Photoacoustic speckle pattern interferometry for detecting cracks of different sizes.

A system and method for non-destructive detection of cracks of different width and depths based on digital speckle interferometry coupled with pulsed laser excitation is introduced and tested. Based on photoacoustic effect, acoustic waves are induced onto the rear of the samples by pumping a pulsed laser beam on it. The generated mechanical wave propagates from the rear surface of the sample to the front while front surface is monitored by speckle interferometry. In order to acquire information about surface deformation, the front surface is illuminated by continuous wave laser and interference are imaged onto the camera as speckle images. After processing the produced fringe patterns, it indicates the presence and location of the cracks in qualitative way. In this study, the system and method mentioned above are validated by detecting medium density fiberboard with simulated cracks. The fringe patterns from areas with or without defects are compared and discussed. Besides, the system and method to distinguish and predict cracks sizes is proposed and validated.

The seasonal and spatial variations in diatom communities and the influence of environmental factors on three temperate reservoirs in Shandong province, China.

Diatoms play an important role as ecological indicators, and some species of diatoms can easily cause water blooms, thereby decreasing the production capacity of water treatment plants and endangering drinking water safety. Mastering the diatom community dynamics is crucial for water supply. In this study, diatom composition, spatial distribution and succession were investigated in Datun Reservoir, Donghu Reservoir and Shuangwangcheng Reservoir, which are important drinking water sources in Shandong province, China. Results showed that the three reservoirs could be classified as being between mesotrophic and moderately eutrophic. The diatom community in each of the three reservoirs exhibited no obvious seasonal succession. The diatom communities in the three reservoirs were relatively simple in composition, with Synedra and Cyclotella being the most dominant groups all year round. Synedra had a negative relationship with NO2-N. Cyclotella had a positive association with NO3-N, but was negatively associated with NH4-N and CODMn in the three reservoirs. Through the analysis of diatom and environmental factors, the three reservoirs have the potential of hosting diatom blooms in summer, when the higher temperature combines with reduced water flow.

A promising application of chitosan quaternary ammonium salt to removal of Microcystis aeruginosa cells from drinking water.

This work was aimed toward studying the new application of chitosan quaternary ammonium salt (HTCC), a water-soluble chitosan derivative, on removal of Microcystis aeruginosa (M. aeruginosa) cells during HTCC coagulation and floc storage. Results showed that all cells were removed without damage under optimum coagulation conditions: HTCC dosage 1.5mg/L, rapid mixing for 0.5min at 5.04g and slow mixing for 30min at 0.20g. The high removal efficiency was due to the large size and compact structure of flocs formed by HTCC, which readily settled. During floc storage, HTCC could induce production of reactive oxygen species (ROS), which would accelerate M. aeruginosa cell lysis. But the flocs, into which the cells aggregated, could protect cells from cellular oxidative damage caused by ROS, thus keeping the cells intact for a longer time.