FEM Optimisation of Seepage Control System Used for Base Stability of Excavation

With the existence of a high groundwater level, the head difference between the inside and outside of an excavation may lead to the loss of stability of the excavation’s surface. Hence, a fundamental understanding of this occurrence is important for the design and construction of water-retaining structures. In some cases, the failure mechanism cannot be predicted exactly because of its mechanical complexity as well as a major lack of protection systems and not adopting effective countermeasures against this phenomenon. The article took a tranche from an 80 km long open sewer located in the Ruhr area, Germany as an example to establish a hydro-geological model and analyse the instability of the excavation base surface caused by the groundwater flow at 45m deep and to present the effectivity of an adopted drainage system inside the excavation pit as 39 columns of sand to relax the pore water pressure. By using the Finite Element Method (FEM) analysis, the failure mechanism was investigated before applying any countermeasures, and the total length of the adopted countermeasure system was minimised. Also, various position tests were performed on the adopted drainage system to confirm the optimised position. The results of this numerical study allowed the deduction of the importance of the used drainage system by achieving 44% more in the excavating process. After achieving the required excavation depth, a further increase of the sand columns’ penetration may be considered non-economic because, after adding extra depth, all the situations have the same safety factor. In addition, this can provide a reference for the optimised position of the sand columns where they must be applied right by the wall and limited by a critical distance, D/2, half of the embedded depth of the wall.

Purification and Characterization of a Novel Bacteriocin Pediocin Z-1 Produced by Pediococcus Pentosaceus Z-1 Screened From Jinhua Ham

Background: Lactic acid bacteria (LAB) can produce bacteriostatic substances, among which bacteriocins attracted wide attention in food preservation for decades. Up to date, nisin (class I bacteriocins) has been considered to be the only bacteriocin produced by Lactococcus lactis strains for commercial use. Moreover, there are many other reports concerning the isolated bacteriocins for potential application in food industry while some exhibited a narrow bactericidal spectrum, thermal stability and low acid-base stability. Jinhua ham is a representative of traditional dry-cured meat product in China. The microbial community structure and diversity was speculated to be responsible for flavor and quality formation of Jinhua ham, protecting from the spoilage microorganisms contamination. However, no studies was performed to investigate the bacteriocin from LAB in Jinhua ham. Thus, the objective of this study was to screen out high-efficiency, safe and non-toxic bacteriocin-producing lactic acid bacteria (LAB) from Jinhua Ham and subsequently perform the purification, identification and characterization of its bacteriocin. Results: The bacteriocin-producing LAB was screened from Jinhua ham and then designated as Pediococcus pentosaceus Z-1 by colony morphology and 16S rDNA sequencing. The bacteriocin was then crudely extracted from the bacterial cell-free supernatant by pH adsorption, and further purified by cellulose DEAE-52 ion exchange and Sephadex G-50 chromatography columns. The tricine-SDS-PAGE electrophoresis showed a highly purified protein band with 8227.35 Da with 60 amino acids identified by MALDI-TOF-MS analysis. The bacteriocin was named as pediocin Z-1 and its antibacterial activity exhibited an acid-base stability between pH 2-10 and a thermal stability at a range of 50-110°C. The pediocin Z-1 was sensitive to proteases and showed an inhibitory effect against Gram-positive bacteria and Gram-negative bacteria, including Listeria monocytogenes, Staphylococcus aureus, Salmonella typhimurium, Salmonella potsdam and Escherichia coli. Conclusions: Our data suggest that pediocin Z-1 has a comparable effect of antibacterial activity with nisin and it is promising that pediocin Z-1 has great potential for application prospect in the food industry.

Study of the stress state of the sleeper base and sleepers of rail track with accounting variable conditions of their resting

The live problem of the stress state of the sleeper base and rail sleepers is considered in the article with taking into account specific normal and specific shear stresses under variable conditions of the sleepers resting on the base. The methodology is aimed at the determination of the mutual influence of normal (compressive) and tangential (shear) specific stresses on formation of stability due to the displacement of individual parts of the base. Stability zones and shear zones of the sleeper base parts are also determined by the authors at different conditions of the sleeper resting on the base. Further, zones with insecure position of the base under the sleepers are found when they and their under-rail parts continuously rest on the base. It is stated that insecure position of the base is formed when specific shear stresses excess specific stresses of shear resistance, which consists of specific friction and specific cohesion between the parts in the base. It is also established that loss of stability of the ballast particles causes their displacement in the direction of the action of specific shear stresses. In these zones, density and rigidity of the sleeper base decreases leading to a gradual redistribution of reactive resistance of the base along the sleeper, and, depending on this redistribution, a change in the bending moments acting on the sleeper occurs. It is found that when the sleepers rest only by their under-rail parts, shear stresses and forces, as well as stresses and shear resistance forces under the middle part of the sleepers are distributed in such a way that shear forces exceed resistance forces up to the depth of 60 cm from the sleepers sole. This phenomenon leads to the displacement of ballast particles under the middle part of the sleeper, consolidation of the ballast and resting of the sleepers by their middle part with possible cracks formation. In the end sections of the sleepers, there is also a loss of ballast stability. Recommendations for improving stability indicators of the sleeper base and strength of the sleepers are given. The obtained results of the study can be used for the mine, industrial and railway transport.

Stability of ionic liquids in Brønsted-basic media

The stability of ionic liquids towards strong Brønsted bases is reviewed from a fundamental perspective, and approaches for improving the base stability of various classes of ionic liquids are discussed.

Cooperative proton transportation based on the reversible single crystal–single crystal transformation in a highly water-stable Cu-MOF with its facile and scalable preparation

A Cu-MOF with excellent acid–base stability in boiling water was constructed under mild conditions. This MOF was very suitable for scaled-up preparation, and exhibits distinct proton conductivity at temperatures above and below 75 °C.