Inflation Targeting, Price-Path Targeting and Output Variability

The dramatic improvement in macroeconomic outcomes during the 1990s - stable, low inflation and high, stable growth - can be at least partly ascribed to improved monetary policy. Central banks became more independent and many of them adopted inflation targeting. This paper examines the potential for further improvements by refining the concept of inflation targeting. We construct a general model that encompasses a broad array of possible target regimes, and apply it to the data. Our results suggest that the vast majority of countries could benefit from moving to pricepath targeting, where the central bank makes up for periods of above (below) target inflation with later periods of below (above) target inflation.

Asset Price Bubbles and Challenges to Central Banks

The experience from the 2007 - 2009 global financial crisis was a wake-up call for central bankers. In the past decade, central bankers around the world have become more confident that they can control economic fluctuations including inflation. Many countries have adopted inflation targeting as their monetary policy framework. The success of inflation targeting in combating inflation led central bankers to believe not only that they have conquered inflation but also that they can even flatten business cycles, ups and downs of economic activities such as consumption and investment. Inflation was well managed around what many believe as a level close to price stability, business cycles were mitigated, and a few isolated incidences of financial crises responded well to active interventions undertaken by central banks and governments.

Variability in GRMHD simulations of Sgr A∗^*: Implications for EHT closure phase observations

The observable quantities that carry the most information regarding the structures of the images of black holes in the interferometric observations with the Event Horizon Telescope are the closure phases along different baseline triangles. We use long time span, high cadence, GRMHD+radiative transfer models of Sgr A$^*$ to investigate the expected variability of closure phases in such observations. We find that, in general, closure phases along small baseline triangles show little variability, except in the cases when one of the triangle vertices crosses one of a small regions of low visibility amplitude. The closure phase variability increases with the size of the baseline triangle, as larger baselines probe the small-scale structures of the images, which are highly variable. On average, the jet-dominated MAD models show less closure phase variability than the disk-dominated SANE models, even in the large baseline triangles, because the images from the latter are more sensitive to the turbulence in the accretion flow. Our results suggest that image reconstruction techniques need to explicitly take into account the closure phase variability, especially if the quality and quantity of data allow for a detailed characterization of the nature of variability. This also implies that, if image reconstruction techniques that rely on the assumption of a static image are utilized, regions of the $u-v$ space that show a high level of variability will need to be identified and excised.Comment: submitted to apj. 12 pages, 12 figure

GRMHD simulations of visibility amplitude variability for Event Horizon Telescope images of Sgr A*

Synthesis imaging of the black hole in the center of the Milky Way, Sgr A*, with the Event Horizon Telescope (EHT) rests on the assumption of a stationary image. We explore the limitations of this assumption using high-cadence GRMHD simulations of Sgr A*. We employ analytic models that capture the basic characteristics of the images to understand the origin of the variability in the simulated visibility amplitudes. We find that, in all simulations, the visibility amplitudes for baselines oriented perpendicular to the spin axis of the black hole typically decrease smoothly over baseline lengths that are comparable to those of the EHT. On the other hand, the visibility amplitudes for baselines oriented parallel to the spin axis show significant structure with one or more minima. This suggests that fitting EHT observations with geometric models will lead to reasonably accurate determination of the orientation of the black-hole on the plane of the sky. However, in the disk-dominated models, the locations and depths of the minima in the visibility amplitudes depend primarily on the width and asymmetry of the crescent-like images and are highly variable. In the jet-dominated models, the locations of the minima are determined by the separation of the two image components but their depths depend primarily on the relative brightness of the two components and are also variable. This suggests that using time-independent models to infer additional black-hole parameters, such as the shadow size or the spin magnitude, will be severely affected by the variability of the accretion flow.Comment: replaced to match published version, new figure added, results unchange

Bridging the Health Disparity of African Americans Through Conversational Agents

African Americans have faced health disparities in terms of access to health care and treatment of illnesses. The novel coronavirus disease 2019 pandemic exacerbates those disparities caused by limited access to medical care and healthy lifestyles, vulnerability to misleading information, and mistrust of the medical profession, all of which disproportionately affect the African American population in terms of infection and mortality. Conversational agents (CAs) are a technological intervention with the potential to narrow the disparities because they make health care more accessible, are effective in disseminating health information among a population with low health literacy, and can increase users’ trust in health information. However, designing CAs for this population presents challenges with regard to embodying the African American culture into CAs and addressing privacy and security concerns. This commentary discusses some advantages and challenges of using CAs to help African Americans protect themselves against coronavirus disease 2019, and calls for more research in this area.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/167148/1/Kim et al. 2020 Published.pdfDescription of Kim et al. 2020 Published.pdf : Published VersionSEL

Tonal signal detection in passive sonar systems using atomic norm minimization

Frequency estimation of a tonal signal in passive sonar systems is crucial to the identification of the marine object. In the conventional techniques, a basis mismatch error caused by the discretization of the frequency domain is unavoidable, resulting in a severe degradation of the object detection quality. To overcome the basis mismatch error, we propose a tonal frequency estimation technique in the continuous frequency domain. Towards this end, we formulate the frequency estimation problem as an atomic norm minimization problem. From the numerical experiments, we show that the proposed technique is effective in identifying the tonal frequency components of marine objects.This work was supported by the Agency for Defense Development (ADD) in Korea under the contract No. UD190005DD