Doping driven magnetic instabilities and quantum criticality of NbFe2_{2}

Using density functional theory we investigate the evolution of the magnetic ground state of NbFe$_{2}$ due to doping by Nb-excess and Fe-excess. We find that non-rigid-band effects, due to the contribution of Fe-\textit{d} states to the density of states at the Fermi level are crucial to the evolution of the magnetic phase diagram. Furthermore, the influence of disorder is important to the development of ferromagnetism upon Nb doping. These findings give a framework in which to understand the evolution of the magnetic ground state in the temperature-doping phase diagram. We investigate the magnetic instabilities in NbFe$_{2}$. We find that explicit calculation of the Lindhard function, $\chi_{0}(\mathbf{q})$, indicates that the primary instability is to finite $\mathbf{q}$ antiferromagnetism driven by Fermi surface nesting. Total energy calculations indicate that $\mathbf{q}=0$ antiferromagnetism is the ground state. We discuss the influence of competing $\mathbf{q}=0$ and finite $\mathbf{q}$ instabilities on the presence of the non-Fermi liquid behavior in this material.Comment: 8 pages, 7 figure

Magnetic ordering above room temperature in the sigma-phase of Fe66V34

Magnetic properties of four sigma-phase Fe_(100-x)V_x samples with 34.4<x<55.1 were investigated by Mossbauer spectroscopy and magnetic measurements in the temperature interval 5-300 K. Four magnetic quantities viz. hyperfine field, Curie temperature, magnetic moment and susceptibility were determined. The sample containing 34.4 at% V was revealed to exhibit the largest values found up to now for the sigma-phase for average hyperfine field, B = 12.1 T, average magnetic moment per Fe atom, m = 0.89 mB, and Curie temperature, TC = 315.5 K. The quantities were shown to be strongly correlated with each other. In particular, TC is linearly correlated with m with a slope of 406.5 K/mB, as well as B is so correlated with m yielding 14.3 T/mB for the hyperfine coupling constant.Comment: 15 pages, 11 figures, 1 tabl

Influences of state anxiety on gaze behavior and stepping accuracy in older adults during adaptive locomotion

This article is available open access through the publisher’s website at the link below. Copyright © The Authors 2011.OBJECTIVES: Older adults deemed to be at a high risk of falling transfer their gaze from a stepping target earlier than their low-risk counterparts. The extent of premature gaze transfer increases with task complexity and is associated with a decline in stepping accuracy. This study tests the hypothesis that increased anxiety about upcoming obstacles is associated with (a) premature transfers of gaze toward obstacles (i.e., looking away from a target box prior to completing the step on it in order to fixate future constraints in the walkway) and (b) reduced stepping accuracy on the target in older adults. METHODS: High-risk (9) and low-risk (8) older adult participants walked a 10-m pathway containing a stepping target area followed by various arrangements of obstacles, which varied with each trial. Anxiety, eye movements, and movement kinematics were measured. RESULTS: Progressively increasing task complexity resulted in associated statistically significant increases in measures of anxiety, extent of early gaze transfer, and stepping inaccuracies in the high-risk group. DISCUSSION: These results provide evidence that increased anxiety about environmental hazards is related to suboptimal visual sampling behavior which, in turn, negatively influences stepping performance, potentially contributing to increased falls risk in older adults.Biotechnology and Biological Sciences Research Counci

A new method to measure anatomic knee alignment for large studies of OA: data from the Osteoarthritis Initiative

SummaryObjectiveTo develop and validate a new and improved software method to rapidly determine femur–tibia angle (FTA).MethodsThree readers, two skilled and one unskilled, without any formal medical training, measured FTA in 142 subjects from the Osteoarthritis Initiative (OAI). The reader reliability was assessed using the intra-class correlation coefficient (ICC), root mean square standard deviation (RMSSD), and Bland–Altman plots, comparing the existing and new FTA methods. Gender-specific linear regression assessed the relationship of FTA with the hip–knee–ankle angle (HKA).ResultsThe ICC (RMSSD) for intra- and inter-reader reproducibility of the existing FTA method was 0.96 (0.77°) and 0.92 (1.38°), respectively, and for the new technique was 0.98 (0.25°) and 0.98 (0.37°), with similar results for all three readers. Bland–Altman 95% limits of agreement were greater than ±2° for the existing, and ±1° for the new method. The r-value for the relation of FTA to HKA was 0.68 and 0.72 for the existing and new methods, respectively. Varus (HKA ≤ −2°)/neutral (−2° < HKA < 2°)/valgus (HKA ≥ 2°) alignment based on predicted HKA agreed moderately with measured HKA (weighted kappa = 0.53), and had moderate sensitivity (73%) and specificity (84%) for varus malalignment. The new FTA was related to HKA using a linear equation with a slope of 0.98 and an offset of 4.0°.ConclusionsSince it is largely automated and uses unambiguous anatomical landmarks, the new method is highly reproducible and can be made on a standard posteroanterior (PA) knee radiograph by a relatively unskilled reader

Site Occupancy and Lattice Parameters in Sigma-Phase Co-Cr alloys

Neutron diffraction technique was used to study distribution of Co and Cr atoms over different lattice sites as well as lattice paramaters in sigma-phase Co100-xCrx compounds with x = 57.0, 62.7 and 65.8. From the diffractograms recorded in the temperature range of 4.2 - 300 K it was found that all five sites A, B, C, D and E are populated by both kinds of atoms. Sites A and D are predominantly occupied by Co atoms while sites B, C and E by Cr atoms. The unit cell parameters a and c, hence the unit cell volume, increase with x, the increase being characteristic of the lattice paramater and temperature. Both a and c show a non-linear increase with temperature.Comment: 5 figure