P 097—Metabolic cost of transport in over-ground and treadmill walking of healthy elderly and effects of a treadmill familiarization protocol

Background: Previous research has shown that the mechanics of walking on a treadmill is similar to walking overground. However it might be true that the energetics of walking is not similar between overground and treadmill, especially for older adults. We hypothesized that a lack of or inadequate familiarization on a treadmill would increase the Metabolic Cost of Transport (MCoT) in older adults due to increased levels of anxiety and the novelty of the locomotor task. Methods: 10 healthy elderly (5 males and 5 females, mean age of 75.3 SD(6.3) years) were recruited and they walked first at their overground Preferred Walking Speed (PWS) for 8 min to reach a steady state of oxygen consumption in the morning. After that the same speed was imposed on a dual-belt treadmill and they walked for 15 min to properly familiarize themselves with the treadmill. This was called the familiarization session (Session 1). In the afternoon they repeated both the overground and treadmill walking again in the same order and with the same protocol. This session was called the post-familiarization session (Session 2). Results: The group average of the overground PWS was 1.28 SD(0.11) m/s (4.61 SD(0.40) km/hr). During the familiarization session, the group average of the Gross Cost of Transport (GCoT) was 3.47 SD(0.35) J/kg/m while walking overground and 4 SD(0.65) J/kg/m while walking on a treadmill. The Net Cost of Transport (NCoT) was 2.64 SD(0.37) J/kg/m while walking overground and 3.14 SD(0.64) J/kg/m while walking on a treadmill. During the post-familiarization session, the group average of the GCoT was 3.84 SD(0.35) J/kg/m while walking overground and 3.94 SD(0.67) J/kg/m while walking on a treadmill. The NCoT was 2.76 SD(0.39) J/kg/m while walking overground and 2.90 SD(0.68) J/kg/m while walking on a treadmill. Both the GCoT and NCoT were statistically significantly higher on a treadmill than overground during the familiarization session. This elevation was not present during the post-familiarization session. There were also no statistically significant differences in the Resting Metabolic Rate (RMR) between before walking overground and before walking on a treadmill in either the familiarization or the post-familiarization session. Discussion and Conclusion: This shows that the energetics of walking can be different for even healthy elderly on a treadmill if they are not or inadequately familiarized to it. This underlines the importance of adequate familiarization to treadmill walking for elderly in trying to understand the MCoT in this population

Quantum Phase Transitions in Josephson Junction Chains

We investigate the quantum phase transition in a one-dimensional chain of ultra-small superconducting grains, considering both the self- and junction capacitances. At zero temperature, the system is transformed into a two-dimensional system of classical vortices, where the junction capacitance introduces anisotropy in the interaction between vortices. This leads to the superconductor-insulator transition of the Berezinskii-Kosterlitz-Thouless type, as the ratios of the Josephson coupling energy to the charging energies are varied. It is found that the junction capacitance plays a role similar to that of dissipation and tends to suppress quantum fluctuations; nevertheless the insulator region survives even for arbitrarily large values of the junction capacitance.Comment: REVTeX+5 EPS figures, To appear in PRB Rapid

Exchange-correlation energy of a hole gas including valence band coupling

We have calculated an accurate exchange-correlation energy of a hole gas, including the complexities related to the valence band coupling as occurring in semiconductors like GaAs, but excluding the band warping. A parametrization for the dependence on the density and the ratio between light- and heavy-hole masses is given. We apply our results to a hole gas in an AlxGa1-xAs/GaAs/AlxGa1-xAs quantum well and calculate the two-dimensional band structure and the band-gap renormalization. The inclusion of the valence band coupling in the calculation of the exchange-correlation potentials for holes and electrons leads to a much better agreement between theoretical and experimental data than when it is omitted

Effects of fatigue of plantarflexors on control and performance in vertical jumping

INTRODUCTION: We investigated the effects of a mismatch between control and musculoskeletal properties on performance in vertical jumping. METHODS: Six subjects performed maximum-effort vertical squat jumps before (REF) and after the plantarflexors of the right leg had been fatigued (FAT) while kinematic data, ground reaction forces, and EMG of leg muscles were collected. Inverse dynamics was used to calculate the net work at joints, and EMG was rectified and smoothed to obtain the smoothed rectified EMG (SREMG). The jumps of the subjects were also simulated with a musculoskeletal model comprising seven body segments and 12 Hill-type muscles, and having as only input muscle stimulation. RESULTS: Jump height was approximately 6 cm less in FAT jumps than in REF jumps. In FAT jumps, peak SREMG level was reduced by more than 35% in the right plantarflexors and by approximately 20% in the right hamstrings but not in any other muscles. In FAT jumps, the net joint work was reduced not only at the right ankle (by 70%) but also at the right hip (by 40%). Because the right hip was not spanned by fatigued muscles and the reduction in SREMG of the right hamstrings was relatively small, this indicated that the reduction in performance was partly due to a mismatch between control and musculoskeletal properties. The differences between REF and FAT jumps of the subjects were confirmed and explained by the simulation model. Reoptimization of control for the FAT model caused performance to be partly restored by approximately 2.5 cm. CONCLUSION: The reduction in performance in FAT jumps was partly due to a mismatch between control and musculoskeletal properties. © 2011 The American College of Sports Medicine

3-D kinematic comparison of treadmill and overground running.

Studies investigating the mechanics of human movement are often conducted using the treadmill. The treadmill is an attractive device for the analysis of human locomotion. Studies comparing overground and treadmill running have analyzed discrete variables, however differences in excursion from footstrike to peak angle and range of motion during stance have yet to be examined. This study aimed to examine the 3-D kinematics of the lower extremities during overground and treadmill locomotion to determine the extent to which the two modalities differ. Twelve participants ran at 4.0m/s in both treadmill and overground conditions. 3-D angular kinematic parameters during the stance phase were collected using an eight camera motion analysis system. Hip, knee and ankle joint kinematics were quantified in the sagittal, coronal and transverse planes, then compared using paired t-tests. Of the parameters analyzed hip flexion at footstrike 12° hip range of motion 17°, peak hip flexion 12.7°, hip transverse plane range of motion 8° peak knee flexion 5° and peak ankle excursion range 6.6°, coronal plane ankle angle at toe-off 6.5° and peak ankle eversion 6.3° were found to be significantly different. These results lead to the conclusion that the mechanics of treadmill locomotion cannot be generalized to overground

Effect of Coulomb scattering from trapped charges on the mobility in an organic field-effect transistor

We investigate the effect of Coulomb scattering from trapped charges on the mobility in the two-dimensional channel of an organic field-effect transistor. The number of trapped charges can be tuned by applying a prolonged gate bias. Surprisingly, after increasing the number of trapped charges to a level where strong Coulomb scattering is expected, the mobility has decreased only slightly. Simulations show that this can be explained by assuming that the trapped charges are located in the gate dielectric at a significant distance from the channel instead of in or very close to the channel. The effect of Coulomb scattering is then strongly reduced

Influence of the Characteristics of the STM-tip on the Electroluminescence Spectra

We analyze the influence of the characteristics of the STM-tip (applied voltage, tip radius) on the electroluminescence spectra from an STM-tip-induced quantum dot taking into account the many-body effects. We find that positions of electroluminescence peaks, attributed to the electron-hole recombination in the quantum dot, are very sensitive to the shape and size of the confinement potential as determined by the tip radius and the applied voltage. A critical value of the tip radius is found, at which the luminescence peak positions as a function of the tip radius manifest a transition from decreasing behavior for smaller radii to increasing behavior for larger radii. We find that this critical value of the tip radius is related to the confinement in the lateral and normal direction.Comment: 15 pages, 5 figure

The effect of induced forelimb lameness on thoracolumbar kinematics during treadmill locomotion

Reasons for performing study: Lameness has often been suggested to result in altered movement of the back, but there are no detailed studies describing such a relationship in quantitative terms. Objectives: To quantify the effect of induced subtle forelimb lameness on thoracolumbar kinematics in the horse. Methods: Kinematics of 6 riding horses was measured at walk and at trot on a treadmill before and after the induction of reversible forelimb lameness grade 2 (AAEP scale 1-5). Ground reaction forces (GRF) for individual limbs were calculated from kinematics. Results: The horses significantly unloaded the painful limb by 11.5% at trot, while unloading at walk was not significant. The overall flexion-extension range of back motion decreased on average by 0.2° at walk and increased by 3.3° at trot (P<0.05). Changes in angular motion patterns of vertebral joints were noted only at trot, with an increase in flexion of 0.9° at T10 (i.e. angle between T6, T10 and T13) during the stance phase of the sound diagonal and an increase in extension of the thoracolumbar area during stance of the lame diagonal (0.7° at T13, 0.8° at T17, 0.5° at L1, 0.4° at L3 and 0.3° at L5) (P<0.05). Lameness further caused a lateral bending of the cranial thoracic vertebral column towards the lame side (1.3° at T10 and 0.9° at T13) (P<0.05) during stance of the lame diagonal. Conclusions: Both range of motion and vertebral angular motion patterns are affected by subtle forelimb lameness. At walk, the effect is minimal, at trot the horses increased the vertebral range of motion and changed the pattern of thoracolumbar motion in the sagittal and horizontal planes, presumably in an attempt to move the centre of gravity away from the lame side and reduce the force on the affected limb. Potential relevance: Subtle forelimb lameness affects thoracolumbar kinematics. Future studies should aim at elucidating whether the altered movement patterns lead to back and/or neck dysfunction in the case of chronic lameness

The effect of deuteration on organic magnetoresistance

NOTICE: this is the author’s version of a work that was accepted for publication in Synthetic Metals. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in SYNTHETIC METALS, 161, 7-8, (2011) DOI 10.1016/j.synthmet.2010.11.04