169 research outputs found
Thermal effects on atomic friction
We model friction acting on the tip of an atomic force microscope as it is
dragged across a surface at non-zero temperatures. We find that stick-slip
motion occurs and that the average frictional force follows ,
where is the tip velocity. This compares well to recent experimental work
(Gnecco et al, PRL 84, 1172), permitting the quantitative extraction of all
microscopic parameters. We calculate the scaled form of the average frictional
force's dependence on both temperature and tip speed as well as the form of the
friction-force distribution function.Comment: Accepted for publication, Physical Review Letter
Dynamic condensation of water at crack tips in fused silica glass
Water molecules play a fundamental role in the physics of slow crack
propagation in glasses. It is commonly understood that, during
stress-corrosion, water molecules that move in the crack cavity effectively
reduce the bond strength at the strained crack tip and, thus, support crack
propagation. Yet the details of the environmental condition at the crack tip in
moist air are not well determined. In a previous work, we reported direct
evidence of the presence of a 100 nm long liquid condensate at the crack tip in
fused silica glass during very slow crack propagation (10^-9 to 10^-10 m/s).
These observations are based on in-situ AFM phase imaging techniques applied on
DCDC glass specimens in controlled atmosphere. Here, we discuss the physical
origin of the AFM phase contrast between the liquid condensate and the glass
surface in relation to tip-sample adhesion induced by capillary bridges. We
then report new experimental data on the water condensation length increase
with relative humidity in the atmosphere. The measured condensation lengths
were much larger than what predicted using the Kelvin equation and expected
geometry of the crack tip.Comment: Accepted in JNCS. In pres
3D transient heat transfer numerical analysis of multiple energy piles
This paper presents a three-dimensional (3D) transient heat transfer numerical model for multiple energy piles based on the finite volume method (FVM). The initial and boundary conditions are established and the effects of “thermal short-circulating” between two pipes of a U-tube in energy pile are investigated. Thermal partial differential equations are discretized at the spatial nodal points and solved by linear approximation method. Temperature variations of working fluid, energy pile and its surrounding soil from simulation program are compared with experimental data to validate the developed model. In addition, the influences of fluid flow rate and U-tube shank spacing are analysed. It is established that the shank spacing should be set in a range of 0.06m to 0.10m to reduce heat transfer between the two pipes and meet the structural requirement. Meanwhile, the flow rate should be controlled in a range of 0.5m3/h to 0.7m3/h to avoid the low outlet fluid temperature and decrease the influence of “thermal short-circuiting”
Heat transfer analysis of underground U-type heat exchanger of ground source heat pump system
On the Commonality Between Theoretical Models for Fluid and Solid Friction, Wear and Tribochemistry
Relaxation dans les verres isolants et semiconducteurs
SIGLECNRS T Bordereau / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc
Grafting processes studied with a nanotip: Silane molecules and polymers grafted on silica and silanized silica surfaces
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Grafting processes studied with a nanotip: Silane molecules and polymers grafted on silica and silanized silica surfaces
no abstrac
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