Abstract. The antibacterial activity of the five dimeric quaternary ammonium amphiphiles against Escherichia coli were evaluated by determining the minimum inhibitory concentration (MIC) and compared with one monomeric quaternary ammonium amphiphile. The antibacterial activity of dimeric amphiphiles is superior to the corresponding monomeric amphiphile. The action mechanism was investigated by measuring the activity of β-galactosidase from E. coli and scanning electron microscopy (SEM) imaging of E. coli cells. The result of β-galactosidase activity shows that 12-8-12 disrupts the membrane of E.coli leading to the releasing of intracellular contents and death of bacterial cells. This conclusion was supported by scanning electron microscopy, which imaged the holes on the cell membrane and irregular shape of cells caused by treatment of 12-8-12.

The experimental research on thermal response of LPG tank exposed to fire is carried out. A experimental apparatus to simulate real accident of LPG tank is designed and manufactured. A series of experiments for different fill levels, different type of tanks subjected to different type of fires are performed with this apparatus. From the results of the experiments, the obvious stratification of temperature in the ladings of the tank is observed. And the pressure is increased due to the stratification. Thermal response of the LPG is affected by various factors such as fire type, tank type and fill level etc. The liquid could be superheated or sub-cooled in fire exposure situation. The pressure can be fitted to time by cube polynomial equation.

The finite element model of the concrete mixing truck’s frame is builded by using shell as basic element, and the process of building the finite element model of the balance suspension is introduced in detail. Based on this, frame’s stress on five types of typical operating conditions are calculated by using the finite element analysis software, NASTRAN, and results can show the dangerous position and the maximum stress position on the frame. The analysis result on structural strength can provide the basis for further improving the frame structure.

By employing a dipole defect model, two-dimensional phase field simulations of domain switching in the crack tip vicinity of a crack embedded in a relaxor ferroelectric single crystal, which was subjected to mechanical loading and electric field, have been carried out. The interaction between the dipole defects and crack, the influence of the dipole defect concentration density on the switching process, and the coupling effect of mechanical stress and electric field on domain switching in the vicinity of the crack tip have been studied. Comparing the results obtained from relaxor ferroelectrics with those of normal ferroelectrics, the former showed that, due to the interaction between the dipole defects and crack, polarization switching in the vicinity of the crack tip was suppressed. Moreover, the coupling between applied mechanical stress and electric field can either promote or suppress domain switching in the vicinity of a crack.