Solvent penetration in cured epoxy networks

The kinetics of the sorption characteristics of seven different solvents has been measured at 22°, 40°, and 50°C in several cured epoxies. In addition to water, the organic solvents methanol, acetone, isopropanol, ethyl acetate, 1,2-dichloroethane, and toluene were examined. The resin, diglycidyl ether of bisphenol A, was cured with four hardeners, each one resulting in a different epoxy material. The curing agents include triethylenetetramine, nadic methylanhydride, dicyandiamide and m-phenylenediamine, all commonly used substances. Data were analyzed using Fick's diffusion equation. In general, three types of behavior were observed, Fickian diffusion, Case II diffusion, and anomalous diffusion. Fickian or anomalous behavior dominated at all temperatures. Diffusion was both material and solvent dependent. The anomalous nature of isopropanol was noted. Although chemically similar to methanol and about the same size, as acetone, isopropanol is sorbed at a much lower rate. A combination of physical and chemical effects appeared to be responsible for the observations in the epoxies. Diffusion coefficients were estimated for all penetrants and were mostly in the range of 10^?9 to 10^?11 cm²/s. Where appropriate, apparent activation energies for diffusion were calculated from the kinetic curves.     

Fabrication of switchable liquid crystal devices using surface relief gratings in photopolymer

Holographically recorded surface relief gratings in dry, self-developing acrylamide based photopolymer were used to fabricate two types of switchable liquid crystal (LC) device. One is an electrically switchable LC diffraction grating and the other is an electrically switchable polarization rotator. The electrically switchable diffraction grating was characterized by measuring the dependence of the intensity in the first diffracted order on the applied electric field. The polarization rotator was characterized by studying the influence of the applied electric field on the twist angle and the variation of intensity in the zero and the first orders of diffraction.     

Reduction of ASR-expansion using powders ground from various sources of reactive aggregates

This study assesses the potential of ground reactive aggregates to reduce or suppress expansion associated with ASR. Particular attention is paid to fine admixtures (<80 μm) added to mortars, which contain the reactive aggregates from which the fines were ground. Many varieties of aggregate (quarried and natural, igneous, metamorphic and sedimentary rocks) from different geological settings were subjected to an autoclave test. The replacement of 10–20% of the sand by reactive aggregate powder (RAP) of different surface areas from 11 different reactive aggregates led to the reduction of ASR-expansion by up to 78% compared with control mortars. Increasing the amount of fines led to better performance. No clear relationship was observed between the reactivity degree of the aggregates and the efficiency of their ground powder to reduce expansion. A general trend was found regarding the fineness of ground aggregates: finer particles were more effective in reducing expansion. The reduction of the expansion due to RAP is discussed in terms of parameters affecting its efficiency and of the mechanisms responsible for the reduction.     

A thermal model of the immobilization of low-level radioactive waste as grout in concrete vaults

Salt solution, from radioactive waste generated by the production of plutonium and tritium in nuclear reactors at the Savannah River Site, will be mixed with cement and flyash/slag to form a grout which will be poured into above ground concrete vaults. The curing process is exothermic, and a transient thermal model of the pouring and curing process is herein described. A peak temperature limit of 85 °C for the curing grout restricts the rate at which it can be poured into a vault. The model is used to optimize the pouring.     

Effective strain rate sensitivity of two phase materials

Analytical expressions are derived for the effective strain rate sensitivity exponent of a two phase material when the behavior of both phases and of the composite itself can be described by power law relations between the stress and strain rates. The material is assumed to be plastically isotropic and obey to von-Mises type creep behavior. Two types of boundary conditions are considered: strain or stress-controlled. The obtained formulas are applied to a geological composite material (mixture of camphor and octachloropropane) with the help of different simple models of two phase composites.     

Prussian Blue electrodeposition within an oriented mesoporous silica film: preliminary observations

Prussian Blue (PB) has been electrochemically grown through thin mesoporous silica films of novel generation, exhibiting regular arrays of hexagonally packed mesopores channels (3 nm in diameter) oriented perpendicular to the underlying electrode surface. Due to confinement effects, special care has to be taken to ensure effective permeability of PB precursors through the hard silica template, which was best achieved by pulsed electrodeposition from a high ionic strength medium (2 M KCl). Energy dispersive X-ray spectroscopy associated to electron microscopy was used to evidence the presence of PB in the vertically-aligned mesopores, which was also assessed by their electrocatalytic behavior towards H₂O₂ reduction.     

Numerical simulation of confined pulsating jets in human phonation

Confined pulsating jets in simplified two-dimensional models of the larynx are considered to study human phonation. The jets are generated by periodically oscillating inlet velocities in stationary vocal tracts. The jets are computed by solving the 2D compressible Navier-Stokes equations by a high order finite difference method, which has been constructed to be strictly stable for linear hyperbolic and parabolic problems. Vortex dynamics is investigated.     

How indirect supportive digital help during and after solving physics problems can improve problem-solving abilities

This study investigates the effectiveness of computer-delivered hints in relation to problem-solving abilities in two alternative indirect instruction schemes. In one instruction scheme, hints are available to students immediately after they are given a new problem to solve as well as after they have completed the problem. In the other scheme, hints are only available as worked out problems after students have finished their solution. The instruction schemes are supplied by means of a web-based program, Physhint, which supports the development of strategic knowledge [Pol, H. J., Harskamp, E. G., & Suhre, C. J. M. (2008). The effect of the timing of instructional support in a computer-supported problem-solving program for students in secondary physics education. Computers in Human Behavior, 24, 1156–1178]. This program supports novice problem solvers while undertaking physics problems concerned with forces by providing hints structured in accordance with Schoenfeld’s episodes [Schoenfeld, A. H. (1992). Learning to think mathematically: Problem solving, metacognition, and sense making in mathematics. In D. A. Grouws (Ed.), Handbook of research on mathematics teaching (pp. 224–270). New York: McMillan Publishing].     

Shape Decomposition using Modal Analysis

We introduce a novel algorithm that decomposes a deformable shape into meaningful parts requiring only a single input pose. Using modal analysis, we are able to identify parts of the shape that tend to move rigidly. We define a deformation energy on the shape, enabling modal analysis to find the typical deformations of the shape. We then find a decomposition of the shape such that the typical deformations can be well approximated with deformation fields that are rigid in each part of the decomposition. We optimize for the best decomposition, which captures how the shape deforms. A hierarchical refinement scheme makes it possible to compute more detailed decompositions for some parts of the shape.
Although our algorithm does not require user intervention, it is possible to control the process by directly changing the deformation energy, or interactively refining the decomposition as necessary. Due to the construction of the energy function and the properties of modal analysis, the computed decompositions are robust to changes in pose as well as meshing, noise, and even imperfections such as small holes in the surface.