Statics and dynamics of a cylindrical droplet under an external body force

We study the rolling and sliding motion of droplets on a corrugated substrate by Molecular Dynamics simulations. Droplets are driven by an external body force (gravity) and we investigate the velocity profile and dissipation mechanisms in the steady state. The cylindrical geometry allows us to consider a large range of droplet sizes. The velocity of small droplets with a large contact angle is dominated by the friction at the substrate and the velocity of the center of mass scales like the square root of the droplet size. For large droplets or small contact angles, however, viscous dissipation of the flow inside the volume of the droplet dictates the center of mass velocity that scales linearly with the size. We derive a simple analytical description predicting the dependence of the center of mass velocity on droplet size and the slip length at the substrate. In the limit of vanishing droplet velocity we quantitatively compare our simulation results to the predictions and good agreement without adjustable parameters is found.Comment: Submitted to the Journal of Chemical Physic

Efficiency of donning and doffing medical examination gloves

Quickly donning and doffing medical gloves is of vital importance for high-pressure environments. The efficiency of glove donning, however, is sometimes hindered because of moisture on the hand. A variety of commercial glove coatings exist that are said to enable a smoother donning process, however, no previous studies have examined the differences in time taken to don or doff gloves manufactured using different materials and coatings. The aim of this new study was to compare the efficiency of donning and doffing different glove types. 14 participants were timed on their efficiency to don and doff chlorinated latex and nitrile gloves, as well as polymer coated latex and nitrile gloves. All glove types were studied in both dry and wet hand conditions, leading to a total of 8 different glove condition combinations. The results indicate that polymer coated latex gloves are desirable when a quick glove change is required as there was no statistically significant difference between the average time taken to don these gloves in dry and wet hand conditions. Higher incidences of sticking were found among the wet hands, particularly in the polymer coated nitrile, which took the longest to don. However, little differences were found between all glove types, suggesting that neither the material itself, nor the internal coating, have an effect on the overall donning process when hands are dry. Discrepancies in best fit size were also noticed between the recommended sizes based on anthropometric measurements and the participants preferred glove size

Perceptions and attitudes towards shoulder padding and shoulder injury in rugby union

Objective To develop an understanding of the role of shoulder padding in preventing injuries in rugby by investigating player perceptions and attitudes towards shoulder padding and extending previous research into the nature of shoulder injuries in rugby. Methods A survey was distributed to current rugby players over 13 years old. Questions related to the participants' demographic, attitudes to shoulder padding and shoulder injury history. Results 616 rugby players responded to the survey. 66.1% of respondents had worn shoulder padding at some point during their career. Youth players (13-17 years old) and the older demographic (36+ years old) perceived shoulder padding to be more effective. 37.1% of respondents considered shoulder padding to be effective at preventing cuts and abrasions with 21.9% finding it very effective. 50.3% considered it to be effective at preventing contusion injury with 9.7% finding it very effective. 45.5% wore padding for injury prevention, while 19.2% wore padding to protect from reoccurring injury. 38.6% did not wear shoulder padding because they felt it was not needed for the game of rugby. Sprain/ ligament damage (57.5%) and bruising (55.5%) to the shoulder were the most commonly reported injury. Conclusions Research should focus on quantifying the injury preventive capabilities while also educating the rugby community on shoulder padding. Bruising, cuts and abrasion injuries to the shoulder are prevalent. The ability of shoulder padding to protect from these injuries should be further explored

Probing the liquid-t-gas like phase transition in a cluster via a caloric curve

IP

Understanding the traction of tennis surfaces

The traction provided by a footwear-surface interaction can have an impact on player safety, performance and overall enjoyment of sport. Mechanical test methods used for the testing and categorisation of safe playing surfaces do not tend to simulate loads occurring during participation on the surface, and thus are unlikely to predict human response to the surface. For example, the pendulum system routinely employed by the International Tennis Federation (I.T.F.) utilises a standard rubber ‘foot’, rather than a shoe sole, and does not apply forces comparable to those in real play. There is a requirement for an improved scientific understanding of the tribological interactions at the shoe surface interface and the effects footwear and surface parameters have on the traction mechanism developed. The relationship between normal force and the coefficient of traction for the forefoot of a tennis shoe in contact with different tennis surfaces was examined using a bespoke traction rig. The effects of surface roughness were also examined. A power relationship was found between normal force and traction. As normal force increased differences in surface traction were found. The normal force, stiffness, and roughness of the surfaces affected the adhesive and hysteresis friction mechanisms that contribute to the overall traction force

Reply to the comment on direct experimental evidence for a negative heat capacity in the liquid to gas phase transition in hydrogen cluster ions backbending of the caloric curve

IP

Effect of simulated tennis steps and slides on tread element friction and wear

In hard court tennis, players change direction by either stepping or sliding. The shoe–surface friction during these movements is crucial to player performance. Too little friction when stepping may result in a slip. Too much friction when attempting to slide could cause the player to move only a short distance, or to fail to slide. To understand the influence of tread design on shoe–surface friction in tennis, experiments were performed on individual shoe tread elements that replicated the tribological conditions typically experienced during hard court step and slide movements. Tread element orientation had no effect on the static friction in step movements, but longer tread elements (in the sliding direction) had 9% lower dynamic friction during slide movements (p < 0.001). The friction between tennis shoe tread and hard court tennis surfaces is also shown to be influenced by the tread’s sliding history, and the wearing pattern that forms on the surface of the rubber