2,401 research outputs found
Pulsar magnetospheres: numerical simulations of large amplitude electron-positron oscillations
The numerical simulation of non-linear electron-positron oscillations is reported, showing the evolution of the electric field and the plasma number density for large amplitude disturbances. Sharp density gradients and changes in the oscillation frequency are demonstrated, and a new analytical framework is presented to illustrate these phenomena, particularly in the context of pulsar plasmas
Interactional response during infants’ aquatic sessions
The aim of study was to assess infants’ behaviour during routine
swimming sessions using a naturalistic observation method.
The study sample included 14 infants (13.7 ± 7.5 months old)
with previous aquatic experience. The frequency of occurrences
per unit of time (session) in the different dimensions –
infant’s motor behaviour and social-affective interaction – was
registered over the course of two sessions by two independent
experts. The behaviours most frequently observed were accompanied
displacement (61.1 %) and interaction with others
(41.6 %). Submersions or jumps represented only 8.4 % of the
session. Implementing a child-centred methodology leads to
positive behaviours during this type of sessions, contributing
to the child’s healthy development.info:eu-repo/semantics/publishedVersio
A comparison of load cell and pressure sensors to measure in-water force in young competitive swimmers
The purpose of this study was to compare the in-water force of young competitive swimmers using tethered
swimming and differential pressure sensors. Thirty-one swimmers (16 girls and 15 boys) were randomly assigned
to perform two in-water tests. Swimmers completed two maximum bouts of 25 m front crawl with a differential
pressure system and a 30 s maximum bout with an attached load cell (tethered-swimming). The peak force
(FPEAK, in N) of dominant and non-dominant upper limbs was retrieved for further analysis. Comparison between
methods revealed significant differences in all force variables (p ≤ 0.05) and the biases (mean differences) were
large in girls (FPEAK dominant, 45.89 N; FPEAK non-dominant, 43.79 N) and boys (FPEAK dominant, 67.26 N; FPEAK
non-dominant, 61.78 N). Despite that, simple linear regression models between the two methods showed significant
relationships with a moderate effect in all variables for girls, whereas in boys a high and moderate effect
was verified for FPEAK of dominant and non-dominant limbs (respectively). It seems that using pressure sensors
and tethered swimming leads to different FPEAK values in young competitive, where correction factors are needed
to compare data between both methods.The authors would like to thank all swimming coaches for their
voluntary support as well as all the swimmers involved. This project was
supported by the Portuguese Foundation for Science and Technology
(FCT), I.P., under Grants 2020.08326.BD and UID 04045/2020.info:eu-repo/semantics/publishedVersio
Somatotype is more interactive with strength than fat mass and physical activity in peripubertal children
The purpose of this study was to analyse the interaction between somatotype, body fat and physical activity in
prepubescent children. This was a cross!sectional study design involving 312 children (160 girls, 152 boys) aged
between 10 and 11.5 years old (10.8 ± 0.4 years old). Evaluation of body composition was done determining body mass
index and body fat by means of skin!fold measurements, using the method described by Slaughter. Somatotype was
computed according to the Carter’s method. Physical activity was assessed with the Baecke questionnaire. The physical
activity assessment employed sets of curl!ups, push!ups, standing broad jump, medicine ball throw, handgrip strength
and Margaria!Kalamen power stair. There were negative associations for body fat, endomorphy and mesomorphy with
curl!ups, push!ups and broad jump tests and positive associations with ball throw, handgrip strength and Margaria!
Kalamen power tests. The associations for ectomorphy were the inverse of those for endomorphy and mesomorphy. Non
obese children presented higher values for curl!ups, push!ups and standing broad jump. In medicine ball throw,
handgrip strength and Margaria!Kalamen power test obese children presented higher scores, followed by children who
were overweight. The mesoectomorphic boys and ectomesomorphic girls performed higher in all tests. The morphological
typology presented more interactions with strength than % of body fat and physical activity. These data seem to suggest
that the presence/absence of certain physical characteristics is crucial in the levels of motor provision in prepubescent
children
Can concurrent teaching promote equal biomechanical adaptations at front crawl and backstroke swimming?
The biomechanical adaptations in front crawl and backstroke swimming, as influenced by the implementation of a concurrent teaching programme were analysed. Methods: Sixteen participants (19.75 ± 1.13 years) underwent a 30 weeks intervention characterized by an increasing complexity to accomplish motor skills in the following order: (i) lower limbs propulsion; (ii) lower limbs propulsion synchronized with breathing cycle; (iii) lower limbs propulsion synchronized with one upper limb action; (iv) lower limbs propulsion synchronized with both breathing cycle and one upper limb action; (v) full swimming stroke; (vi) motor trajectory of the arms
stroke. Performance and biomechanics were measured at front crawl and backstroke during three time points throughout the programme. There were improvements in performance over time at front crawl (21.49 s to 19.99 s, p < 0.01) and backstroke (27.15 s to 24.60 s, p = 0.01). Significant improvements were found for velocity at front crawl (1.13 m/s to 1.22 m/s, p < 0.01) and backstroke (0.92 m/s to 1.00 m/s, p < 0.01). Stroke frequency increased at backstroke (0.64 to 0.73 Hz, p = 0.01), while the intra-cyclic variation of the velocity
decreased at front crawl (0.13 to 0.12%, p = 0.02). There was also a moderate-high inter-subject variability in response to the programme. These findings prove that a programme of 30 weeks teaching concurrently front crawl and backstroke is effective to promote similar biomechanical adaptations in low-tier swimmers. However, each subject shows an individual response to better adapt the biomechanical actions and to reach a higher level of expertise.info:eu-repo/semantics/publishedVersio
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Establishment of a room temperature molten salt capability to measure fundamental thermodynamic properties of actinide elements
This is the final report of a six-month, Laboratory Directed Research and Development (LDRD) project at Los Alamos National Laboratory (LANL). The goal of this work was to establish a capability for the measurement of fundamental thermodynamic properties of actinide elements in room temperature molten salts. This capability will be used to study in detail the actinide chloro- and oxo-coordination chemistries that dominate in the chloride-based molten salt media. Uranium will be the first actinide element under investigation
Tentativa preliminar para desenvolver um modelo de análise (path-flow) da performance em jovens nadadoras
O objectivo do presente trabalho foi desenvolver um modelo de análise da
performance (path flow) em jovens nadadoras, com base em parâmetros antropométricos,
hidrodinâmicos, biomecânicos e bioenergéticos
Stability of elite freestyle performance from childhood to adulthood
Stability of athletic performance is important for practitioners and coaches, since it allows the selection of appropriate training
methods and prediction of ages for best results. We performed a longitudinal study of 1694 season-best performances of 242
elite-standard swimmers throughout their careers, from 12 to 18 years of age. Mean stability (descriptive statistics and oneway
repeated-measures ANOVA, followed by a Bonferroni post-hoc test) and normative stability (Cohen’s kappa tracking
index and the Pearson correlation coefficient) were determined for seven consecutive seasons. Performance improvements in
all events were observed (14.36–18.97%). Bonferroni post-hoc tests verified changes in almost all events assessed. Cohen’s
kappa demonstrated low stability (0.17–0.27) in relative performance. Pearson correlations only became high from 15 to 16
years in the 50-m and 100-m events, and from 16 to 17 years in the 200-m, 400-m, and 1500-m events. Our results show that:
(a) swimmers should display a substantial improvement (14–19%) to become elite standard as adults, such as at 18 years; (b)
16 is the age at which the ability to predict adult performance increases markedly
Tracking the freestyle performance from children to adult age
Swimming researchers are, on regular
basis, trying to identify and understand
the factors that can predict
swimming performance. For such
aim most of the research designs
adopted are cross sectional in nature.
There are few longitudinal researches
in swimming science
Monte Carlo study of the critical temperature for the planar rotator model with nonmagnetic impurities
We performed Monte Carlo simulations to calculate the
Berezinskii-Kosterlitz-Thouless (BKT) temperature for the
two-dimensional planar rotator model in the presence of nonmagnetic impurity
concentration . As expected, our calculation shows that the BKT
temperature decreases as the spin vacancies increase. There is a critical
dilution at which . The effective interaction
between a vortex-antivortex pair and a static nonmagnetic impurity is studied
analytically. A simple phenomenological argument based on the pair-impurity
interaction is proposed to justify the simulations.Comment: 5 pages, 5 figures, Revetex fil
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