It Does Matter What You Do: How Practical Choices Reflect Theology

(Excerpt) We would all, I trust, agree with the centrality of baptism for Lutheran theology and its importance for Lutheran liturgical renewal. Yet, how many of us are from parishes where baptisms, if done during the Sunday assembly at all, are at small, out of the way fonts, with a few drops of water, no candles or oil, and little or no congregational involvement? Certainly, the baptism is valid, but is it salutary? Have we done any more than meet the lifetime minimum requirement of grace ? Have we lost a wonderful opportunity to celebrate the richness of grace poured out in baptism, not only on the baptized but on the community

Reflections on becoming a teacher and the challenges of teacher education

In this lecture, the context and conditions of becoming a teacher from the time of being selected into the programme, through the process of training and being retained to teach are discussed within the framework of Teacher Education in Nigeria. First, the concepts and the history of teacher education are examined. Then, some critical issues as well as my personal research efforts on teacher education are discussed. Finally, recommendations for meeting the challenges of Teacher Education in Nigeria are made

Role of vertical migration in biogenic ocean mixing

Recent efforts to empirically measure and numerically simulate biogenic ocean mixing have consistently observed low mixing efficiency. This suggests that the buoyancy flux achieved by swimming animals in the ocean may be negligible in spite of the observed large kinetic energy dissipation rates. The present letter suggests that vertical migration across isopycnals may be necessary in order to generate overturning and subsequent mixing at length scales significantly larger than the individual animals. The animal-fluid interactions are simulated here using a simplified potential flow model of solid spheres migrating vertically in a stably stratified fluid. The interaction of successive solid bodies with each parcel of fluid is shown to lead, under certain conditions, to vertical displacement of the fluid parcels over distances much larger than the individual body size. These regions of displaced fluid are unstably stratified and, hence, amenable to large-scale overturning and efficient mixing

Optimal vortex formation as a unifying principle in biological propulsion

I review the concept of optimal vortex formation and examine its relevance to propulsion in biological and bio-inspired systems, ranging from the human heart to underwater vehicles. By using examples from the existing literature and new analyses, I show that optimal vortex formation can potentially serve as a unifying principle to understand the diversity of solutions used to achieve propulsion in nature. Additionally, optimal vortex formation can provide a framework in which to design engineered propulsions systems that are constrained by pressures unrelated to biology. Finally, I analyze the relationship between optimal vortex formation and previously observed constraints on Strouhal frequency during animal locomotion in air and water. It is proposed that the Strouhal frequency constraint is but one consequence of the process of optimal vortex formation and that others remain to be discovered

Urban droughts and floods in Maiduguri: twin hazards of a variable climate

Maiduguri, an important city in the Sudano-Sahelian zone of West Africa, experiences both drought and floods. Although droughts are more popular, floods are a seasonal occurrence in parts of the city in the average rainy season. Both hazards exert a heavy toll on their victims. Present response to the hazard problems is characterised by a fire-fighting approach which does little about future occurrence. Much of the perception and response is spiritual and stops short of needed structural and organisational programmes for effective mitigation of hazards. Future occurrences of drought and flood may have more adverse effects as land use in the city becomes more complex and agricultural and water supply system comes to depend heavily on surfacial sources. Future effects will also depend on the socio-economic conditions of the people at risk and the capacity of those who help them. Governments and people need to work together to reduce drought and flood hazards

On the estimation of swimming and flying forces from wake measurements

The transfer of momentum from an animal to fluid in its wake is fundamental to many swimming and flying modes of locomotion. Hence, properties of the wake are commonly studied in experiments to infer the magnitude and direction of locomotive forces. The determination of which wake properties are necessary and sufficient to empirically deduce swimming and flying forces is currently made ad hoc. This paper systematically addresses the question of the minimum number of wake properties whose combination is sufficient to determine swimming and flying forces from wake measurements. In particular, it is confirmed that the spatial velocity distribution (i.e. the velocity field) in the wake is by itself insufficient to determine swimming and flying forces, and must be combined with the fluid pressure distribution. Importantly, it is also shown that the spatial distribution of rotation and shear (i.e. the vorticity field) in the wake is by itself insufficient to determine swimming and flying forces, and must be combined with a parameter that is analogous to the fluid pressure. The measurement of this parameter in the wake is shown to be identical to a calculation of the added-mass contribution from fluid surrounding vortices in the wake, and proceeds identically to a measurement of the added-mass traditionally associated with fluid surrounding solid bodies. It is demonstrated that the velocity/pressure perspective is equivalent to the vorticity/vortex-added-mass approach in the equations of motion. A model is developed to approximate the contribution of wake vortex added-mass to locomotive forces, given a combination of velocity and vorticity field measurements in the wake. A dimensionless parameter, the wake vortex ratio (denoted Wa), is introduced to predict the types of wake flows for which the contribution of forces due to wake vortex added-mass will become non-negligible. Previous wake analyses are reexamined in light of this parameter to infer the existence and importance of wake vortex added-mass in those cases. In the process, it is demonstrated that the commonly used time-averaged force estimates based on wake measurements are not sufficient to prove that an animal is generating the locomotive forces necessary to sustain flight or maintain neutral buoyancy