Transport of ions through an elliptic ion-selective membrane

The rate of transport of ions through an annular ion-selective membrane having an elliptic cross section is analyzed. This is a generalization to a hollow-fiber type of device, and represents a wide class of membranes which are capable of providing a large (surface area/volume) ratio for ion transport. The Nernst–Plank equation governing the transport of ions is solved numerically. The results obtained reveal that, if the concentration of fixed charge is high, its current efficiency is insensitive to fixed charge distribution, and the local electroneutrality can be assumed. On the other hand, if the concentration of fixed charge is low, the distribution of fixed charge becomes significant, and assuming local electroneutrality can be inappropriate. In general, the higher the average concentration (or the greater the total amount) of fixed charge of a membrane, the higher its current efficiency. We show that the results for planar and cylindrical membranes can be recovered from the present model.     

Biological agent inactivation in a flowing air stream by photocatalysis

The first decontamination of a flowing air stream polluted by bacteria, via room temperature non-germicidal UV photocatalysis on titania, leads to a simple and 99.1-99.8% efficient process.     

Diffusion of a trace gas into a flowing carrier

Numerical Methods were used to solve the differential equation for diffusion of a trace gas into a flowing carrier gas having a parabolic velocity profile in a cylindrical tube. Steady state solutions are given in the form of contour diagrams of constant trace gas concentration.     

Transport of ions of pyrophosphoric acid through chemically different anion-exchange membranes

Characteristics of mass transport of the anions of pyrophosphoric acid are investigated during electrodialysis through MA-40 and MA-41 anion-exchange membranes. It is established that the rate of mass transport for counterions is greater through the MA-41 membrane than the MA-40 membrane, and thus the former can be used for demineralizing solutions with salts of pyrophosphoric acid. Higher selectivity to pyrophosphate ions is found for the MA-40 membrane compared to the MA-41 membrane in the electrodialysis of mixtures of pyrophosphate and hydropyrophosphate ions, and thus the MA-40 membrane can be regarded as promising for the separation of such mixtures.     

Transport of ions and charged droplets from the atmospheric region into a gas dynamic interface

Transport of charged particles from the region of their generation to vacuum through a transport capillary with various length-to-diameter ratios L/D = 0.8, 32.5 and 420 is studied. It is shown the process is affected mostly by the geometrical features of the transport capillary and the structure of particles, ions, or droplets, due to the method of their generation (ESI and APCI). A method for distinguishing ions and droplets inside a gas dynamic interface is utilized and supported by computational simulation. The droplets are shown to dominate in the current by ESI for all the capillaries studied. It is shown experimentally that space charge effects predominated over diffusion ones for all practically important currents and capillaries. The estimations show that electrostatic repulsion and their attraction to capillary walls because of the mirror charge induced by all particles are close in effect.     

Transport of hydrated nitrate and nitrite ions through graphene nanopores in aqueous medium

Nitrate () and nitrite () ions are naturally occurring inorganic ions that are part of the nitrogen cycle. High doses of these ions in drinking water impose a potential risk to public health. In this work, molecular dynamics simulations are carried out to study the passage of nitrate and nitrite ions from water through graphene nanosheets (GNS) with hydrogen-functionalized narrow pores in presence of an external electric field. The passage of ions through the pores is investigated through calculations of ion flux, and the results are analyzed through calculations of various structural and thermodynamic properties such as the density of ions and water, ion–water radial distribution functions, two-dimensional density distribution functions, and the potentials of mean force of the ions. Current simulations show that the nitrite ions can pass more in numbers than the nitrate ions in a given time through GNS hydrogen-functionalized pore of different geometry. It is found that the nitrite ions can permeate faster than the nitrate ions despite the former having higher hydration energy in the bulk. This can be explained in terms of the competition between the number density of the ions along the pore axis and the free energy barrier calculated from the potential of mean force. Also, an externally applied electric field is found to be important for faster permeation of the nitrite over the nitrate ions. The current study suggests that graphene nanosheets with carefully created pores can be effective in achieving selective passage of ions from aqueous solutions.     

Rapid metal ions shuttling through 1,3-alternate Thiacalix[4]crown tubes

Several new thiacalix[4]monocrown and thiacalix[4]biscrown compounds were synthesized. Their metal ion extractabilities are found to be lower than those of conventional calix[4]crowns. By use of X-ray crystal structures and (1)H NMR spectroscopy, this result is explained by weaker electrostatic interactions of the polyether ring oxygen atoms with the metal ions and diminished pi-metal ion interactions between the metal ions and the aromatic rings of the thiacalix[4]crowns. Temperature-dependent (1)H NMR spectroscopic measurements reveal coalescence temperatures T(c)(intra) and T(c)(inter) for metal ion exchange. In one case, this exchange was rationalized as metal ion shuttling through a thiacalix[4]biscrown tube. Since the metal ions are less tightly complexed by the polyether units in thiacalix[4]biscrowns than in conventional calix[4]biscrowns, more facile metal ion exchange between the two polyether units takes place in the former.     

Diffusion phenomena of a cold gas in a thermal plasma stream

The present study involves both experimental investigation and mathematical modeling of the diffusion process of a cold gas injected into a main plasma stream. The cold gas (nitrogen or helium) was injected axially through a water cooled tube located along the centerline of an induction plasma torch. The 2-D distribution of the temperature, velocity and concentration profiles in the plasma flow were measured using enthalpy probe techniques. The results are compared with the predictions of a 2-D, LTE, turbulent mathematical model. The effects of the nature (composition) of the injected gas and its mass flow rate are investigated. The enthalpy probe measurements and the predictions of the model are in good agreement. The effective (turbulent and molecular) transport properties are estimated from a comparison of the measured and calculated profiles of the temperature, velocity and concentration fields. This study sheds light on the basic diffusion mechanisms involved in a widely used configuration of induction plasma reactors, i.e. in which the material to be treated is injected axially into the plasma, through a central water cooled tube.     

Transport of hydrogen and hydroxyl ions through ion-exchange membranes under overlimiting current densities

A direct method is suggested for measurement of fluxes of hydrogen and hydroxyl ions through ion-exchange membranes under overlimiting modes of electrodialysis. Fluxes of hydrogen and hydroxyl ions are measured for different immobilized membrane ions and counterions. The important role of counterions in generation of hydrogen and hydroxyl ions is shown. Exponential decrease in fluxes of hydroxyl or hydrogen ions is established at an increase in the Gibbs energy of counterion hydration.     

Transport of a heated granular gas in a washboard potential

We study numerically the motion of a one dimensional array of Brownian particles in a washboard potential, driven by an external stochastic force and interacting via short range repulsive forces. In particular, we investigate the role of instantaneous elastic and inelastic collisions on the system dynamics and transport. The system displays a locked regime, where particles may move only via activated processes and a running regime where particles drift along the direction of the applied field. By tuning the value of the friction parameter controlling the Brownian motion we explore both the overdamped dynamics and the underdamped dynamics. In the two regimes we considered the mobility and the diffusivity of the system as functions of the tilt and other relevant control parameters such as coefficient of restitution, particle size, and total number of particles. We find that while in the overdamped regime the results for the interacting systems present similarities with the known noninteracting case, in the underdamped regime the inelastic collisions determine a rich variety of behaviors among which is an unexpected enhancement of the inelastic diffusion.     

Determination of lactate and lactic dehydrogenase by biamperometric monitoring of hexacyanoferrate(II) in a flowing stream

Summary Open tubular carbon electrodes were used to monitor the biamperometric current of hexacyanoferrate(II) ion produced by the LDH catalyzed reaction between hexacyanoferrate(III) ion and lactate, and that produced from the diaphorase catalyzed reaction between hexacyanoferrate(III) ion and NADH, product from the LDH catalyzed reaction between lactate and NAD. Reagents and samples were mixed in a flow stream. Reaction takes place between the mixing point and the electrodes, and measurements are taken after a constant time interval. Lactate and LDH standards in serum control solutions were measured using the NAD dependent reaction.

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Bestimmung von Lactat und Lactatdehydrogenase durch biamperometrische Messung von Hexacyanoferrat(II) im Durchfluß

Zusammenfassung Kohlenstoff-Röhrenelektroden wurden zur Messung des biamperometrischen Stromes des Hexacyanoferrat(II)-ions eingesetzt, das aus der LDH-katalysierten Reaktion zwischen Hexacyanoferrat(III) und Lactat bzw. der Diaphorase-katalysierten Reaktion zwischen Hexacyanoferrat(III) und NADH (Produkt der LDH-katalysierten Reaktion zwischen Lactat und NAD) stammte. Die Reagentien wurden mit den Proben im Durchfluß vermischt. Die Reaktion fand zwischen der Mischungsstelle und den Elektroden statt und die Messungen wurden nach einem Bestimmten Zeitintervall durchgeführt. Mit Hilfe der NAD-abhängigen Reaktion wurden Lactat- und LDH-Standards in Serumkontrollösungen bestimmt.

     

Stabilization of a standard gas mixture generator with diffusion tubes

Summary The generator contains diffusion tubes of known length and internal diameter. Once produced, the mixture of the carrier gas and acetone, the reference material, is sent through a chromatographic flame ionisation detector. Its signal reaches a constant level after a time corresponding to the stabilization time of the generator. The technique described is simple and gives repeatable results.     

Sulphonylium ions in the gas phase

Electron impact mass spectrometry was used to investigate the fragmentation of a series of arenesulphonyl chlorides. Sequential losses of a chlorine atom and sulphur dioxide from the molecular ions occurred and the reverse of these reactions had small critical energies that were generally unaffected by the ring substituent. However, an interesting intramolecular cyclization reaction occurring on the ortho-nitro derivative is discussed with the aid of kinetic energy release measurements on this derivative and on a model compound. Appearance energy measure ments combined with multiple scattering Xα calculations led to an estimate of the sulphur-chlorine bond strength in benzenesulphonyl chloride.     

Transport of calcium and potassium ions in opposite directions in a liquid membrane system

A new type of 18-crown-6 derivative having two carboxylic acids on the side arms transported calcium and potassium ions in opposite directions across a dichloromethane membrane by pH control. Calcium and potassium ions were concentrated in the acidic and the basic phases, respectively. The presence of picrate ion in the acidic phase plays an important role in the transport of potassium ion from the acidic to the basic phase.     

Rheological behavior of POM polymer melt flowing through micro-channels

Determination of the rheological behavior of the polymer melt within micro-structured geometry is vital for accurate simulation modeling of micro-molding. The lack of commercial equipment is one of main hurdles in the investigation of micro-melt rheology. In this study, a melt viscosity measurement system for POM melt flowing through micro-channels was established. For measured pressure drop and volumetric flow rate, both capillary and slit flow models were used for the calculation of viscosity. The calculated results were also compared with those of PS resin to discuss the effect of morphology structure on the viscosity characteristics of polymer within micro-channels. It was found that the measured POM viscosity values in the test ranges are significantly lower (about 29-35% for a channel size of 150 μm) than those obtained with a traditional capillary rheometer. Meanwhile, the percentage reduction in the viscosity value and the ratio of slip velocity relative to mean velocity all increase with decreasing micro-channel size, but less significantly when compared with PS resin. In the present study we emphasize that the rheological behavior of the POM resin in microscopic scale is also different from that of macroscopic scale as PS resin but displays a less significant lower. It also revealed that the wall slip occurs more easily for the PS resin within micro-channels than POM resin due to enlarge the effect of molecular weight.     

Directional Potassium Transport through a Unimolecular Peptide Channel

Three unimolecular peptide channels have been designed and prepared by using the β‐helical conformation of gramicidin A (gA). The new peptides bear one to three NH₃⁺ groups at the N‐end and one to three CO₂^? groups at the C‐end. These zwitterionic peptides were inserted into lipid bilayers in an orientation‐selective manner. Conductance experiments on planar lipid bilayers showed that this orientation bias could lead to observable directional K⁺ transport under multi‐channel conditions. This directional transport behavior can further cause the generation of a current across a planar bilayer without applying a voltage. More importantly, in vesicles with identical external and internal KCl concentrations, the channels can pump K⁺ across the lipid bilayer and cause a membrane potential.