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Summary In previous studies we found that lamp fouling was a major limitation when tubular ultraviolet reactors were used for sterilization of cheese whey over an extended period of time. Heat generation by ultraviolet lamps causes the temperature of the flowing fluid to rise and thus enhances fouling. In this study, the heat generated by a low pressure mercury ultraviolet lamp during continuous sterilization of cheese whey in three tubular reactors having different gap sizes (18, 13 and 6 mm) was calculated using a heat balance formula. The technique quantified the heat produced in and lost from each reactor. The heat balance calculations showed that lamp heat generation decreased with decreasing gap size (50.48, 47.71 and 31.91 kJ/h for 18, 13 and 6 mm gap sizes, respectively). However, the heat gain per unit volume and consequently the steady state temperature of the cheese whey effluent increased with decreasing gap size (91.79, 159.03 and 319.12 kJ/l and 44.5, 53.4 and 62.8 °C for 18, 13 and 6 mm gap sizes, respectively). A strong correlation between the amount of heat gain per unit volume and the amount of fouling material accumulated on the quartz surface was realized. The amount of accumulated fouling material increased with decreasing gap size (14.42, 15.31 and 25.26 g on wet basis for 18, 13 and 6 mm gap sizes, respectively). A new design in which the direct contact between the lamp and the flowing cheese whey is avoided and lamp cooling is introduced should be investigated.  相似文献   
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Use of DNA markers to study bird migration   总被引:2,自引:2,他引:0  
The molecular methods that are presently being used for studying phylogenetics, phylogeography and population genetics can also be applied to study bird migration. They are powerful and can supplement the information obtained from ringing, telemetry, morphometrics, ringing, radar tracking and isotope analysis. This short review describes the principles, scopes and limitations DNA methods and DNA markers that are relevant for migration research, such as DNA sequences, short tandem repeats (microsatellites), single nucleotide polymorphisms, amplified fragment length polymorphism, inter simple sequence repeats and molecular sexing.  相似文献   
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Activities of whole blood glutathione peroxidase (GSH-Px) and erythrocyte superoxide dismutase (SOD) and serum levels of selenium (Se), copper (Cu) and zinc (Zn) were measured in 118 apparently healthy subjects aged 20-60 years from the city of Ponta Delgada, Island of San Miguel, The Azores Archipelago, Portugal. Data were analysed by age/gender, lipid profile and blood pressure as cardiovascular risk factors searching for their relevance when assessing reference values for antioxidant biomarkers. GSH-Px was in the same range, but SOD was significantly lower than in other Portuguese populations. Neither activity differed with gender. GSH-Px activity increased with age, namely in normolipidemic men versus the hyperlipidemic group in which a decrease was observed. This suggests a progressive impairment of GSH-Px with age caused by an enhanced production of oxidant species in hyperlipidemia. GSH-Px was 30% lower in male hypertensives versus normotensives. SOD activity did not relate to age or blood pressure but was 17% higher in the hyperlipidemic men versus the normolipidemic group, suggesting a better antioxidant protection by SOD than by GSH-Px in hyperlipidemia and hypertension. Se was higher in men versus women, particularly in the older subjects, and partly related to hyperlipidemia. Zn levels showed a similar dependency on gender, not related to age or lipid profile. Cu levels were much higher in women than in men in all age or lipid profile classes and decreased in hyperlipidemia. They were lowered with age in both genders, particularly in normolipidemic women. The present research therefore suggests that hyperlipidemia and hypertension do affect antioxidant status and should be considered when assessing antioxidant biomarkers in blood.  相似文献   
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Human housekeeping genes,revisited   总被引:1,自引:0,他引:1  
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We investigated the production of hydrogen peroxide (HOOH) in illuminated seawater media containing a variety of zwitterionic buffers. Production rates varied extensively among buffers, with 4‐(2‐hydroxyethyl)1‐piperazineethanesulfonic acid (HEPES) highest and N‐Tris(hydroxymethyl)methyl‐3‐aminopropanesulfonic acid (TAPS) among the lowest. The rate of HOOH accumulation was remarkably consistent over many days, and increased linearly with buffer concentration, natural seawater concentration, and light level. Concentrations of HEPES commonly used in culture media (1–10 mM) generated enough HOOH to kill the axenic Prochlorococcus strain VOL1 during growth in enriched seawater media at lower, environmentally realistic cell concentrations and/or under high light exposure. We also demonstrated that HEPES can be used experimentally to study the biological effects of chronic exposure to sublethal levels of HOOH such as may be experienced by light‐exposed microorganisms.  相似文献   
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Asian Americans comprise 6.4% of the US population, but account for over 20% of the country’s elite Ivy League students. While researchers have studied mechanisms that promote an “Asian second-generation advantage” in education, including immigrant hyper-selectivity, few have examined whether this advantage extends into the labour market. Focusing on the five largest Asian groups – Chinese, Indians, Filipinos, Vietnamese, and Koreans – we revisit the thesis of Asian second-generation advantage. We argue that how we define advantage – as outcomes or mobility, in education or in occupations – matters. Our analyses reveal that all five second-generation Asian groups attain exceptional educational outcomes, but vary in intergenerational mobility. Second-generation Vietnamese exhibit the greatest intergenerational gains, followed by second-generation Chinese and Koreans; second-generation Indians and Filipinos experience none. Moreover, this advantage disappears in the labour market for all groups, except for Chinese, revealing the domain-specific nature of the Asian second-generation advantage.  相似文献   
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