Rationing can backfire : the day without a car in Mexico City

In November 1989, Mexico City's administration imposed a regulation banning each car from driving on a specific day of the week. The regulation has been both popular and controversial. Some feel that it is a reasonable concession aimed at alleviating congestion and pollution problems. Others feel it is both inefficient and unfair: inefficient in the way most rationing systems are inefficent, and unfair in that it is costly to some and easily avoided or accommodated by others. Some feel that it may also be so inefficient that it is counterproductive. The authors found evidence to support that view. Many households bought an additional car to get additional driving permits, and the amount of driving increased. Greater use of old cars and increased weekend driving may have contributed to the disappointing results of Mexico's one-day ban on driving: high welfare costs and none of the intended benefits.Roads&Highways,Economic Theory&Research,Environmental Economics&Policies,Financial Crisis Management&Restructuring,Country Strategy&Performance,Economic Theory&Research,Environmental Economics&Policies,Roads&Highways,Financial Crisis Management&Restructuring,Transport and Environment

Is demand for polluting goods manageable? an econometric study of car ownership and use in Mexico

Charging for social marginal costs is efficient regardless of price elasticities, but the importance of getting prices"right"is greater the more manageable, or elastic, the demand. In efficient pollution control programs, options to make cars cleaner are combined optimally with demand conservation. The roles played by"cleaner cars"as compared with"fewer trips"are determined by empirical parameters: cheap, clean technologies would imply a great role for cleaner cars, while high demand elasticities lead to a greater role for demand reduction. In seminal research, evisence was found to support the hypothesis that demand for commodities such as gasoline should have lower price elasticities and higher income elasticities in developing than in industrial countries. The authors estimate a model of gasoline demand and car ownership in Mexico, using a panel of annual observations by state. Key features they introduce are instrumental variables on different data and the treatment of (1) possible dynamics, (2) measurement errors in the data, and (3) unobserved characteristics in individual states. They use tests of serial correlation in the residuals to model the dynamics properly. The resulting model is one of almost immediate adjustment, with a short-term price elasticity for gasoline close to the long-term estimate of -0.8. The model displays elasticities that are lower (for income) and higher (for price) than those hypothesized, and are within the range of elasticities found in industrial countries. Byproducts of the model: The elasticity of car purchases with respect to gasoline prices is positive. Scrappage decisions are affected by income and by car and gasoline prices. And these elasticities are not significantly different in the richer states. For policy purposes, these findings do not support"elasticity pessimism"The use of car services is sensitive to pricing, which suggests that consumers, for some of their demand, have reasonably good alternatives to car services. Consideration of external costs - such as accidents, congestion, air pollution, and road damage - thus involve considerable demand conservation.Inequality,Transport and Environment,Energy and Environment,Economic Theory&Research,Environmental Economics&Policies

Curvature Inheritance Symmetry In Riemannian Spaces with Applications to String Cloud and String Fluids

We study, in this paper, curvature inheritance symmetry (CI), $\pounds_{\xi}R_{bcd}^{a}=2\alpha R_{bcd}^{a}$, where $\alpha$ is a scalar function, for string cloud and string fluid in the context of general relativity. Also, we have obtained some result when a proper CI (i.e., $\alpha \neq 0$) is also a conformal Killing vector.Comment: 14 pages, Latex, no figures, to appear in the International Journal of Modern Physics D (IJMPD), Vol.8, No.5(Oct.,1999

Enhancing capacity of coherent optical information storage and transfer in a Bose-Einstein condensate

Coherent optical information storage capacity of an atomic Bose-Einstein condensate is examined. Theory of slow light propagation in atomic clouds is generalized to short pulse regime by taking into account group velocity dispersion. It is shown that the number of stored pulses in the condensate can be optimized for a particular coupling laser power, temperature and interatomic interaction strength. Analytical results are derived for semi-ideal model of the condensate using effective uniform density zone approximation. Detailed numerical simulations are also performed. It is found that axial density profile of the condensate protects the pulse against the group velocity dispersion. Furthermore, taking into account finite radial size of the condensate, multi-mode light propagation in atomic Bose-Einstein condensate is investigated. The number of modes that can be supported by a condensate is found. Single mode condition is determined as a function of experimentally accessible parameters including trap size, temperature, condensate number density and scattering length. Quantum coherent atom-light interaction schemes are proposed for enhancing multi-mode light propagation effects.Comment: 12pages. Laser Physics, in pres

Direct observation of LO phonon-plasmon coupled modes in the infrared transmission spectra of n-GaAs and n-InxGa1-xAs epilayers

The infrared transmission spectrum of Si-doped molecular beam epitaxy (MBE)-grown GaAs epilayers, 2-2.5-mum thick, measured in the oblique (Berreman) geometry, revealed distinct minima in p polarization. Given epilayer thickness \u3c reststrahlen wavelength, the minima are identified as the zone-center transverse optic phonon (omega(TO)) and the high-frequency LO phonon-plasmon coupled mode (omega(+)). Analysis of the experimental data yielded free-carrier concentrations ranging from 2.5x10(17) to 1.4x10(18) cm(-3). The same technique with MBE-grown Si-doped In0.53Ga0.47As epilayers (0.5-1 mum thick) yielded omega(+) modes corresponding to free-carrier concentrations of 8.2x10(16)-2.7x10(19) cm(-3). The observations of the transmission minima in the Berreman geometry and their interpretation demonstrate a direct and simple method for deducing free-carrier concentrations over a wide range

Soap Froths and Crystal Structures

We propose a physical mechanism to explain the crystal symmetries found in macromolecular and supramolecular micellar materials. We argue that the packing entropy of the hard micellar cores is frustrated by the entropic interaction of their brush-like coronas. The latter interaction is treated as a surface effect between neighboring Voronoi cells. The observed crystal structures correspond to the Kelvin and Weaire-Phelan minimal foams. We show that these structures are stable for reasonable areal entropy densities.Comment: 4 pages, RevTeX, 2 included eps figure

Implementing Service Learning in Pre-service Teacher Coursework

Service learning remains a topic of interest in higher education. It has become more prevalent in teacher preparation programs with the intent of providing the opportunity for pre-service teachers to become engaged with individuals who have different life experiences than their own. Lessons can be learned through a review of the literature and the examination of existing models of service learning, including an honest discussion of the advantages and potential barriers for all stakeholders