Residence time distribution in spouted bed drying of maltodextrin solutions on a bed of inert particles

Residence time distributions (RTD) for aqueous maltodextrin solutions were determined in two kinds of spouted bed dryers: (1) conventional spouted bed (CSB) 0.305 m diameter with a bed of polypropylene beads and (2) spout‐fluid bed 0.143 m diameter with draft tube submerged in a bed of FEP® pellets (S‐FBDT). RTD, mean residence time t_m, and spread of the distribution σ², were determined at different drying temperatures, spouting velocities, bed depths, spraying pressures, and feed concentrations. Average values of t_m and σ² were 6.5 min and 26.6 min² for the CSB and 6.9 min and 36 min² for the S‐FBDT, respectively, for all operating conditions except spraying pressure. RTD curves were well represented by the response of an ideal stirred tank with a superimposed bypass of 15% on average for the CSB and 7% on average for the S‐FBDT dryer for all operating conditions. Increase in spraying pressure produced a reduction of t_m and an increase in the bypass fraction of the product in both dryers. © 2011 Canadian Society for Chemical Engineering     

Modification of the Natural Photonic Bandgap of Synthetic Opals via Infilling with Crystalline InP

The growth of high‐quality stoichiometric indium phosphide by atmospheric pressure metal–organic chemical vapor deposition within thin‐film artificial opals has been optimized. The optical properties of these systems have been studied as a function of the filling fraction. A consistent behavior has been found which substantially differs from that of other common infilled opals. The evolution of the InP morphology seems to be strongly correlated with this anomalous photonic response. At the first infiltration stages, the growth leads to the formation of nanocrystallites that eventually, as the infiltration increases, coalesce in single‐crystalline grains of increasing size. The possibility to oxidize the material adds to its potential as a useful optical material.     

Effect of temperature on the aerobic degradation of vitamin C in citric fruit juices

By means of the method of the 2,4-dinitrophenylhydrazine the total ascorbic acid content in lima, lemon, tangerine and grapefruit juices, fresh and kept at four temperatures and different times, was determined. It was confirmed that in all the cases, the aerobic degradation of ascorbic acid follows a kinetic first order and that the values of the reaction rate are different between species and even between varieties of lemon and tangerine. The values of the equation terms are reported, and examples of application given. Within a range from 20 degrees to 92 degrees C, the effect of temperature on the velocity of the ascorbic acid degradation is described satisfactorily following the Arrhenius equation, in accordance with which, the corresponding values of activation energy are calculated to compare them with other published values. With the simple application of the method, in two steps, and considering that the L-ascorbic acid and the L-dehydroascorbic acid are predominant, the results can be used to calculate the vitamin C losses in citric fruit juices, indicated when they are processed by traditional thermal treatments.     

Expression of acetylcholinesterase messenger RNA in human brain: an in situ hybridization study

The distribution of messenger RNA coding for acetylcholinesterase was studied in human post mortem brain and rhesus monkey by in situ hybridization histochemistry and compared to the distribution of acetylcholinesterase activity. Acetylcholinesterase messenger RNA had--similar to acetylcholinesterase enzymatic activity--a widespread distribution in human bain. Acetylcholinesterase messenger RNA positive cells corresponded to perikarya rich in acetylcholinesterase activity in most but not all regions. Examples for mismatches included the inferior olive and human cerebellar cortex. The presence of hybridization signals in cerebral cortex and an enrichment in layer III and V of most isocortical areas confirmed that perikaryal acetylcholinesterase in cerebral cortex is of postsynaptic origin and not derived from cholinergic projections. In striatum the expression of high levels of acetylcholinesterase messenger RNA was restricted to a small population of large striatal neurons. In addition, low levels of expression were found in most medium sized striatal neurons. Cholinergic neurons tended to express high levels of acetylcholinesterase messenger RNA whereas in cholinoceptive neurons the levels were moderate to low. However, some noncholinergic neurons like dopaminergic cells in substantia nigra, noradrenergic cells in locus coeruleus, serotoninergic cells in raphé dorsalis, GABAergic cells in thalamic reticular nucleus, granular cells in cerebellar cortex and pontine relay neurons expressed levels comparable to cholinergic neurons in basal forebrain. It is suggested that neurons expressing high levels of acetylcholinesterase messenger RNA may synthesize acetylcholinesterase for axonal transport whereas neurons with an expression of acetylcholinesterase confined to somatodendritic regions tend to contain lower levels of acetylcholinesterase messenger RNA.     

Influence of the binder on the properties of catalysts based on titanium-vanadium oxides

The influence of the nature of the binder and its concentration in V₂O₅/TiO₂ catalysts on their mechanical and catalytic properties has been studied. The characterization analysis showed that the agglomeration mechanism is different when an inorganic acid, such as H₃PO₄, or a natural silicate, such as sepiolite, were used. Two different patterns are proposed, which explain the effect of these binders on the performance of this type of catalyst in the selective catalytic reduction of NO _x with NH₃.     

Comparison of the ligase chain reaction with solid and liquid culture media for routine detection of Mycobacterium tuberculosis in nonrespiratory specimens

The aim of this study was to compare the results of a commercial assay based on the ligase chain reaction [(LCR) LCx Probe System MTB; Abbott, USA] with those of culture in liquid medium (Septi-Chek AFB; Becton-Dickinson, USA) and culture on the egg-based L?wenstein-Jensen solid medium for the direct detection of Mycobacterium tuberculosis complex in nonrespiratory specimens. The results were analyzed according to the standard definition of a true-positive result. Two hundred thirty-five nonrespiratory samples routinely submitted to rule out tuberculosis were analyzed. All samples were smear-negative. Mycobacterial growth in either culture medium was detected in 18 (7.6%) specimens: Mycobacterium tuberculosis was recovered from seven (38.9%) specimens cultured on L?wenstein-Jensen medium and from 18 (100%) specimens cultured in Septi-Chek AFB. The LCR protocol was positive in 22 specimens. None of the LCR-negative controls showed positive results. All samples positive by culture on L?wenstein-Jensen medium were positive by culture in liquid medium and by the LCR assay. However, Mycobacterium tuberculosis was detected by culture in liquid medium in two specimens that were negative by the LCR assay, whereas six specimens negative by culture in liquid medium were positive by the LCR protocol; three of these were identified as true-positive results of the LCR assay. The sensitivity, specificity, and positive and negative predictive values were 33.3%, 100%, 100%, and 93.8%, respectively, for L?wenstein-Jensen medium; 85.7%, 100%, 100%, and 98.6% for the liquid medium; and 90.4%, 98.5%, 86.3%, and 99% for the LCR assay. These findings indicate that the LCR assay may be a valid method of high diagnostic yield for direct detection of Mycobacterium tuberculosis complex in nonrespiratory specimens.     

The prevalence of antibiotic-resistant faecal Escherichia coli in healthy volunteers in Venezuela

Faecal samples were collected from healthy volunteers in two regions in Venezuela, the village of Grulla (n = 195) and the city of Mérida (n = 181), and analysed for the prevalence of antibiotic resistant faecal Escherichia coli as well as the antibiotic susceptibility of the strains isolated. The highest prevalences of resistance were observed for amoxicillin, oxytetracycline, sulfamethoxazole and trimethoprim. The percentages found for Grulla were 46, 38, 44 and 30%, respectively; for Mérida 39, 65, 56 and 36%, respectively. In Mérida, a significantly higher prevalence of resistance for oxytetracycline was found (P < 0.05). Significant differences in the distribution of the MIC values between Grulla and Mérida were observed for amoxicillin, chloramphenicol and oxytetracycline (P < 0.05). In Grulla, the most frequent pattern was resistance to amoxicillin only and in Mérida to oxytetracycline only. Amoxicillin resistance was due to production of TEM1 beta-lactamase.