Differential Incorporation of Carbon Substrates among Microbial Populations Identified by Field-Based, DNA Stable-Isotope Probing in South China Sea.

To determine the adapted microbial populations to variant dissolved organic carbon (DOC) sources in the marine environment and improve the understanding of the interaction between microorganisms and marine DOC pool, field-based incubation experiments were carried out using supplemental 13C-labeled typical substrates D-glucose and D-glucosamine (D-Glc and D-GlcN, respectively), which are two important components in marine DOC pool in the South China Sea. 13C- and 12C-DNA were then fractionated by ultracentrifugation and the microbial community was analyzed by terminal-restriction fragment length polymorphism and 454 pyrosequencing of 16S rRNA gene. 12C-DNA-based communities showed relatively high similarities with their corresponding in situ communities, and their bacterial diversities were generally higher than 13C-DNA-based counterparts. Distinct differences in community composition were found between 13C- and 12C-DNA-based communities and between two substrate-supplemented 13C-DNA-based communities; these differences distinctly varied with depth and site. In most cases, there were more genera with relative abundances of >0.1% in D-Glc-incorporating communities than in D-GlcN-incorporating communities. The Roseobacter clade was one of the prominent actively substrate-incorporating bacterial populations in all 13C-DNA-based communities. Vibrio was another prominent actively D-GlcN-incorporating bacterial population in most incubations. However notably, different OTUs dominated this clade or genus in different treatments at different depths. Altogether, these results suggested that there were taxa-specific differences in DOC assimilations and, moreover, their differences varied among the typical water masses, which could have been caused by the variant compositions of original bacterial communities from different hydrological environments. This implies that ecologically, the levels of labile or recalcitrance of DOC can be maintained only in a specific environmental context with specific bacterial community composition

Experimental Study on the Bond Performance between Fiber-Reinforced Polymer Bar and Unsaturated Polyester Resin Concrete

Fiber-reinforced polymer (FRP) bar-reinforced unsaturated polyester resin concrete (UPC) can solve the problem of rebar corrosion in ordinary reinforced concrete members. However, it has not been widely used in engineering practice because there have been few studies conducted on the bond behaviors of FRP bar and UPC, and the interaction mechanisms between FRP bar and UPC have not been well understood. A series of pull-out tests are conducted on FRP bar-UPC specimens to study the bond behaviors between these two materials. Parametric studies are also carried out to investigate the effects of FRP bar diameter, fiber type, type of surface treatment, concrete cover thickness, and interfacial bond length between the two. Three failure modes of the specimens are observed from pull-out tests, i.e., FRP bar pull-out, tensile failure of FRP bar, and UPC split. A new constitutive model is, therefore, proposed to predict the bond stress of FRP bar and UPC in the residual stage, and the proposed model is finally verified by test data reported in this study

Phylogenetic tree of representative sequences from dominant OTUs that fell in the genus <i>Vibrio</i> constructed using neighbor-joining method.

<p>Sequences from this study are shown in blue (site SETAS) and green (site D001). Sampling depths are indicated in brackets. Square indicates ¹³C-<i>D</i>-GlcN supplemented incubation. The topology of the phylogenetic tree was evaluated by bootstrap re-sampling method with 1,000 replicates, and bootstrap values greater than 50% are shown.</p

Distribution of DNA in a CsCl density gradient, produced from surface water of site D001 after incubation with supplemental ¹³C-labeled <i>D</i>-GlcN.

<p>Distribution of corresponding natural DNA shown as a negative control. Mixture of ¹²C- and ¹³C-DNA from <i>Escherichia coli</i> shown as a positive standard.</p

Phylogenetic tree of representative sequences from dominant OTUs that fell in the <i>Roseobacter</i> clade constructed using neighbor-joining method.

<p>Sequences from this study are shown in blue (site SETAS) and green (site D001). Sampling depths are indicated in brackets. Square indicates ¹³C-<i>D</i>-GlcN supplemented incubation. Circle indicates ¹³C-<i>D</i>-Glc supplemented incubation. The topology of the phylogenetic tree was evaluated by bootstrap re-sampling method with 1,000 replicates, and bootstrap values greater than 50% are shown.</p

The 2^nd (heavy) to 11^th (light) density gradient fractions were analyzed with T-RFLP among 12 density gradient fractions produced from ultracentrifugation of DNA from surface water of site D001 after incubation with supplemental ¹³C-labeled <i>D</i>-GlcN.

<p>(a) Distribution of DNA concentrations in CsCl density gradients; (b) Relative abundance of T-RFLP peaks (color bars) in each DNA fraction; (c) Community similarity analysis based on T-RFLP fingerprinting.</p

Taxa with relative abundances of >0.1% of total sequences in ¹³C-DNA-based (left axis) and ¹²C-DNA-based (right axis) communities at site D001.

<p>Taxa with relative abundances of >0.1% of total sequences in ¹³C-DNA-based (left axis) and ¹²C-DNA-based (right axis) communities at site D001.</p

Assessment and Prediction Model of GFRP Bars&rsquo; Durability Performance in Seawater Environment

In this study, the performance degradation law and mechanism of glass fiber reinforced polymer (GFRP) bars were investigated by being immersed in natural seawater (denoted as SW), saline-alkali solution (SA), or wrapped with concrete, and then submerged in natural seawater (SWC). A series of short-beam shear tests were conducted to investigate the effects of aging temperature and time on the interlaminar shear strength (ILSS) of GFRP bars. Microstructure changes, glass transition temperature (Tg) difference, and hydrolysis degree of GFRP bars after aging in three environments for 183 days were analyzed using scanning electron microscopy (SEM), differential scanning calorimeter (DSC), and Fourier transform infrared spectroscopy (FTIR). Test results demonstrated that the temperature could accelerate the strength degradation of GFRP bars significantly. After 183-day aging treatment at 60 &deg;C, the ILSS retention rates of GFRP bars in the three environments of SW, SWC, and SA were 66.41%, 53.10%, and 45.36%, respectively; and Tg was 1.7%, 7.0%, 7.8% lower than that of unconditioned sample, respectively. Meanwhile different degrees of damage, such as separation between fiber and resin and few holes in the resin, were observed on the GFRP bars in the SWC and SA environments. It was also found that irreversible hydrolysis took place in some resins. The durability prediction model of GFRP bars serving in the Yellow Sea of China was established by using Arrhenius equation, and the correlation coefficient with the test data was not less than 0.94

Dendrogram constructed using group average model based on Bray-Curtis similarities between communities at D001 (a) and SEATS (b) sites.

<p>Dendrogram constructed using group average model based on Bray-Curtis similarities between communities at D001 (a) and SEATS (b) sites.</p