General purpose computer program for interacting supersonic configurations: Programmer's manual

The program ISCON (Interacting Supersonic Configuration) is described. The program is in support of the problem to generate a numerical procedure for determining the unsteady dynamic forces on interacting wings and tails in supersonic flow. Subroutines are presented along with the complete FORTRAN source listing

General purpose computer program for interacting supersonic configurations. User's manual

The input data required to execute the computer program ISCON are described. The program generates a numerical procedure for the determination of unsteady aerodynamic forces on arbitrarily interacting wings and tails in supersonic flow. A velocity potential gradient method is used. Constant Mach number is assumed throughout the flow field. Lifting surfaces are represented by trapezoidal elements which can be generated automatically by the program. The wake field is represented by rectangular strip elements. The formulation is reviewed as well as input overview and input format. Instruction on how to use ISCON, a sample problem, and the restart feature are discussed. Program size limitations, computer program flow, and error messages are also included along with a description of the SS31 program used to compute the coefficients of surface spline

Collisions and close encounters involving massive main-sequence stars

We study close encounters involving massive main sequence stars and the evolution of the exotic products of these encounters as common--envelope systems or possible hypernova progenitors. We show that parabolic encounters between low-- and high--mass stars and between two high--mass stars with small periastrons result in mergers on timescales of a few tens of stellar freefall times (a few tens of hours). We show that such mergers of unevolved low--mass stars with evolved high--mass stars result in little mass loss ($\sim0.01$ M$_{\odot}$) and can deliver sufficient fresh hydrogen to the core of the collision product to allow the collision product to burn for several million years. We find that grazing encounters enter a common--envelope phase which may expel the envelope of the merger product. The deposition of energy in the envelopes of our merger products causes them to swell by factors of $\sim100$. If these remnants exist in very densely-populated environments ($n\gtrsim10^{7}$ pc$^{-3}$), they will suffer further collisions which may drive off their envelopes, leaving behind hard binaries. We show that the products of collisions have cores rotating sufficiently rapidly to make them candidate hypernova/gamma--ray burst progenitors and that $\sim0.1$ of massive stars may suffer collisions, sufficient for such events to contribute significantly to the observed rates of hypernovae and gamma--ray bursts.Comment: 15 pages, 13 figures, LaTeX, to appear in MNRAS (in press

The Brutal Murder of George J. Bushman

In the fall of 1918 there occurred in Adams County a singularly brutal murder that brought the County and the town of Gettysburg to a shocked standstill. The tentacles of this event would reach into four Pennsylvania counties: Adams, Cumberland, Dauphin, and Philadelphia, and eventually the Pennsylvania Supreme Court. The investigation of the crime and the trial of the perpetrators involved so many public officials and families, as well as the extended judicial system and geographical locations within and without the County, that we have included a Cast of Characters and Locations to assist the reader in following this convoluted tale

NASTRAN level 16 programmer's manual updates for aeroelastic analysis of bladed discs

The programming routines for the NASTRAN Level 16program are presented. Particular emphasis is placed on its application to aeroelastic analyses, mode development, and flutter analysis for turbomachine blades

Estimating the Return to College Selectivity over the Career Using Administrative Earning Data

We estimate the monetary return to attending a highly selective college using the College and Beyond (C&B) Survey linked to Detailed Earnings Records from the Social Security Administration (SSA). This paper extends earlier work by Dale and Krueger (2002) that examined the relationship between the college that students attended in 1976 and the earnings they self-reported reported in 1995 on the C&B follow-up survey. In this analysis, we use administrative earnings data to estimate the return to various measures of college selectivity for a more recent cohort of students: those who entered college in 1989. We also estimate the return to college selectivity for the 1976 cohort of students, but over a longer time horizon (from 1983 through 2007) using administrative data. We find that the return to college selectivity is sizeable for both cohorts in regression models that control for variables commonly observed by researchers, such as student high school GPA and SAT scores. However, when we adjust for unobserved student ability by controlling for the average SAT score of the colleges that students applied to, our estimates of the return to college selectivity fall substantially and are generally indistinguishable from zero. There were notable exceptions for certain subgroups. For black and Hispanic students and for students who come from less-educated families (in terms of their parents’ education), the estimates of the return to college selectivity remain large, even in models that adjust for unobserved student characteristics.return to higher education, college quality, payoff to college selectivity

Ionization--induced star formation V: Triggering in partially unbound clusters

We present the fourth in a series of papers detailing our SPH study of the effects of ionizing feedback from O--type stars on turbulent star forming clouds. Here, we study the effects of photoionization on a series of initially partially unbound clouds with masses ranging from $10^{4}$--$10^{6}$M$_{\odot}$ and initial sizes from 2.5-45pc. We find that ionizing feedback profoundly affects the structure of the gas in most of our model clouds, creating large and often well-cleared bubble structures and pillars. However, changes in the structures of the embedded clusters produced are much weaker and not well correlated to the evolution of the gas. We find that in all cases, star formation efficiencies and rates are reduced by feedback and numbers of objects increased, relative to control simulations. We find that local triggered star formation does occur and that there is a good correlation between triggered objects and pillars or bubble walls, but that triggered objects are often spatially-mixed with those formed spontaneously. Some triggered objects acquire large enough masses to become ionizing sources themselves, lending support to the concept of propagating star formation. We find scant evidence for spatial age gradients in most simulations, and where we do see them, they are not a good indicator of triggering, as they apply equally to spontaneously-formed objects as triggered ones. Overall, we conclude that inferring the global or local effects of feedback on stellar populations from observing a system at a single epoch is very problematic.Comment: 17 pages, 11 figures (mostly degraded to get under the submission size limit), accepted by MNRA

Ionizing feedback from massive stars in massive clusters III: Disruption of partially unbound clouds

We extend our previous SPH parameter study of the effects of photoionization from O-stars on star-forming clouds to include initially unbound clouds. We generate a set of model clouds in the mass range $10^{4}-10^{6}$M$_{\odot}$ with initial virial ratios $E_{\rm kin}/E_{\rm pot}$=2.3, allow them to form stars, and study the impact of the photoionizing radiation produced by the massive stars. We find that, on the 3Myr timescale before supernovae are expected to begin detonating, the fractions of mass expelled by ionizing feedback is a very strong function of the cloud escape velocities. High-mass clouds are largely unaffected dynamically, while lower-mass clouds have large fractions of their gas reserves expelled on this timescale. However, the fractions of stellar mass unbound are modest and significant portions of the unbound stars are so only because the clouds themselves are initially partially unbound. We find that ionization is much more able to create well-cleared bubbles in the unbound clouds, owing to their intrinsic expansion, but that the presence of such bubbles does not necessarily indicate that a given cloud has been strongly influenced by feedback. We also find, in common with the bound clouds from our earlier work, that many of the systems simulated here are highly porous to photons and supernova ejecta, and that most of them will likely survive their first supernova explosions.Comment: 14 pages, 13 figures (some degraded and greyscaled), accepted by MNRA

Estimating the Payoff to Attending a More Selective College: An Application of Selection on Observables and Unobservables

There are many estimates of the effect of college quality on students' subsequent earnings. One difficulty interpreting past estimates, however, is that elite colleges admit students, in part, based on characteristics that are related to their earnings capacity. Since some of these characteristics are unobserved by researchers who later estimate wage equations, it is difficult to parse out the effect of attending a selective college from the students' pre-college characteristics. This paper uses information on the set of colleges at which students were accepted and rejected to remove the effect of unobserved characteristics that influence college admission. Specifically, we match students in the newly colleted College and Beyond (C&B) Data Set who were admitted to and rejected from a similar set of institutions, and estimate fixed effects models. As another approach to adjust for selection bias, we control for the average SAT score of the schools to which students applied using both the C&B and National Longitudinal Survey of the High School Class of 1972. We find that students who attended more selective colleges do not earn more than other students who were accepted and rejected by comparable schools but attended less selective colleges. However, the average tuition charged by the school is significantly related to the students' subsequent earnings. Indeed, we find a substantial internal rate of return from attending a more costly college. Lastly, the payoff to attending an elite college appears to be greater for students from more disadvantaged family backgrounds.