274 research outputs found
Detection of reactive oxygen and nitrogen species by electron paramagnetic resonance (EPR) technique
During the last decade there has been growing interest in physical-chemical oxidation processes and the behavior of free radicals in living systems. Radicals are known as intermediate species in a variety of biochemical reactions. Numerous techniques, assays and biomarkers have been used to measure reactive oxygen and nitrogen species (ROS and RNS), and to examine oxidative stress. However, many of these assays are not entirely satisfactory or are used inappropriately. The purpose of this chapter is to review current EPR (Electron Paramagnetic Resonance) spectroscopy methods for measuring ROS, RNS, and their secondary products, and to discuss the strengths and limitations of specific methodological approaches
Iterative Perturbation Theory for Strongly Correlated Electron Systems with Orbital Degeneracy
A new scheme of the iterative perturbation theory is proposed for the
strongly correlated electron systems with orbital degeneracy. The method is
based on the modified self-energy of Yeyati, et al. which interpolates between
the weak and the strong correlation limits, but a much simpler scheme is
proposed which is useful in the case of the strong correlation with orbital
degeneracy. It will be also useful in the study of the electronic structures
combined with the band calculations.Comment: 6 pages, 3 Postscript figures, to appear in J. Phys. Cond. Matte
Theory for Magnetic Anisotropy of Field-Induced Insulator-to-Metal Transition in Cubic Kondo Insulator YbB_{12}
Magnetization and energy gap of Kondo insulator YbB_{12} are calculated
theoretically based on the previously proposed tight-binding model composed of
Yb 5d and 4f orbitals. It is found that magnetization
curves are almost isotropic, naturally expected from the cubic symmetry, but
that the gap-closing field has an anisotropy: the gap closes faster for the
field in (100) direction than in (110) and (111) directions, in accord with the
experiments. This is qualitatively understood by considering the maximal
eigenvalues of the total angular momentum operators projected on each direction
of the magnetic field. But the numerical calculation based on the band model
yields better agreement with the experiment.Comment: 4 pages, 4 figures, to appear in J. Phys. Soc. Jp
Optical conductivity of filled skutterudites
A simple tight-binding model is constructed for the description of the
electronic structure of some Ce-based filled skutterudite compounds showing an
energy gap or pseudogap behavior. Assuming band-diagonal electron interactions
on this tight-binding model, the optical conductivity spectrum is calculated by
applying the second-order self-consistent perturbation theory to treat the
electron correlation. The correlation effect is found to be of great importance
on the description of the temperature dependence of the optical conductivity.
The rapid disappearance of an optical gap with increasing temperature is
obtained as observed in the optical experiment for Ce-based filled-skutterudite
compounds.Comment: 6 pages, 7 figures, use jpsj2.cls, to appear in J. Phys. Soc. Jpn.
Vol.73, No.10 (2004
Calculation of Optical Conductivity of YbB using Realistic Tight-Binding Model
Based on the previously reported tight-binding model fitted to the LDA+U band
calculation, optical conductivity of the prototypical Kondo insulator
YbB is calculated theoretically. Many-body effects are taken into
account by the self-consistent second order perturbation theory. The gross
shape of the optical conductivity observed in experiments are well described by
the present calculation, including their temperature-dependences.Comment: 6 pages, 7 figures, use jpsj2.cls, to appear in J. Phys. Soc. Jpn.
Vol.73, No.10 (2004
Kondo Effect in Fermi Systems with a Gap: A Renormalization Group Study
We present the results of a Wilson Renormalization Group study of the
single-impurity Kondo and Anderson models in a system with a gap in the
conduction electron spectrum. The behavior of the impurity susceptibility and
the zero-frequency response function, are discussed in the
cases with and without particle-hole symmetry. In addition, for the asymmetric
Anderson model the correlation functions, , are computed.Comment: 10 pages, 10 figure
Absence of Hybridization Gap in Heavy Electron Systems and Analysis of YbAl3 in terms of Nearly Free Electron Conduction Band
In the analysis of the heavy electron systems, theoretical models with c-f
hybridization gap are often used. We point out that such a gap does not exist
and the simple picture with the hybridization gap is misleading in the metallic
systems, and present a correct picture by explicitly constructing an effective
band model of YbAl_3. Hamiltonian consists of a nearly free electron model for
conduction bands which hybridize with localized f-electrons, and includes only
a few parameters. Density of states, Sommerfeld coefficient, f-electron number
and optical conductivity are calculated and compared with the band calculations
and the experiments.Comment: 9 pages, 9 figures, submitted to J. Phys. Soc. Jp
Calculation of Optical Conductivity, Resistivity and Thermopower of Filled Skutterudite CeRuSb based on a Realistic Tight-binding Model with Strong Correlation
The filled-skutterudite compound CeRuSb shows a pseudo-gap
structure in the optical conductivity spectra similar to the Kondo insulators,
but metallic behavior below 80 K. The resistivity shows a large peak at 80 K,
and the Seebeck coefficient is positive and also shows a large peak at nearly
the same temperature. In order to explain all these features, a simplified
tight-binding model, which captures the essential features of the band
calculation, is proposed. Using this model and introducing the correlation
effect within the framework of the dynamical mean field approximation and the
iterative perturbation theory, the temperature dependences of the optical
conductivity, resistivity and the Seebeck coefficient are calculated, which can
explain the experiments.Comment: 4 pages, 6 figure
Indirect and direct energy gaps in the Kondo semiconductor YbB12
Optical conductivity [] of the Kondo semiconductor YbB
has been measured over wide ranges of temperature (=8690 K) and photon
energy ( 1.3 meV). The data reveal the
entire crossover of YbB from a metallic electronic structure at high
into a semiconducting one at low . Associated with the gap development in
, a clear onset is newly found at =15 meV for 20 K. The onset energy is identified as the gap width of YbB
appearing in . This gap in \sigma(\omega)\sigma(\omega)$ is interpreted as arising from the direct gap. The
absorption coefficient around the onset and the mIR peak indeed show
characteristic energy dependences expected for indirect and direct optical
transitions in conventional semiconductors.Comment: 4 pages, 3 figures, submitted to J. Phys. Soc. Jp
Interplay of Spin-Orbit Interaction and Electron Correlation on the Van Vleck Susceptibility in Transition Metal Compounds
We have studied the effects of electron correlation on Van Vleck
susceptibility () in transition metal compounds. A typical
crossover behavior is found for the correlation effect on as
sweeping spin-orbit interaction, . For a small , orbital
fluctuation plays a dominant role in the correlation enhancement of
; however, the enhancement rate is rather small. In contrast,
for an intermediate , shows a substantial increase,
accompanied by the development of spin fluctuation. We will discuss the
behavior of in association with the results of Knight-shift
experiments on SrRuO and an anomalously large magnetic susceptibility
observed for Ir compounds.Comment: 5 pages, 3 figures, to appear in J. Phys. Soc. Jp
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