10,179 research outputs found
Membrane properties revealed by spatiotemporal response to a local inhomogeneity
We study theoretically the spatiotemporal response of a lipid membrane
submitted to a local chemical change of its environment, taking into account
the time-dependent profile of the reagent concentration due to diffusion in the
solution above the membrane. We show that the effect of the evolution of the
reagent concentration profile becomes negligible after some time. It then
becomes possible to extract interesting properties of the membrane response to
the chemical modification. We find that a local density asymmetry between the
two monolayers relaxes by spreading diffusively in the whole membrane. This
behavior is driven by intermonolayer friction. Moreover, we show how the ratio
of the spontaneous curvature change to the equilibrium density change induced
by the chemical modification can be extracted from the dynamics of the local
membrane deformation. Such information cannot be obtained by analyzing the
equilibrium vesicle shapes that exist in different membrane environments in
light of the area-difference elasticity model.Comment: 11 pages, 4 figure
Temporal and Spatial Data Mining with Second-Order Hidden Models
In the frame of designing a knowledge discovery system, we have developed
stochastic models based on high-order hidden Markov models. These models are
capable to map sequences of data into a Markov chain in which the transitions
between the states depend on the \texttt{n} previous states according to the
order of the model. We study the process of achieving information extraction
fromspatial and temporal data by means of an unsupervised classification. We
use therefore a French national database related to the land use of a region,
named Teruti, which describes the land use both in the spatial and temporal
domain. Land-use categories (wheat, corn, forest, ...) are logged every year on
each site regularly spaced in the region. They constitute a temporal sequence
of images in which we look for spatial and temporal dependencies. The temporal
segmentation of the data is done by means of a second-order Hidden Markov Model
(\hmmd) that appears to have very good capabilities to locate stationary
segments, as shown in our previous work in speech recognition. Thespatial
classification is performed by defining a fractal scanning ofthe images with
the help of a Hilbert-Peano curve that introduces atotal order on the sites,
preserving the relation ofneighborhood between the sites. We show that the
\hmmd performs aclassification that is meaningful for the agronomists.Spatial
and temporal classification may be achieved simultaneously by means of a 2
levels \hmmd that measures the \aposteriori probability to map a temporal
sequence of images onto a set of hidden classes
Effect of cerium concentration on corrosion resistance and polymerization of hybrid sol–gel coating on martensitic stainless steel
Stainless steels are increasingly used in the aeronautics field for the manufacture of structural parts. One of them, the X13VD martensitic stainless steel (X12CrNiMoV12-3), known for its good mechanical properties, has a poor corrosion resistance in confined or severe environments. In the past years, Cr(VI) based pre-treatments have been currently used for corrosion protection of different metals, however, they are toxic and due to environmental regulations, they will be definitely banned in a near future. Alternatives to replace Cr(VI) show advantages and drawbacks considering key properties such as: corrosion resistance, adhesion of coatings, fatigue resistance, durability and reliability. However, some of their possible alternatives show high potential. In this paper, a process was developed to improve the corrosion resistance of the martensitic stainless steel. Organic–inorganic hybrid coatings with different cerium concentrations were deposited onto stainless steel by sol–gel process. Corrosion resistance of the coatings was evaluated by electrochemical impedance measurements and it has been proved that cerium concentration of 0.01 M into hybrid coating was an optimal content. Adhesion tests were also carried out by "nanoscratchtest" to characterize the coatings mechanical properties as a function of cerium concentration but results do not clearly show the influence of cerium for the coating adhesion toward the substrate. To try to correlate with the electrochemical properties, liquid 29Si NMR spectroscopy was then performed to investigate hydrolysis and condensation reactions of sol–gel process, and by this method, it was demonstrated that for higher cerium concentration (>0.01 M) there is a modification of the chemical structure of the sol–gel network
Bilayer elasticity at the nanoscale: the need for new terms
Continuum elastic models that account for membrane thickness variations are
especially useful in the description of nanoscale deformations due to the
presence of membrane proteins with hydrophobic mismatch. We show that terms
involving the gradient and the Laplacian of the area per lipid are significant
and must be retained in the effective Hamiltonian of the membrane. We reanalyze
recent numerical data, as well as experimental data on gramicidin channels, in
light of our model. This analysis yields consistent results for the term
stemming from the gradient of the area per molecule. The order of magnitude we
find for the associated amplitude, namely 13-60 mN/m, is in good agreement with
the 25 mN/m contribution of the interfacial tension between water and the
hydrophobic part of the membrane. The presence of this term explains a
systematic variation in previously published numerical data.Comment: 34 pages, 9 figure
New sol-gel formulations to increase the barrier effect of a protective coating against the corrosion of steels
Films were deposited onto AISI 430 stainless steel substrates by dip-coating technique. The aim is to reach the AISI 304L stainless steel anti-corrosion properties by a coated AISI 430 stainless steel system. Sol formulation is done from the starting precursors tetraethylorthosilicate (TEOS) and 3(trimethoxysilyl) propyl methacrylate (MAP). After the hydrolysis of these precursors, sol-gel reactions occur before the addition (or not) of a controlled quantity of cerium nitrate. The addition of the PEG (polyethylene glycol), used as plasticizer has been studied in this paper and both physical and chemical properties of the synthesized hybrid films were studied by varying PEG ratios. Based on SEM observations and mass gain measurements, the thickness of the films has been adjustable. Another parameter plays a key role: the drying step of the whole system. It has been investigated and optimized in this paper to lead to coatings with a high barrier effect. The efficiency of the anti-corrosion protection of hybrid-coated stainless steel was investigated by potentiodynamic polarization curves and electrochemical impedance spectroscopy (EIS) after immersion of the material in a 3.5% NaCl solution.
Double-layered systems were successfully developed and a good compromise between PEG content and drying conditions has been found. Potentiodynamic polarization curves showed that the hybrid coating prepared using a TEOS/MAP/PEG yielded the best anti-corrosion performances. It acts as an efficient barrier similar to AISI 304 stainless steel used as reference, increasing the total impedance and significantly reducing the current densities
Universal amplitudes of the Casimir-like interactions between four types of rods in fluid membranes
The fluctuation-induced, Casimir-like interaction between two parallel rods
of length L adsorbed on a fluid membrane is calculated analytically at short
separations d<<L. The rods are modeled as constraints imposed on the membrane
curvature along a straight line. This allows to define four types of rods,
according to whether the membrane can twist along the rod and/or curve across
it. For stiff constraints, all the interaction potentials between the different
types of rods are attractive and proportional to L/d. Two of the four types of
rods are then equivalent, which yields six universal Casimir amplitudes.
Repulsion can occur between different rods for soft constraints. Numerical
results obtained for all ranges of d/L show that the attraction potential
reaches kT for d/L\simeq0.2. At separations smaller than d_c \approx
L(L/l_p)^(1/3), where l_p is the rod persistence length, two rods with fixed
ends will bend toward each other and finally come into contact because of the
Casimir interaction.Comment: 6 pages, 3 figure
Sol–gel synthesis and characterization of barium (magnesium) aluminosilicate glass sealants for solid oxide fuel cells
Solid oxide fuel cells (SOFC) correspond to efficient energy conversion systems coupled with low emissions of pollutants. In the aim to fabricate high temperature planar SOFC, glass and glass-ceramic sealants are developed to associate several criteria and properties : high thermal expansion (11.0 to 12.0 ⋅ 10− 6 K− 1), high electrical resistance > 2 kΩ/cm2, good thermochemical compatibility with the other active materials of the fuel cell, and stability under H2 and H2O atmospheres at an operation temperature of 800 °C for a long time. According to these requirements, new BAS (BaO–Al2O3–SiO2) and BMAS (BaO–MgO–Al2O3–SiO2) glass-ceramic sealants have been developed by sol–gel route which is a non-conventional process for such applications. By this soft chemistry process, we anticipate a decrease in the glasses processing temperature due to a better homogeneity between cationic precursors in the mixture and a more important reactivity of materials. Experimental results in terms of thermomechanical properties, thermal expansion coefficient, crystalline phase content, and microstructure were discussed. In particular, the influence of the %BaO on the thermomechanical properties of glass-ceramics was described. Changes in properties of glass-ceramics were closely related to the microstructure. The influence of MgO on glass processing temperatures, on the structure and on the microstructure is evaluated in order to confirm that these glass-ceramics are promising candidates to SOFC applications. So, after performing a systematic investigation to the various systems, the properties of suitable glass were proposed
Automatic case acquisition from texts for process-oriented case-based reasoning
This paper introduces a method for the automatic acquisition of a rich case
representation from free text for process-oriented case-based reasoning. Case
engineering is among the most complicated and costly tasks in implementing a
case-based reasoning system. This is especially so for process-oriented
case-based reasoning, where more expressive case representations are generally
used and, in our opinion, actually required for satisfactory case adaptation.
In this context, the ability to acquire cases automatically from procedural
texts is a major step forward in order to reason on processes. We therefore
detail a methodology that makes case acquisition from processes described as
free text possible, with special attention given to assembly instruction texts.
This methodology extends the techniques we used to extract actions from cooking
recipes. We argue that techniques taken from natural language processing are
required for this task, and that they give satisfactory results. An evaluation
based on our implemented prototype extracting workflows from recipe texts is
provided.Comment: Sous presse, publication pr\'evue en 201
Computation of 2-groups of positive classes of exceptional number fields
We present an algorithm for computing the 2-group of the positive divisor
classes of a number field F in case F has exceptional dyadic places. As an
application, we compute the 2-rank of the wild kernel WK2(F) in K2(F) for such
number fields
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