Matthew R. Williams

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We investigated the performance of three user interfaces for restoration of cursor control in individuals with tetraplegia: head orientation, electromyography (EMG) from face and neck muscles, and a standard computer mouse (for comparison). Subjects engaged in a 2-D, center-out, Fitts' Law style task and performance was evaluated using several measures.(More)
We study the positive solutions to steady state reaction diffusion equations with Dirichlet boundary conditions of the forms: u(0) = 0 = u(1), and −u ′′ = λ[au − bu 2 − c], x ∈ (0, 1 2), λ[au − bu 2 ], x ∈ (1 2 , 1), (B) u(0) = 0 = u(1). 1 2. Such steady state equations arise in population dynamics with logistic type growth and constant yield harvesting.(More)
We evaluated the ability of an individual with a high cervical spinal cord injury (SCI) to control a cursor on a computer screen using two different user interfaces: (1) head movements measured via a head-mounted orientation sensor and (2) electromyography (EMG) signals from four head and neck muscles acquired using a 4-channel implanted upper-limb(More)
An above knee amputation can have a significant impact on gait, with substantial deviations in inter-leg symmetry, step length, hip exertion and upper body involvement even when using a current clinical standard of care prosthesis. These differences can produce gait that is less efficient and less comfortable, resulting in slower and shorter distance(More)
The loss of a hand can greatly affect quality of life. A prosthetic device that can mimic normal hand function is very important to physical and mental recuperation after hand amputation, but the currently available prosthetics do not fully meet the needs of the amputee community. Most prosthetic hands are not dexterous enough to grasp a variety of shaped(More)
High cervical spinal cord injuries result in significant functional impairments and affect both the injured individual as well as their family and care givers. To help restore function to these individuals, multiple user interfaces are available to enable command and control of external devices. However, little work has been performed to assess the 3D(More)
We consider a test of an unknown change-point in a Weibull hazard function. We assume that data are subject to staggered entry and type I censoring. We formulate the profile log-likelihood ratio test statistic as a function of the change-point and derive the limiting Gaussian process. From the supremum of the limiting process, we determine critical values(More)
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