H. Figiel

Structural and magnetic properties of TbMn2Hx hydrides

Abstract Powder samples of TbMn 2 H x hydrides, with 0≤ x ≤4.3, are characterised by X-ray analysis and SQUID magnetometry for temperatures ranging between 2 and 375 K. We observed structural phase transformations as a function of the hydrogen concentration and temperature. In particular a spinodal decomposition for x

Structural and magnetic transformations in the GdMn2Hx hydrides

Powder samples of GdMn2Hx hydrides, with 0pxp4.3, have been characterized by X-ray analysis and SQUID magnetometry for temperatures ranging between 4 and 375 K.The observed phase transformations as a function of temperature and hydrogen concentration are discussed and explained.The correlated changes of magnetization and susceptibility have been analyzed and the temperature dependent development of magnetic ordering of Mn and Gd atoms as a function of temperature and hydrogen content has been discussed.The structural and magnetic phase diagrams have been proposed. r 2002 Elsevier Science B.V. All rights reserved.

Micro-imaging of implanted scaffolds using combined MRI and micro-CT

RATIONALE AND OBJECTIVES Thanks to the advanced studies in biomaterial engineering a panoply of polymers can be used to manufacture porous scaffolds for bone tissue regeneration. Suitability of the scaffold for its purpose is determined by factors like size of the pores, its orientation and shape, as well as biocompatibility of the material. Even though a variety of analysis methods is available for in vitro studies, investigating the process of bone reconstruction on implanted scaffold meets with difficulties. METHODS AND MATERIALS Polylactide porous sponges imbued in hydroxyapatite were implanted into long bones of white New Zealand rabbits for 3 months. The bones obtained from the animals were subjected to MRI and μCT imaging. The obtained images were subsequently fused together. RESULTS AND CONCLUSIONS Combined MRI and μCT resulted in high resolution diagnostic images which allow for: implant positioning, inflammation divulgement, rating degree of implant resorption, observation of newly formed trabeculae, texture analysis and other quantitative measurements.

Magnetic ordering in TbMn2D2

The results of neutron diffraction investigations of TbMn2D2 deuteride are presented and analysed. The location of deuterium atoms in the lattice was determined. Magnetic ordering in this compound appears below 300 K. The magnetic structure can be described by the propagation vector [ 1 1 1 ]. The Tb sublattice couples antiferromagnetically, with magnetic moments equal to 4.8 µB, and the Mn sublattice is also coupled antiferromagnetically, with different magnetic moments.

Magnetic ordering of TbMn2D2 - a nuclear magnetic resonance analysis

Nuclear magnetic resonance of 2 D nuclei is measured in the paramagnetic phase of TbMn2D2 powder samples. Static and dynamic contributions of Mn and Tb moments to the nuclear probes are characterized on approach to the ordering temperature TN = 272 K and the possibility of antiferromagnetic correlations between Mn and Tb magnetic moments is analysed. Field and temperature dependence of the magnetization in the ordered state is presented as well.

A theoretical validation of the B-matrix spatial distribution approach to diffusion tensor imaging

The recently presented B-matrix Spatial Distribution (BSD) approach is a calibration technique which derives the actual distribution of the B-matrix in space. It is claimed that taking into account the spatial variability of the B-matrix improves the accuracy of diffusion tensor imaging (DTI). The purpose of this study is to verify this approach theoretically through computer simulations. Assuming three different spatial distributions of the B-matrix, diffusion weighted signals were calculated for the six orientations of a model anisotropic phantom. Subsequently two variants of the BSD calibration were performed for each of the three cases; one with the assumption of high uniformity of the model phantom (uBSD-DTI) and the other taking into account imperfections in phantom structure (BSD-DTI). Several cases of varying degrees of phantom uniformity were analyzed and the distributions of the B-matrix obtained were used for the calculation of the diffusion tensor of a model isotropic phantom. The results were compared with standard diffusion tensor calculation. The simulations confirmed the improvement of accuracy in the determination of the diffusion tensor after the calibration. BSD-DTI improves accuracy independent of both the degree of uniformity of the phantom and the inhomogeneity of the B-matrix. In cases of a relatively good uniformity of the phantom and minor distortions in the spatial distribution of the B-matrix, the uBSD-DTI approach is sufficient.

Quasicritical behaviour of the nuclear magnetic resonance and muon spin-rotation relaxation in cubic ferromagnets and antiferromagnets

At heoretical model describing quasicritical behaviour of the nuclear magnetic resonance (NMR) relaxation rates 1/T1 ,1 /T2 and muon relaxation rate λ for cubic ferromagnets and antiferromagnets with spin fluctuations is presented. The model extends and generalizes the model of Moriya and explains why the observed experimental values of the critical exponents are different from the values predicted by th et heory of critical phenomena. The formulae for the relaxation rates obtained from this model are used for fitting to the experimental NMR data for YMn2Dx ,T bMn 2D2 and the muon spin-rotation (µSR) data for YMn2 ,Y Mn 2Dx ,G dMn 2 and Y(Co1−x Alx )2 (ferromagnetic). It is shown that the dependence of the exchange coupling constant on the wavevector k is important for understanding the observed quasicritical effects. (Some figures in this article are in colour only in the electronic version)

Application of the Digital Curvelet Transform for the Purpose of Image Denoising in MRI

This paper presents a curvelet-based approach on the image denoising in magnetic resonance imaging (MRI). The method is worth of examination, because it has not been tested so far in case of MRI. The results show how the Digital Curvelet Transform method can be used for the noise reduction. The analysis of the Signal to Noise Ratio (SNR), Normal to Mean value (NM) and edge detection quality is applied. The Digital Curvelet Transform application provides additional possibilities like image compression and image fusion, which could be also useful in the MRI application.

Structural and magnetic transformations in HoMn2Hx hydrides

The HoMn2 compound crystallizes in the C15 or C14 Laves phases depending on preparation. The effect of hydrogen absorption on structural, magnetic and thermodynamic properties of HoMn2Hx hydrides for both phases has been investigated by XRD, AC/DC magnetometry, and calorimetry in the temperature range of 80?300 K. In addition to general features revealed by RMn2Hx compounds (R = rare earth or Yttrium), unusual behavior of these hydrides was found. In particular, a transformation from the cubic to the monoclinic structure was detected, which so far has not been reported for other cubic RMn2Hx (R ? rare earth or Yttrium) compounds. The structural transformations are reflected in the magnetic behavior. The change in ordering temperatures indicates a strong correlation between the magnetic interactions and the Mn-Mn distance modified by hydrogen absorption. Tentative magnetic and structural phase diagrams are proposed. The presented results are compared with the properties of other cubic and hexagonal RMn2Hx hydrides.