The effect of multi-step milling and annealing treatments on microstructure and magnetic properties of nanostructured Fe-Si powders

Nanostructured Fe_1−xSi_x (x=0.05, 0.1, 0.15 and 0.2) powders are prepared by different multi-step milling and annealing treatments. The microstructure and magnetic properties are investigated for all alloys. The minimum crystallite size of as-annealed powders (∼40 nm) is found to be larger than in as-milled ones (∼15 nm). It is found that microstrains of 2- and 4-step processes are close to those of the as-received powders. The lattice parameter decreased ∼0.5% and 0.9% for the powders that experienced milling and annealing at the last step, respectively. The Fe₈₀Si₂₀ powders prepared by 1- and 4-step treatments show the maximum (40-125 Oe) and minimum (20-26 Oe) coercivity, respectively. With increase in milling time, mass magnetization increased for all processes. This can be ascribed to diminution in magneto-crystalline anisotropy due to grain refinement. The maximum mass magnetization (160-199 Am²/kg) is achieved for the 4-step process.     

Development of T2-relaxation values in regional brain sites during adolescence

Brain tissue changes accompany multiple neurodegenerative and developmental conditions in adolescents. Complex processes that occur in the developing brain with disease can be evaluated accurately only against normal aging processes. Normal developmental changes in different brain areas alter tissue water content, which can be assessed by magnetic resonance (MR) T2 relaxometry. We acquired proton-density (PD) and T2-weighted images from 31 subjects (mean age±S.D., 17.4±4.9 years; 18 male), using a 3.0-T MR imaging scanner. Voxel-by-voxel T2-relaxation values were calculated, and whole-brain T2-relaxation maps constructed and normalized to a common space template. We created a set of regions of interest (ROIs) over cortical gray and white matter, basal ganglia, amygdala, thalamic, hypothalamic, pontine and cerebellar sites, with sizes of ROIs varying from 12 to 243 mm³; regional T2-relaxation values were determined from these ROIs and normalized T2-relaxation maps. Correlations between R2 (1/T2) values in these sites and age were assessed with Pearson's correlation procedures, and gender differences in regional T2-relaxation values were evaluated with independent-samples t tests. Several brain regions, but not all, showed principally positive correlations between R2 values and age; negative correlations emerged in the cerebellar peduncles. No significant differences in T2-relaxation values emerged between males and females for those areas, except for the mid pons and left occipital white matter; males showed higher T2-relaxation values over females. The findings indicate that T2-relaxation values vary with development between brain structures, and emphasize the need to correct for such age-related effects during any determination of potential changes from control values.     

Comparison of the three-phase oil relative permeability models

A comparative study of seven different methods for predicting three-phase oil relative permeabilities in the presence of gas and water phases is presented. Predicted oil relative permeabilities from these correlations have been compared with published three-phase experimental data obtained in Berea sandstone core samples. Some of the correlations under study have been recently developed and have never been tested against the laboratory data.The comparison shows that the commonly used models such as Stones' often do not give accurate predictions of the experimental data. It is concluded that the recently developed models fit the experimental data as well as or better than the previously developed and widely used three-phase oil relative permeability models.     

Electrochemical determination of tyrosine in the presence of uric acid at a carbon paste electrode modified with multi-walled carbon nanotubes enhanced by sodium dodecyl sulfate

Tyrosine (Tyr) was quantitated with high sensitivity and selectivity in the presence of uric acid (UA) using a carbon paste electrode modified with multi-walled carbon nanotubes. Tyr and UA were catalytically oxidized with diffusion-controlled characteristics. They were determined simultaneously by differential pulse voltammetry with a potential difference of 350 mV. The electrocatalytic currents increase linearly with Tyr and UA concentrations 4×10^?7?1×10^?4 M and 3×10^?7?2×10^?4 M. Their detection limits were 1×10^?7 and 5.1×10^?8 M respectively. In the presence of sodium dodecyl sulfate the Tyr detection limit improved from 1×10^?7 to 6.9×10^?8 M. The electrode was successfully used to quantitate Tyr and UA in serum.      

Solution Construction to a Class of Riemann Problems of Multiphase Flow in Porous Media

Transport in Porous Media - Fluid displacement in porous media can usually be formulated as a Riemann problem. Finding the solution to such a problem helps shed light on the dynamics of flow and...     

Displacement Theory of Low-Tension Gas Flooding

Low-tension gas (LTG) flooding is a promising chemical enhanced oil recovery technique in tight sandstone and carbonate reservoirs where polymer may not be used because of plugging and degradation issues. This process has been the subject of many experimental studies. However, theoretical investigation of the LTG process is scarce in the literature. Hence, in this study, we lay out a displacement theory for LTG flooding, with a constant mobility reduction factor, which lays the groundwork for further theoretical studies. The proposed model is based on the three-phase flow of water, oil, and gas in the presence of a water-soluble surfactant component. Under the developed model, we study the effect of MRF and oil viscosity on the flow dynamics and oil recovery. Moreover, we explain experimental observations on early gas breakthrough that occurs during LTG core floods even in the presence of a stable foam drive.

     

Application of higher-order flux-limited methods in compositional simulation

A higher-order flux-limited finite-difference scheme has been implemented into a compositional simulator to discretize the convection terms of the component conservation equations and the relative permeability terms of the phase fluxes. Harten's total variation diminishing criteria are imposed directly to the finite-difference equations and the bounds of the flux limiters which are suitable for larger Courant numbers and nonuniform grid systems are obtained. A time-correction technique is applied to increase the time accuracy and improve the stability condition.The scheme has been tested for miscible and immiscible flow problems in one and two dimensions, and the results were compared with those using a third-order method without flux limiting and some available analytical solutions.