Fluid circulation and heat extraction from engineered geothermal reservoirs

A large amount of fluid circulation and heat extraction (i.e., thermal power production) research and testing has been conducted on engineered geothermal reservoirs in the past 15 years. In confined reservoirs, which best represent the original Hot Dry Rock concept, the flow distribution at any given time is primarily determined by three parameters: (1) the nature of the interconnected network of pressure-stimulated joints and open fractures within the flow-accessible reservoir region, (2) the mean pressure in the reservoir, and (3) the cumulative amount of fluid circulation—and therefore reservoir cooling—that has occurred. For an initial reservoir rock temperature distribution and mean fluid outlet temperature, the rate of heat extraction (i.e., thermal power) is at first only a function of the production flow rate, since the production temperature can be expected to remain essentially constant for some time (months, or even years). However, as reservoir circulation proceeds, the production temperature will eventually start to decline, as determined by the mean effective joint spacing and the total flow-accessible (i.e., heat-transfer) volume of the reservoir. The rate of heat extraction, which depends on the production flow rate, can also vary with time as a result of continuing changes in the flow distribution arising from reservoir cooling.The thermal power of engineered reservoirs can most readily be increased by increasing the production flow rate, as long as this does not lead to premature cooldown, the development of short-circuit flow paths, or excessive water losses. Generally, an increase in flow rate can be accomplished by increasing the injection pressure within limits. This strategy increases the driving pressure drop across the reservoir and the mean reservoir pressure, which in turn reduces the reservoir flow impedance by increasing the amount of joint dilation. However, the usefulness of this strategy is limited to reservoir operating pressures below the fracture extension pressure, and may lead to excessive water losses, particularly in less-confined reservoirs. Under such conditions, a downhole production-well pump may be employed to increase productivity by recovering more of the injected fluid at lower mean reservoir operating pressures.     

Systems analyses and the sustainable transfer of renewable energy technologies: A focus on remote areas of Africa

Sustainable energy provision is regarded as one of the most significant challenges facing the realm of development, especially in Africa where large proportions of the population still lack access to energy services. Although there have been much efforts to address these problems with renewable energy technologies, there have also been substantial failures and problems. The Intermediate Technology Development Group (ITDG) has developed a manual that seeks to address these implementation issues. The Renewable Energy for Sustainable Rural Livelihoods workgroup has also developed such a framework, termed SURE, which is a multi-criteria decision analysis modelling tool. Both of these frameworks rely heavily on the Sustainable Livelihoods Approach and emphasise the need to rigorously analyse the sub-systems where technologies are to be introduced. These two frameworks have been integrated and assessed in terms of their applicability for the South African rural renewable energy landscape through a Delphi study conducted with several experts in the energy sector. The results indicate that the integrated framework is suitable for the South African context, with additions to the ITDG and SURE frameworks suggested. Finally the paper highlights a potential concern in the South African renewable energy industry in that technology assessment methods that are utilised in practise do not incorporate the concepts of sustainability science adequately; this must be addressed through further case study research efforts.     

Transactive discussions with peers and adults.

Piaget (1932) hypothesized that peer and adult–child discussions of moral dilemmas are qualitatively different and that children are more likely to use reasoning when interacting with peers. To test this hypothesis, the present study compared the interactive styles of child–child and adult–child dyads engaged in discussions of moral dilemmas, focusing on the use of logical operations (transacts). 48 7- and 11-yr-old girls were paired with either a female agemate or their mother. Ss used transacts in a higher proportion of their conversational turns when interacting with peers than when interacting with mothers. Ss produced proportionally more transactive responses when interacting with mothers because mothers produced proportionally more requests for idea clarification than did peer partners. Self-generated transacts, on the other hand, were produced proportionally more often with peers. When paired with peers, Ss produced transactive statements that operated on the partner's logic more often rather than clarifying their own logic. Results support Piaget's contention that moral discussions with peers feature a more spontaneous use of reasoning than do discussions with adults. (21 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Wettability of Surface Oxyfluorinated Polypropylene Fibres and Its Effect on Interfacial Bonding with Cementitious Matrix

The surface of high molecular weight polypropylene monofilament fibre was modified using a oxyfluorination method. The oxyfluorination treatment level was varied and a hydrolysis post-treatment was also applied. Contact angles of oxyfluorinated, hydro-lyzed oxyfluorinated and unmodified polypropylene fibres were obtained by dynamic contact angle (DCA) measurement using three liquids of known dispersion, acid and base surface free energy components. The surface free energies were then calculated according to the acid-base theory developed by Good, van Oss and Chaudhury. Surface oxyfluorination largely increased the acid and base components of the fibres' surface free energy compared with unmodified polypropylene fibres. The oxyfluorinated and unmodified polypropylene fibre surfaces were observed by Scanning Electronic Microscopy and Photoacoustic Infrared Spectroscopy. It was found that the surface oxyfluorination largely increases the roughness of the polypropylene surfaces and the carbonyl group content increases as the treatment level increases. The interfacial shear bond strengths between the cementitious matrix and the polypropylene fibres treated under various conditions were determined by embedded fibre pull-out tests. Results showed that the fibre surface oxyfluorination treatments increase the interfacial bond strengths. The correlations between the shear bond strengths and surface free energy components were established. Results showed that fibre/concrete interfacial bonding was best correlated with the acid component of surface free energy of polypropylene fibres.     

Automated Radiographic Diagnosis via Feature Extraction and Classification of Cardiac Size and Shape Descriptors

One goal of digital processing of radiographic images is to provide the radiologist with quantitative measurements of human anatomy as well as an indication as to whether or not this anatomy is within normal limits. A computer algorithm is described, designed to automatically detect, extract quantitative measurements from, and diagnose the cardiac projection present in full-size anteriorview chest radiographs. A normal-abnormal diagnosis is demonstrated utilizing abnormal data from five classes of heart disease. In addition, normal-abnormal as well as normal-differential diagnoses are demonstrated for the rheumatic heart disease class. A feature extraction algorithm is developed using several ad hoc techniques, some of which were adapted from other feature extraction uses. The extracted features are classified into diagnostic classes using linear and quadratic discriminant functions. A concurrent study of physician diagnostic accuracy is also undertaken using the averaged diagnostic rates of ten radiologists on a representative subset of the radiographs used in the computer study.     

Comparative requirements for electric energy for production of hydrogen fuel and/or recharging of battery electric automobile fleets in New Zealand and the United States

Within the current outlook for sustainable electric energy supply with concomitant reduction in emission of greenhouse gases, accelerated attention is focusing on the long-term development of hydrogen fuel cell and all-electric battery vehicles to provide alternative fuels to replace petroleum-derived fuels for automotive national fleets. The potential varies significantly between large industrially developed nations and smaller industrially developing nations. The requirement for additional electric energy supply from low-specific energy renewable resources and high-specific energy nuclear resources depends strongly on individual national economic, environmental, and political factors. Analysis of the additional electric energy supply required for the two potential large-scale technologies for fueling future national transportation sectors is compared for a large Organization for Economic Co-operation and Development (OECD) nation (USA) with a small OECD nation (New Zealand), normalized on a per-capita basis.     

System Aspects and Realization of Wide-Band Switching in the Local Area

This paper discusses the functional components of nodes in wide-band switching networks. Emphasis is given to the local area where the system's architecture can be considerably simplified. The experimental results are related to this type of application. They demonstrate the availability of all system components for medium-size systems (up to 240 lines). A 16 × 16 highly integrated switch is described as a building block for greater systems. It is capable of handling data streams up to 380 Mbits/s. The maximum jitter amplitude observed after passing one cross point is 0.25 ns.     

User strategies for the interaction with in-vehicle devices while driving

In this study, the efficiency of different strategies for the interaction with in-vehicle devices was analysed. Twenty-four drivers completed a test course in a motion-based driving simulator containing different critical situations. At predetermined points of the route, an additional menu navigation task was offered to the driver. The driver could decide whether the actual situation was suitable to execute a task and when to interrupt it. The results show that drivers are able to adapt their secondary task behaviour to the situational demands. The anticipation of potential conflicts could be shown in secondary task behaviour (complete task rejection or task delay in critical situations). These strategies were successful to maintain driving safety. Adequate situational assessment prior to the start of the task and adequate monitoring of situational development during secondary task execution are identified as relevant processes for situation awareness in this context.     

A Ten-Year Rule to guide the allocation of EU emission allowances

Member States in the European Union (EU) are responsible for National Allocation Plans governing the initial distribution of emission allowances in the CO₂ Emission Trading System, including rules governing allocations to installations that close and to new entrants. The European Commission has provided guidelines to discourage the use of allocation methodologies that provide incentives affecting firms’ compliance behavior, for example by rewarding one type of compliance investment over another. We find that the treatment of closures and new entrants by Member States is inconsistent with the general guidelines provided by the EU. We propose stronger EU guidance regarding closures and new entrants, a more precise compensation criterion on which to justify free allocations, and a Ten-Year Rule as a component of future EU policy that can guide a transition from current practice to an approach that places greater weight on efficiency.