Réhabilitation à l'aide de matériaux composites avancés de poutres en béton armé du système Kahn

Plusieurs structures en béton armé construites il y a maintenant près de 70 ans présentent aujourd'hui des défaillances et une capacité inadéquate ne répondant plus aux besoins dictés par un nouvel usage. La réhabilitation de ces structures présente un défi de taille pour l'ingénieur qui doit trouver des solutions économiques et techniquement viables pour rendre ces bâtiments sécuritaires. Le renforcement des structures en béton armé avec l'aide de matériaux composites avancés (MCA) offre une solution intéressante. Les MCA possèdent des caractéristiques avantageuses et sont d'application facile. Plusieurs structures à travers le monde ont été renforcées avec ce type de matériaux. Nous présentons dans ce mémoire les résultats expérimentaux et théoriques sur le renforcement à l'aide de MCA de poutres armées du système d'armature Kahn. Les poutres, au nombre de trois, proviennent de l'édifice Eaton situé sur la rue Ste-Catherine à Montréal. Des essais à quatre points pour la résistance en flexion et à trois points pour la résistance en cisaillement ont été préalablement effectués dans le but d'évaluer expérimentalement la capacité des poutres avant leur réhabilitation

Miniaturized Low-Voltage Power Converters With Fast Dynamic Response

This paper demonstrates a two-stage approach for power conversion that combines the strengths of variable-topology switched capacitor techniques (small size and light-load performance) with the regulation capability of magnetic switch-mode power converters. The proposed approach takes advantage of the characteristics of complementary metal-oxide-semiconductor (CMOS) processes, and the resulting designs provide excellent efficiency and power density for low-voltage power conversion. These power converters can provide low-voltage outputs over a wide input voltage range with very fast dynamic response. Both design and fabrication considerations for highly integrated CMOS power converters using this architecture are addressed. The results are demonstrated in a 2.4-W dc-dc converter implemented in a 180-nm CMOS IC process and co-packaged with its passive components for high performance. The power converter operates from an input voltage of 2.7-5.5 V with an output voltage of ≤1.2 V, and achieves a 2210 W/in[superscript 3] power density with ≥80% efficiency.Focus Center Research ProgramUnited States. Defense Advanced Research Projects AgencySemiconductor Research CorporationCharles Stark Draper Laborator

Multi-Muscle FES Force Control of the Human Arm for Arbitrary Goals

We present a method for controlling a neuroprosthesis for a paralyzed human arm using functional electrical stimulation (FES) and characterize the errors of the controller. The subject has surgically implanted electrodes for stimulating muscles in her shoulder and arm. Using input/output data, a model mapping muscle stimulations to isometric endpoint forces measured at the subject’s hand was identified. We inverted the model of this redundant and coupled multiple-input multiple-output system by minimizing muscle activations and used this inverse for feedforward control. The magnitude of the total root mean square error over a grid in the volume of achievable isometric endpoint force targets was 11% of the total range of achievable forces. Major sources of error were random error due to trial-to-trial variability and model bias due to nonstationary system properties. Because the muscles working collectively are the actuators of the skeletal system, the quantification of errors in force control guides designs of motion controllers for multi-joint, multi-muscle FES systems that can achieve arbitrary goals

Toward the Restoration of Hand Use to a Paralyzed Monkey: Brain-Controlled Functional Electrical Stimulation of Forearm Muscles

Loss of hand use is considered by many spinal cord injury survivors to be the most devastating consequence of their injury. Functional electrical stimulation (FES) of forearm and hand muscles has been used to provide basic, voluntary hand grasp to hundreds of human patients. Current approaches typically grade pre-programmed patterns of muscle activation using simple control signals, such as those derived from residual movement or muscle activity. However, the use of such fixed stimulation patterns limits hand function to the few tasks programmed into the controller. In contrast, we are developing a system that uses neural signals recorded from a multi-electrode array implanted in the motor cortex; this system has the potential to provide independent control of multiple muscles over a broad range of functional tasks. Two monkeys were able to use this cortically controlled FES system to control the contraction of four forearm muscles despite temporary limb paralysis. The amount of wrist force the monkeys were able to produce in a one-dimensional force tracking task was significantly increased. Furthermore, the monkeys were able to control the magnitude and time course of the force with sufficient accuracy to track visually displayed force targets at speeds reduced by only one-third to one-half of normal. Although these results were achieved by controlling only four muscles, there is no fundamental reason why the same methods could not be scaled up to control a larger number of muscles. We believe these results provide an important proof of concept that brain-controlled FES prostheses could ultimately be of great benefit to paralyzed patients with injuries in the mid-cervical spinal cord

Interprofessional Inconsistencies in the Diagnosis of Shoulder Instability: Survey Results of Physicians and Rehabilitation Providers

Background: Clinicians of many specialties within sports medicine care for athletes with shoulder instability, but successful outcomes are inconsistent. Consistency across specialties in the diagnosis of shoulder instability is critical for care of the athlete, yet the extent of divergence in its diagnosis is unknown. Hypothesis: Physicians differ from rehabilitation providers in which findings they deem clinically important to differentiate shoulder instability from impingement, and in how they diagnose athlete scenarios with atraumatic shoulder instability. Study Design: Cross-sectional study. Methods: Physicians (orthopaedic surgeons, primary care sports medicine physicians) and rehabilitation providers (physical therapists, athletic trainers) were asked via an online survey to rate clinical factors used to diagnose shoulder instability. Clinicians were also asked to diagnose two athlete scenarios with concurrent clinical findings of atraumatic shoulder instability and impingement, differentiated by the absence or presence of a positive sulcus sign. Results: Responses were recorded from 888 clinicians. Orthopaedic surgeons (N=170) and primary care sports medicine physicians (N=108) ranked physical examination factors as more important for the diagnosis of shoulder instability than patient history factors, whereas physical therapists (N=379) and athletic trainers (N=231) preferred patient history factors. Orthopaedic surgeons differed from physical therapists and athletic trainers in their clinical diagnoses for both scenarios (P≤0.001). Conclusion: A lack of consistency exists among sports medicine clinicians in recognizing which clinical factors are important when used to diagnose shoulder instability and in diagnoses given with concurrent findings of impingement. Level of Evidence: Level 3

Haptic Transparency and Interaction Force Control for a Lower-Limb Exoskeleton

Controlling the interaction forces between a human and an exoskeleton is crucial for providing transparency or adjusting assistance or resistance levels. However, it is an open problem to control the interaction forces of lower-limb exoskeletons designed for unrestricted overground walking. For these types of exoskeletons, it is challenging to implement force/torque sensors at every contact between the user and the exoskeleton for direct force measurement. Moreover, it is important to compensate for the exoskeleton's whole-body gravitational and dynamical forces, especially for heavy lower-limb exoskeletons. Previous works either simplified the dynamic model by treating the legs as independent double pendulums, or they did not close the loop with interaction force feedback. The proposed whole-exoskeleton closed-loop compensation (WECC) method calculates the interaction torques during the complete gait cycle by using whole-body dynamics and joint torque measurements on a hip-knee exoskeleton. Furthermore, it uses a constrained optimization scheme to track desired interaction torques in a closed loop while considering physical and safety constraints. We evaluated the haptic transparency and dynamic interaction torque tracking of WECC control on three subjects. We also compared the performance of WECC with a controller based on a simplified dynamic model and a passive version of the exoskeleton. The WECC controller results in a consistently low absolute interaction torque error during the whole gait cycle for both zero and nonzero desired interaction torques. In contrast, the simplified controller yields poor performance in tracking desired interaction torques during the stance phase.Comment: 17 pages, 12 figure

Fluorescent core-shell alloy nanoparticles for cell targeting applications

ABSTRACT: RÉSUMÉ: ABSTRACT

Use of Self-Selected Postures to Regulate Multi-Joint Stiffness During Unconstrained Tasks

The human motor system is highly redundant, having more kinematic degrees of freedom than necessary to complete a given task. Understanding how kinematic redundancies are utilized in different tasks remains a fundamental question in motor control. One possibility is that they can be used to tune the mechanical properties of a limb to the specific requirements of a task. For example, many tasks such as tool usage compromise arm stability along specific directions. These tasks only can be completed if the nervous system adapts the mechanical properties of the arm such that the arm, coupled to the tool, remains stable. The purpose of this study was to determine if posture selection is a critical component of endpoint stiffness regulation during unconstrained tasks.Three-dimensional (3D) estimates of endpoint stiffness were used to quantify limb mechanics. Most previous studies examining endpoint stiffness adaptation were completed in 2D using constrained postures to maintain a non-redundant mapping between joint angles and hand location. Our hypothesis was that during unconstrained conditions, subjects would select arm postures that matched endpoint stiffness to the functional requirements of the task. The hypothesis was tested during endpoint tracking tasks in which subjects interacted with unstable haptic environments, simulated using a 3D robotic manipulator. We found that arm posture had a significant effect on endpoint tracking accuracy and that subjects selected postures that improved tracking performance. For environments in which arm posture had a large effect on tracking accuracy, the self-selected postures oriented the direction of maximal endpoint stiffness towards the direction of the unstable haptic environment.These results demonstrate how changes in arm posture can have a dramatic effect on task performance and suggest that postural selection is a fundamental mechanism by which kinematic redundancies can be exploited to regulate arm stiffness in unconstrained tasks