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In the present study, the effect of short-term salt shocks (13% and 20%) on the performance of a halophilic MBR bioreactor used to treat a hypersaline (5% salt) synthetic wastewater was considered. 13% and 20% salt shocks resulted in a transient and permanent decrease in chemical oxygen demand removal efficiency, respectively which could be correlated with soluble microbial products (SMP) concentration and specific oxygen uptake rate values of the halophilic population. DNA leakage tests suggested that both 13% and 20% short-term salt shocks resulted in some cell structural damage. During both 13% and 20% salt shocks mixed liquor SMP, extracellular polymeric substances (EPS), zeta potential and endogenous respiration increased while relative hydrophobicity, EPS p /EPS c and exogenous respiration decreased; in both cases, however, the pre-shock values for these parameters were restored after the removal of the salt shock. 13% salt shock resulted in a transient increase in the membrane fouling rate and a permanent rise in total membrane resistance (R t). On the other hand, both membrane fouling rate and R t increased during 20% salt shock. Membrane fouling rate initially reduced after the 20% salt shock removal but after 5 days a "TMP jump" occurred. The latter was caused by the higher steady state SMP c and SMP p concentrations after removal of 20% salt shock compared to pre-shock values. This might have either resulted in a decrease in critical flux or an increase in local flux above critical flux in some parts of the membrane. The contribution of cake layer resistance to overall membrane resistance increased after the 13% and 20% salt shocks. The findings of the present study reveal the robustness of halophilic MBRs against salt shocks in the treatment of hypersaline wastewater. However, in cases of very high salt shocks, appropriate membrane fouling reduction strategies should be carried out during its operation. [Display omitted] • 13% salt shock had transient effect on removal performance and membrane fouling. • Membrane fouling worsened in both salt shocks due to change in sludge properties. • TMP jump observed after removal of 20% salt shock and attributed to increased SMP. • 20% salt shock had irreversible effect on removal performance and membrane fouling. • Contribution of cake layer resistance to membrane fouling rose after salt shocks. [ABSTRACT FROM AUTHOR]

For the first time, the oxygen evolution reaction (OER) behavior of commercial catalyst-coated membranes (CCMs) has been studied using an in-house modified rotating disk electrode (MRDE) tip capable of reaching current densities of up to 2 A cm−2. The electrochemical results are comparable with a full PEM electrolysis cell. The kinetic analysis reveals Tafel slopes of about 50 and 60 mV dec−1 for all temperatures with the PEM electrolysis hardware and the MRDE, respectively. The activation energy of the OER obtained with the MRDE and the PEM electrolysis cell are 75 and 68 kJ mol−1, respectively. Detailed cyclic voltammetric measurements of Ir-based CCMs were performed to examine the influence of operating temperature, Ti-based current collectors, the scan rate on the adsorbed charge, and the electro kinetics of the OER. Six different expanded metal Ti current collectors were analyzed in sulfuric acid and their impact on the CCM charging at various temperatures were examined in order to calculate the electrode's inner and outer charge. It was observed that the voltammetric charge is proportional to the coverage of the CCM by the current collector. The MRDE tool presented here is an ideal tool for electrochemical characterization of CCMs and current collectors and allows for an economical and accelerated screening of these important PEM electrolyzer components without the requirement of full cell testing. [ABSTRACT FROM AUTHOR]

Abstract In this research, the ability of preformed aerobic granules, which were formed in slaughterhouse wastewater, was investigated for treatment of real dyeing wastewater. The percentages of real dyeing wastewater in the influent were increased gradually from 50% to 100% in orders to investigate the ability of granules in treating of real dyeing wastewater. According to outcomes, maximum chemical oxygen demand (COD) elimination was up to 87%, while the best percentage of dye removal was about 42.6%. Due to the toxic effect of dyeing wastewater, 43.3% reduction in the amount of specific oxygen uptake rate (SOUR) was observed after 90 day of operation. Furthermore, when the percentages of real dyeing wastewater increased to 100%, the granules collapsed, which lead to decrement of granular ratio (GR). Granules collapsing led to 86.5%, 49.73% and 40% reduction in GR 0.3 , GR 0.5 and GR 1 , respectively. [ABSTRACT FROM AUTHOR]

A novel rotating disk electrode (RDE) tip capable of characterizing catalyst coated substrates and compatible with commercial RDE systems is presented. The RDE tip, which uses a top-oriented Ti-based current collector, is demonstrated with Pt foil and commercial catalyst coated membranes (CCM). The specific activity of the platinum foil for oxygen reduction reaction is about 1.55 mA kinetic cm Pt −2 in 0.1 M HClO 4 at room temperature (20°C), which is in agreement with the measurements reported for polycrystalline Pt. The Ti-based current collector leads to a very small (≈ 5.6%) loss in the electrochemical surface area (ECSA). Hydrodynamic calculations and oxygen reduction measurements confirm that even at the fastest rotation speeds used in this type of measurement (i.e., 1600 rpm), the laminar flow regime (Re ≈ 56) is maintained, allowing one to apply classical RDE analysis. Repeatable and high quality cyclic voltammograms (CVs), oxygen reduction curves, and mass and specific activities for commercial CCMs were obtained in 0.1 M HClO 4 at room temperature (20°C). The activities determined from these experiments are in agreement with those of the H 2 /O 2 fuel cell measurements under equivalent operating conditions. Degradation of the CCM’s catalyst during a 30,000 potential cycling accelerated degradation test (ADT) is performed using a 0.4 mg Pt cm −2 commercial CCM and shows an ECSA loss of ≈ 0.0010 m 2 g Pt −1 cycle −1 and a mass activity loss of ≈ 1.8 × 10 −6 A mg Pt −1 cycle −1 . Details of the design, implementation, and results of this economical and novel approach for characterization of CCMs are presented and discussed. [ABSTRACT FROM AUTHOR]

We demonstrate a new approach that simultaneously converts dissolved carbon dioxide and high salinity waste-water to desalinated water and value-added chemicals in the form of inorganic acids and carbonate salts. A four compartment electrodialysis cell module using anion exchange and cation exchange membranes, and a Pt/Ir-coated Ti anode and Ti mesh cathode was used to produce HCl and NaHCO 3 products from CO 2 and NaCl feed. Cell operation consisted of feeding the cell with carbonic acid (CO 2 dissolved in water) and a saline solution of sodium chloride. Under an applied voltage clear production of inorganic carbon salts and acids was demonstrated. The product fluxes for HCl and NaHCO 3 were ∼0.05 mM cm −2 h −1 on average. A mathematical model for this electrodialysis cell configuration was developed to better understand limitations within the cell which are not available from experimental data including concentration profiles within the intra-membrane channels. [ABSTRACT FROM AUTHOR]

The energy density of lithium metal batteries (LMBs) could be much higher than that of current graphite anode-based LIBs. When a metallic current collector is used for plating/de-plating of lithium (i.e., anode-free lithium metal batteries (AFLMBs)) energy density could be higher by about 70%. However, LMBs suffer from dendritic lithium growth and formation of an unstable solid-electrolyte interface, which requires careful control to improve the cycling performance and the overall safety. The current collector (CC), typically Cu, plays an important role in lithium nucleation/growth, local current density and Li-ion flux distribution. However, the commonly used planar Cu CC does not work satisfactorily, and as such, modifications of Cu CC, for decreasing the local current density, suppressing the lithium dendrite growth, and improving the Coulombic efficiency (CE), have been widely investigated and reported in the literature. This review systematically summarizes the modification methods for Cu CCs and serves as a guide for rational design of modified Cu CCs with tailored structures and properties. Furthermore, misrepresentation and misinterpretation of data, which are often observed in the literature on this topic, are critically discussed and insights into the key challenges and future directions on this topic are presented. [ABSTRACT FROM AUTHOR]

In this study the effect of NaCl, normally found in dye bath wastewaters employing reactive azo dyes, on the performance of sequential anaerobic–aerobic processes for treatment of Reactive Black 5 (RB5) containing media, with concentration in the range 100–500 mg L −1 , was investigated. Three possible scenarios of the sequential anaerobic–aerobic process, namely two stage process and one stage processes employing either anaerobic or activated sludge, were considered. The results showed a statistically significant enhancement of the anaerobic decolourisation efficiency as a result of the addition of 30 g L −1 NaCl to the RB5 containing media for two stage processes and one stage processes employing anaerobic sludge. NaCl at 30 g L −1 concentration also inhibited aerobic colour formation during two stage processes whereas it prevented aerobic decolourisation during one stage processes. HPLC and UV Vis analysis indicated that during anaerobic phase/stage the majority of azo bonds in RB5 molecules cleave whereas the hydrophobicity/MW of the resulting dye reduction metabolites decreases. The same analysis revealed partial mineralisation of RB5 reduction metabolites under aerobic conditions. The results of the present work also showed that the effect of salt on anaerobic decolourisation efficiency, TVFA and methane production was dependent on the exposure history of anaerobic sludge. [ABSTRACT FROM AUTHOR]

Highlights: [•] A MBR with a moderately halophilic consortium used for hypersaline PW treatment. [•] Fairly good O&G and turbidity removal from PWs with no associated membrane fouling. [•] Organic accumulation in the mixed liquor was observed at all salt concentration. [•] Salinity increase caused SVI increase or formation of biomass attached oil bodies. [•] Viscosity and flow behavior index of mixed liquor increased with salt concentration. [Copyright &y& Elsevier]

Highlights: [•] >95% O&G removal from synthetic PW in MBR with halophilic consortium at high OLR. [•] O&G and SMP transient accumulation occurred but did not affect removal performance. [•] Bioflocculation and compressibility of flocs affected by EPS and surface charge. [•] At high OLR non-Newtonain rheology and EPS bulking in the mixed liquor was observed. [•] Membrane fouling mainly due to cake formation at highest OLR of 2.6kgCODm−3 d−1. [Copyright &y& Elsevier]

Highlights: [•] Simple sol–gel synthesis strategy for fabricating multimodal porous carbon. [•] Unique hierarchical macro-, meso-, and micropores and ultrahigh surface area. [•] Stores and releases large electrical charges rapidly whether at a low-mid or high rate. [•] Considerably outperforms carbon black Pearls 2000, CMK-1 and CMK-3. [Copyright &y& Elsevier]

Abstract: Metal oxides such as niobium oxides have been demonstrated as alternative support materials for Pt and non-precious metal catalysts in fuel cells. High surface area and columnar niobium oxide catalyst support structures were produced by the glancing angle deposition (GLAD) technique on 5mm diameter glassy carbon disks. The columnar structures have lengths of about 500nm, diameters of 50nm and an areal density of about 109 cm−2. Annealing under different gas mixtures (Ar/H2) led to the formation of various oxides (Nb2O5, NbO2, or NbO+NbO2). Pt catalyst, with a loading of 0.1mgPt cm−2, was deposited onto these structures by magnetron sputter deposition. Rotating disk electrode characterization of the samples, performed in 0.1M HClO4 electrolyte at room temperature, revealed surface enhancement factors of up to 11 and oxygen reduction specific activities of ≥1mAcm−2 Pt at 0.9V (vs. RHE). The impact of annealing on Nb-O phase formation, conductivity, oxygen reduction activity and stability are discussed. [Copyright &y& Elsevier]

Abstract: The organic redox catalysis of O2 electroreduction to H2O2 in acidic media has been investigated using several quinone and riboflavin catalysts supported on Vulcan XC72 carbon. The synthesis of a novel riboflavinyl–anthraquinone 2-carboxylate ester (RF–AQ) is reported. The activity and selectivity of organic redox catalysts (riboflavin, anthraquinone derivatives and riboflavinyl–anthraquinone 2-carboxylate ester) for the electrosynthesis of H2O2 were investigated by the rotating ring-disk electrode (RRDE) method and potentiostatic electrolysis. Electrodes with 10wt% RF–AQ loading on Vulcan XC-72 showed excellent electrocatalytic activity toward the two-electron oxygen reduction coupled with very good catalyst layer stability. The reaction mechanism for the organic redox catalysis by RF–AQ is discussed. Electroreduction of O2 dissolved in 0.5M H2SO4 under potentiostatic conditions (0.1V vs. RHE) at 21°C using the composite RF–AQ/Vulcan XC72 catalyst (total loading 2.5mgcm−2) deposited on unteflonated Toray® carbon paper, generated H2O2 with an initial rate of 21μmolh−1 cmgeo −2 and a stable current efficiency of 70%. [Copyright &y& Elsevier]

Abstract: Numerous transition metal–carbon composite catalysts (M=V, Zn, Ni, Sn, Ce, Ba, Fe, Cu) have been synthesized and tested for electroreduction of O2 to H2O2, The activity and selectivity of all synthesized catalysts for electrosynthesis of H2O2 were determined by the rotating ring-disk electrode method in acidic and neutral electrolytes. The Co-based catalysts in general showed the highest activity towards H2O2 formation. Experiments with different loading contents of Co showed that the activation overpotential losses of oxygen reduction to H2O2 reduces as loading increases to about 4wt% Co. Addition of Co beyond this level did not seem to impact the overpotential losses. The cobalt-based catalysts, were spray-coated onto 120μm thick Toray® graphite substrates, and were studied in bulk electrolysis cells for up to 100h at potentiostatic conditions (0.25V vs. RHE) in pH 0, 3, and 7 electrolytes. At (25°C and 1bar) with a catalysts loading of about and using dissolved O2 in 0.5M H2SO4, typical H2O2 electrosynthesis rates of about were reached with current efficiencies of about 85±5% at 0.25V (vs. RHE). [Copyright &y& Elsevier]

Abstract: The use of membrane sequencing batch reactors, operated at HRT of 8, 16 and 24h, was considered for the treatment of a synthetic petroleum wastewater. Increase in HRT resulted in statistically significant decrease in MLSS. Removal efficiencies higher than 97% were found for the three model hydrocarbon pollutants at all HRTs, with air stripping making a small contribution to overall removal. Particle size distribution (PSD) and microscopic analysis showed reduction in the protozoan populations in the activated sludge with decreasing HRT. PSD analysis also showed a higher proportion of larger and smaller sized particles at the lowest HRT. The rate of membrane fouling was found to increase with decreasing HRT; SMP, especially carbohydrate SMP, and mixed liquor apparent viscosity also showed a pronounced increase with decreasing HRT, whereas the concentration of EPS and its components decreased. FTIR analysis identified organic compounds as the main component of membrane pore fouling. [Copyright &y& Elsevier]

Abstract: In the present study the performance of anaerobic–aerobic one and two stage processes for the biological treatment of synthetic wastewaters containing Reactive Black 5 (RB5) were studied and compared with each other. In both processes the majority of colour removal by biodegradation occurred under anaerobic environment. The colour change under aerobic conditions was correlated with extent of anaerobic decolourisation in the preceding phase/stage of the process. Partial mineralisation of the anaerobic dye metabolites, roughly to the same extent, was achieved aerobically in both one stage and two stage processes. The majority of COD was removed in the anaerobic stage for two stage processes and aerobic stage in one stage processes. In one stage processes, the exposure of anaerobic sludge to alternating anaerobic–aerobic environment decreased anaerobic decolourisation efficiency and COD removal; when employing activated sludge, the same exposure enhanced anaerobic substrate utilisation whereas the effect on the anaerobic decolourisation efficiency depended on RB5 concentration. The comparative performance of one and two stage processes in terms of overall dye decolourisation depended on RB5 concentration. Both types of processes brought about similar overall COD removal. Increase in RB5 concentration, in the range studied, resulted in decrease in overall COD removal for both processes. [Copyright &y& Elsevier]

Abstract: The kinetics of N2O electroreduction in the absence and presence of methanol was studied between 295 and 333K on polycrystalline Pt and Pd electrodes in 0.1M NaOH. In the absence of methanol the reduction of N2O on Pd is more facile than on Pt as shown by the approximately four times lower apparent activation energy and lower Tafel slope (Pt: 0.111±0.019Vdec−1, Pd: 0.084±0.007Vdec−1 at 295K). Two different electroreduction mechanisms are proposed for Pt and Pd with and without participation of underpotential deposited hydrogen, respectively. The selectivity of Pt and Pd electrodes toward both N2O electroreduction and methanol (0.5 and 1M) oxidation at 295K was also investigated. Pt based electrocatalysts are promising candidates for the anode of a mixed reactant CH3OH–N2O fuel cell due to inhibition of N2O reduction by chemisorbed methanol. Pd on the other hand is a selective cathode electrocatalyst since N2O reduction takes place fairly actively in the presence of 1M methanol, while methanol oxidation is inhibited. [Copyright &y& Elsevier]

Abstract: We report on extensive measurements of oxygen reduction activity of Pt and Pt–Co–Mn electrocatalysts using the rotating ring-disk electrode (RRDE) method. The electrocatalysts were prepared by sputtering from Pt or Pt, Co and Mn targets onto 3M''s nano-structured thin film support (NSTF) structures. The area specific activity of Pt/NSTF, measured in 0.1M HClO4 and at room temperature, is similar to that of bulk Pt. The area specific measurements show a 20mV reduction in the Pt–Co–Mn/NSTF overpotential compared to Pt/NSTF. The corresponding kinetic gain in the area specific activity of the ternary alloy is about a factor of two. This ORR enhancement factor observed in the ternary Pt–Co–Mn/NSTF by RRDE measurements is similar to the results obtained in 50cm2 H2/air fuel cells. [Copyright &y& Elsevier]

At present there is no consensus on the charge-storage mechanism of the positive electrode in the chemistry of the MnO 2 /ZnSO 4 /Zn battery. We report the discovery of a novel, electrochemically active Mn-Zn layered double hydroxide (MnZnLDH), which, is analogous in structure to ZnLDH, and because of this similarity cannot be identified as a discharge product even by the operando XRD techniques used. We were able to synthesize MnZnLDH, for the first time, and, herein, demonstrate that its electrochemical behavior, structure, and Gibbs free energy of formation correspond to the products formed during the first discharge, providing clear evidence that this phase forms during the first discharge reaction through a conversion reaction of MnO 2 and Zn2+. [Display omitted] [ABSTRACT FROM AUTHOR]

The effects of electroless Pt layers (<80 μg Pt cm−2) in the membrane subsurface on hydrogen crossover, ORR kinetics, and overall fuel cell performance are closely investigated. The electroless Pt layer in the membrane subsurface reduces gas crossover for a 17 μm thick membrane in an inversely proportional relationship to the loading, yielding up to >65% reduction. High electroless Pt layer loading reduces proton conductivity and results in less optimal ORR kinetic performance. Given the relationship between kinetic performance, exchange current density, and proton concentration, the impact of electroless Pt layer loading on proton concentration is determined. This correlation sheds light on the relationship between proton concentration, proton conductivity, and Pt loading, and can be useful as a probe for proton concentration diagnostic examinations. Hydrogen fuel cell tests reveal that with an additional membrane Pt loading of <20 μg Pt cm−2, the performance of GDE-based MEAs at low humidity are improved in both polarization and long-term humidity cycling tests, while the performance under wet conditions is still nearly identical to the baseline. This suggests that the addition of electroless Pt in the membrane subsurface at such loadings enhances the operational flexibility of hydrogen fuel cells and reduces hydrogen crossover effects. • Deposition of ≤80 μg Pt cm−2 electroless Pt layer in the membrane subsurface. • Reduction of hydrogen crossover by >65% in hydrogen fuel cell. • Enhanced operational flexibility for H 2 /O 2 polymer electrolyte membrane fuel cell. • Delineation of electroless Pt layer role on proton conductivity and humidity level. [ABSTRACT FROM AUTHOR]

In the present study a membrane sequencing batch reactor (MSBR) was assessed for treatment of petroleum refinery wastewater (PRW). Mean COD, O&G and TPH removal efficiencies of 80%, 82% and 93.4% respectively – achieved during more than three-month operation of the MSBR with real PRW of varying composition – attested to the robustness of the MSBR system for treatment of PRW. The MSBR system was also able to withstand and recover from a toxic shock loading applied during part of its operation. GC/MS analysis revealed that the majority of the organic constituents of the PRW were eliminated as a result of MSBR treatment whereas a minority were only partially biodegraded. The effect of the application of relaxation – a hydraulic membrane cleaning method that has been extensively studied in MBRs but not in MSBRs – on membrane fouling was both quantified and characterised. The finding of the present work showed that, compared to the use of air scouring alone, relaxation results in a significant drop in the rate of membrane fouling in MSBRS and affects the way mixed liquor physicochemical properties influence membrane fouling. Also, the membrane fouling layer at the end of MSBR operation was visually and chemically characterised. [ABSTRACT FROM AUTHOR]

[Display omitted] • An innovative anaerobic hybrid bioreactor was considered for in situ biomethanation. • Low CO 2 content was achieved (below 2%) in EC-UASB within a short time. • Improvement in removal of pollutants and turbidity was achieved in EC-UASB. • No accumulation of volatile fatty acids was observed in EC-UASB. • Hydrogen and higher concentration of iron positively altered microbial community. In this study, the integration of the electrocoagulation (EC) process with anaerobic digestion as a novel in-situ biomethanation approach was considered for the first time. As a result of this integration (iron electrodes, current density of 1.5 mA/cm2 and an exposure mode of 10-min-ON/ 30-min-OFF), the carbon dioxide content of biogas reached below 2%. Also, the methane production rate improved by 18.0 ± 0.4%, whereas the removal efficiencies of chemical oxygen demand, turbidity, phosphate, and sulfate increased by 12.0 ± 1.5%, 30.7 ± 1.7%, > 99%, and 75.7%, respectively. Anaerobic granular sludge characteristics were also improved. Moreover, the EC process stimulated growth and quantity of functional microorganisms, especially Acinetobacter in bacterial and Methanobacterium in archaeal community. Methane concentration, however decreased due to possible excess hydrogen production. The application of the biogas as bio-hythane, and the optimization of the hybrid bioreactor to decrease hydrogen production, are possible avenues for further research. [ABSTRACT FROM AUTHOR]

Abstract: A colloidal silica incorporated porous anodic aluminum oxide (AAO) was utilized as a dual-template to prepare mesoporous carbon nanofibers (MCNFs). Such a strategy is simple because it takes advantage of commercially available materials (i.e., colloidal silica and AAO) and the templates can be removed in one step. The as-prepared MCNF shows a hierarchical nanostructure consisting of open macroporous channel connected with large mesopores and micropores. As a result of the large surface area and unique hierarchical nanoarchitecture which facilitates fast mass and electron transport, the MCNF reveals a discharge capacity of 679 mA h g−1 at 25 mA g−1. This value is significantly greater than that (i.e., 394 mA h g−1) observed for an ordered mesoporous carbon (OMC) with a similar specific surface area. Furthermore, at 3000 mA g−1, the MCNF demonstrates a discharge capacity of 585 mA h g−1, which is about twice that (i.e., 256 mA h g−1) of the OMC. [Copyright &y& Elsevier]

Abstract: In this study, lactulose production with β-galactosidase from Kluyveromyces lactis in aqueous and non-conventional media was studied. The optimisation of the rate of enzymatic lactulose production in aqueous media was carried out using factorial design methodology. The results showed a statistically significant effect of both lactose and fructose levels – as well as their interaction – on the rate of lactulose production. Maximum lactulose production rate was obtained at fructose and lactose concentrations of 25–30% (w/w) and 9–12% (w/w), respectively. The addition of acetone had a negative effect on lactulose production, whereas the incorporation of triethyl phosphate up to a concentration of 30% (w/w) caused an increase of up to 20% in the lactulose production. [Copyright &y& Elsevier]

Abstract: Most neuroimaging studies examining verb morphology have focused on verb tense, with fewer examining agreement morphology, and no previous fMRI studies have investigated distinctions between past and present tense inflection. However, models of language representation and processing suggest differences in where these inflections are instantiated in the phrase structure as well as differences in the linguistic functions they serve, suggesting unique neural networks for these forms. In addition, results of available neuroimaging studies of grammatical morphology vary considerably due to methodological differences. Some studies have used overt production tasks, whereas others have used covert tasks. In the present study we examined brain activation associated with past tense and present tense/agreement morphology under overt and covert production conditions in 13 healthy adults using an event-related functional magnetic resonance imaging (fMRI) design. Production of verbs inflected for past tense (V + -ed) and present tense/agreement (V + -s) was elicited using temporal adverbs (i.e. Yesterday, Nowadays). Results showed that in healthy adults inflecting both past tense and agreement morphology (compared to a verb stem production condition) recruited not only left inferior frontal structures, but also motor and premotor cortices, and posterior parietal regions. Activation also was observed in the basal ganglia, thalamus, and the cingulate gyrus. Past tense and present tense/agreement recruited partially overlapping tissue in these regions, with distinctions observed for the two forms in frontal and parietal brain areas. We also found that activation varied with task demands, with more extensive frontal activation noted in the overt compared to the covert verb inflection task. These results are consistent with the hypothesis that the neural signatures for verb inflection differ from that for verb stems alone and involve a distributed frontal and parietal network of brain regions. Further, the neural tissue recruited for instantiation of past tense versus present tense/agreement morphology is distinct, supporting linguistic theories that differentiate the two forms. [Copyright &y& Elsevier]