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Numerical simulation of macrosegregation during solidification of binary alloys

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Rare Metals 2016年第8期35卷 591-597页

作者： Wu-Tao Tu Hou-fa Shen Bai-Cheng Liu Key Laboratory for Advanced Materials Processing Technology Ministry of Education School of Materials Science and Engineering Tsinghua University

Macrosegregation as a consequence of solidifi- cation of a binary Pb-48 wt% Sn alloy in two-dimensional rectangle cavity was investigated by two-phase model instead of the common used continuum model. The macroscopic transport of mass, momentum, species and energy was cou- pled with the microscopic descriptions of grain nucleation and growth. The mathematic equations of the two-phase model were discretized on staggered grids and solved by the finite volume method. The final tin concentrations along different heights over the bottom face were compared with the ex- periment measurements. Simulations with different mi- crostructure parameters （second dendrite arm spacing （SDAS）） were conducted to ascertain the influence of microstructure on the final macrosegregation. The results show that with the decrease in SDAS value, the drag force as the resistance to relative motion between solid and liquid phase increases, and the macrosegregation during solidification is alleviated.

关键词： Macrosegregation Two-phase model Solidification Second dendrite arm spacing

ANALYSIS OF HABITAT PATTERN CHANGE OF RED-CROWNED CRANES IN THE LIAO HE DELTA USING SPATIAL DIVERSITY INDEX

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Chinese Geographical Science 2003年第2期13卷 164-170页

作者： WANGLing LIXiu-zhen HUYuan-man GUODu-fa CollegeofPopulation ResourcesandEnvironmentShandongNormalUniversityJinan250014P.R.China InstituteofappliedEcology ChineseAcademyofSciencesShenyang110016P.R.China CollegeofLandandEnvironment ShenyangAgriculturalUniversityShenyang110161P.R.China

Habitat pattern change of red-crowned cranes (Grus japonensis) in t he Liaohe Delta between 1988 and 1998 was analyzed with the help of Spatial Dive rsity Index based on remote sensing data and field investigation. The result sho wed that the influence from human activities on the wetland habitat of red-crow ned cranes was prominent with the development of oil and agricultural exploitati on, and the habitat pattern of red-crowned cranes had been obviously changed by the human disturbance during the ten years. The areas with high Spatial Diversi ty values (SD≥0.65) and that with mid-high values (0.5≤SD< 0.65), which const ituted the main part of suitable habitat of red-crowned cranes,had reduced to 9142ha and 5576ha respectively, with the shrinking of natural land cover, such a s reed and Suaeda community. The habitat pattern became more fragmented, which w as caused by roads and wells during oil exploration. It was indicated that the s uitability and quality of habitat for red-crowned cranes in the Liaohe Delta we re degraded in the last decade. The results also showed that diversity index cou ld reflect the habitat suitability of red-crowned cranes quantitatively and des cribe the spatial pattern of the habitat explicitly. This study will provide a s cientific basis for habitat protection of red-crowned cranes and other rare spe cies in wetlands.

关键词： spatial diversity Index red-crowned crane ( GrUS japonensis) habitatpattern the liaohe delta

BOUNDING PYRAMIDS AND BOUNDING CONES FOR TRIANGULAR BEZIER SURfaCES

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Journal of Computational Mathematics 2000年第6期18卷 609-620页

作者： Jian-song Deng fa-lai Chen Li-li Wang Department of Mathematics University of Science and Technology of ChinaHefei 230026China Information Center of Bengbu Bengbu 233000China

This paper describes practical approaches on how to construct bounding pyramids and bounding cones for triangular Bezier surfaces. Examples are provided to illustrate the process of construction and comparison is made between various surface bounding volumes. Furthermore, as a starting point for the construction, we provide a way to compute hodographs of triangular Bezier surfaces and improve the algorithm for computing the bounding cone of a set of vectors. [ABSTRACT FROM AUTHOR]

关键词： triangular Bezier surface patch hodograph bounding pyramid bounding cone

Effect of precipitates on high-temperature strength and irradiation behavior of vanadium-based alloys

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Journal of Iron and Steel Research International 2018年第12期25卷 1270-1277页

作者： Shao-ning Jiang Li-qun Xu fa-rong Wan School of Mechanical and Automotive Engineering Qilu University of Technology (Shandong Academy of Science) Jinan 250353ShandongChina School of Materials Science and Engineering University of Science and Technology BeijingBeijing 100083China

The formation of precipitates and their effect on mechanical properties and irradiation damage in V-4CraTi alloys have been investigated using transmission electron microscope,high-temperature tensile tests and high-voltage electron microscope (HVEM).V-4Cr-4Ti alloys were aged for 20-40 h at 873 K,and extremely fine precipitates were produced during the aging process,which coarsened with aging *** results of high-temperature (773,873 and 973 K)tensile tests showed an increase in strength with increasing aging time (i.e:,increasing size of precipitates)while a decrease in the uniform *** was evidence that presence of precipitates strengthened V-4Cr-4Ti *** situ HVEM observations showed that the precipitates restricted the growth rate of dislocation loops induced during electron irradiation at 773 *** interactions between precipitates and irradiation-induced dislocation loops were *** presence of particles alleviated the increase in irradiation hardening up to an irradiation dose of 3.42 dpa (displacement per atom).The precipitates shrank in size during electron irradiation,which was due to the dissolution of constituent atoms of the precipitates into the alloy matrix.

关键词： Aging Precipitate strengthening Electron irradiation Irradiation defect Dislocation loop

Tensile force correction calculation method for prestressed construction of tension structures

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Journal of Zhejiang University-Science A(Applied Physics & Engineering) 2008年第9期9卷 1201-1207页

作者： Xin ZHUO Guo-fa ZHANG Koichiro ISHIKAWA Dao-an LOU Department of Civtl Engmeermg Zhejiang University Hangzhou 310027 China Department of Architecture and Civil Engineering Fukui University Fukui 910-8507 Japan Zhejiang Zhancheng Construction Group Co. Ltd. Hangzhou 310005 China

factors such as errors during the fabrication or construction of structural components and errors of calculation as- sumption or calculation methods, are very likely to cause serious deviation of many strings’ actual prestressing forces from the designed values during tension structure construction or service period, and further to threaten the safety and reliability of the structure. Aiming at relatively large errors of the prestressing force of strings in a tension structure construction or service period, this paper proposes a new finite element method (FEM), the "tensile force correction calculation method". Based on the measured prestressing forces of the strings, this new method applies the structure from the zero prestressing force status approach to the measured prestressing force status for the first phase, and from the measured prestressing force status approach to the designed prestressing force status for the second phase. The construction tensile force correction value for each string can be obtained by multi-iteration with FEM. Using the results of calculation, the strings’ tensile force correction by group and in batch will be methodic, simple and accurate. This new calculation method can be applied to the prestressed correction construction simulation analysis for tension structures.

关键词： Tension structures Prestressed construction High precision

A Numerical Study of the Effect of Multiple Pouring on Macrosegregation in a 438-Ton Steel Ingot

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Acta Metallurgica Sinica(English Letters) 2015年第9期28卷 1123-1133页

作者： Zhen-Hu Duan Hou-fa Shen Bai-Cheng Liu Key Laboratory for Advanced Materials Processing Technology Ministry of Education School of Materials Science and Engineering Tsinghua University

In present paper, a ladle-tundish-mold CFD model and a macrosegregation model were utilized to investigate the effects of the multiple pouring （MP） process on the macrosegregation in a 438-ton steel ingot. Firstly, the model was partially proved as compared to the measured carbon distributions along the transverse sections in the riser of ingot. Then, the comparison between the single pouring （SP） and MP process has been carried out to study their influences on the macrosegregation in ingot. Besides, the predicted macrosegregation results in MP process which introduced the improved riser fixed with an insulating sleeve were compared with that in traditional MP process. The traditional MP process leads to certain favorable initial carbon distribution in the mold, which has some favorable influence on suppressing the positive segregation in ingot. The holding time of the low carbon in the riser is the main factor to suppress the positive segregation in ingot. Improved insulating sleeve can prolong the holding time of the low carbon in the riser and release the positive segregation in the riser of ingot. Improvement of the insulating effect of the riser is an efficient method to control macrosegregation in large steel ingot.

关键词： Multiple pouring process Macrosegregation Numerical simulation Large steel ingot

Numerical simulation of macrosegregation in steel ingots using a two-phase model

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International Journal of Minerals,Metallurgy and Materials 2012年第9期19卷 787-794页

作者： Wen-sheng Li Hou-fa Shen Bai-cheng Liu The Key Laboratory of the Ministry of Education of China for Advanced Materials Processing Technology Deparanent of Mechanical EngineeringTsinghna UniversityBeijing 100084China

A two-phase model for the prediction of macrosegregation formed during solidification is presented. This model incorporates the descriptions of heat transfer, melt convection, solute transport, and solid movement on the system scale with microscopic relations for grain nucleation and growth. Then the model is used to simulate the solidification of a benchmark industrial 3.3-t steel ingot. Simulations are per- formed to investigate the effects of grain motion and pipe shrinkage formation on the final macrosegregation pattern. The model predictions are compared with experimental data and numerical results from literatures. It is demonstrated that the model is able to express the overall macrosegregation patterns in the ingot. Furthermore, the results show that it is essential to consider the motion of equiaxed grains and the formation of pipe shrinkage in modelling. Several issues for future model improvements are identified.

关键词： steel ingots solidification segregation shrinkage modelling

Inflammation in diabetic retinopathy: possible roles in pathogenesis and potential implications for therapy

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Neural Regeneration Research 2023年第5期18卷 976-982页

作者： Lei Tang Guo-Tong Xu Jing-fa Zhang Department of Ophthalmology of Tongji Hospital Tongji Eye InstituteDepartment of Regenerative Medicineand Department of PharmacologyTongji University School of MedicineShanghaiChina Department of Ophthalmology Shanghai General Hospital(Shanghai First People’s Hospital)Shanghai Jiao Tong UniversityShanghaiChina National Clinical Research Center for Eye Diseases Shanghai Key Laboratory of Ocular Fundus DiseasesShanghai Engineering Center for Visual Science and PhotomedicineShanghai Engineering Center for Precise Diagnosis and Treatment of Eye DiseasesShanghaiChina

Diabetic retinopathy, characterized as a microangiopathy and neurodegenerative disease, is the leading cause of visual impairment in diabetic patients. Many clinical features observed in diabetic retinopathy, such as capillary occlusion, acellular capillaries and retinal non-perfusion, aggregate retinal ischemia and represent relatively late events in diabetic retinopathy. In fact, retinal microvascular injury is an early event in diabetic retinopathy involving multiple biochemical alterations, and is manifested by changes to the retinal neurovascular unit and its cellular components. Currently, intravitreal anti-vascular endothelial growth factor therapy is the firstline treatment for diabetic macular edema, and benefits the patient by decreasing the edema and improving visual acuity. However, a significant proportion of patients respond poorly to anti-vascular endothelial growth factor treatments, indicating that factors other than vascular endothelial growth factor are involved in the pathogenesis of diabetic macular edema. Accumulating evidence confirms that low-grade inflammation plays a critical role in the pathogenesis and development of diabetic retinopathy as multiple inflammatory factors, such as interleukin-1β, monocyte chemotactic protein-1 and tumor necrosis factor-α, are increased in the vitreous and retina of diabetic retinopathy patients. These inflammatory factors, together with growth factors such as vascular endothelial growth factor, contribute to blood-retinal barrier breakdown, vascular damage and neuroinflammation, as well as pathological angiogenesis in diabetic retinopathy, complicated by diabetic macular edema and proliferative diabetic retinopathy. In addition, retinal cell types including microglia, Müller glia, astrocytes, retinal pigment epithelial cells, and others are activated, to secrete inflammatory mediators, aggravating cell apoptosis and subsequent vascular leakage. New therapies, targeting these inflammatory molecules or relate

关键词： anti-inflammation therapy anti-vascular endothelial growth factor diabetic retinopathy hyperreflectivity foci inflammation inflammatory cells inflammatory cytokines leukostasis microglia Müller cells

A Novel Hardware/Software Partitioning Method Based on Position Disturbed Particle Swarm Optimization with Invasive Weed Optimization

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Journal of Computer Science & Technology 2017年第2期32卷 340-355页

作者： Xiao-Hu Yan fa-Zhi He Yi-Lin Chen State Key Laboratory of Software Engineering Wuhan University Wuhan 430072 China School of Computer Science Wuhan University Wuhan 430072 China

With the development of the design complexity in embedded systems, hardware/software （HW/SW） partitioning becomes a challenging optimization problem in HW/SW co-design. A novel HW/SW partitioning method based on position disturbed particle swarm optimization with invasive weed optimization （PDPSO-IWO） is presented in this paper. It is found by biologists that the ground squirrels produce alarm calls which warn their peers to move away when there is potential predatory threat. Here, we present PDPSO algorithm, in each iteration of which the squirrel behavior of escaping from the global worst particle can be simulated to increase population diversity and avoid local optimum. We also present new initialization and reproduction strategies to improve IWO algorithm for searching a better position, with which the global best position can be updated. Then the search accuracy and the solution quality can be enhanced. PDPSO and improved IWO are synthesized into one single PDPSO-IWO algorithm, which can keep both searching diversification and searching intensification. Furthermore, a hybrid NodeRank （HNodeRank） algorithm is proposed to initialize the population of PDPSO-IWO, and the solution quality can be enhanced further. Since the HW/SW communication cost computing is the most time-consuming process for HW/SW partitioning algorithm, we adopt the GPU parallel technique to accelerate the computing. In this way, the runtime of PDPSO-IWO for large-scale HW/SW partitioning problem can be reduced efficiently. Finally, multiple experiments on benchmarks from state-of-the-art publications and large-scale HW/SW partitioning demonstrate that the proposed algorithm can achieve higher performance than other algorithms.

关键词： hardware/software partitioning particle swarm optimization invasive weed optimization communicationcost parallel computing