Load-balancing for mesh-based applications on heterogeneous cluster computers

This paper discusses load-balancing issues when using heterogeneous cluster computers. There is a growing trend towards the use of commodity microprocessor clusters. Although today's microprocessors have reached a theoretical peak performance in the range of one GFLOPS/s, heterogeneous clusters of commodity processors are amongst the most challenging parallel systems to programme efficiently. We will outline an approach for optimising the performance of parallel mesh-based applications for heterogeneous cluster computers and present case studies with the GeoFEM code. The focus is on application cost monitoring and load balancing using the DRAMA library.

Markovian bulk-arriving queues with state-dependent control at idle time

This paper considers a Markovian bulk-arriving queue modified to allow both mass arrivals when the queue is idle and mass departures which allow for the possibility of removing the entire workload. Properties of queues which terminate when the server becomes idle are developed first, since these play a key role in later developments. Results for the case of mass arrivals, but no mass annihilation, are then constructed with specific attention being paid to recurrence properties, equilibrium queue-size structure, and waiting-time distribution. A closed-form expression for the expected queue size and its Laplace transform are also established. All of these results are then generalised to allow for the removal of the entire workload, with closed-form expressions being developed for the equilibrium size and waiting-time distributions.

The collision branching process

We consider a branching model, which we call the collision branching process (CBP), that accounts for the effect of collisions, or interactions, between particles or individuals. We establish that there is a unique CBP, and derive necessary and sufficient conditions for it to be nonexplosive. We review results on extinction probabilities, and obtain explicit expressions for the probability of explosion and the expected hitting times. The upwardly skip-free case is studied in some detail.

Uniqueness criteria for continuous-time Markov chains with general transition structures

We derive necessary and sufficient conditions for the existence of bounded or summable solutions to systems of linear equations associated with Markov chains. This substantially extends a famous result of G. E. H. Reuter, which provides a convenient means of checking various uniqueness criteria for birth-death processes. Our result allows chains with much more general transition structures to be accommodated. One application is to give a new proof of an important result of M. F. Chen concerning upwardly skip-free processes. We then use our generalization of Reuter's lemma to prove new results for downwardly skip-free chains, such as the Markov branching process and several of its many generalizations. This permits us to establish uniqueness criteria for several models, including the general birth, death, and catastrophe process, extended branching processes, and asymptotic birth-death processes, the latter being neither upwardly skip-free nor downwardly skip-free.

Numerical and experimental studies of a substructural identification strategy

For structural health monitoring it is impractical to identify a large structure with complete measurement due to limited number of sensors and difficulty in field instrumentation. Furthermore, it is not desirable to identify a large number of unknown parameters in a full system because of numerical difficulty in convergence. A novel substructural strategy was presented for identification of stiffness matrices and damage assessment with incomplete measurement. The substructural approach was employed to identify large systems in a divide-and-conquer manner. In addition, the concept of model condensation was invoked to avoid the need for complete measurement, and the recovery process to obtain the full set of parameters was formulated. The efficiency of the proposed method is demonstrated numerically through multi-storey shear buildings subjected to random force. A fairly large structural system with 50 DOFs was identified with good results, taking into consideration the effects of noisy signals and the limited number of sensors. Two variations of the method were applied, depending on whether the sensor could be repositioned. The proposed strategy was further substantiated experimentally using an eight-storey steel plane frame model subjected to shaker and impulse hammer excitations. Both numerical and experimental results have shown that the proposed substructural strategy gave reasonably accurate identification in terms of locating and quantifying structural damage.

Capturing teachers' experience of learning design through case studies

This article distinguishes three dimensions to learning design: a technological infrastructure, a conceptual framework for practice that focuses on the creation of structured sequences of learning activities, and a way to represent and share practice through the use of mediating artefacts. Focusing initially on the second of these dimensions, the article reports the key findings from an exploratory study, eLIDA CAMEL. This project examined a hitherto under-researched aspect of learning design: what teachers who are new to the domain perceive to be its value as a framework for practice in the design of both flexible and classroom-based learning. Data collection comprised 13 case studies constructed from participants' self-reports. These suggest that providing students with a structured sequence of learning activities was the major value to teachers. The article additionally discusses the potential of such case studies to function as mediating artefacts for practitioners who are considering experimenting with learning design.

Antioxidant principles of Tanacetum vulgare L. aerial parts

The methanolic extract of aerial parts of Tanacetum vulgare L. (Asteraceae) and its fractions were investigated for antioxidant activity. The crude extract displayed DPPH radical scavenging effects with an EC50 value of 37 +/- 1.2 microg/mL (n=3). Activity-guided fractionations of the crude extract resulted in the isolation of three antioxidant compounds; 3,5-O-dicaffeoylquinic acid (3,5-DCQA), axillarin and luteolin. 3,5-DCQA was the major constituent with antioxidant activity (IC50 = 9.7 microM) comparable with that of the standard quercetin (IC50 = 8.8 microM). Though the isolated compounds were previously known for their antioxidant effects, this is the first report on the identification of 3,5-DCQA from Tanacetum vulgare. The displayed potent antioxidant activity of the crude extract and isolated active principles is in support of the traditional medicinal uses of the plant for disease conditions such as wound healing, rheumatic arthritis and other inflammatory conditions.

Epidemiological and nutrition transition in developing countries: impact on human health and development

Whereas common infectious and parasitic diseases such as malaria and the HIV/AIDS pandemic remain major unresolved health problems in many developing countries, emerging non-communicable diseases relating to diet and lifestyle have been increasing over the last two decades, thus creating a double burden of disease and impacting negatively on already over-stretched health services in these countries. Prevalence rates for type 2 diabetes mellitus and CVD in sub-Saharan Africa have seen a 10-fold increase in the last 20 years. In the Arab Gulf current prevalence rates are between 25 and 35% for the adult population, whilst evidence of the metabolic syndrome is emerging in children and adolescents. The present review focuses on the concept of the epidemiological and nutritional transition. It looks at historical trends in socio-economic status and lifestyle and trends in nutrition-related non-communicable diseases over the last two decades, particularly in developing countries with rising income levels, as well as the other extreme of poverty, chronic hunger and coping strategies and metabolic adaptations in fetal life that predispose to non-communicable disease risk in later life. The role of preventable environmental risk factors for obesity and the metabolic syndrome in developing countries is emphasized and also these challenges are related to meeting the millennium development goals. The possible implications of these changing trends for human and economic development in poorly-resourced healthcare settings and the implications for nutrition training are also discussed.