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Polarization control at the microscopic and electronic structure observatory
The new Microscopic and Electronic Structure Observatory (MAESTRO) at the Advanced Light Source (ALS) in Berkeley provides X-rays of variable polarization, produced by an elliptically polarized undulator (EPU), for angle resolved photoemission (ARPES) and photoemission electron microscopy (PEEM) experiments. The interpretation of photoemission data, in particular of dichroism effects in ARPES, requires the precise knowledge of the exact polarization state. Numerical simulations show that the first harmonics of the EPU at MAESTRO provides soft X-rays of almost 100% on axis polarization. However, the higher harmonics as well as the downstream optical elements of the beamline, have a considerable impact on the polarization of the light delivered to the experimental end-station. Employing a simple reflective polarimeter, the polarization is characterized for variable EPU and beamline settings and the overall degree of polarization in the MAESTRO end-stations is estimated to be on the order of 83%
Quasiparticle Transformation During a Metal-Insulator Transition in Graphene
Here we show, with simultaneous transport and photoemission measurements,
that the graphene terminated SiC(0001) surface undergoes a metal-insulator
transition (MIT) upon dosingwith small amounts of atomic hydrogen. We find the
room temperature resistance increases by about 4 orders of magnitude, a
transition accompanied by anomalies in the momentum-resolved spectral function
including a non-Fermi Liquid behaviour and a breakdown of the quasiparticle
picture. These effects are discussed in terms of a possible transition to a
strongly (Anderson) localized ground state.Comment: 11 pages, 4 figure
Kohn anomaly and interplay of electron-electron and electron-phonon interactions in epitaxial graphene
The interplay of electron-phonon (el-ph) and electron-electron (el-el)
interactions in epitaxial graphene is studied by directly probing its
electronic structure. We found a strong coupling of electrons to the soft part
of the A1g phonon evident by a kink at 150+/-15 meV, while the coupling of
electrons to another expected phonon E2g at 195 meV can only be barely
detected. The possible role of the el-el interaction to account for the
enhanced coupling of electrons to the A1g phonon, and the contribution of el-ph
interaction to the linear imaginary part of the self energy at high binding
energy are also discussed. Our results reveal the dominant role of the A1g
phonon in the el-ph interaction in graphene, and highlight the important
interplay of el-el and el-ph interactions in the self energy of graphene.Comment: accepted to Phys. Rev.
Report in the Grand River Eagle
A report in the Grand River Eagle that a committee was organized in Grand Rapids to help the worthy and enterprising pastor, the Rev. A. C. Van Raalte, and his people in their settlement. Some members of the committee were appointed to visit Holland. E. B. Bostwick was chairman and A. D. Rathbone, secretary.https://digitalcommons.hope.edu/vrp_1840s/1138/thumbnail.jp
Syndecan-2 is a novel target of insulin-like growth factor binding protein-3 and is over-expressed in fibrosis
Extracellular matrix deposition and tissue scarring characterize the process of fibrosis. Transforming growth factor beta (TGFβ) and Insulin-like growth factor binding protein-3 (IGFBP-3) have been implicated in the pathogenesis of fibrosis in various tissues by inducing mesenchymal cell proliferation and extracellular matrix deposition. We identified Syndecan-2 (SDC2) as a gene induced by TGFβ in an IGFBP-3-dependent manner. TGFβ induction of SDC2 mRNA and protein required IGFBP-3. IGFBP-3 independently induced production of SDC2 in primary fibroblasts. Using an ex-vivo model of human skin in organ culture expressing IGFBP-3, we demonstrate that IGFBP-3 induces SDC2 ex vivo in human tissue. We also identified Mitogen-activated protein kinase-interacting kinase (Mknk2) as a gene induced by IGFBP-3. IGFBP-3 triggered Mknk2 phosphorylation resulting in its activation. Mknk2 independently induced SDC2 in human skin. Since IGFBP-3 is over-expressed in fibrotic tissues, we examined SDC2 levels in skin and lung tissues of patients with systemic sclerosis (SSc) and lung tissues of patients with idiopathic pulmonary fibrosis (IPF). SDC2 levels were increased in fibrotic dermal and lung tissues of patients with SSc and in lung tissues of patients with IPF. This is the first report describing elevated levels of SDC2 in fibrosis. Increased SDC2 expression is due, at least in part, to the activity of two pro-fibrotic factors, TGFβ and IGFBP-3. © 2012 Ruiz et al
Dirac dispersion and non-trivial Berry's phase in three-dimensional semimetal RhSb3
We report observations of magnetoresistance, quantum oscillations and
angle-resolved photoemission in RhSb, a unfilled skutterudite semimetal
with low carrier density. The calculated electronic band structure of RhSb
entails a quantum number in analogy to
strong topological insulators, and inverted linear valence/conduction bands
that touch at discrete points close to the Fermi level, in agreement with
angle-resolved photoemission results. Transport experiments reveal an
unsaturated linear magnetoresistance that approaches a factor of 200 at 60 T
magnetic fields, and quantum oscillations observable up to 150~K that are
consistent with a large Fermi velocity ( ms), high
carrier mobility ( /Vs), and small three dimensional hole pockets
with nontrivial Berry phase. A very small, sample-dependent effective mass that
falls as low as bare masses scales with Fermi velocity, suggesting
RhSb is a new class of zero-gap three-dimensional Dirac semimetal.Comment: 9 pages, 4 figure
Anderson Transition in Disordered Graphene
We use the regularized kernel polynomial method (RKPM) to numerically study
the effect disorder on a single layer of graphene. This accurate numerical
method enables us to study very large lattices with millions of sites, and
hence is almost free of finite size errors. Within this approach, both weak and
strong disorder regimes are handled on the same footing. We study the
tight-binding model with on-site disorder, on the honeycomb lattice. We find
that in the weak disorder regime, the Dirac fermions remain extended and their
velocities decrease as the disorder strength is increased. However, if the
disorder is strong enough, there will be a {\em mobility edge} separating {\em
localized states around the Fermi point}, from the remaining extended states.
This is in contrast to the scaling theory of localization which predicts that
all states are localized in two-dimensions (2D).Comment: 4 page
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