Model for the vibration produced by a single point defect in a rolling element bearing

A model is developed to describe the vibration produced by a single point defect on the inner race of a rolling element bearing under constant radial load. The model incorporates the effects of bearing geometry, shaft speed, bearing load distribution, transfer function and the exponential decay of vibration. A comparison of predicted and measured demodulated vibration spectra confirms the satisfactory performance of the model.     

Absence of overshoot in a dichotic masking condition

Brief tonal signals presented soon after the onset of a masking noise are known to be less detectable than signals delayed by several hundred milliseconds. This difference in detectability is known as the "overshoot." Signals of two sorts were studied here--either interaurally in phase (S o) or interaurally out of phase by 180 degrees (S pi). When S omicron signals of 750 Hz and about 14 ms in duration were presented 4 ms after the onset of a diotic, broadband masking noise (N o), detectability was about 6 dB worse than when the signal was presented 325 ms after onset. By contrast, there was no such overshoot when S pi signals were presented at varying times after masker onset; detectability was about the same for all values of signal delay. Accordingly, the difference in performance between N o S o and N o S pi--the masking-level difference or MLD--was large (about 16 dB) with the shortest delays used and diminished (to about 9 dB) as the delay was increased. This absence of overshoot with the S pi signals is in accord with the well-established view that detectability in the dichotic masking conditions is based upon different stimulus information from that used in the diotic masking conditions. Specifically, the evidence confirms the common view that detectability in the diotic conditions is based more or less directly on neural firing rate, whereas, in the dichotic conditions, it is based upon interaural time differences encoded in the periodicity of neural firings.     

Development of a methodology for non-contacting strain measurements in fluid environments using computer vision

Using first order, ray optics theory, a method has been developed and experimentally verified for measurement of surface strains on structures immersed in fluid environments. The methodology utilizes an imaging system that is contained within an air environment and separated from the fluid media by an optical quality, transparent window. Theoretical considerations demonstrate that non-contacting strain measurements in fluid systems are somewhat sensitive to the relative orientation of the transparent window, providing insight into the system setup required to make accurate strain measurements in fluid environments. Underwater experimental measurements using a laboratory-based system are in excellent agreement with theoretical predictions, demonstrating that the proposed methodology is both viable and capable of measuring strains accurately.     

Partial dissociation of spontaneous otoacoustic emissions and distortion products during aspirin use in humans

Otoacoustic emissions (OAEs) of two types--spontaneous and evoked distortion products--were studied before, during, and following a period of aspirin use. As previously reported, aspirin consumption uniformly reduced the spontaneous OAEs (SOAEs) to unmeasurable or extremely low levels. Aspirin consumption also reduced the amplitude of the evoked distortion products (EDPs) but did not eliminate them entirely. The amplitude of the EDP and its change with aspirin consumption were related to both the proximity of the EDP to the frequency of the SOAE and to the level of the primaries producing the EDP. At low primary levels, even with the SOAE absent (due to aspirin consumption, or suppression), EDPs near the SOAE frequency were 10-20 dB higher than when they were 100 Hz away from the SOAE frequency.     

A front-tracking model to predict solidification macrostructures and columnar to equiaxed transitions in alloy castings

The solidified grain structure (macrostructure) of castings is predicted by process simulation using a newly extended front-tracking technique which models the growth of solid dendritic fronts through undercooled liquid during metallic alloy solidification. Such fronts are either constrained, as is the case with directed columnar growth from mould walls, or unconstrained, as is the case for multiple equiaxed growth from individual nucleating particles distributed throughout the liquid. Non-linear latent heat evolution is treated by incorporating the Scheil equation. Thermal conductivity changes with the solid fraction. A log-normal distribution of activation undercooling to initiate free growth from equiaxed nuclei is used, and the routines to deal with such growth followed by impingement of dendritic grains upon one another are verified by comparison with the results of analytical studies of simplified systems. The extensions to the model enable the predictions of equiaxed grain structure and, importantly, the columnar to equiaxed transition in inoculated alloy castings. The model is validated via comparison with experimental results. The front-tracking method is proposed as a suitable formulation for modelling alloy castings that solidify with a dendritic structure, either columnar, equiaxed, or both.     

Temporal decline of masking and comodulation detection differences

Comodulation detection differences (CDDs) were studied using flanking bands that were either gated simultaneously with the signal band (burst) or gated at varying times prior to signal onset (fringed). Used for these experiments were a signal band centered at 1250 Hz and four flanking bands centered at 450, 850, 1650, and 2050 Hz; all bands were 100 Hz wide. In different conditions, the temporal envelope of the signal band was either the same as (correlated), or different from (uncorrelated), the common envelope of the four flanking bands, or the temporal envelopes of all of the bands were different (all-uncorrelated). For 8 of the 13 listeners, signal detectability improved by as much as 25 dB as the temporal fringe of the flanking bands was increased from 5 to about 700 ms. This temporal decline of masking was similar, but not identical, for the correlated, uncorrelated, and all-uncorrelated conditions. Results of this sort are reminiscent of several related findings that have been attributed to auditory adaptation or enhancement, or to a temporally developing critical-band filter. The other 5 of the 13 listeners were generally more sensitive than the majority, and they showed little or no improvement in detectability as fringe duration was varied. Large individual differences of this sort are not uncommon in the adaptation and comodulation literatures. As signal duration was changed from 50 to 240 ms, temporal integration was less in the correlated condition than in the uncorrelated condition, thereby producing a larger CDD with the longer signal. When the fringe followed the observation interval instead of preceding it, the results were equivocal because detectability improved for the majority of subjects and worsened for the minority. In follow-up experiments, different subsets of these four flanking bands were used. When temporal gaps of varying duration were inserted into the flanking band(s) immediately prior to the observation intervals, it was found that a temporal gap as long as 355 ms was not sufficient to reset the mechanisms underlying the temporal decline of masking.