Computer program documentation - SYSTID, system time-domain simulation program

SYSTID computer program for system time-domain simulation program in FORTRAN 5 for Univac 1108 compute

Computerized polar plots by a cathode ray tube/grid overlay method

Overlay is aligned with four calibration dots so it is not affected by CRT drift or changes in vertical or horizontal gain when producing Nyquist /frequency-response phase/amplitude/ plots. Method produces over 50 plots per hour

Aerodynamic characteristics of a 1/6-scale powered model of the rotor systems research aircraft

A wind-tunnel investigation was conducted to determine the effects of the main-rotor wake on the aerodynamic characteristics of the rotor systems research aircraft (RSRA). For the investigation, a 1/6-scale model with a four-blade articulated main rotor was used. Tests were conducted with and without the main rotor. Both the helicopter and the compound helicopter were tested. The latter configuration included the auxiliary thrust engines and the variable-incidence wing. Data were obtained over ranges of angle of attack, angle of sideslip, and main-rotor collective pitch angle at several main-rotor advance ratios. Results are presented for the total loads on the airframe as well as the loads on the rotor, the wing, and the tail. The results indicated that without the effect of the rotor wake, the RSRA had static longitudinal and directional stability and positive effective dihedral. With the effect of the main rotor and its wake, the RSRA exhibited longitudinal instability but retained static directional stability and positive effective dihedral

fMRI correlates of subjective reversals in ambiguous structure-from-motion

We used fMRI to examine the neural correlates of subjective reversals for bistable structure-from-motion. We compared transparent random-dot kinematograms depicting either a cylinder rotating in depth or two flat surfaces translating in opposite directions at apparently different depths. For both such stimuli, the motion of dots on the different apparent depth planes typically appears to reverse direction periodically on prolonged viewing. Yet for cylindrical but not flat stimuli, such subjective reversals also coincide with apparent reversal of 3D rotation direction. We hypothesized that the lateral occipital complex (region LOC), sensitive to 3D form, might show greater event-related activity for subjective reversals of cylindrical than flat stimuli; conversely, motion-sensitive hMT+/V5 should respond in common to subjective reversals for either type of stimuli, as both are perceived as changes in planar motion. We obtained an event-related measure of neural activity associated with subjective reversals after first factoring out block-related differences between cylindrical versus flat stimuli (and thereby the associated low-level blocked stimulus differences). In support of our hypothesis, only the cylindrical stimuli produced reversal-related activity in contralateral human LOC. In contrast, the hMT+/V5 complex was activated alike by subjective reversals for both cylindrical and flat stimuli. Intriguingly, V1 also showed (contralateral) specificity for rotational reversals, suggesting a possible feedback influence from LOC. These results reveal specific neural correlates for subjective switches of 3D rotation versus translation, as distinct from subjective reversals in general

Configuration-specific attentional modulation of flanker target lateral interactions

Elements of a contour are often easier to detect when they possess collinearity, with their local orientations matching the global orientation of the contour. We recently reported attentional modulation of such lateral interactions between a central near-threshold target Gabor patch and flanking high-contrast patches (Freeman et al, 2001 Nature Neuroscience 4 1032-1036). Here, we examined whether such attentional effects reflect specific modulation of mechanisms sensitive to collinear configurations, or instead more general modulation of sensitivity to either the global or local orientation-components of the stimulus. Thresholds for detecting a central Gabor target were measured, while observers also judged the Vernier alignment between one pair of flankers and ignored a second flanker pair (when present). Target contrast-thresholds were facilitated only when attending collinear flankers. There was no facilitation when attending flankers that shared only local orientation with the target, or flankers that fell on a global axis aligned with target orientation but having orthogonal local orientation. Ignored collinear flankers had no effect on target thresholds. These results demonstrate strong and specific attentional modulation of contour-integration mechanisms in early vision sensitive to collinear configurations