A singular perturbation approach to the steady-state 1D Poisson-Nernst-Planck modeling

The reduced 1D Poisson-Nernst-Planck (PNP) model of artificial nanopores in the presence of a permanent charge on the channel wall is studied. More specifically, we consider the limit where the channel length exceed much the Debye screening length and channel's charge is sufficiently small. Ion transport is described by the nonequillibrium steady-state solution of the PNP system within a singular perturbation treatment. The quantities, 1/lambda -- the ratio of the Debye length to a characteristic length scale and epsilon -- the scaled intrinsic charge density, serve as the singular and the regular perturbation parameters, respectively. The role of the boundary conditions is discussed. A comparison between numerics and the analytical results of the singular perturbation theory is presented.Comment: 27 pages, 8 figures, conference: Marian Smoluchowski Symposium on Statistical Physics Zakopane, Poland, September 22-29, 200

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 $I-V$ 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

Rectification in synthetic conical nanopores: a one-dimensional Poisson-Nernst-Planck modeling

Ion transport in biological and synthetic nanochannels is characterized by phenomena such as ion current fluctuations and rectification. Recently, it has been demonstrated that nanofabricated synthetic pores can mimic transport properties of biological ion channels [P. Yu. Apel, {\it et al.}, Nucl. Instr. Meth. B {\bf 184}, 337 (2001); Z. Siwy, {\it et al.}, Europhys. Lett. {\bf 60}, 349 (2002)]. Here, the ion current rectification is studied within a reduced 1D Poisson-Nernst-Planck (PNP) model of synthetic nanopores. A conical channel of a few $\mathrm{nm}$ to a few hundred of nm in diameter, and of few $\mu$m long is considered in the limit where the channel length considerably exceeds the Debye screening length. The rigid channel wall is assumed to be weakly charged. A one-dimensional reduction of the three-dimensional problem in terms of corresponding entropic effects is put forward. The ion transport is described by the non-equilibrium steady-state solution of the 1D Poisson-Nernst-Planck system within a singular perturbation treatment. An analytic formula for the approximate rectification current in the lowest order perturbation theory is derived. A detailed comparison between numerical results and the singular perturbation theory is presented. The crucial importance of the asymmetry in the potential jumps at the pore ends on the rectification effect is demonstrated. This so constructed 1D theory is shown to describe well the experimental data in the regime of small-to-moderate electric currents.Comment: 27 pages, 7 figure

Identification of structural features of condensed tannins that affect protein aggregation

A diverse panel of condensed tannins was used to resolve the confounding effects of size and subunit composition seen previously in tannin-protein interactions. Turbidimetry revealed that size in terms of mean degree of polymerisation (mDP) or average molecular weight (amw) was the most important tannin parameter. The smallest tannin with the relatively largest effect on protein aggregation had an mDP of ~7. The average size was significantly correlated with aggregation of bovine serum albumin, BSA (mDP: r=-0.916; amw: r=-0.925; p<0.01; df=27), and gelatin (mDP: r=-0.961; amw: r=-0.981; p<0.01; df=12). The procyanidin/prodelphinidin and cis-/trans-flavan-3-ol ratios gave no significant correlations. Tryptophan fluorescence quenching indicated that procyanidins and cis-flavan-3-ol units contributed most to the tannin interactions on the BSA surface and in the hydrophobic binding pocket (r=0.677; p<0.05; df=9 and r=0.887; p<0.01; df=9, respectively). Circular dichroism revealed that higher proportions of prodelphinidins decreased the apparent α-helix content (r=-0.941; p<0.01; df=5) and increased the apparent β-sheet content (r=0.916; p<0.05; df=5) of BSA

Brownian dynamics simulations of flicker noise in nanochannels currents

We simulated the single-file motion of ${\rm K}^{+}$ ions through a model channel with the gate which opens and closes under influence of white noise and of interactions with ions present inside the channel. There is a range of the model parameters, in which the power spectrum of the ion net current through the channel has the characteristics of the flicker noise. The flicker noise is accompanied by the long-tail dwell-time distributions. The stochastic analysis of the calculated currents reveals their self-similarity. The open-state currents scale with the scaling exponent β=-1.0±0.15. To our best knowledge, our results are the first derivation of $1/f$ noise directly from Langevin equations with simple electrostatic interactions and white noise

Asbestosis hospitalizations in Poland (2006–2016): results from the National Hospital Discharge Registry

Introduction and objective. Occupational asbestos exposure is one of the major public health issues. Although asbestos use in Poland has decreased, asbestosis continues to remain an important health concern in the area of occupational medicine. The aim of the study is to perform a descriptive analysis of hospitalization cases in patients suffering from asbestosis in Poland. Materials and method. The authors used hospital discharge records to conduct a retrospective, population-based study. To estimate the asbestosis hospitalization rate, data from the Nationwide General Hospital Morbidity Study conducted by the National Institute of Public Health were used. Events were defined as in-patient hospital discharges during 2006–2016. 1,101 hospitalization records of 764 patients were included in the study. Results. In the study group of first-time hospitalized patients, the mean and median ages were 68.1 and 69 years, respectively; CI: 67.3–68.9; SD: 11.1, min-max:16–99 years. In this group, significant gender differences were observed (560 males vs. 204 female; P<0.001). No statistical differences were observed regarding the place of residence. During the observation period, 61 in-hospital deaths were reported (8% of all patients), 40 of whom (5.2 % of all patients) took place during the first-time hospitalizations. Asbestosis hospitalizations were mainly clustered in the south-western region, whereas the highest hospitalization rates were clustered in several areas of Poland. Conclusions. The authors believe this study to be the first evaluation of asbestosis in Poland made on the basis of the hospital morbidity database. The data presented may be helpful in comparative studies on the epidemiology of asbestosis across European countries