Spatially Resolved Nonlinearity Measurements of YBa2_2Cu3_3O7−d_{7-d} Bi-crystal Grain Boundaries

We have developed a near-field microwave microscope to locally excite a superconducting film and measure second and third harmonic responses at microwave frequencies. We study the local nonlinear response of a YBa$_2$Cu$_3$O$_{7-d}$ thin film grown on a bi-crystal SrTiO$_3$ substrate. The location of the bi-crystal grain boundary is clearly identified by the microscope through higher harmonic response, and the spatial resolution is on the order of the magnetic loop probe size, about 500$\mu m$. The harmonic power and spatial resolution are successfully modeled with a one-dimensional extended Josephson junction simulation. From the model, the 2nd order harmonic response is dominated by Josephson vortex generation and flow. A geometry-free nonlinear scaling current density $J_{NL}\simeq 10^4\sim 10^5 A/cm^2$ is also exstracted from the data, indicating that the grain boundary weak link is the dominant nonlinear source in this case.Comment: 4pages, 4figure

Doping dependent time-reversal symmetric nonlinearity of YBa_2Cu_3O_7-d thin films

We have measured the temperature dependent third harmonic response from a series of under-doped YBa_2Cu_3O_7-d thin films to address the mechanism of nonlinearity in these samples. We find that the intrinsic Ginzburg-Landau nonlinearity near Tc is doping dependent, with the sample becoming more nonlinear as it is under-doped. The results are consistent with the doping dependence of the condensation energy of YBa_2Cu_3O_7-d.Comment: 2 pages, 3 figures, submitted to Physica C for M2S-Rio conference pres

Substitutability between Equity REITs and Mortgage REITs

This study extends Seck’s (1996) approach to investigate the degree of substitutability between equity real estate investment trusts (EREITs) and mortgage real estate investment trusts (MREITs). The variance ratio test and the variance decomposition of forecast errors yield results indicating the existence of informational commonality between EREITs and MREITs. The findings indicate that the two types of REITs are substitutable. A direct implication is that investors who believe they have superior forecasting ability will be indifferent to invest in either type of REIT. Another implication is that REITs can be treated as a single asset class in constructing a diversified multi-asset portfolio.

Mean reversion of inflation rates in 19 OECD countries: Evidence from panel Lm unit root tests with structural breaks

The paper applies the recently developed panel LM unit root tests with heterogeneous structural breaks by Im et al., [The Oxford Bulletin of Economics and Statistics, 2005] in order to re-examine the validity of mean reversion in the inflation rates of 19 OECD countries for the time period 1960-2004. Our empirical findings are favorable to the stationarity of the inflation ratesand therefore point to the absence of hyperinflation in the majority of the countries. The results indicate that most shocks to inflation rates are temporary and soon converge when we control for breaks, with the inflation rates showing mean reversion. Overall, some policy implications are obtained in this paper.Inflation