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J Schlappa

Publications and source records attributed to J Schlappa.

3 recordsLinked to original sources
PubMed2005

Spectroscopy of stripe order in La1.8Sr0.2NiO4 using resonant soft x-ray diffraction.

Strong resonant enhancements of the charge-order and spin-order superstructure-diffraction intensities in La1.8Sr0.2NiO4 are observed when x-ray energies in the vicinity of the Ni L2,3 absorption edges are used. The pronounced photon-energy and polarization dependences of these diffraction intensities allow for a critical determination of the local symmetry of the ordered spin and charge carriers. We found that not only the antiferromagnetic order but also the charge-order superstructure resides within the NiO2 layers; the holes are mainly located on in-plane oxygens surrounding a Ni2+ site with the spins coupled antiparallel in close analogy to Zhang-Rice singlets in the cuprates.

Journal Article↗
PubMed2000

Systematic errors in multi-frequency EIT.

Systematic errors have been measured with a multi-frequency data-collection system operating between 10.24 and 81.92 kHz. The errors were present even though a conventional background measurement on a uniform saline phantom had already been subtracted. Errors due to changes in transimpedance between the calibration and the tissue measurements, cable movement and electrode-skin contact impedance were simulated giving a total systematic error estimate equivalent to a 9% change in tissue conductivity. It was shown that more than 89% of the image was above the total error magnitude, indicating that most of the image revealed true changes in tissue conductivity. In three human subjects, the largest conductivity changes were in two regions, located posteriorly on either side of the midline, and were interpreted as due to the erector spinae muscles. These regions showed increases in conductivity of 73-104%. Identification of other anatomical features was difficult because of the poor spatial resolution of the images.

Biometry↗