172 research outputs found
Profound genetic divergence and asymmetric parental genome contributions as hallmarks of hybrid speciation in polyploid toads.
The evolutionary causes and consequences of allopolyploidization, an exceptional pathway to instant hybrid speciation, are poorly investigated in animals. In particular, when and why hybrid polyploids versus diploids are produced, and constraints on sources of paternal and maternal ancestors, remain underexplored. Using the Palearctic green toad radiation (including bisexually reproducing species of three ploidy levels) as model, we generate a range-wide multi-locus phylogeny of 15 taxa and present four new insights: (i) at least five (up to seven) distinct allotriploid and allotetraploid taxa have evolved in the Pleistocene; (ii) all maternal and paternal ancestors of hybrid polyploids stem from two deeply diverged nuclear clades (6 Mya, 3.1-9.6 Mya), with distinctly greater divergence than the parental species of diploid hybrids found at secondary contact zones; (iii) allotriploid taxa possess two conspecific genomes and a deeply diverged allospecific one, suggesting that genomic imbalance and divergence are causal for their partly clonal reproductive mode; (iv) maternal versus paternal genome contributions exhibit asymmetry, with the maternal nuclear (and mitochondrial) genome of polyploids always coming from the same clade, and the paternal genome from the other. We compare our findings with similar patterns in diploid/polyploid vertebrates, and suggest deep ancestral divergence as a precondition for successful allopolyploidization
Magneto-optic Kerr effect in a spin-polarized zero-moment ferrimagnet
The magneto-optical Kerr effect (MOKE) is often assumed to be proportional to
the magnetisation of a magnetically ordered metallic sample; in metallic
ferrimagnets with chemically distinct sublattices, such as rare-earth
transition-metal alloys, it depends on the difference between the sublattice
contributions. Here we show that in a highly spin polarized, fully compensated
ferrimagnet, where the sublattices are chemically similar, MOKE is observed
even when the net moment is strictly zero. We analyse the spectral ellipsometry
and MOKE of Mn 2 Ru x Ga, and show that this behaviour is due to a highly
spin-polarized conduction band dominated by one of the two manganese
sublattices which creates helicity-dependent reflectivity determined by a broad
Drude tail. Our findings open new prospects for studying spin dynamics in the
infra-red.Comment: 7 pages, 7 figure
Dynamical charge density fluctuations pervading the phase diagram of a Cu-based high-Tc superconductor
Charge density waves are a common occurrence in all families of high critical
temperature superconducting cuprates. Although consistently observed in the
underdoped region of the phase diagram and at relatively low temperatures, it
is still unclear to what extent they influence the unusual properties of these
systems. Using resonant x-ray scattering we carefully determined the
temperature dependence of charge density modulations in
(Y,Nd)BaCuO for three doping levels. We discovered
short-range dynamical charge density fluctuations besides the previously known
quasi-critical charge density waves. They persist up to well above the
pseudogap temperature T*, are characterized by energies of few meV and pervade
a large area of the phase diagram, so that they can play a key role in shaping
the peculiar normal-state properties of cuprates.Comment: 34 pages, 4 figures, 11 supplementary figure
C7 is expressed on endothelial cells as a trap for the assembling terminal complement complex and may exert anti-inflammatory function
We describe a novel localization of C7 as a membrane-bound molecule on endothelial cells (ECs). Data obtained by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), Western blot analysis, Northern blot analysis, and mass spectrometry revealed that membrane- associated C7 (mC7) was indistinguish-able from soluble C7 and was associated with vimentin on the cell surface. mC7 interacted with the other late complement components to form membrane-bound TCC (mTCC). Unlike the soluble SC5b-9, mTCC failed to stimulate ECs to express adhesion molecules, to secrete IL-8, and to induce albumin leakage through a monolayer of ECs, and more importantly protected ECs from the proinflammatory effect of SC5b-9. Our data disclose the possibility of a novel role of mC7 that acts as a trap for the late complement components to control excessive inflammation induced by SC5b-9. \ua9 2009 by The American Society of Hematology
Polarization resolved Cu -edge resonant inelastic x-ray scattering of orbital and spin excitations in NdBaCuO
High resolution resonant inelastic x-ray scattering (RIXS) has proven
particularly effective in the determination of crystal field and spin
excitations in cuprates. Its strength lies in the large Cu resonance
and in the fact that the scattering cross section follows quite closely the
single-ion model predictions, both in the insulating parent compounds and in
the superconducting doped materials. However, the spectra become increasingly
broader with (hole) doping, hence resolving and assigning spectral features has
proven challenging even with the highest energy resolution experimentally
achievable. Here we have overcome this limitation by measuring the complete
polarization dependence of the RIXS spectra as function of momentum transfer
and doping in thin films of NdBaCuO. Besides
confirming the previous assignment of and spin excitations (magnon,
bimagnon) in the antiferromagnetic insulating parent compound, we unequivocally
single out the actual spin-flip contribution at all dopings. We also
demonstrate that the softening of excitations is mainly attributed to the
shift of the peak to lower energy loss. These results provide a definitive
assessment of the RIXS spectra of cuprates and demonstrate that RIXS
measurements with full polarization control are practically feasible and highly
informative.Comment: 14 pages, 10 figure
Crystalline and magnetic structure of Ba2CuO3+{\delta} investigated by x-ray absorption spectroscopy and resonant inelastic x-ray scattering
Motivated by the recent synthesis of BaCuO (BCO), a high
temperature superconducting cuprate with putative ground state
symmetry, we investigated its electronic structure by means of Cu x-ray
absorption (XAS) and resonant inelastic x-ray scattering (RIXS) at the Cu
edge on a polycrystalline sample. We show that the XAS profile of BCO is
characterised by two peaks associated to inequivalent Cu sites, and that its
RIXS response features a single, sharp peak associated to crystal-field
excitations. We argue that these observations are only partially compatible
with the previously proposed crystal structure of BCO. Based on our
spectroscopic results and on previously published powder diffraction
measurements, we propose a crystalline structure characterized by two
inequivalent Cu sites located at alternated planes along the axis:
nominally trivalent Cu(1) belonging to very short Cu-O chains, and divalent
Cu(2) in the oxygen deficient CuO planes. We also analyze the
low-energy region of the RIXS spectra to estimate the magnitude of the magnetic
interactions in BCO and find that in-plane nearest neighbor superexchange
exceeds 120~meV, similarly to that of other layered cuprates. Although these
results do not support the pure ground state scenario, they hint
at a significant departure from the common quasi-2D electronic structure of
superconducting cuprates of pure symmetry
Symmetry breaking at the (111) interfaces of SrTiO hosting a 2D-electron system
We used x-ray absorption spectroscopy to study the orbital symmetry and the
energy band splitting of (111) LaAlO/SrTiO and
LaAlO/EuTiO/SrTiO heterostructures, hosting a quasi
two-dimensional electron system (q2DES), and of a Ti-terminated (111)
SrTiO single crystal, also known to form a q2DES at its surface. We
demonstrate that the bulk tetragonal Ti-3d D crystal field is
turned into trigonal D crystal field in all cases. The symmetry
adapted a and e orbitals are non-degenerate in energy and
their splitting, \Delta, is positive at the bare STO surface but negative in
the heterostructures, where the a orbital is lowest in energy.
These results demonstrate that the interfacial symmetry breaking induced by
epitaxial engineering of oxide interfaces has a dramatic effect on their
electronic properties, and it can be used to manipulate the ground state of the
q2DES.Comment: 6 pages article, plus 5 pages supplementary informatio
Depth-resolved resonant inelastic x-ray scattering at a superconductor/half-metallic-ferromagnet interface through standing wave excitation
We demonstrate that combining standing wave (SW) excitation with resonant inelastic x-ray scattering (RIXS) can lead to depth resolution and interface sensitivity for studying orbital and magnetic excitations in correlated oxide heterostructures. SW-RIXS has been applied to multilayer heterostructures consisting of a superconductor La1.85Sr0.15CuO4 (LSCO) and a half-metallic ferromagnet La0.67Sr0.33MnO3 (LSMO). Easily observable SW effects on the RIXS excitations were found in these LSCO/LSMO multilayers. In addition, we observe different depth distribution of the RIXS excitations. The magnetic excitations are found to arise from the LSCO/LSMO interfaces, and there is also a suggestion that one of the dd excitations comes from the interfaces. SW-RIXS measurements of correlated-oxide and other multilayer heterostructures should provide unique layer-resolved insights concerning their orbital and magnetic excitations, as well as a challenge for RIXS theory to specifically deal with interface effects
Gapped collective charge excitations and interlayer hopping in cuprate superconductors
We use resonant inelastic x-ray scattering (RIXS) to probe the propagation of
plasmons in the electron-doped cuprate superconductor
SrLaCuO (SLCO). We detect a plasmon gap of ~120 meV
at the two-dimensional Brillouin zone center, indicating that low-energy
plasmons in SLCO are not strictly acoustic. The plasmon dispersion, including
the gap, is accurately captured by layered -- model calculations. A
similar analysis performed on recent RIXS data from other cuprates suggests
that the plasmon gap is generic and its size is related to the magnitude of the
interlayer hopping . Our work signifies the three-dimensionality of the
charge dynamics in layered cuprates and provides a new method to determine
.Comment: 17 pages, 10 figures, includes Supplemental Material. Accepted for
publication in Physical Review Letter
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