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PubMed1979

Osmotic water flow in leaky epithelia.

I review three currently unsolved and controversial problems in understanding solute-linked water transport in epithelia. 1. Values of osmotic water permeability (Posm) calculated from steady-state osmotic flow in response to a gradient of a probe molecule tend to be underestimates, because of three unstirred-layer (USL) effects. These are: dissipation of the probe's gradient by diffusion in USL's; reduction of the probe's gradient, due to the sweeping-away effect of water flow generated by the probe itself; and solute polarization (creation of an opposing gradient of an initially symmetrically distributed solute by the sweeping-away effect). These errors increase with probe permeability, USL thickness, Posm, and concentration ratio of symmetrically distributed solute to probe, and vary inversely as the fractional area available for water flow (e.g., lateral intercellular space width). The form of an osmotic transient, and the possibility of extracting a true Posm value from the transient, depend on the relative values of three time constants: those for solute diffusion in USL's, for solute polarization by water flow in USL's and for measuring water flow. Sweeping-away effects cause major underestimates (by one or more orders of magnitude) in epithelial Posm determinations, as shown by apparent streaming potentials during osmotic flow and by transiently reversed flows after removal of the proble. True Posm values for leaky epithelia probably exceed 10(-3) or 10(-2) cm/sec.osm. The necessary conditions for resolving osmotic transients are set out. 2. I illustrate the difficulties in deciding what fraction of transepithelial water flow is via the cells, and what fraction via the junctions. There is no existing method for answering this question. 3. Controversies about the validity, or need for modification, of the standing-gradient theory are discussed. Progress in this field requires new methods: to resolve osmotic transients; to separate transcellular and transjunctional water flows; and to measure solute concentrations in lateral intercellular spaces directly.

Animals↗

PubMed1994

MIB-1, Ki67, and PCNA scores and DNA flow cytometry in intermediate grade malignant lymphomas.

AIMS: To verify the correlation between MIB-1, Ki67, and proliferating cell nuclear antigen (PCNA-PC10) scores and S-phase fraction in intermediate grade non-Hodgkin's lymphomas (Working Formulation F); and their reliability in differently processed tissues. METHODS: Forty one non-Hodgkin's lymphomas were classified as (F) intermediate grade malignant lymphomas according to the Working Formulation; mitotic counts and percentage of large cells were assessed for each case. Sections from formalin fixed, paraffin wax embedded tissues were stained with anti MIB-1 monoclonal antibody, after microwave oven processing, and anti-PCNA (PC10) monoclonal antibody using an avidin-biotin immunoperoxidase (ABC) method. One thousand cells from 10 representative fields were scored. Frozen sections from surgical specimens were stained with Ki67 monoclonal antibody using the ABC method; the fraction of Ki67 positive cells was calculated scoring 1000 cells. Flow cytometry analysis (FCM) was performed on cell suspensions from fresh tissues. Correlations between data were estimated using linear regression. RESULTS: A linear correlation was found between MIB-1 and Ki67 scores (r = 0.92; p < 0.00001); between MIB-1 and PCNA scores (r = 0.79; p < 0.00001); and between MIB-1 score and S-phase fraction (r = 0.51; p = 0.0006). A linear correlation was also found between Ki67 and PCNA scores (r = 0.85; p < 0.00001); between Ki67 score and S-phase fraction (r = 0.6; p = 0.0002); and between PCNA score and S-phase fraction (r = 0.74; p < 0.00001). A correlation was found between mitotic counts and MIB-1 (r = 0.56; p = 0.0001), PCNA (r = 0.51; p = 0.0007), or Ki67 scores (r = 0.47; p = 0.002); between the percentage of large cells and MIB-1 (r = 0.49; p = 0.0009), PCNA (r = 0.6; p = 0.00003), and Ki67 scores (r = 0.53; p = 0.0003) and S-phase fraction (r = 0.55; p = 0.0002). CONCLUSION: MIB-1, Ki67, and PCNA (PC10) scores and S-phase fraction are highly correlated and equally well represent the proliferative activity of intermediate grade non-Hodgkin's lymphomas in differently processed material. MIB-1 and PCNA stains can be applied even on small biopsy specimens. MIB-1 produces homogenous staining without background; it also strongly stains mitotic figures. It can be performed on routinely processed tissues, permitting the simultaneous evaluation of the morphology and tumour cell kinetics. The wide standard deviations of the proliferative indices found for intermediate grade NHL suggest that this category probably includes various degrees of malignancy.

Antibodies, Monoclonal↗

PubMed2007

The influence of grafted polymer architecture and fluid hydrodynamics on protein separation by entropic interaction chromatography.

Entropic interaction chromatography (EIC) provides efficient size-based separation of protein mixtures through the entropy change associated with solute partitioning into a layer of hydrophilic homopolymer that has been end-grafted within the pores of a macroporous chromatography support. In this work, surface-initiated atom-transfer radical polymerization (ATRP) is used to prepare a library of EIC stationary phases covering a wide range of grafted-chain densities and molecular weights. Exhaustive chain cleavage and analysis by saponification and GPC-MALLS, respectively, show that the new ATRP synthesis procedure allows for excellent control over graft molecular weight and polydispersity. The method is used to prepare high-density grafts (up to 0.164 +/- 0.005 chains/nm(2)) that extend the range of EIC applications to include efficient buffer-exchange and desalting of protein preparations. Reducing the graft density allows for greater partitioning of high molecular weight solutes, extending the linear range of the selectivity curve. Increasing graft molecular weight also alters selectivity, but more directly affects column capacity by increasing the volume of the grafted layer. Protein partitioning in high-density EIC columns is found to decrease with mobile-phase velocity (u). Although solute mass transfer resistances leading to an increase in plate height can explain this effect, pressure drop data across the column are indicative of weak convective flow through at least a fraction of the grafted architecture. Modeling of the grafted brush properties in the presence of solvent flow by subjecting a self-consistent-field theory representation of the brush to a viscous shear force predicts that the grafted chains will tilt and elongate in the direction of flow. The shear force may therefore act to reduce the number of conformations available to chains, increasing their rigidity without significantly altering the thickness of the grafted layer. A reduction in protein partitioning is then predicted when the dependence on u of the solute entropy loss is stronger than that of the grafted polymer, a condition met at high graft densities.

Chromatography, Gel↗

PubMed1998

Application of free-flow electrophoresis to the purification of trichosanthin from a crude product of acetone fractional precipitation.

The application of free-flow electrophoresis (FFE) to the purification of trichosanthin (TCS) from a crude product of acetone fractional precipitation was investigated. An electrophoresis technique, combining field step electrophoresis (FSE) and zone electrophoresis (ZE) to a one-step procedure, was optimized until a satisfactory purification factor (1.35), high resolution, and purity (>99%) were achieved. Testing several separation buffer systems revealed that a throughput of 14.2 mg/h can be obtained when the very basic TCS (pI 10.1) was dissolved and electrophoresed in a phosphate buffer system of pH 4. The purity of electrophoresed trichosanthin was proved by a variety of analytical methods, such as sodium dodecyl sulfate (SDS)-gel electrophoresis, capillary isoelectric focusing (CIEF), and sequencing of N- and C-termini. The high purity and large throughput achieved at low cost by using FFE indicates that this method can be employed for TCS purification.

Acetone↗

PubMed2005

Plutonium in groundwater at the 100K-Area of the U.S. DOE Hanford Site.

We examined the concentration, size distribution, redox state and isotopic composition of plutonium (Pu) in groundwater at the 100K-Area at the U.S. Department of Energy's (DOE) Hanford Site. Total concentrations of Pu isotopes were extremely low (10(-4) to 10(-6) pCi/kg, approximately 10(4) to 10(6) atoms/kg) but measurable for the first time in the 100K-Area wells using mass spectrometric analyses that are much more sensitive than alpha spectroscopy methods used previously. Size fractionation data from two wells suggest that 7-29% of the Pu is associated with colloids, operationally defined here as particles between 1 kDa-0.2 microm in size. These colloids were collected using a 1 kDa cross-flow ultrafiltration (CFF) system developed specifically for groundwater actinide studies to include careful controls both in the field and during processing to ensure in situ geochemical conditions are maintained and size separations can be well characterized. Pu in this colloidal fraction was exclusively in the more reduced Pu(III/IV) form, consistent with the higher affinity of Pu in the lower oxidation states for particle surfaces. While the overall concentrations of Pu were low, the Pu isotopic composition suggests at least two local sources of groundwater Pu, namely, local Hanford reactor operations at the 100K-Area and spent nuclear fuel from the N-reactor, which was stored in concrete pools at this site. Differences between this site and the Savannah River Site (SRS) are noted, since groundwater Pu at the F-Area seepage basin at SRS has been found using these same methods, to be characterized by lower colloidal abundances and higher oxidation states. This difference is not directly attributable to groundwater redox potential or geochemical conditions, but rather the physical-chemical difference in Pu sources, which at SRS appear to be dominated downstream from the seepage basins by decay of 244Cm, resulting in more oxidized forms of 240Pu. There is no clear evidence for colloid facilitated transport of Pu in groundwater at the Hanford Site, since downstream wells have both an order of magnitude lower concentrations of Pu and a lower fractional colloidal distribution.

Colloids↗

PubMed2000

Invasion percolation with long-range correlations: first-order phase transition and nonuniversal scaling properties

We present the results of extensive Monte Carlo simulations of the invasion percolation model with trapping (TIP) with long-range correlations, a problem which is relevant to multiphase flow in field-scale porous media, such as oil reservoirs and groundwater aquifers, as well as flow in rock fractures. The correlations are generated by a fractional Brownian motion characterized by a Hurst exponent H. We employ a highly efficient algorithm for simulating TIP, and a novel method for identifying the backbone of TIP clusters. Both site and bond TIP are studied. Our study indicates that the backbone of bond TIP is loopless and completely different from that of site TIP. We obtain precise estimates for the fractal dimensions of the sample-spanning cluster (SSC), the minimal path, and the backbone of site and bond TIP, and analyze the size distribution of the trapped clusters, in order to identify all the possible universality classes of TIP with long-range correlations. For site TIP with H > 1/2 the SSC and its backbone are compact, indicating a first-order phase transition at the percolation threshold, while the minimal paths are essentially straigth lines. For H < 1/2 the SSC, its backbone, and the minimal paths are all fractal with fractal dimensions that depend on the Hurst exponent H. The fractal dimension of the loopless backbone for bond TIP is much less than that of site TIP for any H.

Journal Article↗

PubMed2003

Microbial in situ degradation of aromatic hydrocarbons in a contaminated aquifer monitored by carbon isotope fractionation.

We present an approach for characterizing in situ microbial degradation using the 13C/12C isotope fractionation of contaminants as an indicator of biodegradation. The 13C/12C isotope fractionation of aromatic hydrocarbons was studied in anoxic laboratory soil percolation columns with toluene or o-xylene as the sole carbon and electron source, and sulfate as electron acceptor. After approximately 2 months' of incubation, the soil microbial community degraded 32 mg toluene l(-1) and 44 mg o-xylene l(-1) to less than 0.05 mg l(-1), generating a stable concentration gradient in the column. The 13C/12C isotope ratio in the residual non-degraded fraction of toluene and o-xylene increased significantly, corresponding to isotope fractionation factors (alphaC) of 1.0015 and 1.0011, respectively. When the extent of biodegradation in the soil column was calculated based on the measured isotope ratios (R(t)) and an isotope fractionation factor (alphaC=1.0017) obtained from a sulfate-reducing batch culture the theoretical residual substrate concentrations (C(t)) matched the measured toluene concentrations in the column. This indicated that a calculation of biodegradation based on isotope fractionation could work in systems like soil columns. In a field study, a polluted, anoxic aquifer was analyzed for BTEX and PAH contaminants. These compounds were found to exhibit a significant concentration gradient along an 800-m groundwater flow path downstream of the source of contamination. A distinct increase in the carbon isotope ratio (delta13C) was observed for the residual non-degraded toluene (7.2 per thousand ), o-xylene (8.1 per thousand ) and naphthalene fractions (1.2 per thousand ). Based on the isotope values and the laboratory-derived isotope fractionation factors for toluene and o-xylene, the extent to which the residual substrate fraction in the monitoring wells had been degraded by microorganisms was calculated. The results revealed significant biodegradation along the groundwater flow path. In the wells at the end of the plume, the bioavailable toluene and o-xylene fractions had been almost completely reduced by in situ microbial degradation. Although indane and indene showed decreasing concentrations downstream of the groundwater flow path, suggesting microbial degradation, their carbon isotope ratios remained constant. As the physical properties of these compounds are similar to those of BTEX compounds, the constant isotope values of indane and indene indicated that microbial degradation did not lead to isotope fractionation of all aromatic hydrocarbons. In addition, physical interaction with the aquifer material during the groundwater passage did not significantly alter the carbon isotope composition of aromatic hydrocarbons.

Biodegradation, Environmental↗

PubMed1995

Design of a high-precision fraction collector for capillary electrophoresis.

A high-precision fraction collector for capillary electrophoresis has been developed. The device utilizes detection close to the end of the capillary and a sheath liquid at the exit of the capillary, allowing continuous collection (i.e., uninterrupted applied electrical field) of multiple species. The role of the sheath liquid flow rate and position of detection in the column on the collection precision was assessed. Fiber-optic detection at approximately 1 cm before the exit end of the capillary was found effective for precise timing of the collection. Up to 60 fractions of microliter or smaller volumes could be automatically collected into capillaries used as collection vials. The collection capillaries were placed on a cylinder, and a computer-controlled stepping motor aligned the appropriate capillary with the column exit. The effectiveness of the fraction collector was demonstrated in the collection of all 11 fragments of the HaeIII restriction digest of phi X-174 plasmid DNA. Polymerase chain reaction amplification of the 271 and 281 bp fragments revealed an inversion of the size-dependent migration order.

Bacteriophage phi X 174↗

PubMed2005

Controlling cell destruction using dielectrophoretic forces.

Measurements are reported of the main factors, namely the AC voltage frequency and magnitude, that were observed to influence the number of cells destroyed during dielectrophoresis (DEP) experiments on Jurkat T cells and HL60 leukemia cells. Microelectrodes of interdigitated and quadrupolar geometries were used. A field-frequency window has been identified that should be either avoided or utilised, depending on whether or not cell damage is to be minimised or is a desired objective. The width and location of this frequency window depends on the cell type, as defined by cell size, morphology and dielectric properties, and is bounded by two characteristic frequencies. These frequencies are the DEP cross-over frequency, where a cell makes the transition from negative to positive DEP, and a frequency determined by the time constant that controls the frequency dependence of the field induced across the cell membrane. When operating in this frequency window, and for the microelectrode designs used in this work, cell destruction can be minimised by ensuring that cells are not directed by positive DEP to electrode edges where fields exceeding 30-40 kV/m are generated. Alternatively, this field-frequency window can be exploited to selectively destroy specific cell types in a cell mixture.

Cell Fractionation↗

PubMed1986

Deformability and other rheological interactions of red blood cells in electronic cell sizing.

The red blood cell apparent-size spectrum, obtained using resistive pulse spectroscopy (RPS) with typical electrical response times, is characterized by a bimodality, which in turn is quantified by a bimodality index. The magnitude of the index reflects the nonuniformity in distribution of particle trajectories within the orifice, itself a function of cell deformability. In measurements of mixed populations of glutaraldehyde-fixed and native cells, the index is found to be linearly dependent on the fraction of deformable cells. The index, previously known to be a function of flow rate, is now found to be a function of the electric field strength within the orifice as well. Furthermore a previously reported time-dependent loss of bimodality, for the uncounted cells remaining in a counting-vial suspension, appears to be a function of the electric field strength far outside the orifice. The relationship between the pressure drop across the orifice and the average linear fluid velocity through the orifice has been measured, and it is concluded that the flow within the orifice is non-turbulent, at all but the highest flow rates. The non-turbulent flow condition, coupled with the short resident time within the orifice, implies that the observed selection of different trajectories (as a function of cell deformability) must take place well in front of the orifice.

Animals↗

PubMed1998

Mechanism of electroporative dye uptake by mouse B cells.

The color change of electroporated intact immunoglobulin G receptor (Fc gammaR-) mouse B cells (line IIA1.6) after direct electroporative transfer of the dye SERVA blue G (Mr 854) into the cell interior is shown to be dominantly due to diffusion of the dye after the electric field pulse. Hence the dye transport is described by Fick's first law, where, as a novelty, time-integrated flow coefficients are introduced. The chemical-kinetic analysis uses three different pore states (P) in the reaction cascade (C <==> P1 <==> P2 <==> P3), to model the sigmoid kinetics of pore formation as well as the biphasic pore resealing. The rate coefficient for pore formation k(p) is dependent on the external electric field strength E and pulse duration tE. At E = 2.1 kV cm(-1) and tE = 200 micros, k(p) = (2.4 +/- 0.2) x 10(3) s(-1) at T = 293 K; the respective (field-dependent) flow coefficient and permeability coefficient are k(f)0 = (1.0 +/- 0.1) x 10(-2) s(-1) and P0 = 2 cm s(-1), respectively. The maximum value of the fractional surface area of the dye-conductive pores is 0.035 +/- 0.003%, and the maximum pore number is Np = (1.5 +/- 0.1) x 10(5) per average cell. The diffusion coefficient for SERVA blue G, D = 10(-6) cm2 s(-1), is slightly smaller than that of free dye diffusion, indicating transient interaction of the dye with the pore lipids during translocation. The mean radii of the three pore states are r(P1) = 0.7 +/- 0.1 nm, r(P2) = 1.0 +/- 0.1 nm, and r(P3) = 1.2 +/- 0.1 nm, respectively. The resealing rate coefficients are k(-2) = (4.0 +/- 0.5) x 10(-2) s(-1) and k(-3) = (4.5 +/- 0.5) x 10)(-3) s(-1), independent of E. At zero field, the equilibrium constant of the pore states (P) relative to closed membrane states (C) is K(p)0 = [(P)]/[C] = 0.02 +/- 0.002, indicating 2.0 +/- 0.2% water associated with the lipid membrane. Finally, the results of SERVA blue G cell coloring and the new analytical framework may also serve as a guideline for the optimization of the electroporative delivery of drugs that are similar in structure to SERVA blue G, for instance, bleomycin, which has been used successfully in the new discipline of electrochemotherapy.

Animals↗

PubMed2006

Assessment of the multi-scale leaching behaviour of compacted coal fly ash.

Peer experimental-modelling tools were developed and applied in the case of coal fly ashes with the aim to assess the leaching behaviour of ash compacted layers in a use scenario. Laboratory-scale (dissolution kinetics, ANC test, column percolation) and field pilot experimental studies (release monitoring during 18 month, hydrodynamic study, ANC on 44 month leached waste) were performed in order to identify and quantify the main transport phenomena and chemical processes. A quantitative geochemical model was developed taking into account equilibrium chemical reactions as well as kinetic processes for silicate phases like albite, K-feldspar and Ca-olivine. Phases like BaHAsO(4) and a solid solution Ba(x)Sr(1-x)(SO(4))(y)(CrO(4))(1-y) were proposed to explain the complex leaching behaviour of As, Cr, Ba, S; the soluble CaMoO(4) seems to control the Mo concentration. At neutral and acid pH, the model of surface complexation on ferric hydroxides was added for describing the behaviour of As, Cr, and Mo. At each scale the dynamic processes were identified and quantified by modelling. During the first contact with water an equilibration time of about 10 days was identified and then considered in all other laboratory experiments (ANC, column percolation). The hydrodynamic properties of compacted fly ashes were identified: a high water retention capacity (97% of the pores are still filled after draining under normal pressure), a flow regime close to plug type, a low fraction of stagnant zones (<0.03%). The scenario factors like carbonation and rainfall play an important role on the leaching behaviour at field scale. The carbonation diminishes the leachate pH from 11 to 8.5. The alternation of rain periods determines an apparent batch behaviour which slows down the outflow of the initial soluble fraction in pore water, if compared with the laboratory percolation column. The coupled geochemical-transport model was validated by comparison of the simulation results on ANC data obtained on the waste after 44 months of leaching under natural conditions.

Acids↗

PubMed2004

Velocity field measurement in gas-liquid metal two-phase flow with use of PIV and neutron radiography techniques.

To establish reasonable safety concepts for the realization of commercial liquid-metal fast breeder reactors, it is indispensable to demonstrate that the release of excessive energy due to re-criticality of molten core could be prevented even if a severe core damage accident took place. Two-phase flow due to the boiling of fuel-steel mixture in the molten core pool has a larger liquid-to-gas density ratio and higher surface tension in comparison with those of ordinary two-phase flows such as air-water flow. In this study, to investigate the effect of the recirculation flow on the bubble behavior, visualization and measurement of nitrogen gas-molten lead bismuth in a rectangular tank was performed by using neutron radiography and particle image velocimetry techniques. Measured flow parameters include flow regime, two-dimensional void distribution, and liquid velocity field in the tank. The present technique is applicable to the measurement of velocity fields and void fraction, and the basic characteristics of gas-liquid metal two-phase mixture were clarified.

Journal Article↗

PubMed2001

Effect of chronic bladder outlet obstruction on blood flow of the rabbit bladder.

PURPOSE: Previous studies have shown that the initial reaction of the rabbit bladder to partial bladder outlet obstruction is increased blood flow at day 1 and a return to baseline blood flow at 1 week. Mucosal and muscle blood flow followed this pattern but mucosal blood flow was always 4 to 5-fold greater. In this study we examined the effect of 4 weeks of outlet obstruction on bladder blood flow and correlated it with the severity of bladder contractile dysfunction. MATERIALS AND METHODS: A total of 14 male New Zealand White rabbits underwent partial outlet obstruction creation by standard methods. After 4 weeks the rabbits were anesthetized, and blood flow to the muscle and mucosa was determined by standard fluorescent microsphere technique. A section of each detrusor was used for in vitro contractility studies. Contractile responses to field stimulation, carbachol and potassium chloride were determined. A section of each detrusor tissue was fixed in formalin and used to determine the smooth muscle volume fraction. RESULTS: Four weeks of partial bladder outlet obstruction caused a significant and variable increase in bladder weight and a decrease in blood flow to bladder muscle without changes in the blood flow to mucosa. There was a clear correlation between the severity of contractile dysfunction, bladder weight and the magnitude of the decrease in blood flow in muscle. The smooth muscle volume fraction remained stable at approximately 40%. CONCLUSIONS: Bladder decompensation was associated with decreased blood flow to bladder smooth muscle. Because compensated obstructed bladders with relatively normal contractile function are also hypertrophied but have normal blood flow, decreased blood flow in decompensated bladders is not simply a response to bladder hypertrophy. From this study we hypothesize that decreased blood flow to bladder smooth muscle is an etiological factor in bladder contractile dysfunction (bladder decompensation) secondary to partial outlet obstruction.

Animals↗

PubMed1991

Beta-adrenergic stimulation contributes to incretin effect in conscious dogs.

Oral glucose administration increases insulin secretion to a greater extent than peripheral glucose infusion (incretin effect). It also augments protal vein blood flow, hepatic uptake of glucose, and fractional hepatic extraction of insulin. The mechanisms for these various effects are not known but could involve both neurogenic stimuli and gut hormones. The present studies examined the effect of a non-nutrient drink, 1 g/kg body wt oral mannitol, on these parameters during an intravenous glucose infusion in conscious dogs. The dogs had chronically implanted Doppler flow probes on the portal vein and hepatic artery and catheters in the portal vein, hepatic vein, and femoral artery. After a 30-min control period, an infusion of atropine, propranolol, phentolamine, or propranolol and phentolamine was begun. Thirty minutes later, glucose (13 mg.kg-1.min-1) was then infused into a peripheral vein for 120 min with continuation of the atropine and adrenergic blockade. Water or mannitol (10% solution) was administered orally 50 min after the initiation of the glucose infusion. Mannitol, but not water, significantly enhanced the insulin response to intravenous glucose, as indicated by higher insulin concentrations in the portal vein as well as more rapid reduction of the plasma glucose. This incretin effect was significantly attenuated by infusion of propranolol but not by atropine or phentolamine. Mannitol did not increase portal vein blood flow or have any effect on the hepatic uptake of glucose or the fractional hepatic extraction of insulin. Thus absorption of nutrient is not necessary for the incretin effect but is for the increased portal vein blood flow and increased fractional extraction of insulin.(ABSTRACT TRUNCATED AT 250 WORDS)

Administration, Oral↗

PubMed2007

Blood progenitor cell separation from clinical leukapheresis product by magnetic nanoparticle binding and magnetophoresis.

Positive selection of CD34+ blood progenitor cells from circulation has been reported to improve patient recovery in applications of autologous transplantation. Current magnetic separation methods rely on cell capture and release on solid supports rather than sorting from flowing suspensions, which limits the range of therapeutic applications and the process scale up. We tested CD34+ cell immunomagnetic labeling and isolation from fresh leukocyte fraction of peripheral blood (leukapheresis) using the continuous quadrupole magnetic flow sorter (QMS), consisting of a flow channel (SHOT, Greenville, IN) and a quadrupole magnet with a maximum field intensity (B(o)) of 1.42 T and a mean force field strength (S(m)) of 1.45 x 10(8) TA/m(2). Both the sample magnetophoretic mobility (m) and the inlet and outlet flow patterns highly affect the QMS performance. Seven commercial progenitor cell labeling reagent combinations were quantitatively evaluated by measuring magnetophoretic mobility of a high CD34 expression cell line, KG-1a, using the cell tracking velocimeter (CTV). The CD34 Progenitor Cell Isolation Kit (Miltenyi Biotec, Bergisch Gladbach, Germany) showed the strongest labeling of KG-1a cells and was selected for progenitor cell enrichment from 11 fresh and 11 cryopreserved clinical leukapheresis samples derived from different donors. The CD34+ cells were isolated with a purity of 60-96%, a recovery of 18-60%, an enrichment rate of 12-169, and a throughput of (1.7-9.3) x 10(4) cells/s. The results also showed a highly regular dependence of the QMS performance on the flow conditions that agreed with the theoretical predictions based on the CD34+ cell magnetophoretic mobility.

Antigens, CD34↗

PubMed2005

Quasi-static electrorheological properties of hematite/silicone oil suspensions under DC electric fields.

In this work, a modified rheometer has been used to gain information on the "start-up" of the shear flow of an electrorheological (ER) fluid consisting of hematite particles dispersed in silicone oil. The results show that unelectrified suspensions behave essentially as fluids, continuously deforming upon application of shear. However, this behavior changes in the presence of an electric field. For low fields and low volume fractions of solids, a solidlike (drastic increase in shear stress after the strain is applied) behavior is observed for small deformations. If the strain is increased, the yield starts and a transition to a viscoelastic-plastic nature is observed. Finally, a plastic behavior is characteristic of the post-yield regime. If the field strength and solids content are high, a discontinuous flow profile develops. These results, together with direct structural observations, suggest that the observed behavior is compatible with the formation of layers of particles electrophoretically deposited on the electrodes; the layers turn into rings when the shear field is applied. It is the slip of the fluid between these rings that can be considered responsible for the ER effect in these suspensions.

Journal Article↗

PubMed2001

Evaluating non-equilibrium solute transport in small soil columns.

Displacement studies on leaching of bromide and two pesticides (atrazine and isoproturon) were conducted under unsaturated steady state flow conditions in 24 small undisturbed soil columns (5.7 cm in diameter and 10 cm long) each collected from two sites differing in soil structure and organic carbon content in North Germany. There were large and irregular variabilities in the characteristics of both soils, as well as in the shapes of breakthrough curves (BTCs) of different columns, including some with early breakthrough and increased tailing, qualitatively indicating the presence of preferential flow. It was estimated that one preferential flow column (PFC) at site A, and four at site B, contributed, respectively to 11% and 58% of the accumulated leached fraction and to more than 80% of the maximum observed standard deviation (SD) in the field-scale concentration and mass flux of pesticides at two sites. The bromide BTCs of two sites were analyzed with the equilibrium convection-dispersion equation (CDE) and a non-equilibrium two-region/mobile-immobile model. Transport parameters of these models for individual BTCs were determined using a curve fitting program, CXTFIT, and by the time moment method. For the CDE based equilibrium model, the mean values of retardation factor, R, considered separately for all columns, PFCs or non-preferential flow columns (NPFCs) were comparable for the two methods; significant differences were observed in the values of dispersion coefficients of two sites using the two estimation methods. It was inferred from the estimated parameters of non-equilibrium model that 5-12% of water at site A, and 12% at site B, was immobile during displacement in NPFCs. The corresponding values for PFCs of two sites were much larger, ranging from 25% to 51% by CXTFIT and from 24% to 72% by the moment method, suggesting the role of certain mechanisms other than immobile water in higher degrees of non-equilibrium in these columns. Peclet numbers in PFCs of both sites were consistently smaller than five, indicating the inadequacy of the non-equilibrium model to incorporate the effect of all forms of non-equilibrium in PFCs. Overall, the BTCs of individual NPFCs, PFCs and of field average concentration at the two sites were better reproduced with parameters obtained from CXTFIT than by the moment method. The moment method failed to capture the peak concentrations in PFCs, but tended to describe the desorption and tail branches of BTCs better than the curve fitting approach.

Atrazine↗