1,976 research outputs found
Scale-dependent rigidity of polymer-ornamented membranes
We study the fluctuation spectrum of fluid membranes carrying grafted
polymers. Contrary to usual descriptions, we find that the modifications
induced by the polymers cannot be reduced to the renormalization of the
membrane bending rigidity. Instead we show that the ornamented membrane
exhibits a scale-dependent elastic modulus that we evaluate. In ornamented
lamellar stacks, we further show that this leads to a modification of the
Caille parameter characterizing the power-law singularities of the Bragg peaks.Comment: 4 pages, 2 figure
Co-non-solvency: Mean-field polymer theory does not describe polymer collapse transition in a mixture of two competing good solvents
Smart polymers are a modern class of polymeric materials that often exhibit
unpredictable behavior in mixtures of solvents. One such phenomenon is
co-non-solvency. Co-non-solvency occurs when two (perfectly) miscible and
competing good solvents, for a given polymer, are mixed together. As a result,
the same polymer collapses into a compact globule within intermediate mixing
ratios. More interestingly, polymer collapses when the solvent quality remains
good and even gets increasingly better by the addition of the better cosolvent.
This is a puzzling phenomenon that is driven by strong local concentration
fluctuations. Because of the discrete particle based nature of the
interactions, Flory-Huggins type mean field arguments become unsuitable. In
this work, we extend the analysis of the co-non-solvency effect presented
earlier [Nature Communications 5, 4882 (2014)]. We explain why co-non-solvency
is a generic phenomenon that can be understood by the thermodynamic treatment
of the competitive displacement of (co)solvent components. This competition can
result in a polymer collapse upon improvement of the solvent quality. Specific
chemical details are not required to understand these complex conformational
transitions. Therefore, a broad range of polymers are expected to exhibit
similar reentrant coil-globule-coil transitions in competing good solvents
Measuring the importance of the uniform nonsynchronization hypothesis
In this paper we critically reappraise some measures of the importance of time-dependent price setting rules and propose an alternative way to gauge the significance of this type of price setting behaviour. The merits of the proposed measure are highlighted in an application using micro-data. Our results suggest that a large proportion of price trajectories may be compatible with simple time-dependent price setting mechanisms but the strength of this evidence very much depends on the way that is used to evaluate the importance of this type of behaviour. JEL Classification: D40, E31, L11perfect synchronization, Time-dependent price setting models, uniform staggering
Time or state dependent price setting rules? Evidence from Portuguese micro data
In this paper we analyse the ability of time and state dependent price setting rules to explain durations of price spells or the probability of changing prices. Our results suggest that simple time dependent models cannot be seen as providing a reasonable approximation to the data and that state dependent models are required to fully characterise the price setting behaviour of Portuguese firms. Inflation, the level of economic activity and the magnitude of the last price change emerge as relevant variables affecting the probability of changing prices. Moreover, it is seen that the impact differs for negative and positive values of these covariates. JEL Classification: C41, D40, E31CPI data, Hazard functions, inflation
Can adding oil control domain formation in binary amphiphile bilayers?
Bilayers formed of two species of amphiphile of different chain lengths may
segregate into thinner and thicker domains composed predominantly of the
respective species. Using a coarse-grained mean-field model, we investigate how
mixing oil with the amphiphiles affects the structure and thickness of the
bilayer at and on either side of the boundary between two neighbouring domains.
In particular, we find that oil molecules whose chain length is close to that
of the shorter amphiphiles segregate to the thicker domain. This smooths the
surface of the hydrophobic bilayer core on this side of the boundary, reducing
its area and curvature and their associated free-energy penalties. The
smoothing effect is weaker for oil molecules that are shorter or longer than
this optimum value: short molecules spread evenly through the bilayer, while
long molecules swell the thicker domain, increasing the surface area and
curvature of the bilayer core in the interfacial region. Our results show that
adding an appropriate oil could make the formation of domain boundaries more or
less favourable, raising the possibility of controlling the domain size
distribution.Comment: 18 pages including 5 figure
Can amphiphile architecture directly control vesicle size?
Bilayer membranes self-assembled from simple amphiphiles in solution always
have a planar ground-state shape. This is a consequence of several internal
relaxation mechanisms of the membrane and prevents the straightforward control
of vesicle size. Here, we show that this principle can be circumvented and that
direct size control by molecular design is a realistic possibility. Using
coarse-grained calculations, we design tetrablock copolymers that form
membranes with a preferred curvature, and demonstrate how to form
low-polydispersity vesicles while suppressing micellization.Comment: 4 pages, 4 figures. Version 2: Calculations performed for a fuller
range of parameters, accepted for publication in Physical Review Letter
Why are some prices stickier than others? Firm-data evidence on price adjustment lags
Infrequent price changes at the firm level are now well documented in the literature. However, a number of issues remain partly unaddressed. This paper contributes to the literature on price stickiness by investigating the lags of price adjustments to different types of shocks. We find that adjustment lags to cost and demand shocks vary with firm characteristics, namely the firm’s cost structure, the type of pricing policy, and the type of good. We also document that firms react asymmetrically to demand and cost shocks, as well as to positive and negative shocks, and that the degree and direction of the asymmetry varies across firms. JEL Classification: C41, D40, E31Firm heterogeneity, Panel-ordered probit, real rigidities, survey data
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