Effect of liquid wetting on catalyst effectiveness in trickle-bed reactors

The liquid in trickle-bed reactors falls in rivulets down over the catalyst particles. Heretofore, studies of the effect of fractional liquid coverage of the outer surface of the particle on reaction rate have ignored the distribution of the rivulets. A model has been developed in this paper for predicting the effect of number and size of the liquid rivulets. The system of equations has been solved numerically for a first order reaction for two types of reactions: a), one where the rate is determined by the reactant concentration in the liquid, and b), a reaction where the rate is controlled by reactant concentration in the gas phase, as in some hydrogenations. The results show that intraparticle concentration profiles are strongly affected by the distribution and size of the rivulets. However, for both types of reactions the overall rate, as measured by an overall effectiveness factor, is not significantly affected. This result is important since it suggests that distribution and size of the liquid rivulets may be safely ignored in evaluating the effect of liquid coverage, or wetting efficiency, on the rate of reaction     

Quantitative Assessment of a Peer-to-peer Cooperative Infrastructure Using Stochastic Well-Formed Nets

Traditional support tools for software engineers, normally based on a client-server architecture, are unsuitable to deal with the new issues emerging from the current (and future) cooperative work scenarios (where connectivity is intrinsically transient, the number of interacting partners dynamically changes, etc.). This paper presents a quantitative assessment of a fully decentralized, peer-to-peer, cooperative infrastructure. Stochastic Well-Formed Nets (SWNs) modelling the new peer-to-peer architecture, and a traditional (client-server) one, are developed and analysed: we used SWNs for their ability to directly exploit the symmetries intrinsically present in the modelled systems, thus greatly reducing the complexity of the analysis. The main goal is to compare the impact of the two alternative protocols on the collaborative work. Together with the performance figures of interest, methodological issues concerning the choice of the most appropriate model abstraction level, the adoption of a compositional modelling approach, and the management of the model complexity are also discussed.     

Psychiatric illness and family support in children and adolescents with diabetic ketoacidosis: a controlled study

BACKGROUND: In the adult respiratory distress syndrome, nitric oxide (NO) inhalation improves oxygenation through reducing ventilation-perfusion mismatching, but detailed information on the pulmonary effects of NO inhalation in septic shock is scarce. The present study investigated the effects of inhaled NO on alveolar dead space (Vdalv) and venous admixture as well as on respiratory system compliance (Crs) and respiratory system resistance (Rrs) in a porcine model of septic shock. Protective effects of NO are discussed. METHODS: Thirteen anaesthetised and ventilated pigs were given an infusion of endotoxin for an observation time of 220 min to induce acute lung injury (ALI). In the NO-early group (n=6), an inhalation of 60 ppm NO was started simultaneously with the endotoxin infusion and continued for 190 min. In 7 control/NO-late animals, 60 ppm NO was administered for 30 min following 190 min of endotoxin infusion. Haemodynamics, single-breath CO2-, pressure-, and flow signals were recorded. RESULTS: Endotoxin induced haemoconcentration, pulmonary vasoconstriction, and a decrease in Crs, while venous admixture, Vdalv, and Rrs increased. In the NO-early group, the pulmonary vasoconstriction was attenuated, no increase in pulmonary venous admixture or in Vdalv was seen before cessation of NO, and the improvements in oxygenation outlasted the NO inhalation. In the control/NO-late group, the NO inhalation reversed the changes in dead space and venous admixture. NO had no effect on the changes in respiratory mechanics. CONCLUSION: In porcine ALI, 60 ppm NO diminishes pulmonary vasoconstriction and improves gas exchange by reducing pulmonary venous admixture and alveolar dead space, but does not prevent a fall in Crs. NO inhalation may help prevent long-lasting pulmonary failure.     

PCR method for detection and identification of Lactobacillus casei/paracasei bacteriophages in dairy products

Bacteriophage infections of starter lactic acid bacteria (LAB) pose a serious risk to the dairy industry. Nowadays, the expanding use of valuable Lactobacillus strains as probiotic starters determines an increase in the frequency of specific bacteriophage infections in dairy plants. This work describes a simple and rapid Polymerase Chain Reaction (PCR) method that detects and identifies bacteriophages infecting Lactobacillus casei/paracasei, the main bacterial species used as probiotic. Based on a highly conserved region of the NTP-binding genes belonging to the replication module of L. casei phages phiA2 and phiAT3 (the only two whose genomes are completely sequenced), a pair of primers was designed to generate a specific fragment. Furthermore, this PCR detection method proved to be a useful tool for monitoring and identifying L. casei/paracasei phages in industrial samples since specific PCR signals were obtained from phage contaminated milk (detection limit: 10(4) PFU/mL milk) and other commercial samples (fermented milks and cheese whey) that include L. casei/paracasei as probiotic starter (detection limit: 10(6) PFU/mL fermented milk). Since this method can detect the above phages in industrial samples and can be easily incorporated into dairy industry routines, it might be readily used to earmark contaminated milk for use in processes that do not involve susceptible starter organisms, or processes which involve phage-deactivating conditions.     

Wild Lactobacillus strains: Technological characterisation and design of Coalho cheese lactic culture

To design a specific lactic culture for the controlled manufacture of coalho cheese, 13 Lactobacillus rhamnosus, two Lactobacillus fermentum and one Lactobacillus plantarum strains isolated from artisanal coalho cheeses were identified and characterised. Two Lb. rhamnosus, one Lb. plantarum and one Lb. fermentum were selected and grouped in pairs designing four different culture formulations that demonstrated a good performance in cheesemaking experiments at pilot scale. Further studies to adjust the balance of strains used are necessary to attain adequate sensorial and technological attributes as expected for artisanal cheeses.     

A High Viscosity Gelatin

Abstract

The viscosity of gelatin solutions may he increased by the addition of polysaccharides such as carrageenan. The rheology of such a high viscosity mixture is described.