304 research outputs found
Experimental study of the competition between Kondo and RKKY interactions for Mn spins in a model alloy system
The quasicrystal Al-Pd-Mn is a model system for an experimental study of the
competition between Ruderman-Kittel-Kasuya-Yoshida (RKKY) and Kondo
interactions. First, specific of such alloys, only a few Mn atoms carry an
effective spin and their concentration x is tunable over several orders of
magnitude, even though the Mn amount is almost constant. Second, the
characteristic energy scales for the interactions lie in the Kelvin range.
Hence we could study the magnetization on both side of these energy scales,
covering a range of temperatures [0.1-100 K] and magnetic fields (mu_B H/k_B= 0
to 5 K) for 22 samples and x varying over 2 decades. Using very general Kondo
physics arguments, and thus carrying out the data analysis with no preconceived
model, we found a very robust and simple result: The magnetization is a sum of
a pure Kondo (T_K=3.35K) and a pure RKKY contributions, whatever the moment
concentration is and this surprisingly up to the concentration where the RKKY
couplings dominate fully and thus cannot be considered as a perturbation.Comment: 18 pages, 18 figure
Pancreatico-jejunostomy decreases post-operative pancreatic fistula incidence and severity after central pancreatectomy
BACKGROUNDS: Central pancreatectomy (CP) is an alternative to pancreaticoduodenectomy and distal pancreatectomy in benign tumours of pancreatic isthmus management. It is known for a high post-operative pancreatic fistula (POPF) rate. The purpose of this study was to compare POPF incidence between pancreatico-jejunostomy (PJ) and pancreatico-gastrostomy (PG).
METHODS: Fifty-eight patients (mean age 53.9 ± 1.9 years) who underwent a CP in four French University Hospitals from 1988 to 2011 were analysed. The distal pancreatic remnant was either anastomosed to the stomach (44.8%, n = 25) or to a Roux-en-Y jejunal loop (55.2%, n = 35) with routine external drainage allowing a systematic search for POPF. POPF severity was classified according to the International Study Group on Pancreatic Fistula (ISGPF) and Clavien-Dindo classifications.
RESULTS: The groups were similar on sex ratio, mean age, ASA score, pancreas texture, operative time and operative blood loss. Mean follow-up was 36.2 ± 3.9 months. POPF were significantly more frequent after PG (76.9 versus 37.5%, P = 0.003). PG was associated with significantly higher grade of POPF both when graded with ISGPF classification (P = 0.012) and Clavien-Dindo classification (P = 0.044). There was no significant difference in post-operative bleeding (0.918) and delayed gastric emptying (0.877) between the two groups. Hospital length of stay was increased after PG (23.6 ± 3.5 days versus 16.5 ± 1.9 days, P = 0.071). There was no significant difference in incidence of long-term exocrine (3.8 versus 19.2%, P = 0.134) and endocrine (7.7 versus 9.4%, P = 0.575) pancreatic insufficiencies.
CONCLUSION: PG was associated with a significantly higher POPF incidence and severity in CP. We recommend performing PJ especially in older patients to improve CP outcomes
Anomalous dependence of the c-axis polarized Fe B phonon mode with Fe and Se concentrations in FeTeSe
We report an investigation of the lattice dynamical properties in a range of FeTeSe compounds, with special emphasis on the c-axis polarized vibration of Fe with B symmetry, a Raman active mode common to all families of Fe-based superconductors. We have carried out a systematic study of the temperature dependence of this phonon mode as a function of Se and excess Fe concentrations. In parent compound FeTe, we observe an unconventional broadening of the phonon between room temperature and magnetic ordering temperature . The situation smoothly evolves towards a regular anharmonic behavior as Te is substituted for Se and long range magnetic order is replaced by superconductivity. Irrespective to Se contents, excess Fe is shown to provide an additional damping channel for the B phonon at low temperatures. We performed Density Functional Theory (DFT) ab-initio calculations within the local density approximation (LDA) to calcuate the phonon frequencies including magnetic polarization and Fe non-stoichiometry in the Virtual Crystal Approximation (VCA). We obtained a good agreement with the measured phonon frequencies in the Fe-deficient samples, while the effects of Fe excess are poorly reproduced. This may be due to excess Fe-induced local magnetism and low energy magnetic fluctuations that can not be treated accurately within these approaches. As recently revealed by neutron scattering and -SR studies, these phenomena occur in the temperature range where anomalous decay of the B phonon is observed, and suggests a peculiar coupling of this mode with local moments and spin fluctuations in FeTeSe
Heat Transport and the Nature of the Order Parameter in Superconducting
Recent thermal conductivity data on the heavy fermion superconductor
have been interpreted as offering support for an model of the order
parameter as opposed to an model. In this paper, we analyze this issue
from a theoretical standpoint including the detailed effects of Fermi surface
and gap anisotropy. Our conclusion is that although current data put strong
constraints on the gap anisotropy, they cannot definitively distinguish between
these two models. Measurements on samples of varying quality could be decisive
in this regard, however.Comment: 8 pages, revtex, 15 uunencoded postscript figure
High temperature superconductivity (Tc onset at 34K) in the high pressure orthorhombic phase of FeSe
We have studied the structural and superconducting properties of tetragonal
FeSe under pressures up to 26GPa using synchrotron radiation and diamond anvil
cells. The bulk modulus of the tetragonal phase is 28.5(3)GPa, much smaller
than the rest of Fe based superconductors. At 12GPa we observe a phase
transition from the tetragonal to an orthorhombic symmetry. The high pressure
orthorhombic phase has a higher Tc reaching 34K at 22GPa.Comment: 15 pages, 4 figure
Anomalous magnetic field dependence of the thermodynamic transition line in the isotropic superconductor (K,Ba)Bi03
Thermodynamic (specific heat, reversible magnetization, tunneling
spectroscopy) and transport measurements have been performed on high quality
(K,Ba)BiO single crystals. The temperature dependence of the magnetic field
corresponding to the onset of the specific heat anomaly presents a
clear positive curvature. is significantly smaller than the field
for which the superconducting gap vanishes but is closely related to
the irreversibility line deduced from transport data. Moreover, the temperature
dependence of the reversible magnetization present a strong deviation from the
Ginzburg--Landau theory emphasazing the peculiar nature of the superconducting
transition in this material.Comment: 4 pages, 4 figures, 28 reference
Platelet factor-4 and its p17-70 peptide inhibit myeloma proliferation and angiogenesis in vivo
<p>Abstract</p> <p>Background</p> <p>Angiogenesis plays an important role in the development of multiple myeloma (MM). The interaction between MM cells and the bone marrow microenvironment stimulates the proliferation and migration of endothelial progenitor cells (EPCs). Vascular endothelial growth factor (VEGF) contributes to the formation of new blood vessels by actively recruiting circulating EPCs. The production of proangiogenic and antiangiogenic factors is also dysregulated in MM. Platelet factor 4 (PF4) is a potent angiostatic cytokine that inhibits angiogenesis and tumor growth in several animal models.</p> <p>Methods</p> <p>In this study, we stably transfected human myeloma cell lines with the PF4 gene or the sequence encoding its more potent p17-70 peptide and investigated the effects of PF4 and p17-70 on angiogenesis and tumor growth <it>in vitro </it>and in a SCID-rab myeloma model.</p> <p>Results</p> <p>PF4 and p17-70 significantly attenuated VEGF production, both <it>in vitro </it>and <it>in vivo</it>. In a migration study using a Transwell system, PF4 or p17-70 markedly suppressed the migration of co-cultured human endothelial progenitor cells. PF4 or p17-70 also caused a significant reduction in microvessel densities in myeloma xenografts and markedly reduced the tumor volume in the SCID mice. Kaplan-Meier analysis demonstrated that PF4 and p17-70 significantly extended the overall survival of SCID mice bearing human myeloma xenografts.</p> <p>Conclusions</p> <p>Our findings indicate that PF4 or p17-70 could be valuable in combating multiple myeloma by disrupting tumor angiogenesis.</p
Validation of the Meaf Score and Comparaison with Early Allograft Dysfunction Critera on Predicting 3 Months Graft Survival
International audienceno abstrac
On the thermoelectricity of correlated electrons in the zero-temperature limit
The Seebeck coefficient of a metal is expected to display a linear
temperature-dependence in the zero-temperature limit. To attain this regime, it
is often necessary to cool the system well below 1K. We put under scrutiny the
magnitude of this term in different families of strongly-interacting electronic
systems. For a wide range of compounds (including heavy-fermion, organic and
various oxide families) a remarkable correlation between this term and the
electronic specific heat is found. We argue that a dimensionless ratio relating
these two signatures of mass renormalisation contains interesting information
about the ground state of each system. The absolute value of this ratio remains
close to unity in a wide range of strongly-correlated electron systems.Comment: 15 pages, including two figure
Bulk charge density wave and electron-phonon coupling in superconducting copper oxychlorides
Bulk charge density waves (CDWs) are now reported in nearly all
high-temperature superconducting (HTS) cuprates, with the noticeable exception
of one particular family: the copper oxychlorides. Here, we used resonant
inelastic X-ray scattering (RIXS) to reveal a bulk CDW in these materials.
Combining RIXS with non-resonant IXS, we investigate the interplay between the
lattice excitations and the CDW, and evidence bond-stretching (BS) phonon
anomalies at the CDW wave-vector. We propose that such electron-phonon
anomalies occur in the presence of dispersive charge excitations emanating from
the CDW and interacting with the BS phonon. Our observations in a structurally
simple cuprate promises to better connect bulk and surface properties and
bridge the gap between theory and experiment
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