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排序方式: 共有199条查询结果,搜索用时 15 毫秒
31.
Belen Moreno Pablo Lopez‐Crespo Alejandro S. Cruces Jaime Dominguez 《Fatigue & Fracture of Engineering Materials & Structures》2019,42(9):2194-2203
The crack opening/closure load concept is widely used to justify the fatigue crack growth behaviour with different load ratios and the load interaction effects. Many experimental techniques have been proposed to measure crack opening/closure load, and amongst them, compliance offset methods are widely used for their simplicity and consistency. In this paper, a modification of the ASTM method is proposed. The new method has a more general applicability as it can be applied to broadband variable amplitude loads. The method is described in detail and is applied on a 2024‐T351 aluminium alloy. The good correlation of the opening load estimated with the new method and the strip‐yield model implemented in Nasgro indicates that the new method could be used as an alternative for the cases where complex variable amplitude loads occur. 相似文献
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Stabilisation of state‐and‐input constrained nonlinear systems via diffeomorphisms: A Sontag's formula approach with an actual application
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In this work, we provide a new and constructive outlook for the control of state‐and‐input constrained nonlinear systems. Previously, explicit solutions have been mainly focused on the finding of a barrier‐like Lyapunov function, whereas we propose the construction of a diffeomorphism to map all the trajectories of the constrained dynamics into an unconstrained one. Careful analysis has revealed that only some foundations of differential geometry and a technical assumption are necessary to construct the proposed methodology based on the well‐established theories of control Lyapunov functions and Sontag's universal formulae. Altogether, it allows us to obtain an explicit solution that even includes bounded constraints in the control action, giving the designer a way to decide (to some extent) the trade‐off between control saturations and robustness. Moreover, this approach does not rely on the own structure of the system dynamics, therefore covering a broad class of nonlinear systems. The main advantage of this approach is that the use of a diffeomorphism allows the splitting of the mathematical treatment of the constraint and the Lyapunov controller design. The result has been successfully applied to solve the dynamic positioning of an actual ship, where the nonlinear state constraints describe a strait. This approach enabled us to design a control Lyapunov function and thereby use Sontag's formula to solve the stabilisation problem. Realistic simulations have been executed in a real scenario on the simulator owned by an international shipbuilding company. 相似文献
33.
Reproducing the appearance of real‐world materials using current printing technology is problematic. The reduced number of inks available define the printer's limited gamut, creating distortions in the printed appearance that are hard to control. Gamut mapping refers to the process of bringing an out‐of‐gamut material appearance into the printer's gamut, while minimizing such distortions as much as possible. We present a novel two‐step gamut mapping algorithm that allows users to specify which perceptual attribute of the original material they want to preserve (such as brightness, or roughness). In the first step, we work in the low‐dimensional intuitive appearance space recently proposed by Serrano et al. [ SGM*16 ], and adjust achromatic reflectance via an objective function that strives to preserve certain attributes. From such intermediate representation, we then perform an image‐based optimization including color information, to bring the BRDF into gamut. We show, both objectively and through a user study, how our method yields superior results compared to the state of the art, with the additional advantage that the user can specify which visual attributes need to be preserved. Moreover, we show how this approach can also be used for attribute‐preserving material editing. 相似文献
34.
Cover Feature: Directed Evolution of Hyaluronic Acid Synthase from Pasteurella multocida towards High‐Molecular‐Weight Hyaluronic Acid (ChemBioChem 13/2018)
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Solute distributions in the vicinity of grain boundaries in Al–Zn–Mg(–Ag) alloys were studied using a three-dimensional atom probe, in order to elucidate the mechanism of formation of precipitate free zones (PFZs) and the fundamental role of Ag in controlling PFZ width. It is shown that nanoscale clusters are formed within the PFZ in Al–Zn–Mg, despite the solute concentration remaining at the levels in the as-quenched state. Such observations have not previously been possible, and show unambiguously that vacancy depletion is the dominant mechanism of formation of PFZs in this alloy. In the Ag-containing alloy, a narrower PFZ is observed, with a reduced solute level, showing that here the dominant mechanism of PFZ formation is solute depletion. The role of Ag in this change of mechanism appears to be due to its favorable interactions not only with Mg and Zn atoms but also with vacancies. 相似文献
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Effect of Amplicon Length in Propidium Monoazide Quantitative PCR for the Enumeration of Viable Cells of Salmonella in Cooked Ham 总被引:1,自引:0,他引:1
Belen Martin Sergi Raurich Margarita Garriga Teresa Aymerich 《Food Analytical Methods》2013,6(2):683-690
Real-time PCR-based methods have been frequently used to detect and enumerate foodborne pathogens. However, these techniques have a major drawback since they cannot differentiate between DNA from live and dead cells. In this study, we developed a propidium monoazide (PMA)-based PCR method to detect and enumerate viable Salmonella cells in the presence of high number of dead cells (up to 108 CFU/g) in cooked ham. Three different specific PCR targets differing in length (95, 285, and 417 bp) were tested. We found that the inhibition effect was dependent on the PCR amplification product length, and only the longer product achieved suppression of 108 CFU/g of heat-killed cells. SYBR® Green and TaqMan® chemistries were compared to develop a highly efficient PMA-quantitative PCR system targeting the 417-bp fragment. Both chemistries showed similar detection (103 CFU/g) and quantification limits (104 CFU/g), but TaqMan® assay showed higher efficiency (98.6 %) than SYBR® Green assay (92.8 %). PMA-quantitative PCR assay developed is a rapid method for the selective detection and enumeration of viable Salmonella cells with further application in postprocessed meat products and safe shelf-life studies. 相似文献