Science in the Mainstream: Retooling Science Activities     

Kevin D. Finson  Christine K. Ormsbee  Mary Jensen  Donald T. Powers 《Journal of Science Teacher Education》1997,8(3):219-232

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Show‐Jumping     

Pippa Powers  Andrew Harrison 《Sports biomechanics / International Society of Biomechanics in Sports》2013,12(2):135-146

This study examined the effects of the rider on the linear projectile kinematics of show‐jumping horses. SVHS video recordings (50 Hz) of eight horses jumping a vertical fence 1 m high were used for the study. Horses jumped the fence under two conditions: loose (no rider or tack) and ridden. Recordings were digitised using Peak Motus. After digitising the sequences, each rider's digitised data were removed from the ridden horse data so that three conditions were examined: loose, ridden (including the rider's data) and riderless (rider's data removed). Repeated measures ANOVA revealed significant differences between ridden and loose conditions for CG height at take‐off (p < 0.001), CG distance to the fence at take‐off (p = 0.001), maximum CG during the suspension phase (p < 0.001), CG position over the centre of the fence (p < 0.001), CG height at landing (p < 0.001), and vertical velocity at take‐off (p < 0.001). The results indicated that the rider's effect on jumping horses was primarily due to behavioural changes in the horse's motion (resulting from the rider's instruction), rather than inertial effects (due to the positioning of the rider on the horse). These findings have implications for the coaching of riders and horses.  相似文献   

The nature and substantiation of official sexual abuse reports   总被引：1，自引：0，他引：1  

J Eckenrode  J Munsch  J Powers  J Doris 《Child abuse & neglect》1988,12(3):311-319

A representative sample of 796 sexual abuse reports from New York State in 1985 was studied to explore factors associated with the decision to substantiate or unsubstantiate these reports. This study focused on the age, sex, and ethnicity of the subject child, and the source of the report as predictors of case substantiation. Substantiation rates tended to increase with the age of the child although this was more characteristic of reports involving female than male victims. Overall, reports involving female children were more likely to be substantiated than those involving male children. Ethnicity of the child showed no significant relationship to substantiation. Source of report, however, showed a strong relationship to case determination, with mandated reports found to be substantiated at a rate 13% higher than reports from non-mandated sources.  相似文献   

Control of ventilation during submaximal exercise: a brief review     

S K Powers  R E Beadle 《Journal of sports sciences》1985,3(1):51-65

This review discusses the leading hypotheses concerning ventilatory control during submaximal exercise. The ventilatory response at the onset of submaximal exercise has been studied extensively. It is generally agreed that expired ventilation (VE) increases rapidly at the initiation of exercise followed by a slower increase in VE until a steady state is reached. In general, there are four schools of thought concerning the mechanisms that are responsible for the exercise hyperpnoea. Two of the hypotheses relate the increase in VE to neural regulation. One group argues that the increase in VE during work is primarily due to afferent neural feedback to the ventilatory control centre while the other group proposes that efferent neural activity can explain the hyperpnoea. A third group of hypotheses submit that humoral mechanisms must be actively involved in the increase in VE during exercise. The leading hypothesis in this area is based on experiments that suggest that CO2 return to the lung provides a stimulus for ventilatory control. Finally, the fourth supposition is that the exercise hyperpnoea may be due to both neural and humoral mechanisms. In summary, although there is persuasive evidence that both humoral and neural factors may play a role in mediating the exercise hyperpnoea, the basic question of whether the response is due solely to humoral or neural mechanisms remains unresolved.  相似文献   

The educational attainments of deaf students in mainstream programs in England: examination results and influencing factors.     

S Powers 《American annals of the deaf》1999,144(3):261-269

The author reports findings of an investigation into educational outcomes of 16-year-old deaf students in mainstream programs in England in 1995 and 1996. Data on examination results, communication competence, and social acceptance were collected by questionnaire and analyzed against several background factors. All the background factors investigated contributed an effect of about 20% on examination results, emphasizing the need to investigate the effect of other factors. Relatively strong predictors of examination success were family socioeconomic status, presence of any additional learning difficulty, whether English was used as a main language in the home, age at onset of deafness, and parents' hearing status. Degree of hearing loss did not appear to have an important effect on examination success but was linked to other outcomes. The discussion considers how different codings of examination success can affect the results obtained from statistical analysis. Findings on the ethnic status of deaf students are also noted.  相似文献   

Linear kinematics at take-off in horses jumping the wall in an international Puissance competition     

Powers P 《Sports biomechanics / International Society of Biomechanics in Sports》2005,4(2):149-162

Sagittal plane SVHS video recordings (50 Hz) were made of horses jumping the wall at an international Puissance competition. Video sequences were manually digitized and six kinematic variables at take-off were analyzed. Nine horses started the competition with the fence height at 1.80 m, and two horses attempted the fence in the fifth and final round with the fence height at 2.27 m. For successful performances, fence height was correlated with the following take-off variables: vertical velocity of the centre of mass (r = 0.45, p = 0.03); height of centre of mass (r = 0.44, p = 0.04); distance of centre of mass from fence (r = 0.46, p = 0.03); and distance from leading hind limb to centre of mass (r = -0.61, p < 0.01). These results indicated that body position at take-off is the most important aspect when jumping high fences. This is the first known study that has examined horses jumping over a Puissance wall. The results should help horse riders and trainers improve performance in Puissance jumping horses, and perhaps help in the early selection of horses with a talent for jumping high fences.  相似文献   

Participation in extracurricular physical activity programs at middle schools     

Powers HS  Conway TL  McKenzie TL  Sallis JF  Marshall SJ 《Research quarterly for exercise and sport》2002,73(2):187-192

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Effects of the rider on the linear kinematics of jumping horses     

Powers P  Harrison A 《Sports biomechanics / International Society of Biomechanics in Sports》2002,1(2):135-146

This study examined the effects of the rider on the linear projectile kinematics of show-jumping horses. SVHS video recordings (50 Hz) of eight horses jumping a vertical fence 1 m high were used for the study. Horses jumped the fence under two conditions: loose (no rider or tack) and ridden. Recordings were digitised using Peak Motus. After digitising the sequences, each rider's digitised data were removed from the ridden horse data so that three conditions were examined: loose, ridden (including the rider's data) and riderless (rider's data removed). Repeated measures ANOVA revealed significant differences between ridden and loose conditions for CG height at take-off (p < 0.001), CG distance to the fence at take-off (p = 0.001), maximum CG during the suspension phase (p < 0.001), CG position over the centre of the fence (p < 0.001), CG height at landing (p < 0.001), and vertical velocity at take-off (p < 0.001). The results indicated that the rider's effect on jumping horses was primarily due to behavioural changes in the horses motion (resulting from the rider's instruction), rather than inertial effects (due to the positioning of the rider on the horse). These findings have implications for the coaching of riders and horses.  相似文献   

Exploring the information kaleidoscope     

David Thornburg  Roger Minier  Carl Carter  Judy Powers  Hal Gibson  Libby Reeves 《TechTrends》1995,40(6):19-25

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On rectangular systems of differential equations and their application to circuit theory     

Victor Lovass-Nagy  David L. Powers 《Journal of The Franklin Institute》1975,299(6):399-407

A system of differential equations A(d/dt) x = Bx+f, along with the initial condition x(0) = k, is considered where A and B are m x n matrices. Generalized inverses of the matrix A are used to derive algebraic conditions for the existence and uniqueness of a solution. An example is presented to illustrate application of the results to circuit theory.  相似文献