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[en] The patterns left by desiccating droplets of colloidal solutions form an integral part of a gamut of applications in technology, medicine and fundamental science. While almost all attention is reserved for understanding flow dynamics of drying droplets and the resulting dried droplet pattern with respect to variation of a host of parameters, there is almost a total absence of any discussion on the importance of the ‘mixing methods’ of solute and solvent during solution preparation. We demonstrate in this work, that desiccation patterns of colloidal solutions show an amazing variation in details, depending on the manner of solution preparation. The variation is achieved by simple mechanical treatment, namely magnetic stirring and ultrasonication, and for different stirring times. The suitable explanation of the striking variation in the dried droplets on both hydrophilic and hydrophobic substrates lead us to propose that the stirring time corresponding to a particular method adopted for solution preparation, results in varying degrees of paring of aggregates. We establish that a homogeneous colloidal solution can only be achieved by mixing for a minimum time t std, that is a function of a particular mixing procedure and a given solute-solvent combination. The prepared solution may then be used in different applications to obtain faithful standard results. (paper)
[en] The device is designed for calibration of radioisotope gages used for measuring concentrations and/or the specific weight of liquid-solid dispersion systems, i.e., suspensions. The device secures that during the calibration using a particular suspension, the solid is uniformly dispersed throughout the suspension which is contained in the measuring compartment of the gage through which the directed ionizing radiation passes. (Z.S.). 1 fig
[en] The Savannah River Site (SRS) is in the process of removing waste (sludge and salt cake) from million gallon waste tanks. The current practice for removing waste from the tanks is adding water, agitating the tanks with long shaft vertical centrifugal pumps, and pumping the sludge/salt solution from the tank to downstream treatment processes. This practice has left sludge heels (tilde 30,000 gallons) in the bottom of the tanks. SRS is evaluating shrouded axial impeller mixers for removing the sludge heels in the waste tanks. The authors conducted a test program to determine mixer requirements for suspending sludge heels using the shrouded axial impeller mixers. The tests were performed with zeolite in scaled tanks which have diameters of 1.5, 6.0, and 18.75 feet. The mixer speeds required to suspend zeolite particles were measured at each scale. The data were analyzed with various scaling methods to compare their ability to describe the suspension of insoluble solids with the mixers and to apply the data to a full-scale waste tank. The impact of changes in particle properties and operating parameters was also evaluated. The conclusions of the work are: Scaling of the suspension of fast settling zeolite particles was best described by the constant power per unit volume method. Increasing the zeolite particle concentration increased the required mixer power needed to suspend the particles. Decreasing the zeolite particle size from 0.7 mm 0.3 mm decreased the required mixer power needed to suspend the particles. Increasing the number of mixers in the tank decreased the required mixer power needed to suspend the particles. A velocity of 1.6 ft/sec two inches above the tank bottom is needed to suspend zeolite particles
[en] We have produced nanotube-in-oil suspensions and measured their effective thermal conductivity. The measured thermal conductivity is anomalously greater than theoretical predictions and is nonlinear with nanotube loadings. The anomalous phenomena show the fundamental limits of conventional heat conduction models for solid/liquid suspensions. We have suggested physical concepts for understanding the anomalous thermal behavior of nanotube suspensions. In comparison with other nanostructured materials dispersed in fluids, the nanotubes provide the highest thermal conductivity enhancement, opening the door to a wide range of nanotube applications
[en] Lead-free solder paste printing process accounts for majority of the assembly defects in the electronic manufacturing industry. The study investigates rheological behaviour and stencil printing performance of the lead-free solder pastes (Sn/Ag/Cu). Oscillatory stress sweep test was carried out to study the visco-elastic behaviour of the lead-free solder pastes. The visco-elastic behaviour of the paste encompasses solid and liquid characteristic of the paste, which could be used to study the flow behaviour experienced by the pastes during the stencil printing process. From this study, it was found that the solid characteristics (G') is higher than the liquid characteristic (G'') for the pastes material. In addition, the results from the study showed that the solder paste with a large G' = G'' has a higher cohesiveness resulting in poor withdrawal of the paste during the stencil printing process. The phase angles (δ) was used to correlate the quality of the dense suspensions to the formulation of solder paste materials. This study has revealed the value of having a rheological measurement for explaining and characterising solder pastes for stencil printing. As the demand for lead free pastes increases rheological measurements can assist with the formulation or development of new pastes.
[en] We say that a group G acts infinitely transitively on a set X if for every m element of N the induced diagonal action of G is transitive on the cartesian mth power Xm backslash Δ with the diagonals removed. We describe three classes of affine algebraic varieties such that their automorphism groups act infinitely transitively on their smooth loci. The first class consists of normal affine cones over flag varieties, the second of nondegenerate affine toric varieties, and the third of iterated suspensions over affine varieties with infinitely transitive automorphism groups. Bibliography: 42 titles.
[en] We investigate the microstructural and microrheological response to a tracer particle of a two-dimensional colloidal suspension under thermodynamic conditions close to a liquid-gas phase boundary. On the liquid side of the binodal, increasing the velocity of the (repulsive) tracer leads to the development of a pronounced cavitation bubble, within which the concentration of colloidal particles is strongly depleted. The tendency of the liquid to cavitate is characterized by a dimensionless “colloidal cavitation” number. On the gas side of the binodal, a pulled (attractive) tracer leaves behind it an extended trail of colloidal liquid, arising from downstream advection of a wetting layer on its surface. For both situations the velocity dependent friction is calculated
[en] This paper presents a physico-mathematical combustion model of the boron-air suspension. The oxidation mechanism and combustion of boron particles are based on the study by King M. K. The physico-mathematical formulation of the problem implies the approaches by R.I. Nigmatulin for the mechanics of two-phase reactive media. The paper provides numerical investigation on the effect of mass concentration and boron particle size on the apparent and normal combustion front velocity of the boron-air suspension. (paper)
[en] Suspensions of self-propelled particles are studied in the framework of two-dimensional (2D) Stokesean hydrodynamics. A formula is obtained for the effective viscosity of such suspensions in the limit of small concentrations. This formula includes the two terms that are found in the 2D version of Einstein's classical result for passive suspensions. To this, the main result of the paper is added, an additional term due to self-propulsion which depends on the physical and geometric properties of the active suspension. This term explains the experimental observation of a decrease in effective viscosity in active suspensions
[en] Microorganisms compete with other species by secreting antimicrobial compounds. The compact structure of aerobic granules was generally assumed to provide spatial isolation, resulting in the co-occurrence of diverse strains that have similar or dissimilar functions. No studies have investigated whether stable, mature aerobic granules can be formed with two mutually inhibitory strains. The strain Acinetobacter sp. I8 competes with Bacillus sphaericus I5 in a well-mixed environment, but can form stable and mature granules at 400 mg L-1 phenol by repeatedly replenishing fresh medium in a sequencing batch reactor. The supernatants collected from the I8 medium in its exponential-growth phase or from the I5 + I8 medium cultivated for 12 or 24 h significantly inhibited I5 growth. Addition of tightly bound extracellular polymeric substances (TBEPS) or loosely bound extracellular polymeric substances (LBEPS) extracted from I5 + I8 granules effectively suppressed the inhibitory effects of I8 on I5. The TBEPS or LBEPS physically separate strain I5 from I8 in the granule, and effectively adsorb the inhibitory substance(s) in the suspension.