Seabed roughness was measured over an area of the south shore of O'ahu, Hawaii, with a boat-mounted acoustic altimetry system. The study site is characterized by a highly inhomogeneous rough seabed. ...Roughness was resolved in the 40–200-cm range over an area extending from the wave breaking zone to a depth of 20 m. Theory suggests that roughness length scales and distribution both play an important role in wave energy dissipation mechanisms. In this paper, we investigate methods for quantifying bed roughness within this range of scales. Various methods for quantifying roughness are examined, including spectral and statistically derived variables. These methods are compared qualitatively with sidescan imagery and quantitatively via in situ diver-based roughness surveys. Results show that wavenumber spectra can effectively differentiate smooth from rough areas. Results also suggest that the bed roughness in the study site exhibit a high spatial variability within the examined range, with no dominant length scale but with a characteristic spectral slope. In addition, roughness also exhibits variation between the shallow and deep ends of the study site.
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BFBNIB, DOBA, IZUM, KILJ, NMLJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Recently, Smith, Thelen, and colleagues proposed a dynamic systems account of the Piagetian "A-not-B" error in which infants' errors result from general processes that make goal-directed actions to ...remembered locations. Based on this account, the A-not-B error should be a general phenomenon, observable in different tasks and at different points in development. Smith, Thelen, et al.'s proposal was tested using an A-not-B version of a sandbox task. During three training trials and three "A" trials, 2-year-olds watched as a toy was buried in a sandbox at Location A. Following a 10-s delay, children searched for the object. Across five experiments, children's (total N = 92) performance on the A trials was accurate. After the A trials, children watched as a toy was hidden at Location B, 8 to 10 inches from Location A. In all experiments, children's searches after a 10-s delay were significantly biased in the direction of Location A. Furthermore, this bias toward Location A decreased with repeated trials to Location B, as well as when children completed fewer trials to Location A. Together, these data suggest that A-not-B-type errors are pervasive across tasks and development.
Can middle-grades students determine which of two rectangular prisms has a larger volume? Can they do so without using a formula? Geometry, and particularly the concept of volume, is important in ...many subjects, such as physics and chemistry. Carpenter and Romberg (2004) note that students greatly enhance their mathematics knowledge when they make generalizations and construct arguments to justify their methods through problem solving. To realize this goal, teachers should encourage and accept students' self-initiative, allow students' responses to help shape lessons, and inquire about students' understanding of concepts before sharing their own (Brooks and Brooks 1993). We describe a task that requires students to use their own nonformulaic methods and reasoning to investigate volume.
Antlions construct conical, mechanically unstable pits in sand for prey capture. If ants (a major prey item) have difficulty walking on inclined sand surfaces, this may explain the effectiveness of ...their capture by this trap design. We investigated the degree to which locomotion of ants is impaired on sandy slopes. The locomotion of ants, physical characteristics of sand, steepness of antlion pit walls, and sand-size preference of antlion larvae were evaluated using four size fractions of sand (0.1-0.25, 0.25-0.50, 0.50-0.71, and 0.71-1.0 mm diameter). An ant's probability of falling when walking on a sandy slope increased with increasing slope angle or decreasing sand-particle diameter. For a given particle size and angle of inclination, larger ants were more likely to fall and roll uncontrollably than smaller ants. The maximum inclination above horizontal (angle of repose) for sand of different particle sizes was measured. The angle of repose was higher for the finest sand fraction than for the three coarser sand fractions, but did not differ among these three coarser fractions. In each sand fraction, the steepness of pits constructed by antlions was not significantly different from the angle of repose. Antlion larvae preferentially built pits in the two finer sand-size fractions.
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