Rotating-frame nuclear magnetic relaxation of spins diffusing on a disordered lattice: a Monte Carlo model

The rotating-frame nuclear magnetic relaxation rate of spins diffusing on a disordered lattice has been calculated by Monte Carlo methods. The disorder includes not only variation in the distances between neighbouring spin sites but also variation in the hopping rate associated with each site. The presence of the disorder, particularly the hopping rate disorder, causes changes in the time-dependent spin correlation functions which translate into asymmetry in the characteristic peak in the temperature dependence of the dipolar relaxation rate. The results may be used to deduce the average hopping rate from the relaxation but the effect is not sufficiently marked to enable the distribution of the hopping rates to be evaluated. The distribution, which is a measure of the degree of disorder, is the more interesting feature and it has been possible to show from the calculation that measurements of the relaxation rate as a function of the strength of the radiofrequency spin-locking magnetic field can lead to an evaluation of its width. Some experimental data on an amorphous metal - hydrogen alloy are reported which demonstrate the feasibility of this novel approach to rotating-frame relaxation in disordered materials.

Powering the virtual university with standard portal technology

This article describes ongoing research on developing a portal framework based on the OASIS Web Services for Remote Portlets (WSRP) standard for integration of Web-based education contents and services made available through a model for a European Networked University. We first identify the requirements for such a framework that supports integration at the presentation level and collaboration in developing and updating study programmes and course materials. We then outline the architecture design, and report on the initial implementation and preliminary evaluation.

Towards the design of a portal framework for web services integration

Web services based systems have recently found their way into many applications such as e-commerce, corporate integration and e-learning. Construction of new services or introducing new functions to existing services requires composition of web services. Current approaches to service composition often require major programming effort; this is time consuming and requires considerable developer expertise. In this paper, we explore the real and rich scenarios found in e-learning where education services are offered through the Internet by networked universities to potentially millions in the world. These services are derived from existing/emerging business operation processes and commonly offered through a web interface, combined with other services such as email and ftp services, to support partial/full business processes. We identify the requirements for a generic portal framework for easy integration of existing expertise and services of individual institutions (enterprises). We examine the existing technologies and standards, and point out the gaps to be filled in designing the architecture of the framework

Using set operations to deal with the frame problem

This paper presents a simple approach to the so-called frame problem based on some ordinary set operations, which does not require non-monotonic reasoning. Following the notion of the situation calculus, we shall represent a state of the world as a set of fluents, where a fluent is simply a Boolean-valued property whose truth-value is dependent on the time. High-level causal laws are characterised in terms of relationships between actions and the involved world states. An effect completion axiom is imposed on each causal law, which guarantees that all the fluents that can be affected by the performance of the corresponding action are always totally governed. It is shown that, compared with other techniques, such a set operation based approach provides a simpler and more effective treatment to the frame problem.

Application of regularization methods to damage detection in large scale plane frame structures using incomplete noisy modal data

This paper presents an approach for detecting local damage in large scale frame structures by utilizing regularization methods for ill-posed problems. A direct relationship between the change in stiffness caused by local damage and the measured modal data for the damaged structure is developed, based on the perturbation method for structural dynamic systems. Thus, the measured incomplete modal data can be directly adopted in damage identification without requiring model reduction techniques, and common regularization methods could be effectively employed to solve the developed equations. Damage indicators are appropriately chosen to reflect both the location and severity of local damage in individual components of frame structures such as in brace members and at beam-column joints. The Truncated Singular Value Decomposition solution incorporating the Generalized Cross Validation method is introduced to evaluate the damage indicators for the cases when realistic errors exist in modal data measurements. Results for a 16-story building model structure show that structural damage can be correctly identified at detailed level using only limited information on the measured noisy modal data for the damaged structure.