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Using the educational knowledge graph to express the logical characteristics of knowledge, this paper takes project-driven learning in the teaching of "Information Technology in Secondary Schools" as an example and studies the group cooperative teaching mode based on the educational knowledge graph. The relationship between knowledge points in subject courses is described in the form of a knowledge graph, and the learning activities of coordinating the cooperation of each group are completed through the integration process of the knowledge graph. The use of a group cooperation teaching mode in the classroom can not only build a collaborative knowledge system between teachers and students but also help to carry out project-driven learning. The application of the knowledge graph of "Information Technology in Middle School" in the classroom can better show the logic between knowledge, and its graphical structure can help students to structure the knowledge they have learned.

Owing to the occupying tendency of Mn4+ at octahedral sites, doping Mn4+ activators in tetrahedral structures poses challenges and hence is seldom reported. In this work, tetrahedrally sited Mn4+ phosphors were studied. By combining X-ray diffraction (XRD) data with Rietveld refinement analysis, the location of Mn4+ was determined. It was found that by adding excessive raw MgO, the phosphor synthesis temperature can be improved, enhancing the crystallinity of the crystal and thus improving the emission performance of the phosphor. In addition, excessive raw MgO forms a second phase in an LMGO matrix, which does not change the doping site for Mn4+. The Tanabe–Sugano diagram of Mn4+ in the tetrahedral field and the energy-level diagram of these phosphors were constructed for the first time, and the excitation and emission mechanisms are discussed in detail. With 1.2-fold excess of raw MgO, the prepared sample (LMGO-Mn-1.2) shows the best luminescence, demonstrating red emissions peaked at 656 nm and affording an emission intensity enhancement of over 50 times compared to a stoichiometric LMGO:Mn4+ system. At 150 °C, LMGO-Mn-1.2 keeps 90% emission intensity compared to that at room temperature. Finally, a high-efficiency warm white light–emitting diode was built. This work provides new insights into the study of Mn4+-activated phosphors in a tetrahedron crystal field. [ABSTRACT FROM AUTHOR]

The tail rotor of a helicopter, a crucial component, traditionally relies on a complex drive mode involving reducers and transmission gears. This conventional setup, with its lengthy transmission chain and numerous components, hinders miniaturization efforts. In response to this challenge, our paper presents a novel piezoelectric drive approach. Our objective was to suggest an innovative design capable of minimizing the components involved in the tail rotor drive. This design can be adjusted in size according to specific requirements and is effective up to a specified speed. Moreover, it facilitates the process of miniaturization and integration. The piezoelectric actuator's stator comprises an ultrasonic amplitude transformer, a ring, and three drive teeth. Utilizing the rod-like structure of the tail brace, the actuator is simplified by adhering ceramic sheets to it. The rotary piezoelectric actuator combines the first longitudinal mode of a rod with torus bending modes. The drive teeth then amplify the ring's displacement, facilitating rotor rotation. The resonant frequency and modal shape of the actuator were determined using the finite element method. Furthermore, an investigation was conducted to analyze the influence of the drive teeth positioning on the motion trajectory at the contact point. Theoretically, we infer that the declination angle of the drive tooth is a crucial parameter for achieving high speeds. To test our idea, we built three prototype stators with different drive tooth declination angles. Our actuator stands out for its cost-effectiveness, structural simplicity, compatibility with harmonic signals, and ease of miniaturization. It can be considered for the drive of the tail rotor of a microhelicopter. [ABSTRACT FROM AUTHOR]

In order to improve the effective utilization of agricultural irrigation water and to reasonably allocate water resources in irrigation areas, it is necessary to use open channel flow measurement devices that are accurate and easy to carry. In this study, a spring-plate flow measurement device with different plate widths was designed. Through a combination of theoretical analysis and numerical simulation, the measurement characteristics of the device in specific channels under conditions of 20–105 m3/h flow were studied, the relationship between the flow rate and the force acting on the plate surface was fitted, and the hydraulic characteristics of water flow during its use, such as pressure, velocity distribution, and head loss, were analyzed. The results show that in the process of using the spring-plate flow measurement device, the force on the plate surface increases with the increase in the flow rate, and the force on the plate surface is related to the flow rate in the channel by a power of 5/6. The width of the measurement plate impacts the accuracy of flow measurement, and the smaller the plate width, the larger the error in flow measurement. The distribution of pressure on the measurement plate is similar to that of static pressure, and the pressure increases with the increase in the width of the measurement plate. The upstream flow velocity of the device is small, and the water level increases due to obstruction of the measurement plate. When it connects to the downstream water surface, the water level rapidly decreases, and the flow velocity increases. In using the spring-plate flow measurement device to measure flow, head loss will be produced, and the magnitude of this loss increases with the increase in the width of the measurement plate. The research results provide a theoretical basis for the application of spring plate flow-measuring devices in irrigation areas. [ABSTRACT FROM AUTHOR]

Traveling wave rotary ultrasonic motors (TRUMs) are widely used in various industrial processes due to their attractive features, such as compact structure, high accuracy, and fast response. However, the major limiting factors of the operational performance of TRUMs under high-voltage excitation are the nonlinear behavior caused by the nonlinearities of the piezoelectric materials and the friction between the stator and rotor of the motor. In this study, a nonlinear dynamics model and an identification method are presented to directly design the driver circuit for suppressing the nonlinear behavior under high voltage excitation. Firstly, by studying the time–frequency characteristics of the isolated electrode voltage, a single-sided Hertzian contact forced oscillator model of TRUMs is established, involving the nonlinearities of the piezoelectric material and friction. Secondly, a harmonic balance nonlinear identification is proposed in the time domain for TRUMs. The influence of the voltage and preload on the nonlinear phenomena is discussed. Lastly, a novel driver circuit is proposed to suppress the nonlinearities using feedback from the isolated electrode. Experiments showed that the total harmonic distortion decreased by 89.4% under 500 Vpp. The proposed drive circuit design method is used to find a high excitation voltage and preload to achieve greater motor output power. [ABSTRACT FROM AUTHOR]

To meet the requirements of miniaturization, lightweight and precision of space optical instruments, an aperture driven by single-phase piezoelectric motor was designed. The whole structure of the apertures was designed to realize the integration of structure and function. Then, piezoelectric stators with high strength and power density were designed by using piezoelectric ceramics and carbon fiber composite materials. The dynamics characteristics of laminated piezoelectric stators were analyzed by COMSOL finite element software, and the modal frequency consistency was adjusted. The structure optimization and interference mode separation design of the moving rings of diaphragm were also completed. According to the design scheme, the prototype of piezoelectric apertures was manufactured. The mass is only 49 g, aperture range is in 0.5~35 mm.The experimental results show that the full opening and closing time of the apertures are as 89 ms and 92.4 ms respectively, and the minimum angular resolution is as 4x10-5 rad. This study simplifies the composition and control of the diaphragm, making it more compact in structures and smaller in weight while ensuring accuracy. [ABSTRACT FROM AUTHOR]

The traditional dynamic models of linear ultrasonic motor (LUSM) do not consider the influences of the preload force and the roughness of the contact surface of stator/slider on the performance of the motor, which unable to effectively describe the dynamic behavior of the motor. In this paper, a dynamic model is established for a V-shaped LUSM considering the influence of the preload force and the roughness of the contact surface of stator/slider on the dynamic behavior of the motor. The contact mechanism of the stator/slider and the influence of preload force on the stator parameters are studied and analyzed. The effectiveness of the developed model is verified by comparing with the analytical model that ignored the effect of the preload force on the stator parameters. The experimental results shown that the developed model can accurately reflect the dynamic characteristics of the motor, and the model will be helpful for the function prediction and precise control of the motor. [ABSTRACT FROM AUTHOR]

Owing to the occupying tendency of Mn4+ at octahedral sites, doping Mn4+ activators in tetrahedral structures poses challenges and hence is seldom reported. In this work, tetrahedrally sited Mn4+ phosphors were studied. By combining X-ray diffraction (XRD) data with Rietveld refinement analysis, the location of Mn4+ was determined. It was found that by adding excessive raw MgO, the phosphor synthesis temperature can be improved, enhancing the crystallinity of the crystal and thus improving the emission performance of the phosphor. In addition, excessive raw MgO forms a second phase in an LMGO matrix, which does not change the doping site for Mn4+. The Tanabe–Sugano diagram of Mn4+ in the tetrahedral field and the energy-level diagram of these phosphors were constructed for the first time, and the excitation and emission mechanisms are discussed in detail. With 1.2-fold excess of raw MgO, the prepared sample (LMGO-Mn-1.2) shows the best luminescence, demonstrating red emissions peaked at 656 nm and affording an emission intensity enhancement of over 50 times compared to a stoichiometric LMGO:Mn4+ system. At 150 °C, LMGO-Mn-1.2 keeps 90% emission intensity compared to that at room temperature. Finally, a high-efficiency warm white light–emitting diode was built. This work provides new insights into the study of Mn4+-activated phosphors in a tetrahedron crystal field. [ABSTRACT FROM AUTHOR]