Impedance boundary conditions for pseudo-spectral time-domain methods in room acoustics

The pseudo-spectral time-domain (PSTD) method is an alternative time-marching method to classicalleapfrog finite difference schemes in the simulation of wave-like propagating phenomena. It is basedon the fundamentals of the Fourier transform to compute the spatial derivatives of hyperbolic differential equations. Therefore, it results in an isotropic operator that can be implemented in an efficient way for room acoustics simulations. However, one of the first issues to be solved consists on modeling wallabsorption. Unfortunately, there are no references in the technical literature concerning to that problem. In this paper, assuming real and constant locally reacting impedances, several proposals to overcome this problem are presented, validated and compared to analytical solutions in different scenarios.

Impedance boundary conditions for pseudo-spectral time-domain methods in room acoustics

The Pseudo-Spectral Time Domain (PSTD) method is an alternative time-marching method to classical leapfrog finite difference schemes inthe simulation of wave-like propagating phenomena. It is based on the fundamentals of the Fourier transform to compute the spatial derivativesof hyperbolic differential equations. Therefore, it results in an isotropic operator that can be implemented in an efficient way for room acousticssimulations. However, one of the first issues to be solved consists on modeling wall absorption. Unfortunately, there are no references in thetechnical literature concerning to that problem. In this paper, assuming real and constant locally reacting impedances, several proposals toovercome this problem are presented, validated and compared to analytical solutions in different scenarios.

Diseño, implementación y evaluación de un juego educativo basado en puzles con scaffolding orientado a la programación

Existe una falta de interés por parte de los estudiantes en el área de las Tecnologías de la Información y la Comunicación (TIC) que se ve reflejada en el descenso de las matriculaciones en este ámbito. El uso de metodologías de aprendizaje basadas en el Constructivismo combinadas con tecnología software, se ha observado que es una buena solución para afrontar dicha falta de interés. Sin embargo, actualmente no existen aplicaciones software que implementen estas metodologías pedagógicas y que proporcionen a los estudiantes los mecanismos de ayuda necesarios (Scaffolding) para darles soporte durante el aprendizaje de conceptos TIC. Una posible solución a este problema es el uso de juegos educativos, los cuáles implementarán técnicas de Scaffolding que den el soporte necesario al estudiante para alcanzarlos objetivos de aprendizaje fijados. Por tanto, en este proyecto se diseñará e implementará un juego educativo basado en puzles orientado a la Programación que estará basado en un método aprendizaje basado en el Constructivismo en el que el estudiante construye su propio conocimiento. Una vez implementado, será evaluado en un centro escolar por parte deestudiantes de últimos cursos de ESO o Bachillerato.

Free Flows, Limited Diversification: Explaining the Fall and Rise of Stock Market Correlations, 1890-2001

Using a new dataset on capital account openness, we investigate why equity return correlations changed over the last century. Based on a new, long-run dataset on capital account regulations in a group of 16 countries over the period 1890-2001, we show that correlations increase as financial markets are liberalized. These findings are robust to controlling for both the Forbes-Rigobon bias and global averages in equity return correlations. We test the robustness of our conclusions, and show that greater synchronization of fundamentals is not the main cause of increasing correlations. These results imply that the home bias puzzle may be smaller than traditionally claimed.

Discrete devaluations and multiple equilibria in a first generation model of currency crises

The first generation models of currency crises have often been criticized because they predict that, in the absence of very large triggering shocks, currency attacks should be predictable and lead to small devaluations. This paper shows that these features of first generation models are not robust to the inclusion of private information. In particular, this paper analyzes a generalization of the Krugman-Flood-Garber (KFG) model, which relaxes the assumption that all consumers are perfectly informed about the level of fundamentals. In this environment, the KFG equilibrium of zero devaluation is only one of many possible equilibria. In all the other equilibria, the lack of perfect information delays the attack on the currency past the point at which the shadow exchange rate equals the peg, giving rise to unpredictable and discrete devaluations.

A century of global equity market correlations

In this paper, we use a unique long-run dataset of regulatory constraints on capital account openness to explain stock market correlations. Since stock returns themselves are highly volatile, any examination of what drives correlations needs to focus on long runs of data. This is particularly true since some of the short-term changes in co-movements appear to reverse themselves (Delroy Hunter 2005). We argue that changes in the co-movement of indices have not been random. Rather, they are mainly driven by greater freedom to move funds from one country to another. In related work, Geert Bekaert and Campbell Harvey (2000) show that equity correlations increase after liberalization of capital markets, using a number of case studies from emerging countries. We examine this pattern systematically for the last century, and find it to be most pronounced in the recent past. We compare the importance of capital account openness with one main alternative explanation, the growing synchronization of economic fundamentals. We conclude that greater openness has been the single most important cause of growing correlations during the last quarter of a century, though increasingly correlated economic fundamentals also matter. In the conclusion, we offer some thoughts on why the effects of greater openness appear to be so much stronger today than they were during the last era of globalization before 1914.

Judges' cognition and market order

We argue that during the crystallization of common and civil law in the 19th century, the optimal degree of discretion in judicial rulemaking, albeit influenced by the comparative advantages of both legislative and judicial rulemaking, was mainly determined by the anti-market biases of the judiciary. The different degrees of judicial discretion adopted in both legal traditions were thus optimally adapted to different circumstances, mainly rooted in the unique, market-friendly, evolutionary transition enjoyed by English common law as opposed to the revolutionary environment of the civil law. On the Continent, constraining judicial discretion was essential for enforcing freedom of contract and establishing a market economy. The ongoing debasement of pro-market fundamentals in both branches of the Western legal system is explained from this perspective as a consequence of increased perceptions of exogenous risks and changes in the political system, which favored the adoption of sharing solutions and removed the cognitive advantage of parliaments and political leaders.

Firm investment in imperfect capital markets: A structural estimation

We set up a dynamic model of firm investment in which liquidity constraintsenter explicity into the firm's maximization problem. The optimal policyrules are incorporated into a maximum likelihood procedure which estimatesthe structural parameters of the model. Investment is positively related tothe firm's internal financial position when the firm is relatively poor. This relationship disappears for wealthy firms, which can reach theirdesired level of investment. Borrowing is an increasing function of financial position for poor firms. This relationship is reversed as a firm's financial position improves, and large firms hold little debt.Liquidity constrained firms may be unused credits lines and the capacity toinvest further if they desire. However the fear that liquidity constraintswill become binding in the future induces them to invest only when internalresources increase.We estimate the structural parameters of the model and use them to quantifythe importance of liquidity constraints on firms' investment. We find thatliquidity constraints matter significantly for the investment decisions of firms. If firms can finance investment by issuing fresh equity, rather than with internal funds or debt, average capital stock is almost 35% higher overa period of 20 years. Transitory shocks to internal funds have a sustained effect on the capital stock. This effect lasts for several periods and ismore persistent for small firms than for large firms. A 10% negative shock to firm fundamentals reduces the capital stock of firms which face liquidityconstraints by almost 8% over a period as opposed to only 3.5% for firms which do not face these constraints.

Why are capital flows so much more volatile in emerging than in developed countries?

The standard deviations of capital flows to emerging countries are 80 percent higher than those to developed countries. First, we show that very little of this difference can be explained by more volatile fundamentals or by higher sensitivity to fundamentals. Second, we show that most of the difference in volatility can be accounted for by three characteristics of capital flows: (i) capital flows to emerging countries are more subject to occasional large negative shocks ( crises ) than those to developed countries, (ii) shocks are subject to contagion, and (iii) the most important one shocks to capital flows to emerging countries are more persistent than those to developed countries. Finally, we study a number of country characteristics to determine which are most associated with capital flow volatility. Our results suggest that underdevelopment of domestic financial markets, weak institutions, and low income per capita, are all associated with capital flow volatility.

On the timing of balance of payments crises: Disaggregated information and interest rate policy

This paper proposes a dynamic framework to study the timing of balance of paymentscrises. The model incorporates two main ingredients: (i) investors have private information; (ii)investors interact in a dynamic setting, weighing the high returns on domestic assets against the incentives to pull out before the devaluation. The model shows that the presence of disaggregated information delays the onset of BOP crises, giving rise to discrete devaluations. It also shows that high interest rates can be eective in delaying and possibly avoiding the abandonment of the peg. The optimal policy is to raise interest rates sharply as fundamentals become very weak. However, this policy is time inconsistent, suggesting a role for commitment devices such as currency boards or IMF pressure.

Speculative securities

A speculative security is an asset whose payoff depends on a random shock uncorrelated with economic fundamentals (a sunspot) about which some traders have superior information. In this paper we show that agents may find it desirable to trade such a security in spite of the fact that it is a poorer hedge against their endowment risks as the time oftrade, and has an associated adverse selection cost. In the specific institutional setting of innovation of futures contracts, we show that a futures exchange may not have an incentive to introduce a speculative security even when all traders favor it.

Genomics: more than genes

The fundamentals of Real-time Polymerase Chain Reaction,Automated capillary electrophoresis -Sanger sequencing and Fragmentanalysis- and "Next-generation" sequencing are reviewed. An overview ofapplications is presented using our own examples carried out in our facility.

Exchange rate predictability

The main goal of this article is to provide an answer to the question: "Does anything forecast exchange rates, and if so, which variables?". It is well known thatexchange rate fluctuations are very difficult to predict using economic models, andthat a random walk forecasts exchange rates better than any economic model (theMeese and Rogoff puzzle). However, the recent literature has identified a series of fundamentals/methodologies that claim to have resolved the puzzle. This article providesa critical review of the recent literature on exchange rate forecasting and illustratesthe new methodologies and fundamentals that have been recently proposed in an up-to-date, thorough empirical analysis. Overall, our analysis of the literature and thedata suggests that the answer to the question: "Are exchange rates predictable?" is,"It depends" -on the choice of predictor, forecast horizon, sample period, model, andforecast evaluation method. Predictability is most apparent when one or more of thefollowing hold: the predictors are Taylor rule or net foreign assets, the model is linear, and a small number of parameters are estimated. The toughest benchmark is therandom walk without drift.

Man-bites-dog business cycles

The newsworthiness of an event is partly determined by how unusual it isand this paper investigates the business cycle implications of this fact. In particular, weanalyze the consequences of information structures in which some types of signals are morelikely to be observed after unusual events. Such signals may increase both uncertainty anddisagreement among agents and when embedded in a simple business cycle model, can helpus understand why we observe (i) occasional large changes in macro economic aggregatevariables without a correspondingly large change in underlying fundamentals (ii) persistentperiods of high macroeconomic volatility and (iii) a positive correlation between absolutechanges in macro variables and the cross-sectional dispersion of expectations as measuredby survey data. These results are consequences of optimal updating by agents when theavailability of some signals is positively correlated with tail-events. The model is estimatedby likelihood based methods using individual survey responses and a quarterly time seriesof total factor productivity along with standard aggregate time series. The estimated modelsuggests that there have been episodes in recent US history when the impact on outputof innovations to productivity of a given magnitude was more than eight times as largecompared to other times.

Economics breeds culture

Several recent papers document the influence and long lasting effects of technology on preferences. Simultaneously, cultural factors are often invoked to explain heterogeneity in preferences. These two ideas suggest that culture determines the short run equilibrium values of economic variables, but, in the long run, culture changes in response to the underlying economic fundamentals. We build a model in which preferences are endogenous and the diversity in preferences (the "cultural" diversity) is explained by the variation in the relevant economic fundamentals. This can help explain observed differences in labor market attachment among groups defined e.g., by citizenship, ethnicity or gender.