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A Remark on the Symplectic Blow-up in Dimension 4

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Acta mathematica Sinica,English Series 1996年第4期12卷 379-384页

作者： ma renyi department of applied mathematics tsinghua university beijing, 100084 China department of applied mathematics Tsinghua University Beijing China

In this note, we prove that the symplectic blow-up or blow-down in the dimension 4 is rigid, i.e. the symplectic area of the divisor does not exceed the symplectic radius of the neighbourhood on which we do the blow-u... 详细信息

关键词： J-Holomorphic disc Contact manifold Symplectic blow-up

On Minimal Graph Evolutions in the Hyperbolic Space

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Acta mathematica Sinica,English Series 1999年第3期15卷 371-374页

作者： Li ma department of applied mathematics, tsinghua university, beijing 100084, P. R. China department of applied mathematics Tsinghua University Beijing P. R. China

We study here minmal graph evolutions in the hyperbolic space and prove that there exists a unique smooth solution.

关键词： Minimal graph evolution Apriori estimate

Effect of helmet-wearing regulation on electric-bike riders:a case study of two cities in China

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Transportation Safety and Environment 2024年第3期6卷 62-70页

作者： Wenxin ma Zhiyong Liu Ruimin Li department of Civil Engineering Tsinghua UniversityBeijing 100084China School of Traffic and Transportation Beijing Jiaotong UniversityBeijing 100044China

Objectives:Electric bikes(e-bikes)are widely used for commuting and delivery in *** the rapid increase in e-bikes on the road,related accidents have become crucial issues threatening the *** research aims to explore the protective effect of helmet-wearing regulation and to investigate some factors influencing head injury with reference to two case cities in China,obtaining information to protect e-bike ***:The traffic police-reported crash data cover the periods before and after the implementation of helmet-wearing regulations in Taizhou(with data from 2017 to 2019)and Nanning(with data in 2020)of *** statistical analysis,logistic regression and chi-square test with a Bonferroni correction were applied in the ***:A lack of helmets was common among victims in the context of a high helmet-wearing rate among general e-bike riders in Taizhou,indicating that fatality could be avoided to some extent by wearing ***,helmet wearing could reduce the probability of suffering fatal head injury by 6.4%.After the regulation implementation in Taizhou,the proportion of fatal head injuries decreased from 89%to 79%,remaining at a high level,which indicates that other measures in addition to helmet-wearing regulations should be *** to the results from Nanning,mandatory regulation worked more effectively than encouraged regulation in terms of reducing head ***:mandatory helmet-wearing regulations are highly recommended to policymakers to reduce head injury among e-bike *** in addition to helmet-wearing regulation,*** law-abiding awareness and improving road infrastructure,should be considered to further protect e-bike riders.

关键词： e-bike safety accident analysis helmet-wearing regulation head injury

Conductive edge-warping graphite mesas for robust structural superlubricity

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Science China(Technological Sciences) 2024年第7期67卷 2040-2049页

作者： FENG WeiJia LIU Ying ma Ming PENG DeLi NIE JinHui State Key Laboratory of Tribology in Advanced Equipment&department of Mechanical Engineering Tsinghua UniversityBeijing 100084China Center for Nano and Micro Mechanics Tsinghua UniversityBeijing 100084China Institute of Superlubricity Technology Research Institute of Tsinghua University in ShenzhenShenzhen 518057China

Structural superlubricity(SSL) refers to a state of ultralow friction and zero wear when two solid surfaces slide against each other. Recent investigations have identified amorphous carbon at the edge of the graphite mesa as the primary source of friction in such SSL systems. Here, the tensile stress of metal thin film is exploited to engineer vertically conductive edge-warping graphite mesas(EWGM). Through this approach, robust SSL performance is realized, demonstrated by sliding an 8 μm side length square EWGM on an atomically smooth Au substrate for 10000 cycles at a constant voltage of 1 m V. In this SSL system,differential friction coefficients lower than 1.5 × 10^(-4) are achieved, with static contact resistance between EWGM and Au substrate as low as 28Ω and sliding contact resistance as low as 32Ω. Moreover, the EWGM exhibits SSL behavior on polished Si wafer substrates. Furthermore, because of the no-edge contact with the substrate during sliding, friction is independent of the sliding speed of the EWGM. This study presents the first successful fabrication of conductive EWGM. Remarkably, in both EWGM-Au and EWGM-Si SSL systems, the measured frictions are more than one order of magnitude lower than those of ordinary self-retracting graphite mesas with no-edge warping, and no wear is observed during extended current-carrying ***, these findings establish a solid groundwork for the future realization of macroscale conductive SSL systems.

关键词： structural superlubricity graphite mesa contact resistance tensile stress edge warping

Experimental Studieson Gas－Particle Flows and Coal Combustion in New Generation Spouting－Cyclone Combustor

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Journal of Thermal Science 1996年第2期5卷 132-137页

作者： D.X. Wang Z.H. ma X.L. Wang L.X. Zhou(department of Engineering Mechanics,tsinghua university, beijing 100084, China) department of Engineering Mechanics Tsinghua University Beijing China

Based on previous studies,an improved non-slagging spouting-cyclone combustor with two-stage combustion, organized in perpendicularly vortexing flows, is developed for clean coal combustion applied in small-size industrial furnaces and domestic furnaces. The isothermal model test and the combustion test give some encouraging results. In this studyt further improvement of the geometrical configuration was made, a visualizatiou method and a LDA system were used to study the gas-particle flow behavior,and the temperature and gas composition in combustion experiments were measured by using thermocouples and a COSA-6000-CD Portable Stack Analyzer. Stronger recirculation in the spouting zone and the strongly swirling effect in the cyclone zone were obtained in the improved combustor. The combustion temperature distribution is uniform. These results indicate that the improved geometrical configuration of the combustor is favorable to the stabilization of coal flame and the intensification of coal combustion, and it provides a basis for the practical application of this technique.

关键词： strongly swirling flows LDA measurement combustion

Optoelectronic Synapses Based on MXene/Violet Phosphorus van der Waals Heterojunctions for Visual‑Olfactory Crossmodal Perception

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Nano-Micro Letters 2024年第6期16卷 38-52页

作者： Hailong ma Huajing Fang Xinxing Xie Yanming Liu He Tian Yang Chai Center for Advancing materials Performance From the Nanoscale(CAMP‑Nano) State Key Laboratory for Mechanical Behavior of MaterialsXi’an Jiaotong UniversityXi’an 710049People’s Republic of China Institute of Microelectronics and beijing National Research Center for Information Science and Technology(BNRist) Tsinghua UniversityBeijing 100084People’s Republic of China department of applied Physics The Hong Kong Polytechnic UniversityHong KongPeople’s Republic of China

The crossmodal interaction of different senses,which is an important basis for learning and memory in the human brain,is highly desired to be mimicked at the device level for developing neuromorphic crossmodal perception,but related researches are ***,we demonstrate an optoelectronic synapse for vision-olfactory crossmodal perception based on MXene/violet phosphorus(VP)van der Waals *** from the efficient separation and transport of photogenerated carriers facilitated by conductive MXene,the photoelectric responsivity of VP is dramatically enhanced by 7 orders of magnitude,reaching up to 7.7 A W^(−1).Excited by ultraviolet light,multiple synaptic functions,including excitatory postsynaptic currents,pairedpulse facilitation,short/long-term plasticity and“learning-experience”behavior,were demonstrated with a low power ***,the proposed optoelectronic synapse exhibits distinct synaptic behaviors in different gas environments,enabling it to simulate the interaction of visual and olfactory information for crossmodal *** work demonstrates the great potential of VP in optoelectronics and provides a promising platform for applications such as virtual reality and neurorobotics.

关键词： Violet phosphorus MXene Van der Waals heterojunctions Optoelectronic synapses Crossmodal perception

Experimental investigation of interface curing stresses between PMma and composite using digital speckle correlation method

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Theoretical & applied Mechanics Letters 2011年第5期1卷 14-17页

作者： Yinji ma,Tiechui Xiong,and Xuefeng Yao department of Engineering Mechanics,applied Mechanics Laboratory,tsinghua university,beijing 100084,China department of Engineering Mechanics Applied Mechanics Laboratory Tsinghua University Beijing 100084 China

This paper studies the interface curing stresses between polymethyl methacrylate (PMma) and composite by means of digital speckle correlation method (DSCM).A new method by combining DSCM with the marker points is developed to measure the interface curing stresses,and the measurement principle is *** interface curing stresses between PMma and composite with different curing bonding conditions are measured and analyzed,this indicates that the residual stress for furnace heating and furnace cooling is the ***,the measurement error is discussed by means of finite element method,the influences of glass microsphere between adhesive and PMma can be ignored.

关键词： interface stress cure adhesive layer digital speckle correlation method

Flexible,high-density,laminated ECoG electrode array for high spatiotemporal resolution foci diagnostic localization of refractory epilepsy

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Bio-Design and manufacturing 2024年第4期7卷 388-398页

作者： Yafeng Liu Zhouheng Wang Yang Jiao Ying Chen Guangyuan Xu Yinji ma Xue Feng applied Mechanics Laboratory Department of Engineering MechanicsTsinghua UniversityBeijing 100084China Laboratory of Flexible Electronics Technology Tsinghua UniversityBeijing 100084China College of Artificial Intelligence Southwest UniversityChongqing 400715China Institute of Flexible Electronics Technology of THU Jiaxing 314000China Qiantang Science and Technology Innovation Center Hangzhou 310016China School of Artificial Intelligence Beijing University of Posts and TelecommunicationsBeijing 100876China

High spatiotemporal resolution brain electrical signals are critical for basic neuroscience research and high-precision focus diagnostic localization,as the spatial scale of some pathologic signals is at the submillimeter or micrometer *** entails connecting hundreds or thousands of electrode wires on a limited *** study reported a class of flexible,ultrathin,highdensity electrocorticogram(ECoG)electrode *** challenge of a large number of wiring arrangements was overcome by a laminated structure design and processing technology *** flexible,ultrathin,high-density ECoG electrode array was conformably attached to the cortex for reliable,high spatial resolution electrophysiologic *** minimum spacing between electrodes was 15μm,comparable to the diameter of a single *** hundred electrodes were prepared with an electrode density of 4444 mm^(-2).In focal epilepsy surgery,the flexible,high-density,laminated ECoG electrode array with 36 electrodes was applied to collect epileptic spike waves inrabbits,improving the positioning accuracy of epilepsy lesions from the centimeter to the submillimeter *** flexible,high-density,laminated ECoG electrode array has potential clinical applications in intractable epilepsy and other neurologic diseases requiring high-precision electroencephalogram acquisition.

关键词： Electrocorticogram(ECoG)electrode Epilepsy High density High resolution Laminated structure

MODE SPACE SMOOTHING ALGORITHM TO ESTImaTE DOA OF COHERENT SIGNALS IMPINGING ON UNIFORM CIRCULAR ARRAY

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Journal of Electronics(China) 1998年第4期15卷 289-295页

作者： ma Changlin Peng Yingning Tian Lisheng Liu Jianhua(department of Electronic Engineering, tsinghua university, beijing 100084)

A novel method to estimate DOA of coherent signals impinging on a uniform circular array( UCA) is presented in this paper. A virtual uniform linear array (VULA) is first derived by using spatial DFT technique, transforming the UCA from element space to phase mode space to obtain the properties of ordinary ULA, and then the well known spatial smoothing technique is applied to the VULA so that the lost rank of covariance matrix due to signal coherence can be retrieved. This method makes it feasible to use the simple MUSIC algorithm to estimate DOA of coherent signals impinging on a UCA without heavy computation burden. Simulation results strongly verify the effectiveness of the algorithm.

关键词： Mode space Virtual uniform linear array Spatial smoothing