Duplex systems

Duplex kidneys occur in 0.8% of the general population, many of whom are asymptomatic. Children with duplex kidneys may be prone to urinary tract infections because of vesico-ureteric reflux or obstruction. Surgical management is usually required once symptoms occur. Increasing numbers of duplex kidneys are now prenatally diagnosed by ultrasound, resulting in the development of early postnatal strategies to try and reduce morbidity. Copyright © 2001 John Wiley & Sons, Ltd.     

Evolution of mycorrhiza systems

 Most terrestrial plants live in mutualistic symbiosis with root-infecting mycorrhizal fungi. Fossil records and molecular clock dating suggest that all extant land plants have arisen from an ancestral arbuscular mycorrhizal condition. Arbuscular mycorrhizas evolved concurrently with the first colonisation of land by plants some 450–500 million years ago and persist in most extant plant taxa. Ectomycorrhizas (about 200 million years ago) and ericoid mycorrhizas (about 100 million years ago) evolved subsequently as the organic matter content of some ancient soils increased and sclerophyllous vegetation arose as a response to nutrient-poor soils respectively. Mycorrhizal associations appear to be the result of relatively diffuse coevolutionary processes. While early events in the evolution of mycorrhizal symbioses may have involved reciprocal genetic changes in ancestral plants and free-living fungi, available evidence points largely to ongoing parallel evolution of the partners in response to environmental change.     

Sustainable waste management systems

Waste management is viewed as part of a generation, collection and disposal system. A systems approach that reveals its relationship to other parts of the system is examined in the light of producing more sustainable practice.The move to a more sustainable society requires greater sophistication to manage waste. A traditional reductionist approach is unsustainable as it lacks flexibility and long term thinking.A sustainable waste management system incorporates feedback loops, is focused on processes, embodies adaptability and diverts wastes from disposal.Transitioning to a sustainable waste management system requires identification and application of leverage points which effect change.     

Bioreactor systems for thermophilic fermentative hydrogen production: evaluation and comparison of appropriate systems

Numerous different bioreactor systems are applied for hydrogen production by dark fermentation. Thermophilic fermentations are gaining an increased interest due to the high hydrogen yields associated with them. In order to reach the best thermophilic fermentation system, 2 types of bioreactors, a trickling bed and a fluidized bed system, were constructed and operated under similar conditions. Both systems were designed to meet the requirements of thermophilic fermentations, such as reduction of hydrogen partial pressure, system immanence as its best as well as increasing cell densities. For comparing the 2 systems, the extreme thermophilic organism Caldicellulosiruptor owensensis OL^T and a glucose-containing medium were employed. Parameters like hydraulic retention time, glucose concentration and stripping gas amount were varied. Each bioreactor system exhibited certain advantages; the trickling bed system enabled yields close to 3 mol-H₂ (mol-glucose)^?1 and productivities of 0.2 L L^?1 h^?1, but the application of stripping gas seemed to be obligatory. The fermentations in the fluidized bed system were characterized by slightly higher productivities (0.25 L L^?1 h^?1), but generally lower yields. However, operation of this system without stripping gas was possible.     

X-ray sources in binary systems

After a short introduction mainly concerned with the discoveries of the UHURU satellite, we proceed to a discussion of the observed properties of binary X-ray sources. Interpretation of the data in the framework of currently discussed models is given in the last section.     

Hydrogen storage and distribution systems

Hydrogen storage and transportation or distribution is closely linked together. Hydrogen can be distributed continuously in pipelines or batch wise by ships, trucks, railway or airplanes. All batch transportation requires a storage system but also pipelines can be used as pressure storage system. Hydrogen exhibits the highest heating value per weight of all chemical fuels. Furthermore, hydrogen is regenerative and environment friendly. There are two reasons why hydrogen is not the major fuel of toady’s energy consumption: First of all, hydrogen is just an energy carrier. And, although it is the most abundant element in the universe, it has to be produced, since on earth it only occurs in the form of water. This implies that we have to pay for this energy, which results in a difficult economic task, because since the industrialization we are used to consuming energy for free. The second difficulty with hydrogen as an energy carrier is the low critical temperature of 33 K, i.e. hydrogen is a gas at room temperature. For mobile and in many cases also for stationary applications the volumetric and gravimetric density of hydrogen in a storage system is crucial. Hydrogen can be stored by six different methods and phenomena: high pressure gas cylinders (up to 800 bar), liquid hydrogen in cryogenic tanks (at 21 K), adsorbed hydrogen on materials with a large specific surface area (at T < 100 K), absorbed on interstitial sites in a host metal (at ambient pressure and temperature), chemically bond in covalent and ionic compounds (at ambient pressure), oxidation of reactive metals e.g. Li, Na, Mg, Al, Zn with water. These metals easily react with water to the corresponding hydroxide and liberate the hydrogen from the water. Finally, the metal hydroxides can be thermally reduced to the metals in a solar furnace.     

Farming systems and insect predators

Predatory carabids, staphylinids and spiders were monitored from 1981 to 1987 in a Dutch project concerning the development of arable farming systems. During this period epigeic predators in the conventional, integrated and organic systems were sampled using pitfall traps. The effects of crop type and farming system on species diversity, abundance and guild structure was analysed using trap data from wheat, pea, sugar beet, potato, onion and carrot fields. Predator abundance and species composition were found to be clearly affected by the farming system. However, in most cases the type of crop appeared to be of greater importance. Crops with a greater cover early in the season, like winter wheat and peas appeared to be more favourable than late and open crops like onions or carrots. Both system and crop effects were more apparent in carabids than in spiders or staphylinids. Only minor effects of farm management were found on species richness. Again, the crop itself seemed to be the main structuring factor. It is concluded that the presence and quality of predator populations is mainly determined by crop structure and crop-related factors. The role of favourable crops and field size in predator enhancement is discussed in relation to the agroecological infrastructure of the landscape.     

Alternative crops for sustainable agricultural systems

The lack of suitable and appropriate crops has been a poorly recognized obstacle to the application of sound agroecological practices in some temperate and tropical regions. Cultivation of traditional hybrid crops in inherently hostile environments forces increased managerial and economic expenditures. Selection of ecologically harmonious crops exploits, rather than opposes natural forces. Based in part on US-AID funded research, we have identified three crops suitable for temperate/tropical cultivation. Amaranthus is recognized in Asia and Central and South America as a food crop that can be grown as a leafy vegetable or as a seed grain in mixed croppings. It does well under a wide variety of conditions using established cultural methods. It is nutritious and highly palatable and, in many areas, is well recognized in the market place. Prosopis species (mesquite) leguminous trees occur worldwide in arid and semi-arid areas. As phreatophytes, they are resistant to drought and high temperature extremes and produce abundant yields of edible beanlike pods. Using the beans from the tree, a variety of attractive, marketable food products have been prepared. We have also identified intermediate wheat-grass, a perennial relative of wheat, as an ecologically and economically attractive alternate crop. It is already a well-established range crop; grown for seed, it becomes a useful grain intercrop. The wholegrain or endosperm mill fractions make excellent tasting, appetizing and attractive baked products. Ongoing agronomic studies indicate it is especially suitable for balancing ecologically unstable areas.     

Neurosecretion: peptidergic systems in insects

 Insect neuropeptides are produced in less than 1% of the cells of the central nervous system. Despite this, they are important messenger molecules which influence nearly all physiological processes, including behaviour. They can act as transmitters, modulators and classical hormones, and often exhibit pleiotropic functions when released into the haemolymph. The large number of neuropeptides that has been identified from some of the model organisms among insects underlines the complexity of the neurosecretory system; studies about the coordinated actions of these substances are in their preliminary stages. Recent advances in insect neuropeptide research will be reviewed here, concentrating on the distribution of multiple peptide forms in the central nervous system and adjacent neurohaemal organs, and the role of neuropeptides in eclosion behaviour.     

Renewable financial support systems and cost-effectiveness

This paper analyses the performance of ‘market-based’ and ‘feed-in tariff’ systems of renewable energy procurement, and comments on the impact of different procurement systems on investment in renewable energy. The ‘market-based’ British Renewables Obligation (RO) is not more cost-effective compared to the German feed in tariff. Although the nominal rates of payment per kWh of renewable energy are higher in Germany, this is more than offset by lower wind speeds in Germany producing a lower return on investment compared to the UK. A harmonised, EU-wide market-based system, would not improve cost-effectiveness, and may serve to reduce, rather than increase, local investment in renewable energy. On the other hand, nationally based green electricity certificate systems like the RO are not intrinsically biased against locally owned or co-operative ventures. Systems are needed which encourage a diversity of investment in renewable energy from local as well as institutional sources.     

Unusual ring systems in organic chemistry

The Science of Nature - In this article several compounds with unusual ring systems are surveyed briefly. Saturated and unsaturated monocyclic compounds, polycyclic compounds, and unconventional...     

Preventive environmental strategies for product systems

The paper describes a model for environmental quality and resource efficiency parameters to be used in evaluation of options for improvement of product systems in a life cycle and system perspective. Four main preventive strategies for product system improvements are described and discussed in the paper. (1) Reformulating user needs and requirements to the system; (2) improvement of product system performance; (3) substitution of the whole product systems or system components on different levels; (4) optimization within and between system units and components. These main strategies are discussed with respect to the structure of the product system (the domain theory), and with respect to efficiency in general. It is concluded that at present, it is not possible to make any definite rank of priorities between the different strategies, but that this should be evaluated when more systematic studies of cases are available.     

Energy inputs in agricultural systems of China

An analysis of the energy inputs in corn, rice, sorghum, wheat, soybean, and millet in northeastern China indicates that most of the crops are produced with about one half the fossil energy inputs compared with those in the United States. The inputs of labor, however, are 10–100-fold greater than those in the United States. China also uses 85 to more than 500 h of horse power per hectare in producing its crop and this helps reduce the fossil energy inputs in crop production. A small increase in the use of machinery energy (3%) at appropriate times in the cropping systems could reduce labor inputs by about one third.