Graded Signal Functions for ARTMAP Neural Networks

This study presents an analysis of a modified ARTMAP neural network in which a graded signal function replaces the standard choice-by-difference function. The modifications are introduced mathematically and the performance of the system is studied on two benchmark examples. It is shown that the modified ARTMAP system achieves classification accuracy superior to that of standard ARTMAP, while retaining comparable complexity of the internal code.Office of Naval Research and the Defense Advanced Research Projects Agency (N00014-95-1-0409, N00014-1-95-0657

Subcultural and social innovations in the campaign for nuclear disarmament

In times of war and rumours of peace, when ‘terrorism’ and ‘torture’ are being revisited and redefined, one of the things some of us should be doing is talking and writing about cultures of peace. In what follows, I ask questions about the place of culture in protest by considering the cluster of issues around the Campaign for Nuclear Disarmament (CND) from its founding in London in 1958. I look at instances of (sub)cultural innovation within the social and political spaces CND helped make available during its two high periods of activity and membership: the 1950s (campaigning against the hydrogen bomb) and the 1980s (campaigning against U.S.-controlled cruise missiles). What particularly interests me here is tracing the reticence and tensions within CND to the (sub)cultural practices with which it had varying degrees of involvement or complicity. It is not my wish to argue in any way that there was a kind of dead hand of CND stifling cultural innovation from within; rather I want to tease out ambivalences in some of its responses to the intriguing and energetic cultural practices it helped birth. CND was founded at a significant moment for emerging political cultures. Its energies and strategies contributed to the rise of the New Left, to new postcolonial identities and negotiations in Britain, and to the Anti-Apartheid Movement. In what ways did it attempt to police the ‘outlaw emotions’ it helped to release

A normalised seawater strontium isotope curve: possible implications for Neoproterozoic-Cambrian weathering rates and the further oxygenation of the Earth

The strontium isotope composition of seawater is strongly influenced on geological time scales by changes in the rates of continental weathering relative to ocean crust alteration. However, the potential of the seawater 87Sr/86Sr curve to trace globally integrated chemical weathering rates has not been fully realised because ocean 87Sr/86Sr is also influenced by the isotopic evolution of Sr sources to the ocean. A preliminary attempt is made here to normalise the seawater 87Sr/86Sr curve to plausible trends in the 87Sr/86Sr ratios of the three major Sr sources: carbonate dissolution, silicate weathering and submarine hydrothermal exchange. The normalised curve highlights the Neoproterozoic-Phanerozoic transition as a period of exceptionally high continental influence, indicating that this interval was characterised by a transient increase in global weathering rates and/or by the weathering of unusually radiogenic crustal rocks. Close correlation between the normalised 87Sr/86Sr curve, a published seawater δ34S curve and atmospheric pCO2 models is used here to argue that elevated chemical weathering rates were a major contributing factor to the steep rise in seawater 87Sr/86Sr from 650 Ma to 500 Ma. Elevated weathering rates during the Neoproterozoic-Cambrian interval led to increased nutrient availability, organic burial and to the further oxygenation of Earth's surface environment. Use of normalised seawater 87Sr/86Sr curves will, it is hoped, help to improve future geochemical models of Earth System dynamics

The mystery of the cosmic vacuum energy density and the accelerated expansion of the Universe

After a short history of the $\Lambda$-term it is explained why the (effective) cosmological constant is expected to obtain contributions from short-distance-physics, corresponding to an energy scale of at least 100 GeV. The actual tiny value of the cosmological constant in any natural scale of units represents, therefore, one of the deepest mysteries of present day fundamental physics. We also briefly discuss recent astronomical evidence for a cosmologically significant vacuum energy density causing an accelerating expansion of the universe. This arises mainly from the Hubble diagram of type Ia supernovae and from the observed temperature fluctuations of the cosmic microwave background radiation. If this should become an established fact, we are also confronted with a disturbing {\it cosmic coincidence} problem.Comment: 12 pages, 2 figures, iopart macros include

Quantization in Control Systems and Forward Error Analysis of Iterative Numerical Algorithms

The use of control theory to study iterative algorithms, which can be considered as dynamical systems, opens many opportunities to find new tools for analysis of algorithms. In this paper we show that results from the study of quantization effects in control systems can be used to find systematic ways for forward error analysis of iterative algorithms. The proposed schemes are applied to the classical iterative methods for solving a system of linear equations. The obtained bounds are compared with bounds given in the numerical analysis literature

A vertex-based finite volume method applied to non-linear material problems in computational solid mechanics

A vertex-based finite volume (FV) method is presented for the computational solution of quasi-static solid mechanics problems involving material non-linearity and infinitesimal strains. The problems are analysed numerically with fully unstructured meshes that consist of a variety of two- and three-dimensional element types. A detailed comparison between the vertex-based FV and the standard Galerkin FE methods is provided with regard to discretization, solution accuracy and computational efficiency. For some problem classes a direct equivalence of the two methods is demonstrated, both theoretically and numerically. However, for other problems some interesting advantages and disadvantages of the FV formulation over the Galerkin FE method are highlighted