Epifluorescence optical microscopy: a sensitive tool for determining the spatial distribution of europium-dihalide precipitates in KCl : KBr : Eu2+ crystals

The spatial distribution of europium-dihalide-type precipitates in KCl?:?KBr?:Eu²⁺ single crystals annealed at 200°C for long periods of time was determined by epifluorescence optical microscopy. Laue-type patterns and optical spectroscopy were used to test the degree of long-range ordering of the specimens and to monitor the precipitation during annealing, respectively. Precipitates smaller than about 0.08?µm were found (2.84?×?10¹² precipitates cm^?3) all across the host, whereas larger precipitates of about 0.17?µm were found (2.9?×?10⁴ precipitates cm^?1) along certain linear structural singularities of the matrix. These singularities, identified as crystal dislocations, were observed to terminate always either at a triple node of singularities or at the crystal surface, forming a three-dimensional network of crystal singularities (2.0?×?10⁶ singularities cm^?2), identified as the Frank network. The presence of europium exhaustive matrix zones accompanying the observed europium-decorated paths indicates that impurity segregation processes, occurring during annealing, favour the precipitation phenomena.     

Stability of the F2-(Al-Pd-Mn) phase

The stability of the F2-(Al-Pd-Mn) phase has been studied by in-situ neutron diffraction on a single quasicrystal with composition Al_69.8Pd_21.4Mn_8.8. We find that the F2 phase is not stable and corresponds to a transient state in the process of the transformation of the icosahedral phase to the F2_M phase. The icosahedral-to-F2_Mphase transition occurs at around 715^oC. In the F2 phase a large amount of diffuse scattering is located close to the icosahedral Bragg reflection in place of the S ₁ superstructure reflections characteristic of the F2_m phase.     

Theoretical explanation for Raman and ESR spectra of V3+ ions in salt guanidinium vanadium sulfate hexahydrate

The Raman spectra and electronic spin resonance (ESR) parameters (spin-Hamiltonian parameter g factors, zero-field splitting parameter D, and hyperfine structure constant A) for the trigonal V³⁺ centers in salt guanidinium vanadium sulfate hexahydrate (GVSH) are calculated from the complete diagonalization (of energy matrix) method. The theoretical results are in agreement with the experimental findings and the trigonal crystal-field parameters are determined. The difficulty in explaining ESR parameters of V³⁺ in GVSH is removed.     

Toward an understanding of aging in plutonium from direct measurements of stored energy

ABSTRACT

We present here the first direct measurement of the radiation-damage-induced energy stored in δ-phase plutonium. The primary mode of radioactive decay of ²³⁹Pu occurs with a time constant of τ=1.1?×?10¹²?s. Each decay imparts about 85?keV of recoil energy to the uranium byproduct, 5.2?Mev to the alpha particle, and a spectrum of mostly low energy gamma rays with the most probable at 51?keV [1]. Most of the decay energy is converted immediately to heat, releasing about 1.9?mW/g. However, some thermally-recoverable energy remains trapped. Reported here are measurements of that stored energy using differential scanning calorimetry (DSC) applied to ²³⁹Pu-2.0 at.%Ga δ-phase alloy. Retained energy of ～2 J/g saturates at about 5 months and is unchanged after 30 years. The magnitude of the stored energy agrees with a short-bond defect model that that we present here. This model treats radiation damage as a Pu impurity with shortened bond lengths. It explains the change in known properties with age and predicts that density increases with age, contrary to current thinking. The short-bond impurities proposed are expected to act like other impurities, affecting strength, phase transitions, grain boundaries and other metallurgical properties.     

A study of the spin-Hamiltonian parameters for Cr5+ at the rhombically-distorted tetrahedral P5+ site of Ca2PO4Cl crystal using a two-mechanism model

The complete high-order perturbation formulae of spin-Hamiltonian (SH) parameters (g factors g_i and hyperfine structure constants A_i , where i = x, y, z) containing contributions from both the crystal-field (CF) and charge-transfer (CT) mechanisms (the latter mechanism is neglected in the widely-used CF theory) are established for d¹ ions in rhombic tetrahedra. From these formulae, the SH parameters of Cr⁵⁺ ion at the rhombically-distorted tetrahedral P⁵⁺ site of Ca₂PO₄Cl crystal are calculated. The CF and CT energy levels used in the calculation are obtained from the optical spectra of the studied Ca₂PO₄Cl : Cr⁵⁺ crystal. The calculated results showed reasonable agreement with the experimental values. The signs of the hyperfine structure constants A_i and the relative importance of the CT mechanism to SH parameters are acquired from the calculations.     

Absorption and photoluminescence spectroscopy of Er3+-doped SrAl2O4 ceramic phosphors

A spectroscopic characterization of Er³⁺-doped SrAl₂O₄ phosphor materials synthesized by a solid-state reaction method with Er concentrations varying from 0.1 to 1?mol% has been performed by studying photoluminescence (PL) in the temperature range 10 to 360?K and absorption spectra. PL signals containing five emission bands at 1492, 1529, 1541, 1558, and 1600?nm, respectively, have been observed at room temperature for Er³⁺ transitions in the near infrared region. The samples exhibit a main luminescence peak at 1.54?µm, which is assigned to recombination via an intra-4f Er³⁺ transition. Sharp bands centered at around 378, 488, 521, 651, 980, 1492, and 1538?nm in the absorption spectra can be associated with transitions from ⁴I_15/2 level to ²H_9/2, ⁴F_7/2, ²H_11/2, ⁴F_9/2, ⁴I_11/2, ²H_11/2, and ⁴I_13/2 levels, respectively. The sharp emission peaks and excellent luminescence properties show that SrAl₂O₄ is a suitable host for rare-earth-doped phosphors, which may be suitable for optical applications.     

Electron diffraction and lattice imaging study of La2Cu0.925V0.075O4 + d

The superconducting compound La₂Cu_0.925V_0.075O_{4 +}      

Commensurate-incommensurate phase transition in muthmannite,AuAgTe2: first evidence of a modulated structure at low temperature

To study the temperature-dependent structural changes and to analyze the crystal chemical behavior of silver as a function of temperature, a crystal of muthmannite, AuAgTe₂, has been investigated by X-ray single-crystal diffraction methods at 300 K and 110 K. At room temperature, muthmannite was confirmed as belonging to the space group P2/m, while at low temperature (110 K) it undergoes a reversible commensurate–incommensurate phase transition with a modulation wave vector q = 0.215(1)a* + 0.379(2)c*. Muthmannite reconverts to the commensurate type upon returning to room temperature, thus indicating that the phase transition is completely reversible in character. The average structure of the low-temperature muthmannite remains monoclinic, space group P2/m, and shows only normal thermal compression over the entire temperature range investigated. Crystal-chemical characteristics are compared with published data on the other members of the system Au–Ag–Te. Speculations on the possible origin of the modulated structure at low temperature are also given.     

Averaged Eshelby tensor and elastic strain energy of a superspherical inclusion with uniform eigenstrains

A shape described by (x²1)^p/2 + (x²2) ^p/2 + (x²3) ^p/2     

Transmission electron microscopy characterization of the high-Tc superconductor HgBa2Ca3Cu4O 10+ delta

The structures of HgBa3Ca4Cu4O10+ delta(Hg-1234) samples have been characterized by means of high-resolution electron microscopy, electron diffraction, X-ray energy-dispersive spectroscopy (XEDS) and electron-energy-loss spectroscopy (EELS) techniques. A modulated structure with a modulation vector of q = (0.036-0.048) b* + 0.5c* was found for Hg-1234. High-resolution electron microscopy on the modulated structure revealed slight displacements of atomic layers along the c direction. The anomalous contrast induced by the modulation was observed to be distributed asymmetrically between the HgOdelta layers, leading to the breakdown of the (001) mirror symmetry of the basic structure. XEDS compositional analyses showed a depletion of mercury for the modulated Hg1234 compared with the unmodulated Hg-1234, while EELS analysis suggested the presence of carbon in the modulated Hg-1234 phase. In addition, a sidecentred ordered (Cu, Hg)-1223 phase with low mercury content was identified as one of the major impurity phases in the Hg-1234 samples.     

Yield drop in high-strain-rate superplastic deformation of ZrO2-30 vol% MgAl2O4 spinel composite

The origin of a sudden yield drop in a tetragonal ZrO₂ dispersed with 30 vol% MgAl₂O₄ spinel composite has been examined. The present ZrO₂-spinel composite exhibits yield drop in superplastic flow at high strain rates of 0.2s^?1 or greater, where the flow behaviour is characterized by a stress exponent of about 3.5 and a grain-size exponent of about 1.0. Experimental examination suggests that a sudden increase in the mobile dislocation density within spinel grains is responsible for the yield drop.     

PbO compensation in the growth of PbWO4: Y3+ crystals

The light yield of Y³⁺-doped PbWO₄ crystals increases after low-dose-rate irradiation with?γ?rays, and the radiation hardness is sensitive to annealing temperature. In the PWO growth procedure, an excess of PbO in the starting materials is a convenient method of compensating for PbO volatility. The relationship between the excess of PbO and the abnormal radiation behaviour has been investigated. The mechanism of the normal excess of PbO in the growth of PWO: Y³⁺ is discussed.     

Effects of Ag and Pd on the nucleation and growth of the nano-icosahedral phase in Zr65Al7.5Ni10Cu7.5M10 (M = Ag or Pd) metallic glasses

The nucleation and growth of a nano-icosahedral phase from a supercooled liquid region of Zr₆₅Al_7.5Ni₁₀Cu_7.5M₁₀ (M = Ag or Pd) glasses have been examined by differential scanning calorimetry and transmission electron microscopy. The growth rate of the icosahedral phase is nearly constant at the initial stage and much slower than that of the Zr₂Ni phase in the Zr₆₅Al_7.5Ni₁₀Cu_17.5 metallic glass. The homogeneous nucleation rate has a maximum value of 4.4 x 10²⁰ m^-3 s^-1 at 695 K in the Zr₆₅Al_7.5Ni₁₀Cu_7.5Ag₁₀ glass, which is approximately 10² times higher than that for the formation of quasicrystalline phase in the Zr_69.5Al_7.5Ni₁₁Cu₁₂ glass and 10⁴ times higher than that of the Zr₂Ni phase in the Zr₆₅Al_7.5Ni₁₀Cu_17.5 glass. With increasing Pd content, the nucleation rate of the primary phase increases significantly and the growth rate decreases at the crystallization temperature. Thus, the addition of Ag and Pd is effective for an increase in the number of nucleation sites and the suppression of grain growth, which is the main reason for the formation of icosahedral nanoparticles. The significant increase in the nucleation rate is due to an increase in the number of nucleation sites resulting from the short-range ordering consisting of Zr-(Ag or Pd) strong pairs. It is implied that the strong pair Zr-(Ag or Pd) also contributes to the restraint of the long-range rearrangements of the constitutional elements. The formation of the nanoicosahedral phase suggests that icosahedral short-range order exists in the glassy state in the present alloys.     

Psychosocial mediators of a theory-based resistance training maintenance intervention for prediabetic adults

Objective: Examine psychosocial mediators of the effects of high vs. low-dose resistance training (RT) maintenance interventions among older (ages 50–69), overweight and pre-diabetic adults.

Design: Participants (N = 123) completed a three-month supervised RT initiation phase and were subsequently randomised (time 1) to high or low-dose six-month unsupervised RT maintenance interventions (time 2), followed by a six-month no-contact phase (time 3).

Main Outcome Measures: Online measures of putative mediators and RT behaviour.

Results: RT intervention condition (high vs. low dose) had significant effects on change from time 1 to time 2 in behavioural expectation, self-regulation and perceived satisfaction (f² = .04–.08), but not outcome expectancies, RT strategies or behavioural intentions (f² ≤ .02). Change in each of the putative mediators, except for outcome expectancies (f² ≤ .02), had significant effects on RT behaviour at times 2 (f² = .12–.27) and 3 (f² = .23–.40). In a multiple mediation model, behavioural expectation (f² = .11) and self-regulation (f² = .06) mediated the effects of RT intervention condition on time 2 RT behaviour, whereas perceived satisfaction did not (f² = .01). Self-regulation was a significant mediator of intervention effects on time 3 RT behaviour (f² = .11), but behavioural expectation and perceived satisfaction were not (f² = .04).

Conclusions: Findings suggest that behavioural expectation and self-regulation are appropriate targets for RT maintenance interventions among at-risk older adults.     

Mindfulness on Daily Life Coping in People Experiencing Psychosis: A Randomized Controlled Trial

Background/ObjectiveCognitive Behavior Therapy for psychosis (CBTp) is a recommended treatment for psychoses whose effect is mediated by coping. Mindfulness (MBI) have shown positive effects in psychosis. This study examines the hypothesis that combining CBTp+MBI could improve coping with day-to-day life in psychosis better than CBTp alone in people attending a public community rehabilitation center.MethodFifty-six outpatients were recruited and randomly allocated either to CBTp or CBTp+MBI. Measures comprised PANSS interview and COPE Inventory. Data were analyzed using a repeated measures ANOVA and RCI calculation.ResultsThere were no statistical differences between groups at pre-treatment. Significant statistical differences were found for the interaction Treatment x Time in Mental disengagement (F = 5.65, p = .021, η² = .102), Acceptance (F = 7.69, p = .008, η² = .133), and Suppressing competing activities (F = 4.62, p = .037, η² = .085).ConclusionsMBI promotes specific coping styles in people who experience psychosis that otherwise are not improved with CBTp. Only the MBI group improved acceptance of the presence of the stressor and reduced mental disengagement from the context. The intervention is feasible and effective for public healthcare settings.     

Oxygen self-diffusion in corundum (alpha-Al2O3): A conundrum

Recent point-defect calculations for Al2O3 by Lagerlof and Grimes have been used to rationalize oxygen diffusion in undoped, MgO-doped and TiO2-doped Al2O3. The amphoteric nature of Al2O3 is emphasized by the calculations; oxygen and aluminium diffusion will be dominated by oxygen vacancies and aluminium interstitials, or oxygen interstitials or aluminium vacancies, depending on whether divalent or tetravalent impurities are present in greater abundance. The oxygen diffusion data can be rationalized in a reasonably quantitative manner by the calculated concentrations of oxygen vacancies and oxygen interstitials. Oxygen vacancies appear to be 2-2.5 times more mobile than oxygen interstitials, whereas aluminium interstitials appear to be 103 to 104 times more mobile than oxygen vacancies. However, these calculations suggest migration energies of the oxygen point defects of 4.5-5.9eV. These values are large, and it is not known whether they have any physical significance.     

Parafoveal processing in reading: Manipulating n+1 and n+2 previews simultaneously

The boundary paradigm (Rayner, 1975) with a novel preview manipulation was used to examine the extent of parafoveal processing of words to the right of fixation. Words n+1 and n+2 had either correct or incorrect previews prior to fixation (prior to crossing the boundary location). In addition, the manipulation utilized either a high or low frequency word in word n+1 location on the assumption that it would be more likely that n+2 preview effects could be obtained when word n+1 was high frequency. The primary findings were that there was no evidence for a preview benefit for word n+2 and no evidence for parafoveal-on-foveal effects when word n+1 is at least four letters long. We discuss implications for models of eye-movement control in reading.     

Effects of ball milling and annealing of an alloy in the Al-Fe-Cu system: Implications for phase equilibria

An icosahedral quasicrystalline alloy in the Al-Fe-Cu system has been mechanically milled in a high-energy ball mill (Szegvari attritor) for 1, 3, 6 and 10 h. Samples were characterized by X-ray diffraction and transmission electron microscopy. The evolution of nanosize crystallites of the disordered B2 phase (bcc; a = 0.29 nm), coexisting with either the parent icosahedral phase or an amorphous phase, occurs during milling. Isothermal heat treatment of milled powder at various temperatures (200, 500, 600, 700, 800 and 850°C) leads in all cases, except at 200°C, to the transformation from disordered B2 and amorphous phases to an ordered B2 phase with a high degree of long-range ordering. The maximum degree of superlattice ordering was found after isothermal treatment at 800^oC. The implications of these results are discussed with reference to phase equilibria existing between crystalline and quasicrystalline phases in the Al-Fe-Cu system.     

Investigations of the optical spectra and local structure for nickel(II) ions in XF2 (X = Mg,Zn) single crystals

A complete diagonalization energy matrix method (CDM) is proposed for 3d ⁸ ions in orthorhombic site (D _{2 h} ) symmetry. As an application, the optical spectra of XF₂ : Ni²⁺ (X = Mg, Zn) is well explained on the basis of both the CDM and the semi-self-consistent field d-orbital (semi-SCF d-orbital) theory. In addition, by establishing the relationship between the optical spectra and local structure, it has been possible to calculate the crystal structure parameters for XF₂:Ni²⁺ from optical measurements on Ni²⁺ ions. The theoretical results are in good agreement with experimental findings.