bluuebunny/crossref_metadata_2025_split huggingface dataset:
Continua of states in boundary-layer flows
Authors: HEWITT R. E. , DUCK P. W. , STOW S. R. 
Published: October 2002

We consider a class of three-dimensional boundary-layer flows, which may be viewed
as an extension of the Falkner–Skan similarity form, to include a cross-flow velocity
component, about a plane of symmetry. In general, this provides a range of three-
dimensional boundary-layer solutions, parameterized by a Falkner–Skan similarity
parameter, n, together with a further parameter, Ψ∞, which is associated with a
cross-flow velocity component in the external flow. In this work two particular cases
are of special interest: for n = 0 the similarity equations possess a family of solutions
related to the Blasius boundary layer; for n = 1 the similarity solution provides an
exact reduction of the Navier–Stokes equations corresponding to the flow near a
saddle point of attachment. It is known from the work of Davey (1961) that in
this latter class of flow, a continuum of solutions can be found. The continuum
arises (in general) because it is possible to find states with an algebraic, rather than
exponential, behaviour in the far field. In this work we provide a detailed overview
of the continuum states, and show that a discrete infinity of ‘exponential modes’ are
smoothly embedded within the ‘algebraic modes’ of the continuum. At a critical value
of the cross-flow, these exponential modes appear as a cascade of eigensolutions to
the far-field equations, which arise in a manner analogous to the energy eigenstates
found in quantum mechanical problems described by the Schrödinger equation.The presence of a discrete infinity of exponential modes is shown to be a generic
property of the similarity equations derived for a general n. Furthermore, we show
that there may also exist non-uniqueness of the continuum; that is, more than one
continuum of states can exist, that are isolated for fixed n and Ψ∞, but which are
connected through an unfolded transcritical bifurcation at a critical value of the
cross-flow parameter, Ψ∞.The multiplicity of states raises the question of solution selection, which is addressed
using two stability analyses that assume the same basic symmetry properties as the
base flow. In one case we consider a steady, algebraic form in the ‘streamwise’
direction, whilst in the other a temporal form is assumed. In both cases it is possible
to extend the analysis to consider a continuous spectrum of disturbances that decay
algebraically in the wall-normal direction. We note some obvious parallels that exist
between such stability analyses and the approach to the continua of states described
earlier in the paper.We also discuss the appearance of analogous non-unique states to the Falkner–Skan
equation in the presence of an adverse pressure gradient (i.e. n < 0) in an appendix.
Enzyme Reaction Engineering: Effect of Methanol on the Synthesis of Antibiotics Catalyzed by Immobilized Penicillin G Acylase under Isothermal and Non‐Isothermal Conditions
Authors: Travascio P. , Zito E. , Portaccio M. , Diano N. , Grano V. , Martino S. Di , Bertolini T. , Rossi S. , Mita D. G. 
Published: October 2002

AbstractThe effect of methanol on the kinetically controlled synthesis of cephalexin by free and immobilized penicillin G acylase (PGA) was investigated. Catalytic and hydrophobic membranes were obtained by chemical grafting, activation, and PGA immobilization on hydrophobic nylon supports. Butyl methacrylate (BMA) was used as graft monomer. Increasing concentrations of methanol were found to cause a greater deleterious effect on the activity of free than on that of the immobilized enzyme. Methanol, however, improved the kinetic stability of cephalexin synthesized by free PGA, resulting in higher maximum yields. By contrast, immobilized PGA reached 100% yields even in the absence of the cosolvent. Cephalexin synthesis by the catalytic membrane was also performed in a non‐isothermal bioreactor. Under these conditions, a 94% increase of the synthetic activity and complete conversion of the limiting substrate to cephalexin were obtained. The addition of methanol reduced the non‐isothermal activity increase. The physical cause responsible for the non‐isothermal behavior of the hydrophobic catalytic membrane was identified in the process of thermodialysis.
Feedback Stabilization of Fed‐Batch Bioreactors: Non‐Monotonic Growth Kinetics
Authors: Smets Ilse Y. , Bastin Georges P. , Van Impe Jan F. 
Published: October 2002

AbstractThis paper deals with the design of a feedback controller for fed‐batch microbial conversion processes that forces the substrate concentration CS to a desired setpoint CS*, starting from an arbitrary (initial) substrate concentration when non‐monotonic growth kinetics apply. This problem is representative for a lot of industrial fermentation processes, with the baker's yeast fermentation as a well‐known example. It is assumed that the specific growth rate μ is function of the substrate concentration only. A first approach exploits the availability of on‐line measurements of both the substrate and biomass concentration. A second approach is merely based on on‐line measurements of the biomass concentration, which provide an estimate for the specific growth rate. After a reformulation of the substrate concentration setpoint into a specific growth rate setpoint, it is demonstrated that the fed‐batch process can still be stabilized around any desired operating point along the non‐monotonic kinetics.
Pulse Experiments as a Prerequisite for the Quantification of in Vivo Enzyme Kinetics in Aromatic Amino Acid Pathway of Escherichia coli
Authors: Schmitz M. , Hirsch E. , Bongaerts J. , Takors R. 
Published: October 2002

AbstractGlucose pulse experiments were performed to elucidate their effects on the carbon flux into the aromatic amino acid pathway in different Escherichia coli strains. Using a 3‐deoxy‐d‐ arabino‐heptulosonate 7‐phosphate (DAHP, aroB‐)‐producing strain, a fed‐batch fermentation strategy specialized for glucose pulse experiments was developed and further applied for 3‐dehydroshikimate (DHS, aroE‐)‐ and shikimate 3‐phosphate (S3P, aroA‐)‐producing E. coli strains. The strains overexpress a feedback‐resistant DAHP synthase and additional enzymes to prevent rate‐limiting steps in the aromatic amino acid pathway. Changes of carbon flux into the aromatic amino acid pathway were determined via extracellular metabolite accumulations using 1H NMR and HPLC measurements. As an important result, a close relationship between pulse intensity and aromatic metabolite formation rates was identified. The more downstream an aromatic pathway intermediate was located, the stronger the glucose pulse intensity had to be in order to detect significant changes in product formation. However, with the experimental conditions chosen, changes after pulse were detected even for shikimate 3‐phosphate, the most downstream accumulating metabolite of this experimental series. Hence glucose pulse experiments are assumed to be a promising tool even for the analysis of final pathway products such as, for example, l‐phenylalanine.
Validation and Use of an Enzymic Time‐Temperature Integrator to Monitor Thermal Impacts Inside a Solid/Liquid Model Food
Authors: Guiavarc'h Yann P. , Dintwa Edward , Van Loey Ann M. , Zuber François T. , Hendrickx Marc E. 
Published: October 2002

AbstractHeat denaturation kinetics of Bacillus licheniformis α‐amylase, equilibrated at 81% equilibrium relative humidity at 4 °C (BLA81), was studied with help of isothermal and nonisothermal conditions by monitoring the decrease in enthalpy associated with the heat denaturation of the enzyme. Due to its low water content, BLA81 denaturation could be studied in the range of 118–124 °C. Two batches of BLA81 were successfully validated under nonisothermal conditions allowing the determinations of process values (reference temperature of 121.1 °C) in the range of 1–15 min. In a second step, BLA81 was used as a time‐temperature integrator (TTI) to investigate potential differences of process values received by freely moving spherical particles as compared to a centrally fixed particle (single‐position impact) inside cans containing water as brine. Results showed that the process value received by freely moving particles can be from 5.6% (4 rpm) to 19.7% (8 rpm) smaller than the process value received by the centrally fixed sphere. This means that evaluating the process value by means of a particle fixed at the critical point in a package can lead to potentially overestimations of the actual process value with possible hazardous quality/safety implications. These results highlight the potentials of the TTI technology to monitor the safety of heat‐processed agitated solid/liquid foodstuffs.
Picoliter‐Scale Protein Microarrays by Laser Direct Write
Authors: Ringeisen B. R. , Wu P. K. , Kim H. , Piqué A. , Auyeung R. Y. C. , Young H. D. , Chrisey D. B. , Krizman D. B. 
Published: October 2002

AbstractWe demonstrate the accurate picoliter‐scale dispensing of active proteins using a novel laser transfer technique. Droplets of protein solution are dispensed onto functionalized glass slides and into plastic microwells, activating as small as 50‐μm diameter areas on these surfaces. Protein microarrays fabricated by laser transfer were assayed using standard fluorescent labeling techniques to demonstrate successful protein and antigen binding. These results indicate that laser transfer does not damage the active site of the dispensed protein and that this technique can be used to successfully fabricate a functioning protein microarray. Also, as a result of the efficient nature of the process, material usage is reduced by two to four orders of magnitude compared to conventional pin dispensing methods for protein spotting.
Using a CFD Model To Understand the Fluid Dynamics Promoting E. coli Breakage in a High‐Pressure Homogenizer
Authors: Miller J. , Rogowski M. , Kelly W. 
Published: October 2002

AbstractA Computational Fluid Dynamic (CFD) model of flow in a high‐pressure homogenizing valve (APV Gaulin model 30CD) was developed with the Fluent software. The 2D model consists of an unstructured hexagonal mesh, dense in the regions of high gradients. The flow (single‐phase) was modeled as laminar upstream of and in the channel (gap) and turbulent downstream of the channel exit. Applying a realizable κ‐ϵ turbulence model, the CFD model accurately predicted the effect of gap space on fluid dynamic conditions upstream (inlet pressure and pressure gradient) and downstream (impact pressure) of the channel for a valve with a standard (CD‐0) impact distance (0.25 mm) and a 1 cP fluid. This CFD model was then used to estimate the magnitude of the fluid dynamic parameters (except cavitation effects) presumed to be responsible for cell breakage, as a function of gap space, impact distance and fluid viscosity. The CFD models predicted that for a given volumetric flowrate the upstream fluid conditions (inlet pressure gradient, maximum channel strain rate) and the maximum energy dissipation rate in the post‐gap jet depend only on the gap space and the fluid viscosity and not on the impact distance. The impact pressure however depends on the gap spacing, the fluid viscosity and especially the impact distance. Experimental results indicate that higher inlet pressures are required to break cells, if the impact distance is increased. By conducting experiments to isolate individual cell breakage mechanisms for a single pass, threshold values were identified for breaking Escherichia coli cells: pressure gradient, 1.2 × 1012 Pa/m; energy dissipation rate, 1.0 × 1010 m3/s2; and impact pressure, 160 psig. By isolating the wall impact as the sole mechanism responsible for breaking the E. coli cells between 3000 and 6000 psig inlet pressure, a relationship between E. coli cell breakage rate and maximum wall impact pressure was established (eq 5).
Factors Affecting the Composition of Oligosaccharides Produced in Chitosan Hydrolysis Using Immobilized Chitosanases
Authors: Kuroiwa Takashi , Ichikawa Sosaku , Hiruta Osamu , Sato Seigo , Mukataka Sukekuni 
Published: October 2002

AbstractThe hydrolysis reaction of chitosan using immobilized chitosanases with regard to the composition of its products and the yield of the intermediate target products, pentamer and hexamer of chitosan oligosaccharides, was investigated. Chitosanase was immobilized onto agar or agarose gel particles by the multipoint attachment method. In batch experiments, surface enzyme density, support particle size, temperature, agitator speed, and initial substrate concentration significantly affected the composition of the oligosaccharides produced. It was believed that these factors all related to the reaction rate and mass transfer rate at the surface of the support materials immobilizing the enzymes. These effects were summarized as a correlation with Damköhler number ( Da), defined as the ratio of the maximum reaction rate to the maximum mass transfer rate. The result showed that the reaction conditions that give a low value of Da provide a high yield of pentamer and hexamer oligosaccharides.
Polymerization of Glucans by Enzymatically Active Membranes
Authors: Becker Margot , Provart Nicholas , Lehmann Ingeburg , Ulbricht Mathias , Hicke Hans‐Georg 
Published: October 2002

AbstractConventional enzyme membrane reactors are not appropriate for a continuous synthesis of macromolecules and simultaneous product release. By immobilizing the enzyme in sufficiently large pores of a membrane an ensemble of miniaturized bioreactors is created. Product molecules are continuously removed from the enzyme by the flow of the reaction mixture across the membrane. Additionally, by varying the flow rate, it ought to be possible to influence the substrate as well as the enzyme‐product residence times and thereby the product macromolecule's size. In this paper we present the first results of experiments involving enzymatic 1,4‐α‐glucan synthesis, using sucrose as substrate, maltooligosaccharides (DP 3–6) as primers, and membrane‐immobilized amylosucrase. Epoxy groups for a covalent enzyme immobilization were generated on polypropylene microfiltration membranes by heterogeneous photoinitiated graft polymerization of glycidyl methacrylate. The influence of primer concentration and flow rate through the enzyme‐membrane on amylosucrase activity, molecule growth, and coupling efficiency for glucose (% of coupled glucose versus free glucose) were investigated. The enzymatically mediated chain elongation of maltooligosaccharides by the successive addition of glucose units was achieved for the first time in a transmembrane process utilizing amylosucrase membranes.
Adaptive, Model‐Based Control by the Open‐Loop‐Feedback‐Optimal (OLFO) Controller for the Effective Fed‐Batch Cultivation of Hybridoma Cells
Authors: Frahm Björn , Lane Paul , Atzert Hendrik , Munack Axel , Hoffmann Martin , Hass Volker C. , Pörtner Ralf 
Published: October 2002

AbstractAlthough fed‐batch suspension culture of animal cells continues to be of industrial importance for the large scale production of pharmaceutical products, existing control concepts are still insufficient. Changes in cell metabolism during cultivation and between similar cultivations, the complexity of the cell metabolism, and the lack of on‐line state variables restrict the transfer of available control strategies established in bioprocess engineering. A process control strategy designed to achieve optimized process control must account for all these difficulties and fit sophisticated requirements toward adaptability and flexibility. The combination of a fed‐batch process and an Open‐Loop‐Feedback‐Optimal (OLFO) control provides a new approach for cell culture process control that couples an efficient cultivation concept to a capable process control strategy. The application of an adaptive, model‐based OLFO controller to a hybridoma cultivation and experimental results are presented.
Enzyme‐Carrying Polymeric Nanofibers Prepared via Electrospinning for Use as Unique Biocatalysts
Authors: Jia Hongfei , Zhu Guangyu , Vugrinovich Bradley , Kataphinan Woraphon , Reneker Darrell H. , Wang Ping 
Published: October 2002

AbstractImprovement of catalytic efficiency of immobilized enzymes via materials engineering was demonstrated through the preparation of bioactive nanofibers. Bioactive polystyrene (PS) nanofibers with a typical diameter of 120 nm were prepared and examined for catalytic efficiency for biotransformations. The nanofibers were produced by electrospinning functionalized PS, followed by the chemical attachment of a model enzyme, α‐chymotrypsin. The observed enzyme loading as determined by active site titration was up to 1.4% (wt/wt), corresponding to over 27.4% monolayer coverage of the external surface of nanofibers. The apparent hydrolytic activity of the nanofibrous enzyme in aqueous solutions was over 65% of that of the native enzyme, indicating a high catalytic efficiency as compared to other forms of immobilized enzymes. Furthermore, nanofibrous α‐chymotrypsin exhibited a much‐improved nonaqueous activity that was over 3 orders of magnitude higher than that of its native counterpart suspended in organic solvents including hexane and isooctane. It appeared that the covalent binding also improved the enzyme's stability against structural denaturation, such that the half‐life of the nanofibrous enzyme in methanol was 18‐fold longer than that of the native enzyme.
Production of a Polyester Degrading Extracellular Hydrolase from Thermomonospora fusca
Authors: Gouda Mona K. , Kleeberg Ilona , van den Heuvel Joop , Müller Rolf‐Joachim , Deckwer Wolf‐Dieter 
Published: October 2002

AbstractThe production of a polyester‐degrading hydrolase from the thermophilic actinomycete Thermomonospora fusca was investigated with regard to its potential technical application. Only in the presence of a polyester (random aliphatic‐aromatic copolyester from 1,4‐butanediol, terephthalic acid, and adipic acid with around 40–50 mol % terephthalic acid in the acid component), the excretion of the extracellular enzyme could be achieved with an optimized synthetic medium using pectin and NH4Cl as nitrogen source. Compared to complex media, a significantly higher specific activity at comparable volumetric yields could be obtained, thus reducing the expenditure for purification. The activity profile in the medium is controlled by a complex process involving (1) induction of enzyme excretion, (2) enzyme adsorption on the hydrophobic polyester surface, (3) inhibition of enzyme generation by monomers produced by polyester cleavage, and (4) enzyme denaturation. Diafiltration with cellulose acetate membranes as the sole downstream processing step led to a product of high purity and with sufficient yield (60% of total activity). Scaling‐up from shaking flasks to a fermentor scale of 100 L revealed no specific problems. However, the excretion of the hydrolase by the actinomycete turned out to be inhibited by the degradation products (monomers) of the aliphatic‐aromatic copolyester used as inductor for the enzyme production. The crude enzyme exhibited generally similar properties (temperature and pH optimum) as the highly purified hydrolase described previously; however, the storage capability and thermal stability is improved when the crude enzyme solution is diafiltrated.
Microbial Hydrogen Production with Immobilized Sewage Sludge
Authors: Wu Shu‐Yii , Lin Chi‐Num , Chang Jo‐Shu , Lee Kuo‐Shing , Lin Ping‐Jei 
Published: October 2002

AbstractMunicipal sewage sludge was immobilized to produce hydrogen gas under anaerobic conditions. Cell immobilization was essentially achieved by gel entrapment approaches, which were physically or chemically modified by addition of activated carbon (AC), polyurethane (PU), and acrylic latex plus silicone (ALSC). The performance of hydrogen fermentation with a variety of immobilized‐cell systems was assessed to identify the optimal type of immobilized cells for practical uses. With sucrose as the limiting carbon source, hydrogen production was more efficient with the immobilized‐cell system than with the suspended‐cell system, and in both cases the predominant soluble metabolites were butyric acid and acetic acid. Addition of activated carbon into alginate gel (denoted as CA/AC cells) enhanced the hydrogen production rate ( vH2) and substrate‐based yield ( YH2/sucrose) by 70% and 52%, respectively, over the conventional alginate‐immobilized cells. Further supplementation of polyurethane or acrylic latex/silicone increased the mechanical strength and operation stability of the immobilized cells but caused a decrease in the hydrogen production rate. Kinetic studies show that the dependence of specific hydrogen production rates on the concentration of limiting substrate (sucrose) can be described by Michaelis‐Menten model with good agreement. The kinetic analysis suggests that CA/AC cells may contain higher concentration of active biocatalysts for hydrogen production, while PU and ALSC cells had better affinity to the substrate. Acclimation of the immobilized cells led to a remarkable enhancement in vH2 with a 25‐fold increase for CA/AC and ca. 10‐ to 15‐fold increases for PU and ALSC cells. However, the ALSC cells were found to have better durability than PU and CA/AC cells as they allowed stable hydrogen production for over 24 repeated runs.
Cell Population Modeling and Parameter Estimation for Continuous Cultures of Saccharomyces cerevisiae
Authors: Mhaskar Prashant , Hjortsø Martin A. , Henson Michael A. 
Published: October 2002

AbstractSaccharomyces cerevisiae is known to exhibit sustained oscillations in chemostats operated under aerobic and glucose‐limited growth conditions. The oscillations are reflected both in intracellular and extracellular measurements. Our recent work has shown that unstructured cell population balance models are capable of generating sustained oscillations over an experimentally meaningful range of dilution rates. A disadvantage of such unstructured models is that they lack variables that can be compared directly to easily measured extracellular variables. Thus far, most of our work in model development has been aimed at achieving qualitative agreement with experimental data. In this paper, a segregated model with a simple structured description of the extracellular environment is developed and evaluated. The model accounts for the three most important metabolic pathways involved in cell growth with glucose substrate. As compared to completely unstructured models, the major advantage of the proposed model is that predictions of extracellular variables can be compared directly to experimental data. Consequently, the model structure is well suited for the application of estimation techniques aimed at determining unknown model parameters from available extracellular measurements. A steady‐state parameter selection method developed in our group is extended to oscillatory dynamics to determine the parameters that can be estimated most reliably. The chosen parameters are estimated by solving a nonlinear programming problem formulated to minimize the difference between predictions and measurements of the extracellular variables. The efficiency of the parameter estimation scheme is demonstrated using simulated and experimental data.