The stability of supermassive stars in the Parametrized Post-Newtonian framework

The binding energy and stability of supermassive stars (SMS's) is examined in the framework of the Parametrized Post-Newtonian (PPN) formalism of Will and Nordvedt. The PPN formalism encompasses the post-Newtonian limit of virtually every theory of gravity, differentiating between theories by means of nine PPN parameters. A general expression is derived for the energy integral in the PPN framework, and it is found that only in those theories in which the parameters ₁=₂=₃=₄=₃=0 will the energy be conserved. In all such theories, a SMS of radius less than a critical radius will be unstable against adiabatic radial perturbations. Present experimental limits on the PPN parameters and do not exclude the possibility of the existence of stable, non-rotating, hydrogen-burning SMS's of masses an order of magnitude larger than the upper limit for the mass of such stars predicted in general relativity.     

Pro-poor sanitation technologies

It is estimated that at least two billion people have inadequate sanitation. The current situation in water and sanitation services for millions of peri-urban residents is starkly anti-poor and represents a major challenge for the 21st century. By virtue of its cost and water requirements, we would argue that conventional sewerage is an implicitly anti-poor technology. This paper summarises low-cost sanitation technologies that have been developed by engineers from around the world, and seeks to provide evidence that there is such a thing as a pro-poor technology. We argue that simplified sewerage is often the only sanitation technology that is technically feasible and economically appropriate for low income, high-density urban areas. Simplified sewerage will only truly be a pro-poor technology if issues such as lack of investment in sanitation, insufficient cost recovery for sanitation services, conservative technical standards favoured over innovation, low-cost technologies perceived as second class provision, the nature of peri-urban settlements, and lack of engagement with users, are addressed. So often, peri-urban sanitation schemes fail to exist, fail to be sustainable, or fail to be pro-poor. The challenge is for engineers, social scientists and other professionals to work together to make pro-poor sanitation a reality and interdisciplinarity the norm.     

Explosive activity and generation mechanisms of pyroclastic flows at Arenal volcano, Costa Rica between 1987 and 2001

Explosive activity at Arenal and associated tephra fall that has occurred over the 14-year period from 1987–2001 is described. Explosions have been notably variable in both frequency and size. A marked decrease in both frequency and quantity of tephra fallout occurred in early 1998 until the end of 2001. Grainsize distributions of cumulative tephra samples collected once a month are typically bimodal. Aggregation causing premature fallout of fine ash and possibly fallout from ash plumes produced by pyroclastic flows are considered responsible for the bimodality of fallout. Scanning electron microscopy of the glass component of tephra from single explosions show predominantly blocky and blocky/fluidal clast types, interpreted as being the product of vulcanian type explosions. Fragmentation of a mainly rigid, degassed magma body, and a minor molten component is inferred for these explosions. Pyroclastic flows were produced either associated with the larger explosions by a mechanism of column collapse (1987–1990), or unrelated to explosions by partial collapse of the crater wall (1993, 1998, 2000, 2001). Pyroclastic flow activity has migrated from west to north during the period reported. Pyroclastic flow deposits are variable in the quantity of juvenile material and any associated surge component. Large juvenile blocks were partially molten on emplacement and many have a typical cauliform texture. Blocks with both juvenile and lithic textures indicate that at the summit magma was in intimate contact with the pre-existing edifice, rather than as a simple open crater or lava pool. Crater wall collapse may have been promoted by the reduction in explosive activity, which has increased the lava accumulation at the summit and in turn increased instability of the summit region. Thus although explosive activity has waned, if the lava output is maintained, the hazard of pyroclastic flows is likely to continue.Editorial responsibility: R. Cioni     

North American Natural Gas: Data Show Supply Problems

Natural gas is increasingly the fuel of choice for domestic and industrial use and for electric power generation. With pipelines in all 50 states, gas now fuels more than one-half of United States homes. Demand for all uses is projected to rise. United States production peaked in 1971, and is in decline. The United States in 2002 imported 15% of its gas from Canada, which amount was 56% of Canada's production. However, Canada's production now also is in decline. Mexico's production declined from 1999 to 2002 against rising demand. Mexico is increasingly a net gas importer from the United States. In both the United States and Canada, intensive drilling is being offset by high depletion rates. Frontiers for more production include deep basin drilling, improved exploration and reservoir development technology, increased coalbed methane exploitation, and access to lands not now accessible because of environmental and other restrictions. Stranded gas in Arctic regions of the United States and Canada offer some potential for additional supplies, but pipeline access is at least five years to ten years or more away. Additional LNG landing facilities are needed, and are planned, but these are several years away in significant numbers. For the immediate future, rationing of available gas by the market mechanism of higher prices seems the only option. In the longer term, it seems North America will be increasingly dependent on LNG.     

Toponymy and the Communist city: Street names in Bucharest, 1948–;1965

Past studies of the Socialist/Communist city have paid only limited attention to the ways in which Communist regimes mobilised a wide variety of symbols in the urban landscape in order to legitimate and institutionalise the ideology of revolutionary socialism. This paper considers the role of street names in this process with particular reference to Bucharest, Romania during the 1948–1965 period. When the Communist regime came to power it embarked on widespread renaming of streets as one means of both `decommemorating' the pre-socialist regime and proclaiming the agenda and ideology of the Communist state. The new street names commemorated a variety of events and personalities from the history of Romanian and Soviet Communism. The impact of street names was amplified further through practices such as multiple namings and the spatial clustering of street names of high ideological resonances. The paper argues that Bucharest's street names can be `read' as a mirror of ideological change, changing constructions of national identity, and Romania's macro-political orientation (especially its changing relations with the Soviet Union).     

The evolution from Miocene potassic to Quaternary sodic magmatism in western Turkey: implications for enrichment processes in the lithospheric mantle

New K-Ar dating and major- and trace-element analyses from the U ak-Selendi-Emet (USE) area constrain the timing of changes in the nature of volcanism in the Miocene in western Turkey. The data reveal a change from dominantly calc-alkaline and silicic in the Early Miocene to largely alkaline and more mafic volcanism in the Middle Miocene. This probably reflects a decreasing amount of crustal contamination with time, a result of extensional tectonics. High levels of various incompatible elements (including K) in the more mafic members, suggest an enriched subcontinental lithospheric source region for the Middle Miocene USE lavas. Highly variable Nb/Y, Ti/Y and Th/Nb ratios suggest a lithospheric mantle heterogeneously enriched by two processes: (1) enrichment by subduction-related processes producing high Th/Nb but low Nb/Y and Ti/Y; and (2) enrichment by small degree melts of depleted upper mantle producing low Th/Nb but high Nb/Y and Ti/Y. Both of these enrichment processes have variably contributed to Middle Miocene K-rich lavas in the USE area. The mechanism which initiated the melting of the enriched lithosphere is considered to be extension which produced decompression melting. Comparisons with the nearby Kula lavas reveals that by the Pliocene to Quaternary, volcanism, although still enriched in incompatible elements, had become sodic. It seems likely that continued extension up to this time thinned the lithosphere to such an extent that asthenospheric melts were produced which ascended and mixed with previously enriched lithosphere.