Actively evolving subglacial conduits and eskers initiate ice shelf channels at an Antarctic grounding line.

Ice-shelf channels are long curvilinear tracts of thin ice found on Antarctic ice shelves. Many of them originate near the grounding line, but their formation mechanisms remain poorly understood. Here we use ice-penetrating radar data from Roi Baudouin Ice Shelf, East Antarctica, to infer that the morphology of several ice-shelf channels is seeded upstream of the grounding line by large basal obstacles indenting the ice from below. We interpret each obstacle as an esker ridge formed from sediments deposited by subglacial water conduits, and calculate that the eskers' size grows towards the grounding line where deposition rates are maximum. Relict features on the shelf indicate that these linked systems of subglacial conduits and ice-shelf channels have been changing over the past few centuries. Because ice-shelf channels are loci where intense melting occurs to thin an ice shelf, these findings expose a novel link between subglacial drainage, sedimentation and ice-shelf stability.

Inverse-dynamics based assessment of gait using a robotic orthosis.

Body-weight supported treadmill training following neurological disorders such as stroke and spinal cord injuries (SCI) has become an integral part of rehabilitation for treating gait disorders. Unfortunately techniques for selecting important training parameters, such as walking speed and body-weight support, have not been established. Here we present a 3-D inverse-dynamics based approach for evaluating an individual's ability to ambulate, in terms of evaluating the magnitude and timing of joint moments at the ankle, knee and hip. This technique, which utilizes an instrumented gait robot, allows clinicians and researchers the ability to determine the training parameters in which subjects generate joint moments at the proper phases of the gait cycle which when combined with electromyographic recordings, can help establish and then progress training parameters for individuals on a subject-by-subject basis. We believe that training subjects at their preferred walking speed and body-weight support will lead to higher functional outcomes.

Limb alignment and kinematics inside a Lokomat robotic orthosis.

The use of robotic gait training systems has become commonplace world-wide. In particular, the Lokomat robotic orthosis (Hocoma AG, Volketswil, Switzerland) is in use at nearly 75 facilities treating patients with spinal cord injury, stroke, and other neurological impairments. Despite the extensive use of the device, no studies have reported the leg kinematic trajectories while walking in the device. Furthermore, because the subject's legs are not rigidly coupled to the device, there is the potential for significant leg movement inside the device which also has not been reported. Here we report differences in kinematic trajectories between walking in the Lokomat and walking on a treadmill, as well as the relative limb motion within the Lokomat for a single representative subject. Using high-speed motion analysis, it was found that while similar knee and hip angle patterns were produced when walking on the treadmill and while walking in the Lokomat, there were significant differences (p<.0.01) in percent time spent in swing phase, maximum hip and knee flexion, and maximum hip extension. There was also a larger amount of misalignment at the hip (18.2 mm) than at the knees (12 mm) when the joint positions in space were compared.