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VGQ-Vor： extending virtual grid quadtree with Voronoi diagram for mobile k nearest neighbor queries over mobile objects

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Frontiers of Computer Science 2013年第1期7卷 44-54页

作者： Botao WANG Jingwei QU Xiaosong WANG Guoren WANG Masaru KITSUREGAWA Department of Information Science and Engineering Northeastern University Shenyang 110004 China Institute of Industrial Science the University of Tokyo Tokyo 153-8505 Japan

Performing mobile k nearest neighbor （MkNN） queries whilst also being mobile is a challenging problem. All the mobile objects issuing queries and/or being queried are mobile. The performance of this kind of query relies heav- ily on the maintenance of the current locations of the objects. The index used for mobile objects must support efficient up- date operations and efficient query handling. This study aims to improve the performance of the MkNN queries while re- ducing update costs. Our approach is based on an observa- tion that the frequency of one region changing between being occupied or not by mobile objects is much lower than the frequency of the position changes reported by the mobile ob- jects. We first propose an virtual grid quadtree with Voronoi diagram （VGQ-Vor）, which is a two-layer index structure that indexes regions occupied by mobile objects in a quadtree and builds a Voronoi diagram of the regions. Then we propose a moving k nearest neighbor （kNN） query algorithm on the VGQ-Vor and prove the correctness of the algorithm. The ex- perimental results show that the VGQ-Vor outperforms the existing techniques （Bx-tree, Bdual-tree） by one to three or- ders of magnitude in most cases.

关键词： location based services mobile k nearest neigh- bor query mobile object index Voronoi diagram

Evaluation of high-temperature tensile behavior for metal foils by a novel resistance heating assisted tensile testing system using samples with optimized structures

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Journal of Materials Science & Technology 2021年第35期94卷 216-229页

作者： Qiu Zheng Tsuyoshi Furushima Department of Mechanical and Biofunctional Systems Institute of Industrial ScienceThe University of Tokyo4-6-1 KomabaMeguro 153-8505TokyoJapan

To evaluate the tensile behavior of metal foils by resistance heating(RH)assisted tensile testing system accurately,this study proposed to embed a digital image correlation(DIC)system with laser speckles for the measurement of full-field strain ***,the sample structures were optimized to achieve uniform temperature and strain *** infrared camera was used to monitor the temperature *** samples instead of dog-bone shaped samples were proposed.A model for calculating the temperature distribution was established to optimize the sample *** parameters that influence the temperature distribution and tensile behavior were *** results,compared to the strain measured by a non-contact extensometer,the maximum deviation of the strain measured by DIC was less than 6%when the nominal strain was larger than *** is confirmed that the proposed tensile testing system is reliable for measuring the temperature and full-field strain *** shape influenced temperature distributions of smaller samples while it almost had no influence on the temperature distributions of larger *** temperature difference was not affected by the material type but by the sample *** proposed rectangular shape was validated to be feasible for RH assisted tensile *** sample length was successfully optimized for a more uniform temperature distribution by the established *** the tensile deformation was not influenced by the sample shape,the temperature distribution resulted in a non-uniform strain distribution before achieving ultimate tensile *** effective sample length between two clamping jigs contributed to a more uniform temperature distribution and material deformation.A more accurate evaluation of high-temperature tensile behavior for metal foils can be achieved by the proposed RH assisted tensile testing system using rectangular samples with an optimized structure.

关键词： High temperature Metal foil Resistance heating Sample structure Tensile behavior

Effect of microstructure on outer surface roughening of magnesium alloy tubes in die-less mandrel drawing

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Journal of Magnesium and Alloys 2022年第10期10卷 2730-2744页

作者： Takuma Kishimoto Peihua Du Tsuyoshi Furushima Department of Mechanical and Biofunctional Systems Institute of Industrial ScienceThe University of Tokyo4-6-1 KomabaMeguroTokyo 153-8505Japan

The crystal orientation and outer surface roughening of magnesium alloy tubes were evaluated to clarify the effect of the mandrel on the microstructure and outer surface roughness in die-less mandrel drawing. Locally heated ZM21 tubes with an outer diameter of 6.0 mm and an inner diameter of 3.8 mm were drawn with and without a mandrel. The outer surface roughness and crystal orientation were evaluated in the same measurement area. The results indicated that the outer surface becomes rougher in the die-less mandrel drawing than in die-less drawing for a given outer circumferential strain. The outer surface roughness developed when there was large difference in the pyramidal slip system Schmid factor. Therefore, the slip deformation of the pyramidal slip system seems to be mainly responsible for the outer surface roughening in the die-less mandrel drawing. Furthermore, the crystal grain with the {2110} crystal plane vertical to the normal direction of outer surface had a larger Schmid factor than the other crystal grains. The large number of crystal grains with the {2110} crystal plane in the die-less mandrel drawing is one of the reasons that the outer surface roughness develops more in the die-less mandrel drawing than in die-less drawing for a given outer circumferential strain. These results will contribute significantly to the development of fabrication process of the microtube with high surface quality, which prevents rapid corrosion of biomedical applications.

关键词： Tube forming Die-less drawing Surface roughness Crystal plasticity Magnesium alloy Electron backscatter diffraction

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智能网联汽车多目标预测优化换道决策方法

同济大学学报（自然科学版） 2024年第7期52卷 1109-1117页

作者：程硕夏新 NAKANO Kimihiko 东京大学生产技术研究所东京153-0041日本加州大学洛杉矶分校土木与环境工程系洛杉矶90095美国

换道决策是智能网联汽车的核心难题之一,其面临着高动态、复杂交通场景下需要综合考虑行驶安全及效率等目标的巨大挑战。提出一种多目标预测优化的换道决策方法,主要包括动力学矩阵建模及多目标预测优化问题解算。基于智能网联汽车的通... 详细信息

换道决策是智能网联汽车的核心难题之一,其面临着高动态、复杂交通场景下需要综合考虑行驶安全及效率等目标的巨大挑战。提出一种多目标预测优化的换道决策方法,主要包括动力学矩阵建模及多目标预测优化问题解算。基于智能网联汽车的通讯大数据信息构建交通流矩阵模型,然后分别设计表征车辆换道安全、行驶效率的动力学模型,通过多目标综合预测优化方法,求解条件约束下预测优化问题从而优化出最优换道决策指令。结果表明,所提出的预测优化换道方法较其他方法提高了智能汽车的行驶安全性和效率。

关键词：智能网联汽车换道决策多目标优化预测优化

Microstructure and performance of biodegradable magnesium alloy tubes fabricated by local-heating-assisted dieless drawing

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Journal of Magnesium and Alloys 2020年第3期8卷 614-623页

作者： Peihua Du Shusaku Furusawa Tsuyoshi Furushima Department of Mechanical and Biofunctional Systems Institute of Industrial ScienceThe University of Tokyo4-6-1KomabaMeguroTokyo 153-8505

Magnesium(Mg)alloy stents are expected to be the next generation of stents because of good biocompatibility and *** with cold drawing,dieless drawing with local heating is an effective method for manufacturing the Mg alloy microtubes since a large reduction in area can be achieved in a single ***,the microstructure and properties of dieless drawn tubes have not been clarified,leading to the problems in practical application of dieless drawn *** this study,the microstructure and performance of dieless drawn tubes are *** results show that temperature and speed in the dieless drawing process are two factors in determining the grain size of dieless drawn tubes since decreasing the temperature or increasing the speed promotes the generation of fine-grained *** are also generated during the dieless drawing process,which 1)disintegrates grains leading to refinement and 2)causes Hall-Petch law effect on dieless drawn *** tests show that grain size is the main factor in determining the mechanical properties of dieless drawn tubes,namely,0.2%proof stress 135-180MPa,ultimate tensile strength(UTS)200-250MPa,and elongation 8-12%.In 0.9 wt%NaCl solution,localized corrosion is the key factor in initiating the corrosion of dieless drawn tubes,but refined grains and fewer twins can alleviate local *** results imply that dieless drawn tubes are promising in the clinical application of Mg alloy stents for cardiovascular disease.

关键词： Dieless drawing Magnesium alloy tube Microstructure Mechanical properties Corrosion properties

Numerical prediction of colloidal phase separation by direct computation of Navier–Stokes equation

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npj Computational Materials 2019年第1期5卷 806-814页

作者： Michio Tateno Hajime Tanaka Department of Fundamental Engineering Institute of Industrial ScienceUniversity of Tokyo4-6-1 KomabaMeguro-kuTokyo 153-8505Japan

Numerical prediction of out-of-equilibrium processes in soft and bio matter containing liquids is highly ***,it is quite challenging primarily because the motions of the components at different hierarchical levels(e.g.,large colloids and small solvent molecules)are spatio-temporally coupled in a complicated manner via momentum *** we critically examine the predictability of numerical simulations for colloidal phase separation as a prototype example of self-organization of soft materials containing a *** use coarse-grained hydrodynamic simulations to tackle this problem,and succeed in almost perfectly reproducing the structural and topological evolution experimentally observed by three-dimensional confocal microscopy without any adjustable ***,comparison with non-hydrodynamic simulations shows the fundamental importance of many-body hydrodynamic interactions in colloidal phase *** predictive power of our computational approach may significantly contribute to not only the basic understanding of the dynamical behavior and self-organization of soft,bio and active matter but also the computer-aided design of colloidal materials.

关键词： materials. separation hydrodynamic

Advances in quantum dots for classical and non-classical light sources Invited Paper

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Chinese Optics Letters 2008年第10期6卷 718-723页

作者： Yasuhiko Arakawa Satoshi Iwamoto Satoshi Kako Masahiro Nomura Denis Guimard Research Center for Advanced Science and Technology Institute for Nano Quantum Information ElectronicsThe University of Tokyo4-6-1 Meguro-ku153-8505 TokyoJapan

Recent advances in quantum dots （QDs） for classical and non-classical light sources are presented. We have established metal organic chemical vapor deposition （MOCVD） technology for InAs-based QD lasers at 1.3 μm and achieved ultralow threshold in QD lasers with photonic crystal （PhC） nanocavity. In addition, single photon emitters at 1.55 μm, GaN-based single photon sources operating at 200 K, and high-Q PhC nanocavity have been demonstrated.

关键词： QDs Advances in quantum dots for classical and non-classical light sources Invited Paper AIN InAs

A phononic rectifier based on carbon schwarzite host–guest system

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Chinese Physics B 2020年第12期29卷 50-55页

作者： Zhongwei Zhang Yulou Ouyang Jie Chen Sebastian Volz Center for Phononics and Thermal Energy Science School of Physics Science and EngineeringTongji UniversityShanghai 200092China China-EU Joint Laboratory for Nanophononics Tongji UniversityShanghai 200092China Institute of Industrial Science The University of TokyoTokyo 153-8505Japan Laboratory for Integrated Micro and Mechatronic Systems CNRS-IIS UMI 2820The University of TokyoTokyo 153-8505Japan

Thermal rectification is a promising way to manipulate the heat flow,in which thermal phonons are spectrally and collectively *** phononic devices are mostly relying on monochromatic phonons,in this work we propose a phononic rectifier based on the carbon schwarzite host–guest *** using molecular dynamic simulations,we demonstrate that the phononic rectification only happens at a specific frequency of the hybridized mode for the host–guest system,due to its strong confinement ***,a significant rectification efficiency,~134%,is observed,which is larger than most of the previously observed *** study of length and temperature effects on the phononic rectification shows that the monochromaticity and frequency of the rectified thermal phonons depend on the intrinsic anharmonicity of the host–guest system and that the on-center rattling configuration with weak anharmonicity is *** study provides a new perspective on the rectification of thermal phonons,which would be important for controlling monochromatic thermal phonons in phononic devices.

关键词： thermal rectification phonon thermal transport

Tribologically induced nanostructural evolution of carbon materials: A new perspective

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Friction 2024年第1期12卷 144-163页

作者： Guilherme Oliveira NEVES Nicolás ARAYA Diego Berti SALVARO Thiago de Souza LAMIM Renan Oss GIACOMELLI Cristiano BINDER Aloisio Nelmo KLEIN JoséDaniel Biasoli de MELLO Laboratório de Materiais Universidade Federal de Santa CatarinaSanta Catarina 88040-900Brazil Departamento de Ingeniería Mecánica Facultad de IngenieríaUniversidad del Bío-BíoConcepcion 4070-386Chile Universidad de Concepción Concepcion 4070-386Chile SENAI Innovation Institute for Laser Processing Santa Catarina 89218-153Brazil Universidade Federal de Uberlândia Minas Gerais 38408-100Brazil

Carbon-based solid lubricants are excellent options to reduce friction and wear,especially with the carbon capability to adopt different allotropes *** the macroscale,these materials are sheared on the contact along with debris and contaminants to form tribolayers that govern the tribosystem *** a recently developed advanced Raman analysis on the tribolayers,it was possible to quantify the contactinduced defects in the crystalline structure of a wide range of allotropes of carbon-based solid lubricants,from graphite and carbide-derived carbon particles to multi-layer graphene and carbon *** addition,these materials were tested under various dry sliding conditions,with different geometries,topographies,and solid-lubricant application *** of the initial tribosystem conditions and allotrope level of atomic ordering,there is a remarkable trend of increasing the point and line defects density until a specific saturation limit in the same order of magnitude for all the materials tested.

关键词： carbon nanostructures tribology Raman spectroscopy defects quantification tribolayer solid lubrication