A systematic study of interfacial properties of binary mixtures of simple fluids was carried out by molecular dynamics (MD) simulation and density gradient theory (DGT). The fluids are described by the Lennard-Jones truncated and shifted potential with truncation radius of 2.5 diameters (LJTS fluid). The following interfacial properties were studied: surface tension, relative adsorption, enrichment, and interfacial thickness. A recently developed equation of state for the LJTS fluid (PeTS EOS) was used as basis for the DGT. Six binary mixtures (components 1 + 2) were studied at a constant temperature, which was chosen such that the high-boiling component 1 is subcritical while the low-boiling component 2 is either subcritical or supercritical. Furthermore, a parameter ξ in the combination rule for the unlike dispersive interaction was varied such that the resulting mixtures showed three types of behavior: high-boiling azeotrope, ideal, and low-boiling azeotrope. The parameters of the LJTS potential, including ξ, were also used in the PeTS EOS without any adjustment. Despite this simple approach, excellent agreement between the results of the PeTS EOS and the MD results for the phase equilibrium and the interfacial properties is observed. Enrichment at the interface is only found for the low-boiling component 2. The enrichment increases with decreasing concentration of component 2 and is favored by high boiling point differences of the pure components 1 and 2 and positive deviations from Raoult's law for the mixture 1 + 2.

Literature data on thermophysical properties of the Lennard-Jones fluid, which were sampled with Molecular Dynamics and Monte Carlo simulations, were reviewed and assessed. The literature data was complemented by simulation data from the present work that was taken in regions in which previously only sparse data was available. Data on homogeneous state points (for given temperature T and density ρ: pressure p, thermal expansion coefficient α, isothermal compressibility β, thermal pressure coefficient γ, internal energy u, isochoric heat capacity c v , isobaric heat capacity c p , Grüneisen coefficient Γ, Joule-Thomson coefficient µ JT , speed of sound w, Helmholtz energy a, chemical potential µ, surface tension γ) was considered as well as data on the vapor-liquid equilibrium (for given T : vapor pressure p s , saturated liquid and vapor densities ρ and ρ , enthalpy of vaporization ∆h v). The entire set of available data, which contains about 35,000 data points, was digitalized and included in a database, which is made available in the electronic supplementary material of this paper. Different consistency tests were applied to assess the accuracy and precision of the data. The data on homogeneous states were evaluated point-wise using data from their respective 1 vicinity and equations of state. Approximately 5% of all homogeneous bulk data were discarded as outliers. The vapor-liquid equilibrium data were assessed by tests based on the compressibility factor, the Clausius-Clapeyron equation, and by an outlier test. Seven particularly reliable vapor-liquid equilibrium data sets were identified. The mutual agreement of these data sets is approximately ±1% for the vapor pressure, ±0.2% for the saturated liquid density, ±1% for the saturated vapor density, and ±0.75% for the enthalpy of vaporizationexcluding the region close to the critical point.

Background Emerging studies indicate that some COVID-19 patients suffer from persistent symptoms including breathlessness and chronic fatigue; however the long-term immune response in these patients presently remains ill-defined. Methods Here we describe the phenotypic and functional characteristics of B and T cells in hospitalised COVID-19 patients during acute disease and at 3-6 months of convalescence. Findings We report that the alterations in B cell subsets observed in acute COVID-19 patients were largely recovered in convalescent patients. In contrast, T cells from convalescent patients displayed continued alterations with persistence of a cytotoxic programme evident in CD8 + T cells as well as elevated production of type-1 cytokines and IL-17. Interestingly, B cells from patients with acute COVID-19 displayed an IL-6/IL-10 cytokine imbalance in response to toll-like receptor activation, skewed towards a pro-inflammatory phenotype. Whereas the frequency of IL-6 + B cells was restored in convalescent patients irrespective of clinical outcome, recovery of IL-10 + B cells was associated with resolution of lung pathology. Conclusions Our data detail lymphocyte alterations in previously hospitalized COVID-19 patients up to 6 months following hospital discharge and identify 3 subgroups of convalescent patients based on distinct lymphocyte phenotypes, with one subgroup associated with poorer clinical outcome. We propose that alterations in B and T cell function following hospitalisation with COVID-19 could impact longer term immunity and contribute to some persistent symptoms observed in convalescent COVID-19 patients. Funding Provided by UKRI, Lister Institute of Preventative Medicine, The Wellcome Trust, The Kennedy Trust for Rheumatology Research and 3M Global Giving.

An equation of state is presented for describing thermodynamic properties of the Lennard-Jones truncated and shifted (LJTS) potential with a cut-off radius of 2.5 σ. It is developed using perturbation theory with a hard sphere reference term and labelled with the acronym PeTS (perturbed truncated and shifted). The PeTS equation of state describes the properties of the bulk liquid and vapour and the corresponding equilibrium of the LJTS fluid well. Furthermore, it is developed so that it can be used safely in the entire metastable and unstable region, which is an advantage compared to existing LJTS equations of state. This makes the PeTS equation of state an interesting candidate for studies of interfacial properties. The PeTS equation of state is applied here in two theories of interfaces, namely density gradient theory (DGT) and density functional theory (DFT). The influence parameter of DGT as well as the interaction averaging diameter of DFT are fitted to data of the surface tension of the LJTS fluid obtained from molecular simulation. The results from both theories agree very well with those from the molecular simulations.

Thermodynamic properties are often modeled by classical force fields which describe the interactions on the atomistic scale. Molecular simulations are used for retrieving thermodynamic data from such models, and many simulation techniques and computer codes are available for that purpose. In the present round robin study, the following fundamental question is addressed: Will different user groups working with different simulation codes obtain coinciding results within the statistical uncertainty of their data? A set of 24 simple simulation tasks is defined and solved by five user groups working with eight molecular simulation codes: DL_POLY, GROMACS, IMC, LAMMPS, ms2, NAMD, Tinker, and TOWHEE. Each task consists of the definition of (1) a pure fluid that is described by a force field and (2) the conditions under which that property is to be determined. The fluids are four simple alkanes: ethane, propane, n-butane, and iso-butane. All force fields consider internal degrees of freedom: OPLS, TraPPE, and a modified OPLS version with bond stretching vibrations. Density and potential energy are determined as a function of temperature and pressure on a grid which is specified such that all states are liquid. The user groups worked independently and reported their results to a central instance. The full set of results was disclosed to all user groups only at the end of the study. During the study, the central instance gave only qualitative feedback. The results reveal the challenges of carrying out molecular simulations. Several iterations were needed to eliminate gross errors. For most simulation tasks, the remaining deviations between the results of the different groups are acceptable from a practical standpoint, but they are often outside of the statistical errors of the individual simulation data. However, there are also cases where the deviations are unacceptable. This study highlights similarities between computer experiments and laboratory experiments, which are both subject not only to statistical error but also to systematic error.

Enrichment at vapour–liquid interfaces can be interpreted as a wetting transition in the vicinity of a three phase equilibrium.

The MolMod database is presented, which is openly accessible at http://molmod.boltzmann-zuse.de/ and contains presently intermolecular force fields for over 150 pure fluids. It was developed and is maintained by the Boltzmann-Zuse Society for Computational Molecular Engineering (BZS). The set of molecular models in the MolMod database provides a coherent framework for molecular simulations of fluids. The molecular models in the MolMod database consist of Lennard-Jones interaction sites, point charges, and point dipoles and quadrupoles, which can be equivalently represented by multiple point charges. The force fields can be exported as input files for the simulation programs ms2 and ls1 mardyn, Gromacs, and LAMMPS. To characterise the semantics associated with the numerical database content, a force-field nomenclature is introduced that can also be used in other contexts in materials modelling at the atomistic and mesoscopic levels. The models of the pure substances that are included in the data base were generally optimised such as to yield good representations of experimental data of the vapour-liquid equilibrium with a focus on the vapour pressure and the saturated liquid density. In many cases, the models also yield good predictions of caloric, transport, and interfacial properties of the pure fluids. For all models, references to the original works in which they were developed are provided. The models can be used straightforwardly for predictions of properties of fluid mixtures using established combination rules. Input errors are a major source of errors in simulations. The MolMod database contributes to reducing such errors. KEYWORDS

Introduction The avascular nature of the human intervertebral disc (IVD) is thought to play a major role in disc pathophysiology by limiting nutrient supply to resident IVD cells. In the human IVD, the central IVD cells at maturity are normally chondrocytic in phenotype. However, abnormal cell phenotypes have been associated with degenerative disc diseases, including cell proliferation and cluster formation, cell death, stellate morphologies, and cell senescence. Therefore, we have examined the relative influence of possible blood-borne factors on the growth characteristics of IVD cells in vitro.