The flow stress contribution of the dislocation 'forest' in bcc lattices

The athermal flow stress contribution by junction reactions of a glide dislocation with a 'forest' of density rho is usually written as tau = alpha mu b rho ^1/2. The strength coefficient alpha has been computed for the bcc lattice by virtual displacement of triple nodes following the method of Puschl et al. (1982, Physica status solidi (a), 74, 211). In the isotropic approximation, the values for glide dislocations with 0, 30, 60 and 90^o character are as alpha = 0.18, 0.21, 0.19 and 0.22 respectively. A comparison with values calculated previously by Frydman is made, and good agreement is found when differences in the cut-off radii of the linear elastic solution are accounted for.     

Plastic deformation behaviour of decagonal Al70Ni15Co15 single quasicrystals

High-temperature deformation experiments have been performed on decagonal Al₇₀Ni₁₅Co₁₅ single quasicrystals at a constant strain rate of 10^-5s^-1 in the temperature range between 700 and 860°C. The samples were deformed in compression with the compression axis in different orientations, parallel to, inclined by 45° and perpendicular to the tenfold symmetry axis. Stress relaxation tests and temperature changes were carried out to determine thermodynamic activation parameters. The flow stress and the activation enthalpy were found to depend on the sample orientation whereas dependences of the activation volume and the stress exponent on the orientation were not observed. Additionally, deformation tests were performed on samples of the basic Co-rich modification of the decagonal phase at the temperature of 860°C in the same three orientations. The deformation behaviours of the two different modifications of the decagonal phase are discussed.     

No Relationship Between Joint Position Sense and Force Sense at the Shoulder

In practice, a single test is used to quantify an individual's proprioception. Previous studies have not found a correlation between joint position sense (JPS) and force sense (FS), which are submodalities of proprioception. The purpose of the present study is to determine if root mean square (RMS) error in JPS and FS are related at the shoulder, controlling for external load and elevation angle. Active shoulder angle and force reproduction protocols were performed. No correlation was found between JPS and FS (r = –.019, p = .941) nor were any individual angle and load combinations significant. The main effect for angle in JPS was significant (p < .001). Follow-up contrast demonstrated a significant (p < .001) decrease in RMS error with increased elevation. A significant load by angle interaction was found for FS (p = .014). Follow-up simple effects tests by angle demonstrated RMS error decreased with load at 50° and 70° but not at 90°. By load, RMS error only decreased for 120% between 50° and 90°. JPS and FS demonstrate different behavior with load and angle. This differing behavior is more likely responsible for the lack of correlation than angle and load differences in JPS and FS protocols.     

Strain localization in nickel single crystals cyclically deformed at 77 K

Nickel monocrystals oriented for single slip have been cyclically deformed at 77 K at plastic strain amplitude between 5 x 10^-4 and 1 x 10^-2 up to saturation of the stress amplitude. After unloading from maximum compression, the slip markings on the surface of the specimens were removed and the deformation continued for one half cycle in tension. As previously observed for room-temperature deformation, the plastic strain was found to be localized in narrow slip bands (SBs). Using atomic force microscopy at a given imposed strain amplitude, a wide spectrum of local plastic strains was found. The averaged resolved shear strain of the SBs was found to be independent of the imposed plastic strain amplitude and turned out to be a factor of three larger than the upper plateau strain limit of the cyclic stress-strain curve.     

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.     

Tilted InSb nanostructures fabricated by off-normal ion beam irradiation

ABSTRACT

Using a two-step focused ion beam irradiation process, tilted InSb nanostructures have been fabricated using a off-normal angle of irradiation. In the first step, a well-focused ion beam was used to irradiate the surface of the structure to achieve top-down sputtering. In the second step, the ion beam was used to irradiate the entire surface to promote bottom-up nanostructure growth through the migration of ion-beam-induced interstitial atoms. The formation of a nanostructure with a 46° tilt and an aspect ratio of 0.5 was achieved using ion beam irradiation at an angle of 45° in both steps of the process. The 2% concentration of point defects obtained by changing the volume of the nanostructure before and after irradiation contributed to the growth of the structure. The results showed that many point defects did not recombine, and survived to contribute toward the growth of the wall structure.     

The role of central and peripheral vision in postural control duringwalking

Three hypotheses have been proposed for the roles of central and peripheral vision in the perception and control of self-motion: (1) peripheral dominance, (2) retinal invariance, and (3) differential sensitivity to radial flow. We investigated postural responses to optic flow patterns presented at different retinal eccentricities during walking in two experiments. Oscillating displays of radial flow (0° driver direction), lamellar flow (90°), and intermediate flow (30°, 45°) patterns were presented at retinal eccentricities of 0°, 30°, 45°, 60°, or 90° to participants walking on a treadmill, while compensatory body sway was measured. In general, postural responses were directionally specific, of comparable amplitude, and strongly coupled to the display for all flow patterns at all retinal eccentricities. One intermediate flow pattern (45°) yielded a bias in sway direction that was consistent with triangulation errors in locating the focus of expansion from visible flow vectors. The results demonstrate functionally specific postural responses in both central and peripheral vision, contrary to the peripheral dominance and differential sensitivity hypotheses, but consistent with retinal invariance. This finding emphasizes the importance of optic flow structure for postural control regardless of the retinal locus of stimulation.     

Strain rate response of a Ni–Ti shape memory alloy after hydrogen charging

In this work, we investigate the susceptibility of Ni–Ti superelastic wires to the strain rates during tensile testing after hydrogen charging. Cathodic hydrogen charging is performed at a current density of 10?A/m² during 2–12?h in 0.9% NaCl solution and aged for 24?h at room temperature. Specimens underwent one cycle of loading-unloading reaching a stress value of 700 MPa. During loading, strain rates from 10^?6 to 5?×?10^?2?^?s^?1 have been achieved. After 8?h of hydrogen charging, an embrittlement has been detected in the tensile strain rate range of 10^?6 to 10^?4?s^?1. In contrast, no embrittlement has been detected for strain rates of 10^?3?s^?1 and higher. However, after 12?h of hydrogen charging and 24?h of annealing at room temperature, the embrittlement occurs in the beginning of the austenite-martensite transformation for all the studied strain rate values. These results show that for a range of critical amounts of diffused hydrogen, the embrittlement of the Ni–Ti superelastic alloy strongly depends on the strain rate during the tensile test. Moreover, it has been shown that this embrittlement occurs for low values of strain rates rather than the higher ones. This behaviour is attributed to the interaction between the diffused hydrogen and growth of the martensitic domain.     

Retrospective coping strategies during sexual identity formation and current biopsychosocial stress

Background: Lesbian, gay men, and bisexual individuals (LGBs) often experience distress related to the recognition, self-acceptance, and disclosure of their sexual orientation. Objectives and Design: Retrospectively reported coping strategies enacted during sexual identity formation among LGBs were assessed in relation to current stress indices measured using environmental (frequency of perceived daily hassles), psychological (perceived distress), and biological (allostatic load [AL] levels representing physiological dysregulations) perspectives. Methods: Forty-six healthy LGBs between the ages of 18 and 45 (M = 23.91, SE = .80) participated. Questionnaires included the Ways of Coping Checklist adapted to disclosure milestones, Daily Hassles Inventory, and Perceived Stress Scale. AL was calculated using 21 biomarkers of neuroendocrine, immune, cardiovascular, and metabolic functioning. Results: Avoidance coping during sexual identity formation was positively associated with frequency of daily hassles (β = .598, p < .001), perceived stress (β = .361, p = .015), and AL (β = .405, p = .006). By contrast, seeking social support was negatively associated with perceived stress (β = –.598, p = .048). Conclusions: Emotion-focused coping strategies during LGB sexual identity development are associated with current indices of biopsychosocial stress.     

The role of central and peripheral vision in postural control during walking

Three hypotheses have been proposed for the roles of central and peripheral vision in the perception and control of self-motion: (1) peripheral dominance, (2) retinal invariance, and (3) differential sensitivity to radial flow. We investigated postural responses to optic flow patterns presented at different retinal eccentricities during walking in two experiments. Oscillating displays of radial flow (0 degree driver direction), lamellar flow (90 degrees), and intermediate flow (30 degrees, 45 degrees) patterns were presented at retinal eccentricities of 0 degree, 30 degrees, 45 degrees, 60 degrees, or 90 degrees to participants walking on a treadmill, while compensatory body sway was measured. In general, postural responses were directionally specific, of comparable amplitude, and strongly coupled to the display for all flow patterns at all retinal eccentricities. One intermediate flow pattern (45 degrees) yielded a bias in sway direction that was consistent with triangulation errors in locating the focus of expansion from visible flow vectors. The results demonstrate functionally specific postural responses of both central and peripheral vision, contrary to the peripheral dominance and differential sensitivity hypotheses, but consistent with retinal invariance. This finding emphasizes the importance of optic flow structure for postural control regardless of the retinal locus of stimulation.     

Stress relaxation in cobalt between 15 and 300 K

Abstract

The slope of the logarithmic stress–relaxation curve for a well-annealed cobalt polycrystal of 99·999% purity has been measured as a function of the initial stress level from which relaxation at constant strain was allowed to start at a given temperature between 15 and 300 K. A pronounced undulation was observed in the plot of the relation between the inverse of the stress sensitivity of the relaxation rate and temperature, with a maximum and a minimum at about 75 and 50 K, respectively. The ‘classically unexpected’ behaviour below about 80 K seems to arise from the progressive inhibition of dynamic recovery process as T→0 K, which necessitates the use of stresses higher than that applied in the basic equations describing the mode of deformation.     

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.     

Fireman's job stress: Integrating work/non-work conflict with Job Demand-Control-Support model

IntroductionHeavy working load and uncontrollable schedule often lead firemen to face to conflict between work and non-work life.ObjectiveThis study aims to examine the mediating role of work/non-work conflict between firemen's job stress and job demand, job control, job support and family support.MethodQuestionnaire survey was used for data collection. Four hundred and twenty-two firemen returned completed questionnaires. Structure equation modelling was employed for data analysis.ResultsWork/leisure conflict (WLC) and work/family conflict (WFC) mediate partially the relationship between job demand and job control, job support and job stress. The relationship between family support and job stress is fully mediated by WLC and WFC.ConclusionWFC and WLC are integrated into Job Demand-Control-Support model model in current research to narrow the gap of job stress theory.     

Maximum isokinetic familiarization of the knee: Implication on bilateral assessment

PurposeFamiliarization is necessary for an accurate strength assessment as it reduces confounding factors such as learning and training effects. However, the number of contractions required for familiarization and whether cross-limb transfer during familiarization could affect bilateral assessment are unknown. This study aimed at identifying the number of maximum contractions required for isokinetic knee extension and flexion familiarization in both dominant (D) and non-dominant limb (ND).MethodsTwenty-eight right-limb dominant males (age: 22.64 ± 2.60 years, BMI: 23.82 ± 2.85 kg/m²) performed a total of 6 sets (each consisted of 5 continuous maximum contractions) at 60^o/s for each limb.ResultsThe number of sets required for familiarization is determined when the average peak torque achieved stabilization from the series of contractions of each limb. For knee extension, 3 sets (15 contractions) were required for familiarization, whereas 2 sets (10 contractions) for knee flexion in both limbs. Interestingly, for knee extension in ND, the number of sets required for familiarization was reduced to 2 following contralateral contractions in D, however, for knee extension in D, there was no difference in the number of sets required for familiarization following contralateral contractions in ND. While for knee flexion, no cross-limb transfer was observed. These observations suggest the presence of cross-limb transfer from D to ND during familiarization which implies the involvement of the central nervous system.ConclusionsPractically, familiarization for bilateral isokinetic strength assessment for knee extension and flexion at 60^o/s should begin with the dominant limb for 3 sets to obtain accurate and reliable measurements.     

Effect of grain orientation and local strain on the quality of polycrystalline YBa 2 Cu 3 O 7 superconductive films

The critical current densities of superconducting thin films and their dependence on the film structural characteristics has been a major research interest for more than a decade. Controlling this relationship is crucial if large-scale high-quality YBa 2 Cu 3 O 7 (YBCO) tapes are to be produced. Two major keystones of information have been established in this field. Firstly, there is a direct relationship between the critical current density and the grain-boundary angle in polycrystalline YBCO films. Grain boundaries with a mismatch angle higher than 5° usually result in reduced critical current densities. This detrimental effect of large-angle grain boundaries to the quality of YBCO films has been attributed to strain fields resulting from such grain boundaries. Secondly, the quality of the YBCO film can be enhanced by straining its lattice in specific direction. Here, we report, for the first time, direct experimental results coupling local grain orientation and local strain maps of thin YBCO films deposited on a (001) biaxially textured nickel substrate. These results were correlated to the quality of the film and showed how grain structure in the nickel substrate affects the grain structure in the YBCO films even in the presence of several buffer layers. More importantly, the data show that highquality films with high critical current densities can be produced, in spite of large-angle grain boundaries, if the film is compressed in the range of 0.5% strain normal to the a axis.     

Strain-induced submicrocrystalline grains developed in austenitic stainless steel under severe warm deformation

Strain-induced grain evolution in a 304 type austenitic stainless steel has been studied in multiple compression with the loading direction being changed in each pass. The tests were carried out to total strains above 6 at 873 K (0.5 T _m) at a strain rate of about 10^-3 s^-1. Multiple deformation promotes the rapid formation of many mutually crossing subboundaries because various slip systems operate from pass to pass. The gradual rise in misorientations across dislocation subboundaries with increasing strain finally leads to the evolution of very fine grains with large-angle boundaries. It is concluded that a new grained structure can result from a kind of continuous reaction during deformation, namely continuous dynamic recrystallization. Such deformation-induced grains are characterized by relatively low densities of dislocations, and considerable lattice curvatures developed in their interiors. The latter observations suggest that high elastic distortions are developed in the grain interiors and so such strain-induced grain structures are in a non-equilibrium state.     

Anisotropic perception of visual angle: Implications for the horizontal-vertical illusion,overconstancy of size,and the moon illusion

Three experiments investigated anisotropic perception of visual angle outdoors. In Experiment 1, scales for vertical and horizontal visual angles ranging from 20° to 80° were constructed with the method of angle production (in which the subject reproduced a visual angle with a protractor) and the method of distance production (in which the subject produced a visual angle by adjusting viewing distance). In Experiment 2, scales for vertical and horizontal visual angles of 5°–30° were constructed with the method of angle production and were compared with scales for orientation in the frontal plane. In Experiment 3, vertical and horizontal visual angles of 3°-80° were judged with the method of verbal estimation. The main results of the experiments were as follows: (1) The obtained angles for visual angle are described by a quadratic equation, θ′=a+bθ+cθ² (where θ is the visual angle; θ′, the obtained angle;a, b, andc, constants). (2) The linear coefficientb is larger than unity and is steeper for vertical direction than for horizontal direction. (3) The quadratic coefficientc is generally smaller than zero and is negatively larger for vertical direction than for horizontal direction. And (4) the obtained angle for visual angle is larger than that for orientation. From these results, it was possible to predict the horizontal-vertical illusion, over-constancy of size, and the moon illusion.     

Scaling relationships in indentation of power-law creep solids using self-similar indenters

We use dimensional analysis to derive scaling relationships for self-similar indenters indenting solids that exhibit power-law creep. We identify the parameter that represents the indentation strain rate. The scaling relationships are applied to several types of indentation creep experiment with constant displacement rate, constant loading rate or constant ratio of loading rate over load. The predictions compare favourably with experimental observations reported in the literature. Finally, a connection is found between creep and 'indentation-size effect' (i.e. changing hardness with indentation depth or load).     

A novel method for constructing the mean field of grain-orientation-dependent residual stress

The heterogeneity of grain-orientation-dependent residual stress (ODRS) in polycrystalline materials has received a great deal of attention in the past few years. This letter describes a novel method, called the spherical harmonics approach (SHA), for analysing ODRS. The stress orientation distribution function (SODF) is defined to describe quantitatively the mean field of the residual stress as a function of grain orientation in the Euler space. This stress field can be expanded in terms of generalized spherical harmonics, and its series coefficients can be determined directly from lattice strain maps (strain pole figures). While solving the deconvolution problem of this stress field, the stress or strain equilibrium between neighbouring grains is considered simultaneously by implementing a self-consistent model in the iterative algorithm. The application of the SHA is illustrated by the construction of the SODF for a cold-rolled and annealed austenite stainless steel, using strain pole figures obtained by neutron diffraction.     

Effect of Force Sense to Active Joint Position Sense and Relationships between Active Joint Position Sense,Force Sense,Jumping and Muscle Strength

Abstract

We aimed to investigate the effect of external load on the joint position sense (JPS) accuracy and its relation to the target jump height. The present study also aimed to explore the relationship between force sense (FS) and maximum voluntary isometric contraction (MVIC). Participants’ MVIC levels were determined during the 45-degree knee extension task. Then, participants were asked to execute a knee JPS task with external load (EL-JPS) and with no-load (EL-JPS). To assess jumping accuracy participants were instructed to jump with their 50% of maximum jump height. Results indicated that EL-JPS error values were lower than NL-JPS. EL-JPS was correlated to jumping errors. However, the relationship between NL-JPS and jumping errors was not significant. A significant correlation was found between MVIC and FS errors.