveying, robotics, computer vision, or navigation.
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    Topogenous orders and closure operators on posets
    (TÜBITAK, 2024-05-10) Šlapal, Josef; Richmond, Tom; Iragi, Minani
    We introduce the notion of topogenous orders on a poset X to be certain endomaps on X. We build on a Galois connection between endomaps and binary relations on X and study relationships between endomap properties and corresponding relational properties. In particular, we determine the topogenous orders that are in a one-to-one correspondence with (idempotent) closure operators. Extending our considerations to the categorical level, we find a cartesian closed category of topogenous systems.
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    Application of Dual-target Computed Tomography for Material Decomposition of Low-Z Materials
    (SPRINGER/PLENUM PUBLISHERS, 2024-06-01) Mikuláček, Pavel; Zemek, Marek; Štarha, Pavel; Zikmund, Tomáš; Kaiser, Jozef
    The extension of conventional computed tomography known as spectral computed tomography involves utilizing the variations in X-ray attenuation, driven by spectral and material dependencies. This technique enables the virtual decomposition of scanned objects, revealing their elemental constituents. The resultant images provide quantitative information, such as material concentration within the scanned volume. Enhancements in results are achievable through methods that capitalize on the strong correlation among decomposed images, effectively minimizing noise and artifacts. The Rigaku nano3DX submicron tomograph uses a dual-target source, which allows the generation of two distinct X-ray spectra through different target materials. This configuration holds promise for high-resolution applications in spectral tomography, particularly for low-Z materials, where it offers high contrast in the acquired images. The potential of this setup in the context of spectral computed tomography is explored in this contribution, delving into its applications for materials characterized by low atomic numbers.
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    A precise asymptotic description of half-linear differential equations
    (WILEY-V C H VERLAG GMBH, 2024-04-08) Řehák, Pavel
    We study asymptotic behavior of solutions of nonoscillatory second-order half-linear differential equations. We give (in some sense optimal) conditions that guarantee generalized regular variation of all solutions, where no sign condition on the potential is assumed. For all of these solutions, we establish precise asymptotic formulas, where positive as well as negative potential is considered. We examine, as consequences, also equations with regularly varying coefficients, or with the coefficients viewed as perturbations of exponentials, or the equations under certain critical (double roots) settings. We make also asymptotic analysis of Poincare-Perron solutions. Many of our results are new even in the linear case.