Uma aproximação à forma como os alunos do ensino primário formulam problemas

Problem posing is an excellent strategy for teaching problem solving in Mathematics. This research describes and analyzes the problem posing developed by students of Primary Education (11 years). The methodology for this educational stage was designed in a collaborative environment (PIE-Educational Research Project). Students will have different scenarios to formulate various types of mathematical problems (arithmetic, geometric, itinerary and orientation in space). The study and analysis applied has been cut-off qualitatively within the interpretive paradigm. Highlights of this analysis the students ' ability to identify problematic situations in mathematics, formulating problems varied and rich in terms of conditions, unknowns and data provided in their statements.La formulación de problemas es una excelente estrategia para la enseñanza de la resolución de problemas en Matemáticas. Esta investigacióndescribe y analiza la formulación de problemas desarrollada por alumnos de Educación Primaria (11 años). La metodología a aplicar para esta etapa educativa se diseñó en un entorno colaborativo (el PIE: Proyecto de Investigación Educativa); los alumnos disponían de diferentes escenarios para formular distintos problemas matemáticos (aritméticos, geométricos, de itinerario y de orientación espacial), y el estudio y análisis aplicado han sido de corte cualitativo, dentro del paradigma interpretativo. Se destaca de dicho análisis la capacidad de los alumnos para identificar situaciones problemáticas matemáticas, formulando problemas variados y ricos en cuantoa condiciones, incógnitas y datos aportados en sus enunciados.A formulação de problemas é uma excelente estratégia para o ensino de a resolução de problemas em Matemática. Esta pesquisa descreve e analisa a formulação de problemas desenvolvidos por alunos do Ensino Fundamental (11 anos). A metodologia para este estágio educacional foi projetada em um ambiente colaborativo (PIE-EducationalResearch Project). Os alunos tiveram diferentes cenários para formular diferentes problemas matemáticos (aritmética, geométrica, itinerário e orientação espacial). O estudo e análise aplicada tem sido qualitativos no paradigma interpretativo. Destaca-Se neste contexto a capacidade dos alunos para identificar situações problemáticas matemática, formulando problemas variados e ricos no que respeita a condições, incógnitas e dados fornecidos em seus enunciados

Propiedades mecánicas de carburo de silicio poroso de estructura celular abierta

VIII Congreso de Propiedades Mecánicas de Sólidos. Comunicaciones en: http://www.upv.es/pms2002/Hemos estudiado las propiedades mecánicas y la microestructura de un material de SiC poroso de estructura celular abierta. El tamaño de celda típico es 2.4 mm. Las celdas abiertas ocupan el 80% del volumen y las aristas que conforman la estructura sólida tienen una densidad de 2.53 g/cm3 , es decir un 79% de la densidad teórica del SiC. Se han realizado ensayos de compresión uniaxial hasta rotura a velocidad de compresión constante de 20 mm/min, sobre muestras de 20x20x30 mm aproximadamente, cargando a lo largo de la dimensión mayor. Los ensayos se han realizado a temperatura ambiente y a altas temperaturas, entre 1150ºC y 1400ºC. La resistencia en compresión a rotura se ha encontrado en el rango 369 kPa y 558 kPa. Se comparan estos resultados con los de otros materiales celulares

post high intensity pull-over semi-tethered swimming potentiation in national competitive swimmers

BacKGround: The swimming community has shown considerable interest in using dry-land warm-ups as a method of impacting perfor- mance. This study compared the effects of high-resistance pull-over and swimming warm-up in semi-tethered resisted swimming. MeThodS: an incremental-load semi-tethered swimming test was individually administered in 20 national-competitive swimmers to deter- mine the load maximizing swimming power. in different sessions, participants tested such a load 6 min after a swimming warm-up (SWu) or a dry-land warm-up (dlWu: 3 pull-over reps at 85% of the one-repetition maximum). Kinetic variables (velocity, force, acceleration, impulse, power rate of force development [rfd] and intra-cycle variation), were obtained with a linear encoder through trapezoidal integration regarding time. Kinematic variables (distance, time, stroke-rate and stroke-length), were obtained by video recordings. The differences between protocols were observed by paired-samples t-test (ANOVA). Pearson’s coefficient explored correlations between kinetics and kinematics variables; sig- nificance was set at P<0.05. reSulTS: dlWu increased rfd (34.52±16.55 vs. 31.29±13.70 N/s; Δ=9.35%) and stroke-rate (64.70±9.84 vs. 61.56±7.07 Hz; Δ=5.10%) compared to SWu, but decreased velocity, force, acceleration, impulse and power. during the incremental-load test velocity and power were higher than obtained after SWu (1.21±0.14 vs. 1.17±0.12 m/s; Δ=3.06%), (51.38±14.93 vs. 49.98±15.40 W; Δ=2.72%), suggesting enhance- ments prompted by the test itself. Correlations between stroke-length with impulse (r=0.76) and power (r=0.75) associated kinetics with kine- matics. CONCLUSIONS: Potentiation responses were present after the dry-land warm-up. However, swimmers may benefit more from submaximal prolonged conditioning activities such as resisted swimming rather than high-resistance dry-land sets to obtain performance enhancements

Pull-over potentiation in semi-tethered swimming

BACKGROUNDː The swimming community has shown considerable interest in using dry-land warm-ups as a method of impacting performance. This study compared the effects of high-resistance pull-over and swimming warm-up in semi-tethered resisted swimming. METHODSː An incremental-load semi-tethered swimming test was individually administered in 20 national-competitive swimmers to determine the load maximizing swimming power. In different sessions, participants tested such a load 6 min after a swimming warm-up (SWU) or a dry-land warm-up (DLWU: 3 pull-over reps at 85% of the one-repetition maximum). Kinetic variables (velocity, force, acceleration, impulse, power rate of force development (RFD) and intra-cycle variation), were obtained with a linear encoder through trapezoidal integration regarding time. Kinematic variables (distance, time, stroke-rate and stroke-length), were obtained by video recordings. The differences between protocols were observed by paired-samples T-test (ANOVA). Pearson’s coefficient explored correlations between kinetics and kinematics variables; significance was set at P<0.05. RESULTSː DLWU increased RFD (34.52±16.55 vs. 31.29±13.70 N/s; Δ=9.35%) and stroke-rate (64.70±9.84 vs. 61.56 ± 7.07 Hz; Δ=5.10%) compared to SWU, but decreased velocity, force, acceleration, impulse and power. During the incremental-load test velocity and power were higher than obtained after SWU (1.21±0.14 vs. 1.17±0.12 m/s; Δ=3.06%), (51.38±14.93 vs. 49.98±15.40 W; Δ=2.72%), suggesting enhancements prompted by the test itself. Correlations between stroke-length with impulse (r=0.76) and power (r=0.75) associated kinetics with kinematics. CONCLUSIONSː Potentiation responses were present after the dry-land warm-up. However, swimmers may benefit more from submaximal prolonged conditioning activities such as resisted swimming rather than high-resistance dry-land sets to obtain performance enhancements.CTS-527: Actividad física y deportiva en el medio acuátic

Postactivation potentiation in sprint swimming performance

Introduction: In sprint swimming, every instant is critical. Nowadays, is common to see how sprint swimmers prepare for racing by activating themselves on many different ways such as doing ballistic stretching, by increasing their breathing and heart rate, or by strongly clapping their chest or limbs. Therefore, it cannot be rejected the fact that sprint swimmers need to create an extra activation on their neuromuscular system in order to race at the best of their capacities. Many of those methods have been based on post-activation potentiation (PAP). A procedure which improves muscle contractility both in strength and speed through previously applying maximal or submaximal conditioning exercises on the muscle system. The aim of this study was testing different PAP protocols on sprint swimming performance. Methods: This study received the approval of the ethics committee of the research board’s university and all the protocols accomplished with the declaration of Helsinki regarding the use of human subjects. Thirty trained swimmers volunteered to participate on this study and signed informed consent. First of all, all the swimmers were obtained the maximal repetition lifting load (RM), through strength tests consisting on an incremental load repetition test both for lower and upper limbs. In order to obtain results related to specific swimming-movements, PAP methods were extrapolated from experimental conditions and tested on a swimming start performance. Free-weight load lifting and maximal eccentric flywheel contractions simulating the movement of a swimming start were tested. Kinetic and kinematic variables of performance were obtained through a dynamometer experimental block start station and by photogrammetry. Individual’s strength index were also discussed and related to the results. Finally, conditioning exercises simulating arm strokes in swimming through free-weight and eccentric flywheel were tested on the variables of competition of a swimming race. Results: Swimming starts were able of being improved through PAP as velocity at take-off was higher, specially after eccentric warm-up protocols. These improvements would come from improvements on the vertical vectors of force/impulse developed by the lower limbs on the block. In fact, stronger athletes seemed to react better to PAP protocols, possibly because myosin phosphorylation (main PAP precursor) is more frequent on type II fibers. The first meters of a swimming race might be improved by using PAP. However, some swimming patterns as stroke length might be deteriorated along the race. Conclusion: Fatigue and potentiation co-exists as responses of PAP, therefore, it generates very individualized responses, specially in males. Positive results might be obtained from applying PAP methods on the swimming start impulse although is still needed finding a suitable intensity for the conditioning exercises applied on upper limbs. Acknowledgements: DEP2014-59707-P: SWIM: Specific Water Innovative Measurements, applied to the development of International Swimmers in Short Swimming Events (50and100m).CTS-527: Actividad física y deportiva en el medio acuátic

Lower fatigue and faster recovery of ultra-short race-pace swimming training sessions

Ultra-short race-pace training (USRPT) is a high-intensity training modality used in swimming for the development of the specific race-technique. However, there is little information about the fatigue associated to this modality. In a crossover design, acute responses of two volume-equated sessions (1000-m) were compared on 14 national swimmers: i) USRPT: 20×50-m; ii) RPT: 10×100-m. Both protocols followed an equivalent work recovery ratio (1:1) based on individual 200-m race-pace. The swimming times and the arm-strokes count were monitored on each set and compared by mixed-models. Blood lactate [La-] and countermovement jump-height (CMJ) were compared within and between conditions 2 and 5 min after the protocols. The last bouts in RPT were 1.5–3% slower than the target pace, entailing an arm-strokes increase value of ~0.22 for every second increase in swimming time. USRPT produced lower [La-] ([Mean ± standard deviation], 2 min: 8.2±2.4 [p = 0.021]; 5 min: 6.9±2.8 mM/L [p = 0.008]), than RPT (2 min: 10.9±2.3; 5 min: 9.9±2.4 mM/L). CMJ was lowered at min 2 after RPT (-11.09%) and USRPT (-5.89%), but returned to the baseline in USRPT at min 5 of recovery (4.07%). In conclusion, lower fatigue and better recovery were achieved during USRPT compared to traditional high-volume set.CTS-52

Does jumping conducted before the swimming start elicit underwater enhancement?

The effects of pre-activation exercises on undulatory underwater swimming (UUS) have not been studied. This research aimed to: 1) assess the effects of a jumping-exercise strategy upon UUS performance and kinematics variables; 2) test the different effects on males and females, and; 3) to explore if stronger participants exhibit greater post-activation performance enhancement (PAPE). Ninety-two age-group national level swimmers randomly assigned into control (17 males and 18 females) and experimental groups (27 males and 30 females) took part in a cross-sectional study designed to test two maximal 15-m UUS performance efforts. The experimental group performed four maximal tuck jumps before the first or the second UUS effort. Performance and kinematics variables were analyzed using instantaneous velocity data via speedometer. Maximal lower-limbs force was obtained during a countermovement jump through a linear-encoder. Two-way repeated measures ANOVA test and linear regression analysis were used to explore variable interactions between baseline and PAPE, and the association between the PAPE response and strength of the swimmers, respectively. Despite trends toward improvements in push-off velocity (Δ = 1.33%; d = 0.12), the results did not show enhancements nor deterioration in UUS performance and kinematics after the tuck jumps. No specific PAPE responses modulated by sex or by the strength level of the swimmers were observed for this age-group (p < 0.05). Four tuck jump repetitions executed prior to diving could be insufficient to acutely enhance UUS performance. The fact that the exercise performed during warm-up was a body-weight based exercise, was possibly not enough to evoke PAPE

Electrical properties of biomorphic SiC ceramics and SiC/Si composites fabricated from medium density fiberboard

A study has been made of the dependences of the electrical resistivity and the Hall coefficient on the temperature in the range 1.8–1300 K and on magnetic fields of up to 28 kOe for the biomorphic SiC/Si (MDF-SiC/Si) composite and biomorphic porous SiC (MDF-SiC) based upon artificial cellulosic precursor (MDF – medium density fiberboards). It has been shown that electric transport in MDF-SiC is effected by carriers of n-type with a high concentration of ∼1020 cm−3 and a low mobility of ∼0.4 cm2 V−1 s−1. The specific features in the conductivity of MDF-SiC are explained by quantum effects arising in disordered systems and requiring quantum corrections to conductivity. The TEM studies confirmed the presence of disordering structural features (nanocrystalline regions) in MDF-SiC. The conductivity of MDF-SiC/Si composite originates primarily from Si component in the temperature range 1.8–500 K and since ∼500 to 600 K the contribution of MDF-SiC matrix becomes dominant

Rendimiento en natación después de un protocolo de entrenamiento excéntrico de posactivación

Aplicar ejercicios de acondicionamiento máximo mejora de forma temporal la contractilidad muscular gracias a la potenciación estimulada (PAPE). Sin embargo, se desconoce si el sistema puede mejorar su adaptabilidad al procedimiento mediante un entrenamiento basado en los propios ejercicios de acondicionamiento. Este estudio puso a prueba un protocolo de PAPE en 14 nadadores antes y después de un periodo de entrenamiento. Inicialmente, se evaluó la fuerza de los participantes tanto en extremidades inferiores como superiores. Posteriormente, se estudiaron los efectos de dos tipos de calentamiento en una prueba de natación de 50 metros, uno de ellos estándar y otro de PAPE que incluía repeticiones máximas ejecutadas en máquinas de entrenamiento excéntrico. A continuación, se aplicó un protocolo de entrenamiento de 6 semanas (2 días/semana), en el que se llevaron a cabo repeticiones máximas ejecutadas en máquinas de entrenamiento excéntrico y se volvieron a estudiar los efectos, tanto en los test de fuerza como tras la realización de ambos calentamientos. El rendimiento mejoró a los 15 m tras el PAPE en comparación con la situación estándar, pero no en las marcas posteriores. Tras las 6 semanas, se registraron incrementos en la fuerza de extremidades inferiores (14.46 %) y superiores (12.40 %). Después de aplicar el calentamiento de PAPE, aumentó la velocidad de despegue en la salida de natación y mejoró el tiempo y la velocidad de nadar a los 25, 40 y 50 metros, lo que sugiere que los participantes fueron capaces de alcanzar un mejor balance entre fatiga y potenciación.Este estudio fue financiado por los proyectos: DEP2014- 59707-P “SWIM: Specific Water Innovative Measurements applied to the development of international swimmers in short swimming events (50 and 100m)” y por: PGC2018- 102116-B-100 “SWIM II: Specif Water Innovative Measurements: applied to the improvement in performance”, financiados por el Ministerio de Economía, Industria y Competitividad (Agencia Española de Investigación) y la European Regional Development Fund (ERFD