342 research outputs found
Development of intermolecular potential models for electrolyte solutions using an electrolyte SAFT-VR Mie equation of state
We present a theoretical framework and parameterisation of intermolecular potentials for aqueous electrolyte solutions using the statistical associating fluid theory based on the Mie interaction potential (SAFT-VR Mie), coupled with the primitive, non-restricted mean-spherical approximation (MSA) for electrolytes. In common with other SAFT approaches, water is modelled as a spherical molecule with four off-centre association sites to represent the hydrogen-bonding interactions; the repulsive and dispersive interactions between the molecular cores are represented with a potential of the Mie (generalised Lennard-Jones) form. The ionic species are modelled as fully dissociated, and each ion is treated as spherical: Coulombic ionāion interactions are included at the centre of a Mie core; the ionāwater interactions are also modelled with a Mie potential without an explicit treatment of ionādipole interaction. A Born contribution to the Helmholtz free energy of the system is included to account for the process of charging the ions in the aqueous dielectric medium. The parameterisation of the ion potential models is simplified by representing the ionāion dispersive interaction energies with a modified version of the London theory for the unlike attractions. By combining the Shannon estimates of the size of the ionic species with the Born cavity size reported by Rashin and Honig, the parameterisation of the model is reduced to the determination of a single ionāsolvent attractive interaction parameter. The resulting SAFT-VRE Mie parameter sets allow one to accurately reproduce the densities, vapour pressures, and osmotic coefficients for a broad variety of aqueous electrolyte solutions; the activity coefficients of the ions, which are not used in the parameterisation of the models, are also found to be in good agreement with the experimental data. The models are shown to be reliable beyond the molality range considered during parameter estimation. The inclusion of the Born free-energy contribution, together with appropriate estimates for the size of the ionic cavity, allows for accurate predictions of the Gibbs free energy of solvation of the ionic species considered. The solubility limits are also predicted for a number of salts; in cases where reliable reference data are available the predictions are in good agreement with experiment
Towards the computer-aided molecular design of organic rankine cycle systems with advanced fluid rheories
Organic Rankine cycle (ORC) power-generation systems are increasingly being deployed for heat recovery and conversion from geothermal reservoirs and in several industrial settings. Using a case study of an exhaust flue-gas stream, an ORC power output in excess of 20 MW is predicted at thermal efficiencies ranging between 5% and 15%. The considerable influence on cycle performance of the choice of the working fluid is illustrated with alkane and perfluoroalkane systems modelled using the SAFT-VR Mie equation of state (EoS); in general, the more-volatile pure components (n-butane or n-perfluorobutane) are preferred although some mixtures perform better at restricted cycle conditions. The development of computer-aided molecular design (CAMD) platforms for ORC systems requires both cycle and working-fluid models to be incorporated into a single framework, for the purposes of whole-system design and optimization. Using pure alkanes and their mixtures as a case study, we test the suitability of the recent group-contribution SAFT- Mie EoS method for describing the thermodynamic properties of working fluids relevant to the analysis of ORC systems. The theory is shown to predict accurately the relevant properties of these fluids, thereby suggesting that this SAFT-based CAMD approach is a promising approach towards working-fluid design of ORC power systems
The Shared Experience of Caring: A Study of Care-workersā Motivations and Identifications at Work
AcceptedThis article presents an analysis of long-term care workersā work motivation that examines the way this is shaped by the social contexts in which they operate. We conducted a thematic analysis of 19 in-depth interviews with care-workers. Three core themes were identified as
underpinning their motivation: those of āfulfilmentā, ābelongingā and āvaluingā, and together these contributed to a central theme of āprideā. We also found an overarching theme of āshared experienceā to be integral to the way in which care workers made sense of their motivation and work experience. We draw on the social identity approach to provide a conceptual framework through which to understand how this shared experience shapes careworkersā motivation and the quality of care they deliver. In particular, we note the importance that care-workersā attach to their relationships with clients/patients and highlight the way in which this relational identification shapes their collective identification with their occupation and organisation and, through this, their motivation.European Social Research CouncilSomerset Care Ltd
Working-fluid selection and performance investigation of a two-phase single-reciprocating-piston heat-conversion engine
We employ a validated first-order lumped dynamic model of the Up-THERM converter, a two-phase unsteady heat-engine that belongs to a class of innovative devices known as thermofluidic oscillators, which contain fewer moving parts than conventional engines and represent an attractive alternative for remote or off-grid power generation as well as waste-heat recovery. We investigate the performance the Up-THERM with respect to working-fluid selection for its prospective applications. An examination of relevant working-fluid thermodynamic properties reveals that the saturation pressure and vapour-phase density of the fluid play important roles in determining the performance of the Up-THERM ā the device delivers a higher power output at high saturation pressures and has higher exergy efficiencies at low vapour-phase densities. Furthermore, working fluids with low critical temperatures, high critical pressures and exhibiting high values of reduced pressures and temperatures result in designs with high power outputs. For a nominal Up-THERM design corresponding to a target application with a heat-source temperature of 360 ā¦C, water is compared with forty-five other pure working fluids. When maximizing the power output, R113 is identified as the optimal fluid, followed by i-hexane. Fluids such as siloxanes and heavier hydrocarbons are found to maximize the exergy and thermal efficiencies. The ability of the Up-THERM to convert heat over a range of heat-source temperatures is also investigated, and it is found that the device can deliver in excess of 10 kW when utilizing thermal energy at temperatures above 200 ā¦C. Of all the working fluids considered here, ammonia, R245ca, R32, propene and butane feature prominently as optimal and versatile fluids delivering high power over a wide range of heat-source temperatures
Profiling of Glycan Receptors for Minute Virus of Mice in Permissive Cell Lines Towards Understanding the Mechanism of Cell Recognition
The recognition of sialic acids by two strains of minute virus of mice (MVM), MVMp (prototype) and MVMi (immunosuppressive), is an essential requirement for successful infection. To understand the potential for recognition of different modifications of sialic acid by MVM, three types of capsids, virus-like particles, wild type empty (no DNA) capsids, and DNA packaged virions, were screened on a sialylated glycan microarray (SGM). Both viruses demonstrated a preference for binding to 9-O-methylated sialic acid derivatives, while MVMp showed additional binding to 9-O-acetylated and 9-O-lactoylated sialic acid derivatives, indicating recognition differences. The glycans recognized contained a type-2 GalĪ²1-4GlcNAc motif (Neu5AcĪ±2-3GalĪ²1-4GlcNAc or 3ā²SIA-LN) and were biantennary complex-type N-glycans with the exception of one. To correlate the recognition of the 3ā²SIA-LN glycan motif as well as the biantennary structures to their natural expression in cell lines permissive for MVMp, MVMi, or both strains, the N- and O-glycans, and polar glycolipids present in three cell lines used for in vitro studies, A9 fibroblasts, EL4 T lymphocytes, and the SV40 transformed NB324K cells, were analyzed by MALDI-TOF/TOF mass spectrometry. The cells showed an abundance of the sialylated glycan motifs recognized by the viruses in the SGM and previous glycan microarrays supporting their role in cellular recognition by MVM. Significantly, the NB324K showed fucosylation at the non-reducing end of their biantennary glycans, suggesting that recognition of these cells is possibly mediated by the Lewis X motif as in 3ā²SIA-LeX identified in a previous glycan microarray screen
Interfacial tensions of systems comprising water, carbon dioxide and diluent gases at high pressures: experimental measurements and modelling with SAFT-VR Mie and square-gradient theory
Experimental interfacial tensions of the systems (H2O+CO2), (H2O+N2), (H2O+Ar), (H2O+CO2 +N2) and (H2O+CO2 +Ar) are compared with calculations based on the statistical associating fluid theory for variable range potentials of the Mie form (SAFT-VR Mie) in combination with the square-gradient theory (SGT). Comparisons are made at temperatures from (298 to 473)K and at pressures up to 60MPa. Experimental data for the systems (H2O+CO2), (H2O+N2) and (H2O+CO2 +N2) are taken from the literature. For the (H2O+Ar) and (H2O+CO2 +Ar) systems, we report new experimental interfacial-tension data at temperatures of (298.15-473.15)K and pressures from (2 to 50)MPa, measured by the pendant-drop method. The expanded uncertainties at 95% confidence are 0.05K for temperature, 70kPa for pressure, 0.016Ć Ī³ for interfacial tension in the binary (Ar+H2O) system and 0.018Ć Ī³ for interfacial tension in the ternary (CO2 +Ar+H2O) system. The parameters in the SAFT-VR Mie equation of state are estimated entirely from phase-equilibrium data for the pure components and binary mixtures. For pure water, the SGT influence parameter is determined from vapour-liquid surface-tension data, as is common practice. Since the other components are supercritical over most or the entire temperature range under consideration, their pure-component influence parameters are regressed by comparison with the binary interfacial-tension data. A geometric-mean combining rule is used for the unlike influence parameter in mixtures without incorporation of adjustable binary parameters. The SAFT-VR Mie+SGT approach is found to provide an excellent correlation of the surface tension of water and of the interfacial tensions of the binary systems comprising H2O with CO2 or Ar or N2. When applied to predict the interfacial tensions of the two ternary systems, generally good results are found for (H2O+CO2 +N2) while, for (H2O+CO2 +Ar), the theory performs well at high temperatures but significant deviations are found at low temperatures. Overall, the SAFT-VR Mie+SGT approach can be recommended as a means of modelling the interfacial properties of systems comprising water, carbon dioxide and diluent gases
Aspects of asphaltene aggregation obtained from coarse-grained molecular modeling
We have performed a molecular-simulation-based
study to explore
some of the underlying mechanisms of asphaltene aggregation. The daunting
complexity of the crude oil + asphaltene system precludes any type
of meaningful molecular simulation unless some assumptions are made
with respect to the key physical and chemical properties that must
be explicitly described. In the present work, we focus on molecular
simulations of a coarse-grained model of asphaltene molecules in pure
solvents, which are based on the assumption that the general size
asymmetry and asphaltene morphology play a key role in the aggregation
process. We use simple single isotropic Lennard-Jones sites to represent
paraffinic and aromatic C<sub>6</sub> segments, which are used as
building blocks for the description of continental asphaltene models
and solvent moieties. The energy and size parameters for the intermolecular
models (Īµ and Ļ) for solute and solvent molecules are
chosen to reproduce the experimental density of the liquid phase for
different mixtures. An explicit pure solvent is considered, and the
relationship between the aggregation mechanism and the solvent nature
is investigated through direct simulation of the aggregation process.
The results reproduce accurately expected trends observed for more-complex
models as well as experiments, for example, strong aggregation of
asphaltene molecules in <i>n-</i>heptane and high solubility
in toluene. Different asphaltene models based on different geometries
reveal that even at this level of simplification the topology of the
molecules (number and position of aliphatic branches) does affect
the way molecules aggregate
Glyco-engineered MDCK cells display preferred receptors of H3N2 influenza absent in eggs used for vaccines
Evolution of human H3N2 influenza viruses driven by immune selection has narrowed the receptor specificity of the hemagglutinin (HA) to a restricted subset of human-type (Neu5AcĪ±2-6āGal) glycan receptors that have extended poly-LacNAc (GalĪ²1-4GlcNAc) repeats. This altered specificity has presented challenges for hemagglutination assays, growth in laboratory hosts, and vaccine production in eggs. To assess the impact of extended glycan receptors on virus binding, infection, and growth, we have engineered N-glycan extended (NExt) cell lines by overexpressing Ī²3-Ī-acetylglucosaminyltransferase 2 in MDCK, SIAT, and hCK cell lines. Of these, SIAT-NExt cells exhibit markedly increased binding of H3 HAs and susceptibility to infection by recent H3N2 virus strains, but without impacting final virus titers. Glycome analysis of these cell lines and allantoic and amniotic egg membranes provide insights into the importance of extended glycan receptors for growth of recent H3N2 viruses and relevance to their production for cell- and egg-based vaccines
Continuum-scale modelling of polymer blends using the Cahn-Hilliard equation: transport and thermodynamics
The CahnāHilliard equation is commonly used to study multi-component soft systems such as polymer blends at continuum scales. We first systematically explore various features of the equation system, which give rise to a deep connection between transport and thermodynamics-specifically that the Gibbs free energy of mixing function is central to formulating a well-posed model. Accordingly, we explore how thermodynamic models from three broad classes of approach (lattice-based, activity-based and perturbation methods) can be incorporated within the CahnāHilliard equation and examine how they impact the numerical solution for two model polymer blends, noting that although the analysis presented here is focused on binary mixtures, it is readily extensible to multi-component mixtures. It is observed that, although the predicted liquidāliquid interfacial tension is quite strongly affected, the choice of thermodynamic model has little influence on the development of the morphology
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