Study of iron-borate materials systems processed in space

It was calculated that an FeBO3B2O3 glass-ceramic containing only 1 mole% FeBO3 would be equivalent for magnetooptic application to a YIG crystal of equal thickness. An Fe2O3B2O3 composition containing 2 mole% FeBO3 equivalent (98B) could be converted largely to a dense green, though opaque, FeBO3 glass-ceramic through suitable heat treatments. However, phase separation (and segregation) and Fe+3 reduction could not be entirely avoided with the various procedures that were employed. From light scattering calculations, it was estimated that about 100 A to allow 90% light transmission through a 1 cm thick sample. However, the actual FeBO3 crystallite sizes obtained in 98B were of the order of 1 micron or greater

Neutron diffraction studies on liquids

The above examples serve to illustrate the extent to which neutron diffraction isotopic substitution methods have been used to determine interatomic structure in a wide range of liquid and amorphous systems. The direct determination of pair radial functions not only offers a means of characterising the different structures in liquids, but also provides theorists with information to construct more realistic model potentials which can be used to explore properties in regimes not currently accessible to experiment.\ud \ud It is anticipated that the NDIS methods will continue to be developed and applied to a wider range of systems. The construction and commissioning of new diffractometers with higher count rates, such as D20 and D4C at ILL, and GEM at ISIS with an optimised sample environment for work at non-ambient conditions will enable new and more extensive research to be undertaken. Besides the many problems of immediate interest suggested at the end of some sections, there are several investigations which will become feasible in the longer term as the technology develops. These include: (i) the use of isotopes such as 12C and 13C which will enable detailed and extensive structural studies to be carried out on a wide range of biologically significant materials, and (ii) the exploitation of higher count rates to investigate changes of structure as a chemical reaction occurs

Development of improved amorphous materials for laser systems

Crystallization calculations were performed in order to determine the possibility of forming a particular type of laser glass with the avoidance of devitrification in an outer space laboratory. It was demonstrated that under the homogenuous nucleating conditions obtainable in a zero gravity laboratory this laser glass may be easily quenched to a virtually crystal-free product. Experimental evidence is provided that use of this material as a host in a neodymium glass laser would result in more than a 10 percent increase in efficiency when compared to laser glass rods of a similar composition currently commercially available. Differential thermal analysis, thermal gradient oven, X-ray diffraction, and liquidus determination experiments were carried out to determine the basics of the crystallization behavior of the glass, and small-angle X-ray scattering and splat-cooling experiments were performed in order to provide additional evidence for the feasibility of producing this laser glass material, crystal free, in an outer space environment

Neutron and X-ray diffraction studies on complex liquids

The above examples illustrate the extent to which present day neutron and X-ray diffraction methods are being used to determine interatomic structure in a wide range of liquid and amorphous systems. The determination of pair radial distribution functions not only offers a means to characterise different structures in liquids, but also provides theorists with information to construct realistic model potentials that can be used to calculate macroscopic behaviour and structural properties in regimes not currently accessible to experiment.\ud The well-established NDIS difference methods remain superior to all other methods for the determination of interatomic pairwise structure. The relatively new AXD (or DAS) difference methods have the potential to answer long-standing questions about the structure around species with mass number greater than about 30. However, the relatively low X-ray scattering power from light elements such as hydrogen, carbon, nitrogen etc. means that it will never be possible to resolve completely structures of biologically important liquids by X-ray methods alone. EXAFS spectroscopy has the distinct advantage over both diffraction techniques as it can be used to study local structure around particular species at high dilution. Therefore studies which combine reference data from AXD or NDIS, with extensive EXAFS data, are likely to be useful in studies of structure in regimes which prove difficult for AXD and NDIS. \ud It is clear that no one method will be sufficient to resolve structure at the required level of detail around all species in a complex liquid. Instead one must rely on a full complement of diffraction and other techniques including computer simulation to determine the complete atomic structure of a complex liquid or amorphous system.\ud On the technical front, the construction and commissioning of new neutron diffractometers with higher count rates, such as D20 and D4C at ILL, and GEM at ISIS with an optimised sample environment for work at non-ambient conditions, will enable new and more extensive research to be undertaken. Additionally, the new custom-built X-ray diffractometer for liquids proposed for the DIAMOND synchrotron being established at RAL will provide a much-needed boost for wide-ranging AXD and EXAFS investigations of complex liquids. \ud Besides the many studies of immediate interest suggested at the end of some sections, there are several investigations that will become feasible in the longer term as the technology develops. These include 1. the use of isotopes such as 12C and 13C and 33S and 32S which will enable detailed and extensive structural studies to be carried out on a wide range of biologically significant materials, and 2. the exploitation of higher neutron and X-ray count rates to facilitate real time experiments to investigate changes of structure as a chemical or biochemical reaction occurs. \ud The one strong theme which emerges from all the work described in this paper is that diffraction, especially that based on difference techniques, remains the best means to determine structure at atomic resolution in complex liquids

Preschool Children\u27s Development in Number, Geometry, and Executive Function: A Cross-Lagged Examination

Children develop rapidly during early childhood, and this includes their mathematics and executive function (EF) skills. Past research has focused on connections between early mathematics and EF, but more work was needed to fully understand these relations. In particular, past studies have generally used numeracy-based measures to assess early mathematics, although professional guidelines indicate a more comprehensive construct that includes geometry. The research herein addresses some of the gaps of previous work as it examines unique connections between early number, geometry, and EF. One hundred eighteen preschool children from urban and rural communities, being an average age of 53 months at the beginning of the preschool year, were assessed at both the beginning and end of the preschool year. Using the TEAM, a measure of early mathematics inclusive of number and geometry, and the Head Toes Knees Shoulders (HTKS), a measure of early EF with elements of working memory, inhibition, and cognitive shift, relationships between number, geometry, and EF were examined across the preschool year, using a cross-lagged panel model. Three-way ANOVAs were also used to examine differences based on demographic factors, specifically gender, maternal education, household income, and urbanicity (defined by USDA Rural-Urban Continuum Codes). Findings indicate demographic factors played a limited role; household income was significantly associated with number skills and urbanicity with EF skills at the beginning of the preschool year. No other significant relationships based on demographic variables were found. Number skills at Time 1 universally contributed to number, geometry, and EF performance at Time 2; geometry at Time 2 was universally influenced by number, geometry, and EF at Time 1. EF played a mixed role; Time 1 EF significantly predicted Time 2 geometry, and Time 2 EF was significantly predicted by Time 1 number skills. These findings suggest that geometry is an important area of early mathematics to consider, and the relationship between mathematics and EF may be more nuanced than previously understood

The strange evolution of the Large Magellanic Cloud Cepheid OGLE-LMC-CEP1812

Classical Cepheids are key probes of both stellar astrophysics and cosmology as standard candles and pulsating variable stars. It is important to understand Cepheids in unprecedented detail in preparation for upcoming GAIA, JWST and extremely-large telescope observations. Cepheid eclipsing binary stars are ideal tools for achieving this goal, however there are currently only three known systems. One of those systems, OGLE-LMC-CEP1812, raises new questions about the evolution of classical Cepheids because of an apparent age discrepancy between the Cepheid and its red giant companion. We show that the Cepheid component is actually the product of a stellar merger of two main sequence stars that has since evolved across the Hertzsprung gap of the HR diagram. This post-merger product appears younger than the companion, hence the apparent age discrepancy is resolved. We discuss this idea and consequences for understanding Cepheid evolution.Comment: 5 pages, 3 figures, accepted to A&

Classical Cepheids Require Enhanced Mass Loss

Measurements of rates of period change of Classical Cepheids probe stellar physics and evolution. Additionally, better understanding of Cepheid structure and evolution provides greater insight into their use as standard candles and tools for measuring the Hubble constant. Our recent study of the period change of the nearest Cepheid, Polaris, suggested that it is undergoing enhanced mass loss when compared to canonical stellar evolution model predictions. In this work, we expand the analysis to rates of period change measured for about 200 Galactic Cepheids and compare them to population synthesis models of Cepheids including convective core overshooting and enhanced mass loss. Rates of period change predicted from stellar evolution models without mass loss do not agree with observed rates whereas including enhanced mass loss yields predicted rates in better agreement with observations. This is the first evidence that enhanced mass loss as suggested previously for Polaris and delta Cephei must be a ubiquitous property of Classical Cepheids.Comment: 6 pages, 4 figures, Accepted for publication in ApJ Letter