Myoelectric activity along human gastrocnemius medialis: Different spatial distributions of postural and electrically elicited surface potentials

It has recently been shown that motor units in human medial gastrocnemius (MG), activated during standing, occupy relatively small territories along the muscle's longitudinal axis. Such organisation provides potential for different motor tasks to produce differing regional patterns of activity. Here, we investigate whether postural control and nerve electrical stimulation produce equal longitudinal activation patterns in MG. Myoelectric activity, at different proximal-distal locations of MG, was recorded using a linear electrode array. To ensure differences in signal amplitude between channels did not result from local, morphological factors two experimental protocols were completed: (i) quiet standing; (ii) electrical stimulation of the tibial nerve. Averaged, rectified values (ARVs) were calculated for each channel in each condition. The distribution of signals along electrode channels was described using linear regression and differences between protocols at each channel determined as the ratio between mean ARV from standing: stimulation protocols. Ratio values changed systematically across electrode channels in seven (of eight) participants, with larger values in distal channels. The distribution of ARV along MG therefore differed between experimental conditions. Compared to fibres of units activated during MG nerve stimulation, units activated during standing may have a tendency to be more highly represented in the distal muscle portion. © 2012 Elsevier Lt

Seleção efetiva para o caráter número de afilhos em populações segregantes de trigo Selection eficiency for tillerning in segregating wheat populations

O ganho genético obtido com a seleção em gerações segregantes é dependente do cruzamento, das condições experimentais e do caráter alvo de seleção. O objetivo deste trabalho foi determinar o ganho com a seleção em planta espaçada, na geraç��o F2 para número de afilhos, utilizando diferentes critérios de seleção, além de verificar a efetividade destas seleções na geração subseqüente, nos métodos de semeadura deplanta espaçada e linha cheia. As gerações segregantes foram desenvolvidos em 2006 (F2) e 2007 (F2 e F3), sendo a geração F3 avaliada em planta espaçada e linha cheia. Foram empregados três critérios de seleção: a) elevado número de afilhos e alta produção de grãos; b) reduzido número de afilhos com elevada produção de grãos e c) bulk da população. Foram testadas 15 combinações envolvendo genitores com diferente potencial de afilhamento. Os resultados indicam que mesmo em reduzida magnitude, as estimativas de herdabilidade para estimar a média da próxima geração, revelaram eficiência, porém, somente quando as gerações utilizadas foram desenvolvidas em iguais condições de ambiente e manejo. A seleção para elevado ou reduzido número de afilhos e em bulk, foram dependentes do sistema de manejo em que a população segregante tenha sido submetida. A seleção para elevado número de afilhos revelou o maior ganho genético para produção de grãos, porém, a efetividade da seleção em planta espaçada não proporcionou o mesmo comportamento em competição. O melhor desempenho em rendimento de grãos foi detectado na seleção para reduzido número de afilhos, com média elevada para massa de grãos em competição.<br>The genetic gain obtained with the selection in segregating generations depends on the cross, experimental conditions and the target trait selected. The objective of this work was to determine the genetic gain with selection in spaced plants, in the F2 generation for the character number of tillers, using different selection criteria. In addition it aimed at to verify the effectiveness of these selections by looking at next generations of plants selected by the spaced plant and full row methods. The segregating generations were conducted in the years 2006 (F2) and 2007 (F2 and F3), being the F3 generation evaluated as spaced plant and full row. Three selection criteria were used: i) high tiller number and grain production; ii) low tiller number with high grain production and iii) a bulk of 15 parental genotypes with different tillering potential. The results pointed out that heritability estimates were efficient for the prediction of next generation means when the generations used were under the same environmental and management conditions. The efficiency of the selection for high or low tillering ability and the bulk selection were dependent of the crop management system used. The selection for high tiller number was associated to a higher genetic gain for grain production. However, the efficiency of the selection was different when spaced and competing plants are compared. The best performance for grain yield was achieved selecting for low tiller number in competing plants, resulted in higher total grain weight

Conductividad hidráulica en un suelo aluvial en respuesta al porcentaje de sodio intercambiable Saturated hydraulic conductivity of an alluvial soil with different exchangeable sodium percentages

El efecto del porcentaje de sodio intercambiable (PSI) sobre la conductividad hidráulica de un suelo saturado, fue estudiado en condiciones de laboratorio a través de la determinación de las relaciones entre la conductividad hidráulica medida en un suelo normal y las medidas en suelos con diferentes PSI. Los resultados muestran una gran reducción de la conductividad hidráulica con el aumento de sodio en el suelo, llegando esta reducción a ser en las muestras más sodificadas de casi 100%, cuando comparadas con las muestras sin sodio, hecho probablemente acontecido debido al efecto dispersante del sodio sobre las partículas del suelo.<br>The effect of different exchangeable sodium percentages (ESP) on the saturated hydraulic conductivity of a soil was studied under laboratory conditions by determining the relationship between the hydraulic conductivity of a normal soil and that measured on soil with different ESP. The results show a great reduction in the saturated hydraulic conductivity with the increase of the exchangeable sodium percentage in the soil, this reduction being as great as 100% on the highly sodified samples when compared with those which did not receive sodium treatment. This fact is explained due to the dispersing effect of the exchangeable sodium on the soil particles