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Decidability of linearizabilities for relaxed data structures

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Science China(Information Sciences) 2018年第1期61卷 113-122页

作者： Chao WANG Yi lv Peng WU State Key Laboratory of Computer Science Institute of Software Chinese Academy of Sciences University of Chinese Academy of Sciences

Many recent implementations of concurrent data structures relaxed their linearizability requirements for better performance and scalability. Quasi-linearizability, k-linearizability and regular-relaxed linearizability are three quantitative relaxation variants of linearizability that have been proposed as correctness conditions of relaxed data structures, yet preserving the intuition of linearizability. Quasi-linearizability has been proved undecidable. In this paper, we first show that k-linearizability is undecidable for a bounded number of processes, by reducing quasi-linearizability into it. We then show that regular-relaxed linearizability is decidable for a bounded number of processes. We also find that the number of the states of a relaxed specification is exponential to the number of the states of the underlying specification automaton(representing its relaxation strategy), and polynomial to the number of the states of the underlying quantitative sequential specification and the number of operations.

关键词： concurrent data structures quantitative relaxation linearizability decidability finite automata

Effects of hypoxia on the biological behavior of MSCs seeded in demineralized bone scaffolds with different stiffness

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Acta Mechanica Sinica 2019年第2期35卷 309-320页

作者： Yuanyuan Sun Guobao Chen Yonggang lv Key Laboratory of Biorheological Science and Technology (Chongqing University) Ministry of Education Bioengineering College Chongqing University Chongqing 400044 China Mechanobiology and Regenerative Medicine Laboratory Bioengineering College Chongqing University Chongqing 400044 China

Matrix stiffness has been demonstrated in many studies to adjust the biological behaviors of mesenchymal stem cells (MSCs). However, in the initial phase of bone restore, MSCs will encounter a hypoxic microenvironment. Studying the connection existing between the matrix stiffness and biological behavior of MSCs under hypoxic condition can better simulate the microenvironment at the prime period of bone repairment. In this work, three-dimensional (3D) decalcified bone scaffolds with diverse stiffness (high stiffness (66.06 ± 27.83) MPa, medium stiffness (26.90 ± 13.16) MPa, and low stiffness (0.67 ± 0.14) MPa) but same microstructure have been prepared by controlling decalcification time. In addition, the decellularized bone scaffold was regard as control group and its stiffness was (230.93 ± 72.65) MPa. The viability, proliferation, infiltration, and osteogenic differentiation of MSCs seeded into these 3D demineralized bone scaffolds were systematically investigated under 100 μM CoCl2-simulated hypoxic and normoxic environments. The results showed that the viability, proliferation, and extracellular matrix (ECM) secretion of MSCs had no significant difference on scaffolds with diverse stiffness but the degree of collagen deposition of MSCs gradually increased with the increase of scaffold stiffness both under normoxia and hypoxia. Compared to normoxia, the viability, proliferation, ECM secretion, vascular endothelial growth factor (VEGF) expression, and osteogenis of MSCs on the scaffolds with the same stiffness were evidently inhibited by hypoxia. Additionally, under hypoxic condition, the expression of VEGF and hypoxia inducible factor 1α(HIF-1α) in MSCs on the low stiffness scaffold was markedly increased comparing to those on other groups. In summary, we found that the low stiffness scaffold can improved the proliferation and osteoginic differentiation of MSCs under hypoxic environment, which may help to explore efficient methods for bone defect repairing.

关键词： Mesenchymal stem cells Hypoxia Matrix stiffness Demineralized bone scaffold Osteogenic differentiation

Event-triggered sliding mode control of linear repetitive processes and its application in metal rolling process

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Science China(Information Sciences) 2024年第3期67卷 167-181页

作者： Xinyu lv Yugang NIU James LAM Key Laboratory of Smart Manufacturing in Energy Chemical Process (East China University of Science and Technology) Ministry of Education Department of Mechanical Engineering The University of Hong Kong

This paper investigates the design problem of a sliding mode controller for linear repetitive processes(LRPs) with a finite pass length on each pass. Under limited communication resources, an eventtriggered mechanism is implemented from the sensors to the controller, whose triggered sequence is consistent with the evolution direction of LRPs. To periodically orchestrate communication between the controller and actuator, a round-robin scheduling mechanism is established based on the pass length. A sliding function involving the state and pass profile is constructed, and the sliding mode controller is designed using triggered states and pass profile signals. Feasible controller gains are attained to ensure the stability of the resultant closed-loop system. Finally, the proposed strategy is implemented for a multi-roll metal rolling process.

关键词： event-triggered mechanism linear repetitive processes metal rolling process round-robin scheduling sliding mode control

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Photocatalytic degradation of perfluorooctanoic acid with β-Ga_2O_3 in anoxic aqueous solution

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Journal of Environmental Sciences 2012年第4期24卷 774-780页

作者： Baoxiu Zhao Mou lv Li Zhou School of Environmental and Municipal Engineering Qingdao Technological UniversityQingdao 266033China State Key Joint Laboratory of Environment Simulation and Pollution Control Department of Environmental Science and EngineeringTsinghua UniversityBeijing 100084China

Perfluorooctanoic acid （PFOA） is a new-found hazardous persistent organic pollutant, and it is resistant to decomposition by hydroxyl radical （HO.） due to its stable chemical structure and the high electronegativity of fluorine. Photocatalytic reduction of PFOA with β-Ga2O3 in anoxic aqueous solution was investigated for the first time, and the results showed that the photoinduced electron （ecb） coming from the β-Ga2O3 conduction band was the major degradation substance for PFOA, and shorter-chain perfluorinated carboxylic acids （PFCAs, CnF2n＋1COOH, 1 ≤ n ≤ 6） were the dominant products. Furthermore, the concentration of F- was measured by the IC technique and defluorination efficiency was calculated. After 3 hr, the photocatalytic degradation efficiency was 98.8% and defluorination efficiency was 31.6% in the presence of thiosulfate and bubbling N2. The degradation reaction followed first-order kinetics （k = 0.0239 min-1, t1/2 = 0.48 hr）. PFCAs （CnF2n＋xCOOH, 1 ≤ n≤ 7） were detected and measured by LC-MS and LC-MS/MS methods. It was deduced that the probable photocatalytic degradation mechanism involves ec-b attacking the carboxyl of CnF2n＋1COOH, resulting in decarboxylation and the generation of CnFzn＋1. The produced CnF2n＋1 reacted with H2O, forming CnF2n＋1OH, then CnF2n＋1OH underwent HF loss and hydrolysis to form CnF2,＋1COOH.

关键词： perfluorooctanoic acid β-Ga2O3 photocatalytic degradation defluorination photoinduced electron

Influence of confi ning pressure and impact loading on mechanical properties of amphibolite and sericite-quartz schist

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Earthquake Engineering and Engineering Vibration 2014年第2期13卷 215-222页

作者： Liu Shi Xu Jinyu lv Xiaocong Department of Airfi eld and Building Engineering Air Force Engineering University College of Mechanics and Civil Architecture Northwest Polytechnic University

In order to investigate the dynamic mechanical properties of amphibolite and sericite-quartz schist under confi ning pressure, two rocks are subjected to impact loadings with different strain rates and confi ning pressures by using split Hopkinson pressure bar equipment with a confi ning pressure device. Based on the experimental results, the stress-strain curves are analyzed and the effects of confi ning pressure and strain rates on the dynamic compressive strength, peak strain and failure mode are summarized. The results show that:(1) The characteristics of two rocks in the ascent stage of the stressstrain curve are basically the same, but in the descent stage, the rocks gradually show plastic deformation characteristics as the confi ning pressure increases.(2) The dynamic compressive strength and peak strain of two rocks increase as the strain rate increases and the confi ning pressure effects are obvious.(3) Due to the effect of confi ning pressure, the normal stress on the damage surface of the rock increases correspondingly, the bearing capacity of the crack friction exceeds the material cohesion and the slippage of the fractured rock is controlled, which all lead to the compression and shear failure mode of rock. The theoretical analysis and experimental methods to study the dynamic failure mode and other related characteristics of rock are useful in developing standards for engineering practice.

关键词： rock mechanics SHPB with confi ning pressure device confi ning pressure strain rate impact loading

Characterization of N-nitrosodimethylamine formation from the ozonation of ranitidine

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Journal of Environmental Sciences 2017年第8期29卷 116-126页

作者： Juan lv Lin Wang Yongmei Li School of Environment and Architecture University of Shanghai for Science and Technology State Key Laboratory of Pollution Control and Resource Reuse College of Environmental Science and EngineeringTongji University

N-nitrosodimethylamine（NDMA） is an emerging disinfection by-product which is formed during water disinfection in the presence of amine-based precursors. Ranitidine, as one kind of amine-based pharmaceuticals, has been identified as NDMA precursor with high NDMA molar conversion during chloramination. This study focused on the characterization of NDMA formation during ozonation of ranitidine. Influences of operational variables（ozone dose, pH value） and water matrix on NDMA generation as well as ranitidine degradation were evaluated. The results indicate high reactivity of ranitidine with ***（DMA） and NDMA were generated due to ranitidine oxidation. High pH value caused more NDMA accumulation. NDMA formation was inhibited under acid conditions（pH ≤ 5） mainly due to the protonation of amines. Water matrix such as HCO-3and humic acid impacted NDMA generation due to UOH scavenging. Compared with UOH,ozone molecules dominated the productions of DMA and NDMA. However, UOH was a critical factor in NDMA degradation. Transformation products of ranitidine during ozonation were identified using gas chromatography–mass spectrometry. Among these products, just DMA and N,N-dimethylformamide could contribute to NDMA formation due to the DMA group in the molecular structures. The NDMA formation pathway from ranitidine ozonation was also proposed.

关键词： Ranitidine N-nitrosodimethylamine(NDMA) Ozone Influencing factor NDMA formation pathway

Structure-aware fusion network for 3D scene understanding

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Chinese Journal of Aeronautics 2022年第5期35卷 194-203页

作者： Haibin YAN Yating lv Venice Erin LIONG School of Automation Beijing University of Posts and TelecommunicationsBeijing 100876China Interdisciplinary Graduate School Nanyang Technological UniversitySingapore 639798Singapore

In this paper,we propose a Structure-Aware Fusion Network(SAFNet)for 3D scene *** 2D images present more detailed information while 3D point clouds convey more geometric information,fusing the two complementary data can improve the discriminative ability of the *** is a very challenging task since 2D and 3D data are essentially different and show different *** existing methods first extract 2D multi-view image features and then aggregate them into sparse 3D point clouds and achieve superior ***,the existing methods ignore the structural relations between pixels and point clouds and directly fuse the two modals of data without *** address this,we propose a structural deep metric learning method on pixels and points to explore the relations and further utilize them to adaptively map the images and point clouds into a common canonical space for *** experiments on the widely used ScanNetV2 and S3DIS datasets verify the performance of the proposed SAFNet.

关键词： 3D point clouds Data fusion Structure-aware 3D scene understanding Deep metric learning

Numerical simulation of sedimentation of rectangular particle in Newtonian fluid

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Particuology 2012年第1期10卷 79-88页

作者： Hong lv Shengli Tang Wenping Zhou Department of Power Engineering Chongqing University Chongqing 400030 PR China

The sedimentation of a rectangular particle falling in a two-dimensional channel filled with Newtonian fluid was simulated with finite element arbitrary Lagrangian-Eulerian domain method. The numerical procedure was validated by comparison of the simulation results with existing numerical work. Morea over, good agreement was obtained between the simulation results and experimental measurements performed in the current study. The equilibrium position, stable orientation and drag coefficient ofa rect- angular particle for different particle Reynolds numbers （Rep） were studied. The results show that there is a critical particle Reynolds number for the preferred orientation of a rectangular particle falling in a Newtonian fluid. When Rep is smaller than the critical value, the particle fails with its long side parallel to gravity; otherwise the particle fails with its long side perpendicular to gravity. The critical particle Reynolds number is a decreasing function of the blockage ratio and aspect ratio. The distributions of pressure and shear stress on rectangular particle surface were analyzed. Moreover, the drag coefficient of the rectangular particle decreases as Rep or the blockage ratio increases; however, it appears to be independent of aspect ratio.

关键词： Rectangular particleDrag coefficientSedimentationALE methodDirect numerical simulation

Analysis of pressure characteristics under laminar and turbulent flow states inside the pilot stage of a deflection flapper servo-valve:Mathematical modeling with CFD study and experimental validation

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Chinese Journal of Aeronautics 2020年第3期33卷 1107-1118页

作者： Bijan Krishna SAHA Songjing LI Xinbei lv Department of Fluid Control and Automation Harbin Institute of TechnologyHarbin 150001China

Electro-hydraulic servo-valves are widely used components in the mechanical industry,aerospace and aerodynamic devices which precisely control the airplane or missile *** to the small size and complex structure in the pilot stage of deflection flapper servo-valves,accurate mathematical models for the flow and pressure characteristics have always been very difficult to be *** this paper,mathematical models for the pilot stage of deflection flapper servo-valve are investigated to overcome some gaps between the theoretical formulation and overall performance of the valve by considering different flow ***,a mathematical model of the velocity distribution at the flapper groove exit is established by using Schlichting velocity equations for incompressible laminar fluid ***,when the flow becomes turbulent,a mathematical model of pressure characteristics in the receiving ports is built on the basis of the assumption of the collision between the liquid and the jet as the impact of the jet on a moving block of fluid *** verify the analytical models for both laminar and turbulent flows,the pressure characteristics of the deflection flapper pilot stage are calculated and tested by using numerical simulation and *** verification of the theory is also *** computed numerical and analytical results show a good agreement with experimental data.

关键词： Computational fluid dynamics(CFD) Deflection flapper servovalve Laminar flow Pressure characteristics Servo-valve Turbulent submerged jet