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

Analytical Investigation of Innovation Dynamics Considering Stochasticity in the Evaluation of Fitness

We investigate a selection-mutation model for the dynamics of technological innovation,a special case of reaction-diffusion equations. Although mutations are assumed to increase the variety of technologies, not their average success ("fitness"), they are an essential prerequisite for innovation. Together with a selection of above-average technologies due to imitation behavior, they are the "driving force" for the continuous increase in fitness. We will give analytical solutions for the probability distribution of technologies for special cases and in the limit of large times. The selection dynamics is modelled by a "proportional imitation" of better technologies. However, the assessment of a technology's fitness may be imperfect and, therefore, vary stochastically. We will derive conditions, under which wrong assessment of fitness can accelerate the innovation dynamics, as it has been found in some surprising numerical investigations.Comment: For related work see http://www.helbing.or

Osmotic pressure of matter and vacuum energy

The walls of the box which contains matter represent a membrane that allows the relativistic quantum vacuum to pass but not matter. That is why the pressure of matter in the box may be considered as the analog of the osmotic pressure. However, we demonstrate that the osmotic pressure of matter is modified due to interaction of matter with vacuum. This interaction induces the nonzero negative vacuum pressure inside the box, as a result the measured osmotic pressure becomes smaller than the matter pressure. As distinct from the Casimir effect, this induced vacuum pressure is the bulk effect and does not depend on the size of the box. This effect dominates in the thermodynamic limit of the infinite volume of the box. Analog of this effect has been observed in the dilute solution of 3He in liquid 4He, where the superfluid 4He plays the role of the non-relativistic quantum vacuum, and 3He atoms play the role of matter.Comment: 5 pages, 1 figure, JETP Lett. style, version accepted in JETP Letter

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 $T=0.77 K$, 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

Surface Region of Superfluid Helium as an Inhomogeneous Bose-Condensed Gas

We present arguments that the low density surface region of self-bounded superfluid $^4$He systems is an inhomogeneous dilute Bose gas, with almost all of the atoms occupying the same single-particle state at $T = 0$. Numerical evidence for this complete Bose-Einstein condensation was first given by the many-body variational calculations of $^4$He droplets by Lewart, Pandharipande and Pieper in 1988. We show that the low density surface region can be treated rigorously using a generalized Gross-Pitaevskii equation for the Bose order parameter.Comment: 4 pages, 1 Postscript figur

To wet or not to wet: that is the question

Wetting transitions have been predicted and observed to occur for various combinations of fluids and surfaces. This paper describes the origin of such transitions, for liquid films on solid surfaces, in terms of the gas-surface interaction potentials V(r), which depend on the specific adsorption system. The transitions of light inert gases and H2 molecules on alkali metal surfaces have been explored extensively and are relatively well understood in terms of the least attractive adsorption interactions in nature. Much less thoroughly investigated are wetting transitions of Hg, water, heavy inert gases and other molecular films. The basic idea is that nonwetting occurs, for energetic reasons, if the adsorption potential's well-depth D is smaller than, or comparable to, the well-depth of the adsorbate-adsorbate mutual interaction. At the wetting temperature, Tw, the transition to wetting occurs, for entropic reasons, when the liquid's surface tension is sufficiently small that the free energy cost in forming a thick film is sufficiently compensated by the fluid- surface interaction energy. Guidelines useful for exploring wetting transitions of other systems are analyzed, in terms of generic criteria involving the "simple model", which yields results in terms of gas-surface interaction parameters and thermodynamic properties of the bulk adsorbate.Comment: Article accepted for publication in J. Low Temp. Phy