Oxygen uptake rate (OUR) control strategy for improving avermectin B1a production during fed-batch fermentation on industrial scale (150 m3)

Glucose metabolism plays a crucial role in the process of avermectin B1a biosynthesis. Controlling glucose feeding based on oxygen uptake rate (OUR) was established to improve the efficiency of avermectin B1a  production. The result showed that avermectin B1a production was greatly enhanced by OUR control strategy. In the glucose feeding phase, OUR was maintained at approximate 12 mmol/L/h, which was conducive to avermectin B1a biosynthesis. Using this OUR control strategy, an adequate supply of organic acid precursors produced avermectin B1a 5228 U/mL, which was 22.8% higher than that of the control (batch fermentation, 4256 U/mL) on industrial scale.Key words: Avermectin B1a, glucose feeding, oxygen uptake rate, industrial scale

2-(4-Methyl­benzo­yl)benzoic acid monohydrate

In the title compound, C15H12O3·H2O, the two rings are oriented at a dihedral angle of 69.12 (3)°. In the crystal structure, intermolecular O—H⋯O hydrogen bonds link the mol­ecules into a three-dimensional framework

Evaluation of nano-frictional and mechanical properties of a novel Langmuir-Blodgett monolayer/self-assembly monolayer composite structure

A novel stearic acid (SA)/3-aminopropyltrethoxysilane (APS) composite structure was fabricated using the combined method of the Langmuir-Blodgett technique and self-assembly monolayer (SAM) technique. Its frictional, adhesive properties and interface contact types between the atomic force microscope tip and the samples were evaluated based on Amonton's laws and the general Carpick's transition equation, respectively. The results showed that the tip-sample contacts corresponded to the Johnson-Kendall-Robert/Derjaguin-Muller-Toporov (DMT) transition model for SiO2, APS-SAMs, and the unheated SA-APS composite structure, and for the heated SA-APS bilayer to the DMT model. Frictional forces for the four samples were linearly dependent on external loads at higher loads, and at lower loads they were significantly affected by adhesive forces. Frictional and scratching tests showed that the heated SA-APS composite structure exhibited the best lubricating properties and adhesion resistance ability, and its wear resistance capacity was greatly improved due to the binding-mode conversion from hydrogen bonds to covalent bonds. Thus, this kind of composite bilayer might be promising for applications in the lubrication of nano/microelectromechanical systems. I.Comment: 8 pages, 8 figure

Failure Characteristics and Scale in a Sandstone Joint Subjected to Direct Shear Testing: Experimental Investigation with Acoustic Emission Monitoring

AbstractAn in-depth recognition of the failure characteristics and scale of joints is of great significance for the stability assessment in rock engineering. Unfortunately, due to the close fitting of the upper and lower blocks of the joint under direct shear tests, the shear failure of joints are difficult to observe directly during the shear process. Thus, in this work, direct shear tests were carried out on sandstone joints subjected to three levels of normal stress while the acoustic emission (AE) in the rock is synchronously monitored. The failure characteristics of rock joints were then investigated by calibrating the AE system and combining them with the AE location results and shear load curves. A method was established to determine the failure scale of the rock joint that uses the AE moment tensor and first law of thermodynamics. The results show that the degree of failure of the rock joints increases as the normal stress increases. Also, the shear failure of the rock joints is localized and occurs synchronously, rather than sequentially in different areas. The average length of the microfractures formed in the shear process correlates with the average mineral grain size. On the other hand, the maximum length of the microfractures appears to have different values depending on the normal stress present. Our results have significant reference value for the precursory identification of shear disaster in engineering rock masses

(4,6-Dibromo-m-phenyl­enedimethyl­idyne) tetra­acetate

The title mol­ecule, C16H16Br2O8, lies on a crystallographic twofold axis. Weak intra­molecular C—H⋯O hydrogen bonds may, in part, control the conformation of the mol­ecule. In the crystal structure, mol­ecules are connected into a two-dimensional network via weak inter­molecular C—H⋯O hydrogen bonds