72 research outputs found
Non-universal ordering of spin and charge in stripe phases
We study the interplay of topological excitations in stripe phases: charge
dislocations, charge loops, and spin vortices. In two dimensions these defects
interact logarithmically on large distances. Using a renormalization-group
analysis in the Coulomb gas representation of these defects, we calculate the
phase diagram and the critical properties of the transitions. Depending on the
interaction parameters, spin and charge order can disappear at a single
transition or in a sequence of two transitions (spin-charge separation). These
transitions are non-universal with continuously varying critical exponents. We
also determine the nature of the points where three phases coexist.Comment: 4 pages, 3 figure
Covalency effects on the magnetism of EuRh2P2
In experiments, the ternary Eu pnictide EuRh2P2 shows an unusual coexistence
of a non-integral Eu valence of about 2.2 and a rather high Neel temperature of
50 K. In this paper, we present a model which explains the non-integral Eu
valence via covalent bonding of the Eu 4f-orbitals to P2 molecular orbitals. In
contrast to intermediate valence models where the hybridization with
delocalized conduction band electrons is known to suppress magnetic ordering
temperatures to at most a few Kelvin, covalent hybridization to the localized
P2 orbitals avoids this suppression. Using perturbation theory we calculate the
valence, the high temperature susceptibility, the Eu single-ion anisotropy and
the superexchange couplings of nearest and next-nearest neighbouring Eu ions.
The model predicts a tetragonal anisotropy of the Curie constants. We suggest
an experimental investigation of this anisotropy using single crystals. From
experimental values of the valence and the two Curie constants, the three free
parameters of our model can be determined.Comment: 9 pages, 5 figures, submitted to J. Phys.: Condens. Matte
Anisotropic effect of field on the orthorhombic-to-tetragonal transition in the striped cuprate (La,Nd)_{2-x}Sr_xCuO_4
The Nd-doped cuprate La_{2-y-x}Nd_ySr_xCuO_4 displays a first-order phase
transition at T_d (= 74 K for x=0.10, y = 0.60) to a low-temperature tetragonal
(LTT) phase. A magnetic field H applied || the a-axis leads to an increase in
T_d, whereas T_d is decreased when H || c. These effects show that magnetic
ordering involving both Nd and Cu spins plays a key role in driving the LTO-LTT
transition. Related anisotropic effects are observed in the uniform
susceptibility and the in-plane magnetoresistance.Comment: 5 pages, 5 figure
Local Magnetic Order vs. Superconductivity in a Layered Cuprate
We report on the phase diagram for charge-stripe order in
La(1.6-x)Nd(0.4)Sr(x)CuO(4), determined by neutron and x-ray scattering studies
and resistivity measurements. From an analysis of the in-plane resistivity
motivated by recent nuclear-quadrupole-resonance studies, we conclude that the
transition temperature for local charge ordering decreases monotonically with
x, and hence that local antiferromagnetic order is uniquely correlated with the
anomalous depression of superconductivity at x = 1/8. This result is consistent
with theories in which superconductivity depends on the existence of
charge-stripe correlations.Comment: 4 pages, 4 figures; introduction revised, Fig. 3 removed, last figure
replace
MiRNA expression patterns predict survival in glioblastoma
<p>Abstract</p> <p>Background</p> <p>In order to define new prognostic subgroups in patients with glioblastoma a miRNA screen (> 1000 miRNAs) from paraffin tissues followed by a bio-mathematical analysis was performed.</p> <p>Methods</p> <p>35 glioblastoma patients treated between 7/2005 - 8/2008 at a single institution with surgery and postoperative radio(chemo)therapy were included in this retrospective analysis. For microarray analysis the febit biochip "Geniom<sup>® </sup>Biochip MPEA homo-sapiens" was used. Total RNA was isolated from FFPE tissue sections and 1100 different miRNAs were analyzed.</p> <p>Results</p> <p>It was possible to define a distinct miRNA expression pattern allowing for a separation of distinct prognostic subgroups. The defined miRNA pattern was significantly associated with early death versus long-term survival (split at 450 days) (p = 0.01). The pattern and the prognostic power were both independent of the MGMT status.</p> <p>Conclusions</p> <p>At present, this is the first dataset defining a prognostic role of miRNA expression patterns in patients with glioblastoma. Having defined such a pattern, a prospective validation of this observation is required.</p
Effect of a magnetic field on the spin- and charge-density wave order in La1.45Nd0.4Sr0.15CuO4
The spin-density wave (SDW) and charge-density wave (CDW) order in
superconducting La1.45Nd0.4Sr0.15CuO4 were studied under an applied magnetic
field using neutron and X-ray diffraction techniques. In zero field,
incommensurate (IC) SDW order appears below ~ 40 K, which is characterized by
neutron diffraction peaks at (1/2 +/- 0.134, 1/2 +/- 0.134, 0). The intensity
of these IC peaks increases rapidly below T_Nd ~ 8 K due to an ordering of the
Nd^3+ spins. The application of a 1 T magnetic field parallel to the c-axis
markedly diminishes the intensity below T_Nd, while only a slight decrease in
intensity is observed at higher temperatures for fields up to 7 T. Our
interpretation is that the c-axis field suppresses the parasitic Nd^3+ spin
order at the incommensurate wave vector without disturbing the stripe order of
Cu^2+ spins. Consistent with this picture, the CDW order, which appears below
60 K, shows no change for magnetic fields up to 4 T. These results stand in
contrast to the significant field-induced enhancement of the SDW order observed
in superconducting La2-xSrxCuO4 with x ~ 0.12 and stage-4 La2CuO4+y. The
differences can be understood in terms of the relative volume fraction
exhibiting stripe order in zero field, and the collective results are
consistent with the idea that suppression of superconductivity by vortices
nucleates local patches of stripe order.Comment: 7 pages, 5 figure
Bisulfite-free epigenomics and genomics of single cells through methylation-sensitive restriction
CFTR Function Restoration upon Elexacaftor/Tezacaftor/Ivacaftor Treatment in Patient-Derived Intestinal Organoids with Rare CFTR Genotypes
Cystic fibrosis (CF) is caused by mutations in the Cystic Fibrosis Transmembrane conductance Regulator (CFTR) gene. The combination of the CFTR modulators elexacaftor, tezacaftor, and ivacaftor (ETI) enables the effective rescue of CFTR function in people with the most prevalent F508del mutation. However, the functional restoration of rare CFTR variants remains unclear. Here, we use patient-derived intestinal organoids (PDIOs) to identify rare CFTR variants and potentially individuals with CF that might benefit from ETI. First, steady-state lumen area (SLA) measurements were taken to assess CFTR function and compare it to the level observed in healthy controls. Secondly, the forskolin-induced swelling (FIS) assay was performed to measure CFTR rescue within a lower function range, and to further compare it to ETI-mediated CFTR rescue in CFTR genotypes that have received market approval. ETI responses in 30 PDIOs harboring the F508del mutation served as reference for ETI responses of 22 PDIOs with genotypes that are not currently eligible for CFTR modulator treatment, following European Medicine Agency (EMA) and/or U.S. Food and Drug Administration (FDA) regulations. Our data expand previous datasets showing a correlation between in vitro CFTR rescue in organoids and corresponding in vivo ppFEV1 improvement upon a CFTR modulator treatment in published clinical trials, and suggests that the majority of individuals with rare CFTR variants could benefit from ETI. CFTR restoration was further confirmed on protein levels using Western blot. Our data support that CFTR function measurements in PDIOs with rare CFTR genotypes can help to select potential responders to ETI, and suggest that regulatory authorities need to consider providing access to treatment based on the principle of equality for people with CF who do not have access to treatment.</p
Phase Separation Models for Cuprate Stripe Arrays
An electronic phase separation model provides a natural explanation for a
large variety of experimental results in the cuprates, including evidence for
both stripes and larger domains, and a termination of the phase separation in
the slightly overdoped regime, when the average hole density equals that on the
charged stripes. Several models are presented for charged stripes, showing how
density waves, superconductivity, and strong correlations compete with quantum
size effects (QSEs) in narrow stripes. The energy bands associated with the
charged stripes develop in the middle of the Mott gap, and the splitting of
these bands can be understood by considering the QSE on a single ladder.Comment: significant revisions: includes island phase, 16 eps figures, revte
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