Hotelling模型再探讨     

高建刚 《太原理工大学高等教育研究》2006,24(4):22-26

文章修改Hotelling模型的基本假定，假定厂商边际生产成本为正，交通成本由消费者负担，厂商区位可以为内生变量，也可以为外生变量，在此假定前提下，分析厂商的最优的区位一价格策略，以探讨最大差异化原则或者最小差异化原则何时成立，或者不成立。  相似文献   

外源流水对流域地貌的重塑:河流下切与流域袭夺     

李伊菲  石耀霖  张怀 《中国科学院大学学报》2022,39(3):309-320

自新近纪晚期和第四纪早期以来,许多内流盆地转换成了外流盆地。内流湖水突然外泄,给下游流域带来大量的水。外源流水的注入重塑流域地貌并影响流域内河流的演化。基于有限体积方法,对外源流水对隆升河流地貌的重塑过程进行数值实验分析。主要结论为:外源流水注入后,下游主河道被深切。支流受侵蚀基准点下降的影响开始加速下切,整体流域的高程逐渐降低。当外源流水流量较大时,下游流域会袭夺相邻流域。河流下切系数控制流域开始袭夺的时间。河流下切系数和外源流水流量控制流域袭夺速度。流域重塑后的平均高程依赖于地表隆升速率、河流下切系数和外源流水流量。外源流水引起的流域袭夺过程可用于解释晋陕黄河与汾河流域的演化过程。  相似文献   

Effect of type II collagen treatment on the antioxidant status in immune tissues of adjuvant induced arthritic rats     

Nalini Ganesan  Hariprasad Chegu  A. N. Chandrasekaran 《Indian journal of clinical biochemistry : IJCB》2003,18(2):216-222

Adjuvant induced arthritis (AIA) is a model widely used to study Rheumatoid arthritis (RA). In the present study, lipid peroxides level in spleen and thymus of AIA rats was observed to be significantly high compared to normal rats. A significant decrease in ascorbic acid (ASA), reduced glutathione (GSH), superoxide dismutase activity (SOD) was also observed in spleen and thymus of AIA rats compared to normal rats. There was also a steady increase in the circulating immune complex level (CIC) throughout the experimental period in serum of AIA rats. In the present investigation, it was decided to study the effect of pre and post treatment with TYPE II collagen on the antioxidant status and the circulating immune complex level in AIA rats. The results from the present work indicates that the pretreatment with TYPE II collagen was effective in bringing significant changes on all the parameters studied in AIA rats. The post treatment with TYPE II collagen was effective in bringing significant changes on the CIC immune complex level and GSH content in the thymus tissue of AIA rats. The present work suggests that the pre treatment with TYPE II collagen was more effective in suppressing the disease than the post treatment.  相似文献   

Effects of pre-competitional rapid weight loss on nutrition,vitamin status and oxidative stress in elite boxers     

Dejan Reljic  Joachim Jost  Kirsten Dickau  Ralf Kinscherf  Gabriel Bonaterra  Birgit Friedmann-Bette 《Journal of sports sciences》2015,33(5):437-448

Dietary intake, vitamin status and oxidative stress were evaluated in 17 elite male boxers. Ten of them frequently reduced body weight rapidly before competitions (Weight Loss Group) and 7 did not practice rapid weight loss (Control Group). Food record checklists, blood samples for determination of vitamin status and plasma glutathione levels were obtained during a week of weight maintenance, a pre-competition week and a post-competition week. The average dietary intakes in both groups were 33 ± 8 kcal·kg^?1, 3.7 ± 1.1 g·kg^?1 carbohydrates, 1.5 ± 0.4 g·kg^?1 protein, 1.2 ± 0.4 g·kg^?1 fat and 2.2 ± 1.0 L water per day (excluding pre-competition week in Weight Loss Group). Energy (18 ± 7 kcal·kg^?1), carbohydrate (2.2 ± 0.8 g·kg^?1), protein (0.8 ± 0.4 g·kg^?1), fat (0.6 ± 0.3 g·kg^?1) and water (1.6 ± 0.6 L) consumption (P-values <0.001) and intakes of most vitamins (P-values < 0.05) were significantly reduced during the pre-competition week in the Weight Loss Group. In both groups, the intakes of vitamins A, E and folate were below recommended values throughout the three periods; however, blood vitamin and plasma glutathione levels did not change significantly. Our findings indicate a low-caloric and low-carbohydrate diet in elite boxers, regardless of participating in rapid weight loss or not. Apparently, the pre-competitional malnutitrition in the Weight Loss Group did not induce alterations in the vitamin and glutathione status.  相似文献