As an important pathway for movement of rainfall or sprinkler irrigation water through a crop canopy to the ground, stemflow is of great significance for utilization efficiency of sprinkler irrigation water and for crop growth. In this study, under simulated indoor artificial rainfall, the stemflow rates (SF) of corn plants (Zea mays) in different corn growth stages (V4 stage $ VT stage) under different rainfall intensities (I) were observed, and the relationships among stemflow, leaf area (LA), and I were analyzed. Based on these results, stemflow models were developed. The results showed that for all corn growth stages, the average SF of a single corn plant was about 55.69 mL/ min, accounting for 45% of total rainfall. SF increased as a power function of corn LA and I, and the percentage of stemflow in total rainfall increased as a power function of corn LA. Theoretical, semi-empirical, and empirical models of corn SF and stemflow proportion (SR) of total rainfall were established by analyzing the relationships among LA, I, and stemflow. All three models were used to estimate SF and SR in different corn growth stages and achieved desired accuracy. The semi-empirical and empirical models were more accurate in predicting and simulating corn SF, but the calculation and application of the semi-empirical model was relatively simpler. The empirical model of SR enabled a more accurate calculation of the percentage of stemflow in total rainfall.

Ultrasonic linear motor, Piezoelectricity, Rectangular vibrator, Traveling wave Abstract. With the aim of realizing quasi-traveling wave drive in ultrasonic linear micro motors, a novel quasi-traveling wave ultrasonic linear motor using a ring type rectangular vibrator with the sizes of 39mm×6mm×12.7mm is proposed. The quasi-traveling wave is excited and propagates along the ring type rectangular vibrator depending on the superposition of two orthogonal flexural-vibration modes with a spatial phase shift of 90 degrees. 7 piezoelectric ceramic elements are used to excite two working modes of the vibrator. The vibrator structure was designed and eigenfrequency degeneration was realized by Finite Element Analysis (FEA) method. The modal test shows that the design scheme was tenable. The excitation and propagation of quasi-traveling wave were proved by laser vibration test. The trial motor gave a maximum driving velocity of 162.5mm/s and a maximum load of 8.5N, while the excitation frequency was 66 KHz and voltage was 160Vpp.

There are parametric uncertainties, nonlinearities including the hysteresis effect, and other un-modeled disturbances existing in piezoelectric actuator systems. A terminal sliding mode control methodology is proposed in this paper. By using nonlinear TSM manifold, the system errors can converge to zero in finite time. So high-precision tracking performance can be achieved. Simulation results are presented to validate the design.