Several simple mono- and disaccharides have been assessed for their ability to inhibit ice recrystallization. Two carbohydrates were found to be effective recrystallization inhibitors. D-galactose (1) was the best monosaccharide and D-melibiose (5) was the most active disaccharide. The ability of each carbohydrate to inhibit ice growth was correlated to its respective hydration number reported in the literature. A hydration number reflects the number of tightly bound water molecules to the carbohydrate and is a function of carbohydrate stereochemistry. It was discovered that using the absolute hydration number of a carbohydrate does not allow one to accurately predict its ability to inhibit ice recrystallization. Consequently, we have defined a hydration index in which the hydration number is divided by the molar volume of the carbohydrate. This new parameter not only takes into account the number of water molecules tightly bound to a carbohydrate but also the size or volume of a particular solute and ultimately the concentration of hydrated water molecules. The hydration index of both mono- and disaccharides correlates well with experimentally measured RI activity. C-Linked derivatives of the monosaccharides appear to have RI activity comparable to that of their O-linked saccharides but a more thorough investigation is required. The relationship between carbohydrate concentration and RI activity was shown to be noncolligative and a 0.022 M solution of D-galactose (1) and C-linked galactose derivative (10) inhibited recrystallization as well as a 3% DMSO solution. The carbohydrates examined in this study did not possess any thermal hysteresis activity (selective depression of freezing point relative to melting point) or dynamic ice shaping. As such, we propose that they are inhibiting recrystallization at the interface between bulk water and the quasi liquid layer (a semiordered interface between ice and bulk water) by disrupting the preordering of water.
RESUMOIntrodução: Analisar as tendências seculares ao nível da antropometria e aptidão física das crianças portuguesas. Material e Métodos: Um grupo de 1819 crianças (881 rapazes e 938 raparigas) entre os 10 e os 11 anos de idade, foi avaliado no 5º e 6º ano de escolaridade durante 20 anos. A ANCOVA foi usada para analisar as variações de antropometria (índice de massa corporal, peso e altura) e aptidão física (sentar e alcançar, força abdominal, salto horizontal e corrida de velocidade) durante quatro quinquénios (1993 -1998; 1998 -2003; 2003 -2008 e 2008 -2013 (1993 -1998; 1998 -2003; 2003 -2008; 2008 -2013).Results: Secular trends showed the presence of heavier boys and girls with higher body mass index in the 5 th and 6 th grade throughout the last 20 years. There was also a presence of taller girls but just until the 3 rd quinquennial. Both boys and girls were able to perform better on the core strength test and sprint time but become less flexible over the years. Mean jumping performance remained unchanged for both genders. Discussion: The present study provides novel data on anthropometrics and physical fitness trends over the last two decades in young Portuguese children, consistent with the results reported in other developed countries. Conclusion: Evidence for the start of a positive secular trend in body mass index and in some physical fitness components over the last two decades among the Portuguese youth.
We introduce a method for quantification of movement sway--spontaneous migrations of the center of pressure (COP) during its voluntary shifts. Subjects stood on a force platform or on a board with a narrow support surface ("unstable board") and performed voluntary cyclic shifts of the COP at different frequencies. Movement sway was typically higher than postural sway; sway in the mediolateral direction was particularly increased. Movement sway showed a drop with the frequency of voluntary COP shifts. During standing on the unstable board, postural sway increased while movement sway decreased. The effects of task parameters were stronger on the sway component in the direction of the voluntary COP shift than in the orthogonal direction. We interpret changes in movement sway with task parameters as partly resulting from modulation of the search function of sway during voluntary COP shifts.
The aim of this study was to analyse the relative age effect (RAE) in competitive swimming. The best 50 Portuguese swimmers (12- to 18-year-olds) for the main individual swimming pool events of both genders were considered. Analysis was conducted on 7813 swimming event participants, taking account of respective swimmer birth dates and the Fédération Internationale de Natation points gained. Differences in the distribution of birth dates by quarter year were determined using the Chi-square. A one-way analysis of variance ANOVA was used to test for differences measured in points between individuals by quarterly birth year intervals. A two-way analysis of variance ANOVA was also conducted to test the interaction between gender and seasonal birth date with regard to performance. The results show an inequitable distribution (p<0.01) of birth dates by quarter for almost all age groups and both genders. However, the distribution of birth dates by quarter for each considered swim event shows that RAE seems to exist only for 12-year-old females and 12- to 15-year-old males. Analysing mean swimming performance, post-hoc results (p<0.01) show no consistency in RAE. Higher performance occurs among older swimmers only in 100 m butterfly (female 1998, 1st≠2nd quarter, p=0.003). The results also show no interaction between gender and seasonal birth date (p<0.01). Findings of this study show that a higher number of swimmers, particular males, are born in the first two quarters of the year, although there is mostly no effect of seasonal birth date on performance differences within the top 50 swimmers.
The aim of the study was to assess deep and shallow water teaching methods in swimming lessons for preschool children and identify variations in the basic aquatic skills acquired. The study sample included 32 swimming instructors (16 from deep water programs and 16 from shallow water programs) and 98 preschool children (50 from deep water swimming pool and 48 from shallow water swimming pool). The children were also studied regarding their previous experience in swimming (6, 12 and 18 months or practice). Chi-Square test and Fisher’s exact test were used to compare the teaching methodology. A discriminant analysis was conducted with Λ wilk’s method to predict under what conditions students are better or worse (aquatic competence).Results suggest that regardless of the non-significant variations found in teaching methods, the water depth can affect aquatic skill acquisition - shallow water lessons seem to impose greater water competence particularly after 6 months of practice. The discriminant function revealed a significant association between groups and all predictors for 6 months of swimming practice (p<0.001). Body position in gliding and leg displacements were the main predictors. For 12 and 18 months of practice, the discriminant function do not revealed any significant association between groups. As a conclusion, it seems that the teaching methodology of aquatic readiness based on deep and shallow water programs for preschoolers is not significantly different. However, shallow water lessons could be preferable for the development of basic aquatic skills.
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