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RISS 인기검색어
- 검색키워드
- 저자 : De’an Sun (검색결과 6 건)
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An elastoplastic model for structured clays
Chen, Bo,Xu, Qiang,Sun, De'an Techno-Press 2014 Geomechanics & engineering Vol.7 No.2
An elastoplastic model for structured clays, which is formulated based on the fact that the difference in mechanical behavior of structured and reconstituted clays is caused by the change of fabric in the post-yield deformation range, is present in this paper. This model is developed from an elastoplastic model for overconsolidated reconstituted clays, by considering that the variation in the yield surface of structured clays is similar to that of overconsolidated reconstituted clays. However, in order to describe the mechanical behavior of structured clays with precision, the model takes the bonding and parabolic strength envelope into consideration. Compared with the Cam-clay model, only two new parameters are required in the model for structured clays, which can be determined from isotropic compression and triaxial shear tests at different confining pressures. The comparison of model predictions and results of drained and undrained triaxial shear tests on four different marine clays shows that the model can capture reasonable well the strength and deformation characteristics of structured clays, including negative and positive dilatancy, strain-hardening and softening during shearing.
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Bifurcation analysis of over-consolidated clays in different stress paths and drainage conditions
Sun, De'an,Chen, Liwen,Zhang, Junran,Zhou, Annan Techno-Press 2015 Geomechanics & engineering Vol.9 No.5
A three-dimensional elastoplastic constitutive model, also known as a UH model (Yao et al. 2009), was developed to describe the stress-strain relationship for normally consolidated and over-consolidated soils. In this paper, an acoustic tensor and discriminator of bifurcation for the UH model are derived for the strain localization of saturated clays under undrained and fully and partially drained conditions. Analytical analysis is performed to illustrate the points of bifurcation for the UH model with different three-dimensional stress paths. Numerical analyses of cubic specimens for the bifurcation of saturated clays under undrained and fully and partially drained conditions are conducted using ABAQUS with the UH model. Analytical and numerical analyses show the similar bifurcation behaviour of overconsolidated clays in three-dimensional stress states and various drainage conditions. The results of analytical and numerical analyses show that (1) the occurrence of bifurcation is dependent on the stress path and drainage condition; and (2) bifurcation can appear in either a strain-hardening or strain-softening regime.
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Bansal, Varun,De, Debojyoti,An, Jieun,Kang, Tong Mook,Jeong, Hyeon-Ju,Kang, Jong-Sun,Kim, Kyeong Kyu Elsevier 2019 Biomaterials Vol.193 No.-
<P><B>Abstract</B></P> <P>Use of stem cells in regenerative medicine holds great promise in treating people suffering from various otherwise incurable ailments. Direct conversion of somatic cells to other lineages thereby bypassing the intermediate pluripotent state has enormous applicability with respect to time requirement for conversion as well as safety issues. Among various approaches, chemical induced cell conversion is safe yet effective, and the use of small molecules has thus increased greatly in recent years in regenerative fields due to easy applicability, efficient scalability, and consistent reproducibility. Here we report a combination of small molecules capable of converting mouse fibroblasts into skeletal muscle-like cells (SMLCs) without requiring ectopic transcription factor expression. We observed that a combination of chemicals is necessary and sufficient to convert mouse fibroblast to SMLCs that have functional similarity to skeletal muscles. In addition, we also found that cytokines responsible for modulating several key signaling pathways enhance the maturation of converted SMLCs into multinucleated myocytes. Epigenetic analysis revealed that this conversion is accomplished by an epigenetic overhaul, followed by activation of key signal pathways responsible for activating skeletal specific loci. We further observed that human adipocyte-derived stem cells can be converted into SMLCs under conditions similar to that of fibroblasts. This study not only provides an example of chemical induced direct conversion, but also underlines the key signaling pathways that are needed to induce mesodermal lineages and muscles from pleotropic type cells.</P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
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Wu, Yajun,Kong, Gangqiang,Lu, Yitian,Sun, De'an Techno-Press 2017 Geomechanics & engineering Vol.13 No.2
This vacuum preloading combined with polyacrylamide (PAM) flocculation was proposed to separating solid-liquid in waste slurry and to improving bearing capacity of soft soil ground. By using waste slurry taken from drilled shaft construction site in Shanghai, China, a series of settling column tests with four typical flocculants and one normal for waste slurry were carried out for comparative analysis. The optimal amounts for each flocculant were obtained from the column tests. Then, model tests on vacuum preloading with anionic polyacrylamide (APAM) flocculation and without flocculants were carried out. The out of water and the settlement of slurry surface ground were monitored during the model tests, and the changes in water content, particle-size and pore-size distributions in different positions after the model tests were measured and discussed. It is found that water content of the waste slurry without APAM flocculation changed from 204 to 195% by 24 hours standing and 15 hours vacuum preloading, while the water content of the waste slurry with APAM flocculation was declined from 163 to 96% by 24 hours standing, and was further reduced into 37% by 136 hours vacuum preloading, which shows that the combined method is feasible and effective.
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A New Method for Determination of 3D Active Earth Pressure of Unsaturated Backfills
Long Wang,Meijuan Xu,Jie Li,Wenhua Liu,De’an Sun 대한토목학회 2021 KSCE JOURNAL OF CIVIL ENGINEERING Vol.25 No.12
Determinations of active earth pressures are commonly performed two-dimensionally (2D) based on completely saturated and/or dry assumptions, though the soil in cases of geotechnical interest is mostly unsaturated and the earth pressures are usually of conspicuous three-dimensional (3D) features. In this paper, a novel finite prismoid element method (FPEM) for calculating the lateral earth pressures acting against the retaining wall is suggested. The main feature of the FPEM is that the whole backfill is discretized into numerous horizontally distributed prismoid elements that might characterized with different soil properties. For unsaturated backfills, the prismoid elements are characterized with various soil cohesions and unit soil weights. Upper bound solutions to active earth pressures under 2D and 3D conditions with and without suction are both calculated and compared with several other analytical ones, indicating the reliability and applicability of the proposed method. The responses of unsaturated backfills to surcharge loads on the crest are numerically studied and discussed. An illustrative example is reexamined to further demonstrate the practical use of the technique.
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