21,617 research outputs found
Effective diffusion constant in a two dimensional medium of charged point scatterers
We obtain exact results for the effective diffusion constant of a two
dimensional Langevin tracer particle in the force field generated by charged
point scatterers with quenched positions. We show that if the point scatterers
have a screened Coulomb (Yukawa) potential and are uniformly and independently
distributed then the effective diffusion constant obeys the
Volgel-Fulcher-Tammann law where it vanishes. Exact results are also obtained
for pure Coulomb scatterers frozen in an equilibrium configuration of the same
temperature as that of the tracer.Comment: 9 pages IOP LaTex, no figure
Taxing a Commodity With and Without Revenue Neutrality: An Exploration Using a Calibrated Theoretical Consumer Equilibrium Model
It has long been recognized that taxing a commodity that generates negative externalities can be used to reduce the consumption of that commodity. A variant involves the imposition of revenue neutrality but that may alter the tax rate required to meet a consumption reduction target. We explore the relationships among the commodity tax rate, the demand and supply elasticities, and the revenue offsets by calibrating a theoretical consumer equilibrium model and then recalibrating it with alternative parameter configurations. For each configuration we simulate equilibrium for three policy scenarios: no neutrality, neutrality achieved by subsidizing other commodities, and neutrality achieved by income transfer.Consumer Market Equilibrium; Commodity Taxation; Revenue Neutrality
Barrier island erosion and overwash study -- effect of seawalls. Volume 2
This is the second of a pair of reports documenting the effects of storms on beach systems
including the presence of seawalls. With the aim of simulating the effects of overwash on
barrier islands with seawalls and characterizing their response, a series of eight experiments
was conducted at the Coastal Engineering Laboratory of the University of Florida. The barrier
island was simulated by a 400 feet wide horizontal crest and an initially uniform mildly-sloped
(1:19) beach. The effects of positioning the seawall at two different locations as well as the effects
of various storm surge levels and accompanying overtopping were investigated. Experiments
were conducted with both regular and irregular storm waves. With the seawall located at the
slope break between the crest and the sloping beach of the barrier island, and the crest of the
seawall just submerged in sand, the effects on the sediment transport process were found to be
minimal. For the same position of the seawall but with the crest of the seawall raised above the
surrounding ground level, overtopping caused washover of sand indicating substantial transport
in suspension. Increased levels of overtopping tended to accentuate bed profile changes but
supress bar formation (as did irregular waves). Positioning the seawall at the Mean Sea Level
shoreline caused significant scour both immediately landward as well as immediately seaward
of the seawall. A prominent scour trough developed further seaward. The longshore bar was
highly three-dimensional. It appears that seawalls need to be located adequately landward of the
shoreline to discharge their function effectively without adverse effect to the beach. In addition,
concerns for safety warrant the presence of an adequate buffer-zone between the seawall and
the upland property. (61 pp.
Aggregation and Other Biases in the Calculation of Consumer Elasticities for Models of Arbitrary Rank
Consumer-related policy decisions often require analysis of aggregate responses or mean elasticities. However, in practice these mean elasticities are seldom used. Mean elasticities can be approximated using aggregate data, but that introduces aggregation bias for full and compensated price elasticities, though interestingly not for expenditure elasticities. The biases corresponding to incorrect approximations of mean elasticities depend on the type of data (micro or aggregate), the type and rank of the model, and generalized measures of income inequality. These biases are distinct from the biases (already noted in the literature) when using aggregate data to estimate micro elasticites at mean income.Aggregate price and expenditure elasticities, aggregation bias, consumer demand, generalized measures of income inequality, income distribution
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