60 research outputs found
Intelligence and neural activation : a test of the relationship between the neural efficiency hypothesis and repetition suppression
No full texthonors thesisCollege of Social & Behavioral SciencePsychologyMatthew J. EulerThe Neural Efficiency Hypothesis (NEH) states that individuals with higher measured intelligence exhibit less neural activation on relatively simple tasks compared to those with lower intelligence (Haier et al., 1988). Furthermore, this phenomenon may interact with repetition suppression, or the reduction of neural activity following repeat stimulus exposure (Grill-Spector et al., 2006). The current study examined the relationship between intelligence and event-related EEG amplitudes and latencies during the third of three task conditions, a visual repetition paradigm. Full Scale IQ (FSIQ) scores from the Wechsler Adult Intelligence Scale III (WAIS-III; Wechsler, 1997) were collected on 30 participants, 18 of whom had sufficient numbers of EEG trials for further analysis (FSIQ: M = 111.56, SD = 13.28, range = 91 to 131). During EEG recording, participants were asked to respond to randomized line drawings representing one of three stimulus conditions from the previous two tasks: Repeated stimuli, Once-viewed, and Novel stimuli. Time-frequency analyses were conducted to identify peak phase-locked activity in the theta (4-7 Hz) and alpha (8-12 Hz) bands between 0 and 500 milliseconds poststimulus. Results demonstrated no significant effects of IQ or stimulus condition on peak theta and alpha amplitudes. However, difference scores between Novel and Once-viewed conditions in peak theta latency showed a strong positive correlation with IQ (r[16] = .712, p < .01). These findings appear consistent with the NEH in suggesting that higher IQ individuals may process previously-seen stimuli more efficiently than lower IQ individuals, as evidenced by shorter peak latencies relative to stimulus onset
Conversion of a double crystal diffractometer to a high resolution triple crystal diffractometer
No full textTriple crystal x-ray diffraction analysis of chemical-mechanical polished gallium arsenide
No full textApplication of statistical dynamical diffraction theory to highly defective ion implanted SiGe heterostructures
No full textHigh Resolution Triple Axis X-Ray Diffraction Analysis of II-VI Semiconductor Crystals
No full textThe objective of this research program is to develop methods of structural analysis based on high resolution triple axis X-ray diffractometry (HRTXD) and to carry out detailed studies of defect distributions in crystals grown in both microgravity and ground-based environments. HRTXD represents a modification of the widely used double axis X-ray rocking curve method for the characterization of grown-in defects in nearly perfect crystals. In a double axis rocking curve experiment, the sample is illuminated by a monochromatic X-ray beam and the diffracted intensity is recorded by a fixed, wide-open detector. The intensity diffracted by the sample is then monitored as the sample is rotated through the Bragg reflection condition. The breadth of the peak, which is often reported as the full angular width at half the maximum intensity (FWHM), is used as an indicator of the amount of defects in the sample. This work has shown that high resolution triple axis X-ray diffraction is an effective tool for characterizing the defect structure in semiconductor crystals, particularly at high defect densities. Additionally, the technique is complimentary to X-ray topography for defect characterization in crystals
Triple‐crystal x‐ray diffraction analysis of reactive ion etched gallium arsenide
No full textThis is the published version. Copyright 1994 American Institute of PhysicsThe effect of BCl3 reactive ion etching on the structural perfection of GaAs has been studied with diffuse x‐ray scattering measurementsconducted by high‐resolution triple‐crystal x‐ray diffraction. While using a symmetric 004 diffraction geometry revealed no discernible differences between etched and unetched samples, using the more surface‐sensitive and highly asymmetric 113 reflection revealed that the reactive ion etched samples etched displayed less diffusely scattered intensity than unetched samples, indicating a higher level of structural perfection. Increasing the reaction ion etch bias voltage was found to result in decreased diffuse scattering initially, until an apparent threshold voltage was reached, after which no further structural improvement was observed. Furthermore, we have shown that this reduction in process‐induced surfacestructural damage is not due merely to the removal of residual chemical‐mechanical polishing damage
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