Detection, numerical simulation and approximate inversion of optoacoustic signals generated in multi-layered PVA hydrogel based tissue phantoms.

Optoacoustic (OA) measurements can not only be used for imaging purposes but as a more general tool to "sense" physical characteristics of biological tissue, such as geometric features and intrinsic optical properties. In order to pave the way for a systematic model-guided analysis of complex objects we devised numerical simulations in accordance with the experimental measurements. We validate our computational approach with experimental results observed for layered polyvinyl alcohol hydrogel samples, using melanin as the absorbing agent. Experimentally, we characterize the acoustic signal observed by a piezoelectric detector in the acoustic far-field in backward mode and we discuss the implication of acoustic diffraction on our measurements. We further attempt an inversion of an OA signal in the far-field approximation.

Magnetic structure of La2O3FeMnSe2: neutron diffraction and physical property measurements.

We report on the characterization of the mixed layered lanthanum iron manganese oxyselenide La(2)O(3)FeMnSe(2), where Fe and Mn share the same crystallographic position. The susceptibility data show a magnetic transition temperature of 76 K and a strong difference between field cooled and zero field cooled (ZFC) data at low fields. While the ZFC magnetization curve exhibits negative values below about 45 K, hysteresis measurement reveals, after an initial negative magnetic moment, a hysteresis loop typical for ferromagnetic material, pointing to competing ferromagnetic and antiferromagnetic interactions. Resistivity and dielectric permittivity measurements indicate that La(2)O(3)FeMnSe(2) is a semiconductor. We performed x-ray diffraction at 295 K and neutron diffraction at 90 and 1.7 K. The nuclear and magnetic structure was refined in the space group I4/mmm with a = 4.11031 (3) Å and c = 18.7613 (2) Å at 295 K. We did not detect a structural distortion and the Fe and Mn atoms were randomly distributed. The magnetic order was found to be antiferromagnetic, with a propagation vector q = (0,0,0) and magnetic moments of 3.44 (5) µ(B) per Fe/Mn atom aligned within the a-b plane. This magnetic order is different with respect to the pure Fe or Mn compositions reported in other studies.