Set Of Recent Observations Research Articles

Detecting Changes in the Environment Based on Full Posterior Distributions Over Real-Valued Grid Maps

To detect changes in an environment, one has to decide whether a set of recent observations is incompatible with a set of previous observations. For binary, lidar-based grid maps, this is essentially the case when the laser beam traverses a voxel that has been observed as occupied, or when the beam is reflected by a voxel that has been observed as empty. However, in real-world environments, some voxels are neither completely occupied nor completely free. These voxels have to be modeled by real-valued variables, whose estimation is an inherently statistical process. Thus, it is nontrivial to decide whether two sets of observations emerge from the same underlying true map values, and hence from an unchanged environment. Our main idea is to account for the statistical nature of the estimation by leveraging the full map posteriors instead of only the most likely maps. Closed-form solutions of posteriors over real-valued grid maps have been introduced recently. We leverage a similarity measure on these posteriors to score each point in time according to the probability that it constitutes a change in the hidden map value. While the proposed approach works for any type of real-valued grid map that allows the computation of the full posterior, we provide all formulas for the well-known reflection maps and the recently introduced decay-rate maps. We introduce and compare different similarity measures and show that our method significantly outperforms baseline approaches in simulated and real-world experiments.

CEO age and gender: Subsequent market performance

AbstractThe issue of CEO age and gender vs. concurrent performance is extensively examined, but the association with subsequent performance has limited treatment in the financial literature, and with conflicting findings. In the current study, we examine the association between CEO age and gender, and subsequent company market performance using a more recent set of observations and the standard four-factor model to estimate future cumulative abnormal shareholder returns. We find that subsequent abnormal shareholder returns are marginally significantly higher for female CEOs than for their male counterparts, but no material pattern is observed between CEO age and subsequent abnormal shareholder return performance.

Stabilising falling liquid film flows using feedback control

Falling liquid films become unstable due to inertial effects when the fluid layer is sufficiently thick or the slope sufficiently steep. This free surface flow of a single fluid layer has industrial applications including coating and heat transfer, which benefit from smooth and wavy interfaces, respectively. Here, we discuss how the dynamics of the system are altered by feedback controls based on observations of the interface height, and supplied to the system via the perpendicular injection and suction of fluid through the wall. In this study, we model the system using both Benney and weighted-residual models that account for the fluid injection through the wall. We find that feedback using injection and suction is a remarkably effective control mechanism: the controls can be used to drive the system towards arbitrary steady states and travelling waves, and the qualitative effects are independent of the details of the flow modelling. Furthermore, we show that the system can still be successfully controlled when the feedback is applied via a set of localised actuators and only a small number of system observations are available, and that this is possible using both static (where the controls are based on only the most recent set of observations) and dynamic (where the controls are based on an approximation of the system which evolves over time) control schemes. This study thus provides a solid theoretical foundation for future experimental realisations of the active feedback control of falling liquid films.

Square Root Receding Horizon Information Filters for Nonlinear Dynamic System Models

New nonlinear filtering algorithms are designed based on a receding horizon strategy, i.e., a finite impulse response (FIR) structure, and square root information filtering to achieve high accuracy and good performance in empirical error covariance tests. The new nonlinear receding horizon filters reduce approximation errors in nonlinear filtering by considering a set of recent observations with non-informative initial conditions. By applying information filtering, we are able to manage the non-informative initial conditions, and thus propose the square root version of the algorithm as a means of retaining the positive definiteness of the error covariance. Based on the proposed strategy, we then implement known nonlinear filtering frameworks. Simulation results confirm that the new nonlinear receding horizon filters outperform existing nonlinear filters in well-known nonlinear examples.

Receding horizon filtering for discrete-time linear systems with state and observation delays

In this study, the authors consider the receding horizon filtering problem for discrete-time linear systems with state and observation time delays. Novel filtering algorithm is proposed based on the receding horizon strategy in order to achieve high estimation accuracy and stability under parametric uncertainties. New receding horizon filter uses a set of recent observations with appropriately chosen initial horizon conditions. The key contribution is the derivation of Lyapunov-like equations for receding horizon mean and covariance of system state with an arbitrary number of time delays. The authors demonstrate how the proposed algorithm robust against dynamic model uncertainties comparing with Kalman and Lainiotis filters with time delays. Superior performance of the proposed filter is illustrated through two numerical examples when the system modelling uncertainties appear.

A Three Body Solution for the DI Her System

The DI Herculis system has been extensively studied over the past few decades because its observed rate of apsidal advance is less than a quarter of that which is expected from its physical and orbital properties. Work by Khaliullin et al. (1991) proposed that this slow rate of apsidal advance is a result of the presence of a third (stellar mass) body orbiting the system, however, observations by Guinan et al. (1994) severely restrict the orbital properties of such a solution. We show that a planetary mass object in a highly inclined orbit relative to the binary is capable of producing the observed apsidal motion, while remaining within the bounds of the most recent set of observations. A wide range of stable solutions are possible.

Community Change and Patterns of Delinquency

One of the most important findings of the classic Shaw and McKay delinquency research was that the distributional pattern of delinquency in Chicago remained relatively stable over time despite processes of ethnic and racial invasion and succession. This paper re-examines this proposal during three 10-year periods spanning 1940-70 using Shaw and McKay's own data as well as a more recent set of observations. Evidence is presented that their model is tenable only between 1940 and 1950; since 1950, changing neighborhoods tend to be characterized by changing levels of delinquency. Historical shifts in the nature of ecological processes that may account for this divergence are discussed.