476 research outputs found
AplicaciĂłn de la biologĂa molecular a la detecciĂłn de portadores de fibrosis quĂstica de pĂĄncreas
Foaming properties of protein/pectin electrostatic complexes and foam structure at the nanoscale
The foaming properties, foaming capacity and foam stability, of soluble
complexes of pectin and a globular protein, napin, have been investigated with
a "Foamscan" apparatus. Complementary, we also used SANS with a recent method
consisting in an analogy between the SANS by foams and the neutron reflectivity
of films to measure in situ film thickness of foams. The effect of ionic
strength, of protein concentration and of charge density of the pectin has been
analysed. Whereas the foam stability is improved for samples containing soluble
complexes, no effect has been noticed on the foam film thickness, which is
almost around 315 {\AA} whatever the samples. These results let us specify the
role of each specie in the mixture: free proteins contribute to the foaming
capacity, provided the initial free protein content in the bulk is sufficient
to allow the foam formation, and soluble complexes slow down the drainage by
their presence in the Plateau borders, which finally results in the
stabilisation of foams
Statistical distributions in the folding of elastic structures
The behaviour of elastic structures undergoing large deformations is the
result of the competition between confining conditions, self-avoidance and
elasticity. This combination of multiple phenomena creates a geometrical
frustration that leads to complex fold patterns. By studying the case of a rod
confined isotropically into a disk, we show that the emergence of the
complexity is associated with a well defined underlying statistical measure
that determines the energy distribution of sub-elements,``branches'', of the
rod. This result suggests that branches act as the ``microscopic'' degrees of
freedom laying the foundations for a statistical mechanical theory of this
athermal and amorphous system
Spatial structure and composition of polysaccharide-protein complexes from Small Angle Neutron Scattering
We use Small Angle Neutron Scattering (SANS), with an original analysis
method, to obtain both the characteristic sizes and the inner composition of
lysozyme-pectin complexes depending on the charge density. Lysozyme is a
globular protein and pectin a natural anionic semiflexible polysaccharide with
a degree of methylation (DM) 0, 43 and 74. For our experimental conditions
(buffer ionic strength I = 2.5 10-2 mol/L and pH between 3 and 7), the
electrostatic charge of lysozyme is always positive (from 8 to 17 depending on
pH). The pectin charge per elementary chain segment is negative and can be
varied from almost zero to one through the change of DM and pH. The weight
molar ratio of lysozyme on pectin monomers is kept constant. The ratio of
negative charge content per volume to positive charge content per volume, -/+,
is varied between 10 and 0.007. On a local scale, for all charged pectins, a
correlation peak appears at 0.2 {\AA}-1 due to proteins clustering inside the
complexes. On a large scale, the complexes appear as formed of spherical
globules with a well defined radius of 10 to 50 nm, containing a few thousands
proteins. The volume fraction Phi of organic matter within the globules derived
from SANS absolute cross-sections is around 0.1. The protein stacking, which
occurs inside the globules, is enhanced when pectin is more charged, due to pH
or DM. The linear charge density of the pectin determines the size of the
globules for pectin chains of comparable molecular weights whether it is
controlled by the pH or the DM. The radius of the globules varies between 10 nm
and 50 nm. In conclusion the structure is driven by electrostatic interactions
and not by hydrophobic interactions. The molecular weight also has a large
influence on the structure of the complexes since long chains tend to form
larger globules. This maybe one reason why DM and pH are not completely
equivalent in our system since DM 0 has a short mass, but this may not be the
only one. For very low pectin charge (-/+ = 0.07), globules do not appear and
the scattering signals a gel-like structure. We did not observe any
beads-on-a-string structure
La remonte d'une unité mehariste : son caractÚre polymorphe. Conditions d'une homogénéité moyenne
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ââLozengeââ contour plots in scattering from polymer networks
We present a consistent explanation for the appearance of âlozengeâ shapes in contour plots of the two dimensional scattering intensity from stretched polymer networks. By explicitly averaging over quenched variables in a tube model, we show that lozenge patterns arise as a result of chain material that is not directly deformed by the stretch. We obtain excellent agreement with experimental data
Secular resonance sweeping of the main asteroid belt during planet migration
We calculate the eccentricity excitation of asteroids produced by the
sweeping secular resonance during the epoch of planetesimal-driven
giant planet migration in the early history of the solar system. We derive
analytical expressions for the magnitude of the eccentricity change and its
dependence on the sweep rate and on planetary parameters; the sweeping
leads to either an increase or a decrease of eccentricity depending on an
asteroid's initial orbit. Based on the slowest rate of sweeping that
allows a remnant asteroid belt to survive, we derive a lower limit on Saturn's
migration speed of \sim0.15\AU\My^{-1} during the era that the
resonance swept through the inner asteroid belt (semimajor axis range
2.1--2.8\AU). This rate limit is for Saturn's current eccentricity, and
scales with the square of Saturn's eccentricity; the limit on Saturn's
migration rate could be lower if Saturn's eccentricity were lower during its
migration. Applied to an ensemble of fictitious asteroids, our calculations
show that a prior single-peaked distribution of asteroid eccentricities would
be transformed into a double-peaked distribution due to the sweeping of the
. Examination of the orbital data of main belt asteroids reveals that
the proper eccentricities of the known bright () asteroids may be
consistent with a double-peaked distribution. If so, our theoretical analysis
then yields two possible solutions for the migration rate of Saturn and for the
dynamical states of the pre-migration asteroid belt: a dynamically cold state
(single-peaked eccentricity distribution with mean of ) linked with
Saturn's migration speed \sim 4\AU\My^{-1}, or a dynamically hot state
(single-peaked eccentricity distribution with mean of ) linked with
Saturn's migration speed \sim 0.8\AU\My^{-1}.Comment: 32 pages, 7 figures. Accepted for publication in ApJ on Mar. 1, 201
The galaxy luminosity function of the Abell 496 cluster and its spatial variations
We investigate the LF in the very relaxed cluster Abell 496. Our analysis is
based on deep images obtained at CFHT with MegaPrime/MegaCam in four bands
(ugri) covering a 1x1 deg2 region, which is centered on the cluster Abell 496
and extends to near its virial radius. The LFs are estimated by statistically
subtracting a reference field taken as the mean of the 4 Deep fields of the
CFHTLS survey. Background contamination is minimized by cutting out galaxies
redder than the observed Red Sequence in the g-i versus i colour-magnitude
diagram. In Abell 496, the global LFs show a faint-end slope alpha=-1.55+/-0.06
and vary little with observing band. Without colour cuts, the LFs are much
noisier but not significantly steeper. The faint-end slopes show a
statistically significant steepening from alpha=-1.4+/-0.1 in the central
region (extending to half a virial radius) to -1.8+/-0.1 in the Southern
envelope of the cluster. Cosmic variance and uncertain star-galaxy separation
are our main limiting factors in measuring the faint-end of the LFs. The
large-scale environment of Abell 496, probed with the fairly complete 6dFGS
catalogue, shows a statistically significant 36 Mpc long filament at PA=137
deg, but we do not find an enhanced LF along this axis. Our LFs do not display
the large number of dwarf galaxies (alpha ~ -2) inferred by several authors,
whose analyses may suffer from field contamination caused by inexistent or
inadequate colour cuts. Alternatively, different clusters may have different
faint-end slopes, but this is hard to reconcile with the wide range of slopes
found for given clusters and for wide sets of clusters.Comment: Accepted in A&A. 13 pages, 11 figure
An optical view of the filament region of Abell 85
We compare the distribution of optically and Halpha (Ha) selected galaxies in
the Southern half of the nearby Abell 85 (A85) cluster with the recently
discovered X-ray filament (XRF). We search for galaxies where star formation
(SF) may have been triggered by interactions with intracluster gas or tidal
pressure due to the cluster potential when entering the cluster. Our analysis
is based on images obtained with CFHT MegaPrime/MegaCam (1x1 deg2 field) in
four bands (ugri) and ESO 2.2mWFI (38'x36' field) in a narrow band filter
corresponding to the redshifted Halpha (Ha) line and in a broad R-band filter.
The LFs are estimated by statistically subtracting a reference field.
Background contamination is minimized by cutting out galaxies redder than the
observed red sequence in the g-i vs. i colour-magnitude diagram. The galaxy
distribution shows a significantly flattened cluster, whose principal axis is
slightly offset from the XRF. The analysis of the broad band LFs shows that the
filament region is well populated. The filament is also independently detected
as a gravitationally bound structure by the Serna & Gerbal hierarchical method.
101 galaxies are detected in Ha, among which 23 have spectroscopic redshifts in
the cluster, 2 have spectroscopic redshifts higher than the cluster and 58 have
photometric redshifts that tend to indicate that they are background
objects.The 23 galaxies with spectroscopic redshifts in the cluster are mostly
concentrated in the South part of the cluster and along the filament. We find a
number of galaxies showing evidence for SF in the XRF, and all our results are
consistent with the previous hypothesis that the XRF in A85 is a
gravitationally bound structure made of groups falling on to the main cluster.Comment: Accepted in A&A. 39 pages, 107 figures. Full resolution images
available at ftp://ftp.iap.fr/pub/from_users/gam/A85
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