Renormalized mean-field analysis of antiferromagnetism and d-wave superconductivity in the two-dimensional Hubbard model

We analyze the competition between antiferromagnetism and superconductivity in the two-dimensional Hubbard model by combining a functional renormalization group flow with a mean-field theory for spontaneous symmetry breaking. Effective interactions are computed by integrating out states above a scale Lambda_{MF} in one-loop approximation, which captures in particular the generation of an attraction in the d-wave Cooper channel from fluctuations in the particle-hole channel. These effective interactions are then used as an input for a mean-field treatment of the remaining low-energy states, with antiferromagnetism, singlet superconductivity and triplet pi-pairing as the possible order parameters. Antiferromagnetism and superconductivity suppress each other, leaving only a small region in parameter space where both orders can coexist with a sizable order parameter for each. Triplet pi-pairing appears generically in the coexistence region, but its feedback on the other order parameters is very small.Comment: 28 pages, 14 figure

Demand and Pricing in Electricity Markets: Evidence from San Diego During California's Energy Crisis

We study the electricity consumption of San Diego-area households following a series of price changes and related events during California's energy crisis in 2000-01. The analysis uses a five-year panel of disaggregate billing and weather data for a random sample of 70,000 households. In contrast to prior work, these data allow us to proceed without behavioral assumptions regarding a consumer's knowledge of energy prices. We find that after a rapid price increase in summer 2000, consumption fell substantially over about 60 days, averaging 12% per household; consumption then rebounded to within 3% of pre-crisis levels after a price cap was imposed. Under the price cap public appeals for energy conservation and a remunerative voluntary conservation program had significant, but transitory, effects. Further, a large share of households reduced electricity consumption substantially (over 10%) but saved small monetary amounts ($10 or less). Overall, the results indicate consumers may be far more responsive to pecuniary and non-pecuniary incentives for altering their energy use than is commonly believed.

Evaluating Welfare with Nonlinear Prices

This paper examines how to evaluate consumer welfare when consumers face nonlinear prices. This problem arises in many settings, such as devising optimal pricing strategies for firms, assessing how price discrimination affects consumers, and evaluating the efficiency costs of many transfer programs in the public sector. We extend prior methods to accommodate a broad range of modern pricing practices, including menus of pricing plans. This analysis yields a simpler and more general technique for evaluating exact consumer surplus changes in settings where consumers face nonlinear prices. We illustrate our method using recent changes in mobile phone service plans.

Tracking the GLOMR satellite

The task of day-to-day low orbiting satellite tracking utilizing the NAVSPASUR orbital elements is discussed and methods for improving pass time predictions are presented. Estimates are needed for preprogramming of satellite-initiated communications scheduling which requires an accuracy of approximately 30 seconds. This can be achieved by removing the variance associated with the NAVSPASUR D sub 2 (decay) term. Finally, the shock evidenced in GLOMR's orbit on February 7, 1986 is documented and attributed to a severe solar storm with immediately enhanced drag. GLOMR's life expectancy in orbit is now estimated to have dropped approximately 17% by the end of orbit in early February, 1987

Household Electricity Demand, Revisited

Recent efforts to restructure and partially deregulate electricity markets have renewed interest in understanding how consumers respond to price changes. Several interrelated problems complicate demand analyses of these markets, including nonlinear pricing, heterogeneity in households' price sensitivities, and data aggregation. This paper formulates a model of household electricity demand that addresses these difficulties. We estimate the model using data for a representative sample of California households, and summarize how electricity demand elasticities vary in that state. We then use the model to analyze the electricity consumption and expenditure effects of recent tariff structure changes in California.

Osmotic force resisting chain insertion in a colloidal suspension

We consider the problem of inserting a stiff chain into a colloidal suspension of particles that interact with it through excluded volume forces. The free energy of insertion is associated with the work of creating a cavity devoid of colloid and sufficiently large to accomodate the chain. The corresponding work per unit length is the force that resists the entry of the chain into the colloidal suspension. In the case of a hard sphere fluid, this work can be calculated straightforwardly within the scaled particle theory; for solutions of flexible polymers, on the other hand, we employ simple scaling arguments. The forces computed in these ways are shown, for nanometer chain and colloid diameters, to be of the order of tens of pN for solution volume fraction for biophysical processes such as the ejection of DNA from viral capsids into the cell cytoplasm.Comment: 16 pages,3 figures. Accepted for publication in European Physical Journal

Preliminary characterization of a one-axis acoustic system

The acoustic fields and levitation forces produced along the axis of a single-axis resonance system were measured. The system consisted of a St. Clair generator and a planar reflector. The levitation force was measured for bodies of various sizes and geometries (i.e., spheres, cylinders, and discs). The force was found to be roughly proportional to the volume of the body until the characteristic body radius reaches approximately 2/k (k = wave number). The acoustic pressures along the axis were modeled using Huygens principle and a method of imaging to approximate multiple reflections. The modeled pressures were found to be in reasonable agreement with those measured with a calibrated microphone

Method and apparatus for shaping and enhancing acoustical levitation forces

A method and apparatus for enhancing and shaping acoustical levitation forces in a single-axis acoustic resonance system wherein specially shaped drivers and reflectors are utilized to enhance to levitation force and better contain fluid substance by means of field shaping is described

Visual representations of women in a Jamaican school science textbook

The gender gap in post-compulsory science education remains a key concern for educators in many countries. Over the last two decades significant effort has been placed in a number of initiatives aimed not only at raising the profile of science in schools, but also at widening female participation. Despite these initiatives, the rate of female participation in science has typically remained below that of males. Although many reasons have been advanced to explain this, visual representations in school science textbooks remain under-researched. Against a background of gender disparity in the Jamaican education system, this article examines the extent to which visual representations in a widely used school science textbook reinforce or ameliorate gender stereotypes. The results indicate that the textbook presents implicit support for gender-biased messages, though in ways that are more subtle than might be supposed. There were a number of ways in which the images did not favour males over females but there were also other ways in which males were more likely to be portrayed as powerful and in high-status ‘positions’, while females were more likely to be depicted in inferior situations. Such gender representations may affect how students see themselves in relation to science