Change in throwing pattern: critical values for control parameter of velocity

The purpose of this study was to determine the critical values at which throwing patterns change when scaling up on the control parameter of velocity. Thirty-six participants (ages: 6-12 years) were categorized into four throwing levels according to patterns represented by temporal joint lag. Each participant was required to complete 5 overhand throws at each of 10 relative velocities for a total of 50 trials per participant. The lowest velocity was 10% of maximum, with increases in increments of 10% up to a maximum effort. Quantitative and qualitative analyses indicated that critical values varied according to throwing category and joint. Generally, lower skilled throwers (Levels 1 and 2) had less stable joint lag and changed patterns at lower velocities than higher skilled (Levels 3 and 4) throwers.     

Changes in limb striking pattern: effects of speed and accuracy

This study investigated the changes in an arm striking pattern as a result of practice and the effects of speed and accuracy requirements on such changes. The task was to strike a baseball-size foam ball from a batting tee adjusted to the height of each subject's iliac crest. Ten righthanded subjects, initially displaying an inefficient striking pattern, volunteered for this study. All subjects performed the task according to the following conditions: (1) speed, (2) accuracy, and (3) speed and accuracy. Each subject completed 10 trials in each condition (randomly ordered) for five consecutive days. A high-speed camera (64 fps) was used to photograph subjects' striking patterns for each condition over the 5-day period. Analysis of variance of joint angles at arm reversal and contact and velocity of hand relative to the glenohumeral axis at contact revealed that subjects initially constrained limb segments to act in a unitary fashion; then, with practice, a more efficient pattern was developed. The requirement of speed was found to enhance a change in limb configuration, whereas the requirement of accuracy, and subsequent reduction in speed, impeded the development of a more efficient striking pattern. Analysis of radial error revealed no differences in accuracies to the target by either condition or day of practice. A graphic analysis of segmental angular momentum versus relative time showed that joint angle changes allowed subjects to transfer angular momentum and thereby increase the velocity of the hand at contact.     

“Why Does Rain Fall?”: Children Prefer to Learn From an Informant Who Uses Noncircular Explanations

These two studies explored 3‐ and 5‐year‐olds' evaluation of noncircular and circular explanations, and their use of such explanations to determine informant credibility. Although 5‐year‐olds demonstrated a selective preference for noncircular over circular explanations (Experiment 1: Long Explanations; Experiment 2: Short Explanations), 3‐year‐olds only demonstrated a preference for the noncircular when the explanations were shortened (Experiment 2). Children's evaluation of the explanations extended to their inferences about the informants' future credibility. Both age groups demonstrated a selective preference for learning novel explanations from an informant who had previously provided noncircular explanations—although only 5‐year‐olds also preferred to learn novel labels from her. The implications and scope of children's ability to monitor the quality of an informant's explanation are discussed.     

Crafting cosmopolitan nationalism: Ellen Johnson Sirleaf’s rhetorical leadership*

This essay analyzes the rhetoric of Ellen Johnson Sirleaf, president of post-conflict Liberia, for how it transformed national citizenship into cosmopolitan citizenship. Specifically, she promoted cosmopolitan values to global and regional audiences; codified cosmopolitan values into national policies and initiatives; and enabled Liberian women as citizens whose cosmopolitan practices fortified national, regional, and global communities. Through these concrete cosmopolitan practices, Liberian women performed as ideal citizens of the new democracy. Thus, this essay demonstrates how rhetorical scholars can turn to cosmopolitan theory to explain how rhetorical leaders can transform how and what it means to belong, especially for women.     

Warm-up with baseball bats of varying moments of inertia: effect on bat velocity and swing pattern

The purpose of this study was to determine if warm-up with baseball bats of different moments of inertia has an effect on swing pattern and bat velocity. Ten experienced baseball players (ages 20-25 years) voluntarily participated in this study. Each participant was required to complete 10 dry swings (5 warm-up and 5 postwarm-up) at maximum effort within 3 different conditions. Post warm-up was always with a standard bat (I = .27 kgm2; 83.8 cm, 9.1 N). Warm-up for Condition 1 was with the standard bat. Condition 2 required participants to warm up with a standard bat plus a 6.1 N lead donut (I = .49 kgm2, 83.8 cm, 15.6 N). Condition 3 required participants to warm up with a hollow plastic bat (I = .08 kgm2; 83.8 cm, 3.34 N). Quantitative and qualitative analyses indicated that following warm-up with the weighted bat (largest moment of inertia), swing pattern was significantly altered, and post warm-up velocity was the lowest of the three conditions.     

An optically transparent membrane supports shear stress studies in a three-dimensional microfluidic neurovascular unit model

We report a microfluidic blood-brain barrier model that enables both physiological shear stress and optical transparency throughout the device. Brain endothelial cells grown in an optically transparent membrane-integrated microfluidic device were able to withstand physiological fluid shear stress using a hydrophilized polytetrafluoroethylene nanoporous membrane instead of the more commonly used polyester membrane. A functional three-dimensional microfluidic co-culture model of the neurovascular unit is presented that incorporates astrocytes in a 3D hydrogel and enables physiological shear stress on the membrane-supported endothelial cell layer.