12,016 research outputs found
To Wet or Not to Wet? Dispersion Forces Tip the Balance for Water Ice on Metals
Despite widespread discussion, the role of van der Waals dispersion forces in wetting remains unclear. Here we show that nonlocal correlations contribute substantially to the water-metal bond and that this is an important factor in governing the relative stabilities of wetting layers and 3D bulk ice. Because of the greater polarizability of the substrate metal atoms, nonlocal correlations between water and the metal exceed those between water molecules within ice. This sheds light on a long-standing problem, wherein common density functional theory exchange-correlation functionals incorrectly predict that none of the low temperature experimentally characterized icelike wetting layers are thermodynamically stable
Unemployment duration among immigrants and natives: unobserved heterogeneity in a multi-spell duration model
This paper studies whether the unemployment dynamics of immigrants differ from those of
natives, paying special attention to the impact of accounting for unobserved heterogeneity
among individuals. Using a large administrative data set for Spain, we estimate multiple-spell
discrete duration models which disentangle unobserved heterogeneity from duration
dependence. Specifically, we estimate random effects models assuming that the distribution of
the effects is discrete with finite support, and fixed effects models in which the distribution of the
unobserved effects is left unrestricted. Our results show the importance of accounting for
unobserved heterogeneity and that mistaken policy implications can be derived due to improper
treatment of unmeasured variables. We find that lack of control for unobserved heterogeneity
leads to the conclusion that immigrant males have a higher probability of leaving unemployment
than natives and that the negative effect of unemployment benefits for immigrants lasts longer
than for natives. Nonetheless, the estimates which do control for unobserved heterogeneity
show the opposite results
The Five-Loop Four-Point Amplitude of N=4 super-Yang-Mills Theory
Using the method of maximal cuts, we construct the complete D-dimensional
integrand of the five-loop four-point amplitude of N = 4 super-Yang-Mills
theory, including nonplanar contributions. In the critical dimension where this
amplitude becomes ultraviolet divergent, we present a compact explicit
expression for the nonvanishing ultraviolet divergence in terms of three vacuum
integrals. This construction provides a crucial step towards obtaining the
corresponding amplitude of N = 8 supergravity useful for resolving the general
ultraviolet behavior of supergravity theories.Comment: 5 pages, 4 figures, RevTex. Ancillary file included. v2 minor
corrections, corrected references and overall phase in eq. (5), matching
journal versio
Kardar-Parisi-Zhang growth on one-dimensional decreasing substrates
Recent experimental works on one-dimensional (1D) circular
Kardar-Parisi-Zhang (KPZ) systems whose radii decrease in time have reported
controversial conclusions about the statistics of their interfaces. Motivated
by this, we investigate here several 1D KPZ models on substrates whose size
changes in time as , focusing on the case . From
extensive numerical simulations, we show that for there exists a
transient regime in which the statistics is consistent with that of flat KPZ
systems (the case), for both . Actually,
for a given model, and , we observe that a difference between
ingrowing () systems arises only at long
times (), when the expanding surfaces cross over to
the statistics of curved KPZ systems, whereas the shrinking ones become
completely correlated. A generalization of the Family-Vicsek scaling for the
roughness of ingrowing interfaces is presented. Our results demonstrate that a
transient flat statistics is a general feature of systems starting with large
initial sizes, regardless their curvature. This is consistent with their recent
observation in ingrowing turbulent liquid crystal interfaces, but it is in
contrast with the apparent observation of curved statistics in colloidal
deposition at the edge of evaporating drops. A possible explanation for this
last result, as a consequence of the very small number of monolayers analyzed
in this experiment, is given. This is illustrated in a competitive growth model
presenting a few-monolayer transient and an asymptotic behavior consistent,
respectively, with the curved and flat statistics.Comment: 5 pages, 3 figure
Width and extremal height distributions of fluctuating interfaces with window boundary conditions
We present a detailed study of squared local roughness (SLRDs) and local
extremal height distributions (LEHDs), calculated in windows of lateral size
, for interfaces in several universality classes, in substrate dimensions
and . We show that their cumulants follow a Family-Vicsek
type scaling, and, at early times, when ( is the correlation
length), the rescaled SLRDs are given by log-normal distributions, with their
th cumulant scaling as . This give rise to an
interesting temporal scaling for such cumulants , with . This scaling is analytically
proved for the Edwards-Wilkinson (EW) and Random Deposition interfaces, and
numerically confirmed for other classes. In general, it is featured by small
corrections and, thus, it yields exponents 's (and, consequently,
, and ) in nice agreement with their respective universality
class. Thus, it is an useful framework for numerical and experimental
investigations, where it is, usually, hard to estimate the dynamic and
mainly the (global) roughness exponents. The stationary (for ) SLRDs and LEHDs of Kardar-Parisi-Zhang (KPZ) class are also investigated
and, for some models, strong finite-size corrections are found. However, we
demonstrate that good evidences of their universality can be obtained through
successive extrapolations of their cumulant ratios for long times and large
's. We also show that SLRDs and LEHDs are the same for flat and curved KPZ
interfaces.Comment: 11 pages, 10 figures, 4 table
Localized Dispersive States in Nonlinear Coupled Mode Equations for Light Propagation in Fiber Bragg Gratings.
Dispersion effects induce new instabilities and dynamics in the weakly nonlinear description of light propagation in fiber Bragg gratings. A new family of dispersive localized pulses that propagate with the group velocity is numerically found, and its stability is also analyzed. The unavoidable different asymptotic order of transport and dispersion effects plays a crucial role in the determination of these localized states. These results are also interesting from the point of view of general pattern formation since this asymptotic imbalance is a generic situation in any transport-dominated (i.e., nonzero group velocity) spatially extended system
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