超滤技术分离双低油菜ACE抑制肽及其性能研究

采用超滤技术对双低油菜酶解物中的ACE抑制肽进行了分离提纯研究,考核了分离参数对分离效果的影响,分析了不同分子质量段多肽HPLC肽谱的变化,研究了双低油菜高ACE抑制活性多肽的耐消化性、酸碱稳定性和耐热性。结果表明,超滤分离能明显提高双低油菜ACE抑制肽的活性,截留分子质量为3 ku的超滤膜透过液IC50值下降了15%,活性多肽回收率超过58%,酶解物中有4个高活性的组分峰,小于3 ku分子质量段的ACE抑制肽有良好的耐热性、酸碱稳定性和耐消化性。     

Structural analysis of value creation in software service platforms

As software service platforms grow in number of users and variety of service offerings, it raises the question of how this phenomenon impacts the value obtained by users. This paper identifies system usability, service variety, and personal connectivity to be the major determinants that contribute to the value offered to users on mobile software service platforms. A structural equation model, which is based on utility theory, technology acceptance theory, and the theory of network externalities, has been constructed from seven observed constructs, reflecting the three determinants and the user value. The lower bound of user value is estimated through the user’s willingness-to-pay for services and the user’s willingness to spend time on using services. For the validation, a co-variance-based structural equation analysis has been conducted on online survey data of 210 users of mobile service platforms (e.g., Android, iOS). The results show that the number of services used and the number of active user connections were found to be the strongest constructs explaining user value. Perceived usefulness did not explain user value as much. In total, they can explain 49 % of the value that the user receives from the platform. The implication of this result is that users’ value from a software service platform cannot be explained by the technology acceptance model itself. Instead, an approach that, as used in this research, of integrating network externality theory, utility theory, and technology acceptance theory is necessary.     

Tempo‐spatial land use/cover change in Zeway,Ketar and Bulbula sub‐basins,Central Rift Valley of Ethiopia

Understanding tempo‐spatial dynamics of land‐use/cover (LULC) and its drivers is instrumental in synthesizing knowledge for informed natural resource management planning and associated decisions. The present study investigates tempo‐spatial LULC changes, their drivers and the associated impacts in three sub‐basins (Zeway, Ketar and Bulbula) in the Central Rift Valley (CRV) of Ethiopia. Satellite imageries of different periods in ArcGIS, field observations, focus group discussions (FGDs) and secondary data were used to analyse the LULC dynamics, their drivers and associated impacts from 1973 to 2014. The overall accuracy of 1973, 2003 and 2014 classification maps was 88.7%, 88.9% and 91.6%, respectively. The analysis results revealed a continuous increase of farmland and town built‐up areas at the expense of grasslands, shrub‐bush land and woodlands. It further indicated area of open irrigated agriculture, increasing from none to 2.61% of the total area. The FGDs demonstrated agricultural land expansion, resettlement and wood extraction were proximate causes of the observed LULC changes. Population increases, changes in land tenure system and decreased farmland productivity were determined to be the underlying causes of the changes. The FGDs further indicated these changes have negatively affected the natural resources. The present study findings indicate the need to reconsider land‐use decision tradeoffs between economic, social and environmental demands, and their implications for other similar areas in Ethiopia and beyond. Quantitative analysis and periodic evaluation of the drivers of such change and the impacts of existing and emerging land‐uses in the face of changing climate is recommended to facilitate sustainable use of the fragile ecosystems in the Ethiopian CRV.