Controlling process parameters of lost foam casting （LFC） enables this process to produce defect-free complex shape castings. An experimental investigation on lost foam casting of an A1-Si-Cu cast alloy was carried ...Controlling process parameters of lost foam casting （LFC） enables this process to produce defect-free complex shape castings. An experimental investigation on lost foam casting of an A1-Si-Cu cast alloy was carried out. The effects of pouting temperature, slurry viscosity, vibration time and sand size on surface finish, shrinkage porosity and eutectic silicon spacing of thin-wall casting were investigated. A full two-level factorial design of experimental technique was used to identify the significant manufacturing factors affecting the properties of casting. Pouring temperature was found as the most significant factor affecting A1-Si-Cu lost foam casting quality. It was shown that flask vibration time interacted with pouring temperature influenced euteetic silicon spacing and porosity percentage significantly. The results also revealed that the surface quality of the samples cast in fine sand moulds at higher pouring temperatures was almost unchanged, while those cast in coarse sand moulds possessed lower surface qualities. Furthermore, variation in slurry viscosity showed no significant effect on the evaluated properties compared to other parameters.展开更多
We study global asymptotic stability for an SIS epidemic model with maturation delay proposed by K. Cooke, P. van den Driessche and X. Zou, Interaction of maturation delay and nonlinear birth in population and epidemi...We study global asymptotic stability for an SIS epidemic model with maturation delay proposed by K. Cooke, P. van den Driessche and X. Zou, Interaction of maturation delay and nonlinear birth in population and epidemic models, J. Math. Biol. 39（4） （1999） 332-352. It is assumed that the population has a nonlinear birth term and disease causes death of infective individuals. By using a monotone iterative method, we establish sufficient conditions for the global stability of an endemic equilibrium when it exists dependently on the monotone property of the birth rate function. Based on the analysis, we further study the model with two specific birth rate functions BI（N） = be-aN and B3（N） = A/N ＋ c, where N denotes the total population. For each model, we obtain the disease induced death rate which guarantees the global stability of the endemic equilibrium and this gives a positive answer for an open problem by X. Q. Zhao and X. Zou, Threshold dynamics in a delayed SIS epidemic model, J. Math. Anal. Appl. 257（2） （2001） 282-291.展开更多
OBJECTIVE： To assess toxicities of the air in Chinese medicine clinics polluted by moxa-burning smoke due to moxibustion-derived burning products （MBP）. METHODS： Both acute and chronic toxicity studies were conduc...OBJECTIVE： To assess toxicities of the air in Chinese medicine clinics polluted by moxa-burning smoke due to moxibustion-derived burning products （MBP）. METHODS： Both acute and chronic toxicity studies were conducted. For the acute toxicity study, five groups of Wistar rats （n = 16/group, male： female = 1 ： 1） were exposed to five different concentrations （95%, 90%, 85%, 80% and 75%, respectively） of MBP for 2 h. For the chronic toxicity study, another three groups of male rats （n = 21/group） were ex- posed to MBP in three concentrations （10%, 40% and 70%, respectively） and one control group ex- posed to clean air 20 min/d for 144 d. Routine ex- aminations were performed and analyzed by analy- sis of variance and dose-response relationship. RESULTS： In the acute toxicity study, the number of dead rats in the 95%, 90%, 85%, 80% and 75% groups were 16, 13, 7, 6 LDS0 of 86.274% after or and 3, respectively, with during the 2 h exposure. In the chronic toxicity study, MBP exposure induced a decline in activity of the rats. Rats in the 10% group showed no signs of toxicity, while those in the 40% MBP group showed toxicity effects on the body weights （P 〈 0.05） and lung. Rats in the 70% MBP group also presented with reversible damage in the blood coagulation system （P 〈 0.05）. CONCLUSION： Exposure to 10% MBP, which is equivalent to 27.45 mg/m^3 was under the critical threshold for male rats＇safety. Exposure to MBP above that limit induced lung damage. MBP in clinics need to be reduced to a safe level with enhanced ventilation.展开更多
基金the Ministry of Higher Education of Malaysia (MOHE) for the financial support under the vote GUP-Q.J130000.2501.04H18
文摘Controlling process parameters of lost foam casting （LFC） enables this process to produce defect-free complex shape castings. An experimental investigation on lost foam casting of an A1-Si-Cu cast alloy was carried out. The effects of pouting temperature, slurry viscosity, vibration time and sand size on surface finish, shrinkage porosity and eutectic silicon spacing of thin-wall casting were investigated. A full two-level factorial design of experimental technique was used to identify the significant manufacturing factors affecting the properties of casting. Pouring temperature was found as the most significant factor affecting A1-Si-Cu lost foam casting quality. It was shown that flask vibration time interacted with pouring temperature influenced euteetic silicon spacing and porosity percentage significantly. The results also revealed that the surface quality of the samples cast in fine sand moulds at higher pouring temperatures was almost unchanged, while those cast in coarse sand moulds possessed lower surface qualities. Furthermore, variation in slurry viscosity showed no significant effect on the evaluated properties compared to other parameters.
文摘We study global asymptotic stability for an SIS epidemic model with maturation delay proposed by K. Cooke, P. van den Driessche and X. Zou, Interaction of maturation delay and nonlinear birth in population and epidemic models, J. Math. Biol. 39（4） （1999） 332-352. It is assumed that the population has a nonlinear birth term and disease causes death of infective individuals. By using a monotone iterative method, we establish sufficient conditions for the global stability of an endemic equilibrium when it exists dependently on the monotone property of the birth rate function. Based on the analysis, we further study the model with two specific birth rate functions BI（N） = be-aN and B3（N） = A/N ＋ c, where N denotes the total population. For each model, we obtain the disease induced death rate which guarantees the global stability of the endemic equilibrium and this gives a positive answer for an open problem by X. Q. Zhao and X. Zou, Threshold dynamics in a delayed SIS epidemic model, J. Math. Anal. Appl. 257（2） （2001） 282-291.
基金Supported by the National Natural Science Foundation of China:effect of Moxibustion on"Longevity Gene"SIRT1 Regulation in Aged Mice(No.81403449)NSFC Project:effect of Moxibustion and its Therapeutic Factors on Mitochondrial Energy Metabolism and Apotosis Pathyway in APP/PS1Transgenic Alzheimer's Disease Mouse Model(No.8157-4068)National Program on Key Basic Research Project(973 Program):the Study of Components and Mecha-nisms of Artemisia and the Product and Moxibustion and Safety Evaluation(No.2009CB522906)
文摘OBJECTIVE： To assess toxicities of the air in Chinese medicine clinics polluted by moxa-burning smoke due to moxibustion-derived burning products （MBP）. METHODS： Both acute and chronic toxicity studies were conducted. For the acute toxicity study, five groups of Wistar rats （n = 16/group, male： female = 1 ： 1） were exposed to five different concentrations （95%, 90%, 85%, 80% and 75%, respectively） of MBP for 2 h. For the chronic toxicity study, another three groups of male rats （n = 21/group） were ex- posed to MBP in three concentrations （10%, 40% and 70%, respectively） and one control group ex- posed to clean air 20 min/d for 144 d. Routine ex- aminations were performed and analyzed by analy- sis of variance and dose-response relationship. RESULTS： In the acute toxicity study, the number of dead rats in the 95%, 90%, 85%, 80% and 75% groups were 16, 13, 7, 6 LDS0 of 86.274% after or and 3, respectively, with during the 2 h exposure. In the chronic toxicity study, MBP exposure induced a decline in activity of the rats. Rats in the 10% group showed no signs of toxicity, while those in the 40% MBP group showed toxicity effects on the body weights （P 〈 0.05） and lung. Rats in the 70% MBP group also presented with reversible damage in the blood coagulation system （P 〈 0.05）. CONCLUSION： Exposure to 10% MBP, which is equivalent to 27.45 mg/m^3 was under the critical threshold for male rats＇safety. Exposure to MBP above that limit induced lung damage. MBP in clinics need to be reduced to a safe level with enhanced ventilation.
