66 research outputs found
Multiconfigurational nature of 5f orbitals in uranium and plutonium intermetallics
Uranium and plutonium's 5f electrons are tenuously poised between strongly
bonding with ligand spd-states and residing close to the nucleus. The unusual
properties of these elements and their compounds (eg. the six different
allotropes of elemental plutonium) are widely believed to depend on the related
attributes of f-orbital occupancy and delocalization, for which a quantitative
measure is lacking. By employing resonant x-ray emission spectroscopy (RXES)
and x-ray absorption near-edge structure (XANES) spectroscopy and making
comparisons to specific heat measurements, we demonstrate the presence of
multiconfigurational f-orbital states in the actinide elements U and Pu, and in
a wide range of uranium and plutonium intermetallic compounds. These results
provide a robust experimental basis for a new framework for understanding the
strongly-correlated behavior of actinide materials.Comment: 30 pages, concatenated article and supporting information, 10 figure
Valence and magnetic ordering in intermediate valence compounds : TmSe versus SmB6
The intermediate valent systems TmSe and SmB6 have been investigated up to 16
and 18 GPa by ac microcalorimetry with a pressure (p) tuning realized in situ
at low temperature. For TmSe, the transition from an antiferromagnetic
insulator for p<3 GPa to an antiferromagnetic metal at higher pressure has been
confirmed. A drastic change in the p variation of the Neel temperature (Tn) is
observed at 3 GPa. In the metallic phase (p>3 GPa), Tn is found to increase
linearly with p. A similar linear p increase of Tn is observed for the
quasitrivalent compound TmS which is at ambiant pressure equivalent to TmSe at
p=7 GPa. In the case of SmB6 long range magnetism has been detected above p=8
GPa, i.e. at a pressure slightly higher than the pressure of the insulator to
metal transition. However a homogeneous magnetic phase occurs only above 10
GPa. The magnetic and electronic properties are related to the renormalization
of the 4f wavefunction either to the divalent or the trivalent configurations.
As observed in SmS, long range magnetism in SmB6 occurs already far below the
pressure where a trivalent Sm3+ state will be reached. It seems possible, to
describe roughly the physical properties of the intermediate valence
equilibrium by assuming formulas for the Kondo lattice temperature depending on
the valence configuration. Comparison is also made with the appearance of long
range magnetism in cerium and ytterbium heavy fermion compounds.Comment: 22 pages including figure
Primary cutaneous B-cell lymphoma other than marginal zone: clinicopathologic analysis of 161 cases: Comparison with current classification and definition of prognostic markers.
Valence Fluctuations Revealed by Magnetic Field Scan: Comparison with Experiments in YbXCu_4 (X=In, Ag, Cd) and CeYIn_5 (Y=Ir, Rh)
The mechanism of how critical end points of the first-order valence
transitions (FOVT) are controlled by a magnetic field is discussed. We
demonstrate that the critical temperature is suppressed to be a quantum
critical point (QCP) by a magnetic field. This results explain the field
dependence of the isostructural FOVT observed in Ce metal and YbInCu_4.
Magnetic field scan can lead to reenter in a critical valence fluctuation
region. Even in the intermediate-valence materials, the QCP is induced by
applying a magnetic field, at which the magnetic susceptibility also diverges.
The driving force of the field-induced QCP is shown to be a cooperative
phenomenon of the Zeeman effect and the Kondo effect, which creates a distinct
energy scale from the Kondo temperature. The key concept is that the closeness
to the QCP of the FOVT is capital in understanding Ce- and Yb-based heavy
fermions. It explains the peculiar magnetic and transport responses in CeYIn_5
(Y=Ir, Rh) and metamagnetic transition in YbXCu_4 for X=In as well as the sharp
contrast between X=Ag and Cd.Comment: 14 pages, 9 figures, OPEN SELECT in J. Phys. Soc. Jp
A negative-U interpretation of the femto-second laser pulse induced crystallographic expansion of a cuprate HTSC material reported recently by Gedik et al
Gedik et al have very recently demonstrated using a pump/probe femto-second
laser technique that the c-axis lattice parameter of LaCuO4+d temporarily
becomes expanded by as much as 2.5% following pulsed laser optical excitation
at 1.55 eV. Access to an out-of-equilibrium metastable excited state is
observed to develop on a time scale of 30 ps. Subsequently the latter state
decays displaying a still longer half-life of just over 300 ps. Observation of
the temperature independence of this laser induced interstate transfer and of
the linear dependence of the production of the metastable population upon the
energy delivered per unit area by the initiating light pulse (beyond a key
threshold fluence) have been interpreted by Gedik et al within the framework of
standard p-to-d, O-to-Cu, charge transfer excitations. By contrast these same
data are reinterpreted here in terms of pumped local pairs, within a negative-U
scenario of cuprate HTSC behaviour long advocated by the current author. The
d8-to-d10 laser-induced augmentation in the negative-U state population
(10CuIII2-) brings marked c-axis expansion by virtue of (i) the local
electrostatic charge imbalance, (ii) the increased antibonding nature of the
electron double-loading d10(p6) configuration created at pair-receptive CuIII
coordination units, and (iii) the layered nature of the cuprate crystal
structure. The new observations are related through to Rohlers striking,
standard crystallographic observations, to the stripe domain formation, and to
previous pump/probe experiments.Comment: 14 pages, 1 figur
BaVS probed by V L edge X-ray absorption spectroscopy
Polarization dependent vanadium L edge X-ray absorption spectra of BaVS
single crystals are measured in the four phases of the compound. The difference
between signals with the polarization \textbf{E}\textbf{c} and
\textbf{E}\textbf{c} (linear dichroism) changes with temperature.
Besides increasing intensity of one of the maxima, a new structure appears in
the pre-edge region below the metal-insulator transition. More careful
examination brings to light that the changes start already with pretransitional
charge density wave fluctuations. Simple symmetry analysis suggests that the
effect is related to rearrangements in and states, and is
compatible with the formation of four inequivalent V sites along the V-S chain.Comment: 6 pages, 6 figure
Ramipril and Risk of Hyperkalemia in Chronic Hemodialysis Patients
Angiotensin converting enzyme (ACE) inhibitors provide well known cardiorenal-protective benefits added to antihypertensive
effects in chronic renal disease. These agents are underused in management of patients receiving hemodialysis
(HD) because of common concern of hyperkalemia. However, few studies have investigated effect of renin angiotensin
aldosterone system (RAAS) blockade on serum potassium in hemodialysis patients. We assessed the safety of ramipril in
patients on maintenance HD. We enrolled 28 adult end stage renal disease (ESRD) patients treated by maintenance HD
and prescribed them ramipril in doses of 1.25 to 5 mg per day. They underwent serum potassium concentration measurements
before ramipril introduction and in 1 to 3 months afterwards. No significant increase in kalemia was found. Results
of our study encourage the use of ACE inhibitors in chronically hemodialyzed patients, but close potassium monitoring
is mandatory
Methods for high-dimensonal analysis of cells dissociated from cyropreserved synovial tissue
Background: Detailed molecular analyses of cells from rheumatoid arthritis (RA) synovium hold promise in identifying cellular phenotypes that drive tissue pathology and joint damage. The Accelerating Medicines Partnership RA/SLE Network aims to deconstruct autoimmune pathology by examining cells within target tissues through multiple high-dimensional assays. Robust standardized protocols need to be developed before cellular phenotypes at a single cell level can be effectively compared across patient samples. Methods: Multiple clinical sites collected cryopreserved synovial tissue fragments from arthroplasty and synovial biopsy in a 10% DMSO solution. Mechanical and enzymatic dissociation parameters were optimized for viable cell extraction and surface protein preservation for cell sorting and mass cytometry, as well as for reproducibility in RNA sequencing (RNA-seq). Cryopreserved synovial samples were collectively analyzed at a central processing site by a custom-designed and validated 35-marker mass cytometry panel. In parallel, each sample was flow sorted into fibroblast, T-cell, B-cell, and macrophage suspensions for bulk population RNA-seq and plate-based single-cell CEL-Seq2 RNA-seq. Results: Upon dissociation, cryopreserved synovial tissue fragments yielded a high frequency of viable cells, comparable to samples undergoing immediate processing. Optimization of synovial tissue dissociation across six clinical collection sites with ~ 30 arthroplasty and ~ 20 biopsy samples yielded a consensus digestion protocol using 100 μg/ml of Liberase™ TL enzyme preparation. This protocol yielded immune and stromal cell lineages with preserved surface markers and minimized variability across replicate RNA-seq transcriptomes. Mass cytometry analysis of cells from cryopreserved synovium distinguished diverse fibroblast phenotypes, distinct populations of memory B cells and antibody-secreting cells, and multiple CD4+ and CD8+ T-cell activation states. Bulk RNA-seq of sorted cell populations demonstrated robust separation of synovial lymphocytes, fibroblasts, and macrophages. Single-cell RNA-seq produced transcriptomes of over 1000 genes/cell, including transcripts encoding characteristic lineage markers identified. Conclusions: We have established a robust protocol to acquire viable cells from cryopreserved synovial tissue with intact transcriptomes and cell surface phenotypes. A centralized pipeline to generate multiple high-dimensional analyses of synovial tissue samples collected across a collaborative network was developed. Integrated analysis of such datasets from large patient cohorts may help define molecular heterogeneity within RA pathology and identify new therapeutic targets and biomarkers
Disentangling electronic, lattice, and spin dynamics in the chiral helimagnet Cr1/3Nb S2
We investigate the static and ultrafast magneto-optical response of the hexagonal chiral helimagnet Cr1/3NbS2 above and below the helimagnetic ordering temperature. The presence of a magnetic easy plane contained within the crystallographic ab plane is confirmed, while degenerate optical pump-probe experiments reveal significant differences in the dynamic between the parent, NbS2, and Cr-intercalated compounds. Time-resolved magneto-optical Kerr effect measurements show a two-step demagnetization process, where an initial, subpicosecond relaxation and subsequent buildup (τ>50ps) in the demagnetization dynamic scale similarly with increasing pump fluence. Despite theoretical evidence for partial gapping of the minority spin channel, suggestive of possible half-metallicity in Cr1/3NbS2, such a long demagnetization dynamic likely results from spin-lattice relaxation as opposed to minority state blocking. However, comparison of the two-step demagnetization process in Cr1/3NbS2 with other 3d intercalated transition metal dichalcogenides reveals a behavior that is unexpected from conventional spin-lattice relaxation, and may be attributed to the complicated interaction of local moments with itinerant electrons in this material system
- …