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Microstructure evaluation of shear bands of microcutting chips in AA6061 alloy under the mechanochemical effect

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Journal of Materials Science & Technology 2021年第32期91卷 178-186页

作者： jiayi zhang Yan Jin Lee Hao Wang Department of Mechanical Engineering Faculty of EngineeringNational University of Singapore9 Engineering Drive 1Singapore 117575Singapore

The mechanochemical effect on the microcutting of AA6061 alloy is studied through characterization on the chip. A pronounced reduction of machining forces and chip thickness was observed with mechanochemical effect during microcutting. Furthermore, electron backscattered diffraction(EBSD) and transmission electron microscopy(TEM) observations were performed on the chips and shear bands. The result reveals much coarser grains(24.6 μm in size) in the surfactant-affected chip than that in the surfactant-free chip(13.5 μm). Different grain orientations are induced by microcutting. {100} and{110} grain orientations are majority for surfactant-free chip, and {110} and {100}dominate most for all grain orientations for surfactant-affected chip. Additionally, since less localized shear strain and lower temperature are generated inside the shear band with mechanochemical effect,almost no recrystallization phenomena can be observed in this region. TEM analysis shows that fewer subgrains and dislocations could be observed inside the shear band of the surfactant-affected chip in comparison with the surfactant-free chip. Based on the high-resolution transmission electron microscopic(HRTEM) observations, dislocations were observed at the atomic scale. The results show that the main dislocation motion mode in shear bands of surfactant-free and surfactant-affected chips are dislocation climb and dislocation glide, respectively.

关键词： Mechanochemical effect Microcutting Shear band Chip formation Dislocation

Mechanochemical effect on the microstructure and mechanical properties in ultraprecision machining of AA6061 alloy

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Journal of Materials Science & Technology 2021年第10期69卷 228-238页

作者： jiayi zhang Yan Jin Lee Hao Wang Department of Mechanical Engineering Faculty of EngineeringNational University of Singapore9 Engineering Drive 1Singapore 117575Singapore

The mechanochemical effect on the microcutting of AA6061 alloy is studied through characterization on the microgroove *** is a reduction in cutting and thrust forces with the application of ink during ***,the microhardness of the ink-affected microgroove is lower than that of the ink-free *** substructured grains exist in the ink-affected microgroove zone whilst deformed grains dominate in the ink-free microgroove zone produced by ***,the mechanochemical effect can facilitate the nucleation of precipitates in the microgroove zone and induce the formation of subgrains with multiple *** to the analysis and calculation,the main texture components of the ink-affected sample are Goss{110}and R{124},and that of the ink-free sample are Brass{110},Copper{112}and S{123}.Besides,a clear difference of slip systems is found between the ink-free and ink-affected microgrooves,and the results show that R texture is easier to form on the ink-affected microgroove.

关键词： Mechanochemical effect Microhardness Texture Nucleation Microcutting

Activation of Parvalbumin-Positive Neurons in Both Retina and Primary Visual Cortex Improves the Feature-Selectivity of Primary Visual Cortex Neurons

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Neuroscience Bulletin 2017年第3期33卷 255-263页

作者： Jinggang Duan Hang Fu jiayi zhang Institutes of Brain Science State Key Laboratory of Medical NeurobiologyCollaborative Innovation Center of Brain ScienceFudan UniversityShanghai 200032China

Several recent studies using either viral or transgenic mouse models have shown different results on whether the activation of parvalbumin-positive（PV~＋）neurons expressing channelrhodopsin-2（ChR2） in the primary visual cortex（V1） improves the orientation-and direction-selectivity of V1 neurons. Although this discrepancy was thoroughly discussed in a follow-up communication, the issue of using different models to express ChR2 in V1 was not mentioned. We found that ChR2 was expressed in retinal ganglion cells（RGCs） and V1 neurons in ChR2fl/~＋; PV-Cre mice. Our results showed that the activation of PV~＋RGCs using white drifting gratings alone significantly decreased the firing rates of V1 neurons and improved their direction-and orientation-selectivity. Longduration activation of PV~＋interneurons in V1 further enhanced the feature-selectivity of V1 neurons in anesthetized mice, confirming the conclusions from previous findings. These results suggest that the activation of both PV~＋RGCs and V1 neurons improves feature-selectivity in mice.

关键词： Parvalbumin neurons Primary visual cortex Retinal ganglion cells Optogenetics

Generalized Physical Layer Channel Model for RelayBased Super Dense Networks

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China Communications 2015年第8期12卷 123-131页

作者： zhang Lingwen LIU Chang zhang jiayi WU Faen Institute of Broadband Wireless Mobile Communications Beijing Jiaotong University Department of Electronic Engineering Tsinghua University School of Electronics and Information Engineering Beijing Jiaotong University

The κ-μ fading model is an advanced channel model in super dense wireless *** this paper,we evaluate the performance of the system over κ-μ fading channel in super dense relay networks with consideration of multiple independent but not necessarily identically distributed(i.n.i.d.) cochannel interference(CCI) under interferencelimited *** specifically,we derive a useful and accurate cumulative distribution function(CDF) expression of the end-to-end signal-to-interference plus noise(SINR) ***,we derive novel analytical expressions of the outage probability(OP),average bit error probability(ABEP) and average capacity for binary modulation types and arbitrary positive values of κ-and μ of such ***,we propose asymptotic analysis for both the OP and ABEP to give physical insights.A simplified analytical form for the ABEP at high-SNR regimes is provided as ***,the accuracy of the derived expressions is well validated by Monte Carlo simulations.

关键词： super dense generalized fadingmodel relay co-channel interference decode-and-forward outage probability average biterror probability average capacity.

Generating Real Random Numbers with Uncertainty Principle

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Instrumentation 2020年第3期7卷 43-49页

作者： zhang jiayi School of physical science and technology Lanzhou university730000LanzhouGansuChina

The real random number generation is a critical problem in computer *** current generation methods are either too dangerous or too expensive,such as using decays of some radioactive *** are also hard to *** the declaration of uncertainty principles in quantum mechanics,real probabilistic events can be substituted by easier and safer processes,such as electron diffraction,photon diffraction and *** key to solve the problem of Schr?dinger’s cat is to identify that the atom stays in different states after and before the decay,and the result of the decay is probabilistic according to the wave packet co llapse *** matter is able to possess different kinds of properties such as wave-particle duality due to that it can stay in various states,and which state will the matter stay is determined by the chosen set of physical quantities(or mechanical quantities).One eigenstate of a set of physical quantities can be a superpos ition of other eigenstates of different sets of physical quantities,and the collapse from a superposition to an eigenstate it contains is really *** this randomness,real random number can be generated more easily.

关键词： Uncertainty Principle Wave Packet Real Random Duality Superposition Matter Wave

Modification of X-ray Generator by Energy Reusing

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Instrumentation 2020年第1期7卷 58-65页

作者： zhang jiayi School of physical science and technology Lanzhou University730000China

X-ray is an important tool for charactering and analyzing ***,current X-ray generation is cost with low *** X-ray tube,which is mostly used in laboratories,only has an energy usage of 1%with all other energy dissipated into tremendous heats,and it needs continuous cool water flows to cool down the *** generates X-ray by the bremsstrahlungofhighenergy electronsbombardingonthecathodetarget,thebremsstrahlungwouldcontainX-raywith sufficiently high energy of the *** most part of the electron energy becomes *** order to generate X-ray more cheaply with higher efficiency,methods about reusing the released heats during the working of the X-ray tube are brought *** the photovoltaic effect,nonequilibrium carriers could also be injected via thermion emission when heating a metal,such injection is same to that of photonic injection which produces electromotive in a photovoltaic *** a photovoltaic cell the electron-hole pair generated by incident photons are nonequilibrium carriers that causes electromotive,while the thermion emission creates such electron-hole pairs via thermal *** metals suitable for thermion emission from the cathode into the p-n junction so that thermions as nonequilibrium carriers can be well injected into the p-n junction when the metals are heated by the cathode,with Thomson effect which enhances such injection,a thermal voltaic cell can be constructed and it can produce electricity only by heating the metals *** such thermal voltaic cell into current X-ray tube,it would produce electricity while absorbing the tremendous heats emerges when X-ray tube is *** flows are still used to control the temperature,but letting them boiling to keep the cathode at a temperature best for thermal voltaic cell,and the vapor may be used to drive a mini thermal power *** this way,the energy usage could be modified to a higher *** up-conversion is possib

关键词： X-ray Thermion Semiconductor Device Thermal Voltaic p-n Junction Nonequilibrium Carriers Thermal Electricity Conversion

A survey on user-centric cell-free massive MIMO systems

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Digital Communications and Networks 2022年第5期8卷 695-719页

作者： Shuaifei Chen jiayi zhang Jing zhang Emil Björnson Bo Ai School of Electronic and Information Engineering Beijing Jiaotong UniversityBeijing100044China Frontiers Science Center for Smart High-speed Railway System Beijing Jiaotong UniversityBeijing100044China Department of Computer Science KTH Royal Institute of TechnologySE-16440KistaSweden Department of Electrical Engineering(ISY) Linköping UniversitySE-58183LinköpingSweden State Key Laboratory of Rail Traffic Control and Safety Beijing Jiaotong UniversityBeijing100044China

The mobile data traffic has been exponentially growing during the last several *** was enabled by the densification of the network infrastructure in terms of increased cell density(i.e.,Ultra-Dense Network(UDN))and/or the increased number of active antennas per Access Point(AP)(i.e.,massive Multiple-Input Multiple-Output(mMIMO)).However,neither UDN nor mMIMO will meet the increasing demand for the data rate of the Sixth Generation(6G)wireless communications due to the inter-cell interference and large quality-of-service ***-Free(CF)mMIMO,which combines the best aspects of UDN and mMIMO,is viewed as a key solution to this *** such systems,each User Equipment(UE)is served by a preferred set of surrounding APs *** this paper,we provide a survey of the state-of-the-art literature on CF *** a starting point,the significance and the basic properties of CF mMIMO are *** then present the canonical framework to discuss the essential details(i.e.,transmission procedure and mathematical system model).Next,we provide a deep look at the resource allocation and signal processing problems related to CF mMIMO and survey the up-to-date schemes and *** that,we discuss the practical issues in implementing CF mMIMO and point out the potential future ***,we conclude this paper with a summary of the key lessons learned in this field.

关键词： 6G network User-centric cell-free network Massive multiple-input multiple-output

Wireless Powered IoE for 6G: Massive Access Meets Scalable Cell-Free Massive MIMO

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China Communications 2020年第12期17卷 92-109页

作者： Shuaifei Chen jiayi zhang Yu Jin Bo Ai School of Electronic and Information Engineering Beijing Jiaotong UniversityBeijing 100044China State Key Laboratory of Rail Traffic Control and Safety Beijing Jiaotong UniversityBeijing 100044China Henan Joint International Research Laboratory of Intelligent Networking and Data Analysis Zhengzhou UniversityZhengzhou 450001China

A key challenge to the scalable deployment of the energy self-sustainability(ESS)Internet of Everything(IoE)for sixth-generation(6G)networks is juggling massive connectivity and high spectral efficiency(SE).Cell-free massive multiple-input multiple-output(CF mMIMO)is considered as a promising solution,where many wireless access points perform coherent signal processing to jointly serve the ***,massive connectivity and high SE are difficult to obtain at the same time because of the limited pilot *** solve this problem,we propose a new framework for ESS IoE networks where the user activity detection(UAD)and channel estimation are decoupled.A UAD detector based on deep convolutional neural networks,an initial access scheme,and a scalable power control policy are proposed to enable the practical scalable CF mMIMO *** derive novel and exact closed-form expressions of harvested energy and SE with maximum ratio(MR)*** local partial minimum mean-square error and MR combining,simulation results prove that the proposed framework can serve more users,improve the SE performance,and achieve better user fairness for the considered ESS IoE networks.

关键词： 6G network cell-free massive MIMO energy self-sustainability Internet of Everything

Performance of Relay Networks in Fading Environments with Dominant Specular Components

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China Communications 2016年第12期13卷 69-78页

作者： Lingwen zhang Chang Liu jiayi zhang Faen Wu Wenkao Yang School of Electronics and Information Engineering Beijing Jiaotong University School of Information and Communication Engineering Beijing University of Posts and Telecommunications School of Science Beijing Jiaotong University

Radio propagation in dense and super dense wireless networks as well as indoor-to-outdoor picocell networks can have multiple line-of-sight or multiple specular components. The performance of a dual-hop decode-and-forward relaying system over multiple specular components fading channels(MSCC)with multiple Rayleigh distributed co-channel interferers in an interference-limited environment is investigated. The MSCC fading model is designed to allow direct and meaningful comparisons to be made between line-of-sight channels and non-line-of-sight channels, with exact parameter correspondences. Comparisons of outage and bit error performance between Nakagami-m/Rayleigh and MSCC/Rayleigh fading environments show that the MSCC model is needed to describe line-of-sight channels that cannot be accurately modeled by the Nakagami-m, or other fading models.

关键词： Multiple Specular Components Channel(MSCC) cochannel interference decode-and-forward relay outage probability average bit error probability