On the diffusive water transport through polyelectrolyte-based membranes

Experiments were done for indentification and localization of certain structural changes at different levels of jejunal villus of the hamster during positive and negative water transport across the intestine in vivo and in vitro. Positive transport occurred when the mucosal surface of the intestine was bathed (in vitro experiments) or perfused (in vivo experiments) with isotonic Krebs-Ringer bicarbonate solution containing 10 mM glucose, and negative water transport was achieved by rendering this solution hypertonic with 150 mM mannitol. Results indicate that during positive net water transport the intestine in vivo transported more fluid and exhibited a more conspicuous dilatation of the lateral intercellular spaces (L.I.S.) than did the in vitro preparation. Dilatation of the L.I.S. in both preparations was present only in the apical part of the villus, suggesting that this is the principal site of water absorption. When the mucosal solution was made hypertonic with mannitol, the L.I.S. in the in vivo intestine totally collapsed, whereas in the in vitro intestine these spaces remained open very slightly. These morphological changes correspond well with our finding that in the presence of the hypertonic mucosal solution there was a greater net negative water transport in vivo than in vitro. Incubation of the intestine in the isotonic mucosal solution produced subnuclear swelling of the mid-villus epithelial cells, and this morphological change was associated with an increase in the water content of the tissue. Perfusion of the in vivo intestine with the isotonic solution produced neither the swellings nor the increase in water content of the tissue. In the presence of hypertonic mucosal solution there was a water loss from the tissue both in vivo and in vitro, and these swellings were not observed. These results are discussed in relation to intestinal sugar transport and to the maturity of the epithelial cells, and it is concluded that transport studies on in vitro preparations may provide valid information on a qualitative basis, if not on a strictly quantitative basis.

The absorption of volatile fatty acids (VFA) and the influence of VFA on the net transport of inorganic electrolytes and water were examined in the temporarily isolated colon of the conscious goat. Perfusion of the colon with a solution similar in content to that normally present in the cecal outflow showed that the net absorption of VFA was more rapid than that of any other ion present in the solution. When the VFA were replaced with Cl, the net absorption of Na and water was reduced nearly twofold. Increasing the pH of the solution from 6.0 to 7.4 in the presence of VFA also resulted in a twofold decreased in the net transport of Na and water. Perfusion of the colon with a hypertonic solution resulted in approximately zero net water transport; however, the net absorption of Na and VFA continued at similar rates as before. These results support the concept that the colon primarily conserves solute followed by the passive movement of water. They also demonstrate that VFA are rapidly absorbed from the goat colon and indicate a striking influence of VFA on the net transport of Na and water. The presence of VFA in the large intestine may be important for normal absorptive function.

Lymphatic and Venous Transport of Water From Rat Jejunum: A Vascular Perfusion Study

Modeling water transport in polymer electrolyte membrane electrolyzers using a one-dimensional transport model

Non-equilibrium molecular dynamics (NEMD) and NPT Monte Carlo simulations were carried out for two non-ideal Lennard-Jones/spline mixtures at supercritical temperatures. The systems were chosen so that one of them showed positive and the other negative excess volumes and enthalpies on mixing. A strong composition gradient was generated in the NEMD simulations, such that the entire composition range from pure component 1 to pure component 2 was covered in the molecular dynamics cell. A series of Monte Carlo simulations was made, covering the same composition range. The temperatures and pressures used in the MC simulations were chosen equal to the results from the NEMD simulations. The excess volumes and enthalpies on mixing from the two simulations showed excellent agreement, leading to the conclusion that the NEMD simulations were performed under local equilibrium despite the lack of overall equilibrium in the system. Excess and partial molar quantities were computed by the two methods, sand the data were...

In meat brining, the concentration of brine could affect both water and NaCl transport and, consequently, the total length of the treatment and the final quality of the product. In the present work, the kinetics of water and NaCl transport during the brining of pork loin slices in different brine concentrations (50, 100, 150, 200, 240 and 280 kg/m3) were determined (5±1 °C). In the case of moisture content, the brine concentrations of under 200 kg/m3 led to significant (p < 0.05) sample hydration. Close to this concentration, no net water transport took place, and above it, samples were dehydrated. As regards the evolution of NaCl content, the higher the concentration of brine used, the greater the NaCl content in the sample. The identified effective moisture diffusivity showed a tendency to decrease when the brine concentration rose, changing from positive (hydration) to negative values (dehydration). For NaCl, the identified effective diffusivity remained constant with brine concentration (1.90±0.28) 10–10 m2/s.KeywordsMass transportOsmotic treatmentModelingDiffusivity

The shear viscosity of molten NaCl and KCl was calculated through equilibrium (EMD) and nonequilibrium molecular-dynamics (NEMD) simulations in the canonical (N,V,T) ensemble. Two rigid-ion potentials were investigated, namely, the Born-Mayer-Huggins-Tosi-Fumi potential and the Michielsen-Woerlee-Graaf-Ketelaar potential with the parameters proposed by Ladd. The NEMD simulations were performed using the SLLOD equations of motion [D. J. Evans and G. P. Morriss, Phys. Rev. A 30, 1528 (1984)] with a Gaussian isokinetic thermostat and the results are compared with those obtained from Green-Kubo EMD (N,V,T) simulations and experimental shear viscosity data. The NEMD zero strain rate shear viscosity, eta(0), was obtained by fitting a simplified Carreau-type equation and by application of mode-coupling theory, i.e., a eta-gamma(1/2) linear relationship. The values obtained from the first method are found to be significantly lower than those predicted by the second. The agreement between the EMD and NEMD results with experimental data is satisfactory for the two potentials investigated. The ion-ion radial distribution functions obtained with the two rigid-ion potentials for both molten salts are discussed in terms of the differences between the two models.

Investigation of the thermal behaviors of folded graphene by non-equilibrium molecular dynamics simulation

Mechanism of Enhanced Mechanical Stability of Retroviral Kissing-Loops Elucidated by Non-Equilibrium Molecular Dynamics Simulations

Determination of the absolute binding free energies of HIV-1 protease inhibitors using non-equilibrium molecular dynamics simulations

Atomic-level characterization of the human immunodeficiency virus type 1 envelope glycoproteins using molecular dynamic simulations.

In this work, we study the impact of the phonon thermal conductivity of Silver (Ag) and Gold (Au) on the interface resistance of metal-nonmetal contacts at room temperature. The thermal conductivity of both metals is determined for bulk and thin films of varying thickness using non-equilibrium molecular dynamics (NEMD) simulations. Likewise, we determine the thermal interface resistance due to phonons of metal films embedded in a nonmetal layer composed of Silicon (Si). Based on a two-temperature model (TTM) for electrons and phonons, we determine the thermal resistance due to electron-phonon interactions and the variation of the film resistance of Ag and Au layers as a function of their thickness. The latter considering the estimated phonon contribution to the thermal conductivity of the studied metals obtained with our NEMD simulations. Two important results are presented in this work. First, we have found for the studied metals that at room temperature phonons contribute less than 1.0 % to the bulk thermal conductivity; and that their relative contribution to the conductivity and its variation with the film thickness significantly impacts the overall film resistance of metallic films.

Effect of interfacial structures on ionic conductivity in particle-dispersed composite electrolytes

Individual molecule dynamics have been shown to influence significantly the bulk rheological and microstructural properties of short-chain, unentangled, linear polyethylene liquids undergoing high strain-rate flows. The objective of this work was to extend this analysis to a linear polyethylene composed of macromolecules of a much greater length and entanglement density; i.e., a liquid consisting of C400H802 molecules, with approximately ten kinks per chain at equilibrium, as calculated by the Z1 code of Kröger [Comput. Phys. Commun. 168, 209–232 (2005)]. To achieve this, we performed nonequilibrium molecular dynamics (NEMD) simulations of a model system using the well-established potential model of Siepmann et al. [Nature 365, 330–332 (1993)] for a wide range of Weissenberg numbers (Wi) under steady shear flow. A recent study by Baig et al. [Macromolecules 43, 6886–6902 (2010)] examined this same system using NEMD simulations, but focused on the bulk rheological and microstructural properties as calculated from ensemble averages of the chains comprising the macromolecular liquids. In so doing, some key features of the system dynamics were not fully elucidated, which this article aims to highlight. Specifically, it was found that this polyethylene liquid displays multiple timescales associated with not only the decorrelation of the end-to-end vector (commonly related to the Rouse time or disengagement time, depending on the entanglement density of the liquid), but also ones associated with the retraction and rotation cycles of the individual molecules. Furthermore, when accounting for these individual chain dynamics, the “longest” relaxation time of the system was higher by a factor of 1.7, independent of shear rate, when calculated self-consistently due to the coupling of relaxation modes. Brownian dynamics (BD) simulations were also performed on an analogous free-draining bead-rod chain model to compare the rotation and retraction dynamics of a single chain in dilute solution with individual molecular motions in the melt. These BD simulations revealed that the dynamics of the free-draining chain are qualitatively and quantitatively similar to those of the individual chains comprising the polyethylene melt at strain rates in excess of Wi ≈ 50, implying a possible breakdown of reptation theory in the high shear limit. An examination of the bulk-average properties revealed the effects of the chain rotation and retraction cycles upon commonly modeled microstructural properties, such as the distribution function of the chain end-to-end vector and the entanglement number density.

A mean-field anisotropic diffusion model for unentangled polymeric liquids and semi-dilute solutions: Model development and comparison with experimental and simulation data