Robert John Newport

Variability in young stellar objects (YSOs) is one of their primary characteristics. Long-term, multifilter, high-cadence monitoring of large YSO samples is the key to understand the partly unusual light curves that many of these objects show. Here we introduce and present the first results of the HOYS-CAPS citizen science project that aims to perform such monitoring for nearby (d < 1 kpc) and young (age < 10 Myr) clusters and star-forming regions, visible from the northern hemisphere, with small telescopes. We have identified and characterized 466 variable (413 confirmed young) stars in eight young, nearby clusters. All sources vary by at least 0.2 mag in V, have been observed at least 15 times in V, R, and I in the same night over a period of about 2 yr, and have a Stetson index of larger than 1. This is one of the largest samples of variable YSOs observed over such a time span and cadence in multiple filters. About two-thirds of our sample are classical T-Tauri stars, while the rest are objects with depleted or transition discs. Objects characterized as bursters show by far the highest variability. Dippers and objects whose variability is dominated by occultations from normal interstellar dust or dust with larger grains (or opaque material) have smaller amplitudes. We have established a hierarchical clustering algorithm based on the light-curve properties that allows the identification of the YSOs with the most unusual behaviour and to group sources with similar properties. We discuss in detail the light curves of the unusual objects V2492 Cyg, V350 Cep, and 2MASS J21383981+5708470.

Bioactive sol‐gel calcia‐silica glasses can regenerate damaged or diseased bones due to their ability to stimulate bone growth. This capability is related to the formation of a hydroxyapatite layer on the glass surface, which bonds with bone, and the release of soluble silica and calcium ions in the body fluid which accelerates bone growth. The addition of silver ions imbues the glass with antibacterial properties due to the release of antibacterial Ag ⁺ ion. The antibacterial activity is therefore closely dependent on the dissolution properties of the glasses which in turn are related to their atomic‐level structure. Structural characterization of the glasses at the atomic level is therefore essential in order to investigate and control the antibacterial properties of the glass. We have used neutron diffraction to investigate the structure of silver‐containing calcia‐silica sol‐gel bioactive glasses with different Ag ₂ O loading (0, 2, 4, 6 mol%). The presence of the silver had little effect on the host glass structure, although some silver metal nanoparticles were present. Results agreed with previous computer simulations.

Sol–gel‐synthesized bioactive glasses may be formed via a hydrolysis condensation reaction, silica being introduced in the form of tetraethyl orthosilicate (TEOS), and calcium is typically added in the form of calcium nitrate. The synthesis reaction proceeds in an aqueous environment; the resultant gel is dried, before stabilization by heat treatment. These materials, being amorphous, are complex at the level of their atomic‐scale structure, but their bulk properties may only be properly understood on the basis of that structural insight. Thus, a full understanding of their structure‐property relationship may only be achieved through the application of a coherent suite of leading‐edge experimental probes, coupled with the cogent use of advanced computer simulation methods. Using as an exemplar a calcia–silica sol–gel glass of the kind developed by Larry Hench, in the memory of whom this paper is dedicated, we illustrate the successful use of high‐energy X‐ray and neutron scattering (diffraction) methods, magic‐angle spinning solid‐state NMR, and molecular dynamics simulation as components to a powerful methodology for the study of amorphous materials.

NXFitis a program for obtaining optimized structural parameters from amorphous materials by simultaneously fitting X-ray and neutron pair-distribution functions. Partial correlation functions are generated inQspace, summed and Fourier transformed for comparison with the experimental data inrspace.NXFituses the Nelder–Mead method to vary a set of `best guess' parameters to achieve a fit to experimentally derived data. The output parameters fromNXFitare coordination number, atomic separation and disorder parameter for each atomic correlation used in the fitting process. The use ofNXFithas been demonstrated by fitting both X-ray and neutron diffraction data from two quite different amorphous materials: a melt-quenched (Na₂O)_0.5(P₂O₅)_0.5glass and a (TiO₂)_0.18(SiO₂)_0.82sol–gel.

In this study, amorphous (Na₂O) _x(CaO)_{0.50− x}(P₂O₅)_0.50· yH₂O (where x = ∼0.15 and y = ∼3) samples were prepared by a coacervate method. Thermal analysis showed that two types of water molecules were present in the coacervate structures: one type loosely bound and the other part of the phosphate structure. Structural studies using Fourier transform infrared spectroscopy (FTIR) and X-ray total diffraction revealed the samples to have very similar structures to melt-quenched glasses of comparable composition. Furthermore, no significant structural differences were observed between samples prepared using calcium nitrate as the calcium source or those prepared from calcium chloride. A sample containing ∼1 mol% Ag₂O was prepared to test the hypothesis that calcium phosphate coacervate materials could be used as delivery agents for antibacterial ions. This sample exhibited significant antibacterial activity against the bacterium Psuedomonas aeruginosa. FTIR data revealed the silver-doped sample to be structurally akin to the analogous silver-free sample.

Rare-earth co-doping in inorganic materials has a long-held tradition of facilitating highly desirable optoelectronic properties for their application to the laser industry. This study concentrates specifically on rare-earth phosphate glasses, (R₂O₃)_x(R′₂O₃)_y(P₂O₅)_1−(x+y), where (R, R′) denotes (Ce, Er) or (La, Nd) co-doping and the total rare-earth composition corresponds to a range between metaphosphate, RP₃O₉, and ultraphosphate, RP₅O₁₄. Thereupon, the effects of rare-earth co-doping on the local structure are assessed at the atomic level. Pair-distribution function analysis of high-energy X-ray diffraction data (Q_max = 28 Å⁻¹) is employed to make this assessment. Results reveal a stark structural invariance to rare-earth co-doping which bears testament to the open-framework and rigid nature of these glasses. A range of desirable attributes of these glasses unfold from this finding; in particular, a structural simplicity that will enable facile molecular engineering of rare-earth phosphate glasses with ‘dial-up’ lasing properties. When considered together with other factors, this finding also demonstrates additional prospects for these co-doped rare-earth phosphate glasses in nuclear waste storage applications. This study also reveals, for the first time, the ability to distinguish between P–O and PO bonding in these rare-earth phosphate glasses from X-ray diffraction data in a fully quantitative manner. Complementary analysis of high-energy X-ray diffraction data on single rare-earth phosphate glasses of similar rare-earth composition to the co-doped materials is also presented in this context. In a technical sense, all high-energy X-ray diffraction data on these glasses are compared with analogous low-energy diffraction data; their salient differences reveal distinct advantages of high-energy X-ray diffraction data for the study of amorphous materials.

Calcium phosphate based biomaterials are extensively used in the context of tissue engineering: small changes in composition can lead to significant changes in properties allowing their use in a wide range of applications. Samples of composition (Al2O3)x(Na2O)0.11-x(CaO)0.445(P2O5)0.445, where x = 0, 0.03, 0.05, and 0.08, were prepared by melt quenching. The atomic-scale structure has been studied using neutron diffraction and solid state 27Al MAS NMR, and these data have been rationalised with the determined density of the final glass product. With increasing aluminium concentration the density increases initially, but beyond about 3 mol. % Al2O3 the density starts to decrease. Neutron diffraction data show a concomitant change in the aluminium speciation, which is confirmed by 27Al MAS NMR studies. The NMR data reveal that aluminium is present in 4, 5, and 6-fold coordination and that the relative concentrations of these environments change with increasing aluminium concentration. Materials containing aluminium in 6-fold coordination tend to have higher densities than analogous materials with the aluminium found in 4-fold coordination. Thus, the density changes may readily be explained in terms of an increase in the relative concentration of 4-coordinated aluminium at the expense of 6-fold aluminium as the Al2O3 content is increased beyond 3 mol. %.