Biomedical subjects

JR Schneider

Publications and source records attributed to JR Schneider.

11 recordsLinked to original sources

PubMed2000

First observation of self-amplified spontaneous emission in a free-electron laser at 109 nm wavelength

We present the first observation of self-amplified spontaneous emission (SASE) in a free-electron laser (FEL) in the vacuum ultraviolet regime at 109 nm wavelength (11 eV). The observed free-electron laser gain (approximately 3000) and the radiation characteristics, such as dependency on bunch charge, angular distribution, spectral width, and intensity fluctuations, are all consistent with the present models for SASE FELs.

Journal Article↗

PubMed2000

Local magnetic order vs superconductivity in a layered cuprate

We report on the phase diagram for charge-stripe order in La1.6-xNd0. 4SrxCuO4, determined by neutron and x-ray scattering studies and resistivity measurements. From an analysis of the in-plane resistivity motivated by recent nuclear-quadrupole-resonance studies, we conclude that the transition temperature for local charge ordering decreases monotonically with x, and hence that local antiferromagnetic order is uniquely correlated with the anomalous depression of superconductivity at x approximately 1 / 8. This result is consistent with theories in which superconductivity depends on the existence of charge-stripe correlations.

Journal Article↗

PubMed2000

Topological analyses of cuprite, Cu2O, using high-energy synchrotron-radiation data

Topological analyses were performed on room-temperature and low-temperature high-energy synchrotron-radiation data from cuprite, Cu(2)O, using both single-exponential and analytical functions in the multipole model. Differences between the refinements of the data sets turned out to be small and the data were found to be well suited for the analyses and for evaluations of further properties, e. g. the electrostatic potential and the Laplacian. The ionic character of the copper-oxygen bond was impressively underlined by the results. On the 'empty' tetrahedral sites, minima of the charge density were always found.

Journal Article↗

PubMed1999

Diffraction of 100 to 200 keV X-rays from an Si1-xGex gradient crystal: comparison with results from dynamical theory.

In a large Czochralski-grown Si(1-x)Ge(x) (0.02 </= x </= 0.07) gradient crystal, diffraction patterns have been measured in symmetrical Laue geometry using synchrotron radiation in the energy range 100-200 keV. The experimental data are in very good agreement with the results from geometrical optics theory for distorted crystals, if the creation of new wavefields for strain gradients larger than a critical value is taken into account. In this sense, the crystal behaves like an ideal gradient crystal. If the normal absorption is disregarded, for reflection 111 and 100 keV energy, the full width at half-maximum values and the peak reflectivities of the diffraction patterns range from 14.6" and 97%, respectively, to 70.9" and 74%, respectively, for a variation in the Ge concentration from 3.5 to 5.3 at.%.

Journal Article↗

PubMed1996