Dyadic Green's Functions and Guided Surface Waves for a Surface Conductivity Model of Graphene

An exact solution is obtained for the electromagnetic field due to an electric current in the presence of a surface conductivity model of graphene. The graphene is represented by an infinitesimally-thin, local and isotropic two-sided conductivity surface. The field is obtained in terms of dyadic Green's functions represented as Sommerfeld integrals. The solution of plane-wave reflection and transmission is presented, and surface wave propagation along graphene is studied via the poles of the Sommerfeld integrals. For isolated graphene characterized by complex surface conductivity, a proper transverse-electric (TE) surface wave exists if and only if the imaginary part of conductivity is positive (associated with interband conductivity), and a proper transverse-magnetic (TM) surface wave exists when the imaginary part of conductivity is negative (associated with intraband conductivity). By tuning the chemical potential at infrared frequencies, the sign of the imaginary part of conductivity can be varied, allowing for some control over surface wave properties.Comment: 9 figure

Models of genetic drift as limiting forms of the Lotka-Volterra competition model

The relationship between the Moran model and stochastic Lotka-Volterra competition (SLVC) model is explored via timescale separation arguments. For neutral systems the two are found to be equivalent at long times. For systems with selective pressure, their behavior differs. It is argued that the SLVC is preferable to the Moran model since in the SLVC population size is regulated by competition, rather than arbitrarily fixed as in the Moran model. As a consequence, ambiguities found in the Moran model associated with the introduction of more complex processes, such as selection, are avoided.Comment: 5 pages, 4 figure

The Role of Partnerships in Economic Development and Labor Markets in the United States

This paper describes the role of local partnerships in the delivery of workforce and economic development services in the United States. Partnerships include both public and private organizations and increasingly depend upon local business people for leadership. With grassroots organizations traditionally taking the lead in addressing local issues and a long history of decentralized government, it is not surprising that a labyrinth of partnerships characterize the provision of public services. This paper grew out of a study tour that the Upjohn Institute conducted in conjunction with the Local Employment and Economic Development (LEED) Committee of the Organization for Economic Co-Operation and Development (OECD). Delegates from 16 European countries visited nearly two dozen partnership organizations in the U.S. Midwest. The paper summarizes the history of local partnerships in the United States, tracks the separate evolution of workforce and economic development activities, describes the leadership roles of the federal and state governments in fostering partnerships, and provides case studies of current public-private partnerships that the delegates visited on the tour. The paper concludes by drawing lessons learned from the tour regarding the efficiency of partnerships, the efficiency of service delivery, the local management of programs, and the proper roles of federal, state, and local governments. A version of the paper appears in an OECD volume on partnerships entitled Local Partnerships for Better Governance, prepared by Sylvain Giguereworkforce, economic, development, OECD, partnerships, Eberts, Erickcek, Upjohn

Learning about Risk and Return: A Simple Model of Bubbles and Crashes

This paper demonstrates that an asset pricing model with least-squares learning can lead to bubbles and crashes as endogenous responses to the fundamentals driving asset prices. When agents are risk-averse they need to make forecasts of the conditional variance of a stock¡¯s return. Recursive updating of both the conditional variance and the expected return implies several mechanisms through which learning impacts stock prices. Extended periods of excess volatility, bubbles and crashes arise with a frequency that depends on the extent to which past data is discounted. A central role is played by changes over time in agents¡¯ estimates of risk.Risk, Asset Pricing, Bubbles, Adaptive Learning.

Liquidity Traps, Learning and Stagnation

We examine global economic dynamics under learning in a New Keynesian model in which the interest-rate rule is subject to the zero lower bound. Under normal monetary and fiscal policy, the intended steady state is locally but not globally stable. Large pessimistic shocks to expectations can lead to deflationary spirals with falling prices and falling output. To avoid this outcome we recommend augmenting normal policies with aggressive monetary and fiscal policy that guarantee a lower bound on inflation. In contrast, policies geared toward ensuring an output lower bound are insufficient for avoiding deflationary spirals

The role of commercial real estate investments in the banking crisis of 1985-92

This article examines the role of commercial real estate investments in the banking crisis of 1985-92, an unprecedented period during which more than 1,300 banks failed. Bank failures are fundamentally important because of the unique role played by financial institutions in the provision of business credit. We discover three striking features of banks failing during this period. First, commercial real estate was only a factor in the bank failures of 1988-92. Second, construction loans played a much larger role in bank failures than permanent loans, and the relationship is strongest with construction loans booked during 1983-1985. Third, other ex ante risk measures are systematically related to banking failure throughout the sample period. These results suggest that risk-seeking banks brought about their own demise and commercial real estate, especially construction lending, was one of the vehicles.bank; bank failure; commercial bank; commercial real estate; construction lending; real estate

Reports and Maps of the Geological Survey Released Only in the Open Files, 1966

There is a reference to the Espey "Some effects on urbanization on storm runoff, Waller Creek".Waller Creek Working Grou

Bond disproportionation and dynamical charge fluctuations in the perovskite rare earth nickelates

We present a theory describing the local electronic properties of the perovskite rare earth nickelates--materials which have negative charge transfer energies, strong O $2p$ -- Ni $3d$ covalence, and breathing mode lattice distortions at the origin of highly studied metal-insulator and antiferromagnetic ordering transitions. Utilizing a full orbital, full correlation double cluster approach, we find strong charge fluctuations in agreement with a bond disproportionation interpretation. The unique double cluster formulation permits the inclusion of necessary orbital degeneracies and Coulomb interactions to calculate resonant x-ray spectral responses, with which we find excellent agreement with well-established experimental results. This previously absent, crucial link between theory and experiment provides validation of the recently proposed bond disproportionation theory, and provides an analysis methodology for spectroscopic studies of engineered phases of nickelates and other high valence transition metal compounds