Unique characterization of the Bel-Robinson tensor

We prove that a completely symmetric and trace-free rank-4 tensor is, up to sign, a Bel-Robinson type tensor, i.e., the superenergy tensor of a tensor with the same algebraic symmetries as the Weyl tensor, if and only if it satisfies a certain quadratic identity. This may be seen as the first Rainich theory result for rank-4 tensors.Comment: extended version, 13 pages, shorter version published in Class.Quant.Gra

Evaluative Perception: Introduction

In this Introduction we introduce the central themes of the Evaluative Perception volume. After identifying historical and recent contemporary work on this topic, we discuss some central questions under three headings: (1) Questions about the Existence and Nature of Evaluative Perception: Are there perceptual experiences of values? If so, what is their nature? Are experiences of values sui generis? Are values necessary for certain kinds of experience? (2) Questions about the Epistemology of Evaluative Perception: Can evaluative experiences ever justify evaluative judgments? Are experiences of values necessary for certain kinds of justified evaluative judgments? (3) Questions about Value Theory and Evaluative Perception: Is the existence of evaluative experience supported or undermined by particular views in value theory? Are particular views in value theory supported or undermined by the existence of value experience

Magnetism in Co1−x_{1-{\rm x}}Fex_{\rm x}Sb3_{3} skutterudites from density functional theory

We have investigated the electronic and magnetic properties of Co$_{1-{\rm x}}$Fe$_{\rm x}$Sb$_{3}$ skutterudites from density functional theory and Monte Carlo simulations. We find that above a certain threshold in the Fe concentration, somewhere between x=0.125 and x=0.25, Co$_{1-{\rm x}}$Fe$_{\rm x}$Sb$_{3}$ is ferromagnetic with an atomic moment which increases asymptotically towards about 1 $\mu_{B}$/Fe and a non-zero Curie temperature which reaches 70 K for FeSb$_{3}$. Ferromagnetism is favored due to a Stoner instability in the electronic structure, where a large density of states at the Fermi-level makes it favorable to form the ferromagnetic ground state

Index

Allt fler blir allt äldre i Sverige och äldreomsorgen står inför en stor utmaning när resurser i form av ekonomiska medel och rätt personal blir allt svårare att konkurrera om. I eHälsans tidsålder utvecklas det på många håll smarta tekniska lösningar för att effektivisera och kvalitetshöja omsorgsinsatser, något som allt fler aktörer får upp ögonen för. Denna uppsats utreder behovsbilden för att kunna skapa en ny kontaktyta mellan omsorgstagare, närstående och utförare inom äldreomsorg. Uppsatsens resultat är en del av det Vinnova-finansierade projektet BoNUS VO som undersöker förutsättningarna för en sådan kontaktyta. IKT-stödet ska underlätta delaktighet i den egna omsorgen såväl som stödja yrkesutövare i arbetsuppgifter. Data samlades in genom en observationsstudie av hemtjänstarbete, deltagande i gruppsamtal med närstående till omsorgstagare samt kvalitativa intervjuer med 13 informanter som hade erfarenhet av äldreomsorg. Resultatet av dataanalysen visar på att det i dagsläget finns problem som skulle kunna undvikas genom att underlätta kommunikation och informationsdelning mellan användargrupperna. Resultaten visar också på att det finns många diskussionspunkter vad gäller nytta, motsättningar i behov och avvägningen mellan ett översiktligt eller komplext system. Studien konstaterar att det finns utrymme för vidare forskning inom området.Sweden’s population is steadily growing older and while the demand for care of senior citizens is increasing, care givers are forced to cope with diminishing resources in terms of money and qualified staff. Many put hope in new eHealth technology, as a means of raising efficiency and quality in the every day working situation. This thesis aims to study needs regarding communication, information and interaction between care takers, dependants and caregivers in geriatric care, in order to create a foundation upon which an ICT system may be built to fulfill those needs. The results presented are part of a research project focusing on future ICT systems in healthcare. Data was collected through an observational study, group discussions with informants related to care takers, and qualitative interviews with 13 informants who have extensive experience of geriatric care. The results imply there are existing problems that may be avoided by facilitating information sharing between the aforementioned groups. The study also presents some important points of discussion regarding usefulness, clashing needs of different users, and the balance between simplicity of use and system size

Density functional theory study of the electronic structure of fluorite Cu2_{2}Se

We have investigated the electronic structure of fluorite Cu$_{2}$Se using density functional theory calculations within the LDA, PBE and AM05 approximations as well as with the non-local hybrid PBE0 and HSE approximations. Our results show that Cu$_{2}$Se is a zero gap semiconductor when using either a local or semi-local density functional approximation while there exists a gap when using the PBE0 functional. For the HSE approximation, we find that the presence of a gap depends on the range separation for the non-local exchange within the HSE approximation. For the occupied states we find that the LDA, PBE, AM05, PBE0 and HSE agrees when regarding the overall structure, however, the hybrid functionals are shifted towards lower energy values compared to the LDA, PBE and AM05. The valence bands obtained using the hybrid functionals are in good agreement with experimental valence band spectra. We also find that the PBE, PBE0 and HSE approximations give similar results regarding bulk properties, such as lattice constants and bulk modulus. In addition, we have investigated the localization of the Cu d-states and its effect on the band gap in the material using the LDA+U approach. We find that a gap is opened up by increasing the $U$, however, the $U$ values required for a gap opening is unrealistically high

Algebraic and differential Rainich conditions for symmetric trace-free tensors of higher rank

We study Rainich-like conditions for symmetric and trace-free tensors T. For arbitrary even rank we find a necessary and sufficient differential condition for a tensor to satisfy the source free field equation. For rank 4, in a generic case, we combine these conditions with previously obtained algebraic conditions to obtain a complete set of algebraic and differential conditions on T for it to be a superenergy tensor of a Weyl candidate tensor satisfying the Bianchi vacuum equations. By a result of Bell and Szekeres this implies that in vacuum, generically, T must be the Bel-Robinson tensor of the spacetime. For the rank 3 case we derive a complete set of necessary algebraic and differential conditions for T to be the superenergy tensor of a massless spin 3/2 field satisfying the source free field equation.Comment: 14 pages, with corrections, to appear in Proc. Roy. Soc. London

Thermo-magnonic diode: rectification of energy and magnetization currents

We investigate the dynamics of two coupled macrospins connected to thermal baths at different temperatures. The system behaves like a diode which allows the propagation of energy and mag- netization currents in one direction only. This effect is described by a simple model of two coupled nonlinear oscillators interacting with two independent reservoirs. It is shown that the rectification phenomenon can be interpreted as a a stochastic phase synchronization of the two spin-oscillators. A brief comparison with realistic micromagnetic simulations is presented. This new effect yields promising opportunities in spin-caloritronics devices.Comment: 7 pages, 8 figure

Realistic finite temperature simulations of magnetic systems using quantum statistics

We have performed realistic atomistic simulations at finite temperatures using Monte Carlo and atomistic spin dynamics simulations incorporating quantum (Bose-Einstein) statistics. The description is much improved at low temperatures compared to classical (Boltzmann) statistics normally used in these kind of simulations, while at higher temperatures the classical statistics are recovered. This corrected low-temperature description is reflected in both magnetization and the magnetic specific heat, the latter allowing for improved modeling of the magnetic contribution to free energies. A central property in the method is the magnon density of states at finite temperatures and we have compared several different implementations for obtaining it. The method has no restrictions regarding chemical and magnetic order of the considered materials. This is demonstrated by applying the method to elemental ferromagnetic systems, including Fe and Ni, as well as Fe-Co random alloys and the ferrimagnetic system GdFe$_3$