BACTERICIDAL EFFICIENCIES OF COMMERCIAL DISINFECTANTS AGAINST LISTERIA MONOCYTOGENES ON SURFACES

The efficiencies of potassium persulphate, isopropanol, hydrogen peroxide and peracetic acid, quaternary ammonium compound, hypochlorite, sodium dichloroisocyanurate, ethanol and phenol derivatives, tertiary alkylamines and dimethyl alamine betaine-based disinfectants and a hypochlorite-based disinfecting cleaning agent were evaluated against eight Listeria monocytogenes strains representing three different ribotypes. All the disinfectants were effective in a suspension test with an exposure time of 30 s at the lowest concentrations recommended by the manufacturer. The efficiencies on surfaces were reduced. However, on clean surfaces all the agents were considered effective when the exposure time was 5 min and the concentration was the average recommended by the manufacturer. Five of nine disinfectants and the disinfecting cleaning agent were considered effective in soiled conditions in the surface test. The most efficient agent was isopropanol-based and the least effective was the disinfectant containing tertiary alkylamine and dimethyl alamine betaine. Differences in bactericidal efficiencies of disinfectants against different L. monocytogenes strains on meat soiled surfaces were found.     

Matrix criterion robust linear quadratic control problem

This paper studies a robust linear quadratic (LQ) control problem with multiple quadratic performance indices. Specifically, a linear model is assumed to be available for each of a prespecified set of operating points of a system. A vector-valued quadratic control performance index is given at each operating point. It is then desired to find the constant feedback gains of a linear controller to obtain satisfactory control performance over all the operating points. This is a realistic case involving the minimization of a vector criterion of vector criteria, i.e. a matrix-valued criterion. The matrix-valued criterion gives insight into standard robust LQ design, and leads to several related vector minimization problems, and to natural procedures for computing a satisfactory non-inferior solution to the matrix-valued minimization problem.