Monte Carlo simulations of copolymers at homopolymer interfaces: Interfacial structure as a function of the copolymer density

By means of extensive Monte Carlo simulations of the bond fluctuation model, we study the effect of adding AB diblock copolymers on the properties of an interface between demixed homopolymer phases. The parameters are chosen such that the homopolymers are strongly segregated, and the whole range of copolymer concentrations in the two phase coexistence region is scanned. We compare the ``mushroom'' regime, in which copolymers are diluted and do not interact with each other, with the ``wet brush'' regime, where copolymers overlap and stretch, but are still swollen by the homopolymers. A ``dry brush'' regime is never entered for our choice of chain lengths. ``Intrinsic'' profiles are calculated using a block analysis method introduced by us in earlier work. We discuss density profiles, orientational profiles and contact number profiles. In general, the features of the profiles are similar at all copolymer concentrations, however, the profiles in the concentrated regime are much broader than in the dilute regime. The results compare well with self-consistent field calculations.Comment: to appear in J. Chem. Phy

Long swings in Japan’s current account and in the yen

The yen has experienced several big swings over recent decades. This paper argues that the fluctuations of the Japanese exchange rate resulted mainly from corresponding movements in the current account, which affected the demand for yen relative to other currencies. The paper builds a vector error correction model for the exchange rate and the current account, based on the idea that the exchange rate and its economic fundamental do not move too far apart over time. In addition, the model allows for a Markov-switching stochastic trend in the current account. Regime changes occur at uncertain dates, possibly in response to exchange rate changes. Bayesian estimation proceeds using an innovative Gibbs-sampling procedure. The empirical results suggest that recurrent structural breaks in the yen’s fundamentals account for the large fluctuations of the Japanese exchange rat

Balance of payments flows and exchange rate prediction in Japan

Monetary models of exchange rates tend to focus on inflation differentials to explain exchange rate movements. This paper assesses the ability of currency flows to predict exchange rate changes. The focus is on Japan. Currency flows are assumed to depend on the level of the current account and on the international investment position, where the latter is used as a proxy for international debt repayments. A state space model is used to predict simultaneously the exchange rate and its determinants. Using rolling regressions and out-of-sample predictions, it is shown that a model featuring currency flows can predict the direction of exchange rate movements better than a random walk (with or without drift). However, as happens with standard macroeconomic models, the model is not able to outperform a random walk in terms of the mean square prediction error criterio

Spin effects in deeply virtual Compton scattering

We consider the azimuthal angle dependence in the cross section of the hard leptoproduction of a photon on a nucleon target. We show that this dependence allows to define observables that isolate the twist-two and twist-three sectors in the deeply virtual Compton scattering amplitude. All twist-two and twist-three Compton form factors can be extracted from measurements of the charge odd part of the polarized cross section and give access to all generalized parton distributions.Comment: 6 pages, LaTeX, 1 figure, Talk given at IX International Workshop on Deep Inelastic Scattering Bologna, 27 April - 1 May 200

Echo spectroscopy of Anderson localization

We propose a conceptually new framework to study the onset of Anderson localization in disordered systems. The idea is to expose waves propagating in a random scattering environment to a sequence of short dephasing pulses. The system responds through coherence peaks forming at specific echo times, each echo representing a particular process of quantum interference. We suggest a concrete realization for cold gases, where quantum interferences are observed in the momentum distribution of matter waves in a laser speckle potential. This defines a challenging, but arguably realistic framework promising to yield unprecedented insight into the mechanisms of Anderson localization.Comment: 14 pages, 7 figures; published versio