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[1] A new method of determining the parameters of an aggregated dead zone model (ADZ) to predict longitudinal dispersion in rivers is presented. The method is based on the frequency response analysis (FRA) of observed field tests, which consist of tracer injections (input) and measurement of tracer in downstream sampling points (output) located downstream from the injection point. The ADZ is a combination of plug and completely mixed flow compartments. The ADZ parameters (number of compartments, mean residence time, and delay time) are evaluated by means of Bode plots that give the system order (number of compartments), gain, time constant (mean residence time of each compartment) and delay time. The FRA-ADZ method was checked with tracer data runs in two Spanish rivers, the Tagus and the Ebro rivers. The experimental tracer concentration versus time distributions were compared with the ADZ predicted curves, which were calculated using parameters obtained from the FRA method, and with curves predicted by several classical models. The residence time of several reaches within the two studied rivers was predicted by the FRA-ADZ method with a relative error lower than 10%. The method is generally applicable to ideal and nonideal inputs and is particularly well suited to arbitrary-shaped initial source concentration distributions.Citation: Lambertz, P., M. C. Palancar, J. M. Aragón, and R. Gil (2006), Determining the dispersion characteristics of rivers from the frequency response of the system, Water Resour. Res., 42, W09414,

The comparatively cheap and mechanically accessible Chinese dakadaka diesel engines and their shotteur Z-drives have enabled wooden baleinières to significantly impact waterborne mobility, trade and transportation on the Congo River and its tributaries. While baleinières are artisanal watercraft made of local building materials, their engines are globally circulating technologies, which are able to unfold their economic, hydrodynamic and socio-technical affordances thanks to a number of local technical adaptations. On the basis of ethnographic fieldwork in Tshopo province (DR Congo) foregrounding the engines' use, the article discusses the adaptations the Chinese engines and their propulsion system undergo to enable a felicitous engagement of their intrinsic engineered forces with the muscular, natural, and social forces present in their local riverine habitat. While this entanglement of forces depends on the distributed character of collective onboard engine care, it also encourages the emergence of baleinière owners (armateurs) as a new group of local entrepreneurs.These insights help us understand why, despite frequent breakdowns, the engines and the boats they propel enable, and democratise the access to, new forms of connectivity and mobility for large parts of Congo's riverine and travelling urban populations. In a context of enduring economic precarity, the technical gesture of 'removing the [engine's] backward gear' (Li. kolongolá marche arrière) is therefore also of metaphoric significance.

The Japanese “new religions” ( Shin Shūkyō) active in Kinshasa (DR Congo) nearly all perform healing through the channeling of invisible divine light. In the case of Sekai Kyūseikyō (Church of World Messianity), the light of Johrei cannot be visually apprehended, but is worn as an invisible aura on the practitioner’s body. This article discusses the trans-cultural resonances between Japan and Central Africa regarding the ontology of spiritual force, regimes of subjectivity, and the gradual embodiment of Johrei divine light as a protection against (suspicions of) witchcraft. Meanwhile, I argue that religious multiplicity in urban Africa encourages cultural reflexivity about concepts of health and healing, self-responsibility, and Pentecostal suspicion-mongering of occult sciences. Thus, Johrei divine light not only feeds into a longstanding local tradition of spiritual healing; within the religiously multiple city, it is also a discursive space for, and an experience and performance of, emic critique.