486 research outputs found
Involvement of Cyclin-Dependent Kinase-Like 2 in Cognitive Function Required for Contextual and Spatial Learning in Mice
Cyclin-dependent kinase-like 2 (Cdkl2) is a cdc2-related serine/threonine protein kinase that is postnatally expressed in various brain regions, including the cerebral cortex, entorhinal cortex, hippocampus, amygdala, and dorsal thalamus. The extremely high Cdkl2 expression in these regions suggests that it has a role in cognition and emotion. Recent genetic studies indicate that mutations of Cdkl family kinases are associated with neurodevelopmental and neuropsychiatric disorders in humans. To elucidate the physiologic role of Cdkl2, we behaviorally analyzed Cdkl2LacZ/LacZ mice lacking Cdkl2. Cdkl2LacZ/LacZ mice had reduced latencies to enter the dark compartment after electric footshock in an inhibitory avoidance task and attenuated contextual fear responses when exposed to mild training conditions. Hippocampal spatial learning in the Morris water maze was slightly anomalous with mice exhibiting an abnormal swimming pattern. The aversive response in a two-way avoidance task was slightly, but not significantly, enhanced. On the other hand, Cdkl2LacZ/LacZ mice did not exhibit altered sensitivity to aversive stimuli, such as electric footshock and heat, or deficits in the elevated plus maze or rotating rod test. These findings suggest that Cdkl2 is involved in cognitive function and provide in vivo evidence for the function of Cdkl family kinases expressed in terminally differentiated neurons in mice
The CoESCA station at BESSY: Auger electron–photoelectron coincidences from surfaces demonstrated for Ag MNN
In this work, we present the CoESCA station for electron–electron coincidence spectroscopy from surfaces, built in a close collaboration between Uppsala University and Helmholtz-Zentrum Berlin at the BESSY II synchrotron facility in Berlin, Germany. We start with a detailed overview of previous work in the field of electron–electron coincidences, before we describe the CoESCA setup and its design parameters. The system is capable of recording shot-to-shot resolved 6D coincidence datasets, i.e. the kinetic energy and the two take off angles for both coincident electrons. The mathematics behind extracting and analysing these multi-dimensional coincidence datasets is introduced, with a focus on coincidence statistics, resulting in fundamental limits of the signal-to-noise ratio and its implications for acquisition times and the size of the raw data stream. The functionality of the CoESCA station is demonstrated for the example of Auger electron–photoelectron coincidences from silver surfaces for photoelectrons from the Ag 3d core levels and their corresponding MNN Auger electrons. The Auger spectra originating from the different core levels, 3d and 3d could be separated and further, the two-hole state energy distributions were determined for these Auger decay channels
Origins of large critical temperature variations in single layer cuprates
We study the electronic structures of two single layer superconducting
cuprates, TlBaCuO (Tl2201) and
(BiPb)(SrLa)CuO (Bi2201) which
have very different maximum critical temperatures (90K and 35K respectively)
using Angular Resolved Photoemission Spectroscopy (ARPES). We are able to
identify two main differences in their electronic properties. First, the shadow
band that is present in double layer and low T single layer cuprates
is absent in Tl2201. Recent studies have linked the shadow band to structural
distortions in the lattice and the absence of these in Tl2201 may be a
contributing factor in its T.Second, Tl2201's Fermi surface (FS)
contains long straight parallel regions near the anti-node, while in Bi2201 the
anti-nodal region is much more rounded. Since the size of the superconducting
gap is largest in the anti-nodal region, differences in the band dispersion at
the anti-node may play a significant role in the pairing and therefore affect
the maximum transition temperature.Comment: 6 pages, 5 figures,1 tabl
Kagome silicene: a novel exotic form of two-dimensional epitaxial silicon
Since the discovery of graphene, intensive efforts have been made in search
of novel two-dimensional (2D) materials. Decreasing the materials
dimensionality to their ultimate thinness is a promising route to unveil new
physical phenomena, and potentially improve the performance of devices. Among
recent 2D materials, analogs of graphene, the group IV elements have attracted
much attention for their unexpected and tunable physical properties. Depending
on the growth conditions and substrates, several structures of silicene,
germanene, and stanene can be formed. Here, we report the synthesis of a Kagome
lattice of silicene on aluminum (111) substrates. We provide evidence of such
an exotic 2D Si allotrope through scanning tunneling microscopy (STM)
observations, high-resolution core-level (CL) and angle-resolved photoelectron
spectroscopy (ARPES) measurements, along with Density Functional Theory
calculations.Comment: 13 pages, 6 figure
Expression and trans-specific polymorphism of self-incompatibility RNases in Coffea (Rubiaceae)
Self-incompatibility (SI) is widespread in the angiosperms, but identifying the biochemical components of SI mechanisms has proven to be difficult in most lineages. Coffea (coffee; Rubiaceae) is a genus of old-world tropical understory trees in which the vast majority of diploid species utilize a mechanism of gametophytic self-incompatibility (GSI). The S-RNase GSI system was one of the first SI mechanisms to be biochemically characterized, and likely represents the ancestral Eudicot condition as evidenced by its functional characterization in both asterid (Solanaceae, Plantaginaceae) and rosid (Rosaceae) lineages. The S-RNase GSI mechanism employs the activity of class III RNase T2 proteins to terminate the growth of "self" pollen tubes. Here, we investigate the mechanism of Coffea GSI and specifically examine the potential for homology to S-RNase GSI by sequencing class III RNase T2 genes in populations of 14 African and Madagascan Coffea species and the closely related self-compatible species Psilanthus ebracteolatus. Phylogenetic analyses of these sequences aligned to a diverse sample of plant RNase T2 genes show that the Coffea genome contains at least three class III RNase T2 genes. Patterns of tissue-specific gene expression identify one of these RNase T2 genes as the putative Coffea S-RNase gene. We show that populations of SI Coffea are remarkably polymorphic for putative S-RNase alleles, and exhibit a persistent pattern of trans-specific polymorphism characteristic of all S-RNase genes previously isolated from GSI Eudicot lineages. We thus conclude that Coffea GSI is most likely homologous to the classic Eudicot S-RNase system, which was retained since the divergence of the Rubiaceae lineage from an ancient SI Eudicot ancestor, nearly 90 million years ago.United States National Science Foundation [0849186]; Society of Systematic Biologists; American Society of Plant Taxonomists; Duke University Graduate Schoolinfo:eu-repo/semantics/publishedVersio
Competition between magnetic interactions and structural instabilities leading to itinerant frustration in the triangular lattice antiferromagnet LiCrSe2
LiCrSe2 constitutes a recent valuable addition to the ensemble of two-dimensional triangular lattice antiferromagnets. In this work, we present a comprehensive study of the low temperature nuclear and magnetic structure established in this material. Being subject to a strong magnetoelastic coupling, LiCrSe2 was found to undergo a first order structural transition from a trigonal crystal system (P3 \uaf m1) to a monoclinic one (C2/m) at T s = 30 K. Such restructuring of the lattice is accompanied by a magnetic transition at T N = 30 K. Refinement of the magnetic structure with neutron diffraction data and complementary muon spin rotation analysis reveal the presence of a complex incommensurate magnetic structure with a up-up-down-down arrangement of the chromium moments with ferromagnetic double chains coupled antiferromagnetically. The spin axial vector is also modulated both in direction and modulus, resulting in a spin density wave-like order with periodic suppression of the chromium moment along the chains. This behavior is believed to appear as a result of strong competition between direct exchange antiferromagnetic and superexchange ferromagnetic couplings established between both nearest neighbor and next nearest neighbor Cr3+ ions. We finally conjecture that the resulting magnetic order is stabilized via subtle vacancy/charge order within the lithium layers, potentially causing a mix of two co-existing magnetic phases within the sample
Single domain stripe order in a high-temperature superconductor
The coupling of spin, charge and lattice degrees of freedom results in the
emergence of novel states of matter across many classes of strongly correlated
electron materials. A model example is unconventional superconductivity, which
is widely believed to arise from the coupling of electrons via spin
excitations. In cuprate high-temperature superconductors, the interplay of
charge and spin degrees of freedom is also reflected in a zoo of charge and
spin-density wave orders that are intertwined with superconductivity. A key
question is whether the different types of density waves merely coexist or are
indeed directly coupled. Here we use a novel neutron diffraction technique with
superior beam-focusing that allows us to probe the subtle spin-density wave
order in the prototypical high-temperature superconductor La1.88Sr0.12CuO4
under applied uniaxial pressure to demonstrate that it is immediately coupled
with charge-density wave order. Our result shows that suitable models for
high-temperature superconductivity must equally account for charge and spin
degrees of freedom via uniaxial charge-spin stripe fluctuations
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