Search

The brown planthopper (BPH), Nilaparvata lugens, is one of the most destructive rice pests in Asia. It has already developed a high level of resistance to many commonly used insecticides including nitenpyram (NIT), which is a main synthetic insecticide that is used to control BPH with a much shorter persistence compared to other neonicotinoid insecticides. Recently, we found that an exogenous supplement of paclobutrazol (PZ) could significantly enhance the efficacy of NIT against BPH, and the molecular mechanism underlying this synergistic effect was explored. The results showed that the addition of a range of 150–300 mg/L PZ increased the toxicity of NIT against BPH with the highest mortalities of 78.0–87.0% on the 16th day after treatments, and PZ could also significantly prolong the persistence of the NIT efficacies. Further investigation suggested that PZ directly increased the content of flavonoids and H2O2 in rice and increased the activity of polyphenol oxidase, which might be involved in the constitutive defense of rice in advance. Additionally, there was an interaction between PZ and BPH infestation, indicating that PZ might activate the host defense responses. Therefore, PZ increased the efficacy of NIT against the brown planthoppers by enhancing the constitutive and inducible defense responses of rice. Our study showed for the first time that PZ could contribute to improving the control effects of insecticides via inducing the defense responses in rice plants against BPH, which provided an important theoretical basis for developing novel pest management strategies in the field.

The two-dimensional particle image velocimetry (PIV) data are inevitably contaminated by noise due to various imperfections in instrumentation or algorithm, based on which the well-established vortex identification methods often yield noise or incomplete vortex structure with a jagged boundary. To make up this deficiency, a novel method was proposed in this paper and the efficiency of the new method was demonstrated by its applications in extracting the two-dimensional spanwise vortex structures from 2D PIV data in open-channel flows. The new method takes up a single vortex structure by combining model matching and vorticity filtering, and successfully locates the vortex core and draws a streamlined vortex boundary. The new method shows promise as being more effective than commonly used schemes in open-channel flow applications.

The measurement of instantaneous sediment concentration remains a challenging task. In this study, a three-step procedure is proposed to estimate instantaneous sediment concentration using acoustic backscatter from Acoustic Doppler Velocimeter (ADV). The influences of acoustic noise and particle diameter on an ADV׳s performance was first tested in the laboratory, then the three-step procedure was verified based on field measurements in the Zhongxian and Fengjie reaches in the Three Gorges Reservoir. The first step involves reconstructing the backscatter signal time series. Due to contamination from both the noise floor and spurious spikes, the denoising-despiking method was applied instead of the traditional velocity-despiking methods, and this approach performed well based on spectrum analysis. The second step involves calibrating the sediment concentration against the backscatter signal. A linear relation, whose slope and intercept were calibrated to be dependent on particle diameter, is proposed in double logarithmic coordinates. The third step involves calculating the instantaneous sediment concentration using reconstructed instantaneous backscatter based on the proposed relation. The accuracy of the proposed method was evaluated through consideration of the concentration spectrum and sediment flux, indicating that the proposed three-step procedure is effective for the measurement of instantaneous sediment concentration.

An experimental apparatus driven by horizontal oscillating grids in a water tank is proposed for generating shear-free turbulence, which is measured using Particle Image Velocimetry (PIV). The performances of the proposed apparatus are investigated through the instantaneous and root-mean-square (RMS) velocity, Reynolds stress, length and time scale, frequency spectra and dissipation rate. Results indicate that the turbulence at the core region of the water tank, probably 8 cm in length, is identified to be shear-free. The main advantage of the turbulence driven by horizontal oscillating mode is that the ratios of the longitudinal turbulent intensities to the vertical values are between 1.5 and 2.0, consistent with those ratios in open-channel flows. Additionally, the range of the length scale can span the typical sizes of suspended particles in natural environments, and the dissipation rate also agrees with those found in natural environments. For convenience of experimental use, a formula is suggested to calculate the RMS flow velocity, which is linearly proportional to the product of oscillating stroke and frequency. The proposed experimental method in this study appears to be more appropriate than the traditional vertical oscillating mode for studying the fundamental mechanisms of vertical migratory behavior of suspended particles and contaminants in turbulent flows.

The Three Gorges Reservoir (TGR) is suffering from unexpected fine sediment deposition, to better understand the fine sediment transport processes, field measurements were conducted at the Zhongxian and Fengjie reaches. A method based on the sediment diffusion equation was proposed to measure the settling velocities using the Acoustic Doppler Velocimeter (ADV). The backscatter acoustic intensities (BSI) received from the ADV were calibrated against the sediment concentrations measured via water sampling, suggesting a linear relationship in double logarithmic coordinate system. The instantaneous sediment concentration was calculated using the derived relationship, and then the settling velocity was obtained through the proposed procedure. The settling velocities of the fine particles in the TGR were found to vary with the water depth. Most of the effective settling velocities were within the range of 0.1–10 mm/s, which were larger than those of the primary particles, indicating that the flocculation was likely to occur in the TGR. Additionally, it is suggested that the turbulent motion played an important role in the flocculation in the TGR.

Sedimentation in the Three Gorges Reservoir (TGR) has been studied with a primary focus on the amount due to the decrease in sediment inflow caused by water and soil conservation projects a...

A high accuracy experimental system has been established for unsteady open-channel flow. Then 40 experiments were conducted to study the propagating characteristics of unsteady open-channel flow. From the experimental data, the variation law of propagating velocity, wave deformation rate, flow depth of wave peak and bottom, and other parameters were obtained. The experimental results show the followings. 1) The propagating velocity of unsteady open-channel flows can be expressed by the sum of flow velocity and micro-amplitude wave velocity at wave peak. 2) The waveform of an unsteady flow would deform when it propagates, with the rising stage becoming longer and the falling stage shorter; the deformation rate is a function of distance, period and relative amplitude of discharge. 3) The flow depths of wave peak and bottom have a close relationship with the period of the unsteady flow. When the period is short, water depths of wave peak and bottom are both close to those of the average discharge in the condition of uniform flow. For a long period unsteady flow, the water depth of wave peak is close to that of the maximal discharge in the condition of uniform flow, while at the flow wave bottom, it is close to the depth of the minimum discharge in an uniform flow. 4) Propagating characteristic of discharge is analogous to that of flow depth for unsteady flow.