A mean-field theory for strongly disordered non-frustrated antiferromagnets

Motivated by impurity-induced magnetic ordering phenomena in spin-gap materials like TlCuCl₃, we develop a mean-field theory for strongly disordered antiferromagnets, designed to capture the broad distribution of coupling constants in the effective model for the impurity degrees of freedom. Based on our results, we argue that in the presence of random magnetic couplings the conventional first-order spin-flop transition of an anisotropic antiferromagnet is split into two transitions at low temperatures, associated with separate order parameters along and perpendicular to the field axis. We demonstrate the existence of either a bicritcal point or a critical endpoint in the temperature–field phase diagram, with the consequence that signatures of the spin flop are more pronounced at elevated temperature.     

Diterpenoids from Coprinus heptemerus

Seven diterpenoids, isolated due to their ability to inhibit spore germination in the plant pathogenic fungus Magnaporthe grisea, were obtained from cultures of the basidiomycete Coprinus heptemerus. The structures of the compounds, named heptemerones A-G, were determined with spectroscopic techniques.     

Antifading embedding media in confocal immunoflourescence microscopy

Fading or bleaching of fluorescence intensity during continuous illumination of stained objects is a serious problem in fluorescence microscopy. Fluorescence intensity as well as bleaching characteristics of dyes are dependent primarily upon physical parameters such as molecular constants (absorption rate and quantum efficiency), excitation energy and brightness (causes photon saturation), and environmental parameters (pH, ions, binding to proteins, etc.) that can strongly influence the properties of fluorochrome molecules. We have studied the effect of various antifading reagents on the behavior of the common dyes fluorescein isothiocyanate (FITC) and phycoerythrin (PE) using immunofluorescent-stained living cells in suspension or membrane-permeabilized dried cells as test systems. As expected, fading cannot be completely eliminated but may be reduced to varying degrees. In our hands, the most efficient antifading reagent for FITC isn-propyl gallate (NPG) dissolved in glycerol. No additive was found to retard fading, but complete dehydration of the cell suspension reduces this effect.     

Über das Fortsetzungsproblem für Prozesse mit unabhängigen Zuwächsen

Ohne Zusammenfassung     

Single crystal diffraction under high pressure with synchrotron radiation and a diamond anvil cell

Abstract

A single crystal study on AlPO₄ was performed at 2.90 GPa with synchrotron radiation with a wavelength of only 0.54 ?. The diffracted intensity was high enough to measure even weak reflections with sufficient counting statistics. However, the search for the reflections needed to setup the orientation matrix required a lot of beamtime. A feasibility study was carried out using a proportional area counter to reduce this search time. The results demonstrate that such counters can considerably reduce the time needed for the orientation of the crystal and the data collection.

Presented at the IUCr Workshop on ‘Synchrotron Radiation Instrumentation for High Pressure Crystallography’. Daresbury Laboratory 20-21 July 1991     

UV-induced immobilization of tethered zirconocenes on H-terminated silicon surfaces

A tethered ethylenebis(indenyl) zirconocene was covalently immobilized on H-terminated Si(111) surfaces using UV-mediated alkene hydrosilylation, thus making possible the development of structured catalytic surfaces with highly controlled properties.     

Precision of Raman depolarization and optical attenuation measurements of sound tooth enamel

The demineralization of enamel that is associated with early caries formation affects the optical properties of the enamel. Polarized Raman spectroscopy and optical coherence tomography have been used to detect these changes and potentially offer a means to detect and monitor early caries development. The total optical attenuation coefficient as measured by optical coherence tomography and the polarization anisotropy of the Raman peak arising from the symmetric ν₁ vibration of at approximately 959 cm⁻¹ have been demonstrated as being sensitive markers of early caries. This ex vivo study on extracted human teeth demonstrates that these measurements can be made with reasonable precision with concomitantly good repeatability and reproducibility in sound enamel. Such reliability is crucial for these techniques to have a practical clinical value.