Digital Control of a Continuous Stirred Tank Reactor

We project a novel digital control law for continuous stirred tank reactors, based on sampled measures of temperatures and reactant concentration, as it happens in practice. The methodology of relative degree preservation under sampling is used. It is proved that a suitably approximated sampled system, obtained by Taylor series expansion and truncation, in closed loop with the projected control law, is asymptotically stable, provided that a condition on the sampling period is verified. Such condition allows for values of the sampling period larger than necessary in practical implementation with usual technology. Many simulations show the high performance of the proposed digital control law

Interestingness of traces in declarative process mining: The janus LTLPf Approach

Declarative process mining is the set of techniques aimed at extracting behavioural constraints from event logs. These constraints are inherently of a reactive nature, in that their activation restricts the occurrence of other activities. In this way, they are prone to the principle of ex falso quod libet: they can be satisfied even when not activated. As a consequence, constraints can be mined that are hardly interesting to users or even potentially misleading. In this paper, we build on the observation that users typically read and write temporal constraints as if-statements with an explicit indication of the activation condition. Our approach is called Janus, because it permits the specification and verification of reactive constraints that, upon activation, look forward into the future and backwards into the past of a trace. Reactive constraints are expressed using Linear-time Temporal Logic with Past on Finite Traces (LTLp f). To mine them out of event logs, we devise a time bi-directional valuation technique based on triplets of automata operating in an on-line fashion. Our solution proves efficient, being at most quadratic w.r.t. trace length, and effective in recognising interestingness of discovered constraints

Preliminary notes on invasion and proliferation of foodborne Listeria monocytogenes strains

In this study, virulence properties of L. monocytogenes strains isolated from food and food environments were evaluated. In particular, adhesion and invasion efficiencies were tested in a cell culture model (HeLa). Half of the isolates (9/18) exhibited a high invasion index. In particular, the strain isolated from smoked salmon had the highest invasion index. The remaining isolates showed an intermediate invasion index. All environmental isolates belonged to this group. Finally, no isolates revealed a low invasion index. Regarding intracellular growth, all tested isolates had a replication time between 2 and 6 hours. For this reason, they can be considered virulent. In spite of its capability to invade HeLa cells with a medium/high invasion index, a non-haemolytic rabbit isolate did not show any intracellular growth. In conclusion, differences in invasion efficiency and intracellular growth did not seem strictly related to the origin of the strains. Moreover, invasiveness of an organism is not the only requirement for establishing an infection. Virulence of L. monocytogenes also depends on ability to grow intracellularly and to spread from cell to cell. For these reasons, PCR detection of known virulence genes has the potential to gain additional insight into their pathogenic potential. A comprehensive comparative virulence characterization of different L. monocytogenes strains in studies that include tissue culture models and PCR detection of virulence genes will be necessary to investigate differences in human-pathogenic potentials among the subtypes of this bacterium

Listeria monocytogenes: biofilm in food processing

Contamination of food by Listeria monocytogenes (L.m) frequently occurs in food processing environments, where cells persist due to their ability to attach to surfaces. L.m is able to attach and colonize environmental surfaces by producing a three-dimensional matrix of extracellular polymeric substances (EPS) called biofilm; such structures are dynamic systems. Once established, biofilms can serve as a source of product contamination. Moreover, L.m in the biofilm state shows a reduced susceptibility to antimicrobial agents. The present review focuses on L.m biofilms in food processing environments. In addition, some aspects of biofilm control and eradication are highlighted

METHICILLIN - RESISTANT STAPHYLOCOCCUS AUREUS IN PIG PRODUCTION CHAIN

The aims of this study were (i) to estimate the prevalence of Staphylococcus aureus (S.a) in pig farm environments; (ii) to evaluate the presence of S.a in pork processing environments (iii) to detect the presence of methicillin-resistant (MRSA) among isolated strains. Samples of pig stool, farm environment and pork processing environment were collected. These samples were submitted to detection of S.a following the international method: UNI EN ISO 6888-2 and the Minimum Inhibitory Concentrations (MIC) tests were performed by using the automated VITEK 2 system. In addition, a PCR for the detection of the mecA gene was applied. Overall, S. aureus were more frequently detected from pig farms than from pork processing environments. Among the n.51 isolated strains, n. 49 (96%) were methicillin resistant (MRSA) and only n.2 strains were methicillin sensitive (MSSA). The results of the present study highlighted that further studies are needed to elucidate transmission routes of MRSA in pig production chain

THE MANAGEMENT OF THE DOMESTIC REFRIGERATION: HYGIENIC AND SANITARY CHARACTERISTICS OF REFRIGERATORS FROM NORTHEN AND CENTRAL ITALY

This study aimed to provide information on the consumer management of refrigerated food. N° 469 interviews were carried out and the results obtained were subjected to descriptive statistical analysis and further processed with the Multiple Correspondence Analysis and Cluster Analysis. Five homogeneous groups were obtained. In each of them a significant number of refrigerators (60) were tested to assess the temperature and the microbiological status (TVC, Enterobacteriaceae, Salmonella spp. and Listeria spp.). Listeria monocytogenes and Salmonella spp. were not recovered; Listeria innocua was recovered (3.3%). Regarding the TVC values, the 30% of the tested refrigerators was classified as not appropriate (28.3%) or not acceptable (1.7%). Consumer education should be focused in order to reduce foodborne disease. Only safety-conscious consumers can become active partners within the food safety chain