Tribological, thermal and mechanical coupling aspects of the dry sliding contact

An original experimental set-up, made of two coaxial rings in relative motion, a sapphire and steel, enabled temperature measurements on both sides of the third body at the friction interface. Hot spots have been identified and temperature gradient across the third body accurately measured. Infrared camera and thermocouples have shown to be an effective tool for this research.Investigations conducted using SEM enabled detailed analysis of friction interfaces of both components, the sapphire and steel rings. Two types of third body (layers) have been identified, the compact, smooth micro-plates—where the actual contact occurs, and granular—which seem to accumulate in depressions or against material obstacles. There are also clear indications that the hot spots and depressions on steel friction surface are directly related. These areas of contact seem to be ‘shrinking’ in height after the application and complete component cooling.The investigation of the third body phenomenon and its influence on interface temperatures has direct relation to the observations made in automotive disc brakes.A thermal numerical model, which was also developed, introduced the third body as a uniform layer with energy storage and conduction. The obtained thermal gradients seem to be accurate, when compared with measurements conducted. The results are also similar to those found in literature. In addition, when only a fraction (1/1000th and 1/2000th) of the total nominal friction surface was considered to be in the actual contact, experimental temperature results were exactly within the predicted range. This indicates that the actual contact area varies during application.     

Contact of a Finger on Rigid Surfaces and Textiles: Friction Coefficient and Induced Vibrations

The tactile information about object surfaces is obtained through perceived contact stresses and friction-induced vibrations generated by the relative motion between the fingertip and the touched object. The friction forces affect the skin stress-state distribution during surface scanning, while the sliding contact generates vibrations that propagate in the finger skin activating the receptors (mechanoreceptors) and allowing the brain to identify objects and perceive information about their properties. In this article, the friction coefficient between a real human finger and both rigid surfaces and fabrics is retrieved as a function of the contact parameters (load and scanning speed). Then, the analysis of the vibration spectra is carried out to investigate the features of the induced vibrations, measured on the fingernail, as a function of surface textures and contact parameters. While the friction coefficient measurements on rigid surfaces agree with empirical laws found in literature, the behaviour of the friction coefficient when touching a fabric is more complex, and is mainly the function of the textile constructional properties. Results show that frequency spectrum distribution, when touching a rigid surface, is mainly determined by the relative geometry of the two contact surfaces and by the contact parameters. On the contrary, when scanning a fabric, the structure and the deformation of the textile itself largely affect the spectrum of the induced vibration. Finally, some major features of the measured vibrations (frequency distribution and amplitude) are found to be representative of tactile perception compared to psychophysical and neurophysiologic works in literature.     

Bright green fluorescence of Asian paper wasp nests

An exceptionally bright fluorescent biomatter was discovered when exploring, with UV-A light, the nests of several oriental paper wasp species of the genus Polistes, a genus of diurnal social insects. Fluorescence spectra of the cocoon cap membranes revealed narrow emission bands in the green range of the visible spectrum. Large Stokes shifts of around 160 nm and high fluorescence quantum yields of up to 35% were measured. Transmission spectra were recorded in order to estimate the contribution of the fluorescence to the visible light transmitted through the cocoon cap membrane. The nest fluorescence of the Vietnamese wasps was compared with a European and an American species. Potential biological functions of these interesting fluorescence properties of the studied biomaterial are discussed. The discovery of this striking example of a fluorescent terrestrial biomaterial may contribute to the debate on adaptive biological functions of natural fluorescence and falls in line with the growing interest in biodiversity and bio-inspiration.     

Quantitative and qualitative hydrologic balance for a suburban watershed with a separate sewer system (Nantes, France).

A qualitative and quantitative budget at the outlet of the storm-water runoff system of a small suburban watershed is presented together with some data regarding waste-water. 445,000 m3 (34% of the rain-water volume) were drained by the storm-water runoff system and 40,879 m3 by the waste-water system from September 2002 to March 2004. Storm-water runoff is generally not heavily polluted with regard to trace metals but concentrations occasionally exceed the standards for surface water of good quality. On the contrary, pesticides (diuron and glyphosate) have very high concentrations especially in spring and autumn when their use is maximum. As the St Joseph storm-water runoff is finally discharged into the Erdre River, measures to reduce the use of these pollutants should be considered.     

Current problems of lead poisoning]

In collaboration with private associations and public services, we screened a targeted population for serum lead levels and observed lead poisoning (serum Pb > 100 micrograms/l) in 6 out 44 children living in precarious conditions in Poitiers, France. This observation underscores some of the major problems encountered in the battle against lead poisoning in western countries. First, the social, economical or legal situation of the population at risk often results in exclusion from the normal health care network. If after a coordinated effort based on mutual trust, children exposed to lead poisoning can be identified, the second problem is to identify the source of intoxication. Scaling paint in the current housing may be incriminated, but how can the true source be identified when the populations concerned change residence often and may be unwilling to disclose their previous residence due to fear of reprisals for themselves or the new occupants? And if the source is identified, the cost of rehabilitation or the illegal situation of the family may raise further problems requiring adapted solutions. The prevention of lead poisoning calls for a targeted screening program, combined efforts of public authorities and health care workers, and close cooperation with private associations. All intoxicated children should be removed from the source of exposure and their families protected from the risk of sanctions. Only an active and practical public health policy can provide the solution to this continuing public health problem.     

Consequences of Ti-, Li-, and Er-ion implantations on the optical properties of single layers of Ta(2)O(5)

Tantalum pentoxide (Ta(2)O(5)) layers made by ion plating are implanted with a high fluence of keV Ti, Li, and Er ions. The resulting refractive-index profiles are given from the analysis of guided-wave propagation conditions. A comparison with spectrophotometric measurements is presented. All the implanted layers present low losses (extinction coefficient of some 10(-6)) after thermal annealing in air. Ti-implanted layers exhibit an increase in refractive index, whereas Li- and Er-implanted layers present a slight decrease in refractive index. Er-implanted layers present photoluminescent properties.     

Numerical investigation on the electrical transmission ability of a shearing powder layer

Recent developments in powder technology gave birth to a new lubricant—powder lubricant. Compared to liquid lubricant, powder lubricant like graphite powder has several advantages, such as good electrical conductivity and good thermal resistance. Such advantages are especially appreciated in sliding electrical contacts. Thus, the study of the electrical transmission ability of a shearing powder layer under different dynamical constraints appears to have a great interest. Recent works allowed to model the coupling of mechanical and electrical effects in a discrete medium. This algorithm was extended to study the electrical properties of a shearing powder layer with discrete element method. The mechanical and electrical behaviors of the sample were studied in different dynamical regimes, characterized by the inertial number I. The results exhibit an interesting relationship between the average contact resistance and the inertial number I. An exponential increase of the sample’s electrical resistance as well as the induced electrical noise are observed closed to the dense flow limit. Such observations underline the fact that to ensure the electrical transmission ability of the powder layer, one must keep the particle size and shear rate small, and a sufficiently large pressure.     

Where's the ball? Two- and three-year-olds reason about unseen events.

Children 2, 2?, and 3 years of age engaged in a search task in which they opened 1 of 4 doors in an occluder to retrieve a ball that had been rolled behind the occluder. The correct door was determined by a partially visible wall placed behind the occluder that stopped the motion of the unseen ball. Only the oldest group of children was able to reliably choose the correct door. All children were able to retrieve a toy that had been hidden in the same apparatus if the toy was hidden from the front by opening a door. Analysis of the younger children's errors indicated that they did not search randomly but instead used a variety of strategies. The results are consistent with the Piagetian view that the ability to use representations to guide action develops slowly over the first years of life. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Honeypot forensics, part II: analyzing the compromised host

Although flows are an effective method for monitoring honeypots in real time, they are not sufficient if we want to learn more about the intruder. To accomplish this goal, we must investigate the compromised host itself. In this article, we show how to build two timelines of events: one from network clues and the other from what the host tells us. We can then merge these timelines and answer additional questions.