Unraveling the origin of ferroelectric resistance switching through the interfacial engineering of layered ferroelectric-metal junctions

Ferroelectric memristors have found extensive applications as a type of nonvolatile resistance switching memories in information storage, neuromorphic computing, and image recognition. Their resistance switching mechanisms are phenomenally postulated as the modulation of carrier transport by polarization control over Schottky barriers. However, for over a decade, obtaining direct, comprehensive experimental evidence has remained scarce. Here, we report an approach to experimentally demonstrate the origin of ferroelectric resistance switching using planar van der Waals ferroelectric α-In2Se3 memristors. Through rational interfacial engineering, their initial Schottky barrier heights and polarization screening charges at both terminals can be delicately manipulated. This enables us to find that ferroelectric resistance switching is determined by three independent variables: ferroelectric polarization, Schottky barrier variation, and initial barrier height, as opposed to the generally reported explanation. Inspired by these findings, we demonstrate volatile and nonvolatile ferroelectric memristors with large on/off ratios above 104. Our work can be extended to other planar long-channel and vertical ultrashort-channel ferroelectric memristors to reveal their ferroelectric resistance switching regimes and improve their performances.

Score-Driven Time Series Models

The construction of score-driven filters for nonlinear time series models is described, and they are shown to apply over a wide range of disciplines. Their theoretical and practical advantages over other methods are highlighted. Topics covered include robust time series modeling, conditional heteroscedasticity, count data, dynamic correlation and association, censoring, circular data, and switching regimes. Expected final online publication date for the Annual Review of Statistics and Its Application, Volume 9 is March 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Expansionary or restrictive policies in the Eurozone? Dominating trends in the first two decades

Our aim is to identify periods of restrictive versus expansionary economic policy in the euro area in the last two decades. We firstly conducted the study for identifying the dominant trend in fiscal policies and then in monetary policies. We studied several fiscal outputs, focusing on the cyclical adjusted primary balance. We also analysed the European long-term and short-term interest rates. The study was conducted for several windows, namely for 3-, 4- and 5-year periods. Additional procedures were conducted for robustness checks, namely the study of structural breaks in the analysed time series as well as a study of them recurring to Markov-Switching Regimes models. For most of the analysed periods and subperiods of the series, we concluded for the presence of expansionary policies either in the fiscal or in monetary European domains. Finally, the results and the analysis of dependencies in the euro area economy favour the evidence that economic authorities in the euro area have sought to coordinate monetary and fiscal policy to stabilise the economy.

Price transmission on agricultural markets: methodological approaches

The phenomenon of price transmission on various agricultural markets has attracted the attention of scientists in the 21-st century. Empirical studies of price relationships at various market levels can be found in recent publications. In this scientific review the survey was carried out as to the existing empirical literature on price transmission in agricultural markets of European, Asian, North and South American countries. The paper also presents the analysis of the most important methodological approaches, which are very heterogeneous in the aspects of econometric models, asymmetry types and empirical results. The article provides a detailed analysis of applied research in the field of the linear and nonlinear concepts of cointegration, also the most popular econometric price transmission models have been assessed in the light of the main advantages and disad-vantages with a special focus on autoregressive models with distributed lags, error correction models, nonlinear models with switching regimes and vector autoregressive models. In recent years nonlinear and nonparametric methodological approaches and techniques have become widely used in applied research of market integration and price transmission.

Monetary policy effectiveness in the liquidity trap: a switching regimes approach

Liquidity trap economics seems to have fared particularly well on all counts of its predictions, in the aftermath of the 2008 global financial crisis. Therefore, in this paper we evaluate formally the effectiveness of unconventional monetary policy in a liquidity trap, based on data from Japan, the USA, and the eurozone over periods of liquidity trap conditions (1994–2018 for Japan and 2009–2018 for the USA and the eurozone). Under effective unconventional policies, changes in the base money-growth regime should be associated with similar regime changes in either inflation or investment expenditure growth and the estimation of a switching regimes model allows us to test whether significant joint regime shifts occur in the data. Also, a test of liquidity trap conditions is based on a discrepancy of regime shifts between growth rates of base money and broad money, since this implies a collapse of the money multiplier. Our findings show that drastic shifts in the growth rate of the monetary base do not produce similar behavior for the inflation rate, investment expenditure growth, and broad money growth, thus pointing to liquidity trap conditions and unconventional monetary policy ineffectiveness.

Infinite-Horizon Optimal Switching Regions for a Pair-Trading Strategy with Quadratic Risk Aversion Considering Simultaneous Multiple Switchings: A Viscosity Solution Approach

Very few studies have explored the structure of optimal switching regimes. We extend the existing research on the infinite-horizon multiple-regime switching problem with an arbitrary number of switch options by replacing the linear running reward function with a quadratic function in the objective function. To make our analysis more rigorous, we establish the theoretical basis for the application of the simultaneous multiple-regime switches to the problem with the extended objective function, and provide the sufficient condition under which each certain separated region in the space includes, at most, one single connected optimal switching region, which determines the structure of the optimal switching regions, and we identify the structure of the optimal switching regions for the particular problem.

Switching environments, synchronous sex, and the evolution of mating types

While facultative sex is common in sexually reproducing species, for reasons of tractability most mathematical models assume that such sex is asynchronous in the population. In this paper, we develop a model of switching environments to instead capture the effect of an entire population transitioning synchronously between sexual and asexual modes of reproduction. We use this model to investigate the evolution of the number of self-incompatible mating types in finite populations, which empirically can range from two to thousands. When environmental switching is fast, we recover the results of earlier studies that implicitly assumed populations were engaged in asynchronous sexual reproduction. However when the environment switches slowly, we see deviations from previous asynchronous theory, including a lower number of mating types at equilibrium and bimodality in the stationary distribution of mating types. We provide analytic approximations for both the fast and slow switching regimes, as well as a numerical scheme based on the Kolmogorov equations for the system to quickly evaluate the model dynamics at intermediate parameters. Our approach exploits properties of integer partitions in number theory. We also demonstrate how additional biological processes such as selective sweeps can be accounted for in this switching environment framework, showing that beneficial mutations can further erode mating type diversity in synchronous facultatively sexual populations.

Forecasting extreme risk using regime-switching GARCH models: a case from an energy commodity

PurposeThe purpose of this paper is to investigate regime-switching and single-regime GARCH models for the extreme risk forecast of the developed and the emerging crude oil markets.Design/methodology/approachThe regime-switching GARCH-type models and their single-regime counterparts are used in risk forecast of crude oil.FindingsThe author finds that the regime-switching GARCH-type models are suitable for the developed and the emerging crude oil markets in that they effectively measure the extreme risk of crude oil in different cases. Meanwhile, the model with switching regimes captures dynamic structures in financial markets, and these models are just only better than the corresponding single-regime in terms of long position risk forecast, instead of short position. That is, it just outperforms the single-regime on the downside risk forecast.Originality/valueThis study comprehensively compares risk forecast of crude oil in different situations through the competitive models. The obtained findings have strong implications to investors and policymakers for selecting a suitable model to forecast extreme risk of crude oil when they are faced with portfolio selection, asset allocation and risk management.