Fatigue of boron-aluminum composites bonds and joints

Study examines effects of boron filament diameter on bonds and joints in boron-aluminum composite. Data include static strength, fatigue, and dynamic moduli of elasticity. Manson-Coffin analyses and metallurgical and fracture surface evaluation were also performed

The American Middle Class, Income Inequality, and the Strength of Our Economy

Analyzes 1979-2007 income growth by income group and how the state of the middle class and level of income inequality affect factors shaping the economy, such as human capital, demand for goods and services, entrepreneurship, and inclusive institutions

Effects of grazing flow on the steady-state flow resistance and acoustic impedance of thin porous-faced liners

The effects of grazing flow on the steady state flow resistance and acoustic impedance of seven Feltmetal and three Rigimesh thin porous faced liners were studied. The steady-state flow resistance of the ten specimens was measured using standard fluid mechanical experimental techniques. The acoustic impedance was measured using the two microphone method. The principal findings of the study are that the effects of grazing flow were measured and found to be small; small differences were measured between steady-state and acoustic resistance, and a semi-empirical model was derived that correlated the steady-state resistance data of the seven Feltmetal liners and the face sheet reactance of both the Feltmetal and Rigimesh liners

Fluid mechanical model of the acoustic impedance of small orifices

A fluid mechanical model of the acoustic behavior of small orifices is presented which predicts orifice resistance and reactance as a function of incident sound pressure level, frequency, and orifice geometry. Agreement between predicted and measured values is excellent. The model shows the following: (1) The acoustic flow in immediate neighborhood of the orifice can be modeled as a locally spherical flow. Within this near field, the flow is, to a first approximation, unsteady and incompressible. (2) At very low sound pressure levels, the orifice viscous resistance is directly related to the effect of boundary-layer displacement along the walls containing the orifice, and the orifice reactance is directly related to the inertia of the oscillating flow in the neighborhood of the orifice. (3) For large values of the incident acoustic pressure, the impedance is dominated by nonlinear jet-like effects. (4) For low values of the pressure, the resistance and reactance are roughly equal

Fluid mechanical model of the Helmholtz resonator

A semi-empirical fluid mechanical model of the acoustic behavior of Helmholtz resonators is presented which predicts impedance as a function of the amplitude and frequency of the incident sound pressure field and resonator geometry. The model assumes that the particle velocity approaches the orifice in a spherical manner. The incident and cavity sound fields are connected by solving the governing oscillating mass and momentum conservation equations. The model is in agreement with the Rayleigh slug-mass model at low values of incident sound pressure level. At high values, resistance is predicted to be independent of frequency, proportional to the square root of the amplitude of the incident sound pressure field, and virtually independent of resonator geometry. Reactance is predicted to depend in a very complicated way upon resonator geometry, incident sound pressure level, and frequency. Nondimensional parameters are defined that divide resonator impedance into three categories corresponding to low, moderately low, and intense incident sound pressure amplitudes. The two-microphone method was used to measure the impedance of a variety of resonators. The data were used to refine and verify the model

Sound propagation in choked ducts

The linearized equations describing the propagation of sound in variable area ducts containing flow are shown to be singular when the duct mean flow is sonic. The singularity is removed when previously ignored nonlinear terms are retained. The results of a numerical study, for the case of plane waves propagating in a one-dimensional converging-diverging duct, show that the sound field is adequately described by the linearized equations only when the axial mean flow Mach number at the duct throat M sub th 0.6. For M sub th 0.6, the numerical results showed that acoustic energy flux was not conserved. An attempt was made to extend the study to include the nonlinear behavior of the sound field. Meaningful results were not obtained due, primarily, to numerical difficulties

Why China Grew: Understanding the Financial Structure of Late Development

This dissertation explores how economic institutions governing finance and investment have con- tributed to growth in reform-era China. Economic and political reforms greatly transformed China\u27s prior centrally-planned economy. Although reforms incorporated elements of market institutions and private enterprise, China\u27s state institutions exercising extensive authority over a wide range of eco- nomic affairs critically and fundamentally played a central role in transforming this economy from one of the world\u27s poorest to the world\u27s second largest in the span of one generation. I explain the emergence of a unique configuration of institutions supportive of industrial policy implemented by largely autonomous local government officials. In combination with state-directed bank credit, this local government industrial policy finance have played a significant and positive role in development of exports in China. Foreign direct investment, too, was positively and significantly associated with export development, though on a more geographically-limited basis. Though private entrepreneurs are often seen as dynamic engines of growth in China\u27s reform-era economy, I show that the vast majority of entrepreneurs are low-skilled, low-productivity, and exhibit non-positive rates of capital accumulation. Most entrepreneurs would experience higher earnings were they not segmented into self-employment occupations by adverse socioeconomic conditions. Rather than engines of growth, China\u27s entrepreneurs resemble more the vast numbers of informal sector self-employment prevalent in many developing countries

Technical and managerial support for the performance standardization working group of the interagency chemical rocket propulsion group Final report

Performance standardization working group for analytical and experimental evaluation of performance of liquid propellant rocket engine