Search results for "fusion"
showing 10 items of 4513 documents
Transport of Mobile Particles in an Immobile Environment: Computer Simulations of Sodium Silicates
2007
Molecular dynamics (MD) simulations of various sodium silicate melts, (Na2O)x(SiO2) with x=2, 3, 20, are presented. In these systems, the mobility of sodium ions is much higher, often by orders of magnitude, than that of the silicon and oxygen atoms forming a tetrahedral network structure. We show that the high mobility of sodium is intimately related to the chemical ordering in sodium silicates. A network of percolating sodium-rich channels is formed in the static structure that serve as diffusion channels for the sodium ions. This channel network is revealed in static structure factors by a prepeak at the wavenumber q=0.95 A-1. Inelastic neutron scattering experiments of sodium silicate m…
Reoperations After First Lumbar Disk Herniation Surgery with or without Implantation of Mechanical Annular Closure Device
2019
Lumbar diskectomy is a widely performed surgical procedure in patients affected by lumbar disk herniation (LDH). Such a surgical procedure is considered to be safe and able to provide a consistent symptomatic relief in most patients. However, perioperative complications have been reported, ranging from 13% to 15%, and pose a considerable financial burden among patients, hospitals, and national health care agencies. The most common perioperative complication following lumbar diskectomy for disk herniation is the recurrence. Although the recurrence rate of LDH has been reported to be 5%−15%, its exact incidence may be underestimated. Recurrent lumbar disk herniation (rLDH) is defined as disk …
Growth of Ice Particles by Accretion and Ice Particle Melting
2010
In Chapter 13, we discussed the growth of snow crystals by vapor diffusion, and in Chapter 14, we described the manner with which snow crystals interact with other snow crystals and with drops. In this chapter, we shalllook closer at the growth of ice particles by the accretion of supercooled drops, at the formation of snow flakes by the collision of snow crystals, and also consider the physics of melting of individual ice particles.
New insights into seismic absorption imaging
2020
Abstract In recent years, attenuation has been used as a marker for source and dynamic Earth processes due to its higher sensitivity to small variations of lithospheric properties compared to seismic velocity. From seismic hazard analysis to oil and gas exploration and rock physics, many fields need a better reconstruction of energy absorption, a constituent of seismic attenuation generally considered a reliable marker of fluid saturation in space. Here, we propose absorption tomography (AT), a technique grounded on the principles of scattering tomography and Multiple Lapse Time Window Analysis. We benchmark its efficiency to image absorption in space by comparing its results with those obt…
Protein diffusion through charged nanopores with different radii at low ionic strength
2014
[EN] The diffusion of two similar molecular weight proteins, bovine serum albumin (BSA) and bovine haemoglobin (BHb), through nanoporous charged membranes with a wide range of pore radii is studied at low ionic strength. The effects of the solution pH and the membrane pore diameter on the pore permeability allow quantifying the electrostatic interaction between the chargedpore and the protein. Because of the large screening Debye length, both surface and bulk diffusion occur simultaneously. By increasing the pore diameter, the permeability tends to the bulk self-diffusion coefficient for each protein. By decreasing the pore diameter, the charges on the pore surface electrostatically hinder …
Dynamic anomalies at the glass transition of organic van der Waals liquids
1993
Abstract The paper discusses the question of whether there is a characteristic temperature T c above the calorimetric glass transition temperature T g . Mode-coupling theory (MCT) predicts a crossover from liquid- to solid-like dynamics at T c . Neutron scattering and gradient NMR experiments have been carried out to test MCT using the molecular van der Waals liquid ortho -terphenyl as a model system. A significant anomaly of the Debye—Waller factor and a “decoupling” of self-diffusion from viscosity support the MCT predictions. A critical discussion of the relevance of such tests and of the limitations of neutron scattering is presented.
Heterogeneity at the Glass Transition: Translational and Rotational Self-Diffusion
1997
Self-diffusion coefficients, D, have been measured in the glass forming liquids salol, glycerol, phenolphthaleine dimethyl ether (PDE), cresolphthaleine dimethyl ether (CDE), and ααβ-trinaphthylbenzene (TNB) in the supercooled regime. The NMR static magnetic field gradient technique was applied where D >10-14 m2 s-1 can be attained. The results are similar to previous diffusion experiments where an enhancement of translational diffusion was found in comparison with rotational diffusion and shear viscosity. Various models of spatial heterogeneity are related to a phenomenological environmental fluctuation model in view of recent diffusion and relaxation data close to the glass transition.
Surface Self-Diffusion and Mean Displacement of Hydrogen on Graphite and a PEM Fuel Cell Catalyst Support
2009
International audience; Quasielastic neutron scattering (QENS) measurements together with equilibrium molecular dynamic (EMD) simulations have been performed to investigate the surface interaction between hydrogen molecules and a carbon material commonly used in polymer electrolyte membrane fuel cells (PEMFC), called XC-72. Half a monolayer of molecular hydrogen was adsorbed on to the carbon material at 2 K. QENS spectra were recorded at the time-of-flight spectrometer IN5 at 40, 45, 50, 60, 70, 80, and 90 K. Simultaneously the pressure was measured as a function of time to monitor the equilibrium surface coverage at each temperature. By using the Chudley and Elliott model for jump diffusio…
Collective and self diffusion of PS microgels in solution as observed by thermal diffusion forced Rayleigh scattering
2007
Thermal diffusion in solutions of polystyrene micro-network spheres (microgels) in toluene has been studied by the holographic scattering technique of thermal diffusion forced Rayleigh scattering (TDFRS) and by photon correlation spectroscopy (PCS). Size distributions of microgels of different crosslink ratios are obtained from TDFRS measurements on dilute solutions at very low q-values around 4000cm−1. At low concentrations a single diffusive mode is observed and the diffusion coefficient increases with concentration. It is attributed to the collective diffusion of the microgels and the solvent. At high concentrations an additional slow mode appears whose diffusion coefficient decreases wi…
Si self-diffusion in cubic B20-structured FeSi
2008
Self-diffusion of implanted 31Si in the e-phase FeSi (cubic B20-structure) has been determined in the temperature range 660–810 °C using the modified radiotracer technique. With an activation enthalpy of 2.30 eV and a pre-exponential factor of 15×10−8 m2 s−1 the silicon diffusivity was found to be slightly slower than Ge impurity diffusion in FeSi. This difference is proposed to originate from attractive elastic interactions prevailing between the slightly oversized Ge atoms and the Si sublattice vacancies. The results confirm the argument that 71Ge radioisotopes may be used to substitute the short-lived 31Si radiotracers when estimating self-diffusion in silicides.