bluuebunny/crossref_metadata_2025 huggingface dataset:
Brief report: Risk‐taking behaviors in a non‐western urban adolescent sample
Authors: Bayar Nalan , Sayıl Melike
Published: March 2005

This study analyzes the age and gender related risk‐taking behaviors of Turkish adolescents in an urban sample. A self‐report risk taking scale was administered to 280 adolescents between the ages of 12–21. Results revealed that both the type and the frequency of risk‐taking behaviors were changed according to age and gender. All risky behaviors except hitchhiking increased until the college level and than decreased. Boys outperformed the girls in most of the risk‐taking behaviors.
Optimal Temperature Control Policy for a Two‐Stage Recombinant Fermentation Process
Authors: Hortacsu Amable , Ryu Dewey D. Y.
Published: March 2005

The optimal temperature control policy to be followed in the operation of a two‐stage fermentation system in which gene expression is induced by a temperature‐sensitive gene switching system was studied. A genetically structured model was used to describe product formation, and kinetic equations based on experimental data were used to quantify the specific gene expression rate and parameters that affect plasmid instability. A constant temperature control policy and temperature profiling control policy including temperature cycling were studied and compared. Maximum average production rate was obtained from a temperature control policy in which the second stage was operated initially at about 40.5 °C and the temperature decreased slightly to a constant value at 40.0 °C. The maximum average production rate, which corresponds to the optimal temperature control policy, for an operation of 180 h was 29.7 units of protein (mg of cells)−1 h−1.
Intact Chemoreceptor‐Based Biosensors
Authors: Barker Todd Q. , Buch R. Michael , Rechnitz Garry A.
Published: March 2005

A receptrode biosensor is presented that uses intact chemoreceptor‐based molecular recognition from antennular structures of the Hawaiian swimming crab species Por‐tunis sanguinolentus. The sensor is coupled to a learning, pattern recognition calculation for performing analytical chemistry. Action potential waveforms are used to establish the identity of individual action potential types that can be associated to particular analytes. The pattern recognition calculations used are referred to as cluster analysis (CA) and principal component analysis (PCA). Action potential similarities are determined by using a dendrogram plot of the cluster analysis results and further elucidated by using principal component scores plots. Quantitative analysis was performed after classification of analyte and background responses. Chemoresponses to salinity and trimethylamine N‐oxide, two chemical constituents that are found in the crustacean living environment, were investigated and gave analytic responses over several orders of magnitude.
Monitoring Cell Concentration and Activity by Multiple Excitation Fluorometry
Authors: Li J.‐K. , Asali E. C. , Humphrey A. E. , Horvath J. J.
Published: March 2005

Four key cellular metabolic fluorophores‐tryptophan, pyridoxine, NAD(P)H, and riboflavin‐were monitored on‐line by a multiple excitation fluorometric system (MEFS) and a modified SLM 8000C scanning spectrofluorometer in three model yeast fermentation systems‐bakers' yeast growing on glucose, Candida utilis growing on ethanol, and Saccharomyces cerevisiae RTY110/pRB58 growing on glucose. The measured fluorescence signals were compared with cell concentration, protein concentration, and cellular activity. The results indicate that the behavior and fluorescence intensity of various fluorophores differ in the various fermentation systems. Tryptophan fluorescence is the best signal for the monitoring of cell concentration in bakers' yeast and C. utilis fermentations. Pyridoxine fluorescence is the best signal for the monitoring of cell concentration in the S. cerevisiae RTY110/pRB58 fermentation. In bakers' yeast fermentations the pyridoxine fluorescence signal can be used to monitor cellular activity. The NAD(P)H fluorescence signal is a good indicator of cellular activity in the C. utilis fermentation. For this fermentation NAD(P)H fluorescence can be used to control ethanol feeding in a fed‐batch process.
Phase Transitions of Mixtures of Amorphous Polysaccharides and Sugars
Authors: Roos Yrjö , Karel Marcus
Published: March 2005

Maltodextrins of varying molecular weights, maltose, and sucrose were used to study the effect of molecular weight, water plasticization, and composition on glass transition temperature (Tg). All maltodextrins were plasticized by water, and the decrease of Tg was linear with water activity over the range of 0.11–0.85. The plasticization effect of water was similar for maltodextrins having various molecular weights. Effects of molecular weight and composition on the Tg of maltodextrins could be correlated by using relationships reported previously for polymers. The quantitative results obtained can be applied to formulate food and related materials having desired processability and storage stability.
Novel N‐Halamine Disinfectant Compounds
Authors: Tsao Te‐Chen , Williams Delbert E. , Worley Christopher G. , Worley S. Davis
Published: March 2005

A new series of N‐halamine compounds has been synthesized and tested for stability in aqueous solution and efficacy in inactivating several species of bacteria and algae. The compounds, which are N,N′‐dihalo‐4‐imidazolidinones, are inexpensive to synthesize and appear to have considerable potential as general‐purpose disinfectants. They have greater stability in the laboratory, as well as outdoors in direct sunlight, than do current commercial swimming pool biocides. They also are efficient at sterilizing hard surfaces (stainless steel) and could thus be useful for a variety of household and medical disinfection applications.
Fermentative Production of Injectable‐Grade Calcium Gluconate
Authors: Shah Deepak N. , Kothari Raman M.
Published: March 2005

Optimized economical procedures for the submerged batchwise (250‐L scale) production and recovery of injectable‐grade calcium gluconate are devised. While the optimal parameters of production envisaged the use of Aspergillus niger, salts‐fortified dextrose‐rich production medium, pH 6.5±0.1, 29±1°C, 250±10 rpm, 1.0‐1.5 vol of air (vol of medium)−1 min−1 aeration rate over 24±2h duration, and intermittent neutralization with calcium carbonate, the optimal recovery procedure consisted of charcoal decolorization, vacuum filtration, methanol‐aided precipitation, centrifugation, vacuum drying, and pulverization to provide 85% recovery of calcium gluconate, passing Indian/British pharmacopeial tests for the injectable‐grade preparation.
Determination of Antigenic Characteristics and Stabilities of Mycoplasma hyopneumoniae
Authors: Weng C. N. , Lin S. Y. , Tzan Y. L. , Lee C. J.
Published: March 2005

The aim of this study was to find a titering method that could rapidly and accurately determine the antigenic activities of Mycoplasma hyopneumoniae under specific conditions. By using the enzyme‐linked immunosorbent assay (ELISA) method, the activity of M. hyopneumoniae was found to be affected by acidic environment, temperature, and the existence of trypsins.
Theoretical Analysis of the Effect of Cell Recycling on Recombinant Cell Fermentation Processes
Authors: Park Tai Hyun , Hong Juan , Lim Henry C.
Published: March 2005

A cell recycle system is studied for two‐stage continuous fermentation. Cell recycle around the second stage provides higher cell concentrations than processes without recycle and a longer residence time of the cell, which is necessary for inducible products, especially in recombinant cell fermentation. Residence time distribution of the cell in the fermentor is important for the optimization of inducible products. The residence time distributions are studied for the cases with and without significant cell growth in the second stage. With cell growth in the second stage, three cases are considered. These are the cases of (1) zero residence time for two daughter cells after the cell division, (2) zero residence time of one daughter cell after the cell division and inherited residence time for the other daughter cell from the mother cell after the cell division, and (3) two daughter cells having the residence time of the mother cell after the cell division.
Enzyme Engineering for Nonaqueous Solvents. II. Additive Effects of Mutations on the Stability and Activity of Subtilisin E in Polar Organic Media
Authors: Chen Keqin , Robinson Amy C. , Van Dam Mariana E. , Martinez Pascal , Economou Chariklia , Arnold Frances H.
Published: March 2005

Single amino acid substitutions increase the activity and stability of subtilisin E in mixtures of organic solvents and water, and the effects of these mutations are additive. A variant of subtilisin E that exhibits higher activity in mixtures of dimethylformamide (DMF) and water (Q103R) was created by random mutagenesis combined with screening for improved activity (K. Chen and F. H. Arnold, in preparation). Another mutation, N218S, known to improve both the activity and stability of subtilisin BPN′, also improves the activity and stability of subtilisin E in the presence of DMF. The effects of the two substitutions on transition‐state stabilization are additive. Furthermore, the Q103R mutation that improves activity has no deleterious effect on subtilisin stability. The double mutant Q103R+N218S is 10 times more active than the wild‐type enzyme in 20% (v/v) DMF and twice as stable in 40% DMF. Although the effects of single mutations can be impressive, a practical strategy for engineering enzymes that function in nonaqueous solvents will most likely require multiple changes in the amino acid sequence. These results demonstrate the excellent potential for engineering nonaqueoussolvent‐compatible enzymes.
Elution Conditions and Degradation Mechanisms in Long‐Term Immunoadsorbent Use
Authors: Antonsen K. Pickard , Colton Clark K. , Yarmush Martin L.
Published: March 2005

The limited life of immunoadsorbents used for the large‐scale purification of biological macromolecules poses a significant limitation to the more widespread application of this technology. In this study, the binding activity of a monoclonal antibody (MAb) to bovine serum albumin (BSA) was measured as a function of pH, ionic strength, and varying concentrations of KSCN, ethylene glycol, or DMSO. Low pH (2.5) and 3 M KSCN each reduced the antibody binding constant below 6×105 L/mol, meeting criteria derived from a simple chromatographic model for identifying effective eluents. A panel of six MAb to BSA was exposed repeatedly to adsorption conditions and the two eluents. Four MAb lost less than 50% of their initial binding capacity over 100 cycles. The other two lost 75% of their initial capacity. One MAb was stable when exposed to low pH but lost binding capacity with KSCN. In all cases, the equilibrium constant was unchanged. The loss of capacity was also shown to be a strong function of antibody loading: at 14.5 mg/mL, 98% of the initial binding capacity of one MAb was lost within 40 cycles, versus 75 % loss at 1 mg/mL. Antibody leakage and nonspecific adsorption of contaminants were not responsible for significant loss of antibody activity over time.
Water Diffusivity in Starches at High Temperatures and Pressures
Authors: Karathanos Vaios T. , Vagenas George K. , Saravacos George D.
Published: March 2005

The method of distance‐concentration curves was applied to the estimation of water diffusivities in starches at high temperatures (25‐140 °C) and pressures (up to 40 atm). Temperature had a positive (Arrhenius) effect on the water diffusivity. Pressure decreased the water diffusivity and caused an increase of the energy of activation for diffusion of water in starch, especially at pressures of 1–10 bar. Water diffusivities varied from 0.3×10−10 to 30×10−10 m2/s, and they were higher in hydrated starches than in gels, evidently due to the higher porosity. The water diffusivity in hydrated granular starch decreased with increasing moisture content, due to their lower porosity.
Flow Cytometry and Cell Cycle Kinetics in Continuous and Fed‐Batch Fermentations of Budding Yeast
Authors: Alberghina L. , Ranzi B. M. , Porro D. , Martegani E.
Published: March 2005

Cell size distributions, obtained either as protein distribution by flow cytometry or as cell volume distribution by a Coulter counter, give relevant information about the growth conditions of populations of budding yeast Saccharomyces cerevisiae. We have previously found a good correlation between these distributions and the growth rate in continuous cultures (Ranzi et al., Biotechnol. Bioeng. 1986, 28, 185–190). We now present determinations of the protein distributions and cell volume distributions during different fed‐batch fermentations performed with a simple on/off controller. Since during the fed‐batch fermentation a true steady state is not obtained, the distributions continuously change with time, but nevertheless we observed a good correlation between the average of both distributions and the actual growth rate. The behavior of the cell size distributions can be interpreted on the basis of a two‐threshold cell cycle model in which both the critical protein content at budding (Ps) and the critical protein content for cell division (Pm) are differently modulated by the growth rate. Additional findings will be presented showing that this model can be used to successfully explain the insurgence and the maintenance of oscillatory states in continuous cultures.
In Vivo NMR Analysis of the Influence of Pyruvate Decarboxylase and Alcohol Dehydrogenase of Zymomonas mobilis on the Anaerobic Metabolism of Escherichia coli
Authors: Ricci Juan C. Diaz , Hitzmann Bernd , Bailey James E.
Published: March 2005

Phosphorus‐31 NMR studies of Escherichia coli expressing cloned pyruvate decarboxylase (pdc) and alcohol dehydrogenase (adh) genes from Zymomonas mobilis revealed significant changes in the concentration of intracellular metabolites. The intracellular concentrations of phosphate, sugar phosphates, NAD(H), NTP, NDP, and UDPG of the strain HB101 expressing pdc, adh, or both genes were analyzed at quasi steady state during the anaerobic catabolism of glucose. The evolution of the intracellular pH and extracellular pH during glucose consumption showed a constant value of ΔpH equal to 0.2 pH unit that did not depend on the expression of the Zymomonas genes. The strains expressing PDC only exhibited greatest changes in intracellular composition with significantly decreased inorganic phosphate, NAD(H), NTP, and UDPG and significantly increased sugar phosphates. Analysis of the fermentation products during the NMR experiments provided further information about the physilogical changes observed in the cells. Two plasmid effects on the host metabolism are reported, one induced by the plasmid utilized as control (pUCl9), and the other induced by the expression of the pet operon. In both cases an enhancement of the glucose uptake rate was observed. Although the plasmid carrying adh induces a rapid metabolic inhibition, the expression of pdc does not. The expression of pdc and adh together showed a physiological enhancement that is attributable not to effects on external pH but rather to the effect of the switch in pathways from mixed acid to ethanol fermentation.
Up‐Flow Attached‐Bed Bioreactor for Continuous Ethanol Fermentation
Authors: Chen Hung‐Chang
Published: March 2005

Ethanol fermentation was carried out in an up‐flow attached‐bed (UFAB) continuous fermentor using different microorganisms, substrates, and attachment supports. When Saccharomyces fragilis was attached to cellulose acetate to ferment deproteinized and concentrated acid whey, ethanol productivity as high as 6.9 g/(L.h), 10 times that of a batch reactor, was obtained in a continuous UFAB bioreactor. When Zymomonas mobilis was attached to vermiculite in a continuous UFAB bioreactor to ferment a 10% glucose feed, ethanol productivity as high as 105.7 g/(L.h) was achieved with a dilution rate of 3.6 h−1 and an ethanol concentration of 29.0 g/L.
Block Copolymer Microdomains: A Novel Medium for Enzymatic Reactions
Authors: Gupte A. , Nagarajan R. , Kilara A.
Published: March 2005

Block copolymers exhibit the phenomenon of microdomain formation in pure states as well as in solutions. The microdomains vest the block copolymer assemblies with the intriguing characteristics of microheterogeneous media. We demonstrate that this microheterogeneity in hydrophobic‐hydrophilic block copolymer systems can be exploited for immobilizing enzymes and to carry out enzymatic reactions. Examples involving cholesterol oxidase and horseradish peroxidase are provided here. The observed changes in the enzymatic activity in block copolymer microdomains from that in the aqueous media are interpreted in terms of the hydrophobicity of the reaction microenvironment. The block copolymer microdomains are simple to generate, well defined, and easily reproducible. Therefore, they hold significant potential as media for enzymatic biosynthetic reactions when the substrates or the reaction products are water insoluble.
Kinetic Model for Substrate Utilization and Methane Production in the Anaerobic Digestion of Organic Feeds
Authors: Barthakur Archana , Bora Munindra , Singh H. Devendra
Published: March 2005

A kinetic model for anaerobic digestion of organic substrates is presented. Two complementary kinetic equations, one each for substrate utilization and methane production, are derived. The model equations take into account extracellular hydrolysis of complex substrates and consider the hydrolyzed products as the limiting substrates for cell growth and product formation according to Monod kinetics. The equations are applied to the experimental data on the anaerobic digestion of a variety of feeds reported in the literature with reasonable agreement of the predicted and observed values. When substrate hydrolysis is poor and rate limiting, the equations are reduced to a Contoistype equation. On the other hand, if no hydrolysis of the substrate is involved as in the case of simple and soluble substrate, the equations take the form of a Monod‐type relationship. Thus, the equations represent a generalized kinetic expression for fermentation relating the Monod and Contois equations, which hold good in two extreme cases.
Production and Deactivation of Biosurfactant by Bacillus licheniformis JF‐2
Authors: Lin Sung‐Chyr , Sharma Mukul M. , Georgiou George
Published: March 2005

Bacillus licheniformis JF‐2 produces a lipopeptide surfactant with excellent interfacial properties (Lin et al., 1990, 1992). An HPLC assay was developed to monitor the concentration of the lipopeptide in the fermentation broth and was employed to determine the effect of the composition of the growth medium on biosurfactant production. A maximum concentration of 110 mg/L lipopeptide was obtained in optimized media with 1.0% (w/v) glucose as the carbon source. The maximum amount of surfactant was obtained in early stationary‐phase cultures, but subsequently decreased rapidly and disappeared completely from the fermentation broth within 8 h. It was shown that the surfactant is chemically stable in the culture supernatant but becomes internalized by stationary‐phase cells. The apparent rate of surfactant internalization was not inhibited by carbonyl cyanide (m‐chlorophenyl) hydrazone (CCCP), an uncoupler of oxidative phosphorylation, suggesting that it is not dependent on the availability of ATP and/or a charged membrane. A variety of physical and chemical treatments failed to release the surfactant from the cells. In minimal media the rate of surfactant internalization could be reduced by optimizing the concentration of phosphate and by increasing the amount of magnesium, whereas the nitrogen source, calcium, and trace salts had no effect. Since a related lipopeptide has been shown to be responsible for DNA transformation competence in certain Bacillus subtilis strains, it is possible that the internalization of the B. licheniformis JF‐2 surfactant may be a developmentally important process related to the ability of the cells to take up extraneous DNA.
Stochastic Simulation of 2μ Multicopy Plasmid Amplification in Yeast
Authors: Shaw Mark R. , Schiek Richard , Wittrup K. Dane
Published: March 2005

The 2μ plasmid of Saccharomyces cerevisiae has been used extensively as a vector for foreign protein expression because of its natural amplification to 60–100 copies per cell. The amplification of the 2μ plasmid occurs through a recombinational mechanism which we have simulated using two free parameters: the FLP recombinase DNA‐binding probability and FLP specific enzymatic activity. Model results indicate that a single plasmid amplifies to 5.5–7 copies on average at maximal FLP concentrations and that amplification is approximately proportional to the probability of FLP attachment but independent of its specific enzymatic activity. Thus, FLP overexpression should lead to maximal plasmid amplification. The model predicts the existence of topologically novel replication intermediates.
Biomass Estimation in Plant Cell Cultures Using an Extended Kalman Filter
Authors: Albiol Joan , Robusté Jordi , Casas Carles , Poch Manel
Published: March 2005

Use of carbohydrate concentration measurements linked to a digital filter was studied for biomass estimation in plant cell cultures. Due to the high complexity of the biological system, the strategy followed has been to work with a simple model and to rely on the filter to adapt the values of the model parameters to changes in the system behavior. Results obtained with this approach have shown the method to be efficient for biomass estimation, both in Erlenmeyer flasks and in bioreactors with changing operational conditions.
An Extended Model for Open‐Ended Fluorosensor Probes
Authors: Ladén Gunnar , Niklasson Claes
Published: March 2005

Measurements on pure solutions of NADH (8–800 μM) were made at different path lengths (0–140 mm) with an open‐ended fluorosensor. It was shown that a geometric factor must be included in a model to quantitatively explain the results. A mathematical expression for this factor was found, and parameter estimations were made. It was shown that the often‐used implicit assumption of a completely directed emitted light is not correct, A better fit was obtained by assuming the emitted light to be uniformly distributed in all directions. However, it was necessary to consider the slight divergence of the excitation light beams in the model.
Low‐Temperature Transitions in Fresh and Osmotically Dehydrated Plant Materials
Authors: Anglea Stacey A. , Karathanos Vaios , Karel Marcus
Published: March 2005

Phase transitions in several plant materials were studied using differential scanning calorimetry (DSC) and small oscillatory amplitude rheology. The glass transition temperature of the unfrozen phase, recrystallization peak of water, and melting point of ice, in fresh plant materials as well as in samples osmotically dehydrated in 15, 30, and 45% sucrose solutions, were identified using both thermal and mechanical analysis. Mechanical analysis showed that the glass transition temperature of the unfrozen phase was approximately ‐45°C for fresh and osmotically dehydrated plant materials at all concentrations. Thermal analysis showed that the glass transition of the unfrozen phase in osmotically dehydrated potato samples varied depending on the amount of freeze‐concentration achieved.
Characterization of Water Distribution in Cell Pellets Using Nonlabeled Sodium Thiosulfate as an Interstitial Space Marker
Authors: Larroche Christian , Besson Isabelle , Dussap Claude‐Gilles , Bourrust Francois , Gros Jean‐Bernard
Published: March 2005

A procedure for determination of the intracellular water content of cells using a single, nonlabeled solute as an interstitial space marker is proposed. Sodium thiosulfate, which can be accurately assayed by a tritrimetric method, is found to be a good compound for this purpose. Cells are recovered both by filtration and centrifugation; the two techniques gave the same value for internal water, i.e., 650 mg of H2O/g of wet matter for Corynebacterium melassecola and 390 mg of H2O/g of wet matter for Penicillium roquefortii spores. The methodology of data handling, based on a regression technique, is also described. It allows one to obtain very reliable results and should be useful for any marker.
Advances in Metabolic Control Analysis
Authors: Liao James C. , Delgado Javier
Published: March 2005

A methodology for characterizing metabolic systems using the response, control, and elasticity coefficients has emerged since the early 1970s. This methodology, termed metabolic control analysis, aims to characterize the sensitivity of metabolic responses with respect to changes in enzyme activities or parameters without the use of full mathematical models. It takes advantage of several relationships among the coefficients at the steady state. These relationships facilitate the experimental determination of the coefficients and serve as a consistency test when the coefficients are determined independently. Both the theoretical and experimental aspects of this analysis are reviewed, with an emphasis on recent developments and issues commonly discussed in the literature.
Effect of Chelatants on Gellan Gel Rheological Properties and Setting Temperature for Immobilization of Living Bifidobacteria
Authors: Camelin I. , Lacroix C. , Paquin C. , Prévost H. , Cachon R. , Divies C.
Published: March 2005

The effect of various concentrations of sequestrants (sodium citrate, sodium meta‐phosphate, and BDTA) was studied on gellan gel (1.5–2.5% (w/v)) setting temperature and rheological properties. Addition of EDTA between 0 and 0.8% (w/v) led to a progressive decrease of setting temperature. Citrate and metaphosphate decreased this parameter when added up to 0.4 or 0.6%, depending on gellan gum concentration, eventually resulting in the absence of gel formation at room temperature for the 1.5% gellan solution containing 0.4% citrate. This effect was accompanied by a significant decrease of gel strength and stiffness and might be attributed to the binding of the divalent cations required for chain association during gelation by chelatants. With the aim of lowering the gel setting temperature during the cell entrapment process while maintaining high mechanical properties, a gel made of 2.5% gellan gum and 0.2% sodium citrate was used to entrap Bifidobacterium longum ATCC15707. Ions and pH of the inoculum during the immobilization step influenced the long‐term mechanical stability of the gel beads during continuous fermentation in a stirred tank reactor. High stability as well as high biocatalyst activity was obtained when a washed cell suspension was used as the inoculum. Gellan gel produced by dissolving gellan gum in a sodium citrate solution may be a promising entrapment matrix for temperature‐sensitive cells such as mesophilic lactic acid bacteria and eukaryotic cells.
Fractional Factorial Study of Hybridoma Behavior. 1. Kinetics of Growth and Antibody Production
Authors: Gaertner John G. , Dhurjati Prasad
Published: March 2005

A comprehensive approach was taken toward the quantitative study of hybridoma growth and antibody production. A fractional factorial experimental method was used to identify important variables and variable interactions affecting hybridoma behavior. The variables studied include temperature, pH, dissolved oxygen, glucose, glutamine, base medium, serum, lactate, and ammonium. The growth rate was strongly affected by the levels of dissolved oxygen, pH, temperature, and base medium. Interactions between temperature, pH, and dissolved oxygen were important. The optimal pH for growth depends upon the temperature and dissolved oxygen concentration. In general, growth was fastest at low dissolved oxygen levels. The growth rate was very sensitive to low concentrations of base medium, but was relatively insensitive to the serum concentration at levels above 2.5%. Antibody production was stimulated by high concentrations of base medium and serum and inhibited by ammonium and lactate. Antibody production increased linearly with serum concentration. In general, conditions that favored a high growth rate also favored a high specific rate of antibody production. The functional dependencies of antibody production on base medium and ammonium were similar to those for cell growth; however, antibody production and cell growth exhibited different dependencies on serum. Mathematical descriptions of cell growth and antibody production were developed. These experimental results have significant implications for the optimization of hybridoma growth in bioreactors.
A Computer Model for Intracellular pH Regulation in Chinese Hamster Ovary Cells
Authors: Wu P. , Ray N. G. , Shuler M. L.
Published: March 2005

A single‐cell model for Chinese hamster ovary (CHO) cells has been extended to study the regulation of intracellular pH. This model provides for the first time a direct mechanistic linkage between intracellular pH control and cellular metabolism. Among the known mechanisms that regulate and disturb pHi, the Na/H antiport, effect of lactate and ammonia, proton leakage, and external pH have been included in the model. The ability of the model to predict both steady‐state and transient pHi has been tested against experimental studies. The “regular model” that has been used to predict cell growth in suspension and batch cultures can predict the steady‐state pHi and the transient response of pHi to an alkaline load well, but it had to be modified in terms of the maximum activity of the Na/H antiport in order to simulate the transient response of pHi to an acid load. The modification indicates the possibility that a cell could activate the Na/H antiport under acute acid load but return to its basal level of Na/H antiport activity under steady‐state conditions, even when the cell interior is under low‐pH conditions (6.7–7.0).
Application of Oxygen Microbubbles for in Situ Biodegradation of p‐Xylene‐Contaminated Groundwater in a Soil Column
Authors: Jenkins Kristen B. , Michelsen Donald L. , Novak John T.
Published: March 2005

In situ biodegradation of p‐xylene was studied in a 7‐cm (2.75‐in.) soil column using oxygen microbubbles to supply the electron acceptor. Pseudomonas putida continuously degraded p‐xylene below detectable limits until the oxygen supply was exhausted. Retention time in the biodegradation zone was approximately 45 min. Vent losses claimed 5–10% of the injected oxygen, with 71–82 % being utilized. The pressure drops resulting from increased biomass showed a slight increase over the first few days followed by a gradual decline, indicating that the biomass will not plug the soil matrix under the conditions of this test. The addition of ferrous iron in the feed and its subsequent oxidation to ferric hydroxide did not affect biodegradation, nor did it cause appreciable soil plugging. In order to precipitate the ferrous iron before it reached the microbubbles, an air‐sparging section was added. This resulted in volatilization of p‐xylene with very little ferrous oxidation until the groundwater reached the oxygen microbubbles.
5‐Aminolevulinic Acid: A Potential Herbicide/Insecticide from Microorganisms
Authors: Sasikala Ch. , Ramana Ch. V. , Rao P. Raghuveer
Published: March 2005

5‐Aminolevulinic acid (ALA), an intermediate of the biological tetrapyrrole synthesis, can be used as a photodynamic herbicide/insecticide. Among the various microorganisms capable of its production, anoxygenic phototrophic bacteria produce ALA in considerable amounts, making it worthwhile to work toward commercial exploitation. Knowledge of the biochemical synthesis of ALA and its physiological and genetic regulation in microorganisms can enable the biotechnologist to manipulate them for enhancing ALA production for possible practical applications.
Optimal Experimental Design for Parameter Estimation in Unstructured Growth Models
Authors: Baltes M. , Schneider R. , Sturm C. , Reuss M.
Published: March 2005

A method of optimal experimental design for parameter estimation in unstructured growth models is presented. The approach is based on a method suggested by Munack (1991) for application in fed‐batch processes. In a critical analysis of this method, special emphasis is given to the model validity, because unstructured growth models often are not valid under transient conditions. In consequence, a combined object function has been introduced, which considers model validity and the accuracy of the kinetic parameters to be estimated. The application of this method for fed‐batch processes leads to satisfactory results. Investigations of different fed‐batch strategies regarding model validity and the quality of parameter estimation are presented. In addition, an experimental verification has been performed with fermentations of the yeast Trichosporon cutaneum.
Three‐Dimensional Mammalian Cell Growth on Nonwoven Polyester Fabric Disks
Authors: Petti Stacy A. , Lages Ana C. , Sussman Martin V.
Published: March 2005

Small disks of nonwoven polyester fabric (NWPF), similar to Fibra‐Cel carriers, were surface treated with strong acid and used as a high surface area support matrix for in vitro culture of anchorage dependent MRC‐5 cells. The disks can be autoclaved, and require inocula concentrations of only 2–5% of the final cell densities, which have reached 108 cells/mL of disk bed volume. Scanning electron microscopy photographs shown herein reveal that cells grow in a multilayered fashion between the randomly arrayed fibers of the nonwoven fabric, emulating in vivo growth.
Cost Analysis of Ethanol Production from Willow Using Recombinant Escherichia coli
Authors: Sivers Margareta Von , Zacchi Guido , Olsson Lisbeth , Hahn‐Hügerdal Bärbel
Published: March 2005

This study comprises a technical and economic analysis of the production of fuel ethanol by fermentation of a pentose‐rich hydrolysate with recombinant Escherichia coli, strain KO11. Hydrolysate from steam‐pretreated willow was used as raw material in calculations regarding the fermentation. The calculations were based on a feed capacity of 10 metric tons of dry willow per hour to the pretreatment stage, providing 35 metric tons of hydrolysate per hour, consisting of 45 g of sugars/L, to the pentose fermentation plant. A detoxification step was included, since the hydrolysate has been shown to have an inhibitory effect on the E. coli KO11. The technical data used in the calculations were based on a kinetic fermentation model, which was developed from laboratory‐scale experiments in a previous study. The economic analysis predicted an ethanol production cost of 48¢/L in the pentose fermentation plant, indicating potentially good economy. The detoxification cost constitutes 22% of this cost. Sensitivity analyses revealed that if the concentration of sugars in the feed to the fermentation was decreased by 40% to 27 g/L, the ethanol production cost was increased to 54 ¢/L. The production cost was increased to 50 ¢/L ethanol if the cell mass was recirculated to the fermentation stage 5 times instead of 20.
Predictions of energetic particle radiation in the close Martian environment
Authors: McKenna‐Lawlor Susan M. P. , Dryer M. , Fry C. D. , Sun W. , Lario D. , Deehr C. S. , Sanahuja B. , Afonin V. A. , Verigin M. I. , Kotova G. A.
Published: March 2005

Intense, prolonged solar flare activity during March 1989 was used to provide a retrospective scenario for predictions of associated interplanetary shocks and accompanying particle radiation at planet Mars. Shocks from five major flares were simulated to hit both the Earth and Mars during the interval 9–23 March 1989. The simulated scenario was provided by the Hakamada‐Akasofu‐Fry version 2 (HAFv.2) solar wind model. Since part of the generally required inputs for the model (specifically metric radio Type II coronal shock speeds) were not available, the shock speeds were iteratively determined via a “calibration” that uses limited IMP 8 particle and sudden storm commencement (SSC) data as proxies for shock arrival at the Earth. The shocks from four major solar flares were, thereby, found to arrive at Mars at times that are appropriate to explain solar energetic particle (SEP) and energetic storm particle (ESP) events recorded in situ by the particle radiation detector experiments Solar Low Energy Detector (SLED) and Low Energy Telescope (LET) aboard Phobos‐2. Supporting measurements were provided by the magnetometer (MAGMA) and plasma spectrometer (TAUS) experiments. A gap in the spacecraft records occurred at the simulated time of arrival of the fifth flare‐associated shock. There were some uncertainties attending the selection of certain of the events deemed to be “parent” flares. Such uncertainty can be expected in view of the incomplete set of energetic particle, plasma, and magnetic field measurements made at relevant times at both the Earth and Mars (the latter planet was then located at a distance of 1.6 AU, at about 78° east of the Sun‐Earth line). Use of the HAFv.2 solar wind model affords a 4‐day lead time between predicted and measured space weather events at Mars, with an error of approximately ±12 hours. Solar radiation events of the magnitude studied occur often enough to warrant consideration in the design of both manned and unmanned expeditions to Mars.
Physics of saturation of collisionless tearing mode as a function of guide field
Authors: Karimabadi Homa , Daughton William , Quest Kevin B.
Published: March 2005

The tearing instability has been the subject of much study in space and laboratory plasmas and is thought to play a role as an onset mechanism for reconnection at the magnetotail and at the magnetopause. However, the nonlinear evolution is not completely understood. Here we employ a combination of theory and full particle simulations, including one for realistic mass ratio, to address the saturation of a single, linearly unstable tearing mode as a function of guide field. For the parameter regime considered, we find no agreement with any of the previous theories of tearing mode saturation. There are marked differences in the electron behavior and the associated saturation mechanism in the antiparallel (zero guide field) and finite guide field cases. Electrons become nongyrotropic and also develop temperature anisotropies in the antiparallel case, whereas they remain isotropic in the presence of a guide field. In the antiparallel limit there are two competing saturation mechanisms. One is due to preferential parallel heating of electrons which leads to a saturation amplitude of ws ∼ 2.9 ρe, where ρe is the electron gyroradius in the asymptotic magnetic field and ws is the half‐width of the magnetic island. The other saturation mechanism is electron trapping in the magnetic island which leads to a saturation amplitude comparable to the singular layer thickness (ΔNS). Electron parallel heating is usually the dominant saturation mechanism. However, in the presence of sufficiently fast electron pitch angle scattering, caused either by current‐aligned Weibel instability or turbulence, the second saturation mechanism due to trapping becomes dominant. In the presence of a guide field, the only saturation mechanism is electron trapping which leads to a saturation amplitude of ws ∼ 1.8 ρeG in the strong guide field and ws ∼ (2ρeGΔNS)1/2 in the intermediate regime. Here ρeG is the electron gyroradius in the guide field. The predicted saturation amplitudes for all cases, including the antiparallel regime, are much smaller than the thickness of the magnetopause current layer. Thus a single tearing mode saturates at too small of an amplitude to be of relevance to reconnection in the magnetosphere.
Ozonolysis of α-pinene and β-pinene: Kinetics and mechanism
Authors: Zhang Dan , Zhang Renyi
Published: March 2005

A combined quantum-chemical and RRKM/ME (ME—master equation) approach is employed to investigate the structures, energetics, and kinetics of intermediate and stable species, and the yields of stabilized carbonyl oxides and OH radicals from the α-pinene and β-pinene ozonolysis reactions. The cycloaddition of O3 is highly exothermic, with the reaction energies of 55.1 and 51.1kcalmol−1 for α- and β-pinenes, respectively. Cleavage of primary ozonides yields carbonyl oxides with the barrier height of 12.2–17.5kcalmol−1. For the prompt reactions of carbonyl oxides from α- and β-pinene ozonolysis, H migration to hydroperoxides represents the dominant pathway over ring closure to dioxiranes. The kinetic calculations indicate a significant portion of stabilization for α- and β-carbonyl oxides. The yields of stabilized carbonyl oxides are estimated to be 0.34 for α-pinene and 0.22 for β-pinene. The applicability of theoretical methods for investigation of oxidation reactions of large hydrocarbon molecules is demonstrated.
Infrared water vapor continuum absorption at atmospheric temperatures
Authors: Cormier John G. , Hodges Joseph T. , Drummond James R.
Published: March 2005

We have used a continuous-wave carbon dioxide laser in a single-mode realization of cavity ring-down spectroscopy to measure absorption coefficients of water vapor at 944cm−1 for several temperatures in the range 270–315 K. The conventional description of water vapor infrared absorption is applied, in which the absorption is modeled in two parts consisting of local line absorption and the remaining residual absorption, which has become known as the water vapor continuum. This water vapor continuum consists of distinct water-water, water-nitrogen, and water-oxygen continua. The water-water continuum absorption coefficient is found to have a magnitude of Cs(296K)=(1.82±0.02)×10−22cm2molecule−1atm−1, and the water-nitrogen coefficient has a magnitude of Cn(296K)=(7.3±0.4)×10−25cm2molecule−1atm−1. The temperature dependences of both the water-water and the water-nitrogen continua are shown to be well represented by a model describing the expected behavior of weakly bound binary complexes. Using this model, our data yield dissociation energies of De=(−15.9±0.3)kJ∕mole for the water dimer and De=(−3.2±1.7)kJ∕mole for the water-nitrogen complex. These values are in excellent agreement with recent theoretical predictions of De=−15.7kJ∕mole (water dimer) and De=−2.9kJ∕mole (water-nitrogen complex), as well as the experimentally determined value of De=(−15.3±2.1)kJ∕mole for the water dimer obtained by investigators employing a thermal conductivity technique. Although there is reasonably good agreement with the magnitude of the continuum absorption coefficients, the agreement on temperature dependence is less satisfactory. While our results are suggestive of the role played by water dimers and water complexes in producing the infrared continuum, the uncertain spectroscopy of the water dimer in this spectral region prevents us from making a firm conclusion. In the meantime, empirical models of water vapor continuum absorption, essential for atmospheric radiative transfer calculations, should be refined to give better agreement with our low-uncertainty continuum absorption data.
Analytical current–voltage relationships for electron tunneling across rough interfaces
Authors: Kogut L. , Komvopoulos K.
Published: March 2005

Conductive rough surfaces separated by an insulating ultrathin film comprise the core of various engineering and scientific systems. Electron tunneling through the potential barrier imposed by the insulating film is the main mechanism of charge transport across these interfaces. The strong dependence of the tunnel current on the characteristics of the interface provides an in situ means of studying the electromechanical behavior of hindered interfaces in terms of the current–voltage response. Analytical relationships for the current density versus applied voltage that include the real tunneling area are used to characterize the electrical and mechanical properties of the interfaces of rough conductive surfaces coated by an insulating thin film. It is shown that the contact load, real contact area, surface topography, mechanical properties, and insulating film characteristics, such as thickness, dielectric constant, and potential barrier, can be determined from simple electrical measurements and the use of the present analytical approach.
Microstructure of Co-doped TiO2(110) rutile by ion implantation
Authors: Wang C. M. , Shutthanandan V. , Thevuthasan S. , Droubay T. , Chambers S. A.
Published: March 2005

Co-doped rutile TiO2 was synthesized by injecting Co ions into single crystal rutile TiO2 using high energy ion implantation. Microstructures of the implanted specimens were studied in detail using high-resolution transmission electron microscopy (HRTEM), energy dispersive x-ray spectroscopy, electron diffraction, and HRTEM image simulations. The spatial distribution and conglomeration behavior of the implanted Co ions, as well as the point defect distributions induced by ion implantation, show strong dependences on implantation conditions. Uniform distribution of Co ions in the rutile TiO2 lattice was obtained by implanting at 1075K with a Co ion fluence of 1.25×1016Co∕cm2. Implanting at 875K leads to the formation of Co metal clusters. The precipitated Co metal clusters and surrounding TiO2 matrix exhibit the orientation relationships Co⟨110⟩‖TiO2[001] and Co{111}‖TiO2(110). A structural model representing the interface between Co metal clusters and TiO2 is developed based on HRTEM imaging and image simulations.
The subgrid-scale models based on coherent structures for rotating homogeneous turbulence and turbulent channel flow
Authors: Kobayashi Hiromichi
Published: March 2005

The subgrid-scale (SGS) models based on the coherent structure in grid-scale flow fields are proposed and are applied to (non-)rotating homogeneous turbulences and turbulent channel flows. The eddy viscosity is modeled by a coherent structure function (CSF) with a fixed model-parameter. The CSF is defined as the second invariant normalized by the magnitude of a velocity gradient tensor and plays a role of wall damping. The probability density function of the CSF is non-Gaussian showing an intermittency effect. The model parameter is locally determined, and it is always positive and has a small variance. These models satisfy a correct asymptotic behavior to a wall for incompressible flows. It is shown that the SGS models with an energy-decay suppression function which indicates also a pseudo-backscatter are consistent with the asymptotic material frame indifference in a rotating frame. Since the CSF characterizing turbulent flows has relation to the SGS energy dissipation, the present SGS models are applicable not only to (non-)rotating homogeneous and shear turbulences but also to laminar flows. The proposed models have almost the same performance as the dynamic Smagorinsky model for (non-)rotating homogeneous turbulences and turbulent channel flows, but these models do not need to average or clip the model parameter, use an explicit wall-damping function, or change the fixed-parameter, so that they are suitable for engineering applications of large-eddy simulation.
Comparative studies of temperature dependence of G-band peak in single walled carbon nanotube and highly oriented pyrolytic graphite
Authors: Atashbar Massood Z. , Singamaneni Srikanth
Published: March 2005

Thermal stability and temperature-dependent properties of carbon nanotubes are very important for the fabrication of carbon nanotube-based devices. High purity of carbon nanotube matrix was achieved by sieving through Anatop filters. The temperature dependence of G-band in single-wall-carbon-nanotubes matrices and highly oriented pyrolytic graphite is investigated. It was found that the former had significantly higher magnitude of temperature coefficient (−0.044cm−1∕K) compared to the latter (−0.031cm−1∕K). A hypothesis is proposed based on their structural differences in C–C bonds for explaining this variation.