727,754 research outputs found
Ion transport through confined ion channels in the presence of immobile charges
We study charge transport in an ionic solution in a confined nanoscale
geometry in the presence of an externally applied electric field and immobile
background charges. For a range of parameters, the ion current shows
non-monotonic behavior as a function of the external ion concentration. For
small applied electric field, the ion transport can be understood from simple
analytic arguments, which are supported by Monte Carlo simulation. The results
qualitatively explain measurements of ion current seen in a recent experiment
on ion transport through a DNA-threaded nanopore (D. J. Bonthuis et. al., Phys.
Rev. Lett, vol. 97, 128104 (2006)).Comment: 5 pages, 3 figure
Visualization of lithium-ion transport and phase evolution within and between manganese oxide nanorods.
Multiple lithium-ion transport pathways and local phase changes upon lithiation in silver hollandite are revealed via in situ microscopy including electron diffraction, imaging and spectroscopy, coupled with density functional theory and phase field calculations. We report unexpected inter-nanorod lithium-ion transport, where the reaction fronts and kinetics are maintained within the neighbouring nanorod. Notably, this is the first time-resolved visualization of lithium-ion transport within and between individual nanorods, where the impact of oxygen deficiencies is delineated. Initially, fast lithium-ion transport is observed along the long axis with small net volume change, resulting in two lithiated silver hollandite phases distinguishable by orthorhombic distortion. Subsequently, a slower reaction front is observed, with formation of polyphase lithiated silver hollandite and face-centred-cubic silver metal with substantial volume expansion. These results indicate lithium-ion transport is not confined within a single nanorod and may provide a paradigm shift for one-dimensional tunnelled materials, particularly towards achieving high-rate capability
Quantitative description of ion transport via plasma membrane of yeast and small cells
Modeling of ion transport via plasma membrane needs identification and
quantitative understanding of the involved processes. Brief characterization of
main ion transport systems of a yeast cell (Pma1, Ena1, TOK1, Nha1, Trk1, Trk2,
non-selective cation conductance) and determining the exact number of molecules
of each transporter per a typical cell allow us to predict the corresponding
ion flows. In this review a comparison of ion transport in small yeast cell and
several animal cell types is provided. The importance of cell volume to surface
ratio is emphasized. The role of cell wall and lipid rafts is discussed in
respect to required increase in spatial and temporal resolution of
measurements. Conclusions are formulated to describe specific features of ion
transport in a yeast cell. Potential directions of future research are outlined
based on the assumptions.Comment: 22 pages, 6 figures, 1 tabl
Global effects on neoclassical transport in the pedestal with impurities
We present a numerical study of collisional transport in a tokamak pedestal
in the presence of non-trace impurities, using the radially global
neoclassical solver PERFECT [M. Landreman et al. 2014 Plasma Phys. Control.
Fusion 56 045005]. It is known that in a tokamak core with non-trace impurities
present the radial impurity flux opposes the bulk ion flux to provide an
ambipolar particle transport, with the electron transport being negligibly
small. However, in a sharp density pedestal with sub-sonic ion flows the
electron transport can be comparable to the ion and impurity flows.
Furthermore, the neoclassical particle transport is not intrinsically
ambipolar, and the non-ambipolarity of the fluxes extends outside the pedestal
region by the radial coupling of the perturbations. The neoclassical momentum
transport, which is finite in the presence of ion orbit-width scale profile
variations, is significantly enhanced when impurities are present in non-trace
quantities, even if the total parallel mass flow is dominated by the bulk ions
Mechanism of NaCl transport-stimulated prostaglandin formation in MDCK cells
Recently we have found that stimulation of NaCl transport in high-resistance MDCK cells enhances their prostaglandin formation. In the present study, we investigated the mechanisms by which prostaglandin formation could be linked to the ion transport in these cells. We found that stimulation of transport caused a transient stimulation of prostaglandin formation lasting 5-10 min. The rise in prostaglandin formation was paralleled by a rise of free intracellular arachidonic acid. Analysis of membrane lipids revealed that the rise of free arachidonic acid was paralleled by a loss of arachidonic acid from polyphosphoinositides. We failed to obtain indications for the stimulation of calcium-dependent phospholipase A2. However, we did obtain evidence that the incorporation of arachidonic acid into phospholipids was diminished during stimulation of ion transport, indicating a decreased rate of reesterification. Despite the fact that there was no significant fall in total cellular ATP on stimulation of ion transport, we found a high and transient rise of lactate production of the cells on stimulation of the ion transport indicating an alteration of the ADP/ATP ratio. Moreover, prostaglandin formation and lactate formation were linearly correlated in this situation. When glucose utilization was inhibited by mannoheptulose, the rise in lactate formation was abolished, whereas that of PG formation was unaltered, indicating that lactate formation and prostaglandin formation were not causally linked on stimulation of ion transport. Our results suggest that an increase in the rate of sodium chloride transport by MDCK cells stimulates formation by an inhibition of reesterification of free arachidonic acid.(ABSTRACT TRUNCATED AT 250 WORDS
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Direct Measurement of Vanadium Crossover in an Operating Vanadium Redox Flow Battery
Measurements of Vanadium diffusion coefficients for transport across cation exchange membranes using dialysis cells have been reported in the literature. However, to date direct measurement of crossover coefficients in an operating Vanadium redox flow battery (VRB) cell have not been reported. Results are reported in this paper on experiments utilizing a special VRB cell which allows measurement of Vanadium ion transport across ion exchange membranes with and without the presence of current. The cell utilizes two additional flow regions which collect Vanadium ions which diffuse from the positive and negative half cells. The effects of the magnitude and direction of electrical current on transport can be measured directly with this cell. We observe that transport is greatly enhanced when the direction of the hydrogen ion flux is in the same direction as the density gradient driven vanadium flux and suppressed when the hydrogen ion flux is in the opposite direction. The cell has been used to of investigate the effects on transport of current densities up to 900 mA/cm(2).US Department of Energy ARPA-E program DE-AR00000149Materials Science and Engineerin
How the asymmetry of internal potential influences the shape of I-V characteristic of nanochannels
Ion transport in biological and synthetic nanochannels is characterized by
such phenomena as ion current fluctuations, rectification, and pumping.
Recently, it has been shown that the nanofabricated synthetic pores could be
considered as analogous to biological channels with respect to their transport
characteristics \cite{Apel, Siwy}. The ion current rectification is analyzed.
Ion transport through cylindrical nanopores is described by the Smoluchowski
equation. The model is considering the symmetric nanopore with asymmetric
charge distribution. In this model, the current rectification in asymmetrically
charged nanochannels shows a diode-like shape of characteristic. It is
shown that this feature may be induced by the coupling between the degree of
asymmetry and the depth of internal electric potential well. The role of
concentration gradient is discussed
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