137 research outputs found
Wetting and Growth Behaviors in Adsorbed Systems with Long-Range Forces
The growth and possible wetting behaviors of an adsorbed film are studied employing a solid-on-solid model in the presence of a hard wall and external potential V(h) which is of long range. The model is analyzed with the use of position-space renormalization-group methods within the Migdal approximation. The existence of wetting transitions and their nature depends on the asymptotic behavior of V(h) at large distances. We find that critical wetting cannot take place in this model. From what is known of V(h), we conclude that wetting can be observed only along the gas-liquid phase boundary; however, first-order transitions between thin and thick films, which may be experimentally difficult to distinguish from wetting, can be observed along any phase boundary. The nature of the global phase diagram depends on the form of V(h) and several general behaviors are presented. In particular, in the layering subregime we find that the limit of layering critical points is indeed the bulk roughening temperature as had been suggested by de Oliveira and Griffiths. The scaling of these layering critical points is given explicitly
Universal Long-time Behavior of Nuclear Spin Decays in a Solid
Magnetic resonance studies of nuclear spins in solids are exceptionally well
suited to probe the limits of statistical physics. We report experimental
results indicating that isolated macroscopic systems of interacting nuclear
spins possess the following fundamental property: spin decays that start from
different initial configurations quickly evolve towards the same long-time
behavior. This long-time behavior is characterized by the shortest ballistic
microscopic timescale of the system and therefore falls outside of the validity
range for conventional approximations of statistical physics. We find that the
nuclear free induction decay and different solid echoes in hyperpolarized solid
xenon all exhibit sinusoidally modulated exponential long-time behavior
characterized by identical time constants. This universality was previously
predicted on the basis of analogy with resonances in classical chaotic systems.Comment: 4 pages main paper + 3 pages supporting material, 3 figure
Bose-Einstein Condensation at a Helium Surface
Path Integral Monte Carlo was used to calculate the Bose-Einstein condensate
fraction at the surface of a helium film at , as a function of
density. Moving from the center of the slab to the surface, the condensate
fraction was found to initially increase with decreasing density to a maximum
value of 0.9 before decreasing. Long wavelength density correlations were
observed in the static structure factor at the surface of the slab. Finally, a
surface dispersion relation was calculated from imaginary-time density-density
correlations.Comment: 8 pages, 5 figure
Bunching Transitions on Vicinal Surfaces and Quantum N-mers
We study vicinal crystal surfaces with the terrace-step-kink model on a
discrete lattice. Including both a short-ranged attractive interaction and a
long-ranged repulsive interaction arising from elastic forces, we discover a
series of phases in which steps coalesce into bunches of n steps each. The
value of n varies with temperature and the ratio of short to long range
interaction strengths. We propose that the bunch phases have been observed in
very recent experiments on Si surfaces. Within the context of a mapping of the
model to a system of bosons on a 1D lattice, the bunch phases appear as quantum
n-mers.Comment: 5 pages, RevTex; to appear in Phys. Rev. Let
Adsorption in non interconnected pores open at one or at both ends: A reconsideration of the origin of the hysteresis phenomenon
We report on an experimental study of adsorption isotherme of nitrogen onto
porous silicon with non interconnected pores open at one or at both ends in
order to check for the first time the old (1938) but always current idea based
on Cohan's description which suggests that the adsorption of gaz should occur
reversibly in the first case and irreversibly in the second one. Hysteresis
loops, the shape of which is usually associated to interconnections in porous
media, are observed whether the pores are open at one or at both ends in
contradiction with Cohan's model.Comment: 5 pages, 4 EPS figure
High resolution carotid black-blood 3T MR with parallel imaging and dedicated 4-channel surface coils
Cooperation, Norms, and Revolutions: A Unified Game-Theoretical Approach
Cooperation is of utmost importance to society as a whole, but is often
challenged by individual self-interests. While game theory has studied this
problem extensively, there is little work on interactions within and across
groups with different preferences or beliefs. Yet, people from different social
or cultural backgrounds often meet and interact. This can yield conflict, since
behavior that is considered cooperative by one population might be perceived as
non-cooperative from the viewpoint of another.
To understand the dynamics and outcome of the competitive interactions within
and between groups, we study game-dynamical replicator equations for multiple
populations with incompatible interests and different power (be this due to
different population sizes, material resources, social capital, or other
factors). These equations allow us to address various important questions: For
example, can cooperation in the prisoner's dilemma be promoted, when two
interacting groups have different preferences? Under what conditions can costly
punishment, or other mechanisms, foster the evolution of norms? When does
cooperation fail, leading to antagonistic behavior, conflict, or even
revolutions? And what incentives are needed to reach peaceful agreements
between groups with conflicting interests?
Our detailed quantitative analysis reveals a large variety of interesting
results, which are relevant for society, law and economics, and have
implications for the evolution of language and culture as well
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