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Investigation of flow characteristics in a rotor-stator cavity under crossflow using wall-modelled large-eddy simulation

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Journal of Zhejiang University-Science A(Applied Physics & Engineering) 2023年第6期24卷 473-496页

作者： Lei Xie Qiang DU Guang LIU Zengyan LIAN Yaguang xie Yifu LUO Key Lab of Light-duty Gas-turbine Institute of Engineering ThermophysicsChinese Academy of SciencesBeijing 100190China University of Chinese Academy of Sciences Beijing 100049China Innovation Academy for Light-duty Gas Turbine Chinese Academy of SciencesBeijing 100190China

Rotor-stator cavities are frequently encountered in engineering applications such as gas turbine engines.They are usually subject to an external hot mainstream crossflow which in general is highly swirled under the effect of the nozzle guide vanes.To avoid hot mainstream gas ingress,the cavity is usually purged by a stream of sealing flow.The interactions between the external crossflow,cavity flow,and sealing flow are complicated and involve all scales of turbulent unsteadiness and flow instability which are beyond the resolution of the Reynolds-average approach.To cope with such a complex issue,a wall-modeled large-eddy simulation(WMLES)approach is adopted in this study.In the simulation,a 20°sector model is used and subjected to a uniform pre-swirled external crossflow and a stream of radial sealing flow.It is triggered by a convergent Reynoldsaveraged Navier-Stokes(RANS)result in which the shear stress transport(SST)turbulent model is used.In the WMLES simulation,the Smagoringsky sub-grid scale(SGS)model is applied.A scalar transportation equation is solved to simulate the blending and transportation process in the cavity.The overall flow field characteristics and deviation between RANS and WMLES results are discussed first.Both RANS and WMLES results show a Batchelor flow mode,while distinct deviation is also observed.Deviations in the small-radius region are caused by the insufficiency of the RANS approach in capturing the small-scale vortex structures in the boundary layer while deviations in the large-radius region are caused by the insufficiency of the RANS approach in predicting the external crossflow ingestion.The boundary layer vortex and external ingestion are then discussed in detail,highlighting the related flow instabilities.Finally,the large-flow structures induced by external flow ingress are analyzed using unsteady pressure oscillation signals.

关键词： Wall-modeled large-eddy simulation(WMLES) Rotor-stator cavity Flow instability Reynolds-averaged Navier-Stokes(RANS)

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Optimizing the Perceptual Quality of Time-Domain Speech Enhancement with Reinforcement Learning

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Tsinghua Science and Technology 2022年第6期27卷 939-947页

作者： Xiang Hao Chenglin Xu Lei Xie Haizhou Li School of Computer Science Northwestern Polytechnical UniversityXi'an 710000China Department of Electrical and Computer Engineering National University of SingaporeSingapore 710129Singapore

In neural speech enhancement,a mismatch exists between the training objective,i.e.,Mean-Square Error(MSE),and perceptual quality evaluation metrics,i.e.,perceptual evaluation of speech quality and short-time objective intelligibility.We propose a novel reinforcement learning algorithm and network architecture,which incorporate a non-differentiable perceptual quality evaluation metric into the objective function using a dynamic filter module.Unlike the traditional dynamic filter implementation that directly generates a convolution kernel,we use a filter generation agent to predict the probability density function of a multivariate Gaussian distribution,from which we sample the convolution kernel.Experimental results show that the proposed reinforcement learning method clearly improves the perceptual quality over other supervised learning methods with the MSE objective function.

关键词： speech enhancement neural networks dynamic filter reinforcement learning

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Polyhedral Feasible Set Computation of MPC-Based Optimal Control Problems

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IEEE/CAA Journal of Automatica Sinica 2018年第4期5卷 765-770页

作者： Lantao xie Lei Xie Hongye Su Jingdai Wang State Key Laboratory of Industrial Control Technology Institute of Cyber-Systems and ControlZhejiang UniversityHangzhou 310027China College of Chemical and Biological Engineering Zhejiang UniversityHangzhou 310027China IEEE

Feasible sets play an important role in model predictive control(MPC) optimal control problems(OCPs). This paper proposes a multi-parametric programming-based algorithm to compute the feasible set for OCP derived from MPC-based algorithms involving both spectrahedron(represented by linear matrix inequalities) and polyhedral(represented by a set of inequalities) constraints. According to the geometrical meaning of the inner product of vectors, the maximum length of the projection vector from the feasible set to a unit spherical coordinates vector is computed and the optimal solution has been proved to be one of the vertices of the feasible set. After computing the vertices,the convex hull of these vertices is determined which equals the feasible set. The simulation results show that the proposed method is especially efficient for low dimensional feasible set computation and avoids the non-unicity problem of optimizers as well as the memory consumption problem that encountered by projection algorithms.

关键词： Feasible set computation linear matrix inequalities(LMIs) model predictive control(MPC) polyhedron

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Improved Plasticity of Fe_(25)Co_(25)Ni_(25)(Si_(0.3)B_(0.7))_(25) High Entropy Bulk Metallic Glass through the Addition of Cu

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Acta Metallurgica Sinica(English Letters) 2023年第3期36卷 417-425页

作者： Xueru Fan Lei Xie Qiang Li Chuntao Chang Hongxiang Li School of Physics Science and Technology Xinjiang UniversityUrumqi 830046China School of Mechanical Engineering Dongguan University of TechnologyDongguan 523808China State Key Laboratory for Advanced Metals and Materials University of Science and Technology BeijingBeijing 100083China

This work was focused on enhancement in the plasticity of Fe_(25)Co_(25)Ni_(25)(Si_(0.3)B_(0.7))_(25) high entropy bulk metallic glass(HE-BMG)by adding minor Cu(0–1.2,in at.%).It is found that the appropriate addition of Cu can efficiently improve the plasticity of the present HE-BMG while the excessive addition of Cu will deteriorate again the plasticity,and especially,the plastic strain of the present HE-BMG is improved from 0.8%for the Cu-free alloy to 4.7%for the 0.3 at.%Cu-added alloy.The transmission electron microscopy observation shows that there are manyα-Fe(Co,Ni)clusters with sizes of less than 5 nm dispersed in the glassy matrix in the 0.3 and 0.6 at.%Cu-added alloys,which may account for the significant improvement in the plasticity of the two alloys,and further increase in Cu content more than 0.9 at.%leads to the precipitation ofα-Fe(Co,Ni)and Fe(Co,Ni)B compound grains with diameters of tens of nanometers,in which the plasticity of the present HE-BMGs has deteriorated rapidly.

关键词： High entropy alloys Bulk metallic glasses Glass forming ability Nano-crystallization Plasticity Microstructure

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Antibacterial hydrogel with pH-responsive microcarriers of slow-release VEGF for bacterial infected wounds repair

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Journal of Materials Science & Technology 2023年第13期144卷 198-212页

作者： Xiaofei xie Huan lei Daidi Fan Shaanxi Key Laboratory of Degradable Biomedical Materials School of Chemical EngineeringNorthwest UniversityXi’an 710069China Shaanxi R&D Center of Biomaterials and Fermentation Engineering School of Chemical EngineeringNorthwest UniversityXi’an 710069China Biotech.&Biomed.Research Institute Northwest UniversityXi’an 710069China

Bacterial infection causes wound inflammation and makes angiogenesis difficult.It is urgent to develop effectively antibacterial and pro-vascularizing dressings for wound healing.The hydrogel is developed with pH-responsive drug-releasing microcarriers which were loaded with vascular endothelial growth factor(VEGF)that promotes angiogenesis and actively respond to wound pH for control and prolong VEGF release.The surfaces of the microcarriers were coated with polydopamine which can reduce the silver nanoparticles(AgNPs)in situ,and dynamically crosslink with the polyacrylamide,which forms a stable slow-release system with different release behavior for the VEGF and AgNPs.The hydrogel inhib-ited bacterial formation and accelerated wound healing.With the hydrogel dressing,83.3%±4.29%of the wound heals at day 7,which is 40.9%±8.5%higher than the non-treatment group in defect infected model.The antibacterial properties of hydrogel down-regulate early inflammation-related cytokines,and the release of VEGF in the middle and late phases of wound healing in response to pH changes pro-motes angiogenesis and up-regulate the expression of angiogenesis-associated cytokine.The sequential release of antibacterial agents and pro-vascularizing agents in response to the change in wound microen-vironmental cues facilitate temporally controlled therapy that suites the need of different wound healing phases.Collectively,the hydrogel loaded with multifunctional microcarriers that enable controlled release of AgNPs and VEGF is an effective system for treating infected wounds.

关键词： Antibacterial pH-responsive microcarriers Slow-release Infected wound repair

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Progress and prospect of Pt-based catalysts for electrocatalytic hydrogen oxidation reactions

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Nano Research 2024年第3期17卷 960-981页

作者： Xu Zhang Ying xie lei Wang Key Laboratory of Functional Inorganic Material Chemistry Ministry of Education of the People’s Republic of ChinaHeilongjiang UniversityHarbin 150080China

To achieve the goals of the peak carbon dioxide emissions and carbon neutral,the development and utilization of sustainable clean energy are extremely important.Hydrogen fuel cells are an important system for converting hydrogen energy into electrical energy.However,the slow hydrogen oxidation reaction(HOR)kinetics under alkaline conditions has limited its development.Therefore,elucidating the catalytic mechanism of HOR in acidic and alkaline media is of great significance for the construction of highly active and stable catalysts.In terms of practicality,Pt is still the primary choice for commercialization of fuel cells.On the above basis,we first introduced the hydrogen binding energy theory and bifunctional theory used to describe the HOR activity,as well as the pH dependence.After that,the rational design strategies of Pt-based HOR catalysts were systematically classified and summarized from the perspective of activity descriptors.In addition,we further emphasized the importance of theoretical simulations and in situ characterization in revealing the HOR mechanism,which is crucial for the rational design of catalysts.Moreover,the practical application of Pt-based HOR catalysts in fuel cells was also presented.In closing,the current challenges and future development directions of HOR catalysts were discussed.This review will provide a deep understanding for exploring the mechanism of highly efficient HOR catalysts and the development of fuel cells.

关键词： Pt-based catalysts hydrogen oxidation reaction(HOR) electrocatalytic mechanism hydrogen binding energy theory bifunctional theory

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Rail pressure controller design of GDI basing on predictive functional control

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Control Theory and Technology 2019年第2期17卷 176-182页

作者： Zhiming ZHANG Lei Xie Hongye SU State Key Laboratory of Industrial Control Technology Zhejiang UniversityHangzhou Zhejiang 310027China

Gasoline direct injection(GDI)is a pivotal technique for a highly efficient engine.However,how to maintain a stable rail pressure which offers good fuel economy and low emissions,is still a challengeable work.In this paper,a rail pressure controller is designed basing on predictive functional control(PFC),a model predictive control(MPC)method,to surmount the nonlinearity and disc on tinuity brought by the common rail pressure system(CRPS).A control-oriented piecewise linear model is prese nted to simplify the CRPS.The simulation results on a benchmark show that rail pressure tracks the setpoint accurately even with some perturbations.Profiting from the conciseness of PFC algorithm,the controller can compute the online solution in a short time,which makes it possible to realize the strategy on a fast response system.

关键词： Rail pressure control model based predictive control predictive functional control

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Novel E2E-QoE Metric for PHY Optimization:A Cross-Layered Framework

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China Communications 2023年第4期20卷 167-179页

作者： lei Ji Hao Wang Hongxiang xie Huawei No.156.Beiqing RoadHaidian DistrictBeijing 100095China

Existing systems use key performance indicators(KPIs)as metrics for physical layer(PHY)optimization,which suffers from the problem of overoptimization,because some unnecessary PHY enhancements are imperceptible to terminal users and thus induce additional cost and energy waste.Therefore,it is necessary to utilize directly the quality of experience(QoE)of user as a metric of optimization,which can achieve the global optimum of QoE under cost and energy constraints.However,QoE is still a metric of application layer that cannot be easily used to design and optimize the PHY.To address this problem,we in this paper propose a novel end-to-end QoE(E2E-QoE)based optimization architecture at the user-side for the first time.Specifically,a cross-layer parameterized model is proposed to establish the relationship between PHY and E2E-QoE.Based on this,an E2E-QoE oriented PHY anomaly diagnosis method is further designed to locate the time and root cause of anomalies.Finally,we investigate to optimize the PHY algorithm directly based on the E2E-QoE.The proposed frameworks and algorithms are all validated using the data from real fifth-generation(5G)mobile system,which show that using E2E-QoE as the metric of PHY optimization is feasible and can outperform existing schemes.

关键词： quality of experience(QoE) performance metric physical layer optimization cross-layer framework

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Comparison between Minimally Invasive Transforaminal Lumbar Interbody Fusion and Conventional Open Transforaminal Lumbar Interbody Fusion： An Updated Meta-analysis

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Chinese Medical Journal 2016年第16期129卷 1969-1986页

作者： Lei Xie Wen-Jian Wu Yu Liang Department of Orthopedics Ruijin Hospital Shanghai Jiao Tong University School of Medicine Shanghai 200025 China Shanghai Key Laboratory for Prevention and Treatment of Bone and Joint Diseases with Integrated Chinese-Western Medicine Shanghai Institute of Traumatology and Orthopedics Ruijin Hospital Shanghai Jiao Tong University School of Medicine Shanghai 200025 China

Background： The previous studies agree that minimally invasive transforaminal lumbar interbody fusion （MIS-TLIF） has better function outcomes, less blood loss, and shorter hospital stay, when compared to open-TLIF. However, there are no significance differences on operative time, complication, and reoperation rate between the two procedures. This could be from less relative literatures and lower grade evidence. The further meta-analysis is needed with more and higher grade evidences to compare the above two TLIF procedures. Methods： Prospective and retrospective studies that compared open-TLIF and MIS-TLIF were identified by searching the Medline, Embase, Web of Science, China National Knowledge Infrastructure, Wanfang, and VIP database （the literature search comprised Medical Subject Heading terms and key words or Emtree term）. The retrieval time ranged from the date when the database was founded to January 2015. Pooled risk ratios （RRs） and weighted mean differences （WMDs） with 95% confidence intervals were calculated for the clinical outcomes and perioperative data. Results： Twenty-four studies （n =1967 patients） were included in this review （n =951, open-TLIF, n 1016, MIS-TLIF）. MIS-TLIF was associated with a significant decrease in the visual analog score （VAS）-back pain score （WMD 0.44; P= 0.001）, Oswestry Disabilities Index （WMD 1.57; P =0.005）, early ambulation （WMD = -1.77; P = 0.0001）, less blood loss （WMD = -265.59; P 〈 0.00001）, and a shorter hospital stay （WMD =-1.89; P 〈 0.0001）. However, there were no significant differences in the fusion rate （RR =0.99; P = 0.34）, VAS-leg pain （WMD = -0.10; P = 0.26）, complication rate （RR = 0.84; P = 0.35）, operation time （WMD = 5.23; P = 0.82）, or reoperation rate （RR = 0.73; P = 0.32）. Conclusions： MIS-TLIF resulted in a similar fusion rate with better functional outcome, less blood loss, shorter ambulation, and hospital stay; furthermore, it did not increase the complication or reoperation rate based on the existing evidence.

关键词： Clinical Outcomes Meta-analysis Minimally lnvasive Surgery Transforaminal Lumbar Interbody Fusion

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Investigation on effect of drag models on flow behavior of power-law fluid–solid two-phase flow in fluidized bed

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Particuology 2022年第11期70卷 43-54页

作者： Zihan Yuan Shuyan Wang Baoli Shao Lei Xie Yujia Chen Yimei Ma Key Laboratory of Enhanced Oil Recovery of Ministry of Education School of Petroleum EngineeringNortheast Petroleum UniversityDaqing 163318China

In this study,a Eulerian-Eulerian two-fluid model combined with the kinetic theory of granular flow is adopted to simulate power-law fluid–solid two-phase flow in the fluidized bed.Two new power-law liquid–solid drag models are proposed based on the rheological equation of power-law fluid and pressure drop.One called model A is a modified drag model considering tortuosity of flow channel and ratio of the throat to pore,and the other called model B is a blending drag model combining drag coefficients of high and low particle concentrations.Predictions are compared with experimental data measured by Lali et al.,where the computed porosities from model B are closer to the measured data than other models.Furthermore,the predicted pressure drop rises as liquid velocity increases,while it decreases with the increase of particle size.Simulation results indicate that the increases of consistency coefficient and flow behavior index lead to the decrease of drag coefficient,and particle concentration,granular temperature,granular pressure,and granular viscosity go down accordingly.

关键词： Power-law liquid-solid drag models Power-law fluid Liquid-solid two-phase flow Eulerian-Eulerian two-fluid model

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