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     

Advanced oxidation and adsorption technologies for organic micropollutant removal from lake water used as drinking-water supply

The goal of this research is to evaluate the effectiveness of innovative drinking-water treatments designed to remove toxic and mutagenic organic micropollutants from lake waters used for human consumption. The widely used adsorption on granular activated carbon (GAC) filter technique was compared with the more innovative resin column techniques (XAD4 and Ambersorb-563) and with the advanced oxidation processes (AOPs) with UV/O3 and UV/O3/ H2O2. The water samples, collected from lake Como, treated with these techniques were analysed for mutagenic activity using Ames assay, toxicity using bioluminescent bacteria and organic compound were characterized using the GC-MS technique. The results found a decrease of the mutagenic and toxic activities of the lake water after adsorption on GAC and resins, while the AOP process generally increased these parameters. The absence of mutagenic activity was found only when a GAC adsorption step was performed in addition to the AOP process. Similar results were obtained by the toxicological and chemical analyses. In addition, the GC-MS analysis identified some possible mutagenic agents.     

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.     

Italian multicentre study on microbial environmental contamination in dental clinics: a pilot study

The dental practice is associated with a high risk of infections, both for patients and healthcare operators, and the environment may play an important role in the transmission of infectious diseases. A microbiological environmental investigation was carried out in six dental clinics as a pilot study for a larger multicentre study that will be performed by the Italian SItI (Society of Hygiene, Preventive Medicine and Public Health) working group "Hygiene in Dentistry". Microbial contamination of water, air and surfaces was assessed in each clinic during the five working days of the week, before and during treatments. Air and surfaces were also examined at the end of the daily activity. A wide variation was found in microbial environmental contamination, both within the participating clinics and relative to the different sampling times. Microbial water contamination in Dental Unit Water Systems (DUWS) reached values of up to 26 × 10⁴ cfu/mL (colony forming units per millilitre). P. aeruginosa was found in 33% of the sampled DUWS and Legionella spp. in 50%. A significant decrease in the Total Viable Count (TVC) was recorded during the activity. Microbial air contamination showed the highest levels during dental treatments and tended to decrease at the end of the working activity (p < 0.05). Microbial buildup on surfaces increased significantly during the working hours. As these findings point out, research on microbial environmental contamination and the related risk factors in dental clinics should be expanded and should also be based on larger collections of data, in order to provide the essential knowledge aimed at targeted preventive interventions.     

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.     

Quality assessment of bed sediments of the Po River (Italy)

Comprehensive and contemporary evaluations of physical, chemical and toxicological endpoints have been performed on bed sediments of the Po River, the major Italian watercourse. Two extensive sampling campaigns were conducted in summer and winter low-flow conditions. Composite sediment samples were collected from ten reaches of the main river: the first was located in the upper region (ambient control), and the others downstream of the confluences of nine principal tributaries. The two sampling programs were paralleled by contemporary investigations on the macroinvertebrate community. The particle-size composition along the Po River showed a relatively uniform distribution of fine sand, a progressive downstream decrease of coarse sands and a corresponding increase of fine materials. The levels of polychlorinated biphenyls (PCB), polycyclic aromatic hydrocarbons (PAH), extractable organo halides (EOX), Cd, Cr, Cu, Hg, Ni, Pb and Zn were determined in sediment fine particles (< 63 microm), and showed marked changes across the ten river reaches. Their longitudinal trends, as those of organic carbon and total nitrogen, were very similar and largely independent of the survey season. Sediment quality benchmarks were used to evaluate sediment chemistry, and, although the overall level of contamination was from moderate to low, the reaches located downstream of the tributaries Dora Riparia, Dora Baltea, Lambro and Oglio were considered to be at risk. Sediments were tested for toxicity on Oncorhynchus mykiss, Ceriodaphnia dubia, Raphidocelis subcapitata and Vibrio fischeri. The toxicity tests were conducted both with sediment extracts and whole samples. Sediment extracts showed toxic potentials that were consistent with the spatial distribution of contaminants. Whole-sediment toxicity showed moderate/low effects which also included false positives and negatives. Alterations of the macroinvertebrate community were found for many kilometers downstream of Dora Riparia, and with a seasonal dependence, also in other reaches of the Italian river. Principal component analysis (PCA) was used to describe the longitudinal and temporal changes of the Po River, and allowed the selection of the most useful and discriminating indicators.