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Discrete Phase Shifts Control and Beam Selection in RIS-Aided MISO System via Deep Reinforcement Learning

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China Communications 2023年第8期20卷 198-208页

作者： Dongting Lin Yuan Liu School of Electronic and Information Engineering South China University of TechnologyGuangzhou 510641China

Reconfigurable intelligent surface(RIS)for wireless networks have drawn lots of attention in both academic and industry communities.RIS can dynamically control the phases of the reflection elements to send the signal in the desired direction,thus it provides supplementary links for wireless networks.Most of prior works on RIS-aided wireless communication systems consider continuous phase shifts,but phase shifts of RIS are discrete in practical hardware.Thus we focus on the actual discrete phase shifts on RIS in this paper.Using the advanced deep reinforcement learning(DRL),we jointly optimize the transmit beamforming matrix from the discrete Fourier transform(DFT)codebook at the base station(BS)and the discrete phase shifts at the RIS to maximize the received signal-to-interference plus noise ratio(SINR).Unlike the traditional schemes usually using alternate optimization methods to solve the transmit beamforming and phase shifts,the DRL algorithm proposed in the paper can jointly design the transmit beamforming and phase shifts as the output of the DRL neural network.Numerical results indicate that the DRL proposed can dispose the complicated optimization problem with low computational complexity.

关键词： reconfigurable intelligent surface discrete phase shifts transmit beamforming deep reinforcement learning

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A weighted fuzzy C-means clustering method for hardness prediction

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Journal of Iron and Steel Research(International) 2023年第1期30卷 176-191页

作者： Yuan Liu Shi-zhong Wei School of Materials Science and Engineering Henan University of Science and TechnologyLuoyang 471003HenanChina School of Aerospace Engineering Zhengzhou University of AeronauticsZhengzhou 450015HenanChina National Joint Engineering Research Center for Abrasion Control and Molding of Metal Materials Henan University of Science and TechnologyLuoyang 471003HenanChina

The hardness prediction model was established by support vector regression(SVR).In order to avoid exaggerating the contribution of very tiny alloying elements,a weighted fuzzy C-means(WFCM)algorithm was proposed for data clustering using improved Mahalanobis distance based on random forest importance values,which could play a full role of important features and avoid clustering center overlap.The samples were divided into two classes.The top 10 features of each class were selected to form two feature subsets for better performance of the model.The dimension and dispersion of features decreased in such feature subsets.Comparing four machine learning algorithms,SVR had the best performance and was chosen to modeling.The hyper-parameters of the SVR model were optimized by particle swarm optimization.The samples in validation set were classified according to minimum distance of sample to clustering centers,and then the SVR model trained by feature subset of corresponding class was used for prediction.Compared with the feature subset of original data set,the predicted values of model trained by feature subsets of classified samples by WFCM had higher correlation coefficient and lower root mean square error.It indicated that WFCM was an effective method to reduce the dispersion of features and improve the accuracy of model.

关键词： Hardness prediction Weighted fuzzy C-means algorithm Feature selection Particle swarm optimization Support vector regression Dispersion reduction

High-Porosity Foam-Based Iontronic Pressure Sensor with Superhigh Sensitivity of 9280 kPa^(-1)

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Nano-Micro Letters 2022年第2期14卷 12-23页

作者： Qingxian liu Yuan Liu Junli Shi Zhiguang liu Quan Wang Chuan Fei Guo School of Astronautics Harbin Institute of TechnologyHarbin 150001HeilongjiangPeople’s Republic of China Department of Materials Science and Engineering Southern University of Science and TechnologyShenzhen 518055People’s Republic of China Department of Mechanics and Aerospace Engineering Southern University of Science and TechnologyShenzhen 518055GuangdongPeople’s Republic of China Department of Civil and Environmental Engineering Shantou UniversityShantou 515063GuangdongPeople’s Republic of China Department of Mechanical Engineering Massachusetts Institute of TechnologyCambridgeMA 02139USA Department of Physics and TcSUH University of HoustonHoustonTX 77204USA Guangdong Provincial Key Laboratory of Functional Oxide Materials and Devices Southern University of Science and TechnologyShenzhen 518055GuangdongPeople’s Republic of China Present Address:320 Crescent Village Circle Unit 1413 San JoseCA 95134USA

Flexible pressure sensors with high sensitivity are desired in the fields of electronic skins,human-machine interfaces,and health monitoring.Employing ionic soft materials with microstructured architectures in the functional layer is an effective way that can enhance the amplitude of capacitance signal due to generated electron double layer and thus improve the sensitivity of capacitive-type pressure sensors.However,the requirement of specific apparatus and the complex fabrication process to build such microstructures lead to high cost and low productivity.Here,we report a simple strategy that uses open-cell polyurethane foams with high porosity as a continuous three-dimensional network skeleton to load with ionic liquid in a one-step soak process,serving as the ionic layer in iontronic pressure sensors.The high porosity(95.4%) of PU-IL composite foam shows a pretty low Young's modulus of 3.4 kPa and good compressibility.A superhigh maximum sensitivity of 9,280 kPa^(-1) in the pressure regime and a high pressure resolution of 0.125% are observed in this foam-based pressure sensor.The device also exhibits remarkable mechanical stability over 5,000 compression-release or bending-release cycles.Such high porosity of composite structure provides a simple,cost-effective and scalable way to fabricate super sensitive pressure sensor,which has prominent capability in applications of water wave detection,underwater vibration sensing,and mechanical fault monitoring.

关键词： High porosity Elastic modulus Compression deformation Iontronic pressure sensor Superhigh sensitivity

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Synthesis of Stimuli-Responsive Block Copolymers and Block Copolymer Nano-assemblies

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Chinese Journal of Chemistry 2022年第8期40卷 965-972页

作者： Yuan Liu Yu Sun Wangqing Zhang Key Laboratory of Functional Polymer Materials of the Ministry of Education Institute of Polymer ChemistryCollege of ChemistryNankai UniversityTianjin 300071China

Block copolymers have aroused much interest,and their application has been rapidly expanded.In recent years,our group has committed to exploring synthesis and self-assembly of block copolymers.We have designed and synthesized several new thermo-responsive polymers and photo-responsive polymers by living/controlled radical polymerization(LCRP)and investigated their stimuli-responsive properties.Aiming at convenient and efficient synthesis of block copolymer nano-assemblies,we have developed several methods based on polymerization-induced self-assembly(PISA).Herein,we give a short summary of our research in these years.The aim of this account is to stimulate innovative synthesis strategies of block copolymer nano-assemblies,and promote more scientific research cooperation to face the exciting opportunities and challenges encountered in block copolymers.

关键词： Block copolymers Living/controlled radical polymerization(LCRP) Stimuli-responsive Self-assembly Nanostructures

Cellular strategies to induce immune tolerance after liver transplantation:Clinical perspectives

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World Journal of Gastroenterology 2024年第13期30卷 1791-1800页

作者： Ai-Wei Zhou Jing Jin Yuan Liu Department of Liver Surgery Renji Hospital Affiliated to Shanghai Jiao Tong University School of MedicineShanghai 200127China Department of Nursing Renji Hospital Affiliated to Shanghai Jiao Tong University School of MedicineShanghai 200127China Department of Liver Transplantation Shanghai Immune Therapy InstituteShanghai 200127China

Liver transplantation(LT)has become the most efficient treatment for pediatric and adult end-stage liver disease and the survival time after transplantation is becoming longer due to the development of surgical techniques and perioperative management.However,long-term side-effects of immunosuppressants,like infection,metabolic disorders and malignant tumor are gaining more attention.Immune tolerance is the status in which LT recipients no longer need to take any immunosuppressants,but the liver function and intrahepatic histology maintain normal.The approaches to achieve immune tolerance after transplantation include spontaneous,operational and induced tolerance.The first two means require no specific intervention but withdrawing immunosuppressant gradually during follow-up.No clinical factors or biomarkers so far could accurately predict who are suitable for immunosuppressant withdraw after transplantation.With the understanding to the underlying mechanisms of immune tolerance,many strategies have been developed to induce tolerance in LT recipients.Cellular strategy is one of the most promising methods for immune tolerance induction,including chimerism induced by hematopoietic stem cells and adoptive transfer of regulatory immune cells.The safety and efficacy of various cell products have been evaluated by prospective preclinical and clinical trials,while obstacles still exist before translating into clinical practice.Here,we will summarize the latest perspectives and concerns on the clinical application of cellular strategies in LT recipients.

关键词： Cellular therapy Induced tolerance Liver transplantation Regulatory T cells Regulatory dendritic cells

Efflux pump gene hefA of Helicobacter pylori plays an important role in multidrug resistance

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World Journal of Gastroenterology 2008年第33期14卷 5217-5222页

作者： Zhi-Qiang liu Peng-yuan Zheng Ping-Chang Yang Department of Gastroenterology the Second Affiliated Hospital of Zhengzhou University Zhengzhou 450014 Henan Province China Department of Pathology and Molecular Medicine McMaster University Hamilton Ontario L8N 4A6 Canada

AIM: To determine whether efflux systems contribute to multidrug resistance of H pylori. METHODS: A chloramphenicol-induced multidrug resistance model of six susceptible H pylori strains (5 isolates and H pylori NCTC11637) was developed. Multidrug-resistant (MDR) strains were selected and the minimal inhibitory concentration (MIC) of eryth-romycin, metronidazole, penicillin G, tetracycline, and ciprofloxacin in multidrug resistant strains and their parent strains was determined by agar dilution tests. The level of mRNA expression of hefA was assessed by fluorescence real-time quantitative PCR. A H pylori LZ1026 knockout mutant (ΔH pylori LZ1026) for (puta-tive) efflux protein was constructed by inserting the kanamycin resistance cassette from pEGFP-N2 into hefA, and its susceptibility profiles to 10 antibiotics were evaluated. RESULTS: The MIC of six multidrug-resistant strains (including 5 clinical isolates and H pylori NCTC11637) increased signifi cantly (≥ 4-fold) compared with their parent strains. The expression level of hefA gene was significantly higher in the MDR strains than in their parent strains (P = 0.033). A H pylori LZ1026 mutant was successfully constructed and the ΔH pylori LZ1026 was more susceptible to four of the 10 antibiotics. All the 20 strains displayed transcripts for hefA that con-fi rmed the in vitro expression of these genes.CONCLUSION: The efflux pump gene hefA plays an important role in multidrug resistance of H pylori.

关键词：消化系统疾病多药物抗性幽门 hefA基因突变异种

Graphene-based vertical thin film transistors

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Science China(Information Sciences) 2020年第10期63卷 42-53页

作者： Liting liu Yuan Liu Xiangfeng DUAN Key Laboratory for Micro-Nano Optoelectronic Devices of Ministry of Education School of Physics and ElectronicsHunan University Department of Chemistry and Biochemistry University of California

Vertical field effect transistors(VFETs), where the channel material is sandwiched between source-drain electrodes and the channel length is simply determined by its body thickness, have attracted considerable interest for high performance electronics owning to their intrinsic short channel length. To enable the effective gate modulation and current switching behavior, the electrode of conventional VFET is largely based on perforated metals, in which the gate electrical field could penetrate through. Recently,with the emerge of graphene, a new type of graphene based VFETs has been developed. With finite density of states and the weak electrostatic screening effect, graphene exhibits a field-tunable work-function and partial electrostatic transparency, it can thus function as an "active" contact with tunable graphene-channel junction, enabling entirely new transistor functions or higher device performance not previously possible.In this review, we discuss the research progresses of graphene-based VFET, including the its basic device structure, carrier transport mechanism, device performance and novel properties demonstrated.

关键词： graphene electrode vertical transistors thin film transistors van der Waals heterostructures

Multiple Ergodicity For Reversible Markov Chains

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Acta Mathematicae Applicatae Sinica 2018年第4期34卷 863-868页

作者： Yuan Liu Academy of Mathematics and Systems Science Chinese Academy of Sciences University of Chinese Academy of Sciences

Inspired by the multiple recurrence and multiple ergodic theorems for measure preserving systems,we discuss an analogous question for measure preserving semigroups. In this note, we deal with the symmetric semigroups ... 详细信息

关键词： Multiple recurrence reversible Markov chain

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Long Period Grating Imprinted on a Flat-Shaped Plastic Optical Fiber for Refractive Index Sensing

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Photonic Sensors 2023年第4期13卷 39-49页

作者： Yuan Liu Yanfei ZHOU Haiyang BAO Jie ZHENG State Key Laboratory of Integrated Optoelectronics College of Electronic Science and EngineeringJilin UniversityChangchun 130012China Changchun Institute of Optics Fine Mechanics and PhysicsChinese Academy of SciencesChangchun 130012China

A corrugated surface long period grating(LPG)was fabricated on a flat-shaped plastic optical fiber(POF)as a refractive index(RI)sensor by a simple pressing with the heat pressure and mechanical die press print method.The light propagation characteristics of an LPG imprinted on a multi-mode POF were analyzed by the method of geometrical optics.Theoretical and experimental results showed that the structural parameters of the sensor affected the RI sensing performance,and the sensor with a thinner flat thickness,a deeper groove depth of the corrugated surface LPG,and a longer LPG exhibited better RI sensing performance.When the POF with a diameter of 1 mm was pressed with the heat pressure to a flat shape with a thickness of 600μm,an LPG with a period of 300μm,a groove depth of 200μm,and a length of 6 cm was fabricated on it,and the RI sensitivity of 1447%/RIU was obtained with a resolution of 5.494×10^(−6) RIU.In addition,the influences of the POF cladding,tilting of LPG,and bending of the sensing structure were investigated.The results demonstrated that after removing the cladding and tilting or bending the LPG,the RI sensing performance was improved.When the LPG imprinted on the flat-shaped POF was bent with a curvature radius of 6/πcm,the highest sensitivity of 6563%/RIU was achieved with a resolution of 2.487×10^(−9) RIU in the RI range of 1.3330–1.4230.The proposed sensor is a low-cost solution for RI measurement with the features of easy fabrication,high sensitivity,and intensity modulation at the visible wavelengths.

关键词： Plastic optical fiber fiber optic sensor flat-shaped optical fiber long period grating refractive index sensing