Ferromagnetic transition in a double-exchange system

We study ferromagnetic transition in three-dimensional double-exchange model. The influence of strong spin fluctuations on conduction electrons is described in coherent potential approximation. In the framework of thermodynamic approach we construct for the system "electrons (in a disordered spin configuration) + spins" the Landau functional, from the analysis of which critical temperature of ferromagnetic transition is calculated.Comment: 4 pages, 1 eps figure, LaTeX2e, RevTeX. References added, text change

TRY plant trait database – enhanced coverage and open access

Plant traits—the morphological, anatomical, physiological, biochemical and phenological characteristics of plants—determine how plants respond to environmental factors, affect other trophic levels, and influence ecosystem properties and their benefits and detriments to people. Plant trait data thus represent the basis for a vast area of research spanning from evolutionary biology, community and functional ecology, to biodiversity conservation, ecosystem and landscape management, restoration, biogeography and earth system modelling. Since its foundation in 2007, the TRY database of plant traits has grown continuously. It now provides unprecedented data coverage under an open access data policy and is the main plant trait database used by the research community worldwide. Increasingly, the TRY database also supports new frontiers of trait‐based plant research, including the identification of data gaps and the subsequent mobilization or measurement of new data. To support this development, in this article we evaluate the extent of the trait data compiled in TRY and analyse emerging patterns of data coverage and representativeness. Best species coverage is achieved for categorical traits—almost complete coverage for ‘plant growth form’. However, most traits relevant for ecology and vegetation modelling are characterized by continuous intraspecific variation and trait–environmental relationships. These traits have to be measured on individual plants in their respective environment. Despite unprecedented data coverage, we observe a humbling lack of completeness and representativeness of these continuous traits in many aspects. We, therefore, conclude that reducing data gaps and biases in the TRY database remains a key challenge and requires a coordinated approach to data mobilization and trait measurements. This can only be achieved in collaboration with other initiatives

Correlated electrons in heavy fermion and double exchange systems

The metamagnetic state of the Anderson model is investigated with the intent of explaining anomalous de Haas-van Alphen experiments on the heavy fermion system CeRu_2Si_2. Working in the Landau quantised basis a variational quasiparticle ansatz modelling magnetic polaron formation is used to obtain the self-energy. The oscillatory magnetisation M-tilde is calculated following Luttinger and the usual Lifschitz-Kosevich formula is obtained. Owing to the large mass enhancement the oscillatory part of the self-energy #SIGMA#-tilde is not negligible here however, and the effects of #SIGMA#-tilde on M-tilde are calculated. A new oscillatory paramagnetic term and a splitting of the spectral peaks into subharmonics is predicted, but the anomalous experimental results are not explained. The double exchange model is studied in order to resolve controversy over whether it suffices to model the colossal magnetoresistance manganites or whether additional physics is required. The one-electron Green function is obtained using a Hubbard-III type equation of motion decoupling approximation approximation exact in the atomic limit, regarded as a dynamic many-body coherent potential approximation. The paramagnetic state resistivity is calculated and found to be much smaller than that measured, and the reason for disagreement over its magnitude is explained. The magnetic susceptibility is studied for spin 1/2 and it is found that ferromagnetism does not exist in this approximation. At low temperature and half-filling the susceptibility deviates from the physical Curie law behaviour and methods of remedying this problem are considered. (author)SIGLEAvailable from British Library Document Supply Centre-DSC:DXN034068 / BLDSC - British Library Document Supply CentreGBUnited Kingdo

Schur complements and state space realizations

AbstractMotivated by state space realizations of transfer functions from system theory, a number of operations on Schur complements are introduced and studied. These operations are equivalence, extension, multiplication, inversion, and factorization. Together they form an algebraic framework which is of independent interest, and also useful in solving problems in analysis

In vivo assessment of optimal viewing angles from X-ray coronary angiography

Aims: To propose and validate a novel approach to determine the optimal angiographic viewing angles for a selected coronary (target) segment from X-ray coronary angiography, without the need to reconstruct the entire coronary tree in three-dimensions (3D), such that subsequent interventions are carried out from the best view. Methods and results: The approach starts with standard quantitative coronary angiography (QCA) of the target vessel in two angiographic views. Next, the target vessel is reconstructed in 3D, and in a very simple and intuitive manlier, the possible overlap of the target vessel and other vessel segments can be assessed, resulting in the best view with minimum foreshortening and overlap. A retrospective study including 67 patients was set up for the validation. The overlap prediction result was compared with the true overlap on the available angiographic views (TEST views). The foreshortening for the views proposed by the new approach software viewing angle (SVA) and the views used during the stent deployment software viewing angle (EVA) were compared. Two experienced interventional cardiologists visually evaluated the success of SVA with respect to EVA. The evaluation results were graded into five values ranging from -2 to 2. The overlap prediction algorithm successfully predicted the overlap condition for all 235 TEST views. EVA was associated with more foreshortening than SVA (8.9%+/- 8.2% vs. 1.6%+/- 1.5%, p<0.001). The average evaluated point for the success of SVA was 0.94 +/- 0.80 (p<0.001), indicating that the evaluators were in favor of the optimal views determined by the proposed approach versus the views used during the actual intervention. Conclusions: The proposed approach is able to accurately and quickly determine the optimal viewing angles for the online support of coronary interventions.Cardiovascular Aspects of Radiolog