Real-Time Planning with Primitives for Dynamic Walking over Uneven Terrain

We present an algorithm for receding-horizon motion planning using a finite family of motion primitives for underactuated dynamic walking over uneven terrain. The motion primitives are defined as virtual holonomic constraints, and the special structure of underactuated mechanical systems operating subject to virtual constraints is used to construct closed-form solutions and a special binary search tree that dramatically speed up motion planning. We propose a greedy depth-first search and discuss improvement using energy-based heuristics. The resulting algorithm can plan several footsteps ahead in a fraction of a second for both the compass-gait walker and a planar 7-Degree-of-freedom/five-link walker.Comment: Conference submissio

Liquidity, Volatility, and Equity Trading Costs Across Countries and Over Time

Actual investment performance reflects the underlying strategy of the portfolio manager and the execution costs incurred in realizing those objectives. Execution costs, especially in illiquid markets, can dramatically reduce the notional return to an investment strategy. This paper examines the interactions between cost, liquidity, and volatility, and analyzes their determinants using panel-data for 42 countries from September 1996 to December 1998. We document wide variation in trading costs across countries; emerging markets in particular have significantly higher trading costs even after correcting for factors affecting costs such as market capitalization and volatility. We analyze the inter-relationships between turnover, equity trading costs, and volatility, and investigate the impact of these variables on equity returns. In particular, we show that increased volatility, acting through costs, reduces a portfolio's expected return. However, higher volatility reduces turnover also, mitigating the actual impact of higher costs on returns. Further, turnover is inversely related to trading costs, providing a possible explanation for the increase in turnover in recent years. The results demonstrate that the composition of global efficient portfolios can change dramatically when cost and turnover are taken into account.http://deepblue.lib.umich.edu/bitstream/2027.42/39706/3/wp322.pd

Dynamical phase transitions in one-dimensional hard-particle systems

We analyse a one-dimensional model of hard particles, within ensembles of trajectories that are conditioned (or biased) to atypical values of the time-averaged dynamical activity. We analyse two phenomena that are associated with these large deviations of the activity: phase separation (at low activity) and the formation of hyperuniform states (at high activity). We consider a version of the model which operates at constant volume, and a version at constant pressure. In these non-equilibrium systems, differences arise between the two ensembles, because of the extra freedom available to the constant-pressure system, which can change its total density. We discuss the relationships between different ensembles, mechanical equilibrium, and the probability cost of rare density fluctuations.Comment: 11 pages, 11 figure

Liquidity, Volatility, and Equity Trading Costs Across Countries and Over Time

Actual investment performance reflects the underlying strategy of the portfolio manager and the execution costs incurred in realizing those objectives. Execution costs, especially in illiquid markets, can dramatically reduce the notional return to an investment strategy. This paper examines the interactions between cost, liquidity, and volatility, and analyzes their determinants using panel-data for 42 countries from September 1996 to December 1998. We document wide variation in trading costs across countries; emerging markets in particular have significantly higher trading costs even after correcting for factors affecting costs such as market capitalization and volatility. We analyze the inter-relationships between turnover, equity trading costs, and volatility, and investigate the impact of these variables on equity returns. In particular, we show that increased volatility, acting through costs, reduces a portfolio's expected return. However, higher volatility reduces turnover also, mitigating the actual impact of higher costs on returns. Further, turnover is inversely related to trading costs, providing a possible explanation for the increase in turnover in recent years. The results demonstrate that the composition of global efficient portfolios can change dramatically when cost and turnover are taken into account.privatization, government priorities, auctions, revenue maximization, probit analysis, selection bias.

Launch of Digitized Journal and Abstract of Proceedings of Sydney University Engineering Society and Minutes of Proceedings of the Engineers’ Association of New South Wales

Presentation for the launch of the Journal and abstract of proceedings of the Sydney University Engineering Society . This journal was digitised as part of a partnership project involving the University of Sydney Library and the Australian Society for History of Engineering and Technology.Australian Society for History of Engineering and Technology and the University of Sydney Librar

In Memoriam Maureen Byrne

A tribute to Maureen Byrne

Fairness Through Counterfactual Utilities

Group fairness definitions such as Demographic Parity and Equal Opportunity make assumptions about the underlying decision-problem that restrict them to classification problems. Prior work has translated these definitions to other machine learning environments, such as unsupervised learning and reinforcement learning, by implementing their closest mathematical equivalent. As a result, there are numerous bespoke interpretations of these definitions. Instead, we provide a generalized set of group fairness definitions that unambiguously extend to all machine learning environments while still retaining their original fairness notions. We derive two fairness principles that enable such a generalized framework. First, our framework measures outcomes in terms of utilities, rather than predictions, and does so for both the decision-algorithm and the individual. Second, our framework considers counterfactual outcomes, rather than just observed outcomes, thus preventing loopholes where fairness criteria are satisfied through self-fulfilling prophecies. We provide concrete examples of how our counterfactual utility fairness framework resolves known fairness issues in classification, clustering, and reinforcement learning problems. We also show that many of the bespoke interpretations of Demographic Parity and Equal Opportunity fit nicely as special cases of our framework

Functional Hyperaemia of Skeletal Muscle

1. Blood flow was recorded through the cat gastrocnemius and soleus muscles at rest and during stimulation at physiological frequencies. Deficiencies in the experimental set-up are discussed and the results compared with the findings of other workers who have recorded blood flow through "fast" and "slow" muscle. 2. ATP and adenosine were shown to be vasodilators of the vascular bed of the cat gastrocnemius and soleus muscles. Potassium, hypertonic glucose and inorganic phosphate were not vasodilator. These findings are discussed in relation to the identity of the vasodilator agent in functional hyperaemia of skeletal muscle. 3. ATP was detected in the plasma and Krebs perfusate from the resting and stimulated cat soleus muscle. This is discussed in relation to the hypothesis that ATP could be the vasodilator agent in functional hyperaemia. 4. APT was shown to be rapidly removed from cat blood in vitro. This is discussed in relation to a possible extracellular role for ATP

AF C∗C^*-algebras from non AF groupoids

We construct ample groupoids from certain categories of paths, and prove that their $C^*$-algebras coincide with the continued fraction AF algebras of Effros and Shen. The proof relies on recent classification results for simple nuclear $C^*$-algebras. The groupoids are not principal. This provides examples of Cartan subalgebras in the continued fraction AF algebras that are isomorphic, but not conjugate, to the standard diagonal subalgebras.Comment: 41 pages, a few tikz pictures. Version 2 (19 July 2021): several typos and minor errors correcte