Search results for "Diffusion"

Nitrogen Gas on Graphene: Pairwise Interaction Potentials

2018

We investigate different types of potential parameters for the graphene-nitrogen interaction. Interaction energies calculated at DFT level are fitted with the semi-emperical Improved Lennard-Jones potential. Both a pseudo-atom potential and a full atomistic potential are considered. Furthermore, we consider the influence of the electrostatic part on the parameters using different charge schemes found in the literature as well as optimizing the charges ourselves. We have obtained parameters for both the nitrogen dimer and the graphene-nitrogen system. For the former, the four-charges Cracknell scheme reproduces with high precision the CCSD(T) interaction energy as well as the experimental di…

Diffusion and sensitivity characteristics of a chemically cross-linked PVA-Fricke gel dosimeter

2016

Characterization process to measure the electrical contact resistance of Gas Diffusion Layers under mechanical static compressive loads

2016

AEM2016. International conference on Advanced Energy Materials, University of Surrey, Guildford, ROYAUME-UNI, 12-/09/2016 - 14/09/2016; Recent research has identified the mechanical properties of the fuel cell internal components (in particular, the Gas Diffusion Layers - GDLs) as key-parameters to obtain high final performances of the generator. The mechanical compression modulus of these components, the stability of their mechanical properties with respect to temperature and humidity, and their ability to interact with water have an impact on the electrical contact resistances in the stack and, by consequence, on the overall performance of the electric generator. Reducing the losses by co…

Ab initioand semiempirical calculations ofH−centers in MgO crystals

1999

The atomic and electronic structure of ${\mathrm{H}}^{\ensuremath{-}}$ ions substituting for ${\mathrm{O}}^{2\ensuremath{-}}$ ions in regular sites in MgO crystals are calculated using an ab initio Hartree-Fock (HF) cluster approach and its semiempirical version, intermediate neglect of the differential overlap. The theoretical optical absorption energy is predicted to be 10 eV, which is supported by analysis of experimental data for the ${\mathrm{H}}^{\ensuremath{-}}$ centers in a series of ionic crystals. The HF simulations of ${\mathrm{H}}^{\ensuremath{-}}$ ion diffusion via direct interstitial hops along the [100] axis predict an activation energy of about 3 eV.

Modeling of primary defect aggregation in tracks of swift heavy ions in LiF

2001

To simulate aggregation of primary F centers created along the path of swift heavy ions in LiF, Monte Carlo simulations were developed. Parameters relevant for defect aggregation as a result of their random hopping, such as the migration energy, temperature in the track, initial defect concentration, and diffusion time, were estimated from available experimental data. It is estimated that in the electronically excited state and under temperature locally increased up to 1200 K F centers are mobile enough to make several tens of hops. Most of the F aggregates formed are extremely small and consist only of two or three F centers. The fraction of larger F clusters ~with more than 10 defects! is…

Pre-Stressed Sub-Surface Contribution on Bulk Diffusion in Metallic Solids

2011

Our recent modelling works and corresponding numerical simulations realized to describe the UO2 oxidation processes confirm the theory showing that an applied mechanical strain can strongly affect the local oxygen diffusion in a stressed solid. This result allows us to assume that stress field, previously applied at the surface of a metallic sample on several microns, will delay the degradation during its oxidation. Considering this hypothesis, we implemented a FEM simulation code developed in our laboratory to numerically investigate some different stress fields applied on a sample sub-surface, that might significantly modify the volume diffusion of oxygen during the oxidation process. The…

Gas Selective Ultrathin Organic Covalent Networks Synthesized by iPECVD: Does the Central Metal Ion Matter?

2017

The potential of porphyrin-derived metal organic covalent networks (OCN) thin films on light gas separations has been recently demonstrated. However, whether or not the central metal ion of the porphyrin plays a key role on separation performance has yet to be elucidated. Here, one metal-free and three metal-containing (zinc(II), manganese(III), and cobalt(II)) porphyrin-derived OCN thin films are successfully deposited on various substrates via an easily scalable initiated plasma-enhanced chemical vapor deposition approach. Among these four porphyrin-derived OCN thin films exhibiting superior light gas separation performances, three of them are synthesized for the first time. The gas perme…

In Vitro–In Vivo Fluctuation Spectroscopies

2010

Fluorescence correlation spectroscopy (FCS) was first developed for biophysical studies in analogy with photon scattering correlation spectroscopy. Although it is mainly devoted to the study of freely diffusing particles, FCS is actually able to discern between different kinds of motions, such as diffusion, anomalous diffusion, or drift motions. The frontier application of FCS nowadays is in medical studies both within cells and on the cell membranes, and in the investigation of single molecules in solid matrices. In this field, FCS originated also image correlation spectroscopy methods. The whole field can be unified under the name of fluorescence fluctuation spectroscopy (FFS). We present…

The Effect of Spectral Diffusion on the Saturation Transient Regime

1985

Saturation kinetics of inhomogeneous resonance lines has been investigated in very dilute ruby samples at T=4.2°K by the saturation transient technique. Experimental evidence of the effectiveness of intraline spectral diffusion is reported. Satisfactory agreement is found between the experimental results and a theoretical model in which spectral diffusion is ascribed to the time fluctuations of the hyperfine field. Spectral diffusion times of the order of 10-5 sec are determined.

Friction Stir Processing of NiTi Shape Memory Alloy: Microstructural Characterization

2010

Shape Memory Alloys (SMA) are metal materials that, after being strained, come back to their original shape at a designated temperature. Welding NiTi alloys is not simple because when the material is melted, due to the high reactivity of the alloy elements, the typical shape memory properties may disappear. The solid state welding process, such as friction stir welding, is thus attractive for SMA joining and it exhibits potentials for achieving welded joints affected by microstructural changes that preserve the shape memory properties. The present study investigates the feasibility of friction stir welding process to join NiTi shape memory alloys; in order to analyse the welding process, it…