Nonlinear internal models for output regulation

In this paper we show how nonlinear internal models can be effectively used in the design of output regulators for nonlinear systems. This result provides a significant enhancement of the non-equilibrium theory for output regulation, which we have presented in the recent paper entitled "Limit Sets, Zero Dynamics, and Internal Models in the Problem of Nonlinear Output Regulation"

Simultaneous stabilization and simultaneous pole placement by nonswitching dynamic compensation

The 'simultaneous stabilization problem' is defined and theorems are proposed for its solution. The problem consists in answering the question: given an r-tuple G sub 1(s), G sub r(s) of p x m proper transfer functions, does there exist a compensator K(s) such that the closed loop systems G sub 1(s) (I+K(s)G sub 1(s)) (-1), G sub r(s) (I+K(s) G sub r(s)) (-1) are (internally) stable. This question arises in reliability theory, where G sub 2(s), G sub r(s) represents a plant G sub 1(s) operating in various modes of failure and K(s) is a nonswitching stabilizing compensator. It is important in the stability analysis and design of a plant which can be switched into various operating modes. The simultaneous stabilization problem can also apply to the stabilization of a nonlinear system which is linearized at several equilibria. Conditions are defined for pole placement and the generalized Sylvestor matrix is discussed

Gravity and non-gravity mediated couplings in multiple-field inflation

Mechanisms for the generation of primordial non-Gaussian metric fluctuations in the context of multiple-field inflation are reviewed. As long as kinetic terms remain canonical, it appears that nonlinear couplings inducing non-gaussianities can be split into two types. The extension of the one-field results to multiple degrees of freedom leads to gravity mediated couplings that are ubiquitous but generally modest. Multiple-field inflation offers however the possibility of generating non-gravity mediated coupling in isocurvature directions that can eventually induce large non-Gaussianities in the metric fluctuations. The robustness of the predictions of such models is eventually examined in view of a case study derived from a high-energy physics construction.Comment: 14 pages, 3 figures, invited review for CQG issue on non-linear cosmolog

Communication: Essential Element at International Centers

The first international agricultural research center began operations less than 20 years ago. Not even the most optimistic and enthusiastic supporter of the International Rice Research Institute (IRRI), the first center, would have dared to dream, let alone predict, either its dramatic success or the consequences for peoples and other commodities around the world

Is this Belt One Size Fits All? China\u27s Belt and Road Initiative

Widely considered one of the largest and most ambitious infrastructure projects in human history, China’s Belt and Road Initiative [BRI] has made major headway since its inception in 2013. Although the BRI is formally adopted under the Chinese Communist Party Constitution as an initiative to secure “shared growth through discussion and collaboration,” the BRI is much more than these words convey. This Comment briefly introduces an overview of the BRI, including its components and early research on its effects on participating countries and regions. The Comment then conducts an in-depth analysis of four countries who have participated in the BRI with varying degrees of success. Next, the Comment discusses various international concerns surrounding the BRI, including possible debt diplomacy and military motivations. Finally, the Comment concludes that although the BRI should be applauded for its bold aspirations and developments, it should also be closely monitored by the international community to mitigate any deleterious effects incurred by BRI participants

Extreme Value Theory and Backtest Overfitting in Finance

In order to identify potentially profitable investment strategies, hedge funds and asset managers can use historical market data to simulate a strategy\u27s performance, a process known as backtesting. While the abundance of historical stock price data and powerful computing technologies has made it feasible to run millions of simulations in a short period of time, this process may produce statistically insignificant results in the form of false positives. As the number of configurations of a strategy increases, it becomes more likely that some of the configurations will perform well by chance alone. The phenomenon of backtest overfitting occurs when a model interprets market idiosyncrasies as signal rather than noise, and is often not taken into account in the strategy selection process. As a result, the finance industry and academic literature are rife with skill-less strategies that have no capability of beating the market. This paper explores the development of a minimum criterion that managers and investors can use during the backtesting process in order to increase confidence that a strategy\u27s performance is not the result of pure chance. To do this we will use extreme value theory to determine the probability of observing a specific result, or something more extreme than this result, given that multiple configurations of a strategy were tested

What\u27s Happening on the International Scene?

Twenty-eight years ago, AAACE was meeting at Mo Ranch in the wilds of Texas

Dilemmas of the Communication Consultant Abroad

When first invited to talk here, I suggested the title: Mom, are them green things oranges? While neither professional nor academic, the title rather vividly describes the Dilemmas of the Communication Consultant Abroad

Small-scale movement and migration cues of Australian bass (Percalates novemaculeata) in an urbanised river

Urban river catchments are often severely affected by human activities but may still retain significant biodiversity. Surprisingly little is known about the behaviour of urban fishes, even those popular with anglers. Key environmental variables that trigger fish behaviour, such as river flow, are highly affected by instream structures including weirs and changes in the natural flow regime. Here, we used acoustic telemetry to examine the movements of Australian bass in a river located in suburban Sydney, Australia. We found that fish tended to be nocturnally active, however, small-scale movements were highly idiosyncratic and less associated with river flow than other factors. Larger-scale movements associated with spawning migrations were strongly correlated with winter floods. Half of the tagged fish migrated to the confluence of the river with Sydney Harbour to breed. Their return migration was hampered by a weir, but the provision of a new fish way facilitated successful return to freshwater at high tide. Despite occupying a highly affected, urban catchment fish behaviour showed similarity to those occupying more natural drainages. Our results highlight the importance of maintaining natural river flows in urban catchments and sustaining fish movement and migration capabilities through the installation of appropriate fish passage devices