Polarized neutron scattering studies of the kagome lattice antiferromagnet KFe3(OH)6(SO4)2

We report polarized neutron scattering studies of spin-wave excitations and spin fluctuations in the S=5/2 kagome lattice antiferromagnet KFe3(OH)6(SO4)2 (jarosite). Inelastic polarized neutron scattering measurements at 10 K on a single crystal sample reveal two spin gaps, associated with in-plane and out-of-plane excitations. The polarization analysis of quasi-elastic scattering at 67 K shows in-plane spin fluctuations with XY symmetry, consistent with the disappearance of the in-plane gap above the Neel temperature T_N = 65 K. Our results suggest that jarosite is a promising candidate for studying the 2D XY universality class in magnetic systems.Comment: 3 pages, 3 figures, Proceeding to the 7th International Workshop on Polarized Neutrons for Condensed Matter Investigations and 2nd International Symposium of Quantum Beam Science Directorat

Ensaios mecânicos de um sistema de fixação pedicular com barra transversal Mechanical assay of a pedicular fixation system with transversal rod

Foi realizado estudo biomecânico de um protótipo de sistema de fixação vertebral que utiliza o pedículo vertebral como ponto de ancoragem dos implantes, associado a hastes que conectam transversalmente os parafusos pediculares. De modo diferente dos sistemas convencionais, nos quais os parafusos são conectados no sentido longitudinal, no sistema desenvolvido as hastes são conectadas transversalmente aos parafusos. Foram realizados ensaios mecânicos (flexo-compressão, flexão lateral e torção) utilizando-se corpos de prova de madeira em máquina universal de testes, com a finalidade de comparar a resistência desse sistema de fixação com o sistema convencionalmente utilizado. Os testes biomecânicos mostraram que o sistema desenvolvido apresentou menor resistência nos ensaios mecânicos realizados, quando comparado com o sistema de fixação convencional.<br>A biomechanical study of a spine fixation prototype was performed. This system uses vertebral pedicle as anchor point of the implants in association with transversally connecting rods. This is different form the usual systems where longitudinally placed rods connect the pedicular screws. Mechanical assays were performed (flexo-compression, lateral flexion, torsion) using probe wood pieces in an universal testing machine, aiming to compare the resistance of this system of fixation to the conventionally used ones. Biomechanical tests showed that the system was less resistant to the mechanical assays when compared to conventional systems

Testing a detection dog to locate bumblebee colonies and estimate nest density

Bumblebee nests are difficult to find, hampering ecological studies. Effective population size of bumblebees is determined by nest density, so the ability to quantify nest density would greatly aid conservation work. We describe the training and testing of a dog to find bumblebee nests. The dog was trained by the British army, using B. terrestris nest material. Its efficacy in finding buried nest material of a range of bumblebee species was 100%, and no false positives were recorded, suggesting that the dog was able to generalize across Bombus species. The dog was then used to locate bumblebee nests in four different habitats on the island of Tiree, west Scotland. The dog located 33 nests, and nest densities recorded varied from 0 to 1.86 nests per hectare, according to species and habitat. Habitat preferences appeared to be evident among the bumblebee species, with most B. muscorum nests in machair and all of the B. distinguendus nests being in dunes. We conclude that the technique has great potential, but note that using a dog to detect nests in more densely vegetated habitats may be less successful

The Operator Fejér-Riesz Theorem

The Fejér-Riesz theorem has inspired numerous generalizations in one and several variables, and for matrix- and operator-valued functions. This paper is a survey of some old and recent topics that center around Rosenblum’s operator generalization of the classical Fejér-Riesz theorem