Understanding the friction mechanisms between the human finger and flat contacting surfaces in moist conditions

Human hands sweat in different circumstances and the presence of sweat can alter the friction between the hand and contacting surface. It is, therefore, important to understand how hand moisture varies between people, during different activities and the effect of this on friction. In this study, a survey of fingertip moisture was done. Friction tests were then carried out to investigate the effect of moisture. Moisture was added to the surface of the finger, the finger was soaked in water, and water was added to the counter-surface; the friction of the contact was then measured. It was found that the friction increased, up until a certain level of moisture and then decreased. The increase in friction has previously been explained by viscous shearing, water absorption and capillary adhesion. The results from the experiments enabled the mechanisms to be investigated analytically. This study found that water absorption is the principle mechanism responsible for the increase in friction, followed by capillary adhesion, although it was not conclusively proved that this contributes significantly. Both these mechanisms increase friction by increasing the area of contact and therefore adhesion. Viscous shearing in the liquid bridges has negligible effect. There are, however, many limitations in the modelling that need further exploration

Human finger contact with small, triangular ridged surfaces

Ridges are often added to surfaces to improve grip of objects such as sports equipment, kitchen utensils, assistive technology, etc. Although considerable work has been carried out to study finger friction generally, not much attention has been paid to understanding and modelling the effects of surface texture. Previous studies indicate that at low roughness values friction decreases as roughness increases, but then a sharp increase is seen after a threshold level of roughness is reached. This is thought to be due to interlocking. In this study an analytical model was developed to analyse the different mechanisms of friction of a fingerpad sliding against triangular-ridged surfaces that incorporated adhesion, interlocking and hysteresis. Modelling was compared with experimental results from tests on five different triangular-ridged surfaces, manufactured from aluminium, brass and steel. Model and experiment compared well. The study showed that at low ridge height and width the friction was dominated by adhesion. However, above a ridge height of 42.5 μm, interlocking friction starts to contribute greatly to the overall friction. Then at a height of 250 μm, a noticeable contribution from hysteresis, of up to 20% of the total friction, is observed

Skin friction at the interface between hands and sports equipment

The friction between the finger pad/palm and items of sports equipment strongly influences how well an athlete is able to perform. It not only determines how well equipment can be gripped and manipulated, but also how the equipment feels to use and the perceived level of performance. In this paper various fundamental aspects of finger pad friction are reviewed, including the effects of applied force, skin moisture, material, surface texture etc., and the influence that they have on friction mechanisms such as adhesion, deformation, interlocking and hysteresis. A number of applied case studies are then outlined. The first is rugby balls and the effect the ball surface pimple pattern has on friction. Initially high speed video was used to establish how the hand interacts with a ball. Friction tests were then carried out with different hand conditions and pimple patterns and the link between friction and pass accuracy was explored. The second study relates to friction modifiers used in sports such as rock climbing and athletics. These can be affected by hand and environmental conditions so a focus was placed on tests with moist hands or wet surfaces. Finally Frisbee interactions were investigated. The impact of loss of feel as a result of wearing gloves was studied to see if any improvements in wet conditions with gloves were offset by the reduced feedback from the Frisbee interface. The fundamentals of skin tribology can play a key role in developing optimised sports equipment, gaps still exist, however, in the understanding and modelling of surface texture and how important feel/comfort are, which are both important for sports equipment design

An assessment of the performance of grip enhancing agents used in sports applications

The performances of four grip enhancing agents, powdered and liquid chalk, rosin and Venice turpentine, were assessed using a bespoke finger friction rig and compared against an agent-free finger. The effectiveness of these agents was measured in dry, damp and wet conditions, to simulate the different environments in which the agents are used. The tests were first done on a polished steel surface and then the powdered and liquid chalk and agent-free finger were tested on sandstone. The tests on the steel showed that in a dry condition, only the Venice turpentine significantly increased the coefficient of friction, compared to no application of agent, with the rosin and powdered chalk actually decreasing the coefficient of friction. It is thought that the reduction in the coefficient of friction is caused by the solid particles acting as a lubricant between the two surfaces. When the fingers were wet, only the granular powder-based agents increased the coefficient of friction. This is because the Venice turpentine cannot adhere well to a wet finger, and therefore is not as effective. When the surface is wet, there is very little difference between the agents due to the water separating the finger surface from the steel. The tests on the sandstone showed no real difference between the lubricants or the different conditions, except for the dry, chalk-free finger, which had a decreased coefficient of friction due to the lubricating properties of the sandstone particles. These results highlight that the use of grip enhancing agents should take into account the moisture in the contact, as in dry conditions, the grip may be optimum when there is no agent used. It also shows that in different sports, different grip enhancing agents should be used

Evidence for suppressed mid-Holocene northeastern Australian monsoon variability from coral luminescence

Summer monsoon rainfall in northeastern (NE) Australia exhibits substantial interannual variability resulting in highly variable river flows. The occurrence and magnitude of these seasonal river flows are reliably recorded in modern inshore corals as luminescent lines. Here we present reconstructed annual river flows for two ~120 year mid-Holocene windows based on luminescence measurements from five cores obtained from three separate coral colonies. We were able to cross-date the luminescence signatures in four cores from two of the colonies, providing confidence in the derived reconstruction. Present-day NE Australian rainfall and river flow are sensitive to El Niño–Southern Oscillation (ENSO) variability, with La Niña (El Niño) events typically associated with wetter (drier) monsoon seasons. Thus, our replicated and annually resolved coral records provide valuable insights into the northern Australian summer monsoon and ENSO variability at a key period (6 ka) when greenhouse gas levels and ice sheet cover were comparable to the preindustrial period but orbital forcing was different. Average modern and mid-Holocene growth characteristics were very similar, suggesting that sea surface temperatures off NE Australia at 6 kyr were also close to present values. The reconstructed river flow record suggests, however, that the mid-Holocene Australian summer monsoon was weaker, less variable from year to year (possibly indicative of reduced ENSO variability), and characterized by more within-season flood pulses than present. In contrast to today, the delivery of moisture appears to have been dominated by eastward propagating convective coupled waves associated with the Madden-Julian Oscillation

Characterising variations in the salinity of deep groundwater systems: A case study from Great Britain (GB)

Study region The study region is Great Britain (GB), a small non-continental island landmass in North West Europe Study focus Data for Total Dissolved Solids (TDS) from groundwater samples can be used to characterise regional-scale variations in the quality of deep groundwater systems. Combined with information about typical well-depths, TDS data can be used to identify the presence of currently undeveloped fresh or brackish groundwater at depth that may require protection. This study considers the distribution of TDS with depth relative to sea level in the main GB aquifers and selected other key hydrogeological units, and demonstrates how useful insights can be obtained from data-led analyses of depth variations in groundwater chemistry if the regional context of hydrogeological systems is taken into account. New hydrogeological insights In GB, TDS varies over about five orders of magnitude, up to about 330,000 mg/L, with a general increase in mineralisation with depth. Overall, there is a transition from fresh 10,000 mg/L groundwater at about 700 m. Given that the 95 %tile depth of water wells is about 200 m, it is evident that there is currently undeveloped fresh groundwater at depth across large parts of the study area that may require protection, although it is inferred that TDS is not the only factor limiting exploitation and use of these deeper resources. As in this study, previous data-led analyses of fresh groundwater at depth have typically analysed TDS as depth below surface. However, if TDS data is analysed relative to sea level and in the context of regional hydrogeological information or models, additional insights can be gained on the distribution and controls on fresh groundwater at depth. Projecting TDS data into a 3D hydrogeological model of the study area shows that fresh groundwater at depth exhibits spatial coherence and is generally associated with relatively dee

A model structure for coloured operads in symmetric spectra

We describe a model structure for coloured operads with values in the category of symmetric spectra (with the positive model structure), in which fibrations and weak equivalences are defined at the level of the underlying collections. This allows us to treat R-module spectra (where R is a cofibrant ring spectrum) as algebras over a cofibrant spectrum-valued operad with R as its first term. Using this model structure, we give suficient conditions for homotopical localizations in the category of symmetric spectra to preserve module structures.Comment: 16 page

Geographic and species association of hepatitis B virus genotypes in non-human primates

AbstractInfection with hepatitis B virus (HBV) has been detected in human populations thoughout the world, as well as in a number of ape species (Pan troglodytes, Gorilla gorilla, gibbons [Nomascus and Hylobates species] and Pongo pygmaeus). To investigate the distribution of naturally occurring HBV infection in these species and other African Old World monkey species (Cercopithecidae), we screened 137 plasma samples from mainly wild caught animals by polymerase chain reaction (PCR) using several of highly conserved primers from the HB surface (HBs) gene, and for HBs antigen (HBsAg) by ELISA. None of the 93 Cercopithecidae screened (6 species) showed PCR or serology evidence for HBV infection; in contrast 2 from 8 chimpanzees and 5 from 22 gibbons were PCR-positive with each set of primers.Complete genome sequences from each of the positive apes were obtained and compared with all previously published complete and surface gene sequences. This extended phylogenetic analysis indicated that HBV variants from orangutans were interspersed by with HBV variants from southerly distributed gibbon species (H. agilis and H. moloch) occupying overlapping or adjacent habitat ranges with orangutans; in contrast, HBV variants from gibbon species in mainland Asia were phylogenetically distinct. A geographical rather than (sub)species association of HBV would account for the distribution of HBV variants in different subspecies of chimpanzees in Africa, and explain the inlier position of the previously described lowland gorilla sequence in the chimpanzee clade. These new findings have a number of implication for understanding the origins and epidemiology of HBV infection in non-human primates

Investigating how faculty social networks and peer influence relate to knowledge and use of evidence-based teaching practices

Background: Calls for science education reform have been made for decades in the USA. The recent call to produce one million new science, technology, engineering, and math (STEM) graduates over 10 years highlights the need to employ evidence-based instructional practices (EBIPs) in undergraduate STEM classes to create engaging and effective learning environments. EBIPs are teaching strategies that have been empirically demonstrated to positively impact student learning, attitudes, and achievement in STEM disciplines. However, the mechanisms and processes by which faculty learn about and choose to implement EBIPs remain unclear. To explore this problem area, we used social network analysis to examine how an instructor’s knowledge and use of EBIPs may be influenced by their peers within a STEM department. We investigated teaching discussion networks in biology and chemistry departments at three public universities. Results: We report that tie strength and tie diversity vary between departments, but that mean indegree is not correlated with organizational rank or tenure status. We also describe that teaching discussion ties can often be characterized as strong ties based on two measures of tie strength. Further, we compare peer influence models and find consistent evidence that peer influence in these departments follows a network disturbances model. Conclusions: Our findings with respect to tie strength and tie diversity indicate that the social network structures in these departments vary in how conducive they might be to change. The correlation in teaching practice between discussion partner and peer influence models suggest that change agents should consider local social network characteristics when developing change strategies. In particular, change agents can expect that faculty may serve as opinion leaders regardless of their academic rank and that faculty can increase their use of EBIPs even if those they speak to about teaching use EBIPs comparatively less

Multiwavelength monitoring of a very active dwarf nova AX J1549.8-5416 with an unusually high duty cycle

We present the results of our analysis of new optical, ultraviolet (UV) and X-ray observations of a highly variable source − AX J1549.8−5416. Both the detection of several fast rise, exponential decay outbursts in the optical light curve and the lack of He II emission lines in the optical spectra suggest AX J1549.8−5416 is a cataclysmic variable of the dwarf nova (DN) type. The multiwavelength analysis of three mini-outbursts and one normal outburst represent one of the most complete multiwavelength studies of a DN and help to refine the relationship between the X-ray, UV and optical emission in this system. We find that the UV emission is delayed with respect to the optical by 1.0–5.4 d during the rising phase of the outburst. The X-ray emission is suppressed during the peak of the optical outburst and recovers during the end of the outburst. From our analysis of archival Swift, Chandra and XMM–Newton observations of AX J1549.8−5416, we estimate this DN has a high duty cycle (∼50 per cent), suggesting a quiescent X-ray luminosity larger than 1032 erg/s. We also find the X-ray and UV flux are roughly anticorrelated. Furthermore, we find that, at low X-ray fluxes, the X-ray spectrum is well described by a single temperature thermal plasma model, while at high X-ray fluxes, an isobaric cooling flow model also works. We find that the maximum temperature of the plasma in quiescence is significantly higher than that in outburst.Instituto de Astrofísica de La Plat