Search

The influence of the resonant vibrational excitation of the ethylene wagging mode (υ7, 949.3 cm-1) on the combustion chemical vapor deposition of diamond was studied via femtosecond laser-induced filamentation (FLIF) spectroscopy. The O2-C2H2-C2H4 flame filaments were sampled within the diamond-formation zones to investigate the evolution of the diamond-formation-related species. In addition to higher diamond growth rates, increasing the incident laser power density led to the transitions of diamond crystal facets and quality as the results of competition between carbon-containing and OH-containing species. Evaluated using the C2/OH number density ratio, {100}-faceted diamond crystals were obtained at the C2/OH ratio of 110.00, while {111}-faceted diamond crystals were produced at the C2/OH ratio of 133.34. [ABSTRACT FROM AUTHOR]

Legionella pneumophila, the most commonly identified causative agent in drinking water associated with disease outbreaks, can be harbored by and released from drinking water biofilms. In this study, the release of biofilm-associated L. pneumophila under simulated drinking water flow containing a disinfectant residual was examined. Meanwhile, the inactivation and infectivity (to amoebae) of the released L. pneumophila were studied. To simulate drinking water system conditions, biofilms were prepared under either disinfectant exposure (predisinfected biofilms) or disinfectant-free (untreated biofilms) conditions, respectively. For experiments with water flow containing a disinfectant to release the biofilm-associated L. pneumophila from these two types of biofilms, the L. pneumophila release kinetics values from predisinfected and untreated biofilms under flow condition were not statistically different (one-way ANOVA, p > 0.05). However, inactivation of the L. pneumophila released from predisinfected biofilms was 1-2 times higher and amoeba infectivity was 2-29 times lower than that from untreated biofilms. The higher disinfectant resistance of L. pneumophila released from untreated biofilms was presumably influenced by the detachment of a larger amount of biofilm material (determined by 16S rRNA qPCR) surrounding the released L. pneumophila. This study highlights the interaction among disinfectant residual, biofilms, and L. pneumophila, which provides guidelines to assess and control pathogen risk. [ABSTRACT FROM AUTHOR]

Mechanical and structural properties of biofilms influence the accumulation and release of pathogens in drinking water distribution systems (DWDS). Thus, understanding how long-term residual disinfectants exposure affects biofilm mechanical and structural properties is a necessary aspect for pathogen risk assessment and control. In this study, elastic modulus and structure of groundwater biofilms was monitored by atomic force microscopy (AFM) and optical coherence tomography (OCT) during three months of exposure to monochloramine or free chlorine. After the first month of disinfectant exposure, the mean stiffness of monochloramine- or free-chlorine-treated biofilms was 4 to 9 times higher than those before treatment. Meanwhile, the biofilm thickness decreased from 120 ± 8 µm to 93 ± 6-107 ± 11 μm. The increased surface stiffness and decreased biofilm thickness within the first month of disinfectant exposure was presumably due to the consumption of biomass. However, by the second to third month during disinfectant exposure, the biofilm mean stiffness showed a 2- to 4-fold decrease, and the biofilm thickness increased to 110 ± 7-129 ± 8 μm, suggesting that the biofilms adapted to disinfectant exposure. After three months of the disinfectant exposure process, the disinfected biofilms showed 2-5 times higher mean stiffness (as determined by AFM) and 6-13-fold higher ratios of protein over polysaccharide, as determined by differential staining and confocal laser scanning microscopy (CLSM), than the nondisinfected groundwater biofilms. However, the disinfected biofilms and nondisinfected biofilms showed statistically similar thicknesses (t test, p > 0.05), suggesting that long-term disinfection may not significantly remove net biomass. This study showed how biofilm mechanical and structural properties vary in response to a complex DWDS environment, which will contribute to further research on the risk assessment and control of biofilm-associated-pathogens in DWDS. [ABSTRACT FROM AUTHOR]

Biofilms in drinking water distribution systems (DWDS) could exacerbate the persistence and associated risks of pathogenic Legionella pneumophila (L. pneumophila), thus raising human health concerns. However, mechanisms controlling adhesion and subsequent detachment of L. pneumophila associated with biofilms remain unclear. We determined the connection between L. pneumophila adhesion and subsequent detachment with biofilm physical structure characterization using optical coherence tomography (OCT) imaging technique. Analysis of the OCT images of multispecies biofilms grown under low nutrient condition up to 34 weeks revealed the lack of biofilm deformation even when these biofilms were exposed to flow velocity of 0.7 m/s, typical flow for DWDS. L. pneumophila adhesion on these biofilm under low flow velocity (0.007 m/s) positively correlated with biofilm roughness due to enlarged biofilm surface area and local flow conditions created by roughness asperities. The preadhered L. pneumophila on selected rough and smooth biofilms were found to detach when these biofilms were subjected to higher flow velocity. At the flow velocity of 0.1 and 0.3 m/s, the ratio of detached cell from the smooth biofilm surface was from 1.3 to 1.4 times higher than that from the rough biofilm surface, presumably because of the low shear stress zones near roughness asperities. This study determined that physical structure and local hydrodynamics control L. pneumophila adhesion to and detachment from simulated drinking water biofilm, thus it is the first step toward reducing the risk of L. pneumophila exposure and subsequent infections. [ABSTRACT FROM AUTHOR]

Seed-free growth of diamond patterns on Si surfaces wasrealizedby surface patterning via femtosecond laser direct writing followedby laser-assisted combustion synthesis in open air. Prepatterned Sisurfaces provide active nucleation sites for diamond growth. The dimensionand shape of the diamond patterns can be precisely controlled at micrometerscales. Field-enhanced thermionic emission current was measured tomonitor diamond nucleation and growth process in real time. The diamondnucleation density and quality depend strongly on the surface roughnessof the prepatterned Si patterns. A higher surface roughness leadsto more nucleation sites and higher nucleation density. However, highlocal temperature at peaks due to a large exposed surface to the flameon an excessively rough surface degrades the diamond quality. Theeasy fabrication of diamond patterns on nondiamond surfaces suggestspotential applications such as cutting tools, protective coatings,heat sinks, etc. [ABSTRACT FROM AUTHOR]

The article focuses on the applications and synthesis of helicenes, polycyclic aromatic compounds having nonplanar screw-shaped skeletons. It says that the Diels-Alder synthetic approach has brought a large number helicenes derivatives, and the enantioselectivities have been developed. It mentions that the helicenes used as chiral reagents or chiral auxiliaries in different diastereoselective reactions including hydroxyamination, epoxidation, and the ene reaction.

Traditional ceramic-based, high-temperature electrode materials (e.g., lanthanum chromate) are severely limited due to their conditional electrical conductivity and poor stability under harsh circumstances. Advanced composite structures based on vertically aligned carbon nanotubes (VACNTs) and high-temperature ceramics are expected to address this grand challenge, in which ceramic serves as a shielding layer protecting the VACNTs from the oxidation and erosive environment, while the VACNTs work as a conductor. However, it is still a great challenge to fabricate VACNT/ceramic composite structures due to the limited diffusion of ceramics inside the VACNT arrays. In this work, we report on the controllable fabrication of infiltrated (and noninfiltrated) VACNT/silicon composite structures via thermal chemical vapor deposition (CVD) [and laser-assisted CVD]. In laser-assisted CVD, low-crystalline silicon (Si) was quickly deposited at the VACNT subsurfaces/surfaces followed by the formation of high-crystalline Si layers, thus resulting in noninfiltrated composite structures. Unlike laser-assisted CVD, thermal CVD activated the precursors inside and outside the VACNTs simultaneously, which realized uniform infiltrated VACNT/Si composite structures. The growth mechanisms for infiltrated and noninfiltrated VACNT/ceramic composites, which we attributed to the different temperature distributions and gas diffusion mechanism in VACNTs, were investigated. More importantly, the as-farbicated composite structures exhibited excellent multifunctional properties, such as excellent antioxidative ability (up to 1100 °C), high thermal stability (up to 1400 °C), good high velocity hot gas erosion resistance, and good electrical conductivity (∼8.95 Sm -1 at 823 K). The work presented here brings a simple, new approach to the fabrication of advanced composite structures for hot electrode applications.

Carbon soot (CS) has the advantages of cost-effectiveness and production scalability over other carbons (i.e., graphene, CNTs) in their synthesis. However, little research has been conducted to explore the potential applications of CS. In this study, we demonstrated that a common daily waste-CS-can be used for developing a cost-effective absorbent (CS-sponge) to remove oil contaminants from water. The CS was synthesized by an ethylene-oxygen combustion flame. The CS-sponge was prepared via a dip-coating method. Without further surface modification and pretreatments, the CS-sponge demonstrates high absorption capacities (up to 80 times its own weight) for a broad spectrum of oils and organic solvents with a recyclability of more than 10 times. These research results show evidence that the CS-sponge is promising in environmental remediation for large-scale, low-cost removal of oils from water.