Effect of texture and heat treatment on high temperature deformation of Zircaloy-2

Cylindrical specimens machined from Zircaloy-2 plate have been tested under compression at 295, 675 and 1075 K. The plate was in three conditions (a) as hot rolled, (b) oil quenched from 1130 K. and (c) oil quenched from 1340 K. These conditions simulate the structures in fuel cladding in regions near brazed spacers. The structures and crystallographic textures of the material in these conditions were characterized. Specimens with axes along the longitudinal, transverse and thickness directions were tested to determine the effect of temperature, texture and structure on the mechanical properties, particularly with respect to postulated LOCA conditions. The tests showed that (i) factors for mechanical anisotropy derived from room temperature results should be valid for LOCA analysis, (ii) anisotropy factors from the results are consistent with about 67% prism and 33% basal slip in the early stages of deformation and (iii) oil quenching from 1130 K changes the texture and strength in a minor way, while quenching from 1340 K (β phase) gives an almost random texture, little mechanical anisotropy and a small change in the average strength.     

Effect of deformation on ferrite nucleation and growth in a plain carbon and two microalloyed steels

Isothermal compression tests were carried out on plain C, Mo, and Mo−Nb−V microalloyed steels in order to study the effect of austenite deformation on the ferrite nucleation and growth rates. The nucleation rate increases with deformation and the degree of supersaturation, Ae₃−T; it appears to be reduced by the substitutional elements Mo, Nb, and V through reduction of the austenite grain boundary energy. The growth rate increases with the degree of supersaturation and is also reduced by these elements, apparently through the solute drag-like effect. Under static conditions, increasing the prestraining strain rate increases the nucleation rate, but this increase is small compared to the effect of concurrent deformation. The growth rate under static conditions decreases as the deformation or the strain rate is increased. E. E, formerly with the Department of Metallurgical Engineering, McGill University     

Ti(CN) precipitation in microalloyed austenite during stress relaxation

Stress relaxation tests were carried out on a 0.05 pct C-0.007 pct N-0.25 pct Ti steel preheated to 1260 °C and then held in the temperature range 900 to 1050 °C. The precipitation of Ti(CN) that took place was followed by extraction replication. Dense precipitates were observed when stress plateaus appeared on the relaxation curves. The cube-shaped Ti(CN) precipitates were heterogeneously distributed in either a chain-like or a cell-like manner, indicating that the precipitates were nucleated on dislocations or on dislocation substructures. The changes in the size distribution of the precipitates during relaxation were also followed and analyzed in terms of the Zener diffusion controlled particle growth theory. The results suggest that Ti(CN) precipitation under the present experimental conditions proceeds in three sequential stages: (i) nucleation and growth according to a parabolic law; (ii) nucleation site saturation accompanied by growth alone; and (iii) Ostwald ripening. The time dependence of the mean Ti(CN) particle size is nonlinear during the first, and becomes linear during the second stage.     

Dependence of gas adsorption rates on carbon granule size and linear flow velocity

A study was made of the dependence of the adsorption rate constant of an activated carbon for dimethyl methylphosphonate vapor on carbon granule size and superficial linear velocity using the adsorption kinetics equation to calculate the rate constant from critical bed weight values. Over a 30-fold range of velocities and a 7-fold range of granule diameters it was found, in accord with adsorption kinetics theory, that although the adsorption capacity for the vapor was invariant, the time for vapor breakthrough of the bed varied because of the effects of linear flow velocity and carbon granule size on the adsorption rate constant. In general, the rate constant increased nonlinearly with increase in velocity and decrease in carbon granule size. The slowest adsorption kinetics existed for the largest granule size at the lowest linear flow velocity, becoming increasingly faster as the velocity was increased and/or the granule size was decreased. For the smallest granule size the rate constant reached a limiting value of 2600 sec^?1 becoming essentially independent of linear velocity due to a change in the rate controlling step.     

Time-resolved NIR spectroscopy for quantitative analysis of intact pharmaceutical tablets

Near-infrared (NIR) spectroscopy is a useful technique for quantitative measurements of intact tablets, but it suffers from limitations due to the fact that changes in the physical properties of a sample strongly affect the recorded spectrum. In this work, time-resolved transmission NIR spectroscopy was utilized to conduct quantitative measurements of intact tablets. The technique enables separation of the absorption properties of the sample from the scattering properties and can therefore handle changes of the physical parameters of the samples in a better way than conventional NIR transmission spectroscopy. The experiments were conducted using a pulsed Ti:sapphire laser coupled into a nonlinear photonic crystal fiber as light source. The light transmitted through the sample was measured by a time-resolving streak camera. A comparison of the results from the time-resolved technique with the results from conventional transmission NIR spectroscopy was made using tablets containing different concentrations of iron oxide and manufactured with different thicknesses. A PLS model made with data from the time-resolved technique predicted samples 5 times better than a PLS model made data from the conventional NIR transmission technique. Furthermore, an improvement to predict samples with physical properties outside those included in the calibration set was demonstrated.     

Solid-phase diffusion mechanism for GaAs nanowire growth

Controllable production of nanometre-sized structures is an important field of research, and synthesis of one-dimensional objects, such as nanowires, is a rapidly expanding area with numerous applications, for example, in electronics, photonics, biology and medicine. Nanoscale electronic devices created inside nanowires, such as p-n junctions, were reported ten years ago. More recently, hetero-structure devices with clear quantum-mechanical behaviour have been reported, for example the double-barrier resonant tunnelling diode and the single-electron transistor. The generally accepted theory of semiconductor nanowire growth is the vapour-liquid-solid (VLS) growth mechanism, based on growth from a liquid metal seed particle. In this letter we suggest the existence of a growth regime quite different from VLS. We show that this new growth regime is based on a solid-phase diffusion mechanism of a single component through a gold seed particle, as shown by in situ heating experiments of GaAs nanowires in a transmission electron microscope, and supported by highly resolved chemical analysis and finite element calculations of the mass transport and composition profiles.     

Optical manipulation in combination with multiphoton microscopy for single-cell studies

We demonstrate how optical tweezers can be incorporated into a multiphoton microscope to achieve three-dimensional imaging of trapped cells. The optical tweezers, formed by a cw 1064 nm Nd:YVO4 laser, were used to trap live yeast cells in suspension while the 4',6-diamidino-2-phenylindole-stained nucleus was imaged in three dimensions by use of a pulsed femtosecond laser. The trapped cell was moved in the axial direction by changing the position of an external lens, which was used to control the divergence of the trapping laser beam. This gives us a simple method to use optical tweezers in the laser scanning of confocal and multiphoton microscopes. It is further shown that the same femtosecond laser as used for the multiphoton imaging could also be used as laser scissors, allowing us to drill holes in the membrane of trapped spermatozoa.     

Focal volume confinement by submicrometer-sized fluidic channels

Microfluidic channels with two lateral dimensions smaller than 1 microm were fabricated in fused silica for high-sensitivity single-molecule detection and fluorescence correlation spectroscopy. The effective observation volumes created by these channels are approximately 100 times smaller than observation volumes using conventional confocal optics and thus enable single-fluorophore detection at higher concentrations. Increased signal-to-noise ratios are also attained because the molecules are restricted to diffuse through the central regions of the excitation volume. Depending on the channel geometries, the effective dimensionality of diffusion is reduced, which is taken into account by simple solutions to diffusion models with boundaries. Driven by electrokinetic forces, analytes could be flowed rapidly through the observation volume, drastically increasing the rate of detection events and reducing data acquisition times. The statistical accuracy of single-molecule characterization is improved because all molecules are counted and contribute to the analysis. Velocities as high as 0.1 m/s were reached, corresponding to average molecular residence times in the observation volume as short as 10 micros. Applications of these nanofabricated devices for high-throughput, single-molecule detection in drug screening and genomic analysis are discussed.     

Projective texture atlas construction for 3D photography

The use of attribute maps for 3D surfaces is an important issue in geometric modeling, visualization and simulation. Attribute maps describe various properties of a surface that are necessary in applications. In the case of visual properties, such as color, they are also called texture maps. Usually, the attribute representation exploits a parametrization g:U??²→?³ of a surface in order to establish a two-dimensional domain where attributes are defined. However, it is not possible, in general, to find a global parametrization without introducing distortions into the mapping. For this reason, an atlas structure is often employed. The atlas is a set of charts defined by a piecewise parametrization of a surface, which allows local mappings with small distortion. Texture atlas generation can be naturally posed as an optimization problem where the goal is to minimize both the number of charts and the distortion of each mapping. Additionally, specific applications can impose other restrictions, such as the type of mapping. An example is 3D photography, where the texture comes from images of the object captured by a camera [4]. Consequently, the underlying parametrization is a projective mapping. In this work, we investigate the problem of building and manipulating texture atlases for 3D photography applications. We adopt a variational approach to construct an atlas structure with the desired properties. For this purpose, we have extended the method of Cohen–Steiner et al. [6] to handle the texture mapping set-up by minimizing distortion error when creating local charts. We also introduce a new metric tailored to projective maps that is suited to 3D photography.