Measuring strain at the atomic-scale with Differential X-ray Absorption Spectroscopy

Strain-inducing phenomena, such as magnetostriction, lie at the heart of transducer technologies. Knowledge of their origin and mechanics, and how they manifest themselves in different materials, underpins the development and optimisation of sensor and actuator devices. DiffXAS has been developed to permit strain measurements at an atomic-scale, and thus verify theoretical models for transducer behaviour.Submitted versio

Local Structure and Spin Transition in Fe2O3 Hematite at High-Pressure

The pressure evolution of the local structure of Fe2O3 hematite has been determined for the first time by extended x-ray absorption fine structure up to 79 GPa. The comparison to the different high-pressure forms proposed in the literature suggests that the orthorhombic structure with space group Aba2 is the most probable. The crossover from Fe high-spin to low-spin states with pressure increase has been monitored from the pre-edge region of the Fe K-edge absorption spectra. The "simultaneous" comparison with the local structural changes allows us to definitively conclude that it is the electronic transition that drives the structural transition and not viceversa

Unexpected effect of Ru-substitution in lightly doped manganites

In this Communication we report about the unexpected effect of ruthenium doping in sodium ligthly-doped manganites. This effect seems to be in contrast with the usual model applied to describe the effect of this magnetic ion into the manganite structure. We propose a possible compensation mechanism which seems also able to describe other peculiar features encountered in these materials.Comment: 3 pages, 2 Figures to appear in ChemCom

Pressure induced bcc to hcp transition in Fe: Magnetism-driven structure transformation

The pressure induced bcc to hcp transition in Fe has been investigated via ab-initio electronic structure calculations. It is found by the disordered local moment (DLM) calculations that the temperature induced spin fluctuations result in the decrease of the energy of Burgers type lattice distortions and softening of the transverse $N$-point $TA_1$ phonon mode with $[\bar{1}10]$ polarization. As a consequence, spin disorder in an system leads to the increase of the amplitude of atomic displacements. On the other hand, the exchange coupling parameters obtained in our calculations strongly decrease at large amplitude of lattice distortions. This results in a mutual interrelation of structural and magnetic degrees of freedom leading to the instability of the bcc structure under pressure at finite temperature

Shoulder posture and median nerve sliding

Background: Patients with upper limb pain often have a slumped sitting position and poorshoulder posture. Pain could be due to poor posture causing mechanical changes (stretch; localpressure) that in turn affect the function of major limb nerves (e.g. median nerve). This studyexamines (1) whether the individual components of slumped sitting (forward head position, trunkflexion and shoulder protraction) cause median nerve stretch and (2) whether shoulderprotraction restricts normal nerve movements.Methods: Longitudinal nerve movement was measured using frame-by-frame cross-correlationanalysis from high frequency ultrasound images during individual components of slumped sitting.The effects of protraction on nerve movement through the shoulder region were investigated byexamining nerve movement in the arm in response to contralateral neck side flexion.Results: Neither moving the head forward or trunk flexion caused significant movement of themedian nerve. In contrast, 4.3 mm of movement, adding 0.7% strain, occurred in the forearm duringshoulder protraction. A delay in movement at the start of protraction and straightening of thenerve trunk provided evidence of unloading with the shoulder flexed and elbow extended and thescapulothoracic joint in neutral. There was a 60% reduction in nerve movement in the arm duringcontralateral neck side flexion when the shoulder was protracted compared to scapulothoracicneutral.Conclusion: Slumped sitting is unlikely to increase nerve strain sufficient to cause changes tonerve function. However, shoulder protraction may place the median nerve at risk of injury, sincenerve movement is reduced through the shoulder region when the shoulder is protracted andother joints are moved. Both altered nerve dynamics in response to moving other joints and localchanges to blood supply may adversely affect nerve function and increase the risk of developingupper quadrant pain

Dynamics of the magnetic and structural a -> e phase transition in Iron

We have studied the high-pressure iron bcc to hcp phase transition by simultaneous X-ray Magnetic Circular Dichroism (XMCD) and X-ray Absorption Spectroscopy (XAS) with an X-ray dispersive spectrometer. The combination of the two techniques allows us to obtain simultaneously information on both the structure and the magnetic state of Iron under pressure. The magnetic and structural transitions simultaneously observed are sharp. Both are of first order in agreement with theoretical prediction. The pressure domain of the transition observed (2.4 $\pm$ 0.2 GPa) is narrower than that usually cited in the literature (8 GPa). Our data indicate that the magnetic transition slightly precedes the structural one, suggesting that the origin of the instability of the bcc phase in iron with increasing pressure is to be attributed to the effect of pressure on magnetism as predicted by spin-polarized full potential total energy calculations

High pressure polymorphism of ?-TaON

The high pressure behavior of TaON was studied using a combination of Raman scattering, synchrotron X-ray diffraction, and X-ray absorption spectroscopy in diamond anvil cells to 70 GPa at ambient temperature. A Birch–Murnaghan equation of state fit for baddeleyite structured ?-TaON indicates a high bulk modulus value Ko = 328 ± 4 GPa with K?o = 4.3. EXAFS analysis of the high pressure XAS data provides additional information on changes in the Ta–(O,N) and Ta–Ta distances. Changes in the X-ray diffraction patterns and Raman spectra indicate onset of a pressure induced phase transition near 33 GPa. Our analysis indicates that the new phase has an orthorhombic cotunnite-type structure but that the phase transition may not be complete even by 70 GPa. Similar sluggish transformation kinetics are observed for the isostructural ZrO2 phase. Analysis of compressibility data for the new cotunnite-type TaON phase indicate a very high bulk modulus Ko 370 GPa, close to the theoretically predicted value.<br/

Interplay of the electronic and lattice degrees of freedom in A_{1-x}Fe_{2-y}Se_{2} superconductors under pressure

The local structure and electronic properties of Rb$_{1-x}$Fe$_{2-y}$Se$_2$ are investigated by means of site selective polarized x-ray absorption spectroscopy at the iron and selenium K-edges as a function of pressure. A combination of dispersive geometry and novel nanodiamond anvil pressure-cell has permitted to reveal a step-like decrease in the Fe-Se bond distance at $p\simeq11$ GPa. The position of the Fe K-edge pre-peak, which is directly related to the position of the chemical potential, remains nearly constant until $\sim6$ GPa, followed by an increase until $p\simeq 11$ GPa. Here, as in the local structure, a step-like decrease of the chemical potential is seen. Thus, the present results provide compelling evidence that the origin of the reemerging superconductivity in $A_{1-x}$Fe$_{2-y}$Se$_2$ in vicinity of a quantum critical transition is caused mainly by the changes in the electronic structure

Emotional Regulation Questionnaire (ERQ): psychometric indicators and affective relations in an elderly sample

Examinou-se indicadores psicométricos do Questionário de Regulação Emocional (QRE) e suas relações com medidas de experiência afetiva, satisfação com a vida e depressão em idosos. Cento e cinquenta e três idosos (M= 66,8 anos; DP=±5,20, 71,2% feminino) de uma Universidade Aberta à Terceira Idade responderam ao QRE, ao Positive and Negative Affect Schedule (PANAS) e à escala satisfação com a vida e de depressão (GDS-15). Dois fatores (Reavaliação Cognitiva; Supressão Emocional) explicaram 50,1% da variância e os índices de consistência interna e de estabilidade temporal foram acima de 0,70. Houve relações positivas entre Reavaliação Cognitiva, satisfação com a vida e afetos positivos e relações negativas com depressão. Maior uso da Reavaliação Cognitiva é indicativo de saúde emocional em idososWe examined psychometric indicators of the Emotional Regulation Questionnaire (ERQ) and their relationship with measures of affective experience, satisfaction with life and depression in the elderly. One hundred and fifty-three elderly people (M = 66.8 years, SD = 5.20, 71.2% female) of an Open University for Seniors responded to the ERQ, the Positive and Negative Affect Schedule (PANAS), the Life Satisfaction Scale and the Geriatric Depression Scale (GDS-15). Two factors (Cognitive Reappraisal and Emotional Suppression) explained 50.1% of variance; internal consistency and temporal stability were above .70. There were positive relations between Cognitive Reappraisal and life satisfaction and positive affect; and there were negative relations with depression. Increased use of Cognitive Reappraisal is an indication of emotional health in the elderl