Fatigue-crack-propagation thresholds in a nickel-base superalloy at high frequencies and temperatures

Fatigue-crack-propagation (FCP) tests were conducted on the powder metallurgy nickel-base superalloy KM4 at temperatures of 20 °C, 550 °C, and 650 °C. Two different heat treatments were investigated, one yielding a relatively coarse grain size of 55 μm and another yielding a fine grain size of 6 μm. Tests were conducted at 100 Hz and 1000 Hz and at load ratios between 0.3 and 0.7. In the Paris regime, trends observed at high frequencies for KM4 were identical to those observed by earlier investigators at lower frequencies: coarse grains, low load ratios, low temperatures, and higher frequencies generally resulted in lower crack-propagation rates. However, in contrast to the Paris-regime behavior, thresholds were a complicated function of microstructure, load ratio, temperature, and frequency, and the only variable that resulted in a consistent trend in threshold was the load ratio. For example, thresholds increased from 100 to 1000 Hz for the fine-grained material at 550 °C, but decreased with the same frequency variation at 650 °C. One reason for this complexity was a change to intergranular fracture in the fine-grained microstructure at 650 °C, which was beneficial for high-frequency thresholds. Higher load ratios and lower frequencies promoted intergranular fracture. However, not all of the complexity could be explained by changing fracture mechanisms. Scanning electron microscope (SEM) stereofractography was utilized to determine quantitative measures of fracture-surface roughness. The most useful quantitative measure was found to be the standard deviation of the fracture-surface height, which is a physically meaningful length parameter and which corresponded to about half the grain size during room-temperature fatigue at near-threshold ΔK levels. The roughness of the fracture surface was found to increase as the load ratio was increased for both microstructures. For the coarse-grained microstructure, there was a direct correlation between fracture-surface roughness and FCP threshold over the entire range of temperatures, frequencies, and load ratios. However, measurements of closure loads indicated that roughness-induced closure was not the sole reason for the varying FCP thresholds.     

Proton MAS NMR spectra at high magnetic fields and high spinning frequencies: spectral simulations using floquet theory

We examined the relationship quality of 55 (27 girls) 9-year-old children with their mothers, teachers, and friends as rated by teachers and by the children themselves. The goal of this longitudinal study was to examine stability and continuity in the quality of children's relationships between infancy and 9 years of age. At age 9, children's perception of their relationships with their teachers was associated with their current teachers' ratings of their relationships with the children. Children's perceptions of their relationships with their mothers were consistent with earlier ratings of attachment security. Children's perceptions of their relationships with teachers were predicted by the quality of their attachment relationships with their first teachers. Children's perceptions of their friendship quality was predicted by preschool teacher ratings of friendship quality and the quality of their attachment relationships with their first teachers.     

Figure/ground segregation from temporal delay is best at high spatial frequencies

Two experiments investigated the role of spatial frequency in performance of a figure/ground segregation task based on temporal cues. Figure orientation was much easier to judge when figure and ground portions of the target were defined exclusively by random texture composed entirely of high spatial frequencies. When target components were defined by low spatial frequencies only, the task was nearly impossible except with long temporal delay between figure and ground. These results are inconsistent with the hypothesis that M-cell activity is primarily responsible for figure/ground segregation from temporal delay. Instead, these results point to a distinction between temporal integration and temporal differentiation. Additionally, the present results can be related to recent work on the binding of spatial features over time.     

Simulation of convection and macrosegregation in a large steel ingot

Melt convection and macrosegregation in casting of a large steel ingot are numerically simulated. The simulation is based on a previously developed model for multicomponent steel solidification with melt convection and involves the solution of fully coupled conservation equations for the transport phenomena in the liquid, mush, and solid. Heat transfer in the mold and insulation materials, as well as the formation of a shrinkage cavity at the top, is taken into account. The numerical results show the evolution of the temperature, melt velocity, and species concentration fields during solidification. The predicted variation of the macrosegregation of carbon and sulfur along the vertical centerline is compared with measurements from an industrial steel ingot that was sectioned and analyzed. Although generally good agreement is obtained, the neglect of sedimentation of free equiaxed grains prevents the prediction of the zone of negative macrosegregation observed in the lower part of the ingot. It is also shown that the inclusion of the shrinkage cavity at the top and the variation of the final solidification temperature due to macrosegregation is important in obtaining good agreement between the predictions and measurements.     

Fatigue damage and crack nucleation mechanisms at intermediate strain amplitudes

Polycrystalline copper was fatigued in rotary bending at constant intermediate surface strain amplitudes at 26 Hz under ambient conditions. The specimens were interrupted at various life fractions, their surfaces prepared metallographically and scrutinised to ascertain the types of fatigue damages, namely, short cracks which are confined to individual grains or isolated grain boundary facets, and their role in fatal crack formation. The results show that, at intermediate strain amplitudes, slip band and twin boundary crack damages predominate during early stages of cycling, while grain boundary crack damages remain relatively insignificant even at the stage when fatal cracks have developed. However, depending on the strain amplitude level, the transgranular crack damages may or may not be instrumental in fatal crack formation. At the lower amplitude end of the transition region, fatal cracks are formed by interlinkage of slip band and twin boundary damages. At the higher amplitude end, even though grain boundary damages are negligible initially, they degenerate rapidly on further cycling and eventually evolve into fatal cracks. The present findings show that some 0.05% plastic strain amplitude is required to propagate intergranular cracks. Once the above condition is met, cracks would propagate rapidly along the interface and the crack nucleation mode would change from transgranular to intergranular.     

Psychoanalysis conducted at reduced frequencies.

This paper explores the clinical indications for an optimal psychoanalysis conducted at reduced frequencies. Among other purposes psychoanalysis is an engagement that serves to demystify experience. The structure of multiple session frequency applied a priori and in the absence of other considerations may contribute to mystification of the analytic process itself. Particularly for those patients presenting with limited ego-capacity for reflection, impulsive or compulsive behaviors, inhibition of thinking processes, blunting of emotions, and rudimentary capacity for therapeutic cooperation, analyses of multiple frequencies can contribute to false compliance or resistance. Clinically the frequency of sessions can be determined on an empirical basis. An analysand's ability to self-reflect occurs in the same measure as one's tolerance for emotional contact with the analyst and the unconscious. An optimal psychoanalysis understood as a maturational process is conducted initially for some clinical varieties of transference at reduced frequency, which is then expanded over time as the person's capacity for thoughtful self-reflection and interpersonal contact with the analyst develops. In this way actual unconscious processes are privileged over taken-for-granted therapeutics and addressed as an empirical reality. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Auditory filters measured at neighboring center frequencies

Auditory filters were derived in 20 normal-hearing human listeners at center frequencies (CFs) of 913, 1095, 3651, and 4382 Hz using the roex (p,r) method. Comparisons were made between slopes of the filters' skirts at the neighboring CFs with filter output levels of 45 and 70 dB. The same comparisons were made with regard to filter equivalent rectangular bandwidth (ERB). In the 1000-Hz region, the low-frequency slopes (Pl) of filters centered at 913 and 1095 Hz were significantly correlated at both stimulus levels, while the high-frequency slopes (Pu) were similar only at the high test level. In the 4000-Hz region, for sinusoids of 3651 and 4382 Hz, the level effect was clearer as both Pu and Pl values diverged at the low level but were related at high levels. The ERBs centered at the same CFs displayed a similar level dependence. At the stimulus level most likely to be affected by an active feedback mechanism, auditory filters centered at nearly the same frequency displayed quite distinct frequency selectivity, and this trend was stronger in the 4000-Hz region than the 1000-Hz region. The findings suggest that a saturating, active cochlear mechanism may not be distributed evenly, or contribute to peripheral tuning with equal effectiveness throughout the length of the partition.     

Low and high spatial frequencies are most useful for drawing.

What perceptual information do artists use to accurately render what they see? To answer this question, we investigated the utility of low, middle, and high spatial frequency bands for drawing. Untrained artists drew portraits from four spatial frequency bands (unfiltered, low, middle, and high). Raters judged the accuracy of those drawings compared to images of either the same or an unfiltered version of the face. Contrary to predictions based on the useful spatial frequencies for face recognition, which favor middle spatial frequencies (MSFs), the results showed that low spatial frequencies (LSFs) and high spatial frequencies (HSFs) were more useful for drawing, and the unfiltered condition produced the best drawings. Thus, the information most useful for drawing faces is not the same as that for recognizing faces. Specifically, artists may utilize the global configuration information carried in LSFs and the edge and detail information carried in HSFs to render accurate drawings. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Fast and slow voltage modulation of apical Cl- permeability in toad skin at high [K+

The influence of voltage on the conductance of toad skin was studied to identify the time course of the activation/deactivation dynamics of voltage-dependent Cl- channels located in the apical membrane of mitochondrion-rich cells in this tissue. Positive apical voltage induced an important conductance inhibition which took a few seconds to fully develop and was instantaneously released by pulse inversion to negative voltage, indicating a short-duration memory of the inhibiting factors. Sinusoidal stimulation at 23.4 mM [Cl-] showed hysteresis in the current versus voltage curves, even at very low frequency, suggesting that the rate of voltage application was also relevant for the inhibition/releasing effect to develop. We conclude that the voltage modulation of apical Cl- permeability is essentially a fast process and the apparent slow components of activation/deactivation obtained in the whole skin are a consequence of a gradual voltage build-up across the apical membrane due to voltage sharing between apical and basolateral membranes.