The haemodynamic effect of an adjustable band in an arteriovenous fistula

A number of treatment approaches exist for excessive flowrate arteriovenous fistulae. Banding has a number of advantages, yet there is concern over its use due to reported high post-surgery thrombosis rates. A computational study is conducted of a new technique, to elucidate the hemodynamics present in the process. The key improvement involves the use of an adjustable band which can be used to optimise the flowrate during the surgery. The pressure and flowrate changes are apparent from the computational results and the computational results also demonstrate that further optimization may be possible. We then present a small cohort of five cases where the new banding procedure has been implemented with success. The new technique was combined with intra-operative ultrasound flow monitoring.     

The effect of flow direction and magnitude on the initial distribution of Pseudomonas aeruginosa cells attached to glass

The effect of flowrate and Reynolds Number, Re, on the spatial distribution of individual Pseudomonas aeruginosa cells during their initial attachment to glass flowcells was observed in a series of time-lapse images obtained over a 56-h period. It was shown that flow affected the distribution at Re > 245. Under laminar flow conditions, Re = 96, the distribution of bacterial cells in 200 sub-areas was accurately predicted by using the Poisson distribution and was not dependent on the orientation or shape of the sub-areas. Under turbulent flow conditions, Re = 2220, cells initially attached in streaks along the line of flow. As bacterial cells accumulated on the surface, the streaks broadened and the distribution became more uniform. Analyses showed that, initially, flow had an effect on cell distribution in the flowcell with Re = 245, with significantly greater effects at higher Re. As the cell surface densities increased, the effect of flow direction on cell distribution decreased. It is concluded that the visco-elastic properties of the extracellular polymeric substances (EPS) in which the cells are embedded, significantly affect the distribution of attaching cells.     

Use and optimization of a dual-flowrate loading strategy to maximize throughput in protein-a affinity chromatography

The effect of an alternate strategy employing two different flowrates during loading was explored as a means of increasing system productivity in Protein-A chromatography. The effect of such a loading strategy was evaluated using a chromatographic model that was able to accurately predict experimental breakthrough curves for this Protein-A system. A gradient-based optimization routine is carried out to establish the optimal loading conditions (initial and final flowrates and switching time). The two-step loading strategy (using a higher flowrate during the initial stages followed by a lower flowrate) was evaluated for an Fc-fusion protein and was found to result in significant improvements in process throughput. In an extension of this optimization routine, dynamic loading capacity and productivity were simultaneously optimized using a weighted objective function, and this result was compared to that obtained with the single flowrate. Again, the dual-flowrate strategy was found to be superior.     

Influence of pH, temperature, and urea molar flowrate on Arthrospira platensis fed-batch cultivation: a kinetic and thermodynamic approach

Arthrospira platensis was cultivated photoautotrophically at 6.0 klux light intensity in 5.0-L open tanks, using a mineral medium containing urea as nitrogen source. Fed-batch experiments were performed at constant flowrate. A central composite factorial design combined to response surface methodology (RSM) was utilized to determine the relationship between the selected response variables (cell concentration after 10 days, X(m), cell productivity, P(X), and nitrogen-to-cell conversion factor, Y(X/N)) and codified values of the independent variables (pH, temperature, T, and urea flowrate, K). By applying the quadratic regression analysis, the equations describing the behaviors of these responses as simultaneous functions of the selected independent variables were determined, and the conditions for X(m) and P(X) optimization were estimated (pH 9.5, T = 29 degrees C, and K = 0.551 mM/day). The experimental data obtained under these conditions (X(m) = 749 mg/L; P(X) = 69.9 mg/L.day) were very close to the estimated ones (X(m) = 721 mg/L; P(X) = 67.1 mg/L.day). Additional cultivations were carried out under the above best conditions of pH control and urea flowrate at variable temperature. Consistently with the results of RSM, the best growth temperature was 29 degrees C. The maximum specific growth rates at different temperatures were used to estimate the thermodynamic parameters of growth (DeltaH* = 59.3 kJ/mol; DeltaS* = -0.147 kJ/mol.K; DeltaG* = 103 kJ/mol) and its thermal inactivation (DeltaH(D) (o) = 72.0 kJ/mol; DeltaS(D) (o) = 0.144 kJ/mol.K; DeltaG(D) (o) = 29.1 kJ/mol).     

A new kinetic Monte Carlo scheme with Gibbs ensemble to determine vapour–liquid equilibria

We present a new kinetic Monte Carlo scheme, as an alternative to the Gibbs ensemble Monte Carlo (GEMC) method, to determine vapour–liquid equilibria using a canonical ensemble in a system composed of two boxes. To illustrate the method, we have tested it with two systems: (1) argon over a range of temperatures from below the triple point to close to the critical point; (2) methane and ethane mixtures of various compositions at 180 K. The advantage of the new scheme is that chemical potentials of all components are accurately determined in both boxes. In particular, the chemical potential in the liquid box is determined much more accurately than with the Widom method employed in conventional GEMC simulations.     

Combined effects of pulsatile flow and dynamic curvature on wall shear stress in a coronary artery bifurcation model

A three-dimensional model with simplified geometry for the branched coronary artery is presented. The bifurcation is defined by an analytical intersection of two cylindrical tubes lying on a sphere that represents an idealized heart surface. The model takes into account the repetitive variation of curvature and motion to which the vessel is subject during each cardiac cycle, and also includes the phase difference between arterial motion and blood flowrate, which may be nonzero for patients with pathologies such as aortic regurgitation. An arbitrary Lagrangian Eulerian (ALE) formulation of the unsteady, incompressible, three-dimensional Navier-Stokes equations is employed to solve for the flow field, and numerical simulations are performed using the spectral/hp element method. The results indicate that the combined effect of pulsatile inflow and dynamic geometry depends strongly on the aforementioned phase difference. Specifically, the main findings of this work show that the time-variation of flowrate ratio between the two branches is minimal (less than 5%) for the simulation with phase difference angle equal to 90 degrees, and maximal (51%) for 270 degrees. In two flow pulsatile simulation cases for fixed geometry and dynamic geometry with phase angle 270 degrees, there is a local minimum of the normalized wall shear rate amplitude in the vicinity of the bifurcation, while in other simulations a local maximum is observed.     

A New Method for Mercury Removal

A method is desibed for the removal of mercury from solution by using the off-gas produced from aerobic cultures of Klebsiella pneumoniae M426. Cells growing in Hg-supplemented medium produced a black precipitate containing mercury and sulphur. The ratio of Hg:S was determined as ~1:1 by analysis using proton-induced X-ray emission, suggesting precipitation of HgS within the culture. The outlet gases produced by a mercury-unsupplemented aerated culture were bubbled into an external chamber supplemented with up to 10 mg HgCl₂/ml. A yellowish-white precipitate formed, corresponding to 99% removal of the mercury from solution within 120 min. Energy dispersive X-ray microanalysis showed that this metal precipitate consisted of mercury, carbon and sulphur. Formation of mercury carbonate was discounted since similar precipitation occurred at pH 2 and no oxygen was detected in the solid, which gave an X-ray powder pattern suggesting an amorphous material, with no evidence of HgS. Precipitation of mercury with a volatile organosulphur compound is suggested. Bio-precipitation of heavy metals by using culture off-gas is a useful approach because it can be used with concentrated or physiologically incompatible solutions. Since the metal precipitate is kept separate from the bacterial biomass, it can be managed independently.     

Pulsed microwave discharge in a capillary filled with atmospheric-pressure gas

A pulsed microwave coaxial capillary plasma source generating a thin plasma filament along the capillary axis in an atmospheric-pressure argon flow is described. The dynamics of filament formation is studied, and the parameters of the gas and plasma in the contraction region are determined. A physical model of discharge formation and propagation is proposed. The model is based on the assumption that, under the conditions in which the electric fields is substantially below the threshold value, the discharge operates in a specific form known as a self-sustained-non-self-sustained (SNS) microwave discharge.     

Non-Newtonian flow patterns associated with an arterial stenosis.

A non-Newtonian constitutive equation for blood has been introduced in this paper. Using this equation, blood flow attributes such as velocity profiles, flowrate, pressure gradient, and wall shear stress in both straight and stenotic (constricted) tubes have been examined. Results showed that compared with Newtonian flow at the same flowrate, the non-Newtonian normally features larger pressure gradient, higher wall shear stress, and different velocity profile, especially in stenotic tube. In addition, the non-Newtonian stenotic flow appears to be more stable than Newtonian flow.     

An assessment of the reaction energetics for cytochrome P450-mediated reactions

Regioselectivity is used to determine the absolute energetic differences for four different reactions catalyzed by P450. Abstraction of a hydrogen from a benzylic carbon containing a chlorine has a 1.0 kcal/mol lower barrier than abstraction from a simple benzylic carbon, which in turn is 0.4 to 0.9 kcal/mol lower than abstraction from the methyl group of an aromatic ether and 0.1 to 0.6 kcal/mol easier than aromatic hydroxylation. Isotope effects are used to determine if the enzyme-substrate complexes leading to each product, from a given substrate, are in rapid equilibrium. For all enzymes isotopically sensitive branching is observed from the benzylic carbon upon deuterium incorporation at that position to each of the other positions, indicating that each product arises from the same active oxygen species. The energetic differences determined experimentally are accurately reproduced by theoretical hydrogen atom abstractions at both the AM1 semiempirical and DFT levels of theory.     

Determination of in vivo oxygen uptake and carbon dioxide evolution rates from off-gas measurements under highly dynamic conditions

In vivo kinetics of Saccharomyces cerevisiae are studied, in a time window of 150 s, by analyzing the response of O(2) and CO(2) in the fermentor off-gas after perturbation of chemostat cultures by metabolite pulses. Here, a new mathematical method is presented for the estimation of the in vivo oxygen uptake rate (OUR) and carbon dioxide evolution rate (CER) directly from the off-gas data in such perturbation experiments. The mathematical construction allows effective elimination of delay and distortion in the off-gas measurement signal under highly dynamic conditions. A black box model for the fermentor off-gas system is first obtained by system identification, followed by the construction of an optimal linear filter, based on the identified off-gas model. The method is applied to glucose and ethanol pulses performed on chemostat cultures of S. cerevisiae. The estimated OUR is shown to be consistent with the independent dissolved oxygen measurement. The estimated in vivo OUR and CER provide valuable insights into the complex dynamic behavior of yeast and are essential for the establishment and validation of in vivo kinetic models of primary metabolism.     

Photoproduction of Hydrogen by the Marine Heterocystous Cyanobacterium Anabaena Species TU37-1 Under a Nitrogen Atmosphere

Hydrogen production rates by Anabaena sp. strain TU37-1 obtained after an initial 1-day incubation period were approximately 70 to 80 and 3 to 9 µmol (mg chl)^–1 h^–1 under argon and nitrogen atmospheres, respectively. Hydrogen production under argon was not enhanced by addition of carbon dioxide, but was enhanced to some extent under nitrogen by increasing the initial carbon dioxide concentration. Rates of hydrogen and oxygen production during the initial 7-hour period were 15 and 220 µmol (mg chl)^–1 h^–1, respectively, in vessels with 18.5% initial carbon dioxide. Hydrogen production under nitrogen was enhanced by addition of carbon monoxide (1%). The rate obtained from the initial 1-day incubation period was about 40 µmol (mg chl)^–1 h^–1, which corresponded to about 60% of that under argon. On the basis of these observations, a possible strategy for hydrogen production by nitrogen-fixing cyanobacteria under nitrogen in the presence of carbon monoxide is indicated.     

Application of a pulsed electric field to cross-flow ultrafiltration of protein solution

The application of pulsed electric field was investigated in the crossflow ultrafiltration of BSA (bovine serum albumn) to economize the application time of electric current as well as to avoid inherent problems of long-term application of electric field. During the application of various cyclic patterns of pulsed electric current, the averaged filtration flowrate and the degree of concentration were maintained higher than those obtained in the absence of electric current application. The temperature increase, pH change, and BSA loss by electrodeposition were all negligible during the operation. The averaged filtration flowrate increased as the ON/OFF duration ratio of electric current was higher and as the period of ON/OFF cycle was shorter. The re-establishment of concentration polarization was dependent to the duration of current OFF state and, therefore, a longer duration of OFF state was not favorable in maintaining higher filtration flow rate. Although the averaged filtration flowrate was enhanced as the magnitude of electric current increased, the flowrate enhancement became smaller as the magnitude of current increased because there exists a current value above which the degree of electrokinetic depolarization is no further improved.     

Numerical analysis of a microwave torch with axial gas injection

The characteristics of a microwave discharge in an argon jet injected axially into a coaxial channel with a shortened inner electrode are numerically analyzed using a self-consistent equilibrium gas-dynamic model. The specific features of the excitation and maintenance of the microwave discharge are determined, and the dependences of the discharge characteristics on the supplied electromagnetic power and gas flow rate are obtained. The calculated results are compared with experimental data.     

A simple flow meter for bioreactors applicable to oscillating feed systems

Summary A new simple electronic device for liquid flowrate measurement in laboratory or semipilot scale fermenters is presented. The flow meter is also applicable to pulsing or oscillating flow rates. This system allows either a direct measurement of the flow or implementation on a data acquisition system, if available.     

On the Structure and Intensity of Vortex in RF Inductively Coupled Argon Plasma

Numerical simulation of a specific technical RF inductively coupled argon plasma with three coils, discharge current in the range of J_coil = 100–250 A, and generator frequency 3 MHz is presented. The temperature, pressure, and velocity fields are obtained under different discharge currents and different flow rates of central gas. A reversed flow (vortex) is found between the injected cool gas and high-temperature plasma-forming gas. The formation mechanisms of such a vortex and the influence of the discharge current and flow rate of central gas on the vortex structure and intensity are studied. Special attention is paid to investigating two different kinds of vortex flow patterns—Benard and toroidal. A critical flow rate of central gas above which the flow pattern would transform from Benard to toroidal is determined and approximated as a function of the discharge current by theoretical calculations and numerical simulations. The maximum negative velocities along the axis in the vortex zone are also determined under different discharge currents and different flow rates of central gas.     

Evaluation of oxygen transfer rates in stirred-tank bioreactors for clinical manufacturing

Several methods are available for determining the volumetric oxygen transfer coefficient in bioreactors, though their application in industrial bioprocess has been limited. To be practically useful, mass transfer measurements made in nonfermenting systems must be consistent with observed microbial respiration rates. This report details a procedure for quantifying the relationship between agitation frequency and oxygen transfer rate that was applied in stirred-tank bioreactors used for clinical biologics manufacturing. The intrinsic delay in dissolved oxygen (DO) measurement was evaluated by shifting the bioreactor pressure and fitting a first-order mathematical model to the DO response. The dynamic method was coupled with the DO lag results to determine the oxygen transfer rate in Water for Injection (WFI) and a complete culture medium. A range of agitation frequencies was investigated at a fixed air sparge flow rate, replicating operating conditions used in Pichia pastoris fermentation. Oxygen transfer rates determined by this method were in excellent agreement with off-gas calculations from cultivation of the organism (P = 0.1). Fermentation of Escherichia coli at different operating parameters also produced respiration rates that agreed with the corresponding dynamic method results in WFI (P = 0.02). The consistency of the dynamic method results with the off-gas data suggests that compensation for the delay in DO measurement can be combined with dynamic gassing to provide a practical, viable model of bioreactor oxygen transfer under conditions of microbial fermentation.     

Analysis of biological wastewater treatment processes using multicomponent gas phase mass balancing.

A reactor system using off-gas analysis was developed for analyzing wastewater treatment process reactions. Using a mass spectrometer for the gas analysis provides the ability to simultaneously measure several gas components (such as oxygen, nitrogen, carbon dioxide, and argon). One of the benefits of the reactor design was the precise control of the dissolved oxygen concentration, uncoupled from the system turbulence, which was controlled via a gas recycle loop. This feature allowed control of the turbulence within the reactor without any need for mechanical stirring. Using oxygen as the test gas, the reactor was shown to perform well in the measurement of oxygen uptake rate of nitrifying activated sludge. The oxygen uptake rate calculations were made using a simple calibration method developed for the reactor system. The reactor was able to provide precise and accurate results for this test case. Furthermore, the system was capable of measuring under dynamic process conditions, as well as when the process rates were constant (steady state).     

Immunofluorescence measurement in a flow cytometer using low-power helium-neon laser excitation

Helium-neon lasers are economical and efficient light sources; their utility in flow cytometry to date has been limited by the lack of fluorescent probes that can be excited at 633 nm. Allophycocyanin (APC), a highly fluorescent phycobiliprotein, can be used as an antibody label and has spectral characteristics suitable for use with He-Ne lasers; we undertook to resolve whether a low-power (7 mW) He-Ne laser could provide sufficient excitation to permit flow cytometric detection of APC-labeled antibodies on cell surfaces. We made an APC conjugate of monoclonal antibody 4F2, which reacts with an antigen abundant on the surfaces of activated human T-lymphocytes; APC-4F2 was used to stain blood mononuclear cells that had been cultured with and without phytohemagglutinin (PHA). Cells so stained were examined in a flow cytometer with orthogonal illumination at 633 nm from a 7 mW He-Ne laser; antibody-bearing cells were detectable by fluorescence emission above 665 nm. Cells from the same cultures were stained with fluorescein-labeled 4F2 antibody and examined in a flow cytometer with argon ion laser excitation at 488 nm. Percentages of antibody-bearing cells determined from APC fluorescence and from fluorescein fluorescence were in good agreement. It thus appears that He-Ne lasers and APC-antibodies are usable for immunofluorescence measurements; the sensitivity attainable with this technique remains to be determined.     

Respiratory response to formaldehyde and off-gas of urea formaldehyde foam insulation.

In 18 subjects, 9 of whom had previously complained of various nonrespiratory adverse effects from the urea formaldehyde foam insulation (UFFI) in their homes, pulmonary function was assessed before and after exposure in a laboratory. On separate occasions formaldehyde, 1 part per million (ppm), and UFFI off-gas yielding a formaldehyde concentration of 1.2 ppm, were delivered to each subject in an environmental chamber for 90 minutes and a fume hood for 30 minutes respectively. None of the measures of pulmonary function used (forced vital capacity, forced expiratory volume in 1 second or maximal midexpiratory flow rate) showed any clinically or statistically significant response to the exposure either immediately after or 8 hours after its beginning. There were no statistically significant differences between the responses of the group that had previously complained of adverse effects and of the group that had not. There was no evidence that either formaldehyde or UFFI off-gas operates as a lower airway allergen or important bronchospastic irritant in this heterogeneous population.