Professor Paolo G. Radaelli OSI

Abstract:

Aim of the LISA Test‐flight Package on board the LISA Pathfinder mission is to provide in‐flight demonstration of some of the LISA critical technologies in achieving the free‐fall condition of a LISA‐like test‐mass in the bandwidth from 1 to 30mHz. Accordingly, owing to high inertial loads arising during the launch phase the test‐mass needs to be firmly secured to the GRS, in order to avoid collision with the surrounding electrodes and housing parts. After the launch and orbit commissioning, the test‐mass must be released to floating conditions, in compliance with strict requirements of initial position and velocity, due to the low force and torque authority made available by the capacitive actuation system. The Caging Mechanism Assembly is being designed by Alcatel Alenia Space Italia and it constitutes the GRS subsystem dedicated to cage and release the test‐mass. The release phase to floating conditions has been identified as critical for the entire mission, therefore a ground‐based verification of such a function has been deemed necessary. The verification approach adopted is to set both test‐mass and release‐dedicated plunger mock‐ups in representative tribological conditions of the in‐flight situation. An effort is being made to build a facility that enables to characterize the momentum transfer between the two suspended bodies and verify the compliance of the design of the release‐dedicated mechanism subsystem of the Grabbing Positioning and Release Mechanism of the CMA. The proposed experiment and the facility status are here presented and discussed.

Abstract:

The local and intermediate structure of La1 - x Cax MnO3 has been studied in the orthorhombic (O) and pseudo-cubic (O^′) phases, both as a function of temperature (x = 0.00), and as a function of Ca content (at 310 K). Neutron powder diffraction-based high real space resolution atomic pair distribution function (PDF) analysis shows that the Jahn Teller distortion of the MnO6 octahedra persists locally deep in the O^′ phase in both cases studied, contrary to the average crystallographic view. The O to O^′ structural phase transformation does have a local structural signature evidenced as a dramatic change in a PDF peak at 10.3 Å sensitive to the rotations of the MnO6 octahedra, providing further evidence that the nature of the transformation is orbital order to disorder regardless of whether the phase boundary is crossed as a function of T or x. © 2006 Elsevier B.V. All rights reserved.

Abstract:

Texture analysis by time-of-flight neutron diffraction, carried out on a multidetector instrument, requires just a few sample orientations. Moreover, on a diffractometer like GEM at ISIS with sufficiently high detector coverage a quantitative bulk texture analysis can be performed even on a stationary sample in a matter of minutes. A 'single-shot', rapid texture measurement on a high-count-rate instrument can be of considerable benefit for studying materials at non-ambient conditions or for bulky samples that cannot be mounted on a goniometer. The capabilities of GEM for texture analysis are demonstrated with results on copper texture standards, which were studied to accompany diffraction analyses of archaeological objects. © 2006 Elsevier B.V. All rights reserved.