Josephson Coupling through a Quantum Dot

We derive, via fourth order perturbation theory, an expression for the Josephson current through a gated interacting quantum dot. We analyze our expression for two different models of the superconductor-dot-superconductor (SDS) system. When the matrix elements connecting dot and leads are featureless constants, we compute the Josephson coupling J_c as a function of the gate voltage and Coulomb interaction. In the diffusive dot limit, we compute the probability distribution P(J_c) of Josephson couplings. In both cases, pi junction behavior (J_c < 0) is possible, and is not simply dependent on the parity of the dot occupancy.Comment: 9 pages; 3 encapsulated PostScript figure

Entry, Descent, and Landing with Propulsive Deceleration: Supersonic Retropropulsion Wind Tunnel Testing and Shock Phenomena

The future exploration of the Solar System will require innovations in transportation and the use of entry, descent, and landing (EDL) systems at many planetary landing sites. The cost of space missions has always been prohibitive, and using the natural planetary and planet's moon atmospheres for entry, and descent can reduce the cost, mass, and complexity of these missions. This paper will describe some of the EDL ideas for planetary entry and survey the overall technologies for EDL that may be attractive for future Solar System missions. Future EDL systems may include an inflatable decelerator for the initial atmospheric entry and an additional supersonic retropropulsion (SRP) rocket system for the final soft landing. A three engine retropropulsion configuration with a 2.5 in. diameter sphere-cone aeroshell model was tested in the NASA Glenn Research Center's 1- by 1-ft (11) Supersonic Wind Tunnel (SWT). The testing was conducted to identify potential blockage issues in the tunnel, and visualize the rocket flow and shock interactions during supersonic and hypersonic entry conditions. Earlier experimental testing of a 70deg Viking-like (sphere-cone) aeroshell was conducted as a baseline for testing of a SRP system. This baseline testing defined the flow field around the aeroshell and from this comparative baseline data, retropropulsion options will be assessed. Images and analyses from the SWT testing with 300- and 500-psia rocket engine chamber pressures are presented here. In addition, special topics of electromagnetic interference with retropropulsion induced shock waves and retropropulsion for Earth launched booster recovery are also addressed

Computational Methods for Stability and Control (COMSAC): The Time Has Come

Powerful computational fluid dynamics (CFD) tools have emerged that appear to offer significant benefits as an adjunct to the experimental methods used by the stability and control community to predict aerodynamic parameters. The decreasing costs for and increasing availability of computing hours are making these applications increasingly viable as time goes on and the cost of computing continues to drop. This paper summarizes the efforts of four organizations to utilize high-end computational fluid dynamics (CFD) tools to address the challenges of the stability and control arena. General motivation and the backdrop for these efforts will be summarized as well as examples of current applications

Aerospace Fuels From Nonpetroleum Raw Materials

Recycling human metabolic and plastic wastes minimizes cost and increases efficiency by reducing the need to transport consumables and return trash, respectively, from orbit to support a space station crew. If the much larger costs of transporting consumables to the Moon and beyond are taken into account, developing waste recycling technologies becomes imperative and possibly mission enabling. Reduction of terrestrial waste streams while producing energy and/or valuable raw materials is an opportunity being realized by a new generation of visionary entrepreneurs; several relevant technologies are briefly compared, contrasted and assessed for space applications. A two-step approach to nonpetroleum raw materials utilization is presented; the first step involves production of supply or producer gas. This is akin to synthesis gas containing carbon oxides, hydrogen, and simple hydrocarbons. The second step involves production of fuel via the Sabatier process, a methanation reaction, or another gas-to-liquid technology, typically Fischer-Tropsch processing. Optimization to enhance the fraction of product stream relevant to transportation fuels via catalytic (process) development at NASA Glenn Research Center is described. Energy utilization is a concern for production of fuels whether for operation on the lunar or Martian surface, or beyond. The term green relates to not only mitigating excess carbon release but also to the efficiency of energy usage. For space, energy usage can be an essential concern. Another issue of great concern is minimizing impurities in the product stream(s), especially those that are potential health risks and/or could degrade operations through catalyst poisoning or equipment damage; technologies being developed to remove heteroatom impurities are discussed. Alternative technologies to utilize waste fluids, such as a propulsion option called the resistojet, are discussed. The resistojet is an electric propulsion technology with a powered thruster to vaporize and heat a propellant to high temperature, hot gases are subsequently passed through a converging-diverging nozzle expanding gases to supersonic velocities. A resistojet can accommodate many different fluids, including various reaction chamber (by-)products

SWIFT Code Assessment for Two Similar Transonic Compressors

One goal of the NASA Fundamental Aeronautics Program is the assessment of computational fluid dynamic (CFD) codes used for the design and analysis of many aerospace systems. This paper describes the assessment of the SWIFT turbomachinery analysis code for two similar transonic compressors, NASA rotor 37 and stage 35. The two rotors have identical blade profiles on the front, transonic half of the blade but rotor 37 has more camber aft of the shock. Thus the two rotors have the same shock structure and choking flow but rotor 37 produces a higher pressure ratio. The two compressors and experimental data are described here briefly. Rotor 37 was also used for test cases organized by ASME, IGTI, and AGARD in 1994-1998. Most of the participating codes over predicted pressure and temperature ratios, and failed to predict certain features of the downstream flowfield. Since then the AUSM+ upwind scheme and the k- turbulence model have been added to SWIFT. In this work the new capabilities were assessed for the two compressors. Comparisons were made with overall performance maps and spanwise profiles of several aerodynamic parameters. The results for rotor 37 were in much better agreement with the experimental data than the original blind test case results although there were still some discrepancies. The results for stage 35 were in very good agreement with the data. The results for rotor 37 were very sensitive to turbulence model parameters but the results for stage 35 were not. Comparison of the rotor solutions showed that the main difference between the two rotors was not blade camber as expected, but shock/boundary layer interaction on the casing

PAB3D: Its History in the Use of Turbulence Models in the Simulation of Jet and Nozzle Flows

This is a review paper for PAB3D s history in the implementation of turbulence models for simulating jet and nozzle flows. We describe different turbulence models used in the simulation of subsonic and supersonic jet and nozzle flows. The time-averaged simulations use modified linear or nonlinear two-equation models to account for supersonic flow as well as high temperature mixing. Two multiscale-type turbulence models are used for unsteady flow simulations. These models require modifications to the Reynolds Averaged Navier-Stokes (RANS) equations. The first scheme is a hybrid RANS/LES model utilizing the two-equation (k-epsilon) model with a RANS/LES transition function, dependent on grid spacing and the computed turbulence length scale. The second scheme is a modified version of the partially averaged Navier-Stokes (PANS) formulation. All of these models are implemented in the three-dimensional Navier-Stokes code PAB3D. This paper discusses computational methods, code implementation, computed results for a wide range of nozzle configurations at various operating conditions, and comparisons with available experimental data. Very good agreement is shown between the numerical solutions and available experimental data over a wide range of operating conditions

Regional Bank Efficiency and its Effect on Regional Growth in "Normal" and "Bad" Times

The financial crisis affected regions in Europe in a different magnitude. We examine whether regions which incorporate banks with a higher intermediation quality grow faster using a sample which includes the aftermath of the financial crisis. We measure the intermediation quality of a bank by estimating a its profit and cost efficiency. Next, we aggregate the efficiencies of all banks within a NUTS 2 region to obtain a regional proxy for financial quality in twelve European countries. Our results show that relatively more profit efficient banks foster the economic growth in their region. The link between financial quality and growth is valid in normal times as well as in bad ones

Wage Inequality and Wage Mobility in Europe

Using data from the European Union Statistics on Income and Living Conditions (EU-SILC), this paper investigates wage inequality and wage mobility in Europe. Decomposing inequality into within and between group inequality, we analyse to what extent wage inequality and mobility can be explained by observable characteristics. Furthermore, we investigate which individual and household characteristics determine transitions within the wage distribution. Finally, we examine the importance of institutions for wage inequality, wage mobility, and wage transitions. We find that overall, mobility reduces wage inequality. While a large part of wage inequality is due to unobservable characteristics, the equalizing effect of mobility mainly occurs within groups. Furthermore, both personal and household characteristics play an important role for wage transitions. Finally, our findings reveal large cross-country differences across Europe, which are partly linked to the institutional set-up of the national labour markets.Auf Grundlage der Statistik der Europäischen Union über Einkommen und Lebensbedingungen wird in diesem Papier die Lohnungleichheit und die Lohnmobilität in Europa untersucht. Eine Zerlegung der Ungleichheit in Ungleichheit innerhalb und zwischen Bevölkerungsgruppen liefert Erkenntnisse darüber, inwiefern Lohnungleichheit und -mobilität durch beobachtbare Eigenschaften erklärt werden können. Darüber hinaus werden die Bedeutung von individuellen und Haushaltscharakteristika für Transitionen innerhalb der Lohnverteilung analysiert. Letztlich wird der Zusammenhang von Institutionen mit Lohnungleichheit, Lohnmobilität und Lohntransitionen untersucht. Die Ergebnisse der Analyse lauten wir folgt. Mobilität verringert Lohnungleichheit. Obwohl ein hoher Anteil der Lohnungleichheit auf unbeobachtbare Faktoren zurückzuführen ist, findet der ausgleichende Effekt von Mobillität hauptsächlich zwischen den Bevölkerungsgruppen statt. Zudem spielen sowohl individuelle als auch Haushaltscharakteristika eine wichtige Rolle für Lohntransitionen. Letztlich zeigen die Ergebnisse große Unterschiede zwischen den europäischen Ländern, die sich teilweise auf die institutionellen Gegebenheiten der nationalen Arbeitsmärkte zurückführen lassen

Macroeconomic Effects of Credit Deepening in Latin America

This paper augments a relatively standard dynamic general equilibrium model with financial frictions in order to quantify the macroeconomic effects of the credit deepening process observed in many Latin American (LA) countries in the last decade, most notably in Brazil. In the model, a stylized banking sector intermediates credit from patient households to impatient households and firms. The key novelty of the paper, motivated by the Brazilian experience, is to model the credit constraint faced by (impatient) households as a function of future labor income. In the calibrated model, credit deepening generates only modest abovetrend growth in consumption, investment, and GDP. Since Brazil has experienced one of the most intense credit deepening processes in Latin America, it is argued that the quantitative effects for other LA economies are unlikely to be sizeable