Fluid balance of elite Brazilian youth soccer players during consecutive days of training     

Silva RP  Mündel T  Natali AJ  Bara Filho MG  Lima JR  Alfenas RC  Lopes PR  Belfort FG  Marins JC 《Journal of sports sciences》2011,29(7):725-732

In this study we investigated pre-training hydration status, fluid intake, and sweat loss in 20 elite male Brazilian adolescent soccer players (mean?±?s: age 17.2?±?0.5 years; height 1.76?±?0.05?m; body mass 69.9?±?6.0?kg) on three consecutive days of typical training during the qualifying phase of the national soccer league. Urine specific gravity (USG) and body mass changes were evaluated before and after training sessions to estimate hydration status. Players began the days of training mildly hypohydrated (USG?>?1.020) and fluid intake did not match fluid losses. It was warmer on Day 1 (33.1?±?2.4°C and43.4?±?3.2% relative humidity; P?相似文献   

Statistical analysis of the TULSA database, 1965–1994     

Rafael E. Ubico  John A. Bailey  Pamela J. Weaver 《Publishing Research Quarterly》1995,11(3):138-144

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School district administrators’ perspectives on the professional activities and influence of special educators in Norway and Sweden     

David Lansing Cameron  Gunilla Lindqvist 《International Journal of Inclusive Education》2013,17(7):669-685

The purpose of this study is to investigate school district administrators' perspectives concerning the professional activities and influence of special educators in Norway (n?=?266) and Sweden (n?=?290). We examine three themes drawn from a survey of practices and policies in each country: (a) the organisational arrangements in which special educators work, (b) perceived changes in special educators' activities, and (c) ratings of special educators' influence on the content of instruction and the availability of resources for children with special needs. Findings suggest that special educators frequently work in teams, function largely as advisors, and spend less time working with individual students than in previous years. There appears to be a more pronounced increase in special educators’ time devoted to advising and documentation in Sweden than in Norway. Swedish special educators were also more frequently described as working in multidisciplinary teams. Participants in both countries rated the influence of special educators significantly higher than that of parents and teachers on the availability and distribution of resources; and significantly higher than politicians, public officials, teachers, and parents with regard to influence over the content of instruction. We discuss these findings in relation to the goals and development of inclusive education in Scandinavia.  相似文献   

Kinematic comparisons of 1996 Olympic baseball pitchers     

Rafael F. Escamilla  Glenn S. Fleisig  Nigel Zheng  Steven W. Barrentine  James R. Andrews 《Journal of sports sciences》2013,31(9):665-676

The aim of this study was to compare and evaluate the kinematics of baseball pitchers who participated in the 1996 XXVI Centennial Olympic Games. Two synchronized video cameras operating at 120 Hz were used to video 48 pitchers from Australia, Japan, the Netherlands, Cuba, Italy, Korea, Nicaragua and the USA. All pitchers were analysed while throwing the fastball pitch. Twenty-one kinematic parameters were measured at lead foot contact, during the arm cocking and arm acceleration phases, and at the instant of ball release. These parameters included stride length, foot angle and foot placement; shoulder abduction, shoulder horizontal adduction and shoulder external rotation; knee and elbow flexion; upper torso, shoulder internal rotation and elbow extension angular velocities; forward and lateral trunk tilt; and ball speed. A one-way analysis of variance (P ? 0.01) was used to assess kinematic differences. Shoulder horizontal adduction and shoulder external rotation at lead foot contact and ball speed at the instant of ball release were significantly different among countries. The greater shoulder horizontal abduction observed in Cuban pitchers at lead foot contact is thought to be an important factor in the generation of force throughout the arm cocking and arm acceleration phases, and may in part explain why Cuban pitchers generated the greatest ball release speed. We conclude that pitching kinematics are similar among baseball pitchers from different countries.  相似文献   

The development of mental rotation abilities through robotics-based instruction: An experience mediated by gender     

José Antonio González-Calero  Ramón Cózar  Rafael Villena  José Miguel Merino 《British journal of educational technology : journal of the Council for Educational Technology》2019,50(6):3198-3213

The research literature on the topic of “spatial ability” reveals that it has a major influence on achievement in the fields of science, technology, engineering and mathematics. Additionally, previous studies indicate the existence of a gender gap in spatial ability in favour of males. Mental rotation, one subskill of spatial ability, is an area in which gender differences are greater. At the same time, educational robotics is seen as one of the more promising technologies in educational contexts for the future. We conducted a quasi-experimental study with 142 seven- and eight-year-old students aimed at analysing whether robotics-based instruction may produce greater learning gains on mental rotation abilities compared to traditional instruction. The intervention was developed in the context of map-reading tasks, which are part of the curricular content in Mathematics and Social Sciences at this age. The results showed that for males, the robotics-based instruction promoted a significantly greater improvement in students’ mental rotation abilities compared to the control group. By contrast, no significant differences were observed for females. Although this study provides empirical evidence of the potential of robotics-based instruction, future studies need to deeply analyse the existence of gender differences in the learning gains obtained through educational robotics.  相似文献   

Training load and submaximal heart rate testing throughout a competitive period in a top-level male football team     

Vincenzo Rago  Peter Krustrup  Rafael Martín-Acero  António Rebelo 《Journal of sports sciences》2020,38(11-12):1408-1415

ABSTRACT

The aim of this study was to investigate training load and cardiorespiratory fitness in a top-level Spanish (LaLiga) football team (n = 17). The submaximal Yo-Yo intermittent recovery test level 1 (Yo-Yo IR1_SUB) was performed in four moments of the competitive period from early February (E1) to early May (E4). Training load was quantified using a 10-Hz global positioning system and heart rate (HR) recording (n = 837 individual training sessions), while match load was quantified using semi-automated cameras (n = 216 individual match observations). Cardiorespiratory fitness moderately improved as the season progressed (P < 0.05; effect sizes = 0.8 to 1.2). Cumulative total distance covered during training between E1 and E4 was negatively correlated with percentage of changes in mean HR during the last 30 s of Yo-Yo IR1_SUB (P = 0.049; r = ?0.47 [?0.71; ?0.14]; moderate). HR during the last 30 s of Yo-Yo IR1_SUB was negatively correlated to total distance covered during the match (P = 0.024; r = ?0.56 [?0.80; ?0.17]; moderate). Yo-Yo IR_SUB can be used to monitor seasonal changes in cardiorespiratory fitness without the need to have players work until exhaustion. Cardiorespiratory fitness given by mean HR during the last 30 s of the test seems meaningful in relation to match performance.  相似文献   

Using the Web as corpus for self-training text categorization     

Rafael Guzmán-Cabrera  Manuel Montes-y-Gómez  Paolo Rosso  Luis Villaseñor-Pineda 《Information Retrieval》2009,12(3):400-415

Most current methods for automatic text categorization are based on supervised learning techniques and, therefore, they face the problem of requiring a great number of training instances to construct an accurate classifier. In order to tackle this problem, this paper proposes a new semi-supervised method for text categorization, which considers the automatic extraction of unlabeled examples from the Web and the application of an enriched self-training approach for the construction of the classifier. This method, even though language independent, is more pertinent for scenarios where large sets of labeled resources do not exist. That, for instance, could be the case of several application domains in different non-English languages such as Spanish. The experimental evaluation of the method was carried out in three different tasks and in two different languages. The achieved results demonstrate the applicability and usefulness of the proposed method.  相似文献   

Pre-game hydration status, sweat loss, and fluid intake in elite Brazilian young male soccer players during competition     

Da Silva RP  Mündel T  Natali AJ  Bara Filho MG  Alfenas RC  Lima JR  Belfort FG  Lopes PR  Marins JC 《Journal of sports sciences》2012,30(1):37-42

In this study, we assessed the pre-game hydration status and fluid balance of elite young soccer players competing in a match played in the heat (temperature 31.0 ± 2.0 ° C, relative humidity 48.0 ± 5.0%) for an official Brazilian soccer competition. Fluid intake was measured during the match, as were urine specific gravity and body mass before and after the game to estimate hydration status. Data were obtained from 15 male players (age 17.0 ± 0.6 years, height 1.78 ± 0.06 m, mass 65.3 ± 3.8 kg); however, data are only analysed for 10 players who completed the full game. The mean (± s) sweat loss of players amounted to 2.24 ± 0.63 L, and mean fluid intake was 1.12 ± 0.39 L. Pre-game urine specific gravity was 1.021 ± 0.004, ranging from 1.010 to 1.025. There was no significant correlation between sweat loss and fluid intake (r = 0.504, P = 0.137) or between urine specific gravity and fluid intake (r = -0.276, P = 0.440). We conclude that young, native tropical soccer players started the match hypohydrated and replaced about 50% of the sweat lost. Thus, effective strategies to improve fluid replacement are needed for players competing in the heat.  相似文献   

Mixed order robust adaptive control for general linear time invariant systems     

Javier A. Gallegos  Manuel A. Duarte-Mermoud  Rafael Castro-Linares 《Journal of The Franklin Institute》2018,355(8):3399-3422

We provide a solution to the adaptive control problem of an unknown linear system of a given derivation order, using a reference model or desired poles defined in a possibly different derivation order and employing continuous adjustment of parameters ruled by possibly another different derivation order. To this purpose, we present an extension for the fractional settings of the Bezout’s lemma and gradient steepest descent adjustment. We analyze both the direct and indirect approaches to adaptive control. We discuss some robustness advantages/disadvantages of the fractional adjustment of parameters in comparison with the integer one and, through simulations, the possibility to define optimal derivation order controllers.  相似文献   

The Nobel Exhibition Cultures of Creativity: the Centennial Exhibition of the Nobel Prize, 1901–2001     

Svante Lindqvist 《Minerva》2001,39(4):461-465

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