Creep Deformation and the Grain-Boundary Resistivity of Tetragonal Zirconia Polycrystalline Materials

The grain-boundary resistivity of tetragonal zirconia polycrystals, which had undergone creep with different applied compressive loads and at different temperatures, has been measured with impedance spectroscopy. A stress exponent of unity was determined from strain rate versus stress data. The grain-boundary resistivity decreased significantly with increasing stress at a constant creep temperature indicating squeezing out of the glassy phase from interfaces between grains. This, however, had no effect on the activation energy for the grain-boundary resistivity.     

Methods of non-linear stochastic dynamics for the assessment of structural fragility

Some of the external events which can significantly contribute to the overall risk of a nuclear power plant, give rise to a dynamic excitation of the structural components which form the plant. The computation of the risk associated with these external events requires an investigation of the behaviour of the structural components beyond the elastic limit. The stochastic nature of the excitation, then, leads one to deal with a non-linear stochastic dynamic problem.

No general method of solution exists for such a problem when large structural systems are considered, although classical methods of propagating uncertainty have been successfully employed. This paper investigates the possibility of formulating an approach founded on a suitable equivalent linearization technique. In particular the authors make operative a new method of fragility analysis to be applied directly to the linearized system.

The numerical example considers a framed structural component: its aim is to show the degree of accuracy that can be reached by the approach formulated in the paper.     

Computer-assisted preoperative planning of a novel design of total ankle replacement

Computer-assisted preoperative planning are particularly sought for enhancing surgical implantation and improving clinical outcome of ankle joint replacement arthroplasty. A planning tool was designed to enhance the surgical implantation of a novel ligament-compatible three-component prosthesis. The tool includes a geometric and mechanical model of the ankle complex. The geometry of the articular surfaces and of main ligaments is defined from digitisation on a scanned lateral radiographs of the joint. From the expected movement arc and from component dimensions, a mechanical model of the ligaments is used to select the optimal size and the position the three prosthesis components. The planning is based on the minimisation of ligament change in length and of bone stock to be removed. The main output report is a detailed picture of the replaced ankle with indications of component locations and quantitative measure of bone cuts. An advanced report also superimposes the resulting prediction of prosthesis component kinematics at the replaced joint to the original radiographs.     

Controlling and investigating cellular automaton behavior via interactive inversion and visualization of the search space

An interactive genetic algorithm (IGA) provides a means to optimize the input parameters controlling the behavior of a cellular automaton (CA). The result is one or more combinations of parameters that allow the CA to reproduce geological patterns of fluid flow and chemical reactions in fractured media. Via the IGA, the user can provide subjective feedback on the quality of the CA results, which would otherwise be difficult to express numerically. A simple modification to the IGA ranking process, combined with a self-organizing map, enables the rapid on-line visualization of the highdimensional parameter space, and consequent control over the inversion itself. The insights into the topology of the parameter space offer an understanding of which parameters control different CA behaviors. Fabio Boschetti, Ph.D.: He obtained his Ph.D. in Mathematical Geophysics at the University of Western Australia in 1996. His main expertise lies in global optimisation, evolutionary computation, image processing, visualisation of multivariate data and human-computer interaction. Currently he works for CSIRO, Australia, focussing on forward and inverse modelling of geological processes.     

Synchronization support and group-membership services for reliable distributed multimedia applications

We describe a collection of algorithms designed to support reliable synchronization and group membership services for distributed multimedia applications. In particular, we consider those applications that require interactivity, isochronous rendering of multimedia data, and high reliability. We show that the algorithms we propose (i) provide reliable support for the synchronization of multimedia data streams, despite the occurrence of possible communication failures, (ii) maintain a consistent view of the relative group membership of all the nonfaulty application components, (iii) guarantee time-bounded delay of component failure detection and join, and (iv) meet effectively possible scalability requirements of the applications.     

Estimation of molecular weight distribution of poly(vinylpyrrolidone) from diaphragm-cell diffusion measurements

Viscometry, gel permeation chromatography (GPC) and diffusion measurements on three samples of poly(vinylpyrrolidone) (PVP) were made. The diffusion measurements were carried out by means of a Stokes cell. An equation with five parameters was derived, linking the difference in PVP amount between the two compartments of the cell to the time of the experiment: three parameters are related to the diffusional behavior of the macromolecules and the other two define the molecular weight distribution (the Tung expression has been chosen). A least-squares procedure allowed us to obtain the five parameters and the calculated weight average molecular weights agree with the ones evaluated by viscometry and GPC. The ratio M _w/M _n (heterogeneity of the polymer) calculated from the parameter z of the Tung expression is very different from the one obtained from GPC.     

Isotopic measurements of uranium using inductively coupled plasma cavity ringdown spectroscopy

Inductively coupled plasma cavity ringdown spectroscopy (ICP-CRDS) is applied to isotopic measurements of uranium. We have successfully obtained the isotopic-resolved spectra of uranium at three different atomic/ionic transition lines, 286.57, 358.49, and 409.01 nm. Of the three lines, the largest isotope shift of approximately 9 pm was measured at the 286.57 ionic line. Isotopic-resolved spectra were recorded in ratio of 1:1 (235U/238U, 2.5 micrograms/mL) and at the natural abundance ratio of 0.714% (235U/238U, 1.25 micrograms/mL 235U). The smallest measurable isotope shift of approximately 3 pm was determined for the 409.01 nm ion spectral line. Detection limits (DL) were obtained under optimized ICP operating conditions to be in the range of 70-150 ng/mL, except for the 238U component of the 286.57 nm line (300 ng/mL). This latter result was determined to be due to a strong, previously unreported, absorption interference from the argon plasma. The 235U isotope component (DL 70 ng/mL) was found to be unaffected. This work demonstrates the applicability of ICP-CRDS for uranium isotopic measurements. The potential of development of a field-deployable, on-line uranium isotope monitor using plasma-CRDS is discussed.     

Authentication and Authorization Mechanisms for Multi-Domain Grid Environments

This article discusses the authentication and the authorization aspects of security in grid environments spanning multiple administrative domains. Achievements in these areas are presented using the EU DataGrid project as an example implementation. It also gives an outlook on future directions of development.     

Bayesian relevance feedback for content-based image retrieval

Despite the efforts to reduce the so-called semantic gap between the user's perception of image similarity and the feature-based representation of images, the interaction with the user remains fundamental to improve performances of content-based image retrieval systems. To this end, relevance feedback mechanisms are adopted to refine image-based queries by asking users to mark the set of images retrieved in a neighbourhood of the query as being relevant or not. In this paper, the Bayesian decision theory is used to estimate the boundary between relevant and non-relevant images. Then, a new query is computed whose neighbourhood is likely to fall in a region of the feature space containing relevant images. The performances of the proposed query shifting method have been compared with those of other relevance feedback mechanisms described in the literature. Reported results show the superiority of the proposed method.     

Monitoring forest conditions in a protected Mediterranean coastal area by the analysis of multiyear NDVI data

The operational utilization of remote sensing techniques for monitoring terrestrial ecosystems is often constrained by problems of under-sampling in space and time, particularly in heterogeneous and unstable Mediterranean environments. The current work deals with the use of the NOAA-AVHRR and Landsat-TM/ETM+ images to produce long-term NDVI data series characterising coniferous and broadleaved forests in a protected coastal area in Tuscany (Central Italy). Two methods to extract NDVI values of relatively small vegetated areas from NOAA-AVHRR data were first evaluated by comparison to estimates from higher resolution Landsat-TM/ETM+images. The optimal method was then applied to multitemporal AVHRR data series to derive 10-day NDVI profiles of coniferous and broadleaved forests over a 15-year period (1986-2000). Trend analyses performed on these data series showed that notable NDVI decreases occurred during the study period, particularly for the coniferous forest in summer and early fall. Further analysis carried out on local meteorological measurements led to identify the likely causes of these negative trends in contemporaneous winter rainfall decreases which were significantly correlated with the found NDVI variations.