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991.
District heating is a technology for distributing centrally produced heat for space heating and sanitary hot-water generation for residential and commercial uses. The objectives are to identify which subsystems and components of a district heating grid are the main contributors to the overall impact of the infrastructure; and provide environmentally oriented design strategies for the future eco-redesign of these kinds of infrastructures. This paper performs a life-cycle assessment (LCA) to determine the environmental impacts of a district heating infrastructure in an urban neighbourhood context. The analysis covers seven subsystems (power plant, main grid, auxiliary components of the main grid, trench works, service pipes, buildings and dwellings) and twelve standard components. The results for the subsystems show that the sources of impact are not particularly located in the main grid (less than 7.1% contribution in all impact categories), which is the focus of attention in the literature, but in the power plants and dwelling components. These two subsystems together contribute from 40% to 92% to the overall impact depending on the impact categories. Concerning the components, only a reduced number are responsible for the majority of the environmental impact. This facilitates identifying effective strategies for the redesign of the infrastructure. 相似文献
992.
An important consideration when applying neural networks is the sensitivity to weights and threshold in strict separating systems representing a linearly separable function. Perturbations may affect weights and threshold so that it is important to estimate the maximal percentage error in weights and threshold, which may be allowed without altering the linearly separable function. In this paper, we provide the greatest allowed bound which can be associated to every strict separating system representing a linearly separable function. The proposed bound improves the tolerance that Hu obtained. Furthermore, it is the greatest bound for any strict separating system. This is the reason why we call it the greatest tolerance. 相似文献
993.
David Jiménez Xavier Cartoixà Enrique Miranda Jordi Suñé Ferney Alveiro Chaves Stephan Roche 《Journal of Computational Electronics》2006,5(4):361-364
We present here a physics-based drain current model for Schottky-barrier carbon nanotube field-effect transistors. The model
captures a number of features exhibited by these transistors such as thermionic and tunnel emission, ambipolar conduction,
ballistic transport, multimode propagation and electrostatics dominated by the nanotube capacitance 相似文献
994.
995.
An effective method of growing single crystals of organic photoconductors such as phthalocyanine in the presence of doping
impurity such as iodine by vacuum sublimation is discussed in this paper. This method is very useful especially when an organic
material does not have a melting point but decomposes above a particular temperature. So far, doping has been done by exposing
the previously grown organic single crystals to the dopant vapour, but growing the crystal in the presence of dopant vapour
makes the doped-crystal more efficient and stable. The photosensitivity as well as the photoconductivity of the doped crystals
by this method increases significantly. 相似文献
996.
We present a collection of simple on-the-fly techniques to generate small Büchi automata from Linear Time Logic formulas. These techniques mainly involve syntactic characterizations of formulas, and yet allow efficient computations. Thus heavily relying on such proof-theoretic issues, we can omit the classical formula pre-simplification step, and also simulation-based post-simplification steps (aka model-theoretic issues).Although closely related to other similar recent works in the same topic, our ideas have led to an implementation that performs significantly better than some of the best available tools, such as Wring or LTL2BA. We compare our tool BAOM (“Büchi Automata Once More”) with others, on formulas commonly found in the literature, and on randomly generated testbenchs. 相似文献
997.
Didier Lasseux Azita Ahmadi Xavier Cleis Jean Garnier 《Chemical engineering science》2004,59(10):1949-1964
In this work, we study the possibility of deriving a macroscopic model to describe reaction and transport by diffusion and convection of two species within a porous medium as encountered during in vitro tissue growth. The starting point is a boundary value problem of diffusion-advection and reaction in a three-phase system, the two species being identified as the nutrient for cell growth and the metabolic product within the framework of tissue culture. The method of volume averaging is applied to the set of microscopic equations. Under the local mass equilibrium assumption and a series of constraints on the parameters of the system that are identified, one obtains a one-equation macroscopic model corresponding to a dispersion-reaction equation. Associated closure problems allowing the computation of effective coefficients that appear in this macroscopic model are provided. 相似文献
998.
Xavier Escriva 《International Journal of Heat and Mass Transfer》2003,46(13):2471-2483
The main topic of this paper is the analysis of momentum and heat transfer mechanisms occurring inside a disturbed boundary layer. This analysis is carried out based on a phenomenological decomposition using von Karman’s integral equations, in which appear terms that account for several contributions: the flat plate term, and the unsteady and external gradient terms.This method is applied to the interaction between a single transverse vortex and a boundary layer developing on a flat plate. Based on numerical simulations, we present a qualitative and quantitative study of the behavior of momentum and heat wall transfer described by the terms resulting from the phenomenological decomposition. Finally, the time-dependent behavior of the analogy factor is investigated. 相似文献
999.
The presence of intraspecific variation in toxicity and its relationship with biological or ecological factors were studied in the spongeCrambe crambe. Within-specimen (periphery and central part), between-size (<1000 mm2 in area, between 1000 and 10,000 mm2 and >10,000 mm2) and between-habitat (well-illuminated and dark communities) variations in toxicity were evaluated by the Microtox bioassay. Quantitative differences were detected that were not attributable to within-specimen variation but to size and habitat effects. Habitat comparisons showed that sponges in the shaded habitat were significantly more toxic than those of the well-illuminated community. Sponges of the smaller size classes displayed significantly less toxicity than the medium-sized specimens. Results are interpreted under the optimal defense theory and their ecological implications are considered. 相似文献
1000.
Xavier Font Gloria Caminal Xavier Gabarrell Silvia Romero M Teresa Vicent 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2003,78(5):548-554
Black liquors from a soda pulping mill were treated with the white‐rot fungus Trametes versicolor to detoxify and reduce colour, aromatic compounds and chemical oxygen demand (COD). The fungus was used in the form of pellets in aerated reactors (fluidized, stirred and air‐pulsed reactors). Reductions in colour and aromatic compounds of 70–80% and in COD of 60% were achieved. During the different experiments, laccase activity was detected but neither lignin peroxidase (LiP) nor manganese peroxidase activities were detected, although T versicolor is able to produce these enzymes. Experiments also showed a LiP activity inhibitory effect produced by lignin. From the results obtained, it can be concluded that there is a relationship between laccase production and toxicity reduction. This correlation responds to the equation Laccase production = 1.57 LN (toxicity reduction) ?16.40. Copyright © 2003 Society of Chemical Industry 相似文献