逆转录病毒转移的β－半乳糖苷酶基因在成纤维细胞中的表达

为了研究逆转录病毒载体转移外源基因的实用性，我们采用小鼠白血病病毒（ＭｏＭＬＶ）载体将大肠杆菌的β－半乳糖苷酶基因（ｌａｃＺ）和抗新霉素（ＮｅｏＲ）基因转移到大鼠成纤维细胞内，对整合后的前病毒结构和基因表达进行了酶活性测定和ＤＮＡ分析。结果表明：ｌａｃＺ基因可以在大鼠皮肤成纤维细胞和２０８Ｆ细胞株中较长时间地表达；前病毒整合位点、靶细胞特性和整合后的载体结构与转入基因表达的稳定性紧密相关。     

Use of duration models for predicting vehicular delay at a US/Canadian border crossing

Delays caused by congestion at the US/Canadian border crossing between Washington state and British Columbia have underscored the need for some sort of intervention. One obvious congestion-mitigation measure would be to estimate delay times and then relay this information to motorists so that they could select among alternative border crossing sites, or delay their trips. This paper applies duration models to estimate vehicular delay and demonstrates the usefulness of such models as a basis for a fully automated motorist information system. The paper also explores the flexibility of duration models, in providing estimates of vehicle delay, by using alternate parametric forms and assessing prediction accuracy.     

The evolution of U.S. rail freight pricing in the post-deregulation era: revenues versus marginal costs for five commodity types

There have now been over three decades of experience with rate-making freedom for all modes of intercity freight transport in the United States. Most evidence suggests that regulatory change has been beneficial for the rail industry and its users. Despite evidence of positive impacts of regulatory reform of U.S. freight transport, there is limited evidence related to long-term pricing trends by commodity in the deregulated era. Moreover, U.S. shipper groups have called for increased regulation of U.S. railroads, citing increased rates and profits, and monopoly pricing to “captive shippers.” This study estimates U.S. railroad revenue-marginal cost ratios for seven different commodities between 1986 and 2008. Interestingly, we find no significant increase in revenue-cost margins for commodities thought to be “most captive” (coal and chemicals), while finding large increases for some commodities thought to be “non-captive.” These results may provide insight into the impacts of regulatory reform in other countries, where there are similar concerns of equitable pricing and financial viability. They suggest that a move toward a more market-based pricing system can enhance railroad viability without harming those with fewer transport options.