Multigrid preconditioned conjugate-gradient method for large-scale wave-front reconstruction

We introduce a multigrid preconditioned conjugate-gradient (MGCG) iterative scheme for computing open-loop wave-front reconstructors for extreme adaptive optics systems. We present numerical simulations for a 17-m class telescope with n = 48756 sensor measurement grid points within the aperture, which indicate that our MGCG method has a rapid convergence rate for a wide range of subaperture average slope measurement signal-to-noise ratios. The total computational cost is of order n log n. Hence our scheme provides for fast wave-front simulation and control in large-scale adaptive optics systems.     

Effect of platelet-activating factor on the electrophysiology of the human Fallopian tube: early mediation of embryo-maternal dialogue?

Platelet-activating factor (PAF) is produced by preimplantation embryos and may be involved in the earliest stages of embryo-maternal dialogue. This study explored the potential effects of PAF acting as a signalling agent on human Fallopian tubal epithelial cells grown as a polarized layer in primary culture. The response of the tubal epithelium was assessed in terms of the transepithelial potential difference and short-circuit current (I(scc)), which were recorded using a modified Ussing chamber. Resistance was calculated from the measurements of potential difference and I(scc). PAF (1.9 nmol to 1.9 micromol l(-1)) administered to the apical surface of the cells produced a marked, transient increase in both potential difference and I(scc) in a dose-dependent manner. The mode of action of PAF on the electrophysiological responses of human tubal epithelial cells was investigated. Blockers of Na(+), K(+) and voltage-operated Ca(2+) channels had little effect on PAF action. However, incubation of the epithelial cells in Cl(-)free medium or with a blocker of the Na(+)-K(+)-2Cl(-) cotransporter (Furosemide) reduced the effect of PAF. Blockade of chloride-bicarbonate channels with 4-acetamido-4'-iso-thiocyanostilbene-2.2'-disulphonic acid (SITS) reduced the effect of low doses of PAF only. These results indicate that PAF influences the movement of chloride ions across the tubal epithelial cell and is a candidate molecule for initial embryo-maternal dialogue.     

Performance of hardcoded finite automata

We study the performance of a hardcoded algorithm for recognizing strings of a finite automaton's language and compare it with the use of the more conventional table‐driven algorithm. In both cases, performance depends on the finite automaton's dimensions such as alphabet size and the number of states. However, the respective processing mechanisms that influence the performance, in particular cache memory usage, depend on the details of the processor's underlying architecture. In the hardcoded case, the automaton's dimensions determine the size of the code which is, in turn, the primary determinant of the way in which cache memory is used. In the table‐driven case, cache memory usage is primarily determined by the way in which portions of the transition table are stored in it. Using statistical regression analysis, we provide multivariate equations to model the observed time efficiency of both methods. The equations obtained are cross‐compared and conclusions are drawn. Copyright © 2006 John Wiley & Sons, Ltd.     

Sex differences in electrophysiological and behavioral responses to NaCl taste.

We tested the hypothesis that sex differences in preference for NaCl are attributable to estrogen-mediated alterations in gustatory processing. Electrophysiological responses of the chorda tympani nerve to NaCl were blunted by estrogen treatment in ovariectomized female rats, suggesting that females are less sensitive to concentrated NaCl solutions during high estrogen conditions. In contrast, after a taste aversion was conditioned to 150-mM NaCl, estrogen- and oil-treated ovariectomized rats generalized the aversion to a lower concentration of NaCl than did males, suggesting that females are more sensitive to the taste of dilute NaCl solutions regardless of estrogen. Thus, sex differences in NaCl preferences may be attributable to differences in NaCl taste processing that involve both acute and developmental effects of estrogen. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

NMDA receptor antagonism impairs reversal learning in developing rats.

Four experiments examined the effect of dizocilpine maleate (MK-801), a noncompetitive N-methyl-Daspartate (NMDA) receptor antagonist, on reversal learning during development. On postnatal days (PND) 21, 26, or 30, rats were trained on spatial discrimination and reversal in a T-maze. When MK-801 was administered (intraperitoneally) before both acquisition and reversal, 0.18 mg/kg generally impaired performance, whereas doses of 0.06 mg/kg and 0.10 mg/kg, but not 0.03 mg/kg, selectively impaired reversal learning (Experiments 1 and 3). The selective effect on reversal was not a result of sensitization to the second dose of MK-801 (Experiment 2) and was observed when the drug was administered only during reversal in an experiment addressing state-dependent learning (Experiment 4). Spatial reversal learning is more sensitive to NMDA-receptor antagonism than is acquisition. No age differences in sensitivity to MK-801 were found between PND 21 and 30. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Communication patterns during synchronous Web-based military training in problem solving

The nature of communication among geographically dispersed groups of learners using text messaging in a military training environment was assessed. A total of 6601 acts of chat were coded into one of three interaction content categories (social, task, or technology-related) and analyzed for frequency and relative change over time. Results indicated shifting patterns of interaction over the 6-month course; while technology concerns gradually diminished, on task discussion peaked in the middle months and social interactions were higher at the start and end of the training. Overall, student chats were categorized as on-task 55%, social 30%, or technology-related 15%. Examples of chats and focus group data indicated that there was an emphasis on fostering student problem solving within the online course.     

Simulation of the mechanical properties of an aluminum matrix composite using X-ray microtomography

Aluminum-based particulate-reinforced metal matrix composites (PMMCs) frequently have a heterogeneous distribution of reinforcement particles whether produced by a powder or liquid processing route. The applicability of X-ray microtomography (XMT) for the characterization of this heterogeneity, and its influence on final properties, was investigated for the case of a powder blended and extruded AA2124 matrix with Ni particulate. Three-dimensional image analysis techniques were used to quantify the embedded Ni particle size distribution and the extent and texture of clusters formed. The XMT data were exploited as a rapid method to generate a microstructurally accurate and robust three-dimensional mesh for input for finite-element modeling. Simulation of the elastoplastic response of the material showed excellent correlation with experimental results. This article is based on a presentation made in the symposium “Computational Aspects of Mechanical Properties of Materials,” which occurred at the 2005 TMS Annual Meeting, February 13–17, 2005, in San Francisco, CA, under the auspices of the MPMD-Computational Materials Science & Engineering (Jt. ASM-MSCTS) Committee.