Driven waves in a two-fluid plasma

We study the physics of wave propagation in a weakly ionised plasma, as it applies to the formation of multifluid, MHD shock waves. We model the plasma as separate charged and neutral fluids which are coupled by ion-neutral friction. At times much less than the ion-neutral drag time, the fluids are decoupled and so evolve independently. At later times, the evolution is determined by the large inertial mismatch between the charged and neutral particles. The neutral flow continues to evolve independently; the charged flow is driven by and slaved to the neutral flow by friction. We calculate this driven flow analytically by considering the special but realistic case where the charged fluid obeys linearized equations of motion. We carry out an extensive analysis of linear, driven, MHD waves. The physics of driven MHD waves is embodied in certain Green functions which describe wave propagation on short time scales, ambipolar diffusion on long time scales, and transitional behavior at intermediate times. By way of illustration, we give an approximate solution for the formation of a multifluid shock during the collision of two identical interstellar clouds. The collision produces forward- and reverse J shocks in the neutral fluid and a transient in the charged fluid. The latter rapidly evolves into a pair of magnetic precursors on the J shocks, wherein the ions undergo force free motion and the magnetic field grows monotonically with time. The flow appears to be self similar at the time when linear analysis ceases to be valid.Comment: 18 pages including 24 figures, accepted by MNRA

Estimating Brand Level Demand Elasticities and Measuring Market Power for Regular Carbonated Soft Drinks

This paper reports econometric estimation of brand level demand (AIDS) elasticities for regular carbonated soft drinks using Information Resources, Inc. panel data. Own and cross price elasticities are used to measure actual and hypothetical market power that would arise from potential mergers or collusive pricing arrangements.Demand and Price Analysis, Marketing,

The possible effects of lunar mascons on lunar magnetic and electromagnetic experiments Final report

Electromagnetic and magnetic response study of lunar mascons using gravity mode

Dynamic Consistency in Denmark: A Longitudinal Field Experiment

Evidence that individuals have dynamically consistent preferences is usually generated by studying the discount rates of the individual over different horizons, but where those rates are elicited at a single point in time. If these elicited discount rates vary by horizon the individual is typically claimed to have preferences that imply a dynamic inconsistency, although this inference requires additional assumptions such as intertemporal separability. However, what one really wants to know is if the same subject has the same discount rate function when that individual is asked at a later point in time. Such panel tests then require than one allow for possible changes in the states of nature that the subject faces, since they may confound any in-sample comparisons of discount rate functions at different points in time. We report the results of a large-scale panel experiment undertaken in the field that allows us to examine this issue. In June 2003 we elicited subjective discount rates from 253 subjects, representative of the adult Danish population. Between September 2003 and November 2004 we re-visited 97 of these subjects and repeated these tasks. In each visit we also elicited information on their individual characteristics, as well as their expectations about the state of their own economic situation and macroeconomic variables. We find evidence in favor of dynamic consistency.

Latent Process Heterogeneity in Discounting Behavior

We show that observed choices in discounting experiments are consistent with roughly one-half of the subjects using exponential discounting and one-half using quasi-hyperbolic discounting. We characterize the latent data generating process using a mixture model which allows different subjects to behave consistently with each model. Our results have substantive implications for the assumptions made about discounting behavior, and also have significant methodological implications for the manner in which we evaluate alternative models when there may be complementary data generating processes.

Risk Attitudes, Randomization to Treatment, and Self-Selection Into Experiments

Randomization to treatment is fundamental to statistical control in the design of experiments. But randomization implies some uncertainty about treatment condition, and individuals differ in their preferences towards taking on risk. Since human subjects often volunteer for experiments, or are allowed to drop out of the experiment at any time if they want to, it is possible that the sample observed in an experiment might be biased because of the risk of randomization. On the other hand, the widespread use of a guaranteed show-up fee that is non-stochastic may generate sample selection biases of the opposite direction, encouraging more risk averse samples into experiments. We undertake a field experiment to directly test these hypotheses that risk attitudes play a role in sample selection. We follow standard procedures in the social sciences to recruit subjects to an experiment in which we measure their attitudes to risk. We exploit the fact that we know certain characteristics of the population sampled, adults in Denmark, allowing a statistical correction for sample selection bias using standard methods. We also utilize the fact that we have a complex sampling design to provide better estimates of the target population. Our results suggest that randomization bias is not a major empirical problem for field experiments of the kind we conducted if the objective is to identify marginal effects of sample characteristics. However, there is evidence that the use of show-up fees may have generated a sample that was more risk averse than would otherwise have been observed.

Estimating Risk Attitudes in Denmark

We estimate individual risk attitudes using controlled experiments in the field in Denmark. These risk preferences are elicited by means of field experiments involving real monetary rewards. The experiments were carried out across Denmark using a representative sample of 253 people between 19 and 75 years of age. Risk attitudes are estimated for various individuals differentiated by socio-demographic characteristics such as income and age. Our results indicate that the average Dane is risk averse, and that risk neutrality is an inappropriate assumption to apply. We also find that risk attitudes do vary significantly with respect to several important socio-demographic variables. These conclusions are robust to the use of relatively flexible specifications of risk preferences. When individual characteristics of the sample are ignored, relative risk aversion appears not to be constant over the domain of income considered here, and rises rapidly as income increases above "small" amounts. However, relative risk aversion appears to be constant when one corrects for individual heterogeneity, although there is considerable uncertainty in the characterization of risk attitudes for low stakesRisk preferences, field experiments, heterogeneity

Theory, Experimental Design and Econometrics Are Complementary (And So Are Lab and Field Experiments)

Experiments are conducted with various purposes in mind including theory testing, mechanism design and measurement of individual characteristics. In each case a careful researcher is constrained in the experimental design by prior considerations imposed either by theory, common sense or past results. We argue that the integration of the design with these elements needs to be taken even further. We view all these elements that make up the body of research methodology in experimental economics as mutually dependant and therefore take a systematic approach to the design of our experimental research program. Rather than drawing inferences from individual experiments or theories as if they were independent constructs, and then using the findings from one to attack the other, we recognize the need to constrain the inferences from one by the inferences from the other. Any data generated by an experiment needs to be interpreted jointly with considerations from theory, common sense, complementary data, econometric methods and expected applications. We illustrate this systematic approach by reference to a research program centered on large artefactual field experiments we have conducted in Denmark. An important contribution that grew out of our work is the complementarity between lab and field experiments.

Trade Wars and Trade Negotiations in Agriculture

We employ a numerical equilibrium model to evaluate the payoffs to agricultural and non-agricultural interests in the EC and the US. A government objective function for each region is calibrated as a weighted sum of the payoffs to the two interest groups with weights corresponding to the benchmark political influence. The objective function is employed by each government to determine the level of agricultural support. The influence weights on agricultural interests that would rationalize the existing protection system with these objective functions are 72% in the EC and 61% in the US. A negotiated outcome which fulfills certain economic efficiency criteria with this disagreement point could result in partial liberalization of the CAP by 75% while simultaneously allowing US agriculture to gain an additional 50% protection. There are, however, alternatives to direct negotiations that could result in partial CAP liberalization. A marginal change in the political influence weights of European interest groups would also result in a 75% liberalization of the CAP. A complete liberalization of the CAP would nonetheless require substantial changes in these political weights. Even if the EC were indifferent to income distributional aspects of the outcome, corresponding to 50:50 weights, these would be an efficiency argument in favor of unilaterally keeping some endogenous protection in place. Complete liberalization would therefore, to some extent, require a reversal of the bias in income distributional considerations that now favors agricultural interests