Effect of Time Step Size and Turbulence Model on the Open Water Hydrodynamic Performance Prediction of Contra-Rotating Propellers

A growing interest has been devoted to the contra-rotating propellers （CRPs） due to their high propulsive efficiency, torque balance, low fuel consumption, low cavitations, low noise performance and low hull vibration. Compared with the single-screw system, it is more difficult for the open water performance prediction because forward and aft propellers interact with each other and generate a more complicated flow field around the CRPs system. The current work focuses on the open water performance prediction of contra-rotating propellers by RANS and sliding mesh method considering the effect of computational time step size and turbulence model. The validation study has been performed on two sets of contra-rotating propellers developed by David W Taylor Naval Ship R ＆ D center. Compared with the experimental data, it shows that RANS with sliding mesh method and SST k-ω turbulence model has a good precision in the open water performance prediction of contra-rotating propellers, and small time step size can improve the level of accuracy for CRPs with the same blade number of forward and aft propellers, while a relatively large time step size is a better choice for CRPs with different blade numbers.

Mineralogical and Active Mechanical Excitation Characteristics of Filled Fly Ash Cementitious Materials

To reveal the influence of mechanical activation on the performance of fly ash, the microanalysis（the energy spectroscopy, XRD and SEM）, the distribution size of particle of fly ash and cement paste intensity of various age for different grinding time were studied. The relationships of the activity and the composition of fly ash, microstructure and the distribution of particle size by mechanical activation of fly ash were obtained. The internal glass beads with activity were released by grinding fly ash for a certain time. The particle specific surface area was improved and the hydration reaction of the interface and the surface active center was increased by grinding. The granularity distributing of fly-ash trended towards optimization. The polar molecules or ions were easier to intrude into the internal cavity of the vitreous body. The active silica and alumina of fly ash were rapidly depolymerized. Each performance index of fly ash was increased before grinding for 20 min. Cement paste intensity of various age increased along with the grinding time, and the early strength increase range was big, but the later period intensity increase range hastened slightly. The internal part of vitreous of fly ash was destroyed if the fly ash continued to be ground and the activity of fly ash was reduced. It is suggested that Guozhuang＇s fly ash should be ground for 20 min.

Significance of neuroglobin in serum of acute atherosclerotic cerebral infarction patients

This study sought to examine neuroglobin （NGB） in the serum of acute cerebral infarction patients with double-antibody sandwich enzyme-linked immunosorbent assay to identify all risk factors, calculate infarct size, assess neurological impairment, and analyze the relation between NGB and each of these factors. The double-antibody sandwich assay indicated that levels of NGB in serum were unaltered within 6 hours following acute cerebral infarction compared with normal levels. NGB levels then underwent a distinct change, peaking at 24 hours then returning to normal levels in 72 hours. The results suggest that the level of NGB might be related to infarct size and low-density lipoprotein at 24 hours after acute cerebral infarction. There were no significant differences in neurological impairment scores and infarct size at different periods following infarction. The findings indicated that the level of NGB in serum of acute cerebral infarction patients was correlated with infarct time.

Effect of a Bone Graft Substitute β Tricalcium Phosphate on Osteoblastic Genes mRNA Exprssion

To investigate the molecular aspects of osteoblastic interactions with β tricalcium phosphate （β-TCP） particles, human osteoblast-like MG-63 cells were cultured with β-TCP particles at a density of 6 mg/mL culture medium for 48 h. Then, the mRNA expression of selected genes were quantified by real-time polymerase chain reaction （PCR）, including the attachment-related genes （α integrin and actin）, the proliferation-related gene （c-jun）, and the osteoblastic markers genes （type I collagen, osteonectin, alkaline phosphatase, RUNX2 and osteoclain）. The results showed that β-TCP particles （the average size 809 nm） significantly promote the attachment and the proliferation of MG-63 cells, and slightly enhance the osteoblastic differentiation based on the analyses of the related genes expression. This study provided scientific evidences to better reveal the underlines of functions of β-TCP in bone repair.

Effect of time bin size on accuracy of streak tube imaging lidar

Streak tube imaging lidar （STIL） is an active imaging system that has a high range accuracy with tile use of a pulsed lapser transmitter and streak tube receiver to produce 3D range inlages. This work investigates the effect of tile time bin size oil the range accuracy of STIL systems based on the peak detection algorithm. The nunlerical simulation indicates that the time bin size has a significant effect on the range aceuracy, resulting in a modified analytical estimate of the range error. An indoor experilnent with a planar target is carried out to validate the theory that shows the linear relationship between tile range error and the time bin size. Finer 3D depth iinages of a fist model are acquired by using a smaller time bin size and the best range error of 0.003 In is achieved with the optimal time bin size of 0.07 ns.