Joint Moments and Powers in Healthy Young Adults During Stair Negotiation

The primary objective of this study was to determine lower limb joint moments and powers of stair negotiation in healthy young individuals. These results will provide baseline information for future studies with elderly and clinical populations designed to prevent falls that occur during stair negotiation. In previous stair negotiation studies, researchers investigated joint moments and powers initiating stair ascent in front of the stairway. Starting farther away from the stairway allows individuals to stabilize gait velocity and thus, exclude the influence of velocity on joint moments and powers generated during stair ascent. Ten young, healthy individuals underwent gait analysis during stair negotiation. Two way repeated measures ANOVA was used to determine the differences between two different conditions, starting farther away from the stairway (C1) and starting in front of the stairway (C2), for two consecutive steps (s1 and s2) on the stairway performed by the same leg. A motion analysis system was used to collect the three-dimensional spatial trajectories of the markers (joint angle data). Ground reaction forces were collected using two AMTI force platforms embedded in the first and the third stair treads. Our results demonstrated that ankle power absorption (PA1) was significantly higher during the s1 and s2 in C1 than during the s1 in C2. PA1 was significantly greater during s2 than during s1 in condition 2. Ankle power generation (PA2) was significantly higher during s2 than s1 in C1. The hip power absorption (PH2) was significantly higher during s1 in C1 than during s2 in C1, and s1 and s2 in C2. PH2 was significantly higher during s1 in C2 than s2 in both C1 and C2. These findings iv showed that the way individuals approach stairs will have a different affect on the ankle and the hip joints which has to be considered in future studies in stair negotiation

Discrete-Time Sliding Mode Control with Integral Compensation of Output Error

In this paper, a simple new design method of the sliding mode control based on the integral compensation of an output error is described. The key to this method is to obtain a control with a switching function. The proposed linear control input is robust against plant parameter deviations and external disturbances. We confirmed the effectiveness of the proposed method through simulation of a second and a third order plant

A Discrete-Time Sliding Mode Controller for the Fermentation Process

This paper proposes a discrete-time sliding mode controller for the fermentation process, which is adequately approximated by the first-order plus dead time model. The contribution of the paper is an investigation into the suitable approximation of the time delay for discrete-time sliding mode controller. The dead time is considered in two ways by the first-order Taylor series approximation and the first-order Pade approximation. In the first case, the discrete-time sliding mode controller is based on the integral compensation of an output error, and in the second case, the stable system centre method is used. Numerical simulation examples of the yeast fermentation process are given to show the effectiveness of these two methods

Energy metabolism in human pluripotent stem cells and their differentiated counterparts

Background: Human pluripotent stem cells have the ability to generate all cell types present in the adult organism, therefore harboring great potential for the in vitro study of differentiation and for the development of cell-based therapies. Nonetheless their use may prove challenging as incomplete differentiation of these cells might lead to tumoregenicity. Interestingly, many cancer types have been reported to display metabolic modifications with features that might be similar to stem cells. Understanding the metabolic properties of human pluripotent stem cells when compared to their differentiated counterparts can thus be of crucial importance. Furthermore recent data has stressed distinct features of different human pluripotent cells lines, namely when comparing embryo-derived human embryonic stem cells (hESCs) and induced pluripotent stem cells (IPSCs) reprogrammed from somatic cells. Methodology/Principal Findings: We compared the energy metabolism of hESCs, IPSCs, and their somatic counterparts. Focusing on mitochondria, we tracked organelle localization and morphology. Furthermore we performed gene expression analysis of several pathways related to the glucose metabolism, including glycolysis, the pentose phosphate pathway and the tricarboxylic acid (TCA) cycle. In addition we determined oxygen consumption rates (OCR) using a metabolic extracellular flux analyzer, as well as total intracellular ATP levels by high performance liquid chromatography (HPLC). Finally we explored the expression of key proteins involved in the regulation of glucose metabolism. Conclusions/Findings: Our results demonstrate that, although the metabolic signature of IPSCs is not identical to that of hESCs, nonetheless they cluster with hESCs rather than with their somatic counterparts. ATP levels, lactate production and OCR revealed that human pluripotent cells rely mostly on glycolysis to meet their energy demands. Furthermore, our work points to some of the strategies which human pluripotent stem cells may use to maintain high glycolytic rates, such as high levels of hexokinase II and inactive pyruvate dehydrogenase (PDH). © 2011 Varum et al