2,204 research outputs found
Dzyaloshinsky-Moriya interaction in vesignieite: A route to freezing in a quantum kagome antiferromagnet
We report an electron spin resonance investigation of the geometrically
frustrated spin-1/2 kagome antiferromagnet vesignieite,
BaCuVO(OH). Analysis of the line widths and line shifts
indicates the dominance of in-plane Dzyaloshinsky-Moriya anisotropy that is
proposed to suppress strongly quantum spin fluctuations and thus to promote
long-range ordering rather than a spin-liquid state. We also evidence an
enhanced spin-phonon contribution that might originate from a lattice
instability and discuss the origin of a low-temperature mismatch between
intrinsic and bulk susceptibility in terms of local inhomogeneity
Symmetric and antisymmetric exchange anisotropies in quasi-one-dimensional CuSeO as revealed by ESR
We present an electron spin resonance (ESR) study of single-crystalline spin
chain-system CuSeO in the frequency range between 9 GHz and 450 GHz. In
a wide temperature range above the N\'{e}el temperature K we observe
strong and anisotropic frequency dependence of a resonance linewidth. Although
sizeable interchain interaction ( is the intrachain
interaction) is present in this system, the ESR results agree well with the
Oshikawa-Affleck theory for one-dimensional Heisenberg antiferromagnet.
This theory is used to extract the anisotropies present in CuSeO. We
find that the symmetric anisotropic exchange and the
antisymmetric Dzyaloshinskii-Moriya (DM) interaction are
very similar in size in this system. Staggered-field susceptibility induced by
the presence of the DM interaction is witnessed in the macroscopic
susceptibility anisotropy.Comment: 8 pages, 7 figures, 2 tables, published in Phys. Rev.
Large Horizontal Displacements of Houses in Rotterdam
In 1983 it was established that six blocks of terrace houses in Rotterdam had undergone large horizontal displacements. These displacements were caused by insufficient stability of the adjacent quay and as a result one of the blocks had moved as much as 2.5 m since 1958. The foundation piles of the houses were not designed to resist any horizontal loading. As a result of these large horizontal movements the piles had deflected to such an extent that complete failure was feared. This paper describes the remedial measures that were taken to improve the stability of the quay and foundations of the houses. The present displacement behaviour is compared with the horizontal displacement predicted from creep analysis
High-frequency electron paramagnetic resonance investigation of the Fe3+ impurity center in polycrystalline PbTiO3 in its ferroelectric phase
The intrinsic iron(III) impurity center in polycrystalline lead titanate was
investigated by means of high-frequency electron paramagnetic resonance (EPR)
spectroscopy in order to determine the local-environment sensitive fine
structure parameter D. At a spectrometer frequency of 190 GHz, spectral
analysis of a powder sample was unambiguously possible. The observed mean value
D = +35.28 GHz can be rationalized if Fe3+ ions substitute for Ti4+ at the
B-site of the perovskite ABO3 lattice forming a directly coordinated iron -
oxygen vacancy defect associate. A consistent fit of the multi-frequency data
necessitated use of a distribution of D values with a variance of about 1 GHz.
This statistical distribution of values is probably related to more distant
defects and vacancies.Comment: 6 pages, 3 figures, 1 table, to appear in J. App. Phys, 96 (2004
The cholesterol-raising diterpenes from coffee beans increase serum lipid transfer protein activity levels in humans
Cafestol and kahweol–diterpenes present in unfiltered coffee— strongly raise serum VLDL and LDL cholesterol and slightly reduce HDL cholesterol in humans. The mechanism of action is unknown. We determined whether the coffee diterpenes may affect lipoprotein metabolism via effects on lipid transfer proteins and lecithin:cholesterol acyltransferase in a randomized, double-blind cross-over study with 10 healthy male volunteers. Either cafestol (61–64 mg/day) or a mixture of cafestol (60 mg/day) and kahweol (48–54 mg/day) was given for 28 days. Serum activity levels of cholesterylester transfer protein, phospholipid transfer protein and lecithin:cholesterol acyltransferase were measured using exogenous substrate assays. Relative to baseline values, cafestol raised the mean (±S.D.) activity of cholesterylester transfer protein by 18±12% and of phospholipid transfer protein by 21±14% (both P<0.001). Relative to cafestol alone, kahweol had no significant additional effects. Lecithin:cholesterol acyltransferase activity was reduced by 11±12% by cafestol plus kahweol (P=0.02). It is concluded that the effects of coffee diterpenes on plasma lipoproteins may be connected with changes in serum activity levels of lipid transfer proteins
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