133 research outputs found
A moving thermal dielectric crack in piezoelectric ceramics with a shearing force applied on its surface
No full textThis article conducts an exact analysis of a thermal dielectric crack moving in piezoelectric materials. Self-generating thermal and electric loadings by the crack interior are exerted on the crack surfaces as well as various external loadings including a shearing force. Fundamental solutions of the thermal and electro-elastic coupling fields are given by determining a temperature function and a harmonic function with eigenvalues properties due to material properties considered. Analytical expressions are obtained benefiting evaluation of key parameters. Numerical analysis is done and some interesting observations are found. There is a critical crack velocity within and beyond which the electric loading exerts different influences on the thermal flux of crack interior and the thermal stress intensity factor. (C) 2018 Elsevier Inc. All rights reserved.The authors are grateful for Professor Fengjun Li for his helpful discussion in the revision process. This work was supported by the National Natural Science Foundation of China (11472193, 11572227 and 11261042 as 61662060), the Major Innovation Projects for Building First-class Universities in China's Western Region (ZKZD2017009), and the Fundamental Research Funds for the Central Universities (1330219162)
Tractor and Semitrailer Scheduling with Time Windows in Highway Ports with Unbalanced Demand Under Network Conditions
No full textTo address the challenges of unbalanced demand and high operational costs in highway port logistics, this study investigates the scheduling of tractors and semitrailers under time window constraints in a networked environment, where geographically distributed ports are interconnected by fixed routes, and tractors dynamically transport semitrailers between ports to balance asymmetric demands. A mathematical optimization model is developed, incorporating multiple car yards, diverse transport demands, and temporal constraints. To solve the model efficiently, an Adaptive Large Neighborhood Search (ALNS) algorithm is proposed and benchmarked against an improved Ant Colony System (IACS). Simulation results show that, compared to traditional scheduling methods, the proposed approach reduces the number of required tractors by up to 61% and operational costs by up to 21%, depending on tractor working hours. The tractor-to-semitrailer ratio improves from 1.00:1.10 to 1.00:2.59, demonstrating the enhanced resource utilization enabled by the ALNS algorithm. These findings offer practical guidance for optimizing tractor and semitrailer configurations in highway port operations under varying conditions
The Effect of Mental Toughness on Learning Burnout of Junior Middle School Students: Putting School Adaptation as a Mediator Variable
No full textLearning burnout has always been a key problem in school education. Junior high school students, as an important part of the student population, cannot be ignored. To explore the impact of resilience, school adaptation on learning burnout is helpful to improve students’ learning level and reduce learning burnout. In this study, the junior high school students in A city were selected as the research objects, and questionnaires were used to explore the effect of mental toughness on learning burnout and the mediating effect of school adaptation. Statistical analysis methods such as descriptive statistics, correlation analysis, and regression were used. Based on the theoretical model of job burnout, data analysis showed that mental toughness of junior high school students in A city could significantly negatively predict learning burnout. Adolescent mental toughness can significantly affect the prediction of school adjustment school adjustment has a significant negative impact on learning burnout, and mental toughness can indirectly affect learning burnout through school adjustment
Research on Improved Recovery Method by Composed Synergistic Action of Well Pattern and Tertiary Recovery
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Fatigue Test and Unified Fatigue Life Calculation of Q460C Steel Notched Plates
No full textIn the present study, a total of 20 fatigue tests on notched plates of Q460C steel were carried out, where the effects of relative stress amplitude, Δσ/fy, and relative nominal maximum stress, σmax/fy, on the fatigue life of these notched plates were carefully examined. Theoretical analyses and numerical simulations were subsequently conducted, based on an ellipsoidal fracture model originally proposed by the second author, which has been validated for use as a fracture criterion of fatigue crack, to investigate the fatigue cracking in the Q460C steel notched plates. The theoretical model was further developed to estimate the fatigue life of the Q460C steel notched plates using a unified crack growth approach originally proposed by the second author. Based on the theoretical and simulated results, the accuracy of the unified crack growth approach, and the allowable stress fatigue life formula recommended in China’s code GB50017-2017, were assessed. The comparisons indicate that the unified crack growth approach is able to provide a reliable fatigue life assessment for the Q460C steel notched plates
Frequency octupling millimeter wave generated by polarization modulators and distributed by fiber without bit walk-off effect and carrier reuse with pilot
No full textAn optical polarization modulator (PoIM) is the key device to generate frequency multiplication millimeter waves (MMW) in the radio over fiber (ROF) system. A novel frequency octupling MMW ROF system is designed. The frequency octupling MMW is generated by beating the ±4th order sidebands, which are generated by a DP-PoIM, in a photodetector. By adopting the composite radio frequency (RF) signal as the PoIM’s RF driving signal, the downlink data can be modulated only on the +4th order optical sideband. The composite RF signal is formed by combining two beam signals: One is the modulated RF driving signal by downlink data with a phase modulator (PM), and the other is the amplified downlink data by the electrical gainer (EG). In the central station, a part of the optical carrier is split out and used as a pilot. In the base station, the pilot is filtered out and used as the uplink optical carrier for carrier reuse. To verify the feasibility of our scheme, the operation principle is analyzed, and a simulation experiment is built. The simulation results are in good agreement with the theoretical analysis. When the key parameters of the devices in the system diverge from their theoretical or default values, their influence on the bit error rate (BER) is also analyzed. Our scheme can effectively overcome the bit walk-off effect caused by optical fiber chromatic dispersion, greatly increase the fiber transmission distance, significantly improve the downlink performance and the tunability of the system. It has important application prospects in MMW ROF systems
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