Exclusion Phenomena Research Articles

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.

Exclusion services in smart city knowledge portal

Exclusion phenomenon denotes processes in which some group of people or individuals is permanently blocked from resources (mostly considered as social exclusion). The discussed phenomenon can be considered in many aspects: identifying exclusion as a process, multidimensional research in this area and presenting solutions useful in solving problems. Real support of the processes in overtaking exclusion phenomenon can be offered from Information and Communication Technologies area. The aim of this paper is the presentation of smart city portals content in order to support services devoted to exclusion processes neutralization. Several existing portals of selected smart cities are taken into account. The contents of the research sample will be analysed to investigate the state of the art solutions in the area and confronted with the concept of knowledge portal. The paper consists of five parts, including Introduction and Conclusions. The three merit parts describe exclusion phenomena, then general concept of knowledge portal devoted to services is presented and the last part demonstrates existing solutions in this area.

MOCVD grown HgCdTe device structure for ambient temperature LWIR detectors

The authors report on advanced metalorganic chemical vapor deposition (MOCVD) grown HgCdTe device structure for an ambient temperature long wavelength infrared radiation (LWIR) detector application. MOCVD technology with a wide range of composition and donor/acceptor doping and without post grown annealing seems to be an excellent tool for HgCdTe heterostructure epitaxial growth structure. The N+/G/π/G/P+/G/n+ (where G denotes graded interface region) HgCdTe photovoltaic device concept of a specific barrier bandgap architecture integrated with Auger-suppression is a good solution for high operating temperature (HOT) infrared detectors. Selected problems of photodiode designing are indicated. Theoretical modelling using APSYS platform supports design and better understanding of the carrier transport mechanism in the photodiode structures. SIMS profiles allowed comparing projected and obtained structures and revealed diffusion processes in the structures. The negative differential resistance, clearly visible on current–voltage characteristics, evidences for Auger-suppression due to exclusion and extraction phenomena. It is shown that the thickness and arsenic doping of the active region influence the reverse bias dark current minimum and the response time of LWIR HOT HgCdTe photodiodes. Reverse bias highly (up to 50 times) increases responsivity that could reach 6 A/W at 300 K.

Ceramic membrane as a pretreatment for reverse osmosis: interaction between marine organic matter and metal oxides

Scaling and (bio)fouling phenomena can severely alter the performance of the reverse osmosis process during desalination of seawater. Pretreatments must be applied to efficiently remove particles, colloids, and also precursors of the organic fouling and biofouling. Ceramic membranes offer a lot of advantages for micro and ultrafiltration pretreatments because their initial properties can be recovered using more severe cleaning procedure. The study focuses on the interaction between metal oxides and marine organic matter. Experiments were performed at laboratory scale. The first series of experiments focus on the filtration of different fractions of natural organic matter and model compounds solutions on flat disk ceramic membranes (47 mm of diameter) characterized with different pore size and composition. Direct filtration experiments were conducted at 0.7 bar or 2 bars and at room temperature (20 ± 0.5°C). The efficiency of backflush and alkaline cleaning were evaluated. The second series of experiments were carried out with metal oxide particles of the same composition than the disk ceramic membranes. Isotherm adsorption and adsorption kinetics of different fractions of organic matter with different concentration and physico-chemical characteristics were studied (pH, temperature, and ionic strength). Metal oxides studied are aluminum, zirconium, and titanium oxides. Each metal oxide corresponds to a specific pore size for the disk ceramic membranes: 80, 60, and 30 nm. Different sizes of metal oxide particles are used to measure the impact of the surface area on the adsorption of the organic matter. Seawaters from the Arabian Gulf and from the Red Sea were collected during algal blooms. Cultures of algae were also performed in the laboratory and in cooperation with woods hole oceanographic institute. Solutions of algal exudates were obtained after a couple of weeks of cultivation followed by sonication. Solutions were successively filtered through GFF (0.7 μm) and 0.45μm membrane filters before use. The dissolved organic carbon (DOC) concentration of final solution was between 1 and 4 mg/L and showed strong hydrophilic character. These various solutions were prepared with the objective to mimic the dissolved organic matter composition of seawater subjected to algal bloom. Characterization of the solutions of filtration experiments (feed water, permeate water, and backwashes) and batch experiments (raw solution and supernatant solutions) included fluorescence, UV, total organic carbon, total nitrogen, and Liquid Chromatography – Organic Carbon Detection measurements. In comparison to seawater under normal condition, seawaters collected during algal bloom and algal exudates solutions led to very severe fouling of all ceramic membranes (with some DOC removal of 10–20%). It is important to indicate that algal exudate permeates still exert fouling properties when filtered through similar new (virgin) membrane. These results indicate that both size exclusion and adsorption phenomena occur (on surface, inside pores). In all cases, the backflush (performed with MilliQ [MQ]) showed minor or no effect and the cleaning backwash was not able to recover the initial flux (30–60%). Analyses performed on the backflush solution (performed with MQ) and on the alkaline cleaning solution revealed the retention of both high and low molecular organics on the different metal oxides. Unfortunately, analyses of membrane surface using imaging various tools are not providing informative results in term of foulant/adsorbed material composition.

Gli interventi di "mitigazione" del "disagio sociale" nel quadro della programmazione della Regione Autonoma della Sardegna

This contribution brings to the attention of the scientific community some of the results developed by the Evaluation Unit of the Regional Administration of Sardinia, regarding plausibility and effectiveness profiles of the actions undertaken in the social exclusion area based on the 2000-2006 European Funding. After obtaining a picture of the phenomena by means of a Principal Components Analysis on available data, we observe many critical points regarding the devising and effectiveness of the policy. First of all, there appears no matching between the municipalities benefitting of the program and the intensity of the phenomena. Furthermore, perhaps because of the scarcity of available funds, we find that the Heckman (1979) two-stage procedure does not signal the policy as effective in affecting the performance of the municipalities in the control of the social exclusion phenomena.

Chromatographic NMR with size exclusion chromatography stationary phases

Chromatographic NMR describes the use of stationary phases or solvent additives, such as polymers, to modify the diffusion properties of analyte molecules and thereby improve the observed resolution in the diffusion domain. This paper demonstrates similar ideas using size exclusion chromatographic media and characterises the changes in the observed diffusion coefficient using a series of polymer molecular weight reference standards of known polydispersity. The results are interpreted in terms of a simple description of the size exclusion phenomena.

Assessment of dielectric contribution in the modeling of multi-ionic transport through nanofiltration membranes

In the present work, a knowledge model is used to investigate the possibility of predicting the separation of ionic mixtures. In the model, the transfer through the membrane is based upon the classical vision coupling the Donnan, steric and dielectric exclusions at the interfaces with the extended Nernst–Planck transport equation within the pores. The prediction of selectivity between ions requires the knowledge of the interfacial partitioning which results of three contributions, i.e. steric, electric and dielectric. Each contribution can be assessed by means of a parameter describing the exclusion phenomena. The mean pore radius ( r p ) and the membrane charge density ( X d ) which govern respectively steric and electric exclusions are usually experimentally identified by microscopy or neutral solute rejection and zetametry. The dielectric contribution through the dielectric constant of the solution within the pores ( ɛ p ) is usually fitted from rejection curves. In this paper, an experimental method based upon the membrane potential measurements is also implemented to assess ɛ p -value. The identified values are compared with those obtained by fitting experimental ternary mixtures. The agreement found between these two sets of values indicates that the theory of ionic transfer seems to be coherent and let foresee the possibility of a fully predictive model.

Edukacja międzykulturowa wobec zjawisk wykluczenia społecznego i piętna

Edukacja międzykulturowa wobec zjawisk wykluczenia społecznego i piętna

Transport of salt mixtures through nanofiltration membranes: Numerical identification of electric and dielectric contributions

In this paper, a knowledge model is used to describe the rejection of ionic components in various proportions obtained by mixing two salts (NaCl and Na 2SO 4 or NaCl and MgCl 2). This model is based on a description of the transport within the pores via the extended Nernst–Planck equation and the steric, electric and dielectric exclusion phenomena at the membrane/solution interfaces. Electric and dielectric contributions on the separation selectivity are investigated from experimental results by estimating, respectively, the membrane charge density X d and the solvation energy through the dielectric constant within the pores ɛ p . A new way of numerical identification is presented in this paper, which consists in identifying simultaneously this couple of parameters ( ɛ p , X d ) from mixture experiments. This method appears to be particularly convenient, as it does not require additional assumption to decouple their influences on rejection. The obtained values are discussed with respect to the mixture type and its composition. It was found that the values of both ɛ p and X d are physically consistent and show monotonous behaviors with the proportions of ions. In particular, ɛ p decreases linearly when the proportion of divalent ions increases.

Investigations of mobile phase contributions to enantioselective anion- and zwitterion-exchange modes on quinine-based zwitterionic chiral stationary phases

Novel chiral stationary phases (CSPs) based on zwitterionic Cinchona alkaloid-type low-molecular mass chiral selectors (SOs), as they have been reported recently, were investigated in HPLC towards effects on their chromatographic behavior by mobile phase composition. Mobile phase characteristics like acid-to-base ratio and type of acidic and basic additives as well as effect of type of bulk solvents in nonaqueous polar organic and aqueous reversed-phase (RP) eluent systems were varied in order to illustrate the variability and applicability of zwitterionic CSPs with regard to mobile phase aspects. Chiral SOs of the five zwitterionic CSPs investigated herein contained weak and strong cation-exchange (WCX, SCX) sites at C9- and C6′-positions of the Cinchona alkaloid scaffold which itself accommodated the weak anion-exchange (WAX) site. The study focused on zwitterion-exchange (ZX) operational mode and chiral amino acids as target analytes. Besides, also the anion-exchange (AX) mode for chiral N-blocked amino acid analytes was considered, because of the intramolecular counterion (IMCI) property available in AX mode. Overall, most general and successful conditions in ZX mode were found to be weakly acidic methanolic mobile phases. In aqueous eluents RP contributions to retention came into play but only at low organic modifier content because of the highly polar character of zwitterionic analytes. At higher acetonitrile content, HILIC-related retention phenomena were observed. When using weakly basic eluent system in AX mode remarkably fast enantiomer separations involving exclusion phenomena were possible with one enantiomer eluting before and the other after void volume.

Conjugal properties of the Sinorhizobium meliloti plasmid mobilome

The biology and biochemistry of plasmid transfer in soil bacteria is currently under active investigation because of its central role in prokaryote adaptation and evolution. In this work, we examined the conjugal properties of the cryptic plasmids present in a collection of the N(2)-fixing legume-symbiont Sinorhizobium meliloti. The study was performed on 65 S. meliloti isolates recovered from 25 humic soils of Argentina, which were grouped into 22 plasmid-profile types [i.e. plasmid operational taxonomic units (OTUs)]. The cumulative Shannon index calculated for the observed plasmid profiles showed a clear saturation plateau, thus indicating an adequate representation of the S. meliloti plasmid-profile types in the isolates studied. The results show that isolates of nearly 14% of the plasmid OTUs hosted transmissible plasmids and that isolates of 29% of the plasmid OTUs were able to retransfer the previously characterized mobilizable-cryptic plasmid pSmeLPU88b to a third recipient strain. It is noteworthy that isolates belonging to 14% of the plasmid OTUs proved to be refractory to the entrance of the model plasmid pSmeLPU88b, suggesting either the presence of surface exclusion phenomena or the occurrence of restriction incompatibility with the incoming replicon. Incompatibility for replication between resident plasmids and plasmid pSmeLPU88b was observed in c. 20% of the OTUs. The results reported here reveal a widespread compatibility among the conjugal functions of the cryptic plasmids in S. meliloti, and this fact, together with the observed high proportion of existing donor genotypes, points to the extrachromosomal compartment of the species as being an extremely active plasmid mobilome.

Prediction of physical properties of nanofiltration membranes using experiment and theoretical models

Two commercial nanofiltration (NF) membranes, viz., Desal-HL and NF 700 MWCO were investigated experimentally using neutral and charged solutes, viz., glucose, sodium chloride and magnesium chloride. Effect of pH was studied for sodium chloride rejection and isoelectric point of the membrane was deduced. Experimental results were analyzed using Donnan steric pore and dielectric exclusion models. Dielectric exclusion arises due to the difference in dielectric constant between the bulk and the nano-pore. Born dielectric effect was used as dielectric exclusion phenomena in the present investigation. Stokes–Einstein, Born effective and Pauling radii were used for theoretical simulation, which accurately predicted different charge densities. Empirical correlations were proposed between charge density, concentration and pH for each radius. Charge density decreased drastically when dielectric exclusion term was included in the theoretical model, which showed the real physical characteristics of the membranes employed. Charge density and radius of pore was found to be an important surface parameter in predicting the separation effects in NF membranes.

Hofmeister Effects on Poly(NIPAM) Microgel Particles: Macroscopic Evidence of Ion Adsorption and Changes in Water Structure

The term Hofmeister effects is broadly used to refer to ionic specificities in many different physical, chemical and biological phenomena. The origin of this ionic specificity is sought in two interdependent microscopic sources: 1) the peculiarities of the solvent structure near surfaces and around the ions, and 2) specific ion adsorption-exclusion mechanisms near a surface. In this work, Hofmeister effects on poly(N-isopropylacrylamide) [poly(NIPAM)]-based microgels are examined. Poly(NIPAM) particles are thermally sensitive microgels exhibiting volume-phase transitions with temperature. This temperature-sensitive system seems to be suitable for the independent observation of the two microscopic sources of Hofmeister effects. On the one hand, volume-phase transition, evaluated by photon correlation spectroscopy (PCS), gives information about how the presence of ions changes the water structure around the poly(NIPAM) chains. On the other hand, electrokinetic studies show relevant data about ionic adsorption-exclusion phenomena at the polymer surface.

International knowledge and innovation networks for European integration, cohesion, and enlargement*

Nowadays, it is widely accepted that knowledge and learning are the core of competitiveness, international division of labour and agglomeration and exclusion phenomena. Yet we are still in need of a better understanding of the processes which allow access by individual regions both to codified knowledge and RTD networks as well as tacit knowledge and know‐how at the international/interregional level. This paper will discuss possible approaches to analyse the mechanisms which operate at the international/interregional level and lead to higher forms of integration of industrial and service firms, not only in a commercial or financial perspective but also in knowledge and innovation networks. It will point to a need to develop policy strategies in support of institutions that create and transfer knowledge on a European scale and outline open questions for the creation of the necessary institutional background for the creation and the support of knowledge and innovation networks at this level and for the conditions of its transferability to Objective 1 regions and the EU new member states and candidate countries.

A non-commutativen-particle 3D Wigner quantum oscillator

An n-particle 3-dimensional Wigner quantum oscillator model is constructed explicitly. It is non-canonical in that the usual coordinate and linear momentum commutation relations are abandoned in favour of Wigner's suggestion that Hamilton's equations and the Heisenberg equations are identical as operator equations. The construction is based on the use of Fock states corresponding to a family of irreducible representations of the Lie superalgebra sl(1|3n) indexed by an A-superstatistics parameter p. These representations are typical for p\geq 3n but atypical for p<3n. The branching rules for the restriction from sl(1|3n) to gl(1) \oplus so(3) \oplus sl(n) are used to enumerate energy and angular momentum eigenstates. These are constructed explicitly and tabulated for n\leq 2. It is shown that measurements of the coordinates of the individual particles gives rise to a set of discrete values defining nests in the 3-dimensional configuration space. The fact that the underlying geometry is non-commutative is shown to have a significant impact on measurements of particle separation. In the atypical case, exclusion phenomena are identified that are entirely due to the effect of A-superstatistics. The energy spectrum and associated degeneracies are calculated for an infinite-dimensional realisation of the Wigner quantum oscillator model obtained by summing over all p. The results are compared with those applying to the analogous canonical quantum oscillator.

Dissociation of Colloidal Spheres According to LMO Law

New detailed results for ionic distributions around charged spherical surfaces in electrolyte solutions are presented using the formulation of dissociative electrical double layers (DEDL) with the Lubetkin, Middleton, and Ottewill dissociative law. Wide ranges of spherical radii and ionic strengths are considered. From these theoretical results the extent of ionic atmosphere and the number of ions contained therein are calculated to give an estimate of how many ions interact with a colloidal sphere. A new measure of the range of electrostatic repulsions is defined as the sum of the Debye length and the thickness of the co-ion exclusion shell. New results for extremely low charge densities indicate a possibility of significant electrostatic effects in such systems. These results, representing a synthesis of the classical theory of Debye−Hückel interionic interactions with the Derjaguin−Landau−Verwey−Overbeek (DLVO) theory, provide new insights into the co-ion exclusion phenomena in colloidal dispersions and related consequences. The DEDL theoretical approach, with emphasis on electrostatic consistency, has shown a greater explanatory power than the classical DLVO theory. The latter contradicts Maxwellian electrostatics unnecessarily.

Streaming potential and protein transmission ultrafiltration of single proteins and proteins in mixture: β-lactoglobulin and lysozyme

A study of single proteins, β-lactoglobulin and lysozyme of different sizes and electrical characteristic as a function of pH, ionic strength and nature of salt (NaCl or CaCl 2) allows to evaluate the filtration performances. Streaming potential measurements confirm that proteins contribute to the net charge of the system and that the protein tranfer through mineral membranes is governed by ionic and steric exclusion phenomena. This work shows the correlation between protein transmission and streaming potential values which takes into account steric and ionic exclusion. The ionic repulsion decreases the transmission. This one depends on membrane net charge characterised by streaming potential, which depends on the solution composition. This model, which does not take into account interactions between protein and membrane fouling leads to an overestimation of calculated transmission values when proteins are in a mixture. However, it allows a correct estimation of transmission variations versus the studied variables: pH and ionic strength.

Study of Ion Exclusion Using Artificial Reference Samples for Rocks

AbstractMatrix diffusion in rocks has been extensively studied experimentally with various methods including tracer experiments. Comparing the rock-capacity factors (α) for Cl-36 to corresponding values for H-3, an anion-exclusion tendency has been observed in many cases. This study uses a well-characterized reference material: porous silica (Geltech Inc.), with pore diameters of 2.5, 5, 7.5 and 20 nanometers. The equilibration-leaching method and tracers H-3 (H-3) and Cl-36 (Cl−) were used to determine the capacity factors of the samples in three molarities of NaCl solution: 0.0026, 0.01 and 0. 1 mol/liter. The ratio αcl/αH-3 gives the anion exclusion for each solution/pore diameter combination. A clear anion-exclusion tendency was seen both as a function of the decreasing pore diameter and liquid molarity.The modeling was based on the assumption that the silica surface acts as a proton donor according to SiOH = SiO− + H+. The pore dimensions are also included in the calculations. In the case of the silica samples, good agreement was found when comparing the experimental and calculated values of chloride exclusion. This suggests that the surface complexation model for matrix diffusion can explain the observed exclusion phenomena in rocks although the parameters needed for the application of the model are difficult to obtain in the case of rocks.

Introduction and spread of Thiara granifera (Lamarck, 1822) in Martinique, French West Indies

We followed the invasion dynamics of the Oriental thiarid snail Thiara granifera on the Martinique island, French Antilles. This freshwater species was first discovered in 1991 in the Charpentier River, and its spread has since been analysed based on a yearly survey of the malacological fauna at more than 100 sites covering the whole island and representing 50 river systems and three pools. Four river systems were sampled at many sites. Thirteen river systems were colonized by 1997. Colonization within river systems occurred at a speed greater than 1km per year, probably resulting from both active and passive dispersal. Our results can, on the whole, be explained by a simple diffusion process. However, stratified diffusion has to be invoked in at least one river. Moreover, colonization was faster downstream than upstream, suggesting that current velocity plays a significant role in dispersal. Dispersal also occurred between river systems at a mean distance of almost 10km, though with a large variance, in accordance with the scattered colony model of stratified diffusion. The relative frequencies of T. granifera and Melanoides tuberculata, another recent invader of Martinique, were followed at three sites on the Lezarde River. The first species quickly outnumbered the second, though never wiped it out. The data therefore do not support any exclusion phenomena between these two parthenogenetic invaders. Our analysis does not indicate any obvious influence of the rise of T. granifera on the local freshwater fauna.

Effect of adherent Lactobacillus spp. on in vitro adherence of salmonellae to the intestinal epithelial cells of chicken.

Single strains of Lactobacillus acidophilus and Lact. fermentum, isolated from chicken intestine, were used to study in vitro interactions with Salmonella enteritidis, Salm. pullorum or Salm. typhimurium in an ileal epithelial cell (IEC) radioactive assay. Exclusion, competition and displacement phenomena were investigated by respectively incubating (a) lactobacilli and IEC together, prior to addition of salmonellae, (b) lactobacilli, IEC and salmonellae together, and (c) salmonellae and IEC, followed by the lactobacilli. Lactobacilli were selected for study because of their strong ability to adhere to IEC and poor aggregation with salmonellae. The results demonstrated that Lact. acidophilus significantly reduced (P < 0.05) the attachment of Salm. pullorum to IEC in the tests for exclusion and competition, but not in the displacement tests. Lactobacillus fermentum was found to have some ability to reduce the attachment of Salm. typhimurium to IEC under the conditions of exclusion (P < 0.08), competition (P < 0.09), but not displacement. However, both Lact. acidophilus and Lact. fermentum were unable to reduce the adherence of Salm. enteritidis to IEC under any of the conditions.