bluuebunny/crossref_metadata_2025_split huggingface dataset:
Measurement and theoretical modeling of protein mobility through membranes
Authors: Ho A. K. , Perera J. M. , Dunstan D. E. , Stevens G. W. , Nyström M. 
Published: April 2004

AbstractThe electrophoretic mobilities of hemoglobin and lysozyme were measured through polycarbonate track‐etched membranes of different pore sizes. Together with the zeta potential of the protein‐fouled membranes, and measurements of the free‐solution mobilities, protein sizes, and membrane pore sizes, the theory of Ennis et al. was tested. The presence of the membrane offered little hindrance to protein transfer when the membrane pore size was large in comparison with the protein size and the thickness of the electrical double layers. Under some solution conditions, protein agglomeration was significant and the interactions between the larger particles, and the membrane pore walls caused a more pronounced reduction in the protein mobility from its free‐solution value. Good agreement with the theoretical model was found only for cases where the solution remained as a monodispersed suspension of protein monomers.
Worst‐case performance analysis of optimal batch control trajectories
Authors: Ma David L. , Chung Serena H. , Braatz Richard D. 
Published: April 2004

AbstractIn open‐loop optimal control, inputs to a dynamic system are computed that optimize a specified performance criterion. A novel approach is proposed that quantifies the impact of parameter and control implementation inaccuracies on the performance of open‐loop control policies. Such information can be used to decide whether more laboratory experiments are needed to produce parameter estimates of higher accuracy, or to define performance objectives for lower‐level control loops that implement the optimal control trajectory. The novel features of the approach include (1) computational efficiency; (2) the parametric uncertainty description, which is produced by most process identification algorithms; and (3) addressing of control implementation inaccuracies. The merits of the approach are illustrated on a batch crystallization process.
Crystal growth kinetics of calcite in a dense fluidized‐bed crystallizer
Authors: Tai Clifford Y. , Chien W.‐C. , Chen C.‐Y. 
Published: April 2004

AbstractThe growth kinetics of calcite crystals are studied in a batch‐fluidized‐bed crystallizer, which is maintained at a constant pH. The growth experiments are conducted in the metastable region explored as part of this research. The crystal growth rates are evaluated from the consumption rates of calcium ions, using the cured natural calcite or silica sand as seeding materials. Several operation variables are investigated, including supersaturation, pH, ionic strength, superficial velocity, and particle size and type of seed. The significant factors that affect the crystal growth rate are identified. Then the crystal growth data of constant pH and ionic strength are analyzed by the two‐step growth model. The mass‐transfer coefficients are obtained and compared at various crystal sizes and superficial velocities. Finally, a growth‐rate equation of calcite crystal, which is based on the two‐step growth model, is proposed for design purposes.
Modular representation synthesis framework for homogeneous azeotropic separation
Authors: Ismail Soraya Rahim , Pistikopoulos Efstratios N. , Papalexandri Katerina P. 
Published: April 2004

AbstractThe synthesis and design of separation systems for nonideal azeotropic mixtures traditionally utilize graphical methods, focusing on separation feasibility within a sequential design framework. Once promising systems have been identified, sequencing and design are optimized in a second stage, limited by the separation feasibility region defined in the first stage. A generalized modular representation proposed for the synthesis of nonideal separations can simultaneously explore entrainer and sequencing alternatives. A multipurpose mass/heat exchange module, introduced in earlier work, is employed to investigate separation units and structures as mass‐ and heat‐exchange possibilities. Process units, separation sequences, and entrainers that aid the separation are examined within one separation problem rather than in a sequential manner. Promising separation schemes can be further considered for detailed design optimization.
Optimal‐grade transition strategies for multistage polyolefin reactors
Authors: Takeda Makoto , Ray W. Harmon 
Published: April 2004

AbstractPolymer‐producing companies normally produce many polymer grades in each polymerization reactor train according to customer demands; therefore, many grade‐transition operations are necessary. However, the determination of these optimal strategies is difficult. To solve this problem, several sample simulations showing the optimal solutions of grade‐transition strategies for multistage olefin polymerization reactors with bimodal products were performed. The methodology utilized a dynamic process simulator, POLYRED, coupled to a sequential quadratic programming, nonlinear optimization algorithm, by using two different objective functions with and without state constraints. It is shown that the most beneficial case of using the optimization technology is the grade transition where the hydrogen content in a reactor must be decreased and/or constraints are imposed on state variables.
Three‐dimensional image analysis of mixing in stirred vessels
Authors: Li Lin , Wei James 
Published: April 2004

AbstractSeveral analytical methods were applied to the 3‐D electrical resistance tomography (ERT) image of stirred‐vessel experiments of Holden et al. to characterize the mixing behavior and to measure mixing quantitatively. Based on the time resolved 3‐D ERT results, the centroid and variance of the concentration distribution in three dimensions can be obtained as a time series to track the movement, dispersion, stretch and rotation of the concentration distribution in the tank. By sampling at different scales and locations, the ratios of standard deviations to means and the entropy of corresponding volumes can be calculated to examine the degrees of uniformity. The 3‐D wavelet decomposition provides an effective method of analyzing the mixing process at various scales. The wavelet difference coefficients reflect the concentration gradients of specific volumes along different directions. These methods of analysis promise to guide the design of better mixing schemes and to monitor the process for optimal operation.
Kinetics of oil dispersion in the absence and presence of block copolymers
Authors: Polat H. , Polat M. , Chander S. 
Published: April 2004

AbstractA phenomenological model proposed describes droplet breakup in the turbulently agitated lean oil‐in‐water dispersions and provides a correlation between the median droplet size in an agitated vessel of standard geometry and the time of dispersion. It was assumed that the droplet breakup takes place in the dispersion‐only region and coalescence is negligible. The model described the data from this study and the literature quite satisfactorily under these conditions. The effect of adding triblock PEO/PPO/PEO copolymeric surfactants on the dispersion kinetics of oil was also investigated. Addition of surfactant reduced the median oil droplet size significantly, and the extent of this reduction was a strong function of surfactant concentration. Application of the model on these data demonstrated that the change in the median droplet size could be divided into two distinct regions. The breakage rate was high initially, most probably due to continuous adsorption of surfactant molecules at the oil/water interface. A lower breakage rate was attained at longer times, as the surfactant molecules were depleted from the solution. The time of transition between the two was affected strongly by the concentration of the surfactant added. Furthermore, the time of addition of the surfactant did not affect the final droplet‐size distribution in the system.
Process boundary approach to separations synthesis
Authors: Pressly Thomas G. , Ng Ka M. 
Published: April 2004

AbstractA method for synthesizing separation processes for multicomponent mixtures is presented which identifies the regions, boundaries, and the lower dimensional varieties in an N‐dimensional space. Both thermodynamic and equipment boundaries, which may block or limit a proposed separation step, are considered. To facilitate process synthesis, process boundaries are approximated as linear hyperplanes if appropriate, while nonlinear boundaries are represented using a set of linear hyperplanes. In conjunction with the available separation task selection methods, a step‐by‐step procedure is proposed to generate complete flowsheet alternatives, which allow bypassing both thermodynamic and equipment boundaries to achieve a given separations objective. Several example problems are solved using a spreadsheet program to illustrate the simplicity and applicability of this approach.
Robust PI stabilization of a class of continuously stirred‐tank reactors
Authors: Alvarez‐Ramirez Jose 
Published: April 2004

AbstractThis article deals with the stabilization of continuously stirred‐tank reactors in the face of control input saturations and uncertain chemical kinetics. Using ideas from modeling‐error compensation techniques, a first‐order compensator is designed, and its ability to stabilize the reactor temperature at an arbitrary setpoint is shown. The dynamic part of the proposed controller is interpreted as a type of robust integral action to accommodate the modeling error.
Visualization test for neutralization of acids by marine cylinder lubricants
Authors: Wu Rong Chang , Papadopoulos Kyriakos D. , Campbell Curt B. 
Published: April 2004

AbstractThe combustion of high‐level‐sulfur (2–5%) fuels generates large amounts of sulfuric acid in slow‐speed crosshead marine diesel engines. In this study, a video‐microscope imaging technique is used to develop an experimental protocol for ranking the ability of marine cylinder lubricants to neutralize sulfuric acid within microcapillaries. The technique was applied to several oils with known rates of acid‐neutralization ability to predict these rates. The optical observations allow one to propose a plausible mechanism by which the overbased detergent additive system performs the task of acid neutralization. According to this mechanism, the overbased sulfonate reverse micelles are the site for the neutralization reaction, which occurs at the oil‐acid interface. The results confirm that the detergent surfactants are chemically bound to the micellar core. In the case of overbased calcium‐carbonate detergents reacting with sulfuric acid, the formation of solid crystals was observed which may form a protective antiwear film on engine metal surfaces.
Variable structure NARX models: Application to dissolved‐oxygen bioprocess
Authors: Sargantanis Ioannis G. , Karim M. N. 
Published: April 2004

AbstractSelecting the best structure of nonlinear autoregressive models with exogeneous inputs (NARX) is important for good parameter estimation and control. If the process is also time varying, the best structure selection procedure should be done in an on‐line fashion. Simultaneous model selection and parameter estimation can be achieved by employing the Givens forward selection with exponential windowing (GFEX) algorithm. An on‐line implementation yields a variable‐structure NARX‐model identification, which can be used for control of a dissolved‐oxygen (DO) process. The results of an adaptive DO control scheme, which uses a fixed model structure and was applied to a batch Bacillus subtilis fermentation, were used in this study. Time‐dependent patterns of selected terms were observed that roughly corresponded to different fermentation stages. Fitting and prediction capabilities for the adaptively selected NARX model were compared with fixed ARX and NARX models. The effect of the forgetting factor and the model order was investigated. Performance is satisfactory for short‐step‐ahead prediction, and avoiding overparametrization can stabilize the long‐step‐ahead prediction.
Improvement and validation of the fluoroptic temperature‐measurement method
Authors: Janse Arthur M. C. , de Jong Xander A. , Prins Wolter , van Swaaij Wim P. M. 
Published: April 2004

AbstractThe fluoroptic measurement method, recently developed by Wagenaar and coworkers to determine in a contactless manner the temperature of moving particles, has been improved. It now has a higher accuracy (approximately 5%) and can be used for particles that move at higher speeds. In addition, the technique has become much less labor‐intensive. Validation has been realized by comparing experimentally determined heat‐transfer coefficients for a cylinder in crossflow with predictions of several well‐known correlations from the literature. A consistent deviation of less than 10% is observed. This comparison therefore shows the reliability of the fluoroptic measurement method.
Hierarchical approach for simulation of binary adsorption in silicalite
Authors: Czaplewski Kenneth F. , Snurr Randall Q. 
Published: April 2004

AbstractA hierarchical molecular modeling approach presented predicts adsorption thermodynamics of single components and binary mixtures in zeolites. Atomistic simulations that capture details at the molecular level are performed to calculate the free energies of molecules at discrete adsorption sites. Then a more coarse‐grained lattice model is used to calculate the equilibrium loading of adsorbates based on these free energies, and thermodynamic properties can be predicted. Sorbate–sorbate free energies beyond nearest‐neighbor interactions are introduced and their impact on the lattice model is investigated. By adding these free energies, the model is better able to accurately describe single‐component and binary adsorption of sulfur hexafluoride and neopentane in silicalite. The results from the lattice model agree well with full atomistic grand canonical Monte Carlo simulations performed for the same systems, but the hierarchical approach saves an order of magnitude of computational effort.
Evaluation of a locus of azeotropes by molecular simulation
Authors: Pandit Sandeep P. , Kofke David A. 
Published: April 2004

AbstractThe technique proposed here for the evaluation of azeotrope lines by molecular simulation builds on ideas used to devise the Gibbs‐Duhem integration (GDI) technique for evaluating phase equilibria by molecular simulation. Beginning with a known azeotropic state point, the method integrates a differential equation for the locus of azeotropes with a single semigrand‐ensemble molecular simulation performed at each integration state point. Unlike the standard GDI method, fluctuation quantities are needed to conduct the integration. Although these quantities are measured less precisely than simple ensemble averages, the integration is not adversely affected by this difficulty. The method is demonstrated by applying to three model Lennard‐Jones binaries. Among these mixtures is one in which the molecular diameter of one species is varied along the azeotrope line. This application shows how details of the intermolecular interactions affect azeotropic behavior. Such an understanding might be useful in formulating additives to break an azeotrope.
Predicting geometrical properties of random packed beds from computer simulation
Authors: Nandakumar K. , Shu Yiqiang , Chuang K. T. 
Published: April 2004

AbstractUsing advances in computational geometry and collision‐detection algorithms, an algorithm was developed to analyze and predict the geometrical properties of a randomly packed structure using packing objects of arbitrary shape. A 3‐D polygonal model was used to describe an arbitrarily complex packing object and a simple container object. The dynamics of the packing process is not simulated, but a search algorithm finds stable equilibrium positions for the packing objects of arbitrary shapes using a collision‐detection algorithm in a 3‐D space. A modified conjugate gradient optimization method determines the packing object's final packing location and orientation. Once the bed is packed, both macroscopic quantities like the overall porosity, the specific surface area, and the number of packing objects per unit volume and microscopic properties like the porosity variation in any direction could be determined. For accurate porosity calculation inside a given 3‐D polygonal sample space, the Sutherland‐Hodgman polygon clipper algorithm was used. Predicted results are validated against available experimental data for spheres, Raschig rings, Pall rings, and cascade minirings.
Growth and aggregation rates for calcite and calcium oxalate monohydrate
Authors: Collier Alan P. , Hounslow Michael J. 
Published: April 2004

AbstractSeeded batch experiments were conducted at low magma densities and moderate ionic strength to determine the growth and aggregation rate constants for calcite precipitation in a stirred vessel. The growth was found to be surface‐reaction‐limited, and the growth rates agreed broadly with other studies of calcite precipitation. Aggregation rates have rarely been presented for calcite. The aggregation rate constant studied here was directly proportional to the instantaneous growth rate and inversely proportional to the average shear rate in the vessel. The results were also compared with similar work carried out on calcium oxalate monohydrate. It was found that the relationship between the aggregation rate constant and stirrer speed was virtually identical in the two cases, despite almost an order of magnitude difference in the growth rate constants.
Entry mass transfer in axial flows through randomly packed fiber bundles
Authors: Bao L. , Liu B. , Lipscomb G. G. 
Published: April 2004

AbstractAn analysis of the effects of nonuniform fiber packing on external mass‐transfer coefficients for axial flows through bundles of parallel, axially oriented fibers is presented in the entry mass‐transfer limit. In this limit, one can obtain an analytic solution to the mass‐transfer boundary‐layer equations in terms of the velocity gradient on the fiber surface for either a constant wall flux or constant wall concentration. To explicitly calculate mass‐transfer coefficients, a numerical approximation for the velocity gradient is obtained from the conservation of momentum equations using the boundary‐element method. Results indicate that the effective mass‐transfer coefficient depends strongly on fiber packing. Regions of higher fiber packing have lower flows and lower mass‐transfer coefficients than regions of lower packing. The net effect is a dramatic decrease in overall mass‐transfer coefficient relative to mass‐transfer coefficients in regularly packed fiber bundles.
Radial reactor for trichloroethylene steam reforming
Authors: Moates F. Craig , McMinn Timothy E. , Richardson James T. 
Published: April 2004

AbstractA ceramic foam radial reactor was used to convert trichloroethylene by steam reforming, using 0.5 wt. % Pt as a catalyst. With a quartz enclosure heated externally by infrared lamps, the inlet temperature to the catalyst bed was low enough to suppress pyrolysis, but high conversions (0.99999+) were achieved at the exit. Stable operation up to 600 h with a space velocity of 5.6 × 104 h−1 was achieved, but reactant breakthrough then occurred, and the catalyst quickly deactivated. Although the deactivated catalyst was regenerated with carbon burning, activity decline was more rapid due to platinum sintering and washcoat degradation. Measured temperature profiles and model calculations indicated a large gradient in the bed and suggested that stable operation could be extended at lower space velocities. Axial temperature profiles were not uniform, since preferential flow occurred in the middle and lower regions of the radial bed. Potential improvements for future designs are suggested.
Mass‐transfer parameters in gas‐solid reactive media to identify permeability of IMPEX
Authors: Lu Hui‐Bo , Mazet Nathalie 
Published: April 2004

AbstractLu et al.'s modeling of gas‐solid reaction demonstrated the significant influence of mass transfer on the global transformation of consolidated porous reactive media with reactive gas at low pressure and low permeability. Their model coupled mass transfer with chemical kinetics at the grain level and heat transfer with mass transfer at the pellet level. The comparison between simulation results and recent experiments demonstrated that the value of the material permeability varies during the reaction process. This study presents the permeability decrease during the synthesis process. A correlation representing the nonlinear evolution of permeability was identified for different reactive materials used for experiments. These mechanisms can satisfactorily explain both the experimental measurements of global advancement and local temperature profiles.
Residence‐time distribution model for twin‐screw extruders
Authors: Gao Jun , Walsh Gregory C. , Bigio David , Briber Robert M. , Wetzel Mark D. 
Published: April 2004

AbstractA model for the residence‐time distribution (RTD) is validated by the analysis of data collected from the extrusion of polyethylene on a 30‐mm Krupp Werner and Pfleiderer (W&P) corotating twin‐screw extruder. Transformation of the RTD to give both the residence‐volume distribution (RVD) and the residence‐revolution distribution (RRD) yields new physical insights into the extrusion process. It is observed that operating conditions with equivalent specific throughput result in an equivalent RVD and RRD, and for a given screw configuration the axial mixing of extrusion material as measured by a tracer is essentially the same for all operating conditions. This allows the experimental RVD curves to be superimposed to form a single master curve for a given screw geometry. These new tools motivate the development of a simple residence model that characterizes the partially filled and fully filled screw sections and is capable of distinguishing between screw configurations and operating conditions. A least‐square error‐fit method used to identify the parameters of the RTD model indicated that the model function is appropriate to describe the RTD experimental data.
Mechanisms of pulsating combustion during synthesis of advanced materials
Authors: Mukasyan Alexander S. , Rogachev Alexander S. , Varma Arvind 
Published: April 2004

AbstractGasless combustion is a specific type of combustion, where all initial reactants, as well as intermediate and final products, remain in condensed (solid or liquid) state. This process is of great interest because of its prospective applications in combustion synthesis of advanced materials. The stability of combustion wave propagation is an important factor in determining the quality of materials produced by combustion synthesis. In this work, a digital high‐speed microscopic video recording method is used for direct observation and quantitative characterization of pulsating combustion in several gasless systems. The experimental data quantitatively describe, for the first time, oscillations of local instantaneous velocity at length scale about 10 μm and time scale ∼10;minus;3 s. Three systems investigated were: Ta‐C, Nb‐B, and Ti‐C. Two new mechanisms of pulsating combustion were identified: crack‐induced oscillations occur in Nb + B and Ta + C systems, while ignition‐extinction oscillations take place during reaction in Ti + xC system.