Studies examining rapid spine loading have documented the influence of steady-state trunk preload... more Studies examining rapid spine loading have documented the influence of steady-state trunk preloads, and the resulting levels of trunk muscle preactivation, on the control of spine stability. However, the effects of different levels of muscle coactivation, and resulting spine loads, on the response to a perturbation of the externally unloaded trunk are unclear. Fourteen male subjects coactivated the abdominal muscles at four different levels (approximately 0%, 10%, 20% and 30% of the maximal voluntary contraction) monitored by an electromyography biofeedback system while semi-seated in a neutral lumbar spine position. They were loaded posteriorly in two directions (0 degrees and 30 degrees from the sagittal plane) and with two different loads (6.80 and 9.07 kg). Force perturbation, spine displacement and electromyography activity were measured, and torso compression and stability were modeled. Abdominal coactivation significantly increased spine stability and reduced the movement of the lumbar spine after perturbation, but at the cost of increasing spinal compression. Preactivation also reduced the frequency and magnitude, and delayed the onset of muscle reactions, mainly for the back muscles and the internal oblique. The higher magnitude load and the load applied in an oblique direction both showed more potentially hazardous effects on the trunk. Torso coactivation increases spinal stiffness and stability and reduces the necessity for sophisticated muscle responses to perturbation. Although further investigation is needed, it appears there is an asymptotic function between coactivation and both stiffness and stability. There also appears to be more hazard when buttressing twisting components of a sudden load compared to sagittal components. Patients with trunk instability and intolerance to spine compression may benefit from low to moderate levels of coactivation.
Accretion rates were measured in fringe and basin mangrove forests in river and tidally dominated... more Accretion rates were measured in fringe and basin mangrove forests in river and tidally dominated sites in Terminos Lagoon, Mexico, and a basin mangrove forest in Rookery Bay, Florida, USA. Accretion rates were determined using the radionuclides210Pb and137Cs. Consolidation-corrected accretion rates for the Rookery Bay cores, ranged from 1.4 to 1.7 mm yr−1, with an average rate of 1.6 mm yr−1. Rates at the Mexico sites ranged from 1.0 to 4.4 mm yr−1, with an average of 2.4 mm yr−1. Determination of rates in these mangrove forests was greatly affected by the consolidation corrections which decreased the apparent accretion rate by over 50% in one case. Accretion rates at basin sites compare favorably with a reported 1.4 to 1.6 mm yr−1 rate of sea-level rise, indicating little or no subsidence at inland locations. Accretion rates in fringe sites are generally greater than basin sites, indicating greater subsidence rates in these sediments over longer time intervals.
Oral Surgery Oral Medicine Oral Pathology Oral Radiology and Endodontology, 2000
Nerve sheath myxoma is a benign peripheral nerve sheath tumor that rarely occurs in the oral cavi... more Nerve sheath myxoma is a benign peripheral nerve sheath tumor that rarely occurs in the oral cavity; experience with these lesions is therefore limited. The lesion described in this report appeared clinically as a gradually enlarging, painless growth arising on the tongue of a newborn girl. Microscopically, the lesion was characterized by nodules of spindle-shaped cells with abundant myxoid stroma. Immunohistochemical studies were consistent with a nerve sheath neoplasm.
Studies examining rapid spine loading have documented the influence of steady-state trunk preload... more Studies examining rapid spine loading have documented the influence of steady-state trunk preloads, and the resulting levels of trunk muscle preactivation, on the control of spine stability. However, the effects of different levels of muscle coactivation, and resulting spine loads, on the response to a perturbation of the externally unloaded trunk are unclear. Fourteen male subjects coactivated the abdominal muscles at four different levels (approximately 0%, 10%, 20% and 30% of the maximal voluntary contraction) monitored by an electromyography biofeedback system while semi-seated in a neutral lumbar spine position. They were loaded posteriorly in two directions (0 degrees and 30 degrees from the sagittal plane) and with two different loads (6.80 and 9.07 kg). Force perturbation, spine displacement and electromyography activity were measured, and torso compression and stability were modeled. Abdominal coactivation significantly increased spine stability and reduced the movement of the lumbar spine after perturbation, but at the cost of increasing spinal compression. Preactivation also reduced the frequency and magnitude, and delayed the onset of muscle reactions, mainly for the back muscles and the internal oblique. The higher magnitude load and the load applied in an oblique direction both showed more potentially hazardous effects on the trunk. Torso coactivation increases spinal stiffness and stability and reduces the necessity for sophisticated muscle responses to perturbation. Although further investigation is needed, it appears there is an asymptotic function between coactivation and both stiffness and stability. There also appears to be more hazard when buttressing twisting components of a sudden load compared to sagittal components. Patients with trunk instability and intolerance to spine compression may benefit from low to moderate levels of coactivation.
Accretion rates were measured in fringe and basin mangrove forests in river and tidally dominated... more Accretion rates were measured in fringe and basin mangrove forests in river and tidally dominated sites in Terminos Lagoon, Mexico, and a basin mangrove forest in Rookery Bay, Florida, USA. Accretion rates were determined using the radionuclides210Pb and137Cs. Consolidation-corrected accretion rates for the Rookery Bay cores, ranged from 1.4 to 1.7 mm yr−1, with an average rate of 1.6 mm yr−1. Rates at the Mexico sites ranged from 1.0 to 4.4 mm yr−1, with an average of 2.4 mm yr−1. Determination of rates in these mangrove forests was greatly affected by the consolidation corrections which decreased the apparent accretion rate by over 50% in one case. Accretion rates at basin sites compare favorably with a reported 1.4 to 1.6 mm yr−1 rate of sea-level rise, indicating little or no subsidence at inland locations. Accretion rates in fringe sites are generally greater than basin sites, indicating greater subsidence rates in these sediments over longer time intervals.
Oral Surgery Oral Medicine Oral Pathology Oral Radiology and Endodontology, 2000
Nerve sheath myxoma is a benign peripheral nerve sheath tumor that rarely occurs in the oral cavi... more Nerve sheath myxoma is a benign peripheral nerve sheath tumor that rarely occurs in the oral cavity; experience with these lesions is therefore limited. The lesion described in this report appeared clinically as a gradually enlarging, painless growth arising on the tongue of a newborn girl. Microscopically, the lesion was characterized by nodules of spindle-shaped cells with abundant myxoid stroma. Immunohistochemical studies were consistent with a nerve sheath neoplasm.
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