Preparation of controlled particulate mixtures with glass beads of different sizes

A method of mixing/preparing binary and ternary mixtures of glass beads was developed using a viscous solution of glycerol in water. After mixing, the mixture was transferred to a prismatic vessel and glycerol was washed out. The different sized beads were differently coloured and digital pictures taken from each face were automatically treated by image analysis to determine the coloured fraction present in each face. Statistical analysis showed that no significant deviation existed in the colour distribution of each of the four faces.Achi-square test showed that a uniform distribution could be accepted for the beads, no segregation of bead size nearby the edges was observed and that no wall effect was present. The two-dimensional picture obtained by image analysis was converted to the corresponding three-dimensional distribution, from which the expected bed porositywas inferred. The porosity previously estimatedwas compared with the experimental porosity determined by gravimetry directly on the bed.Nosignificant deviations were found, thereby proving that the mixing method developed was reliable. Hundreds of experiments were done showing a very high reproducibility. The developed methodwas further used for studies on mixing of binary and ternary mixtures. In certain conditions (mixtures enriched with large size particles and having a significant difference in size) a segregation layering effect took place and the bottom layer presented a composition corresponding to the packing with the smallest porosity possible.Fundação para a Ciência e a Tecnologia (FCT) e FEDER - POCTI/EQU/37500/2001

Validation of a stochastic digital packing algorithm for porosity prediction in fluvial gravel deposits

Porosity as one of the key properties of sediment mixtures is poorly understood. Most of the existing porosity predictors based upon grain size characteristics have been unable to produce satisfying results for fluvial sediment porosity, due to the lack of consideration of other porosity-controlling factors like grain shape and depositional condition. Considering this, a stochastic digital packing algorithm was applied in this work, which provides an innovative way to pack particles of arbitrary shapes and sizes based on digitization of both particles and packing space. The purpose was to test the applicability of this packing algorithm in predicting fluvial sediment porosity by comparing its predictions with outcomes obtained from laboratory measurements. Laboratory samples examined were two natural fluvial sediments from the Rhine River and Kall River (Germany), and commercial glass beads (spheres). All samples were artificially combined into seven grain size distributions: four unimodal distributions and three bimodal distributions. Our study demonstrates that apart from grain size, grain shape also has a clear impact on porosity. The stochastic digital packing algorithm successfully reproduced the measured variations in porosity for the three different particle sources. However, the packing algorithm systematically overpredicted the porosity measured in random dense packing conditions, mainly because the random motion of particles during settling introduced unwanted kinematic sorting and shape effects. The results suggest that the packing algorithm produces loose packing structures, and is useful for trend analysis of packing porosity

The Genes Coding for the Conversion of Carbazole to Catechol Are Flanked by IS6100 Elements in Sphingomonas sp. Strain XLDN2-5

BACKGROUND: Carbazole is a recalcitrant compound with a dioxin-like structure and possesses mutagenic and toxic activities. Bacteria respond to a xenobiotic by recruiting exogenous genes to establish a pathway to degrade the xenobiotic, which is necessary for their adaptation and survival. Usually, this process is mediated by mobile genetic elements such as plasmids, transposons, and insertion sequences. FINDINGS: The genes encoding the enzymes responsible for the degradation of carbazole to catechol via anthranilate were cloned, sequenced, and characterized from a carbazole-degrading Sphingomonas sp. strain XLDN2-5. The car gene cluster (carRAaBaBbCAc) and fdr gene were accompanied on both sides by two copies of IS6100 elements, and organized as IS6100::ISSsp1-ORF1-carRAaBaBbCAc-ORF8-IS6100-fdr-IS6100. Carbazole was converted by carbazole 1,9a-dioxygenase (CARDO, CarAaAcFdr), meta-cleavage enzyme (CarBaBb), and hydrolase (CarC) to anthranilate and 2-hydroxypenta-2,4-dienoate. The fdr gene encoded a novel ferredoxin reductase whose absence resulted in lower transformation activity of carbazole by CarAa and CarAc. The ant gene cluster (antRAcAdAbAa) which was involved in the conversion of anthranilate to catechol was also sandwiched between two IS6100 elements as IS6100-antRAcAdAbAa-IS6100. Anthranilate 1,2-dioxygenase (ANTDO) was composed of a reductase (AntAa), a ferredoxin (AntAb), and a two-subunit terminal oxygenase (AntAcAd). Reverse transcription-PCR results suggested that carAaBaBbCAc gene cluster, fdr, and antRAcAdAbAa gene cluster were induced when strain XLDN2-5 was exposed to carbazole. Expression of both CARDO and ANTDO in Escherichia coli required the presence of the natural reductases for full enzymatic activity. CONCLUSIONS/SIGNIFICANCE: We predict that IS6100 might play an important role in the establishment of carbazole-degrading pathway, which endows the host to adapt to novel compounds in the environment. The organization of the car and ant genes in strain XLDN2-5 was unique, which showed strong evolutionary trail of gene recruitment mediated by IS6100 and presented a remarkable example of rearrangements and pathway establishments

Prediction of attrition in agitated particle beds

The majority of pharmaceutical powders produced through crystallisation are dried in agitated dryers. The rotation of the impeller causes shear deformation of the bed, which enhances the drying rate, but also leads to particle breakage. A method of predicting the extent of breakage occurring due to agitation is described and applied for Paracetamol in a small-scale dryer. The distributions of stresses and strains in the bed are estimated using the Distinct Element Method (DEM). The information obtained here is then coupled with the measured attrition of Paracetamol in an annular shear cell in order to predict the attrition in the agitated bed. The experiments are carried out on dry material so as to establish purely the effect of stresses and strains on attrition, whilst keeping moisture content and temperature constant.The shear cell provides uniform condition for stresses and strains so that the breakage taking place under relatively well-defined conditions is quantified. In contrast, the prevailing shear stresses and strains in the agitated bed have wide distributions, as little shearing takes place near the impeller shaft, whilst there are considerable shearing stresses near the impeller tip. Therefore, the bed is divided into a number of segments for which the extent of attrition can be evaluated for each segment, based on the shear cell data. A good quantitative agreement is found between the predictions and experimental results obtained for the attrition of Paracetamol in the small scale dryer. The resulting prediction also suggests that, for a given number of impeller rotations, the extent of breakage is independent of impeller speed in the range tested (20-78. rpm). This is expected as the prevailing strain rates are too low for the inertial effects to be dominating and the shear stresses are independent of shear rates within the range investigated. The attrition prediction suggest that over half of the attrition occurs in the bottom third of the bed, with increased attrition at greater radial distances. The attrition is also predicted to occur predominantly within the region extending from 30° in front of to 30° behind the impeller