The properties of thin-section, four-point-contact ball bearings in space

Thin section, four-point-contact ball bearings are increasinly employed in spacecraft mechanisms because of the potential advantages they offer. However, litte was previously known of their torque, thermal conductance and stiffness properties at conditions anticipated for their use in space. An investigation of these properties are described. It was found that frictional (Coulomb) torque, thermal conductance and stiffness all show marked dependence on the bearing preload, the housing design, the bearing external fit (i.e., free fit or interference) and on the thermal gradient across the races. Optimum bearing performance is achieved only if these properties are well understood. The necessary data to understand these properties are provided

The Evil of sluits : a re-assessment of soil erosion in the Karoo of South Africa as portrayed in century-old sources

Deep, linear gullies are a common feature of the present landscape of the Karoo of South Africa, where they were known locally in the early twentieth century as ‘sluits’. Recent research has shown that many of these features are now stable and are no longer significant sediment sources, although they are efficient connectors in the landscape. Because most of the gully networks predate the first aerial photographs, little is known in the scientific literature about the timing of their formation. One secondary source, however, throws interesting light on the origin of these features, and the early response by landowners to their rehabilitation. The Agricultural Journal of the Cape of Good Hope at the turn of the Twentieth Century carried a number of articles by farmers and agricultural officers concerning the "evil of sluits". The authors gave accounts of widespread incision of valley bottoms by deep, wide gullies. Many of these gullies had been in existence for some thirty years but apparently had formed within living memory. A number of attempts to prevent further erosion had been put in place at the time of writing. This paper presents a review of land degradation, specifically gully erosion, and rehabilitation recommendations as given by authors writing in this journal. It reflects on the findings in the context of assessing land degradation processes through the local knowledge portrayed in the journal

Exploring the political geoecology of African Drainage Basins

[From the text] Many people in Africa rely directly on their natural ecosystems for their livelihoods. A key driver of these ecosystems is water, which in Africa has a high spatial and temporal variability. Water comes from rainfall, but the availability of that water depends on the way that it is processed through the landscape unit known as a drainage basin. Drainage basins are the "home" of rivers; rivers which sustain ecosystems and their dependents (human society). Humans and ecosystems cannot live apart from one another, but the relationship can be exploitative and degrading, or harmonious and protective. Throughout history human activity has been subject to direct controls and indirect pressures subjected by the larger society, through political, economic and cultural forces that are often intertwined. Rivers are especially sensitive to the geography of this relationship. Being longitudinal ecosystems that transfer water and other materials from the source of the river to the oceans, activities in upstream areas have a direct impact on downstream areas. To explore these socio-ecological relationships within the context of an African drainage basin I have developed the concept of political geoecology that is explored in this address

Water allocation strategies for the Kat Basin in South Africa : comparing negotiation tools and game theory models

Governments and developing agencies promote participatory approaches in solving common pool resource problems, such as in the water sector. Two main participatory approaches have been applied separately, namely negotiation and mediation. In this paper the authors apply the Role-Playing Game that is a component of the Companion Modeling approach, a negotiation procedure, and the Cooperative Game Theory (Shapley value and the Nucleolus solution concepts) that can be mirrored as a mediated mechanism to a water allocation problem in the Kat watershed in South Africa. While the absolute results of the two approaches differ, the negotiation and the cooperative game theory provide similar shares of the benefit allocated to the players from various cooperative arrangements. By evaluating the two approaches, the authors provide useful tips for future extension for both the Role-Playing Games and the Cooperative Game Theory applications.Water Supply and Systems,Water Supply and Sanitation Governance and Institutions,Environmental Economics&Policies,Water Conservation,Town Water Supply and Sanitation

TO NEGOTIATE OR TO GAME THEORIZE: Negotiation vs. Game Theory Outcomes for Water Allocation Problems in the Kat Basin, South Africa

The 6th MEETING ON GAME THEORY AND PRACTICE Zaragoza, Spain 10-12 July 2006Negotiation, Role-playing game, Core, Nucleolus, Shapley value, Water allocation, Economic efficiency, Planning models, Resource /Energy Economics and Policy, C61, C71, C78, Q25, Q56, R14,