Sunspots and Credit Frictions

We examine a general equilibrium model with collateral constraints and increasing returns to scale in production. The utility function is nonseparable, with no income effect on the consumer's choice of leisure. Unlike this model without a collateral constraint, we find that indeterminacy of equilibria is possible. Hence, business cycles can be driven by self-fulfilling expectations. This is the case for more realistic parametrizations than in previous, similar models without these features.business cycles, credit markets, collateral constraint, sunspots

Indeterminacy with No-Income-Effect Preferences and Sector-Specific Externalities

We examine a two-sector real business cycle model with sector-specific externalities in the production of distinct consumption and investment goods. In addition, the household utility is postulated to exhibit no income effect on the demand for leisure. Unlike in the one-sector counterpart, we show that equilibrium indeterminacy can result with sufficiently high returns-to-scale in the production of investment goods. We also find that the smaller the labor supply elasticity, the lower the threshold level of returns-to-scale needed for generating indeterminacy and sunspots. This finding turns out to be exactly the opposite of that in all existing RBC-based indeterminacy studies.Indeterminacy, Income Effect, Sector-Specific Externalities

Chaos, Sunspots, and Automatic Stabilizers

We study a one-sector growth model which is standard except for the presence of an externality in the production function. The set of competitive equilibria is large. It includes constant equilibria, sunspot equilibria, cyclical and chaotic equilibria, and equilibria with deterministic or stochastic regime switching. The efficient allocation is characterized by constant employment and a constant growth rate. We identify an income tax-subsidy schedule that supports the efficient allocation as the unique equilibrium outcome. That schedule has two properties: (i) it specifies the tax rate to be an increasing function of aggregate employment, and (ii) earnings are subsidized when aggregate employment is at its efficient level. The first feature eliminates inefficient, fluctuating equilibria, while the second induces agents to internalize the externality.

Utilization of VAS satellite data in the initialization of an oceanic-cyclogenesis simulation

A series of experiments was performed to test various method of incorporating Visible Infrared Spin Scan Radiometer Atmospheric Sounder (VAS)-sounding data into the initial conditions of the Penn State University/National Center for Atmospheric mesoscale model. The VAS data for this ocean-cyclogenesis case consist of 110 irregularly distributed temperature and humidity soundings located over the North Pacific Ocean and apply at approximately 1200 GMT 10 November 1981. Various methods of utilizing VAS data in the initial condition of a mesoscale model were evaluated

The end of HIV: Still a very long way to go, but progress continues.

In an Editorial accompanying PLOS Medicine's Special Issue on Advances in Prevention, Treatment and Cure of HIV/AIDS, Guest Editors Steven Deeks, Sharon Lewin, and Linda-Gail Bekker discuss priorities in the field and the content of the issue

Cost-Offsets of New Medications for Treatment of Schizophrenia

Broad claims are frequently made that new medications will offset all or part of their costs by reducing other areas of Medicaid spending. In this paper we examine the net impact on spending for new drugs used to treat schizophrenia. We extend research in this area by taking a new approach to identification of spending impacts of new drugs. We specify and estimate models of spending on treatment of schizophrenia using 7 years of Florida Medicaid data. The estimates indicate that use of the new drugs result in net spending increases. This may be due to increased adherence to treatment.

Spike frequency adaptation affects the synchronization properties of networks of cortical oscillators

Oscillations in many regions of the cortex have common temporal characteristics with dominant frequencies centered around the 40 Hz (gamma) frequency range and the 5–10 Hz (theta) frequency range. Experimental results also reveal spatially synchronous oscillations, which are stimulus dependent (Gray&Singer, 1987;Gray, König, Engel, & Singer, 1989; Engel, König, Kreiter, Schillen, & Singer, 1992). This rhythmic activity suggests that the coherence of neural populations is a crucial feature of cortical dynamics (Gray, 1994). Using both simulations and a theoretical coupled oscillator approach, we demonstrate that the spike frequency adaptation seen in many pyramidal cells plays a subtle but important role in the dynamics of cortical networks. Without adaptation, excitatory connections among model pyramidal cells are desynchronizing. However, the slow processes associated with adaptation encourage stable synchronous behavior

Dielectric response of modified Hubbard models with neutral-ionic and Peierls transitions

The dipole P(F) of systems with periodic boundary conditions (PBC) in a static electric field F is applied to one-dimensional Peierls-Hubbard models for organic charge-transfer (CT) salts. Exact results for P(F) are obtained for finite systems of N = 14 and 16 sites that are almost converged to infinite chains in deformable lattices subject to a Peierls transition. The electronic polarizability per site, \alpha_{el} = (\partial P/\partial F)_0, of rigid stacks with alternating transfer integrals t(1 +/- \delta) diverges at the neutral-ionic transition for \delta = 0 but remains finite for \delta > 0 in dimerized chains. The Peierls or dimerization mode couples to charge fluctuations along the stack and results in large vibrational contributions, \alpha_{vib}, that are related to \partial P/\partial \delta and that peak sharply at the Peierls transition. The extension of P(F) to correlated electronic states yields the dielectric response \kappa of models with neutral-ionic or Peierls transitions, where \kappa peaks >100 are found with parameters used previously for variable ionicity \rho and vibrational spectra of CT salts. The calculated \kappa accounts for the dielectric response of CT salts based on substituted TTFs (tetrathiafulvalene) and substituted CAs (chloranil). The role of lattice stiffness appears clearly in models: soft systems have a Peierls instability at small \rho and continuous crossover to large \rho, while stiff stacks such as TTF-CA have a first-order transition with discontinuous \rho that is both a neutral-ionic and Peierls transition. The transitions are associated with tuning the electronic ground state of insulators via temperature or pressure in experiments, or via model parameters in calculations.Comment: 10 pages, 9 figures; J.Chem.Phys., in pres

High reflectivity grating waveguide coatings for 1064nm

We propose thin single-layer grating waveguide structures to be used as high-reflectivity, but low thermal noise, alternative to conventional coatings for gravitational wave detector test mass mirrors. Grating waveguide (GWG) coatings can show a reflectivity of up to 100% with an overall thickness of less than a wavelength. We theoretically investigate GWG coatings for 1064nm based on tantala (Ta2O5) on a Silica substrate focussing on broad spectral response and low thickness