Optimal Image Reconstruction in Radio Interferometry

We introduce a method for analyzing radio interferometry data which produces maps which are optimal in the Bayesian sense of maximum posterior probability density, given certain prior assumptions. It is similar to maximum entropy techniques, but with an exact accounting of the multiplicity instead of the usual approximation involving Stirling's formula. It also incorporates an Occam factor, automatically limiting the effective amount of detail in the map to that justified by the data. We use Gibbs sampling to determine, to any desired degree of accuracy, the multi-dimensional posterior density distribution. From this we can construct a mean posterior map and other measures of the posterior density, including confidence limits on any well-defined function of the posterior map.Comment: 41 pages, 11 figures. High resolution figures 8 and 9 available at http://www.astro.uiuc.edu/~bwandelt/SuttonWandelt200

The Enrollment Effects of Merit-Based Financial Aid: Evidence from Georgia's HOPE Scholarship

This paper examines the effects of Georgia's merit-based HOPE Scholarship on college enrollment. Introduced in 1993, the HOPE Scholarship covers tuition, fees, and book expenses for students attending Georgia public colleges, and provides a subsidy of comparable value to students attending in-state private colleges, without any income restrictions. Treating HOPE as a natural experiment, we contrast college enrollment in Georgia with those in the other member states of the Southern Regional Educational Board using IPEDS data for the period 1988-97. We estimate that the HOPE increased total freshmen enrollment by 5.9 percent, with the gains concentrated in 4-year schools. For freshmen recently graduated from high school attending 4-year colleges, two-thirds of the program effect is explained by a decrease in students leaving the state. Both white and black enrollments increased because of HOPE, with the state's historically-black institutions playing an important role. Finally, the total HOPE-induced enrollment increase represents only 15 percent freshmen scholarship recipients.Higher Education, Enrollment, HOPE, Merit-based Aid

Non-cognitive Skills and the Gender Disparities in Test Scores and Teacher Assessments: Evidence from Primary School

We extend the analysis of early-emerging gender differences in academic achievement to include both (objective) test scores and (subjective) teacher assessments. Using data from the 1998-99 ECLS-K cohort, we show that the grades awarded by teachers are not aligned with test scores, with the disparities in grading exceeding those in testing outcomes and uniformly favoring girls, and that the misalignment of grades and test scores can be linked to gender differences in non-cognitive development. Girls in every racial category outperform boys on reading tests and the differences are statistically significant in every case except for black fifth-graders. Boys score at least as well on math and science tests as girls, with the strongest evidence of a gender gap appearing among whites. However, boys in all racial categories across all subject areas are not represented in grade distributions where their test scores would predict. Even those boys who perform equally as well as girls on reading, math and science tests are nevertheless graded less favorably by their teachers, but this less favorable treatment essentially vanishes when non-cognitive skills are taken into account. White boys who perform on par with white girls on these subject-area tests and exhibit the same non-cognitive skill level are graded similarly. For some specifications there is evidence of a grade "bonus" for white boys with test scores and behavior like their girl counterparts. While the evidence is a little weaker for blacks and Hispanics, the message is essentially the same.gender differences, test scores, grades, educational attainment

Student Responses to Merit Retention Rules

A common justification for HOPE-style merit-aid programs is to promote and reward academic achievement, thereby inducing greater investments in human capital. However, grade-based eligibility and retention rules encourage other behavioral responses. Using the longitudinal records of all undergraduates who enrolled at the University of Georgia (UGA) between 1989 and 1997, we estimate the effects of HOPE on course enrollment, withdrawal and completion, and the diversion of course taking from the academic year to the summer, treating non-residents as a control group. First, we find that HOPE decreased full-load enrollments and increased course withdrawals among resident freshmen. The combination of these responses results in an 11\% lower probability of full-load completion and an annual average reduction in credits completed of 1.0. The latter implies that between 1993 and 1997 Georgia-resident freshmen completed 15,710 fewer credit hours or 3,142 individual course enrollments than non-residents. Second, the scholarship's influence on course-taking behavior is concentrated on students with GPAs on or below the scholarship-retention margin. Third, the effect increased as the income cap was lifted and more students became eligible for the award. Fourth, these freshmen credit-hour reductions represent an intertemporal substitution, not a general slowdown in academic progress. Finally, residents diverted an average of 1.65 more credits from the regular academic year to the first summer term after their matriculation, which amounts to a 72\% rise in summer course taking.Education, Merit-based aid, Education Finance, HOPE Scholarship

Displacement- and Timing-Noise Free Gravitational-Wave Detection

Motivated by a recently-invented scheme of displacement-noise-free gravitational-wave detection, we demonstrate the existence of gravitational-wave detection schemes insusceptible to both displacement and timing (laser) noises, and are thus realizable by shot-noise-limited laser interferometry. This is possible due to two reasons: first, gravitational waves and displacement disturbances contribute to light propagation times in different manners; second, for an N-detector system, the number of signal channels is of the order O(N^2), while the total number of timing- and displacement-noise channels is of the order O(N).Comment: 4 pages, 3 figures; mistake correcte

Magnitude of Hazards Associated with the Rail Transport of Crude Oil and LPG

PresentationOver the past several years, the volume of crude oil being transported by rail has dramatically increased. With this increase, the number of train accidents involving crude oil rail cars has also increased. A common perception of the public is that the risk associated with “crude-by-rail” has increased. This may be true due to an increase in rail car shipments but has the magnitude of hazards associated with crude by rail transport changed? Arguments have been made that the compositions of specific crudes make them more hazardous than conventional crude. Is there a basis for this claim? As the volume of crude transported by rail has increased, so has the volume of liquefied petroleum gases (LPGs) transported by rail, albeit with different types of rail cars than those used for crude oil. This paper will investigate the magnitude of hazards associated with rail transport of a range of crude oils and LPGs. The release mechanisms will be affected by the type of rail car employed (DOT-112, DOT-111, and the modified DOT-111 called the 1232) and the fluid condition upon release. The result of the overall analysis will be a side-by-side comparison of hazard magnitude as a function of the transported fluid and the rail car employed

What API RP 752 Does Not Tell You – But People Will Ask

PresentationOver the past several years, Quest Consultants Inc. has conducted building siting studies per API RP 752 for a range of facilities in the United States and abroad. This paper summarizes several of the issues encountered when applying the guidance provided by API RP 752. While the API recommended practices may not address the full range of hazards a building occupant could experience, other codes such as 29 CFR 1910 do require their evaluation under the “general duty clause” and the Process Safety Management (PSM) program. What will be outlined in this paper are the “holes” in the API RP 752 guidance as well as possible approaches to address these missing elements. Questions that are simple to ask (e.g., What happens to your siting study if a new facility moves in just past your fence line?) may be difficult or impossible to answer. However, if an impact is realized, do you have to move your building due to your new neighbor’s operation? This is only one example of a host of scenarios that will be addressed in this paper

Quantitative Risk Calculations for a U.S. DOT Natural Gas Pipeline Using Population Classifications

PresentationOver the past several years, Quest Consultants Inc. has conducted quantitative risk analysis (QRA) and risk assessment studies for a range of pipelines in the United States and abroad. In most instances, the risk acceptance or tolerability criteria are defined by the individual risk (IR) to a person; often this risk is presented as location specific individual risk (LSIR). The LSIR is a measure of the risk to a person who is continuously at a specific location. In recent years, there has been increasing dependence on the use of societal risk acceptance or tolerability criteria, including the risk associated with pipelines. Pipelines are often described as linear sources of risk, like highways and rail lines. The risk analysis methodology used to calculate the risk associated with fixed facilities (e.g., refineries and chemical plants) cannot be directly applied to linear risk sources. This paper presents a risk calculation methodology that can be applied to linear risk sources, like natural gas pipelines, and compares the societal risk indices for U.S. DOT pipeline classes