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At least 397 records · Page 22Linked to original sources
PubMed2003

Experiment and simulation of laminar and turbulent ferrofluid pipe flow in an oscillating magnetic field.

Laminar and turbulent pipe flow of a ferrofluid with an imposed linearly polarized, oscillating, magnetic field is examined here. Experimental results show a fractional pressure drop dependence on flow rate, magnetic field strength, and oscillation frequency. Calculations are presented, which show that ferrofluid theory can explain the flow phenomena in laminar and turbulent pipe flow. The model requires an initial fit of key parameters but then shows predictive capability in both laminar and turbulent flow. Simulation results are found to be essentially independent of the spin boundary condition due to an approximation of spin viscosity that is very small. A low Reynolds number k-epsilon model is used to model the turbulent pipe flow.

Journal Article↗
PubMed2006

Impact of flow path length and flow rate on phosphorus loss in simulated overland flow from a humic gleysol grassland soil.

In this overland flow simulation experiment, the relationships between flow path length, flow rate and the concentration of different P fractions were investigated. Overland flow was simulated using a 3 mx0.12 m laboratory flume. To remove the impact of rainfall on P lost in overland flow, simulated rainfall was not used during these experiments. Instead overland flow was generated by pumping water into the flume at the surface of the grass sod. The experimental setup allowed for the variation in flow path length and flow rate between and during experimental runs. The results demonstrated that an increase in flow path length caused an increase in Total Dissolved P (TDP), Dissolved Reactive P (DRP) and Total Reactive P (TRP) concentration in overland flow (p<0.01) while an increase in flow rate resulted in a decrease in the concentration of these P fractions in overland flow due to dilution (p<0.01). Total P (TP), Particulate P (PP) and Dissolved Organic P were not affected by the variables tested during this study. When flow path length was increased in conjunction with flow rate, there was an increase in TDP, DRP, and TRP concentrations despite the impact of greater dilution. The results indicate that variations in flow path length during a rainfall event may play a role in determining the concentration of dissolved P fractions in overland flow at field scale.

Phosphorus↗
PubMed2006

Continuous flow magnetic cell fractionation based on antigen expression level.

Cell separation is important in medical and biological research and plays an increasingly important role in clinical therapy and diagnostics, such as rare cancer cell detection in blood. The immunomagnetic labeling of cells with antibodies conjugated to magnetic nanospheres gives rise to a proportional relationship between the number of magnetic nanospheres attached to the cell and the cell surface marker number. This enables the potential fractionation of cell populations by magnetophoretic mobility (MM). We exploit this feature with our apparatus, the Dipole Magnet Flow Fractionator (DMFF), which consists of an isodynamic magnetic field, an orthogonally-oriented thin ribbon of cell suspension in continuous sheath flow, and ten outlet flows. From a sample containing a 1:1 mixture of immunomagnetically labeled (label+) and unlabeled (label-) cells, we achieved an increase in enrichment of the label+ cell fraction with increasing outlet numbers in the direction of the magnetic field gradient (up to 10-fold). The total recovery of the ten outlet fractions was 90.0+/-7.7%. The mean MM of label+ cells increased with increasing outlet number by up to a factor of 2.3. The postulated proportionality between the number of attached magnetic beads and the number of cell surface markers was validated by comparison of MM measured by cell tracking velocimetry (CTV) with cell florescence intensity measured by flow cytometry.

Antigens↗
PubMed2000

Characterising phosphorus loss in surface and subsurface hydrological pathways

The magnitude and composition of the phosphorus (P) load transported in surface and subsurface hydrological pathways from a grassland catchment depends on the discharge capacity of the flow route and the frequency with which the pathway operates. Surface runoff is an important pathway for P loss, but this pathway is spatially limited and temporarily confined to high magnitude, high intensity rainfall events. High P concentrations (mean: 1.1 mg TP l(-1)) were recorded, with most P transported in the dissolved fraction. Preferential flow pathways, particularly soil macropores and field drains, are important contributors to the overall P load; most P is transported in the particulate fraction and associated with organic or colloidal P forms. High P concentrations (mean: 1.2 mg TP l(-1)) were recorded in macropore flow in the upper 0-15 cm of a grassland soil, and generally declined with increasing soil depth. On average, P concentrations in drainflow were over six times greater in stormflow compared to baseflow. Stormflow P losses in drainflow were predominantly in the particulate fraction; significant correlation (P < 0.01) was recorded with suspended sediment concentrations in drainflow. Phosphorus concentrations in groundwater were low (< 0.2 mg TP l(-1) at 150 cm), although this pathway may contribute to stream flow for the majority of the year.

Journal Article↗
PubMed1993

Erythrocyte behavior in free-flow electrophoresis is independent of erythrocyte age.

Enzyme activities (acetylcholinesterase, fluorescein diacetate hydrolase, superoxide dismutase), membrane protein band 4.1a/4.1b ratio and density of various fractions of rabbit erythrocytes separated did not show differences between various fractions of erythrocytes separated by free-flow electrophoresis. Also, electric field deflection of lightest and densest fractions of erythrocytes did not differ. These results point to the lack of changes in surface charge density during in vivo erythrocyte aging.

Acetylcholinesterase↗
PubMedDate not supplied

Migrainous cerebral infarction: a tomographic study of cerebral blood flow and oxygen extraction fraction with the oxygen-15 inhalation technique.

A patient with migraine who had a permanent visual field defect was studied by angiography and CT scan. He also had a tomographic study of cerebral blood flow (CBF) and oxygen extraction fraction (EO2) using the non-invasive continuous oxygen-15 (15O) inhalation technique. Angiography was normal. CT scan revealed an area of decreased density with contrast enhancement suggestive of a recent infarct in the left occipital lobe. The 15O inhalation technique showed a decrease in CBF and EO2, typical of recent infarcts, in the corresponding area, an increase in CBF with normal EO2 in the left temporal lobe, and a decrease in CBF with increased EO2 in the right occipital cortex. These findings illustrate the unusual nature and extent of the ischemic process underlying migrainous cerebral infarction.

Cerebral Angiography↗
PubMed2000

Electroosmotic capillary flow with nonuniform zeta potential

The present work is an analytical and experimental study of electroosmotic flow (EOF) in cylindrical capillaries with nonuniform wall surface charge (zeta-potential) distributions. In particular, this study investigates perturbations of electroosmotic flow in open capillaries that are due to induced pressure gradients resulting from axial variations in the wall zeta-potential. The experimental inquiry focuses on electroosmotic flow under a uniform applied field in capillaries with an EOF-suppressing polymer adsorbed onto various fractions of the total capillary length. This fractional EOF suppression was achieved by coupling capillaries with substantially different zeta-potentials. The resulting flow fields were imaged with a nonintrusive, caged-fluorescence imaging technique. Simple analytical models for the velocity field and rate of sample dispersion in capillaries with axial zeta-potential variations are presented. The resulting induced pressure gradients and the associated band-broadening effects are of particular importance to the performance of chemical and biochemical analysis systems such as capillary electrokinetic chromatography and capillary zone electrophoresis.

Journal Article↗
PubMed2000

Modulation of the mechanical properties of tissue engineered cartilage.

Cartilaginous constructs have been grown in vitro using chondrocytes, biodegradable polymer scaffolds, and tissue culture bioreactors. In the present work, we studied how the composition and mechanical properties of engineered cartilage can be modulated by the conditions and duration of in vitro cultivation, using three different environments: static flasks, mixed flasks, and rotating vessels. After 4-6 weeks, static culture yielded small and fragile constructs, while turbulent flow in mixed flasks induced the formation of an outer fibrous capsule; both environments resulted in constructs with poor mechanical properties. The constructs that were cultured freely suspended in a dynamic laminar flow field in rotating vessels had the highest fractions of glycosaminoglycans and collagen (respectively 75% and 39% of levels measured in native cartilage), and the best mechanical properties (equilibrium modulus, hydraulic permeability, dynamic stiffness, and streaming potential were all about 20% of values measured in native cartilage). Chondrocytes in cartilaginous constructs remained metabolically active and phenotypically stable over prolonged cultivation in rotating bioreactors. The wet weight fraction of glycosaminoglycans and equilibrium modulus of 7 month constructs reached or exceeded the corresponding values measured from freshly explanted native cartilage. Taken together, these findings suggest that functional equivalents of native cartilage can be engineered by optimizing the hydrodynamic conditions in tissue culture bioreactors and the duration of tissue cultivation.

Animals↗
PubMed2004

Void fraction and velocity measurement of simulated bubble in a rotating disc using high frame rate neutron radiography.

To evaluate measurement error of local void fraction and velocity field in a gas-molten metal two-phase flow by high-frame-rate neutron radiography, experiments using a rotating stainless-steel disc, which has several holes of various diameters and depths simulating gas bubbles, were performed. Measured instantaneous void fraction and velocity field of the simulated bubbles were compared with the calculated values based on the rotating speed, the diameter and the depth of the holes as parameters and the measurement error was evaluated. The rotating speed was varied from 0 to 350 rpm (tangential velocity of the simulated bubbles from 0 to 1.5 m/s). The effect of shutter speed of the imaging system on the measurement error was also investigated. It was revealed from the Lagrangian time-averaged void fraction profile that the measurement error of the instantaneous void fraction depends mainly on the light-decay characteristics of the fluorescent converter. The measurement error of the instantaneous local void fraction of simulated bubbles is estimated to be 20%. In the present imaging system, the light-decay characteristics of the fluorescent converter affect the measurement remarkably, and so should be taken into account in estimating the measurement error of the local void fraction profile.

Journal Article↗
PubMed1977

Development and application of a fully automated continuous flow radioimmunoassay system.

A fully automated, continuous flow radioimmunoassay system is described. The antibodies are covalently linked to a magnetic cellulose solid phase and separation of bound and free antigen is achieved by applying an external electromagnetic field. The bound fraction, after washing, is counted in a flow-through gamma counter chamber. The system employing Auto Analyzer modules, is highly reproducible and allows assays to be performed without equilibrium being reached, and only 10 minutes incubation time is required. The method is universally applicable to the assay of ligands, either protein, hormone, or drug, and for obtaining information about binding proteins. A new approach to the latter has been developed and is illustrated by a fully automated thyroid hormone uptake test which gives better discrimination between normal and pathological states than existing assays. The system operates at 30 samples/h and is characterised by the high precision, speed, and minimal carry-over which can be achieved.

Antigens↗
PubMed2004

Observation of multipactor in an alumina-based dielectric-loaded accelerating structure.

We report a new regime of single-surface multipactor that was observed during high-power testing of an 11.424-GHz alumina-based dielectric-loaded accelerating structure. Previous experimental observations of single-surface multipactor on a dielectric occurred in cases for which the rf electric field was tangential and the rf power flow was normal to the dielectric surface (such as on rf windows) and found that the fraction of power absorbed at saturation is approximately 1%, independent of the incident power. In this new regime, in which strong normal and tangential rf electric fields are present and the power flow is parallel to the surface, the fraction of power absorbed at saturation is an increasing function of the incident power, and more than half of the incident power can be absorbed. A simple model is presented to explain the experimental results.

Journal Article↗
PubMedDate not supplied

Assessment of mitral regurgitation by magnetic resonance imaging.

To evaluate the potential of magnetic resonance imaging (MRI) in detection and quantification of mitral regurgitation, 26 pts. with echocardiographically or angiographically documented mitral regurgitation were examined using a 0.5 Tesla superconducting magnet. In each patient a multislice-multiphase study in a sagittal-coronal double angulated projection (four-chamber view equivalent) was performed to assess left and right ventricular volumes, ejection fraction and regurgitant fraction. Additionally a blood flow sensitive cine-study (fast field echo: FFE) was done to visualize direction and area of regurgitant jet. MRI data were compared with quantitative and quantitative assessment of mitral regurgitation by angiography, 2D echocardiography, Doppler sonography and color flow mapping. Using the FFE mode MRI was able to detect the regurgitant jet as a typical signal loss within the left atrium in all patients. The ratio of regurgitant jet area/left atrium area as determined by MRI showed a correlation with a comparable ratio from color Doppler sonography of R = 0.87 (p less than 0.001). There was also good agreement in semiquantitative grading of mitral regurgitation between MRI and angiography (R = 0.77, p less than 0.001). The determination of left and right ventricular stroke volume allowed the calculation of the regurgitant fraction, which showed a correlation with invasively determined regurgitation fraction of R = 0.84 (p less than 0.001). These data provide additional information that MRI may be useful as a noninvasive technique to detect and quantify mitral regurgitation.

Adult↗
PubMed1995

The acceleration and collimation of jets.

I will discuss several issues related to the acceleration, collimation, and propagation of jets from active galactic nuclei. Hydromagnetic stresses provide the best bet for both accelerating relativistic flows and providing a certain amount of initial collimation. However, there are limits to how much "self-collimation" can be achieved without the help of an external pressurized medium. Moreover, existing models, which postulate highly organized poloidal flux near the base of the flow, are probably unrealistic. Instead, a large fraction of the magnetic energy may reside in highly disorganized "chaotic" fields. Such a field can also accelerate the flow to relativistic speeds, in some cases with greater efficiency than highly organized fields, but at the expense of self-collimation. The observational interpretation of jet physics is still hampered by a dearth of unambiguous diagnostics. Propagating disturbances in flows, such as the oblique shocks that may constitute the kiloparsec-scale "knots" in the M87 jet, may provide a wide range of untapped diagnostics for jet properties.

Journal Article↗
PubMed2005

Continuous-flow fractionation of animal cells in microfluidic device using aqueous two-phase extraction.

Monitoring of live cells is important in the field of medical science, diagnostics, biology, and the pharmaceutical industry. In this study, live and dead CHO-K1 (Chinese Hamster Ovary) cells were fractionated by continuous-flow extraction in a microfluidic device using immiscible aqueous two-phase extraction technique. The polymer solutions offered stable two-phase flows in microchannel without diffusive mixing. The fundamentals of aqueous two-phase extraction can support stable and reproducible recovery and separation of biomolecules in microfluidic devices. Polyethylene glycol 8000 (PEG 8000, 4%) and dextran T 500 (5%) were selected as model polymer solutions. The appropriate flow rates of polymer and cell solutions were suggested. The fractionation efficiency of live and dead CHO K-1 cells from the culture broth was compared in normal macroscale system and microfluidic device. The optimum pH for the fractionation was 6.6 in both the normal and micro-scale systems. The loss of target live cells by sedimentation was circumvented in microfluidic device because of the negligible effect of gravity on the sedimentation. Most live cells were distributed to PEG-rich phase, while dead cells were found at the interface of two polymer solutions in microchannel. In this case, the recovery and fractionation efficiency of live cells in the PDMS-based microfluidic device was 100% and 97.0%, respectively.

Animals↗
PubMed1999

Magnetic cell sorting is a fast and effective method of enriching viable spermatogonia from Djungarian hamster, mouse, and marmoset monkey testes.

Germ cell transplantation, which offers promising new approaches for research and clinical applications, has focused interest on spermatogonia. This paper describes a procedure that permits the isolation of large quantities of viable spermatogonia. The immunomagnetic isolation procedure was applied to testicular cell suspensions from photoinhibited and photostimulated Djungarian hamsters, mice, and marmoset monkeys. The cells were incubated with a polyclonal rabbit anti-c-kit IgG, binding of which was characterized by immunohistochemical staining. For magnetic labeling, a secondary anti-rabbit IgG conjugated to ferromagnetic microbeads was used. Separation columns allowed the retention of magnetically labeled cells within the matrix. The magnetic fractions were eluted after removal of the column from the magnetic field. All fractions were analyzed for cellular morphology and by flow cytometry. The final enrichment of c-kit-positive cells in the magnetic fraction using fully active testes was in the range of 25-55% with a viability rate of 80-90%. The magnetic fractions of all three species were characterized by high numbers of diploid cells. Cytological analysis revealed a strong enrichment of spermatogonia. No haploid cells were retained in the magnetic fraction. In comparison to conventional procedures, magnetic cell separation is an efficient and fast approach for isolation of spermatogonia.

Animals↗
PubMed2002

Isotopic fractionation during reductive dechlorination of trichloroethene by zero-valent iron: influence of surface treatment.

During reductive dechlorination of trichloroethene (TCE) by zero-valent iron, stable carbon isotopic values of residual TCE fractionate significantly and can be described by a Rayleigh model. This study investigated the effect of observed reaction rate, surface oxidation and iron type on isotopic fractionation of TCE during reductive dechlorination. Variation of observed reaction rate did not produce significant differences in isotopic fractionation in degradation experiments. However, a small influence on isotopic fractionation was observed for experiments using acid-cleaned electrolytic iron versus experiments using autoclaved electrolytic iron, acid-cleaned Peerless cast iron or autoclaved Peerless cast iron. A consistent isotopic enrichment factor of epsilon = -16.7/1000 was determined for all experiments using cast iron, and for the experiments with autoclaved electrolytic iron. Column experiments using 100% cast iron and a 28% cast iron/72% aquifer matrix mixture also resulted in an enrichment factor of -16.9/1000. The consistency in enrichment factors between batch and column systems suggests that isotopic trends observed in batch systems may be extrapolated to flowing systems such as field sites. The fact that significant isotopic fractionation was observed in all experiments implies that isotopic analysis can provide a direct qualitative indication of whether or not reductive dechlorination of TCE by Fe0 is occurring. This evidence may be useful in answering questions which arise at field sites, such as determining whether TCE observed down-gradient of an iron wall remediation scheme is the result of incomplete degradation within the wall, or of the dissolved TCE plume by passing the wall.

Carbon Isotopes↗
PubMed2005

Study on the wind field and pollutant dispersion in street canyons using a stable numerical method.

A stable finite element method for the time dependent Navier-Stokes equations was used for studying the wind flow and pollutant dispersion within street canyons. A three-step fractional method was used to solve the velocity field and the pressure field separately from the governing equations. The Streamline Upwind Petrov-Galerkin (SUPG) method was used to get stable numerical results. Numerical oscillation was minimized and satisfactory results can be obtained for flows at high Reynolds numbers. Simulating the flow over a square cylinder within a wide range of Reynolds numbers validates the wind field model. The Strouhal numbers obtained from the numerical simulation had a good agreement with those obtained from experiment. The wind field model developed in the present study is applied to simulate more complex flow phenomena in street canyons with two different building configurations. The results indicated that the flow at rooftop of buildings might not be assumed parallel to the ground as some numerical modelers did. A counter-clockwise rotating vortex may be found in street canyons with an inflow from the left to right. In addition, increasing building height can increase velocity fluctuations in the street canyon under certain circumstances, which facilitate pollutant dispersion. At high Reynolds numbers, the flow regimes in street canyons do not change with inflow velocity.

Air Pollutants↗