Symmetry, regression design, and sampling distributions

When values of regressors are symmetrically disposed, many M-estimators in a wide class of models have a reflection property, namely, that as the signs of the coefficients on regressors are reversed, their estimators' sampling distribution is reflected about the origin. When the coefficients are zero, sign reversal can have no effect. So in this case, the sampling distribution of regression coefficient estimators is symmetric about zero, the estimators are median unbiased and, when moments exist, the estimators are exactly uncorrelated with estimators of other parameters. The result is unusual in that it does not require response variates to have symmetric conditional distributions. It demonstrates the potential importance of covariate design in determining the distributions of estimators, and it is useful in designing and interpreting Monte Carlo experiments. The result is illustrated by a Monte Carlo experiment in which maximum likelihood and symmetrically censored least-squares estimators are calculated for small samples from a censored normal linear regression, Tobit, model. © 1994, Cambridge University Press. All rights reserved

Scaling Reinforcement Learning Paradigms for Motor Control

Reinforcement learning offers a general framework to explain reward related learning in artificial and biological motor control. However, current reinforcement learning methods rarely scale to high dimensional movement systems and mainly operate in discrete, low dimensional domains like game-playing, artificial toy problems, etc. This drawback makes them unsuitable for application to human or bio-mimetic motor control. In this poster, we look at promising approaches that can potentially scale and suggest a novel formulation of the actor-critic algorithm which takes steps towards alleviating the current shortcomings. We argue that methods based on greedy policies are not likely to scale into high-dimensional domains as they are problematic when used with function approximation – a must when dealing with continuous domains. We adopt the path of direct policy gradient based policy improvements since they avoid the problems of unstabilizing dynamics encountered in traditional value iteration based updates. While regular policy gradient methods have demonstrated promising results in the domain of humanoid notor control, we demonstrate that these methods can be significantly improved using the natural policy gradient instead of the regular policy gradient. Based on this, it is proved that Kakade’s ‘average natural policy gradient’ is indeed the true natural gradient. A general algorithm for estimating the natural gradient, the Natural Actor-Critic algorithm, is introduced. This algorithm converges with probability one to the nearest local minimum in Riemannian space of the cost function. The algorithm outperforms nonnatural policy gradients by far in a cart-pole balancing evaluation, and offers a promising route for the development of reinforcement learning for truly high-dimensionally continuous state-action systems. Keywords: Reinforcement learning, neurodynamic programming, actorcritic methods, policy gradient methods, natural policy gradien

Relationship between antihypertensive medications and cognitive impairment: Part II. Review of Physiology and animal studies

Purpose of Review There is an established association between hypertension and increased risk of poor cognitive performance and dementia including Alzheimer’s disease; however, associations between antihypertensive medications (AHM) and dementia risk are less clear. An increased interest in AHM has resulted in expanding publications; however, none of the recent reviews provide comprehensive review. Our extensive review includes 24 mechanistic animal and human studies published over the last 5 years assessing relationship between AHM and cognitive function. Recent Findings All classes of AHM showed similar result patterns in animal studies. The mechanism by which AHM exert their effect was extensively studied by evaluating well-established pathways of AD disease process, including amyloid beta (Aβ), vascular, oxidative stress and inflammation pathways, but only few studies evaluated the blood pressure lowering effect on the AD disease process. Summary Methodological limitations of the studies prevent comprehensive conclusions prior to further work evaluating AHM in animals and larger human observational studies, and selecting those with promising results for future RCTs

Thermal Insulative Elastomers for Clustered Large Liquid Propellant Rocket Engines

As thrust levels increase and as rocket engines fire for longer periods of time, the difficulties encountered in the protection of critical components from the effects of excessively high temperatures greatly increase. To protect these components a series of filled elastomeric composites have been evaluated. A brief discussion is presented of the problems of hot gas recirculation, radiation, and base plane heating with particular reference to large, clustered, liquid propellant rocket engines. The effect on components is discussed and an evaluation of a series of insulators based on filled elastomeric composites is presented. The evaluations are based on specialized thermal tests which were designed to simulate as far as possible, conditions during flight. The most promising of these elastomeric composites are compared to three alternative insulative systems, a filled, castable ceramic, a metal foil-silica fiber batting, and an asbestos-inconel wire mesh composite, in terms of weight, cost, and ease of fabrication and repair

Relationship between antihypertensive medications and cognitive impairment: Part I. review of human studies and clinical trials

Purpose of review: There is an established association between hypertension and increased risk of poor cognitive performance and dementia including Alzheimer’s disease; however, associations between antihypertensive medications (AHMs) and dementia risk are less consistent. An increased interest in AHM has resulted in expanding publications; however, none of the recent reviews are comprehensive. Our extensive review includes 15 observational and randomized controlled trials (RCTs) published over the last 5 years, assessing the relationship between AHM and cognitive impairment. Recent findings: All classes of AHM showed similar result patterns in human studies with the majority of study results reporting point estimates below one and only a small number of studies (N = 15) reporting statistically significant results in favor of a specific class. Summary: Only a small number of studies reported statistically significant results in favor of a specific class of AHM. Methodological limitations of the studies prevent definitive conclusions. Further work is now needed to evaluate the class of AHM and cognitive outcomes in future RCTs, with a particular focus on the drugs with the promising results in both animals and human observational studies

Process Evaluation Insights on Program Implementation

This white paper has the explicit intention to draw lessons learned from the past 30 years of energy efficiency program evaluation in order to facilitate improved program design and implementation going forward. The discussion in this white paper is developed based on interviews with 43 individuals who are either practitioners or users of process and market evaluation. In addition, we obtained references to published materials from our contacts and reviewed conference proceedings dating from 1992 to 2008, which resulted in a review of nearly 100 articles or reports documenting the results of, or commenting on, process and market evaluations