Body sway,aim point fluctuation and performance in rifle shooters: inter- and intra-individual analysis

In this study, we examined the relationships between body sway, aim point fluctuation and performance in rifle shooting on an inter- and intra-individual basis. Six elite shooters performed 20 shots under competition conditions. For each shot, body sway parameters and four aim point fluctuation parameters were quantified for the time periods 5 s to shot, 3 s to shot and 1 s to shot. Three parameters were used to indicate performance. An AMTI LG6-4 force plate was used to measure body sway parameters, while a SCATT shooting analysis system was used to measure aim point fluctuation and shooting performance. Multiple regression analysis indicated that body sway was related to performance for four shooters. Also, body sway was related to aim point fluctuation for all shooters. These relationships were specific to the individual, with the strength of association, parameters of importance and time period of importance different for different shooters. Correlation analysis of significant regressions indicated that, as body sway increased, performance decreased and aim point fluctuation increased for most relationships. We conclude that body sway and aim point fluctuation are important in elite rifle shooting and performance errors are highly individual-specific at this standard. Individual analysis should be a priority when examining elite sports performance.     

The vibrational mode structure of a golf ball

In this paper, we report the discrete frequencies at which golf balls can vibrate, the mode patterns of these vibrations and how these modes can be excited. There are two broad classes of modes: those that radiate sound waves and those that do not. Both silent and acoustic modes are excited by tangential (i.e. spin-producing) impact forces; only acoustic modes are excited by radial impact forces. Exact analytical results for a homogeneous ball core are compared with finite element numerical results for both a core and a model two-piece ball. Correspondences are readily established for the important low-frequency modes, and the good agreement suggests the validity of these results for real golf balls. The results potentially provide the basis for a rapid, simple and non-destructive method of measuring the effective high-frequency elastic shear modulae of balls (and ball cores) as well as a method for 'tuning' the performance of balls for specific clubs. Some of these aspects are explored further in our companion paper in this issue.     

The Use of the Analysis of Co‐variance in Educational Research: panacea or pitfall for the unwary?

The theory underlying the analysis of covariance is outlined and certain common misuses delineated. The technique is severely limited in its applications while invalid applications may lead to false inferences. It is shown that it cannot make non‐experimental designs experimental and that invalid assumptions regarding the slope of the regression lines may also lead the educational researcher astray.     

How Niche Magazines Survive and Thrive Through an Industry in Turmoil

In recent years, many general-interest magazine publishers have had problems maintaining stability. What can these publications learn from smaller, niche titles that have  remained successful through the same industry changes? This paper will examine three major strengths for niche magazines that general-interest magazine publishers lack: their reader devotion, their careful approaches to digitalization, and their use of paid digital content. These strengths are analyzed in three case studies from different sub-genres of niche publishing: a city magazine, a luxury product magazine, and a hobby magazine. This paper offers practical suggestions general-interest magazines can implement. Looking at the successful practices suggests the potential to address industry-wide problems and to potentially yield more stable magazine publishing environments.