2,265 research outputs found
Direct evidence for charge stripes in a layered cobalt oxide
Recent experiments indicate that static stripe-like charge order is generic to the hole-doped copper oxide superconductors and competes with superconductivity. Here we show that a similar type of charge order is present in La5/3 Sr1/3 CoO4 , an insulating analogue of the copper oxide superconductors containing cobalt in place of copper. The stripe phase we have detected is accompanied by short-range, quasi-one-dimensional, antiferromagnetic order, and provides a natural explanation for the distinctive hour- glass shape of the magnetic spectrum previously observed in neutron scattering mea- surements of La2βxSrx CoO4 and many hole-doped copper oxide superconductors. The results establish a solid empirical basis for theories of the hourglass spectrum built on short-range, quasi-static, stripe correlations
Refining rodent models of spinal cord injury.
This report was produced by an Expert Working Group (EWG) consisting of UK-based researchers, veterinarians and regulators of animal experiments with specialist knowledge of the use of animal models of spinal cord injury (SCI). It aims to facilitate the implementation of the Three Rs (Replacement, Reduction and Refinement), with an emphasis on refinement. Specific animal welfare issues were identified and discussed, and practical measures proposed, with the aim of reducing animal use and suffering, reducing experimental variability, and increasing translatability within this critically important research field
New Chiral Phases of Superfluid 3He Stabilized by Anisotropic Silica Aerogel
A rich variety of Fermi systems condense by forming bound pairs, including
high temperature [1] and heavy fermion [2] superconductors, Sr2RuO4 [3], cold
atomic gases [4], and superfluid 3He [5]. Some of these form exotic quantum
states having non-zero orbital angular momentum. We have discovered, in the
case of 3He, that anisotropic disorder, engineered from highly porous silica
aerogel, stabilizes a chiral superfluid state that otherwise would not exist.
Additionally, we find that the chiral axis of this state can be uniquely
oriented with the application of a magnetic field perpendicular to the aerogel
anisotropy axis. At suffciently low temperature we observe a sharp transition
from a uniformly oriented chiral state to a disordered structure consistent
with locally ordered domains, contrary to expectations for a superfluid glass
phase [6].Comment: 6 pages, 4 figure, and Supplementary Informatio
Electron-Spin Excitation Coupling in an Electron Doped Copper Oxide Superconductor
High-temperature (high-Tc) superconductivity in the copper oxides arises from
electron or hole doping of their antiferromagnetic (AF) insulating parent
compounds. The evolution of the AF phase with doping and its spatial
coexistence with superconductivity are governed by the nature of charge and
spin correlations and provide clues to the mechanism of high-Tc
superconductivity. Here we use a combined neutron scattering and scanning
tunneling spectroscopy (STS) to study the Tc evolution of electron-doped
superconducting Pr0.88LaCe0.12CuO4-delta obtained through the oxygen annealing
process. We find that spin excitations detected by neutron scattering have two
distinct modes that evolve with Tc in a remarkably similar fashion to the
electron tunneling modes in STS. These results demonstrate that
antiferromagnetism and superconductivity compete locally and coexist spatially
on nanometer length scales, and the dominant electron-boson coupling at low
energies originates from the electron-spin excitations.Comment: 30 pages, 12 figures, supplementary information include
Universality of pseudogap and emergent order in lightly doped Mott insulators
It is widely believed that high-temperature superconductivity in the cuprates
emerges from doped Mott insulators. The physics of the parent state seems
deceivingly simple: The hopping of the electrons from site to site is
prohibited because their on-site Coulomb repulsion U is larger than the kinetic
energy gain t. When doping these materials by inserting a small percentage of
extra carriers, the electrons become mobile but the strong correlations from
the Mott state are thought to survive; inhomogeneous electronic order, a
mysterious pseudogap and, eventually, superconductivity appear. How the
insertion of dopant atoms drives this evolution is not known, nor whether these
phenomena are mere distractions specific to hole-doped cuprates or represent
the genuine physics of doped Mott insulators. Here, we visualize the evolution
of the electronic states of (Sr1-xLax)2IrO4, which is an effective spin-1/2
Mott insulator like the cuprates, but is chemically radically different. Using
spectroscopic-imaging STM, we find that for doping concentration of x=5%, an
inhomogeneous, phase separated state emerges, with the nucleation of pseudogap
puddles around clusters of dopant atoms. Within these puddles, we observe the
same glassy electronic order that is so iconic for the underdoped cuprates.
Further, we illuminate the genesis of this state using the unique possibility
to localize dopant atoms on topographs in these samples. At low doping, we find
evidence for much deeper trapping of carriers compared to the cuprates. This
leads to fully gapped spectra with the chemical potential at mid-gap, which
abruptly collapse at a threshold of around 4%. Our results clarify the melting
of the Mott state, and establish phase separation and electronic order as
generic features of doped Mott insulators.Comment: This version contains the supplementary information and small updates
on figures and tex
Novel role for the innate immune receptor toll-like receptor 4 (TLR4) in the regulation of the wnt signaling pathway and photoreceptor apoptosis
Recent evidence has implicated innate immunity in regulating neuronal survival in the brain during stroke and other neurodegenerations. Photoreceptors are specialized light-detecting neurons in the retina that are essential for vision. In this study, we investigated the role of the innate immunity receptor TLR4 in photoreceptors. TLR4 activation by lipopolysaccharide (LPS) significantly reduced the survival of cultured mouse photoreceptors exposed to oxidative stress. With respect to mechanism, TLR4 suppressed Wnt signaling, decreased phosphorylation and activation of the Wnt receptor LRP6, and blocked the protective effect of the Wnt3a ligand. Paradoxically, TLR4 activation prior to oxidative injury protected photoreceptors, in a phenomenon known as preconditioning. Expression of TNFΞ± and its receptors TNFR1 and TNFR2 decreased during preconditioning, and preconditioning was mimicked by TNFΞ± antagonists, but was independent of Wnt signaling. Therefore, TLR4 is a novel regulator of photoreceptor survival that acts through the Wnt and TNFΞ± pathways. Β© 2012 Yi et al
Superconductivity in the Intercalated Graphite Compounds C6Yb and C6Ca
In this letter we report the discovery of superconductivity in the
isostructural graphite intercalation compounds C6Yb and C6Ca, with transition
temperatures of 6.5K and 11.5K respectively. A structural characterisation of
these compounds shows them to be hexagonal layered systems in the same class as
other graphite intercalates. If we assume that all the outer s-electrons are
transferred from the intercalant to the graphite sheets, then the charge
transfer in these compounds is comparable to other superconducting graphite
intercalants such as C8K 1,2 . However, the superconducting transition
temperatures of C6Yb and C6Ca are up to two orders of magnitude greater.
Interestingly, superconducting upper critical field studies and resistivity
measurements suggest that these compounds are significantly more isotropic than
pure graphite. This is unexpected as the effect of introducing the intercalant
is to move the graphite layer further apart.Comment: 2 Figures. Please see accompanying theoretical manuscript,
"Electronic Structure of the Superconducting Graphite Intercalates" by Csanyi
et al., cond-mat/050356
Changed epitopes drive the antigenic drift for influenza A (H3N2) viruses
<p>Abstract</p> <p>Background</p> <p>In circulating influenza viruses, gradually accumulated mutations on the glycoprotein hemagglutinin (HA), which interacts with infectivity-neutralizing antibodies, lead to the escape of immune system (called antigenic drift). The antibody recognition is highly correlated to the conformation change on the antigenic sites (epitopes), which locate on HA surface. To quantify a changed epitope for escaping from neutralizing antibodies is the basis for the antigenic drift and vaccine development.</p> <p>Results</p> <p>We have developed an epitope-based method to identify the antigenic drift of influenza A utilizing the conformation changes on epitopes. A changed epitope, an antigenic site on HA with an accumulated conformation change to escape from neutralizing antibody, can be considered as a "key feature" for representing the antigenic drift. According to hemagglutination inhibition (HI) assays and HA/antibody complex structures, we statistically measured the conformation change of an epitope by considering the number of critical position mutations with high genetic diversity and antigenic scores. Experimental results show that two critical position mutations can induce the conformation change of an epitope to escape from the antibody recognition. Among five epitopes of HA, epitopes A and B, which are near to the receptor binding site, play a key role for neutralizing antibodies. In addition, two changed epitopes often drive the antigenic drift and can explain the selections of 24 WHO vaccine strains.</p> <p>Conclusions</p> <p>Our method is able to quantify the changed epitopes on HA for predicting the antigenic variants and providing biological insights to the vaccine updates. We believe that our method is robust and useful for studying influenza virus evolution and vaccine development.</p
A System-Wide Investigation of the Dynamics of Wnt Signaling Reveals Novel Phases of Transcriptional Regulation
Aberrant Wnt signaling has been implicated in a wide variety of cancers and many components of the Wnt signaling network have now been identified. Much less is known, however, about how these proteins are coordinately regulated. Here, a broad, quantitative, and dynamic study of Wnt3a-mediated stimulation of HEK 293 cells revealed two phases of transcriptional regulation: an early phase in which signaling antagonists were downregulated, providing positive feedback, and a later phase in which many of these same antagonists were upregulated, attenuating signaling. The dynamic expression profiles of several response genes, including MYC and CTBP1, correlated significantly with proliferation and migration (P<0.05). Additionally, their levels tracked with the tumorigenicity of colon cancer cell lines and they were significantly overexpressed in colorectal adenocarcinomas (P<0.05). Our data highlight CtBP1 as a transcription factor that contributes to positive feedback during the early phases of Wnt signaling and serves as a novel marker for colorectal cancer progression
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