Torque maximisation of the PMAC motor for high performance, low inertia operation

This paper describes the techniques applied to maximise the torque en- velope of the permanent magnet AC (PMAC) motor operating under current and voltage constraints. Standard steady-state descriptions of the system are often suitable for control purposes when the rotor velocity is varying rela- tively slowly. In low inertia applications such as clutchless gearchange opera- tions, where in the pursuit of driveability, the motor is required to accelerate and decelerate its own rotor inertia as quickly as possible. In this case, the voltage drop due to the current dynamics start to become significant. This paper presents a method to reserve voltage headroom dynamically in the field-weakening region in order to maximise the torque envelope when the effective inertia is low. Experimental results show the effectiveness of this approach

The Grizzly, April 19, 2007

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Somatosensory and motor evoked potentials in dogs with chronic severe thoracolumbar spinal cord injury

ome dogs that become paraplegic after severe spinal cord injury regain ambulation on the pelvic limbs despite permanent loss of pelvic limb sensation, a phenomenon termed ‘spinal walking’. Plastic changes in spinal cord circuitry are thought to mediate this form of recovery but the precise circumstances that favor its development are not known. More information on this phenomenon would be helpful because it might be possible to coax more function in chronically paraplegic animals so improving their, and their owners’, quality of life. We analysed the correlation of ‘spinal walking’ and pelvic limb pain sensation with recordings of scalp and spinal somatosensory and transcranial magnetic motor evoked potentials. We prospectively examined 94 paraplegic dogs (including 53 Dachshunds) that had sustained T10 to L3 spinal cord injury (including 78 dogs with acute intervertebral disc herniation) at a median time of 12.0 months from injury. Nine dogs exhibited ‘spinal walking’ and nine other individuals had intact pelvic limb pain sensation. Of 34 tested, 12 dogs had recordable scalp somatosensory evoked potentials. Fifty-three of 59 tested dogs had recordable spinal somatosensory evoked potentials, but only six had recordable potentials cranial to the lesion. Twenty-two of 94 tested dogs had recordable transcranial magnetic motor evoked potentials in the pelvic limb(s). There was no apparent association between intact evoked potential recording and either spinal walking or intact pain sensation. We conclude that factors other than influence, or lack of influence, of input carried by spinal cord long tracts mediate recovery of spinal walking

Part I. Improvements in the rotation-rate step experiment for the evaluation of diffusion coefficients at rotating disk electrodes. Part II. Ion-pairing and electric field effects on electron hopping in the Nafion-tris(2,2'-bipyridine)osmium(3+/2+) system

Part I: An improved description of the current transient produced by an abrupt change in the rate of rotation of a rotating disk electrode has been obtained by the method of orthogonal collocation. The procedure provides a formula that accurately describes the expected current transient for at least 90% of its duration. If the final rotation rate is chosen to be ca. 58% of the initial rotation rate, the resulting current transient exhibits simple exponential decay, thereby facilitating data analysis. A simple offset in the time scale of the experiment proves effective in compensating for the effects of both hydrodynamic relaxation and imperfections in the response of the electrode rotator. Part II: The high ionic content and low dielectric constant that prevail in the interior of many redox polymers are expected to promote ionic association between the polyelectrolyte and counterions. The present study is an attempt to evaluate the influence of ion-pairing interactions on charge propagation within polyelectrolyte films. The system under investigation consists of the Os(bpy)3(3+/2+) redox couple incorporated into Nafion, where ion-pairing between the osmium complex and pendant sulfonate groups is argued to be responsible for the irreversible retention of the complex within the film. The apparent diffusion coefficient characterizing the dynamics of electron propagation through the redox polymer exhibits a remarkably sudden increase as the film approaches electrostatic saturation with the Os(bpy)3(3+) complex. Existing models, even those taking into account the presence of electric fields within the film, do not account satisfactorily for the observed behavior of the apparent diffusion coefficients. The introduction of ion-pairing into the model for charge transport leads to predictions that are consistent with the observed behavior. Key ingredients in the successful model are the assumptions that the predominant forms of the Os(bpy)3(3+/2+) complex incorporated in Nafion are neutral aggregates resulting from the formation of triple or double ion-pairs and that the triply ion-paired Os(bpy)3(3+) species dissociates into a singly charged species containing the same number of sulfonate groups as the predominant form of the Os(bpy)3(2+) complex, thereby providing a low-energy pathway for electron self-exchange. The dissociation of the triply ion-paired Os(bpy)3(3+) complex provides a natural explanation for the steep increase in the apparent diffusion coefficient, i.e., the rate of electron propagation, as the concentration of the osmium complex comes close to saturation, because as saturation is approached the ion-pairing equilibrium shifts to favor the formation of the doubly ion-paired form of Os(bpy)3(3+) that is the best partner for accepting an electron from the doubly ion-paired Os(bpy)3(2+) complex. The inevitable presence of electric fields within the polyelectrolyte films also affects the observed behavior, especially as the concentration of the incorporated cation is increased

The origin of the neural activity responsible for canine chorea

Call number: LD2668 .T4 1969 B528Master of Scienc