532 research outputs found
Resonant X-ray diffraction studies on the charge ordering in magnetite
Here we show that the low temperature phase of magnetite is associated with
an effective, although fractional, ordering of the charge. Evidence and a
quantitative evaluation of the atomic charges are achieved by using resonant
x-ray diffraction (RXD) experiments whose results are further analyzed with the
help of ab initio calculations of the scattering factors involved. By
confirming the results obtained from X-ray crystallography we have shown that
RXD is able to probe quantitatively the electronic structure in very complex
oxides, whose importance covers a wide domain of applications.Comment: 4 pages 4 figures, accepted for publication in PR
Health effects of acid aerosols formed by atmospheric mixtures.
Under ambient conditions, sulfur and nitrogen oxides can react with photochemical products and airborne particles to form acidic vapors and aerosols. Inhalation toxicological studies were conducted, exposing laboratory animals, at rest and during exercise, to multicomponent atmospheric mixtures under conditions favorable to the formation of acidic reaction products. Effects of acid and ozone mixtures on early and late clearance of insoluble radioactive particles in the lungs of rats appeared to be dominated by the oxidant component (i.e., the mixture did cause effects that were significantly different from those of ozone alone). Histopathological evaluations showed that sulfuric acid particles alone did not cause inflammatory responses in centriacinar units of rat lung parenchyma (expressed in terms of percent lesion area) but did cause significant damage (cell killing followed by a wave of cell replication) in nasal respiratory epithelium, as measured by uptake of tritiated thymidine in the DNA of replicating cells. Mixtures of ozone and nitrogen dioxide, which form nitric acid, caused significant inflammatory responses in lung parenchyma (in excess of effects seen in rats exposed to ozone alone), but did not damage nasal epithelium. Mixtures containing acidic sulfate particles, ozone, and nitrogen dioxide damaged both lung parenchyma and nasal epithelia. In rats exposed at rest, the response of the lung appeared to be dominated by the oxidant gas-phase components, while responses in the nose were dominated by the acidic particles. In rats exposed at exercise, however, mixtures of ozone and sulfuric acid particles significantly (2.5-fold) elevated the degree of lung lesion formation over that seen in rats exposed to ozone alone under an identical exercise protocol
Resonant X-Ray Scattering on the M-Edge Spectra from Triple-k Structure Phase in U_{0.75}Np_{0.25}O_{2} and UO_{2}
We derive an expression for the scattering amplitude of resonant x-ray
scattering under the assumption that the Hamiltonian describing the
intermediate state preserves spherical symmetry. On the basis of this
expression, we demonstrate that the energy profile of the RXS spectra expected
near U and Np M_4 edges from the triple-k antiferromagnetic ordering phase in
UO_{2} and U_{0.75}Np_{0.25}O_{2} agree well with those from the experiments.
We demonstrate that the spectra in the \sigma-\sigma' and \sigma-\pi' channels
exhibit quadrupole and dipole natures, respectively.Comment: 3 pages, 3 figures, to be published in J. Phys. Soc. Jpn. Supp
Evidence for Octupole Order in CeLaB from Resonant X-ray Scattering
The azimuthal angle dependence observed in the resonant X-ray scattering in
phase IV of CeLaB is analyzed theoretically. It is shown
that the peculiar angle dependence observed in the E2 channel is consistent
with the Gamma_{5u}-type octupole order with principal axis along (111) and
equivalent directions. Under the assumption that the four equivalent octupole
domains are nearly equally populated in the sample, the observed angle
dependences are reproduced by calculation for both sigma-sigma' and sigma-pi'
polarizations. The calculation for various symmetries of order parameters
excludes unambiguously other order parameters than the Gamma_{5u}-type
octupole.Comment: 4 pages, 2 figures, 3 tables, in JPSJ forma
Satellite holmium M-edge spectra from the magnetic phase via resonant x-ray scattering
Developing an expression of resonant x-ray scattering (RXS) amplitude which
is convenient for investigating the contributions from the higher rank tensor
on the basis of a localized electron picture, we analyze the RXS spectra from
the magnetic phases of Ho near the absorption edges. At the
edge in the uniform helical phase, the calculated spectra of the absorption
coefficient, the RXS intensities at the first and second satellite spots
capture the properties the experimental data possess, such as the spectral
shapes and the peak positions. This demonstrates the plausibility of the
adoption of the localized picture in this material and the effectiveness of the
spectral shape analysis. The latter point is markedly valuable since the
azimuthal angle dependence, which is one of the most useful informations RXS
can provides, is lacking in the experimental conditions. Then, by focusing on
the temperature dependence of the spectral shape at the second satellite spot,
we expect that the spectrum is the contribution of the pure rank two profile in
the uniform helical and the conical phases while that is dominated by the rank
one profile in the intermediate temperature phase, so-called spin slip phase.
The change of the spectral shape as a function of temperature indicates a
direct evidence of the change of magnetic structures undergoing. Furthermore,
we predict that the intensity, which is the same order observed at the second
satellite spot, is expected at the fourth satellite spot from the conical phase
in the electric dipolar transition.Comment: 24 pages, 5 figure
Detection of Neutron Scattering from Phase IV of Ce0.7La0.3B6: A Confirmation of the Octupole Order
We have performed a single crystal neutron scattering experiment on
Ce0.7La0.3B6 to investigate the order parameter of phase IV microscopically.
Below the phase transition temperature 1.5 K of phase IV, weak but distinct
superlattice reflections at the scattering vector (h/2,h/2,l/2) (h, l = odd
number) have been observed by neutron scattering for the first time. The
intensity of the superlattice reflections is stronger for high scattering
vectors, which is quite different from the usual magnetic form factor of
magnetic dipoles. This result directly evidences that the order parameter of
phase IV has a complex magnetization density, consistent with the recent
experimental and theoretical prediction in which the order parameter is the
magnetic octupoles Tbeta with Gamma5 symmetry of point group Oh. Neutron
scattering experiments using short wavelength neutrons, as done in this study,
could become a general method to study the high-rank multipoles in f electron
systems.Comment: 4 pages, 4 figure
Multipole correlations in low-dimensional f-electron systems
By using a density matrix renormalization group method, we investigate the
ground-state properties of a one-dimensional three-orbital Hubbard model on the
basis of a j-j coupling scheme. For , where is a parameter
to control cubic crystalline electric field effect, one orbital is itinerant,
while other two are localized. Due to the competition between itinerant and
localized natures, we obtain orbital ordering pattern which is sensitive to
, leading to a characteristic change of quadrupole state
into an incommensurate structure. At , all the three orbitals are
degenerate, but we observe a peak at in quadrupole
correlation, indicating a ferro-orbital state, and the peak at in
dipole correlation, suggesting an antiferromagnetic state. We
also discuss the effect of octupole on magnetic anisotropy.Comment: 4 pages, 3 figures, Proceedings of ASR-WYP-2005 (September 27-29,
2005, Tokai
Resonant magnetic x-ray and neutron diffuse studies of transition metal multilayers
Electron scattering mechanisms within metallic multilayers are affected by both structural and magnetic disorders. Off-specular x-ray scattering has long been used to probe the structural interfaces, and it is only recently that it has been applied to the study of magnetic disorder. We compare the resonant magnetic x-ray scattering with off-specular neutron studies from magnetron-sputtered Co/Cu and Co/Ru multilayers grown at the second antiferromagnetic coupling peak. Both techniques yield similar results for the Cu system, and a simple domain model can be applied to extract the magnetic interface morphological parameters. For the Cu system, the in-plane correlation length is field dependent and is 880+/-20 Ã… after saturation along the hard axis, but increases to 7000+/-100 Ã… after saturation along the orthogonal easy axis. Both systems show strong out-of-plane correlations in both the structural and magnetic disorders. In all cases, the out-of-plane correlation length for the structural interfaces is 200-250 Ã…, but the ratio of the magnetic to structural correlations length is dependent on the magnitude of the exchange coupling and ranges from 0.4 to 1.4.
Inhalation exposure methodology.
Modern man is being confronted with an ever-increasing inventory of potentially toxic airborne substances. Exposures to these atmospheric contaminants occur in residential and commercial settings, as well as in the workplace. In order to study the toxicity of such materials, a special technology relating to inhalation exposure systems has evolved. The purpose of this paper is to provide a description of the techniques which are used in exposing laboratory subjects to airborne particles and gases. The various modes of inhalation exposure (whole body, head only, nose or mouth only, etc.) are described at length, including the advantages and disadvantages inherent to each mode. Numerous literature citations are included for further reading. Among the topics briefly discussed are the selection of appropriate animal species for toxicological testing, and the types of inhalation studies performed (acute, chronic, etc.)
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