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A vertical track nonlinear energy sink

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Applied Mathematics and Mechanics(English Edition) 2024年第6期45卷 931-946页

作者： Meng LI Hu ding Shanghai Key Laboratory of Mechanics in Energy Engineering School of Mechanics and Engineering ScienceShanghai Frontier Science Center of MechanoinformaticsShanghai UniversityShanghai 200444China

Eliminating the effects of gravity and designing nonlinear energy sinks(NESs)that suppress vibration in the vertical direction is a challenging task with numerous damping *** this paper,the dynamic design of a vertical track nonlinear energy sink(VTNES)with zero linear stiffness in the vertical direction is proposed and realized for the first *** motion differential equations of the VTNES coupled with a linear oscillator(LO)are *** the strong nonlinearity considered of the VTNES,the steady-state response of the system is analyzed with the harmonic balance method(HBM),and the accuracy of the HBM is verified *** this basis,the VTNES prototype is manufactured,and its nonlinear stiffness is *** damping effect and dynamic characteristics of the VTNES are studied theoretically and *** results show that the VTNES has better damping effects when strong modulation responses(SMRs)***,even for small-amplitude vibration,the VTNES also has a good vibration suppression *** sum up,in order to suppress the vertical vibration,an NES is designed and developed,which can suppress the vertical vibration within certain ranges of the resonance frequency and the vibration intensity.

关键词： track nonlinear energy sink(TNES) vertical direction gravity nonlinear stiffness harmonic balance method(HBM) vibration control

Exceptional mechanical performance and macroscale superlubricity enabled by core-shell-like MoS_(2)/B_(4)C film

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Science China(Technological Sciences) 2024年第7期67卷 2018-2030页

作者： REN SiMing GAO ZhenRong FAN Xin WANG HaiXin WANG liping Key Laboratory of Advanced Marine Materials Ningbo Institute of Materials Technology and EngineeringChinese Academy of SciencesNingbo 315201China

Molybdenum disulfide(MoS_(2)) films are widely deployed in industrial applications owing to their inherent interlayer slip characteristics, offering energy consumption savings and prolonged mechanical part performance. Nevertheless, their practical utility is limited by environmental constraints and the limitations of preparation techniques, which hinder the attainment of robust superlubricity(friction coefficient ding them with outstanding mechanical properties and efficient lubrication over a wide range of temperatures. Remarkably, such film achieves robust macroscale superlubricity and an ultralow wear rate(1.7 ×10^(-8)mm^(3)N-1m^(-1)) under high contact stress in a mild vacuum environment. This noteworthy outcome is primarily attributable to the self-segmentation of the macroscale contact interface during the friction process, involving:(1) a large amount of wear debris is embedded into the wear track to create extensive micro-sized asperities;(2) a nanolayer of amorphous carbon enriched with oxide nanoparticles is formed on the uppermost part of these asperities;(3) numerous incommensurate nanocontacts comprising nanoparticles and highly oriented MoS_(2)nanosheets are established, culminating in the achievement of robust superlubricity. Our pioneering design, coupled with the elucidation of the underlying superlubricity mechanism, holds significant promise for advancing the development of robust and high-performance lubricants.

关键词： MoS_(2)/B_(4)C nanocomposites core-shell-like structure H/E ratio high-temperature friction macroscale superlubricity

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正整数方幂和的多项式表示

纺织高校基础科学学报 2015年第1期28卷 21-26页

作者：田清丁丽萍西安建筑科技大学理学院陕西西安710055

研究正整数方幂和Sk(n)=n∑a=1ak的多项式表示.结合初等数论及组合的方法,证明了正整数方幂和S2k-1(n)可展开为包含因子n(n+1)且关于n(n+1)的k阶有理多项式;S2k(n)可展n开为包含因子n(n+1)(2n+1)且关于n(n+1)的k阶有理多项式,并且给出Sk... 详细信息

研究正整数方幂和Sk(n)=n∑a=1ak的多项式表示.结合初等数论及组合的方法,证明了正整数方幂和S2k-1(n)可展开为包含因子n(n+1)且关于n(n+1)的k阶有理多项式;S2k(n)可展n开为包含因子n(n+1)(2n+1)且关于n(n+1)的k阶有理多项式,并且给出Sk(n)=n∑a=1ak展开成多项式后系数的确切计算公式.

关键词：正整数方幂和多项式表示系数计算

Capturing metal clusters at the strong-interaction region to reverse Ostwald ripening

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Science China Materials 2024年第4期67卷 1363-1364页

作者： Shuheng Tian ding Ma Beijing National Laboratory for Molecular Sciences New Cornerstone Science LaboratoryCollege of Chemistry and Molecular EngineeringPeking UniversityBeijing 100871China

High-temperature interactions induce sintering of metal nanoparticles(NPs) on heterogeneous catalyst surfaces, leading to reduced surface area and active site loss through Ostwald ripening [1]. This irreversible deactivation necessitates costly catalyst replacement, notably impacting metals like copper in hydrogenation and reforming reactions [2].

关键词： catalyst reforming irreversible

Towards human-leveled vision systems

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Science China(Technological Sciences) 2024年第8期67卷 2331-2349页

作者： ding JianHao HUANG TieJun State Key Laboratory of Multimedia Information Processing School of Computer SciencePeking UniversityBeijing 100871China

The human visual system is a complex and interconnected network comprising billions of neurons. It plays an essential role in translating environmental light stimuli into information that guides and shapes human perception and action. Research on the visual system aims to uncover the underlying neural structure principles of human visual perception and their possible ***, there are two main approaches: biological system analysis and simulation, artificial intelligence models based on deep learning. Here we aim to discuss the two approaches to human-level vision systems. Deep learning has significantly impacted the field of vision with achievements in representation, modeling, and hardware design. However, there is still a significant gap between deep learning models and the human visual system in terms of scalability, transferability, and sustainability. The progress of the biological visual system can help fill the gap by further understanding the properties and functions of different components of the system. We take the efforts of reconstructing the retina as an example to illustrate that even if we are unable to replicate the visual system on a computer right now, we can still learn a lot by combining existing research outcomes in neuroscience. At the end of the paper, we suggest tracing back to gradually build visual systems from the computational counterpart of biological structures to achieve a human-level vision system in the future.

关键词： human-leveled vision system deep learning biological visual system

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A newly unraveled 13.6-year oscillation from GPS displacements and its potential implications for the dynamic reference frame

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Science China Earth Sciences 2024年第10期67卷 3204-3212页

作者： Hao ding Weiping JIANG School of Geodesy and Geomatics Hubei Luojia LaboratoryWuhan UniversityWuhan 430079China GNSS Research Center Wuhan UniversityWuhan 430079China

Numerous practical geodetic and geophysical applications necessitate precise measurements of GNSS displacements at the millimeter or sub-millimeter level. To attain such precision, it is imperative to identify and analyze the unidentified decadal signals inherent in the GPS displacements. In this research, we employ the optimal sequence estimation method to effectively detect an about 13.6-year oscillational signal with an excited amplitude of 3.6±1.2 mm in the U-components of the GPS displacements. It is noteworthy that this signal demonstrates a consistent spatial pattern characterized by the spherical harmonic Y_(2,-2). We conduct a comparative analysis with the 13.6-year oscillation observed in length-of-day variations(and geomagnetic records), finding that they are in reverse phase. After eliminating the Earth's external excitation sources through the utilization of two distinct in-situ hydrological records, we suggest that the 13.6-year GPS signal may come from the internal motions within the Earth. However, the specific excitation source and the detailed physical mechanism remain uncertain. Additionally, we develop a mathematical displacement model to explain the 13.6-year signal. Our findings indicate that this signal can result in displacements of up to 1.37 mm and velocity effects of 0.63 mm/yr(for U-component) at maximum. These results underscore the necessity of incorporating this 13.6-year signal into the construction and maintenance of a dynamic reference frame at the millimeter level.

关键词： GPS displacements Decadal changes 13.6-year oscillation Displacement model Dynamic reference frame

Deep Learning based Efficient Edge Slicing for System Cost Minimization in Wireless Networks

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Journal of Communications and Information Networks 2024年第2期9卷 162-175页

作者： Wei Jiang Daquan Feng liping Qian Yao Sun College of Information Engineering Zhejiang University of TechnologyHangzhou 310023China Shenzhen Key Laboratory of Digital Creative Technology Guangdong Province Engineering Laboratory for Digital Creative TechnologyCollege of Electronics and Information EngineeringShenzhen UniversityShenzhen 518060China James Watt School of Engineering University of GlasgowG128QQScotlandUK

It is widely recognized that the future wireless networks are able to efficiently slice heterogeneous resources to provide customized services for various use cases. However, it is challenging to meet the diverse requirements of ever-growing applications, especially the stringent requirements of numerous delay-sensitive and/or computation-intensive applications. To tackle this challenge, we should not only consider user admission control to cope with resource limitations, but also make resource management more intelligent and flexible to meet diverse service needs. Taking advantages of mobile edge computing(MEC)and network slicing, in this paper, we propose deep edge slicing(DES),to jointly optimize user admission control and resource scheduling with the aim of minimizing the system cost while guaranteeing multitudinous quality-of-service (QoS) requirements. Specifically, we first apply a deep reinforcement learning approach to select the optimal set of access users with different service requests for maximizing resource *** a deep learning algorithm is employed to predict traffic data for allocating the communication and computing resources to different slices in advance. Finally, we realize the dynamic scheduling of heterogeneous resources by solving the optimization problem of minimizing the system cost. Simulation results demonstrate that DES can greatly reduce the system cost compared to other benchmarks.

关键词： deep learning mobile edge computing user admission control resource scheduling

From London buses to activity trackers:A reflection of 70 years of physical activity research

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Journal of Sport and Health Science 2024年第6期13卷 736-738页

作者： ding ding Ulf Ekelund Prevention Research Collaboration Sydney School of Public HealthFaculty of Medicine and HealthThe University of SydneyCamperdownNSW 2006Australia Charles Perkins Centre The University of SydneyCamperdownNSW 2006Australia Department of Sports Medicine Norwegian School of Sports SciencesOslo 0806Norway Department of Chronic Diseases Norwegian Institute of Public HealthOslo 0213Norway

In 1953,Morris et al.^(1)published their ground-breaking findings among London bus drivers and conductors,linking physical activity to a major chronic disease for the first *** seminal paper marked the birth of a new field—physical activity epidemiology.^(1)Since then,the field has flourished,evidenced by mounting scientific publications.^(2)Our knowledge about the role of physical activity in disease prevention has expanded from coronary heart disease in Morris et al.’s^(1)initial study to dozens of additional diseases and conditions,such as diabetes,cancers,and dementia.^(3)More than 7 decades and thousands of publications later,we critically reflect on several aspects of the progress in physical activity epidemiology.

关键词： epidemiology prevention linking

New advances in the study of Tethyan Geodynamic System

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Science China Earth Sciences 2024年第3期67卷 874-878页

作者： Lin ding State Key Laboratory of Tibetan Plateau Earth System Science(LATPES) Institute of Tibetan Plateau ResearchChinese Academy of SciencesBeijing 100101China

Tethyan Ocean was initially proposed by Austrian geologist Eduard Suess in 1893. The study of the Tethyan evolution by European geologists has led to the development of modern geology, but not to the establishment of plate tectonics theory(Trümpy, 2001). With the progress in various studies, the concept of Tethys has evolved from a Mesozoic ocean into three long-term evolving oceans:Proto-Tethys, Paleo-Tethys, and Neo-Tethys (Figure 1), and their life cycles cover the entire Phanerozoic era (Wu et al., 2020).

关键词： geology Mesozoic ocean