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Now showing items 1 - 16 of 419

  • Study on the shear property of nano-MgO-modified soil

    Lei Gao   Ke-yi Ren   Zhen Ren   Xiang-juan Yu  

    To study the relationship between nano-MgO and soil shear property, the nano-MgO was evenly mixed in the soil to perform the triaxial consolidation draining shear test. Then the microscopic soil granules on the shear planes were observed through the scanning electron microscope. The soil water content was 10% and soil dry density was 1.5 g/cm3, different dosages of nano-MgO, i.e., 0, 2, 4, and 6% were put into the soil samples. The result of triaxial consolidation draining shear test showed that, under low confining pressure and more nano-MgO dosage, the stress–strain relationship of nano-MgO-modified soil turned from hardening to softening. The incorporation of nano-MgO can effectively improve the soil failure strength and cohesive force, and the increasing dosages of nano-MgO had a positive effect on soil shear strength and cohesive force, but little effect on internal friction angle. The analysis of scanning electron microscopy showed that the dosage of nano-MgO can reduce the void ratio of soil and reinforce the cementation between soil granules to change the shear property of soil.
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  • Staged financing: a trade-off theory of holdup and option value

    Lei Gao  

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  • An improved error bound for linear complementarity problems forB-matrices

    Lei Gao   Chaoqian Li  

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  • Hot deformation behavior of as-cast Mg–Zn–Mn–Ce alloy in compression

    Lei Gao   Alan A. Luo  

    ZME200 (Mg-2.3Zn-0.4Mn-0.2Ce 1) is a newly-developed magnesium sheet alloy for automobile closure and structure applications. The hot deformation behavior of as-cast ZME200 alloy was investigated by compression tests at temperatures (T) ranging from 250 to 450degC and strain rates (epsilondot) between 0.001 and 10s -1. Most of the stress-strain curves exhibited typical dynamic recrystallization (DRX) behavior with a single peak stress followed by a gradual fall toward a steady-state stress. The flow behavior (hot working characteristics) can be described by the hyperbolic sine function, epsilondot=A[sinh(alphasigma)] nexp(-Q/RT), where A, alpha, and n are material constants, sigma is the applied stress, Q is the activation energy, R is the gas constant. Light metallography and electron backscattered diffraction (EBSD) were conducted to investigate the microstructure evolution under various deformation conditions. The results suggested that dynamic recrystallization was the main softening mechanism during the hot compression process. Both discontinuous and continuous DRX were the operating DRX mechanisms at temperatures between 300degC and 450degC. The former predominates mainly at low strains, while the latter dominates at moderate and higher strains. Twinning deformation and twin DRX were operative at relatively high strain rates of (1.0-10s -1). [All rights reserved Elsevier].
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  • Enhancement of ductility in high strength Mg-Gd-Y-Zr alloy

    Lei GAO   Rong-shi CHEN   En-hou HAN  

    A high strength GW94 alloy with fully recrystallized microstructure and equiaxed ultrafine grains of submicron size was produced by multiaxial forging and ageing. The alloy exhibits an ultimate tensile strength of 377 MPa, proof stress of 295 MPa and elongation to failure of 21.7%. The ductility is improved in comparison with that of the conventional extrusion processing. Superplastic ductility is achieved in tensile testing at 573 K with a maximum elongation of 450%. These high ductility and high strength are attributed to the coexistence of fully recrystallized grains and nanoscale Mg5(Gd, Y) particles dynamically precipitated at grain boundaries.
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  • Enhancement of ductility in high strength Mg-Gd-Y-Zr alloy

    Lei GAO   Rong-shi CHEN   En-hou HAN  

    A high strength GW94 alloy with fully recrystallized microstructure and equiaxed ultrafine grains of submicron size was produced by multiaxial forging and ageing. The alloy exhibits an ultimate tensile strength of 377 MPa, proof stress of 295 MPa and elongation to failure of 21.7%. The ductility is improved in comparison with that of the conventional extrusion processing. Superplastic ductility is achieved in tensile testing at 573 K with a maximum elongation of 450%. These high ductility and high strength are attributed to the coexistence of fully recrystallized grains and nanoscale Mg5(Gd, Y) particles dynamically precipitated at grain boundaries.
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  • Temporal stability of soil water storage in diverse soil layers

    Lei Gao   Mingan Shao  

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  • Fracture behavior of high strength Mg-Gd-Y-Zr magnesium alloy

    Lei GAO   Rong-shi CHEN   En-hou HAN  

    The fracture behavior of a permanent mould casting Mg-8.57Gd-3.72Y-0.54Zr (mass fraction,%) (GW94) alloy was investigated under different thermal conditions, including as-cast, solution-treated, peak-aged, and over-aged states. Scanning electron microscopy (SEM) and optical microscopy (OM) were employed to examine the crack nucleation and fracture model. The results indicate that the GW94 alloy shows different behaviors of crack initiation and fracture under different thermal conditions. During tensile test at room temperature, the fracture model of the as-cast GW94 alloy is quasi-cleavage, while that of the solution-treated alloy is transgranular cleavage. It is a mixed pattern of transgranular and intergranular fracture for both the aged conditions. Large cavities formed at grain boundaries are observed in the peak-aged sample tested at 300 °C, corresponding to the intergranular fracture. Localized plastic deformation at grain boundaries is also observed and corresponds to the high elongation at 300 °C.
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  • Fracture behavior of high strength Mg-Gd-Y-Zr magnesium alloy

    Lei GAO   Rong-shi CHEN   En-hou HAN  

    The fracture behavior of a permanent mould casting Mg-8.57Gd-3.72Y-0.54Zr (mass fraction,%) (GW94) alloy was investigated under different thermal conditions, including as-cast, solution-treated, peak-aged, and over-aged states. Scanning electron microscopy (SEM) and optical microscopy (OM) were employed to examine the crack nucleation and fracture model. The results indicate that the GW94 alloy shows different behaviors of crack initiation and fracture under different thermal conditions. During tensile test at room temperature, the fracture model of the as-cast GW94 alloy is quasi-cleavage, while that of the solution-treated alloy is transgranular cleavage. It is a mixed pattern of transgranular and intergranular fracture for both the aged conditions. Large cavities formed at grain boundaries are observed in the peak-aged sample tested at 300 °C, corresponding to the intergranular fracture. Localized plastic deformation at grain boundaries is also observed and corresponds to the high elongation at 300 °C.
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  • Load-carrying capacity of high-strength steel box-sections I: Stub columns

    Lei Gao   Hongcai Sun   Fengnian Jin   Hualin Fan  

    To study the load-carrying capacity of thin-walled box-section stub columns fabricated by high strength steel 18Mn2CrMoBA, uniaxial compression experiments of specimens with different geometrical dimensions were carried out. Compared with the predicted values by the AISI Code, the tested load-carrying capacities of the stub columns are much greater, which suggests that the existing effective width method should not be applicable for high strength steel stub columns. The finite element analysis based on ANSYS code was employed to simulate the deformation curves and predict the load-carrying capacities. The numerical values were generally in good agreement with the experimental values. Parameter analysis was performed to investigate the ultimate strength of the high strength steel stub column. The values obtained indicate that the width–thickness ratio of the flange and the section side ratio should be the main factors to decide the ultimate strength of the stub column. Taking the width–thickness ratio and the section side ratio as parameters, a formula to predict the loading capacity of the high strength steel stub column was put forward and proved to be effective by the tested and numerical values.
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  • Load-carrying capacity of high-strength steel box-sections I: Stub columns

    Lei Gao   Hongcai Sun   Fengnian Jin   Hualin Fan  

    To study the load-carrying capacity of thin-walled box-section stub columns fabricated by high strength steel 18Mn2CrMoBA, uniaxial compression experiments of specimens with different geometrical dimensions were carried out. Compared with the predicted values by the AISI Code, the tested load-carrying capacities of the stub columns are much greater, which suggests that the existing effective width method should not be applicable for high strength steel stub columns. The finite element analysis based on ANSYS code was employed to simulate the deformation curves and predict the load-carrying capacities. The numerical values were generally in good agreement with the experimental values. Parameter analysis was performed to investigate the ultimate strength of the high strength steel stub column. The values obtained indicate that the width-thickness ratio of the flange and the section side ratio should be the main factors to decide the ultimate strength of the stub column. Taking the width-thickness ratio and the section side ratio as parameters, a formula to predict the loading capacity of the high strength steel stub column was put forward and proved to be effective by the tested and numerical values. [All rights reserved Elsevier].
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  • Checkpoint-free in log mining for distributed information sharing

    Techniques for replicating data between database systems without taking checkpoints are provided. In an embodiment, a capture process restarts. Upon restarting, the capture process reestablishes an association with an apply process. A particular logical time maintained by the apply process is then communicated to the capture process. Upon receiving the particular logical time, the capture process restarts mining from this particular logical time.
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  • Preparation and photoluminescence properties of electrospun nanofibers of C60/PVK

    Lei Gao   Congju Li  

    Ultrafine fullerene (C60)/poly(N-vinylcarbazole) (PVK) composite fibers with 1 mum diameter were prepared by electrospinning C60/PVK blend solutions in solvent mixtures of N,N-dimethylformamide (DMF)/toluene. The UV absorption spectra of nanofibers have a similar behavior as observed in the thin films for the same doping condition. It is interesting to observe that the PVK nanofibers have a very strong blue-violet luminescence, while `bright spots' due to C60 can be observed on the C60/PVK fibers under UV irradiation in a fluorescence optical microscope. Compared to the emission spectra of PVK thin films, the photoluminescence of the PVK nanofibers shows a new emission peak at 437 nm. Efficient energy transfer was observed in C60/PVK thin films, as well as in blend nanofibers. [All rights reserved Elsevier].
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  • An agent-based simulation system for evaluating gridding urban management strategies

    Lei Gao   Bohdan Durnota   Yongsheng Ding   Hua Dai  

    Traditional means of urban management are not satisfying the new demands placed by a modern city. Gridding urban management (GUM) seems to be a promising model for urban management in the 21st century. But the GUM must be more than ldquoinfrastructurerdquo- it needs to support effective management strategies. This paper outlines our initial attempt of examining urban problems within a GUM framework and studying strategy choices. To this end, we construct an agent-based simulation system, namely DeciUrban, to explore GUM and strategy development. This paper proposes the architecture of DeciUrban and describes its core agent-based model using a model documentation protocol. A simulation of grid inspecting activities in Shanghai GUM is conducted with the purpose of assessing different inspecting strategies. The strategies involve district-first, community-first, cooperative, and random inspecting strategies. The results show how the effectiveness of strategies and the distribution of their impacts can be very different from what one would expect without the benefit of a simulation model. These simulations are presented as a demonstration that DeciUrban can help urban strategy developers understand a multitude of local interactions in cities, explore strategies, and improve community wellbeing without always designing field experiments. To sum up, simulation systems similar to DeciUrban could be valuable tools for addressing the challenges in the further development of GUM. [All rights reserved Elsevier].
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  • Automatic discovery of relevant data in massive datasets

    An approach for discovery of relevant data in massive datasets. Compare datasets including compare key fields, compare data fields and a core dataset including target data field(s) and core field(s) are received. The compare datasets are categorized into direct and indirect related dataset pools based on the target data field(s) correlation strength with matching compare and core fields. The direct related dataset pool and the core dataset are transformed into reduction datasets based on statistical measure of values of target data fields, shared key fields and compare data fields. Target correlations of the reduction datasets are creating based on a reduction compare and target data fields. Statistical relationship strength of core dataset and the direct related dataset pool are created based on a statistical mean of target correlations and a relevancy data store is created.
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  • Multi-standard network convergence method, device, and system

    The present invention discloses a multi-standard network convergence method, device, and system and relates to the field of communications technologies. The method includes: acquiring an AC mapping parameter corresponding to an RLC packet; performing encapsulation on the AC mapping parameter and the RLC packet; and forwarding an encapsulated packet to a second network, so that the second network acquires a corresponding AC according to the AC mapping parameter in the encapsulated packet, and places the RLC packet into a transmission queue corresponding to the AC for transmission. According to the present invention, an AC mapping parameter and an RLC packet are encapsulated and then sent to a second network, so that the second network may determine a corresponding AC according to the AC mapping parameter, so as to accurately place the RLC packet into a corresponding transmission queue for transmission and further implement multi-standard network convergence.
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