Fluid flow in porous systems

Nuclear magnetic resonance (NMR) measurements of water velocity flowing through glass bead packs with a bead diameter of 10 mm have been made using the phi echo-planar imaging (PEPI) sequence. These results indicate that for various flow rates the flow variance is proportional to the mean flow velocity in agreement with the Mansfield-Issa equation. The velocity distributions are approximately Gaussian. Investigation of the slopes of the variance vs. velocity curves as a function of slice thickness indicate some coherence effects in the connectivity of the glass bead system. An extension of an earlier intervoxel coupling model is presented, which seems to explain the observed coherence effects.     

Susceptibility effects in unsaturated porous silica

Nuclear magnetic resonance proton line widths have been studied as the saturation level of water in a porous silica system is varied. Two silica samples were used with nominal pore sizes of 60 and 140 A. It was found that the line width increased with saturation level for both systems; this is consistent with the saturation process suggested by Allen et al. At low saturation levels the peak shift, from bulk water, increased with the saturation level reaching a maximum at filling factors of approximately 40% and 20% for the 60- and 140-A samples, respectively, after which point it began to decrease. Analysis is currently under way to try to model this system to determine whether these results are also consistent. It is anticipated that further analysis will give information on the pore morphology of the system.     

NMR relaxation studies of porous sol-gel glasses

Dual energy X-ray absorptiometry (DXA) was used to measure human body composition on a high speed fan beam scanner. High and low energy attenuation pairs, produced by the various combinations of fat mass and fat-free mass in the human body, were compared to attenuation values produced by standard materials (aluminum and acrylic). These standards were measured in various combinations to construct calibration curves for fat and fat-free mass. Primary calibration of the aluminum/acrylic combinations was achieved by direct comparison to the dual energy attenuation produced by stearic acid and pure water. Whole body examinations were accomplished using three 45 s longitudinal passes of the fan beam. These passes were acquired and assembled to create a giant, isocentric fan beam with a single center of focus. In vivo precision was 0.009 g/cm2 for BMD and 425 g for fat mass and fat-free mass (s.d.).     

Fluid transport in glass beads phantoms: spatial velocity measurements and confirmation of the stochastic model

A stochastic model of fluid flow in porous rocks has been previously developed to explain the measured distribution of local velocity. The theoretical predictions of this model agree well with experimental results obtained from the magnetic resonance imaging-based measurements of the spatial variation of velocity of water permeating through Bentheimer and Clashach sandstones. To further verify previous results, we have performed new velocity measurement experiments using an efficient velocity encoded pi-echo planar imaging sequence on glass bead phantoms that exhibit more regular pore size distribution than rocks. The results show that velocity distributions in glass bead phantoms also exhibit Gaussian profiles and the linear relationship between the velocity variance and the mean velocity (the Mansfield-Issa equation).     

溶胶-凝胶法制备SiO2薄膜的研究

采用溶胶-凝胶法,研究了催化剂和反应温度对正硅酸乙脂溶胶-凝胶过程中胶凝时间的影响,观察了不同基材上制得的SiO2薄膜的表面形貌.发现催化剂是制备良好薄膜的关健因素,反应温度可明显缩短胶凝时间,并在玻璃和金属粉末基体上制得了具有网状结构的SiO2薄膜.     

Dowel space preparation in root canals filled with glass ionomer cement

To assist beginners in the microsurgical practices of handling instruments and tying knots before using an animal model, the authors suggest the use of colored beads. These beads will diminish eyestrain and secondary fatigue. Also, working with colored beads might be a little more amusing and enjoyable for beginners in learning microsurgical techniques during preliminary studies to achieve the necessary orientation for working under the operating microscope.     

Behavior of silica inclusions in a partially solidified iron base alloy

Experiments are reported on the behavior of primary silica inclusions during the growth by isothermal coarsening of iron dendrites. The base alloy employed was Fe-50 pct Cu, chosen because of its wide freezing range. The inclusions are “pushed” by the growing dendrites. Also, the initially spherical inclusions collide and join with one another to form stringy “multimembered” inclusions. Partial coalescence occurs between touching inclusion members. A limited amount of diffusional coarsening of inclusions also occurs. It is suggested similar phenomena occur during dendritic solidification. Formerly Graduate Student, Massachusetts Institute of Technology, Cambridge, Mass.