<b>Background:</b> Shallow wells and boreholes are vital sources of potable water in Hargeisa. This water can be polluted by runoff, in particular during the rainy season, causing outbreaks of waterborne i...<b>Background:</b> Shallow wells and boreholes are vital sources of potable water in Hargeisa. This water can be polluted by runoff, in particular during the rainy season, causing outbreaks of waterborne infections. <b>Objectives:</b> This research aimed at evaluating the microbial quality of shallow wells and boreholes water around Hargeisa, Somaliland. <b>Methods:</b> The total coliform and <i>Escherichia coli</i> count were done by using the membrane filtration method. Overall, 100 ml of each water sample was filtered via a 0.45 μm membrane filter, and then the filters were put on m-Endo agar plates that were incubated at 37°C for 24 to 48 hours. <b>Results:</b> The mean value of total coliform counts for the boreholes and shallow wells ranged from 1.288 × 10<sup>3</sup> to 8.8 × 10<sup>3</sup> CFU/100ml, while the mean value of total <i>E. coli</i> counts also ranged from 3.5 × 10<sup>2</sup> to 4.429 × 10<sup>3</sup> CFU/100ml. Results from this study have demonstrated that all water sources (Arabsiyo, Dararweyne, Darasalaam, Dabaraqas, and Jaleelo) don’t comply with the WHO guideline for drinking water. Results from the analysis of water samples of 28 wells demonstrated a significant correlation between total coliform and <i>E. coli</i> counts (P = 0.01). Therefore, this water is not fit for human consumption unless it is treated. <b>Conclusion:</b> This study has demonstrated that all results of both mean values of total coliform and <i>E. coli</i> counts from groundwater of selected shallow wells and boreholes were beyond WHO standards, so water from Arabsiyo, Jaleelo, Dabaraqas, Dararweyne, and Darasalaam requires treatment before human consumption.展开更多
Billet optimization can greatly improve the forming quality of the transitional region in the isothermal local loading forming （ILLF） of large-scale Ti-alloy ribweb components. However, the final quality of the tran...Billet optimization can greatly improve the forming quality of the transitional region in the isothermal local loading forming （ILLF） of large-scale Ti-alloy ribweb components. However, the final quality of the transitional region may be deteriorated by uncontrollable factors, such as the manufacturing tolerance of the preforming billet, fluctuation of the stroke length, and friction factor. Thus, a dual-response surface method （RSM）-based robust optimization of the billet was proposed to address the uncontrollable factors in transi- tional region of the ILLF. Given that the die underfilling and folding defect are two key factors that influence the forming quality of the transitional region, minimizing the mean and standard deviation of the die underfilling rate and avoiding folding defect were defined as the objective function and constraint condition in robust optimization. Then, the cross array design was constructed, a dual-RSM model was established for the mean and standard deviation of the die underfilling rate by considering the size parameters of the billet and uncontrollable factors. Subsequently, an optimum solution was derived to achieve the robust optimization of the billet. A case study on robust optimization was conducted. Good results were attained for improving the die filling and avoiding folding defect, suggesting that the robust optimization of the billet in the transitional region of the ILLF was efficient and reliable.展开更多
该文通过分析三重移相(triple phase shift,TPS)控制下双主动全桥(dual active bridge,DAB)变换器的等效电路,推导出传输功率以及电感电流有效值与控制量输入之间的统一模型,并根据控制量之间的关系,划分DAB变换器的6种工作模式。然后,...该文通过分析三重移相(triple phase shift,TPS)控制下双主动全桥(dual active bridge,DAB)变换器的等效电路,推导出传输功率以及电感电流有效值与控制量输入之间的统一模型,并根据控制量之间的关系,划分DAB变换器的6种工作模式。然后,通过揭示控制量的扰动对于传输功率及电感电流有效值的影响,提出针对电流有效值的全局最优化条件,统一不同功率段和不同工作模式的优化问题。全局最优化条件的解即为电感电流有效值最小的控制策略。最后搭建实验平台进行验证,实验结果证明了文中理论分析的正确性和控制策略的有效性。展开更多
文摘<b>Background:</b> Shallow wells and boreholes are vital sources of potable water in Hargeisa. This water can be polluted by runoff, in particular during the rainy season, causing outbreaks of waterborne infections. <b>Objectives:</b> This research aimed at evaluating the microbial quality of shallow wells and boreholes water around Hargeisa, Somaliland. <b>Methods:</b> The total coliform and <i>Escherichia coli</i> count were done by using the membrane filtration method. Overall, 100 ml of each water sample was filtered via a 0.45 μm membrane filter, and then the filters were put on m-Endo agar plates that were incubated at 37°C for 24 to 48 hours. <b>Results:</b> The mean value of total coliform counts for the boreholes and shallow wells ranged from 1.288 × 10<sup>3</sup> to 8.8 × 10<sup>3</sup> CFU/100ml, while the mean value of total <i>E. coli</i> counts also ranged from 3.5 × 10<sup>2</sup> to 4.429 × 10<sup>3</sup> CFU/100ml. Results from this study have demonstrated that all water sources (Arabsiyo, Dararweyne, Darasalaam, Dabaraqas, and Jaleelo) don’t comply with the WHO guideline for drinking water. Results from the analysis of water samples of 28 wells demonstrated a significant correlation between total coliform and <i>E. coli</i> counts (P = 0.01). Therefore, this water is not fit for human consumption unless it is treated. <b>Conclusion:</b> This study has demonstrated that all results of both mean values of total coliform and <i>E. coli</i> counts from groundwater of selected shallow wells and boreholes were beyond WHO standards, so water from Arabsiyo, Jaleelo, Dabaraqas, Dararweyne, and Darasalaam requires treatment before human consumption.
基金Acknowledgements The authors would like to gratefully acknowledge the support given by the National Natural Science Foundation of China （Grant No. 51575449）, Research Fund of the State Key Laboratory of Solidification Processing （NWPU）, China （Grant No. 104-QP-2014）, 111 Project （Grant No. B08040）, and Fundamental Research Funds for the Central Universities （Grant No. 3102015AX004）.
文摘Billet optimization can greatly improve the forming quality of the transitional region in the isothermal local loading forming （ILLF） of large-scale Ti-alloy ribweb components. However, the final quality of the transitional region may be deteriorated by uncontrollable factors, such as the manufacturing tolerance of the preforming billet, fluctuation of the stroke length, and friction factor. Thus, a dual-response surface method （RSM）-based robust optimization of the billet was proposed to address the uncontrollable factors in transi- tional region of the ILLF. Given that the die underfilling and folding defect are two key factors that influence the forming quality of the transitional region, minimizing the mean and standard deviation of the die underfilling rate and avoiding folding defect were defined as the objective function and constraint condition in robust optimization. Then, the cross array design was constructed, a dual-RSM model was established for the mean and standard deviation of the die underfilling rate by considering the size parameters of the billet and uncontrollable factors. Subsequently, an optimum solution was derived to achieve the robust optimization of the billet. A case study on robust optimization was conducted. Good results were attained for improving the die filling and avoiding folding defect, suggesting that the robust optimization of the billet in the transitional region of the ILLF was efficient and reliable.
文摘该文通过分析三重移相(triple phase shift,TPS)控制下双主动全桥(dual active bridge,DAB)变换器的等效电路,推导出传输功率以及电感电流有效值与控制量输入之间的统一模型,并根据控制量之间的关系,划分DAB变换器的6种工作模式。然后,通过揭示控制量的扰动对于传输功率及电感电流有效值的影响,提出针对电流有效值的全局最优化条件,统一不同功率段和不同工作模式的优化问题。全局最优化条件的解即为电感电流有效值最小的控制策略。最后搭建实验平台进行验证,实验结果证明了文中理论分析的正确性和控制策略的有效性。
