Drag Reduction by Polymers in Wall Bounded Turbulence

We address the mechanism of drag reduction by polymers in turbulent wall bounded flows. On the basis of the equations of fluid mechanics we present a quantitative derivation of the "maximum drag reduction (MDR) asymptote" which is the maximum drag reduction attained by polymers. Based on Newtonian information only we prove the existence of drag reduction, and with one experimental parameter we reach a quantitative agreement with the experimental measurements.Comment: 4 pages, 1 fig., included, PRL, submitte

Identification and Calculation of the Universal Maximum Drag Reduction Asymptote by Polymers in Wall Bounded Turbulence

Drag reduction by polymers in wall turbulence is bounded from above by a universal maximal drag reduction (MDR) velocity profile that is a log-law, estimated experimentally by Virk as $V^+(y^+)\approx 11.7 \log y^+ -17$. Here $V^+(y)$ and $y^+$ are the mean streamwise velocity and the distance from the wall in "wall" units. In this Letter we propose that this MDR profile is an edge solution of the Navier-Stokes equations (with an effective viscosity profile) beyond which no turbulent solutions exist. This insight rationalizes the universality of the MDR and provides a maximum principle which allows an ab-initio calculation of the parameters in this law without any viscoelastic experimental input.Comment: 4 pages, 1 fig. Phys. Rev. Letts., submitte

Shortening of the Short Refractory Periods in Short QT Syndrome.

BACKGROUND: Diagnosis of short QT syndrome (SQTS) remains difficult in case of borderline QT values as often found in normal populations. Whether some shortening of refractory periods (RP) may help in differentiating SQTS from normal subjects is unknown. METHODS AND RESULTS: Atrial and right ventricular RP at the apex and right ventricular outflow tract as determined during standard electrophysiological study were compared between 16 SQTS patients (QTc 324±24 ms) and 15 controls with similar clinical characteristics (QTc 417±32 ms). Atrial RP were significantly shorter in SQTS compared with controls at 600- and 500-ms basic cycle lengths. Baseline ventricular RP were significantly shorter in SQTS patients than in controls, both at the apex and right ventricular outflow tract and for any cycle length. Differences remained significant for RP of any subsequent extrastimulus at any cycle length and any pacing site. A cut-off value of baseline RP <200 ms at the right ventricular outflow tract either at 600- or 500-ms cycle length had a sensitivity of 86% and a specificity of 100% for the diagnosis of SQTS. CONCLUSIONS: Patients with SQTS have shorter ventricular RP than controls, both at baseline during various cycle lengths and after premature extrastimuli. A cut-off value of 200 ms at the right ventricular outflow tract during 600- and 500-ms basic cycle length may help in detecting true SQTS from normal subjects with borderline QT values

Longevity and mortality of cats attending primary care veterinary practices in England

Enhanced knowledge on longevity and mortality in cats should support improved breeding, husbandry, clinical care and disease prevention strategies. The VetCompass research database of primary care veterinary practice data offers an extensive resource of clinical health information on companion animals in the UK. This study aimed to characterise longevity and mortality in cats, and to identify important demographic risk factors for compromised longevity. Crossbred cats were hypothesised to live longer than purebred cats. Descriptive statistics were used to characterise the deceased cats. Multivariable linear regression methods investigated risk factor association with longevity in cats that died at or after 5 years of age. From 118,016 cats attending 90 practices in England, 4009 cats with confirmed deaths were randomly selected for detailed study. Demographic characterisation showed that 3660 (91.7%) were crossbred, 2009 (50.7%) were female and 2599 (64.8%) were neutered. The most frequently attributed causes of mortality in cats of all ages were trauma (12.2%), renal disorder (12.1%), non-specific illness (11.2%), neoplasia (10.8%) and mass lesion disorders (10.2%). Overall, the median longevity was 14.0 years (interquartile range [IQR] 9.0–17.0; range 0.0–26.7). Crossbred cats had a higher median longevity than purebred cats (median [IQR] 14.0 years [9.1–17.0] vs 12.5 years [6.1–16.4]; P \u3c0.001), but individual purebred cat breeds varied substantially in longevity. In cats dying at or after 5 years (n = 3360), being crossbred, having a lower bodyweight, and being neutered and non-insured were associated with increased longevity. This study described longevity in cats and identified important causes of mortality and breed-related associations with compromised longevity

Spatial Resolution of a Micromegas-TPC Using the Charge Dispersion Signal

The Time Projection Chamber (TPC) for the International Linear Collider will need to measure about 200 track points with a resolution close to 100 $\mu$m. A Micro Pattern Gas Detector (MPGD) readout TPC could achieve the desired resolution with existing techniques using sub-millimeter width pads at the expense of a large increase in the detector cost and complexity. We have recently applied a new MPGD readout concept of charge dispersion to a prototype GEM-TPC and demonstrated the feasibility of achieving good resolution with pads similar in width to the ones used for the proportional wire TPC. The charge dispersion studies were repeated with a Micromegas TPC amplification stage. We present here our first results on the Micromegas-TPC resolution with charge dispersion. The TPC resolution with the Micromegas readout is compared to our earlier GEM results and to the resolution expected from electron statistics and transverse diffusion in a gaseous TPC.Comment: 5 pages, 8 figures, to appar in the Proceedings of the 2005 International Linear Collider Workshop (LCWS05), Stanford, 18-22 March 200

Avec leur statut original, quels rôles pour les sociétés d'aménagement régional dans les politiques de l'eau et de l’irrigation ?

Les sociétés d’aménagement régional (SAR) opérateurs régionaux de la gestion de l’eau avec un mandat d’aménagement du territoire ont un statut original de sociétés commerciales. Elles jouent un rôle majeur dans la réalisation des investissements nécessaires à l’irrigation dans le Sud de la France. Une interview de trois cadres de ces sociétés permet de cerner comment elles peuvent jouer ce rôle. La relation avec les irrigants se fait par des contrats de droit privé impliquant généralement un comptage des quantités d’eau distribuée et une attention particulière au prix de l’eau. La vente d’eau à différents usagers agricole, urbain ou industriel permet d’équilibrer les comptes. Ces sociétés apportant à l’État la garantie d’organisations structurées, la répartition de l’eau, la création de ressource avant l’équipement des exploitations irrigantes, le conseil d’État recommande de leur donner plus de poids. / Regional development companies (SAR), regional organizations of water management with a role of regional planning and development have, in France, an original status of corporations. They play a major role in making the necessary investments in irrigation in the South of France. An interview with three managers of these companies can identify how they can play this role. Relationship with irrigators is done by private contracts generally involving water measurement and special attention to water price. The sale of water to different users agricultural, urban or industrial balances the accounts. As these companies bring to the state the guaranty of structured organizations, balanced distribution of water, creating resource before farm equipment, the State Council recommends to give them more weight

Saturation of Turbulent Drag Reduction in Dilute Polymer Solutions

Drag reduction by polymers in turbulent wall-bounded flows exhibits universal and non-universal aspects. The universal maximal mean velocity profile was explained in a recent theory. The saturation of this profile and the crossover back to the Newtonian plug are non-universal, depending on Reynolds number Re, concentration of polymer $c_p$ and the degree of polymerization $N_p$. We explain the mechanism of saturation stemming from the finiteness of extensibility of the polymers, predict its dependence on $c_p$ and $N$ in the limit of small $c_p$ and large Re, and present the excellent comparison of our predictions to experiments on drag reduction by DNA.Comment: 4 pages, 4 figs., included, PRL, submitte

Co-engineering participatory water management processes: theory and insights from Australian and Bulgarian interventions

Broad-scale, multi-governance level, participatory water management processes intended to aid collective decision making and learning are rarely initiated, designed, implemented, and managed by one person. These processes mostly emerge from some form of collective planning and organization activities because of the stakes, time, and budgets involved in their implementation. Despite the potential importance of these collective processes for managing complex water-related social-ecological systems, little research focusing on the project teams that design and organize participatory water management processes has ever been undertaken. We have begun to fill this gap by introducing and outlining the concept of a co-engineering process and examining how it impacts the processes and outcomes of participatory water management. We used a hybrid form of intervention research in two broad-scale, multi-governance level, participatory water management processes in Australia and Bulgaria to build insights into these coengineering processes. We examined how divergent objectives and conflict in the project teams were negotiated, and the impacts of this co-engineering on the participatory water management processes. These investigations showed: (1) that language barriers may aid, rather than hinder, the process of stakeholder appropriation, collective learning and skills transferal related to the design and implementation of participatory water management processes; and (2) that diversity in co-engineering groups, if managed positively through collaborative work and integrative negotiations, can present opportunities and not just challenges for achieving a range of desired outcomes for participatory water management processes. A number of areas for future research on co-engineering participatory water management processes are also highlighted

Approche méthodologique de la modélisation du transport des HAP dans les sols et les eaux

Afin de préciser le cadre d'utilisation de codes de transport de polluants dans les sols et les eaux, un programme d'intercomparaison de méthodes et de codes a été mis en oeuvre avec la collaboration de huit équipes appartenant à des instituts de recherche ou des bureaux d'études. Parmi les types de polluants étudiés, les hydrocarbures aromatiques polycycliques (HAP) ont fait l'objet de simulations par deux groupes de travail. Le premier groupe, composé de cinq équipes, s'est intéressé à leur comportement en phase dissoute à partir d'un cas réel de pollution. Disposant des mêmes données d'étude, chaque équipe avait pour mission de concevoir un modèle conceptuel (description géologique, définition de la source, paramètres d'écoulement et de transport) et de simuler la pollution de la nappe avec le code de son choix. Les résultats obtenus montrent des différences significatives qui trouvent leur explication dans les paramètres des modèles conceptuels adoptés plus que dans les simulateurs choisis. Cet exercice a confirmé l'importance des paramètres suivants qui sont souvent incertains mais justifieraient d'être mieux appréciés lors de diagnostics : paramètres hydrodynamiques (détermination du champ de vitesse), coefficient de partition (pour chaque horizon géologique), temps de demi-vie du ou des polluants, extension de la source de pollution. Le second groupe a étudié les écoulements en phase libre (phase liquide non aqueuse) sur un cas théorique inspiré d'un cas réel de déversement massif de naphtalène. La modélisation a été conduite par trois équipes avec trois codes polyphasiques différents (SIMUSCOPP, TOUGH/T2VOC, UTCHEM). Cet exercice comprend le suivi du déversement et de la migration du naphtalène sous formes liquide et dissoute sur une distance de 300 m et une durée de 10 ans. Le naphtalène révèle un comportement d'hydrocarbure " lourd " avec une phase huile (partiellement miscible) qui tend à descendre à travers la nappe. Ce comportement a été reproduit par chacune des équipes, de manière plus ou moins complète en fonction des possibilités de modélisation offertes par les codes. Les résultats obtenus permettent de vérifier la cohérence des différentes approches polyphasiques entre elles. Bien que plus complexe (paramètres plus nombreux, difficulté numérique accrue), l'approche polyphasique se justifie pour mieux comprendre et déterminer la répartition spatiale de HAP en profondeur dans une nappe