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| 2. |
- Jiang, Qiyun, et al.
(författare)
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Development and Validation of a Risk Score Screening Tool to Identify People at Risk for Hypertension in Shanghai, China.
- 2022
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Ingår i: Risk management and healthcare policy. - 1179-1594. ; 15, s. 553-562
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Tidskriftsartikel (refereegranskat)abstract
- This study aimed to develop a screening tool based on a risk scoring approach that could identify individuals at high risk for hypertension in Shanghai, China.A total of 3147 respondents from the 2013 Shanghai Chronic Disease and Risk Factor Surveillance were randomly divided into the derivation group and validation group. The coefficients obtained from multivariable logistic regression were used to assign a score to each variable category. The receiver operating characteristic (ROC) curve was used to find the optimal cut-off point and to evaluate the screening performance.Age, family history of hypertension, having diabetes, having dyslipidemia, body mass index, and having abdominal obesity contributed to the risk score. The area under the ROC curve was 0.817 (95% CI: 0.797-0.836). The optimal cut-off value of 20 had a sensitivity of 83.4%, and a specificity of 64.3%, demonstrating good performance.We developed a simple and valid screening tool to identify individuals at risk for hypertension. Early detection could be beneficial for high-risk groups to better manage their conditions and delay the progression of hypertension and related complications.
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| 3. |
- Ma, Yueqiang, et al.
(författare)
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Roles of heat and stress transfer in triggering fault instability in conjugate faulted reservoirs
- 2024
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Ingår i: International Journal of Rock Mechanics And Mining Sciences. - : Elsevier. - 1365-1609 .- 1873-4545. ; 180
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Tidskriftsartikel (refereegranskat)abstract
- The presence of multiple conjugate but non-intersecting faults in geothermal reservoirs presents issues related to fault interaction in the presence of complex coupled thermo-hydro-mechanical (THM) processes in influencing the triggering of seismicity. We examine alternate strategies in stimulating such a conjugate-faulted geothermal reservoir analogous to that hosting the Mw 5.5 Pohang earthquake (2017). We evaluate the response of the reservoir to both short-term stimulation (1y) and long-term production (10y), both with and without thermal effects - for a large fault (F1) adjacent to a non-intersecting smaller fault (F2) and in a reverse faulting stress regime. Results suggest that the slip on either fault impacts the stress state on the other fault through stress transfer. Reactivation of the minor fault (F2) transfers stress towards to the upper part of primary fault (F1), inducing instability. The slip of the major fault is delayed by positioning the location of injection away from the junction between the two faults - decreasing the injection depth from 4087.5 m to 3712.5 m delays the time to slip by 2.61 y. Furthermore, thermal stress plays a decisive role in prompting late-stage fault reactivation for long-term fluid circulation where pore pressures have already reached steady state. The pattern of thermal unloading follows the path of fluid transport and heat transfer along the faults. Overall, this study not only advances our understanding of mechanisms of injection-induced fault instability in EGS reservoirs with multiple and closely-interacting faults, but also provides insights into how different injection strategies can delay or mitigate induced seismicity.
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| 4. |
- Xia, Zhisheng, et al.
(författare)
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Fabrication and Tribological Properties of Nickel-Based Cellular Structure Self-Lubricating Composites by Selective Laser Melting and Metal Infiltration
- 2023
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Ingår i: Tribology Transactions. - 1040-2004 .- 1547-397X. ; 66:4, s. 670-682
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Tidskriftsartikel (refereegranskat)abstract
- The service life of Inconel 718 (IN718) nickel-based superalloys under extreme working conditions is limited due to their poor tribological properties. In this study, IN718 cellular structure self-lubricating composites were fabricated by selective laser melting (SLM) and multi-soft metal (Sn-Pb-Ag) infiltration. Different cellular structures were verified by means of numerical simulation and experiment. The effects of pore diameter and temperature on tribological properties of the selective-laser-melted (SLMed) IN718 with Sn-Pb-Ag (INSPA) infiltration self-lubricating composites were investigated. Results show that INSPA samples of cellular structure with a pore diameter of 1.4 mm (INSPA3) exhibited excellent tribological properties compared to the two other pore diameters of 1.2 mm (INSPA2) and 1.0 mm (INSPA1). The tribological properties test results at different temperatures indicate that the coefficient of friction (COF) of INSPA3 was decreased from 0.29 to 0.13 as the temperature of 25 °C rose to 350 °C. The reason is that more Sn-Pb-Ag lubricant was stored in the Ф1.4-mm holes, which were heated and expanded to the worn surface during the friction process to realize self-compensation lubrication. At 350 °C, the friction product of Pb2O was decomposed into PbO and other multicomponent friction oxides were generated, which improves the wear resistance of the SLMed INSPA self-lubricating composites. This study demonstrates a potential approach to enhance the tribological properties and service life of IN718 superalloys used in harsh friction conditions.
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| 5. |
- Zhang, Xu, et al.
(författare)
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Impact of fracture shear dilation on long-term heat extraction in Enhanced Geothermal Systems: Insights from a fully-coupled thermo-hydro-mechanical simulation
- 2021
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Ingår i: Geothermics. - : Elsevier BV. - 0375-6505 .- 1879-3576. ; 96, s. 102216-102216
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Tidskriftsartikel (refereegranskat)abstract
- Shear dilation of fractures has been recognized as a main mechanism of permeability enhancement by hydraulic stimulation in Enhanced Geothermal Systems (EGSs); however, the interactive role of fracture shear dilation and thermo-hydro-mechanical (THM) coupling processes in long-term heat extraction performance of EGSs remains unclear. In this study, we develop a novel THM coupling model based on the discrete fracture network approach, which can realistically capture important processes including hybrid normal-shear deformation of fractures, thermal expansion of rocks, fluid flow in both fractures and rocks, and heat convection/conduction as well as local thermal non-equilibrium effect and changes in physical parameters of fluid. We quantitatively investigate the effects of fracture network geometries and geomechanical boundary constraints on fracture shear dilatancy, and the resulting heat transfer characteristics of EGSs. Numerical results reveal that shear dilation of fractures can be triggered by transient pore pressurization and thermal stress under anisotropic in-situ stress condition, and would severely engender flow channeling as well as anisotropic heat transfer, which strongly impact the heat extraction performance. The production temperature tends to be overestimated while the thermal production rate may be underestimated, if the shear dilatational behavior is not incorporated. Increased in-situ stress ratio and injection/production pressure would magnify the effects of shear dilation, and lead to considerable enhancement of fracture permeability, eventually resulting in much earlier and quicker temperature drop. Excessive increase of fracture density and the location of injection-production wells parallel to potential channelized flow paths, formed by intersected fractures preferentially oriented for shear sliding, tend to form short circulating flow paths and reduce the heat extraction performance. Our study demonstrates the importance of considering fracture shear dilation and fully-coupled THM behaviors when evaluating the long-term performance and efficiency of heat extraction in EGSs.
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| 6. |
- Zhang, Xu, et al.
(författare)
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Improving heat extraction performance of enhanced geothermal systems: Insights from critical fracture network parameter and multi-objective optimization method
- 2022
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Ingår i: Applied Thermal Engineering. - : Elsevier BV. - 1359-4311 .- 1873-5606. ; 213
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Tidskriftsartikel (refereegranskat)abstract
- The generation of a highly permeable fracture network in Enhanced Geothermal Systems (EGSs) is a prerequisite to develop such geothermal reservoirs efficiently. However, it lacks a quantitative geometrical metric to evaluate what kind of fracture network is preferable for geothermal production. To address this problem, we use our previously developed high-fidelity Thermo-Hydro-Mechanical (THM) coupling model to investigate the joint influence of fracture geometry and thermal stress on the THM behaviors of EGSs. Results show that the geometrical connectivity of fracture networks plays a dominant role in determining the THM processes and the thermal performance of EGSs, in which the network connectivity integrates multiple properties of fracture networks including the fracture length, intensity, location and orientation. Satisfactory thermal performance tends to be achieved when the connectivity of fracture systems ranges from 15 to 35. We focus on such fracture networks and design an appropriate production scenario for optimizing multiple objectives (i.e. maximum EGS service life, heat extraction rate, and global thermal power). The overall heat extraction performance of EGSs under the optimum scenario gets improved by 77.7% compared with the base case. This research provides an effective workflow and feasible methods for evaluating and optimizing energy exploitation efficiency of EGSs.
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