497 research outputs found
PANDALP : a new penetrometer for snow investigation
This paper presents a new tool for snow investigation, issued from a portable dynamic penetrometer Panda with variable energy for soil investigation. After a brief presentation of this apparatus, a comparable study between this tool and other tests is carried out. The application of this apparatus in different sights shows that in couple with other tests such us nivological test or temperature test, we could use this portable machine to make snow investigation
Influence of cysteine to cysteic acid oxidation on the collision-activated decomposition of protonated peptides: evidence for intraionic interactions
AbstractOxidation of cysteine residues to cysteic acids in C-terminal arginine-containing peptides (such as those derived by tryptic digestion of proteins) strongly promotes the formation of multiple members of the Y″ series of fragment ions following low energy collision-activated decomposition (CAD) of the protonated peptides. Removal of the arginine residue abolishes the effect, which is also attenuated by conversion of the arginine to dimethylpyrimidylornithine. The data indicate the importance of an intraionic interaction between the cysteic acid and arginine side-chains. Low energy CAD of peptides which include cysteic acid and histidine residues, also provides evidence for intraionic interactions. It is proposed that these findings are consistent with the general hypothesis that an increased heterogeneity (with respect to location of charge) of the protonated peptide precursor ion population is beneficial to the generation of a high yield of product ions via several charge-directed, low energy fragmentation pathways. Furthermore, these data emphasize the significance of gas-phase conformations of protonated peptides in determining fragmentation pathways
Shifting of the magnetic resonance peak to lower energy in the superconducting state of underdoped YBa_2Cu_3O_{6.8}
Inelastic neutron scattering has been used to determine the dynamic spin
fluctuations in an underdoped high temperature superconductor YBCO_{6.8} single
crystal. The magnetic resonance, that occurs around 40 meV in overdoped
samples, is shifted to a lower energy, E_r= 34 meV. A constant ratio, , almost independent of the doping level, is found. According
to numerous theoretical approaches, this finding supports the idea that the
resonance energy is proportional (approximately twice) to the superconducting
gap.Comment: 8 pages, 3 figures, accepted in Europhysics Lette
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
European guidance for the diagnosis and management of osteoporosis in postmenopausal women
Kramers degeneracy in a magnetic field and Zeeman spin-orbit coupling in antiferromagnets
In this article, I analyze the symmetries and degeneracies of electron
eigenstates in a commensurate collinear antiferromagnet. In a magnetic field
transverse to the staggered magnetization, a hidden anti-unitary symmetry
protects double degeneracy of the Bloch eigenstates at a special set of
momenta. In addition to this `Kramers degeneracy' subset, the manifold of
momenta, labeling the doubly degenerate Bloch states in the Brillouin zone, may
also contain an `accidental degeneracy' subset, that is not protected by
symmetry and that may change its shape under perturbation. These degeneracies
give rise to a substantial momentum dependence of the transverse g-factor in
the Zeeman coupling, turning the latter into a spin-orbit interaction.
I discuss a number of materials, where Zeeman spin-orbit coupling is likely
to be present, and outline the simplest properties and experimental
consequences of this interaction, that may be relevant to systems from chromium
to borocarbides, cuprates, hexaborides, iron pnictides, as well as organic and
heavy fermion conductors.Comment: 16+ pages, extended version of arXiv:0805.0378; revised versio
Interpocket polarization model for magnetic structures in rare-earth hexaborides
The origin of peculiar magnetic structures in cubic rare-earth (R)
hexaborides RB_6 is traced back to their characteristic band structure. The
three sphere-like Fermi surfaces induce interpocket polarization of the
conduction band as a part of a RKKY-type interaction. It is shown for the
free-electron-like model that the interpocket polarization gives rise to a
broad maximum in the intersite interaction I(q) around q=(1/4,1/4,1/2) in the
Brillouin zone. This maximum is consistent with the superstructure observed in
R=Ce, Gd and Dy. The wave-number dependence of I(q) is independently extracted
from analysis of the spin-wave spectrum measured for NdB_6. It is found that
I(q) obtained from fitting the data has a similarly to that derived by the
interpocket polarization model, except that the absolute maximum now occurs at
(0,0,1/2) in consistency with the A-type structure. The overall shape of I(q)
gives a hint toward understanding an incommensurate structure in PrB_6 as well.Comment: 5 pages, 3 figures, submitted to J.Phys.Soc.Jp
Effects of Uniaxial Stress on Antiferromagnetic Moment in the Heavy Electron Compound URu_2Si_2
We have performed the elastic neutron scattering experiments under uniaxial
stress \sigma along the tetragonal [100], [110] and [001] directions for
URu2Si2. For \sigma // [100] and [110], the antiferromagnetic moment \mu_o is
strongly enhanced from 0.02 \mu_B (\sigma=0) to 0.22 \mu_B (\sigma=2.5 kbar) at
1.5 K. The rate of increase d\mu_o/d\sigma is roughly estimated to be ~ 0.1
\mu_B/kbar, which is much larger than that for the hydrostatic pressure (~
0.025 \mu_B/kbar). Above 2.5 kbar, \mu_o shows a tendency to saturate similar
to the behavior in the hydrostatic pressure. For \sigma // [001], on the other
hand, \mu_o shows only a slight increase to 0.028 \mu_B (\sigma = 4.6 kbar)
with a rate of ~ 0.002 \mu_B/kbar. The observed anisotropy suggests that the
competition between the hidden order and the antiferromagnetic state in URu2Si2
is strongly coupled with the tetragonal four-fold symmetry and the c/a ratio,
or both.Comment: 3 pages, 3 eps figures, Proceedings of Int. Conf. on Strongly
Correlated Electrons with Orbital Degrees of Freedom (Sendai, Japan,
September 11-14, 2001
Non-Collinear Magnetism due to Orbital Degeneracy and Multipolar Interactions
The origin of non-collinear magnetism under quadrupolar ordering is
investigated with CeB6 taken as a target system. The mode-mixing effect among
15 multipoles is analyzed based on the Ginzburg-Landau free energy. Then the
lower magnetic transition temperature and the order parameters are derived
within the mean-field approximation. In the presence of pseudo-dipole-type
interactions for the next-nearest neighbors, the observed pattern of
non-collinear ordering is indeed stabilized for certain set of interaction
parameters. The stability of the phase III' in the magnetic field is also
explained, which points to the importance of the next-nearest-neighbor
octupole-octupole interaction. Concerning the phase IV in CexLa1-xB6 with x ~
0.75, a possibility of pure octupole ordering is discussed based on slight
modifications of the strength of interactions.Comment: 12 pages, 7 figures, 3 tables, to appear in J. Phys. Soc. Jpn. 70 (6)
(2001
Magnetic order and multipole interactions in CexPr1-xB6 solid solutions
Magnetic ordering phenomena in CexPr1-xB6 solid solutions have been studied
using both powder and single-crystal neutron diffraction. A variety of magnetic
structures are observed depending on temperature and Ce concentration. Over a
broad composition range (x 0.7), Pr-Pr interactions play a dominant role,
giving rise to incommensurate structures with wave vectors of the form
k{IC1}=(1/4-delta, 1/4, 1/2) or k{IC2}=(1/4-delta, 1/4-delta, 1/2). The
crossover to a CeB6-like regime takes place near x = 0.7-0.8. For the latter
composition, the antiferroquadrupolar phase transition observed in transport
measurements precedes the onset, at lower temperature, of a commensurate
magnetic order similar to that existing in CeB6. However, unlike in the pure
compound, an incommensurate magnetic order is formed at even higher temperature
and persists in the antiferroquadrupolar phase down to the lock-in transition.
These results are shown to reflect the interplay between various type of dipole
exchange and higher multipole interactions in this series of compounds.Comment: Abstract of submission changed to get rid of LaTeX code Minor
differences exist between this version and that published in PRB (corrections
introduced by publisher
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