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

Aeroelastic simulation of higher harmonic control

This report describes the development of an aeroelastic analysis of a helicopter rotor and its application to the simulation of helicopter vibration reduction through higher harmonic control (HHC). An improved finite-state, time-domain model of unsteady aerodynamics is developed to capture high frequency aerodynamic effects. An improved trim procedure is implemented which accounts for flap, lead-lag, and torsional deformations of the blade. The effect of unsteady aerodynamics is studied and it is found that its impact on blade aeroelastic stability and low frequency response is small, but it has a significant influence on rotor hub vibrations. Several different HHC algorithms are implemented on a hingeless rotor and their effectiveness in reducing hub vibratory shears is compared. All the controllers are found to be quite effective, but very differing HHC inputs are required depending on the aerodynamic model used. Effects of HHC on rotor stability and power requirements are found to be quite small. Simulations of roughly equivalent articulated and hingeless rotors are carried out, and it is found that hingeless rotors can require considerably larger HHC inputs to reduce vibratory shears. This implies that the practical implementation of HHC on hingeless rotors might be considerably more difficult than on articulated rotors

The speed of innovation diffusion in social networks

New ways of doing things often get started through the actions of a few innovators, then diffuse rapidly as more and more people come into contact with prior adopters in their social network. Much of the literature focuses on the speed of diffusion as a function of the network topology. In practice, the topology may not be known with any precision, and it is constantly in flux as links are formed and severed. Here, we establish an upper bound on the expected waiting time until a given proportion of the population has adopted that holds independently of the network structure. Kreindler and Young (2014) demonstrated such a bound for regular networks when agents choose between two options: the innovation and the status quo. Our bound holds for directed and undirected networks of arbitrary size and degree distribution, and for multiple competing innovations with different payoffs

Financial Market Intermediaries and Information Asymmetry in Equity Markets

This dissertation examines the relationship between financial market intermediaries and information asymmetry. Chapters 5, 6, and 7 re-examines issues raised in the literature, but extends this research by using unique datasets not previously available to researchers. Overall, the results show that (i) market intermediaries help reduce information asymmetry in upstairs markets by filtering out information-motivated trades, (ii) market intermediaries produce information which is valuable to clients who are able to trade ahead of the market, and iii) market intermediaries are heterogeneously informed, and are therefore affected differently by a change in market structure

Active and Passive Helicopter Noise Reduction Using the AVINOR/HELINOIR Code Suite

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/143085/1/1.C034519.pd

The HELINOIR Aeroacoustic Code and its Application to Active/Passive Helicopter Noise Reduction

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/143060/1/6.2017-1179.pd

Comprehensive Numerical Assessment of Rotorcraft Vibration and Noise Control Using Microflaps

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/140642/1/1.c033448.pd

The Bridgwater Infant Welfare Centre, 1922-1939: from an authoritarian concern with 'welfare mothers' to a more inclusive community health project?

The infant welfare movement in Britain has received considerable scholarly attention but continues to generate controversy and debate. Many of the services began with nineteenth-century voluntary initiative but were later developed by local authorities. Critics have drawn attention to the limitations of such provision; arguing that it was predicated on unattractive assumptions about class and gender roles. Under this interpretation working-class mothers were viewed with suspicion and targeted for advice aimed at inculcating middle-class standards of childcare and housekeeping. This paper accepts that there was an authoritarian character to much of the early welfare work but suggests that over time this gave way to more inclusive approaches that sought to provide clients with the services that met their real rather than assumed needs. This paper reviews the recent historiography, develops an overview of national trends, and then takes a detailed look at the Bridgwater Infant Welfare Centre. The case study benefi ts from unusually comprehensive records and, by drawing on evidence from a small Somerset town, adds to our understanding of infant welfare work that has previously been developed from research on major urban centres.Wellcome Trust Fellowshi

Faster decline of pitch memory over time in congenital amusia

Congenital amusia (amusia, hereafter) is a developmental disorder that impacts negatively on the perception of music. Psychophysical testing suggests that individuals with amusia have above average thresholds for detection of pitch change and pitch direction discrimination; however, a low-level auditory perceptual problem cannot completely explain the disorder, since discrimination of melodies is also impaired when the constituent intervals are suprathreshold for perception. The aim of the present study was to test pitch memory as a function of (a) time and (b) tonal interference, in order to determine whether pitch traces are inherently weaker in amusic individuals. Memory for the pitch of single tones was compared using two versions of a paradigm developed by Deutsch (1970a). In both tasks, participants compared the pitch of a standard (S) versus a comparison (C) tone. In the time task, the S and C tones were presented, separated in time by 0, 1, 5, 10, and 15 s (blocked presentation). In the interference task, the S and C tones were presented with a fixed time interval (5 s) but with a variable number of irrelevant tones in between: 0, 2, 4, 6, and 8 tones (blocked presentation). In the time task, control performance remained high for all time in tervals, but amusics showed a performance decrement over time. In the interference task, controls and amusics showed a similar performance decrement with increasing number of irrelevant tones. Overall, the results suggest that the pitch representations of amusic individuals are less stable and more prone to decay than those of matched non-amusic individuals