132 research outputs found
Electron spin dynamics and electron spin resonance in graphene
A theory of spin relaxation in graphene including intrinsic, Bychkov-Rashba,
and ripple spin-orbit coupling is presented. We find from spin relaxation data
by Tombros et al. [Nature 448, 571 (2007).] that intrinsic spin-orbit coupling
dominates over other contributions with a coupling constant of 3.7 meV.
Although it is 1-3 orders of magnitude larger than those obtained from first
principles, we show that comparable values are found for other honeycomb
systems, MgB2 and LiC6; the latter is studied herein by electron spin resonance
(ESR). We predict that spin coherence is longer preserved for spins
perpendicular to the graphene plane, which is beneficial for spintronics. We
identify experimental conditions when bulk ESR is realizable on graphene
Field Dependent Superfluid Density in the Optimally Doped SmFeAsO_(1-x)F_y Superconductor
The magnetic field dependence of the in-plane magnetic penetration depth for
optimally doped SmFeAsO_(1-x)F_y was investigated by combining torque
magnetometry, SQUID magnetometry, and muon-spin rotation. The results obtained
from these techniques show all a pronounced decrease of the superfluid density
as the field is increased up to 1.4 T. This behavior is analysed within a
two-band model with self-consistently derived coupled gaps, where the
superfluid density related to the larger gap is field independent and the
superfluid density related to the smaller gap is strongly suppressed with
increasing field.Comment: 7 pages, 5 figure
Synthesis and characterization of Sn‑doped TiO2 flm for antibacterial applications
Simple sol–gel method has been exploited to deposit Sn-doped TiO2 thin flms on glass substrates. The resultant coatings
were characterized by X-ray difraction (XRD), UV–visible techniques (UV–Vis), Fourier transform infrared spectroscopy
(FTIR), and photoluminescence analysis (PL). The XRD pattern reveals an increase in crystallite size of the prepared samples
with the increasing doping concentration. A decrease in doping concentrating resulted in the decrease in bandgap values. The
diferent chemical bonds on these flms were identifed from their FTIR spectra. The photoluminescence analysis shows an
increase in the emission peak intensity with increasing dopant concentration, and this can be attributed to the efect created
due to surface states. The prepared samples were tested as antibacterial agent toward both Gram-positive and Gram-negative
bacteria like S.aureus (Staphylococcus aureus) and E.coli (Escherichia coli), respectively. The size of the inhibition zones
indicates that the sample shows maximum inhibitory property toward E.coli when compared to S.aureus
The Double-stranded RNA–dependent Protein Kinase Differentially Regulates Insulin Receptor Substrates 1 and 2 in HepG2 Cells
The RNA-dependent protein kinase (PKR), initially known as a virus infection response protein, is found to differentially regulate two major players in the insulin signaling pathway, IRS1 and IRS2. PKR up-regulates the inhibitory phosphorylation of IRS1 and the expression of IRS2 at the transcriptional level
Spin-lattice relaxation time of conduction electrons in MgB2
The spin-lattice relaxation time, T-1, of conduction electrons is measured as a function of temperature and magnetic field in MgB2 in the normal and superconducting states. The method is based on the detection of the z component of the conduction electron magnetization under electron-spin-resonance conditions with amplitude-modulated microwave excitation. Measurement of T-1 below T-c at 0.32 T allows us to disentangle contributions from the two Fermi surfaces of MgB2, as this field restores the normal state on the part of the Fermi surface with pi symmetry only.This article is published as Simon, F., F. Murányi, T. Fehér, A. Jánossy, L. Forró, C. Petrovic, S. L. Bud’ko, and P. C. Canfield. "Spin-lattice relaxation time of conduction electrons in Mg B 2." Physical Review B 76, no. 2 (2007): 024519.
DOI: 10.1103/PhysRevB.76.024519.
Copyright 2007 American Physical Society.
Posted with permission
Generalized Elliott-Yafet Theory of Electron Spin Relaxation in Metals: Origin of the Anomalous Electron Spin Lifetime in MgB2
The temperature dependence of the electron-spin relaxation time in MgB2 is anomalous as it does not follow the resistivity above 150 K; it has a maximum around 400 K and decreases for higher temperatures. This violates the well established Elliot-Yafet theory of spin relaxation in metals. The anomaly occurs when the quasiparticle scattering rate (in energy units) is comparable to the energy difference between the conduction and a neighboring bands. The anomalous behavior is related to the unique band structure of MgB2 and the large electron-phonon coupling. The saturating spin relaxation is the spin transport analogue of the Ioffe-Regel criterion of electron transport.This article is published as Simon, F., B. Dóra, F. Murányi, A. Jánossy, S. Garaj, L. Forró, S. Bud’ko, C. Petrovic, and P. C. Canfield. "Generalized Elliott-Yafet Theory of Electron Spin Relaxation in Metals: Origin of the Anomalous Electron Spin Lifetime in MgB 2." Physical Review Letters 101, no. 17 (2008): 177003.
DOI: 10.1103/PhysRevLett.101.177003.
Copyright 2008 American Physical Society.
Posted with permission
Generalized Elliott-Yafet Theory of Electron Spin Relaxation in Metals: Origin of the Anomalous Electron Spin Lifetime in MgB<sub>2</sub>
A viral ER resident glycoprotein inactivates the MHC encoded peptide transporter.
AbstractHuman cytomegalovirus inhibits peptide import into the endoplasmic reticulum (ER) by the MHC-encoded TAP peptide transporter. We identified the open reading frame US6 to mediate this effect. Expression of the 21 kDa US6 glycoprotein in human cytomegalovirus–infected cells correlates with the inhibition of peptide transport during infection. The subcellular localization of US6 is ER restricted and is identical with TAP. US6 protein is found in complexes with TAP1/2, MHC class I heavy chain, β2-microglobulin, calnexin, calreticulin, and tapasin. TAP inhibition, however, is independent of the presence of class I heavy chain and tapasin. The results establish a new mechanism for viral immune escape and a novel role for ER-resident proteins to regulate TAP via its luminal face
Determinants of the in vivo folding of the prion protein - A bipartite function of helix 1 in folding and aggregation
Misfolding of the mammalian prion protein (PrP) is implicated in the pathogenesis of prion diseases. We analyzed wild type PrP in comparison with different PrP mutants and identified determinants of the in vivo folding pathway of PrP. The complete N terminus of PrP including the putative transmembrane domain and the first beta-strand could be deleted without interfering with PrP maturation. Helix 1, however, turned out to be a major determinant of PrP folding. Disruption of helix 1 prevented attachment of the glycosylphosphatidylinositol (GPI) anchor and the formation of complex N-linked glycans; instead, a high mannose PrP glycoform was secreted into the cell culture supernatant. In the absence of a C-terminal membrane anchor, however, helix 1 induced the formation of unglycosylated and partially protease-resistant PrP aggregates. Moreover, we could show that the C-terminal GPI anchor signal sequence, independent of its role in GPI anchor attachment, mediates core glycosylation of nascent PrP. Interestingly, conversion of high mannose glycans to complex type glycans only occurred when PrP was membrane-anchored. Our study indicates a bipartite function of helix 1 in the maturation and aggregation of PrP and emphasizes a critical role of a membrane anchor in the formation of complex glycosylated PrP
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