Calculation of shock-separated turbulent boundary layers

Numerical solutions of the complete, time-averaged conservation equations using several eddy-viscosity models for the Reynolds shear stress to close the equations are compared with experimental measurements in a compressible, turbulent separated flow. An efficient time-splitting, explicit difference scheme was used to solve the two-dimensional conservation equations. The experiment used for comparison was a turbulent boundary layer that was separated by an incident shock wave in a Mach 2.93 flow with a unit Reynolds number of 5.7 x 10 to the seventh power m. Comparisons of predicted and experimental values of surface pressure, shear stress along the wall, and velocity profiles are shown. One of the tested eddy-viscosity models which allows the shear stress to be out of equilibrium with the mean flow produces substantially better agreement with the experimental measurements than the simpler models. A tool is thereby provided for inferring additional information about the flow, such as static pressures in the stream, which might not be directly obtainable from experiments

Cotton spinning to climbing gear: practical aspects of design evolution in Lancashire and the North West of England

This article looks at the role of path dependency in the design of outdoor clothing and equipment, from the perspective of changing and overlapping industrial clusters in Lancashire and Sheffield, from the 1960s. It demonstrates that, unlike the fashion market, design in mountaineering clothing and equipment was originally based heavily upon functionality and hence on user innovation. It shows that skills and knowledge which evolved during the industrial revolution, in both industrial areas, were vitally important to the development of internationally competitive mountaineering equipment firms. It was, however, the way in which these sources of knowledge were combined with sporting expertise that contributed to the design of innovative functional products. In addition, fundamental changes occurred in the relationship between manufacturers and their customers and these were vital to the success of this process, marking a departure from past practice

Trends in Outcomes for Young People with Disabilities: Are We Making Progress?

This paper uses the Current Population Survey (CPS) from 1981-2000 to compare long term trends in socio-economic outcomes for youth (aged 15-21) and young adults (aged 22-29) with work limitations to those for youth and young adults without work limitations. We focus on the years 1988 and 1999: years that roughly correspond to the peaks of successive business cycles. We find that prevalence of work limitations declined for males but increased for females, mostly accounted for by growth for African American females. Despite a substantial reduction in the educational attainment gap between young adults with and without disabilities, gaps in employment, earnings, dependency on public programs and poverty widened substantially. These trends could be due to factors that determine whether individuals report themselves to be work-limited, factors that affect individual outcomes regardless of self-reported work limitation status, or both sets of factors

Control of broad-area vertical-cavity surface emitting laser emission by optically induced photonic crystals

We control the emission properties of a broad-area vertical-cavity surface emitting laser by coupling it to an external feedback cavity containing a photorefractive crystal with an optically induced photonic lattice. The periodic modulation of the refractive index serves as a tunable filter and enables the dynamic suppression of unwanted spatial instabilities and modes, as originally suggested by Gomila et al

Spin Coherence and 14^{14}N ESEEM Effects of Nitrogen-Vacancy Centers in Diamond with X-band Pulsed ESR

Pulsed ESR experiments are reported for ensembles of negatively-charged nitrogen-vacancy centers (NV$^-$) in diamonds at X-band magnetic fields (280-400 mT) and low temperatures (2-70 K). The NV$^-$ centers in synthetic type IIb diamonds (nitrogen impurity concentration $<1$~ppm) are prepared with bulk concentrations of $2\cdot 10^{13}$ cm$^{-3}$ to $4\cdot 10^{14}$ cm$^{-3}$ by high-energy electron irradiation and subsequent annealing. We find that a proper post-radiation anneal (1000$^\circ$C for 60 mins) is critically important to repair the radiation damage and to recover long electron spin coherence times for NV$^-$s. After the annealing, spin coherence times of T$_2 = 0.74$~ms at 5~K are achieved, being only limited by $^{13}$C nuclear spectral diffusion in natural abundance diamonds. At X-band magnetic fields, strong electron spin echo envelope modulation (ESEEM) is observed originating from the central $^{14}$N nucleus. The ESEEM spectral analysis allows for accurate determination of the $^{14}$N nuclear hypefine and quadrupole tensors. In addition, the ESEEM effects from two proximal $^{13}$C sites (second-nearest neighbor and fourth-nearest neighbor) are resolved and the respective $^{13}$C hyperfine coupling constants are extracted.Comment: 10 pages, 5 figure

Five Principles for Vertical Merger Enforcement Policy

There seems to be consensus that the Department of Justice’s 1984 Vertical Merger Guidelines do not reflect either modern theoretical and empirical economic analysis or current agency enforcement policy. Yet widely divergent views of preferred enforcement policies have been expressed among agency enforcers and commentators. Based on our review of the relevant economic literature and our experience analyzing vertical mergers, we recommend that the enforcement agencies adopt five principles: (i) The agencies should consider and investigate the full range of potential anticompetitive harms when evaluating vertical mergers; (ii) The agencies should decline to presume that vertical mergers benefit competition on balance in the oligopoly markets that typically prompt agency review, nor set a higher evidentiary standard based on such a presumption; (iii) The agencies should evaluate claimed efficiencies resulting from vertical mergers as carefully and critically as they evaluate claimed efficiencies resulting from horizontal mergers, and require the merging parties to show that the efficiencies are verifiable, merger-specific and sufficient to reverse the potential anticompetitive effects; (iv) The agencies should decline to adopt a safe harbor for vertical mergers, even if rebuttable, except perhaps when both firms compete in unconcentrated markets; (v) The agencies should consider adopting rebuttable anticompetitive presumptions that a vertical merger harms competition when certain factual predicates are satisfied. We do not intend these presumptions to describe all the ways by which vertical mergers can harm competition, so the agencies should continue to investigate vertical mergers that raise concerns about input and customer foreclosure, loss of a disruptive or maverick firm, evasion of rate regulation or other threats to competition, even if the specific factual predicates of the presumptions are not satisfied

High Accuracy Fuel Flowmeter, Phase 1

Technology related to aircraft fuel mass - flowmeters was reviewed to determine what flowmeter types could provide 0.25%-of-point accuracy over a 50 to one range in flowrates. Three types were selected and were further analyzed to determine what problem areas prevented them from meeting the high accuracy requirement, and what the further development needs were for each. A dual-turbine volumetric flowmeter with densi-viscometer and microprocessor compensation was selected for its relative simplicity and fast response time. An angular momentum type with a motor-driven, spring-restrained turbine and viscosity shroud was selected for its direct mass-flow output. This concept also employed a turbine for fast response and a microcomputer for accurate viscosity compensation. The third concept employed a vortex precession volumetric flowmeter and was selected for its unobtrusive design. Like the turbine flowmeter, it uses a densi-viscometer and microprocessor for density correction and accurate viscosity compensation