Depth distribution of oxygen vacancies in 1 MeV Li + -irradiated KTiOPO 4

Electron-energy-loss spectra have been recorded from cross-sectional transmission electron microscopy samples of Li + -irradiated KTiOPO 4 single crystals. By evaluating the intensity in the pre-edge shoulder of the OK ionization edge, the depth distribution of O vacancies in radiation-damaged KTiOPO 4 was monitored. Li + irradiation at 295K and Li + irradiation at 100K generate very similar defect profiles except for an additional superficial maximum in the room-temperature-irradiated sample. Vacancy distributions in the O sublattice can be monitored on the nanometre scale by the method introduced. The methodology is potentially applicable to a wide range of materials, when pertinent defect-sensitive features in electron-energy-loss spectra are evaluated, and its sensitivity is expected to become further improved with the availability of monochromated electron sources in transmission electron microscopes.     

Anisotropic BaTiO3 thin films grown on MgO-buffered R-plane sapphire

Epitaxial BaTiO₃ thin films grown on MgO-buffered R-plane-cut Al₂O₃ substrates show a non-uniform distribution of planar defects. Transmission electron microscopy allows the determination of the distributions of planar defects with respect to the Al₂O₃ substrate. The BaTiO₃ film, the MgO buffer and the Al₂O₃ substrate have an orientation relationship of [100]_BaTiO3//[100]_MgO//[1120]_Al2O3, (010)_BaTiO3//(010)_MgO//(1104)_Al2O3 and (001)_BaTiO3//(001)_MgO// ≈ (1102)_Al2O3 (about 5°; deviation). Under the above relationship, most of the {111} stacking faults occur on (111) and (111) planes, that is two of four sets of {111}_BaTiO3, whereas cracks in the BaTiO₃ film (and MgO buffer) are situated on the (100) planes. The anisotropic distribution of planar defects is regarded as a consequence of an anisotropic stress in the films generated during their fabrication.     

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.     

Evaluation of the threshold stress for creep deformation in a 3 mol% Y 2 O 3 -stabilized tetragonal ZrO 2 polycrystal

The origin of the increase in the stress exponent from n , 2.0 to with decreasing stress in 3 mol% Y 2 O 3 -stabilized tetragonal ZrO 2 has been examined. The present data show that the increase in the n value arises from the existence of a threshold stress that depends on the grain size and temperature. Careful examination of earlier creep data confirms that evaluation of the threshold stress is sensitive to the accuracy of the creep data and the value of n chosen for the compensation of the data. Inspection of the present results and some recent observations of the deformed microstructure suggests that the threshold stress is associated with intragranular dislocation motion.     

Associations between heart rate,perceived heart rate,and anxiety during acute psychological stress

ABSTRACT

Background: Acute psychological stress elicits increases in heart rate (HR) and anxiety. Theories propose associations between HR, perceived HR, and anxiety during stress. However, anxiety is often measured as a unidimensional construct which limits a comprehensive understanding of these relationships.

Objectives: This research explored whether HR reactivity or perceived HR change was more closely associated with cognitive and somatic anxiety during acute psychological stress.

Design: Two laboratory-based studies were conducted.

Methods: In a single laboratory session, healthy male (N?=?71; study 1) and female (N?=?70; study 2) university students completed three laboratory psychological stress tasks (counterbalanced), each with a preceding baseline. Heart rate, perceived HR change, and cognitive and somatic anxiety intensity and interpretation of anxiety symptoms were assessed immediately following each task. Data were aggregated across tasks.

Results: Actual HR change was unrelated to anxiety intensity, but was associated with more debilitative interpretations of anxiety (study 2). Perceptions of HR change were consistently associated with greater intensity of cognitive (study 1) and somatic (study 1 and 2) anxiety.

Conclusions: Perceived HR rather than actual HR is more closely associated with anxiety intensity during psychological stress. The findings have implications for stress management and the clinical treatment of anxiety symptoms.     

Crystal structure of the ξ phase in the Al-Si-Mg-Fe system studied by electron channelling

We have re-examined the structure of the ~ phase in a quaternary alloy previously found to have the composition Al 8 Si 6 Mg 3 Fe. Electron probe microanalysis shows that the composition of the phase is actually Al 9 Si 5 Mg 3 Fe and, based on this new chemical formula, we propose a revision of the atomic positions which does not require any substitutional disorder within the hexagonal crystal unit cell with space group P ¥ 62 m (no. 189). These Wyckoff positions are as follows: for Al, 6i and 3f; for Si, 4h and 1b; for Mg, 3g; and for Fe, 1a. Results from electron channelling experiments are consistent with these new positions while ruling out those previously reported in the literature.     

The orientation and temperature dependences of dislocation velocity in Ni 3 Al single crystals

The average velocities of screw dislocations in Ni 3 Al single crystals have been directly measured as a function of resolved shear stress (RSS) and orientation in the temperature domain of the flow stress anomaly using the etch-pit technique. The velocity was found to be extremely sensitive to the RSS in all cases. In contrast with ordinary metals, the screw dislocation velocities in Ni 3 Al show anomalous behaviour; under a constant RSS, the velocities decrease dramatically with increasing temperature. Furthermore, the velocities and the tension-compression asymmetry of the velocities depend on the orientation of applied stress.     

Stress anomaly in Al-rich Ti-Al single crystals deformed by the motion of 1/2«110] ordinary dislocations

The microstructure and plastic deformation behaviour of Al-rich Ti-Al single crystals containing 54.7 and 58.0 at.% Al have been examined, focusing on the effect of chemical ordering of a Al5Ti3 superstructure on anomalous strengthening. Fine precipitates with the Al5Ti3 superstructure were developed in the L10 matrix of the Ti-58.0 at.% Al alloy. The size and volume fraction of the precipitates varied depending on temperature. An anomalous increase in the yield stress of the two alloys appeared at around 800oC. This strengthening mechanism is discussed on the basis of the difference in antiphase-boundary energies on (111), (110) and (001) planes in the Al5Ti3 phase.     

Epitaxial decagonal thin films on crystalline substrates

Al-Cu-Fe-Cr quasicrystalline thin films were grown on atomically flat Al 2 O 3 sapphire (0001) substrates by single-target magnetron sputtering followed by annealing. A decagonal phase with the tenfold axis A 10 parallel to the substrate surface normal was observed. The epitaxial decagonal film had two different unique orientations: a twofold P axis A 2P and a twofold D axis A 2D parallel to of the substrate. These two configurations were explained using a coincidence reciprocal lattice planes model for the interface energy. We show that this classic approach for crystal-crystal epitaxy can be applied to quasicrystal-crystal systems.     

Formation of self-assembled Cu-γ-Al 2 O 3 nanocomposite

We report here the formation of a novel 'self-assembled' three-dimensional nanocomposite consisting of uniformly sized, evenly spaced spherical Cu nanoparticles embedded within a polycrystalline n -Al 2 O 3 matrix. This was discovered serendipitously during the examination of an ion-beam-milled ZrO 2 specimen in a transmission electron microscope. This nanocomposite was deposited as a coating during ion-beam milling by the co-sputtering of Cu and Al from the ion-mill hardware in the presence of O. The mechanism by which this highly organized nanocomposite forms is discussed, together with broader implications of these types of metal-ceramic nanocomposite and the possibility of using sputter deposition as a generic method for making them.     

Keep your eyes open: dispositional vigilance moderates the relationship between operational police stress and stress symptoms

Background: Vigilant coping is characterized by a deep processing of threat-related information. In many cases, vigilant coping increases stress symptoms, whereas avoidant coping decreases negative affect. However, vigilance may be beneficial when stress-eliciting situations involve a risk of injury or escalation as is usually the case in police operations. Design: We investigated the roles of vigilance and cognitive avoidance in police operations in a cross-sectional survey. Methods: The participants were 137 students (104?men, M_age?=?28.54, SD?=?8.04) from the Federal University of Applied Administrative Sciences; 76 of them were already police officers (work experience: M?=?12.59?years), and 61 were police officer candidates who had completed a 3- to 6-month police internship. Participants completed a paper-and-pencil survey and reported their operational stress, dispositional vigilance and cognitive avoidance in police operations, and stress symptoms. Results: We found that vigilance was negatively associated with stress symptoms and moderated the relationship between operational stress and stress symptoms. Cognitive avoidance, on the other hand, just missed the level of statistical significance in our test of whether it was positively associated with stress symptoms. Conclusions: Our findings demonstrate that vigilance may protect against the negative consequences of stress in police operations.     

Associations of perceived stress and state anger with symptom burden and functional status in patients with heart failure

Abstract

Background: Psychosocial stress and anger trigger cardiovascular events, but their relationship to heart failure (HF) exacerbations is unclear. We investigated perceived stress and anger associations with HF functional status and symptoms.

Methods and Results: In a prospective cohort study (BETRHEART), 144 patients with HF (77% male; 57.5?±?11.5 years) were evaluated for perceived stress (Perceived Stress Scale; PSS) and state anger (STAXI) at baseline and every 2 weeks for 3 months. Objective functional status (6-min walk test; 6MWT) and health status (Kansas City Cardiomyopathy Questionnaire; KCCQ) were also measured biweekly. Linear mixed model analyses indicated that average PSS and greater than usual increases in PSS were associated with worsened KCCQ scores. Greater than usual increases in PSS were associated with worsened 6MWT. Average anger levels were associated with worsened KCCQ, and increases in anger were associated with worsened 6MWT. Adjusting for PSS, anger associations were no longer statistically significant. Adjusting for anger, PSS associations with KCCQ and 6MWT remained significant.

Conclusion: In patients with HF, both perceived stress and anger are associated with poorer functional and health status, but perceived stress is a stronger predictor. Negative effects of anger on HF functional status and health status may partly operate through psychological stress.     

site determination of dilute Cu in beta-phase NiAl by 63Cu nuclear magnetic resonance and X-ray emission channelling patterns

A sharply bimodal lattice site distribution of dilute Cu in both Ni-deficient and Al-deficient beta-phase Ni-Al alloys has been observed in the 63Cu nuclear magnetic resonance (NMR) spectra. These NMR results are correlated with results derived from incoherent channelling patterns (ICPs) formed by variations in characteristic X-ray emission as a function of incident fast electron orientation. Statistical analysis of ICP data, generated near a 210 zone axis, indicates that Cu occupies substitutional sites; Cu is exclusively on the Al sublattice sites in the Al-deficient alloy, whilst the partition ratio of Ni : Al sublattice sites for Cu in the Ni-deficient alloy is about 80 : 20. Comparison of ICP contrast from Cu X-ray emission with ICPs from the host lattice enables the two peaks in the 63Cu NMR spectrum to be individually identified as originating from Cu on Ni sublattice sites, and from Cu on Al sublattice sites. The respective NMR line intensities from the Ni-deficient alloy yields a Ni : Al sublattice site occupancy ratio which is in good agreement with the partitioning ratios derived from channelling patterns     

Short-range order in Al-rich 𝛄-TiAl alloys studied by high-resolution transmission electron microscopy with image processing

The atomic arrangements of short-range order (SRO) in two Al-rich γ-TiAl alloys with 62.5 and 60.0at.%Al respectively have been investigated by high-resolution transmission electron microscopy with image processing. For both alloys, SRO structures are formed in Ti-rich (002) layers of the L1₀ ordered γ-TiAl matrix, in the course of the phase transformation from the Al₅ Ti₃ long-period superstructure phase at lower temperatures to the h-Al₂ Ti phase at higher temperatures. The SRO structures are composed of three types of ordered cluster: Ti₄ Al type (square shaped), Ti₃ Al type (fat rhombus shaped) and Ti₂ Al type (lean rhombus shaped). The ordered clusters form local microdomains of the Al₅ Ti₃ and Al₃ Ti₂ superstructures in addition to the Al₅ Ti₃ and h-Al₂ Ti superstructures, by different methods of tiling the ordered clusters. Such ordered clusters or microdomains tend to be in contact with each other through common {310) boundaries. This results in peculiar diffuse streaks in diffraction connecting intensity maxima arising from the long-period superstructures.     

Acute stress disorder among civilians during a war and post-traumatic growth six years later: the impact of personal and social resources

Background and Objectives: Various studies suggest a link between stress response to a traumatic event and post-traumatic growth (PTG), but little is known about their long-term relationship. In this study, the relationship between acute stress disorder (ASD) among civilians during a war on the home front and PTG six years later was examined for the first time. Based on the conservation of resources (COR) theory, the role of personal and social resource loss and gain as moderating factors was investigated. Design and Methods: At Time 1 of the research (the Second Lebanon War in 2006), a structured questionnaire was administered to 370 civilians living within rocket range. At Time 2, 6 years later, 301 participants from Time 1 were again examined. The data analysis refers to the 301 respondents who participated at Time 2. Results: The findings indicate a significant relationship between ASD and PTG. Examination of the interaction revealed that resource gain (but not resource loss) moderates (strengthens) the relationship between the two. Conclusions: These findings are not consistent with the COR view that resource loss has a greater effect on stress responses than resource gain.     

Identifying the character of intrinsic stacking faults in the A15 compound Nb3Al

The character of intrinsic stacking faults on {001} in the A15 intermetallic compound Nb₃Al has been investigated using energy-dispersive X-ray spectroscopy in a field-emission-gun transmission electron microscope. Line scans were obtained across edge-on faults with an electron beam of approximate diameter 0.5 nm and it was found that the Al concentration is enhanced at the fault. Taken in conjunction with crystallographic data obtained previously, this implies that a {004} layer composed of Nb atoms only is removed to form these intrinsic stacking faults in Nb₃Al. The configuration of these faults implies that they may form by Nb vacancy coalescence and could act as embryonic nuclei for the precipitation of the D8_bcompound Nb₂Al.     

Hair cortisol in relation to acute and post-traumatic stress symptoms in children and adolescents

Background: We report on the preliminary results of two independent studies that (1) compare the hair cortisol concentrations (HCC) of healthy controls with patients displaying post-traumatic stress symptoms (PTSS, study 1+2), (2) investigate whether pre-trauma HCC are predictive for the development of acute stress symptoms (ASS) and PTSS (study 1) and (3) determine whether HCC correlate with PTSS in a clinical sample of children (study 2).

Methods: In study 1, the clinical symptoms of 35 minors were examined one (T1) and seven weeks (T2) after surgery following an accident. Hair samples were taken after the accident that reflect cortisol secretion over the past three months before the accident (healthy controls). In study 2, HCC and PTSS symptoms were cross-sectionally assessed in 22 minors who had experienced a psychological trauma.

Results: The HCC of patients with PTSS were lower than the HCC of healthy controls (study 1+2). Secondary analyses showed that HCC were significantly lower in male PTSS patients than in male healthy controls, whereas the HCC in females were comparably low in both groups. Pre-trauma HCC did not predict the total ASS and PTSS scores (study 1) and HCC were not directly related to the total PTSS scores (study 2).     

A randomized controlled pilot trial of acceptance and commitment training (ACT) for preventing stress-related ill health among future nurses

Background: Levels of stress and burnout increase during nursing education. This development has consequences for nursing students' health, learning, competence, and interest in quality issues in health care. Design: In a randomized controlled pilot trial with a sample of 113 nursing students the effect of an intervention using techniques from acceptance and commitment training (ACT) to prevent the development of stress and burnout was evaluated. Method: The 6 × 2-hour program was compared to standard treatment (reflection seminars) post-intervention and at a three-month follow-up using longitudinal analysis of mean response profiles. Mechanisms of change were investigated using a baseline-post intervention two-mediator model. Results: The intervention resulted in increased mindful awareness and decreased experiential avoidance, as well as decreased perceived stress and burnout. Levels of mindful awareness and perceived stress were sustained at follow-up. The proposed mechanisms of change were partly supported by the data. Conclusion: This study shows that techniques from ACT might have the potential to contribute to preventing the development of stress and burnout during nursing education. However, additional studies are needed to validate these results.     

Selective attention as a protagonist in contemporary workplace stress: implications for the interruption age

Background and Objectives: The ubiquity of instant messages and email notifications in contemporary work environments has opened a Pandora's Box. This box is filled with countless interruptions coming from laptops, smartphones, and other devices, all of which constantly call for employees’ attention. In this interruption era, workplace stress is a pervasive problem. To examine this problem, the present study hypothesizes that the three-way interaction among the frequency with which interrupting stimuli appear, their salience, and employees’ deficits in inhibiting attentional responses to them impacts mental workload perceptions, ultimately leading to stress. The study, further, probes a related form of self-efficacy as a potential suppressor of interruption-based stress. Design: The study used a 2 (low vs. high frequency) × 2 (low vs. high salience) mixed model design. Methods: The 128 subjects completed a test of their inhibitory deficits and rated their mental workload perceptions and experiences of stress following a computer-based task. Results: Inhibitory deficits and increased interruption salience can alter the perception of mental workload in contemporary work environments for the worse, but interruption self-efficacy can help offset any resulting interruption-based stress. Conclusions: This study extends the literatures on work interruptions as well as on stress and coping in the workplace.