2,562 research outputs found
Thin film instability with thermal noise
We study the effects of stochastic thermal fluctuations on the instability of
the free surface of a flat liquid film upon a solid substrate. These
fluctuations are represented as a standard Brownian motion that can be added to
the deterministic equation for the film thickness within the lubrication
approximation. Here, we consider that while the noise term is white in time, it
is coloured in space. This allows for the introduction of a finite correlation
length in the description of the randomized intermolecular interaction.
Together with the expected spatial periodicity of the flow, we find a
dimensionless parameter, , that accounts for the relative importance of
the spatial correlation. We perform here the linear stability analysis (LSA) of
the film under the influence of both terms, and find the corresponding power
spectra for the amplitudes of the normal modes of the instability. We compare
this theoretical result with the numerical simulations of the complete
non-linear problem, and find a good agreement for early times. For late times,
we find that the stochastic LSA predictions on the dominant wavelength remains
basically valid. We also use the theoretical spectra to fit experimental data
from a nanometric melted copper film, and find the corresponding times of the
evolution as well as the values of the parameter,
Drops with non-circular footprints
In this paper we study the morphology of drops formed on partially wetting
substrates, whose footprint is not circular. This type of drops is a
consequence of the breakup processes occurring in thin films when anisotropic
contact line motions take place. The anisotropy is basically due to hysteresis
effects of the contact angle since some parts of the contact line are wetting,
while others are dewetting. Here, we obtain a peculiar drop shape from the
rupture of a long liquid filament sitting on a solid substrate, and analyze its
shape and contact angles by means of goniometric and refractive techniques. We
also find a non--trivial steady state solution for the drop shape within the
long wave approximation (lubrication theory), and compare most of its features
with experimental data. This solution is presented both in Cartesian and polar
coordinates, whose constants must be determined by a certain group of measured
parameters. Besides, we obtain the dynamics of the drop generation from
numerical simulations of the full Navier--Stokes equation, where we emulate the
hysteretic effects with an appropriate spatial distribution of the static
contact angle over the substrate
Thin films dewetting with phase separation: Dependence of surface tension and Hamaker constant on concentration
We study the instability of a thin film composed of two miscible fluids
(binary fluid) placed on a solid planar surface. We include the fact that both
the free surface and wetting energies depend on the mixture concentration. By
assuming a linear relationship between these energies and both the bulk and
surface concentrations, we analyze their effect on the phase separation of the
constituent fluids. The problem is formulated within the gradient dynamics
formulation applied to the thin film limit of the Cahn-Hilliard Navier-Stokes
equations. The dependence of the free surface energy on concentration leads to
a Marangoni type of effect, while the wetting energy resulting from
fluid--solid interaction between the film and the substrate is described by a
concentration dependent Hamaker constant. The linear stability analysis
uncovers that both monotonous and oscillatory evolution is possible. While our
problem formulation applies to any binary mixture that can be consistently
modeled via the presented approach, a particular interpretation of the results
is provided for the case of liquid metal alloy films on nanoscale. In this
context, we find that rich dynamics is possible, including the evolution that
may lead to formation of drops of the Janus--type as well as of core-shell
configurations
Electroreactivity of isopropanol on platinum in acids studied by DEMS and FTIRS
The reactivity of isopropanol on polycrystalline Pt in acid solutions was investigated using in-situ Fourier transform IR spectroscopy (FTIRS) and on-line differential electrochemical mass spectrometry (DEMS). The electro-oxidation products are acetone and CO2; the former is observed when isopropanol is present in the bulk of the solution, and the latter is produced from strongly adsorbed species. Both bulk and adsorbed isopropanol electro-reduction yield propane. H-D exchange is observed during propane formation when the reaction takes place in a D2O + DCIO4 solution. This observation suggests the formation of adsorbates bonded to the surface through the C ∝ atom of the isopropanol molecule. FTIR spectra of adsorbed species show the presence of -CH3 and -COH groups. The most probable adsorbate structures are (CH3-C-CH3)Pt, (CH3-CH-CH3)Pt and (CH3-COH-CH3)Pt, presumably accompanied by (CH3-CO-CH3)Pt.Instituto de Investigaciones Fisicoquímicas Teóricas y AplicadasFacultad de Ciencias Exacta
Electroreactivity of isopropanol on platinum in acids studied by DEMS and FTIRS
The reactivity of isopropanol on polycrystalline Pt in acid solutions was investigated using in-situ Fourier transform IR spectroscopy (FTIRS) and on-line differential electrochemical mass spectrometry (DEMS). The electro-oxidation products are acetone and CO2; the former is observed when isopropanol is present in the bulk of the solution, and the latter is produced from strongly adsorbed species. Both bulk and adsorbed isopropanol electro-reduction yield propane. H-D exchange is observed during propane formation when the reaction takes place in a D2O + DCIO4 solution. This observation suggests the formation of adsorbates bonded to the surface through the C ∝ atom of the isopropanol molecule. FTIR spectra of adsorbed species show the presence of -CH3 and -COH groups. The most probable adsorbate structures are (CH3-C-CH3)Pt, (CH3-CH-CH3)Pt and (CH3-COH-CH3)Pt, presumably accompanied by (CH3-CO-CH3)Pt.Instituto de Investigaciones Fisicoquímicas Teóricas y AplicadasFacultad de Ciencias Exacta
Crystallographic control of the fabrication of an extremely sophisticated shell surface microornament in the glass scallop Catillopecten
The external surface microornament of the glass scallops Catillopecten natalyae and malyutinae is
made by calcitic spiny projections consisting of a stem that later divides into three equally spaced
and inclined branches (here called aerials). C. natalyae contains larger and smaller aerials, whereas
C. malyutinae only secreted aerials of the second type. A remarkable feature is that aerials within
each type are fairly similar in size and shape and highly co-oriented, thus constituting a most
sophisticated microornament. We demonstrate that aerials are single crystals whose morphology is
strongly controlled by the crystallography, with the stem being parallel to the c-axis of calcite, and
the branches extending along the edges of the {104} calcite rhombohedron. They grow epitaxially
onto the foliated prisms of the outer shell layer. The co-orientation of the prisms explains that of the
aerials. We have developed a model in which every aerial grows within a periostracal pouch. When
this pouch reaches the growth margin, the mantle initiates the production of the aerial. Nevertheless,
later growth of the aerial is remote, i.e. far from the contact with the mantle. We show how such an
extremely sophisticated microornament has a morphology and co-orientation which are determined
by crystal growth.Instituto de Salud Carlos III
Spanish Government CGL2017-85118-P
PID2020-116660GB-I00Unidad Cientifica de Excelencia of the University of Granada UCE-PP2016-05Junta de Andalucia RNM363Ministry of Science, ICT & Future Planning, Republic of Korea 13.1902.21.001
075-15-2020-79
Evolution of the anti-truncated stellar profiles of S0 galaxies since in the SHARDS survey: I - Sample and Methods
The controversy about the origin of the structure of S0--E/S0 galaxies may be
due to the difficulty of comparing surface brightness profiles with different
depths, photometric corrections and PSF effects (almost always ignored). We aim
to quantify the properties of Type-III (anti-truncated) discs in a sample of S0
galaxies at 0.2<z<0.6. In this paper, we present the sample selection and
describe in detail the methods to robustly trace the structure in their
outskirts and correct for PSF effects. We have selected and classified a sample
of 150 quiescent galaxies at 0.2<z<0.6 in the GOODS-N field. We perform a
quantitative structural analysis of 44 S0-E/S0 galaxies. We corrected their
surface brightness profiles for PSF distortions and analysed the biases in the
structural and photometric parameters when the PSF correction is not applied.
Additionally, we have developed Elbow, an automatic statistical method to
determine whether a possible break is significant - or not - and its type and
made it publicly available. We found 14 anti-truncated S0-E/S0 galaxies in the
range 0.2<z<0.6 (~30% of the final sample). This fraction is similar to the
those reported in the local Universe. In our sample, ~25% of the Type-III
breaks observed in PSF-uncorrected profiles are artifacts, and their profiles
turn into a Type I after PSF correction. PSF effects also soften Type-II
profiles. We found that the profiles of Type-I S0 and E/S0 galaxies of our
sample are compatible with the inner profiles of the Type-III, in contrast with
the outer profiles. We have obtained the first robust and reliable sample of 14
anti-truncated S0--E/S0 galaxies beyond the local Universe, in the range
0.2<z<0.6. PSF effects significantly affect the shape of the surface brightness
profiles in galaxy discs even in the case of the narrow PSF of HST/ACS images,
so future studies on the subject should make an effort to correct them.Comment: Accepted for publishing in Astronomy & Astrophysics. 75 pages, 57
figure
Energetic metabolism in fasting sheep: regularization of metabolic profile by treatment with oral glucose, with prior handling of gastric groove
The objective of this research was to evaluate a possible corrective measure against negative metabolic states, as occurs in the advanced stage of gestation in ewes, and that sometimes produces a disease called pregnancy toxaemia. In the present research, we found that the joint administration of i.v. lysine-vasopressin (0.08 IU/kg body weight, BW) and an oral glucose solution (50 g) produces an increase in blood glucose, which persists for some time (up to 6 h); therefore, it could be used in the treatment of pregnancy toxaemia. This therapy is based on the fact that lysine-vasopressin induces gastric groove closure in adult ruminants, enabling orally administered glucose to reach the abomasum directly, from where it rapidly passes into the intestine and is immediately absorbed. We can say that the tested treatment causes a significant increase in blood glucose in ewes affected by toxaemia caused by fasting, which, although less marked than conventional therapy with intravenous drip glucose, remains longer, regularizing other parameters indicative of energy metabolism in fasting ewes
Spectral problem for the complex mKdV equation: singular manifold method and Lie symmetries
This article addresses the study of the complex version of the modified
Korteweg-de Vries equation using two different approaches. Firstly, the
singular manifold method is applied in order to obtain the associated spectral
problem, binary Darboux transformations and -functions. The second part
concerns the identification of the classical Lie symmetries for the spectral
problem. The similarity reductions associated to these symmetries allow us to
derive the reduced spectral problems and first integrals for the ordinary
differential equations arising from such reductions.Comment: This article is intended to be published in the special issue
dedicated to Prof. Decio Levi (in Open Communications in Nonlinear
Mathematical Physics
- …