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Combined surface acoustic wave and surface plasmon resonance measurement of collagen and fibrinogen layers
We use an instrument combining optical (surface plasmon resonance) and
acoustic (Love mode acoustic wave device) real-time measurements on a same
surface for the identification of water content in collagen and fibrinogen
protein layers. After calibration of the surface acoustic wave device
sensitivity by copper electrodeposition, the bound mass and its physical
properties -- density and optical index -- are extracted from the complementary
measurement techniques and lead to thickness and water ratio values compatible
with the observed signal shifts. Such results are especially usefully for
protein layers with a high water content as shown here for collagen on an
hydrophobic surface. We obtain the following results: collagen layers include
70+/-20 % water and are 16+/-3 to 19+/-3 nm thick for bulk concentrations
ranging from 30 to 300 ug/ml. Fibrinogen layers include 50+/-10 % water for
layer thicknesses in the 6+/-1.5 to 13+/-2 nm range when the bulk concentration
is in the 46 to 460 ug/ml range.Comment: 50 pages, 8 figures, 1 tabl
Front propagation directed by a line of fast diffusion: large diffusion and large time asymptotics
The system under study is a reaction-diffusion equation in a horizontal
strip, coupled to a diffusion equation on its upper boundary via an exchange
condition of the Robin type. This class of models was introduced by H.
Berestycki, L. Rossi and the second author in order to model biological
invasions directed by lines of fast diffusion. They proved, in particular, that
the speed of invasion was enhanced by a fast diffusion on the line, the
spreading velocity being asymptotically proportional to the square root of the
fast diffusion coefficient. These results could be reduced, in the logistic
case, to explicit algebraic computations. The goal of this paper is to prove
that the same phenomenon holds, with a different type of nonlinearity, which
precludes explicit computations. We discover a new transition phenomenon, that
we explain in detail
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