Synchronisation Properties of Trees in the Kuramoto Model

We consider the Kuramoto model of coupled oscillators, specifically the case of tree networks, for which we prove a simple closed-form expression for the critical coupling. For several classes of tree, and for both uniform and Gaussian vertex frequency distributions, we provide tight closed form bounds and empirical expressions for the expected value of the critical coupling. We also provide several bounds on the expected value of the critical coupling for all trees. Finally, we show that for a given set of vertex frequencies, there is a rearrangement of oscillator frequencies for which the critical coupling is bounded by the spread of frequencies.Comment: 21 pages, 19 Figure

Nomad, a naval message understanding system

We are building systems to automatically analyze Navy messages. Such messages typically are terse and use many abbreviations and Navy jargon. As a result, they are more difficult to understand than everyday English.The NOMAD system interacts with a message sender to ensure that only unambiguous and reasonably correct messages are generated. The VOX system will allow a human tutor to interactively extend the knowledge base of NOMAD

Are There Thresholds of Current Account Adjustment in the G7?

We find evidence of threshold behavior in current account adjustment for the G7 countries, such that the dynamics of adjustment towards equilibrium depend upon whether the current-account/ net-output ratio breaches estimated, country specific current account surplus or deficit thresholds. Both the speeds of adjustment and the size of the thresholds are found to differ significantly across countries. In addition, we also find evidence of shifts in means and variances of exchange rate changes, stock returns, and interest differentials that coincide with the current account adjustment regimes identified by the model.

Remittances, Inequality and Poverty: Evidence from Rural Mexico

Economic research has produced conflicting findings on the distributional impacts of migrant remittances, and there has been little research on the effects of changes in remittances on poverty. This paper utilizes new data from the Mexico National Rural Household Survey, together with inequality and poverty decomposition techniques, to explore the impacts of remittances on rural inequality and poverty. Our findings suggest that remittances from international migrants become more equalizing (or less unequalizing), as well as more effective at reducing poverty, as the prevalence of migration increases.Labor and Human Capital,

The Term Structure of Forward Exchange Rates and the Forecastability of Spot Exchange Rates: Correcting the Errors

This paper revisits one of the oldest questions in international finance: does the forward exchange rate contain useful information about of the future path of the spot exchange rate? We present a theoretical framework and provide evidence that challenges the common view (Mussa (1979); Dornbusch (1980); Frenkel (1981); Cumby-Obstfeld (1984) that forward premia contain little information regarding subsequent changes in the spot exchange rate. Using weekly dollar-DM and dollar-sterling data on spot exchange rates and 1, 3, 6., and 12 month forward exchange rates, we find that, as predicted by the theoretical framework the term structure of forward exchange rates together with the spot exchange rate comprise a system that is well represented by a vector vector correction model. Employing Johansen's (1991) maximum likelihood approach, we test and confirm for each country the existence of 4 cointegrating relationships as predicted by the theory. We then test and confirm for each country the joint hypothesis that a basis for this cointegrating space is the vector of 4 forward premia. We next test, and reject for each country, the hypothesis that the spot exchange rate is weekly exogenous with respect to the term structure of forward rates. Out-of-sample simulations indicate that the information contained in the term structure of forward premia can be used to reduce the mean squared error in forecasting the spot rate by at least 33 percent at 6 month horizon and 50 percent at a 1 year horizon

A RESTful API for exchanging Materials Data in the AFLOWLIB.org consortium

The continued advancement of science depends on shared and reproducible data. In the field of computational materials science and rational materials design this entails the construction of large open databases of materials properties. To this end, an Application Program Interface (API) following REST principles is introduced for the AFLOWLIB.org materials data repositories consortium. AUIDs (Aflowlib Unique IDentifier) and AURLs (Aflowlib Uniform Resource locator) are assigned to the database resources according to a well-defined protocol described herein, which enables the client to access, through appropriate queries, the desired data for post-processing. This introduces a new level of openness into the AFLOWLIB repository, allowing the community to construct high-level work-flows and tools exploiting its rich data set of calculated structural, thermodynamic, and electronic properties. Furthermore, federating these tools would open the door to collaborative investigation of the data by an unprecedented extended community of users to accelerate the advancement of computational materials design and development.Comment: 22 pages, 7 figure