Synchronization properties of self-sustained mechanical oscillators

We study, both analytically and numerically, the dynamics of mechanical oscillators kept in motion by a feedback force, which is generated electronically from a signal produced by the oscillators themselves. This kind of self-sustained systems may become standard in the design of frequency-control devices at microscopic scales. Our analysis is thus focused on their synchronization properties under the action of external forces, and on the joint dynamics of two to many coupled oscillators. Existence and stability of synchronized motion are assessed in terms of the mechanical properties of individual oscillators --namely, their natural frequencies and damping coefficients-- and synchronization frequencies are determined. Similarities and differences with synchronization phenomena in other coupled oscillating systems are emphasized.Comment: To appear in Phys. Rev.

Dollarization and Economic Performance: What Do we Really Know?

In this paper we analyze the macroeconomic record of dollarized economies. In particular, we investigate whether, as its supporters’ claim, dollarization is associated with lower inflation and faster growth. We analyze this issue by using a matching estimator technique developed in the training evaluation literature. Our findings suggest that inflation has been significantly lower in dollarized nations than in non-dollarized ones. We also find that dollarized nations have had a lower rate of economic growth than non-dollarized ones. Finally, we find that macroeconomic volatility is not significantly different across dollarized and non-dollarized economies. We conjecture that the lower rate of economic growth in dollarized countries is due, at least in part, to these countries’ difficulties in accommodating external disturbances, such as major term of trade and capital flows shocks.

Independent Currency Unions, Growth, and Inflation

During the last few years, there has been a renewed interest in currency unions. This is the result both of the recent wave of currency crises as well as the implementation of the euro. In this paper, the authors use panel data for 1970-98 to investigate economic performance under historical independent currency unions (ICUs) along three dimensions: GDP per capital growth, growth volatility, and inflation. They use a treatment effects model that estimates jointly the probability of having a common currency and its effect on performance. The authors find that ICU countries have had a significantly lower rate of inflation, but macroeconomic volatility has been higher. Also, ICU countries have grown faster than with currency nations, but the East Caribbean Currency Area countries are found to be the driving force behind this result.

Strict Dollarization and Economic Performance: An Empirical Investigation

In this paper we analyze the macroeconomic record of 'strictly dollarized' economies. In particular we investigate whether dollarized countries have historically exhibited faster growth and lower volatility than countries with a domestic currency. We analyze this issue by using a treatment regression analysis that estimates jointly the probability of being a dollarized country, and outcome equations. Our analysis indicates that the probability of being a dollarized country depends on regional, geographical, political and structural variables. Our results also suggest GDP per capita growth has not been statistically different in dollarized and in non-dollarized ones. We also find that volatility has been significantly higher in dollarized than in non-dollarized economies. These results are robust to the estimation technique, and to the sample used.

Ultrabright Linearly Polarized Photon Generation from a Nitrogen Vacancy Center in a Nanocube Dimer Antenna

We demonstrate an exceptionally bright photon source based on a single nitrogen- vacancy center (NV-center) in a nanodiamond (ND), placed in the nanoscale gap between two monocrystalline silver cubes in a dimer configuration. The system is operated near saturation at a stable photon rate of 850 kcps, while we further achieve strongly polarized emission and high single photon purity, evident by the measured auto-correlation with a g(2)(0)-value of 0.08. These photon source features are key parameters for quantum technological applications, such as secure communication based on quantum key distribution. The cube antenna is assembled with an atomic force microscope, which allows us to predetermine the dipole orientation of the NV-center and optimize cube positioning accordingly, while also tracking the evolution of emission parameters from isolated ND to the 1 and 2 cube configuration. The experiment is well described by finite element modelling, assuming an instrinsic quantum efficiency of 0.35. We attribute the large photon rate of the assembled photon source, to increased quantum efficiency of the NV-center and high antenna efficiency