257 research outputs found
Correlation-function structure in square-gradient models of the liquid-gas interface: Exact results and reliable approximations
In a recent article, we described how the microscopic structure of density-density correlations in the fluid interfacial region, for systems with short-ranged forces, can be understood by considering the resonances of the local structure factor occurring at specific parallel wave vectors q [Nat. Phys. 15, 287 (2019)]. Here we investigate
this further by comparing approximations for the local structure factor and pair correlation function against three new examples of analytically solvable models within square-gradient theory. Our analysis further demonstrates that these approximations describe the pair correlation function and structure factor across the whole spectrum of
wave vectors, encapsulating the crossover from the Goldstone mode divergence (at small q) to bulklike behavior (at larger q). As shown, these approximations are exact for some square-gradient model potentials and never more than a few percent inaccurate for the others. Additionally, we show that they describe very accurately the correlation function structure for a model describing an interface near a tricritical point. In this case, there are no analytical solutions for the correlation functions, but the approximations are nearly indistinguishable from the numerical solutions of the Ornstein-Zernike equation.A.O.P. acknowledges the EPSRC, UK, for Grant No. EP/L020564/1 (Multiscale Analysis of Complex Interfacial Phenomena). C.R. acknowledges the support of Grant No. PGC2018-096606-B-I00 (MCIU/AEI/FEDER, UE)
Microscopic determination of correlations in the fluid interfacial region in the presence of liquid-gas asymmetry
In a recent article, we showed how the properties of the density-density correlation function and its integral,
the local structure factor, in the fluid interfacial region, in systems with short-ranged forces, can be understood
microscopically by considering the resonances of the local structure factor [A. O. Parry and C. Rascón, Nat.
Phys. 15, 287 (2019)]. Here, we illustrate, using mean-field square-gradient theory and the more microscopic
Sullivan density functional model, and how this approach generalizes when there is liquid-gas asymmetry, i.e.,
when the bulk correlation lengths of the coexisting liquid and gas phases are different. In particular, we are
able to express the correlation function exactly as a simple average of contributions arising from two effective
Ising-symmetric systems referred to as the symmetric gas and symmetric liquid. When combined with our earlier
results, this generates analytical approximations for the correlation function and the local structure factor, which
are near indistinguishable from the numerical solution to the Ornstein-Zernike equations over the whole range of
wave vectors. Our results highlight how asymmetry affects the correlation function structure and describes the
crossover from a long-ranged Goldstone mode to short-ranged properties determined by the local density as the
wave vector increases.A.O.P. acknowledges the EPSRC, UK for Grant No.
EP/L020564/1 (multiscale analysis of complex interfacial
phenomena). C.R. acknowledges the support from Grant No.
PGC2018-096606-B-I00 (MCIU/AEI/FEDER, UE)
Capillary contact angle in a completely wet groove
We consider the phase equilibria of a fluid confined in a deep capillary groove of width L with identical side walls and a bottom made of a different material. All walls are completely wet by the liquid. Using density functional theory and interfacial models, we show that the meniscus separating liquid and gas phases at two phase capillary coexistence meets the bottom capped end of the groove at a capillary contact angle thetacap(L) which depends on the difference between the Hamaker constants. If the bottom wall has a weaker wall-fluid attraction than the side walls, then thetacap>0 even though all the isolated walls are themselves completely wet. This alters the capillary condensation transition which is now first order; this would be continuous in a capped capillary made wholly of either type of material. We show that the capillary contact angle thetacap(L) vanishes in two limits, corresponding to different capillary wetting transitions. These occur as the width (i) becomes macroscopically large, and (ii) is reduced to a microscopic value determined by the difference in Hamaker constants. This second wetting transition is characterized by large scale fluctuations and essential critical singularities arising from marginal interfacial interactions.A. O. P. wishes to thank the support of the EPSRC UK for Grant No. EP/J009636/1. A. M. thanks the Czech Science Foundation for Grant No. 13-09914S. C. R. acknowledges support from Grants No. FIS2010-22047-C05 and No. MODELICO
¿Es posible la clasificación de individuos perinatales a partir de caracteres objetivos?
X Congreso Nacional de Paleopatología. Univesidad Autónoma de Madrid, septiembre de 200
Estado, frontera y ciudadanía. El Septentrión entre el Antiguo Regimen y la formación de la nación mexicana
The study explores the specific historical circumstances in which
the Mexican state of Chihuahua was created and became integrated into
the Mexican federation. Usually, historiography has considered 1821 as a
starting point for the integration of this state to the Mexican nation
when Independence was proclaimed in this country. The same happens with
the independence studies that generally start in 1810 when the uprising
of insurgent forces began. Thus, those temporal arcs form real
historiographical boundaries which are difficult to cross. The author
argues that in order to achieve a deeper analysis of the creation of the
state of Chihuahua, we need to trespass those boundaries. For this
purpose, he explores a series of events which took already place during
the Spanish colonial rule. He provides an in-depth study of two
fundamental events that marked the evolution of the Northern part of
present-day of Mexico. Both events originated in Spain in 1767: the
Jesuit expulsion and the Sierra Morena colonization project in Spain
that was implemented in the internal provinces of Northern Mexico.
He concludes that the new ethos of rationality does not begin at the
declaration of independence as a new nation project definition; its
ideological foundation had already been defined in the old colonial
regime. In this manner, there is continuity between the expressions of
the old on the Hapsburg model and the new, based in Bourbon impositions,
and they were passed down to the new Republican regime.Political Culture and National Identit
Interfacial Structural Changes and Singularities in Non-Planar Geometries
We consider phase coexistence and criticality in a thin-film Ising magnet
with opposing surface fields and non-planar (corrugated) walls. We show that
the loss of translational invariance has a strong and unexpected non-linear
influence on the interface structure and phase diagram. We identify 4
non-thermodynamic singularities where there is a qualitative change in the
interface shape. In addition, we establish that at the finite-size critical
point, the singularity in the interface shape is characterized by two distint
critical exponents in contrast to the planar case (which is characterised by
one). Similar effects should be observed for prewetting at a corrugated
substrate. Analogy is made with the behaviour of a non-linear forced oscillator
showing chaotic dynamics.Comment: 13 pages, 3 figure
Geometry dominated fluid adsorption on sculptured substrates
Experimental methods allow the shape and chemical composition of solid
surfaces to be controlled at a mesoscopic level. Exposing such structured
substrates to a gas close to coexistence with its liquid can produce quite
distinct adsorption characteristics compared to that occuring for planar
systems, which may well play an important role in developing technologies such
as super-repellent surfaces or micro-fluidics. Recent studies have concentrated
on adsorption of liquids at rough and heterogeneous substrates and the
characterisation of nanoscopic liquid films. However, the fundamental effect of
geometry has hardly been addressed. Here we show that varying the shape of the
substrate can exert a profound influence on the adsorption isotherms allowing
us to smoothly connect wetting and capillary condensation through a number of
novel and distinct examples of fluid interfacial phenomena. This opens the
possibility of tailoring the adsorption properties of solid substrates by
sculpturing their surface shape.Comment: 6 pages, 4 figure
Quality of life associated with treatment adherence in patients with type 2 diabetes: a cross-sectional study
<p>Abstract</p> <p>Background</p> <p>Despite certain contradictions, an association has been identified between adherence to drug treatment and the quality of life in patients with type 2 diabetes. The contradictions observed emphasize the importance of using different methods to measure treatment adherence, or the association of psychological precursors of adherence with quality of life. For this reason, we have used an indirect method to measure adherence (pill count), as well as two adherence behaviour precursors (attitude and knowledge), to assess the association between adherence and the quality of life in type 2 diabetes patients.</p> <p>Methods</p> <p>A cross-sectional comparative study on a random sample of 238 type 2 diabetic patients was carried out over one year in four family medicine units of the Mexican Institute of Social Security (IMSS) in Aguascalientes, Mexico. Treatment adherence was measured using the indirect method of pill count to assess adherence behaviour, obtaining information at two home visits. In the first we recorded the medicine prescribed and in the second, we counted the medicine remaining to determine the proportion of the medicine taken. We also assessed two adherence behaviour precursors: the patients' knowledge regarding their medical prescription measured through a structured questionnaire; and attitudes to treatment adherence using a Likert scale. Quality of life was measured through the WHOQOL-100 (the WHO Quality of Life questionnaire). Information concerning both knowledge and attitude was obtained through interviews with the patients. A multiple linear regression model was constructed to establish the relationship between each quality of life domain and the variables related to adherence, controlling for covariates.</p> <p>Results</p> <p>There was no association between quality of life and treatment adherence behaviour. However, the combination of strong knowledge and a positive attitude was associated with five of the six quality of life domains.</p> <p>Conclusion</p> <p>The results suggest that it is important to explore psychological precursors of treatment adherence behaviour in type 2 diabetic patients. Indeed, we consider that it will be useful to carry out interventions that change negative attitudes towards treatment adherence and that promote medical prescription knowledge, which may help to improve the quality of life of such patients.</p
Ion size effects on the electrokinetics of salt-free concentrated suspensions in ac fields
We analyze the influence of finite ion size effects in the response of a
salt-free concentrated suspension of spherical particles to an oscillating
electric field. Salt-free suspensions are just composed of charged colloidal
particles and the added counterions released by the particles to the solution,
that counterbalance their surface charge. In the frequency domain, we study the
dynamic electrophoretic mobility of the particles and the dielectric response
of the suspension. We find that the Maxwell-Wagner-O'Konski process associated
with the counterions condensation layer, is enhanced for moderate to high
particle charges, yielding an increment of the mobility for such frequencies.
We also find that the increment of the mobility grows with ion size and
particle charge. All these facts show the importance of including ion size
effects in any extension attempting to improve standard electrokinetic models.Comment: J. Colloid Interface Sci., in press, 13 pages, 9 figure
Stability of Colloidal Quasicrystals
Freezing of charge-stabilized colloidal suspensions and relative stabilities
of crystals and quasicrystals are studied using thermodynamic perturbation
theory. Macroion interactions are modelled by effective pair potentials
combining electrostatic repulsion with polymer-depletion or van der Waals
attraction. Comparing free energies -- counterion terms included -- for
elementary crystals and rational approximants to icosahedral quasicrystals,
parameters are identified for which one-component quasicrystals are stabilized
by a compromise between packing entropy and cohesive energy.Comment: 6 pages, 4 figure
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