Protection of personal information Act No. 4 of 2013: Implications for biobanks

The Protection of Personal Information Act (POPIA) No. 4 of 2013 is the first comprehensive data-protection regulation to be passed in South Africa (SA). Its objectives include giving effect to the constitutional right to privacy by regulating the way in which personal information must be processed, balancing the right to privacy against other rights, and establishing an Information Regulator to ensure that the rights protected by POPIA are respected. POPIA will have an impact on health research, including biobanks. As sharing of samples and data is a central feature of biobanks, POPIA could change the way in which data are obtained, shared and exported. In particular, the provisions regarding data minimisation, requirements pertaining to the transfer of data abroad, consent provisions and identification of the 'responsible person' will impact the operation of biobanks in SA. With POPIA soon to come into force, it is now time to consider its implications for biobanks in SA

Temperature-dependent magnetocrystalline anisotropy of rare earth/transition metal permanent magnets from first principles : the light RCo5 (R = Y, La-Gd) intermetallics

Computational design of more efficient rare earth/transition metal (RE-TM) permanent magnets requires accurately calculating the magnetocrystalline anisotropy (MCA) at finite temperature, since this property places an upper bound on the coercivity. Here, we present a first-principles methodology to calculate the MCA of RE-TM magnets which fully accounts for the effects of temperature on the underlying electrons. The itinerant electron TM magnetism is described within the disordered local moment picture, and the localized RE-4f magnetism is described within crystal field theory. We use our model, which is free of adjustable parameters, to calculate the MCA of the RCo5 (R=Y, La-Gd) magnet family for temperatures 0–600 K. We correctly find a huge uniaxial anisotropy for SmCo5 (21.3MJm−3 at 300 K) and two finite temperature spin reorientation transitions for NdCo5. The calculations also demonstrate dramatic valency effects in CeCo5 and PrCo5. Our calculations provide quantitative, first-principles insight into several decades of RE-TM experimental studies

Rare-earth transition-metal magnets at finite temperature : self-interaction-corrected relativistic density functional theory in the disordered local-moment picture

Atomic-scale computational modeling of technologically-relevant permanent magnetic materials faces two key challenges. First, a material's magnetic properties depend sensitively on temperature, so the calculations must account for thermally-induced magnetic disorder. Second, the most widely-used permanent magnets are based on rare-earth elements, whose highly-localized 4f electrons are poorly described by standard electronic structure methods. Here, we take two established theories --- the disordered local moment picture of thermally-induced magnetic disorder and self-interaction-corrected density-functional theory --- and devise a computational framework to overcome these challenges. Using the new approach, we calculate magnetic moments and Curie temperatures of the rare-earth cobalt (RECo5) family for RE=Y--Lu. The calculations correctly reproduce the experimentally-measured trends across the series and confirm that, apart from the hypothetical compound EuCo5, SmCo5 has the strongest magnetic properties at high temperature. An order parameter analysis demonstrates that varying the RE has a surprisingly strong effect on the Co--Co magnetic interactions determining the Curie temperature, even when the lattice parameters are kept fixed. We propose the origin of this behavior is a small contribution to the density from f-character electrons located close to the Fermi level

On the Jacobi Equation and Manifolds with Multiple Conjugate Points

We investigate the phenomenon of multiple conjugate points along a geodesic. In the first instance, we investigate conjugate points in the context of the Jacobi equation, a second order ordinary differential equation, which captures precisely the geometry of conjugate points on surfaces. We then construct geometric examples which exhibit similar properties in higher dimensions

Crystal field coefficients for yttrium analogues of rare-earth/transition-metal magnets using density-functional theory in the projector-augmented wave formalism

We present a method of calculating crystal field coefficients of rare-earth/transition-metal (RE-TM) magnets within density-functional theory (DFT). The principal idea of the method is to calculate the crystal field potential of the yttrium analogue ("Y-analogue") of the RE-TM magnet, i.e. the material where the lanthanide elements have been substituted with yttrium. The advantage of dealing with Y-analogues is that the methodological and conceptual difficulties associated with treating the highly-localized 4<i>f</i> electrons in DFT are avoided, whilst the nominal valence electronic structure principally responsible for the crystal field is preserved. In order to correctly describe the crystal field potential in the core region of the atoms we use the projector-augmented wave formalism of DFT, which allows the reconstruction of the full charge density and electrostatic potential. The Y-analogue crystal field potentials are combined with radial 4<i>f</i> charge densities obtained in self-interaction-corrected calculations on the lanthanides to obtain crystal field coefficients. We demonstrate our method on a test set of 10 materials comprising 9 RE-TM magnets and elemental Tb. We show that the calculated easy directions of magnetization agree with experimental observations, including a correct description of the anisotropy within the basal plane of Tb and NdCo<sub>5</sub>. We further show that the Y-analogue calculations generally agree quantitatively with previous calculations using the open-core approximation to treat the 4<i>f</i> electrons, and argue that our simple approach may be useful for large-scale computational screening of new magnetic materials

On the Jacobi Equation and Manifolds with Multiple Conjugate Points

We investigate the phenomenon of multiple conjugate points along a geodesic. In the first instance, we investigate conjugate points in the context of the Jacobi equation, a second order ordinary differential equation, which captures precisely the geometry of conjugate points on surfaces. We then construct geometric examples which exhibit similar properties in higher dimensions

Metallic magnetism at finite temperatures studied by relativistic disordered moment description: Theory and applications

We develop a self-consistent relativistic disordered local moment (RDLM) scheme aimed at describing finite temperature magnetism of itinerant metals from first principles. Our implementation in terms of the Korringa--Kohn--Rostoker multiple scattering theory and the coherent potential approximation allows to relate the orientational distribution of the spins to the electronic structure, thus a self-consistent treatment of the distribution is possible. We present applications for bulk bcc Fe, L1$_0$-FePt and FeRh ordered in the CsCl structure. The calculations for Fe show significant variation of the local moments with temperature, whereas according to the mean field treatment of the spin fluctuations the Curie temperature is overestimated. The magnetic anisotropy of FePt alloys is found to depend strongly on intermixing between nominally Fe and Pt layers, and it shows a power-law behavior as a function of magnetization for a broad range of chemical disorder. In case of FeRh we construct a lattice constant vs. temperature phase diagram and determine the phaseline of metamagnetic transitions based on self-consistent RDLM free energy curves.Comment: 11 pages, 8 figure