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engineering behaviour of in situ cored deep cement mixed marine deposits subjected to undrained and drained shearing

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journal of Rock Mechanics and Geotechnical engineering 2024年第5期16卷 1749-1760页

作者： Wei Li chung Yee Kwok Faculty of engineering China University of GeosciencesWuhan430074China Department of Civil engineering The University of Hong Kong999000Hong Kong SARChina

The deep cement mixing(DCM)is used to improve the capacity and reduce the settlement of the soft ground by forming cemented clay *** investigation on the mechanical behaviour of the DCM samples is limited to either laboratory-prepared samples or in-situ samples under unconfined *** this study,a series of drained and undrained triaxial shearing tests was performed on the in-situ cored DCM samples with high cement content to assess their mechanical *** is found that the drainage condition affects significantly the stiffness,peak and residual strengths of the DCM samples,which is mainly due to the state of excess pore water pressure at different strain levels,*** positive before the peak deviatoric stress and negative after the peak deviatoric stress,in the undrained *** slope of the failure envelope changes obviously with the confining pressures,being steeper at lower stress levels and flatter at higher stress *** strength parameters,effective cohesion and friction angle obtained from lower stress levels(c′0 andφ′0)are 400 kPa and 58°,respectively,which are deemed to be true for design in most DCM applications where the in-situ stress levels are normally at lower values of 50-200 ***,the computed tomography(CT)scanning system was adopted to visualize the internal structures of DCM *** is found that the clay pockets existing inside the DCM samples due to uneven mixing affect markedly their stress-strain behaviour,which is one of the main reasons for the high variability of the DCM samples.

关键词： Deep cement mixing(DCM) In-situ cored sample Triaxial shearing Drainage condition Confining pressure Computed tomography(CT)

Are hydrides under high-pressure-high-temperature superconductors?

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National Science Review 2024年第7期11卷 9-12页

作者： j.e.Hirsch Department of Physics University of California

Contrary to the current consensus, I argue that the existing evidence for high-temperature superconductivity in hydrides under high pressure is not compelling. I suggest that the focus of the field should urgently shift to establish unequivocally experimentally whether or not superconductivity in pressurized hydrides exists, instead of continuing to search for new materials that might show elusive signals of unproven superconductivity at ever higher temperatures. The implications of a negative finding for the theoretical understanding of superconductivity are discussed.

关键词： Hydrides

ensemble Wind Power Prediction Interval with Optimal Reserve Requirement

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journal of Modern Power Systems and Clean energy 2024年第1期12卷 65-76页

作者： Hamid Rezaie Cheuk Hei chung Nima Safari the Saskatchewan Power Corporation(SaskPower) ReginaSaskatchewanCanada the Department of electrical and Computer engineering and Department of Human Biology University of TorontoTorontoON M5S 3G4Canada the Alberta electric System Operator(AeSO) CalgaryAlbertaCanada

Wind power prediction interval(WPPI)models in the literature have predominantly been developed for and tested on specific case ***,wind behavior and characteristics can vary significantly across ***,a prediction model that performs well in one case might underperform in *** address this shortcoming,this paper proposes an ensemble WPPI framework that integrates multiple WPPI models with distinct characteristics to improve *** important and often overlooked factor is the role of probabilistic wind power prediction(WPP)in quantifying wind power uncertainty,which should be handled by operating *** reserve in WPPI frameworks enhances the efficacy of *** this regard,the proposed framework employs a novel bi-layer optimization approach that takes both WPPI quality and reserve requirements into *** analysis with different real-world datasets and various benchmark models validates the quality of the obtained WPPIs while resulting in more optimal reserve requirements.

关键词： ensemble model linear programming operating reserve optimal reserve requirement prediction interval probabilistic prediction renewable integration uncertainty representation wind power prediction(WPP)

Small-signal Stability Criteria in Power electronics-dominated Power Systems:A Comparative Review

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journal of Modern Power Systems and Clean energy 2024年第4期12卷 1003-1018页

作者： Qifan Chen Siqi Bu Chi Yung chung Department of electrical and electronic engineer The Hong Kong Polytechnic UniversityHong KongChina Department of electrical and electronic engineering Shenzhen Research InstituteCentre for Grid ModernisationInternational Centre of Urban Energy NexusCentre for Advances in Reliability and SafetyResearch Institute for Smart Energyand Policy Research Centre for Innovation and TechnologyThe Hong Kong Polytechnic UniversityHong KongChina

To tackle emerging power system small-signal stability problems such as wideband oscillations induced by the large-scale integration of renewable energy and power electronics,it is crucial to review and compare existing small-signal stability analysis *** this basis,guidance can be provided on determining suitable analysis methods to solve relevant small-signal stability problems in power electronics-dominated power systems(PeDPSs).Various mature methods have been developed to analyze the small-signal stability of PeDPSs,including eigenvalue-based methods,Routh stability criterion,Nyquist/Bode plot based methods,passivity-based methods,positive-net-damping method,lumped impedance-based methods,bifurcation-based methods,*** this paper,the application conditions,advantages,and limitations of these criteria in identifying oscillation frequencies and stability margins are reviewed and compared to reveal and explain connections and discrepancies among ***,efforts are devoted to mathematically proving the equivalence between these small-signal stability ***,the performance of these criteria is demonstrated and compared in a 4-machine 2-area power system with a wind farm and an Ieee 39-bus power system with 3 wind farms.

关键词： Impedance-based method oscillation analysis power electronic converter power electronics-dominated power system renewable power generation small-signal stability

Interplay of laser power and pore characteristics in selective laser melting of ZK60 magnesium alloys:A study based on in-situ monitoring and image analysis

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journal of Magnesium and Alloys 2024年第4期12卷 1346-1366页

作者： Weijie Xie Hau-chung Man Chi-Wai Chan Department of Industrial and Systems engineering The Hong Kong Polytechnic UniversityHong KongChina School of Mechanical and Aerospace engineering Queen’s UniversityBelfast BT95AHUK Research Institute for Advanced Manufacturing The Hong Kong Polytechnic UniversityHong KongChina

This study offers significant insights into the multi-physics phenomena of the SLM process and the subsequent porosity characteristics of ZK60 Magnesium(Mg)***-speed in-situ monitoring was employed to visualise process signals in real-time,elucidating the dynamics of melt pools and vapour plumes under varying laser power conditions specifically between 40 W and 60 *** morphological analysis was performed using Scanning-electron Microscopy(SeM),demonstrating a critical correlation between laser power and pore *** laser power led to increased pore coverage,whereas a denser structure was observed at higher laser *** laser power influence on porosity was further confirmed via Optical Microscopy(OM)conducted on both top and cross-sectional surfaces of the *** increase in laser power resulted in a decrease in pore coverage and pore size,potentially leading to a denser printed part of Mg alloy.X-ray Computed Tomography(XCT)augmented these findings by providing a 3D volumetric representation of the sample internal structure,revealing an inverse relationship between laser power and overall pore *** laser power appeared to favour the formation of interconnected pores,while a reduction in interconnected pores and an increase in isolated pores were observed at higher *** interplay between melt pool size,vapour plume effects,and laser power was found to significantly influence the resulting porosity,indicating a need for effective management of these factors to optimise the SLM process of Mg alloys.

关键词： Selective laser melting(SLM) Magnesium(Mg)alloys Biodegradable implants Porosity In-situ monitoring

100 W-class green hydrogen production from ammonia at a dual-layer electrode containing a Pt-Ir catalyst for an alkaline electrolytic process

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journal of energy Chemistry 2024年第6期93卷 352-360,I0009页

作者： Donghyun Yoon Sunki chung Minjun Choi eunhyeok Yang jaeyoung Lee School of earth Sciences and environmental engineering Gwangju Institute of Science and Technology(GIST)Gwangju 61005Republic of Korea International Future Research Center of Chemical energy Storage and Conversion Processes GISTGwangju 61005Republic of Korea ertl Center for electrochemistry and Catalysis GISTGwangju 61005Republic of Korea TKG Huchems Co.Ltd 963Sangam-roYeosu-siJeollanam-do 59614Republic of Korea

Ammonia allows storage and transport of hydrogen over long distances and is an attractive potential hydrogen *** decomposition has recently been used for the conversion of ammonia to hydrogen and is regarded as a future technology for production of CO_(2)-free pure ***,a heterostructural Pt-Ir dual-layer electrode is developed and shown to achieve successful long-term operation in an ammonia electrolyzer with an anion exchange membrane(AeM).This electrolyzer consisted of eight membra ne electrode assemblies(MeAs)with a total geometric area of 200 cm~2 on the anode side,which resulted in a hydrogen production rate of 25 L h~(-1).We observed the degradation in MeA performance attributed to changes in the anode catalyst layer during hydrogen production via ammonia ***,we demonstrated the relationship between the ammonia oxidation reaction(AOR)and the oxygen evolution reaction(OeR).

关键词： Ammonia oxidation Dual-layer catalyst Green hydrogen electrolytic process Oxygen evolution reaction

Supergravity effects on flame propagation and structure in hydrogen/air mixtures

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Acta Mechanica Sinica 2024年第6期40卷 31-38页

作者： Wenkai Liang chung K.Law Center for Combustion energy Department of Energy and Power EngineeringTsinghua UniversityBeijing100080China Department of Mechanical and Aerospace engineering Princeton UniversityPrinceton08544USA

In the current work,we investigated hydrogen/air flame propagation under supergravity *** show that when gravity is in the same/opposite direction as flame propagation,it leads to acceleration/deceleration of the flame,and that such an effect could substantially modify the flame propagation and structure at high gravity ***,for the absolute and relative flame propagation speeds,the gravity-affected flame speed shows opposite trends as the absolute flame speed is more affected by the local induced flow field,while the relative flame speeds are controlled by the super-adiabatic or sub-adiabatic flame *** gravity-affected thermal and chemical flame structures are also examined through the influence of the mixture equivalence ratio,pressure,and flame stretch.

关键词： Supergravity Flame acceleration Laminar flame speed Flame stretch Hydrogen

Data-driven Static equivalence with Physics-informed Koopman Operators

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CSee journal of Power and energy Systems 2024年第1期10卷 432-438页

作者： Wei Lin Changhong Zhao Maosheng Gao C.Y.chung Department of electrical engineering The Hong Kong Polytechnic UniversityHong Kong SARChina Department of Information engineering The Chinese University of Hong KongHong Kong SARChina School of electrical engineering Chongqing UniversityChongqing 400044China

With deployment of measurement units,fitting static equivalent models of distribution networks(DNs)by linear regression has been recognized as an effective method in power flow analysis of a transmission *** volatility of measurements caused by variable distributed renewable energy sources makes it more difficult to accurately fit such equivalent *** tackle this challenge,this letter proposes a novel data-driven method to improve equivalency accuracy of DNs with distributed energy *** letter provides a new perspective that an equivalent model can be regarded as a mapping from internal conditions and border voltages to border power *** mapping can be established through 1)Koopman operator theory,and 2)physical features of power flow equations at the root node of a *** of the proposed method is demonstrated on the Ieee 33-bus and Ieee 136-bus test systems connected to a 661-bus utility system.

关键词： Data-driven distribution network Koopman operator theory static equivalent model

Hierarchical Control Strategy for Load Regulation Based on Stackelberg Game Theory Considering Randomness

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CSee journal of Power and energy Systems 2024年第3期10卷 929-941页

作者： Tingyu jiang Ping ju C.Y.chung Yuzhong Gong College of energy and electrical engineering Hohai UniversityNanjing 211100China Department of electrical engineering City University of Hong KongHong Kong CF624China Department of electrical and Computer engineering University of SaskatchewanSaskatoonSK S7N 5A9Canada CSee Ieee

Demand response has been recognized as a valuable functionality of power systems for mitigating power *** paper proposes a hierarchical control strategy among the distribution system operator(DSO),load aggregators(LAs),and thermostatically controlled loads(TCLs);the strategy includes a scheduling layer and an executive layer to provide load *** the scheduling layer,the DSO(leader)offers compensation price(CP)strategies,and the LAs(followers)respond to CP strategies with available regulation power(ARP)*** of the DSO and LAs are modeled according to their behaviors during the load regulation *** game is adopted to capture interactions among the players and leader and to obtain the optimal strategy for each participant to achieve ***,considering inevitable random factors in practice,e.g.,renewable generation and behavior of users,two different stochastic models based on sample average approximation(SAA)and parameter modification are formulated with improved scheduling *** the executive layer,distributed TCLs are triggered based on strategies determined in the scheduling layer.A self-triggering method that does not violate user privacy is presented,where TCLs receive external signals from the LA and independently determine whether to alter their operation *** simulations are performed on the modified Ieee-24 bus system to verify effectiveness of the proposed strategy.

关键词： Demand response hierarchical control load regulation self-triggering method Stackelberg game