Overview of the Plasma Science and Innovation Center (PSI – Center)

The principal goal of the Plasma Science and Innovation Center (PSI – Center) is to achieve significantly improved computational predictive capability for smaller-scale devices. This is being accomplished through the refinement of existing computational tools through adding sufficient physics modeling, boundary conditions, and geometric capabilities while benchmarking results against experimental data. The work emphasizes the modeling needs of emerging concept (EC) experiments, but improved simulation capabilities for all innovative confinement concepts (ICC) are expected. A special emphasis is placed on physics effects that may extend beyond the standard analysis applied to the mainline programs.     

Salience and awareness in the Jacoby-Whitehouse effect.

L. L. Jacoby and K. Whitehouse (1989) observed that false recognition of new test words was biased by the nature and duration of preceding context words. With very brief exposures to context words, participants were more likely to call a test item "old" when the prior context word was identical than when there was a mismatch. At longer durations, the reverse pattern was obtained. In the present experiment, test items were preceded by the rapid visual presentation of 7 supraliminal context items, 1 of which might or might not match the test item. Participants either looked for matches (high salience) or tried to remember the context items (low salience). The results closely resemble those for long and short exposure durations, suggesting that the crucial variable is the salience of matches rather than perceptual subliminality of context items. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A modeling study predicts the presence of voltage gated Ca2+ channels on myelinated central axons

The objective of this current study was to investigate whether voltage gated Ca(2+) channels are present on axons of the adult rat optic nerve (RON). Simulations of axonal excitability using a Hodgkin-Huxley based one-compartment model incorporating I(Na), I(K) and leak currents were used to predict conditions under which the potential contribution of a Ca(2+) current to an evoked action potential could be measured. Under control conditions the inclusion of a high threshold Ca(2+) current (I(Ca)) in the model had a negligible effect on the action potential. Reducing I(K), by decreasing the value of g(K), elongated the repolarizing phase of the action potential, increasing its duration. Subsequent incorporation of I(Ca) in the model revealed a significant I(Ca) contribution to the repolarizing phase of the action potential. The simulation thus suggests that Ca(2+) channels may be present on RON axons, but that pharmacological intervention is required to unmask their presence. Experiments based on the simulations revealed that there was no significant contribution of I(Ca) to the control action potential. However, as predicted by the simulation, reducing the repolarizing effect of I(K) by adding the K(+) channel blocker 4-AP revealed a Ca(2+) component on the repolarizing phase of the action potential that was blocked by the Ca(2+) channel inhibitor nifedipine.     

Experimental evaluation of a spherical aberration-corrected TEM and STEM

We have successfully developed a spherical aberration (Cs)-corrected electron microscope for probe- and image-forming systems using hexapole correctors. The performance of the microscope has been evaluated experimentally. The point resolution attained using the image-forming Cs-corrector is better than 0.12 nm. For scanning transmission electron microscopy, the Ronchigram flat area was >40 mrad in half-angle using the probe-forming Cs-corrector.     

DNA multilayer films on planar and colloidal supports: sequential assembly of like-charged polyelectrolytes

Multilayer films comprising solely negatively charged polyelectrolytes were sequentially assembled based on DNA hybridization. Films prepared from alternating layers of two-block homopolymeric nucleotides (polyA(20)G(20)/polyT(20)C(20)) grew linearly with increasing layer number, as verified by quartz crystal microgravimetry, UV-vis spectrophotometry and optical microscopy. Urea treatment of the films induced morphological changes, while exposure to low ionic strength solutions resulted in film disassembly. DNA multilayer films were also formed on silica particles, and DNA hollow capsules were obtained following dissolution of the template core.     

Alloy solidification in systems containing a liquid miscibility gap

Directional solidification methods have been used to examine the growth of fibrous, or tubular, composite samples in alloys close to the monotectic reaction: Liquid 1 Solid + Liquid 2. The binary systems Al-In, Cu-Pb and Cd-Ga have been examined and some use made of a transparent analogue, succinnonitrile-water. The solidification behavior appears to relate to the height of the miscibility gap in such systems and it is demonstrated how ternary additions which change this height (Sn to Al-In, Al to Cu-Pb) modify the microstructures dramatically. These structural changes are discussed with reference to the relative surface energies between two immiscible liquids and a third (solid) phase. The phase spacings and transitions in microstructure are discussed in terms of diffusion processes at the monotectic front. Formerly with University of Wisconsin-Milwaukee     

Growing and characterizing one-dimensional crystals within single-walled carbon nanotubes

Single-walled carbon nanotubes (SWNTs) have been used as growth templates for spatially confined crystal growth. The comparative crystallization and high-resolution transmission electron microscopy imaging properties of simple binary halides formed by the alkali iodides MI (M = Li, K, Na, Rb and Cs) within SWNTs are described. The most common structure type observed within SWNTs was the rocksalt archetype, although CsI was observed to form both body-centred cubic (bcc) and rocksalt structure types. ThCl4 was found to form a chain structure of Th[Cl]8 polyhedra. HgI2 crystallized within nanotubes with ultra-narrow (i.e. 0.8 nm) capillaries was observed to form helical 2 x 1 layer crystals.     

Numerical Error in Weighting Function-Based Unsteady Friction Models for Pipe Transients

The accurate simulation of pressure transients in pipelines and pipe networks is becoming increasingly important in water engineering. Applications such as inverse transient analysis for condition assessment, leak detection, and pipe roughness calibration require accurate modeling of transients for longer simulation periods that, in many situations, requires improved modeling of unsteady frictional behavior. In addition, the numerical algorithm used for unsteady friction should be highly efficient, as inverse analysis requires the transient model to be run many times. A popular model of unsteady friction that is applicable to a short-duration transient event type is the weighting function-based type, as first derived by Zielke in 1968. Approximation of the weighting function with a sum of exponential terms allows for a considerable increase in computation speed using recursive algorithms. A neglected topic in the application of such models is evaluation of numerical error. This paper presents a discussion and quantification of the numerical errors that occur when using weighting function-based models for the simulation of unsteady friction in pipe transients. Comparisons of numerical error arising from approximations are made in the Fourier domain where exact solutions can be determined. Additionally, the relative importance of error in unsteady friction modeling and unsteady friction itself in the context of general simulation is discussed.