Factors affecting Confidence Index in EBSD analysis.

Automated EBSD analysis systems have been used for over two decades relying on the fact that the correctness of a particular orientation solution could be assessed through the calculation of a Confidence Index. However, such an index only reports whether a particular solution stands out among any other possible solutions, by receiving a larger number of votes than others, and does not necessarily imply that the corresponding orientation is correct. This issue is addressed in the present paper, where the correctness of solutions and the factors that might affect it have been studied for single crystal Si and polycrystalline Zn. The results were compared to those presented in previous papers where this matter was studied in particular for an FCC material. It was observed that about 90% of the solutions were correct if they were obtained using a confidence index of 0.1 using at least 8 Hough bands regardless of the crystallographic structure or orientation.

The trianvil test apparatus: measurement of shear strength under pressure.

An experimental apparatus has been developed for performing shear tests on specimens held under moderately high hydrostatic pressures (up to the order of 10 GPa). This testing procedure experimentally determines the pressure dependent shear strength of thin foil specimens. This information is necessary for models of materials subjected to extreme pressures and can assist in model validation for models such as discrete dislocation dynamics simulations, among others. This paper reports the development of the experimental procedures and the results of initial experiments on thin foils of polycrystalline Ta performed under hydrostatic pressures ranging from 2 to 4 GPa. Subsequent characterization of the samples held under pressure established that the procedure described herein represents a reliable method to impose nearly uniform hydrostatic pressure on thin foil specimens. Both yielding and hardening behavior of Ta are observed to be sensitive to the imposed pressure.

Analysis of local orientation gradients in deformed single crystals.

Grain fragmentation and local orientation gradients in deformed single crystals are characterized using electron backscatter diffraction (EBSD) to obtain statistically reliable information. Interrogation of the dislocation substructure is accomplished by extracting information gleaned from small point-to-point misorientations as measured by EBSD. Along with an estimate of the geometrically necessary dislocation (GND) content, the point-to-point deviation from an average grain orientation is described by an orientation difference vector defined in Rodrigues space. Mapping of parameters such as GND, and divergence and gradient fields created from analysis of the difference vectors provide an alternative approach to obtain quantitative information and images from EBSD data.

Changing behavior within session: cyclicity and perseverance produced by varying the minimum ratio of a variable-ratio schedule.

Four pigeons repeatedly chose between a fixed-ratio (FR) 20 and a variable-ratio (VR) 40 schedule of reinforcement, in which the minimum ratio of the VR cycled within each session. The minimum ratio ascended and descended (ASCDESC), descended and ascended (DESCASC), or remained constant (unchanging). In Phase 1, 2 birds (Group 1) were exposed to ASCDESC series and 2 birds (Group 2) were exposed to the DESCASC series. Choice proportions changed with the cycling minimum ratio for Group 2 but not for Group 1. In Phase 2, Group 1 subjects were exposed to the DESCASC series and Group 2 subjects were exposed to the unchanging condition. Although Group 1's choice proportions appeared to be undifferentiated in Phase 2, Group 2's choice proportions continued to cycle for more than 100 sessions. Group 2 subjects were then moved to the ASCDESC series in the third phase, and choice proportions cycled with the minimum ratio as in the first phase. The descending portion of the series was the more powerful determinant of cyclicity. Response rates also changed with the minimum component ratio, a finding that goes against the claim of universality of a rise-and-fall within-session pattern of responding. That preference varied despite the constancy of the average ratio requirement suggests nonlinear averaging in quantitatively representing a variable schedule's value. The strong perseverance observed also lends support to a growing body of literature on history effects.

Prism adaptation to dynamic events.

In the present study, we explored adaptation to prism-displaced dynamic and static events under conditions of minimal information. Many of our interactions with the world are dynamic and involve reaching for or intercepting moving objects. The consequences (or feedback) of those interactions entail the presence or absence of physical contact with the moving objects. In this study, humans learned, with only heptic feedback, to intercept optically displaced falling balls. To eliminate visual feedback, the falling balls disappeared behind an occluder (which systematically varied in size across groups) prior to either striking or missing a subject's hand. As occluder size decreased, adaptation increased. With minimum occluder sizes, the greatest adaptation occurred around the training position, and adaptation decreased as distance between training and testing positions increased. The results can best be described in terms of a generalization gradient centered around the training position. This generalization gradient was not present when subjects were trained with ecologically similar static arrays. Implications for models of adaptation are discussed.

Preference between variable-ratio and fixed-ratio schedules: local and extended relations.

Although it has repeatedly been demonstrated that pigeons, as well as other species, will often choose a variable schedule of reinforcement over an equivalent (or even richer) fixed schedule, the exact nature of that controlling relation has yet to be fully assessed. In this study pigeons were given repeated choices between concurrently available fixed-ratio and variable-ratio schedules. The fixed-ratio requirement (30 responses) was constant throughout the experiment, whereas the distribution of individual ratios making up the variable-ratio schedule changed across phases: The smallest and largest of these components were varied gradually, with the mean variable-ratio requirement constant at 60 responses. The birds' choices of the variable-ratio schedule tracked the size of the smallest variable-ratio component. A minimum variable-ratio component at or near 1 produced strong preference for the variable-ratio schedule, whereas increases in the minimum variable-ratio component resulted in reduced preference for the variable-ratio schedule. The birds' behavior was qualitatively consistent with Mazur's (1984) hyperbolic model of delayed reinforcement and could be described as approximate maximizing with respect to reinforcement value.

Exchange delays and impulsive choice in adult humans.

Choice responding by adult humans in a discrete-trial task was examined as a function of conditions that manipulated either the delay to point delivery or the delay between points and their exchange for money. In point-delay conditions, subjects chose between an "impulsive" alternative that provided a small amount of points immediately and a "self-control" alternative that provided a larger amount of points delayed by 15, 30, or 60 s. Points were exchanged for money immediately following the session. Subjects preferred the self-control alternative. In exchange-delay conditions, subjects chose between a small amount of points exchangeable for money immediately following the session and a larger amount of points exchangeable for money after 1 day, 3 weeks, or 6 weeks. A self-control preference observed for all subjects in the 1-day exchange-delay condition reversed to exclusive impulsive preference for 4 of the 6 subjects when choice conditions involved exchange delays of 3 or 6 weeks. These results show that human choice is sensitive to the manipulation of exchange delays and that impulsive preference can be obtained with exchange delays on the order of weeks.

Functions of the environment in behavioral evolution.

This paper explores some of the ways in which the environment functions with respect to behavior within an explanatory framework analogous to that of evolutionary biology. In both the behavioral and organic domains, the environment functions differently with respect to individual occurrences and evolutionary units. Within the behavioral domain, the problem of accounting for an occurrence of an operant instance differs from that of accounting for the existence of the operant unit of which the instance is a part. Maintaining these distinctions in levels of analysis within the behavioral domain, we focus first on operant units and operant instances as products of evolutionary processes occurring in the behavioral domain and second upon the causal role of the environment with respect to the existence of operant units and the occurrence of operant instances. The environment's function is selective with respect to origin, maintenance, suppression, and extinction of behavioral populations. At the level of operant instances, the environment has instantiating functions-evocative or alterative. Evocative functions are exemplified by discriminative relations, and alterative functions include both conditional and motivative relations. Implications are considered regarding extension of the analogy to more complex behavior-environment relations.