7,326 research outputs found
Price Dispersion and Accessibility: A Case study of Fast Food
This study examines spatial variation in the price and accessibility of fast food across a major urban area. We use novel data on the price of a representative fast food meal and the location of fast food restaurants belonging to one of three major chains in the District of Columbia and its surrounding suburbs. These data are used to test a structural model of spatial competition. The results of this study are easily interpreted and compared with a past analysis. We find that spatial differences in costs and demand conditions drive variation in the number of firms operating in a market, which in turn affects prices.food prices, food accessibility, spatial competition, price dispersion, fast food
Running-mass models of inflation, and their observational constraints
If the inflaton sector is described by softly broken supersymmetry, and the
inflaton has unsuppressed couplings, the inflaton mass will run strongly with
scale. Four types of model are possible. The prediction for the spectral index
involves two parameters, while the COBE normalization involves a third, all of
them calculable functions of the relevant masses and couplings. A crude
estimate is made of the region of parameter space allowed by present
observation.Comment: Latex file, 20 pages, 11 figures, uses epsf.sty. Comment on the
observation of the spectral index scale dependence added; Fig. 3-6 improve
Differential variational inequalities
International audienceThis paper introduces and studies the class of differential variational inequalities (DVIs) in a finite-dimensional Euclidean space. The DVI provides a powerful modeling paradigm for many applied problems in which dynamics, inequalities, and discontinuities are present; examples of such problems include constrained time-dependent physical systems with unilateral constraints, differential Nash games, and hybrid engineering systems with variable structures. The DVI unifies several mathematical problem classes that include ordinary differential equations (ODEs) with smooth and discontinuous right-hand sides, differential algebraic equations (DAEs), dynamic complementarity systems , and evolutionary variational inequalities. Conditions are presented under which the DVI can be converted, either locally or globally, to an equivalent ODE with a Lipschitz continuous right-hand function. For DVIs that cannot be so converted, we consider their numerical resolution via an Euler time-stepping procedure, which involves the solution of a sequence of finite-dimensiona
An Assessment of Panel vs. Individual Instructor Ratings of Student Speeches
This study addressed the possibility of utilizing a panel of instructors to evaluate student speeches. Forty-six public speaking students were videotaped during an informative speech assignment. Instructor panels evaluated each speech using the same criteria as the real instructor. This study found that trait error exists in panel grading as it does in individual instructor evaluation. Panel and individual instructor ratings were generally similar but inferior speeches were graded lower by the panel than the real instructor. This suggests that panels may be less likely to experience leniency error and may give more accurate evaluations of weaker speeches. Considerations are offered for the possible use of panel evaluations
Comments on gauge-invariance in cosmology
We revisit the gauge issue in cosmological perturbation theory, and highlight
its relation to the notion of covariance in general relativity. We also discuss
the similarities and differences of the covariant approach in perturbation
theory to the Bardeen or metric approach in a non-technical fashion.Comment: 7 pages, 1 figure, revtex4; v3: minor changes, typos corrected,
discussion extended; v4: typos corrected, corresponding to published versio
A -medoids Approach to Exploring Districting Plans
Researchers and legislators alike continue the search for methods of drawing
fair districting plans. A districting plan is a partition of a state's
subdivisions (e.g. counties, voting precincts, etc.). By modeling these
districting plans as graphs, they are easier to create, store, and operate on.
Since graph partitioning with balancing populations is a computationally
intractable (NP-hard) problem most attempts to solve them use heuristic
methods. In this paper, we present a variant on the -medoids algorithm
where, given a set of initial medoids, we find a partition of the graph's
vertices to admit a districting plan. We first use the -medoids process to
find an initial districting plan, then use local search strategies to fine-tune
the results, such as reducing population imbalances between districts. We also
experiment with coarsening the graph to work with fewer vertices. The algorithm
is tested on Iowa and Florida using 2010 census data to evaluate the
effectiveness.Comment: 25 pages, 7 figures, and 6 table
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