Video Prioritization for Unequal Error Protection

We analyze the effect of packet losses in video sequences and propose a lightweight Unequal Error Protection strategy which, by choosing which packet is discarded, reduces strongly the Mean Square Error of the received sequenc

Demand for Reserves Under International Capital Mobility

In this research, I assess the determinants of foreign exchange reserves under endogenous capital flows. I consider a model where reserves represent collateral to international borrowing, which is endogenously determined by risk averse foreign investors. This is a departure from usual models of reserve accumulation, that focus solely on the portfolio decision of a central bank along the lines of optimal inventory control models or precautionary saving. In contrast to this view, I find that the expected effect on reserves of changes in the international interest rate or the volatility of the terms of trade is ambiguous if actions are simultaneous. However, if foreign investors and the central bank act sequentially, this ambiguity breaks down. Empirical evidence from OECD and non-OECD economies is suggestive: while LIBOR and terms of trade volatility positively affects the demand for reserves in OECD economies, the effects are reversed in non-OECD countries. This indicates that commitment issues are an important factor in the determination of reserves in non-OECD countries.

A Simple Global Perspective on the US Slowdown, Boom-Bust Cycles and the Rise of Protectionism

The global economy has experienced several significant developments during the recent years: the rising role of giant Asian economies in international trade; the 2008 financial crisis and the ensuing Great Recession in the US, with its propagation to the rest of the world; the sharp rise and subsequent burst of commodity prices over 2006-2009. In this paper we use a multi-region DSGE model for the global economy as a simple framework to understand the global response to these shocks and the importance of the propagation to different regions. The model is equipped to jointly determine exchange rates, trade balances and commodity prices across the world. We carry out several simulations with the model. First, we consider the US slowdown and its international propagation. Second, we explore a global boom-bust cycle driven by overoptimistic forecasts for productivity and their relationship with current account rebalancing. Finally, we analyze the global economic consequences of protectionism. We find that the effects in commodity prices, global output and demand tend to be amplified if the real exchange rates and real wages are more sluggish to adjust in some regions.

Exact and efficient calculation of Lagrange multipliers in constrained biological polymers: Proteins and nucleic acids as example cases

In order to accelerate molecular dynamics simulations, it is very common to impose holonomic constraints on their hardest degrees of freedom. In this way, the time step used to integrate the equations of motion can be increased, thus allowing, in principle, to reach longer total simulation times. The imposition of such constraints results in an aditional set of Nc equations (the equations of constraint) and unknowns (their associated Lagrange multipliers), that must be solved in one way or another at each time step of the dynamics. In this work it is shown that, due to the essentially linear structure of typical biological polymers, such as nucleic acids or proteins, the algebraic equations that need to be solved involve a matrix which is banded if the constraints are indexed in a clever way. This allows to obtain the Lagrange multipliers through a non-iterative procedure, which can be considered exact up to machine precision, and which takes O(Nc) operations, instead of the usual O(Nc3) for generic molecular systems. We develop the formalism, and describe the appropriate indexing for a number of model molecules and also for alkanes, proteins and DNA. Finally, we provide a numerical example of the technique in a series of polyalanine peptides of different lengths using the AMBER molecular dynamics package.Comment: 29 pages, 10 figures, 1 tabl

Fiscal and Monetary Policy Rules: The Recent Chilean Experience

This paper describes monetary and fiscal rules used in Chile in recent years. On monetary policy rules, we present both the framework for monetary policy rate assumptions that guide the construction of inflation and growth forecasts, as well as the broad characteristics of Taylor-Type Rules that reflect recent monetary policy actions. The role of the assumptions on the neutral policy rate as well as issues as what inflation index or time horizon to consider are included in the discussion. On fiscal rules, this paper presents the structural balance methodology used by the Chilean public sector since 2001. This rule implies that expenditures should evolve according to the dynamics of structural fiscal income, which is consistent with full employment and a long-term copper price. The key assumptions underlying the trend GDP growth and the long-term copper price are not set in a discretional way but rather follow the recommendations of two panels of independent experts. We conclude with a positive assessment of the recent Chilean experience with monetary and fiscal policy rules. This positive assessment is driven by the prominent role of monetary policy as the stabilizing macroeconomic instrument under a credible inflation targeting regime, and the avoidance of pro cyclical fiscal policies. In spite of tumultuous external conditions between 1999 and 2003, the Chilean economy managed to sustain positive rates of growth, record-low domestic interest rates and sovereign spreads, stable external public debt, as well as low inflation. The recent upswing in 2004 and 2005 has been accompanied by a smooth normalization of monetary conditions and a substantial improvement in fiscal balances.

Large Hoardings of International Reserves: Are They Worth It?

We empirically assess the contribution of international reserves vis- à -vis institutional variables in reducing the risk of a currency crisis. We find that the ratio of reserves to short-term debt is robust in explaining international crisis, even after controlling for financial development and political variables. Based on our estimates on crisis probabilities we compute the optimal level of reserves for a set of East Asian economies and for Chile. The results of this exercise turn out to be very sensitive to the data utilized and to the assumptions regarding the cost of a crisis. For our benchmark estimate we conclude that the current stocks of reserves for most of the cases are consistent with an optimal selfinsurance policy under reasonable assumptions regarding the cost of a crisis.

On the role of chemical synapses in coupled neurons with noise

We examine the behavior in the presence of noise of an array of Morris-Lecar neurons coupled via chemical synapses. Special attention is devoted to comparing this behavior with the better known case of electrical coupling arising via gap junctions. In particular, our numerical simulations show that chemical synapses are more efficient than gap junctions in enhancing coherence at an optimal noise (what is known as array-enhanced coherence resonance): in the case of (nonlinear) chemical coupling, we observe a substantial increase in the stochastic coherence of the system, in comparison with (linear) electrical coupling. We interpret this qualitative difference between both types of coupling as arising from the fact that chemical synapses only act while the presynaptic neuron is spiking, whereas gap junctions connect the voltage of the two neurons at all times. This leads in the electrical coupling case to larger correlations during interspike time intervals which are detrimental to the array-enhanced coherence effect. Finally, we report on the existence of a system-size coherence resonance in this locally coupled system, exhibited by the average membrane potential of the array.Comment: 7 pages, 7 figure