57,127 research outputs found
Comparative evaluation of three alternative power cycles for waste heat recovery from the exhaust of adiabatic diesel engines
Three alternative power cycles were compared in application as an exhaust-gas heat-recovery system for use with advanced adiabatic diesel engines. The power cycle alternatives considered were steam Rankine, organic Rankine with RC-1 as the working fluid, and variations of an air Brayton cycle. The comparison was made in terms of fuel economy and economic payback potential for heavy-duty trucks operating in line-haul service. The results indicate that, in terms of engine rated specific fuel consumption, a diesel/alternative-power-cycle engine offers a significant improvement over the turbocompound diesel used as the baseline for comparison. The maximum imporvement resulted from the use of a Rankine cycle heat-recovery system in series with turbocompounding. The air Brayton cycle alternatives studied, which included both simple-cycle and compression-intercooled configurations, were less effective and provided about half the fuel consumption improvement of the Rankine cycle alternatives under the same conditions. Capital and maintenance cost estimates were also developed for each of the heat-recovery power cycle systems. These costs were integrated with the fuel savings to identify the time required for net annual savings to pay back the initial capital investment. The sensitivity of capital payback time to arbitrary increases in fuel price, not accompanied by corresponding hardware cost inflation, was also examined. The results indicate that a fuel price increase is required for the alternative power cycles to pay back capital within an acceptable time period
A Cause Lost, a Story Being Written: Explaining Black and White Commemorative Difference in the Postbellum South
This paper addresses the disparate commemorative modes and purposes employed by black and white Southerners following the Civil War, in their competing efforts to control the cultural narrative of the war’s legacy. I attempt to explain commemorative difference in the post-war era by evaluating the historical and rhetorical implications of the white Confederate monument, in contrast with the black freedom celebration. The goal of this research is to understand why monuments to the Confederacy proliferate in the South, while similar commemorative markers of the prominent role of slavery in the Civil War are all but nonexistent. I conclude that, while a white supremacist system denied black Southerners the economic and political capital to commission monuments, black Southerners organized public commemorative celebrations not only because they were denied monuments but because celebration and oration presented themselves as powerful strategies to advance black interests. White Southerners favored monuments as a commemorative form because, in the face of a culturally devastating loss, they sought to establish permanent testaments to a pre-war cultural landscape; however, the initial victory of emancipation, with its promise of not only freedom but equality, led black Southerners to seek communion about the past as a tool for understanding and shaping their future, and so celebration and oration became important strategies for consolidating historical narratives and collective imaginations about the place of blacks in a new America
Electromagnetic analysis for large reflector antennas
A comparison is made between the measured E and H plane patterns of the 35 GHz offset paraboloidal reflector and the calculated patterns for the same reflector using the 200 points to describe the surface. The accuracy of the computer prediction is quite good considering that the only description of the surface was the coordinates of a finite number of points on the reflector. The results indicate the possibility of acceptable accuracy in the prediction of electromagnetic performance for arbitrarily distorted reflectors using the coordinates of a practical number of measured points. An optimization of the number and distribution of points, and experimental verification for a distorted reflector are planned
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Predicting Category Intuitiveness With the Rational Model, the Simplicity Model, and the Generalized Context Model
Naïve observers typically perceive some groupings for a set of stimuli as more intuitive than others. The problem of predicting category intuitiveness has been historically considered the remit of models of unsupervised categorization. In contrast, this article develops a measure of category intuitiveness from one of the most widely supported models of supervised categorization, the generalized context model (GCM). Considering different category assignments for a set of instances, the authors asked how well the GCM can predict the classification of each instance on the basis of all the other instances. The category assignment that results in the smallest prediction error is interpreted as the most intuitive for the GCM—the authors refer to this way of applying the GCM as “unsupervised GCM.” The authors systematically compared predictions of category intuitiveness from the unsupervised GCM and two models of unsupervised categorization: the simplicity model and the rational model. The unsupervised GCM compared favorably with the simplicity model and the rational model. This success of the unsupervised GCM illustrates that the distinction between supervised and unsupervised categorization may need to be reconsidered. However, no model emerged as clearly superior, indicating that there is more work to be done in understanding and modeling category intuitiveness
Migration Flows in Regeneration Outcome Agreement Areas: an analysis of Census migration data for the Scottish Executive
Effect of shaping sensor data on pilot response
The pilot of a modern jet aircraft is subjected to varying workloads while being responsible for multiple, ongoing tasks. The ability to associate the pilot's responses with the task/situation, by modifying the way information is presented relative to the task, could provide a means of reducing workload. To examine the feasibility of this concept, a real time simulation study was undertaken to determine whether preprocessing of sensor data would affect pilot response. Results indicated that preprocessing could be an effective way to tailor the pilot's response to displayed data. The effects of three transformations or shaping functions were evaluated with respect to the pilot's ability to predict and detect out-of-tolerance conditions while monitoring an electronic engine display. Two nonlinear transformations, on being the inverse of the other, were compared to a linear transformation. Results indicate that a nonlinear transformation that increases the rate-or-change of output relative to input tends to advance the prediction response and improve the detection response, while a nonlinear transformation that decreases the rate-of-change of output relative to input tends to lengthen the prediction response and make detection more difficult
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