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Residual chlorine is often required to remain present in public drinking water supplies during distribution to ensure water quality. It is essential to understand how bacteria respond to long-term chlorine exposure, especially with the presence of assimilable organic carbon (AOC). This study aimed to investigate the effects of chlorination on Pseudomonas aeruginosa in low AOC medium by both conventional plating and culture-independent methods including flow cytometry (FCM) and quantitative PCR (qPCR). In a simulated chlorinated system using a bioreactor, membrane damage and DNA damage were measured by FCM fluorescence fingerprint. The results indicated membrane permeability occurred prior to DNA damage in response to chlorination. A regrowth of P. aeruginosa was observed when the free chlorine concentration was below 0.3 mg/L. The bacterial response to long-term exposure to a constant low level of free chlorine (0.3 mg/L) was subsequently studied in detail. Both FCM and qPCR data showed a substantial reduction during initial exposure (0–16 h), followed by a plateau where the cell concentration remained stable (16–76 h), until finally all bacteria were inactivated with subsequent continuous chlorine exposure (76–124 h). The results showed three-stage inactivation kinetics for P. aeruginosa at a low chlorine level with extended exposure time: an initial fast inactivation stage, a relatively stable middle stage, and a final stage with a slower rate than the initial stage. A series of antibiotic resistance tests suggested long-term exposure to low chlorine level led to the selection of antibiotic-resistant P. aeruginosa. The combined results suggest that depletion of residual chlorine in low AOC medium systems could reactivate P. aeruginosa, leading to a possible threat to drinking water safety.

Abstract. Bacteria with low nucleic acid content (LNA) and high nucleic acid content (HNA) are widely distributed in aquatic environments. Most of the current understanding of these two subgroups is derived from studies in marine environments. In comparison, information on the spatial distribution of these two subgroups in freshwater environments is very limited. The present study analysed the biogeographical pattern of those two groups on a large-river scale (i.e. the Songhua River catchment, .1000 km). The results showed that the concentrations of LNA and HNA bacteria were distributed over a wide range from 5.45 Â 10 4 to 4.43 Â 10 6 cells mL À1 , and from 1.35 Â 10 5 to 4.37 Â 10 6 cells mL À1 respectively. The two groups have almost equal proportions in the Songhua River, with the average contribution of LNA bacteria reaching 47.0%. In comparison, the abundance of LNA bacteria in the mainstream was significantly higher than in the tributaries. The cytometric expressions (green fluorescence and side scatter) within LNA and HNA were strongly covaried, which implies that these two subgroups are intrinsically linked. Multivariate redundancy analysis indicated that both the abundance and cytometric characteristics of co-occurring LNA and HNA bacteria were regulated differently in the Songhua River. This suggests that LNA and HNA bacteria play different ecological roles in river ecosystems.

Infrared photodetectors are gaining remarkable interest due to their widespread civil and military applications. Low-dimensional materials such as quantum dots, nanowires, and two-dimensional nanolayers are extensively employed for detecting ultraviolet to infrared lights. Moreover, in conjunction with plasmonic nanostructures and plasmonic waveguides, they exhibit appealing performance for practical applications, including sub-wavelength photon confinement, high response time, and functionalities. In this review, we have discussed recent advances and challenges in the prospective infrared photodetectors fabricated by low-dimensional nanostructured materials. In general, this review systematically summarizes the state-of-the-art device architectures, major developments, and future trends in infrared photodetection.

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Recently, we have carried out a detailed Raman analysis to investigate the inhomogeneous crystallization of a-Si thin films irradiated by femtosecond (Fs) laser. As expected, there are many etched spots overlapping each other, which features the surface morphology of the irradiated films. It is observed clearly that there has generated an inhomogeneous crystallization inside a-Si thin film induced by Fs laser, and the crystalline volume fraction in one irradiated spot varies depending on different areas from the center to the edge. It is hard to observe any crystallization at the spot center where maximum energy of Fs laser is injected; however, there is an increasing crystalline volume fraction when the site varies from the center to the edge of the irradiated spot.More importantly, as the site varies from the center to the edge, the TO mode of Si nanocrystals (NCs; first-order Si-Si peak at~520.5 cm −1 ) is asymmetrically broadened towards the low wavenumber and exhibits a dip on the high wavenumber. A model has been proposed to explain this inhomogeneous crystallization inside the a-Si thin films induced by Fs laser, and both phonon confinement model and Fano model have been employed to discuss the origin of asymmetric line shapes of TO mode of Si NCs, and we prefer to attribute the asymmetry of TO mode to Fano effect. Our present research results provide a deep insight into the origin of asymmetric broadening for the Raman TO mode of Si NCs inside a-Si thin films irradiated by Fs laser.KEYWORDS a-Si thin film, asymmetric TO mode, femtosecond laser, inhomogeneous crystallization