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Characterization of the tribologically relevant cover layers formed on copper in oxygen and oxygen-free conditions

Friction 2023年第8期11卷 1505-1521页

作者： Selina RAUMEL Khemais BARIEnTI Hoang-Thien LUU nina MERKERT Folke DEnCKER florian nürnberger Hans Jürgen MAIER Marc Christopher WURZ Institute of Micro Production Technology Leibniz Universität HannoverGarbsen 30823Germany Institut für Werkstoffkunde(Materials Science) Leibniz Universität HannoverGarbsen 30823Germany Institute of Applied Mechanics Clausthal University of TechnologyClausthal-Zellerfeld 38678Germany

Engineering in vacuum or under a protective atmosphere permits the production of materials, wherever the absence of oxygen is an essential demand for a successful processing. However, very few studies have provided quantitative evidence of the effect of oxidized surfaces to tribological properties. In the current study on 99.99% pure copper, it is revealed that tribo-oxidation and the resulting increased abrasive wear can be suppressed by processing in an extreme high vacuum (XHV) adequate environment. The XHV adequate atmosphere was realized by using a silane-doped shielding gas (1.5 vol% SiH4 in argon). To analyse the influence of the ambient atmosphere on the tribological and mechanical properties, a ball–disk tribometer and a nanoindenter were used in air, argon, and silane-doped argon atmosphere for temperatures up to 800 ℃. Resistance measurements of the resulting coatings were carried out. To characterize the microstructures and the chemical compositions of the samples, the scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD) were used. The investigations have revealed a formation of η-Cu3Si in silane-doped atmosphere at 300 ℃, as well as various intermediate stages of copper silicides. At temperatures above 300 ℃, the formation of γ-Cu5Si were detected. The formation was linked to an increase in hardness from 1.95 to 5.44 GPa, while the Young’s modulus increased by 46% to 178 GPa, with the significant reduction of the wear volume by a factor of 4.5 and the suppression of further oxidation and susceptibility of chemical wear. In addition, the relevant diffusion processes were identified using molecular dynamics (MD) simulations.

关键词： wear behavior tribochemical reaction oxidation behavior surface analysis molecular dynamics(MD)simulation

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On a Variant of Giuga numbers

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Acta Mathematica Sinica,English Series 2012年第4期28卷 653-660页

作者： Jos María GRAU florian LUCA Antonio M. OLLER-MARCn Departmento de Matemáticas Universidad de Oviedo Avda. Calvo Sotelo s/n Instituto de Matemáticas Universidad Nacional Autnoma de México The John Knopfmacher Centre for Applicable Analysis and number Theory University of the Witwatersrand Centro Universitario de la Defensa Academia General Militar Ctra. Huesca s/n

In this paper, we characterize the odd positive integers n satisfying the congruence ∑j=1^n-1 j n-1/2 We show that the set of such positive integers has an asymptotic densitywhich turns out to be slightly larger than... 详细信息

关键词： Congruence Giuga numbers asymptotic density

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Modeling public holidays in load forecasting: a German case study

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Journal of Modern Power Systems and Clean Energy 2018年第2期6卷 191-207页

作者： florian ZIEL Fakultat fur Wirtschaftswissenschaften insb.Okonomik erneuerbarer EnergienUniversitat Duisburg-Essen

We address the issue of public or bank holidays in electricity load modeling and forecasting. Special characteristics of public holidays such as their classification into fixed-date and weekday holidays are discussed in detail. We present state-of-the-art techniques to deal with public holidays such as removing them from the data set,treating them as Sunday dummy or introducing separate holiday dummies. We analyze pros and cons of these approaches and provide a large load forecasting study for Germany that compares the techniques using standard performance and significance measures. Finally, we give general recommendations for the treatment of public holidays in energy forecasting to suggest how the drawbacks particular to most of the state-of-the-art methods can be mitigated. This is especially useful, as the incorporation of holiday effects can improve the forecasting accuracy during public holidays periods by more than 80%, but even for non-holidays periods, the forecasting error can be reduced by approximately 10%.

关键词： Public holidays Bank holidays Special day effects Forecasting Electricity load Holiday dummy

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Using the DEM-CFD method to predict Brownian particle deposition in a constricted tube

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Particuology 2014年第4期12卷 94-106页

作者： florian Chaumeil Martin Crapper School of Engineering The University of EdinburghEdinburgh EH9 3JLUnited Kingdom

Modelling of the agglomeration and deposition on a constricted tube collector of colloidal size particles immersed in a liquid is investigated using the discrete element method （DEM）. The ability of this method to represent surface interactions allows the simulation of agglomeration and deposition at the particle scale. The numerical model adopts a mechanistic approach to represent the forces involved in colloidal suspensions by including near-wall drag retardation, surface interaction and Brownian forces. The model is implemented using the commercially available DEM package EDEM 2.3~, so that results can be repli- cated in a standard and user-friendly framework. The effects of various particle-to-collector size ratios, inlet fluid flow-rates and particle concentrations are examined and it is found that deposition efficiency is strongly dependent on the inter-relation of these parameters. Particle deposition and re-suspension mechanisms have been identified and analyzed thanks to EDEM＇s post processing capability. One-way coupling with computational fluid dynamics （CFD） is considered and results are compared with a two- way coupling between EDEM 2.3 and FLUEnT 12.1. It is found that two-way coupling requires circa 500% more time than one-way coupling for similar results.

关键词： Discrete element method DEM Colloids Agglomeration Deposition Simulation

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Analysis of stresses at the center of transversely isotropic Brazilian disk

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Journal of Rock Mechanics and Geotechnical Engineering 2023年第3期15卷 618-629页

作者： Ali Aminzadeh florian Amann Institute of Geology of the Czech Academy of Sciences PragueCzech Republic Chair of Engineering Geology RWTH Aachen UniversityAachenGermany

This article presents the stresses at the center of a Brazilian disk(BD)for transversely isotropic *** is shown that the solution of stresses at the center of an anisotropic disk is a function of the disk radius and the magnitude of applied load,as well as the material orientation with respect to the load axis and two dimensionless ratios with specific physical meanings and *** two dimensionless parameters are the ratios of Young’s modulus and apparent shear modulus,although the ratio of apparent shear modulus will be eliminated if the Saint-Venant assumption is *** finite element simulations are carried out to find the stresses at the disk center concerning the material orientation and the two dimensionless ***,an approximate formula obtained from analytical results,previously proposed in the literature for solving the tensile and compressive stresses at the disk center,is re-written and simplified based on these new *** results of the approximate formula fitted to the analytical results are compared to those obtained from numerical solutions,suggesting a good agreement between the numerical and analytical *** approximate equation for the shear stress at the disk center is also formulated based on the numerical ***,the influence of the assumptions for simplification of the proposed formula for the tensile,compressive,and shear stresses at the disk center is discussed,and simple and practical equations are proposed as estimations for the stresses at the center of the BD specimen for low to moderate anisotropic *** highly anisotropic rocks,the reference plots can be used for more accuracy.

关键词： Brazilian test Transverse isotropy Rock anisotropy Anisotropic disk Tensile stress Shear stress

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Malaria modeling: In vitro stem cells vs in vivo models

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World Journal of Stem Cells 2016年第3期8卷 88-100页

作者： florian noulin Department of Microbiology and Molecular Genetics The Kuvin Center for the Study of Infectious and Tropical Diseases IMRIC The Hebrew University-Hadassah Medical School

The recent development of stem cell research and the possibility of generating cells that can be stably and permanently modified in their genome open a broad horizon in the world of in vitro modeling. The malaria field is gaining new opportunities from this importantbreakthrough and novel tools were adapted and opened new frontiers for malaria research. In addition to the new in vitro systems, in recent years there were also significant advances in the development of new animal models that allows studying the entire cell cycle of human malaria. In this paper, we review the different protocols available to study human Plasmodium species either by using stem cell or alternative animal models.

关键词： Malaria Stem cells In vitro models Animal models Humanized mice

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Optimal trajectory design accounting for the stabilization of linear time-varying error dynamics

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Chinese Journal of Aeronautics 2022年第7期35卷 55-66页

作者： Patrick PIPREK Haichao HOnG florian HOLZAPFEL Institute of Flight System Dynamics Technical University of MunichGarching D-85748Germany

This study is dedicated to the development of a direct optimal control-based algorithm for trajectory optimization problems that accounts for the closed-loop stability of the trajectory tracking error dynamics already during the ***,the trajectory is designed such that the Linear Time-Varying(LTV)dynamic system,describing the controller’s error dynamics,is stable,while additionally the desired optimality criterion is optimized and all enforced constraints on the trajectory are *** is achieved by means of a Lyapunov stability analysis of the LTV dynamics within the optimization problem using a time-dependent,quadratic Lyapunov function *** care is taken with regard to ensuring the correct definiteness of the ensuing matrices within the Lyapunov stability analysis,specifically considering a numerically stable formulation of these in the numerical *** developed algorithm is applied to a trajectory design problem for which the LTV system is part of the path-following error dynamics,which is required to be *** main benefit of the proposed scheme in this context is that the designed trajectory trades-off the required stability and robustness properties of the LTV dynamics with the optimality of the trajectory already at the design phase and thus,does not produce unstable optimal trajectories the system must follow in the real application.

关键词： LTV error dynamics LTV stability Optimal control-based LTV stabilization Path-following error controller Trajectory generation Trajectory optimization

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Saturated Hydraulic Conductivity from Field Measurements Compared to Pedotransfer Functions in a Heterogeneous Arable Landscape

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Journal of Earth Science 2010年第6期21卷 923-930页

作者： florian Winter Markus Disse Institute of Hydro Sciences Universitt der Bundeswehr München

A high degree of uncertainty with regard to soil parameterisation limits the significance of physically-based simulation of distributed flood control measures, which affect the runoff generation process, such as land-use changes or differing soil tillage practices. In this study, the soil measurement data from the hillslope scale at the Scheyern research farm were compared to demonstrate this uncertainty. To account for the spatial variability of soils in the investigation area of Scheyern, different approaches were applied to estimate soil hydraulic properties and saturated hydraulic conductivity, and were compared to field measurements

关键词： hydraulic conductivity pedotransfer function hood infiltrometer uncertainty distributed flood control measures.

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Bayesian inference-based wear prediction method for plain bearings under stationary mixed-friction conditions

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Friction 2024年第6期12卷 1272-1282页

作者： florian KÖnIG florian WIRSInG Georg JACOBS Rui HE Zhigang TIAn Ming J.ZUO Institute for Machine Elements and Systems Engineering RWTH Aachen UniversityAachen 52062Germany Department of Mechanical Engineering University of AlbertaEdmonton T6G1H9Canada Qingdao International Academician Park Research Institute Qingdao 266000China

This study introduces a method to predict the remaining useful life(RUL)of plain bearings operating under stationary,wear-critical *** this method,the transient wear data of a coupled elastohydrodynamic lubrication(mixed-EHL)and wear simulation approach is used to parametrize a statistical,linear degradation *** method incorporates Bayesian inference to update the linear degradation model throughout the runtime and thereby consider the transient,system-dependent wear progression within the RUL prediction.A case study is used to show the suitability of the proposed *** results show that the method can be applied to three distinct types of post-wearing-in behavior:wearing-in with subsequent hydrodynamic,stationary wear,and progressive wear *** hydrodynamic operation leads to an infinite lifetime,the method is successfully applied to predict RUL in cases with stationary and progressive wear.

关键词： plain bearings wear modeling remaining useful life prediction Bayesian inference

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numerical prediction of the frictional losses in sliding bearings during start-stop operation

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Friction 2021年第3期9卷 583-597页

作者： florian KÖnIG Christopher SOUS Georg JACOBS Institute for Machine Elements and Systems Engineering Rheinisch-Westfälische Technische Hochschule Aachen UniversitySchinkelstraße 10Aachen 52062Germany

With the increased use of automotive engine start-stop systems,the numerical prediction and reduction of frictional losses in sliding bearings during starting and stopping procedures has become an important *** engineering practice,numerical simulations of sliding bearings in automotive engines are performed with statistical asperity contact models with empirical values for the necessary surface *** aim of this study is to elucidate the applicability of these approaches for the prediction of friction in sliding bearings subjected to start-stop *** this purpose,the friction performance of sliding bearings was investigated in experiments on a test rig and in transient mixed elasto-hydrodynamic simulations in a multi-body simulation environment(mixed-EHL/MBS).In mixed-EHL/MBS,the extended Reynold’s equation with flow factors according to Patir and Cheng has been combined on the one hand with the statistical asperity contact model according to Greenwood and Tripp and on the other hand with the deterministic asperity contact model according to *** detailed comparison of simulation and experimental results clarifies that the application of statistical asperity contact models with empirical values of the necessary inputs leads to large deviations between experiment and *** actual distribution and position of surface roughness,as used in deterministic contact modelling,is necessary for a reliable prediction of the frictional losses in sliding bearings during start-stop operation.

关键词： sliding bearing friction wearing-in contact model,mixed elasto-hydrodynamic simulation

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