沂南县饮食业菜刀细菌污染的调查

为了解本县部分餐饮业菜刀细菌污染情况,采用纸片粘贴法采样192把菜刀,用发酵培养法检测,并对生熟切菜刀的细菌污染状况进行比较。结果,103把切生菜刀大肠菌群几何均数为1.0×103 cfu/cm2,89把切熟菜刀为6.4 cfu/cm2;切生菜刀致病菌检出率为7.29％,切熟菜刀检出率为1.12％,前者污染率明显高于后者。经统计学处理,有非常显著性差异(P<0.001)。

STUDY OF REFLECTION FROM GRADUAL TRANSITION SOUND ABSORBERS

Ⅰ. THEORY The problem of reflection from a gradual transition sound absorber has been investigated, in general, by finding the solution of a differential equation of the Riccati type, and also by experiment. We have dealt with this problem as a boundary value problem of the wave equation. The expression for the reflection factor of a gradual transition lining - (Fig. 1) is given