Incremental and Decremental Maintenance of Planar Width

We present an algorithm for maintaining the width of a planar point set dynamically, as points are inserted or deleted. Our algorithm takes time O(kn^epsilon) per update, where k is the amount of change the update causes in the convex hull, n is the number of points in the set, and epsilon is any arbitrarily small constant. For incremental or decremental update sequences, the amortized time per update is O(n^epsilon).Comment: 7 pages; 2 figures. A preliminary version of this paper was presented at the 10th ACM/SIAM Symp. Discrete Algorithms (SODA '99); this is the journal version, and will appear in J. Algorithm

Two Approaches to Building Time-Windowed Geometric Data Structures

Given a set of geometric objects each associated with a time value, we wish to determine whether a given property is true for a subset of those objects whose time values fall within a query time window. We call such problems time-windowed decision problems, and they have been the subject of much recent attention, for instance studied by Bokal, Cabello, and Eppstein [SoCG 2015]. In this paper, we present new approaches to this class of problems that are conceptually simpler than Bokal et al.\u27s, and also lead to faster algorithms. For instance, we present algorithms for preprocessing for the time-windowed 2D diameter decision problem in O(n log n) time and the time-windowed 2D convex hull area decision problem in O(n alpha(n) log n) time (where alpha is the inverse Ackermann function), improving Bokal et al.\u27s O(n log^2 n) and O(n log n loglog n) solutions respectively. Our first approach is to reduce time-windowed decision problems to a generalized range successor problem, which we solve using a novel way to search range trees. Our other approach is to use dynamic data structures directly, taking advantage of a new observation that the total number of combinatorial changes to a planar convex hull is near linear for any FIFO update sequence, in which deletions occur in the same order as insertions. We also apply these approaches to obtain the first O(n polylog n) algorithms for the time-windowed 3D diameter decision and 2D orthogonal segment intersection detection problems

Dynamics of Attention in Depth: Evidence from Mutli-Element Tracking

The allocation of attention in depth is examined using a multi-element tracking paradigm. Observers are required to track a predefined subset of from two to eight elements in displays containing up to sixteen identical moving elements. We first show that depth cues, such as binocular disparity and occlusion through T-junctions, improve performance in a multi-element tracking task in the case where element boundaries are allowed to intersect in the depiction of motion in a single fronto-parallel plane. We also show that the allocation of attention across two perceptually distinguishable planar surfaces either fronto-parallel or receding at a slanting angle and defined by coplanar elements, is easier than allocation of attention within a single surface. The same result was not found when attention was required to be deployed across items of two color populations rather than of a single color. Our results suggest that, when surface information does not suffice to distinguish between targets and distractors that are embedded in these surfaces, division of attention across two surfaces aids in tracking moving targets.National Science Foundation (IRI-94-01659); Office of Naval Research (N00014-95-1-0409, N00014-95-1-0657

Engineering study for a mass memory system for advanced spacecrafts Final report, 1 Dec. 1969 - 1 Jul. 1970

Mass memory system for advanced spacecraf

Deployable antenna demonstration project

Test program options are described for large lightweight deployable antennas for space communications, radar and radiometry systems

Integrated Power/Attitude Control System (IPACS) study. Volume 2: Conceptual designs

For abstract, see N74-22706

ALTERNATE FOOT PLACEMENT: INVESTIGATING THE ROLE OF GAIT PARAMETERS, PLANAR OBSTACLE COMPLEXITY, AND ATHLETIC TRAINING

On a daily basis modifications, based upon environmental demands and the capabilities of the individual, are made to the locomotor pattern to enable avoidance of undesirable landing areas (i.e. planar obstacles). Athletes and dancers have been suggested to have superior perception-action coupling compared to non-athletes, allowing them to perform various tasks at a greater speed without a loss of precision (Federici et al., 2005; Gerin-Lajoie et al. (2007). The current study assessed non-athletes, dancers, and field athletes to investigate whether training influences the maintenance of forward progression and stability in relation to alternate foot placement during planar obstacle avoidance. Eleven field athletes (22± 2.68 years) having recent/ current sport participation, 10 individuals (21.1± 1.1 years) with previous/current dance training, and 12 non-athletes (21.75± 1.54 years) with no participation in organized sport in \u3e5 years were asked to walk to a goal (~13 m away) at a self-selected pace, avoiding any obstacle(s) when present (50% of trials; 15cm wide x 70cm long rectangles, projected ~8m from the start position). Obstacle conditions were: 1) Single obstacle appearance (SIN) where the obstacle (at N) appeared when the participant was 2 steps away from the first obstacle (N-2) ; 2) Double obstacle appearance was delayed (DDEL) until at N-2; and 3) Double obstacle appearance after participants reached steady state (i.e. ~3 steps from start)(DSS). All participants, regardless of training, stepped medially during SIN. Avoidance during double obstacle conditions was variable (i.e. medial-medial, medial-lateral, and lateral-medial). The variability of behaviour, computed as a coefficient of unalikeability (the proportion of possible comparisons which are unalike), had significant moderate positive correlations with the minimum Dynamic Stability Margin at N-1 for DSS and DDEL (r = 0.36; r = 0.44, respectively, p\u3c0.001) and a significant weak positive relationship with ML COM variability (r = 0.28, p\u3c0.05) during DDEL. To a degree, greater ML COM variability leads to avoidance behaviour that exploits forward progression more so than stability, as stepping medially perturbs the COM the least from its forward momentum but narrows the BOS creating instability that must be offset in the following step. Avoidance of planar obstacles at a comfortable walk lacked context specificity to dance or field sport training to elicit any behavioural differences

Study of optoelectronic switch for satellite-switched time-division multiple access

The use of optoelectronic switching for satellite switched time division multiple access will improve the isolation and reduce the crosstalk of an IF switch matrix. The results are presented of a study on optoelectronic switching. Tasks include literature search, system requirements study, candidate switching architecture analysis, and switch model optimization. The results show that the power divided and crossbar switching architectures are good candidates for an IF switch matrix