A new instantaneous mobile bed thickness model is presented for sediment transport in skewed asymmetric oscillatory sheet flows. The proposed model includes a basic bed load part and a suspended load part related to t...A new instantaneous mobile bed thickness model is presented for sediment transport in skewed asymmetric oscillatory sheet flows. The proposed model includes a basic bed load part and a suspended load part related to the Shields parameter, and takes into account the effects of mass conservation, phase-lag, and asymmetric boundary layer development, which are important in skewed asymmetric flows but usually absent in classical models. The proposed model is validated by erosion depth and sheet flow layer thickness data in both steady and unsteady flows, and applied to a new instantaneous sediment transport rate formula. With higher accuracy than classical empirical models in steady flows, the new formula can also be used for instantaneous sediment transport rate prediction in skewed asymmetric oscillatory sheet flows.展开更多
Hospital linen is clearly recognized as a potential reservoir for microorganisms and could be a vector of disease transmission. The aim of this study was to isolate, count and identify fungi and bacteria from differen...Hospital linen is clearly recognized as a potential reservoir for microorganisms and could be a vector of disease transmission. The aim of this study was to isolate, count and identify fungi and bacteria from different kinds of clean and dirty linen in a hospital. Microbiological samples have been collected on clean bed linen (n = 200), dirty bed linen (n = 192) and staff uniforms (n = 192) by using contact plates. 55% of samples from clean bed linen were contaminated before contact with the patient, with a mean count of 3 cfu/25 cm2 (range: 1-117 cfu) when contaminated. Virtually all samples from dirty bed linen carried microorganisms, with a mean count of 23 cfu/25 cm2 (range 1-191 cfu). In addition, staff hospital uniforms showed the highest contamination rates in the study, with an average of 45 cfu/25 cm2 (range: 1-218 cfu). Microbial species were mostly bacteria commonly found in the environment or on human skin, such as staphylococci or micrococci. Nevertheless, 57% of the identified species may be opportunistic pathogens for humans, representing a risk for people with a deficient or weakened immune system, especially in cases of superinfection. Since contamination of linen seems to occur after washing, actively antimicrobial textiles would represent a valuable measure to prevent textiles from being a vehicle for transfer of microorganisms.展开更多
Nikuradse roughness(ks) is very important in the sediment transport prediction because it is related to the evaluations of the velocity distribution, shear stress and erosion depth. Dimensionless Nikuradse roughness(k...Nikuradse roughness(ks) is very important in the sediment transport prediction because it is related to the evaluations of the velocity distribution, shear stress and erosion depth. Dimensionless Nikuradse roughness(ks/D,where D is the sediment diameter) is usually given 1–2.5 on the immobile plan bed or at low shear stress. But it behaves differently on the mobile plan bed at high shear stress with much sediment picked up to movement when the Shields parameter(Θ) is larger than 0.8–1.0. The effective Nikuradse roughness on the mobile plan bed was derived indirectly from the erosion depth correlated to the mobile plan bed thickness considering the mass conservation in the present study. The proposed erosion depth confirmed the relation to the Shields parameters with an extra factor consisting of suspended sediment and its damping to turbulence. The decrement of the erosion depth caused by the increment of the sediment diameter at large shear stress was obtained, which was usually absent in classical empirical formulas based on the bedload theory. Good agreement with experiments was achieved by the present prediction of the Nikuradse roughness, erosion depth and sediment transport rate. Discussion was mainly focused on the prediction improvement caused by considering the impact of suspended sediment and its damping to turbulence.展开更多
基金supported by the National Natural Science Foundation of China (Grants 51609244, 11472156, and 51139007)the National Science-Technology Support Plan of China (Grant 2015BAD20B01)
文摘A new instantaneous mobile bed thickness model is presented for sediment transport in skewed asymmetric oscillatory sheet flows. The proposed model includes a basic bed load part and a suspended load part related to the Shields parameter, and takes into account the effects of mass conservation, phase-lag, and asymmetric boundary layer development, which are important in skewed asymmetric flows but usually absent in classical models. The proposed model is validated by erosion depth and sheet flow layer thickness data in both steady and unsteady flows, and applied to a new instantaneous sediment transport rate formula. With higher accuracy than classical empirical models in steady flows, the new formula can also be used for instantaneous sediment transport rate prediction in skewed asymmetric oscillatory sheet flows.
文摘Hospital linen is clearly recognized as a potential reservoir for microorganisms and could be a vector of disease transmission. The aim of this study was to isolate, count and identify fungi and bacteria from different kinds of clean and dirty linen in a hospital. Microbiological samples have been collected on clean bed linen (n = 200), dirty bed linen (n = 192) and staff uniforms (n = 192) by using contact plates. 55% of samples from clean bed linen were contaminated before contact with the patient, with a mean count of 3 cfu/25 cm2 (range: 1-117 cfu) when contaminated. Virtually all samples from dirty bed linen carried microorganisms, with a mean count of 23 cfu/25 cm2 (range 1-191 cfu). In addition, staff hospital uniforms showed the highest contamination rates in the study, with an average of 45 cfu/25 cm2 (range: 1-218 cfu). Microbial species were mostly bacteria commonly found in the environment or on human skin, such as staphylococci or micrococci. Nevertheless, 57% of the identified species may be opportunistic pathogens for humans, representing a risk for people with a deficient or weakened immune system, especially in cases of superinfection. Since contamination of linen seems to occur after washing, actively antimicrobial textiles would represent a valuable measure to prevent textiles from being a vehicle for transfer of microorganisms.
基金financially supported by the National Natural Science Foundation of China(Grant Nos.51836010 and 51609244)the National Science-Technology Support Plan Projects(Grant No.2015BAD20B01)
文摘Nikuradse roughness(ks) is very important in the sediment transport prediction because it is related to the evaluations of the velocity distribution, shear stress and erosion depth. Dimensionless Nikuradse roughness(ks/D,where D is the sediment diameter) is usually given 1–2.5 on the immobile plan bed or at low shear stress. But it behaves differently on the mobile plan bed at high shear stress with much sediment picked up to movement when the Shields parameter(Θ) is larger than 0.8–1.0. The effective Nikuradse roughness on the mobile plan bed was derived indirectly from the erosion depth correlated to the mobile plan bed thickness considering the mass conservation in the present study. The proposed erosion depth confirmed the relation to the Shields parameters with an extra factor consisting of suspended sediment and its damping to turbulence. The decrement of the erosion depth caused by the increment of the sediment diameter at large shear stress was obtained, which was usually absent in classical empirical formulas based on the bedload theory. Good agreement with experiments was achieved by the present prediction of the Nikuradse roughness, erosion depth and sediment transport rate. Discussion was mainly focused on the prediction improvement caused by considering the impact of suspended sediment and its damping to turbulence.
