132 research outputs found
BCS theory for s+g-wave superconductivity borocarbides Y(Lu)NiBC
The s+g mixed gap function \Delta_k=\Delta {[(1-x)-x\sin^4\theta\cos4\phi]}
(x: weight of g-wave component) has been studied within BCS theory. By suitable
consideration of the pairing interaction, we have confirmed that the
coexistence of s- and g-wave, as well as the state with equal s and g
amplitudes (i.e., x=1/2) may be stable. This provides the semi-phenomenological
theory for the s+g-wave superconductivity with point nodes which has been
observed experimentally in borocarbides YNi_2B_2C and possibly in LuNi_2B_2C.Comment: 5 pages, 3 figure
Reentrant charge ordering caused by polaron formation
Based on a two-dimensional extended Hubbard model with electron-phonon
interaction, we have studied the effect of polaron formation on the charge
ordering (CO) transition. It is found that for fully ferromagnetically ordered
spins the CO state may go through a process of appearance, collapse and
reappearance with decreasing temperature. This is entirely due to a
emperature-dependent polaron bandwidth. On the other hand, when a paramagnetic
spin state is considered, only a simple reentrant behavior of the CO transition
is found, which is only partly due to polaron effect. This model is proposed as
an explanation of the observed reentrant behavior of the CO transition in the
layered manganite LaSrMnO.Comment: 4 pages, 2 eps figures, revised version accepted by Phys. Rev. Let
Phase diagram of a generalized Hubbard model applied to orbital order in manganites
The magnetic phase diagram of a two-dimensional generalized Hubbard model
proposed for manganites is studied within Hartree-Fock approximation. In this
model the hopping matrix includes anisotropic diagonal hopping matrix elements
as well as off-diagonal elements. The antiferromagnetic (AF), ferromagnetic
(F), canted (C) and paramagnetic (P) states are included in the analysis as
possible phases. It is found that away from half-filling only the canted and F
states may exist and AF and P states which are possible for the usual Hubbard
model do not appear. This is because the F order has already developed for
on-site repulsion U=0 due to the hopping matrix of the generalized model. When
applied for manganites the orbital degree is described by a pseudospin. Thus
our ``magnetic'' phase diagram obtained physically describes how orbital order
changes with and with doping for manganites. Part of our results are
consistent with other numerical calculations and some experiments.Comment: 5 eps figures; a note added, to appear in Phys. Rev.
Spin-Peierls transition in an anisotropic two-dimensional XY model
The two-dimensional Jordan-Wigner transformation is used to investigate the
zero temperature spin-Peierls transition for an anisotropic two-dimensional XY
model in adiabatic limit. The phase diagram between the dimerized (D) state and
uniform (U) state is shown in the parameter space of dimensionless interchain
coupling and spin-lattice coupling . It is found
that the spin-lattice coupling must exceed some critical value
in order to reach the D phase for any finite . The dependence of on
is given by for and the transition between U and D
phase is of first-order for at least .Comment: 2 eps figures, considerable revisions were mad
Magnetic field dependence of superconducting energy gaps in YNi2B2C: Evidence of multiband superconductivity
We present results of in field directional point contact spectroscopy (DPCS)
study in the quaternary borocarbide superconductor YNi2B2C, which is
characterized by a highly anisotropic superconducting gap function. For I||a,
the superconducting energy gap (D), decreases linearly with magnetic field and
vanishes around 3.25T which is well below the upper critical field (Hc2~6T)
measured at the same temperature (2.2K). For I||c, on the other hand, D
decreases weakly with magnetic field but the broadening parameter (G) increases
rapidly with magnetic field with the absence of any resolvable feature above
3.5T. From an analysis of the field variation of energy gaps and the zero bias
density of states we show that the unconventional gap function observed in this
material could originate from multiband superconductivity.Comment: 19 pages including figures (final version
Impurity effects on s+g-wave superconductivity in borocarbides Y(Lu)Ni_2B_2C
Recently a hybrid s+g-wave pairing is proposed to describe the experimental
observation for a nodal structure of the superconducting gap in borocarbide
YNiBC and possibly LuNiBC. In this paper the impurity effects
on the s+g-wave superconductivity are studied in both Born and unitarity limit.
The quasiparticle density of states and thermodynamics are calculated. It is
found that the nodal excitations in the clean system are immediately prohibited
by impurity scattering and a finite energy gap increases quickly with the
impurity scattering rate. This leads to an activated behavior in the
temperature dependence of the specific heat. Qualitative agreement with the
experimental results is shown. Comparison with d-wave and some anisotropic
s-wave studied previously is also made.Comment: 6 pages, 6 eps figure
Structure and Luminescence Properties of Eu3+-Doped Cubic Mesoporous Silica Thin Films
Eu3+ ions-doped cubic mesoporous silica thin films with a thickness of about 205 nm were prepared on silicon and glass substrates using triblock copolymer as a structure-directing agent using sol–gel spin-coating and calcination processes. X-ray diffraction and transmission electron microscopy analysis show that the mesoporous silica thin films have a highly ordered body-centered cubic mesoporous structure. High Eu3+ ion loading and high temperature calcination do not destroy the ordered cubic mesoporous structure of the mesoporous silica thin films. Photoluminescence spectra show two characteristic emission peaks corresponding to the transitions of5D0-7F1 and 5D0-7F2 of Eu3+ ions located in low symmetry sites in mesoporous silica thin films. With the Eu/Si molar ratio increasing to 3.41%, the luminescence intensity of the Eu3+ ions-doped mesoporous silica thin films increases linearly with increasing Eu3+ concentration
Thermosensitive Nanocables Prepared by Surface-Initiated Atom Transfer Radical Polymerization
Thermosensitive nanocables consisting of Au nanowire cores and poly(N-isopropylacrylamide) sheaths (denoted as Au/PNIPAAm) were synthesized by surface-initiated atom transfer radical polymerization (SI-ATRP). The formation of PNIPAAm sheath was verified by Fourier transform infrared (FTIR) and hydrogen nuclear magnetic resonance (1H NMR) spectroscopy. Transmission electron microscope (TEM) results confirmed the core/shell structure of nanohybrids. The thickness and density of PNIPAAm sheaths can be adjusted by controlling the amount of cross-linker during the polymerization. Signature temperature response was observed from Au/cross-linked-PNIPAAm nanocables. Such smart nanocables show immense potentials as building blocks for novel thermosensitive nanodevices in future
Naloxone inhibits immune cell function by suppressing superoxide production through a direct interaction with gp91phox subunit of NADPH oxidase
<p>Abstract</p> <p>Background</p> <p>Both (-) and (+)-naloxone attenuate inflammation-mediated neurodegeneration by inhibition of microglial activation through superoxide reduction in an opioid receptor-independent manner. Multiple lines of evidence have documented a pivotal role of overactivated NADPH oxidase (NOX2) in inflammation-mediated neurodegeneration. We hypothesized that NOX2 might be a novel action site of naloxone to mediate its anti-inflammatory actions.</p> <p>Methods</p> <p>Inhibition of NOX-2-derived superoxide by (-) and (+)-naloxone was measured in lipopolysaccharide (LPS)-treated midbrain neuron-glia cultures and phorbol myristate acetate (PMA)-stimulated neutrophil membranes by measuring the superoxide dismutase (SOD)-inhibitable reduction of tetrazolium salt (WST-1) or ferricytochrome c. Further, various ligand (<sup>3</sup>H-naloxone) binding assays were performed in wild type and gp91<it><sup>phox-/- </sup></it>neutrophils and transfected COS-7 and HEK293 cells. The translocation of cytosolic subunit p47<it><sup>phox </sup></it>to plasma membrane was assessed by western blot.</p> <p>Results</p> <p>Both (-) and (+)-naloxone equally inhibited LPS- and PMA-induced superoxide production with an IC50 of 1.96 and 2.52 μM, respectively. Competitive binding of <sup>3</sup>H-naloxone with cold (-) and (+)-naloxone in microglia showed equal potency with an IC50 of 2.73 and 1.57 μM, respectively. <sup>3</sup>H-Naloxone binding was elevated in COS-7 and HEK293 cells transfected with gp91<sup><it>phox</it></sup>; in contrast, reduced <sup>3</sup>H-naloxone binding was found in neutrophils deficient in gp91<sup><it>phox </it></sup>or in the presence of a NOX2 inhibitor. The specificity and an increase in binding capacity of <sup>3</sup>H-naloxone were further demonstrated by 1) an immunoprecipitation study using gp91<sup><it>phox </it></sup>antibody, and 2) activation of NOX2 by PMA. Finally, western blot studies showed that naloxone suppressed translocation of the cytosolic subunit p47<sup><it>phox </it></sup>to the membrane, leading to NOX2 inactivation.</p> <p>Conclusions</p> <p>Strong evidence is provided indicating that NOX2 is a non-opioid novel binding site for naloxone, which is critical in mediating its inhibitory effect on microglia overactivation and superoxide production.</p
Modulation, Bioinformatic Screening, and Assessment of Small Molecular Peptides Targeting the Vascular Endothelial Growth Factor Receptor
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