The Least of These: American Evangelical Parachurch Missions to the Poor, 1947-2005

This dissertation narrates the historical development of American evangelical missions to the poor from 1947-2005 and analyzes the discourse of its main parachurch proponents, especially World Vision, Compassion International, Food for the Hungry, Samaritan's urse, Sojourners, Evangelicals for Social Action, and the Christian Community Development Association. Although recent scholarship on evangelicalism has been prolific, much of the historical work has focused on earlier periods. Sociological and political scientific scholarship on the postwar period has been attracted mostly to controversies surrounding the Religious Right, leaving evangelicalism's resurgent concern for the poor relatively understudied. This dissertation addresses these lacunae. The study consists of three chronological parts, each marked by a distinctive model of mission to the poor. First, the 1950s were characterized by compassionate charity for individual emergencies, a model that cohered neatly with evangelicalism's individualism and emotionalism. This model should be regarded as the quintessential, bedrock evangelical theory of mission to the poor. It remained strong throughout the entire postwar period. Second, in the 1970s, a strong countercurrent emerged that advocated for penitent protest against structural injustice and underdevelopment. In contrast to the first model, it was distinguished by going against the grain of many aspects of evangelical culture, especially its reflexive patriotism and individualism. Third, in the 1990s, an important movement towards developing potential through hopeful holism gained prominence. Its advocates were confident that their integration of biblical principles with insights from contemporary economic development praxis would contribute to drastic, widespread reductions in poverty. This model signaled a new optimism in evangelicalism's engagement with the broader world. The increasing prominence of missions to the poor within American evangelicalism led to dramatic changes within the movement's worldview: by 2005, evangelicals were mostly unified in their expressed concern for the physical and social needs of the poor, a position that radically reversed their immediate postwar worldview of near-exclusive focus on the spiritual needs of individuals. Nevertheless, missions to the poor also paralleled, reinforced, and hastened the increasing fragmentation of evangelicalism's identity, as each missional model advocated for highly variant approaches to poverty amelioration that were undergirded by diverse sociological, political, and theological assumptions.

Nonlinear Acoustics in Underwater and Biomedical Applications: Array Performance Degradation and Time Reversal Invariance

This dissertation describes a model for acoustic propagation in inhomogeneous flu- ids, and explores the focusing by arrays onto targets under various conditions. The work explores the use of arrays, in particular the time reversal array, for underwater and biomedical applications. Aspects of propagation and phasing which can lead to reduced focusing effectiveness are described. An acoustic wave equation was derived for the propagation of finite-amplitude waves in lossy time-varying inhomogeneous fluid media. The equation was solved numerically in both Cartesian and cylindrical geometries using the finite-difference time-domain (FDTD) method. It was found that time reversal arrays are sensitive to several debilitating factors. Focusing ability was determined to be adequate in the presence of temporal jitter in the time reversed signal only up to about one-sixth of a period. Thermoviscous absorption also had a debilitating effect on focal pressure for both linear and nonlinear propagation. It was also found that nonlinearity leads to degradation of focal pressure through amplification of the received signal at the array, and enhanced absorption in the shocked waveforms. This dissertation also examined the heating effects of focused ultrasound in a tissue-like medium. The application considered is therapeutic heating for hyperther- mia. The acoustic model and a thermal model for tissue were coupled to solve for transient and steady temperature profiles in tissue-like media. The Pennes bioheat equation was solved using the FDTD method to calculate the temperature fields in tissue-like media from focused acoustic sources. It was found that the temperature-dependence of the medium's background prop- erties can play an important role in the temperature predictions. Finite-amplitude effects contributed excess heat when source conditions were provided for nonlinear ef- fects to manifest themselves. The effect of medium heterogeneity was also found to be important in redistributing the acoustic and temperature fields, creating regions with hotter and colder temperatures than the mean by local scattering and lensing action. These temperature excursions from the mean were found to increase monotonically with increasing contrast in the medium's properties.

Simulations of X and Y Retinal Ganglion Cell Behavior with a Nonlinear Push-pull Model of Spatiotemporal Retinal Processing

This article describes a nonlinear model of neural processing in the vertebrate retina, comprising model photoreceptors, model push-pull bipolar cells, and model ganglion cells. Previous analyses and simulations have shown that with a choice of parameters that mimics beta cells, the model exhibits X-like linear spatial summation (null response to contrast-reversed gratings) in spite of photoreceptor nonlinearities; on the other hand, a choice of parameters that mimics alpha cells leads to Y-like frequency doubling. This article extends the previous work by showing that the model can replicate qualitatively many of the original findings on X and Y cells with a fixed choice of parameters. The results generally support the hypothesis that X and Y cells can be seen as functional variants of a single neural circuit. The model also suggests that both depolarizing and hyperpolarizing bipolar cells converge onto both ON and OFF ganglion cell types. The push-pull connectivity enables ganglion cells to remain sensitive to deviations about the mean output level of nonlinear photoreceptors. These and other properties of the push-pull model are discussed in the general context of retinal processing of spatiotemporal luminance patterns.