Helium Incorporation into Scandium Fluoride, a Model Negative Thermal Expansion Material

Scandium trifluoride is a model negative thermal expansion (NTE) material. Its simple structure can be described as an A-site vacant perovskite, and it shows isotropic NTE over a very wide temperature range (up to ∼1100 K), due to transverse vibrational motion of the fluoride. Like many framework NTE materials, it undergoes a phase transition at low pressures, adopting a rhombohedral (R3̅c) structure at >0.7 GPa and 300 K in commonly used nonpenetrating pressure media, such as silicone oil. High pressure X-ray diffraction data and gas uptake/release measurements indicate that, on compression in helium above ∼200 K, helium is inserted into ScF3 to form the defect perovskite HexScF3. The incorporation of helium stiffens the structure and changes its phase behavior. At room temperature, complete filling of the structure with helium does not occur until >1.5 GPa. On compression, a cubic perovskite structure is maintained until ∼5 GPa. As the pressure was increased to ∼9.5 GPa, a further transition occurred at ∼7 GPa. The first transition at ∼5 GPa is likely to a tetragonal (P4/mbm) perovskite, but the detailed structure of the perovskite phase formed on compression above ∼7 GPa is unclear. Cooling down from 300 to 100 K in helium at ∼0.4 GPa leads to an approximate composition of He0.1ScF3. High pressure neutron diffraction measurements, in the temperature range 15–150 K show that the incorporation of helium increases the pressure at which the cubic (Pm3̅m) to rhombohedral (R3̅c) putative quantum structural phase transition occurs from close to 0 GPa to ∼0.2 GPa at 0 K

Replicable Associations between Common Mental Distress and Suicide Risk in Young People: Implications for Clinical Practice and Population Suicide Prevention

Background. Recent evidence suggests that multiple symptoms or diagnoses, partucularly when co-ocuring with non-suicidal self-harm, predict suicide risk more strongly than single diagnosis. / Method. Suicidal thought (ST) and non-suicidal self-injury (NSSI) were studies in two independent longitudinal UK samples of young people: the Neuroscience in Psychiatry (NSPN) 2400 cohort (n=2403) and the ROOTS cohort (n=1074). Participants, age 14-24 years, were recruited from primary health care registers, schools and colleges, and advertisements to complete quotas in age-sex strata. We calculated a score on a latent construct Common Mental Distress (the summary measure indexing a broad range of symptoms conventionally seen as components of distinct disorders). We examined the relative prevalence of ST and NSSI over the population distribution of mental distress; we used logistic regressions, IRT and ROC analyses to determine associations between suicide risks and mental distress (in continuous and above-the-norm categorical format); and pathway mediation models to examine longitudinal associations. / Outcomes. We found a dose-response relationship between levels of mental distress and suicide risk. In both cohorts the majority of all subjects experiencing ST (78% and 76%) and NSSI (66% and 71%) had scores on mental distress no more than two standard deviations above the population mean; higher scores indicated highest risk but were, by definition, infrequent. Mental distress contributed to the longitudinal persistence of ST and NSSI. / Interpretation. Universal prevention strategies reducing levels of mental distress in the whole population (in addition to screening) may prevent more suicides than approaches targeting youths with psychiatric disorders

Lipidomics of homeoviscous adaptation to low temperatures in Staphylococcus aureus utilizing exogenous straight-chain unsaturated fatty acids

Abstract It is well established that Staphylococcus aureus can incorporate exogenous straight-chain unsaturated fatty acids (SCUFAs) into membrane phospho- and glyco-lipids from various sources in supplemented culture media, and when growing in vivo in an infection. Given the enhancement of membrane fluidity when oleic acid (C18:1Δ9) is incorporated into lipids, we were prompted to examine the effect of medium supplementation with C18:1Δ9 on growth at low temperatures. C18:1Δ9 supported the growth of a cold-sensitive, branched-chain fatty acid (BCFA)-deficient mutant at 12°C. Interestingly, we found similar results in the BCFA-sufficient parental strain. We show that incorporation of C18:1Δ9 and its elongation product C20:1Δ9 into membrane lipids was required for growth stimulation and relied on a functional FakAB incorporation system. Lipidomics analysis of the phosphatidylglycerol (PG) and diglycosyldiacylglycerol (DGDG) lipid classes revealed major impacts of C18:1Δ9 and temperature on lipid species. Growth at 12°C in the presence of C18:1Δ9 also led to increased production of the carotenoid pigment staphyloxanthin; however, this was not an obligatory requirement for cold adaptation. Enhancement of growth by C18:1Δ9 is an example of homeoviscous adaptation to low temperatures utilizing an exogenous fatty acid. This may be significant in the growth of S. aureus at low temperatures in foods that commonly contain C18:1Δ9 and other SCUFAs in various forms