The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Xiaoyu Tang - One of the best experts on this subject based on the ideXlab platform.
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degradation induced evolution of particle Roundness and its effect on the shear behaviour of railway ballast
Transportation geotechnics, 2020Co-Authors: Zongtang Zhang, Wenhua Gao, Xiang Wang, Junqi Zhang, Xiaoyu TangAbstract:Abstract Ballast degradation has a strong effect on railway track performance (including accumulative deformation, ballast resistance, and drainage). The main objective of this research is to determine the evolution of Roundness during ballast degradation and investigate the mechanical properties of real ballast shape at different abrasion stages. To this end, the Los Angeles (LA) abrasion test is conducted on three groups of fresh ballast materials with different sizes (i.e., 25–30 mm, 40–50 mm, and 50–60 mm). Then, a homemade image-acquisition platform is used to extract ballast outlines from multiple projection directions. Next, the corner sharpness of the degraded ballast is quantified by particle Roundness. The LA abrasion test shows that particle Roundness gradually increases with increasing abrasion. Subsequently, biaxial shear tests are performed on ballasts with different Roundness characteristics based on the discrete element method (DEM). The shear behaviours of degraded ballasts with different degrees of Roundness are investigated through macroscopic (e.g., the shear strength and dilatancy response) to microscopic (e.g., the mean coordination number, the ratio of sliding contacts, and the mean particle contact moment) analyses. The results show that the shear strength slightly increases in the peak state, while a substantial reduction in shear strength is observed in the residual state with increasing Roundness. Moreover, the microscopic analysis shows that greater Roundness results in a smaller mean coordination number, as well as decreases in the ratio of sliding contacts and the mean particle contact moment.
Xiang Wang - One of the best experts on this subject based on the ideXlab platform.
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degradation induced evolution of particle Roundness and its effect on the shear behaviour of railway ballast
Transportation geotechnics, 2020Co-Authors: Zongtang Zhang, Wenhua Gao, Xiang Wang, Junqi Zhang, Xiaoyu TangAbstract:Abstract Ballast degradation has a strong effect on railway track performance (including accumulative deformation, ballast resistance, and drainage). The main objective of this research is to determine the evolution of Roundness during ballast degradation and investigate the mechanical properties of real ballast shape at different abrasion stages. To this end, the Los Angeles (LA) abrasion test is conducted on three groups of fresh ballast materials with different sizes (i.e., 25–30 mm, 40–50 mm, and 50–60 mm). Then, a homemade image-acquisition platform is used to extract ballast outlines from multiple projection directions. Next, the corner sharpness of the degraded ballast is quantified by particle Roundness. The LA abrasion test shows that particle Roundness gradually increases with increasing abrasion. Subsequently, biaxial shear tests are performed on ballasts with different Roundness characteristics based on the discrete element method (DEM). The shear behaviours of degraded ballasts with different degrees of Roundness are investigated through macroscopic (e.g., the shear strength and dilatancy response) to microscopic (e.g., the mean coordination number, the ratio of sliding contacts, and the mean particle contact moment) analyses. The results show that the shear strength slightly increases in the peak state, while a substantial reduction in shear strength is observed in the residual state with increasing Roundness. Moreover, the microscopic analysis shows that greater Roundness results in a smaller mean coordination number, as well as decreases in the ratio of sliding contacts and the mean particle contact moment.
T. Sato - One of the best experts on this subject based on the ideXlab platform.
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effects of process parameters on workpiece Roundness in tangential feed centerless grinding using a surface grinder
Journal of Materials Processing Technology, 2010Co-Authors: Weixing Xu, Yongbo Wu, T. SatoAbstract:Abstract The present authors proposed a new centerless grinding method using a surface grinder in their previous study [Wu, Y., Kondo, T., Kato, M., 2005. A new centerless grinding technique using a surface grinder. J. Mater. Process. Technol. 162–163, 709–717]. In this method, a compact centerless grinding unit composed mainly of an ultrasonic elliptic-vibration shoe is installed onto the worktable of a multipurpose surface grinder to perform tangential-feed centerless grinding operations. However, for the complete establishment of the new method it is crucial to clarify the workpiece rounding process and the effects of process parameters such as the worktable feed rate, the stock removal and the workpiece rotational speed on the machining accuracy, i.e., workpiece Roundness, so that the optimum grinding conditions can be determined. In this paper, the effects of the process parameters on workpiece Roundness are investigated by simulation and experiments. For the simulation analysis, a grinding model taking into account the elastic deformation of the machine is created. Then, a practical way to determine the machining-elasticity parameter is developed. Further, simulation analysis is carried out to predict the variation of workpiece Roundness during grinding and to discover how the process parameters affect the Roundness. Finally, actual grinding operations are performed by installing the previously constructed unit onto a CNC surface grinder to confirm the simulation results. The obtained results indicate that: (1) a slower worktable feed rate and higher workpiece rotational speed give better Roundness; (2) better Roundness can be also obtained when the stock removal is set at a larger value; (3) the workpiece Roundness was improved from an initial value of 23.9 μm to a final value of 0.84 μm after grinding.
Pierreolivier Weill - One of the best experts on this subject based on the ideXlab platform.
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measuring the financial soundness of u s firms 1926 2012
Research in Economics, 2017Co-Authors: Andrew Atkeson, Andrea L Eisfeldt, Pierreolivier WeillAbstract:We measure the distribution of firms’ financial soundness over most of the last century for a broad cross section of firms. We highlight three main findings for this key aggregate state variable. First, the three worst recessions between 1926 and 2012 coincided with sharp deteriorations in the financial soundness of all firms, but other recessions did not. Second, fluctuations in total asset volatility, rather than fluctuations in leverage, appear to drive most of the variation in the distribution of firms’ financial soundness. Finally, the distribution of financial soundness for large financial firms 1962–2007 largely resembles that for large nonfinancial firms.
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measuring the financial soundness of u s firms 1926 2012
Staff Report, 2013Co-Authors: Andrew Atkeson, Andrea L Eisfeldt, Pierreolivier WeillAbstract:Building on the Merton (1974) and Leland (1994) structural models of credit risk, we develop a simple, transparent, and robust method for measuring the financial soundness of individual firms using data on their equity volatility. We use this method to retrace quantitatively the history of firms' financial soundness during U.S. business cycles over most of the last century. We highlight three main findings. First, the three worst recessions between 1926 and 2012 coincided with insolvency crises, but other recessions did not. Second, fluctuations in asset volatility appear to drive variation in firms' financial soundness. Finally, the financial soundness of financial firms largely resembles that of nonfinancial firms.
Mingshu Tang - One of the best experts on this subject based on the ideXlab platform.
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soundness evaluation of concrete with mgo
Construction and Building Materials, 2007Co-Authors: Peiwei Gao, Min Deng, Pinghua Lin, Mingshu TangAbstract:Abstract A new test method – delayed autoclave expansion test – has been used in this study to evaluate the soundness of concrete that contains intrinsic dead-burnt MgO and adscititious lightly burnt MgO. The autoclave expansion value and strength of that concrete were investigated and the relationships between the expansion or strength and the soundness were discussed. The results of this study showed that it was unsuitable to apply a standard for the soundness evaluation of cement with MgO to that of concrete. Unlike the MgO content upper limit 5% in cement, more than 5% in concrete is acceptable. The soundness of concrete can be evaluated on the basis of expansion rate or strength changes after autoclave and it will be better to use changes in strength to express the volume soundness of concrete.
