Expanding the exergy concept to the urban water cycle

The world is urbanizing fast and this increases the pressure on available resources. In a world of cities, it is therefore crucial to take a new look at the way urban systems function: where do the resources come from and where do the wastes end up? It is essential to find ways to minimize urban impacts on resource depletion and environmental impacts and also to improve cycles within the systems. Energy and water cycles are vital to support urban life. Over the last decades, important advances have been made separately in the field of integrated water management and energy efficiency in urban areas. However, for urban planning purposes a shared framework is required that allows planners to model and understand the dynamics of the broader system to achieve an integrated management of the resources. Natural energy and water cycles are modified by metabolic profiles of the cities. The metabolic profile varies with the local resource availability and the level of technological development. To cope with this complexity, the concept of Exergy, based on Thermodynamic laws, and defined as the non-used fraction of energy, has been used to understand the energy cycle in the built environment. This will lead to new approaches towards urban planning and better resources use. This paper aims to find out if the exergy concept can be expanded to the water cycle defined as the use of the non-used water(-fraction). This way the cycle can be optimized and closed at a high efficiency level. In order to achieve this, we want to study to what extend the energy and water cycles are comparable, and how they can learn from each other in order to optimize their management

Modeling and Energy Optimization of LDPC Decoder Circuits with Timing Violations

This paper proposes a "quasi-synchronous" design approach for signal processing circuits, in which timing violations are permitted, but without the need for a hardware compensation mechanism. The case of a low-density parity-check (LDPC) decoder is studied, and a method for accurately modeling the effect of timing violations at a high level of abstraction is presented. The error-correction performance of code ensembles is then evaluated using density evolution while taking into account the effect of timing faults. Following this, several quasi-synchronous LDPC decoder circuits based on the offset min-sum algorithm are optimized, providing a 23%-40% reduction in energy consumption or energy-delay product, while achieving the same performance and occupying the same area as conventional synchronous circuits.Comment: To appear in IEEE Transactions on Communication

The millimeter-wave properties of superconducting microstrip lines

We have developed a novel technique for making high quality measurements of the millimeter-wave properties of superconducting thin-film microstrip transmission lines. Our experimental technique currently covers the 75-100 GHz band. The method is based on standing wave resonances in an open ended transmission line. We obtain information on the phase velocity and loss of the microstrip. Our data for Nb/SiO/Nb lines, taken at 4.2 K and 1.6 K, can be explained by a single set of physical parameters. Our preliminary conclusion is that the loss is dominated by the SiO dielectric, with a temperature-independent loss tangent of 5.3 ± 0.5 x 10^(-3) for our samples

Strategic investment in protection in networked systems

We study the incentives that agents have to invest in costly protection against cascading failures in networked systems. Applications include vaccination, computer security and airport security. Agents are connected through a network and can fail either intrinsically or as a result of the failure of a subset of their neighbors. We characterize the equilibrium based on an agent's failure probability and derive conditions under which equilibrium strategies are monotone in degree (i.e. in how connected an agent is on the network). We show that different kinds of applications (e.g. vaccination, airport security) lead to very different equilibrium patterns of investments in protection, with important welfare and risk implications. Our equilibrium concept is flexible enough to allow for comparative statics in terms of network properties and we show that it is also robust to the introduction of global externalities (e.g. price feedback, congestion)

Electrochemical properties of nicotinamide derivatives in aqueous solution - Part IV. Oxidation of N1 -alkyl-1,4-dihydronicotinamides

International audienceThe electrochemical reduction of nicotinamide—adenine-dinucleotide (NAD+) and model compounds has been extensively studied1-3 ; on the other hand very few papers have been published on the electrochemical oxidation of nicotinamide—adenine-dinucleotide reduced (NADH) in aqueous solution. Haas4 reported the occurrence of an oxidation wave of NADH at pH 8.6 at rotating platinum and glassy carbon disk electrodes (with respective half-wave potentials 0.90 ± 0.02 and 0.67 ± 0.03 V vs. NHE); macroscale electrolyses lead to NAD+ by a two-electron oxidation4'5. In this paper we shall present the features of the electrochemical oxidation of model compounds of NADH, namely Ni-benzyl-and NL-propyl-l,4-dihydronicotinamide (NBzNH and NPrNH) in aqueous solution, buffered within a large pH range; a possible mechanism is deduced from these data. Extensive studies have shown the occurrence of a "primary acid modification" of aqueous NADH solutions or its models below pH 7 (ref. 6); the common explanation put forward is a saturation of the 5-6 double bond in the pyridinic ring, the u.v. absorption band being shifted from 355 to 290 nm. Therefore the results and discussions presented here only concern the pH range 7 to 13. Experimental All products used were prepared in this laboratory, according to published methods, namely NBzNTP (ref. 7), NBzNH and NPrN+Br~ (ref. 8), NPrNH (ref. 9). The purity and concentration of the freshly prepared aqueous solutions were checked by u.v. spectrophotometry with a Cary 14 apparatus. Drop-time controlled portography and voltammetry were carried out with Tacussel equipment (PRT 500 LC\ Servovit 9 B, S6 RZ millivoltmeter) and a Sefram "Luxy trace" bigalvanometric recorder. A Tacussel IG 4-100 electronic integrator was used for coulometry. At the beginning of all macroelectrolyses a Fontaine A 60 power-supply was connected between the counter-electrode and the generator. All aqueous solutions were thermostated at 25.0 ± 0.1°C during the experiments

Reaching the hydrodynamic regime in a Bose-Einstein condensate by suppression of avalanche

We report the realization of a Bose-Einstein condensate (BEC) in the hydrodynamic regime. The hydrodynamic regime is reached by evaporative cooling at a relative low density suppressing the effect of avalanches. With the suppression of avalanches a BEC containing 120.10^6 atoms is produced. The collisional opacity can be tuned from the collisionless regime to a collisional opacity of more than 3 by compressing the trap after condensation. In the collisional opaque regime a significant heating of the cloud at time scales shorter than half of the radial trap period is measured. This is direct proof that the BEC is hydrodynamic.Comment: Article submitted for Phys. Rev. Letters, 6 figure

Gestion intégrée de l'eau au sein d'un bassin versant

Dans la vallée du Merguellil, le barrage d'el Haouareb sépare le haut-bassin, très varié dans sa géologie, sa morphologie et son hydrologie, de la vaste plaine alluviale, plus homogène, élément de la plaine de Kairouan. Le barrage construit en 1989 bloque tous les écoulements vers l'aval et provoque involontairement l'infiltration des eaux de surface vers un karst puissant, lui-même en contact avec plusieurs aquifères. Les interactions entre les diverses composantes hydrologiques régionales sont nombreuses et encore insuffisamment quantifiées. Nous donnons ici l'état des connaissances actuelles et les prochaines recherches à entreprendre. Comme attendu en milieu méditerranéen semi-aride, les apports au barrage sont très variables dans le temps. A plus de 60 %, ils disparaissent dans le karst. La recharge des aquifères, qui s'effectuait autrefois lors des crues les plus fortes du Merguellil, connaît donc un nouveau régime. Les années les plus humides induisent toujours une remontée des piézométries des nappes adjacentes (Aïn el Beidha à l'amont, alluvions de la plaine de Kairouan à l'aval). Cependant, le trait régional majeur est la surexploitation de la nappe alluviale par des forages de plus en plus nombreux répondant à une forte extension de l'irrigation. La baisse de cette nappe dépasse 1 m/an par endroits et rien ne peut présumer une diminution de cette chute dans les prochaines années. (Résumé d'auteur