A spaceship with a thruster - one body, one force

A spaceship with one thruster producing a constant magnitude force is analyzed for various initial conditions. This elementary problem, with one object acted upon by one force, has value as a challenge to one's physical intuition and in demonstrating the benefits and limitations of dimensional analysis. In addition, the problem can serve to introduce a student to special functions, provide a mechanical model for Fresnel integrals and the associated Cornu spiral, or be used as an example in a numerical methods course. The problem has some interesting and perhaps unexpected features.Comment: 8 pages, 12 figures. Submitted to the American Journal of Physics. After it is published, it will be found at http://scitation.aip.org/aj

Strong Evidence for a Buried AGN in UGC 5101: Implications for LINER-Type Ultra-Luminous Infrared Galaxies

We report on the results of 3--4 $\mu$m spectroscopy of the ultra-luminous infrared galaxy (ULIRG) UGC 5101. It has a cool far-infrared color and a LINER-type optical spectrum, and so, based on a view gaining some currency, would be regarded as dominated by star formation. However, we find that it has strong 3.4 $\mu$m carbonaceous dust absorption, low-equivalent-width 3.3 $\mu$m polycyclic aromatic hydrocarbon (PAH) emission, and a small 3.3 $\mu$m PAH to far-infrared luminosity ratio. This favors an alternative scenario, in which an energetically dominant AGN is present behind obscuring dust. The AGN is plausibly obscured along all lines of sight (a `buried AGN'), rather than merely obscured along our particular line of sight. Such buried AGNs have previously been found in thermal infrared studies of the ULIRGs IRAS 08572+3915 and IRAS F00183$-$7111, both classified optically as LINERs. We argue that buried AGNs can produce LINER-type optical spectra, and that at least some fraction of LINER-type ULIRGs are predominantly powered by buried AGNs.Comment: 11 pages, 1 figure, accepted by ApJ Lette

Assessment and manipulation of training practices in adolescent athletes

Adolescent athletic development is a complex process. There are a number of challenges adolescent athletes face that influence their training practices. As such, this thesis aimed to 1) investigate the methods of monitoring and the distribution of training practices of adolescent athletes and examine the relationship with changes in physical qualities; and 2) assess how manipulating task-constraints (i.e., pitch size and player numbers) can influence the physical, technical and subjective task-load demands of training. To investigate these aims, 81 individuals were recruited across four study in conjunction with the industry partner, St Joseph’s Nudgee College. Study one systematically examined the research assessing internal and external methods of monitoring training load and changes in physical qualities, injury, or illness in adolescent athletes. The most reported load monitoring tools were session ratings of perceived exertion (n = 29) and training duration (n = 22). Results of the best-evidence synthesis identified moderate evidence of positive relationships between resistance training volume load and improvement in strength, and between throw count (i.e., number of pitches or bowls) and injury. However, evidence for other relationships between training load and change in physical qualities, injury, or illness were limited or inconsistent. Study two quantified the training loads in adolescent rugby players, as well as the relationship between training loads and changes in physical qualities, and the changes in levels of stress and recovery throughout an 8-week pre-season period. Subjects completed (mean ± S.D) 5.60 ± 1.60 total training sessions per week, with 2.45 ± 0.34 resistance training sessions and 2.73 ± 0.54 field training sessions. Conditioning drills had the greatest running intensity (145.2 ± 47.8 m/min), whereas small-sided games (SSG) had the greatest acceleration density (0.46 ± 0.13 AU/min). Significant improvements (p 10). Relationships between training load variables and changes in physical qualities were assessed using elastic net regression, with number of full body exercises having the greatest importance. As identified in study two, the IMTP is a commonly implemented method of assessing strength. Study three investigated the validity and reliability of strapped and taped grip, figure eight straps, and bare hand grip during the IMTP. Compared to the straps and tape condition, using only bare hands to grasp the bar reduced peak force (p < 0.01) while the figure eight strap condition allowed for similar (p = 0.42; ES = 0.08 ± 1.14) outcomes. All conditions were found to have acceptable reliability (CV% = 5.36 - 5.67%) for peak force, but all rate of force development (RFD) and impulse outcome measures were not reliable irrespective of grip. These findings demonstrate that practitioners who wish to use the IMTP to assess peak force should use either straps and tape, or figure eight straps. It is advised that practitioners use figure eight straps, as was used in study two, due to their equivalence in reliability, but increased efficiency and practicality. Study four assessed the variability of physical, technical, and subjective task-load demands in SSG, and the effect of manipulating of pitch size and player numbers in SSG on these demands in adolescent Rugby Union players. This study was conducted as SSG were the most commonly used conditioning tool evidenced in study two. In each condition subjects played 4 × 3-min periods of an SSG. Games were completed with either 4 × 4, 6 × 6 or 12 × 12 players on either a small (W: 25 m, L: 30 m), medium (W: 30 m, L: 40 m), or large (W: 35 m, L: 50 m) sized pitch. A substantial range of variability was observed in technical (CV = 25.00 to 52.38%), physical (CV = 4.12 to 51.18%) and subjective task-loads (CV = 7.65 to 17.14%) between identical games. Reducing player numbers increased physical demands such as m/min (ES range = 0.44 to 1.45; p = <0.01), technical exposures such as total involvements (ES range = 0.04 to 0.63; p range = <0.01 to 0.64) and effort, physical and temporal task-loads. Increasing pitch size caused greater movement demands such as m/min (ES range = 0.11 to 0.79; p = <0.01 to 0.62), but did not change the technical demands

The case for TIPS: an examination of the costs and benefits

Slightly more than a decade has passed since the introduction of the Treasury Inflation-Protected Securities (TIPS) program, through which the U.S. Treasury Department issues inflation-indexed debt. Several studies have suggested that the program has been a financial disappointment for the Treasury and by extension U.S. taxpayers. Relying on ex post analysis, the studies argue that a more cost-effective strategy remains the issuance of nominal Treasury securities. This article proposes that evaluations of the TIPS program be more comprehensive, and instead focus on the ex ante costs of TIPS issuance compared with nominal Treasury issuance. The authors contend that ex ante analysis is a more effective way to assess the costs of TIPS over the long run. Furthermore, relative cost calculations--whether ex post or ex ante--are just one aspect of a comprehensive analysis of the costs and benefits of the TIPS program. TIPS issuance provides other benefits that should be taken into account when evaluating the program, especially when TIPS are only marginally more expensive or about as expensive to issue as nominal Treasury securities.Treasury bonds ; Debt

Empirical development of a scale of patience

Patience is a construct not directly studied in the literature. Studies in the psychological literature have typically spoken of patience only as the converse of impatience. The assumption of these studies is that patience exists in the absence of impatience. However, other research proposes a multidimensional model of patience based on qualitative studies. It follows from the multidimensional model that patience exists on a continuum with the potential for different levels or amounts of patience across different situations. The purpose of this study was to develop an objective measure of patience.;To develop a measure of patience an item pool was constructed and reviewed, and then 347 undergraduate students completed items. Factor analysis of this initial administration identified nine factors. A final measure was developed and administered to 312 undergraduate students. To assess validity of the patience scale, students completed the Boredom Proneness Scale, the Student Version of the Jenkins Activity Scale, and a modified version of the Questionnaire Measure of Emotional Empathy in addition to the patience measure. Forty undergraduate students completed the measures at a four-week interval to assess temporal stability. Factor analysis utilized the Scree test and Kaiser eigenvalue rule in determining the number of factors to retain. Equamax rotation was the orthogonal method of factor rotation.;A six-factor model of patience was found with strong reliability for the measure as a whole (alpha = .7993) and adequate for individual factors (alpha = .7334--.5226). The six factors explained 48.282 percent of the variance. Temporal stability was high (r = .893). Support was found for convergent validity. Factor labels are postponement, even-tempered, composure, time abundance, tolerance, and limits of patience.;The Patience Scale is discussed in comparison to a sociotemporal model of patience and the other measures used in the study. Future directions for the use of the scale are discussed