586 research outputs found
Effective transport and optical properties of composite materials
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Intrinsic Friction of Monolayers Adsorbed on Solid Surfaces
We overview recent results on intrinsic frictional properties of adsorbed
monolayers, composed of mobile hard-core particles undergoing continuous
exchanges with a vapor phase. In terms of a dynamical master equation approach
we determine the velocity of a biased impure molecule - the tracer particle
(TP), constrained to move inside the adsorbed monolayer probing its frictional
properties, define the frictional forces exerted by the monolayer on the TP, as
well as the particles density distribution in the monolayer.Comment: 12 pages, 5 figures, talk at the MRS Fall 2003 Meeting, Boston,
December 1-5, 200
La vallée de l'Escaut à Pont-à -Chin
The sudden opening of a karst pipe in the abandoned bed of the Scheldt River has exposed 8 m ofHolocene deposits; their stratigraphy, archaeological contents, fossil fauna and flora are studied here. A well dated early occupation is from the First Iron Age to Early La Tène (around 650-450 B.C.), a second one from Roman times (around 50-200 A.D.); they permit a close control of the14 C dates, which are systematically too old, due to reworking in the stream. Vertebrate and molluscan assemblages are discussed separatel
Metastable wetting
Consider a droplet of liquid on top of a grooved substrate. The wetting or
not of a groove implies the crossing of a potential barrier as the interface
has to distort, to hit the bottom of the groove. We start with computing the
free energies of the dry and wet states in the context of a simple
thermodynamical model before switching to a random microscopic version
pertaining to the Solid-on-Solid (SOS) model. For some range in parameter space
(Young angle, pressure difference, aspect ratio), the dry and wet states both
share the same free energy, which means coexistence. We compute these
coexistence lines together with the metastable regions. In the SOS case, we
describe the dynamic transition between coexisting states in wetting. We show
that the expected time to switch from one state to the other grows
exponentially with the free energy barrier between the stable states and the
saddle state, proportional to the groove's width. This random time appears to
have an exponential-like distribution
Collaborative research and development (R&D) for climate technology transfer and uptake in developing countries: Towards a needs driven approach
While international cooperation to facilitate the transfer and uptake of climate technologies in developing countries is an ongoing part of climate policy conversations, international collaborative R&D has received comparatively little attention. Collaborative R&D, however, could be a potentially important contributor to facilitating the transfer and uptake of climate technologies in developing countries. But the complexities of international collaborative R&D options and their distributional consequences have been given little attention to date. This paper develops a systematic approach to informing future empirical research and policy analysis on this topic. Building on insights from relevant literature and analysis of empirical data based on a sample of existing international climate technology R&D initiatives, three contributions are made. First, the paper analyses the coverage of existing collaborative R&D efforts in relation to climate technologies, highlighting some important concerns, such as a lack of coverage of lower-income countries or adaptation technologies. Second, it provides a starting point for further systematic research and policy thinking via the development of a taxonomic approach for analysing collaborative designs. Finally, it matches characteristics of R&D collaborations against developing countries’ climate technology needs to provide policymakers with guidance on how to Configure R&D collaborations to meet these needs
Dynamics of Spreading of Chainlike Molecules with Asymmetric Surface Interactions
In this work we study the spreading dynamics of tiny liquid droplets on solid
surfaces in the case where the ends of the molecules feel different
interactions with respect to the surface. We consider a simple model of dimers
and short chainlike molecules that cannot form chemical bonds with the surface.
We use constant temperature Molecular Dynamics techniques to examine in detail
the microscopic structure of the time dependent precursor film. We find that in
some cases it can exhibit a high degree of local order that can persist even
for flexible chains. Our model also reproduces the experimentally observed
early and late-time spreading regimes where the radius of the film grows
proportional to the square root of time. The ratios of the associated transport
coefficients are in good overall agreement with experiments. Our density
profiles are also in good agreement with measurements on the spreading of
molecules on hydrophobic surfaces.Comment: 12 pages, LaTeX with APS macros, 21 figures available by contacting
[email protected], to appear in Phys. Rev.
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