3,512 research outputs found
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
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 -algebras from non AF groupoids
We construct ample groupoids from certain categories of paths, and prove that
their -algebras coincide with the continued fraction AF algebras of Effros
and Shen. The proof relies on recent classification results for simple nuclear
-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
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