ALBERT

Description: In this article, we study the influence of solid-to-fluid density ratio m on the type of vortex-induced oscillation of a square section prism placed inside a two-dimensional channel. We assume that the solid body has neither structural damping nor spring restoring force. Accordingly, the prism equation of motion contains only inertia and aerodynamics forces. The problem is considered in the range of Reynolds numbers Re ε [50 200] (based on the prism cross-section height h) and channel widths H = H'/h ε [2.5 10]. We found that, for each Re and H, there is a critical mass ratio mc that separates two different oscillation regimes. For m 〉 mc, the prism oscillation is periodical and contains a single harmonic. For m 〈 mc, the prism oscillation changes completely and assumes an irregular pattern that is characterized by multiple harmonics that appear to belong to a uniform spectrum. The change from one regime to the other is abrupt and we were not able to observe a transitional regime in which the number of response harmonics grew by finite steps. The value of the critical mass ratio grows along with the Reynolds number and the channel width. © 2009 Cambridge University Press.

Description: We are concerned with the behaviour of a two-dimensional jet that issues from a planar orifice, with a top-hat profile. At the orifice the steady flow is modulated by a time-harmonic fluctuation. A suitably defined Reynolds number is assumed to be large throughout. At large streamwise distances from the orifice, the time-averaged flow yields the classical, Bickley, jet with a suitable virtual origin. This decays algebraically whilst, by contrast, the unsteady component decays exponentially with streamwise distance. An asymptotic theory confirms the exponential decay and provides a good agreement with the numerical solution. © 2009 Copyright Cambridge University Press.

Description: High resolution multiproxy analysis (microcharcoal, pollen, organic carbon, Neogloboquadrina pachyderma (s), ice rafted debris) of the deep-sea record MD04-2845 (Bay of Biscay) provides new insights for understanding mechanisms of fire regime variability of the last glacial period in western France. Fire regime of western France closely follows Dansgaard–Oeschger climatic variability and presents the same pattern than that of southwestern Iberia, namely low fire regime associated with open vegetation during stadials including Heinrich events, and high fire regime associated with open forest during interstadials. This supports a regional climatic control on fire regime for western Europe through fuel availability for the last glacial period. Additionally, each of Heinrich events 6, 5 and 4 is characterised by three episodes of fire regime, with a high regime bracketed by lower fire regime episodes, related to vegetational succession and complex environmental condition changes.

Description: SUMMARYLand use/land cover change (LULC) is a major threat to natural protected areas worldwide. This paper explores the relationships between four estimated LULC parameters for 17 Mexican biosphere reserves (BRs) for 1993–2002 on a GIS platform, and ten socioeconomic factors obtained from census data. These relationships were tested through linear correlations and multivariate analysis. BRs showed lower human demographic pressure, but higher population dispersion, social marginality, percentage of rain-fed agriculture area, and dependence upon agriculture and cattle compared to nationwide values. BRs also varied in their indigenous population, and showed cattle overpopulation, and low immigration and road density. Socioeconomic factors explained 87% of LULC variation. High population and road density, cattle overpopulation and low percentage indigenous population were related to percentage of transformed area (2002). Conversely, small population and road density, large proportion of indigenous population and high dependency on agriculture and cattle, were related to the rate of change in transformed area (1993–2002). High human population growth and urban concentration occurred when BRs suffered higher LULC than their corresponding ecoregions. Including socioeconomic conditions prevailing in BRs and their influence on LULC in reserve management and rural development planning will improve strategies for the confluence of conservation and development goals.

Description: SUMMARYIn the Central Peruvian highlands, potatoes are commonly cultivated by smallholder farmers in fields between 3500 and 4300 m asl. Severe climatic conditions, marginal soils and limited access to inputs and infrastructure define these challenging agro-ecological environments. To prepare an adequate seed bed for the potato and mitigate climatic, topographic and labour constraints, Andean farmers have developed distinct footplough-based tillage systems: barbecho, chiwa and chacmeo. A series of field experiments was conducted in 2005/06 and 2006/07 at four different locations to investigate the effect of three different tillage systems on potato tuber yield, varying factors such as cultivars and types and amounts of fertilizer applied. The objective was to improve understanding of the effect of these factors on potato yield and study the potential advantages and disadvantages of each tillage system.The study showed that the type of tillage influenced a great variety of factors. Farmers often use a combination of tillage systems as a strategy to diversify possible risks, considering trade-offs regarding productivity v. yield stability, internal v. external resource use, labour requirement during peak times v. more uniform distribution or extensive v. intensive production. The chiwa and to some extent the chacmeo tillage systems resulted in relatively constant and stable yields for different environments and genetic materials, whereas the more intensive barbecho system sought to optimize growth conditions for the potato crop but was more liable to stress and required external resources. Currently, farmers often use the barbecho system to produce commercial cultivars for the urban markets investing the greatest share of internal and external resources. They use the chiwa and chacmeo systems to produce diverse native cultivars for their home consumption, valorizing their taste, cooking qualities and lower resource requirements.