Air exchange rate and pollutant dispersion inside compact urban street canyons with combined wind and thermal driven natural ventilations: Effects of non-uniform building heights and unstable thermal stratifications.

In the present work, a delicate CFD research of a multi-street canyon model with varying thermal stratifications and non-uniformities of buildings was conducted to investigate the street ventilation and pollutant dispersion between the compact urban blocks. Non-isothermal turbulent wind flow, temperature field and pollutant dispersion in a two-dimensional computational domain were solved by the Renormalization Group (RNG) k-ε turbulence model along with the enhanced wall treatment. Present numerical results indicated that the variation of ground heating intensity has a significant influence on the airflow pattern in the step-down case, and the distribution of pollutants in the street canyons mainly depends on the variation of the upper clockwise vortex. The canyon ventilation performance became better as the unstable thermal stratification strengthened. Similarly, the increase of ground heating intensity could reduce ADF (atmospheric dispersion factor) in the step-down case and ADF became the lowest when Ri = -3.92 was maintained. Additionally, the increase of building unevenness further complicated the canyon airflow structure, which aggravated the pollution of the canyon. In the step-down configuration, as the standard deviation of adjacent building height gradually increases, canyon ventilation could be further enhanced. For the step-up configuration, the best ventilation performance was found at σH = 16.7 %. ADF of adjacent canyons also varied greatly. When σH = 33.3 % was maintained, the peak and bottom values of ADF were discovered in the step-up and step-down cases, respectively. Present research has provided a theoretical reference for guiding urban design and improve living environment in modern compact cities.

[The tracking of allogenic grafted rat bone marrow stem cells in rat liver and their role on repairing injured liver].

OBJECTIVE: To study the location, immigration of allogenic grafted Feridex-labeled rat bone marrow stem cells (BMSCs) in chemically-induced acute injured livers and their role on repairing the injured liver function. METHODS: The rat models of chemically-induced acute hepatic injury established with CCl4 Feridex-labeled BMSCs were injected into the injured livers. Magnetic resonance imaging (MRI) examination was conducted on rat livers, the levels of ALT, AST and Fe3+ in the serum and hepatic tissues were studied 6 h before and 6 h, 1 w and 5 w after injection. RESULTS: Cellular necrosis, congestion in the hepatic sinusoid and infiltration of inflammatory cells were seen in the model livers. Above 90 percent of the cells were Feridex-labeled BMSCs positive by prussian blue staining and iron particles were found in their endochylema through electron microscopy. MRI examination at the sequence of SE-T2WI showed remarkably low signal changes 6 h after injecting Feridex-labeled BMSCs and the site with signal changes gradually expanded 1 and 5 w after injection. Comparatively, the changes of low signal images at each time point in the injured livers were more obvious than those of the controls at all time points, respectively. Simultaneously, pathological injuries in the livers were ameliorated and the levels of ALT and AST in serums declined: these changes in the Feridex-labeled BMSCs group were more obvious than those in the non-Feridex-labeled BMSCs group. Uniformly, there were no significant differences between the Feridex-labeled BMSCs group and the non-Feridex-labeled BMSCs group in view of histopathological examination and serological examination (including ALT, AST, Fe3+ levels) at all time points. CONCLUSIONS: The liver function in the model of chemically-induced acutely-injured liver may be repaired by BMSCs implantation. Traced by MRI, BMSCs in the injured liver of rats disperse at a higher rate than in the normally fed ones.

[Optimization investigation on the elements in ferrum aluminum silicon alloy by ICP-AES].

A method for the determination of Al, Fe, Ca, Cr, Mn, Ni, Si and Ti elements in ferrum aluminum silicon alloy by inductively coupled plasma atomic emission spectrometry (ICP-AES) was described. The influence of ICP-AES operating conditions, sample dissolution methods and spectral lines were studied. The preferable experimental conditions were examined, and the influences of coexistent elements on the signals were investigated. The method was applied to the determination of elements in ferrum aluminum silicon alloy samples, and the measured results were in good agreement with the recommended values of the standard steel. The detection limits of the method were 0.029 microg x mL(-1) for Al, 0.004 microg x mL(-1) for Fe, 0.0075 microg x mL(-1) for Ca, 0.0015 microg x mL(-1) for Cr, 0.0009 microg x mL(-1) for Mn, 0.0027 microg x mL(-1) for Ni, 0.045 microg x mL(-1) for Si and 0.003 microg x mL(-1) for Ti. The relative standard deviation (n=6) of this method was between 0.3%-1.8%, and the recoveries by standard addition were in the range of 96.7%-102.9%. The method was used to determine the amount of silicon in alloy samples with satisfactory results, which agreed with those by the standard gravimetry. The method is characterized by good precision, easy operation and convenience to apply.