362 research outputs found
Dilational rheology and relaxation properties of the adsorption layers of electrostatic complexes between Eudragit RS and chitosan sulfate at the methylene chloride-water interface.
Convection in a mushy-layer along a heated wall
Motivated by the mushy zones of sea ice, volcanoes, and icy moons of the
outer solar system, we perform a theoretical and numerical study of
boundary-layer convection along a vertical heated wall in a bounded ideal mushy
region. The mush is comprised of a porous and reactive binary alloy with a
mixture of saline liquid in a solid matrix, and is studied in the near-eutectic
approximation. Here we demonstrate the existence of four regions and study
their behavior asymptotically. Starting from the bottom of the wall, the four
regions are (i) an isotropic corner region; (ii) a buoyancy dominated vertical
boundary layer; (iii) an isotropic connection region; and (iv) a horizontal
boundary layer at the top boundary with strong gradients of pressure and
buoyancy. Scalings from numerical simulations are consistent with the
theoretical predictions. Close to the heated wall, the convection in the mushy
layer is similar to a rising buoyant plume abruptly stopped at the top, leading
to increased pressure and temperature in the upper region, whose impact is
discussed as an efficient melting mechanism
Vibrational Instability of Metal-Poor Low-Mass Main-Sequence Stars
We find that low-degree low-order g-modes become unstable in metal-poor
low-mass stars due to the -mechanism of the pp-chain. Since the
outer convection zone of these stars is limited only to the very outer layers,
the uncertainty in the treatment of convection does not affect the result
significantly. The decrease in metallicity leads to decrease in opacity and
hence increase in luminosity of a star. This makes the star compact and results
in decrease in the density contrast, which is favorable to the
-mechanism instability. We find also instability for high order
g-modes of metal-poor low-mass stars by the convective blocking mechanism.
Since the effective temperature and the luminosity of metal-poor stars are
significantly higher than those of Pop I stars, the stars showing
Dor-type pulsation are substantially less massive than in the case of Pop I
stars. We demonstrate that those modes are unstable for about
stars in the metal-poor case.Comment: 4 pages, 4 figures, To be published in Astrophysics and Space Science
Proceedings series (ASSP). Proceedings of the "20th Stellar Pulsation
Conference Series: Impact of new instrumentation and new insights in stellar
pulsations", 5-9 September 2011, Granada, Spai
Si-HPMC hydrogel combining CaCO3 microparticles as hybrid biomaterial for bone and cartilage tissue engineering
National audienc
Sterol composition of three marine sponge species from the genus Cinachyrella
The hitherto undescribed sterol composition of three marine sponge species belonging to the genus #Cynachyrella are reported : #C. alloclada and #C. kukenthali from the Senegalese coast, at two different depths, and C. aff. #schultezei from the lagoon of Nouméa, New Caledonia. (D'après résumé d'auteur
Seismology of beta Cephei stars: differentially-rotating models for interpreting the oscillation spectrum of nu-Eridani
A method for the asteroseismic analysis of beta Cephei stars is presented and
applied to the star nu Eridani. The method is based on the analysis of
rotational splittings, and their asymmetries using differentially-rotating
asteroseismic models. Models with masses around 7.13 M_sun, and ages around
14.9 Myr, were found to fit better 10 of the 14 observed frequencies, which
were identified as the fundamental radial mode and the three L=1 triplets g, p,
and p. The splittings and aymmetries found for these modes recover those
provided in the literature, except for p. For this last mode, all its
non-axysimmetric components are predicted by the models. Moreover, opposite
signs of the observed and predicted splitting asymmetries are found. If
identification is confirmed, this can be a very interesting source of
information about the internal rotation profile, in particular in the outer
regions of the star.
In general, the seismic models which include a description for shellular
rotation yield slightly better results as compared with those given by
uniformly-rotating models. Furthermore, we show that asymmetries are quite
dependent on the overshooting of the convective core, which make the present
technique suitable for testing the theories describing the angular momentum
redistribution and chemical mixing due to rotationally-induced turbulence.Comment: 11 pages, 9 figures, 8 tables. ApJ (in press
Pulsations in M dwarf stars
We present the results of the first theoretical non-radial non-adiabatic
pulsational study of M dwarf stellar models with masses in the range 0.1 to
0.5M_solar. We find the fundamental radial mode to be unstable due to an
\epsilon mechanism caused by deuterium (D-) burning for the young 0.1 and
0.2M_solar models, by non-equilibrium He^3 burning for the 0.2 and 0.25M_solar
models of 10^4Myr, and by a flux blocking mechanism for the partially
convective 0.4 and 0.5M_solar models once they reach the age of 500Myr. The
periods of the overstable modes excited by the D-burning are in the range 4.2
to 5.2h for the 0.1M_solar models and is of order 8.4h for the 0.2M_solar
models. The periods of the modes excited by He^3 burning and flux blocking are
in the range 23 to 40min. The more massive and oldest models are more promising
for the observational detection of pulsations, as their ratio of instability
e-folding time to age is more favourable.Comment: 5 pages, 4 figures, 2 tables. Accepted for publication in MNRAS
Letters on 2011 October 11 Version 2 is the accepted manuscript with changes
in boldfac
Dilational viscoelasticity and relaxation properties of interfacial electrostatic complexes between oppositely charged hydrophobic and hydrophilic polyelectrolytes
Strongly adsorbing hydrophobic cationic polyelectrolyte, Eudragit RS, containing approximately 2.5 mol% of pendent hydrophilic trimethylammonium (TMA) groups irreversibly adsorbs from its methylene chloride (MCl) solution at the MCl/water interface and forms solid-like adsorption layers (ALs). Submitted to periodic dilational deformations with the standard radial frequency omega(0)=0.63 rad/s, these ALs exhibit relatively high dilational storage modulus E\u27 approximately 20 mN/m and practically zero loss modulus E\u27\u27 at the bulk concentration C(Eud)=4 x 10(-3)g/L. The frequency scanning of these ALs in the diapason omega=0.01-0.63rad/s and the approximation of the experimental dependences E\u27(omega) and E\u27\u27(omega) by two relaxation times rheological model makes it possible to estimate the crossing frequency of these ALs determined from the condition E\u27(omega(c))=E\u27\u27(omega(c)) as omega(c) approximately 5 x 10(-4)rad/s. Upon dissolving the hydrophilic anionic polyelectrolyte, chitosan sulfate (ChS), in the water phase (C(ChS)=3 x 10(-2)g/L) the electrostatic interpolyelectrolyte complexes form at the MCl/water interface. The elasticity moduli E\u27 and E\u27\u27 of these mixed AL did not undergo remarkable variations, but the crossing frequency is sharply increased by approximately 10 times becoming equal to omega(c) congruent with 3 x 10(-3)rad/s. The increase of omega(c) certifies for the liquefaction of mixed Eudragit RS/ChS adsorption layers. A remarkable decrease of the storage modulus down to E\u27=8 mN/m and simultaneous increase of the crossing frequency up to omega(c) congruent with 10(-2)rad/s occurs upon increasing the concentrations of both components, Eudragit RS and ChS, up to 0.1g/L. The liquefaction effect in the mixed ALs of oppositely charged polyelectrolytes was explained on the basis of the proposed relaxation mechanism. The effect of the liquefaction of adsorption layers of strongly adsorbing hydrophobic polyelectrolytes by formation of interpolyelectrolyte complexes with hydrophilic polyelectrolytes must be taken into account in the production of nano-capsules and nano-fibers
Expression and function of aquaporins in human skin: Is aquaporin-3 just a glycerol transporter?
AbstractThe aquaporins (AQPs) are a family of transmembrane proteins forming water channels. In mammals, water transport through AQPs is important in kidney and other tissues involved in water transport. Some AQPs (aquaglyceroporins) also exhibit glycerol and urea permeability. Skin is the limiting tissue of the body and within skin, the stratum corneum (SC) of the epidermis is the limiting barrier to water loss by evaporation. The aquaglyceroporin AQP3 is abundantly expressed in keratinocytes of mammalian skin epidermis. Mice lacking AQP3 have dry skin and reduced SC hydration. Interestingly, however, results suggested that impaired glycerol, rather than water transport was responsible for this phenotype. In the present work, we examined the overall expression of AQPs in cells from human skin and we reviewed data on the functional role of AQPs in skin, particularly in the epidermis. By RT-PCR on primary cell cultures, we found that up to 6 different AQPs (AQP1, 3, 5, 7, 9 and 10) may be selectively expressed in various cells from human skin. AQP1, 5 are strictly water channels. But in keratinocytes, the major cell type of the epidermis, only the aquaglyceroporins AQP3, 10 were found. To understand the role of aquaglyceroporins in skin, we examined the relevance to human skin of the conclusion, from studies on mice, that skin AQP3 is only important for glycerol transport. In particular, we find a correlation between the absence of AQP3 and intercellular edema in the epidermis in two different experimental models: eczema and hyperplastic epidermis. In conclusion, we suggest that in addition to glycerol, AQP3 may be important for water transport and hydration in human skin epidermis
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