Inert Spheres Research Articles

Reduction of Iron-Oxide-Carbon Composites: Part III. Shrinkage of Composite Pellets during Reduction

This article involves the evaluation of the volume change of iron-oxide-carbon composite pellets and its implications on reduction kinetics under conditions prevalent in a rotary hearth furnace (RHF) that were simulated in the laboratory. The pellets, in general, were found to shrink considerably during the reduction due to the loss of carbon and oxygen from the system, sintering of the iron-oxide, and formation of a molten slag phase at localized regions inside the pellets due to the presence of binder and coal/wood-charcoal ash at the reduction temperatures. One of the shortcomings of the RHF ironmaking process has been the inability to use multiple layers of composite pellets because of the impediment in heat transport to the lower layers of a multilayer bed. However, pellet shrinkage was found to have a strong effect on the reduction kinetics by virtue of enhancing the external heat transport to the lower layers. The volume change of the different kinds of composite pellets was studied as a function of reduction temperature and time. The estimation of the change in the amount of external heat transport with varying pellet sizes for a particular layer of a multilayer bed was obtained by conducting heat-transfer tests using inert low-carbon steel spheres. It was found that if the pellets of the top layer of the bed shrink by 30 pct, the external heat transfer to the second layer increases by nearly 6 times.

Control of methanol vapours in a biotrickling filter: Performance analysis and experimental determination of partition coefficient

Methanol vapours were treated in a biotrickling filter (BTF) packed with inert polypropylene spheres. The effects of the nitrogen concentration in the nutrient solution, the empty bed residence time (EBRT) and the methanol inlet concentration, on the BTF performance, were all examined. The elimination capacity (EC), the biomass and the carbon dioxide production rates were all increased with the rising of the nitrogen concentration and the EBRT. The EC also rose with increasing methanol inlet load (IL) when the methanol inlet concentration and the EBRT were varied, from 0.3 to 37.0 g m −3, and from 20 to 65 s, respectively. The BTF reached its maximum EC level of 2160 g m −3 h −1 when it was operated at an IL level of 3700 g m −3 h −1. The input methanol was removed through two mechanisms: biodegradation and absorption in the liquid phase. The partition coefficient for the methanol in the BTF was determined at five EBRTs and along the packed bed. It generally followed the Henry model, having an average value of 2.64 × 10 −4 [mol L −1] gas/[mol L −1] liquid

Internal transport properties of macroporous sugar polyacrylate hydrogels: Microsphere diffusion described by phenomenological laws

We have determined the internal transport properties of heterogeneous, macroporous hydrogels based on the regioregular sugar polyacrylate poly(6-acryloyl-beta-O-methyl-galactopyranoside). This was accomplished by measuring the diffusive flux of variously sized polystyrene microspheres and combining these results with solutions of phenomenological transport laws (the Navier-Stokes equations and Fick's Law with an assumption of first-order irreversible sphere capture by the gel polymer). This enabled calculation of gel properties such as average pore diameters (ca. 11.76 microm) and the diffusivities of the polystyrene spheres in the gel. These values range from 76% to 83% of that in free solution and correlate closely with the equilibrium solution content of the gel (82.3%). This approach has also enabled calculation of the sphere capture rates (2.4 x 10(-3) to 9.6 x 10(-5) s(-1)). These low capture rates indicate that the gel is extremely non-adhesive towards the spheres, and a linear correlation with sphere form drag area (r(2) = 1) was found. The pore sizes of the hydrated gel were observed via DIC light microscopy and the visible effective diameters corresponded very closely to the calculated values (11.66 vs. 11.76 microm). The diffusion/capture of inert spheres in the hydrogel can thus be described in a non-destructive manner by straightforward application of phenomenological transport laws. This result is significant in that these laws were intended to describe macroscopic ensembles of very large numbers of particles in continuous media, not small numbers (i.e., hundreds) in discontinuous media.

The rheology of a semi-dilute suspension of swimming model micro-organisms

The rheological properties of a cell suspension may play an important role in the flow field generated by populations of swimming micro-organisms (e.g. in bioconvection). In this paper, a swimming micro-organism is modelled as a squirming sphere with prescribed tangential surface velocity, in which the centre of mass of the sphere may be displaced from the geometric centre (bottom-heaviness). Effects of inertia and Brownian motion are neglected, because real micro-organisms swim at very low Reynolds numbers but are too large for Brownian effects to be important. The three-dimensional movement of 64 identical squirmers in a simple shear flow field, contained in a cube with periodic boundary conditions, is dynamically computed, for random initial positions and orientations. The computation utilizes a database of pairwise interactions that has been constructed by the boundary element method. The restriction to pairwise additivity of forces is expected to be justified if the suspension is semi-dilute. The results for non-bottom-heavy squirmers show that the squirming does not have a direct influence on the apparent viscosity. However, it does change the probability density in configuration space, and thereby causes a slight decrease in the apparent viscosity atO(c2), wherecis the volume fraction of spheres. In the case of bottom-heavy squirmers, on the other hand, the stresslet generated by the squirming motion directly contributes to the bulk stress atO(c), and the suspension shows strong non-Newtonian properties. When the background simple shear flow is directed vertically, the apparent viscosity of the semi-dilute suspension of bottom-heavy squirmers becomes smaller than that of inert spheres. When the shear flow is horizontal and varies with the vertical coordinate, on the other hand, the apparent viscosity becomes larger than that of inert spheres. In addition, significant normal stress differences appear for all relative orientations of gravity and the shear flow, in the case of bottom-heavy squirmers.

In vitro and in vivo comparative study of itraconazole bioavailability when formulated in highly soluble self‐emulsifying system and in solid dispersion

A semisolid self-emulsifying system (SES) of itraconazole consisting of oleic acid, polysorbate 80 and coajuvant (citric acid) was prepared by a hot-melt technique and then compared with hydroxypropylmethylcellulose (HPMC) solid dispersion (SD) coated onto inert sugar spheres as a reference formulation for in vitro and in vivo disposition in rats. The optimal SES greatly increased dissolution rates in gastric (pH 1.2) and intestinal fluid (pH 6.8) by forming a microemulsion (150-250 nm), whereas that of SD was minimal. The tissue uptake of itraconazole from SES in whole intestine, liver and Peyer's patches of the rats was more favorable than that from SD and linearly increased as a function of administering dose. Interestingly, the uptake ratio of Peyer's patches relative to liver also increased linearly in the case of SES while that of SD was almost unchanged. After repeated dosing for 1 week, both SES and SD increased the areas of Peyer's patch region in intestinal tissues but no distinct histopathological damage of the intestine was observed except the hepatocytes. Due to the biopharmaceutical differences of SES in terms of efficient solubilization, easy dispersibility and higher lymphatic transport, the in vivo bioavailability of SES was about twice greater than that of SD in rats.

Technetium and rhenium: coordination chemistry and nuclear medical applications

Coordination compounds of the radioactive element technetium are well established in diagnostic nuclear medicine, and various complexes of the gamma-emitting nuclide 99mTc are routinely used for organ imaging. Modern trends in the radiopharmaceutical chemistry of technetium focus on the 'labeling' of biologically active molecules such as peptides, steroids or other receptor-seeking units. This requires more knowledge about the coordination chemistry of the artificial transition metal, particularly with regard to stable or kinetically inert coordination spheres, which allow couplings to biomolecules following a bioconjugate approach. The dominant role of technetium compounds in diagnostic procedures recommends the beta--emitting rhenium isotopes 186Re and 188Re for applications in nuclear-medical therapy. 188Re is readily available from an 188W/188Re radionuclide generator system and general synthetic approaches can be adopted from the established technetium chemistry.

Valvular interstitial cell mechanobiology: effects of substrate stiffness

During inflammation, neutrophil capture by vascular endothelial cells is dependent on L-selectin and β2-integrin adhesion receptors. One of us (S.I.S.) previously demonstrated that homotypic neutrophil aggregation is analogous to this process in that it is also mediated by these receptors, thus providing a model for studying the dynamics of neutrophil adhesion. In the present work, we set out to confirm the hypothesis that cell–cell adhesion via selectins serves to increase the lifetimes of neutrophil doublets formed through shear-induced two-body collisions. In turn, this would facilitate the engagement of more stable β2-integrin bonds and thus increase the two-body collision efficiency (fraction of collisions resulting in the formation of nonseparating doublets). To this end, suspensions of unstimulated neutrophils were subjected to a uniform shear field in a transparent counter-rotating cone and plate rheoscope, and the formation of doublets and growth of aggregates recorded using high-speed videomicroscopy. The dependence of neutrophil doublet lifetime and two-body collision-capture efficiency on shear rate, G, from 14 to 220 s−1 was investigated. Bond formation during a two-body collision was indicated by doublets rotating well past the orientation predicted for break-up of doublets of inert spheres. A striking dependence of doublet lifetime on shear rate was observed. At low shear (G = 14 s−1), no collision capture occurred, and doublet lifetimes were no different from those of neutrophils pretreated with a blocking antibody to L-selectin, or in Ca++-depleted EDTA buffers. At G ≥ 66 s−1, doublet lifetimes increased, with increasing G reaching values twice those for the L-selectin-blocked controls. This correlated with capture efficiencies in excess of 20%, and, at G ≥ 110 s−1, led to the rapid formation of large aggregates, and this in the absence of exogenous chemotactic stimuli. Moreover, the aggregates almost completely broke up when the shear rate was reduced below 66 s−1. Partial inhibition of aggregate formation was achieved by blocking β2-integrin receptors with antibody. By direct observation of the shear-induced interactions between neutrophils, these data reveal that steady application of a threshold level of shear rate is sufficient to support homotypic neutrophil aggregation.

Origins of Pulsing Regime in Cocurrent Packed-Bed Flows

The mechanism of the formation for cocurrent downflow pulse flow was studied experimentally in a packed bed of inert spheres of 3, 6, and 8 mm using an air−water flow. By measurement of the flow distance until pulses are observed, the spatial growth rate of convective disturbances within the pulsing flow regime were determined. Observations indicate that pulses form from trickling flow as the result of a global convective instability. Further, experiments indicate that an analogous transition exists for the formation of pulses from the dispersed bubble flow regime, except that pulses form as the flow rates are adjusted to become less severe. Existing global instability models based on averaged (dispersed flow) momentum equations were modified to explain experimental results. A key uncertainty in modeling pulse formation from trickle flow is the regularization (i.e., stabilization) force. Re-examination of this issue suggests some mechanistic inconsistencies with surface tension which had been used in previous studies. Consistent with the present experiments, it is proposed that gravity may be the primary restoring force. Incorporating gravity stabilization into the dispersed flow equations provides predictions that are at least as good as the previous models. A similar dispersed flow model is used to explain the bubbly flow to pulse transition. While predictions agree with experimental data for part of the range, model accuracy is limited by the accuracy of constitutive expressions for interaction forces between phases.

Effects of adding inert spheres into the filter bed on the performance of biofilters for gaseous toluene removal

To investigate the effect of adding large size inert materials into natural organic packing media in waste gas treatment, two biofilters, one packed with buckwheat hulls and inert spheres and the other packed with buckwheat hulls only, were used in parallel experiments to treat toluene gas for 305 continuous days. The toluene removal capacities and pressure drops of the two biofilters were compared during the experiments. The physical properties of the filter beds were also investigated by pulse injection technique combined with a mathematical model. In the late phase of the operation with a sufficient supply of nutrients, the biofilter with inert spheres showed a higher toluene removal capacity than the biofilter without inert spheres. This was due to the fact that the biofilter with inert spheres had less bed compaction and a greater increase in specific surface area. The pressure drop of the biofilter with inert spheres was also significantly lower and more stable than that of the biofilter without inert spheres due to its higher bed void fraction. All the experimental results quantitatively showed that adding inert spheres into the filter beds could improve the performance of the biofilter under long-term operation.

Particle Size Distributions of Inert Spheres and Pelletized Pharmaceutical Products by Image Analysis

Image analysis was used to measure particle size distributions (PSDs) of ensembles of 425 to 1400 µm‐size materials. Repeatability of a measurement, suitable sample sizes, and methods of sampling were assessed. Two lots of inert spheres were compared prior to drug layering in a Glatt GPCG‐5 rotor. The differences in PSD in the starting materials were reflected in the rotor‐granulated products. Such detailed information was not available from sieving with U.S. standard wire mesh sieves. The products from the rotor process were polymer‐coated in a Wurster process in a Glatt GPCG‐3, 4‐in. Wurster. The resolution of the technique was sufficient to measure differences in diameter equating to 4‐µm coat thickness, which resulted from applying 2% polymer coat weight. The utility of the technique for monitoring commercial scale processes was demonstrated by measuring diameter after layering drug onto nonpareils in a Glatt RG‐150 rotor, and by measuring the diameter after application of a polymer solution in a Glatt 46‐in. Wurster coating process. The similarity of samples removed from the sample port in situ and samples from the batch suggested that processes in the fluid bed are intensively mixed and inherently random.

Dynamics of Neutrophil Aggregation in Couette Flow Revealed by Videomicroscopy: Effect of Shear Rate on Two-Body Collision Efficiency and Doublet Lifetime

During inflammation, neutrophil capture by vascular endothelial cells is dependent on L-selectin and β 2-integrin adhesion receptors. One of us (S.I.S.) previously demonstrated that homotypic neutrophil aggregation is analogous to this process in that it is also mediated by these receptors, thus providing a model for studying the dynamics of neutrophil adhesion. In the present work, we set out to confirm the hypothesis that cell–cell adhesion via selectins serves to increase the lifetimes of neutrophil doublets formed through shear-induced two-body collisions. In turn, this would facilitate the engagement of more stable β 2-integrin bonds and thus increase the two-body collision efficiency (fraction of collisions resulting in the formation of nonseparating doublets). To this end, suspensions of unstimulated neutrophils were subjected to a uniform shear field in a transparent counter-rotating cone and plate rheoscope, and the formation of doublets and growth of aggregates recorded using high-speed videomicroscopy. The dependence of neutrophil doublet lifetime and two-body collision-capture efficiency on shear rate, G, from 14 to 220 s −1 was investigated. Bond formation during a two-body collision was indicated by doublets rotating well past the orientation predicted for break-up of doublets of inert spheres. A striking dependence of doublet lifetime on shear rate was observed. At low shear ( G = 14 s −1), no collision capture occurred, and doublet lifetimes were no different from those of neutrophils pretreated with a blocking antibody to L-selectin, or in Ca ++-depleted EDTA buffers. At G ≥ 66 s −1, doublet lifetimes increased, with increasing G reaching values twice those for the L-selectin-blocked controls. This correlated with capture efficiencies in excess of 20%, and, at G ≥ 110 s −1, led to the rapid formation of large aggregates, and this in the absence of exogenous chemotactic stimuli. Moreover, the aggregates almost completely broke up when the shear rate was reduced below 66 s −1. Partial inhibition of aggregate formation was achieved by blocking β 2-integrin receptors with antibody. By direct observation of the shear-induced interactions between neutrophils, these data reveal that steady application of a threshold level of shear rate is sufficient to support homotypic neutrophil aggregation.

Mass transfer from a single grain to a fluid in an inert fixed bed

Mass transfer from single grain to fluid moving through assemblage of immobile, identical inert spheres was studied. It is shown that the effective mass transfer rate is strongly dependent on the local bed structure around the irregularly shaped particles. Blending active grains with smaller inert spheres results in an enhancement of the effective transport rate.

MASS TRANSFER FROM SOLID PARTICLES TO FLUID IN GRANULAR BED

Abstract Mass transfer from assemblage of irregularly shaped particles to fluid was analysed using a combination of “cell” and “channel” concepts. The theoretical analysis predicts that blending active grains with inert spheres will result in an enhancement of the mass transfer due to a decrease of the overlapping of the neighbour particles and to a change of the bed geometry. The comparison between the derived relationship and available literature and our own experimental data shows a reasonably good agreement.

Meta-Analysis of Gas Flow Resistance Measurements Through Packed Beds

Measurements of the resistance to flow through packed beds of inert spheres have been reported by a number of authors through relations expressing the coefficient of drag as a function of Reynolds number. A meta-analysis of the data using improved statistical methods is undertaken to aggregate the available experimental results. For Reynolds number in excess of 103 the relation log Fv = 0.49 + 0.90 log Re′ is shown to be a highly effective representation of all available data.

Nuclear assembly with lambda DNA in fractionated Xenopus egg extracts: an unexpected role for glycogen in formation of a higher order chromatin intermediate.

Crude extracts of Xenopus eggs are capable of nuclear assembly around chromatin templates or even around protein-free, naked DNA templates. Here the requirements for nuclear assembly around a naked DNA template were investigated. Extracts were separated by ultracentrifugation into cytosol, membrane, and gelatinous pellet fractions. It was found that, in addition to the cytosolic and membrane fractions, a component of the gelatinous pellet fraction was required for the assembly of functional nuclei around a naked DNA template. In the absence of this component, membrane-bound but functionally inert spheres of lambda DNA were formed. Purification of the active pellet factor unexpectedly demonstrated the component to be glycogen. The assembly of functionally active nuclei, as assayed by DNA replication and nuclear transport, required that glycogen be pre-incubated with the lambda DNA and cytosol during the period of chromatin and higher order intermediate formation, before the addition of membranes. Hydrolysis of glycogen with alpha-amylase in the extract blocked nuclear formation. Upon analysis, chromatin formed in the presence of cytosol and glycogen alone appeared highly condensed, reminiscent of the nuclear assembly intermediate described by Newport in crude extracts (Newport, J. 1987. Cell. 48:205-217). In contrast, chromatin formed from phage lambda DNA in cytosol lacking glycogen formed "fluffy chromatin-like" structures. Using sucrose gradient centrifugation, the highly condensed intermediates formed in the presence of glycogen could be isolated and were now able to serve as nuclear assembly templates in extracts lacking glycogen, arguing that the requirement for glycogen is temporally restricted to the time of intermediate formation and function. Glycogen does not act simply by inducing condensation of the chromatin, since similarly isolated mitotically condensed chromatin intermediates do not form functional nuclei. However, both mitotic and fluffy interphase chromatin intermediates formed in the absence of glycogen can be rescued to form functional nuclei when added to a second extract which contains glycogen. This study presents a novel role for a carbohydrate in nuclear assembly, a role which involves the formation of a particular chromatin intermediate. Potential models for the role of glycogen are discussed.

Critical diameter for the transmission of a detonation wave into a porous medium

An experimental investigation has been undertaken to elucidate the existence of a critical diameter forthe transmission of gaseous detonation into a porous medium. A Chapman-Jouguet (CJ) detonation is first established in a tube and allowed to transmit through an orifice plate into a porous medium comprised of inert spheres of equal diameter. It is found that detonation can successfully transmit past the orifice for diameters much smaller than the normal critical diameter (dc) of the mixture. An immediate transition from detonation to quasi-detonation normally takes place upon wave entry in the porous medium. Failure of detonation is observed to take place downstream of the orifice in the near-limit regime and is followed by deflagration to detonation transition (DDT) within the porous medium. Wave velocities in the porous medium are found to be identical to the corresponding values measured for direct transmission (without an orifice). For subcritical conditions, there is complete quenching of combustion in the pores. The critical composition (lean and rich) for mixtures with high activation energy is found to be practically the same as the propagation limits in the porous medium without an orifice. This indicates that the phenomenon is governed by the smallest physical dimension of the pore size, and thus a local failure mechanism exists. In mixtures highly diluted with argon, i.e., (C2H2−O2)+75% Ar, which have a lower activation energy and for which the “dc=13λ” correlation (where λ is the cell size) is known to break down, the critical composition appears to depend on the orifice diameter. The orifice now introduces a larger controlling length scale at the limits compared to the pore size, indicating that a global failure mechanism may prevail for such mixtures. Present findings are consistent with a local and global failure mechanism for normal detonation failure recently proposed by Lee.

Diffusion of latex spheres through solutions of hydroxypropylcellulose in water

Translational diffusion coefficients of polystyrene latex spheres in solutions of hydroxypropylcellulose (HPC) have been measured using dynamic light scattering. As observed by other workers, latex clustering occurs, involving a bridging interaction of adsorbed HPC, which can be prevented using the nonionic surfactant Triton X-100. In the presence of Triton X-100, the diffusion data serve to test hydrodynamic theories of the Brownian motion of inert spheres in a matrix of entangled polymer chains. As predicted by certain theories, the diffusion data follow a stretched exponential function of the HPC concentration. For two HPC fractions of low molecular weight, we find that probe diffusion coefficients follow the Stokes-Einstein (SE) law, determined by the bulk viscosity of the HPC solution. For two fractions of high-molecular-weight HPC, the microviscosity measured by the SE equation is substantially smaller than the bulk viscosity. Within experimental error, the latter data follow the stretched exponential law D/ D 0 = exp[ α( C ν - C + ν )] with α ∝ M σ R ϵ , where ϵ = 0.7 ± 0.1, σ = 0.8 ± 0.1, and ν = 1.0. The characteristic concentration C + is numerically comparable to incipient overlap of the chains in a hexagonal close-packing arrangement. These results are discussed in terms of different theoretical models for the diffusion of spherical particles through a polymer matrix.

A simple separator to generate half micron aqueous particles for lung imaging

An aerosol of a radionuclide may be used for ventilation imaging as an alternative to radioactive rare gases. For good-quality images as few particles as possible must be deposited in the trachea and bronchi, which means that no, or very few, particles should have aerodynamic diameter of more than 2 micron. We have developed a separator to modify the output of an Acorn jet nebuliser. It reduced the proportion of particles in the aerosol with aerodynamic diameters of more than 2 micron from 60% for the unmodified output of the nebuliser to only 6%; it consisted of a cylinder of perspex with two compartments containing inert spheres, either stainless steel or glass, of diameter 3 mm (the first compartment contained two layers of spheres, and the main section was packed with spheres). To examine the efficiency of the separator system for routine clinical use we compared the images produced and the deposition of the particles in the modified aerosol (using 99TcmDTPA) with the distribution of ventilation of 81Krm in eight subjects. Despite the theoretical differences between the behaviour of a gas molecule and of a particle in the respiratory tree, the images produced using the modified aerosol delivery system were as good as those produced with 81Krm in normal subjects. In abnormal subjects the images produced were only distinguished following the calculation of a penetration index.

Microsphere and magnetic-fluid mixtures as magnetoresistors

A magnetic fluid full of uniform inert spheres behaves like a liquid crystal when it is magnetised. The spheres form long chains, which arrange themselves into a triangular lattice. For a conducting liquid, resistance across the chains can be >30 times that along their length. This active device can be large and self repairing.

Effect on column efficiency of packing capillary columns with inert spheres for use in liquid chromatography

Effect on column efficiency of packing capillary columns with inert spheres for use in liquid chromatography