Master curve of viscoelastic solid: Using causality to determine the optimal shifting procedure,and to test the accuracy of measured data

Viscoelastic solids such as rubber exhibit a complex elastic modulus E(ω), which depends on the frequency ω of the applied stress or strain. The modulus E(ω) can often be determined in a wide frequency range by performing measurements in a limited frequency range for many different temperatures, and then shift the frequency segments horizontally along the frequency axis to obtain a continuous master curve. We show that one can use the spectral representation of E(ω) (or 1/E(ω)), which obeys causality, to determine the optimal shifting procedure, and to test the accuracy of the measured data and the calculated master curve.     

Bi-directional causality in California's electricity and natural-gas markets

The Granger instantaneous-causality test is applied to explore the potential causal relationships between wholesale electricity and natural-gas prices in California. The test shows these relationships to be bi-directional, and reveals California's electricity and natural-gas markets to be as inextricably intertwined as casual observation and theoretical considerations would suggest they ought to be. This meshing of markets exacerbated the effects of California's natural-gas crisis on the contemporaneous electricity crisis, while concurrently the electricity crisis may have contributed to the dysfunction in the national-gas market and helped to precipitate the natural-gas crisis. The finding supports an integrated approach, as opposed to a piecemeal approach, for formulating energy policy recommendations, not just in California but in the world at large.     

The causal relationship between electricity consumption and economic growth in the ASEAN countries

This paper investigates the causal relationship between electricity consumption and economic growth among the Association of South East Asian Nations (ASEAN) 4 members, namely Indonesia, Malaysia, Singapore, and Thailand, using modern time-series techniques for the period 1971–2002. The results indicate that there is a bi-directional causality between electricity consumption and economic growth in Malaysia and Singapore. This means that an increase in electricity consumption directly affects economic growth and that economic growth also stimulates further electricity consumption in the two countries. However, uni-directional causality runs from economic growth to electricity consumption in Indonesia and Thailand without any feedback effect. Thus, electricity conservation policies can be initiated without deteriorating economic side effects in the two countries.     

Market integration and price transmission in the U.S. natural gas market: From the wellhead to end use markets

Examination of the upstream-downstream pricing behavior in U.S. natural gas industry reveals that: (a) natural gas markets are integrated but subject to regime shifts and asymmetric adjustments, suggesting market imperfections. (b) Demand- and supply-side shocks play important roles in determining short-run price movements as evidenced by tests of causality and impulse response functions. (c) The response of end use prices to deviations from equilibrium with wellhead prices vary. Electrical, industrial and city gate prices adjust fast while commercial and residential prices adjust slowly, consistent with the role of administered pricing in later markets. (d) Long-run variations in end use prices are primarily due to their own shocks, while long-run variations in wellhead prices are due to innovations in residential and electrical prices. These findings point to the importance of demand shocks as the primary determinant of natural gas prices in the long-run.     

The integration of China into the world crude oil market since 1998

The integration of China into the world oil market is an important issue for at least two reasons. First, the influence of the country on the world oil market is dependent on the level of the integration. Second, integration into the world oil market means that China is opening itself up to potential disturbances in the world market and this leads to significant energy security concerns for the country. The aim of this paper is to investigate whether or not China is an integral part of the world oil market. By reviewing the relevant trade and pricing policies of the Chinese government as well as the behavior of the Chinese national oil companies, we find that China is actively engaging itself in the world oil market. Our time-series results show that the Chinese oil price is cointegrated with the major oil prices in the world and a high degree of co-movement between the prices is found. Causality between the price pairs is found to be bi-directional in most cases. The empirical results suggest that China is now an integral part of the world oil market.     

Dispositional versus epistemic causality

I put forward several desiderata that a philosophical theory of causality should satisfy: it should account for the objectivity of causality, it should underpin formalisms for causal reasoning, it should admit a viable epistemology, it should be able to cope with the great variety of causal claims that are made, and it should be ontologically parsimonious. I argue that Nancy Cartwright’s dispositional account of causality goes part way towards meeting these criteria but is lacking in important respects. I go on to argue that my epistemic account, which ties causal relationships to an agent’s knowledge and ignorance, performs well in the light of the desiderata. Such an account, I claim, is all we require from a theory of causality.     

The power of logical clock abstractions

Vector and matrix clocks are extensively used in asynchronous distributed systems. This paper asks, how does the clock abstraction generalize? To address this problem, the paper motivates and proposes logical clocks of arbitrary dimensions. It then identifies and explores the conceptual link between such clocks and knowledge. It establishes the necessary and sufficient conditions on the size and dimension of clocks required to attain any specified level of knowledge about the timestamp of the most recent system state for which this is possible without using any messages in the clock protocol. The paper then gives algorithms to determine the timestamp of the latest system state about which a specified level of knowledge is attainable in a given system state, and to compute the timestamp of the earliest system state in which a specified level of knowledge about a given system state is attainable. The results are applicable to applications that deal with a certain class of properties, identified as monotonic properties.Received: 15 March 2002, Accepted: 15 January 2004, Published online: 9 June 2004This material is based on work supported by the National Science Foundation under Grant No. 9875617. A conference version appeared in [14] and the full technical report is in [13].     

Causality and Counterfactuals in the Situation Calculus

Structural causal models offer a popular framework for exploringcausal concepts. However, due to their limited expressiveness,structural models have difficulties coping with such conceptsas actual (event-to-event) causation. In this article, we proposea new type of causal model, based on embedding structural considerationsin the language of situation calculus. By using situation calculusas a basic language, we leverage its power to express complex,dynamically changing situations and, by relying on structuralconsiderations, we can formulate an effective theory of counterfactualswithin the situation-calculus.