科研成果

The effects of flagella and their properties on bacterial transport and deposition behaviors were examined by using four types of Escherichia coli (E. coli) with or without flagella, as well as with normal or sticky flagella. Packed column, quartz crystal microbalance with dissipation, visible parallel-plate flow chamber system, and visible flow chamber packed with porous media system were employed to investigate the deposition mechanisms of bacteria with different properties of flagella. We found that the presence of flagella favored E. coli deposition onto quartz sand/silica surfaces. Moreover, by changing the porous media porosity and directly observing the bacterial deposition process, local sites with high roughness, narrow flow channels, and grain-to-grain contacts were found to be the major sites for bacterial deposition. Particularly, flagella could help bacteria swim near and then deposit at these sites. In addition, we found that due to the stronger adhesive forces, sticky flagella could further enhance bacterial deposition onto quartz sand/silica surfaces. Elution experiments indicated that flagella could help bacteria attach onto sand surfaces more irreversibly. Clearly, flagella and their properties would have obvious impacts on the transport/deposition behaviors of bacteria in porous media. © 2021 American Chemical Society.

When using spectral methods, a consistent method for tuning the expansion order is often required, especially for time-dependent problems in which oscillations emerge in the solution. In this paper, we propose a frequency-dependent p-adaptive technique that adaptively adjusts the expansion order based on a frequency indicator. Using this p-adaptive technique, combined with recently proposed scaling and moving techniques, we are able to devise an adaptive spectral method in unbounded domains that can capture and handle diffusion, advection, and oscillations. As an application, we use this adaptive spectral method to numerically solve Schrödinger’s equation in an unbounded domain and successfully capture the solution’s oscillatory behavior at infinity.

 

To distinctively identify two objects at the deep-subwavelength scales requires sharp superfocusing to overcome the diffraction limit. However, conventional superfocusing effect and information-carrying capacity are limited by the focal length and single focusing field (only electric or magnetic field), which are hard to be apparently improved. Here, we introduce the concept of “dual-foci superfocusing”, an advanced focusing form that can provide either one or two focusing spots, simultaneously converging both electric and magnetic fields and presenting an effect of electromagnetostatic space-division multiplexing. The physical mechanism of the dual-foci superfocusing is analyzed and synthesized by an original theory of shaping functional fields using hybrid-magnitude evanescent modes. Through a terahertz plasmonic array, the dual-foci superfocusing is numerically demonstrated, whose metric (ratio of focal length to focusing-spot size) is sufficiently improved from traditional 1–1.8 up to 2.8. The proposed methodology could be exploited as a platform to investigate the novel concurrent characteristics of superfocusing and might represent an important step toward the development of beam manipulation and sophisticated holography.

Microfluidic droplets are widely applied in various fields such as biomedicine, aerospace, energy utilization, and chemical engineering due to their advantages of large specific surface area, uniform size, stability, and easy control. The double T-shaped microchannel has the characteristics of rapid preparation of microdroplets with controllable size and good uniformity. Through 3D numerical simulation, the influence of the constriction structure of the microchannel on the formation of droplets was studied qualitatively and quantitatively. Compared with ordinary double T-shaped microchannels, the microchannels with a necked structure generate smaller droplets in diameter and faster generation frequency. Among the three structures of rectangular necking, inverted trapezoidal necking, and trapezoidal necking, the microchannel with the latter structure has the best performance, can produce monodisperse droplets of uniform size, and the period is stable.