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

Activity of human hippocampal and amygdala neurons during retrieval of declarative memories

Episodic memories allow us to remember not only that we have seen an item before but also where and when we have seen it (context). Sometimes, we can confidently report that we have seen something (familiarity) but cannot recollect where or when it was seen. Thus, the two components of episodic recall, familiarity and recollection, can be behaviorally dissociated. It is not clear, however, whether these two components of memory are represented separately by distinct brain structures or different populations of neurons in a single anatomical structure. Here, we report that the spiking activity of single neurons in the human hippocampus and amygdala [the medial temporal lobe (MTL)] contain information about both components of memory. We analyzed a class of neurons that changed its firing rate to the second presentation of a previously novel stimulus. We found that the neuronal activity evoked by the presentation of a familiar stimulus (during retrieval) distinguishes stimuli that will be successfully recollected from stimuli that will not be recollected. Importantly, the ability to predict whether a stimulus is familiar is not influenced by whether the stimulus will later be recollected. We thus conclude that human MTL neurons contain information about both components of memory. These data support a continuous strength of memory model of MTL function: the stronger the neuronal response, the better the memory

Detection of Anomalous Reactor Activity Using Antineutrino Count Rate Evolution Over the Course of a Reactor Cycle

This paper analyzes the sensitivity of antineutrino count rate measurements to changes in the fissile content of civil power reactors. Such measurements may be useful in IAEA reactor safeguards applications. We introduce a hypothesis testing procedure to identify statistically significant differences between the antineutrino count rate evolution of a standard 'baseline' fuel cycle and that of an anomalous cycle, in which plutonium is removed and replaced with an equivalent fissile worth of uranium. The test would allow an inspector to detect anomalous reactor activity, or to positively confirm that the reactor is operating in a manner consistent with its declared fuel inventory and power level. We show that with a reasonable choice of detector parameters, the test can detect replacement of 73 kg of plutonium in 90 days with 95% probability, while controlling the false positive rate at 5%. We show that some improvement on this level of sensitivity may be expected by various means, including use of the method in conjunction with existing reactor safeguards methods. We also identify a necessary and sufficient daily antineutrino count rate to achieve the quoted sensitivity, and list examples of detectors in which such rates have been attained.Comment: 9 pages, 7 figures, submitted to J. Appl. Phy

Inflation, Monetary Transparency, and G3 Exchange Rate Volatility

Short-term volatility in G3 bilateral exchange rates has been a fact of life since the beginning of the post-Bretton Woods float. It has been established, surprisingly, that this volatility is not only disproportionately large relative to the variation in relative macroeconomic fundamentals of Germany, Japan, and the United States, but is in fact largely unrelated to them. The apparent disconnect between fundamentals and dollar-yen and dollar-euro exchange rate fluctuations has led to perennial complaints about persistent exchange rate "misalignments," and their real effects on the G3 (and other) economies, giving rise in turn to recurring proposals for government policies to limit this volatility. The idea that volatility reflects nothing more than the (perhaps rational, certainly profit-seeking) behavior of foreign exchange traders seems to give justification for a policy response. Yet, the disjunction between macroeconomic expectations and the volatility seems to indicate as well that some deviation from domestic monetary policy goals would be necessary to intervene against exchange rate swings.