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81.
Heather Windle 《BMJ (Clinical research ed.)》1980,280(6229):1425-1426
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An 11-week crossover study was carried out in which 12 subjects smoked high-nicotine (1·84 mg standard yield) and low-nicotine (0·6 mg) cigarettes after an initial period of smoking their usual brands with a medium-nicotine yield (mean 1·4 mg). Plasma and urine nicotine concentrations, carboxyhaemoglobin (COHb) concentration, puffing behaviour, 24-hour cigarette consumption, and butt nicotine content were measured. The changes in plasma nicotine and blood COHb concentrations showed that the smokers compensated for about two-thirds of the difference in standard yields when switched to either high- or low-nicotine cigarettes. Thus, compared with the medium-nicotine brand, the intake of nicotine and carbon monoxide was only about 10% higher when subjects smoked the high-nicotine cigarettes, which had a standard yield 30-40% higher than the medium brands; and only about 15% lower when they smoked the low-nicotine cigarettes, which had a standard yield about 50% lower than the medium brands. But nicotine content and urine nicotine concentrations followed a similar pattern. Changes in puffing behaviour and in 24-hour cigarette consumption were only slight.The results show clear evidence of both upward and downward self-titration of nicotine and carbon monoxide (and tar) intakes when smokers change to cigarettes with standard yields that differ over the range studied. 相似文献
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Simple agarose gel electrophoretic method for the identification and characterization of plasmid deoxyribonucleic acid. 总被引:225,自引:28,他引:197 下载免费PDF全文
Agarose gel electrophoresis may be employed effectively for the detection and preliminary characterization of plasmid deoxyribonucleic acid (DNA) present in clinical isolates and laboratory strains of gram-negative microorganisms. The method is sensitive and does not require radioisotopes or ultracentrifugation. The estimation of plasmid mass from the extent of DNA migration in gels compares favorably with results obtained by electron microscopy of plasmid DNA purified by equilibrium density centrifugation. The method has proved to be a useful tool for survey work and the epidemiological investigation of plasmid dissemination, as well as an important adjunct to the genetic analysis of plasmids. 相似文献
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Hayley L. Crowell Katherine C. King James M. Whelan Mallory V. Harmel Gennesee Garcia Sebastian G. Gonzales Paul H. Maier Heather Neldner Thomas Nhu John T. Nolan Emily N. Taylor 《Ecology and evolution》2021,11(12):8170
- Most studies on how rising temperatures will impact terrestrial ectotherms have focused on single populations or multiple sympatric species. Addressing the thermal and energetic implications of climatic variation on multiple allopatric populations of a species will help us better understand how a species may be impacted by altered climates.
- We used eight years of thermal and behavioral data collected from four populations of Pacific rattlesnakes (Crotalus oreganus) living in climatically distinct habitat types (inland and coastal) to determine the field‐active and laboratory‐preferred body temperatures, thermoregulatory metrics, and maintenance energetic requirements of snakes from each population.
- Physical models showed that thermal quality was best at coastal sites, but inland snakes thermoregulated more accurately despite being in more thermally constrained environments. Projected increases of 1 and 2°C in ambient temperature result in an increase in overall thermal quality at both coastal and inland sites.
- Population differences in modeled standard metabolic rate estimates were driven by body size and not field‐active body temperature, with inland snakes requiring 1.6× more food annually than coastal snakes.
- All snakes thermoregulated with high accuracy, suggesting that small increases in ambient temperature are unlikely to impact the maintenance energetic requirements of individual snakes and that some species of large‐bodied reptiles may be robust to modest thermal perturbations under conservative climate change predictions.
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Paul Daly Mao Peng Hugh D. Mitchell Young-Mo Kim Charles Ansong Heather Brewer Peter de Gijsel Mary S. Lipton Lye Meng Markillie Carrie D. Nicora Galya Orr Ad Wiebenga Kristiina S. Hildén Mirjam A. Kabel Scott E. Baker Miia R. Mäkelä Ronald P. de Vries 《Environmental microbiology》2020,22(3):1154-1166