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.

Single-File Diffusion of Flagellin in Flagellar Filaments

A bacterial flagellar filament is a cylindrical crystal of a protein known as flagellin. Flagellin subunits travel from the cytoplasm through a 2 nm axial pore and polymerize at the filament’s distal end. They are supplied by a pump in the cell membrane powered by a proton-motive force. In a recent experiment, it was observed that growth proceeded at a rate of approximately one subunit every 2 s. Here, we asked whether transport of subunits through the pore at this rate could be effected by single-file diffusion, which we simulated by a random walk on a one-dimensional lattice. Assuming that the subunits are α-helical, the answer is yes, by a comfortable margin.Molecular and Cellular BiologyPhysic

Growth of Flagellar Filaments of Escherichia coli is Independent of Filament Length

Bacterial flagellar filaments grow at their distal ends, from flagellin that travels through a central channel $\sim 2 nm$ in diameter. The flagellin is extruded from the cytoplasm by a pump powered by a proton motive force (PMF). We measured filament growth in cells near the mid-exponential-phase with flagellin bearing a specific cysteine-for-serine substitution, allowing filaments to be labeled with sulfhydryl-specific fluorescent dyes. We labeled filaments first with a green maleimide dye and then, following an additional period of growth, with a red maleimide dye. The contour lengths of the green and red segments were measured. The average lengths of red segments $(2.3 \mu m)$ were the same regardless of the lengths of the green segments from which they grew (ranging from less than 1 to more than $9 \mu m$ in length). Thus, flagellar filaments do not grow at a rate that decreases exponentially with length, as formerly supposed. If flagellar filaments were broken by viscous shear, the broken filaments continued to grow. Identical results were obtained whether flagellin was expressed from fliC on the chromosome under the control of its native promoter or on a plasmid under the control of the arabinose promoter.Molecular and Cellular BiologyPhysic

Properties of the Scale Invariant O(g4)O(g^4) Lipatov Kernel

We study the scale-invariant $O(g^4)$ kernel which appears as an infra-red contribution in the BFKL evolution equation and is constructed via multiparticle $t$-channel unitarity. We detail the variety of Ward identity constraints and infra-red cancellations that characterize its infrared behaviour. We give an analytic form for the full non-forward kernel. For the forward kernel controlling parton evolution at small-x, we give an impact parameter representation, derive the eigenvalue spectrum, and demonstrate a holomorphic factorisation property related to conformal invariance. The results show that, at next-to-leading-order, the transverse momentum infra-red region may produce a strong reduction of the BFKL small-x behavior.Comment: 41 pages in latex, 16 figs. in a uu-encoded ps-fil

Locating helicopter emergency medical service bases to optimise population coverage versus average response time

__Background:__ New South Wales (NSW), Australia has a network of multirole retrieval physician staffed helicopter emergency medical services (HEMS) with seven bases servicing a jurisdiction with population concentrated along the eastern seaboard. The aim of this study was to estimate optimal HEMS base locations within NSW using advanced mathematical modelling techniques. __Methods:__ We used high resolution census population data for NSW from 2011 which divides the state into areas containing 200-800 people. Optimal HEMS base locations were estimated using the maximal covering location problem facility location optimization model and the average response time model, exploring the number of bases needed to cover various fractions of the population for a 45 min response time threshold or minimizing the overall average response time to all persons, both in green field scenarios and conditioning on the current base structure. We also developed a hybrid mathematical model where average response time was optimised based on minimum population coverage thresholds. __Results:__ Seven bases could cover 98% of the population within 45mins when optimised for coverage or reach the entire population of the state within an average of 21mins if optimised for response time. Given the existing bases, adding two bases could either increase the 45 min coverage from 91% to 97% or decrease the average response time from 21mins to 19mins. Adding a single specialist prehospital rapid response HEMS to the area of greatest population concentration decreased the average state wide response time by 4mins. The optimum seven base hybrid model that was able to cover 97.75% of the population within 45mins, and all of the population in an average response time of 18 mins included the rapid response HEMS model. __Conclusions:__ HEMS base locations can be optimised based on either percentage of the population covered, or average response time to the entire population. We have also demonstrated a hybrid technique that optimizes response time for a given number of bases and minimum defined threshold of population coverage. Addition of specialized rapid response HEMS services to a system of multirole retrieval HEMS may reduce overall average response times by improving access in large urban areas

Vertical Migration, Orientation, Aggregation, and Fecundity of the Freshwater Mussel Lampsilis Siliquoidea

Author Institution: Department of Zoology, Miami UniversityThe decline in freshwater mussels makes it imperative that more information be gathered on their population status, behavior, and habitat requirements. We examined vertical migration, aggregation, and reproductive potential of captive and field populations of Lampsilis siliquoidea. Both captive populations and a field population exhibited vertical migration. This movement was strongly correlated with day length, and somewhat less strongly correlated with water temperature. While captive mussels tended to orient their siphons into the current, no pattern of orientation was detected in the field population. The field population was significantly aggregated in the fall and winter. The spatial patterning of captive mussels was random in the fall and winter, but this result may have been an artifact of the small size of the artificial streams. Weather conditions prevented data collection in the spring and, therefore, no conclusions could be drawn about the relationship between aggregation and glochidia release. The average number of glochidia (parasitic larvae) produced by individuals across a limited size range was not correlated with any maternal or marsupial properties. These results are useful for implementing qualitative sampling methods under optimum conditions and for information on the reproductive potential of Lampsilis siliquoidea

LADEE Preparations for Contingency Operations for the Lunar Orbit Insertion Maneuver

The Lunar Atmosphere and Dust Environment Explorer (LADEE) spacecraft was launched on September 7, 2013 UTC, and completed its mission on April 17, 2014 UTC with a directed impact to the Lunar Surface. Its primary goals were to examine the lunar atmosphere, measure lunar dust, and to demonstrate high rate laser communications. The mission objectives, much of which can be attributed to careful LADEE mission was a resounding success, achieving all planning and preparation. This paper discusses the specific preparations for fault conditions that could occur during a highly-critical phase of the mission, the Lunar Orbit Insertion (LOI). highly critical phase of the mission

School Vouchers: Settled Questions, Continuing Disputes

Provides an assessment of the constitutional principles announced by the Court, following the June 2002 decision in the Cleveland school voucher case. Presents contrasting arguments on educational policy that address key issues about the decision

A Complete Scheme of Ionization Cooling for a Muon Collider

A complete scheme for production and cooling a muon beam for three specified muon colliders is presented. Parameters for these muon colliders are given. The scheme starts with the front end of a proposed neutrino factory that yields bunch trains of both muon signs. Emittance exchange cooling in slow helical lattices reduces the longitudinal emittance until it becomes possible to merge the trains into single bunches, one of each sign. Further cooling in all dimensions is applied to the single bunches in further slow helical lattices. Final transverse cooling to the required parameters is achieved in 50 T solenoids using high Tc superconductor at 4 K. Preliminary simulations of each element are presented.Comment: 3 pages, 6 figure