Identification of functional information subgraphs in complex networks

We present a general information theoretic approach for identifying functional subgraphs in complex networks where the dynamics of each node are observable. We show that the uncertainty in the state of each node can be expressed as a sum of information quantities involving a growing number of correlated variables at other nodes. We demonstrate that each term in this sum is generated by successively conditioning mutual informations on new measured variables, in a way analogous to a discrete differential calculus. The analogy to a Taylor series suggests efficient search algorithms for determining the state of a target variable in terms of functional groups of other degrees of freedom. We apply this methodology to electrophysiological recordings of networks of cortical neurons grown it in vitro. Despite strong stochasticity, we show that each cell's patterns of firing are generally explained by the activity of a small number of other neurons. We identify these neuronal subgraphs in terms of their mutually redundant or synergetic character and reconstruct neuronal circuits that account for the state of each target cell.Comment: 4 pages, 4 figure

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Trace ions rejection tunning in NF by selecting solution composition: Ion permeances estimation

Nanofiltration (NF) is suggested to selectively remove ionic species in aqueous process streams taking benefit of both membrane and aqueous solution composition. The importance of predicting and optimizing selective ion rejections by NF not only of major compounds (e.g. NaCl, Na2SO4, MgCl2, MgSO4) but also of minor ones such as ammonium (NH4+), nitrate (NO3-), bromide (Br-), iodide (I-) typically present in natural and industrial process streams is crucial. The current work explores ion rejection patterns and membrane ion permeances using the phenomenological Solution-Electro-Diffusion-Film (SEDF) model. It makes possible rapid calculations that account for the effects of spontaneously arising electric fields on rejections. Experimental ion rejection data of several inorganic ions species at various transmembrane pressures and at fixed cross-flow velocity have been obtained with NF270 membrane. A number of trace ions (Na+, K+, Cl-, Ca2+, Mg2+, SO42-, NO3-, NH4+, Br-and I-) have been used in combination with various dominant salts (NaCl, MgCl2, MgSO4) as model feed solutions. Results showed that dominant salts were moderately (NaCl) and highly (MgCl2, MgSO4) rejected when some ions are divalent, while trace ions exhibited quite variable rejection, including negative ones mainly at low transmembrane volume flows. The electric field of membrane potential can accelerate or retard the ion flows to the permeate, so negative or unexpectedly high rejections could be observed. Ions transport was shown to be affected by the membrane chemistry (e.g. acid-base properties of the un-crosslinked carboxylic and amine groups) and the dielectric exclusion phenomena. From the modelling procedure, ionic membrane permeances were determined for various multi-ion systems studied. Results showed that nature of dominant salt composition can be used to control the rejection of minor components.Peer ReviewedPostprint (author's final draft

Selectrodialysis and bipolar membrane electrodialysis combination for industrial process brines treatment: Monovalent-divalent ions separation and acid and base production

Chemical industries generate large amounts of wastewater rich in different chemical constituents. Amongst these, salts at high concentrations are of major concern, making necessary the treatment of saline effluents before discharge. Because most of these rejected streams comprise a combination of more than one salt at high concentration, it is reasonable to try to separate and revalorize them to promote circular economy at industry site level. For this reason, ion-exchange membranes based technologies were integrated in this study: selectrodialysis (SED) and electrodialysis with bipolar membranes (EDBM). Different process brines composed by Na2SO4 and NaCl at different concentrations were treated first by SED to separate each salt, and then by EDBM to produce base (NaOH) and acids (HCl and H2SO4) from each salt. The optimum of both electrolyte nature and concentration of the SED stack streams was evaluated. Results indicated that it was possible to separate Cl- and SO42- depending on the anionic membrane, initial electrolytes and concentrations of each stream. Pure NaOH and a mixture of HCl and H2SO4 with different purities could be obtained. Energy consumption evolutions were plotted and an optimal zone work was found where the consumption values were acceptable.Peer ReviewedPostprint (author's final draft

Resíduos de exploração em areeiros de Trás-os-Montes Oriental: potencialidades como matéria prima para a indústria cerâmica de construção

A exploração de sedimentos cenozóicos, para produção de inertes (areia e seixo), efectuada em areeiros da região de Trás-os-Montes Oriental, é geradora de resíduos (fracção dos sedimentos <70µm), aos quais estão associados impactes vários. Neste trabalho apresentam-se parte dos resultados do estudo mineralógico, químico, granulométrico e tecnológico dos resíduos. Os resíduos possuem características que os permitem considerar como Argilas Comuns, com apetência para a produção de cerâmicos de construção, nomeadamente tijolo alveolado e maciço, sendo no entanto necessária a beneficiação de algumas das suas características.The Cenozoic sediments of Eastern Trás-os-Montes region are extracted for the production of sand and gravel, used as row materials in the construction industry. This extraction produce a large amount of waste mud, generating several environmental impacts. The waste mud was submitted to mineralogical, chemical and granulometric analysis. Tecnological tests were also performed with these materials. These studies allowed the classification of the waste mud as common clay, and showed their suitability for aplication in the bricks production, although some technological properties corrections should be made.Fundação para a Ciência Tecnologia - POCTI/CTA/38659/2001