Bubble sorting in a foam under forced drainage

A highly polydisperse foam is subjected to a constant liquid flow from above. For sufficiently high flow rates, large-scale bubble motion is observed, in the course of which large bubbles rise to the top of the foam until a steady state is reached at which the average bubble size increases smoothly with height.     

Boundary effects on forced drainage through aqueous foam

The flow of liquid through foam confined in vertical tubes was investigated by measuring the velocity v_f of the liquid front forced down by gravity for various flow rates Q. The power law relating the velocity to flow rate of the incoming liquid (v_f     

Vertex interactions and film shapes in two-dimensional foam

A model of the structure of two-dimensional foam (cells separated by circular arcs (films) meeting at threefold vertices) is considered. Films that are so curved as to be nearly semicircular arcs are problematic for conventional foam structure computations, which aim to identify the pressures needed to achieve specified bubble areas. When the films have near semicircularity, tiny variations in pressure can lead to large changes in the computed bubble area, and hence a failure to meet the specified targets. A new algorithm for determining foam structure is presented. It is based on 'freezing' most of the system, except the nearly semicircular arcs, and then finding the particular bubble pressures associated with the latter via an analytic approximation. This procedure is shown to work well for structure relaxation in a small bubble cluster. Large relaxed bubble clusters are considered briefly at the end of the paper.     

Properties of three-dimensional bubbles of constant mean curvature

Foam bubbles of constant mean curvature with a number of faces between 3 and 32 have been computer generated. The surface area per unit volume is only weakly dependent upon the number of faces, which allows an approximate equation for the energy of a three-dimensional foam to be derived. A further relation between the rate of change in the volume of a bubble due to gas diffusion and its number of faces is compared with existing theory.     

The effect of strain upon the topology of a soap froth

Abstract

The question of the effect of an imposed strain on the topology of a soap froth is addressed through numerical simulations. Both the standard model of a ‘dry’ twodimensional foam and the case of small liquid fraction are explored. The froths are subjected to both extensional deformation and simple shear. The counter-intuitive result that application of strain can induce ordering in a disordered froth is obtained, quantified and discussed. A qualitative dynamical explanation is proposed.     

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.     

Star-triangle equivalence in two-dimensional soap froths

In two-dimensional foams at equilibrium, triangular bubbles can be freely exchanged with threefold stars, three edges ending at a central vertex. This theorem is deduced here from Moukarzel's duality. Moreover, to probe the method, a few related properties are established: under slow gas diffusion, cell extinction is a continuous process for triangles but not for other types of bubble. In general, the gas flow results in different configurations in the presence of a triangle from those in the presence of a star.     

The surface energy of strained foam clusters

We derive general equations relating the surface energy of strained bubble clusters to the volumes and pressures in the bubbles. These equations generalize a similar equation for free bubble clusters. We apply the equations to periodic clusters, clusters between two parallel walls and clusters enclosed by a wall.     

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.     

Surface energy of free clusters of bubbles: An estimation

We propose an approximate equation for the surface energy of two-dimensional free bubble clusters which we compare with exact calculations of the surface energy of symmetrical clusters consisting of a central bubble surrounded by one or two shells of bubbles of two different areas. The accuracy of the equation is good for relatively narrow distributions of the areas and of the number of sides of the bubbles but underestimates the energy for large widths of those distributions. We propose a similar approximate equation for the surface energy of three-dimensional clusters.     

Differential attrition in health behaviour change trials: A systematic review and meta-analysis

Objective: Attrition is a common problem in health behaviour change (HBC) trials. When the degree of attrition differs between treatment conditions, then this is called differential attrition and is regarded as a major threat to internal validity. The primary research question of this study was: how often and to what degree does differential attrition occur in HBC trials?

Design: A systematic review and meta-analysis of a random selection of HBC trials (k = 60). We meta-analysed the relative attrition rates using a random-effects model and examined the relationship between the relative attrition rates and the potential moderators: the amount of human contact in delivery and the intensity of the intervention/control condition, the type of control condition, and the follow-up intensity and duration.

Main outcome measures: Relative attrition rates.

Results: The average attrition rate was 18% (SD = .15; M = .15) in the intervention and 17% (SD = .13; M = .13) in the control conditions. The estimated average relative attrition rate was 1.10 (95% CI: 1.01–1.20, p = .02), suggesting an overall higher attrition rate of 10% in the intervention conditions. This relative attrition rate was not related to any of the potential moderators.

Conclusion: There is indication of a slightly higher amount of attrition on average in the intervention conditions of HBC trials.     

Demonstration and interpretation of ‘scutoid’ cells formed in a quasi-2D soap froth

ABSTRACT

Recently a novel type of epithelial cell has been discovered and dubbed the ‘scutoid’. It is induced by curvature of the bounding surfaces. We show by simulations and experiments that such cells are to be found in a dry foam subjected to this boundary condition.     

Do meditators and non-meditators have different HRV dynamics?

PurposeThe heart is a complex system and many researchers have been recently studying cardiac behavior using the theory of nonlinear dynamical systems. One of the most appealing tools for analyzing heart function is the heart rate variability (HRV) signal. This study aimed to elucidate the HRV dynamics of six distinct states: spontaneous normal breathing (SNB) and metronomic breathing (MB), as non-meditator groups, before Chinese Chi meditation (CCM), during CCM, before Kundalini yoga meditation (KYM), and during KYM, as meditator groups.MethodsThe HRV data were obtained from the Physionet database. Lagged Poincare indices, Lyapunov exponent (LE), Lempel-Ziv complexity (LZ), and 4 types of entropy were calculated.ResultsThe results showed the greatest discrepancies in the lagged Poincare indices for KYM and CCM. In contrast, the least variations were achieved for MB. Compared to SNB, an enhancement in the log energy entropy and a reduction in the LZ and other entropies were concluded during KYM and CCM practices. In contrast, a reverse pattern was observed for MB. Using support vector machine, HRV dynamics were classified with average accuracies of 99.14 and 98.2% and average sensitivities of 99.87 and 99.57% for pre-KYM and during KYM, respectively.ConclusionIt was shown that the HRV dynamics were significantly different in meditators and non-meditators.     

On the evaporation kinetics of C60/toluene solutions

The increasing interest in fullerene nanoparticles makes the question regarding their effect on liquid evaporation behavior unavoidable. In this study, we used a gravimetric technique to investigate the effect of C₆₀ fullerene nanospheres on the evaporation kinetics of toluene over their entire range of solubility. Saturated solutions showed the highest evaporation rate. The increase in the evaporation rate as a function of concentration is not monotonic, but rather exhibits a maximum and a minimum. The results strongly support the notion of molecular structuring within the liquid toluene depending on fullerene mole fractions.     

New insights on tensile plasticity of ultrafine-grained metallic materials

ABSTRACT

The tensile properties of TiNi_43.5Fe_6.5 alloy samples having different grain sizes (0.16, 0.35, 1.7, 2.3, and 3.9?μm) and fabricated by severe plastic deformation and annealing were investigated. It was observed that both the strength and the elongation of the alloy increase with a decrease in the grain size until the average size reaches 1.7?μm. However, for average grain sizes smaller than 1.7?μm, the elongation decreases continuously with further grain refinement. On the other hand, the strain-hardening rate does not decrease with the decrease in plasticity but instead increases slightly. The poor ductility of the ultrafine-grained TiNi_43.5Fe_6.5 alloy is accompanied by a high degree of strain hardening. This newly observed ductility behaviour of the ultrafine-grained TiNi_43.5Fe_6.5 alloy is elucidated by characterising the intragranular and grain boundaries.     

Integrating models of self-regulation and optimal experiences: A qualitative study into flow and clutch states in recreational distance running

ObjectiveIn this study, we aimed to understand the self-regulatory processes facilitating optimal experiences in running by integrating models of self-regulation with flow and clutch states.MethodUsing an event-focused approach, we interviewed 16 runners less than one day on average after recreational running activities (M = 22.17 hours later, range = 3–46) they described as positive, rewarding experiences. Our analysis drew on principles for thematic and connecting analyses.ResultsWe structured our analysis of the self-regulatory processes facilitating flow and clutch states into three overarching themes: forethought; monitoring; and control. Flow was facilitated by intrinsic experiential motives and non-specific goals, whereas clutch states involved an intrinsic motive to accomplish specific goals. The perceived ease and pleasure during flow motivated runners to continue this experience, which appeared to be aided by active and involuntary distraction. Conversely, clutch states were described as more effortful and less pleasant during the run, with active self-regulation strategies used to exert control over cognition and manage feelings of difficulty. Attending to specific outward or internal sensory stimuli appeared to initiate changes that contributed to the disruption of flow, although many runners described transitioning into a clutch state after flow disruption. No runner reported transitioning from a clutch state into flow.ConclusionsOur study offers novel insights into optimal experiences in running by integrating models of self-regulation with flow and clutch states. We discuss how these insights can inform research and applied practice seeking to develop interventions for promoting optimal experiences during running.     

Executive function during and after acute moderate aerobic exercise in adolescents

ObjectivesIn two experiments, we investigated the effects of acute moderate-intensity exercise on aspects of executive function in adolescents.DesignAn experimental design was used.MethodsFifty-five Japanese adolescents (Experiment 1: N = 28; Experiment 2: N = 27) performed a modified flanker task and a modified n-back task to assess inhibitory control and working memory before, during, and after walking on a treadmill at moderate intensity (Experiment 1: 60% maximal heart rate; Experiment 2: 70% maximal heart rate). In a separate session, the same testing sequence was administered while participants sat in a chair.ResultThe results revealed that reaction time for working memory increased during exercise in both experiments, while response accuracy decreased during exercise only at 70% maximal heart rate. Moderate intensity exercise had no substantial effect on inhibition control. Following cessation of the exercise, no effects were observed for either executive function assessment.ConclusionThese results indicate that moderate intensity exercise selectively affects executive function in adolescents. Further, during physical activity, adolescents maintain inhibitory control, but their working memory declines. Further research is required to reveal the mechanisms underlying this phenomenon and to expand beyond the laboratory setting to the areas of sports and physical activities of daily living.     

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.     

Using an Advance Time Meter display as means to reduce driving speed

ObjectiveTesting an experimental means to reduce motivation to drive fast.BackgroundOne determinant of that motivation may be a wrong presumption, demonstrated here: Time to reach destination declines about linearly to increase in driving speed. Actually, that time is a linear function of advance time, the inverse of speed. It is hypothesized that the behavioral by-product of the popularity of that fallacy could be counteracted by introducing an essential change to the speed-based continuous feedback provided to the driver – from a speedometer displaying instantaneous velocity to a gauge reporting advance time (denoted ATM), so that both average driving speed and speed variance are reduced.MethodIn two driving simulator experiments, driving speed of participants presented with either of the two types of gauge was recorded.ResultsThe main finding is that driving with feedback provided by an ATM gauge following prior briefing led to a significant reduction – ∼11 km/h – in mean speed, as well as to a significant reduction in between-driver speed variability, as compared with driving with an ordinary speedometer. It was also found that no significant difference was observed in the speeding behavior of participants driving with an ATM display for three ∼2-h sessions administered in three different days, so that the last session took place within seven days from the first one.ConclusionThe ATM gauge serves to reduce motivation to speed.ApplicationWidespread use of the ATM gauge may result in reduction in number and intensity of accidents.     

Attention allocation under varied workload and effort perception in rowers

ObjectivesTenenbaum's effort-related model has proposed that as physical workload increases, attention allocation shifts from dissociation to association. Owing to equivocal research results regarding gender and experience differences in attention and perceived exertion reports, this study was designed to examine whether attention allocation varied as a function of perceived effort manipulated by physical workload, and whether gender and experience differences would emerge in regards to attention use.DesignA within-subjects study design was employed using measures of attention, perceived exertion, heart rate, and power output.MethodsSixty high school and collegiate rowers were recruited, and were divided into 30 experienced (15 men and 15 women) and 30 novice rowers (15 men and 15 women). After establishing a maximal power output value for each rower using the rowing ergometer, participants were asked to row at 30%, 50%, and 75% relative workload intensities for 10 min in a counterbalanced order. At each minute, measures of heart rate, attention, and perceived exertion were taken. Participants also recorded their thoughts during the session after each task.ResultsResults demonstrated that attention significantly (p<.01) shifted from dissociation to association as workload increased. The workload increase also resulted in elevated perceived exertion and heart rate. Similarly, thought classifications validated attention shift as workload increased. Experience and gender were not found to be discriminatory factors for attention allocation.ConclusionsAttention shifted from dissociation to association as workload increased; as environmental demands increase, physiological sensations dominate the individual's attention. Attention is forced to shift internally and narrow (i.e., associative) to adapt to these demands. During low or moderate workload, attention can be more flexible and voluntarily shift between associative and dissociative modes because the task demands are not overwhelming.