Redetermination of the lanthanum iron sulfide La52Fe12S90

A redetermination of the structure of `La_32.66Fe₁₁S₆₀' in the trigonal space group Rm led to the new formula La₅₂Fe₁₂S₉₀ and to a redefinition of the structure type. In the structure, the Fe²⁺ cations occur in Fe₂S₉ dimers of face‐sharing octa­hedra (with 3m symmetry). The dimers are linked by face‐ and vertex‐sharing bi‐ and tricapped LaS₆ trigonal prisms (with m symmetry) to form a three‐dimensional network containing two types of cubocta­hedral cavities. The larger cavities remain empty, while the smaller ones accommodate alternative sites for disordered La³⁺ cations.     

Stress relaxation behavior of soda-lime glass between the transformation and softening temperatures

The compressive stress relaxation modulus of a container glass composition was investigated over a wide range of strain, time, modulus, and temperature. It is shown that the glass behaves in a linear viscoelastic manner up to a 2% strain level, and that the relaxation modulus is a smooth function of time, with no pseudo-rubbery plateau apparent down to a modulus of 10⁸ dyn/cm². The data cover roughly five decades of modulus, five decades of time, and a temperature range of 150° C above the glass transition, T_g = 536°C. Within experimental error, the effect of temperature on the stress relaxation behavior is to simply shift the modulus-time curves along the time axis with no change in shape. Temperature dependent shift factor data are expressed in terms of the WLF relation, and are shown to be in good agreement with data found in the literature for other silicate compositions. Viscosity data derived from the generated stress relaxation data agree well with data obtained by more direct methods.     

Plate-based diversity subset screening: an efficient paradigm for high throughput screening of a large screening file

The screening files of many large companies, including Pfizer, have grown considerably due to internal chemistry efforts, company mergers and acquisitions, external contracted synthesis, or compound purchase schemes. In order to screen the targets of interest in a cost-effective fashion, we devised an easy-to-assemble, plate-based diversity subset (PBDS) that represents almost the entire computed chemical space of the screening file whilst comprising only a fraction of the plates in the collection. In order to create this file, we developed new design principles for the quality assessment of screening plates: the Rule of 40 (Ro40) and a plate selection process that insured excellent coverage of both library chemistry and legacy chemistry space. This paper describes the rationale, design, construction, and performance of the PBDS, that has evolved into the standard paradigm for singleton (one compound per well) high-throughput screening in Pfizer since its introduction in 2006.     

Gibbs ensemble simulation of nematic-isotropic coexistence in a liquid crystal mixture

The results are presented of Gibbs ensemble Monte Carlo (GEMC) simulations examining the nematic–isotropic (N–I) coexistence envelope of a liquid crystal mixture. The system studied is a 50:50 mixture of 1000 generalized Gay–Berne particles with axial ratios 2.0:1 and 2.5:1. For this system, stable N–I coexistence is observed over run lengths in excess of 5 x 10⁵ GEMC sweeps. There is unambiguous evidence of fractionation, the mole fractions of long particles in the coexisting phases typically differing by 11%. The measured coexistence envelope does not conform to the lens shape predicted by Onsager theory; qualitative finite size arguments are given in explanation of this distortion.     

Electron energy loss spectroscopy; history and related matters

This paper begins with some historical remarks regarding the author’s early interest in the use of electron energy loss spectroscopy to probe dynamical phenomena on crystal surfaces. We then discuss the physical nature of the interactions responsible for vibrational and spin waves losses, with attention to their role in related phenomena. PACS 61.14.-x; 68.35.Ja; 68.49.Jk; 68.49.Uv     

Australian Synchrotron User Meeting 2014

Synchrotron users and experts from Australia, New Zealand, and further afield congregated in November for the Australian Synchrotron User Meeting 2014. Around 200 members of the synchrotron community attended the highly anticipated meeting held, in conjunction with the New User Symposium, at the Australian Synchrotron's National Centre for Synchrotron Science. Early career researchers played a prominent role at the meeting. Their achievements highlighted the promising capabilities of the region's next generation of synchrotron scientists.     

Potential energy surface intersections for triatomic molecules

The different types of surface intersection which may occur in linear configurations of triatomic molecules are reviewed, particularly with regard to the way in which the degeneracy is split as the molecule bends. The Renner-Teller effect in states of symmetry Π, Δ, Φ, etc., and intersections between Σ and Π, Σ and Δ, and Π and Δ states are discussed. A general method of modelling such intersecting potential surfaces is proposed, as a development of the model previously used by Murrell and Carter and co-workers for single-valued surfaces. Some of the lower energy surfaces of H₂O, NH₂, O₃, C₃, and HNO are discussed as examples.