1,702 research outputs found
Competing charge density waves and temperature-dependent nesting in 2H-TaSe2
Multiple charge density wave (CDW) phases in 2H-TaSe2 are investigated by
high-resolution synchrotron x-ray diffraction. In a narrow temperature range
immediately above the commensurate CDW transition, we observe a multi-q
superstructure with coexisting commensurate and incommensurate order
parameters, clearly distinct from the fully incommensurate state at higher
temperatures. This multi-q ordered phase, characterized by a temperature
hysteresis, is found both during warming and cooling, in contrast to previous
reports. In the normal state, the incommensurate superstructure reflection
gives way to a broad diffuse peak that persists nearly up to room temperature.
Its position provides a direct and accurate estimate of the Fermi surface
nesting vector, which evolves non-monotonically and approaches the commensurate
position as the temperature is increased. This behavior agrees with our recent
observations of the temperature-dependent Fermi surface in the same compound
[Phys. Rev. B 79, 125112 (2009)]
Lifetimes of antiferromagnetic magnons in two and three dimensions: experiment, theory, and numerics
A high-resolution neutron spectroscopic technique is used to measure
momentum-resolved magnon lifetimes in the prototypical two- and
three-dimensional antiferromagnets Rb2MnF4 and MnF2, over the full Brillouin
zone and a wide range of temperatures. We rederived theories of the lifetime
resulting from magnon-magnon scattering, thereby broadening their applicability
beyond asymptotically small regions of wavevector and temperature.
Corresponding computations, combined with a small contribution reflecting
collisions with domain boundaries, yield excellent quantitative agreement with
the data.Comment: 5 pages, 4 figure
The total assessment profile, volume 2
Appendices are presented which include discussions of interest formulas, factors in regionalization, parametric modeling of discounted benefit-sacrifice streams, engineering economic calculations, and product innovation. For Volume 1, see
The total assessment profile, volume 1
A methodology is described for the evaluation of societal impacts associated with the implementation of a new technology. Theoretical foundations for the methodology, called the total assessment profile, are established from both the economic and social science perspectives. The procedure provides for accountability of nonquantifiable factors and measures through the use of a comparative value matrix by assessing the impacts of the technology on the value system of the society
Electronic structure, magnetic and dielectric properties of the edge-sharing copper-oxide chain compound NaCuO
We report an experimental study of \nco, a Mott insulator containing chains
of edge-sharing CuO plaquettes, by polarized x-ray absorption spectroscopy
(XAS), resonant magnetic x-ray scattering (RMXS), magnetic susceptibility, and
pyroelectric current measurements. The XAS data show that the valence holes
reside exclusively on the Cu sites within the copper-oxide spin chains
and populate a -orbital polarized within the CuO plaquettes. The RMXS
measurements confirm the presence of incommensurate magnetic order below a
N\'eel temperature of K, which was previously inferred from
neutron powder diffraction and nuclear magnetic resonance data. In conjunction
with the magnetic susceptibility and XAS data, they also demonstrate a new
"orbital" selection rule for RMXS that is of general relevance for magnetic
structure determinations by this technique. Dielectric property measurements
reveal the absence of significant ferroelectric polarization below , which
is in striking contrast to corresponding observations on the isostructural
compound \lco. The results are discussed in the context of current theories of
multiferroicity.Comment: 7 pages, 7 figure
Ab initio calculation of the KRb dipole moments
The relativistic configuration interaction valence bond method has been used
to calculate permanent and transition electric dipole moments of the KRb
heteronuclear molecule as a function of internuclear separation. The permanent
dipole moment of the ground state potential is found to be
0.30(2) at the equilibrium internuclear separation with excess negative
charge on the potassium atom. For the potential the dipole moment
is an order of magnitude smaller (1 Cm) In addition, we
calculate transition dipole moments between the two ground-state and
excited-state potentials that dissociate to the K(4s)+Rb(5p) limits. Using this
data we propose a way to produce singlet KRb molecules by a
two-photon Raman process starting from an ultracold mixture of doubly
spin-polarized ground state K and Rb atoms. This Raman process is only allowed
due to relativistic spin-orbit couplings and the absence of gerade/ungerade
selection rules in heteronuclear dimers.Comment: 16 pages, 7 figure
Ground state properties of heavy alkali halides
We extend previous work on alkali halides by calculations for the heavy-atom
species RbF, RbCl, LiBr, NaBr, KBr, RbBr, LiI, NaI, KI, and RbI. Relativistic
effects are included by means of energy-consistent pseudopotentials,
correlations are treated at the coupled-cluster level. A striking deficiency of
the Hartree-Fock approach are lattice constants deviating by up to 7.5 % from
experimental values which is reduced to a maximum error of 2.4 % by taking into
account electron correlation. Besides, we provide ab-initio data for in-crystal
polarizabilities and van der Waals coefficients.Comment: accepted by Phys. Rev.
Quantification of Aluminum Increase Factors for Curtain Wall Design Using Finite Element Methods
Abstract not provide
Calcisponges have a ParaHox gene and dynamic expression of dispersed NK homeobox genes
This study was funded by the Sars Centre core budget to M. Adamska. Sequencing was performed at the Norwegian High Throughput Sequencing Centre funded by the Norwegian Research Council. O.M.R. and D.E.K.F. acknowledge support from the BBSRC and the School of Biology, University of St Andrews.Sponges are simple animals with few cell types, but their genomes paradoxically contain a wide variety of developmental transcription factors1,2,3,4, including homeobox genes belonging to the Antennapedia (ANTP) class5,6, which in bilaterians encompass Hox, ParaHox and NK genes. In the genome of the demosponge Amphimedon queenslandica, no Hox or ParaHox genes are present, but NK genes are linked in a tight cluster similar to the NK clusters of bilaterians5. It has been proposed that Hox and ParaHox genes originated from NK cluster genes after divergence of sponges from the lineage leading to cnidarians and bilaterians5,7. On the other hand, synteny analysis lends support to the notion that the absence of Hox and ParaHox genes in Amphimedon is a result of secondary loss (the ghost locus hypothesis)8. Here we analysed complete suites of ANTP-class homeoboxes in two calcareous sponges, Sycon ciliatum and Leucosolenia complicata. Our phylogenetic analyses demonstrate that these calcisponges possess orthologues of bilaterian NK genes (Hex, Hmx and Msx), a varying number of additional NK genes and one ParaHox gene, Cdx. Despite the generation of scaffolds spanning multiple genes, we find no evidence of clustering of Sycon NK genes. All Sycon ANTP-class genes are developmentally expressed, with patterns suggesting their involvement in cell type specification in embryos and adults, metamorphosis and body plan patterning. These results demonstrate that ParaHox genes predate the origin of sponges, thus confirming the ghost locus hypothesis8, and highlight the need to analyse the genomes of multiple sponge lineages to obtain a complete picture of the ancestral composition of the first animal genome.PostprintPeer reviewe
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Sheep as a silvicultural tool in coastal Douglas-fir forest
The International Hill Land Symposium was held at Oregon State University in April 1983.A study was conducted during 1981 and 1982 to evaluate the feasibility of using herded sheep as a silvicultural tool to suppress brush in Douglas-fir plantations of Oregon's coastal mountains. Effects of sheep grazing on vegetation were studied by comparing plants grown on grazed with those on ungrazed portions of five clearcut plantations.
Parameters monitored included sheep live weight gains, utilization of vegetation by sheep, soil moisture, and growth of Douglas-fir trees.
Browsing of Douglas-fir trees by sheep was most intense in the spring, then declined to low levels by July. Douglas-fir trees apparently
benefited from the grazing treatment. Diameter increase of trees
growing in grazed plantations was 7 to 14 percent greater than that of ungrazed controls. Height of trees of the end of the year was not
affected by grazing. Grazing did reduce, however, the amount of brush present on the study clearcuts compared to ungrazed control areas. At the end of the 1982 growing season, current year growth of browse
plants on ungrazed areas was 18 percent to 186 percent less than that in ungrazed areas. Regrowth of herbaceous plants, however, was stimulated by grazing. Soil moisture values for spring-grazed plantations were lower in the upper 60 cm of soil, but higher below 60 cm depth
when compared to control areas
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