Incidence of heavy metal and antibiotic resistance in bacterial isolates from Blue Nile river water in Ethiopian region

Heavy metal pollution of river water has health implications. This study was aimed to test if bacteria that are heavy metal resistant can resist antibiotics. Heavy metal-resistant bacteria were isolated using Nutrient agar plates amended with 100?μg?ml^?1 of metal salts. Isolates were further screened to determine minimal inhibitory concentration against each metal. The isolates belonged to the genera of Neisseria, Bacillus, Pseudomonas, Staphylococcus, Streptococcus, Micrococcus, Corynebacterium and Proteus. Minimum inhibitory concentration of the isolates for heavy metals ranged from 200 to 2300?μg?ml^?1. Isolates of Pseudomonas, Neisseria, Bacillus, Protues, Streptococcus, Staphylococcus and Micrococcus spp. exhibited multiple antibiotic resistance. Statistically significant correlation between metal resistance and antibiotic resistance was observed among bacterial isolates. The present work suggests that some of the isolates could be hazardous to human beings as a result of natural selection of dual resistant mechanisms.     

碳纳米管纱在应力下的压阻效应:现象和影响因素(英文)

碳纳米管因机械应力敏感特性而成为传感器的理想材料。单原子层厚度的石墨烯片卷曲而成的单壁碳纳米管具有大约1 nm的管径。碳纳米管纺丝形成纱,使其能够用于结构组份中。本文研究了碳纳米管纱的几何尺寸、力学性能和准静态应力加载速率对其压阻效应的影响。应力加载速率影响碳纳米管纱的失效机理和机电特性。高应力加载速率导致拉伸强度的增加和正压阻效应,而低应力加载速率引起较高的应力失效与负压阻效应。碳纳米管纱的压阻传感器系数随应力加载速率基本不变,但其对于应力水平和碳纳米管纱的几何尺寸具有高度依赖性。作为传感器所需的线性压阻关系在高应力加载速率下相关系数为0.995,而在低应力加载速率下相关系数只有0.832。     

Agronomic and economic performance of reservoir sediment for rehabilitating degraded soils in Northern Ethiopia

Nutrient export through sediment is, often, not given due attention in improving the fertility of soils. A Randomized Complete Block Design (RCBD) (replicated three times) was conducted to assess the effect of sediment, collected from a microdam, on the yield of a local wheat cultivar (Triticum aestivum) grown on a Luvisol and a Vertisol during cropping season of 2003 and 2004 in Tigray, Ethiopia. In the first season, the treatments consisted of applying 34.3 Mg sediment ha⁻¹ (T1), 0.1 Mg urea ha⁻¹ (T2), 4 Mg manure ha⁻¹ (T3) and a control plot (T4). The experiment was repeated in the 2004 cropping season using the same indicator crop but without the use of T1 and T3 inputs to evaluate the residual effect of these treatments on crop productivity. Plant height, plant density, spike length, straw and grain yield were compared among the treatments. After harvest, surface soil (0–25 cm) samples were taken and analyzed for total Nitrogen (Ntot), available Phosphorous (P), Soil Organic Carbon (SOC), Cation Exchange Capacity (CEC), and porosity to examine treatments effect on these soil properties. Higher CEC, exchangeable bases, SOC, Ntot, available P and micronutrients except Cu characterized sediment compared to the two soils used. Application of sediment increased the average grain and straw yield of wheat by 72% and 12%, respectively, in the Luvisol, and by 38% and 23%, respectively, in the Vertisol relative to the control. However, the application of sediment didn’t change the physicochemical properties of the Vertisol, but in the Luvisol CEC and available P were increased significantly. Like manure, sediment provided marginal rate of return above the minimum acceptable value (100%) by farmers, demonstrating the potential of these resources to improve degraded soils and boost farmers’ income.