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TL;DR: A microprojection protocol using the DuPont Biolistic™ particle delivery system and the β-glucuronidase (GUS) reporter gene fused with the 35S promoter of Cauliflower mosaic virus (CaMV) was developed for Picea mariana callus, and transient GUS gene expression was highest when cells were treated 5 and 6 days after subculturing to fresh media.
Abstract: A microprojection protocol using the DuPont Biolistic™ particle delivery system and the β-glucuronidase (GUS) reporter gene fused with the 35S promoter of Cauliflower mosaic virus (CaMV) was developed for Picea mariana callus. Comparison of four tungsten microprojectile sizes showed the highest transient gene expression with 1.11μm diameter particles. Adsorption of DNA on the microcarriers using calcium chloride led to higher GUS gene activity than using polyethylene glycol. GUS gene activity in P. mariana was the highest when cells were treated 5 and 6 days after subculturing to fresh media. The wheat ABA-inducible Em gene promoter yielded 4.5 times higher GUS gene activity than the 35S CaMV promoter. Comparison of transient GUS gene expression among 10 P. mariana embryogenic cell lines from six different open-pollinated families showed comparable gene activity, with the exception of one family showing no GUS gene activity.
52 citations
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TL;DR: In this article, the synthesis, crystal and magnetic properties and the bulk magnetic properties of Ca2FeCoO5, a brownmillerite type oxide, are presented, and the crystal structure, solved and refined from single crystal X-ray and powder neutron diffraction data, with cell parameters, a = 5.3652(3) A, b = 11.0995(5) A.
Abstract: The synthesis, crystal, and magnetic structures and the bulk magnetic properties of Ca2FeCoO5, a brownmillerite type oxide, are presented. The crystal structure, solved and refined from single crystal X-ray and powder neutron diffraction data, is described in Pbcm with cell parameters, a = 5.3652(3) A, b = 11.0995(5) A, c = 14.7982(7) A. Thus, one axis, b in this setting, is doubled in comparison with the standard brownmillerite structure description giving rise to two sets of octahedral and tetrahedral sites. Aided by the strong scattering contrast between Fe and Co for neutrons, a nearly perfect intralayer cation site ordering, not observed for any brownmillerite before, is detected in the tetrahedral layers. There is a lesser degree of cation site ordering in the octahedral sites. Overall, the Fe/Co site ordering is of the NaCl type both within and between the tetrahedral and octahedral layers. There are also both intra- and interlayer ordering of tetrahedral chain orientations. The left- and right-han...
52 citations
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TL;DR: In this article, a rotated triangular tube bundle of tube-to-diameter ratio of 1.5 was tested over a broad range of void fractions and mass fluxes, and well defined fluidelastic instability, random turbulence excitation, and damping were investigated.
Abstract: Two-phase cross-flow exists in many shell-and-tube heat exchangers. The U-bend region of nuclear steam generators is a prime example. Testing in two-phase flow simulated by air-water provides useful results inexpensively. However, two-phase flow parameters, in particular surface tension and density ratio, are considerably different in air-water than in steam-water. A reasonable compromise is testing in liquid-vapor Freon, which is much closer to steam-water while much simpler experimentally. This paper presents the first results of a series of tests on the vibration behavior of tube bundles subjected to two-phase Freon cross-flow. A rotated triangular tube bundle of tube-to-diameter ratio of 1.5 was tested over a broad range of void fractions and mass fluxes. Fluidelastic instability, random turbulence excitation, and damping were investigated. Well-defined fluidelastic instabilities were observed in continuous two-phase flow regimes. However, intermittent two-phase flow regimes had a dramatic effect on fluidelastic instability. Generally, random turbulence excitation forces are much lower in Freon than in air-water. Damping is very dependent on void fraction, as expected.
52 citations
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TL;DR: The results show that quasiparticles in a system hitherto thought of as "classical" can indeed break down, and all three key features of the nonlinear effects as theoretically predicted are observed, in the inelastic neutron scattering measurements of single crystal LuMnO3.
Abstract: The breakdown of magnons, the quasiparticles of magnetic systems, has rarely been seen. By using an inelastic neutron scattering technique, we report the observation of spontaneous magnon decay in multiferroic ${\mathrm{LuMnO}}_{3}$, a simple two dimensional Heisenberg triangular lattice antiferromagnet, with large spin $S=2$. The origin of this rare phenomenon lies in the nonvanishing cubic interaction between magnons in the spin Hamiltonian arising from the noncollinear 120\ifmmode^\circ\else\textdegree\fi{} spin structure. We observed all three key features of the nonlinear effects as theoretically predicted: a rotonlike minimum, a flat mode, and a linewidth broadening, in our inelastic neutron scattering measurements of single crystal ${\mathrm{LuMnO}}_{3}$. Our results show that quasiparticles in a system hitherto thought of as ``classical'' can indeed break down.
52 citations
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TL;DR: Two B-site ordered double perovskites were investigated as geometrically frustrated antiferromagnets, using x-ray and neutron diffraction, superconducting quantum interference device magnetometry, heat capacity, muon spin relaxation, and magic-angle spinning (MAS) NMR.
Abstract: Two B-site ordered double perovskites, ${\text{La}}_{2}{\text{LiReO}}_{6}$ and ${\text{Ba}}_{2}{\text{YReO}}_{6}$, with $S=1$ were investigated as geometrically frustrated antiferromagnets, using x-ray and neutron diffraction, superconducting quantum interference device magnetometry, heat capacity, muon spin relaxation $(\ensuremath{\mu}\text{SR})$, and $^{89}\text{Y}$ magic-angle spinning (MAS) NMR. ${\text{La}}_{2}{\text{LiReO}}_{6}$ has a monoclinic structure $(\text{P}{2}_{1}/\text{n})$ with cell parameters at room temperature; $a=5.58262(22)\text{ }\text{\AA{}}$, $b=5.67582(20)\text{ }\text{\AA{}}$, $c=7.88586(27)\text{ }\text{\AA{}}$, and $\ensuremath{\beta}=90.240(4)\ifmmode^\circ\else\textdegree\fi{}$. A zero-field cooled/field cooled (ZFC/FC) divergence at 50 K was observed in the susceptibility. The ZFC susceptibility is zero below $\ensuremath{\sim}5\text{ }\text{K}$ for polycrystalline samples, suggesting a cooperative singlet ground state but weak moments are induced by cooling in very small fields $\ensuremath{\sim}1\text{ }\text{mT}$. No evidence of long-range ordering is evident in heat capacity, neutron-diffraction, or $\ensuremath{\mu}\text{SR}$ data. The ZF spin dynamics from $\ensuremath{\mu}\text{SR}$ are anomalous and can be fitted to a stretched exponential rather than the Kubo-Toyabe form expected for random frozen spins but the muon spins are decoupled in longitudinal fields (LF), consistent with spin freezing of the fraction of spins relaxing within the muon time scale. The internal fields sensed by the muons are anomalously small, consistent with an electronic spin-singlet state. ${\text{Ba}}_{2}{\text{YReO}}_{6}$ is found to be cubic (Fm3m) with cell parameter $a=8.36278(2)\text{ }\text{\AA{}}$ at 300 K with no change in symmetry at 3.8 K, at variance with the Jahn-Teller theorem for a ${t}_{2\text{g}}^{2}$ configuration for ${\text{Re}}^{5+}$. $^{89}\text{Y}$ MAS NMR shows a single peak indicating that Y/Re site disorder is at most 0.5%. The susceptibility shows two broad peaks around 50 and 25 K but no evidence for long-range order from heat capacity, neutron diffraction, or $\ensuremath{\mu}\text{SR}$. The ZF $\ensuremath{\mu}\text{SR}$ result shows a two-component ground state with both slow and fast relaxations and decoupling results in a 1 kG LF, indicating spin freezing. These results are in sharp contrast to the long-range AF order found in the $S=3/2$ isostructural materials, ${\text{La}}_{2}{\text{LiRuO}}_{6}$ and ${\text{Ba}}_{2}{\text{YRuO}}_{6}$, indicating that the reduction to $S=1$ plays a major role in ground state determination.
52 citations
Authors
Showing all 2298 results
Name | H-index | Papers | Citations |
---|---|---|---|
Michael D. Guiver | 78 | 288 | 20540 |
Robert J. Birgeneau | 78 | 587 | 22686 |
Mike D. Flannigan | 71 | 211 | 21327 |
Martin T. Dove | 61 | 396 | 14767 |
Luis Rodrigo | 58 | 341 | 12963 |
André Longtin | 56 | 260 | 16372 |
David Mitlin | 56 | 196 | 15479 |
John Katsaras | 55 | 220 | 9263 |
John E. Greedan | 55 | 391 | 12171 |
Gang Li | 48 | 406 | 7713 |
Matthew G. Tucker | 45 | 224 | 7288 |
Bruce D. Gaulin | 45 | 284 | 6698 |
Erick J. Dufourc | 43 | 144 | 5882 |
Norbert Kučerka | 43 | 119 | 7319 |
Stephen J. Skinner | 42 | 194 | 8522 |