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A comprehensive study of the molecular vibrations in solid-state benzylic amide [2]catenane
(Royal Society of Chemistry, 2019) Romero Muñiz, Carlos; Paredes Roibás, Denís; Hernanz, Antonio; Gavira Vallejo, José María
The interpretation of vibrational spectra is often complex but a detailed knowledge of the normal modes responsible for the experimental bands provides valuable information about the molecular structure of the sample. In this work we record and assign in detail the infrared (IR) spectrum of the benzylic amide [2]catenane, a complex molecular solid displaying crimped mechanical bonds like the links of a chain. In spite of the large size of the unit cell, we calculate all the vibrational modes of the catenane crystal using quantum first-principles calculations. The activity of each mode is also evaluated using the Born effective charges approach and a theoretical spectrum is constructed for comparison purposes. We find a remarkable agreement between the calculations and the experimental results without the need to apply any further empirical correction or fitting to the eigenfrequencies. A detailed description in terms of the usual internal coordinates is provided for over 1000 normal modes. This thorough analysis allows us to perform the complete assignment of the spectrum, revealing the nature of the most active modes responsible for the IR features. Finally, we compare the obtained results with those of Raman spectroscopy, studying the effects of the rule of mutual exclusion in vibrational spectroscopy according to the different levels of molecular symmetry embedded in this mechanically interlocked molecular compound.
Assessment of the Potential of Using Nanofiltration Polymeric and Ceramic Membranes to Treat Refinery Spent Caustic Effluents
(MDPI, 2022-06-17) Rita, Ana Isabel; Nabais, Ana Rita; Neves, Luisa A.; Huertas Penela, Rosa María; Santos, María; Madeira, Luis M.; Sanches, Sandra
Spent caustic effluents are very challenging due to their very hazardous nature in terms of toxicity as well as their extreme pH (approximately 12–14). Spent caustic has presented a challenge for wastewater treatment in refineries, due to its composition rich in mercaptans, sulfides and other aromatic compounds. To address such problems, membrane filtration was studied using real effluents from Sines Refinery, in Portugal. The present study attempts to assess the potential for spent caustic treatment with nanofiltration (NF) polymeric and ceramic membranes, assessing membrane life expectancy. For that, membrane aging studies in static mode were performed with the polymeric membrane before attempting NF treatment (dynamic studies). A ceramic membrane was also tested for the first time with this type of effluents, though only in dynamic mode. Although the polymeric membrane performance was very good and in accordance with previous studies, its lifespan was very reduced after 6 weeks of contact with spent caustic, compromising its use in an industrial unit. Contrarily to expectations, the ceramic membrane tested was not chemically more resistant than the polymeric one upon direct contact with spent caustic (loss of retention capacity in less than 1 h in contact with the spent caustic). The results obtained suggest that a pH of 13.9 is very aggressive, even for ceramic membranes.
Assignment of the Raman Spectrum of Benzylic Amide [2]Catenane: Raman Microscopy Experiments and First-Principles Calculations
(American Chemical Society, 2018) Romero Muñiz, Carlos; Paredes Roibás, Denís; Hernanz, Antonio; López García, Concepción; Gavira Vallejo, José María
In this work, we use Raman spectroscopy and quantum first-principles calculations to unveil the experimental spectrum of a complex molecular solid-like benzylic amide [2]catenane, a representative example of a mechanically interlocked molecular architecture. We use large-scale density functional theory calculations to obtain the complete set of vibrational normal modes of the catenane crystal, whose unit cell contains 544 atoms. Subsequently, we demonstrate that these calculations are able to accurately reproduce the experimental Raman spectrum of this molecular compound, without introducing any empirical corrections or fittings in the calculated eigenfrequencies. Thanks to the good agreement between the experimental and theoretical spectra, it is possible to carry out the complete assignment of the main vibrational modes responsible for the whole spectrum. A detailed description in terms of the usual internal coordinates is given for all of these representative modes. This description, rather difficult from the experimental point of view, provides valuable information about the molecular structure of this compound, compatible with experimental evidences reported in the literature.
Can gas hydrate structures be described using classical simulations?
(American Institute of Physics (AIP), 2010-02-13) Conde, M. M.; Vega, Carlos; Noya, Eva G.; Ramírez, Rafael
Quantum path-integral simulations of the hydrate solid structures have been performed using the recently proposed TIP4PQ/2005 model. By also performing classical simulations using this model, the impact of the nuclear quantum effects on the hydrates is highlighted; nuclear quantum effects significantly modify the structure, densities, and energies of the hydrates, leading to the conclusion that nuclear quantum effects are important not only when studying the solid phases of water but also when studying the hydrates. To analyze the validity of a classical description of hydrates, a comparison of the results of the TIP4P/2005 model (optimized for classical simulations) with those of TIP4PQ/2005 (optimized for path-integral simulations) was undertaken. A classical description of hydrates is able to correctly predict the densities at temperatures above 150 K and the relative stabilities between the hydrates and iceIh. The inclusion of nuclear quantum effects does not significantly modify the sequence of phases found in the phase diagram of water at negative pressures, namely, Ih→sII→sH. In fact the transition pressures are little affected by the inclusion of nuclear quantum effects; the phase diagram predictions for hydrates can be performed with reasonable accuracy using classical simulations. However, for a reliable calculation of the densities below 150 K, the sublimation energies, the constant pressure heat capacity, and the radial distribution functions, the incorporation of nuclear quantum effects is indeed required.
Cavity Ring-Down Absorption Spectroscopy: Optical Characterization of ICl Product in Photodissociation of CH2ICl at 248 nm
(American Chemical Society, 2018-10-02) Paredes Roibás, Denís; Balaganesh, Muthiah; Kasai, Toshio; Lin, King Chuen; Gavira Vallejo, José María
Combination of Zinc Oxide Photocatalysis with Membrane Filtration for Surface Water Disinfection
(MDPI, 2023-01-02) Martínez Sosa, Santiago; Huertas Penela, Rosa María; Pereira, Vanessa Jorge
Increase water usage has led to its deterioration. Pollutants are easily found in the aquatic environment and treatment techniques must keep improving to meet the current needs and future demands. Membranes are attractive for water treatment, but limitations like fouling and the highly concentrate produced affect their performance. Combining membrane filtration with photocatalysis provides the opportunity to integrate a self-cleaning step during membrane filtration. In this work, we studied two simple and efficient approaches to combine membrane filtration with zinc oxide nanoparticles (using the catalyst in suspension and immobilized) activated by light emitting diodes (LED) emitting light at 365 nm. Both systems were used to test the disinfection efficiency in real surface water, compared in terms of catalyst concentration in the permeate stream (below the limit of detection) and its recovery after filtration (higher that 74%). The system’s capability to retain and inactivate target bacteria (total coliforms and E. coli) in the retentate stream was tested with samples of real surface water. The results obtained show that both configurations led to an improved performance in comparison to the membrane treatment alone with a higher retention of the bacteria (not detected in the permeate samples) and higher treatment of the retentate. For the modified membranes, different catalyst concentrations and thermal treatments were tested. The performance of all the processes was evaluated in terms of the level of treatment achieved and the permeate flux. All the modified membranes showed an efficient retention of the target bacteria from surface water, with higher performances than the unmodified membrane (96.2% for total coliforms and 94.9% for E. coli). Remarkable retention and treatment of the retentate was achieved using a membrane modified with a catalyst load of 125 mg subject during two hours to a thermal treatment of 300 °C. This modification has a performance comparable to the system with the same catalyst load in suspension. During operation, the permeate flux reduction is lower with the modified membranes which could lead to longer operation times without the need of further cleaning or replacement. The combined system, ceramic membranes modified with zinc oxide and UV-A LEDs proved to be effective to retain and disinfect water quality indicator bacteria present in real surface water matrices.
Development of highly selective composite polymeric membranes for Li+/Mg2+ separation
(Elsevier, 2021-02-15) Saif, Hafiz Muhammad; Huertas Penela, Rosa María; Pawlowski, Sylwin; Crespo, João Goulão; Velizarov, Svetlozar
To meet the exponentially rising demand for lithium, it becomes vital to develop environmentally friendly processes for its recovery from brines, salt lakes and/or seawater. In this work, novel composite lithium transport selective polymeric membranes were developed to separate lithium and magnesium ions. Hydrogen manganese oxide (HMO) (at weight percentage from 0 to 25%), polystyrene sulfonate sodium salt (PSS–Na) and lithium triflate (LiCF3SO3) were added into the sulfonated polyethersulfone (SPES) matrix to prepare composite membranes. The developed membranes showed high mechanical stability and a homogeneous distribution of HMO. The most promising membrane, containing 20% (w/w) of HMO, showed an almost 13 times higher Li+ ionic conductivity (8.28 mS/cm) compared to the control composite membrane (without HMO) and an average ideal selectivity of 11.75 for the Li+/Mg2+ pair. The composite-20% membrane had the lowest intermolecular distance between the polymer chains (according to X-ray diffraction (XRD) analysis), the most flexible structure (lowest Tg) and showed the homogeneous dispersion of HMO (SEM images), which explains its highest Li+/Mg2+ selectivity among the tested membranes. The lithium ion transport performance and separation efficiency were investigated through diffusion dialysis experiments, under different operating conditions. A binary separation factor of 9.10 for Li+/Mg2+ and Li+ molar flux of 0.026 mol/(m2.h) was achieved without applying any external potential difference. When an external potential difference of 0.2 V was applied, the binary separation factor of Li+/Mg2+ pair was 5, while the Li+ molar flux increased almost 5 times. The obtained results provide the basis to design and develop composite lithium transport selective polymeric membranes, thus representing a promising step for future implementation of such membranes to recover lithium from saline streams.
Dielectric and Molecular Dynamics Study of the Secondary Relaxations of Poly(styrene-co-methylmethacrylate) Copolymers: Influence of the Molecular Architecture
(EDP Sciences ; Springer Verlag (Germany) ; Società Italiana di Fisica, 2011-11-07) Encinar, M.; Prolongo, M. G.
The effect of the structure of copolymers (random, alternate or diblock) on their dynamics has been studied by dielectric spectroscopy. Six copolymers of styrene and methyl methacrylate (three diblocks, one alternate and two random) have been studied. The results show that the sub-Tg transitions of the diblock samples can be described by one asymmetric Havriliak-Negami (HN) function, while two are necessary for the rest of the copolymers (β and γ relaxations). The characteristic times of the sub-Tg relaxations show an Arrhenius temperature dependence and there is a strong coupling of the α and β relaxations at high temperatures. The deconvolution of the merging relaxations has been made in the framework of the Williams Ansatz set out in terms of Havriliak-Negami distributions. The γ relaxation may be assigned to the rotation of the methyl methacrylate group in a styrene-rich environment. The Molecular Dynamics simulations of a poly(methyl methacrylate) homopolymer and of the alternate copolymer are in qualitative agreement with the experimental results, although they predict smaller values for the activation energy of the sub-Tg relaxations.
Electropsun non-woven luminescent two-dye pH sensors: Effect of morphology on the sensing performance
(Elsevier, 2024-08-24) Vieira, Tiago; Canejo, João; Huertas Penela, Rosa María; Oliveira, Hugo M.; Godinho, María H.; Crespo, João Goulão; Portugal, Carla A. M.
Electrospun (ES) non-woven matrices are regarded as promising platforms for the development of miniaturized sensing systems with improved detection capacity. Their high specific surface area and void-to-volume ratio are expected to promote higher and faster interaction of the sensing molecular probes with the target stimuli increasing sensor sensitivity and response time. However, the poor light transparency of ES non-woven mats appears as the main limiting effect regarding their use as optical sensor platforms being important to determine to what extent it affects the sensor prediction accuracy. This work addresses this question providing a comparative analysis of the performance of flat cast and ES non-woven cellulose acetate luminescent platforms loaded with a pH sensitive dye-pair, i.e. fluorescein isothiocyanate (FITC) and rhodamine 6 G (R6G). This study follows a comprehensive approach aiming at clarifying the effect of the platform morphology on the sensitivity of their spectral properties to pH and to understand about the advantages of using dual dye systems for pH detection. The presence of R6G improved remarkably the sensitivity of these ES matrices extending the analytical capacity of the probes to the alkaline range. The emission of ES matrices showed stronger sensitivity to pH. However, pH prediction accuracy was found to depend crucially on a synergistic effect from the platform morphology and the signal analysis methodology. ES non-woven matrices allows for accurate pH prediction, characterized by determination errors < 10 % for pH < 10, by exponential analysis of the dye-pair emission at λExc of 450 nm and λEm of 519 nm. Furthermore, it shows a strong reduction of the determination errors, at extremely acidic conditions, resulting in values comparable to that obtained by analysis of the emission signal from flat cast platforms with more complex Förster Resonance Energy Transfer (FRET) methodologies.
Fibrillar morphologies of hydrogels obtained from a lamellar medium
(Elsevier, 2011-10-17) Renamayor, Carmen S.; Esteban Pacios, María Isabel
Hydrogels are suitable for multiple applications and their properties are strongly dependent on their morphology. Sponge-like morphologies are obtained in conventional hydrogels when the polymerization is performed in isotropic media. Fibrillar morphologies imparting new properties to hydrogels are expected when the reacting medium is anisotropic. Here, we synthesize such fibrillar hydrogels by polymerization in a lamellar medium formed by 1,4- bis(2-ethylhexyl)sodium sulfosuccinate (AOT) and water. At high surfactant content this objective is achieved, and the thickness of the obtained fibrils (0.1-1 μm) can be correlated with the physical properties of the lamellar system. At intermediate AOT concentrations, the morphology is hierarchical, with primary closed pores containing a secondary fibrillar structure that fills the pores. For low AOT concentrations, the crosslinking process is unhindered, and the hydrogels are mechanically consistent with a sponge-like morphology having large (10-102 μm) void pores. The time evolution of the mesophase as polymerization advances is followed by small angle X-ray scattering.
Fractionation of polyacrylamide in lamellar mesopashes
(2014-05-16) Agzenai Ben Salem, Yahya; Renamayor, Carmen S.; Esteban Pacios, María Isabel
Heat capacity of water : a signature of nuclear quantum effects
(American Institute of Physics (AIP), 2010-01-03) Vega, Carlos; Conde, M. M.
In this note we present results for the heat capacity at constant pressure for the TIP4PQ/2005 model, as obtained from path-integral simulations. The model does a rather good job of describing both the heat capacity of iceIh and of liquid water. Classical simulations using the TIP4P/2005, TIP3P, TIP4P, TIP4P-Ew, simple point charge/extended, and TIP5P models are unable to reproduce the heat capacity of water. Given that classical simulations do not satisfy the third law of thermodynamics, one would expect such a failure at low temperatures. However, it seems that for water, nuclear quantum effects influence the heat capacities all the way up to room temperature. The failure of classical simulations to reproduce Cp points to the necessity of incorporating nuclear quantum effects to describe this property accurately.
Impact of Depression and Cardiovascular Risk Factors on Cognitive Impairment in patients with Atrial Fibrillation: A Systematic Review and Meta-Analysis
(ELSEVIER, 2024) Del Pino Castillo, Maria; Rivero, Pablo; Taylor, Amy; Gabriel, Rafael S.; https://orcid.org/0009-0002-3990-6849; https://orcid.org/0000-0002-3631-8374
BACKGROUND: Atrial fibrillation (AF) is a common cardiac arrhythmia associated with significant cardiovascular morbidity and mortality, as well as cognitive impairment (CI). The interplay between AF and CI is complex, involving various pathophysiological changes and numerous risk factors. Among them, depression has emerged as a significant contributor to both AF and CI, further complicating the relationship between these conditions. OBJECTIVES: This systematic review and meta-analysis aimed to investigate the influence of depression on the development of cognitive impairment in AF patients and assess the predictive value of the CHA2DS2-VASc score for CI risk. METHOS: We searched PubMed, Scopus, and Web of Science for relevant studies without language or date restrictions. Ten studies, comprising 1,605,577 participants, were included. A random-effects model was used for meta-analysis, and heterogeneity was assessed using I2 statistics. Funnel plots and Egger’s test evaluated publication bias. RESULTS: Depression significantly increased the risk of CI in AF patients (OR: 2.23, 95% CI: 1.54-3.21, p<0.01; I2=99%). This association persisted in studies excluding baseline CI (OR: 1.95, 95% CI: 1.33-2.85, p<0.01; I2=88%). Subgroup analysis confirmed these results for both prospective (OR: 1.78, 95% CI: 0.92-3.44, p=0.02; I2=65%) and retrospective studies (OR: 2.63, 95% CI: 1.75-3.93, p<0.01; I2=100%). Analysis of CHA2DS2-VASc risk factors showed associations with CI, particularly cerebrovascular disease (OR: 1.86, 95% CI: 1.61-2.16). CONCLUSIONS: Our findings support the association between depression and cognitive impairment in AF patients, demonstrating the importance of addressing mental health in cardiovascular care. Future research is necessary for a comprehensive understanding of this association.
Impact of Small Adsorbates in the Vibrational Spectra of Mg- and Zn-MOF-74 Revealed by First-Principles Calculations
(American Chemical Society, 2020) Romero Muñiz, Carlos; Merkling, Patrick; Calero, Sofía; Gavira Vallejo, José María
In this work, we analyze the influence of small adsorbates on the vibrational spectra of Mg- and Zn-metal–organic framework MOF-74 by means of first-principles calculations. In particular, we consider the adsorption of four representative species of different interaction strengths: Ar, CO2, H2O, and NH3. Apart from a comprehensive characterization of the structural and energetic aspects of empty and loaded MOFs, we use a fully quantum ab initio approach to evaluate the Raman and IR activities of the normal modes, leading to the construction of the whole vibrational spectra. Under this approach, not only are we able to proceed with the complete assignment of the spectra in terms of the usual internal coordinates but also we can discern the most relevant vibrational fingerprints of the adsorbates and their impact on the whole MOF spectra. On the one hand, some of the typical vibrational modes of the small molecules are slightly shifted but still visible when adsorbed on the MOFs, especially those appearing at high wavenumbers where the empty MOFs lack IR/Raman signals. On the other hand, some bands arising from the organic ligands are affected by the presence of the absorbates, displaying non-negligible frequency shifts, in agreement with recent experiments. We find a strong correlation between all of these frequency shifts and the interaction strength of the adsorbate with the hosting framework. The findings presented in this work expand the capabilities of vibrational spectroscopy techniques to analyze porous materials and can be useful for the design of sensors and new devices based on MOF technology.
Micro Raman Spectroscopy of Epipalaeolithic Decorated Pebbles from Arroyo Moreras 2 (Parque Darwin, Madrid)
(The Royal Society of Chemistry, 2019-11) Hernanz, Antonio; Bueno Ramírez, Primitiva; Balbín Behrmann, Rodrigo de; Morín de Pablos, Jorge; Juana Ortín, Cristina de; Gavira Vallejo, José María
Pigment vestiges on the three decorated pebbles from the excavation of Parque Darwin (Madrid), level 8470 ± 70 BP have been identified by Micro Raman Spectroscopy. Haematite and amorphous carbon were used as pigments. Microscopic contamination spots with ε-copper-phthalocyanine blue, have been detected. The analysis of the pigments used, together with their previously unknown chronology and open-air location, constitute a new point of reference for the technical and cultural uses of symbology among hunter-gatherers in southern Europe.
Micro-Raman spectroscopy of rock paintings from the Galb Budarga and Tuama Budarga rock shelters, Western Sahara
(Elsevier, 2018-03) Iriarte, Mercedes; Hernanz, Antonio; Sáenz de Buruaga, Andoni; Gavira Vallejo, José María; Martín Fernández, Santiago
Rock paintings of two recent discovered rock shelters, Galb Budarga and Tuama Budarga, from the southeastern area of the Western Sahara, Sahrawi Arab Democratic Republic, have been studied by micro-Raman spectroscopy and scanning electron microscopy coupled with energy dispersive X-ray spectrometry in order to characterize the composition of the materials present in the painting panels. An unusual white pigment has been used in the zoomorphic pictographs of the Galb Budarga shelter which main components are the anhydrite (CaSO4) polymorphs I and II. Red and orange zoomorphic figures and ancient Berber scripts have been painted in the Tuama Budarga rock shelter. Haematite (α-Fe2O3) is the main component of the paints used; amorphous carbon and different manganese oxides have also been detected. Accretions of gypsum (CaSO4·2H2O) and anhydrite have been observed on the shelter wall used to paint. α-Quartz (α-SiO2), albite (NaAlSi3O8), dolomite, CaMg(CO3)2, calcite (CaCO3) and traces of hydroxylapatite (Ca10(PO4)6(OH)2) have been identified in the rocks supporting the paintings of both sites. Layers of calcium oxalates, whewellite (CaC2O4·H2O) and weddellite (CaC2O4·(2 + x)H2O, x ≤ 0.5) cover the pictorial panels of these rock shelters. A microestratrigraphic study of the paint used in the Tuama Budarga shelter revealed that the pigment layer is bracketed between oxalate layers.
Non-stoichiometric polymer-surfactant complexes obtained in a lamellar lyotropic medium
(Springer Verlag (Germany), 2012-03-08) Agzenai Ben Salem, Yahya; Renamayor, Carmen S.; Esteban Pacios, María Isabel
The addition of a polyelectrolyte to lamellar media formed by an oppositely charged surfactant often leads to the coexistence of several phases without macroscopic phase separation, which makes their characterization difficult. Here, the effect of the polydiallyldimethylammonium chloride (PD) on the lamellar liquid crystal formed by the anionic surfactant Aerosol OT (AOT) and water is investigated. SAXS results are discussed regarding the changes in the lamellar spacing as a function on the PD or AOT concentrations. In most of the samples two lamellar phases, without macroscopic phase separation, are detected. One of them is a typical swollen phase, while the other is a collapsed phase, which corresponds to the polymer-surfactant complex. At concentrations of polymer up to 3 %wt the two lamellar phases coexist, however, at a critical concentration higher than 3 %wt, the swollen phase becomes isotropic, and a macroscopic phase separation takes place. A simple model is proposed to calculate the composition of the phases when macroscopic phase separation does not occur. The results thus calculated show that generally the polymer-surfactant complexes are non-stoichiometric containing a lesser amount of polymer than ideally expected.
Occurrence and Treatment of Antibiotic-Resistant Bacteria Present in Surface Water
(MDPI, 2023-04-11) Sério, João; Marques, Ana Paula; Huertas Penela, Rosa María; Crespo, João Goulão; Pereira, Vanessa Jorge
According to the World Health Organization, antibiotic resistance is one of the main threats to global health. The excessive use of several antibiotics has led to the widespread distribution of antibiotic-resistant bacteria and antibiotic resistance genes in various environment matrices, including surface water. In this study, total coliforms, Escherichia coli and enterococci, as well as total coliforms and Escherichia coli resistant to ciprofloxacin, levofloxacin, ampicillin, streptomycin, and imipenem, were monitored in several surface water sampling events. A hybrid reactor was used to test the efficiency of membrane filtration, direct photolysis (using UV-C light emitting diodes that emit light at 265 nm and UV-C low pressure mercury lamps that emit light at 254 nm), and the combination of both processes to ensure the retention and inactivation of total coliforms and Escherichia coli as well as antibiotic-resistant bacteria (total coliforms and Escherichia coli) present in river water at occurrence levels. The membranes used (unmodified silicon carbide membranes and the same membrane modified with a photocatalytic layer) effectively retained the target bacteria. Direct photolysis using low-pressure mercury lamps and light-emitting diode panels (emitting at 265 nm) achieved extremely high levels of inactivation of the target bacteria. The combined treatment (unmodified and modified photocatalytic surfaces in combination with UV-C and UV-A light sources) successfully retained the bacteria and treated the feed after 1 h of treatment. The hybrid treatment proposed is a promising approach to use as point-of-use treatment by isolated populations or when conventional systems and electricity fail due to natural disasters or war. Furthermore, the effective treatment obtained when the combined system was used with UV-A light sources indicates that the process may be a promising approach to guarantee water disinfection using natural sunlight.
On operation of reverse electrodialysis (RED) and membrane capacitive deionisation (MCDI) with natural saline streams: A critical review
(Elsevier, 2020-02-15) Pawlowski, Sylwin; Huertas Penela, Rosa María; Galinha, Cláudia F.; Crespo, João Goulão; Velizarov, Svetlozar
Environment-friendly production of power and clean water is one of the major goals of 2030 Agenda for Sustainable Development, and can be achieved by emerging electromembrane processes, such as reverse electrodialysis (RED) and membrane capacitive deionisation (MCDI). RED generates electricity from salinity gradient energy sources, while MCDI desalinates (mainly) brackish water. However, fouling, scaling, stack channels clogging and undesired uphill ionic transport can reduce the power output and salt removal efficiency in RED and MCDI, respectively. A practical overview of current problems and challenges of operating and monitoring these processes under real conditions is provided. Appropriate mitigation approaches, which might include feed water pre-treatment, in-situ cleaning strategies and/or development of new antifouling ion-exchange membranes (IEMs) are disclosed. First, a description, analysis and (when possible) normalised comparison of the performance of available RED and MCDI stacks, employing natural saline streams, is presented. Afterwards, it is discussed how fouling formation can be detected, monitored and characterised, which is essential to implement effective pre-treatment and cleaning strategies. Finally, sustainable ways for preparation of appropriate IEMs are selected and presented.
On the accurate direct computation of the isothermal compressibility for normal quantum simple fluids : application to quantum hard spheres
(American Institute of Physics (AIP), 2012-06-26) Sesé, Luis M.
A systematic study of the direct computation of the isothermal compressibility of normal quantum fluids is presented by analyzing the solving of the Ornstein-Zernike integral equation (OZ2) for the pair correlations between the path-integral necklace centroids. A number of issues related to the accuracy that can be achieved via this sort of procedure have been addressed, paying particular attention to the finite-N effects and to the definition of significant error bars for the estimates of isothermal compressibilities. Extensive path-integral Monte Carlo computations for the quantum hard-sphere fluid (QHS) have been performed in the (N,V,T) ensemble under temperature and density conditions for which dispersion effects dominate the quantum behavior. These computations have served to obtain the centroid correlations, which have been processed further via the numerical solving of the OZ2 equation. To do so, Baxter-Dixon-Hutchinson’s variational procedure complemented with Baumketner-Hiwatari’s grand-canonical corrections have been used. The virial equation of state has also been obtained and several comparisons between different versions of the QHS equation of state have been made. The results show the reliability of the procedure based on isothermal compressibilities discussed herein, which can then be regarded as a useful and quick means of obtaining the equation of state for fluids under quantum conditions involving strong repulsive interactions.

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