Deformed substructures in fine-grained tetragonal zirconia

Transmission electron microscopy (TEM) has been employed to examine the deformed microstructures of a high-purity tetragonal zirconia polycrystal containing 3mol% yttria. The TEM observations reveal that piled-up and tangled dislocations are developed within grains at a high stress, but such substructures do not appear at a lower stress, except for a small number of isolated dislocations. The stress-dependent deformed microstructures suggest that the dislocation substructures observed at a high stress are not due to any experimental artefacts. Applying a model proposed by Eshelby et al. to the observed pile-up dislocations, it can be estimated that a stress concentration of the order of 14-25 is generated around multiple-grain junctions during deformation.     

Creep behaviour of ice single crystals loaded in torsion explained by dislocation cross-slip

Torsion creep experiments are carried out in order to understand the physics of ice plasticity. A dislocation spreading mechanism based on double cross-slip of basal dislocations is proposed to explain the strong plastic anisotropy and the power law relationship between stress and strain rates. The scenario is tested using three-dimensional dislocation dynamics simulations. Numerical investigations give a stress exponent n?=?2.3 in agreement with experimental measurements. This dislocation spreading mechanism sheds a new light on the interpretation of former experimental observations.     

Interactions between interfacial dislocations and γ/γ′ interface during high temperature – low stress creep in nickel-based single crystal superalloy

ABSTRACT

The interaction between interfacial dislocations and γ/γ′ interface is critical to the high temperature creep properties of single crystal superalloys. However, only a few studies have paid attention to the detailed structure such as local interfacial morphologies and the elemental distribution around interfacial dislocations. In this paper, the interfacial protrusions and related dislocations in a single crystal superalloy after creep at high temperature – low stress have been investigated in detail. It is found that the morphology and size of the interfacial protrusions remain almost the same during the early and middle stages of high temperature creep, which indicates a local equilibrium at the interfacial protrusions. Steps at different height are formed at the γ/γ′ interface at the initial stage of high temperature creep since dislocations could move along the γ/γ′ interface, which indicates that dislocation motion at different creep stage may affect the morphology of γ/γ′ interface.     

Interaction and passing stress of two threading dislocations of opposite sign in a confined channel

The binding and unbinding of two threading dislocations in a channel of width d is considered in the context of the persistent slip band (PSB) problem. It is shown that previous analytical estimates of the overall passing stress between two screw-like threading arms have only qualitative validity. In particular, earlier treatments do not recognize the importance of bowing corrections in all limits, and neglect the effects of the opposing dislocation's misfit arms on the passing stress. As an alternative, accurate numerical escape functions are presented for the case of d?=?1?µm, in a form suitable for approximate scaling to other values of d. Although the numerical prediction for the overall passing stress is in good agreement with experimental values of the flow stress observed in the presence of PSBs, we argue that this in fact represents a disagreement, since it is well known that the flow stress in the soft-channel parts of the inhomogeneous PSB structure is reduced by long-range internal back stresses to values significantly below the average macroscopic flow stress of the PSB structure. We suggest that a statistical treatment including the effects of annihilation and of dislocations interacting over a range of separations can account for the discrepancy.     

Transition from diffusive to ballistic capture related to hydrogen incorporation in amorphous silicon

Three intersection mechanisms with the gliding planes (111)_TB, (001)_TB and (115)_TB respectively have been observed by high-resolution electron microscopy in the type-I twin intersection of gamma-TiAl. It was found that the intersection mechanism that occurred was related to the thickness of the incident twin. The accommodation mechanism on the (111)_TB atomic plane is preferred when the incident twin becomes very thin. The dislocation dissociations of the (111)_TB plane accommodation are the most energetically unfavourable of the dissociations of the three intersection mechanisms; however, the resultant dislocations on the (111)_TB planes are the easiest to propagate away from the intersection area. Accordingly, (111)_TB atomic plane accommodation is considered to be the only mechanism allowing shear transmission under the small local stress of the pile-up of the incident twinning partials.     

HRTEM observation of interfacial dislocations at faceted Al–Pb interfaces

Al–Pb ribbons containing 1?at.%?Pb have been produced by melt-spinning and subsequently investigated by high-resolution transmission electron microscopy. It is shown that the lattice mismatch of about 22% between the nanometre-sized Pb inclusions and the surrounding Al matrix is accommodated by a periodic array of misfit dislocations at the Al–Pb interface. The closing failures of Burgers circuits drawn around misfit dislocations on {111} and {100} facets identify the corresponding Burgers vectors as (a ₀/4)? 211 ? and (a ₀/2)? 110?, respectively. The Burgers vector of (a ₀/4)? 211? corresponds to the projected edge part of a 60° (a ₀/2)? 110? dislocation. The Pb inclusions themselves appear to be free of defects.     

Strengthening parent well‐being at the work—family interface: A German trial on workplace Triple P

This study examines the efficacy of a parenting training (Workplace Triple P (WPTP)) especially designed for the needs of employed parents. The program aims to reduce stress at the work–parenting interface by targeting family risk and protective factors and assisting parents to manage competing work and family demands. Ninety‐seven part‐ and full‐time working parents (74 mothers and 23 fathers; intervention group: n = 42 parents; waitlist‐control group n = 55 parents) from multiple organizations and multiple occupations with children between 2 and 10 years were randomly assigned to an intervention and a waitlist‐control condition. After the training, parents from the intervention condition, compared to those from the waitlist‐control condition, reported a significant reduction in individual and work‐related stress. Additionally, they reported a significant reduction in dysfunctional parenting and significant higher levels of parental and occupational self‐efficacy. Within the intervention condition all effects were maintained at the 3‐ and 6‐month follow‐up examinations. The findings support the notion that WPTP promotes parental well‐being and reduces stress at the work–parenting interface. Given that strengthening parenting skills has the potential to strengthen work, strategies to implement WPTP in organizational resources and community‐based services are discussed. Copyright © 2010 John Wiley & Sons, Ltd.     

Experimental evidence of relaxation arising from the motion of geometrical kinks on screw dislocations in iron

Abstract

Internal friction measurements with a superimposed bias stress have provided evidence for geometrical kink migration on screw dislocations in iron. This intrinsic process causes a relaxation phenomenon in internal friction which has been identified with the occurrence of a subpeak (below 20 K) of the α-peak. The effect of different bias stress has allowed us to evaluate the kink migration energy, E ^m _k ? 0·001eV.     

Dipole of misfit dislocations in axially symmetric structures

The nucleation of a pair of misfit dislocations of Burgers vectors b 1 and b 2 with b 1 + b 2 = 0 has been studied for the case of an axially symmetric two-phase structure. Considering a cylindrical inclusion epitaxially stressed in a unbounded matrix, the variation in the total energy due to the formation of the dipole has first been determined as a function of the radius of the inclusion and the epitaxial stress. The conditions for nucleation of the dipole on the interface have then been investigated as a function of the ratio of the shear modulus and of the misfit stress.     

First-principles investigation of bowing parameter in zinc-blende ScxGa1−xN

Helium generated in materials by the nuclear reaction (n,?α) is generally considered to be harmful. It is well-known that helium prompts not only the nucleation of interstitial-type dislocation loops, but also the nucleation of voids in metals and alloys irradiated with high-energy particles, which degrades their mechanical properties. In this study, however, we find that helium trapped by dislocations in Ni increases both the ultimate tensile strength and total elongation.     

The work–family interface among school psychologists and related school personnel: a test of role conflict and expansionist theories

The purpose was to test of the utility of role conflict and expansionist theories in explaining the work–family interface using psychometrically sound instruments. Participants (n = 74) responded to measures of work–family conflict, work‐related stress, and role quality. In support of the expansionist theory, results indicated that the quality of the life roles was a better predictor of both work–family conflict and work‐related stress than was the number of life roles. For both, results indicated that as quality of the work role increased, work–family conflict and work‐related stress decreased. The implications for the research on the work–family life interface and attracting and retaining the most qualified school psychologists are discussed.     

Relationship between the fatigue cracking probability and the grain-boundary category

In this paper, the probability of fatigue cracking along different kinds of grain boundary (GB) and persistent slip bands (PSBs) is considered in the light of data obtained by cyclic deformation of copper bicrystals and columnar crystals. It is found that, in copper bicrystals, fatigue cracks always nucleate and propagate along large-angle GBs, irrespective of whether the GB is perpendicular, parallel or inclined to the stress axis. On the contrary, for columnar copper crystals containing small-angle GBs, PSB-matrix interfaces become the preferential sites for initiation of fatigue crack; fatigue cracking along the small-angle GBs was never observed. For a special [1-34]/[182^-7] copper bicrystal with a Sigma = 19b GB and a common primary slip plane, GB cracking also results in fatigue failure. Based on the results above, the interactions of dislocations carried by PSBs with GBs, including 'pile-up of dislocations', 'passing through of dislocations' and 'partial passing-through dislocations', are discussed. It is suggested that the probability of fatigue cracking in fatigued copper crystals increases in the order of small-angle GBs, PSBs and large-angle GBs.     

Stress Overload: A New Approach to the Assessment of Stress

The link between stress and health has not received strong empirical support, possibly due to problems in the stress measures used. Here, the first wholly empirical development of a new “Stress Overload Scale” is described. A pool of 150 items was formed to reflect “overload”, a common denominator in stress theories. Then, the results of five sequenced studies, conducted in heterogeneous community samples, were used to pare the item pool. Exploratory (n = 431) and confirmatory (n = 433) analyses revealed two factors (Event Load and Personal Vulnerability) corresponding to theoretical constructs; only the best factor markers were submitted to further construct validity (n = 310) and reliability tests (n = 342). The 24 strongest items were selected for the SOS, which demonstrated criterion validity in predicting who (n = 285) would become sick following a common stressor. The SOS is (1) psychometrically strong, especially in its validity relative to popular measures; (2) appropriate to community research, due to its brevity and fit to a broad demographic spectrum; (3) unique in its ability to cross‐section individuals into risk categories. It should prove useful to community psychologists in determining etiology, diagnosing risk for pathology, and evaluating the efficacy of interventions.     

Determination of Peierls stress from acoustic harmonic generation

The interaction of acoustic waves with dislocations leads to aperiodic oscillations in the magnitude of the acoustic nonlinearity parameter β as a function of the acoustic drive amplitude σ _ampl. The magnitude and spacing of the oscillations depend on the value of the Peierls stress. A least-square curve fit of the β(σ _ampl) equation to experimental data taken of 99.999% pure aluminum monocrystals oriented for wave propagation along the [1?0?0] crystal axis yields the value 6.2?×?10⁴?Pa for the Peierls stress. The value is consistent with the smallest values reported in the literature for aluminum where for both theoretical and experimental studies the reported values range over three orders of magnitude.     

First principles determination of the Peierls stress of the shuffle screw dislocation in silicon

The Peierls stress of the a/2?110? screw dislocation belonging to the shuffle set is calculated for silicon using density functional theory. We have checked the effect of boundary conditions by using two models, the supercell method where one considers a periodic array of dislocations, and the cluster method where a single dislocation is embedded in a small cluster. The Peierls stress is underestimated with the supercell and overestimated with the cluster. These contributions have been calculated and the Peierls stress is determined in the range between 2.4?×?10^?2 and 2.8?×?10^?2?eV?Å^?3. When moving, the dislocation follows the {111} plane going through a low energy metastable configuration and never follows the 100 plane, which includes a higher energy metastable core configuration.     

Cognitive appraisal,vulnerability and coping: An integrative analysis of appraisal and coping mechanisms

Research on stress has generally concluded that stress occurs within the person as a result of their cognitive appraisal of experience. However although a number of cognitive theories of emotion exist, an integrative analysis of cognitive appraisal and vulnerability to stress has not been produced. This report contains two studies. Study 1 draws together the major variables identified in the literature in an analysis of their power to differentiate between a clinical sample (n = 48), a self-help group (n = 54), and a control sample (n = 509). The analysis shows that achievement motivation, attributional style, problem-solving style, emotional reactivity; hopelessness, perceived control and perceived social support are significant discriminators. In a second study the relationship between these variables and aspects of life stress, work stress, life satisfaction, depression, anxiety, and positive affect were investigated. Again the data support an explanatory role for these variables. The suggestion is that these variables can be utilized in an integrative model of cognitive appraisal in the stress process to guide intervention.     

Mobility of c dislocations in Ti3, Al

Abstract

The rôle of dislocations with Burgers vectors, b, given by b = [0001] during deformation of samples of the intermetallic compound Ti₃Al has been assessed. At room temperature, the experimental evidence is consistent with these dislocations being sessile, their density and morphology being similar to that in undeformed samples. In samples deformed at 650°C and above, it is concluded that motion of these dislocations is effected by dislocation climb. The line directions of the various segments of dislocations with b= [0001] are shown to be perpendicular to planes that contain sheets of Ti atoms, with an expected tendency to exhibit a high Peierls stress.     

Effects of mindfulness-based stress reduction on prenatal stress,anxiety and depression

Low well-being is common among Chinese pregnant women but few effective interventions currently exist to improve prenatal stress and negative emotions. Mindfulness-based stress reduction (MBSR) has been proved to be effective in reducing stress and rarely studies were focused on Chinese pregnant women. The aim of the current paper is to investigate the effects of 8-week MBSR on prenatal stress, anxiety and depression among Chinese pregnant women. A sample of 66 pregnant women randomly allocated into either the MBSR group (n=34) or the control group (n=32). Participants in the MBSR group received a group 8-week, 90-min each time intervention. The results found a significant interaction between time and condition for prenatal stress (F=45.51, p<0.001, η ²=0.427), anxiety (F=19.30, p<0.001, η ²=0.240), while depression showed no time-by-group interaction (F=0.29, p=0.589, η ²=0.005). As for the sub-scale of state anxiety, while there was only no time effect (F=3.68, p=0.060, η ²=0.057). The findings of this study preliminary indicated effects of the MBSR intervention on self-reported prenatal stress and anxiety in comparison to a treatment-as-usual control. Effect on depression was not observed may due to the low level of depression of participants. This study provides preliminary evidence that MBSR is suitable for Chinese pregnant women and be effective in decreasing prenatal stress, anxiety.     

Maximal Subalgebras of MVn-algebras. A Proof of a Conjecture of A. Monteiro

For each integer n ≥ 2, MV_n denotes the variety of MV-algebras generated by the MV-chain with n elements. Algebras in MV_n are represented as continuous functions from a Boolean space into a n-element chain equipped with the discrete topology. Using these representations, maximal subalgebras of algebras in MV_n are characterized, and it is shown that proper subalgebras are intersection of maximal subalgebras. When A ∈ MV₃, the mentioned characterization of maximal subalgebras of A can be given in terms of prime filters of the underlying lattice of A, in the form that was conjectured by A. Monteiro. Mathematics Subject Classification (2000): 06D30, 06D35, 03G20, 03B50, 08A30. Presented by Daniele Mundici     

Investigation of the factorial structure and psychometric properties of the Persian version of the Toronto Alexithymia Scale-20 in patients with psychiatric disorders

The aims of this study were to assess the factor structure, validity, and reliability of the Persian translation of the Toronto Alexithymia Scale-20 (TAS-20) and to examine different models of the TAS-20 in Iranian patients with various psychiatric disorders. Participants were 839 patients with psychiatric disorders, including obsessive-compulsive disorder (OCD) (n = 80), schizophrenia (n = 82), bipolar disorder (BD) (n = 100), alcohol dependence (n = 81), major depressive disorder (MDD) (n = 95), psychosomatic disorders (n = 92), anxiety disorders (n = 85), post-traumatic stress disorder (PTSD) (n = 90), attention deficit hyperactivity disorder (ADHD) (n = 55), and suicide attempts (n = 79). Results indicated that the three-factor TAS-16 fit the data well, after removing four items from the externally-oriented thinking (EOT) subscale. In addition, the total score and subscales had strong internal consistency and concurrent validity. An alternative three-factor model and a four-factor model, which both allow the reverse-coded EOT items to load on a separate factor, also had an acceptable fit. The results suggest that after deleting four items from the EOT subscale, the 16-item TAS is a reliable scale among Iranian psychiatric patients. Moreover, the alternative three-factor and four-factor structures may be appropriate to apply among Iranian patients.