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Active and switchable thermal control

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Science China(Physics,Mechanics & Astronomy) 2022年第11期65卷 80-81页

作者： chenhan Liu yunfei chen Micro-and Nano-scale Thermal Measurement and Thermal Management Laboratory School of Energy and Mechanical EngineeringNanjing Normal UniversityNanjing210046China Jiangsu Key Laboratory for Numerical Simulation of Large-Scale Complex Systems Nanjing Normal UniversityNanjing210046China Jiangsu Key Laboratory for Design and Manufacture of Micro-Nano Biomedical Instruments School of Mechanical EngineeringSoutheast UniversityNanjing211100China

In the past century, actively controlling electron transport has led to unprecedented advances in the digital world. Controlling phonon(i.e., thermal) transport like electron transport is a current topic of interest. To realize active and switchable thermal control(Figure 1), numerous studies have been conducted recently due to the emerging challenges in the fields of thermal management, heating and refrigeration.

关键词： thermal transport Figure

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Inter-and intramolecular adhesion mechanisms of mussel foot proteins

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Science China(Technological Sciences) 2020年第9期63卷 1675-1698页

作者： KAN YaJing WEI ZhiYong TAN QiYan chen yunfei Jiangsu Key Laboratory for Design and Manugacture of Micro-Nano Biomedical Iastruments and School of Mchanical Enginering.Southeast UniversityNanjing 211189China School of Mechanical Engineering Nanjing Institute of TechnologyNanjing 211167China

Mussel foot proteins(Mfps) secreted in the byssal plaque of marine mussels are widely researched for their relevance to mussel adhesion in water. As the abundant residue in the amino acid sequences of major adhesive proteins, 3,4-dihydroxyphenylalanine(Dopa) or its catecholic moiety plays a key role in both Mfp binding to surface and cohesive cross-linking of Mfps in byssal plaques. The binding performance of an Mfp significantly depends on the content and redox state of Dopa, whereas the types of interaction vary in line with different surface chemistries and p H conditions. Thorough understanding of mussel adhesion from a molecular perspective is crucial to promote the application of synthetic mussel-bionic adhesives. This article presents a brief review of the research progress on the adhesion mechanisms of Mfps, which further emphasizes the contributions of Dopamediated interactions and considers other amino acids and factors. The involved inter-and intramolecular interactions are responsible for not only the diverse adhesion capacities of an adhesive byssal plaque as mussel's adhesion precursor but also the formation and properties of the plaque structure.

关键词： mussel foot protein adhesion mechanism Dopa catechol surface forces apparatus

Molecular dynamics simulation of ion transport in a nanochannel

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Science China(Technological Sciences) 2008年第7期51卷 921-931页

作者： chen Min chen yunfei ZHONG Wu YANG JueKuan School of Mechanical Engineering Southeast UniversityNanjing 210096China China Education Council Key Laboratory of MEMS Southeast UniversityNanjing 210096China

A molecular dynamics (MD) model of the fluidic electrokinetic transport in a nano-scale channel with two bulk sinks was presented, and the process of ion transport in the nanochannel was simulated in this paper. The model consists of two water sinks at the two ends and a pump in the middle, which is different from a single pump model in previous MD simulations. Simulation results show that the charged surfaces of the nanochannel result in the depletion of co-ions and the enrichment of counterions in the nanochannel. A stable current is induced because of the motion of ions when an external electric field is applied across the nanochannel, and the current in the pump region is mainly induced by the motion of counterions. In addition, the ion number in the pump region rapidly decreases as the external electric field is applied. In the equilibrated system, the electrically neutral character in the pump region is destroyed and this region displays a certain electrical character, which depends on the surface charge. The ion distribution is greatly different from the results predicted by the continuum theory, e.g. a smaller peak value of Na+ concentration appears near the wall. The transport efficiency of counterions (co-ions) can be effectively increased (decreased) by increasing the surface charge density. The simulation results demonstrate that the ion distribution in the electric double layer (EDL) of a nanochannel cannot be exactly described by the classical Gouy-Chapman-Stern (GCS) theory model. The mechanism of some special experimental phenomena in a nanochannel and the effect of the surface charge density on the ion-transport efficiency were also explored to provide some theoretical insights for the design and application of nano-scale fluidic pumps.

关键词： ion transport nanochannel molecular dynamics simulation transport efficiency

Molecular dynamics simulation of the test of single-walled carbon nanotubes under tensile loading

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Science China(Technological Sciences) 2007年第1期50卷 7-17页

作者： FU chenXin chen yunfei JIAO JiWei School of Mechanical Engineering MEMS Key Laboratory of China Educational MinistrySoutheast UniversityNanjing 210096China State Key Laboratory of Transducer Technology Shanghai Institute of Microsystem and Information TechnologyChinese Academy of SciencesShanghai 200050China

Molecular dynamics (MD) simulations were performed to do the test of sin-gle-walled carbon nanotubes (SWCNT) under tensile loading with the use of Bren-ner potential to describe the interactions of atoms in SWCNTs. The Young’s modulus and tensile strength for SWCNTs were calculated and the values found are 4.2 TPa and 1.40―1.77 TPa, respectively. During the simulation, it was found that if the SWCNTs are unloaded prior to the maximum stress, the stress-strain curve for unloading process overlaps with the loading one, showing that the SWCNT’s de-formation up to its fracture point is completely elastic. The MD simulation also demonstrates the fracture process for several types of SWCNT and the breaking mechanisms for SWCNTs were analyzed based on the energy and structure be-havior.

关键词： carbon nanotube molecular dynamics Young’s modulus carbene

The oscillatory damped behavior of double wall carbon nanotube oscillators in gaseous environment

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Science China(Technological Sciences) 2009年第4期52卷 916-921页

作者： LI Jian BI KeDong chen MinHua chen yunfei Jiangsu Key Laboratory for Design and Fabrication of Micro-Nano Biomedical Instruments Southeast UniversityNanjing 211189China Key Laboratory of MEMS of Educational Ministry Southeast UniversityNanjing 211189China

The mechanical oscillatory behaviors of multiwall carbon nanotube oscillators in gaseous environment are investigated using the molecular dynamics method. The effects of ambient gas and temperature on intertube frictional force and oscillation frequency are analyzed. It is found that the intertube frictional force increases with the ambient gas density and temperature. Higher gas density and higher tem- perature cause a more rapid decay in the oscillation amplitude and an increase of the oscillation fre- quency. Compared to the vacuum environmental condition, the collision between gas atoms and the nanotube walls is a main ingredient leading to the increase of the energy dissipation. Gas damping may be the main reason for the failure of carbon nanotube oscillators working in gas environment. The am- bient temperature also has an important effect on oscillations and low temperature is advantageous to sustain oscillations.

关键词： multiwall nanotube gas friction vibration frequency molecular dynamics

Modulation Recognition with Frequency Offset and Phase Offset over Multipath Channels

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China Communications 2023年第10期20卷 58-69页

作者： Mingqian Liu Zhaoxi Wen yunfei chen Ming Li State Key Laboratory of Integrated Service Networks Xidian UniversityShaanxiXi’an 710071China Department of Engineering University of DurhamSouth RoadDH13LEDurhamUK Guilin Changhai Development Co. LtdGuangxiGuilin 541001China

Modulation recognition becomes unreliable at low signal-to-noise ratio(SNR)over fading channel.A novel method is proposed to recognize the digital modulated signals with frequency and phase offsets over multi-path fading channels in this *** method can overcome the effects of phase offset,Gaussian noise and multi-path *** achieve this,firstly,the characteristic parameters search is constructed based on the cyclostationarity of received signals,to overcome the phase offset,Gaussian white noise,and influence caused by multi-path ***,the carrier frequency of the received signal is estimated,and the maximum characteristic parameter is searched around the integer multiple carriers and their ***,the modulation types of the received signal with frequency and phase offsets are classified using decision *** results demonstrate that the performance of the proposed method is better than the traditional methods when SNR is over 5dB,and that the proposed method is robust to frequency and phase offsets over multipath channels.

关键词： cyclic characteristics frequency and phase offset multi-path channels modulation recognition

NOMA-Based UAV Communications for Maritime Coverage Enhancement

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China Communications 2021年第4期18卷 230-243页

作者： Rui Tang Wei Feng yunfei chen Ning Ge Department of Electronic Engineering Tsinghua UniversityBeijing 100084China School of Engineering University of WarwickCoventry CV47ALUK

The lack of communication infrastructure in the ocean inevitably leads to coverage blind *** addition to high-throughput marine satellites,unmanned aerial vehicles(UAVs)can be used to provide coverage for these blind zones along with onshore base *** this paper,we consider the use of UAV for maritime coverage ***,to serve more ships on the vast oceanic area with limited spectrum resources,we employ non-orthogonal multiple access(NOMA).A joint power and transmission duration allocation problem is formulated to maximize the minimum ship throughput,with the constraints on onboard communication *** from previous works,we only assume the slowly time-varying large-scale channel state information(CSI)to reduce the system cost,as the large-scale CSI is locationdependent and can be obtained according to a priori radio *** solve the non-convex problem,we decompose it into two subproblems and solve them in an iterative *** results show the effectiveness of the proposed solution.

关键词： large-scale channel state information(CSI) maritime communications non-orthogonal multiple access(NOMA) unmanned aerial vehicle(UAV)

Secrecy Rate Maximization for 6G Cognitive Satellite-UAV Networks

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China Communications 2023年第1期20卷 246-260页

作者： chengleyang Lei Wei Feng yunfei chen Ning Ge Department of Electronic Engineering Tsinghua UniversityBeijing 100084China Beijing National Research Center for Information Science and Technology Tsinghua UniversityBeijing 100084China School of Engineering University of WarwickCoventry CV47ALUnited Kingdom

To cover remote areas where terrestrial cellular networks may not be available,non-terrestrial infrastructures such as satellites and unmanned aerial vehicles(UAVs)can be utilized in the upcoming sixth-generation(6G)*** the spectrum scarcity problem,satellites and UAVs need to share the spectrum to save costs,leading to a cognitive satellite-UAV *** to the openness of both satellite links and UAV links,communication security has become a major concern in cognitive satelliteUAV *** this paper,we safeguard a cognitive satellite-UAV network from a physical layer security(PLS)*** only the slowlyvarying large-scale channel state information(CSI),we jointly allocate the transmission power and subchannels to maximize the secrecy sum rate of UAV *** optimization problem is a mixed integer nonlinear programming(MINLP)problem with coupling *** propose a heuristic algorithm which relaxes the coupling constraints by the penalty method and obtains a sub-optimal low-complexity solution by utilizing random matrix theory,the max-min optimization tool,and the bipartite graph matching *** simulation results corroborate the superiority of our proposed scheme.

关键词： channel allocation cognitive satellite-UAV network physical layer security power allocation

Characteristics of the short rachillae of rice from archaeological sites dating to 7000 years ago

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Chinese Science Bulletin 2007年第12期52卷 1654-1660页

作者： ZHENG yunfei SUN GuoPing chen XuGao Zhejiang Province Institute of Relics and Archaeology Hangzhou 310014 China

The abscission layer formed on a pedicel situated at the basal part of a short rachilla is an important characteristic for discriminating between wild, japonica, and indica rice. The short rachillae of paddy rice grains excavated from the Kuahuqiao, Luojiajiao, and Tianluoshan sites, located in the lower reaches of the Yangtze River and dating to 7000 years old, were observed. The results showed that the short rachillae could be divided into two types: a wild type and japonica type. These results indicated that the rice had been domesticated, but was a primitive cultivated rice that retained some of the characteristics of wild rice. The results also suggested that the rice was changing to resemble japonica type rice. Based on the ratios of wild and japonica types, it was inferred that rice domestication began 10000 years ago.

关键词：考古学水稻农业生产栽培技术