Application of Multi-Channel Synchronized Dynamic Strain Gauges in Monitoring the Neutral Axis Position and Prestress Loss of Box Girder Bridges.

The aim of this paper was to explore the application of multi-channel synchronized dynamic strain gauges in monitoring the neutral axis (N.A.) position of prestressed concrete box girders. The N.A. position has recently been proposed as an indicator for monitoring the health of bridge structures. Laboratory experiments were conducted on a prestressed T-beam under different prestress level conditions to investigate the correlation between the prestress magnitude and the N.A. position. In the development of the multi-channel synchronized dynamic strain gauges, edge computing was employed to significantly reduce the amount of data transmitted from the sensor nodes on-site. In edge computing, only the dynamic strain response caused by the maximum vehicle load in each minute is transmitted. This approach greatly enhances the monitoring efficiency and enables the realization of on-site non-computer-based monitoring systems. The laboratory test results of the prestressed T-beam showed that the N.A. position tends to move slightly downward as the prestress force increases. In other words, when the prestress force decreases due to loss, the N.A. position exhibits a slight upward movement. This study selected a newly constructed prestressed box girder as the subject for on-site measurement of the N.A. position using multi-channel synchronized dynamic strain gauges shortly after the prestress was applied. The on-site monitoring data indeed revealed a gradual upward movement of the N.A. position. This phenomenon confirmed that soon after the completion of prestressed concrete bridges, there is a gradual loss of prestress due to the significant shrinkage and creep effects of the early-age concrete. The on-site monitoring result aligned with the findings from the laboratory experiments, where the N.A. position was observed to move upward as the prestress decreased.

Priming of soil organic carbon mineralization and its temperature sensitivity in response to vegetation restoration in a karst area of Southwest China.

Plant residue input alters native soil organic carbon (SOC) mineralization through the priming effect, which strongly controls C sequestration during vegetation restoration. However, the effects of different vegetation types on SOC priming and the underlying microbial mechanisms due to global warming are poorly understood. To elucidate these unknowns, the current study quantified soil priming effects using 13C-labeled maize residue amendments and analyzed the community structure and abundances in the soils of a vegetation succession gradient (maize field (MF), grassland (GL), and secondary forest (SF)) from a karst region under two incubation temperatures (15 °C and 25 °C). Results revealed that after 120 d of incubation, vegetation restoration increased the soil priming effects. Compared to MF, the priming effects of SF at 15 °C and 25 °C increased by 142.36 % and 161.09 %, respectively. This may be attributed to a high C/N ratio and low-N availability (NO3-), which supports the "microbial nitrogen mining" theory. Variations in soil priming were linked to changes in microbial properties. Moreover, with vegetation restoration, the relative abundance of Actinobacteria (copiotrophs) increased, while Ascomycota (oligotrophs) decreased, which accelerated native SOC decomposition. Co-occurrence network analysis indicated that the cooperative interactions of co-existing keystone taxa may facilitate SOC priming. Furthermore, structural equation modeling (SEM) indicated that changes in the priming effects were directly related to the fungal Shannon index and microbial biomass C (MBC), which were affected by soil C/N and NO3-. Warming significantly decreased soil priming, which may be attributed to the increase in microbial respiration (qCO2) and decreased MBC. The temperature sensitivity (Q10) of SOC mineralization was higher after residue amendment, but significant differences were not detected among the vegetation types. Collectively, our results indicated that the intensity of priming effects was dependent on vegetation type and temperature. Microbial community alterations and physicochemical interactions played important roles in SOC decomposition and sequestration.

Conversion of rainforest into agroforestry and monoculture plantation in China: Consequences for soil phosphorus forms and microbial community.

Microbial communities and their associated enzyme activities affect quantity and quality of phosphorus (P) in soils. Land use change is likely to alter microbial community structure and feedback on ecosystem structure and function. This study presents a novel assessment of mechanistic links between microbial responses to land use and shifts in the amount and quality of soil phosphorus (P). We investigated effects of the conversion of rainforests into rubber agroforests (AF), young rubber (YR), and mature rubber (MR) plantations on soil P fractions (i.e., labile P, moderately labile P, occluded P, Ca P, and residual P) in Hainan Island, Southern China. Microbial community composition and microbial enzyme were assayed to assess microbial community response to forest conversion. In addition, we also identified soil P fractions that were closely related to soil microbial and chemical properties in these forests. Conversion of forest to pure rubber plantations and agroforestry system caused a negative response in soil microorganisms and activity. The bacteria phospholipid fatty acid (PLFAs) levels in young rubber, mature rubber and rubber agroforests decreased after forest conversion, while the fungal PLFAs levels did not change. Arbuscular mycorrhizal fungi (AMF) (16:1w5c) had the highest value of 0.246µmol(gOC)-1 in natural forest, followed by rubber agroforests, mature rubber and young rubber. Level of soil acid phosphatase activity declined soon (5 years) after forest conversion compared to natural forest, but it improved in mature rubber and agroforestry system. Labile P, moderately labile P, occluded P and residual P were highest in young rubber stands, while moderately labile, occluded and residual P were lowest in rubber agroforestry system. Soil P fractions such as labile P, moderately labile P, and Ca P were the most important contributors to the variation in soil microbial community composition. We also found that soil P factions differ significantly among the four transformation systems. Soil labile P faction and its potential sources (moderately labile P, occluded P, and residual P) were positively correlated with NO3-, but negatively correlated with AMF, suggesting that these properties play key roles in P transformation. Our study indicated that land use had an impact on microbial community composition and functions, which consequently influenced soil phosphorus availability and cycling.

[IR study of the hardening and maturation of glass ionomer cement].

The set reaction of glass ionomer cement has been investigated by means of IR spectra. It has been found that the band intensity around 1413 cm(-1) due to the vibration of polyacrylate salt increased with aging, and the shoulder band at 950 cm(-1) due to the stretching vibration of Si-OH still appeared during the periods studied. The results are consistent with that of mechanical determination of compressive strength, which suggested that the crosslink density increase resulting from the slow diffusion of Ca2+ and Al3+ is responsible for compressive strength increasing with aging, and forming and maturing of interface layer comprising of silica gel also have a significant effect on the properties of glass ionomer cements.

[Biological assessment of a new synthetic macromolecular resin class of comfort denture adhesive].

This article devotes itself to evaluating the biocompatibility of synthetic macromolecular resin class of Comfort denture adhesive, which was developed by the present authors. Acute toxicity, haemolysis, cytotoxicity, sensitization and oral mucous stimulation were tested with standard method (ISO7406-1997 and YY0268-1995). The results showed that no toxic effect was observed with in vivo tests and no cytotoxic effect was observed with in vitro MTT assay. Haemolysis rate of the material (2.95%) indicated good hemaocompatibility. No local mucous membrane irritation reaction was noted after the relevant tests. The developed Comfort denture adhesive exhibited good biocompatiblility.