bluuebunny/crossref_metadata_2025_split huggingface dataset:
Modeling membrane filtration of protein and cell suspensions in a vortex flow filtration system
Authors: Mateus M. , Cabral J. M. S. 
Published: June 2004

AbstractVortex flow filtration experiments with bovine serum albumin (BSA) solutions and Arthrobacter simplex cell suspensions in a rotary membrane device are modeled in the pressure‐dependent flux and mass‐transfer‐controlled regions. An expression for the concentration‐dependent diffusion coefficients accounting for hydrodynamic and long‐range potential interactions between rigid spherical macromolecules is used for BSA. A shear‐induced diffusion coefficient, strongly concentration‐dependent on the cell concentration, is assumed to describe the diffusion behavior of the cell suspensions. The adjusted model parameters for albumin solutions in the pressure‐dependent region of flux predict the permeation flux behavior for A. Simplex cell suspensions. When the mass‐transfer correlation is calculated using cell diffusion coefficients, based on a volumetric cell fraction that is around half of the average value of the calculated membrane surface fractions, the fluxes are estimated within less than 10.5% relative error. In the mass‐transfer‐controlled region of flux, the volume fractions of cells at the membrane surface are between 0.16 and 0.35, depending on bulk concentration and hydrodynamic conditions.
Oscillatory, creep and steady flow behavior of Xanthan‐thickened oil‐in‐water emulsions
Authors: Pal Rajinder 
Published: June 2004

AbstractThe rheological behavior of xanthan gum–thickened oil‐in‐water emulsions is studied with a cone‐and‐plate system using a constant‐stress rheometer. Xanthan gum solutions and xanthan‐thickened oil‐in‐water emulsions are strongly shear‐thinning and viscoelastic in nature. The effects of polymer and oil concentrations on the rheological behavior of emulsions are investigated. The relative viscosity for the thickened emulsions, at any given oil concentration, increases with an increase in the shear rate, whereas the unthickened emulsions show the opposite trend. The theoretical models give reasonable predictions for the relative viscosity, storage modulus, and loss modulus of xan‐than‐thickened emulsions. The ratio of storage to loss moduli increases considerably with the increase in polymer and oil concentrations. The creep/recovery experiments confirm that the xanthan‐thickened emulsions are highly viscoelastic in nature and that the degree of elasticity increase with the increase in polymer and oil concentrations.
Mathematical model of mass transport through dispersed‐phase polymer networks
Authors: Varelas Charalambos G. , Dixon David G. , Steiner Carol A. 
Published: June 2004

AbstractA mathematical model of mass transport through dispersed‐phase networks to be used for the sustained release of drugs or other solutes at steady rates is presented. The drug is assumed to be encapsulated within the dispersed microdomains and transported to the bulk by diffusion across the interface. A drug is released to the surroundings by diffusion through the bulk. The results show that the desired steady flux of a drug to the surroundings may be obtained given appropriate values of structural properties of the network. These properties may be manipulated easily in the fabrication of dispersed‐phase networks reported previously.
Estimation of cross‐directional properties: Scanning vs. Stationary Sensors
Authors: Tyler Matthew L. , Morari Manfred 
Published: June 2004

AbstractPeriodic time‐varying Kalman filter equations for problems involving scanning sensors are solved using “lifting” techniques common for multirate systems. The solution to this problem is used to compare the performance of scanning sensors vs. stationary sensors in the estimation of cross‐directional properties. Furthermore, controller performance is examined when the outputs from the Kalman filter are used as inputs to a state feedback control law. Although adding sensors may significantly enhance the estimates of cross‐directional properties, feedback of these improved estimates may translate to lower levels of improvement in cross‐directional variations.
Characterization of structural inhomogeneities in porous media
Authors: Gladden Lynn F. , Hollewand Michael P. , Alexander Paul 
Published: June 2004

AbstractRecent studies have demonstrated that spatial heterogeneities in voidage and pore size, over lengthscales of 0.1–1 mm, significantly affect the transport of liquids within a given porous medium. Nuclear magnetic resonance imaging is used to probe the structure of porous catalyst support pellets, and four image analysis techniques characterize the degree and nature of heterogeneities observed in the spin‐lattice relaxation‐time images of six pellets taken from the same batch. Power‐spectrum, cluster‐size, and percolation analysis reveal significant differences in spatial correlations and topological characteristics of the six images. The fractal dimension of all the images, however, is the same suggesting that this quantity characterizes the intrinsic heterogeneities associated with the particular batch of porous pellets studied in this work. The results suggest that structural models of such pellets should account for these macroscopic variations in pellet structure, as characterized here.
Organic microporous materials made by bicontinuous microemulsion polymerization
Authors: Burban J. H. , He Mengtao , Cussler E. L. 
Published: June 2004

AbstractMicroporous solids made by polymerizing the organic phase of bicontinuous microemulsions stabilized with didodecyldimethylammonium bromide show surface areas as high as 70 m2/g. Small‐angle X‐ray scattering measurements on microporous copolymers containing polymethylmethacrylate show that these areas result from structures larger than 250 Å that are generated during polymerization. These X‐rays measurements also show that the 17‐Å structures characteristics of the original microemulsion are retained during polymerization, but destroyed when the detergent is extracted and the solid is dried.
Controlled drop tensiometer for measuring dynamic interfacial and film tension
Authors: Nagarajan R. , Koczo Kalman , Erdos Elemer , Wasan Darsh T. 
Published: June 2004

AbstractA dynamic interfacial tensiometer described measures the tension of stressed liquid‐liquid interfaces. In this accurate and controlled method, the time‐dependent pressure difference across the curved interface of a spherical drop, immersed in a second immiscible phase, is measured as a function of time. Dynamic experiments are conducted by varying the drop size, therby stressing the interface. The technique is eminently suited for the measurement of static and dynamic interfacial tensions, the study of the diffusion, adsorption, and desorption kinetics of surfactants, and the rheological behavior of liquid films. These capabilities are demonstrated for n‐dodecane contacted with an aqueous solution of a nonionic surfactant. To explain the phenomena, diffusion models are developed that compare well with the experimental data. The noninvasiveness and versatility make this instrument a useful tool.
Computer simulation of protein refolding pathways and intermediates
Authors: Gupta Prashant , Hall Carol K. 
Published: June 2004

AbstractComputer simulation studies of refolding pathways and the formation of intermediates for a simple, 2–D lattice protein model are presented. The sequence of the 20–bead model protein chain is chosen so that hydrophobic beads will reside in the protein interior in the native state. Nonbonded hydrophobic beads attract each other with strength ϵ decreasing the |ϵ/kT| mimics increasing the concentration of the denaturant. Dynamic Monte Carlo simulations and exhaustive conformational searches have been performed on an isolated model protein sequence at different levels of |ϵ| (different denaturant concentrations). As the denaturant is withdrawn, the model protein exhibits a transition from a random coil state to a compact native state with a hydrophobic core. The refolding process is observed to be cooperative in that the chain does not start folding until the middle section has folded correctly, and proceeds along preferred pathways that are populated by distinct, partially folded intermediates.
Salting out of aqueous proteins: Phase equilibria and intermolecular potentials
Authors: Coen C. J. , Blanch H. W. , Prausnitz J. M. 
Published: June 2004

AbstractSalting‐out phase equilibria are reported for lysozyme and α‐chymotrypsin from concentrated ammonium‐sulfate solutions. Supernatant and dense‐phase protein concentrations and the resulting protein partition coefficients are given as a function of solution pH and ionic strength. Phase equilibria with a trivalent salt (sodium citrate) confirm that ionic strength, rather than salt concentration, is the appropriate variable describing phase equilibria. The salting‐out behavior of a mixture of an aqueous lysozyme and α‐chymotrypsin is independent of the presence of the other protein.Parameters for a molecular‐thermodynamic description of salting‐out behavior are obtained from low‐angle laser‐light scattering (LALLS). Osmotic second virial coefficients from LALLS are reported over a range of pH for dilute chymotrypsin concentrations in aqueous electrolyte solutions at 0.01 and 1.0 M ionic strengths. Effective Hamaker constants, regressed from experimental osmotic second virial coefficients, are determined for models of the protein – protein potential of mean force. In addition to excluded volume, dispersion, and shielded charge – charge potentials, the description of protein ‐ protein interactions includes attractive charge – dipole and dipole – dipole potentials as well as an osmotic‐attraction potential that becomes important at high salt concentrations. Protein dipole – dipole potentials are required to account for the observed pH dependence of osmotic second virial coefficients, especially at low ionic strength.
Molecular thermodynamic model for Helix‐Helix docking and protein aggregation
Authors: Chen Chau‐Chyun , King Jonathan , Wang Daniel I. C. 
Published: June 2004

AbstractThe formation of aggregates, rather than correctly folded polypeptide chains, is a pressing problem in biotechnology that has been difficult to approach quantitatively. The competition between folding and aggregation has been carefully analyzed for bovine growth hormone (bGH) and can be attributed to incorrect helix‐helix docking for this four‐helix bundle protein. An extended molecular thermodynamic model reported here represents Gibbs energy changes associated with intramolecular and intermolecular helix‐helix dockings occurring during protein folding and protein aggregation. The model incorporates (1) a semiempirical local composition Gibbs energy expression to account for the helix‐helix hydrophobic interactions, which favor helix‐helix docking and aggregation and (2) a Flory‐Huggins‐type Gibbs energy expression to describe the configurational entropy of the polypeptide backbone conformation, which favors disaggregation. For the folding and aggregation of bGH, the molecular thermodynamic model provides estimates for the Gibbs energies and thermodynamic stabilities of various conformations of bGH and qualitatively accounts for the competition between aggregation and productive folding. It also successfully describes the inhibition of aggregation found with peptides corresponding to bGH helical sequences and the effect of site‐directed mutagenesis.
Multiple roll systems: Steady‐state operation
Authors: Benjamin Dean F. , Anderson Todd J. , Scriven L. E. 
Published: June 2004

AbstractRoll coaters for applying liquid coating to continuous strip or web are, with some two‐roll exceptions, systems of three or more rolls in which liquid passes through two or more gaps or nips between rolls. Yet most of the literature on roll coating is devoted to some of the 11 distinct flows in individual gaps or nips. This article analyzes how the final coated layer thickness in several types of forward roll transfer and reverse roll coating systems depends, at steady state, on the number of rolls, their speeds, the gaps between roll pairs, and the doctoring of recycle films from the rolls. The inputs to the analysis are elementary mass balances at the gaps, and simple gap performance equations that approximate well the available experimental and theoretical findings about flow rates and film‐splits at individual gaps. The results are fundamentals‐based means of understanding, comparing, predicting, and ultimately designing performance of multiple roll systems.
Aspects of flow of power‐law fluids in porous media
Authors: Shah C. B. , Yortsos Y. C. 
Published: June 2004

AbstractNon‐Newtonian fluid flow in porous media is encountered in a variety of applications. Aspects of single‐phase flow of power‐law fluids in porous media are examined. First, homogenization theory is used to derive a macroscopic law. It is shown that the single‐capillary power law between flow rate and pressure gradient also applies at the macroscopic scale, provided that the Reynolds number is sufficiently small. Homogenization theory confirms the validity of the use of pore network models to describe flow of power‐law fluids, although not necessarily of fluids of a more general rheology. Flow in pore networks is next used to explore various pore geometry effects. Numerical simulations show that approaches based on an effective medium or on the existence of a critical path, which carries most of the flow, are valid in narrow‐ or wide‐pore‐size distributions, respectively. The corresponding expressions agreed well with the numerical results in the respective ranges. An analysis presented for Bethe lattices leads to closed‐form expressions in two limits: for an effective medium and near percolation. The behavior near percolation generalizes the results of Stinchcombe (1974) for the linear (Newtonian) case.
Convective diffusion and adsorption in a swarm of spheroidal particles
Authors: Coutelieris F. A. , Burganos V. N. , Payatakes A. C. 
Published: June 2004

AbstractThe problem of mass transfer from a Newtonian fluid to a swarm of spheroidal adsorbers under creeping flow conditions is considered using the spheroid‐in‐cell model to represent the swarm. The flow field within the fluid envelope for the Kuwabara type of boundary conditions is obtained form the analytical solution of Dassios et al. (1994). The complete convective diffusion equation is used to describe mass transport within the envelope so that moderate and strong diffusional terms can be taken into account. A new set of boundary conditions is used that respects mass flux and concentration continuity across the outer surface of the cell and maximizes the applicability of the spheroid‐in‐cell model in the convection‐to‐diffusion transition regime. The resulting elliptic problem in two dimensions is solved numerically. Results for the upstream and downstream concentration profiles reveal that tangential diffusion is very significant and should not be neglected for moderate and low Peclet number values. Also, the classical Levich‐type of formulation, which is theoretically valid for very weak diffusional terms only, can in practice be modified to predict with fair accuracy the overall Sherwood number and the adsorption efficiency of prolate and oblate spheroids‐in‐cell even in moderate Peclet number cases.
Solvent concentration dependence of solute distribution coefficient
Authors: Ching C. B. , Liu X. P. , Hidajat K. 
Published: June 2004

AbstractA simple method for modeling the solvent concentration dependence of solute distribution coefficient is described. Ideal and modified distribution models are proposed based on the mechanism of multicomponent competitive adsorption and the theory of solvent association. The system cresol‐methanol/water‐β‐CD‐silica is tested using the models, which compared with other experimental results show that the ideal distribution model fails at higher water concentrations and that the modified model can describe well the observed solute distribution behavior over the entire concentration range. The relative impact of nonideal factors in the adsorbed phase and the solvent association in the mobile phase on the distribution dependence shows that the limitation of the ideal model at higher water concentrations results mainly from uneven saturation capacities of the solute and solvent components for the system studied here.
Copper selective adsorption with a microemulsion‐based resin
Authors: Yang James H.‐K. , Burban John H. , Cussler E. L. 
Published: June 2004

AbstractCross‐linked terpolymers of allyl acetylacetone, 2‐hydroxyethyl methacrylate, and ethylene glycol dimethacrylate were synthesized in the oil phase of a bicontinuous microemulsion stabilized with didodecyldimethylammonium bromide. The resulting material is porous, with a surface area of 58 m2/dry g. It selectively adsorbs copper, picking up 0.07 meq/dry g from a 0.1‐M solution. This is less than the total apparent capacity of 0.65 meq/dry g inferred from titration with base and much less than the amount in conventional, nonselective resins, which is typically 5 meq/dry g. Breakthrough curves in packed beds and across membranes of this material seem consistent with uptake controlled by chemical reaction compromised by dispersion. Nonporous membranes of this material do not show facilitated transport.
Numerical studies of multicomponent chromatography using pH gradients
Authors: Frey Douglas D. , Barnes Andrew , Strong John 
Published: June 2004

AbstractA general numerical method is developed for multicomponent chromatography for the case where a pH gradient occurs and several buffering species are present that become adsorbed together with the components being separated through an ion‐exchange mechanism. Acid‐base equilibrium relations are used to determine the ionic compositions in the liquid and adsorbed phases and are solved using a single‐variable Newton's method. The differential material‐balance relations are integrated numerically using the method of characteristics. The transport relations are incorporated using a matrix analog of the linear‐driving‐force approximation. The resulting method accounts for the adsorption of each ionic form of each buffering species, for multicomponent diffusional interactions arising from induced electric fields, for volume and concentration overloading of proteins, and for changes in the adsorption capacity caused by pH variations. Numerical calculations illustrate factors govening the selection of the adsorbent and buffer components for use in separating mixtures of proteins using retained, internally generated pH gradients.
Salt extraction from hydrogen‐sulfide scrubber solution using electrodialysis
Authors: Jamaluddin A. K. M. , Kennedy M. W. , McManus D. , Nazarko T. W. 
Published: June 2004

AbstractThe buildup of undesirable sulfur compounds(sulfates and thiosulfates) reduces the scrubbing effectiveness of the LO‐CAT I autocirculation sulfur recovery process from acid‐gas stream. Among various processes, withdrawing and disposing of a portion of the scrubber solution and replacing this “blowdown” with fresh solution have been the practice in the industry. The application of the electrodialysis system to recycle the blowdown is presented. Experiments were carried out using electrodialysis to separate salts (sulfates and thiosulfates) from the LO‐CAT I autocirculation scrubber solution containing organic chelating agents, iron, and various alkali‐metal inorganic salts. The results indicated that the electrodialysis was successful in removing 50% of the salts from the scrubber solution with less than 8% loss of organic and 8% loss of carbonates. The fluxes of the undesired salt species were high even at low current densities (200 to 400 A/m2).
Transient temperature model for reaction injection molding
Authors: Peebles Samuel M. , Corripio Armando B. 
Published: June 2004

AbstractA model of the temperature response for reaction injection molding (RIM) operation is developed that assumes uniform mold temperature and a very fast reaction with slow heat transfer from the reacting mass to the mold and negligible heat losses to the surroundings. The model parameters are fit to data from a number of RIM experiments that agree well with published values of the physical constants for the reactants. The simple model can be fitted on‐line to data from the RIM apparatus and the results used to detect and correct deviations of the part properties from its desired values which could otherwise result in the production of many defective parts.
Tortuosity of bubble rise path in a liquid‐solid fluidized bed: Effect of particle shape
Authors: Tsuchiya Katsumi , Furumoto Akihiko 
Published: June 2004

AbstractEffects of particle properties on the rise of single bubbles in a liquid‐solid fluidized bed ared studied by focusing on the particle‐shape effect at various bed voidages near incipient fluidization of glass beads and sand particles. Experiments, covering the bubble‐size range 6–37 mm and solids holdups as high as 0.94 times that in the packed state, are conducted in a 2‐D column to directly observe the possible relationship between the rate and tortuous path of bubble rise. The shape effect, being significant when the close‐range (surface‐to‐surface) interactions between particles are predominant, is appreciable for the relative solids holdups exceeding 0.9. Marked reduction in the bubble rise velocity is observed as the bubble size is decreased below 8 and 12 mm for the spherical glass and irregular sand particles, respectively. This anomalous reduction stems partly from the tortuousness in the rise path and partly from the “hesitation” in the net vertical movement. The former, in particular, is quantified in terms of the tortuosity of the 2–D rise path. The results support the peculiar trend in the rise velocity observed, especially for the sand particles.
PSA performance of densely packed adsorbent beds
Authors: Shirley Arthur I. , LaCava Alberto I. 
Published: June 2004

AbstractThe separation of air by pressure swing adsorption is improved by filling the interparticle voids in kineticaly selective adsorbent beds with fine particles of the adsorbent or inert material. He ratio of the average diameter of the coarse adsorbent particles to the average diameter of the fine particles, the size of the fine particles themselves, and the percent of volume of the fine particles in the bed are all critical to optimum PA performance.
Modeling chemically active liquid membranes in tubular inorganic supports
Authors: Yi Jongheop , Tavlarides Lawrence L. 
Published: June 2004

AbstractA numerical model is presented to evaluate the dynamic behavior of mas transfer in the shell‐and‐tube‐type membrane modules for metal ion removal from aqueous streams. The analysis that considers the effects of axial‐flow velocity on the radial pressure difference across the membrane wall permits the specifications of this operating parameter to avoid expression of impregnated carrier from the membranes adn to prevent membrane wall rupture. The model accounts for effects of boundary layer mass‐transfer and kinetic rate resistances at the interfces on membrane flux. The performance of different size membrane modules was estimated for two operating modes of a shell‐and‐tube‐type module: one for the flow of feed solution inside the membrane tube and strip solution flow in the annular region and the other for the flow of strip solution inside the membrane tube and feed solution flow in the annular region of the module. A case system evaluated is copper ion extraction from acidic solutions using 2‐hydroxy‐5‐nonylacetophenone oxime impregnated in α‐alumina/silica ceramic membranes. The performance of shell‐and‐tube‐type membrane modules depends on the sizes and operating methods. In these calculations, the operation condition of no‐pressure difference across the membrane was imposed on the design. This condition is achieved by adjusting the ratio of the flow velocities of the feed and strip solutions within the inside and annular regions of the modules.