bluuebunny/crossref_metadata_2025_split huggingface dataset:
How to analyze the investment–uncertainty relationship in real option models?
Authors: Lund Diderik 
Published: March 2005

AbstractThe real options tradition originally predicted a decreasing relationship between uncertainty and investment, through the positive effect of higher uncertainty on the trigger level for revenue relative to costs. An opposing effect on the probability of reaching the level has been identified, yielding a total effect with ambiguous sign. This paper makes three points. The “opposing” effect is not always opposing. Systematic risk cannot generally be assumed to increase with volatility. A probability is not the best measure of investment. The sign of the total effect is again ambiguous. This ambiguity is illustrated, depending on specification of model and parameters.
Characterization of Transient Cultures of Clostridium acetobutylicum
Authors: Srivastava Ashok K. , Volesky Bohumil 
Published: March 2005

AbstractThe inability of unstructured mathematical models to acknowledge complex intracellular physiological changes limits their applicability for dynamic culture growth conditions. By considering RNA as a bottleneck growth‐limiting compound, a structured model was developed to describe the transient and steady‐state growth of Clostridium acetobutylicum. The linear relationship between the on‐line NADH fluorescence and the sugar utilization specific rates was incorporated in the mathematical model to facilitate in situ assessment of the culture metabolic activity. The improved performance of the proposed structured model was demonstrated. It simulated the transient culture metabolism better than the unstructured Monod model. However, it still failed to simulate the metabolic switchover between acidogenic and solventogenic Clostridium culture behavior.
Enhancement of External Mass Transfer by Gaseous End Products
Authors: Huisman Jan W. , Van Den Heuvel Johannes C. , Ottengraf Simon P. P. 
Published: March 2005

AbstractThe conversion rate of biological particles is affected by the mass transfer rate in the particle and the surrounding liquid film. The influence of gas production on the external mass transfer rate was investigated in an inorganic model system, consisting of strong acid ion‐exchange particles converting a sodium bicarbonate solution. The enhancement by the evolution of carbon dioxide amounted to a factor of 4 compared to sodium hydroxide as a reference. The consequences of the experimental results for biological systems are discussed, and it is concluded that the conversion rate might considerably be influenced under conditions of low turbulence. However, no substantial acceleration by the investigated mechanism is to be expected for suspended biological particles, due to the relatively low gas flux at the surface of the particle.
Effects of Dissolved Oxygen on Hybridoma Cell Growth, Metabolism, and Antibody Production Kinetics in Continuous Culture
Authors: Ozturk Sadettin S. , Palsson Bernhard Ø 
Published: March 2005

AbstractThe effects of dissolved oxygen concentration (DO) on hybridoma cell physiology were examined in a continuous stirred tank bioreactor with a murine hybridoma cell line (167.4G5.3). Dissolved oxygen concentration was varied between 0% and 100% air saturation. Cell growth and viability, carbohydrate, amino acid, and energy metabolism, oxygen uptake, and antibody production rates were investigated. Cell growth was inhibited at both high and low DO. Cells could grow at 0% DO and maintain viability under a nitrogen atmosphere. Cell viability was higher at low DO. Glucose, glutamine, and oxygen consumption rates changed little at DO above 1 % air saturation. However, the metabolic uptake rates changed below 1 % DO, where growth became oxygen limited, and a Km value of 0.6 % DO was obtained for the specific oxygen uptake rate. The metabolic rates of glucose, glutamine, lactate, and ammonia increased 2‐3‐fold as the DO dropped from 1% to 0%. Amino acid metabolism followed the same general pattern as that of glutamine and glucose. Alanine was the only amino acid produced. The consumption rates of amino acids changed little above 1% DO, but under anaerobic conditions the consumption rates of all amino acids increased severalfold. Cells obtained most of their metabolic energy from glutamine oxidation except under oxygen limitation, when glucose provided most of the energy. The calculated ATP production rate was only slightly influenced by DO and rose at 0% DO. Antibody concentration was highest at 35% DO, while the specific antibody production rate was insensitive to DO.
Plant Cell Culture Using a Novel Bioreactor: The Magnetically Stabilized Fluidized Bed
Authors: Bramble Joye L. , Graves David J. , Brodeliust Peter 
Published: March 2005

AbstractA novel bioreactor using magnetically stabilized fluidized bed (MSFB) technology has been developed that has certain advantages for cultivating cells continuously. In this system, the cells are protected from shear and are constrained to move through the fermenter in lock‐step fashion by being immobilized in calcium alginate beads. The MSFB permits good mass transfer, minimizes particle collisions, and allows for the production of cells while maintaining a controlled cell residence time. Details of the experimental system are described. In addition, the experimental performance of an MSFB used to grow plant cells in batch mode is compared to the results obtained in shake flask culture.
Quantitation of Cell Area on Glass and Fibronectin‐Coated Surfaces by Digital Image Analysis
Authors: Truskey George A. , Proulx Timothy L. 
Published: March 2005

AbstractBy using digital image processing and analysis, two procedures were developed to rapidly measure the projected area of a field of adherent 3T3 fibroblasts without staining of cell borders. The cell area of newly attached and rounded cells with well‐resolved borders was obtained by a gray value thresholding procedure. For cells that had undergone an appreciable degree of spreading, cell boundaries were less distinct and a nonlinear spatial Sobel filter was used, followed by thresholding. For both procedures, linear relations were observed between cell areas obtained from image analysis and cell areas obtained by tracing. The areas of a population of traced cells were not statistically different from the area distribution obtained by using the standard curves for the processed images. Uncertainty in the estimated mean area depended only upon the number of cells examined. Approximate numbers of cells required to obtain estimates of the mean are calculated. As an application of these procedures, cell areas were measured for 3T3 cells attached to glass and fibronectin‐coated surfaces and were found to be significantly larger for cells spreading on fibronectin‐coated glass than on glass alone. Increased cell area during spreading on fibronectin‐coated surfaces was proportional to increased cell adhesivity after exposure to a shear stress of 58 dyn/cm2.
Rapid Immunoassay Technique for Process Monitoring of Animal Cell Fermentations
Authors: Jervis E. , Kilburn D. G. 
Published: March 2005

AbstractA calibration and quality control technique suited to process monitoring with immunoassay is demonstrated. The particle concentration fluorescence immunoassay (PC‐FIA) is shown to provide a sensitive and rapid method for the quantification of specific biomolecules in cell cultures. Smoothing of linear calibration parameters is performed by forming weighted averages of standard points as the run progresses. These estimates are then used to determine slope and intercept values for improved calibration. The nonuniformity of the fluorescent signal variance is also considered, and a weight model is developed to describe the relationship between signal fluorescence and signal variance for weighted linear curve fitting. Pooling calibration results over the process run improves overall assay performance as determined by using standard control chart analysis. This method is suitable for semicontinuous monitoring of animal cell fermentations and has been used here to measure cell‐associated and culture supernatant concentrations of monoclonal antibody (Ab) from hybridoma cells. The cell‐associated Ab concentration correlates with cell‐specific production rate. Assay times on the order of 10 min for supernatant and 25–30 min for cell‐associated Ab concentrations can be achieved, making this procedure suitable for process monitoring and control. Under these conditions the assay has a detection limit of approximately 10 ng/mL, providing a sensitive and specific method for the quantification of cell culture constituents.
Protein Recovery from Reversed Micellar Solutions through Contact with a Pressurized Gas Phase
Authors: Phillips John B. , Nguyen Huyen , John Vijay T. 
Published: March 2005

AbstractWe describe a new process for the recovery of encapsulated protein from reversed micellar solution in concentrated form. The method involves desolubilization of the protein by decreasing solvent density through gas dissolution. Under appropriate thermodynamic conditions, the micellar water pool can be converted to clathrate hydrates. Protein recovery is facilitated by clathrate hydrate formation, which causes the desolubilized protein to exist in a solid phase, distinct from the micellar supernatant. The process is carried out without any ionic strength or pH modification.
Enhancing Oxygen Transfer in Bioreactors by Perfluorocarbon Emulsions
Authors: Ju Lu‐Kwang , Lee Jaw Fang , Armiger William B. 
Published: March 2005

AbstractThis work aims to investigate the capability of perfluorocarbon (PFC) emulsions in enhancing oxygen transfer in bioreactors. Based on the penetration theory, a model has been derived for evaluating the potential oxygen transfer enhancement effects of PFC emulsions with very fine PFC particles. Defined as the ratio between the maximum oxygen transfer rates in systems with and without the emulsions, the enhancement factor achievable with dilute PFC emulsions can be estimated as the square root of the product of ratios of oxygen permeability and solubility in media with and without the emulsions. The effect of PFC emulsions on oxygen transfer in low‐shear cultivation systems was further studied experimentally with direct measurements of volumetric oxygen transfer coefficients, 𝔨Lα, in bioreactors and with microbial fermentations conducted under low‐shear conditions. It was found that significantly higher cell populations could be maintained at an aerobic state by using systems supplemented with the investigated emulsions. The experimentally determined values of oxygen transfer enhancement factor compare well with the theoretical values for emulsions with up to 15% (v/v) PFC. The feasibility of enhancing oxygen transfer in bioreactors by introduction of adequate amounts of PFC emulsions was clearly demonstrated.
Protein Isolation by Solution‐Controlled Gel Sorption
Authors: Gehrke Stevin H. , Robeson Julie , Johnson James Fred , Vaid Nitin 
Published: March 2005

AbstractIllustrated are the principles for isolating proteins from solution by sorption into a polymer gel phase, driven by the addition of a water‐soluble polymer to the protein solution. The separation is shown to be analogous to conventional two‐phase aqueous extraction. However, the use of a gel phase rather than a solution for absorbing the protein makes separation of the protein from the polymer and the recycling of the gel phase much simpler. The model system used was linear poly(ethylene glycol) (PEG) and dextran gel. Increasing the molecular weight and concentration of the PEG favored sorption by the gel of ovalbumin, bovine serum albumin, cytochrome c, and hemoglobin. The proteins could be quantitatively recovered by immersing the gel in PEG‐free solution.
A Microperifusion System with Environmental Control for Studying Insulin Secretion by Pancreatic Tissue
Authors: Dionne Keith E. , Colton Clark K. , Yarmush Martin L. 
Published: March 2005

AbstractA continuous flow reactor (perifusion system) was fabricated and tested for measuring the kinetics of insulin secretion from isolated pancreatic islets of Langerhans in response to step changes in the glucose concentration and oxygen partial pressure in the perfusate flowing around the islets. The system was capable of making rapid changes in perfusate glucose concentration and pO2, had rapid dynamic response for measuring the change in insulin secretion rate as a result of these changes in perfusate, and was suitable for studying very small volumes of tissue. Initial experiments with this system demonstrated that (1) the response of isolated rat islets to glucose stimulation was very fast, with the first phase peak occurring in as little as about 10 s, (2) bulk perfusate oxygen partial pressure levels of 30 mmHg or less reduced the second‐phase insulin secretion rate in graded fashion, (3) the reduction in secretion rate began within 1 min following an oxygen partial pressure decrease, and (4) the reduction in secretion rate was reversible, with a burst of insulin secretion occurring during the first minute after partial pressure restoration.
Insect Cell Hosts for Baculovirus Expression Vectors Contain Endogenous Exoglycosidase Activity
Authors: Licari Peter J. , Jarvis Donald L. , Bailey James E. 
Published: March 2005

AbstractFour different insect cell lines that can be used as hosts for baculovirus infection were assayed for the presence of endogenous exoglycosidases. All four cell lines, derived from Spodoptera frugiperda, Trichoplusia ni, Bombyx mori, or Malacosoma disstria, contained N‐acetyl‐β‐glucosaminidase, N‐acetyl‐β‐galactosaminidase, β‐galactosidase, and sialidase activities. Exoglycosidase activities were found in cell lysates as well as cell‐free supernatants from uninfected and wild‐type baculovirus infected cells. Oligosaccharide analysis of cellular glycoproteins using lectins recognizing Galβ1, 3GalNAc, Galβ1, 4GlcNAc, and NeuAcα2, 6Gal demonstrated that only Galβ1,3GalNAc was present. The demonstration that these cells contain exoglycosidases raises the possibility that the oligosaccharides of baculovirus‐expressed glycoproteins are subject to enzymatic degradation.
Transient Stirred‐Tank Reactors Operating with Immobilized Enzyme Systems: Analysis and Simulation Models and Their Experimental Checking
Authors: Santoyo A. Bódalo , Carrasco J. L. Gómez , Gómez E. Gómez , Rodriguez J. Bastida , Morales E. Martinez 
Published: March 2005

AbstractA mathematical model applicable to the analysis, design, and simulation of heterogeneous enzymatic processes reacting in a stirred‐tank reactor has been formulated. The model develops the unsteady‐state design equations for such reactors and also the diffusion reaction equation in the spherical catalyst particles for reversible Michaelis—Menten kinetics. This structured general model provides an overview of almost all of the processes occurring in an immobilized enzyme reactor system. Although the analysis presented here is limited to certain situations, it can be extended to other support geometries, enzyme kinetics, and reactor configurations. To check the model, the experimental data obtained with immobilized β‐galactosidase were compared to those theoretically predicted.
Plasmid Stability in Immobilized Mixed Cultures of Recombinant Escherichia coli
Authors: Dincbas Vildan , Hortacsu Amable , Camurdan Agnes 
Published: March 2005

AbstractThe growth behavior of a mixed culture of plasmid‐free and plasmid‐containing (YEp352) Escher chia coli HB101 cells in free suspension and immobilized conditions was studied experimentally. It was found that immobilization in calcium alginate beads delayed the reduction of the plasmid‐containing fraction for a period of time inversely related to the total number of cells initially immobilized. A simple unstructured model that assumes compartmentalization of cells in the immobilization matrix at the beginning of growth gave a fit which was in good agreement with the data.
Preparation and Characterization of Bifunctional Unilamellar Vesicles for Enhanced Immunosorbent Assays
Authors: Jones Matthew A. , Kilpatrick Peter K. , Carbonell Ruben G. 
Published: March 2005

AbstractSmall unilamellar phospholipid vesicles with covalently attached biotin and horseradish peroxidase (HRP) were prepared and characterized in terms of hydrodynamic diameter, amount and activity of immobilized enzyme, and number of biotin molecules on the outer vesicle surface. In addition, the specific adsorption of these bifunctional vesicles and commercially available biotin‐labeled horseradish peroxidase (B‐HRP) to anti‐biotin antibody (ABA) coated polystyrene microtiter plate welis was examined. At low antibody surface densities, the signal (ΔA/min) generated by the vesicles adsorbed to the surface was approximately 100 times higher than the signal generated by B‐HRP. It was also found that the biotin‐conjugated vesicles were able to compete effectively with free biotin in solution for surface ABA sites. These results indicate that this type of vesicle may be used in competitive and sandwich‐type enzyme‐linked immunoassays to improve the detection limits, increase the signal, and decrease the reaction time necessary to detect a given analyte concentration in solution.
Binding Kinetics of Antigen by Immobilized Antibody or of Antibody by Immobilized Antigen: Influence of Lateral Interactions and Variable Rate Coefficients
Authors: Sadana Ajit , Madugula A. 
Published: March 2005

AbstractKinetic rate expressions are developed for the binding kinetics of antigen by immobilized antibody or of antibody by immobilized antigen. The influence of lateral interactions leads to variable rate coefficients for adsorption, and these provide a more realistic picture of the events occurring on the surface. Emphasis is placed on the similarities and dissimilarities present in the kinetic rate expressions. A general trend in the rate expressions is observed on going from dual‐step binding to dual‐step binding with lateral interactions. This provides physical insights into the reactions occurring at the surface and helps in their control and stability at the surface.
Construction and Characterization of a Specialized Ribosome System for the Overproduction of Proteins in Escherichia coli
Authors: Leipold Robert J. , Dhurjati Prasad 
Published: March 2005

AbstractA recombinant Escherichia coli system was constructed to overexpress proteins using the specialized ribosomes developed by Herman de Boer and co‐workers at Genentech. Specialized ribosomes carry a mutation in the anti‐Shine—Dalgarno region of 16 S ribosomal RNA, which is the site of messenger RNA binding. A complementary mutation in the ribosome binding site (the Shine‐Delgarno region) of a particular mRNA results in specific and efficient translation of this mRNA on the specialized ribosomes. Production of β‐galactosidase with this system was characterized with respect to transcription, translation, plasmid replication, and cell growth rate. Translation of specialized mRNA on specialized ribosomes gave 5 times more enzyme activity than did translation of wild‐type mRNA on wild‐type ribosomes under similar conditions. The system described here offers a number of advantages when compared to a similar system described recently: (1) two separate specialized systems were constructed; (ii) the genes for specialized mRNA and specialized rRNA are on separate plasmids, allowing for different combinations of mRNA and rRNA; and (iii) appropriate controls were constructed for each plasmid.
Effects of Oxygen/Glucose/Glutamine Feeding on Insect Cell Baculovirus Protein Expression: A Study on Epoxide Hydrolase Production
Authors: Wang Min‐Ying , Kwong Simon , Bentley William E. 
Published: March 2005

AbstractThe recombinant protein yields for batch cultures of the insect cell baculovirus expression system have been significantly enhanced by oxygen, glucose, and glutamine feeding. The improvement in both volumetric and specific yields was based on influencing the metabolism of infected cells. Oxygen was absolutely required for viral replication and high protein expression in infected cells. Increases of 200% in volumetric yield and 100% in specific yield of recombinant epoxide hydrolase were achieved by controlling the dissolved oxygen (DO) level to near 35% saturation. An additional 100% increase was achieved by glucose and glutamine feeding. Results indicated that the intracellular metabolite pool was not adequate for recombinant protein overproduction. Finally, the specific protein yield, based on initial infection cell density, in high cell density spinner flasks and bioreactors of spent media with glucose and glutamine feeding was equivalent to that of freshly diluted cultures.
Modular Neural Networks for Identification of Starches in Manufacturing Food Products
Authors: Huang Y. W. , Mithani R. , Takahashi K. , Fan L. T. , Seib P. A. 
Published: March 2005

AbstractNeural network technology, especially that related to or derived from the multilayered Perceptron model with the back‐propagation learning mechanism, has been found to be effective in pattern recognition and classification. Although mentioned infrequently, the number of patterns that can be recognized or classified by a specific neural network based on this technology is inescapably constrained by the network configuration such as the numbers of input, output, and hidden units. A direct expansion, e.g., increasing the numbers of the various units, of an existing network to accommodate additional patterns is usually undesirable for two reasons. First, a complete retraining of the network, incorporating the learned and new patterns as the training set, is necessary. Second, such a retraining almost always proceeds at a decreasing rate and is more difficult to converge. Both of these problems can be circumvented, at least partially, by resorting to the concept of modular neural networks. In the present work, each of two multilayered neural networks is trained to recognize eight types of starches used in foods. Subsequently, the two trained networks are coupled as modules of a final network. The learning rate of the final network is found to be much faster than that of a nonmodularized network with the same configuration.
Evaluation of Column Flotation in the Downstream Processing of Fermentation Products: Recovery of a Genetically Engineered α‐Amylase
Authors: Miranda Everson A. , Berglund Kris A. 
Published: March 2005

AbstractFlotation is a simple, inexpensive, and versatile unit operation with a largely unexplored potential in biotechnology. There is a general lack of research concerning biotechnological applications in this area, especially in the recovery of fermentation products. Moreover, the few reports in the literature do not consider the modern concept of column flotation as practiced in the mineral industry. We report herein the application of column flotation for the recovery of a Bacillus stearothermophilus α‐amylase expressed in Escherichia coli by the use of a food‐grade polymer, (hydroxypropyl)methylcellulose (HPMC), and ammonium sulfate. First, the enzyme was removed from the liquid phase by partition to a salted‐out HPMC phase. The enzyme‐containing polymer floes were then floated from the liquid. Recovery of active enzyme was as high as 90%, with throughput as high as 94 m3/(h.m2). The floatability of the enzyme from a periplasmic extract was higher than extracellular enzyme in the broth due to the presence of depressors of molecular weight lower than 10 000 in the broth.