Surface effect on the screw dislocation mobility over the Peierls barrier

The effect of the image force on the Peierls stress (τ _p ) of a screw dislocation below a free surface is studied via a self-consistent semidiscrete variational Peierls–Nabarro model. The consequence of reduction in elastic energy and increase in stacking fault energy by the presence of the free surface is found to additively increase the Peierls stress (τ _p ). This model gives a physical interpretation of the same tend observed in a recent molecular dynamic study, while previous continuum analysis predicted the opposite.     

One-step synthesis of bulk quantities of graphene from graphite by femtosecond laser ablation under ambient conditions

Bulk synthesis of few-layer graphene (FLG) for industrial applications still remains a challenge for researchers. Here, we report a very simple technique for bulk synthesis of FLG by femtosecond laser ablation of graphite powder suspended in ethanol without the requirement of a controlled environment. Graphite powder, with an average particle size <20 μm, was suspended uniformly in ethanol and ablated at room temperature using fs pulses (wavelength ~800 nm and an input beam diameter ~8 mm) followed by ultrasonication to obtain FLG with a lateral size of ~1 μm. Raman spectroscopy and high-resolution transmission electron microscopy data confirmed the nature and morphology of the FLG. The quality and number of layers in the FLG could be controlled by tuning the laser parameters.     

Experimental investigations of TB2 alloy by pack boriding with rare-earth oxides

ABSTRACT

An orthogonal test with four factors, namely temperature, time, type of rare-earth oxides (REOs) and REO content, was performed to obtain the optimised boriding parameters of TB2 alloy by pack boriding with REOs. It is found that temperature has the strongest effect on the boride layer thickness, while time has the strongest effect on the surface hardness and coefficient of friction. The optimum parameters for pack boriding of TB2 alloy with REO are a temperature of 1373?K, a time of 20?h, La₂O₃ as the REO with a content of 4?wt.%.     

Lower limb kinematic variability in dancers performing drop landings onto floor surfaces with varied mechanical properties

Elite dancers perform highly skilled and consistent movements. These movements require effective regulation of the intrinsic and extrinsic forces acting within and on the body. Customized, compliant floors typically used in dance are assumed to enhance dance performance and reduce injury risk by dampening ground reaction forces during tasks such as landings. As floor compliance can affect the extrinsic forces applied to the body, secondary effects of floor properties may be observed in the movement consistency or kinematic variability exhibited during dance performance. The aim of this study was to investigate the effects of floor mechanical properties on lower extremity kinematic variability in dancers performing landing tasks. A vector coding technique was used to analyze sagittal plane knee and ankle joint kinematic variability, in a cohort of 12 pre-professional dancers, through discrete phases of drop landings from a height of 0.2 m. No effect on kinematic variability was observed between floors, indicating that dancers could accommodate the changing extrinsic floor conditions. Future research may consider repeat analysis under more dynamic task constraints with a less experienced cohort. However, knee/ankle joint kinematic variability was observed to increase late in the landing phase which was predominantly comprised of knee flexion coupled with the terminal range of ankle dorsiflexion. These findings may be the result of greater neural input late in the landing phase as opposed to the suggested passive mechanical interaction of the foot and ankle complex at initial contact with a floor. Analysis of joint coordination in discrete movement phases may be of benefit in identifying intrinsic sources of variability in dynamic tasks that involve multiple movement phases.     

Pictorial depth: intensity and aesthetic surface

Philosophers seldom ask questions regarding how certain phenomena occur, because such questions tend to be the province of the sciences or of technology. However, the question how pictures have depth requires philosophical reflection because it takes place on the surface of pictorial objects and involves both physical and phenomenal, i.e. aesthetic, features of those surfaces. This essay examines how pictures have depth by first separating the aesthetic question from interpretive considerations, and thereby refining the question how pictures have depth. Next it explicates two sorts of conceptual tools required to understand the question: several complex concepts needed to understand surfaces, and the concept of intensity. These are then used to understand how pictures can have depth by showing how intensities produce both an aesthetic surface and depth within it.