THE ROLE OF PREVIOUS ANTERIOR CRUCIATE LIGAMENT INJURY ON THE VARIABILITY OF JOINT KINEMATICS AND COORDINATION DURING A MATCH SPECIFIC LAND-CUT TASK

This study compared the movement and coordination variability of the previously injured leg of ACL injured subjects (ACLr, n=9), against their non-injured leg and a control (nACL, n=9) leg. The variability of lower limb joint angles and couplings were calculated during a land-cut task (n=20). The previously injured leg had less variability than the noninjured leg in the knee rotation–knee abd-adduction coupling, and more variability than the nACL leg in frontal and transverse knee joint angles and hip rotation–knee abdadduction coupling. Reduced coordination variability could produce a more repetitive loading pattern linked to cartilage degeneration. Increased movement and coordination variability may stem from proprioceptive deficits on the previously injured leg and decrease the ability to adapt to perturbations

Local temperature-sensitive mechanisms are important mediators of limb tissue hyperemia in the heat-stressed human at rest and during small muscle mass exercise.

Limb tissue and systemic blood flow increases with heat stress, but the underlying mechanisms remain poorly understood. Here, we tested the hypothesis that heat stress-induced increases in limb tissue perfusion are primarily mediated by local temperature-sensitive mechanisms. Leg and systemic temperatures and hemodynamics were measured at rest and during incremental single-legged knee extensor exercise in 15 males exposed to 1 h of either systemic passive heat-stress with simultaneous cooling of a single leg (n=8) or isolated leg heating or cooling (n=7). Systemic heat-stress increased core, skin and heated leg blood (Tb) temperatures, cardiac output and heated leg blood flow (LBF, 0.6 ± 0.1 l.min(-1); P0.05). Increased heated leg deep tissue BF was closely related to Tb (R(2) = 0.50; P0.05), despite unchanged systemic temperatures and hemodynamics. During incremental exercise, heated LBF was consistently maintained ~ 0.6 l.min(-1) higher than that in the cooled leg (P<0.01), with LBF and vascular conductance in both legs showing a strong correlation with their respective local Tb (R(2) = 0.85 and 0.95, P<0.05). We conclude that local temperature-sensitive mechanisms are important mediators in limb tissue perfusion regulation both at rest and during small-muscle mass exercise in hyperthermic humans.The invasive study was partially funded by Gatorade Sports Science Institute, PepsiCo

Pulper vertical de 12 m3 de capacitat

El present Projecte Final de Carrera té com a títol “Pulper vertical de 12m3 de capacitat” i el principal objectiu que persegueix és la de dissenyar aquesta màquina i donar la informació suficient per a la seva fabricació, si es donés el cas. Un pulper és una màquina que intervé en la fabricació de paper tant si és a partir de cel·lulosa com a partir d’altre paper reciclat. El pulper és la primera d’una llarga cadena de màquines que es necessiten per a obtenir aquest paper i la seva missió és la de fer una primera barreja entre el paper reciclat i/o la cel·lulosa amb aigua al 4-5% de paper. Aquesta barreja posteriorment es millorarà i s’anirà progressivament premsant i assecant fins arribar al paper pròpiament dit. Un pulper consta d’un recipient, que en el nostre cas tindrà un volum operatiu de 12 m3 i estarà fet de xapa d’acer i d’un ròtor (amb eix vertical) que està format per diversos elements com l’hèlix, l’eix, els rodaments, la carcassa, etc. La transmissió d’aquest pulper serà per corretja i també està englobada i dissenyada en aquest projecte. En aquest projecte s’han perseguit també altres objectius a part del de dissenyar pròpiament el pulper, ja sigui per decisió del projectista com per requeriments de la màquina en si mateixa, per tal de que tingui un funcionament idoni. S’ha intentat simplificar la màquina en tot el possible amb diverses accions com la de treure la lubricació posant rodaments autolubricats per tal de facilitar el muntatge i desmuntatge del pulper per a la seva neteja. També s’ha perseguit el proporcionar una superfície el més llisa possible a l’interior del recipient del pulper per evitar problemes amb l’adherència de fibres de paper als diferents òrgans de la màquina i així, una erosió excessivament ràpida. S’han aïllat les zones que contenen líquid per tal de que no hi apareguin fuites que facin perdre rendiment a la màquina i desgastin els diferents elements del pulper. Com a últim objectiu important també citar que s’ha perseguit acabar amb el disseny de la màquina amb un pressupost assumible i competitiu en la mesura de les possibilitats del projectista

The walking robot project

A walking robot was designed, analyzed, and tested as an intelligent, mobile, and a terrain adaptive system. The robot's design was an application of existing technologies. The design of the six legs modified and combines well understood mechanisms and was optimized for performance, flexibility, and simplicity. The body design incorporated two tripods for walking stability and ease of turning. The electrical hardware design used modularity and distributed processing to drive the motors. The software design used feedback to coordinate the system and simple keystrokes to give commands. The walking machine can be easily adapted to hostile environments such as high radiation zones and alien terrain. The primary goal of the leg design was to create a leg capable of supporting a robot's body and electrical hardware while walking or performing desired tasks, namely those required for planetary exploration. The leg designers intent was to study the maximum amount of flexibility and maneuverability achievable by the simplest and lightest leg design. The main constraints for the leg design were leg kinematics, ease of assembly, degrees of freedom, number of motors, overall size, and weight

Charge density plateaux and insulating phases in the t−Jt-J model with ladder geometry

We discuss the occurrence and the stability of charge density plateaux in ladder-like $t-J$ systems (at zero magnetization M=0) for the cases of 2- and 3-leg ladders. Starting from isolated rungs at zero leg coupling, we study the behaviour of plateaux-related phase transitions by means of first order perturbation theory and compare our results with Lanczos diagonalizations for $t-J$ ladders ($N=2\times 8$) with increasing leg couplings. Furthermore we discuss the regimes of rung and leg couplings that should be favoured for the appearance of the charge density plateaux.Comment: 10 pages, 7 figures, RevTex

Cable-Driven Actuation for Highly Dynamic Robotic Systems

This paper presents design and experimental evaluations of an articulated robotic limb called Capler-Leg. The key element of Capler-Leg is its single-stage cable-pulley transmission combined with a high-gap radius motor. Our cable-pulley system is designed to be as light-weight as possible and to additionally serve as the primary cooling element, thus significantly increasing the power density and efficiency of the overall system. The total weight of active elements on the leg, i.e. the stators and the rotors, contribute more than 60% of the total leg weight, which is an order of magnitude higher than most existing robots. The resulting robotic leg has low inertia, high torque transparency, low manufacturing cost, no backlash, and a low number of parts. Capler-Leg system itself, serves as an experimental setup for evaluating the proposed cable- pulley design in terms of robustness and efficiency. A continuous jump experiment shows a remarkable 96.5 % recuperation rate, measured at the battery output. This means that almost all the mechanical energy output used during push-off returned back to the battery during touch-down

Analysis of walking with unilateral exoskeleton assistance compared to bilateral assistance with matched work

The finding of the highest negative metabolic rate versus mechanical work ratio in the Bilateral Matched Total Work condition means that if a constrained amount of mechanical work is available (e.g. from a battery) it is more advanta- geous to distribute this work evenly over both legs. The EMG reductions in the unassisted leg also suggest that if the goal is to maximize assistance to one (impaired) leg it might still be advantageous to use a bilateral exoskeleton, perhaps with a different actuation pattern for each leg that is specifically optimized such that each exoskeleton side assists specific phases in the impaired leg

Understanding the three and four-leg inverter Space Vector

This paper shows a new point of view of the classical voltage space vectors and its implications on three and four-leg converters. It is easy to find in the literature, authors using bi-dimensional and threedimensional representations of the converter states. Nonetheless, the literature rarely specifies what these spaces represent. Therefore, this paper proposes a wide analysis of the state voltages and its references for three-leg, three-leg four-wire and four-leg inverters, in favour of understanding the space vector behaviour under three and four-wire scenarios.Postprint (published version

Don't break a leg: Running birds from quail to ostrich prioritise leg safety and economy in uneven terrain

Cursorial ground birds are paragons of bipedal running that span a 500-fold mass range from quail to ostrich. Here we investigate the task-level control priorities of cursorial birds by analysing how they negotiate single-step obstacles that create a conflict between body stability (attenuating deviations in body motion) and consistent leg force–length dynamics (for economy and leg safety). We also test the hypothesis that control priorities shift between body stability and leg safety with increasing body size, reflecting use of active control to overcome size-related challenges. Weight-support demands lead to a shift towards straighter legs and stiffer steady gait with increasing body size, but it remains unknown whether non-steady locomotor priorities diverge with size. We found that all measured species used a consistent obstacle negotiation strategy, involving unsteady body dynamics to minimise fluctuations in leg posture and loading across multiple steps, not directly prioritising body stability. Peak leg forces remained remarkably consistent across obstacle terrain, within 0.35 body weights of level running for obstacle heights from 0.1 to 0.5 times leg length. All species used similar stance leg actuation patterns, involving asymmetric force–length trajectories and posture-dependent actuation to add or remove energy depending on landing conditions. We present a simple stance leg model that explains key features of avian bipedal locomotion, and suggests economy as a key priority on both level and uneven terrain. We suggest that running ground birds target the closely coupled priorities of economy and leg safety as the direct imperatives of control, with adequate stability achieved through appropriately tuned intrinsic dynamics