Ground reaction forces and kinematics of plant leg position during instep kicking in male and female collegiate soccer players

The players' ability to achieve the greatest distance in kicking is determined by their efficiency in transferring kinetic energy from the body to the ball. The purpose of this study was to compare the kinetics and kinematics of the plant leg position between male and female collegiate soccer players during instep kicking. Twenty-three soccer players (11 males and 12 females) were filmed in both the sagittal and posterior views while performing a maximal instep kick. Plant leg kinetic data were also collected using an AMTI 1000 force platform. There were no significant differences between the sexes in plant leg position, but females had significantly greater trunk lean, plant leg angle, and medial-lateral ground reaction force than the males. Males showed higher vertical ground reaction forces at ball contact, but there were no significant differences in ball speed at take-off between the sexes. Ball speed at take-off was inversely related to peak anterior-posterior ground reaction force (-0.65). The anatomical differences between the sexes were reflected in greater trunk lean and lower leg angle in the females.     

Physiological responses and time-motion characteristics of various small-sided soccer games in youth players

The aim of this study was to examine acute physiological responses and time-motion characteristics associated with three different small-sided soccer game formats in youth players. Sixteen male soccer players aged 16.3+/-0.6 years (mean+/-s) completed three variations of a small-sided game (i.e. 2 vs. 2, 4 vs. 4, and 6 vs. 6 players) in which heart rate, rating of perceived exertion (RPE), blood lactate concentration, and time-motion characteristics were recorded. The pitch size was altered to keep the relative pitch area per player consistent for each game format. The 2 vs. 2 games exhibited greater blood lactate, heart rate, and RPE responses compared with 4 vs. 4 and 6 vs. 6 games (P<0.05). The players travelled less (P<0.05) distance at speeds of 0-7 km.h(-1) in the 4 vs. 4 compared with the 2 vs. 2 games (1128+/-10 m and 1176+/-8 m, respectively). Average maximal sprint distances above 18 km.h(-1) were lower (P<0.05) in 2 vs. 2 than in 4 vs. 4 and 6 vs. 6 games (11.5+/-3.9 m, 15.3+/-5.5 m, and 19.4+/-5.9 m, respectively), and in 4 vs. 4 compared with 6 vs. 6 games. The results show that as small-sided game formats decrease in size and relative pitch area remains constant, overall physiological and perceptual workload increases.     

Permissible control of general constrained mechanical systems

This paper develops a unified approach for modeling and controlling mechanical systems that are constrained with general holonomic and nonholonomic constraints. The approach conceptually distinguishes and separates constraints that are imposed on the mechanical system for developing its physical structure between constraints that may be used for control purposes. This gives way to a general class of nonlinear control systems for constrained mechanical systems in which the control inputs are viewed as the permissible control forces. In light of this view, a new and simple technique for designing nonlinear state feedback controllers for constrained mechanical systems is presented. The general applicability of the approach is demonstrated by considering the nonlinear control of an underactuated system.     

Evaluation of the "under-21 rule": do young adult soccer players benefit?

Young adult soccer players often encounter difficulty progressing from youth competition to being regularly selected for high-level, open-age competition. In an attempt to increase the playing opportunities of semi-professional and amateur under-21 players in first teams, the Royal Belgian Football Association required national division teams to include at least two players younger than 21 in their match selection (under-21 rule). Over four seasons, the following variables were analysed across 2138 semi-professional and amateur soccer players aged 16-39 years: (1) the number of times a player was selected to be in the first team squad; (2) the number of times a player was selected to play in the starting line-up; and (3) the number of minutes played. Chi-square analysis demonstrated that second and third division teams had complied with the new selection regulations. However, two-way analysis of variance of individual player data revealed no increase in the number of playing minutes in the under-21 group. It would appear that many teams had complied with the new regulations by selecting young players as substitutes. The results highlight the difficulties that talented young soccer players experience progressing from youth to senior competition. We conclude that the rule imposed by the Royal Belgian Football Association has failed to improve the playing opportunities of young adult soccer players. Alternative strategies for increasing playing opportunities for young talented players are required.     

Friendship and the Public Stage: Revisiting Hannah Arendt's Resistance to “Political Education”

Hannah Arendt's essays about the 1957 crisis over efforts of a group of youth, the “Little Rock Nine,” to desegregate a high school in Little Rock, Arkansas, reveal a tension in her vision of the “public.” In this article Aaron Schutz and Marie Sandy look closely at the experiences of the youth desegregating the school, especially those of Elizabeth Eckford, drawing upon them to trace a continuum of forms of public engagement in Arendt's work. This ranges from arenas of “deliberative friendship,” where unique individuals collaborate on common efforts, to a more conflictual “public stage,” where groups act in solidarity to change aspects of the public world. While Arendt famously asserted in her essay “The Crisis in Education” that political capacities should not be taught in schools, it makes more sense to see this argument as focused on what she sometimes called the conflictual “public stage,” reflecting the experience of the Little Rock Nine. In contrast, Schutz and Sandy argue that Arendt's own work implies that “deliberative friendship,” as described in her essay “Philosophy and Politics” and elsewhere, should be part of everyday practices in classrooms and schools.     

Droplet confinement and leakage: Causes,underlying effects,and amelioration strategies

The applicability of droplet-based microfluidic systems to many research fields stems from the fact that droplets are generally considered individual and self-contained reaction vessels. This study demonstrates that, more often than not, the integrity of droplets is not complete, and depends on a range of factors including surfactant type and concentration, the micro-channel surface, droplet storage conditions, and the flow rates used to form and process droplets. Herein, a model microfluidic device is used for droplet generation and storage to allow the comparative study of forty-four different oil/surfactant conditions. Assessment of droplet stability under these conditions suggests a diversity of different droplet failure modes. These failure modes have been classified into families depending on the underlying effect, with both numerical and qualitative models being used to describe the causative effect and to provide practical solutions for droplet failure amelioration in microfluidic systems.     

The effects of browse time on the Internet on students’ essay scores

This study examined how 30 minutes of search time on the Web affected students’ essay scores in response to a writing prompt. Expository essays were obtained from 49 fourth- and fifthgrade students enrolled in an elementary school in Virginia, in the United States. Students were placed by random assignment into three groups with the same writing prompt for all three groups. Data analyses using ANOVA indicate that there was statistical significance in two components of writing. The group that received instruction on using the Internet to conduct research in the prewriting phase outperformed the control group in two areas: the total essay score (p=.053) and usage/mechanics (p=.028). The study also produced effect sizes ranging from small to large when the Internet users were compared to the control group. Implications for the future of Internet use in the school system are discussed.     

Partisan Media and Discussion as Enhancers of the Belief Gap

This study examines the roles of partisanship, partisan media use, and political discussion in the development of belief gaps. Using national survey data, we construct models of political identity, media use, and discussion factors predicting beliefs on five contested political issues and find that ideology and partisanship are generally stronger predictors of beliefs than is education. Notably, each has independent effects on belief outcomes. Contrary to some concerns that the Internet especially promotes partisan clustering, use of partisan traditional media—television and radio—is by far the strongest information-related predictor of belief outcomes, whereas partisan social media use and partisan discussion are relatively weak and inconsistent. These findings suggest that political elites continue to exert significant influence over the perceptions of rank and file partisans.     

Stereoscopy in Static Scientific Imagery in an Informal Education Setting: Does It Matter?

Stereoscopic technology (3D) is rapidly becoming ubiquitous across research, entertainment and informal educational settings. Children of today may grow up never knowing a time when movies, television and video games were not available stereoscopically. Despite this rapid expansion, the field’s understanding of the impact of stereoscopic visualizations on learning is rather limited. Much of the excitement of stereoscopic technology could be due to a novelty effect, which will wear off over time. This study controlled for the novelty factor using a variety of techniques. On the floor of an urban science center, 261 children were shown 12 photographs and visualizations of highly spatial scientific objects and scenes. The images were randomly shown in either traditional (2D) format or in stereoscopic format. The children were asked two questions of each image—one about a spatial property of the image and one about a real-world application of that property. At the end of the test, the child was asked to draw from memory the last image they saw. Results showed no overall significant difference in response to the questions associated with 2D or 3D images. However, children who saw the final slide only in 3D drew more complex representations of the slide than those who did not. Results are discussed through the lenses of cognitive load theory and the effect of novelty on engagement.