Diffusion Fundamentals (E-Journal)
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Tortuosity estimate through paramagnetic gas diffusion in rock saturated with two fluids using T2 (z, t) low-field NMR
Get PDFPetrophysical interpretation of 1H NMR relaxation responses from saturated rocks is complicated by paramagnetic species present in fluids. Oxygen dissolved in liquids is one common example. Dipolar interactions of oxygen’s unpaired electron spins with the magnetic moment of fluid nuclei provide a strong relaxation mechanism known as paramagnetic relaxation enhancement (PRE). As a result even low concentrations of dioxygen in its common triplet ground state significantly shorten longitudinal and transverse relaxation times of host fluids. This effect may be employed similarly to any standard tracer technique to study pore connectivity in porous media by detecting a change of oxygen concentration due to diffusion resolved in time and space. Since relaxation enhancement effect is likely stronger in non-wetting phase than in wetting one (where surface relaxation process dominates) this difference can be utilized to study wettability in immiscible multiphase systems. We use a relaxation time contrast between air-saturated and oxygen-free fluids to evaluate oxygen concentration change within two fluid phases saturating rock, to estimate time required to establish equilibrium concentration and to calculate a mutual diffusion coefficient of oxygen. A spatially- and time-resolved T2(z,t) experiment provides the time-dependent oxygen concentration change along the fully- and partially-saturated carbonate core plug exposed to air saturated oil at its inlet. We derive an effective mutual diffusion coefficient of oxygen and accordingly a tortuosity estimate as a function of position along the core and rock saturation. The spatially resolved oxygen diffusion-based tortuosity is compared to simulated conductivitybased tortuosity. The latter is calculated on a high-resolution micro-tomographic image of Mount Gambier limestone by solving the Laplace equation for conductivity
Diffusion of Environmental Awareness
Get PDFA high level of “environmental awareness” in the participating countries will likely raise the success of the Kyoto Protocol negotiated in Paris in 2015. In this context it is of interest to investigate the diffusion of environmental awareness, and also the (economic) factors, on which this diffusion depends. This paper addresses these questions for the regions of the Russian Federation, which are sufficiently diverse regarding cultural and economic issues. From a formal point of view, a “Multiple-Indicator-Multiple-Causes” (MIMIC) approach, based on a variety of “indicators” for environmental awareness, derived from search entries in c Yandex, and a variety of “causes”, economic and socio-economic factors, is applied. The empirical results point first to a strong dependence of environmental awareness on the level of GRP per capita. Moreover, the diffusion seems to spread from the eastern part of Russia towards the western regions
The dependencies of self-diffusion coefficient on the size and shape of the nanocrystal at different P-T-conditions
Get PDFOn the liquid-like local state in deformed metallic materials, relevance to physics of the diffusion and other anomalies
Get PDFEffect of mechanical activation on optimal sintering temperature of ultrafine-grained tungsten heavy alloys
Get PDFA Theory for the Surface Induced Growth of Helium Gas Bubbles in Irradiated and Annealed Copper - Boron Alloys
Get PDFNeutron irradiated copper-boron alloys are employed to study the mutual interaction between metallic crystalline lattices and inert gases. Inert gases precipitate to form gas bubbles and their growth induces dilation of the matrix. This dilation, technically designated as swelling, affects the structural integrity of nuclear fuels during their service. The estimated enthalpy of solution of helium in copper is 5.5 eV/atom. As a Consequence, its solubility in the copper matrix is extremely poor and it cannot enter a copper based matrix via any thermo-chemical route. Hence, recourse to a nuclear reaction is taken to impregnate copper with helium. Helium is produced in situ through neutron irradiation in copper-boron alloys as a result of (n, alpha) nuclear reaction between boron atoms and neutrons. The characteristic feature of the growth of helium gas bubbles driven by isothermal annealing of the metallic matrix is that their rate of growth is highly sensitive to the distance of the bubbles from the external surface of the specimen. The growth of gas bubbles as a function of time and temperature is modulated by the flow of vacancies from the free surface of the specimen. A theory for the surface induced growth of helium gas bubbles in the neutron irradiated copper-boron alloys is presented here
