Ammonium Fluoride as a Hydrogen-disordering Agent for Ice

The removal of residual hydrogen disorder from various phases of ice with acid or base dopants at low temperatures has been a focus of intense research for many decades. As an antipode to these efforts, we now show using neutron diffraction that ammonium fluoride (NH4F) is a hydrogen-disordering agent for the hydrogen-ordered ice VIII. Cooling its hydrogen-disordered counterpart ice VII doped with 2.5 mol% ND4F under pressure leads to a hydrogen-disordered ice VIII with ~31% residual hydrogen disorder illustrating the long-range hydrogen-disordering effect of ND4F. The doped ice VII could be supercooled by ~20 K with respect to the hydrogen-ordering temperature of pure ice VII after which the hydrogen-ordering took place slowly over a ~60 K temperature window. These findings demonstrate that ND4F-doping slows down the hydrogen-ordering kinetics quite substantially. The partial hydrogen order of the doped sample is consistent with the antiferroelectric ordering of pure ice VIII. Yet, we argue that local ferroelectric domains must exist between ionic point defects of opposite charge. In addition to the long-range effect of NH4F-doping on hydrogen-ordered water structures, the design principle of using topological charges should be applicable to a wide range of other 'ice-rule' systems including spin ices and related polar materials.Comment: 23 pages, 4 figures, 2 table

Comprehensive determination of the high-pressure structural behaviour of BaTiO₃

We have mapped the phase diagram of BaTiO3 more extensively than previous attempts using high-pressure neutron-powder diffraction. The mapping of the phase diagram has been performed using isothermal compression at fixed temperatures (175, 225, 290, 480 K) within each of the known crystallographic phases, up to ∼6 GPa using a large volume press. The crystallographic structure of each phase has been measured, and the determined absolute atomic displacements of all atoms within the cell have provided detailed information on the order of the phase transitions observed, and the behaviour of the ferroelectric dipole moment.Publisher PDFPeer reviewe

Tuning energetic properties through co-crystallisation - a high-pressure experimental and computational study of nitrotriazolone:4,4′-bipyridine

We report the preparation of a co-crystal formed between the energetic molecule 3-nitro-1,2,4-triazol-5-one (NTO) and 4,4′-bipyridine (BIPY), that has been structurally characterised by high-pressure single crystal and neutron powder diffraction data up to 5.93 GPa. No phase transitions or proton transfer were observed up to this pressure. At higher pressures the crystal quality degraded and the X-ray diffraction patterns showed severe twinning, with the appearance of multiple crystalline domains. Computational modelling indicates that the colour changes observed on application of pressure can be attributed to compression of the unit cell that cause heightened band dispersion and band gap narrowing that coincides with a shortening of the BIPY π⋯π stacking distance. Modelling also suggests that the application of pressure induces proton migration along an N-H⋯N intermolecular hydrogen bond. Impact-sensitivity measurements show that the co-crystal is less sensitive to initiation than NTO, whereas computational modelling suggests that the impact sensitivities of NTO and the co-crystal are broadly similar.</p

Pressure-induced polymorphism of caprolactam : a neutron diffraction study

Caprolactam, a precursor to nylon-6 has been investigated as part of our studies into the polymerization of materials at high pressure. Single-crystal X-ray and neutron powder diffraction data have been used to explore the high-pressure phase behavior of caprolactam and we have observed two new high pressure solid forms. The transition between each of the forms requires a substantial rearrangement of the molecules and we observe that the kinetic barrier to the conversion can aid retention of phases beyond their region of stability. Form II of caprolactam shows a small pressure region of stability between 0.5 and 0.9 GPa with Form III being stable from 0.9 GPa to 5.4 GPa. The two high-pressure forms have a catemeric hydrogen-bonding pattern compared with the dimer interaction observed in the ambient pressure Form I. The interaction between the chains has a marked effect on the directions of maximal compressibility in the structure. Neither of the high-pressure forms can be recovered to ambient pressure and there is no evidence of any polymerization occurring

The International Prevalence Study on Physical Activity: results from 20 countries

<p>Abstract</p> <p>Background</p> <p>Physical activity (PA) is one of the most important factors for improving population health, but no standardised systems exist for international surveillance. The International Physical Activity Questionnaire (IPAQ) was developed for international surveillance. The purpose of this study was a comparative international study of population physical activity prevalence across 20 countries.</p> <p>Methods</p> <p>Between 2002–2004, a standardised protocol using IPAQ was used to assess PA participation in 20 countries [total N = 52,746, aged 18–65 years]. The median survey response rate was 61%. Physical activity levels were categorised as "low", "moderate" and "high". Age-adjusted prevalence estimates are presented by sex.</p> <p>Results</p> <p>The prevalence of "high PA" varied from 21–63%; in eight countries high PA was reported for over half of the adult population. The prevalence of "low PA" varied from 9% to 43%. Males more frequently reported high PA than females in 17 of 20 countries. The prevalence of low PA ranged from 7–41% among males, and 6–49% among females. Gender differences were noted, especially for younger adults, with males more active than females in most countries. Markedly lower physical activity prevalence (10% difference) with increasing age was noted in 11 of 19 countries for males, but only in three countries for women. The ways populations accumulated PA differed, with some reporting mostly vigorous intensity activities and others mostly walking.</p> <p>Conclusion</p> <p>This study demonstrated the feasibility of international PA surveillance, and showed that IPAQ is an acceptable surveillance instrument, at least within countries. If assessment methods are used consistently over time, trend data will inform countries about the success of their efforts to promote physical activity.</p

The rise and fall of Australian physical activity policy 1996 – 2006: a national review framed in an international context

Background: This paper provides an historical review of physical activity policy development in Australia for a period spanning a decade since the release of the US Surgeon General's Report on Physical Activity and Health in 1996 and including the 2004 WHO Global Strategy on Diet, Physical Activity and Health. Using our definition of 'HARDWIRED' policy criteria, this Australian review is compared with an international perspective of countries with established national physical activity policies and strategies (New Zealand, Canada, Brazil, Scotland, Switzerland, the Netherlands and Finland). Methods comprised a literature and policy review, audit of relevant web sites, document searches and surveys of international stakeholders. Results: All these selected countries embraced multi-strategic policies and undertook monitoring of physical activity through national surveys. Few committed to policy of more than three years duration and none undertook systematic evaluation of national policy implementation. This Australian review highlights phases of innovation and leadership in physical activity-related policy, as well as periods of stagnation and decline; early efforts were amongst the best in the world but by the mid-point of this review (the year 2000), promising attempts towards development of a national intersectoral policy framework were thwarted by reforms in the Federal Sport and Recreation sector. Several well received reviews of evidence on good practices in physical activity and public health were produced in the period but leadership and resources were lacking to implement the policies and programs indicated. Latterly, widespread publicity and greatly increased public and political interest in chronicdisease prevention, (especially in obesity and type 2 diabetes) have dominated the framework within which Australian policy deliberations have occurred. Finally, a national physical activity policy framework for the Health sector emerged, but not as a policy vision that was inclusive of the other essential sectors such as Education,Transport, Urban Planning as well as Sport and Recreation. Conclusion: Despite some progression of physical activity policy in the decade since 1995/6, this review found inconsistent policy development, both in Australia and elsewhere. Arguably, Australia has done no worse than other countries, but more effective responses to physical inactivity in populations can be built only on sustainable multi-sectoral public health policy partnerships that are well informed by evidence of effectiveness and good practice. In Australia and elsewhere prerequisites for success are political support, long-term investment and commitment to program implementation and evaluation. An urgent priority is media and political advocacy for physical activity focussed on these factors