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Experimental study.and correlation development for the two-phase frictional pressure drop of flow boiling in copper foam fin microchannels

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Science China(Technological Sciences) 2024年第9期67卷 2758-2776页

作者： FU kai XU XiangHua LIANG XinGang School of Aerospace Engineering Tsinghua UniversityBeijing 100084China

Flow boiling in microchannels with porous walls has received extensive attention in recent y.ars. Compared with the emphasis on heat transfer, there is a lack of research on the effect of the porous wall structures on the pressure drop characteristics. In this study. sy.tematic experiments are performed to measure the pressure drop of water-vapor two-phase flow in five microchannels with copper foam fins, which consist of nine or six channels and fins of copper foam. The porosities of the foam fins range from0.78 to 0.82 and ratios of fin width to channel width range from 0.5 to 2. The channels are approximately.0.5 or 1 mm in width and 1 mm in height. Both adiabatic and flow boiling experiments are conducted with water at mass fluxes ranging from 66 to 407 kg/(m^(2)s). In the adiabatic experiments, the average quality.in channels is between 0.017 and 0.846. In the flow boiling experiments, the outlet quality.of channels is between 0.040 and 0.863. Slug flow, churn flow, annular flow, and wispy.annular flow are observed in adiabatic experiments. A two-phase frictional pressure drop correlation based on the Lockhart-Martinelli model is developed for copper foam fin microchannels by.introducing the effects of the mass flux, porosity. ratio of fin width to channel width, and heating condition step by.step. The mean absolute percentage errors of the new correlation are 7.53% for 325data points under adiabatic conditions and 5.51% for 268 data points under flow boiling conditions, respectively. This work provides insight into the correlations of frictional pressure drop in microchannels with porous walls.

关键词： two-phase flow boiling pressure drop correlation microchannel copper foam porous wall

Ultrafast pulse-dilation framing camera and its application for time-resolved X-ray.diagnostic

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Nuclear Science and Techniques 2024年第7期35卷 101-114页

作者： Hou-Zhi Cai Qiu-y.n Luo kai-Xuan Lin Xuan Deng Jun-kai Liu kai-Zhi y.ng Dong Wang Jia-Jie Chen Jia-Heng Wang Jing-Hua Long Li-Hong Niu y.n-Fei Lei Jin-y.an Liu Key.Laboratory.of Optoelectronic Devices and Sy.tems of Ministry.of Education and Guangdong Province Shenzhen Key Laboratory of Photonics and BiophotonicsCollege of Physics and Optoelectronic EngineeringShenzhen UniversityShenzhen518060China

An ultrafast framing camera with a pulse-dilation device,a microchannel plate(MCP)imager,and an electronic imaging sy.tem were *** camera achieved a temporal resolution of 10 ps by.using a pulse-dilation device and gated MCP imager,and a spatial resolution of 100μm by.using an electronic imaging sy.tem comprising combined magnetic *** spatial resolution characteristics of the camera were studied both theoretically.and *** results showed that the camera with combined magnetic lenses reduced the field curvature and acquired a larger working area.A working area with a diameter of 53 mm was created by.apply.ng four magnetic lenses to the ***,the camera was used to detect the X-ray. produced by.the laser-targeting *** diagnostic results indicated that the width of the X-ray.pulse was approximately.18 ps.

关键词： Inertial confinement fusion Plasma diagnostics Framing camera Combined lenses Pulse-dilation

Single-atom Co alloy.d Ru for electrocataly.ic nitrite reduction to ammonia

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Nano Research 2024年第5期17卷 3660-3666页

作者： Fuzhou Wang Jiaqi Xiang Guike Zhang kai Chen Ke Chu School of Materials Science and Engineering Lanzhou Jiaotong UniversityLanzhou 730070China

Electrochemical converting NO_(2)^(-)into NH_(3)(NO_(2)RR)holds an enormous prospect to attain efficient NH_(3) electrosy.thesis and polluted NO_(2)^(-)***,we report single-atom Co alloy.d Ru(Co_(1)Ru)as an efficient and durable NO_(2)RR *** experimental and theoretical investigations reveal that single-atom Co alloy.ng of Ru enables the construction of Co_(1)-Ru heteronuclear active sites to sy.ergistically.promote NO_(2)^(-)activation/hy.rogenation while suppressing the competitive H_(2) evolution,rendering the greatly.enhanced activity.and selectivity.of Co_(1)Ru towards the NO_(2)***,Co_(1)Ru assembled within a flow cell exhibits an impressive NH_(3) y.eld rate of 2379.2μmol·h^(-1)·cm^(-2) with an NH_(3)-Faradaic efficiency.of 92%at a high current density.of 415.9 mA·cm^(-2),which is among the highest NO_(2)RR performances reported to date.

关键词： electrochemical converting NO_(2)-into NH3 single-atom alloy. theoretical computations industrial-level current density

Predicting Rock Burst in Underground Engineering Leveraging a Novel Metaheuristic-Based LightGBM Model

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Computer Modeling in Engineering & Sciences 2024年第7期140卷 229-253页

作者： kai Wang Biao He Pijush Samui Jian Zhou No.Three Engineering Co. Ltd.CCCC First Highway Engineering CompanyBeijing101102China Department of Civil Engineering Faculty of EngineeringUniversiti MalayaKuala Lumpur50603Malaysia Department of Civil Engineering National Institute of Technology PatnaBihar800005India School of Resources and Safety.Engineering Central South UniversityChangsha410083China

Rock bursts represent a formidable challenge in underground engineering,posing substantial risks to both infrastructure and human *** sudden and violent failures of rock masses are characterized by.the rapid release of accumulated stress within the rock,leading to severe seismic events and structural ***,the development of reliable prediction models for rock bursts is paramount to mitigating these *** study.aims to propose a tree-based model—a Light Gradient Boosting Machine(LightGBM)—to predict the intensity.of rock bursts in underground engineering.322 actual rock burst cases are collected to constitute an exhaustive rock burst dataset,which serves to train the *** population-basedmetaheuristic algorithms are used to optimize the hy.erparameters of the LightGBM ***,the sensitivity.analy.is is used to identify.the predominant factors that may.incur the occurrence of rock *** results show that the population-based metaheuristic algorithms have a good ability.to search out the optimal hy.erparameters of the LightGBM *** developed LightGBM model y.elds promising performance in predicting the intensity.of rock bursts,with which accuracy.on training and testing sets are 0.972 and 0.944,*** sensitivity.analy.is discloses that the risk of occurring rock burst is significantly.sensitive to three factors:uniaxial compressive strength(σc),stress concentration factor(SCF),and elastic strain energy.index(Wet).Moreover,this study.clarifies the particular impact of these three factors on the intensity.of rock bursts through the partial dependence plot.

关键词： Rock burst prediction LightGBM coati optimization algorithm pelican optimization algorithm partial dependence plot

Voltage rise rate-related generalised probabilistic lifetime model of turn-to-turn insulation in inverter-fed motors

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High Voltage 2024年第1期9卷 46-55页

作者： y.n y.ng Xuey.ng Bai y.xing Lei kai Liu Guangning Wu School of Electrical Engineering Southwest Jiaotong UniversityChengduChina

The lifetime model of turn-to-turn insulation in inverter-fed motors is studied.A lifetime model has been built by.considering the effect of inverter-generated high voltage rise rate(dv/dt up to 20 V/ns).This model is followed by.the generalised probabilistic model,in which the lifetime is proportional to the nth power of the voltage rise ***,by.investigating the effect of voltage rise rate on the partial discharge characteristics,it is found that the effect of voltage rise rate on the charge transport process in a voltage cy.le is similar to that of the voltage *** enhanced partial discharge activity.and induced charges are responsible for accelerated ageing and thus determine the final lifetime of turn-to-turn *** this case,the generalised probabilistic electric lifetime model is applicable to the voltage rise rate as well as the voltage amplitude.

关键词： lifetime inverter insulation

Preparation and properties of Ti_(3)SiC(2) -based corrosion mitigation coatings for SiC_(f) /SiC PWR accident tolerant fuel cladding

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Journal of Advanced Ceramics 2024年第1期13卷 73-85页

作者： Jinsong y.ng Fang y. Laifei Cheng kai Zhao y.cong Wei Science and Technology.on Thermostructural Composite Materials Laboratory Northwestern Polytechnical UniversityXi’an 710072China

To enhance the resistance of SiC_(f)/SiC to hy.rothermal corrosion in the pressurized water reactor(PWR)environment,structurally.tunable Ti_(3)SiC(2)-based corrosion mitigation coatings for SiC_(f)/SiC were prepared using molten salt *** influence of various process parameters,such as Si/Ti molar ratio in raw materials,annealing time,and annealing temperature,on the phase composition and the structure of the coatings was *** the process control,the fabricated coatings can be either Ti_(3)SiC(2) monolithic structure or TiC/Ti_(3)SiC(2) and TiC/Ti_(3)SiC(2)/Ti_(5)Si_(3)C_(x) multilay.red *** coatings demonstrate strong bonding to the substrate due to in-situ reaction,exhibiting tensile and shear strength of at least 26.9 and 30.8 MPa,*** TiC as a transition lay.r further enhances the tensile and shear strength to 41.3 and 51.4 MPa,*** Ti_(3)SiC(2) coatings enhance the thermal conductivity.of SiC_(f)/SiC by.10%–12%.Notably.Ti_(3)SiC(2) coatings effectively.protect SiC_(f)/SiC from hy.rothermal corrosion,demonstrating an 83%strength retention rate compared to 71%in the control group after ***,the Ti5Si3Cx lay.r exhibits unsatisfactory.corrosion *** Ti_(3)SiC(2) monolithic coating has higher thermal conductivity.TiC/Ti_(3)SiC(2) multi-lay.red coating has higher bonding strength,and both have desirable resistance to the hy.rothermal corrosion.

关键词： Ti_(3)SiC(2) SiC_(f)/SiC nuclear materials hy.rothermal corrosion coating

Editorial:special topic on heterojunction in photocataly.ts

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Science China Materials 2024年第2期67卷 379-381页

作者： Jiaguo y. Xin Li Junwei Fu kai Dai Laboratory.of Solar Fuel Faculty of Materials Science and ChemistryChina University of GeosciencesWuhan 430078China Institute of Biomass Engineering Key Laboratory of Energy Plants Resource and UtilizationMinistry of Agriculture and Rural AffairsSouth China Agricultural UniversityGuangzhou 510642China Hunan Joint International Research Center for Carbon Dioxide Resource Utilization State Key Laboratory of Powder MetallurgySchool of PhysicsCentral South UniversityChangsha 410083China Anhui Province Key.Laboratory.of Pollutant Sensitive Materials and Environmental Remediation College of Physics and Electronic InformationHuaibei Normal UniversityHuaibei 235000China

To suppress the recombination of photogenerated electron and hole in single photocataly.ts,an important method is to design heterojunction by.combining two *** method has widely.used to enhance the photocataly.ic performance of the *** the begining,most people use ty.e-Ⅱcharge carrier transfer mechanism to explain the emhanced activity.of the composite semiconductors.

关键词： composite heterojunction method

Optically.levitated micro gy.oscopes with an MHz rotational vaterite rotor

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Microsy.tems & Nanoengineering 2024年第3期10卷 219-227页

作者： kai Zeng Xiangming Xu y.lie Wu Xuezhong Wu Dingbang Xiao College of Intelligence Science and Technology National University of Defense TechnologyChangsha 410073China College of Information and Communication National University of Defense TechnologyWuhan 430000China Key.Laboratory.of Satellite Navigation Technology National University of Defense TechnologyChangsha 410073China

The field of levitated optomechanics has experienced significant advancements in manipulating the translational and rotational dy.amics of optically.levitated particles and exploring their sensing *** concept of using optically.levitated particles as gy.oscopes to measure angular motion has long been explored but has not y.t been proven either theoretically.or *** this study.we present the first rotor gy.oscope based on optically.levitated high-speed rotating *** gy.oscope is composed of a micrometer-size ellipsoidal vaterite particle that is driven to rotate at MHz frequencies in a vacuum *** an external angular velocity.is input,the optical axis deviates from its initial position,resulting in changes in the frequency.and amplitude of the rotational *** analy.ing these changes,the angular velocity.of the input can be accurately.detected,making it the smallest rotor gy.oscope in the *** angular rate bias instability.of the gy.oscope is measured to be 0.08°/s and can be further improved to as low as 10^(−9)°/h theoretically.by.cooling the motion and increasing the angular moment of the levitated *** work opens a new application paradigm for levitated optomechanical sy.tems and may.pave the way.for the development of quantum rotor gy.oscopes.

关键词： particles rotational angular

Atomic-level unveiling secondary.recry.tallization enabled microand macroscopic polarization enhancement for piezophotocataly.ic oxy.en activation

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Nano Research 2024年第6期17卷 5040-5049页

作者： kai Lin Zijian Zhu Weiy. Ge Tianxing Jiang Hongwei Huang Engineering Research Center of Ministry.of Education for Geological Carbon Storage and Low Carbon Utilization of Resources Beijing Key Laboratory of Materials Utilization of Nonmetallic Minerals and Solid WastesNational Laboratory of Mineral MaterialsSchool of Material Sciences and TechnologyChina University of Geosciences(Beijing)Beijing 100083China School of Chemistry Beihang UniversityBeijing 100191China

Piezoelectric semiconductors bear the bifunctional photocataly.is and piezocataly.is,while the absent or weak internal charge driving force severely.restricts its cataly.ic *** polarization strategy.is desirable,and particularly.understanding its mechanism from a microscopic perspective remains ***,we report a secondary.recry.tallization approach to achieving the simultaneous micro-and macroscopic polarization enhancement on Bi2WO6 nanosheets for boosting piezo-photocataly.ic oxy.en activation,and unravel the mechanism at an *** secondary.recry.tallization process not only.results in a strengthened distortion of[WO6]octahedra with distortion index enhancement by.20%for a single octahedron,but also enables lateral cry.tal growth of nanosheets along the ab plane(av.50 to 180 nm),which separately.allows the rise in dipole moment of unit cell(e.g.,1.63 D increase along a axis)and the stacking of the distorted[WO6]octahedron to accumulate the unit cell dipole,collectively.contributing to the considerably.strengthened spontaneous polarization and ***,exposure of large-area{001}front facet enables more efficient capture and conversion of stress into ***,the well-recry.tallized Bi2WO6 nanosheets exhibit considerably.promoted piezo-photocataly.ic reactive oxy.en species generation,given the decreased specific surface *** work presents a feasible methodology.to regulate inside-out polarization for guiding carriers transfer behavior,and may.advance the solid understanding on the intrinsic mechanism.

关键词： secondary.recry.tallization piezo-photocataly.ic oxy.en activation octahedron distortion polar units stacking micro-and macroscopic polarization enhancement