1,494 research outputs found
Interfacial layering in a three-component polymer system
We study theoretically the temporal evolution and the spatial structure of
the interface between two polymer melts involving three different species (A,
A* and B). The first melt is composed of two different polymer species A and A*
which are fairly indifferent to one another (Flory parameter chi_AA* ~ 0). The
second melt is made of a pure polymer B which is strongly attracted to species
A (chi_AB 0). We then show
that, due to these contradictory tendencies, interesting properties arise
during the evolution of the interface after the melts are put into contact: as
diffusion proceeds, the interface structures into several adjacent
"compartments", or layers, of differing chemical compositions, and in addition,
the central mixing layer grows in a very asymmetric fashion. Such unusual
behaviour might lead to interesting mechanical properties, and demonstrates on
a specific case the potential richness of multi-component polymer interfaces
(as compared to conventional two-component interfaces) for various
applications.Comment: Revised version, to appear in Macromolecule
Étude des désexcitations électromagnétiques des niveaux 1- situés à 12,44 et 13,09 MeV dans le noyau 16O
Les désexcitations γ des niveaux 1- situés à 12,44 et 13,09 MeV dans le noyau 16O ont été étudiées et deux nouvelles transitions mises en évidence. En outre au cours de ce travail les paramètres des deux niveaux 1- ont été redéterminés
Light Scattering from Nonequilibrium Concentration Fluctuations in a Polymer solution
We have performed light-scattering measurements in dilute and semidilute
polymer solutions of polystyrene in toluene when subjected to stationary
temperature gradients. Five solutions with concentrations below and one
solution with a concentration above the overlap concentration were
investigated. The experiments confirm the presence of long-range nonequilibrium
concentration fluctuations which are proportional to , where
is the applied temperature gradient and is the wave number of
the fluctuations. In addition, we demonstrate that the strength of the
nonequilibrium concentration fluctuations, observed in the dilute and
semidilute solution regime, agrees with theoretical values calculated from
fluctuating hydrodynamics. Further theoretical and experimental work will be
needed to understand nonequilibrium fluctuations in polymer solutions at higher
concentrations.Comment: revtex, 16 pages, 7 figures. J. Chem. Phys., to appea
Non-monotonous crossover between capillary condensation and interface localisation/delocalisation transition in binary polymer blends
Within self-consistent field theory we study the phase behaviour of a
symmetric binary AB polymer blend confined into a thin film. The film surfaces
interact with the monomers via short range potentials. One surface attracts the
A component and the corresponding semi-infinite system exhibits a first order
wetting transition. The surface interaction of the opposite surface is varied
as to study the crossover from capillary condensation for symmetric surface
fields to the interface localisation/delocalisation transition for
antisymmetric surface fields. In the former case the phase diagram has a single
critical point close to the bulk critical point. In the latter case the phase
diagram exhibits two critical points which correspond to the prewetting
critical points of the semi-infinite system. The crossover between these
qualitatively different limiting behaviours occurs gradually, however, the
critical temperature and the critical composition exhibit a non-monotonic
dependence on the surface field.Comment: to appear in Europhys.Let
Erratum. Maternal ageing impairs mitochondrial DNA kinetics during early embryogenesis in mice
STUDY QUESTION: Does ageing affect the kinetics of the mitochondrial pool during oogenesis and early embryogenesis?
SUMMARY ANSWER: While we found no age-related change during oogenesis, the kinetics of mitochondrial DNA content and the expression of the factors involved in mitochondrial biogenesis appeared to be significantly altered during embryogenesis.
WHAT IS KNOWN ALREADY: Oocyte mitochondria are necessary for embryonic development. The morphological and functional alterations of mitochondria, as well as the qualitative and quantitative mtDNA anomalies, observed during ovarian ageing may be responsible for the alteration of oocyte competence and embryonic development.
STUDY DESIGN, SIZE, DURATION: The study, conducted from November 2016 to November 2017, used 40 mice aged 5-8 weeks and 45 mice aged 9-11 months (C57Bl6/CBA F(1)). A total of 488 immature oocytes, with a diameter ranging from 20 μm to more than 80 μm, were collected from ovaries, and 1088 mature oocytes or embryos at different developmental stages (two PN, one-cell, i.e. syngamy, two-cell, four-cell, eight-cell, morula and blastocyst) were obtained after ovarian stimulation and, for embryos, mating.
PARTICIPANTS/MATERIALS, SETTING, METHODS: Mitochondrial DNA was quantified by quantitative PCR. We used quantitative reverse transcriptase PCR (RT-PCR) (microfluidic method) to study the relative expression of three genes involved in the key steps of embryogenesis, i.e. embryonic genome activation (HSPA1) and differentiation (CDX2 and NANOG), two mtDNA genes (CYB and ND2) and five genes essential for mitochondrial biogenesis (PPARGC1A, NRF1, POLG, TFAM and PRKAA). The statistical analysis was based on mixed linear regression models applying a logistic link function (STATA v13.1 software), with values of P < 0.05 being considered significant.
MAIN RESULTS AND THE ROLE OF CHANCE: During oogenesis, there was a significant increase in oocyte mtDNA content (P < 0.0001) without any difference between the two groups of mice (P = 0.73). During the first phase of embryogenesis, i.e. up to the two-cell stage, embryonic mtDNA decreased significantly in the aged mice (P < 0.0001), whereas it was stable for young mice (young/old difference P = 0.015). The second phase of embryogenesis, i.e. between the two-cell and eight-cell stages, was characterized by a decrease in embryonic mtDNA for young mice (P = 0.013) only (young/old difference P = 0.038). During the third phase, i.e. between the eight-cell and blastocyst stage, there was a significant increase in embryonic mtDNA content in young mice (P < 0.0001) but not found in aged mice (young/old difference P = 0.002). We also noted a faster expression of CDX2 and NANOG in the aged mice than in the young mice during the second (P = 0.007 and P = 0.02, respectively) and the third phase (P = 0.01 and P = 0.008, respectively) of embryogenesis. The expression of mitochondrial genes CYB and ND2 followed similar kinetics and was equivalent for both groups of mice, with a significant increase during the third phase (P < 0.01). Of the five genes involved in mitochondrial biogenesis, i.e. PPARGC1A, NRF1, POLG, TFAM and PRKAA, the expression of three genes decreased significantly during the first phase only in young mice (NRF1, P = 0.018; POLGA, P = 0.002; PRKAA, P = 0.010), with no subsequent difference compared to old mice. In conclusion, during early embryogenesis in the old mice, we suspect that the lack of a replicatory burst before the two-cell stage, associated with the early arrival at the minimum threshold value of mtDNA, together with the absence of an increase of mtDNA during the last phase, might potentially deregulate the key stages of early embryogenesis.
LARGE SCALE DATA: N/A.
LIMITATIONS, REASONS FOR CAUTION: Because of the ethical impossibility of working on a human, this study was conducted only on a murine model. As superovulation was used, we cannot totally exclude that the differences observed were, at least partially, influenced by differences in ovarian response between young and old mice.
WIDER IMPLICATIONS OF THE FINDINGS: Our findings suggest a pathophysiological explanation for the link observed between mitochondria and the deterioration of oocyte quality and early embryonic development with age.
STUDY FUNDING/COMPETING INTEREST(S): This work was supported by the University of Angers, France, by the French national research centres INSERM and the CNRS and, in part, by PHASE Division, INRA. There are no competing interests
Liquid-liquid coexistence in the phase diagram of a fluid confined in fractal porous materials
Multicanonical ensemble sampling simulations have been performed to calculate
the phase diagram of a Lennard-Jones fluid embedded in a fractal random matrix
generated through diffusion limited cluster aggregation. The study of the
system at increasing size and constant porosity shows that the results are
independent from the matrix realization but not from the size effects. A
gas-liquid transition shifted with respect to bulk is found. On growing the
size of the system on the high density side of the gas-liquid coexistence curve
it appears a second coexistence region between two liquid phases. These two
phases are characterized by a different behaviour of the local density inside
the interconnected porous structure at the same temperature and chemical
potential.Comment: 5 pages, 4 figures. To be published in Europhys. Letter
Frequency Dispersion of Sound Propagation in Rouse Polymer Melts via Generalized Dynamic Random Phase Approximation
An extended generalization of the dynamic random phase approximation (DRPA)
for L-component polymer systems is presented. Unlike the original version of
the DRPA, which relates the (LxL) matrices of the collective density-density
time correlation fumctions and the corresponding susceptibilities of polymer
concentrated systems to those of the tracer macromolecules and so-called broken
links system (BLS), our generalized DRPA solves this problem for (5xL)x(5xL)
matrices of the coupled susceptibilities and time correlation functions of the
component number, kinetic energy and flux densities. The presented technique is
used to study propagation of sound and dynamic form-factor in disentangled
(Rouse) monodisperse homopolymer melt. The calculated sound velocity and
absorption coefficient reveal substantial frequency dispersion. The relaxation
time is found to be N times less than the Rouse time (N is the degree of
polymerization), which evidences strong dynamic screening because of interchain
interaction. We discuss also some peculiarities of the Brillouin scattering in
polymer melts. Besides, a new convenient expression for the dynamic structural
function of the Rouse chain in (q,p)-representation is found.Comment: 37 pages, 2 appendices, 48 references, 1 figur
Viscoelasticity of two-layer-vesicles in solution
The dynamic shape relaxation of the two-layer-vesicle is calculated. In
additional to the undulation relaxation where the two bilayers move in the same
direction, the squeezing mode appears when the gap between the two bilayers is
small. At large gap, the inner vesicle relaxes much faster, whereas the slow
mode is mainly due to the outer layer relaxation. We have calculated the
viscoelasticity of the dilute two-layer-vesicle suspension. It is found that
for small gap, the applied shear drives the undulation mode strongly while the
slow squeezing mode is not much excited. In this limit the complex viscosity is
dominated by the fast mode contribution. On the other hand, the slow mode is
strongly driven by shear for larger gap. We have determined the crossover gap
which depends on the interaction between the two bilayers. For a series of
samples where the gap is changed systematically, it is possible to observe the
two amplitude switchings
Interplay between dipole and quadrupole modes of field influence in liquid-crystalline suspensions of ferromagnetic particles
In the framework of continuum theory we study orientational transitions
induced by electric and magnetic fields in ferronematics, i.e., in
liquid-crystalline suspensions of ferromagnetic particles. We have shown that
in a certain electric field range the magnetic field can induce a sequence of
re-entrant orientational transitions in ferronematic layer: nonuniform phase
--- uniform phase --- nonuniform phase. This phenomenon is caused by the
interplay between the dipole (ferromagnetic) and quadrupole (dielectric and
diamagnetic) mechanisms of the field influence on a ferronematic structure. We
have found that these re-entrant Freedericksz transitions exhibit tricritical
behavior, i.e., they can be of the first or the second order. The character of
the transitions depends on a degree of redistribution of magnetic admixture in
the sample exposed to uniform magnetic field (magnetic segregation). We
demonstrate how electric and magnetic fields can change the order of
orientational transitions in ferronematics. We show that electric Freedericksz
transitions in ferronematics subjected to magnetic field have no re-entrant
nature. Tricritical segregation parameters for the transitions induced by
electric or magnetic fields are obtained analytically. We demonstrate the
re-entrant behavior of ferronematic by numerical simulations of the
magnetization and optical phase lag.Comment: 12 pages, 9 figures, to be published in Soft Matte
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