Layered double hydroxide and zirconium phosphate as ion exchangers for the removal of 'black crusts' from the surface of ancient monuments.

The chloride form of MgAl layered double hydroxide (hereafter MgAlCl) as an anion exchanger and the semisodic form of α-zirconium phosphate (hereafter ZrPNaH) as a cation exchanger are proposed as new cleaning agents for the removal of gypsum from ancient monuments. The ability of these exchangers to capture the calcium and sulphate ions of the gypsum powder was first investigated separately and then as a coupled system. MgAlCl/gypsum, ZrPNaH/gypsum and MgAlCl/ZrPNaH/gypsum mixtures were characterized by X-ray powder diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and dispersive X-ray spectroscopy (EDX). ZrPNaH in the form of a wet paste exhibited a rapid uptake of calcium from gypsum powder via Na+ and H+/Ca2+ cation exchange. Gypsum powder was also successfully dissolved by a wet paste of MgAlCl by exploiting the Cl-/SO42- anion exchange reaction. However, the dehydration of the paste favoured the reprecipitation of a secondary gypsum that was characterized by lower crystallinity and smaller particle size than the pristine gypsum. The combination of wet MgAlCl and ZrPNaH showed a synergic effect on the dissolution of gypsum and partially prevented the reprecipitation of gypsum in the dry paste. Finally, a preliminary test of the removal of gypsum crust grown on a sandstone sample was performed.

Microchambers for cell exposure: from the design to applications.

In the last decades, the advances in the micro and nano fabrication techniques have led to the development of microdevices that improved the possibility of analysis at cell level. These devices can be used in different applications (e.g., cell detection and identification, manipulation, cell treatments). The requisites, that are necessary to achieve, are different for various applications and represent the starting point of the project. The numerical multiphysics models can be very advantageous to analyze the performances of such devices and to predict their operation. Aim of this work is to give a look of the design rules of microchamber devices in particular for their application in electric field exposure. Two different applications for cell discrimination and characterization are reported considering time and frequency domain measurements.

A molecular dynamic study of cholesterol rich lipid membranes: comparison of electroporation protocols.

We report on a molecular dynamics (MD) simulation study of the electroporation of lipid bilayers at different cholesterol contents using protocols mimicking "traditional" electroporation, i.e. low intensity millisecond pulses (msEP), and high intensity nanosecond electric pulses (nsEP). The results show that addition of cholesterol in concentrations of lipid:sterol ranging from 20 to 50 mol% enhances substantially the membrane cohesion, which is manifested by an increase of the electroporation threshold (U(thr)). This increase is steady in the case of the nsEP protocol, reaching roughly a factor 2 in the 50 mol% samples. In contrast, for the msEP protocol, U(thr) increases by 50% upon addition of 30 mol% cholesterol then levels off. Furthermore, pores formed under msEP are found to possess morphologies much different from the usually reported hydrophilic "electropores" encountered under the nsEP protocol, which may have profound consequences on the transport properties of "electroporated" membranes. Hence, this study reveals that cell membrane models containing the ubiquitous cholesterol component respond quite differently to the two electroporation techniques, in contrast to what has been found for simple zwitterionic bilayers.

Novel passive element circuits for microdosimetry of nanosecond pulsed electric fields.

Microdosimetric models for biological cells have assumed increasing significance in the development of nanosecond pulsed electric field technology for medical applications. In this paper, novel passive element circuits, able to take into account the dielectric dispersion of the cell, are provided. The circuital analyses are performed on a set of input pulses classified in accordance with the current literature. Accurate data in terms of transmembrane potential are obtained in both time and frequency domains for different cell models. In addition, a sensitivity study of the transfer function for the cell geometrical and dielectric parameters has been carried out. This analysis offers a new, simple, and efficient tool to characterize the nsPEFs' action at the cellular level.

Temperature-dependent dynamics of water confined in nafion membranes.

We performed a neutron scattering study to investigate the dynamical behavior of water absorbed in Nafion at low hydration level as a function of temperature in the range 200-300 K. To single out the spectral contribution of the confined water, the measurements were done on samples hydrated with both H(2)O and D(2)O. Due to the strong incoherent scattering cross section of hydrogen atoms with respect to deuterium, in the difference spectra, the contribution from the Nafion membrane is subtracted out and the signal originates essentially from protons in the liquid phase. The main quantities we extracted as a function of the momentum transfer are the elastic incoherent structure factor (EISF) and the line width of the quasielastic component. Their trend suggests that the motion of hydrogen atoms can be schematized as a random jumping inside a confining region, which can be related to the boundaries of the space where water molecules move in the cluster they form around the sulfonic acid site. Through the calculated EISF, we obtained information on the size of such a region, which increases up to 260 K and then attains a constant value. Above this temperature, the number of water protons that are dynamically activated in the accessible time window increases with a faster rate. The jump diffusion dynamics is characterized by a typical jumping time which is stable at 5.3 ps up to approximately 260 K and then gradually decreases. The ensemble of the findings indicates that, within the limits of the energy resolution of the present experiment, water absorbed in the Nafion membrane undergoes a dynamical transition at around 260 K. We discuss the possible relationship of this dynamical onset with the behavior of the electrical conductivity of the membrane as a function of the temperature.