In this article, our objective is to determine efficient allocations in economies with multiple agents having recursive utility functions. Our main result is to show that in a multiagent economy, the problem of determining efficient allocations can be characterized in terms of a single value function (that of a social planner), rather than multiple functions (one for each investor), as has been proposed thus far (Duffie, Geoffard and Skiadas (1994)). We then show how the single value function can be identified using the familiar technique of stochastic dynamic programming. We achieve these goals by first extending to a stochastic environment Geoffard's (1996) concept of variational utility and his result that variational utility is equivalent to recursive utility, and then using these results to characterize allocations in a multiagent setting.

A 3D finite-difference time-domain simulation of a dispersive, inhomogeneous half-space problem is described. The formulation uses the perfectly matched layer (PML) absorbing boundary condition (ABC) extended to dispersive media. The dispersion is characterized by a two-species Debye model with parameters taken from reported experimental data of soils with different moisture contents. The time-stepping scheme for the electric field uses the piecewise-linear recursive convolution (PLRC) method, For homogeneous half-space problems, the simulation results are compared against results from numerical integration of Sommerfeld-type integrals. To illustrate its applications, the inhomogeneous half-space simulations include results from the ground penetrating radar simulated response of buried objects in realistic soils.

A three-dimensional (3D) time-domain numerical scheme for simulation of ground penetrating radar (GPR) on dispersive and inhomogeneous soils with conductive loss is described. The finite-difference time-domain (FDTD) method is used to discretize the partial differential equations for time stepping of the electromagnetic fields. The soil dispersion is modeled by multiterm Lorentz and/or Debye models and incorporated into the FDTD scheme by using the piecewise-linear recursive convolution (PLRC) technique. The dispersive soil parameters are obtained by fitting the model to reported experimental data. The perfectly matched layer (PML) is extended to match dispersive media and used as an absorbing boundary condition to simulate an open space. Examples are given to verify the numerical solution and demonstrate its applications. The 3D PML-PLRC-FDTD formulation facilitates the parallelization of the code. A version of the code is written for a 32-processor system, and an almost linear speedup is observed.

Layered structures which include the high-temperature superconductor DyBa2Cu3O7-x have been fabricated using molecular beam epitaxy with ozone as the activated oxygen source. A c-axis oriented DyBa2Cu3O7-x thin film with a T(c) of 74 K has been grown on a layer of the rare earth sesquioxide Dy2O3 on a (100) oriented SrTiO3 substrate. Dy2O3 has also been incorporated as a barrier between two layers of DyBa2Cu3O7-x, where the T(c) of the top layer is 89 K. X-ray diffraction reveals oriented growth of both the DyBa2Cu3O7-x and the Dy2O3 layers. Cross-sectional transmission electron microscopy clearly shows the detailed matching of the layers, demonstrating that the interfaces are abrupt, with {100} Dy2O3 planes parallel to {001} DyBa2Cu3O7-x planes. These results are a strong indication that high quality, all high-T(c) superconductor tunneling junctions can be fabricated in this system.

A model for the grain signal is presented, which includes the effect of frequency-dependent scattering and attenuation. This model predicts that the expected frequency increases with scattering and decreases with attenuation. Homomorphic processing was used for spectral smoothing, and the selection of parameters for optimal performance was examined. Experimental results are presented that show both the upward shift in the expected frequency with grain boundary scattering and the downward shift with attenuation. Furthermore, it is shown that the expected frequency shift can be correlated with the grain size of the material. It is important to point out that the quantitative relationship between the average grain size and the expected frequency shift (either upward or downward) is dependent on the type of material, the quality of grain boundaries, and the characteristics of the measuring instruments.

A new group of high gain, wide margin direct injection Josephson junction logic gates including a three Josephson junction OR (3J/OR) and a four Josephson junction AND (4J/AND) was previously described. In the present work, these gates have been fabricated in an improved lead alloy technology using 5μm design rules. The measured threshold curves of the 3J/OR and the 4J/AND are in good agreement with the theoretical predictions despite the fact that current density and sheet resistance of the samples differed from the design values.

Recent measurements of Nb-aSi-Nb Josephson tunnel junctions fabritated using SNAP have demonstrated that this technique is a possible alternative to the Pb alloy technology. In the present work, the results of quasi-static measurements are reported on the first logic gates made using SNAP. The basic gate consists of a JAWS with both junctions having the same critical current. Operating margins in terms of the bias, off-set, and input currents are presented for individual gates and for series strings of gates having fanouts of 1 and 2. Whereas the use of an offset current substantially increases the margin of an individual gate, the increase in margin for a string is considerably less. The data are described well by a simple model taking into account the leakage current in the actual gates, and demonstrate the potential utility of SNAP.

A new type of current switching logic device using three Josephson junctions is described. This device allows the simultaneous optimization of both the gain and the operating margin. It shows an enhanced threshold curve compared with that of the Direct Coupled Logic (DCL) isolation device and the Josephson Atto-Weber Switch (JAWS). Design optimization and simulation results are presented. The devi...