Ionic mass transfer in channel electrodes under laminar flow

The rate of ionic mass tranfer under a Poiseuille profile in channel electrodes involving inert zones has been studied. The electrolysis cell was vertically and horizontally placed, the working electrodes facing either upwards or downwards. An extension of Levich's solution for the convective-diffusion equation in a tube comprising an inert zone was applied. The experimental numerical coefficient lies 10% lower than the one theoretically derived.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

Stationary patterns in star networks of bistable units: theory and application to chemical reactions

We present theoretical and experimental studies on pattern formation with bistable dynamical units coupled in a star network configuration. By applying a localized perturbation to the central or the peripheral elements, we demonstrate the subsequent spreading, pinning, or retraction of the activations; such analysis enables the characterization of the formation of stationary patterns of localized activity. The results are interpreted with a theoretical analysis of a simplified bistable reaction-diffusion model. Weak coupling results in trivial pinned states where the activation cannot propagate. At strong coupling, a uniform state is expected with active or inactive elements at small or large degree networks, respectively. A nontrivial stationary spatial pattern, corresponding to an activation pinning, is predicted to occur at an intermediate number of peripheral elements and at intermediate coupling strengths, where the central activation of the network is pinned, but the peripheral activation propagates toward the center. The results are confirmed in experiments with star networks of bistable electrochemical reactions. The experiments confirm the existence of the stationary spatial patterns and the dependence of coupling strength on the number of peripheral elements for transitions between pinned and retreating or spreading fronts in forced network configurations (where the central or periphery elements are forced to maintain their states)

How closely do changes in surface and column water vapor follow Clausius-Clapeyron scaling in climate change simulations?

The factors governing the rate of change in the amount of atmospheric water vapor are analyzed in simulations of climate change. The global-mean amount of water vapor is estimated to increase at a differential rate of 7.3% K[superscript − 1] with respect to global-mean surface air temperature in the multi-model mean. Larger rates of change result if the fractional change is evaluated over a finite change in temperature (e.g., 8.2% K [superscript − 1] for a 3 K warming), and rates of change of zonal-mean column water vapor range from 6 to 12% K [superscript − 1] depending on latitude. Clausius–Clapeyron scaling is directly evaluated using an invariant distribution of monthly-mean relative humidity, giving a rate of 7.4% K − 1 for global-mean water vapor. There are deviations from Clausius–Clapeyron scaling of zonal-mean column water vapor in the tropics and mid-latitudes, but they largely cancel in the global mean. A purely thermodynamic scaling based on a saturated troposphere gives a higher global rate of 7.9% K [superscript − 1]. Surface specific humidity increases at a rate of 5.7% K [superscript − 1], considerably lower than the rate for global-mean water vapor. Surface specific humidity closely follows Clausius–Clapeyron scaling over ocean. But there are widespread decreases in surface relative humidity over land (by more than 1% K − 1 in many regions), and it is argued that decreases of this magnitude could result from the land/ocean contrast in surface warming

Ionic mass transfer in channel electrodes under laminar flow

The rate of ionic mass tranfer under a Poiseuille profile in channel electrodes involving inert zones has been studied. The electrolysis cell was vertically and horizontally placed, the working electrodes facing either upwards or downwards. An extension of Levich's solution for the convective-diffusion equation in a tube comprising an inert zone was applied. The experimental numerical coefficient lies 10% lower than the one theoretically derived.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

OntoTrader

Modern Web-based Information Systems (WIS) are becoming increasingly necessary to provide support for users who are in different places with different types of information, by facilitating their access to the information, decision making, workgroups, and so forth. Design of these systems requires the use of standardized methods and techniques that enable a common vocabulary to be defined to represent the underlying knowledge. Thus, mediation elements such as traders enrich the interoperability of web components in open distributed systems. These traders must operate with other third-party traders and/or agents in the system, which must also use a common vocabulary for communication between them. This paper presents the OntoTrader architecture, an Ontological Web Trading agent based on the OMG ODP trading standard. It also presents the ontology needed by some system agents to communicate with the trading agent and the behavioral framework for the SOLERES OntoTrader agent, an Environmental Management Information System (EMIS). This framework implements a “Query-Searching/Recovering-Response” information retrieval model using a trading service, SPARQL notation, and the JADE platform. The paper also presents reflection, delegation and, federation mediation models and describes formalization, an experimental testing environment in three scenarios, and a tool which allows our proposal to be evaluated and validated

Changes in Coastal Benthic Algae Succession Trajectories and Assemblages Under Contrasting Nutrient and Grazer Loads

Eutrophication plays a crucial role in coastal systems, driving changes in the composition and abundance of flora and fauna with consequent effects for the entire ecosystem. Sensitive to nutrient levels, micro- and macroalgal blooms serve as valuable indicators of eutrophication. The San Antonio Bay (Northern Argentinean Patagonia, 40° 43′ S, 64° 56′ W) provides an appropriate system to study in situ eutrophication processes on coastal communities. In a multi-scale approach, using two different kind of settlement substrates (micro: polyethylene terephthalate, and macro: ceramic), the present study followed benthic algal dynamics over one year, distinguishing changes in natural succession and seasonality. Strong differences were found in the biofilm assemblages after three days, marked by tube dwelling diatoms and Cocconeis spp. under high nutrient-grazer conditions and needle like diatoms (e.g. Nitzschia spp., Tabularia spp.) under lower nutrient-grazer loads. The succession continued by the colonization of macroalgae, with a higher recruitment rate in the nutrient and grazer rich environment with a concomitant higher diversity. Our results show that under higher nutrient-grazer conditions natural benthic succession not only differs in trajectory but in its final taxa composition promoting higher biodiversity and biomass accumulation. In addition, taxa specific substrate preferences interfere with the observed eutrophication pattern, suggesting substrate dependant interrelations between the bloom forming taxa. These findings provide evidence that nutrient enrichment can not only affect an established assemblage but also affect the early succession stages, changing the succession trajectory and thus the final assemblage.Facultad de Ciencias Naturales y Muse

Designing comparative effectiveness trials of surgical ablation for atrial fibrillation: Experience of the Cardiothoracic Surgical Trials Network

ObjectiveSince the introduction of the cut-and-sew Cox maze procedure for atrial fibrillation, there has been substantial innovation in techniques for ablation. Use of alternative energy sources for ablation simplified the procedure and has resulted in dramatic increase in the number of patients with atrial fibrillation treated by surgical ablation. Despite its increasingly widespread adoption, there is lack of rigorous clinical evidence to establish this procedure as an effective clinical therapy.MethodsThis article describes a comparative effectiveness randomized trial, supported by the Cardiothoracic Surgical Clinical Trials Network, of surgical ablation with left atrial appendage closure versus left atrial appendage closure alone in patients with persistent and long-standing persistent atrial fibrillation undergoing mitral valve surgery. Nested within this trial is a further randomized comparison of 2 different lesions sets: pulmonary vein isolation and the full maze lesion set.ResultsThis article addresses trial design challenges, including how best to characterize the target population, operationalize freedom from atrial fibrillation as a primary end point, account for the impact of antiarrhythmic drugs, and measure and analyze secondary end points, such as postoperative atrial fibrillation load.ConclusionsThis article concludes by discussing how insights that emerge from this trial may affect surgical practice and guide future research in this area

Water vapor and the dynamics of climate changes

Water vapor is not only Earth's dominant greenhouse gas. Through the release of latent heat when it condenses, it also plays an active role in dynamic processes that shape the global circulation of the atmosphere and thus climate. Here we present an overview of how latent heat release affects atmosphere dynamics in a broad range of climates, ranging from extremely cold to extremely warm. Contrary to widely held beliefs, atmospheric circulation statistics can change non-monotonically with global-mean surface temperature, in part because of dynamic effects of water vapor. For example, the strengths of the tropical Hadley circulation and of zonally asymmetric tropical circulations, as well as the kinetic energy of extratropical baroclinic eddies, can be lower than they presently are both in much warmer climates and in much colder climates. We discuss how latent heat release is implicated in such circulation changes, particularly through its effect on the atmospheric static stability, and we illustrate the circulation changes through simulations with an idealized general circulation model. This allows us to explore a continuum of climates, constrain macroscopic laws governing this climatic continuum, and place past and possible future climate changes in a broader context.Comment: 22 pages, 11 figure

Recovery of Meteorological Data for the Observatory of A Guarda, Spain

We herein describe the recovery of a series of data on temperature, humidity, precipitation, evaporation, wind, and local weather conditions from documentary sources obtained from the Jesuit observatory of A Guarda (Galicia, Spain) for the period 1881–1896. The data were digitized and made available in accessible electronic formats. Comparisons were made with present-day meteorological data obtained from two nearby stations. We further believe that the discovery of some new complementary documentary sources made during the present research could be a basis for future data recovery efforts. Among these new results, early ozone data from the period are of outstanding importance to meteorologists