A novel split-and-merge algorithm for hierarchical clustering of Gaussian mixture models

The paper presents a novel split-and-merge algorithm for hierarchical clustering of Gaussian mixture models, which tends to improve on the local optimal solution determined by the initial constellation. It is initialized by local optimal parameters obtained by using a baseline approach similar to k-means, and it tends to approach more closely to the global optimum of the target clustering function, by iteratively splitting and merging the clusters of Gaussian components obtained as the output of the baseline algorithm. The algorithm is further improved by introducing model selection in order to obtain the best possible trade-off between recognition accuracy and computational load in a Gaussian selection task applied within an actual recognition system. The proposed method is tested both on artificial data and in the framework of Gaussian selection performed within a real continuous speech recognition system, and in both cases an improvement over the baseline method has been observed.     

Computation of Saturated Permanent-Magnet AC Motor Performance by Means of Magnetic Circuits

A digital computer evaluation of transient states in a permanent-magnet (PM) machine by means of the flux tubes method is described. The influence of initial rotor phaseshift on transient torque peaks, as well as the influence of saturation on current waveforms, is shown. Several computer runs are carried out to illustrate the applicability of the flux tubes method for computation of PM machine performance.     

Improving the performance of Federated Digital Library services

The number of Digital Libraries (DLs) accessible over the Open Archives Initiative–Protocol for Metadata Harvesting (OAI–PMH) has been constantly increasing in the past years. Earlier efforts in the DL area have concentrated on metadata harvesting and provisioning of value-added Federated Digital Library (FDL) services to the users. FDL services, however, have to meet significant performance and scalability requirements, which is difficult to achieve in centralized metadata harvesting systems. The goal of the present study was to evaluate the benefits of using Web Services Resource Framework (WSRF) compliant grid middleware infrastructure for providing efficient and reliable FDL services. The presented FDL application allows for parallel harvesting of OAI–PMH compliant DLs. The results show that this approach efficiently solves the performance related problems, while it also contributes to greater flexibility of the system. The quality of service is improved as metadata can be updated frequently, and the system does not exhibit a single point of failure.     

Radial stretching of a thin hollow membrane: biaxial tension, tension field and buckling domains

The radial stretching of a hollow thin membrane without compressive strength is considered within the framework of the small strain tension field theory. For each type of the uniform boundary conditions, the loading plane is partitioned into the domains of biaxial tension, tension field and buckling. The extent of these domains critically depends on the value of the Poisson??s coefficient and on the aspect ratio of the membrane. The stress and displacement fields are determined at an arbitrary stage of loading, when the outer biaxially stressed (taut) annulus surrounds the inner (tension field) portion of the membrane, characterized by continuously distributed infinitesimal wrinkles. The growth of the tension field as the loading increases is analyzed. It is shown that, depending on the Poisson??s coefficient and the aspect ratio of the membrane, the tension field may or may not spread throughout the whole membrane. For the fixed outer boundary, and the applied tension or a negative displacement at the inner boundary, and for a particular combination of the material and geometric parameters, the tension field instantly spreads to a specific depth within the membrane, dependent on the Poisson??s ratio and the outer radius of the membrane, remaining constant during further increase of the loading.     

Evaluating energy security in the Asia-Pacific region: A novel methodological approach

This paper establishes an ‘energy security assessment instrument’ based on a new and expanded conceptualisation of energy security. The instrument is a systematic interrogative tool for evaluating energy security of individual states or regions. It consists of eleven broad energy security dimensions associated with the current global energy system. These energy security dimensions take into account numerous quantitative and qualitative attributes of each country’s energy security and policy, and include both traditional energy security concerns and many new factors, such as environmental, socio-cultural and technological. Another dimension, largely absent from previous analyses, is the existence of, and the issues addressed in, energy security policy in each country. This instrument serves as an assessment system with which to evaluate energy security in the Asia-Pacific region. The existing studies on energy security in the Asia-Pacific region suffer from serious limitations. No study to date examines regional energy security policies by adopting a more comprehensive energy security definition as a starting point. Most studies also focus on a single country or issue. Even if they examine energy security in major regional economies, they lack critical comparative analysis. The instrument is valuable as it may be utilised to draw a comprehensive map of regional energy security situation, which can also include comparative analysis of energy security characteristics across the Asia-Pacific region. Ultimately, it may be utilised to set up a framework for improved regional energy cooperation with the aim of providing regional leaders with a blueprint for improving regional energy security and policy.     

Study of multicycle melting and freezing of sodium thiosulphate pentahydrate

The behaviour of sodium thiosulphate pentahydrate in the course of repeated use as a heat-storing medium can be predicted, cycle by cycle, on the basis of a generalised phase-transition equation adapted for incongruently melting material. An indice is derived for this purpose and named ‘coefficient of true phase-transition reversibility’. Its predictive value is shown for three additional incongruently melting materials well known as heat-storing media: CaCl₂.6H₂O, Na₂SO₄.10H₂O and the mixture Na₂SO₄.10H₂O + 2/3NH₄Cl + 2/3NaCJ.     

Initial anisotropy in demineralized bovine cortical bone in compressive cyclic loading–unloading

The mechanical properties of demineralized bovine cortical femur bone were investigated by cyclic loading–unloading compression in three anatomical directions (longitudinal, radial, transverse) within the physiological strain range. The loading responses in the radial and transverse directions were nearly linear up to 2% strain, while the response in longitudinal direction was strongly non-linear in that range. The unloading responses were non-linear for each anatomical direction, giving rise to overall loading–unloading hysteresis and cyclic dissipation of energy. The mechanical properties were observed to be anisotropic: the radial direction was found to be the most energy dissipative, while the longitudinal direction appeared to be the stiffest bone direction. The cyclic loading mostly affects the bone stiffness in the radial and transverse directions, while the longitudinal direction was found to be the least affected. These anisotropic properties can be attributed to the differences in collagen fibers alignment and different microstructural architecture in three different anatomical bone directions.