Face Value

There is growing evidence of systematic heterogeneity in behavior by observable characteristics, such as what one would see in a face. We ask, is there informational value in knowing these characteristics in a strategic interaction? Subjects are given the opportunity to purchase a photograph of their partner in the play of a trust game. Not everyone purchases the photo, even at prices as low as $0.20. Senders (first movers in the game) have a more inelastic demand for pictures than responders (second movers). White senders have a substantially higher demand than nonwhite senders or responders. For responders, there is no difference in demand for pictures across ethnicity or sex. White senders who pay to see the picture of their partner use the information to discriminate, sending significantly less to black responders than to white responders. Overall, responders return a higher percentage of the amount received as offers go up, but they do differentiate that percentage when they see the picture of the sender, returning more to a member of the same ethnicity. A face, it appears, has strategic value, especially for those who will use the information to differentiate their decisions.

Resistive flow in a weakly interacting Bose-Einstein condensate

We report the direct observation of resistive flow through a weak link in a weakly interacting atomic Bose-Einstein condensate. Two weak links separate our ring-shaped superfluid atomtronic circuit into two distinct regions, a source and a drain. Motion of these weak links allows for creation of controlled flow between the source and the drain. At a critical value of the weak link velocity, we observe a transition from superfluid flow to superfluid plus resistive flow. Working in the hydrodynamic limit, we observe a conductivity that is 4 orders of magnitude larger than previously reported conductivities for a Bose-Einstein condensate with a tunnel junction. Good agreement with zero-temperature Gross-Pitaevskii simulations and a phenomenological model based on phase slips indicate that the creation of excitations plays an important role in the resulting conductivity. Our measurements of resistive flow elucidate the microscopic origin of the dissipation and pave the way for more complex atomtronic devices.Comment: Version published in PR

Toward a Clearer Understanding of Privatization

The trend toward privatization in higher education is clearly accelerating, as evidenced in both the scholarly and popular presses. It remains unclear whether governments cannot, or choose not to, provide sufficient resources to public postsecondary education, but intelligence points to a myriad of possible points of contention. For instance, the subprime mortgage crisis, downturns on Wall Street, declining state tax bases, and other recently emerging trends suggest little relief is in sight. Furthermore, higher education and the states most likely won\u27t be relieved by other long-term fiscal pressures. K-12 education and Medicare are frequently factors behind funding shortages. State policy continues to encourage competition not only with private institutions but also with other public institutions on a mounting set of issues. For example, Ohio created a program in which its public institutions compete for a $150 million pot of research funding (Richards, 2007). Institutions continue to compete for students and their mi tion dollars, particularly those students who have the means to pay or to use their state-based merit dollars. The competition for students will be especially acute in states, such as Colorado, that have adopted a voucher-style funding structure. Tuition and vouchers, not state block grants, have become an increasingly important source of revenue for some public research universities. States too are recognizing the funding problem and realize that if they cannot provide the resources for their institutions, they should allow them the autonomy and flexibility to set and keep their tuition and to compete for students, investments, and faculty with little state intervention

Care provision: An experimental investigation

In many principal-agent settings, the effort provided by the agent benefits a third party. In these settings, the quality of the work is determined, at least in part, by pro-social motivations. We present lab experiments that utilize a new three-player trust game to examine one such setting, care provision. Players include a principal, an agent, and a needy recipient. The principal can transfer resources to an agent, who then can transfer resources to the needy recipient; the latter transfers are tripled. As in the two-player version, we find high, but variable, levels of trust and reciprocity (agent transfers to target) in the baseline game. Two treatments allow us to gauge the impact of potential policy interventions to enhance care of the target recipient. The first provides a budget subsidy to the principle, and the second alters the effectiveness (multiplier) of the agent’s transfers. Results show that the behavior of the agent does not vary by treatment, and is determined primarily by the amount received from the principal. Principals, on the other hand, do respond to the policy changes. While budget subsidies increase the expenditure of the principal only slightly, policies impacting the agent’s efficiency increase the amount entrusted to them by principals and significantly impact the well-being of the recipient. Results suggest that policies that increase the effectiveness of care workers (the agents) may significantly impact the quality of work provided. Examples of such policies include increased worker training and reductions in red tape

Oxidation of Carbon Fibers in a Cracked Ceramic Matrix Composite Modeled as a Function of Temperature

The oxidation model simulates the oxidation of the reinforcing carbon fibers within a ceramic matrix composite material containing as-fabricated microcracks. The physics-based oxidation model uses theoretically and experimentally determined variables as input for the model. The model simulates the ingress of oxygen through microcracks into a two-dimensional plane within the composite material. Model input includes temperature, oxygen concentration, the reaction rate constant, the diffusion coefficient, and the crack opening width as a function of the mechanical and thermal loads. The model is run in an iterative process for a two-dimensional grid system in which oxygen diffuses through the porous and cracked regions of the material and reacts with carbon in short time steps. The model allows the local oxygen concentrations and carbon volumes from the edge to the interior of the composite to be determined over time. Oxidation damage predicted by the model was compared with that observed from microstructural analysis of experimentally tested composite material to validate the model for two temperatures of interest. When the model is run for low-temperature conditions, the kinetics are reaction controlled. Carbon and oxygen reactions occur relatively slowly. Therefore, oxygen can bypass the carbon near the outer edge and diffuse into the interior so that it saturates the entire composite at relatively high concentrations. The kinetics are limited by the reaction rate between carbon and oxygen. This results in an interior that has high local concentrations of oxygen and a similar amount of consumed carbon throughout the cross section. When the model is run for high-temperature conditions, the kinetics are diffusion controlled. Carbon and oxygen reactions occur very quickly. The carbon consumes oxygen as soon as it is supplied. The kinetics are limited by the relatively slow rate at which oxygen is supplied in comparison to the relatively fast rate at which carbon and oxygen reactions occur. This results in a sharp gradient in oxygen concentration from the edge where it is supplied to the nearest source of carbon, which is where the oxygen is quickly consumed. A moving reaction front is seen in which the outlaying carbon is consumed before the next inner layer of carbon begins to react

Full density matrix dynamics for large quantum systems: Interactions, Decoherence and Inelastic effects

We develop analytical tools and numerical methods for time evolving the total density matrix of the finite-size Anderson model. The model is composed of two finite metal grains, each prepared in canonical states of differing chemical potential and connected through a single electronic level (quantum dot or impurity). Coulomb interactions are either excluded all together, or allowed on the dot only. We extend this basic model to emulate decoherring and inelastic scattering processes for the dot electrons with the probe technique. Three methods, originally developed to treat impurity dynamics, are augmented to yield global system dynamics: the quantum Langevin equation method, the well known fermionic trace formula, and an iterative path integral approach. The latter accommodates interactions on the dot in a numerically exact fashion. We apply the developed techniques to two open topics in nonequilibrium many-body physics: (i) We explore the role of many-body electron-electron repulsion effects on the dynamics of the system. Results, obtained using exact path integral simulations, are compared to mean-field quantum Langevin equation predictions. (ii) We analyze aspects of quantum equilibration and thermalization in large quantum systems using the probe technique, mimicking elastic-dephasing effects and inelastic interactions on the dot. Here, unitary simulations based on the fermionic trace formula are accompanied by quantum Langevin equation calculations

Regenerative Performance of the NASA Symmetrical Solid Oxide Fuel Cell Design

The NASA Glenn Research Center is developing both a novel cell design (BSC) and a novel ceramic fabrication technique to produce fuel cells predicted to exceed a specific power density of 1.0 kW/kg. The NASA Glenn cell design has taken a completely different approach among planar designs by removing the metal interconnect and returning to the use of a thin, doped LaCrO3 interconnect. The cell is structurally symmetrical. Both electrodes support the thin electrolyte and contain micro-channels for gas flow-- a geometry referred to as a bi-electrode supported cell or BSC. The cell characteristics have been demonstrated under both SOFC and SOE conditions. Electrolysis tests verify that this cell design operates at very high electrochemical voltage efficiencies (EVE) and high H2O conversion percentages, even at the low flow rates predicted for closed loop systems encountered in unmanned aerial vehicle (UAV) applications. For UAVs the volume, weight and the efficiency are critical as they determine the size of the water tank, the solar panel size, and other system requirements. For UAVs, regenerative solid oxide fuel cell stacks (RSOFC) use solar panels during daylight to generate power for electrolysis and then operate in fuel cell mode during the night to power the UAV and electronics. Recent studies, performed by NASA for a more electric commercial aircraft, evaluated SOFCs for auxiliary power units (APUs). System studies were also conducted for regenerative RSOFC systems. One common requirement for aerospace SOFCs and RSOFCs, determined independently in each application study, was the need for high specific power density and volume density, on the order of 1.0 kW/kg and greater than 1.0 kW/L. Until recently the best reported performance for SOFCs was 0.2 kW/kg or less for stacks. NASA Glenn is working to prototype the light weight, low volume BSC design for such high specific power aerospace applications

Matching schemes and public goods : a review

Matching schemes, where a party matches the contribution of others, reduce the effective price of a good and aim to foster its demand. We review the empirical literature on the effectiveness of these schemes in the context of public goods, especially in the field of charitable giving. As different measures of effectiveness are used, we classify results according to (i) the level of public good provision, (ii) the amount of individuals' contributions, (iii) the likelihood to give and (iv) the contribution conditional on contributing a positive amount. Generalizing results is challenging, since context specific factors matter. Predominantly, a match is found to create a significant increase in public good provision without crowding out individuals' contributions, while the effect on the likelihood of giving and contribution condition on contributing a positive amount is nonnegative. The discussion reveals several avenues for future research, as putting stronger emphasizes on long term effects, public good competition or heterogeneity in responses

Oxygen Diffusion and Reaction Kinetics in Continuous Fiber Ceramic Matrix Composites

Previous stressed oxidation tests of C/SiC composites at elevated temperatures (350 C to 1500 C) and sustained stresses (69 MPa and 172 MPa) have led to the development of a finite difference cracked matrix model. The times to failure in the samples suggest oxidation occurred in two kinetic regimes defined by the rate controlling mechanisms (i.e. diffusion controlled and reaction controlled kinetics). Microstructural analysis revealed preferential oxidation along as-fabricated, matrix microcracks and also suggested two regimes of oxidation kinetics dependent on the oxidation temperature. Based on experimental results, observation, and theory, a finite difference model was developed. The model simulates the diffusion of oxygen into a matrix crack bridged by carbon fibers. The model facilitates the study of the relative importance of temperature, the reaction rate constant, and the diffusion coefficient on the overall oxidation kinetics