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Biomedical subjects

L E Erickson

Publications and source records attributed to L E Erickson.

At least 19 recordsLinked to original sources
PubMed2001

Mathematical model development and simulation of in situ stabilization in lead-contaminated soils.

Stabilization and remediation of lead-contaminated soils has received considerable attention recently. Amending Pb-contaminated soils with phosphate as an in situ remediation option has been proposed as an alternative to other remediation options, such as soil removal. Research shows that hydroxyapatite (HA) [Ca(5)(PO(4))(3)OH] can reduce the bioavailability of Pb efficiently and thus is considered as an ideal phosphate source for formation of lead pyromorphite. Environmental models are increasingly being relied upon to help identify the limiting factors in such kind of in situ remediation. In this work, the contaminated aggregates remediation model has been developed and simulated to describe the effects of initial contaminant concentration, diffusion coefficient, and aggregate diameter on the time of remediation which is defined as the time required to reduce the aqueous phase lead concentration to <1 ppb. Results of simulation demonstrate that the aggregate size plays a significant role in remediation. The compartments-in-series model has been used to describe the dynamics of in situ stabilization in a soil bed. Results show that for a shallow bed a single, well-mixed, one compartment model gives approximately the same remediation time as the three compartments-in-series model.

Biological Availability↗
PubMed2001

Transport of methyl tert-butyl ether through alfalfa plants.

Concentrations measured in alfalfa plant stem segments indicated that plants grown in methyl tert-butyl ether (MTBE)-contaminated soil took up the chemical through their roots. Assuming a cylindrical shape for the plant stem, a mathematical model was developed to describe the transport of MTBE through the stems. Simulation results from uniform and nonuniform initial concentration distributions across the stem radius were compared with steady-state experimental data. With known values of plant stem radius, water usage, water content, and the distance over which the concentration decreased by 50%, the diffusion coefficient of MTBE radial transport across the plant stem was estimated with 95% confidence to be in the range of 8.43-16.2 x 10(-8) cm2/s with a mean of 1.23 x 10(-7) cm2/s. When the diffusion coefficient was calculated based on transient experimental data, the values with 95% confidence interval ranged from 4.14 x 10(-7) to 8.00 x 10(-7) cm2/s with a mean value of 6.07 x 10(-7) cm2/s. The difference between these two results can be reduced by more accurate estimation of the water flow velocity through plant stems. The model is applicable to other species including sunflowers and poplars upon substitution of appropriate parameters.

Carcinogens↗
PubMed2000

Selective high-resolution electrodeposition on semiconductor defect patterns.

We report a new principle and technique that allows one to electrodeposit material patterns of arbitrary shape down to the submicrometer scale. We demonstrate that an electrochemical metal deposition reaction can be initiated selectively at surface defects created in a p-type Si(100) substrate by Si (++) focused ion beam bombardment. The key principle is that, for cathodic electrochemical polarization of p-type material in the dark, breakdown of the blocking Schottky barrier at the semiconductor/electrolyte interface occurs at significantly lower voltages at implanted locations than for an unimplanted surface. This difference in the threshold voltages is exploited to achieve selective electrochemical deposition.

Journal Article↗
PubMed2000

Application of mass and energy balance regularities in fermentation. Reprinted from Biotechnology and Bioengineering, Vol. XX, No. 10, Pages 1595-1621 (1978).

Material and energy balances for fermentation processes are developed based on the facts that the heat of reaction per electron transferred to oxygen for a wide variety of organic molecules, the number of available electrons per carbon atom in biomass, and the weight fraction carbon in biomass are relatively constant. Mass-energy balance equations are developed which relate the biomass energetic yield coefficient to sets of variables which may be determined experimentally. Organic substrate consumption, biomass production, oxygen consumption, carbon dioxide production, heat evolution, and nitrogen consumption are considered as measured variables. Application of the balances using direct and indirect methods of yield coefficient estimation is illustrated using experimental results from the literature. Product formation is included in the balance equations and the effect of product formation on biomass yield estimates is examined. Application of mass-energy balances in the optimal operation of continuous single-cell protein production facilities is examined, and the variation of optimal operating conditions with changes in yield are illustrated for methanol as organic substrate.

Electrons↗
PubMed1997

An overview of research on the beneficial effects of vegetation in contaminated soil.

Vegetation can enhance in situ bioremediation processes in many applications. Microbial transformations occur in soil and water external to plant roots. Organic contaminants also enter vegetation and are transformed within plants. Research progress is reviewed with emphasis on recent experimental results and mathematical models of contaminant fate in systems where vegetation is present. Plant evapotranspiration provides a solar driven pump-and-treat system which moves contaminants to the rhizosphere and helps to contain them on site. Significant savings have been reported at several field sites where vegetation has been utilized.

Biodegradation, Environmental↗
PubMed1997

Agonist activation of delta-opioid receptor but not mu-opioid receptor potentiates fetal calf serum or tyrosine kinase receptor-mediated cell proliferation in a cell-line-specific manner.

Activation by opioid receptors of cell proliferation was examined with fibroblast cell lines stably expressing either delta-opioid or mu-opioid receptors. Addition of [D-Ala2, D-Leu5]-enkephalin or [D-Pen2,D-Pen5]-enkephalin to Chinese hamster ovary (CHO) cells transfected with delta-opioid receptor cDNA resulted in an agonist concentration-dependent potentiation of fetal calf serum (FCS)-stimulated cell proliferation. This potentiation by delta-opioid agonists was antagonized by naloxone and was not observed with the kappa-opioid receptor selective agonist U50,488 or the mu-opioid receptor selective agonist [D-Ala2,N-MePhe4, Gly-ol5]-enkephalin. This delta-opioid agonist effect was not observed at FCS concentrations > 0.1% and could be blocked by pretreating cells with pertussis toxin, indicating that Gi/Go were involved in this action. In addition, delta-opioid agonists could potentiate CHO cell proliferation stimulated by those growth factors that are mediated by tyrosine kinase receptors (i.e., insulin, insulin-like growth factor 1, and fibroblast-derived growth factor b). This delta-opioid agonist potentiation of growth apparently was dependent on the level of delta-opioid receptors that were expressed and had cell-line selectivity. Activation of delta-opioid receptors expressed in Rat-1 or NIH3T3 fibroblast did not result in a modulation of the cell growth induced by FCS or by growth factors. Interestingly, in CHO cells transfected with mu-opioid receptor cDNA, activation with agonists did not produce a potentiation of FCS-stimulated proliferation. This lack of mu-opioid receptor effect was not due to the differences among CHO clones. In a CHO cell line transfected with both delta-opioid receptor cDNA and mu-opioid receptor cDNA, activation of delta-but not mu-opioid receptors resulted in a potentiation of growth. These data suggest that delta- and mu-opioid receptors in CHO cells activate similar but divergent second messenger pathways, resulting in the differential regulation of cell growth.

3T3 Cells↗
PubMed1993

A review of the effects of shear and interfacial phenomena on cell viability.

The shear sensitivity of animal and plant cells is a problem often encountered in large-scale cell culture. Such sensitivity varies with different cell lines and the severity of cellular damage may depend on both the magnitude and the duration of the shear stress. In a bioreactor, the shear susceptibility of cells depends on their response to hydrodynamic forces arising from fluid motions of particular scale. Cell damage may be induced by forces in the bulk liquid phase, but fluid motions associated with the gas-liquid interface are especially energetic. The detrimental effects of hydrodynamic forces are abated by the addition of some polymers, such as Pluronic F-68, methylcellulose, or serum; the exact mechanisms of protection are the subject of current research.

Animals↗
PubMed1983

Available electron and energetic yields in fermentation processes.

Microbial growth and product yields have been investigated for several cultures. Available electron and free energy balances may be used to examine the efficiency of microbial energetics. Energetic yields based on free energy analysis were obtained and compared with yields from available electron analysis. Estimates of true growth yields under anaerobic conditions have been obtained using statistical methods and the results were compared with theoretical maximum yields.

Adenosine Triphosphate↗
PubMed1982

Analysis of regularities and process efficiencies in living systems.

In the analysis of microbial growth and product formation, regularities which utilize available electron concepts have been used with considerable success. The facts that the heat of reaction per electron transferred to oxygen, the number of available electrons per carbon atom in microbial biomass and the weight fraction carbon in microbial biomass are relatively constant constitute the regularities. Values of these regularities are presented for carbohydrates, proteins, and fats. The free energy of reaction per electron transferred to oxygen is also examined as a regularity. Results of prior work with regularities in living systems are reviewed. Work on the utilization of these concepts in the analysis of process efficiency in living systems is presented.

Animals↗
PubMed1980

Inhibition of intracellular protein transport in the mouse exocrine pancreas induced by vinblastine.

The effect of vinblastine on the intracellular transport of newly synthesized protein in the mouse exocrine pancreas in vivo was studied by electron microscopic autoradiography after administration of 3H-leucine. Vinblastine (1.1 mumole/mouse; i.v. injection) was in general given 1 h before radioleucine and 2-4 h before fixation of the pancreas by perfusion with glutaraldehyde. Vinblastine causes the disappearance of microtubules, mainly present in controls in the apical portion of the acinar cell. After injection of vinblastine, zymogen granules from clusters located throughout the cell but often associated with Golgi areas. The latter are enlarged mainly due to the accumulation of small vesicles. In addition, Golgi areas are displaced, most often in an apical direction. Electron microscopic autoradiography demonstrated that vinblastine delays the appearance of labeled protein in zymogen granules; even 2 h after injection of radioleucine the majority of silver grains is located over the rough endoplasmic reticulum while very few grains are related to zymogen granules. This finding might be related to the structural changes of the Golgi areas observed. Although intracellular migration of protein is retarded, zymogen granules are formed. However, many of the labeled granules are found in peculiar locations, often distant from the acinar lumen. The present study suggests that vinblastine, possibly due to its effect on microtubules, influences both the formation and the translocation of zymogen granules.

Animals↗
PubMed1977

Characteristics of hydrocarbon uptake in cultures with two liquid phases.

In hydrocarbon fermentation, the efficiency of hydrocarbon uptake by cells is one of the keys to the economical production of single-cell protein. This work is concerned with characterization of cultures with two liquid phases for understanding the hydrocarbon uptake process by cells. Batch cultivation of Candida lipolytica was carried out in shaking flasks and in a tower fermentor with motionless mixers. Microscopic observation and cell and hydrocarbon concentration distribution in batch cultivation showed that some cells are attached to the large oil drops and others are free from them. Interfacila tension between oil and water and Sauter mean drop size decreased as cultivation proceeded. On the basis of the experimental results, the process of hydrocarbon uptake by cells is discussed.

Candida↗
PubMed1977

Oxygen transfer and axial dispersion in an aeration tower containing static mixers.

Oxygen transfer from gas to liquid under steady-state cocurrent flow conditions was modeled using the dispersion model, and the oxygen transfer coefficients were estimated from available data for a column with Koch motionless mixers. The dispersion in the column was estimated for several different gas and liquid flow rates using steady-state tracer experiments. The estimated oxygen transfer coefficients were compared with those estimated using complete mixing and plug flow models. The results indicate that the dispersion model is the most appropriate model for estimating the mass transfer coefficient from the available data.

Absorption↗
PubMed1977

Hydrocarbon uptake in hydrocarbon fermentations.

Candida lipolytica (strain ATCC 8662) was grown on a simple defined medium with n-hexadecane as the main carbon source under batch fementation conditions. The relative importance of the cells growing in the aqueous phase on the overall kinetics was studied. The effect of interfacial tension, unoccupied interfacial area, and pseudosolubility on the specific growth was also studied. Results are presented and discussed here.

Candida↗