Theory of magnetic deflagration

Theory of magnetic deflagration (avalanches) in crystals of molecular magnets has been developed. The phenomenon resembles the burning of a chemical substance, with the Zeeman energy playing the role of the chemical energy. Non-destructive reversible character of magnetic deflagration, as well as the possibility to continuously tune the flammability of the crystal by changing the magnetic field, makes molecular magnets an attractive toy system for a detailed study of the burning process. Besides simplicity, new features, as compared to the chemical burning, include possibility of quantum decay of metastable spin states and strong temperature dependence of the heat capacity and thermal conductivity. We obtain analytical and numerical solutions for criteria of the ignition of magnetic deflagration, and compute the ignition rate and the speed of the developed deflagration front.Comment: 17 Pages, 17 Figure caption

Phonon superradiance and phonon laser effect in nanomagnets

We show that the theory of spin-phonon processes in paramagnetic solids must take into account the coherent generation of phonons by the magnetic centers. This effect should drastically enhance spin-phonon rates in nanoscale paramagnets and in crystals of molecular nanomagnets.Comment: 4 PR pages, 1 Figur

Low-Temperature Features of Nano-Particle Dynamics

In view of better characterizing possible quantum effects in the dynamics of nanometric particles, we measure the effect on the relaxation of a slight heating cycle. The effect of the field amplitude is studied; its magnitude is chosen in order to induce the relaxation of large particles (~7nm), even at very low temperatures (100mK). Below 1K, the results significantly depart from a simple thermal dynamics scenario.Comment: 1 tex file, 4 PostScript figure

DFT Calculations as a Tool to Analyse Quadrupole Splittings of Spin Crossover Fe(II) complexes

Density functional methods have been applied to calculate the quadrupole splitting of a series of iron(II) spin crossover complexes. Experimental and calculated values are in reasonable agreement. In one case spin-orbit coupling is necessary to explain the very small quadrupole splitting value of 0.77 mm/s at 293 K for a high-spin isomer

Chemical Dissection of an Essential Redox Switch in Yeast

SummarySaccharomyces cerevisiae responds to elevated levels of hydrogen peroxide in its environment via a redox relay system comprising the thiol peroxidase Gpx3 and transcription factor Yap1. In this signaling pathway, a central unresolved question is whether cysteine sulfenic acid modification of Gpx3 is required for Yap1 activation in cells. Here we report that cell-permeable chemical probes, which are selective for sulfenic acid, inhibit peroxide-dependent nuclear accumulation of Yap1, trap the Gpx3 sulfenic acid intermediate, and block formation of the Yap1-Gpx3 intermolecular disulfide directly in cells. In addition, we present electrostatic calculations that show cysteine oxidation is accompanied by significant changes in charge distribution, which might facilitate essential conformational rearrangements in Gpx3 during catalysis and intermolecular disulfide formation with Yap1

Oxidation and protection of fiberglass-epoxy composite masts for photovoltaic arrays in the low Earth orbital environment

Fiberglass-epoxy composites are considered for use as structural members for the mast of the space station solar array panel. The low Earth orbital environment in which space station is to operate is composed mainly of atomic oxygen, which has been shown to cause erosion of many organic materials and some metals. Ground based testing in a plasma asher was performed to determine the extent of degradation of fiberglass-epoxy composites when exposed to a simulated atomic oxygen environment. During exposure, the epoxy at the surface of the composite was oxidized, exposing individual glass fibers which could easily be removed. Several methods of protecting the composite were evaluated in an atomic oxygen environment and with thermal cycling and flexing. The protection techniques evaluated to date include an aluminum braid covering, an indium-tin eutectic and a silicone based paint. The open aluminum braid offered little protection while the CV-1144 coating offered some initial protection against atomic oxygen, but appears to develop cracks which accelerate degradation when flexed. Coatings such as the In-Sn eutectic may provide adequate protection by containing the glass fibers even though mass loss still occurs