22 research outputs found
Charge degree of freedom and single-spin fluid model in YBa_2Cu_4O_8
We present a 17O nuclear magnetic resonance study in the stoichiometric
superconductor YBa_2Cu_4O_8. A double irradiation method enables us to show
that, below around 180 K, the spin-lattice relaxation rate of plane oxygen is
not only driven by magnetic, but also significantly by quadrupolar
fluctuations, i.e. low-frequency charge fluctuations. In the superconducting
state, on lowering the temperature, the quadrupolar relaxation diminishes
faster than the magnetic one. These findings show that, with the opening of the
pseudo spin gap, a charge degree of freedom of mainly oxygen character is
present in the electronic low-energy excitation spectrum.Comment: 4 pages, 3 figures, REVTE
Planar Cu and O hole densities in high-Tc cuprates determined with NMR
The electric hyperfine interaction observable in atomic spectroscopy for O
and Cu ions in various configurations is used to analyze the quadrupole
splitting of O and Cu nuclear magnetic resonance (NMR) in La2-xSrxCuO4 and
YBa2Cu3O6+y and to determine the hole densities at both sites as a function of
doping. It is found that in La2-xSrxCuO4 all doped holes (x) reside in the Cu-O
plane but almost exclusively at O. For YBa2Cu3O6+y and y<0.6 doped holes are
found at planar Cu as well as O. For y>0.6 further doping increases the hole
content only for planar O. The phase diagram based on NMR data is presented.
Further implications from the Cu A and B site in La2-xSrxCuO4 and the two
planar O sites in YBa2Cu3O6+y and consequences for the phase diagram are
discussed.Comment: 18 pages, 1 figure, 2 tables, 2 appendice
Neutron powder diffraction and gas volumetry studies of the crystal structure and oxidation properties of Nd<sub>1</sub><sub>.</sub><sub>8</sub><sub>5</sub>Ce<sub>0</sub><sub>.</sub><sub>1</sub><sub>5</sub>CuO<sub>4</sub><sub>-</sub><sub>y</sub>
Probing the Electronic Structure of Y-Ba-Cu-O Superconductors by Cu, O and Ba NQR and NMR
Crystal structure, magnetic susceptibility and thermopower of superconducting and non-superconducting Nd<sub>1</sub><sub>.</sub><sub>8</sub><sub>5</sub>Ce<sub>0</sub><sub>.</sub><sub>1</sub><sub>5</sub>CuO<sub>4</sub><sub>+</sub><sub>#</sub>upsilone#
Molecular study of chromosome 15 in 22 patients with Angelman syndrome
DNA studies in 22 families with Angelman syndrome (AS) were performed using the chromosome 15 marker loci D15S9, D15S10, D15S11, D15S12, D15S13, D15S18, D15S24, D15S86, the alpha-actin gene and the GABA beta 3 receptor gene (GABRB3). Uniparental disomy of chromosome 15 was excluded in all patients. Eighteen AS patients (82%) showed a molecular deletion of chromosome 15q11-q13 with one or more of these markers. No duplications of junction fragments, bridging deletions or duplication breakpoints were observed. The GABRB3 gene was deleted in all deletion-positive patients tested. Analysis of maternal DNA indicated that each deletion was a de novo event. All deletions were of maternal origin; this is in agreement with genomic imprinting in A
Clinical profile of Angelman syndrome at different ages
We describe 47 patients with Angelman syndrome (AS) from Belgium and the Netherlands, including the anamnestic data, the clinical and the behavioral attributes at different ages. The clinical picture of AS is most distinct between the ages of 2-16 years. Most patients of this age group show at least 8 of the major characteristics (bursts of laughter, happy disposition, hyperactive behaviour, microcephaly, brachycephaly, macrostomia, tongue protrusion, mandibular prognathism, widely spaced teeth, stiff and puppetlike movements, typical stature, wide based gait) beside the mental retardation and (almost) absence of speech, which is a universal trait. The diagnosis in infants is based on only a limited number of clinical characteristics or on anamnestic data. However, if these occur in combination, they are indicative of AS. In older patients, the diagnosis may be hampered in part because of the changing behavioral characteristics and the decreasing frequency of fits. Other manifestations, such as scoliosis, may become more pronounced with ag