Work-hardening and recovery mechanisms in gamma-based titanium aluminides

The work-hardening mechanisms in two-phase γ-titanium aluminide alloys were characterized in terms of the glide obstacles determining the velocity and slip path of dislocations, utilizing transmission electron microscopy (TEM) observations and thermodynamic-glide parameters. There was clear evidence that short-range obstacles in the form of dislocation debris and dipoles were produced during plastic deformation at room temperature. These dislocation obstacles contributed significantly to work hardening. The observed strong strain hardening arose from long-range elastic dislocation interactions and the production of dipole and debris defects. The thermal stability of these deformation-induced defects was assessed by isothermal and isochronal annealing. The results indicated that the dipole and debris defects were relatively unstable upon annealing at moderately high temperatures, which led to significant recovery of work hardening. This article is based on a presentation made in the symposium entitled “Fundamentals of Structural Intermetallics,” presented at the 2002 TMS Annual Meeting, February 21–27, 2002, in Seattle, Washington, under the auspices of the ASM and TMS Joint Committee on Mechanical Behavior of Materials.     

High Throughput Primer Walking of cDNA Clones

Primer walking of cloned DNA is a standard research tool. It has been used in the past to determine the sequence of individual clones of interest. With the expansion of DNA sequencing capacity the need to be able to walk larger numbers of clones has become necessary. Our laboratory is a mid-sized genomics facility. In conjunction with the Advanced Biomedical Computing Center (ABCC) we have developed methods for automating the primer selection, DNA sequencing, contig assembly and sequence analysis for clones arrayed in microtiter format. This approach has allowed us to walk 475 clones (five microtiter plates) selected from a cDNA library.     

Localization of Function Within the Dorsal Hippocampus: The Role of the CA3 Subregion in Paired-Associate Learning.

Computational models and electrophysiological data suggest that the CA3 subregion of the hippocampus supports the formation of arbitrary associations; however, no behavioral studies have been conducted to test this hypothesis. Rats with neurotoxin-induced lesions of dorsal dentate gyrus (DG), CA3, or CA1 were tested on object-place and odor-place paired-associate tasks to test whether the mechanism that supports paired-associate learning is localized to the CA3 subregion of the dorsal hippocampus or whether all hippocampal subregions contribute to paired-associate learning. The data indicate that rats with DG or CA1 lesions learned the tasks as well as controls; however, CA3-lesioned rats were impaired in learning the tasks. Thus, the CA3 subregion of the dorsal hippocampus contains a mechanism to support paired-associate learning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Gaming the Regulator: A Survey

Many regulators use benchmarking as part of the incentive-based regulation of natural monopolies so as to reduce the possibilities for gaming. However, the use of benchmarking can lead firms to pursue virtual rather than true performance improvements by gaming the regulator’s benchmarking in a number of ways that are contrary to the intentions of the scheme.     

Biases in Social Comparative Judgments: The Role of Nonmotivated Factors in Above-Average and Comparative-Optimism Effects.

Biases in social comparative judgments, such as those illustrated by above-average and comparative-optimism effects, are often regarded as products of motivated reasoning (e.g., self-enhancement). These effects, however, can also be produced by information-processing limitations or aspects of judgment processes that are not necessarily biased by motivational factors. In this article, the authors briefly review motivational accounts of biased comparative judgments, introduce a 3-stage model for understanding how people make comparative judgments, and then describe how various nonmotivational factors can influence the 3 stages of the comparative judgment process. Finally, the authors discuss several unresolved issues highlighted by their analysis, such as the interrelation between motivated and nonmotivated sources of bias and the influence of nonmotivated sources of bias on behavior. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The pros and cons of qualitative & quantitative analysis of safety systems

There are currently two separate coalitions regarding the analysis of safety/emergency shutdown/interlock systems used in the chemical and petroleum industries. These qualitative versus quantitative differences range from how risk is measured, how safety system performance is measured, and how the two can be related in order to determine which system is appropriate for the application in question. A review of each method is discussed along with their merits and limitations.     

Neural correlates of sexual arousal in homosexual and heterosexual men.

Men exhibit much higher levels of genital and subjective arousal to sexual stimuli containing their preferred sex than they do to stimuli containing only the nonpreferred sex. This study used event-related functional magnetic resonance imaging to investigate how this category-specific pattern would be reflected in the brains of homosexual (n = 11) and heterosexual (n = 11) men. Comparisons of activation to preferred sexual stimuli, nonpreferred sexual stimuli, and sports stimuli revealed large networks correlated with sexual arousal, spanning multiple cortical and subcortical areas. Both homosexual and heterosexual men exhibited category-specific arousal in brain activity. Within the amygdala, greater preference-related activity was observed in homosexual men, but it is unclear whether this is a cause or a consequence of their sexuality. In a subsequent analysis of regions hypothesized to support arousal, both participant groups demonstrated widespread increases in evoked activity for preferred stimuli. Aggregate data from these regions produced significant differences between stimulus types in 16 out of 22 participants. Significant activational differences matched reported sexual orientation in 15 of these 16 participants, representing an advance in psychophysiological measures of arousal. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

What can we learn from the Monte Carlo simulation of the glass transition of polymer melts?

The use of coarse-grained lattice models for the modelling of the glassy freezing in of polymer melts is discussed. The bond-fluctuation model is shown to be a reasonable compromise between simulation efficiency and realistic chemical detail. The potential energy, favoring large values of the length of effective bonds, is at low temperatures in conflict with the tendency for dense packing of the effective monomers and this “geometrical frustration” is responsible for the glass transition of this model. It is shown that many physical properties of the model are in surprisingly close agreement with experiments. Open problems and directions for future research are briefly discussed.     

PAC-learnability of probabilistic deterministic finite state automata in terms of variation distance

We consider the problem of PAC-learning distributions over strings, represented by probabilistic deterministic finite automata (PDFAs). PDFAs are a probabilistic model for the generation of strings of symbols, that have been used in the context of speech and handwriting recognition, and bioinformatics. Recent work on learning PDFAs from random examples has used the KL-divergence as the error measure; here we use the variation distance. We build on recent work by Clark and Thollard, and show that the use of the variation distance allows simplifications to be made to the algorithms, and also a strengthening of the results; in particular that using the variation distance, we obtain polynomial sample size bounds that are independent of the expected length of strings.