A note on the concentrations and bioavailability of selected metals in sediments of Richards Bay Harbour, South Africa

Sediments are considered to be the ultimate sink for most contaminants and therefore pose the highest risk to these aquatic environments. This paper presents the levels of metals in sediments from Richards Bay Harbour, 20 years after the construction of the harbour and studied spatial and temporal, as well as the proportion of the bioavailable metal fraction. Sediment samples were collected from nine sites in Richards Bay Harbour. Sequential extractions of metals were carried out and samples were analysed for aluminium, chromium, copper, iron, manganese and zinc. Metal concentrations in sediment samples varied only slightly between seasons but showed significant spatial variation, which was significantly correlated to sediment particle size composition. Highest metal concentrations were found in sites with substrata dominated by fine mud. Manganese and Zn had more than 50% of this concentrated in the easily reducible fractions. Zinc concentrations were not elevated when compared to historic data. More than 70% of Cr was concentrated in the inert fractions nevertheless concentrations recorded at some sites were still above action levels when considering only the bioavailable fractions. Keywords: sediments, metals, bioavailability, sediment composition, Richards Bay Harbour Water SA Vol. 31(4) 2005: 589-59

Dynamics and equilibria under incremental horizontal differentiation on the Salop circle

We study product differentiation on a Salop circle when firms relocate incrementally due to bounded rationality. We prove that, under common assumptions on demand, firms relocate only when two or more firms target the same niche. In any other case, there is no incentive for any firm to relocate incrementally. We prove that all distributions in which firms are sufficiently far apart in product space are unstable Nash equilibria. We prove, in particular, that the classical equidistant distribution is an unstable Nash equilibrium that cannot emerge from another distribution. However, we show that if each firm is engaged in head-on rivalry with one other competitor, the industry converges to a ’equidistantesque’ equilibrium of clusters of rivals

Capability-based governance patterns over the product life-cycle

We investigate patterns of vertical governance over the product life-cycle as function of the capability regime properties imitability and substitutability. We use a novel neo-Schumpeterian model to study emerging governance patterns. We find that, in the era of incremental change, firms prefer vertical specialization. In the era of ferment, no governance form dominates. Imitability and substitutability, in interplay, determine the governance form preferred. High imitability frustrates appropriation and thereby integration for synergistic advantages. However, firms need not vertically specialize: under low substitutability, incompatibilities reduce the advantages of specialization. When both substitutability and imitability are low, firms can appropriate the value of their inventions and there is no combinatorial advantage of specialization, so firms predominantly integrate. If substitutability is high and imitability is low, the combinatorial advantage of specialization balances with the synergistic advantage of integration

Capability-based governance patterns over the product life-cycle: an agent-based model

In recent literature, there is disagreement over the temporal pattern of vertical governance of firms over the product life-cycle. We use a novel neo-Schumpeterian agent-based simulation model to investigate emerging patterns of vertical governance for different levels of imitability and substitutability of capabilities. We find that, in the mature phase of the product life-cycle, firms generally prefer vertical specialization. However, in the early phase, imitability and substitutability, in interplay, determine the governance form preferred. High imitability frustrates appropriation and thereby discourages integration for synergistic advantages. However, firms need not vertically specialize: under low substitutability, incompatibilities reduce the advantages of specialization. When both substitutability and imitability are low, firms can appropriate the value of their inventions and there is no combinatorial advantage of specialization, so firms predominantly integrate. If substitutability is high and imitability is low, the combinatorial advantage of specialization balances with the synergistic advantage of integration

Optimization of online patient scheduling with urgencies and preferences

We consider the online problem of scheduling patients with urgencies and preferences on hospital resources with limited capacity. To solve this complex scheduling problem effectively we have to address the following sub problems: determining the allocation of capacity to patient groups, setting dynamic rules for exceptions to the allocation, ordering timeslots based on scheduling efficiency, and incorporating patient preferences over appointment times in the scheduling process. We present a scheduling approach with optimized parameter values that solves these issues simultaneously. In our experiments, we show how our approach outperforms standard scheduling benchmarks for a wide range of scenarios, and how we can efficiently trade-off scheduling performance and fulfilling patient preferences

Adaptive resource allocation for efficient patient scheduling

Objective Efficient scheduling of patient appointments on expensive resources is a complex and dynamic task. A resource is typically used by several patient groups. To service these groups, resource capacity is often allocated per group, explicitly or implicitly. Importantly, due to fluctuations in demand, for the most efficient use of resources this allocation must be flexible. Methods We present an adaptive approach to automatic optimization of resource calendars. In our approach, the allocation of capacity to different patient groups is flexible and adaptive to the current and expected future situation. We additionally present an approach to determine optimal resource openings hours on a larger time frame. Our model and its parameter values are based on extensive case analysis at the Academic Medical Hospital Amsterdam. Results and conclusion We have implemented a comprehensive computer simulation of the application case. Simulation experiments show that our approach of adaptive capacity allocation improves the performance of scheduling patients groups with different attributes and makes efficient use of resource capacity

Dynamics and equilibria under incremental horizontal differentiation on the Salop circle

We study product differentiation on a Salop circle when firms relocate incrementally due to bounded rationality. We prove that, under common assumptions on demand, firms relocate only when two or more firms target the same niche. In any other case, there is no incentive for any firm to relocate incrementally. We prove that all distributions in which firms are sufficiently far apart in product space are unstable Nash equilibria. We prove, in particular, that the classical equidistant distribution is an unstable Nash equilibrium that cannot emerge from another distribution. However, we show that if each firm is engaged in head-on rivalry with one other competitor, the industry converges to an ’equidistantesque’ equilibrium of clusters of rivals

Diseño y evaluación de VISP, una aplicación móvil para la práctica de la competencia oral

In this paper a new mobile application (app), called VISP (VIdeos for SPeaking), is introduced. This app is easily accessible and manageable and it is aimed at helping students of English as a foreign language to improve their idiomaticity (lexicon, phraseological competence, syntax) in their oral production. In order to do so, the user is invited to make the audio description (AD) of a clip, as part of an authentic communicative task framed within the task-based learning method. After a brief overview of what has been done in the field of Mobile Assisted Language Learning (MALL) and a description of the basic principles of AD, this paper provides an account of the process followed to create and launch VISP until arriving to the conceptualization of its second version, VISP 2.0. This was accomplished by carrying out several empirical tests to evaluate the app and the learning outcomes that it contributes to achieve. The data obtained up until now allow for the proposal of a theoretical-pedagogical framework that can be applied to a MALL app that is to be used in the context of distance education, thanks to the assessment of the methodological steps that have been taken on the making process of VISP 2.0.En el presente artículo se introduce una nueva aplicación para el móvil, llamada VISP (Videos for Speaking) de fácil acceso y simple manejo, por la que se pretende ayudar a los estudiantes de inglés como lengua extranjera a mejorar su idiomaticidad (léxico, fraseología, sintaxis) en la producción oral, pidiéndoles que hagan una audiodescripción (AD) de un clip, por medio de una tarea comunicativa auténtica, enmarcada dentro del  método basado en tareas. Tras un breve repaso a lo que se ha hecho hasta ahora en el campo de la enseñanza de lenguas basada en dispositivos móviles (a la que nos referimos como MALL,  del inglés “Mobile Assisted Language Learning”), y una descripción de los principios básicos de la AD,  este trabajo da cuenta del proceso de la concepción y lanzamiento de VISP hasta llegar a la versión segunda, VISP 2.0, tras haber realizado una serie de pruebas empíricas para evaluar la app y los resultados de aprendizaje a los que conduce. Los datos obtenidos hasta ahora permiten esbozar el marco teórico-pedagógico en el que se puede enmarcar una aplicación de MALL que se vaya a usar en la educación a distancia, haciendo un balance de  los pasos metodológicos que se han ido siguiendo hasta llegar a VISP 2.0.

Improving patient activity schedules by multi-agent Pareto appointment exchanging

We present a dynamic and distributed approach to the hospital patient scheduling problem: the multi-agent Pareto-improvement appointment exchanging algorithm, MPAEX. It respects the decentralization of scheduling authorities and is capable of continuously adjusting the different patient schedules in response to the dynamic environment. We present models of the hospital patient scheduling problem in terms of th