A simple,explicit formula for the critical pressure of homogenous two-phase nozzle flows

The critical pressure ratio of the homogeneous two-phase nozzle flow model known as the Omega method is expressed in function of the Omega Parameter as the exact numerical solution of a transcendental equation. A well fitting, easy to use, explicit approximation for flashing and non-flashing flows is presented here. The validation against the exact numerical solution proves that this new formula is better fitting than the other ones in the technical literature for both single and two-component flows.     

Teil III: Die Verkehrsbilanz der Universität Osnabrück

One central aspect of the environmental management system for universities developed in Osnabrück is the environmental audit of universities, realized by an ecobalance. This article deals with modelling the material and energy flows caused by the University’s commuters (staff and students), and by the business trips of employees, using the software Umberto^®. The result is the University’s traffic balance. 10,000 MWh of energy are consumed yearly by the University’s traffic. 94% of the consumption is caused by commuters (1,300 employees and 11,500 students) and only 6% by business trips. Compared with the whole energy consumption of the University, the traffic’s share is 32% and therefore lies between the electricity’s share (25%) and that of heat (43%). Similarly related are the CO₂ emissions, caused by traffic (3,160 tons per anno). Compared with the whole CO₂ emissions of the University the traffic’s share is 31%, thus putting it between the heat’s share (27%) and that of electricity (42%). Although the average weekly distance the University’s commuters drive (79 km/student and 84 km/employer) is at the bottom of the range for other comparable universities, a transportation demand management for a further reduction of the traffic-caused CO₂ emissions should be implemented.     

Trace Metal Studies on the Starfish Asterias rubens L. From the Western Baltic Sea

In 1984, 115 samples of the starfish Asterias rubens L. collected in the south-eastern part of Cadet Trench (Mecklenburg Bay/Western Baltic Sea) were analyzed for their contents of a few major (calcium, magnesium) and trace elements (cadmium, copper, iron, mercury, manganese, nickel, lead, selenium and zinc). Distinct differences were found between starfish from different stations, and these are attributed to the composition of the sediments acting as a substrate for their prey (mussels, snails). Except for cadmium, the concentrations of the elements studied all correlated negatively with the diameter and weight of the starfish.

Parallel analyses of starfish arms and the central discs of the same animals showed that iron, zinc, copper and mercury levels were 16 to 30% higher, and selenium, manganese, magnesium, calcium and lead were 4 to 9% higher in the arms. Cadmium concentrations were 20% higher in the central discs than in the arms.

Stock estimations (about 52,000 tons fresh weight) show that starfish play a significant role in the benthic ecosystem of the western Baltic Sea. They can consume up to 200,000 tons of mussels and clams (Mytilus edulis, Macoma baltica) a year and may therefore represent a notable factor in the trace metal balance of the region.     

Integrated relief design for gas-generating reactions: predicted vessel pressure course in dependence on the phase separation model

Pressure relief of a hydrogen peroxide decomposition in a top-vented vessel is simulated numerically using six phase separation models. The results lead to the conclusion that generally a parameter study will be required for relief design by simulation when a gas-generating reaction is considered. None of the phase separation models can be expected to be always conservative in contrast to the case of tempered systems.     

Examining the coupling of carbon and nitrogen cycles in Appalachian streams: the role of dissolved organic nitrogen

Although regional and global models of nitrogen (N) cycling typically focus on nitrate, dissolved organic nitrogen (DON) is the dominant form of nitrogen export from many watersheds and thus the dominant form of dissolved N in many streams. Our understanding of the processes controlling DON export from temperate forests is poor. In pristine systems, where biological N limitation is common, N contained in recalcitrant organic matter (OM) can dominate watershed N losses. This recalcitrant OM often has moderately constrained carbon:nitrogen (C:N) molar ratios (approximately 25-55) and therefore, greater DON losses should be observed in sites where there is greater total dissolved organic carbon (DOC) loss. In regions where anthropogenic N pollution is high, it has been suggested that increased inorganic N availability can reduce biological demand for organic N and therefore increase watershed DON losses. This would result in a positive correlation between inorganic and organic N concentrations across sites with varying N availability. In four repeated synoptic surveys of stream water chemistry from forested watersheds along an N loading gradient in the southern Appalachians, we found surprisingly little correlation between DON and DOC concentrations. Further, we found that DON concentrations were always significantly correlated with watershed N loading and stream water [NO3-] but that the direction of this relationship was negative in three of the four surveys. The C:N molar ratio of dissolved organic matter (DOM) in streams draining watersheds with high N deposition was very high relative to other freshwaters. This finding, together with results from bioavailability assays in which we directly manipulated C and N availabilities, suggests that heterotrophic demand for labile C can increase as a result of dissolved inorganic N (DIN) loading, and that heterotrophs can preferentially remove N-rich molecules from DOM. These results are inconsistent with the two prevailing hypotheses that dominate interpretations of watershed DON loss. Therefore, we propose a new hypothesis, the indirect carbon control hypothesis, which recognizes that heterotrophic demand for N-rich DOM can keep stream water DON concentrations low when N is not limiting and heterotrophic demand for labile C is high.     

Fostering sustainability through sourcing from small businesses: public sector perspectives

This article examines the opportunities for fostering sustainable development through public sector sourcing from small- and medium-sized enterprises (SMEs). Buying from small businesses can make such contributions in a variety of forms, ranging from a contribution to local economic development through providing innovative green products and services, particularly in the food sector, to helping the public sector organisation to better align its operations with its community. Sourcing from small businesses also has implications for the governance of sourcing processes and can benefit from a partnership approach. Barriers to public sector sourcing from small businesses are discussed and suggestions made on how these can be overcome.