The starting transient of solid propellant rocket motors with high internal gas velocities

A comprehensive analytical model which considers time and space development of the flow field in solid propellant rocket motors with high volumetric loading density is described. The gas dynamics in the motor chamber is governed by a set of hyperbolic partial differential equations, that are coupled with the ignition and flame spreading events, and with the axial variation of mass addition. The flame spreading rate is calculated by successive heating-to-ignition along the propellant surface. Experimental diagnostic studies have been performed with a rectangular window motor (50 cm grain length, 5 cm burning perimeter and 1 cm hydraulic port diameter), using a controllable head-end gaseous igniter. Tests were conducted with AP composite propellant at port-to-throat area ratios of 2.0, 1.5, 1.2, and 1.06, and head-end pressures from 35 to 70 atm. Calculated pressure transients and flame spreading rates are in very good agreement with those measured in the experimental system

Thermomechanical Analysis of a Thermal Protection System with Defects and Heat Shorts

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/77124/1/AIAA-2006-2212-827.pd

Characterization of carbon nanotubes produced by arc discharge: Effect of the background pressure

Single walled carbon nanotubes (SWNT) produced by the anodic arc discharge over a range of constant background pressures of helium (100–1000 Torr) were examined under a high-resolution transmission electron microscope, and a Raman spectrometer. It was found that the average SWNT diameter is about 2 nm and fairly independent of the background pressure. Analysis of the relative purity of SWNTs samples suggests that highest SWNT relative concentration can be obtained at background pressure of about 200–300 Torr. Measured anode ablation rate increases linearly with background pressure. The model of the anodic arc discharge was developed. It was found that the predicted anode ablation rate agrees well with experiment suggesting that electron temperature in the anodic arc is about 0.5 eV. © 2004 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/69876/2/JAPIAU-95-5-2749-1.pd

Single-charge detection by an atomic precision tunnel junction

We demonstrate sensitive detection of single charges using a planar tunnel junction 8.5 nm wide and 17.2 nm long defined by an atomically precise phosphorus doping profile in silicon. The conductance of the junction responds to a nearby gate potential and also to changes in the charge state of a quantum dot patterned 52 nm away. The response of this detector is monotonic across the entire working voltage range of the device, which will make it particularly useful for studying systems of multiple quantum dots. The charge sensitivity is maximized when the junction is most conductive, suggesting that more sensitive detection can be achieved by shortening the length of the junction to increase its conductance

Thermomechanical Behavior of Damaged TPS Including Hypersonic Flow Effects

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76198/1/AIAA-2006-7951-158.pd

Effect of gait speed on gait rhythmicity in Parkinson's disease: variability of stride time and swing time respond differently

BACKGROUND: The ability to maintain a steady gait rhythm is impaired in patients with Parkinson's disease (PD). This aspect of locomotor dyscontrol, which likely reflects impaired automaticity in PD, can be quantified by measuring the stride-to-stride variability of gait timing. Previous work has shown an increase in both the variability of the stride time and swing time in PD, but the origins of these changes are not fully understood. Patients with PD also generally walk with a reduced gait speed, a potential confounder of the observed changes in variability. The purpose of the present study was to examine the relationship between walking speed and gait variability. METHODS: Stride time variability and swing time variability were measured in 36 patients with PD (Hoehn and Yahr stage 2–2.5) and 30 healthy controls who walked on a treadmill at four different speeds: 1) Comfortable walking speed (CWS), 2) 80% of CWS 3) 90% of CWS, and 4) 110% of CWS. In addition, we studied the effects of walking slowly on level ground, both with and without a walker. RESULTS: Consistent with previous findings, increased variability of stride time and swing time was observed in the patients with PD in CWS, compared to controls. In both groups, there was a small but significant association between treadmill gait speed and stride time variability such that higher speeds were associated with lower (better) values of stride time variability (p = 0.0002). In contrast, swing time variability did not change in response to changes in gait speed. Similar results were observed with walking on level ground. CONCLUSION: The present results demonstrate that swing time variability is independent of gait speed, at least over the range studied, and therefore, that it may be used as a speed-independent marker of rhythmicity and gait steadiness. Since walking speed did not affect stride time variability and swing time variability in the same way, it appears that these two aspects of gait rhythmicity are not entirely controlled by the same mechanisms. The present findings also suggest that the increased gait variability in PD is disease-related, and not simply a consequence of bradykinesia

Developing Preservice Elementary Teachers' Pedagogical Design Capacity for Reform‐Based Curriculum Design

Teachers use curriculum materials as a guide in their planning, critiquing and adapting them to address reform‐based goals and practices and specific contextual needs. To become well‐started beginners in planning lessons, novice teachers need opportunities to develop their pedagogical design capacity—that is, their ability to use personal and curricular resources in designing instruction for students. This study investigated the use of reform‐based criteria in supporting 24 preservice teachers enrolled in an elementary science methods course. In learning about and applying criteria, the preservice teachers developed aspects of their pedagogical design capacity by expanding their analysis ideas and refining their knowledge and beliefs about curriculum design. However, many struggled with analyzing lesson plans in a reform‐oriented way during student teaching. This occurred, in part, because the preservice teachers navigated different settings that conveyed conflicting ideas about the reasons why teachers make modifications. The methods course emphasized the importance of modifying materials to promote reform‐based science teaching, but few preservice teachers observed their mentor teachers make adaptations for this reason. These findings have important implications for theoretical models on curriculum materials use and the design of science teacher education.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/91354/1/j.1467-873X.2012.00599.x.pd