Use of the Likelihood Ratio Test on the Uniform Distribution

In this article we give a simple procedure to determine the exact distribution of the likelihood ratio test of a statistical hypothesis regarding the parameter of the uniform distribution. The resulting distribution will be shown to serve as an approximation to the distribution of the likelihood ratio statistic for testing the equality of scale parameters of k independent Exponential populations.     

发酵生产S-腺苷-L-蛋氨酸培养条件的优化研究

考察了摇瓶发酵生产S-腺苷-L-蛋氨酸过程中碳源、氮源、无机盐和生长因子以及培养过程中补加L-蛋氨酸时间对S-腺苷-L-蛋氨酸的产量、含量及生物量的影响。并通过均匀实验设计对培养基配方进行优化,在30℃、180 r/m in的培养条件下,得到最后的培养基配方为:葡萄糖30g,酵母粉11g,(NH4)2SO412g,K2HPO4.3H2O 5g,KH2PO410g,MnSO4.H2O 0.09g,ZnSO4.7H2O 0.14g,MgC l20.5g,CaC l20.3g,CuSO40.005g,自来水定容至1L。摇瓶中优化后的S-腺苷-L-蛋氨酸产量可以达到0.9g/L,比优化前产量提高了30%。采用优化后的培养基和培养条件在5L发酵罐中间歇培养,24h后一次性补加24g/L葡萄糖和1.0g/L L-蛋氨酸,继续培养24h后产量可达2.66g/L,生物量23.4g/L。     

A convenient test for lipase activity in aqueous-based solutions

We proposed a convenient and accurate method for the measurement of lipase activity in a uniform aqueous-based substrate solution. In this work, lipase from Candida rugosa was used as the model lipase to test its catalytic ability toward p-nitrophenyl palmitate (p-NPP), which was suspended in a mixture of p-NPP ethanol solution and buffer. An ultraviolet–visible spectrophotometer was used to efficiently measure the liberated p-nitrophenol without extraction or centrifugation. Several factors that affected lipase activity were investigated, such as the ratio of p-NPP ethanol solution to buffer, the concentrations of p-NPP and lipase, as well as the temperature, reaction time, pH and agitation rate. Additionally, enzyme catalytic parameters such as K_m, V_m and “activation energy” were also assessed. We determined the optimal conditions for lipase in this homogeneous system and demonstrated lipase's catalytic performance in this condition followed Michealis–Menten kinetics.     

带饱和项的互惠交错扩散模型整体解的存在性和稳定性

应用能量估计方法和Gagliardo-Nirenberg型不等式证明了带饱和项的Shigesada-Kawasaki-Teramoto两种群互惠模型在齐次Neumann边值条件下整体解的存在唯一性和一致有界性.通过构造Lyapunov函数给出了该模型正平衡点全局渐近稳定的条件.