Finite-Amplitude Instability of the Compressible Laminar Wake. Strongly Amplified Disturbances

The interaction between mean flow and finite‐amplitude disturbances in certain experimentally observed unstable, compressible laminar wakes is considered theoretically without explicitly assuming small amplification rates. Boundary‐layer form of the two‐dimensional mean‐flow momentum, kinetic energy and thermal energy equations and the time‐averaged kinetic energy equation of spatially growing disturbances are recast into their respective von Kármán integral form which show the over‐all physical coupling. The Reynolds shear stresses couple the mean flow and disturbance kinetic energies through the conversion mechanism familiar in low‐speed flows. Both the mean flow and disturbance kinetic energies are coupled to the mean‐flow thermal energy through their respective viscous dissipation. The work done by the disturbance pressure gradients gives rise to an additional coupling between the disturbance kinetic energy and the mean‐flow thermal energy. The compressibility transformation suggested by work on turbulent shear flows is not applicable to this problem because of the accompanying ad hoc assumptions about the disturbance behavior. The disturbances of a discrete frequency which corresponds to the most unstable fundamental component, are first evaluated locally. Subsequent mean‐flow and disturbance profile‐shape assumptions are made in terms of a mean‐flow‐density Howarth variable. The compressibility transformation, which cannot convert this problem into a form identical to the low‐speed problem of Ko, Kubota, and Lees because of the compressible disturbance quantities, nevertheless, yields a much simplified description of the mean flow

Computers, Learning Outcomes, and the Choices Facing Students

We model the tradeoff students face between devoting time to coursework and time for other activities. We show how the model can be used to identify whether computers are productive tools and whether students will learn more when using computers. We present our own empirical findings, in a case study focusing on college composition. Only one-sixth of the students in our study fall into the category indicating that the computer was a productivity enhancing tool even though more than half achieved the same or higher measure of learning.

Invariant Variation Problems

The problems in variation here concerned are such as to admit a continuous group (in Lie's sense); the conclusions that emerge from the corresponding differential equations find their most general expression in the theorems formulated in Section 1 and proved in following sections. Concerning these differential equations that arise from problems of variation, far more precise statements can be made than about arbitrary differential equations admitting of a group, which are the subject of Lie's researches. What is to follow, therefore, represents a combination of the methods of the formal calculus of variations with those of Lie's group theory. For special groups and problems in variation, this combination of methods is not new; I may cite Hamel and Herglotz for special finite groups, Lorentz and his pupils (for instance Fokker), Weyl and Klein for special infinite groups. Especially Klein's second Note and the present developments have been mutually influenced by each other, in which regard I may refer to the concluding remarks of Klein's Note.Comment: M. A. Tavel's English translation of Noether's Theorems (1918), reproduced by Frank Y. Wang. Thanks to Lloyd Kannenberg for corrigend

Psychological and physiological correlates of stress: Performance on a cooperative task

The relationship of personality dimensions to performance was investigated. The personality measure used to select subjects, the Barratt impulsiveness scale, is hypothesized to be related to a style of behavior which should affect the trend of choices which various subjects will make. Personality dimensions were specifically examined during performance of a cooperative task, the Prisoner's Dilemma

POPCORN: a Supervisory Control Simulation for Workload and Performance Research

A multi-task simulation of a semi-automatic supervisory control system was developed to provide an environment in which training, operator strategy development, failure detection and resolution, levels of automation, and operator workload can be investigated. The goal was to develop a well-defined, but realistically complex, task that would lend itself to model-based analysis. The name of the task (POPCORN) reflects the visual display that depicts different task elements milling around waiting to be released and pop out to be performed. The operator's task was to complete each of 100 task elements that ere represented by different symbols, by selecting a target task and entering the desired a command. The simulated automatic system then completed the selected function automatically. Highly significant differences in performance, strategy, and rated workload were found as a function of all experimental manipulations (except reward/penalty)

Do Frictions Matter in the Labor Market? Accessions, Separations and Minimum Wage Effects

We measure labor market frictions using a strategy that bridges design-based and structural approaches: estimating an equilibrium search model using reduced-form minimum wage elasticities identified from border discontinuities and fitted with Bayesian and LIML methods. We begin by providing the first test of U.S. minimum wage effects on labor market flows and find negative effects on employment flows, but not levels. Separations and accessions fall among restaurants and teens, especially those with low tenure. Our estimated parameters of a search model with wage posting and heterogeneous workers and firms imply that frictions help explain minimum wage effects.minimum wage, labor market flows, monopsony, Bayesian estimation

Interactivity within IMS Learning Design and Question and Test Interoperability

We examine the integration of IMS Question and Test Interoperability (QTI) and IMS Learning Design (LD) in implementations of E-learning from both pedagogical and technological points of view. We propose the use of interactivity as a parameter to evaluate the quality of assessment and E-learning, and assess various cases of individual and group study for their interactivity, ease of coding, flexibility, and reusability. We conclude that presenting assessments using IMS QTI provides flexibility and reusability within an IMS LD Unit Of Learning (UOL) for individual study. For group study, however, the use of QTI items may involve coding difficulties if group members need to wait for their feedback until all students have attempted a question, and QTI items may not be able to be used at all if the QTI services are implemented within a service-oriented architecture

Limb Darkening and Planetary Transits: Testing Center-to-limb Intensity Variations and Limb-Darkening Directly from Model Stellar Atmospheres

The transit method, employed by MOST, \emph{Kepler}, and various ground-based surveys has enabled the characterization of extrasolar planets to unprecedented precision. These results are precise enough to begin to measure planet atmosphere composition, planetary oblateness, star spots, and other phenomena at the level of a few hundred parts-per-million. However, these results depend on our understanding of stellar limb darkening, that is, the intensity distribution across the stellar disk that is sequentially blocked as the planet transits. Typically, stellar limb darkening is assumed to be a simple parameterization with two coefficients that are derived from stellar atmosphere models or fit directly. In this work, we revisit this assumption and compute synthetic planetary transit light curves directly from model stellar atmosphere center-to-limb intensity variations (CLIV) using the plane-parallel \textsc{Atlas} and spherically symmetric \textsc{SAtlas} codes. We compare these light curves to those constructed using best-fit limb-darkening parameterizations. We find that adopting parametric stellar limb-darkening laws lead to systematic differences from the more geometrically realistic model stellar atmosphere CLIV of about 50 -- 100 ppm at the transit center and up to 300 ppm at ingress/egress. While these errors are small they are systematic, and appear to limit the precision necessary to measure secondary effects. Our results may also have a significant impact on transit spectra.Comment: 12 pages, 14 figures, accepted for publication in ApJ after revision

An Economic Analysis of the Possible Implications of the Abolition of the Basing Point System of Pricing on the Steel Industry in Utah

The production of iron in America began in a limited area east of the Aleghenies, centered around Philadelphia, which was also a principal port of entry for foreign iron. As early as 1750, pricing was done on a rudimentary basing point structure. Apparently, all prices on domestic iron were quoted on a Philadelphia base and were higher in the outlying territory where the iron was actually made. The manufacturers absorbed freight in order to move their iron to the central market, where it competed with foreign iron. This study will be confined to a discussion of the possible implications of the abandonment of the basing point system of pricing by the steel industry in Utah. For purposes of comparison, a rather detailed discussion of the basing point system will be included, and to clarify the present legal status of delivered pricing, some court history will be summarized. Without doubt, a new pricing policy in the steel industry will have some rather far reaching effects, both on other industries and upon the economy of this region. These possible effects will be discussed. The abandonment of the basing point system of pricing by the steel industry creates many problems as to the adjustments which will be necessary under the new pricing systems. It will be the aim of this sutdy to ascertain the possible nature and extent of these adjustments, and their effect, both upon the Utah steel industry and upon the economy of this area. Since the abandonment of basing point pricing is a rather recent development, this thesis, of necessity, will be in the nature of a prediction as to some of the possible economic implications of this action

Chas. T. Lester to Dr. Silver, 4 September 1963

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