Measurement of Magnetic Flux in a Hall Thruster for Comparison to Mathematical Model

As part of the early development of a Hall-effect thruster, a type of advanced electric propulsion system, a prototype thruster body was built for the purpose of experimentation. To be as close as possible to reality, the prototype was designed and built under the assumption that it would be fireable. As such, it is equipped with a ceramic discharge chamber, as well as with customized electromagnets which use 28 AWG magnet wire and 1010 steel for the cores. The field is measured using Hall sensors for comparison with a mathematical model of the field. Physical systems and mathematical models can be used to iteratively improve one another, so this experiment serves as a beginning to the much larger project of fully developing a fully functional thruster system. Results of this experiment will affect the progress of development, either requiring system modifications or allowing for further system design

Netrin-3 Avoidance and Mitotic Inhibition in \u3cem\u3eTetrahymena thermophila\u3c/em\u3e Involves Intracellular Calcium and Serine/Threonine Kinase Activity

Netrins are a family of signaling proteins ubiquitously expressed throughout the animal kingdom. While netrin-1 has been well characterized, other netrins, such as netrin-3, remain less well understood. In our current study, we characterize the behavior of two netrin-3 peptides, one derived from the N-terminal and one derived from the C-terminal of netrin-3. Both peptides cause avoidance behavior and mitotic inhibition in Tetrahymena thermophila at concentrations as low as 0.5 micrograms (μg) per milliliter. These effects can be reversed by addition of the calcium chelator, EGTA; the intracellular calcium chelator, BAPTA-AM, or the serine/threonine kinase inhibitor, apigenin. The broad spectrum tyrosine kinase inhibitor, genistein, has no effect on netrin-3 signaling, indicating that netrin-3 signaling in this organism uses a different pathway than the previously described netrin-1 pathway. Further studies will allow us to better describe the netrin-3 signaling pathway in this organism

Effects of pediatric obesity on joint kinematics and kinetics during 2 walking cadences

Objective: To determine whether differences existed in lower-extremity joint biomechanics during self-selected walking cadence (SW) and fast walking cadence (FW) in overweight- and normal-weight children.---------- Design: Survey.---------- Setting: Institutional gait study center.---------- Participants: Participants (N=20; mean age ± SD, 10.4±1.6y) from referred and volunteer samples were classified based on body mass index percentiles and stratified by age and sex. Exclusion criteria were a history of diabetes, neuromuscular disorder, or recent lower-extremity injury.---------- Main Outcome Measures: Sagittal, frontal, and transverse plane angular displacements (degrees) and peak moments (newton meters) at the hip, knee, and ankle joints.---------- Results: The level of significance was set at P less than .008. Compared with normal-weight children, overweight children had greater absolute peak joint moments at the hip (flexor, extensor, abductor, external rotator), the knee (flexor, extensor, abductor, adductor, internal rotator), and the ankle (plantarflexor, inverter, external/internal rotators). After including body weight as a covariate, overweight children had greater peak ankle dorsiflexor moments than normal-weight children. No kinematic differences existed between groups. Greater peak hip extensor moments and less peak ankle inverter moments occurred during FW than SW. There was greater angular displacement during hip flexion as well as less angular displacement at the hip (extension, abduction), knee (flexion, extension), and ankle (plantarflexion, inversion) during FW than SW.---------- Conclusions: Overweight children experienced increased joint moments, which can have long-term orthopedic implications and suggest a need for more nonweight-bearing activities within exercise prescription. The percent of increase in joint moments from SW to FW was not different for overweight and normal-weight children. These findings can be used in developing an exercise prescription that must involve weight-bearing activity

Head Position and Football Equipment Influence Cervical Spinal-Cord Space During Immobilization

OBJECTIVE: To assess the effect of head position and football equipment (ie, helmet and shoulder pads) on cervical spinal cord space in individuals lying supine on a spine board. DESIGN AND SETTING: The independent variables were head position (0-cm, 2-cm, and 4-cm occiput elevation with no helmet and shoulder pads and with helmet and shoulder pads) and cervical spine level (C3, C4, C5, C6, and C7). The 3 dependent variables were sagittal space available for the cord (SAC) (mm), sagittal spinal-cord diameter (mm), and cervical-thoracic angle ( degrees ), determined via magnetic resonance imaging. SUBJECTS: Twelve men (age = 24.3 +/- 2.1 years; height = 181.1 +/- 5.7 cm; weight = 93.9 +/- 3.6 kg). MEASUREMENTS: Sagittal space available for the cord was determined by subtracting the sagittal spinal-cord diameter from the corresponding sagittal spinal-canal diameter. The spinal-canal diameter was measured as the shortest distance from the vertebral body to the spinolaminar line at each of the spinal levels. Each measurement was taken 3 times, and the 3 measurements were averaged. RESULTS: Sagittal space available for the cord was significantly greater (P \u3c .01) for 0-cm (mean = 5.50 mm) than for 2-cm (mean = 4.86 mm) and 4-cm (mean = 5.07 mm) occiput elevation. SAC was also significantly greater (P \u3c .01) for the equipment condition (mean = 5.34 mm) than for the 2-cm and 4-cm elevation levels. No significant difference (P = .093) in SAC existed between 0-cm elevation and the equipment condition. CONCLUSIONS: The helmet and shoulder pads should be left on during spine-board immobilization of the injured football player. Similarly, during spine-board immobilization of an individual without football helmet and shoulder pads, the head should be maintained at 0 cm of occiput elevation. Sagittal spinal-cord space is optimized in both of these conditions

Cervical Spine Stenosis Measures in Normal Subjects

Objective: To compare 2 methods of determining cervical spinal stenosis (Torg ratio, space available for the cord [SAC]); determine which of the components of the Torg ratio and the SAC account for more of the variability in the measures; and present standardized SAC values for normal subjects using magnetic resonance imaging (MRI). Design and Setting: The research design consisted of a posttest-only, comparison-group design. The independent variable was method of measurement (Torg ratio and SAC). The dependent variables were Torg ratio and SAC scores. Subjects: Fourteen men (age = 24.4 ± 2.5 years, height = 181.0 ± 5.8 cm, weight = 90 ± 13.5 kg) participated in this study. The C3 to C7 vertebrae were examined in each subject (n = 70). Measurements: The Torg ratio was determined by dividing the sagittal spinal-canal diameter by the corresponding sagittal vertebral-body diameter. The SAC was determined by subtracting the sagittal spinal-cord diameter from the corresponding sagittal spinal-canal diameter. The Torg ratio and SAC were measured in millimeters. Results: The SAC ranged from 2.5 to 10.4 mm and was greatest at C7 in 71% (10 of 14) of the subjects. The SAC was least at C3 or C5 in 71% (10 of 14) of the subjects. A Pearson product moment correlation revealed a significant relationship between the Torg ratio and SAC (r = .53, P < .01). Regression analyses revealed the vertebral body (r (2) = .58) accounted for more variability in the Torg ratio than the spinal canal (r (2) = .48). Also, the spinal canal (r (2) = .66) accounted for more variability in the SAC than the spinal cord (r (2) = .23). Conclusions: The SAC measure relies more on the spinal canal compared with the Torg ratio and, therefore, may be a more effective indicator of spinal stenosis. This is relevant clinically because neurologic injury related to stenosis is a function of the spinal canal and the spinal cord (not the vertebral body). Further research must be done, however, to validate the SAC measure