bluuebunny/crossref_metadata_2025_split huggingface dataset:
MRI investigations of fractures and multiphase flow in fractured media
Authors: Chen Songhua , Yao Xiaoli , Qiao Jinli , Watson A. Ted 
Published: June 2004

AbstractThe new application of nuclear magnetic resonance imaging (MRI) techniques for characterizing fractures and flow in fractured media is investigated. Specifically, a relaxation‐weighted imaging technique is used for selectively highlighting either fracture or porous matrix regions. Many advantages over conventional spin‐density MRI techniques for characterizing fractured media are demonstrated. Its use to speed image acquisition is also demonstrated. In addition, a multislice profile imaging technique is used to investigate imbibition and drainage displacement experiments in fractured porous media. These images demonstrate that the fractures can have profound effects on the fluid distributions in multiphase flow.
Model of crystallization in a confined space applied to iron uptake and release by ferritin
Authors: Courteix Anne , Bergel Alain 
Published: June 2004

AbstractMany living organisms store iron in solid form, Fe(III), as a crystal in the inner cavity of the ferritin molecule. When iron is needed for biosynthesis, a reducing agent reduces Fe(III) into the soluble form Fe2+ released by ferritin. Crystallization and release processes are reversible, and their rates evolve in an identical way as a function of the number n of iron atoms in the molecule. The rate increases with n, showing a maximum value when n is approximately 1,300, and then stabilizes for the highest values of n, which can reach 4,500. On the other hand, plotting the amount of released iron as a function of time gives curves with a sigmoid shape. The proposed model was based on the theoretical description of different steps involved in crystal growth inside the protein shell: several independent crystals grow freely at the inner protein wall, and then a distribution function takes into account possible overlapping of different crystallite clusters, whose further growth is limited by diminution of the available space inside the cavity. The kinetics derived was then used to calculate the release curve as a function of time. Solving the system of differential mass‐balance equations was simplified by describing the ferritin population as a large discrete distribution of species. The model fully fitted and explained the variation in the crystallization rate with n, and the sigmoid shape of the release curve as a function of time obtained experimentally in a thin‐layer electrochemical cell.
Mathematical modeling of a solid‐state limiting current carbon monoxide sensor
Authors: Tan Y. , Tan T. C. 
Published: June 2004

AbstractA solid‐state carbon monoxide sensor was fabricated using a 9% yttria‐stabilized zirconia (YSZ) disc sandwiched between two platinum thin‐film electrodes. One of the electrodes was coated with a thin layer of 7 CuO · 10 ZnO · 3 Al2O3 catalyst. The sensor showed limiting current behavior at an applied voltage between 0.5 and 1.2 V. Linear response was observed with carbon monoxide in a nitrogen–oxygen mixture at high temperature and limiting current conditions. The linear carbon monoxide concentration range increased with increase in the operating temperature and its sensitivity increased from 2.437 mA · atm−1 CO at 1,023 K to 10.771 at 1,093 K. These characteristics were adequately described by the proposed mathematical model relating the response to the rate processes occurring in the catalyst layer and in the electrochemical cell under limiting current conditions. The model showed that effective sensing and high sensitivity are best obtained using a catalyst with high catalytic activity toward the test solute and proper design and fabrication of the sensor to ensure its high diffusivity in the catalyst.
Random walks in prefractal porous media
Authors: Sternberg Steven P. K. , Cushman John H. , Greenkorn Robert A. 
Published: June 2004

AbstractRandom walks are used to examine dispersion between miscible fluids in one‐dimensional, prefractal porous medium. Mixing in such media is anomalous and several nonlocal theories have been proposed to describe this non‐Fickian characteristic. This work simulates dispersion via a random walk in a prefractal media by incorporation local and spatially nonlocal effects and compares the results with laboratory experiments. Results suggest that nonlocal models fit experimental data better than local models.
Permeability of gigaporous particles
Authors: Pfeiffer James F. , Chen John C. , Hsu James T. 
Published: June 2004

AbstractThe volumetric flow rate of liquid and gas through small gigaporous particles was measured by a new method that isolates single particles in a test apparatus. To our knowledge, this is the first direct confirmation of flow through gigaporous particles made at pressure drops experienced during normal operation. High‐performance liquid chromatography particles from 30 to 50 μm in diameter, previously reported to exhibit convection‐enhanced intraparticle mass transfer, were studied. Using a CFD model of the test system, the permeability of individual particles was determined from the pressure‐drop‐flow‐rate relationship. The average measured permeability of the particles studied is 7.89 × 10−15 m2 with no dependence on particle size. This is 4 to 17 times greater than values calculated from models currently used to estimate the permeability of these kinds of particles. No other experimentally measured values of permeability have been reported for particles of this size. The results of this study might imply that the intraparticle structure does not behave like a bed of uniformly packed microspheres, but rather as an inhomogeneous assemblage of microparticles. The measured permeability values offer the possibility of developing better models of the intraparticle flow field under normal operating conditions. Knowledge of the intraparticle flow field is an important step in deriving predictive models of convective mass transfer in these types of particles.
Determining porosity profiles during filtration and expression of sewage sludge by NMR imaging
Authors: La Heij E. J. , Kerkhof P. J. A. M. , Kopinga K. , Pel L. 
Published: June 2004

AbstractThe formation of a filter cake during mechanical dewatering (filtration and expression) of sludge is studied using one‐dimensional nuclear magnetic resonance (NMR) imaging of porosity profiles. The experiments clearly showed the formation of a porosity gradient during filtration and the disappearing of this gradient during expression, forming a cake with a uniform porosity. This technique makes it possible to investigate the material behavior of the porous medium, which is needed before any model calculations can be performed. The results indicate that NMR imaging is useful in nondestructive monitoring of the filtration and expression process of sludge.
Damage detection in composites by ZnO sensors
Authors: Viljoen H. J. , van Rensbure N. F. J. 
Published: June 2004

AbstractThe development of composites with self‐diagnostic capabilities is based on the analysis of a mathematical model of the structure. The method is illustrated for a vibrating cantilevered plate and analyzed considering damping. Damage is modeled as an elastic joint, and the spectrum of natural frequencies is calculated for different positions and magnitudes of the elastic joint. Small sensors consisting of tungsten filaments coated with ZnO are embedded in the plate, and their output is modeled. The solution of the inverse problem depends on the position and extent of damage which can be uniquely solved if the system is not overdamped with respect to the primary frequency. Higher modes have a decreasing contribution to the signal output; when the primary mode is overdamped, only the secondary frequency can be detected reliably. The solution to the inverse problem is no longer unique; there are as many as three different solutions (damage position and extent of damage) all of which produce the same signal output.
Backone family of equations of state: 1. Nonpolar and polar pure fluids
Authors: Müller Andreas , Winkelmann Jochen , Fischer Johann 
Published: June 2004

AbstractThe Helmholtz energy F is written as the sum F = FH + FA + FPol, where FH is the hard‐body contribution, FA the attractive dispersion force contribution, and FPol either the quadrupolar or dipolar contribution. Here, a new expression for FA is constructed by a simultaneous correlation of experimental data of methane, oxygen, and ethane. The resulting equations for F with only three or four substance‐specific parameters are tested for several nonpolar, quadrupolar, and dipolar fluids. In the correlation of large data sets good results are obtained. The significance of the approach, however, is in the good to excellent prediction of all thermodynamic properties in the whole fluid region based on a parameter fit to only four experimental data—two vapor pressures and two saturated liquid densities.
Analysis of cell‐target encounter by random filopodial projections
Authors: Buettner Helen M. 
Published: June 2004

AbstractDynamic projections from the surface of many motile cell types provide for variable contact with the extracellular environment and can be important in regulating cell migration events. For example, during nerve development and regeneration, the sensory motile tip of the axon exhibits long, slender filopodia projecting from the growth cone periphery. Extension and retraction of these filopodia continually remodel the points of contact between axon and surroundings. Experimental studies show that filopodial contact with specific extracellular features can guide subsequent growth cone migration, suggesting a potentially important means of engineering nerve growth to repair nerve injury or construct biological neural networks. A simulation model is presented of the dynamic filopodial structure on the nerve growth cone based on recent experimental characterization. The model is analyzed to obtain quantitative relationships between average filopodial characteristics, which are commonly measured experimental quantities, and the underlying parameters of individual filopodium dynamics. It is then applied to simulate encounter between a growth cone and its target due to filopodial dynamics alone. Filopodial contribution to growth cone‐target encounter is summarized in terms of a mean encounter time that is reminiscent of a first passage time for a diffusing particle. The parametric relationships in this study provide a basis for further investigation of filopodial‐mediated mechanisms in nerve growth and other cellular processes.
Air purification in a reverse‐flow reactor: Model simulations vs. experiments
Authors: van de Beld L. , Westerterp K. R. 
Published: June 2004

AbstractThe behavior of a reverse‐flow reactor was studied for the purification of polluted air by catalytic combustion. A heterogeneous one‐dimensional model was extended with a heat balance for the reactor wall. An overall heat transport term is included to account for the small heat losses in radial direction.The calculations are compared to experimental data without using fit parameters. The agreement between simulations and experiments is generally good. Discrepancies can be explained mainly by inaccurate kinetic data and experimental uncertainties. At low gas velocities and for small reactor diameters, the one‐dimensional model failed and a two‐dimensional model must be developed to improve the predictive potential.
Atomization of dilute polyisobutylene/mineral oil solutions
Authors: Smolinski Joseph M. , Gulari Esin , Manke Charles W. 
Published: June 2004

AbstractAtomization experiments, motivated by the need to suppress misting of machining oils, were conducted on dilute solutions of polyisobutylene (PIB) in mineral oil using a coaxial air blast atomizer and an optical (Fraunhofer diffraction) particle sizer. Polymer concentrations (0.1 to 1.0 kg/m3) and molecular weight (1.0 to 2.2 million) were varied to determine their effects on aerosol drop‐size distributions. The pure oil and PIB ‐ oil solutions were atomized at air/liquid mass ratios near 10 and atomizing air velocities of 150–270 m/s, producing droplet‐size distributions with mass mean diameters (MMD) in the range of 7–15 μm for the pure oil. Under identical atomization conditions, the MMDs of PIB solutions were 20–200% higher than pure oil. These observed increases in MMD correspond to significant reductions in the fraction of droplets falling below 5 μm in diameter that constitute the misting problem in industrial machining applications. Observed effects of PIB on atomization are ascribed to the viscoelastic properties of PIB ‐ oil solutions as characterized by the elongational viscosity ηE. This relationship is examined by correlating the change in MMD caused by PIB addition with the stress‐dependent elongational viscosity of PIB‐oil solutions as predicted by the FENE‐P dumbbell kinetic theory. The increase in MMD due to PIB varies linearly with the predicted ηE at constant atomization tensile stress.
Stability of the liquid‐fluidized magnetically stabilized fluidized bed
Authors: Fee Conan J. 
Published: June 2004

AbstractRosensweig's (1979) analysis of the stability of gas‐fluidized magnetically stabilized fluidized beds (MSFBs) with voidage perturbations is modified to include terms dependent on the fluid density. This allows the stability analysis to be applicable to liquid‐fluidized MSFBs, which have potential use in liquid chromatography. Results show that in systems where the fluid density is not insignificant when compared to the solid‐phase density, the difference in density between the two phases should be used when normalizing the magnetization required to achieve stability. Comparisons between theory and experiment show that although the present analysis improves on Rosensweig's analysis, it still does not give reliable, quantitative predictions of stability behavior. It is suggested that for liquid‐fluidized MSFBs, stability to particle velocity perturbations, rather than to voidage perturbations, is more relevant to chromatographic applications wherein the purpose of magnetic stabilization is to prevent particle mixing as opposed to preventing the occurrence of bubbling and slugging observed in gas‐fluidized beds.
Theoretical model for drop and bubble breakup in turbulent dispersions
Authors: Luo Hean , Svendsen Hallvard F. 
Published: June 2004

AbstractA theoretical model for the prediction of drop and bubble (fluid‐particle) breakup rates in turbulent dispersions was developed. The model is based on the theories of isotropic turbulence and probability and contains no unknown or adjustable parameters. Unlike previous work, this model predicts the breakage rate for original particles of a given size at a given combination of the daughter particle sizes and thus does not need a predefined daughter particle size distribution. The daughter particle size distribution is a result and can be calculated directly from the model. Predicted breakage fractions using the model for the air–water system in a high‐intensity pipeline flow agree very well with the available 1991 experimental results of Hesketh et al. Comparisons of the developed model for specific particle breakage rate with earlier models show it to give breakage‐rate values bracketed by other models. The spread in predictions is high, and improved experimental studies are recommended for verification.
Pore and surface diffusion in multicomponent adsorption and liquid chromatography systems
Authors: Ma Z. , Whitley R. D. , Wang N.‐H. L. 
Published: June 2004

AbstractA generalized parallel pore and surface diffusion model for multicomponent adsorption and liquid chromatography is formulated and solved numerically. Analytical solution for first‐ and second‐order central moments for a pulse on a plateau input is used as benchmarks for the numerical solutions. Theoretical predictions are compared with experimental data for two systems: ion‐exchange of strontium, sodium, and calcium in a zeolite and competitive adsorption of two organics on activated carbon. In a linear isotherm region of single‐component systems, both surface and pore diffusion cause symmetric spreading in breakthrough curves. In a highly nonlinear isotherm region, however, surface diffusion causes pronounced tailing in breakthrough curves; the larger the step change in concentration, the more pronounced tailing, in contrast to relatively symmetric breakthroughs due to pore diffusion. If only a single diffusion mechanism is assumed in analyzing the data of parallel diffusion systems, a concentration‐dependent apparent surface diffusivity or pore diffusivity results; for a convex isotherm, the apparent surface diffusivity increases, whereas the apparent pore diffusivity decreases with increasing concentration. For a multicomponent nonlinear system, elution order can change if pore diffusion dominates for a low‐affinity solute, whereas surface diffusion dominates for a high‐affinity solute.
Robust unconstrained predictive control design with guranteed nominal performance
Authors: Hrissagis Kostas , Crisalle Oscar D. , Sznaier Mario 
Published: June 2004

AbstractA systematic and complete method to design robust predictive controllers for unconstrained linear systems is proposed. The synthesis procedure is based on rigorous theoretical foundations, without resorting to approximations or ad hoc design guidelines, yet it remains a viable tool for practical application. A significant feature is that the robust predictive controller retains the servo performance of a nominal predictive controller designed using conventional methods. In addition, the robust predictive controller can be designed to guarantee perfect steady‐state rejection of asymptotically constant disturbances. The robust design method is developed for systems affected by unmodeled dynamics and is based on solving a discrete‐time model‐matching problem. It is shown that the robust controller can be classified legitimately as a predictive controller because it minimizes the same performance functional as the nominal predictive controller. An illustrative design example is given.
Statistical operating strategies for charging batch reactors
Authors: Tsai Chii‐Shiang , Chang Chuei‐Tin 
Published: June 2004

AbstractTwo critical decisions must be made in the charging sequence of batch reactors: target setting and alarm generation. A number of statistics‐based strategies are proposed in this article to perform these tasks. The off‐line and on‐line target setting procedures developed in this work can be adopted to increase the profit margin of any given batch process without sacrificing reliability. A synthesis method for building optimal alarm logic is also described in detail. Monitoring systems constructed according to this suggested approach are effective in reducing the probability of undetected faulty batches. Extensive simulation studies show that the proposed strategies are suitable for application of manufacturing high‐value‐added products, which is a prevailing practice in batch processes.
Three‐phase reactor model for hydrotreating in pilot trickle‐bed reactors
Authors: Korsten Hans , Hoffmann Ulrich 
Published: June 2004

AbstractA three‐phase reactor model for describing the hydrotreating reactions in a trickle‐bed reactor was developed. It includes correlations for determining mass‐transfer coefficients, solubility data, and properties of the compounds under process conditions. The model, based on the two‐film theory, was tested with regard to the hydrodesulfurization of vacuum gas oil in a new high‐pressure pilot plant operated under isothermal conditions. The sulfur content of the product oil was found to depend strongly on the gas/oil flow ratio within the reactor. This is due to the inhibiting effect of hydrogen sulfide on the chemical reaction rates described by Langmuir–Hinshelwood kinetics. The poor conversion which, in contrast to industrial plants, is often observed in pilot plant reactors can be explained by incomplete catalyst wetting produced by low liquid velocities. The simulation shows a good agreement with the experiments carried out in a wide range of temperature, pressure, space velocity and gas/oil ratio.
Study of instabilities in film blowing
Authors: Ghaneh‐Fard A. , Carreau P. J. , Lafleur P. G. 
Published: June 2004

AbstractBubble instabilities observed in film blowing using four different polyolefins are discussed: high‐density polyethylene (HDPE), low‐density polyethylene (LDPE), linear low‐density polyethylene (LLDPE), and polypropylene (PP). Special attention is given to the effect of the frost line height on the bubble stability, an effect mostly ignored in the literature. A video‐camera system was used to record the bubble shape and oscillations. In general, three forms of instabilities and combinations were observed: (1) axisymmetric periodic variations in the bubble diameter; (2) helical motions of the bubble; and (3) variations in the position of the solidification line. The four resins show different stability behaviors. The LDPE has the most stable operating space and the PP is the most unstable one. No correlation was observed between bubble stability and oscillatory shear rheological properties of the resins. Instability is enhanced by increasing take‐up ratio, increasing blow‐up ratio, and decreasing frost line height. Furthermore, for the LDPE, some operating points were not attainable and multiple steady states were observed. Our results are in a poor agreement with the predictions Cain and Denn's 1988 analysis.
Electrophoresis of a colloidal sphere in a circular cylindrical pore
Authors: Keh Huan J. , Chiou Jinn Y. 
Published: June 2004

AbstractThe electrophoretic motion of a dielectric sphere along the centerline of a long circular cylindrical pore is studied theoretically. The imposed electric field is constant and parallel to the nonconducting pore wall, and the particle and wall surfaces are assumed uniformly charged. Electrical double layers adjacent to solid surfaces are assumed to be thinner than particle radius and gap width between surfaces. The presence of the pore wall affects particle velocity: 1. an electroosmotic flow of the suspending fluid exists due to interaction between the electric field and the charged wall; 2. the local electric field on the particle surface is enhanced by the insulated wall, speeding up the particle; and 3. the wall increases viscous retardation of the moving particle. To solve electrostatic and hydrodynamic governing equations, general solutions are constructed from fundamental solutions in both cylindrical and spherical coordinate systems. Boundary conditions are enforced at the pore wall by Fourier transforms and then on the particle surface by a collocation technique. Typical electric‐field‐line, equipotential‐line and streamline patterns for the fluid phase are exhibited, and corrections to the Smoluchowski equation for particle electrophoretic velocity are presented for various relative separation distances between the particle and wall. The presence of the pore wall always reduces the electrophoretic velocity; however, the net wall effect is quite weak, even for very small gap width between the particle and wall.