| 1. |
- Gu, Guansi, et al.
(author)
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A finite element-based dynamic simulation method for modeling shield-ground interactions : 3D numerical simulations with comparison to physical experiments
- 2024
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In: Computers and geotechnics. - : Elsevier. - 0266-352X .- 1873-7633. ; 169
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Journal article (peer-reviewed)abstract
- In this paper, a novel numerical simulation approach based on the finite element method for dynamically modeling the excavation process of shield tunneling is proposed, with the shield-ground interactions well captured. This method is capable of mimicking the alternating modes of advancing and stopping of a shield boring machine during underground construction, with the important effects of the cutterhead rotation and slurry support pressure considered. Under the cutting action, the soil at the excavation face would experience irreversible deformation and damage, such that additional support needs to be provided by the cutterhead blades and slurry to maintain stability. The impacts of key construction parameters are examined, including cutterhead rotary speed, advance rate, and slurry support pressure, on shield tunneling operations and ground responses. The numerical model is rigorously validated against physical model experiments. This work provides useful insights into the mechanistic processes in the stratum during shield tunneling, including the spatiotemporal evolution of ground deformation patterns and stress redistributions. The results offer valuable guidance for optimizing shield tunneling operations and enhancing tunneling safety and efficiency.
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| 2. |
- Huang, Wei, et al.
(author)
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Substrate Promiscuity, Crystal Structure, and Application of a Plant UDP-Glycosyltransferase UGT74AN3
- 2024
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In: ACS Catalysis. - : American Chemical Society (ACS). - 2155-5435. ; 14:1, s. 475-488
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Journal article (peer-reviewed)abstract
- Glycosyltransferases are effective enzymes for glycosylating natural products (NPs), and some of them have the unusual property of being exceedingly promiscuous catalytically toward a range of substrates. UGT74AN3 is a plant glycosyltransferase identified from Catharanthus roseus in our previous work. In this study, we found that UGT74AN3 exhibits high substrate promiscuity toward 78 acceptors and 6 sugar donors and also exhibits N-/S-glycosylation activity toward simple aromatic compounds. The crystal structures of UGT74AN3 in the complex with various NPs were solved. Sugar donor recognition of UGT74AN3 was altered by structure-based mutagenesis, and the T145V mutant shifted its sugar donor preference from UDP-Glc to UDP-Xyl. Structural analysis reveals that a spacious U-shaped hydrophobic binding pocket accounts for the high substrate promiscuity of UGT74AN3. The residues E85 and F193 might serve as gatekeepers of UGT74AN3 to control substrate binding. In addition, a rare substrate binding mode was discovered in the structure of UGT74AN3, and the process of substrate flipping in the pocket was charted by molecular dynamics simulations. Moreover, a cost-effective one-pot system by coupling UGT74AN3 with AtSuSy, a sucrose synthase, was established for in situ generating and recycling UDP-Glc from sucrose and UDP to glycosylate NPs. Our study reveals the structural basis underlying the substrate promiscuity of UGT74AN3 and provides an efficient and economical enzymatic synthesis strategy for producing valuable glycosides for drug discovery.
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| 3. |
- Huang, Xin, et al.
(author)
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A tensor-based analysis of stress variability in granular media subjected to various loading conditions
- 2019
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In: Powder Technology. - : Elsevier. - 0032-5910 .- 1873-328X. ; 356, s. 581-593
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Journal article (peer-reviewed)abstract
- This paper uses a novel tensor-based approach to characterize the spatial variability and localization of stress fields in granular media derived from three-dimensional discrete element simulations. We use the Euclidean distance of the stress tensor of each particle to the bulk mean stress tensor to quantify local stress fluctuations and use the effective variance of the stress field to quantify the overall dispersion. We observe that the evolutions of both the local stress fluctuation and the bulk stress dispersion strongly depend on the stress state, packing density and shearing process. However, they become constant, and are uniquely related to the deviatoric stress and the void ratio when the sample is at critical state, under which the stress variability reaches an ultimate condition. Multifractal analysis further shows that the local stress field is highly heterogeneous and exhibits self-organized patterns.
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| 4. |
- Huang, Xin, et al.
(author)
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Characterizing stress variability within granular samples upon liquefaction
- 2020
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In: Computers and geotechnics. - : Elsevier BV. - 0266-352X .- 1873-7633. ; 127, s. 103771-103771
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Journal article (peer-reviewed)abstract
- A tensor-based approach is adopted to investigate the evolution of stress variability within granular media based on DEM simulations of both cyclic and static liquefactions. The bulk stress dispersion is evaluated using the effective variance of the entire stress tensor field and the local stress fluctuation is quantified by the Euclidean distance between the stress tensor of individual particles and the global stress tensor. The orientation discrepancies between the local stress tensor and global fabric tensor, and between the local and global stress tensors are examined by their joint invariants. We observe that the bulk stress dispersion decreases but the discrepancy of local stress fluctuation increases upon liquefaction. The initially deviatoric stress-dominated stress variability gradually becomes hydrostatic stress-dominated, and returns to deviatoric stress-dominated again after liquefaction. The liquefaction process is characterized by the degradation of coaxiality between the local stress tensor and the global fabric tensor and that between the local and global stress tensors. There exists a range of threshold values for such coaxiality, below which liquefaction occurs. Particles with coaxiality higher than the threshold value and particles with coaxality lower than the threshold value exhibit different roles in sustaining external loads. However, the discrepancy becomes neutral upon liquefaction.
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| 5. |
- Liang, Jianxin, et al.
(author)
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Mechanistic study of transcription factor Sox18 during heart development
- 2024
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In: General and Comparative Endocrinology. - : Elsevier BV. - 0016-6480 .- 1095-6840. ; 350
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Journal article (peer-reviewed)abstract
- Heart development is a delicate and complex process regulated by coordination of various signaling pathways. In this study, we investigated the role of sox18 in heart development by modulating Wnt/β-Catenin signaling pathways. Our spatiotemporal expression analysis revealed that sox18 is mainly expressed in the heart, branchial arch, pharyngeal arch, spinal cord, and intersegmental vessels at the tailbud stage of Xenopus tropicalis embryo. Overexpression of sox18 in the X. tropicalis embryos causes heart edema, while loss-of-function of sox18 can change the signal of developmental heart marker gata4 at different stages, suggesting that sox18 plays an essential role in the development of the heart. Knockdown of SOX18 in human umbilical vein endothelial cells suggests a link between Sox18 and β-CATENIN, a key regulator of the Wnt signaling pathway. Sox18 negatively regulates islet1 and tbx3, the downstream factors of Wnt/β-Catenin signaling, during the linear heart tube formation and the heart looping stage. Taken together, our findings highlight the crucial role of Sox18 in the development of the heart via inhibiting Wnt/β-Catenin signaling.
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| 6. |
- Pan, Wenbo, et al.
(author)
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Earthquake-induced fracture displacements and transmissivity changes in a 3D fracture network of crystalline rock for spent nuclear fuel disposal
- 2023
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In: Journal of Rock Mechanics and Geotechnical Engineering. - : Elsevier. - 1674-7755. ; 15:9, s. 2313-2329
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Journal article (peer-reviewed)abstract
- During the long service period of a nuclear waste repository in crystalline rock, large earthquake(s) may occur nearby the repository site and coseismically alter the local stress field around pre-existing fractures within the geological formation. The resulting fracture normal/shear displacements may lead to fracture opening and further promote the transport of leaked radionuclides into the groundwater system. Thus, it is of central importance to analyze the consequences of potential future earthquake(s) on the hydrogeological properties of a repository site for spent nuclear fuel disposal. Based on the detailed site characterization data of the repository site at Forsmark, Sweden, we conduct a three-dimensional (3D) seismo-hydro-mechanical simulation using the 3Dimensional Distinct Element Code (3DEC). We explicitly represent a primary seismogenic fault zone and its surrounding secondary fracture network associated with a power-law size scaling and a Fisher orientation distribution. An earthquake with a magnitude of Mw = 5.6 caused by the reactivation of the primary fault zone is modeled by simulating its transient rupture propagating radially outwards from a predefined hypocenter at a specified rupture speed, with the faulting dynamics controlled by a strength weakening law. We model the coseismic response of the off-fault fracture network subject to both static and dynamic triggering effects. We further diagnose the distribution of fracture hydro-mechanical properties (e.g. mechanical/hydraulic aperture, hydraulic transmissivity) before and after the earthquake in order to quantify earthquake-induced hydraulic changes in the fracture network. It is found that earthquake-induced fracture transmissivity changes tend to follow a power-law decay with the distance to the earthquake fault. Our simulation results and insights obtained have important implications for the long-term performance assessment of nuclear waste repositories in fractured crystalline rocks.
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| 7. |
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| 8. |
- Qu, Muchao, et al.
(author)
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Electric Resistance of Elastic Strain Sensors-Fundamental Mechanisms and Experimental Validation
- 2023
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In: Nanomaterials. - : MDPI AG. - 2079-4991. ; 13:12
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Journal article (peer-reviewed)abstract
- Elastic strain sensor nanocomposites are emerging materials of high scientific and commercial interest. This study analyzes the major factors influencing the electrical behavior of elastic strain sensor nanocomposites. The sensor mechanisms were described for nanocomposites with conductive nanofillers, either dispersed inside the polymer matrix or coated onto the polymer surface. The purely geometrical contributions to the change in resistance were also assessed. The theoretical predictions indicated that maximum Gauge values are achieved for mixture composites with filler fractions slightly above the electrical percolation threshold, especially for nanocomposites with a very rapid conductivity increase around the threshold. PDMS/CB and PDMS/CNT mixture nanocomposites with 0-5.5 vol.% fillers were therefore manufactured and analyzed with resistivity measurements. In agreement with the predictions, the PDMS/CB with 2.0 vol.% CB gave very high Gauge values of around 20,000. The findings in this study will thus facilitate the development of highly optimized conductive polymer composites for strain sensor applications.
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| 9. |
- Sun, Zhixue, et al.
(author)
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Combined Effects of Thermal Perturbation and In-situ Stress on Heat Transfer in Fractured Geothermal Reservoirs
- 2021
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In: Rock Mechanics and Rock Engineering. - : Springer. - 0723-2632 .- 1434-453X. ; 54:5, s. 2165-2181
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Journal article (peer-reviewed)abstract
- We develop a new fully coupled thermo-hydro-mechanical (THM) model to investigate the combined effects of thermal perturbation and in-situ stress on heat transfer in two-dimensional fractured rocks. We quantitatively analyze the influence of geomechanical boundary constraints and initial reservoir temperature on the evolutionary behavior of fracture aperture, fluid flow and heat transfer, and further identify the underlying mechanisms dominating the coupled THM processes. The results reveal that, apart from enhancing normal opening of fractures, the transient cooling effect of thermal front may trigger shear dilations under the anisotropic in-situ stress condition. It is found that the applied in-situ stress tends to impose a strong impact on the spatial and temporal variations of fracture apertures and flow rates, and eventually affect heat transfer. The enhancement of reservoir transmissivity during transient cooling tends to be significantly overestimated if the in-situ stress effect is not incorporated, which may lead to unrealistic predictions of heat extraction performance. Our study also provides physical insights into a fundamental thermo-poroelastic behavior of fractured rocks, where fracture aperture evolution during heat extraction tends to be simultaneously governed by two mechanisms: (1) thermal expansion-induced local aperture enlargement and (2) thermal propagation-induced remote aperture variation (can either increase or decrease). The results from our study have important implications for optimizing heat extraction efficiency and managing seismic hazards during fluid injections in geothermal reservoirs.
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| 10. |
- Wang, Cheng-Xiang, et al.
(author)
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On the Road to 6G: Visions, Requirements, Key Technologies, and Testbeds
- 2023
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In: IEEE Communications Surveys and Tutorials. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 1553-877X. ; 25:2, s. 905-974
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Journal article (peer-reviewed)abstract
- Fifth generation (5G) mobile communication systems have entered the stage of commercial deployment, providing users with new services, improved user experiences as well as a host of novel opportunities to various industries. However, 5G still faces many challenges. To address these challenges, international industrial, academic, and standards organizations have commenced research on sixth generation (6G) wireless communication systems. A series of white papers and survey papers have been published, which aim to define 6G in terms of requirements, application scenarios, key technologies, etc. Although ITU-R has been working on the 6G vision and it is expected to reach a consensus on what 6G will be by mid-2023, the related global discussions are still wide open and the existing literature has identified numerous open issues. This paper first provides a comprehensive portrayal of the 6G vision, technical requirements, and application scenarios, covering the current common understanding of 6G. Then, a critical appraisal of the 6G network architecture and key technologies is presented. Furthermore, existing testbeds and advanced 6G verification platforms are detailed for the first time. In addition, future research directions and open challenges are identified to stimulate the on-going global debate. Finally, lessons learned to date concerning 6G networks are discussed.
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