Acoustic metafluids made from three acoustic fluids

Significant reduction in target strength and radiation signature can be achieved by surrounding an object with multiple concentric layers comprised of three acoustic fluids. The idea is to make a finely layered shell with the thickness of each layer defined by a unique transformation rule. The shell has the effect of steering incident acoustic energy around the structure, and conversely, reducing the radiation strength. The overall effectiveness and the precise form of the layering depends upon the densities and compressibilities of the three fluids. Nearly optimal results are obtained if one fluid has density equal to the background fluid, while the other two densities are much greater and much less than the background values. Optimal choices for the compressibilities are also found. Simulations in 2D and 3D illustrate effectiveness of the three fluid shell. The limited range of acoustic metafluids that are possible using only two fluid constituents is also discussed.Comment: 12 pages, 11 figure

The Bayesian sampler : generic Bayesian inference causes incoherence in human probability

Human probability judgments are systematically biased, in apparent tension with Bayesian models of cognition. But perhaps the brain does not represent probabilities explicitly, but approximates probabilistic calculations through a process of sampling, as used in computational probabilistic models in statistics. Naïve probability estimates can be obtained by calculating the relative frequency of an event within a sample, but these estimates tend to be extreme when the sample size is small. We propose instead that people use a generic prior to improve the accuracy of their probability estimates based on samples, and we call this model the Bayesian sampler. The Bayesian sampler trades off the coherence of probabilistic judgments for improved accuracy, and provides a single framework for explaining phenomena associated with diverse biases and heuristics such as conservatism and the conjunction fallacy. The approach turns out to provide a rational reinterpretation of “noise” in an important recent model of probability judgment, the probability theory plus noise model (Costello & Watts, 2014, 2016a, 2017; Costello & Watts, 2019; Costello, Watts, & Fisher, 2018), making equivalent average predictions for simple events, conjunctions, and disjunctions. The Bayesian sampler does, however, make distinct predictions for conditional probabilities and distributions of probability estimates. We show in 2 new experiments that this model better captures these mean judgments both qualitatively and quantitatively; which model best fits individual distributions of responses depends on the assumed size of the cognitive sample

Beyond Bipolar: A Three-Dimensional Assessment of Monetary Frameworks

Recently, great attention has been focused on the impact of exchange rate regimes, just as previous empirical research examined central bank autonomy and announced targets for domestic monetary policy. To date, however, these three elements of monetary frameworks have been assessed in isolation from one another, and all have been viewed in terms of a unidimensional spectrum of fixity versus flexibility. Using a newly-constructed dataset, this paper jointly analyzes and compares all three elements' effects on inflation and exchange rate behavior. The results show that each of the three elements has independent and distinct effects on nominal outcomes. Key findings include: (1) although hard pegs do tend to reduce inflation and attenuate exchange rate fluctuations within some range, they are clearly characterized by large devaluations; (2) central bank autonomy is associated with a more stable exchange rate and lower inflation; and (3) explicit inflation targeting reduces both inflation and its persistence, consistent with the view that inflation targeting increases flexibility through transparency. These results raise the possibility that a combination of central bank autonomy, inflation targeting, and a free float might offer the same benefits as any intermediate exchange rate regime on its own, without the proclivity to occasional large depreciations.monetary policy, exchange rates, central bank independence

Do Markets Care Who Chairs the Central Bank?

This paper assesses the effects of central bank governor appointments on financial market expectations of monetary policy. To measure these effects, we assemble a new dataset of appointment announcements from 15 countries, and conduct an event study analysis on exchange rates, bond yields, and stock prices. The analysis reveals a significant reaction of exchange rates and bond yields to unexpected appointments. The reactions are not unidirectional, and thus do not suggest new governors suffer from a generic credibility problem. Federal Reserve chairman appointments stand out in terms of their unusually pronounced effects on financial markets.Central banking, Monetary policy, Credibility, Financial markets, Event study analysis

The Difficulty of Discerning What's Too Tight: Taylor Rules and Japanese Monetary Policy

Observers have relied increasingly on simple reaction functions, such as the Taylor rule, to assess the conduct of monetary policy. Applying this approach to deflationary or near-zero inflation environments is problematic, however, and this paper examines two shortcomings of particular relevance to the Japanese case of the last decade. One is the unusually high degree of uncertainty associated with potential output in an environment of prolonged stagnation and deflation. Consequently, reaction function-based assessments of Japanese monetary policy are so sensitive to the chosen gauge of potential output as to be unreliable. The second shortcoming is the neglect of policy expectations, which become critically important as nominal interest rates approach zero. Using long-term bond yields, we identify five episodes since 1996 characterized by abrupt declines in Japanese inflation expectations. Policies undertaken by the Bank of Japan during this period did little to stabilize expectations, and the August 2000 interest rate increase appears to have intensified deflationary concerns.Deflation, Monetary Policy, Policy Rules, Taylor Rule, Japan

The Pure Spinor Formulation of Superstrings

In this lectures we outline the construction of pure spinor superstrings. We consider both the open and closed pure spinor superstrings in critical and noncritical dimensions and on flat and curved target spaces with RR flux. We exhibit the integrability properties of pure spinor superstrings on curved backgrounds with RR fluxes.Comment: These lectures have been given in the RTN Winter School on Strings, Supergravity and Gauge Theories, CERN (2008). 32 pages, a typo correcte