Plane-symmetric inhomogeneous magnetized viscous fluid universe with a variable Λ\Lambda

The behavior of magnetic field in plane symmetric inhomogeneous cosmological models for bulk viscous distribution is investigated. The coefficient of bulk viscosity is assumed to be a power function of mass density $(\xi =\xi_{0}\rho^{n})$. The values of cosmological constant for these models are found to be small and positive which are supported by the results from recent supernovae Ia observations. Some physical and geometric aspects of the models are also discussed.Comment: 18 pages, LaTex, no figur

Effort Cost and Energy Optimization in human pathological movement

Movement is a fundamental characteristic of human life; almost every aspect of day-to-day life involves some sort of physical effort. Any movement, by virtue of requiring energy to perform, is aversive and people seek to increase the utility of a movement by performing it in the most energy-efficient way. Neurological conditions such as stroke and Parkinson’s disease (PD) result in impaired movement, and while medications help alleviate the symptoms to some extent in these conditions, rehabilitation is often required to aid in functional recovery. However, current interventions are incapable of restoring movement functionality to a similar level as healthy adults. This thesis takes a multi-dimensional approach to understanding how effort costs and energy optimization is altered in persons with PD and post-stroke, to provide insights into principles that can inform the design of more efficient rehabilitation strategies. In pursuit of these goals, I have used a combinatorial approach utilizing psychophysics, dynamometry, motion capture and expired gas analysis to present a holistic understanding of pathological movement. The first part of this thesis focusses on an investigation into the influence of dopamine (the gold standard treatment for PD) on the translation of physical exertions into subjective effort costs. Using a psychophysics paradigm in persons with PD ON and OFF dopaminergic medication, I determined that dopamine availability mediates the acuity of subjective effort assessment by dampening performance variability with exertion. These increased feelings of effort also increase risk aversion to prospective exertions of physical effort. The rest of the thesis focusses on effort cost of one specific movement: locomotion. Specifically, I demonstrated that persons with PD display reduced sensitivity to minimize the energy cost of walking, and dopamine mediated improvements in gait were correlated with improved energy optimization. Finally, I also assessed why persons post-stroke, despite retaining a preference for maximizing utility of walking, walk with a sub-optimal gait. I identified that there was reduced propulsion and shorter time spent on the affected leg, resulting in energetically expensive compensatory movements. Together, these findings expand on our current understanding of how objective and subjective correlates of effort demonstrate preferences for movement in neurological disorders

Simple within-stride changes in treadmill speed can drive selective changes in human gait symmetry.

Millions of people walk with asymmetric gait patterns, highlighting a need for customizable rehabilitation approaches that can flexibly target different aspects of gait asymmetry. Here, we studied how simple within-stride changes in treadmill speed could drive selective changes in gait symmetry. In Experiment 1, healthy adults (n = 10) walked on an instrumented treadmill with and without a closed-loop controller engaged. This controller changed the treadmill speed to 1.50 or 0.75 m/s depending on whether the right or left leg generated propulsive ground reaction forces, respectively. Participants walked asymmetrically when the controller was engaged: the leg that accelerated during propulsion (right) showed smaller leading limb angles, larger trailing limb angles, and smaller propulsive forces than the leg that decelerated (left). In Experiment 2, healthy adults (n = 10) walked on the treadmill with and without an open-loop controller engaged. This controller changed the treadmill speed to 1.50 or 0.75 m/s at a prescribed time interval while a metronome guided participants to step at different time points relative to the speed change. Different patterns of gait asymmetry emerged depending on the timing of the speed change: step times, leading limb angles, and peak propulsion were asymmetric when the speed changed early in stance while step lengths, step times, and propulsion impulses were asymmetric when the speed changed later in stance. In sum, we show that simple manipulations of treadmill speed can drive selective changes in gait symmetry. Future work will explore the potential for this technique to restore gait symmetry in clinical populations