Coherent Thermoelectric Power from Graphene Quantum Dots

Zhao, Mali,Kim, Dohyun,Nguyen, Van Luan,Jiang, Jinbao,Sun, Linfeng,Lee, Young Hee,Yang, Heejun American Chemical Society 2019 NANO LETTERS Vol.19 No.1

<P>The quantum confinement of charge carriers has been a promising approach to enhance the efficiency of thermoelectric devices, by lowering the dimension of materials and raising the boundary phonon scattering rate. The role of quantum confinement in thermoelectric efficiency has been investigated by using macroscopic device-scale measurements based on diffusive electron transport with the thermal de Broglie wavelength of the electrons. Here, we report a new class of thermoelectric operation originating from quasi-bound state electrons in low-dimensional materials. Coherent thermoelectric power from confined charges was observed at room temperature in graphene quantum dots with diameters of several nanometers. The graphene quantum dots, electrostatically defined as circular n-p-n junctions to isolate charges in the p-type graphene quantum dots, enabled thermoelectric microscopy at the atomic scale, revealing weakly localized and coherent thermoelectric power generation. The conceptual thermoelectric operation provides new insights, selectively enhancing coherent thermoelectric power via resonant states of charge carriers in low-dimensional materials.</P> [FIG OMISSION]</BR>

Fault feature extraction of a rotor system based on local mean decomposition and Teager energy kurtosis

Linfeng Deng,Rongzhen Zhao 대한기계학회 2014 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.28 No.4

Feature extraction is the most important step for machine fault diagnosis, but useful features are very difficult to extract from the vibrationsignals, especially for intelligent fault diagnosis based on data-driven technique. An integral method for fault feature extraction basedon local mean decomposition (LMD) and Teager energy kurtosis (TEK) is proposed in this paper. The raw vibration signals are firstprocessed via LMD to produce a group of product functions (PFs). Then, the Teager energies are computed using the derived PFs. Subsequently,each Teager energy data set is directly used to calculate the corresponding TEK. A vibration experiment was performed on arotor-bearing rig with rub-impact fault to validate the proposed method. The experimental results show that the proposed method canextract different TEKs from the mechanical vibration signals under two different operating conditions. These TEKs can be employed toidentify the normal and rub-impact fault conditions and construct a numerical-valued machine fault decision table, which proves that thismethod is suitable for fault feature extraction of the rotor-bearing system.

Synaptic Computation Enabled by Joule Heating of Single-Layered Semiconductors for Sound Localization

Sun, Linfeng,Zhang, Yishu,Hwang, Geunwoo,Jiang, Jinbao,Kim, Dohyun,Eshete, Yonas Assefa,Zhao, Rong,Yang, Heejun American Chemical Society 2018 NANO LETTERS Vol.18 No.5

<P>Synaptic computation, which is vital for information processing and decision making in neural networks, has remained technically challenging to be demonstrated without using numerous transistors and capacitors, though significant efforts have been made to emulate the biological synaptic transmission such as short-term and long-term plasticity and memory. Here, we report synaptic computation based on Joule heating and versatile doping induced metal-insulator transition in a scalable monolayer-molybdenum disulfide (MoS<SUB>2</SUB>) device with a biologically comparable energy consumption (∼10 fJ). A circuit with our tunable excitatory and inhibitory synaptic devices demonstrates a key function for realizing the most precise temporal computation in the human brain, sound localization: detecting an interaural time difference by suppressing sound intensity- or frequency-dependent synaptic connectivity. This Letter opens a way to implement synaptic computing in neuromorphic applications, overcoming the limitation of scalability and power consumption in conventional CMOS-based neuromorphic devices.</P> [FIG OMISSION]</BR>

RESEARCH ON LOCAL DISTURBANCE COOPERATIVE CONTROL OF HETEROGENEOUS VEHICLE PLATOON BASED ON SITUATION ASSESSMENT

Tingfang Zhang,Qidong Wang,Linfeng Zhao,Wuwei Chen,Bixin Cai,Mingyue Yan 한국자동차공학회 2024 International journal of automotive technology Vol.25 No.2

In the longitudinal driving of a heterogeneous platoon, external disturbances of local vehicles can cause safety problemsof the intended functionality. Therefore, a cooperative control method based on situation assessment is proposed. First, theminimum safe distance is determined according to the state of adjacent vehicles. A novel situation assessment model isestablished to characterize the stability of the platoon. Vehicle spacing, speed, and acceleration are selected as evaluationindicators. Then, an improved active disturbance rejection controller (IADRC) is designed to improve platoon stabilitythrough feedback compensation control. In addition, considering the unnecessary continuous involvement of the IADRC,its intervention time is determined by the situation assessment results. Finally, simulation and hardware-in-the-loop (HIL)experiments are carried out under two communication topologies. The results show that the proposed method can eff ectivelyimprove the stability and safety of the platoon.

Anti-Rollover Control Based on Stable Zone Partition of Counterbalanced Forklift Trucks

Xia Guang,Xia Yan,Tang Xiwen,Zhao Linfeng,Hu Jinfang 한국자동차공학회 2021 International journal of automotive technology Vol.22 No.6

To improve the anti-rollover capacity of a counterbalanced forklift, a two-stage rollover dynamic model is established on the basis of the forklift structure. Stable zones are divided according to the two-stage lateral load transfer rate: stable region, relatively stable region, dangerous zone and abnormal dangerous zone. An anti-rollover layered control strategy based on stable zone partition is proposed, and different anti-rollover control actuators are selected: dynamic balance weight, anti-rollover cylinder and steering cylinder. Anti-rollover controllers consist of the upper stable region identification controller, the middle-level controller based on model predictive control (MPC) and the lower layer executive controller. The upper stable region identification controller performs stable zone recognition based on the two-stage lateral load transfer rate. The middlelevel MPC controller calculates the required control torque with the body’s lateral angle and yaw rate as the control objectives. The lower layer executive controller controls the balance weight, anti-rollover cylinder and the steering cylinder according to the improved chain incremental allocation method to meet the target control torque. Simulation and real vehicle tests based on MATLAB/Simulink show that the anti-rollover control based on stable zone partition can greatly reduce the risk of forklift rollover and improve the forklift safety.

Study on Anti-Rollover of the Counterbalance Forklift Based on Extension Hierarchical Control

Xia Guang,Li Jiacheng,Tang Xiwen,Zhao Linfeng,Sun Baoqun 한국자동차공학회 2021 International journal of automotive technology Vol.22 No.3

The anti-rollover control actuator of a counterbalance forklift is determined by analysing its structural characteristics and roll-over mechanism. An anti-rollover control strategy for counterbalance forklifts based on extension decision is proposed, and the anti-rollover extension hierarchical controller, including the upper-layer extension and lower-layer execution controls, is designed. The upper-layer extension controller divides the forklift anti-rollover control domain into three types, namely, classical domain, extension domain and non-domain, and determines the weight coefficient of the lower layer execution controller. The lower-layer execution controller receives the weight coefficient determined by the upper-layer extension controller, controls the weight distribution on the yaw rate and lateral acceleration controllers and executes the command to obtain the anti-rollover extension control of the counterbalance forklift. The European standard condition simulation and real vehicle test results show that the anti-rollover control strategy of the counterbalance forklift based on the extension decision can effectively reduce the forklift roll range under high-speed emergency steering conditions, prevent the forklift from rolling over and improve the stability and active safety of the counterbalance forklift.

Center of Gravity Position Estimation of Counterbalanced Forklift Truck Based on Multi Model Data Fusion

Xia Guang,Zhang Chenhao,Tang Xiwen,Zhang Yang,Zhao Linfeng 한국자동차공학회 2023 International journal of automotive technology Vol.24 No.5

The center of gravity of a forklift truck, a crucial parameter for vehicle stability, changes with different loads during operation. We propose an estimation algorithm for the center of gravity position suitable for a counterbalanced forklift truck. By installing sensors on the fork, we use an inclinable platform and propose a static joint center of gravity measurement method. For straight-line driving, we establish a longitudinal dynamics model and propose a nonlinear H∞ estimation algorithm. For steering conditions, we establish a roll dynamics model and propose a forgetting factor recursive least square estimation algorithm. A data fusion algorithm for the forklift truck’s center of gravity position under various working conditions is proposed. The fusion of these estimation results yields the best estimated center of gravity height. We validate the algorithm’s effectiveness using a hardware-in-the-loop simulation platform under different working conditions. The experiments demonstrate the algorithm’s fast parameter fitting, wide applicability, and accurate position control within a 5 % error range.

Adaptive Fault-Tolerant Control Considering the Actuator Failure of Forklift Anti-Rollover System

Xia Guang,Li Tao,Tang Xiwen,Zhang Yang,Zhao Linfeng 한국자동차공학회 2023 International journal of automotive technology Vol.24 No.3

An adaptive fault-tolerant anti-rollover fuzzy system is proposed to improve the anti-rollover performance of counterbalanced forklifts. Considering the actual control input, various unpredictable actuator failure models in the system are established. Based on the three degree-of-freedom (DOF) model of a counterbalanced forklift, an anti-rollover Takagi-Sugeno (T-S) fuzzy system is established. The stability of this anti-rollover system is analyzed to ensure its stability under specific control inputs and external disturbances. When the upper limits of actuator faults and disturbances are unknown, an adaptive fault-tolerant control method is designed to update the controller parameters. The sufficient conditions for the stability of the forklift anti-rollover system in the presence of actuator faults and external disturbances are given using the Lyapunov stability theory. Simulation and real vehicle tests based on MATLAB/Simulink show that the anti-rollover system with adaptive fault-tolerant control can reduce impacts effectively and quickly after the actuator fails, thereby improving the safety and reliability of the forklift.