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.     

降血压肽的构效关系研究

降血压肽的活性与其氨基酸组成和氨基酸序列有重要的关系.然而,关于降血压肽的构效关系至今尚未清楚.通过对收集的270种降血压肽的氨基酸组成进行分析,研究降血压肽的构效关系以及如何选择蛋白酶和蛋白原料用酶解方法制备降血压肽.结果表明:降血压肽中,N端氨基酸主要为Arg、Tyr、Gly、Val、Ala、Ile和:Leu;C端氨基酸主要为Tyr、Pro、Trp、Phe和Leu;与降血压肽的N端氨基酸特征相比,其C端氨基酸特征对降血压活性影响更为重要.根据降血压肽的构效关系可以看出,在选择蛋白酶和蛋白原料制备降血压肽时,优先选择酶切位点为Tyr、Pro、Trp、Phe和Leu羧基端的蛋白酶以及富含Tyr、Val、Ala、Ile、Leu、Pro、Trp和Phe的蛋白.     

条斑紫菜蛋白和多糖提取工艺优化

以条斑紫菜为原料，采用超声辅助提取蛋白和多糖、通过单因素试验和正交试验，确定了最佳的提取工艺条件。     

Development of a multiplex real-time PCR assay for the detection of ruminant DNA

The U.S. Food and Drug Administration (FDA) has previously validated a real-time PCR-based assay that is currently being used by the FDA and several state laboratories as the official screening method. Due to several shortcomings to the assay, a multiplex real-time PCR assay (MRTA) to detect three ruminant species (bovine, caprine, and ovine) was developed using a lyophilized bead design. The assay contained two primer or probe sets: a "ruminant" set to detect bovine-, caprine-, and ovine-derived materials and a second set to serve as an internal PCR control, formatted using a lyophilized bead design. Performance of the assay was evaluated against stringent acceptance criteria developed by the FDA's Center for Veterinary Medicine's Office of Research. The MRTA for the detection of ruminant DNA passed the stringent acceptance criteria for specificity, sensitivity, and selectivity. The assay met sensitivity and reproducibility requirements by detecting 30 of 30 complete feed samples fortified with meals at 0.1 % (wt/wt) rendered material from each of the three ruminant species. The MRTA demonstrated 100 % selectivity (0.0 % false positives) for negative controls throughout the assessment period. The assay showed ruggedness in both sample selection and reagent preparation. Second and third analyst trials confirmed the quality of the written standard operating procedure with consistency of results. An external laboratory participating in a peer-verification trial demonstrated 100 % specificity in identifying bovine meat and bone meal, while exhibiting a 0.03 % rate of false positives. The assay demonstrated equal levels of sensitivity and reproducibility compared with the FDA's current validated real-time PCR assay. The assay detected three prohibited species in less than 1.5 h of total assay time, a significant improvement over the current real-time assay. These results demonstrated this assay's suitability for routine regulatory use both as a primary screening tool and as a confirmatory test.     

电池托架有限元分析与轻量化研究

以8 t平台纯电底盘电池托架为研究对象,基于有限元分析,对其强度性能进行了评估,研究了使用高强钢和结构优化等轻量化方法.结果表明:该轻量化方法实现了降重54 kg,经过强度评估后满足设计要求,为纯电底盘的轻量化设计提供了一条可行的途径.     

Radical-Initiated Reaction of Methyl Linoleate with Dialkyl Phosphites

The addition of dialkyl phosphite (methyl, ethyl and n‐butyl) to methyl linoleate (MeLin) double bonds was investigated. The reaction proved to be more challenging than the analogous reaction with methyl oleate (MeOl), due to inhibition of the radical reaction by the bis‐allylic hydrogens of MeLin and the lower reactivity of MeLin double bonds. However, we demonstrated that this self‐inhibition problem can be solved by simply keeping the MeLin reagent at low concentrations, while keeping the dialkyl phosphite at high concentrations. For optimization of the reaction, four different radical initiators were investigated: dilauroyl peroxide (LP), 2,2′‐azobis(2‐methylpropionitrile) (AIBN), tert‐butyl perbenzoate (t‐BP), and tert‐butyl peroxide (TOOT). The initiators were used at temperatures that provided a half‐life of 10 h: 64, 64, 104, and 125 °C respectively for LP, AIBN, t‐BP, and TOOT. The tests showed the reaction to be faster at higher temperatures, but transesterification of the ester groups was also observed at elevated temperatures. t‐BP was chosen as an optimal initiator for carrying the reaction. The apparent order of reactivity of the dimethyl, diethyl and di‐n‐butyl phosphites (Me >Et >n‐Bu) towards MeLin was due to differences in their molar volumes. When the concentrations of dialkyl phosphite were kept the same, the order reversed (n‐Bu > Et~Me). GC–MS spectra of the resulting phosphonates are reported and the main fragments assigned.     

超声降解条斑紫菜多糖的反应动力学

针对多糖化学降解、热裂解和生物降解存在的一些不足,采用超声波技术研究了紫菜多糖（PYPS）的降解问题。研究了以下几个基础问题：（1）PYPS浓度、超声功率和溶液温度对降解过程中反应产物特性粘度随处理时间变化的影响;（2）用于描述PYPS分子量与特性粘度之间关系的Mark-Houwink方程的建立;（3）超声降解反应动力学方程的建立;（4）超声降解反应活化能的计算。结果表明,超声功率和溶液温度的增加有利于PYPS超声降解作用的增强,浓度的影响不是单调变化的,在0.75g/dL时降解较快;PYPS在水溶液中25℃下的Mark-Houwink方程参数为KMH＝7.86×10-3和α＝0.626;超声降解动力学研究发现,反应速率常数与反应时间之间呈显著的指数关系;超声降解反应的活化能为52.13kJ/mol。超声降解反应的活化能的数值小于两例发表的酶解法活化能,初步认为超声降解法优于酶解法。     

Effects of Ultrasound on Mass Transfer Kinetics,Structure, Carotenoid and Vitamin C Content of Osmodehydrated Sweet Potato (Ipomea Batatas)

The effects of ultrasound pretreatments on mass transfer kinetics, microstructure, carotenoid and vitamin C contents of sweet potato were investigated. Sweet potato samples were treated in distilled water with ultrasound (DWU), osmotic dehydration without ultrasound (OD) and ultrasound-assisted osmotic dehydration (UOD). Samples were subjected to ultrasound probe of 2 cm diameter, frequency of 28 kHz at 300 W maximum power at different pretreatment times of 20, 30, 45 and 60 min. The Azuara model used in this study fitted the experimental data well with high coefficient of correlation ranging from 0.92 to 0.98, low values of chi-square (<0.6), root mean square error (<0.9) and percent mean relative deviation (<10%). The results showed that UOD significantly (p < 0.05) had the highest mass transfer coefficient and equilibrium value for water loss and solid gain, compared to DWU and OD. DWU had no significant effect on the structure of sweet potato samples, while UOD had the highest effect on the structure. The samples treated in OD had the highest carotenoid retention compared to DWU and UOD at all pretreatment times. However, ultrasound enhanced the retention of vitamin C (>70%) in sweet potato samples treated in DWU and UOD.