73 research outputs found
An Extended Jahn-Teller Hamiltonian for Large-Amplitude Motion: Application To Vibrational Conical Intersections in CH3SH and CH3OH
An extended Jahn-Teller Hamiltonian is presented for the case where the (slow) nuclear motion extends far from the symmetry point and may be described approximately as motion on a sphere. Rather than the traditional power series expansion in the displacement from the C3v symmetry point, an expansion in the spherical harmonics is employed. Application is made to the vibrational Jahn-Teller effect in CH3XH, with X = S, O, where the equilibrium CXH angles are 83° and 72°, respectively. In addition to the symmetry-required conical intersection (CI) at the C3v symmetry point, ab initio calculations reveal sets of six symmetry-allowed vibrational CIs in each molecule. The CIs for each molecule are arranged differently in the large-amplitude space, and that difference is reflected in the infrared spectra. The CIs in CH3SH are found in both eclipsed and staggered geometries, whereas those for CH3OH are found only in the eclipsed geometry near the torsional saddle point. This difference between the two molecules is reflected in the respective high-resolution spectra in the CH stretch fundamental region
High quality epitaxial thin films and exchange bias of antiferromagnetic Dirac semimetal FeSn
FeSn is a topological semimetal (TSM) and kagome antiferromagnet (AFM)
composed of alternating Fe3Sn kagome planes and honeycomb Sn planes. This
unique structure gives rise to exotic features in the band structures such as
the coexistence of Dirac cones and flatbands near the Fermi level, fully
spin-polarized 2D surface Dirac fermions, and the ability to open a large gap
in the Dirac cone by reorienting the N\'eel vector. In this work, we report the
synthesis of high quality epitaxial (0001) FeSn films by magnetron sputtering.
Using FeSn/Py heterostructures, we show a large exchange bias effect that
reaches an exchange field of 220 Oe at 5 K, providing unambiguous evidence of
antiferromagnetism and strong interlayer exchange coupling in our films. Field
cycling studies show steep initial training effects, highlighting the complex
magnetic interactions and anisotropy. Importantly, our work provides a simple,
alternative means to fabricate FeSn films and heterostructures, making it
easier to explore the topological physics of AFM TSMs and develop FeSn-based
spintronics.Comment: accepted by AP
Anomalous Hall and Nernst effects in epitaxial films of topological kagome magnet Fe3Sn2
The topological kagome magnet (TKM) Fe3Sn2 exhibits unusual topological
properties, flat electronic bands, and chiral spin textures, making it an
exquisite materials platform to explore the interplay between topological band
structure, strong electron correlations, and magnetism. Here we report the
first synthesis of high-quality epitaxial (0001) Fe3Sn2 films with large
intrinsic anomalous Hall effect close to that measured in bulk single crystals.
In addition, we measured a large, anisotropic anomalous Nernst coefficient Syx
of 1.26 {\mu}V/K, roughly 2-5x greater than that of common ferromagnets,
suggesting the presence of Berry curvature sources near the Fermi level in this
system. Crucially, the realization of high-quality Fe3Sn2 films opens the door
to explore emergent interfacial physics and create novel spintronic devices
based on TKMs by interfacing Fe3Sn2 with other quantum materials and by
nanostructure patterning.Comment: accepted by Physical Review Material
Lipid-Induced Toxicity Stimulates Hepatocytes to Release Angiogenic Microparticles That Require Vanin-1 for Uptake by Endothelial Cells.
Angiogenesis is a key pathological feature of experimental and human steatohepatitis, a common chronic liver disease that is associated with obesity. We demonstrated that hepatocytes generated a type of membrane-bound vesicle, microparticles, in response to conditions that mimicked the lipid accumulation that occurs in the liver in some forms of steatohepatitis and that these microparticles promoted angiogenesis. When applied to an endothelial cell line, medium conditioned by murine hepatocytes or a human hepatocyte cell line exposed to saturated free fatty acids induced migration and tube formation, two processes required for angiogenesis. Medium from hepatocytes in which caspase 3 was inhibited or medium in which the microparticles were removed by ultracentrifugation lacked proangiogenic activity. Isolated hepatocyte-derived microparticles induced migration and tube formation of an endothelial cell line in vitro and angiogenesis in mice, processes that depended on internalization of microparticles. Microparticle internalization required the interaction of the ectoenzyme Vanin-1 (VNN1), an abundant surface protein on the microparticles, with lipid raft domains of endothelial cells. Large quantities of hepatocyte-derived microparticles were detected in the blood of mice with diet-induced steatohepatitis, and microparticle quantity correlated with disease severity. Genetic ablation of caspase 3 or RNA interference directed against VNN1 protected mice from steatohepatitis-induced pathological angiogenesis in the liver and resulted in a loss of the proangiogenic effects of microparticles. Our data identify hepatocyte-derived microparticles as critical signals that contribute to angiogenesis and liver damage in steatohepatitis and suggest a therapeutic target for this condition
Kondo physics in antiferromagnetic Weyl semimetal Mn3+xSn1-x films
Topology and strong electron correlations are crucial ingredients in emerging
quantum materials, yet their intersection in experimental systems has been
relatively limited to date. Strongly correlated Weyl semimetals, particularly
when magnetism is incorporated, offer a unique and fertile platform to explore
emergent phenomena in novel topological matter and topological spintronics. The
antiferromagnetic Weyl semimetal Mn3Sn exhibits many exotic physical properties
such as a large spontaneous Hall effect and has recently attracted intense
interest. In this work, we report synthesis of epitaxial Mn3+xSn1-x films with
greatly extended compositional range in comparison with that of bulk samples.
As Sn atoms are replaced by magnetic Mn atoms, the Kondo effect, which is a
celebrated example of strong correlations, emerges, develops coherence, and
induces a hybridization energy gap. The magnetic doping and gap opening lead to
rich extraordinary properties as exemplified by the prominent DC Hall effects
and resonance-enhanced terahertz Faraday rotation
Solution structure of the SGTA dimerisation domain and investigation of its interactions with the ubiquitin-like domains of BAG6 and UBL4A
BACKGROUND: The BAG6 complex resides in the cytosol and acts as a sorting point to target diverse hydrophobic protein substrates along their appropriate paths, including proteasomal degradation and ER membrane insertion. Composed of a trimeric complex of BAG6, TRC35 and UBL4A, the BAG6 complex is closely associated with SGTA, a co-chaperone from which it can obtain hydrophobic substrates. METHODOLOGY AND PRINCIPAL FINDINGS: SGTA consists of an N-terminal dimerisation domain (SGTA_NT), a central tetratricopeptide repeat (TPR) domain, and a glutamine rich region towards the C-terminus. Here we solve a solution structure of the SGTA dimerisation domain and use biophysical techniques to investigate its interaction with two different UBL domains from the BAG6 complex. The SGTA_NT structure is a dimer with a tight hydrophobic interface connecting two sets of four alpha helices. Using a combination of NMR chemical shift perturbation, isothermal titration calorimetry (ITC) and microscale thermophoresis (MST) experiments we have biochemically characterised the interactions of SGTA with components of the BAG6 complex, the ubiquitin-like domain (UBL) containing proteins UBL4A and BAG6. We demonstrate that the UBL domains from UBL4A and BAG6 directly compete for binding to SGTA at the same site. Using a combination of structural and interaction data we have implemented the HADDOCK protein-protein interaction docking tool to generate models of the SGTA-UBL complexes. SIGNIFICANCE: This atomic level information contributes to our understanding of the way in which hydrophobic proteins have their fate decided by the collaboration between SGTA and the BAG6 complex
Systemic Theory for Software Teams: A Perspective
Complex problems involve a concerted effort by the software team and can absorb vital resources, but our
understanding of how the software team forms and succeeds has been minimal. It is not possible to explain the
relationships between team achievement and scale, concentration, and especially team expertise by confound-
ing elements, such as age group, additional participation from other individuals who are not in the team, or
by team structures. This generates a need to understand software teams using systemic theory. This position
paper presents the efforts we have undertaken to study the impact of systemic factors on software development
teams and how systemic theory can be used to understand software teams. Our approach looks at the effect of
psychological and sociological systemic variables on software teams to identify a way to represent software
teams as system
Signal Compartments Mapped from Multi-Echo Gradient Recalled Echo Data Vary across the Corpus Callosum
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