Energy shifts in photoemission lines during the tetragonal- to cubic-phase transition in BaTiO3 single crystals and systems with CoFe2O4 and NiFe2O4 overlayers.

In BaTiO3 the phase transition from tetragonal to cubic is connected with the disappearance of the ferroelectric polarization. In photoelectron spectroscopy huge transient shifts in the binding energies of all core-level photoemission lines have been observed while heating and cooling through the Curie temperature. Excitation energies from 2 keV to 6 keV have been used to show this to be a bulk effect and not a surface effect alone. These observations are discussed in terms of charging, which results from the disappearance of the ferroelectric polarization. This mechanism has previously been proposed as the origin of electron emission in ferroelectric materials. Besides the jump-like shifts, additional permanent shifts in binding energies have been observed for the tetragonal and the cubic phase. These experimental shifts have been related to theoretical ones from ab initio calculations. In addition to BaTiO3 single crystals, systems with CoFe2O4 and NiFe2O4 overlayers on BaTiO3 have been investigated. The low conductivity of these layers sets them apart from metallic overlayers like Fe or Co, where the shifts are suppressed. This difference adds further support for charging as the origin of the effect.

Study of electronic and magnetic properties and related x-ray absorption spectroscopy of ultrathin Co films on BaTiO3.

We present a first-principles study of electronic and magnetic properties of thin Co films on a BaTiO3(0 0 1) single crystal. The crystalline structure of 1-3 monolayer thick Co films was determined and served as input for calculations of the electronic and magnetic properties of the films. The estimation of exchange constants indicates that the Co films are ferromagnetic with a high critical temperature, which depends on the film thickness and the interface geometry. In addition, we calculated x-ray absorption spectra, related magnetic circular dichroism (XMCD) and linear dichroism (XLD) of the Co L 2, 3 edges as a function of Co film thickness and ferroelectric polarization of BaTiO3. We found characteristic features, which depend strongly on the magnetic properties and the structure of the film. While there is only a weak dependence of XMCD spectra on the ferroelectric polarization, the XLD of the films is much more sensitive to the polarization switching, which could possibly be observed experimentally.

Quantifying skeletal muscle properties in cadaveric test specimens: effects of mechanical loading, postmortem time, and freezer storage.

Investigators currently lack the data necessary to define the state of skeletal muscle properties within cadaveric specimens. The purpose of this study is to define the temporal changes in the postmortem properties of skeletal muscle as a function of mechanical loading and freezer storage. The tibialis anterior of the New Zealand white rabbit was chosen for study. Modulus and no-load strain were found to vary significantly from live after eight hours postmortem. Following the changes that occur during rigor mortis, a stable region of postmortem, post-rigor properties occurred between 36 to 72 hours postmortem. A freeze-thaw process was not found to have a significant effect on the post-rigor response. The first loading cycle response of post-rigor muscle was unrepeatable but stiffer than live passive muscle. After preconditioning, the post-rigor muscle response was repeatable. The preconditioned post-rigor response was less stiff than the live passive response due to a significant increase in no-load strain. Failure properties of postmortem muscle were found to be significantly different from live passive muscle with a significant decrease in failure stress (61 percent) and energy (81 percent), while failure strain was unchanged. These results suggest that the post-rigor response of cadaveric muscle is unaffected by freezing but sensitive to even a few cycles of mechanical loading.