Introduction of a Nonlinearity Measure for Principal Component Models

This is the first paper that introduces a nonlinearity test for principal component models. The methodology involves the division of the data space into disjunct regions that are analysed using principal component analysis using the cross-validation principle. Several toy examples have been successfully analysed and the nonlinearity test has subsequently been applied to data from an internal combustion engine.

Statistical Monitoring of Dynamic Multivariate Processes: Part I: Modeling Auto- and Cross-Correlation

The work in this paper is of particular significance since it considers the problem of modelling cross- and auto-correlation in statistical process monitoring. The presence of both types of correlation can lead to fault insensitivity or false alarms, although in published literature to date, only autocorrelation has been broadly considered. The proposed method, which uses a Kalman innovation model, effectively removes both correlations. The paper (and Part 2 [2]) has emerged from work supported by EPSRC grant GR/S84354/01 and is of direct relevance to problems in several application areas including chemical, electrical, and mechanical process monitoring.

Statistical Monitoring of Dynamic Multivariate Processes: Part II: Identifying Fault Magnitude and Signature

This paper builds on work presented in the first paper, Part 1 [1] and is of equal significance. The paper proposes a novel compensation method to preserve the integrity of step-fault signatures prevalent in various processes that can be masked during the removal of both auto- and cross correlation. Using industrial data, the paper demonstrates the benefit of the proposed method, which is applicable to chemical, electrical, and mechanical process monitoring. This paper, (and Part 1 [1]), has led to further work supported by EPSRC grant GR/S84354/01 involving kernel PCA methods.

X-ray and extreme-ultraviolet emission from the coronae of Capella

The primary objective of this work is the analysis and interpretation of coronal observations of Capella obtained in 1999 September with the High Energy Transmission Grating Spectrometer on the Chandra X-ray Observatory and the Extreme Ultraviolet Explorer (EUVE). He-like lines of O (O vii) are used to derive a density of 1.7 x 10(10) cm(-3) for the coronae of the binary, consistent with the upper limits derived from Fe xxi, Ne ix and Mg xi line ratios. Previous estimates of the electron density based on Fe xxi should be considered as upper limits. We construct emission measure distributions and compare the theoretical and observed spectra to conclude that the coronal material has a temperature distribution that peaks around 4-6 MK, implying that the coronae of Capella were significantly cooler than in the previous years. In addition, we present an extended line list with over 100 features in the 5-24 Angstrom wavelength range, and find that the X-ray spectrum is very similar to that of a solar flare observed with SMM. The observed to theoretical Fe xvii 15.012-Angstrom line intensity reveals that opacity has no significant effect on the line flux. We derive an upper limit to the optical depth, which we combine with the electron density to derive an upper limit of 3000 km for the size of the Fe xvii emitting region. In the same context, we use the Si iv transition region lines of Capella from HST/Goddard High-Resolution Spectrometer observations to show that opacity can be significant at T = 10(5) K, and derive a path-length of approximate to 75 kin for the transition region. Both the coronal and transition region observations are consistent with very small emitting regions, which could be explained by small loops over the stellar surfaces.

Charge exchange emission from solar wind helium ions

Charge exchange X-ray and far-ultraviolet (FUV) aurorae can provide detailed insight into the interaction between solar system plasmas. Using the two complementary experimental techniques of photon emission spectroscopy and translation energy spectroscopy, we have studied state-selective charge exchange in collisions between fully ionized helium and target gasses characteristic of cometary and planetary atmospheres (H2O, CO2, CO, and CH4). The experiments were performed at velocities typical for the solar wind (200-1500 km s(-1)). Data sets are produced that can be used for modeling the interaction of solar wind alpha particles with cometary and planetary atmospheres. These data sets are used to demonstrate the diagnostic potential of helium line emission. Existing Extreme Ultraviolet Explorer (EUVE) observations of comets Hyakutake and Hale-Bopp are analyzed in terms of solar wind and coma characteristics. The case of Hale-Bopp illustrates well the dependence of the helium line emission to the collision velocity. For Hale-Bopp, our model requires low velocities in the interaction zone. We interpret this as the effect of severe post-bow shock cooling in this extraordinary large comet.

Relevance of heterometallic binding energy for metal underpotential deposition

We present first-principles calculations for a number of metals adsorbed on several different metallic substrates. Some of these systems are very relevant in electrochemistry, especially in the field of underpotential deposition phenomena. The present studies reveal the existence of a relationship between the excess binding energy and the surface energy difference between substrate and adsorbate. Comparisons with experimental underpotential shifts show that excess binding energies are systematically underestimated. By analyzing experimental information on different systems, we conclude that this discrepancy between our vacuum calculations and experiments carried out in an electrolytic solution is likely to be due to anion adsorption and/or solvent effects.

Monte Carlo simulation of properties of monolayers and metal islands adsorbed on metallic (111) surfaces

To obtain the surface stress changes due to the adsorption of metal monolayers onto metallic surfaces, a new model derived from thermodynamic considerations is presented. Such a model is based on continuum Monte Carlo simulations with embedded atom method potentials in the canonical ensemble, and it is extended to consider the behavior on different islands adsorbed onto (111) substrate surfaces. Homoepitaxial and heteroepitaxial systems are studied. Pseudomorphic growth is not observed for small metal islands with considerable positive misfit with the substrate. Instead, the islands become compressed upon increase of their size. A simple model is proposed to interpolate between the misfits of atoms in small islands and the pseudomorphic behavior of the monolayer.

A combined experimental and theoretical study of the generation of palladium clusters on Au(111) with a scanning tunnelling microscope

Palladium clusters have been deposited on the surface of a Au(111) electrode with the tip of a scanning tunnelling microscope. The distance over which the tip was moved towards the surface has a decisive influence on the properties of the clusters: the larger this distance, the larger the generated clusters, and the more stable they are. These findings are supported by computer simulations, which further suggest that the larger clusters contain a sizable amount of gold, which enhances their stability. Dissolution of the clusters occurs from the edges rather than layer by layer.

Kinetic Monte Carlo study of electrochemical growth in a heteroepitaxial system

Structural and kinetic aspects of 2-D irreversible metal deposition under potentiostatic conditions are analyzed by means of dynamic Monte Carlo simulations employing embedded atom potentials for a model system. Three limiting models, all considering adatom diffusion, were employed to describe adatom deposition. The first model (A) considers adatom deposition on any free substrate site on the surface at the same rate. The second model (B) considers adatom deposition only on substrate sites which exhibit no neighboring sites occupied by adatoms. The third model (C) allows deposition at higher rates on sites presenting neighboring sites occupied by adatoms. Under the proper conditions, the coverage (theta) versus time (t) relationship for the three cases can be heuristically fitted to the functional form theta = 1 - exp(-betat(alpha)), where alpha and beta are parameters. We suggest that the value of the parameter alpha can be employed to distinguish experimentally between the three cases. While model A trivially delivers a = 1, models B and C are characterized by alpha 1, respectively.

Current-induced forces in atomic-scale conductors

We present a self-consistent tight-binding formalism to calculate the forces on individual atoms due to the flow of electrical current in atomic-scale conductors. Simultaneously with the forces, the method yields the local current density and the local potential in the presence of current flow, allowing a direct comparison between these quantities. The method is applicable to structures of arbitrary atomic geometry and can be used to model current-induced mechanical effects in realistic nanoscale junctions and wires. The formalism is implemented within a simple Is tight-binding model and is applied to two model structures; atomic chains and a nanoscale wire containing a vacancy.

On the road from consultation cynicism to energising e-consultation

A major concern in recent political discourse is that government has become both isolated from and unresponsive to its citizens. Democracy, by definition, demands a two-way flow of communication between government and civil society and it is now commonly argued that ICTs have the potential to facilitate such improved flows of communication--hence, e-democracy and e-consultation. The preliminary research findings presented here are part of a larger ongoing research project on e-consultation on the island of Ireland (see http://e-consultation.org). The paper initially draws on focus group discussions on the theme of (e)consultation conducted amongst activist citizens. High levels of frustration, scepticism and cynicism were expressed on the form, nature and process of extant consultation processes. The main focus addressed in this paper, however, is on how these citizens envisage ICT being used in future e-consultations. In general, most focus group participants were open to the use of ICT in future e-consultation processes but the consensus was that community groups did not currently have access to an appropriate level or range of infrastructure, technologies or skills. As a follow up to the focus group findings the research group ran a number of demonstrations on e-consultation technologies with invited activist citizens. Technologies introduced included chat room, video-conferencing, WikiPedia, WebIQ, Zing and others. The main preliminary findings and feedback from one such demonstration, and our own observations, are then presented which suggest that the potential does exist for using e-consultation technologies in local democracy and in local government to drive positive change in the government-citizen relationship. We present no na�¯ve solutions here; we merely point to some possibilities and we acknowledge that ICT alone is very unlikely to be a panacea for the declining levels of citizen participation in most democratic societies.