910 research outputs found
Growth and Characterization of -Mn Structured CoZn Thin Films
Thin films of polycrystalline -Mn structure CoZn have been grown on
thermally oxidized Si substrates by co-sputtering from elemental targets
followed by annealing. A range of films grown with variable Co deposition power
and fixed Zn deposition power were produced, so as to vary the proportions of
the two elements reaching the substrate, which were annealed post-growth.
Whilst all films exhibited a (211) -Mn structure CoZn texture in X-ray
diffraction, transmission electron microscopy showed that the composition with
the highest integrated intensity for that Bragg peak contained large vacancies
and was covered by a thick ZnO cap owing to being Co-deficient overall. CoZn
films deposited at ratios tuned to give the optimal volume fraction of
-Mn were continuous, with crystallites up to 200~nm in size, with a much
thinner ZnO cap layer. Magnetic measurements show that such optimal CoZn films
have a Curie temperature ~K and saturation magnetization
of 120~emu/cm, properties close to those reported for bulk crystals. The
-Mn structure is chiral (P432/P432 space group) and is known
to give rise to a Dzyaloshinkii-Moriya interaction (DMI) that stabilizes
room-temperature skyrmions in the bulk. Our thin films are thus a potential
materials platform, compatible with planar processing technology, for magnetic
skyrmions arising from a bulk DMI.Comment: v2 corrects minor typographical error
The malleability of uranium: manipulating the charge-density wave in epitaxial films
We report x-ray synchrotron experiments on epitaxial films of uranium,
deposited on niobium and tungsten seed layers. Despite similar lattice
parameters for these refractory metals, the uranium epitaxial arrangements are
different and the strains propagated along the a-axis of the uranium layers are
of opposite sign. At low temperatures these changes in epitaxy result in
dramatic modifications to the behavior of the charge-density wave in uranium.
The differences are explained with the current theory for the electron-phonon
coupling in the uranium lattice. Our results emphasize the intriguing
possibilities of producing epitaxial films of elements that have complex
structures like the light actinides uranium to plutonium.Comment: 6 pages, 6 figure
Positional, Reorientational and Bond Orientational Order in DNA Mesophases
We investigate the orientational order of transverse polarization vectors of
long, stiff polymer molecules and their coupling to bond orientational and
positional order in high density mesophases. Homogeneous ordering of transverse
polarization vector promotes distortions in the hexatic phase, whereas
inhomogeneous ordering precipitates crystalization of the 2D sections with
different orientations of the transverse polarization vector on each molecule
in the unit cell. We propose possible scenarios for going from the hexatic
phase, through the distorted hexatic phase to the crystalline phase with an
orthorhombic unit cell observed experimentally for the case of DNA.Comment: 4 pages, 2 figure
TaMSH7: A cereal mismatch repair gene that affects fertility in transgenic barley (Hordeum vulgare L.)
Background: Chromosome pairing, recombination and DNA repair are essential processes during meiosis in sexually reproducing organisms. Investigating the bread wheat (Triticum aestivum L.) Ph2 (Pairing homoeologous) locus has identified numerous candidate genes that may have a role in controlling such processes, including TaMSH7, a plant specific member of the DNA mismatch repair family. Results: Sequencing of the three MSH7 genes, located on the short arms of wheat chromosomes 3A, 3B and 3D, has revealed no significant sequence divergence at the amino acid level suggesting conservation of function across the homoeogroups. Functional analysis of MSH7 through the use of RNAi loss-of-function transgenics was undertaken in diploid barley (Hordeum vulgare L.). Quantitative real-time PCR revealed several T0 lines with reduced MSH7 expression. Positive segregants from two T1 lines studied in detail showed reduced MSH7 expression when compared to transformed controls and null segregants. Expression of MSH6, another member of the mismatch repair family which is most closely related to the MSH7 gene, was not significantly reduced in these lines. In both T1 lines, reduced seed set in positive segregants was observed. Conclusion: Results presented here indicate, for the first time, a distinct functional role for MSH7 in vivo and show that expression of this gene is necessary for wild-type levels of fertility. These observations suggest that MSH7 has an important function during meiosis and as such remains a candidate for Ph2.Andrew H Lloyd, Andrew S Milligan, Peter Langridge, and Jason A Abl
The impact of drought on wheat leaf cuticle properties
BACKGROUND: The plant cuticle is the outermost layer covering aerial tissues and is composed of cutin and waxes. The cuticle plays an important role in protection from environmental stresses and glaucousness, the bluish-white colouration of plant surfaces associated with cuticular waxes, has been suggested as a contributing factor in crop drought tolerance. However, the cuticle structure and composition is complex and it is not clear which aspects are important in determining a role in drought tolerance. Therefore, we analysed residual transpiration rates, cuticle structure and epicuticular wax composition under well-watered conditions and drought in five Australian bread wheat genotypes, Kukri, Excalibur, Drysdale, RAC875 and Gladius, with contrasting glaucousness and drought tolerance. RESULTS: Significant differences were detected in residual transpiration rates between non-glaucous and drought-sensitive Kukri and four glaucous and drought-tolerant lines. No simple correlation was found between residual transpiration rates and the level of glaucousness among glaucous lines. Modest differences in the thickness of cuticle existed between the examined genotypes, while drought significantly increased thickness in Drysdale and RAC875. Wax composition analyses showed various amounts of C31 ß-diketone among genotypes and increases in the content of alkanes under drought in all examined wheat lines. CONCLUSIONS: The results provide new insights into the relationship between drought stress and the properties and structure of the wheat leaf cuticle. In particular, the data highlight the importance of the cuticle’s biochemical makeup, rather than a simple correlation with glaucousness or stomatal density, for water loss under limited water conditions.Huihui Bi, Nataliya Kovalchuk, Peter Langridge, Penny J. Tricker, Sergiy Lopato, and Nikolai Borisju
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