1,217 research outputs found
Charge-Transfer Excitations in the Model Superconductor HgBaCuO
We report a Cu -edge resonant inelastic x-ray scattering (RIXS) study of
charge-transfer excitations in the 2-8 eV range in the structurally simple
compound HgBaCuO at optimal doping ( K).
The spectra exhibit a significant dependence on the incident photon energy
which we carefully utilize to resolve a multiplet of weakly-dispersive ( eV) electron-hole excitations, including a mode at 2 eV. The observation
of this 2 eV excitation suggests the existence of a charge-transfer pseudogap
deep in the superconducting phase. Quite generally, our data demonstrate the
importance of exploring the incident photon energy dependence of the RIXS cross
section.Comment: 5 pages, 3 figure
Unraveling the Nature of Charge Excitations in LaCuO with Momentum-Resolved Cu -edge Resonant Inelastic X-ray Scattering
Results of model calculations using exact diagonalization reveal the orbital
character of states associated with different Raman loss peaks in Cu -edge
resonant inelastic X-ray scattering (RIXS) from LaCuO. The model
includes electronic orbitals necessary to highlight non-local Zhang-Rice
singlet, charge transfer and - excitations, as well as states with apical
oxygen 2 character. The dispersion of these excitations is discussed with
prospects for resonant final state wave-function mapping. A good agreement with
experiments emphasizes the substantial multi-orbital character of RIXS profiles
in the energy transfer range 1-6 eV.Comment: Original: 4.5 pages. Replaced: 4 pages and 4 figures with updated
content and reference
Receptor-independent metabolism of platelet-activating factor by myelogenous cells
AbstractHuman neutrophils incorporate and metabolize platelet-activating factor (PAF). We dissociated these events from PAF binding to its receptors. Cells were pretreated with either pronase, a PAF antagonist (L652731), or excess PAF. This reduced PAF receptor numbers by 70 to almost 100% but had no comparable effect upon the neutrophil's ability to metabolize PAF. Furthermore, HL-60 cells efficiently metabolized, but did not specifically bind, PAF. Thus, PAF receptor availability did not correlate with PAF metabolic capacity and we conclude that myelogenous tissues can process this bioactive ligand by a receptor-independent pathway
Fragmentation of small carbon clusters, a review
An overview of the works devoted to fragmentation of small carbon clusters is given in a first part. Fragmentation of swift neutral and (multi) charged carbon clusters studied with the AGAT spectrometer is presented and discussed in a second part
The global clonal complexity of the murine blood system declines throughout life and after serial transplantation.
Although many recent studies describe the emergence and prevalence of "clonal hematopoiesis of indeterminate potential" in aged human populations, a systematic analysis of the numbers of clones supporting steady-state hematopoiesis throughout mammalian life is lacking. Previous efforts relied on transplantation of "barcoded" hematopoietic stem cells (HSCs) to track the contribution of HSC clones to reconstituted blood. However, ex vivo manipulation and transplantation alter HSC function and thus may not reflect the biology of steady-state hematopoiesis. Using a noninvasive in vivo color-labeling system, we report the first comprehensive analysis of the changing global clonal complexity of steady-state hematopoiesis during the natural murine lifespan. We observed that the number of clones (ie, clonal complexity) supporting the major blood and bone marrow hematopoietic compartments decline with age by ∼30% and ∼60%, respectively. Aging dramatically reduced HSC in vivo-repopulating activity and lymphoid potential while increasing functional heterogeneity. Continuous challenge of the hematopoietic system by serial transplantation provoked the clonal collapse of both young and aged hematopoietic systems. Whole-exome sequencing of serially transplanted aged and young hematopoietic clones confirmed oligoclonal hematopoiesis and revealed mutations in at least 27 genes, including nonsense, missense, and deletion mutations in Bcl11b, Hist1h2ac, Npy2r, Notch3, Ptprr, and Top2b
Craters Hosting Radar-Bright Deposits in Mercury's North Polar Region: Areas of Persistent Shadow Determined from MESSENGER Images
Radar-bright features near Mercury's poles were discovered in Earth-based radar images and proposed to be water ice present in permanently shadowed areas. Images from MESSENGER's one-year primary orbital mission provide the first nearly complete view of Mercury’s north polar region, as well as multiple images of the surface under a range of illumination conditions. We find that radar-bright features near Mercury's north pole are associated with locations persistently shadowed in MESSENGER images. Within 10 degrees of the pole, almost all craters larger than 10 km in diameter host radar-bright deposits. There are several craters located near Mercury's north pole with sufficiently large diameters to enable long-lived water ice to be thermally stable at the surface within regions of permanent shadow. Craters located farther south also host radar-bright deposits and show a preference for cold-pole longitudes; thermal models suggest that a thin insulating layer is required to cover these deposits if the radar-bright material consists predominantly of longlived water ice. Many small (less than 10 km diameter) and low-latitude (extending southward to 66 degrees N) craters host radar-bright material, and water ice may not be thermally stable in these craters for ~1 Gy, even beneath an insulating layer. The correlation of radar-bright features with persistently shadowed areas is consistent with the deposits being composed of water ice, and future thermal modeling of small and low-latitude craters has the potential to further constrain the nature, source, and timing of emplacement of the radar-bright material
Plasma Membrane Factor XIIIA Transglutaminase Activity Regulates Osteoblast Matrix Secretion and Deposition by Affecting Microtubule Dynamics
Transglutaminase activity, arising potentially from transglutaminase 2 (TG2) and
Factor XIIIA (FXIIIA), has been linked to osteoblast differentiation where it is
required for type I collagen and fibronectin matrix deposition. In this study we
have used an irreversible TG-inhibitor to ‘block –and-track’
enzyme(s) targeted during osteoblast differentiation. We show that the
irreversible TG-inhibitor is highly potent in inhibiting osteoblast
differentiation and mineralization and reduces secretion of both fibronectin and
type I collagen and their release from the cell surface. Tracking of the dansyl
probe by Western blotting and immunofluorescence microscopy demonstrated that
the inhibitor targets plasma membrane-associated FXIIIA. TG2 appears not to
contribute to crosslinking activity on the osteoblast surface. Inhibition of
FXIIIA with NC9 resulted in defective secretory vesicle delivery to the plasma
membrane which was attributable to a disorganized microtubule network and
decreased microtubule association with the plasma membrane. NC9 inhibition of
FXIIIA resulted in destabilization of microtubules as assessed by cellular
Glu-tubulin levels. Furthermore, NC9 blocked modification of Glu-tubulin into
150 kDa high-molecular weight Glu-tubulin form which was specifically localized
to the plasma membrane. FXIIIA enzyme and its crosslinking activity were
colocalized with plasma membrane-associated tubulin, and thus, it appears that
FXIIIA crosslinking activity is directed towards stabilizing the interaction of
microtubules with the plasma membrane. Our work provides the first mechanistic
cues as to how transglutaminase activity could affect protein secretion and
matrix deposition in osteoblasts and suggests a novel function for plasma
membrane FXIIIA in microtubule dynamics
Resonant inelastic x-ray scattering in electronically quasi-zero-dimensional CuB2O4
We explore the general phenomenology of resonant inelastic scattering (RIXS)
using CuB2O4, a network of CuO4 plaquettes electronically isolated by B+3 ions.
Spectra show a small number of well-separated features, and we exploit the
simple electronic structure to explore RIXS phenomenology by developing a
calculation which allows for intermediate-state effects ignored in standard
approaches. These effects are found to be non-negligible and good
correspondence between our model and experiment leads to a simple picture of
such phenomenology as the genesis of d-d excitations at the K edge and
intermediate-state interference effects.Comment: Phys. Rev. B 80, 092509 (2009
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