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Abstract: Fitting a mathematical model to data is a fundamental task across all scientific disciplines. FitBenchmarking has been designed to help: Scientists, who want to know the best algorithm for fitting their data to a given model using specific hardware; Scientific software developers, who want to identify the best fitting algorithms and implementations. This allows them to recommend a default solver, to see if it is worth adding a new minimizer, and to test their implementation; Mathematicians and numerical software developers, who want to understand the types of problems on which current algorithms do not perform well, and to have a route to expose newly developed methods to users. Representatives of each of these communities have got together to build FitBenchmarking. We hope this tool will help foster fruitful interactions and collaborations across the disciplines.

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Abstract: Ultra-SAXS can enhance the capabilities of existing synchrotron SAXS/WAXS beamlines. A compact ultra-SAXS module has been developed, which extends the measurable q-range with 0.0015 ≤ q (nm−1) ≤ 0.2, allowing structural dimensions in the range 30 ≤ D (nm) ≤ 4000 to be probed in addition to the range covered by a high-end SAXS/WAXS instrument. By shifting the module components in and out on their respective motor stages, SAXS/WAXS measurements can be easily and rapidly interleaved with USAXS measurements. The use of vertical crystal rotation axes (horizontal diffraction) greatly simplifies the construction, at minimal cost to efficiency. In this paper, the design considerations, realization and synchrotron findings are presented. Measurements of silica spheres, an alumina membrane, and a porous carbon catalyst are provided as application examples.

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Abstract: Understanding interactions between nanoparticles and model membranes is relevant to functional nano-composites and the fundamentals of nanotoxicity. In this study, the effect of polyamidoamine (PAMAM) dendrimers as model nanoparticles (NP) on the mesophase behaviour of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine (POPE) has been investigated using high-pressure small-angle X-ray scattering (HP-SAXS). The pressure-temperature ( p−T ) diagrams for POPE mesophases in excess water were obtained in the absence and presence of G2 and G4 polyamidoamine (PAMAM) dendrimers (29 Å and 45 Å in diameter, respectively) at varying NP-lipid number ratio (ν = 0.0002-0.02) over the pressure range p = 1-3000 bar and temperature range T = 20–80°C. The p−T phase diagram of POPE exhibited the Lβ, Lα and HII phases. Complete analysis of the phase diagrams, including the relative area pervaded by different phases, phase transition temperatures (Tt) and pressures (pt), the lattice parameters (d-spacing), the pressure-dependence of d-spacing (Δd/Δp), and the structural ordering in the mesophase as gauged by the Scherrer coherence length (L) permitted insights into the size- and concentration-dependent interactions between the dendrimers and the model membrane system. The addition of dendrimers changed the phase transition pressure and temperature and resulted in the emergence of highly swollen lamellar phases, dubbed Lβ-den and Lα-den. G4 PAMAM dendrimers at the highest concentration ν = 0.02 suppressed the formation of the HII phase within the temperature range studied, whereas the addition of G2 PAMAM dendrimers at the same concentration promoted an extended mixed lamellar region in which Lα and Lβ phases coexisted.

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Abstract: Understanding the structure of polymer/surfactant mixtures at the air-water interface is of fundamental importance and also of relevance to a variety of practical applications. Here, the complexation between a neutral ’tardigrade’ comb co-polymer (consisting of a hydrophilic polyethylene glycol backbone with hydrophobic polyvinyl acetate grafts, PEG-g-PVAc) with an anionic surfactant (sodium dodecyl sulfate, SDS) at the air-water interface has been studied. Contrast-matched neutron reflectivity (NR) complemented by surface tension measurements allowed elucidation of the interfacial composition and structure of these mixed systems, as well as providing physical insights into the polymer/surfactant interactions at the air-water interface. For both polymer concentrations studied, below and above its critical aggregation concentration, cac, (0.2 cac and 2 cac, corresponding to 0.0002 wt% or 0.013 mM and 0.002 wt% or 0.13 mM respectively), we observed a synergistic cooperative behaviour at low surfactant concentrations with a 1-2 nm mixed interfacial layer; a competitive adsorption behaviour at higher surfactant concentrations was observed where the polymer was depleted from the air-water interface, with an overall interfacial layer thickness ∼1.6 nm independent of the polymer concentration. The weakly associated polymer layer “hanging” proximally to the interface, however, played a role in enhancing foam stability, thus was relevant to the detergency efficacy in such polymer/surfactant mixtures in industrial formulations.

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Abstract: Context. Laboratory analogues can provide physical constraints to the interpretation of astronomical observations of cosmic dust but clearly do not experience the same formation conditions. To distinguish between properties intrinsic to the material and properties imprinted by their means of formation requires extensive characterisation. Aims. Sol-gel methods can produce amorphous silicates with potentially high reproducibility, but often require long drying times (24+ hours) at elevated temperatures in air, controlled atmosphere, or vacuum. We investigate the possibility that microwave drying can be used to form amorphous silicate on a timescale of ∼10 minutes and characterise their structural and spectroscopic properties relative to silicates produced by other drying methods. Methods. Microwave-dried amorphous MgSiO3, Fe 0.1Mg0.9SiO3 and Mg2SiO4 are characterised using X-ray powder diffraction, total X-ray scattering, small angle X-ray scattering and mid-IR FTIR spectroscopy, and compared to samples produced from the same gels, but dried in-air and under vacuum. The development of crystalline structure in the microwave-dried silicates via thermal annealing up to 999 ◦C is also investigated using in situ X-ray powder diffraction. Results. At the inter-atomic level the silicate structures are largely independent of drying method, however largerscale structured domains, ranging from a ∼few×10 ˚A to∼100’s ˚A in size, are observed. These are ordered as mass fractals with discernible variation caused by the drying processes. The mid-IR 10 μm band profile is also found to be influenced by the drying process, likely due to the way removal of water and bonded OH influences the distribution of tetrahedral species. However, microwave drying also allows Fe to be easily incorporated into the silicate structure. In situ annealing shows that for amorphous MgSiO3 crystalline forsterite, enstatite and cristobalite are high temperature phases, while for Mg2SiO4 forsterite crystallises at lower temperatures followed by cristobalite at high temperature. For Fe0.1Mg0.9SiO3 the crystallisation temperature is significantly increased and only forsterite is observed. Crystalline SiO2 may be diagnostic of Mg-rich, Fe-poor grain mineralogies. The results are discussed in relation to the different thermal conditions required for dust to crystallise within protoplanetary disk lifetimes. Conclusions. Sol-gel microwave drying provides a fast and easy method of producing amorphous Mg- and Fe,Mg-silicates of both pyroxene and olivine compositions. Their structure and spectroscopic characteristics although similar to silicates produced using other drying methods, exhibit subtle variations which are particularly manifest spectroscopically in the mid-IR, and structurally over medium- and long-range length scales.