Optimization of commercial net spacers in spiral wound membrane modules

CFD simulations have been used to determine mass transfer coefficients and power consumption of commercial net spacers. The simulations show transversal and longitudinal vortices, vortex shedding and instationary flow behavior leading to the enhanced mass transfer in spacer filled-channels compared to empty channels. The results of the simulations were validated with experiments and compared with data reported in literature, showing satisfactory agreement. Furthermore, CFD simulations were used to optimize the geometry of commercial net spacers in terms of mass transfer and power consumption. The performance of these optimized spacer geometries will be used as reference for future work on the development of new high-performance spacer shapes

Accountability of Central Banks: Aspects and Quantification

This paper starts with a discussion of the various aspects of accountability of central banks. On the basis of this discussion we construct an indicator for accountability for 16 central banks, including the European Central Bank. It is shown that the degree of accountability differs considerably and that the ECB has a rather low score. The indicator is used to examine the relationship between central bank independence and accountability. It is concluded that although there appears to be a negative relationship between independence and accountability, this does certainly not imply that a central bank cannot both be independent and accountable.central bank independence;central bank accountability;European central bank

MIGRATION AND RURAL ASSETS: EVIDENCE FROM SURVEYS IN THREE SEMI-ARID REGIONS IN SOUTH AFRICA, INDIA AND BOTSWANA

Consumer/Household Economics,

Visual pathways from the perspective of cost functions and multi-task deep neural networks

Vision research has been shaped by the seminal insight that we can understand the higher-tier visual cortex from the perspective of multiple functional pathways with different goals. In this paper, we try to give a computational account of the functional organization of this system by reasoning from the perspective of multi-task deep neural networks. Machine learning has shown that tasks become easier to solve when they are decomposed into subtasks with their own cost function. We hypothesize that the visual system optimizes multiple cost functions of unrelated tasks and this causes the emergence of a ventral pathway dedicated to vision for perception, and a dorsal pathway dedicated to vision for action. To evaluate the functional organization in multi-task deep neural networks, we propose a method that measures the contribution of a unit towards each task, applying it to two networks that have been trained on either two related or two unrelated tasks, using an identical stimulus set. Results show that the network trained on the unrelated tasks shows a decreasing degree of feature representation sharing towards higher-tier layers while the network trained on related tasks uniformly shows high degree of sharing. We conjecture that the method we propose can be used to analyze the anatomical and functional organization of the visual system and beyond. We predict that the degree to which tasks are related is a good descriptor of the degree to which they share downstream cortical-units.Comment: 16 pages, 5 figure

Molecular gas in NUclei of GAlaxies (NUGA) XV. Molecular gas kinematics in the inner 3kpc of NGC6951

Within the NUclei of GAlaxies project we have obtained IRAM PdBI and 30m 12CO(1-0) and 12CO(2-1) observations of the spiral galaxy NGC 6951. Previous work shows that there is indirect evidence of gas inflow from 3 kpc down to small radii: a large-scale stellar bar, a prominent starburst ring (r~580 pc) and a LINER/Seyfert 2 nucleus. In this paper we study the gas kinematics as traced by the CO line emission in detail. We quantify the influence of the large-scale stellar bar by constructing an analytical model of the evolution of gas particles in a barred potential. From this model gravitational torques and mass accumulation rates are computed. We compare our model-based gravitational torque results with previous observationally-based ones. The model also shows that the large-scale stellar bar is indeed the dominant force for driving the gas inward, to the starburst ring. Inside the ring itself a nuclear stellar oval might play an important role. Detailed analysis of the CO gas kinematics there shows that emission arises from two co-spatial, but kinematically distinct components at several locations. The main emission component can always be related to the overall bar-driven gas kinematics. The second component exhibits velocities that are larger than expected for gas on stable orbits, has a molecular gas mass of 1.8x10^6Msun, is very likely connected to the nuclear stellar oval, and is consistent with inflowing motion towards the very center. This may form the last link in the chain of gas inflow towards the active galactic nucleus in NGC 6951.Comment: 17 pages, accepted by A&A (17 feb 2011

Water scarcity and institutional change: lessons in adaptive governance from the drought experience of Perth, Western Australia

Urban water systems will be increasingly challenged under future climates and global pressures. Meeting challenges by reconfiguring water systems to integrate supplies and deliver multifunctional uses is technically well described. Adjusting the institutions that frame the management of these systems is not well operationalized in practice or conceptualized in theory. This study seeks to address this gap through an institutional analysis of Perth, Australia, a city where drought crisis has put under pressure both management practices and the institutional setting that underlies them. The study found that while trusted practices moderated water scarcity, the stability of the institutional setting may not facilitate a shift toward adaptable institutional configurations suited to future conditions. The results identified three key ingredients for a flexible institutional setting: (i) feedbacks in the system through better information management, (ii) reflexive dialogue and strategic use of projects to generate greater learning opportunities, and (iii) policy level support for sector-wide collaboration through progressive agendas, incentives for innovation and capacity building in stakeholder and community engagement. Further, the results suggest that a deeper understanding of institutional dynamics is needed to enable adaptive governance. The paper provides an analytical framework for diagnosing how greater adaptive capacity might be mobilized through influencing these dynamics

Natural handicaps in Dutch agricultural areas : assessment of less favoured areas based on economic criteria

Smit en Brouwer (2009) hebben bodems met een landbouwkundige handicap geselecteerd aan de hand van biofysische criteria. De relevante biofysische criteria waren gerelateerd aan bodemeigenschappen: drainage, textuur, aanwezigheid van stenen en chemische eigenschappen. Textuur en aanwezigheid van stenen zijn onderverdeeld in verschillende klassen: grof materiaal, grof en middelgrof zand, zware klei, veengronden, zwel en krimpverschijnselen en het opkomen van stenen uit de ondergrond. Verzilting is de enige chemische eigenschap die relevant is voor Nederland. Naast een selectie van gebieden op grond van biofysische eigenschappen, moet ook een verfijnde selectie worden uitgevoerd. Deze verfijnde selectie is gebaseerd op de verschillen in saldo per hectare tussen gebieden met en zonder de landbouwkundige gevolgen van de biofysische eigenschappen. De belangrijkste landbouwkundige gevolgen voor de verschillende categorieën waren de gevoeligheid voor winderosie bij grof en middelgrof zand; de beperkingen van de bewerkbaarheid van de grond en de beperkingen in het bouwplan op de zware kleigronden en lagere netto productie en de onmogelijkheid om maïs te verbouwen op veengronde

Correlations of record events as a test for heavy-tailed distributions

A record is an entry in a time series that is larger or smaller than all previous entries. If the time series consists of independent, identically distributed random variables with a superimposed linear trend, record events are positively (negatively) correlated when the tail of the distribution is heavier (lighter) than exponential. Here we use these correlations to detect heavy-tailed behavior in small sets of independent random variables. The method consists of converting random subsets of the data into time series with a tunable linear drift and computing the resulting record correlations.Comment: Revised version, to appear in Physical Review Letter

Differential trajectories of tobacco smoking in people at ultra-high risk for psychosis: Associations with clinical outcomes

Objective: People at ultra-high risk (UHR) for psychosis have a high prevalence of tobacco smoking, and rates are even higher among the subgroup that later develop a psychotic disorder. However, the longitudinal relationship between the course of tobacco smoking and clinical outcomes in UHR subjects is unknown. Methods: We investigated associations between tobacco smoking and clinical outcomes in a prospective study of UHR individuals (n = 324). Latent class mixed model analyses were used to identify trajectories of smoking severity. Mixed effects models were applied to investigate associations between smoking trajectory class and the course of attenuated psychotic symptoms (APS) and affective symptoms, as assessed using the CAARMS. Results: We identified four different classes of smoking trajectory: (i) Persistently High (n = 110), (ii) Decreasing (n = 29), (iii) Persistently Low (n = 165) and (iv) Increasing (n = 20). At two-year follow-up, there had been a greater increase in APS in the Persistently High class than for both the Persistently Low (ES = 9.77, SE = 4.87, p = 0.046) and Decreasing (ES = 18.18, SE = 7.61, p = 0.018) classes. There were no differences between smoking classes in the incidence of psychosis. There was a greater reduction in the severity of emotional disturbance and general symptoms in the Decreasing class than in the High (ES = −10.40, SE = 3.41, p = 0.003; ES = −22.36, SE = 10.07, p = 0.027), Increasing (ES = −11.35, SE = 4.55, p = 0.014; ES = −25.58, SE = 13.17, p = 0.050) and Low (ES = −11.38, SE = 3.29, p = 0.001; ES = −27.55, SE = 9.78, p = 0.005) classes, respectively. Conclusions: These findings suggests that in UHR subjects persistent tobacco smoking is associated with an unfavorable course of psychotic symptoms, whereas decrease in the number of cigarettes smoked is associated with improvement in affective symptoms. Future research into smoking cessation interventions in the early stages of psychoses is required to shine light on the potential of modifying smoking behavior and its relation to clinical outcomes.</p