The deformation of soap film junctions by applied forces

The equilibrium configuration of soap films in a tetrahedral frame is well known, and a study is reported here of the displacement of the tetrahedral vertex formed at the junction of the Plateau borders between the films. Applying a force to this junction causes an increase in soap film area, and hence surface energy, which is modelled both theoretically and numerically. In the present work, this force is conceived as being due to the displacement of a small particle at the centre of the vertex and the energy dependence of the configuration on both the size of the particle and the magnitude of the displacement is calculated. The results underline the importance of the curvature of the films in any detailed analysis of the suspension of particles in a foam, as, for example, in the industrial process of foam flotation. The results are relevant also to problems of foam drainage and stability.     

Shared identity content between leader and follower influences intentional mobilization and challenge and threat states

ObjectivesResearchers have examined how leaders' representation of shared identity content allows them to mobilize group members towards success in competitive tasks. However, research is yet to determine the psychological and physiological implications of shared identity content with a leader when approaching competitive tasks. The present research addresses this gap within a two-phase experimental study, examining the effect of shared identity content on follower intentional mobilization, self-efficacy, perceived control, approach and avoidance goals, cardiovascular challenge and threat and motor performance within a competitive task.DesignA 2 × 2 between-participants two-phase experimental design, with two shared and two non-shared conditions.MethodWithin phase one, 220 sport and exercise undergraduate students imagined themselves in one of four scenarios and responded to measures of mobilization (e.g., willingness to invest time on a task). Then, a pre-screening questionnaire was used to evidence the students' authentic identity content when competing in sport, which informed condition within phase two. Of those who consented to phase two, a laboratory experiment with 120 undergraduate sport and exercise students was used. Within this experiment, the sharedness of identity content between leader and follower was manipulated through the students' authentic pre-screening questionnaire responses. Within phase two, competition related self-efficacy, perceived control, approach and avoidance goals, cardiovascular challenge and threat and motor performance was assessed.ResultsPhase one results indicated that when identity content is shared (vs. non-shared) between leader and follower, group members' willingness to invest time on a task is increased within a hypothetical scenario. In phase two, it was evidenced that when identity content is shared (vs. non-shared) between leader and follower, followers reported greater intentional mobilization, self-efficacy and perceived control when approaching a competitive task. Shared identity content with a leader did not predict cardiovascular challenge states nor greater motor performance (relative to non-shared identity content).ConclusionThe present research provides evidence that a leaders' capacity to mobilize effort of group members and enhance psychological appraisal of competitive events is dependent on their ability to build shared identity content.     

Antiphase domains and {011} twins in TiAl

Abstract

Titanium aluminides with a TiAl/Ti₃Al two-phase microstructure exhibit mechanical properties which are superior to those for either single-phase TiAl or Ti₃Al. The TiAl lamella in the two-phase microstructures show differently oriented TiAl regions which are frequently observed to coexist within the same TiAl lamella. The atomic arrangements of these regions are similar to antiphase domains/{011} twins of TiAl. However, the mechanism by which these regions are formed cannot be derived from the TiAl phase alone. This study suggests that, for two-phase titanium aluminides, Ti₃Al has a strong influence on the development of the TiAl microstructure.     

A new high-pressure phase transition in a zirconium-niobium alloy

It is reported for the first time that a g M y transformation can be induced in a g -stabilized zirconium alloy subjected to shock pressure. The y phase formed in the g matrix has been found to have a plate shape akin to martensitic plates. The lattice correspondence between the g and y structures has been found to be the same as that produced by thermal treatment. The formation of the plate-shaped y phase is explained in terms of a mechanism involving shear on <112> planes of the bcc lattice and the mechanical instability of the g phase.     

Mixed-valence impurity in a nanoscale particle

We consider a mixed-valence Anderson impurity with infinite U embedded into a small metallic particle. The nanosize of the system leads to discrete energy levels rather than to a continuum of energy eigenstates for the host. Using the Brillouin-Wigner approximation we show that the magnetic susceptibility, which arises from the van Vleck admixing of the magnetic configuration into the ground state, is only weakly affected by the finite spacing of energy levels, while the specific heat and the entropy display an exponential activation at low temperatures, that is have properties deviating from a Fermi liquid.     

Thermal stability of nanocrystalline fcc and hcp Ni(Si) synthesized by mechanical alloying of Ni90Si10

The thermal stability of nanocrystalline fcc and hcp Ni(Si), obtained by mechanical alloying of Ni₉₀Si₁₀, has been studied. The allotropic transformation from fcc to hcp Ni(Si) is accompanied by a volume expansion of 8.6% and is observed when fcc Ni(Si) reaches a critical crystallite size of 10nm. The hcp phase transforms to stable fcc Ni(Si) at 573K. It has been identified that the lattice distortion in nanometre-sized crystallites from the equilibrium configuration and the decrease in the interfacial energy with grain refinement act as self obstacles in controlling the grain growth of nanocrystalline materials.     

Developing emotion abilities and regulation strategies in a sport organization: An action research intervention

ObjectivesThis study aimed to improve the practice of individuals operating in a sport organization by providing an intervention to develop emotion abilities and strategies.DesignA two-phase action research approach was adopted to facilitate the objective and to assess the intervention's effectiveness.MethodIn the first phase of the intervention, 25 individuals fulfilling a range of roles (i.e., board of directors, chief executive officer, heads of performance and development, staff, administrators, national coaches and team managers, club coaches, national talent academy athletes) attended educational workshops over a 6 month period. In the second phase, three pivotal operators (i.e., national managers) received one-to-one coaching for a further 3 months. Data were collected using a range of self-report and performance measures, participant daily diaries, a researcher's log, and social validation interviews.ResultsFollowing social validation procedures the findings suggest that both phases were effective at improving the practice of participants, with significant improvements in regulation strategy use, perceptions of relationship quality, and closeness. However, only participants receiving the extended one-to-one coaching showed improvement in emotional intelligence ability scores.ConclusionsThe findings indicate that short-term generic interventions to promote the use of adaptive emotion regulation strategies may be effective in sport organizations, but the purposive development of emotional intelligence may require more longitudinal and idiographic approaches.     

Formation of ductile Al-based metallic glasses without rare-earth elements

Al₇₅Cu₁₇Mg₈ is a eutectic composition according to the ternary phase diagram, which can be quenched into a fully amorphous phase by adding 2-8at.% Ni, but the addition of a similar percentage of Gd failed to form the amorphous phase. The amorphous alloys obtained exhibit two broad diffuse peaks in the X-ray diffraction curves and, correspondingly, two halo rings in the electron diffraction patterns, implying that two types of local atom configuration exist. Thermal analysis of the amorphous alloys indicates that the primary crystallization peak shifts to higher temperatures with increasing Ni content. The occurrence of a nucleation and crystal growth peak during isothermal crystallization reveals the amorphous nature of the quenched ribbon alloys. The quenched amorphous ribbons do not break after bending by 180°. Mechanical testing yielded a tensile strength of 810MPa for (Al₇₅Cu₁₇Mg₈)₉₅Ni₅, and a vein structure, characteristic of amorphous fracture, is apparent in scanning electron micrographs. The different effects of Ni and Gd on the glass formation indicate that the large atomic size of Gd is not critical to the glass formation.     

Crystal structure of a hexagonal phase and its relation to a quasicrystalline phase in Zn-Mg-Y alloy

The crystal structure of a Zn-Mg-Y hexagonal phase, considered to be related to that of the quasicrystalline phase, has been determined by single-crystal X-ray diffraction. The atomic model, refined to a final R value of 0.027, has the composition Zn65.22Mg27.92Y6.86 and 92 atoms in a unit cell with lattice constants a = 14.579(2) A and c = 8.687(1) A and the space group P63/mmc. The Y atoms are situated at two different sites; one is fully occupied by Y atoms, while the other is shared with Mg atoms. The structure can be characterized by a layer structure stacked along the c axis, and also viewed as a columnar structure composed of fused Friauf polyhedras sharing hexagonal rings. The similarity of this hexagonal phase to the MgZn2 phase is shown. The structural relationship between this hexagonal phase and the icosahedral phase is also discussed.     

Boron impurities on a vicinal Si(100) surface: A study of structural properties and binding energies

The equilibrium locations of boron on the steps of the Si(100) surface have been studied using the Hartree-Fock method at the semiempirical level. The step is represented by a cluster of silicon atoms whose dangling bonds are saturated by hydrogen atoms. The boron impurity is moved in the step in substitutional and interstitial positions and the optimal configuration of the step containing the impurity is evaluated from a steepest-descent energy minimization. The study focuses on the dependence of the properties of the boron-step interaction on the shape of the step. These effects are analysed in the light of the features of boron absorbed on the flat surfaces and in the bulk, which have been widely studied.     

Planar dissociations and recombination energy of [110] superdislocations in Ni3Al: Generalized Peierls model in combination with ab initioelectron theory

Planar dissociation configurations of the [110] superdislocation in stoichiometric Ni₃Al are investigated by the generalized Peierls model using the {111} γ-surface energies calculated by the ab initio electron theory. The dissociation into four Shockley partials with the formation of an antiphase boundary and two complex stacking fault (CSF) ribbons turned out to be the energetically most favourable configuration. For the edge superdislocation the obtained dissociation widths should be large enough to be resolved in a weakbeam image, whereas for the corresponding configuration of the screw superdislocation the CSF ribbon has a rather small width which may be beyond the limit of the resolution. A twofold dissociation involving a superlattice intrinsic stacking fault is energetically less favourable. The recombination energy of the two Shockley partials in one superpartial is found to be 0.24eV/b.     

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.     

Formation of prismatic loop alignments in crystals deformed in single slip

In γ-TiAl deformed at room temperature in single slip, prismatic loops ar often organized in a staircase-like configuration, called strings whose generation by cross-slip is facilitated by the dislocation tendency to form screw locks as described recently by Grégori and Veyssière. The present letter is aimed at showing that strings may be encountered in virtually any crystal provided that the two impinging dislocations exhibit significantly different velocities. The crossslip annihilation mechanism of crossed dislocations considered by Tetelman is revisited and shown to evolve into a configuration significantly distinct from that originally predicted.     

Transformation-induced elastic strain effect on the precipitation kinetics of ordered intermetallics

Abstract

A transformation-induced elastic strain effect on the decomposition kinetics of a disordered phase into a mixture of ordered and disordered phases was investigated for a prototype binary alloy in two dimensions (2-D) by using a computer simulation technique. The simulation technique not only described simultaneously different processes, such as atomic ordering, clustering, disordering and coarsening, but also produced automatically ordered structures and alloy morphologies. It was found that irrespective of the degree of the crystal lattice mismatch between precipitates and the matrix, the alloy morphologies, developed during the congruent ordering stage which preceded the decomposition, showed no alignment in any of the crystallographic directions. Alignment developed during subbequent decomposition of the congruently ordered single phase, which resulted in the appearance of an equilibrium disordered phase preferentially along the antiphase domain boundaries. It became increasingly pronounced as the time of alloy aging increased. The aligned morphology finally formed the modulated structure found in many alloys. This mechanism of modulated structure formation is new since almost all previous experimentally observed modulated structures were interpreted as a result of a homogeneous spinodal decomposition. The predicted kinetics was found to be in excellent agreement with recent experimental results in a Fe-Si system and should be expected in most two-phase alloys with an ordered intermetallic precipitate whose stress-free lattice constant is significantly different from that of the disordered matrix.     

Direct evidence that an apparent splitting pattern of gamma particles in Ni alloys is a stage of coalescence

High-resolution electron microscopy is used to determine the translation order domains of gamma particles in arrangements formed during Ostwald ripening in the alloy Ni-12at.%Al. Such arrangements have been often identified with the operation of a mechanism of particle splitting in the late stages of the coarsening process, that is when the elastic strain contribution becomes predominant. It is shown that the translation order domains are not identical in such a particle array. This leads to the conclusion that particle splitting is not necessarily the mechanism responsible for the formation of such characteristic particle arrangements. Instead, particle migration can also be considered to be the responsible mechanism for the formation of such a correlated gamma-particle spatial distribution observed in Ni-based alloys.     

Formation of icosahedral quasicrystals in an annealed Zr65Al7.5Ni10Cu12.5Ag5 metallic glass

The formation and thermal stability of an icosahedral quasicrystalline phase in an annealed Zr₆₅Al_7.5Ni₁₀Cu_12.5Ag₅ metallic glass have been investigated by X-ray diffraction and transmission electron microscopy analyses. It was found that the quasicrystalline phase can precipitate from the glassy state and the supercooled liquid of the alloy over a wide range of annealing temperatures. After optimizing the heat-treatment conditions, the volume fraction of the quasicrystalline phase in the alloy can reach as high as about 80%. Investigation of the thermal stability of the quasicrystalline phase demonstrates that it is very stable when the annealing temperature is below the glass transformation temperature T _g of the alloy.     

Postural Stability in Children with High Sacral Level Spina Bifida: Deviations from a Control Group

Abstract

Objective: To assess static and dynamic postural stability changes in children with high sacral level spina bifida.

Methods: Thirty-five children with high sacral level spina bifida and 35 age-matched healthy controls were enrolled. Their lower extremity muscle strengths and static and dynamic postural stability parameters were measured with the use of a dynamometer and the NeuroCom Balance Master^® device, respectively. Functional gait and balance were evaluated using the five times sit-to-stand test (5STS) and the 6-minute walk test (6MWT). Spinal, hip, and ankle deformities of the patient group were measured by radiologic evaluation.

Results: In comparison with controls, patients were found to have lower ankle dorsiflexion and plantar-flexion strength, increased 5STS duration, and decreased 6MWT distance while both static and dynamic postural stability parameters were significantly different. Bilateral ankle muscle strengths were found to be negatively correlated with postural stability parameters. The presence of hydrocephalus or meningomyelocele in the patient group was found to have negative effects on static postural stability.

Conclusion: Static and dynamic postural stability is affected even in children with high sacral level spina bifida who are expected to have best condition in this patient population. The ankle muscle strength is the main factor influencing these changes.     

A quantum-mechanical study of the stability of SnO 2 nanocrystalline grains

The purpose of this study is to gain insight into the instability which is observed, under operative conditions, in SnO 2 nanocrystalline materials. For this purpose, the binding and fragmentation energies of SnO 2 crystalline grains have been evaluated quantum-mechanically at a semiempirical level using the extended Debye-Hückel approximation. The inner structure of the grains is assumed to be an unreconstructed rutile lattice, as in the parent solid. The grain size and shape are variable and a parametric search has been carried out on both quantities. In broad terms the grains show a bulk-like behaviour, as their characteristic energies are approximately independent of their size and shape. However, the increases in the grain size and in the oxygen content may increase the grain stability. These features are discussed in the light of the properties of small clusters formed by tin and oxygen.     

Observation of planar stacking faults in a Ti-rich two-phase Ti-Al alloy after deformation at elevated temperatures

It is a common observation that in two-phase Ti-Al-based binary alloys, deformation of the gamma phase occurs by 1/2<110]-type ordinary dis-location activity and twinning associated with 1/6<112] type partials. In the present study the microstructure of a new Ti-Al-based alloy (Ti-47at.% Al-2at.%Mn-2at.%Nb+ 0.8 vol.% TiB₂) with a duplex microstructure consisting of primary equiaxed gamma grains and lamellar alpha₂+ gamma colonies was studied by transmission electron microscopy (TEM) after deformation at elevated temperatures. Planar stacking faults were found in the gamma laths. A detailed contrast analysis by TEM shows that these planar stacking faults lying on {111} planes are bound by all the fcc variants of the Shockley partial dislocations of type 1/6<121>, in contrast with the observations in stoichiometric binary TiAl alloys, where only 1/6<112]-type Shockley partials are found to be associated with the true twins. It is proposed that the addition of ternary and quaternary elements such as Mn and Nb promotes the other variants of the fcc-like dissociations (not common in L1₀structure) in the present alloy.