Interface Unbinding in Structured Wedges

The unbinding properties of an interface near structured wedges are investigated by discrete models with short range interactions. The calculations demonstrate that interface unbinding take place in two stages: $i$) a continuous filling--like transition in the pure wedge--like parts of the structure; $ii$) a conclusive discontinuous unbinding. In 2$D$ an exact transfer matrix approach allows to extract the whole interface phase diagram and the precise mechanism at the basis of the phenomenon. The Metropolis Monte Carlo simulations performed in 3$D$ reveal an analogous behavior. The emerging scenario allows to shed new light onto the problem of wetting of geometrically rough walls.Comment: 5 pages, 5 figures, to appear in Phys. Rev.

Ground State Wave Function of the Schr\"odinger Equation in a Time-Periodic Potential

Using a generalized transfer matrix method we exactly solve the Schr\"odinger equation in a time periodic potential, with discretized Euclidean space-time. The ground state wave function propagates in space and time with an oscillating soliton-like wave packet and the wave front is wedge shaped. In a statistical mechanics framework our solution represents the partition sum of a directed polymer subjected to a potential layer with alternating (attractive and repulsive) pinning centers.Comment: 11 Pages in LaTeX. A set of 2 PostScript figures available upon request at [email protected] . Physical Review Letter

A Simulation Model Outline for the Hungarian Forest Sector

The model presented in this paper describes the structure of the Hungarian forest sector. The planning of the sector at a national and company level as well as the mechanism of regulation concerning production, investments, and consumption are also investigated and the exports and imports linked. One of the most important objectives is to create this model in order to study the behavior of the system so as to aid the decision making both in strategic and tactical areas. Apart from forestry the model also includes the wood processing activities

Renormalon disappearance in Borel sum of the 1/N expansion of the Gross-Neveu model mass gap

The exact mass gap of the O(N) Gross-Neveu model is known, for arbitrary $N$, from non-perturbative methods. However, a "naive" perturbative expansion of the pole mass exhibits an infinite set of infrared renormalons at order 1/N, formally similar to the QCD heavy quark pole mass renormalons, potentially leading to large ${\cal O}(\Lambda)$ perturbative ambiguities. We examine the precise vanishing mechanism of such infrared renormalons, which avoids this (only apparent)contradiction, and operates without need of (Borel) summation contour prescription, usually preventing unambiguous separation of perturbative contributions. As a consequence we stress the direct Borel summability of the (1/N) perturbative expansion of the mass gap. We briefly speculate on a possible similar behaviour of analogous non-perturbative QCD quantities.Comment: 16 pp., 1 figure. v2: a few paragraphs and one appendix added, title and abstract slightly changed, essential results unchange

Network formation of tissue cells via preferential attraction to elongated structures

Vascular and non-vascular cells often form an interconnected network in vitro, similar to the early vascular bed of warm blooded embryos. Our time-lapse recordings show that the network forms by extending sprouts, i.e., multicellular linear segments. To explain the emergence of such structures, we propose a simple model of preferential attraction to stretched cells. Numerical simulations reveal that the model evolves into a quasi-stationary pattern containing linear segments, which interconnect above the critical volume fraction of 0.2. In the quasi-stationary state the generation of new branches offset the coarsening driven by surface tension. In agreement with empirical data, the characteristic size of the resulting polygonal pattern is density-independent within a wide range of volume fractions

Transient Pattern Formation in an Active Matter Contact Poisoning Model

One of the most notable features in repulsive particle based active matter systems is motility-induced-phase separation (MIPS) where a dense, often crystalline phase coexists with a low density fluid. In most active matter studies, the activity is kept constant as a function of time; however, there are many examples of active systems in which individual particles transition from living or moving to dead or nonmotile due to lack of fuel, infection, or poisoning. Here we consider an active matter particle system at densities where MIPS does not occur. When we add a small number of infected particles that can effectively poison other particles, rendering them nonmotile, we find a rich variety of time dependent pattern formation, including MIPS, a wetting phase, and a fragmented state formed when mobile particles plow through an nonmotile packing. We map out the patterns as a function of time scaled by the duration of the epidemic, and show that the pattern formation is robust for a wide range of poisoning rates and activity levels. We also show that pattern formation does not occur in a random death model, but requires the promotion of nucleation by contact poisoning. Our results should be relevant to biological and active matter systems where there is some form of poisoning, death, or transition to nonmotility.Comment: 7 pages, 6 figure

A Monopole-Antimonopole Solution of the SU(2) Yang-Mills-Higgs Model

As shown by Taubes, in the Bogomol'nyi-Prasad-Sommerfield limit the SU(2) Yang-Mills-Higgs model possesses smooth finite energy solutions, which do not satisfy the first order Bogomol'nyi equations. We construct numerically such a non-Bogomol'nyi solution, corresponding to a monopole-antimonopole pair, and extend the construction to finite Higgs potential.Comment: 11 pages, including 4 eps figures, LaTex format using RevTe

An indole alkaloid from Strychnos erichsonii

Le premier alcaloïde indolique de type vobasine rencontré dans les #Loganiaceae a été isolé des écorces de #Strychnos erichsonii, récoltées en Guyane Française. Sa structure confirmée par cristallographie Rx. (Résumé d'auteur

Integrability in Theories with Local U(1) Gauge Symmetry

Using a recently developed method, based on a generalization of the zero curvature representation of Zakharov and Shabat, we study the integrability structure in the Abelian Higgs model. It is shown that the model contains integrable sectors, where integrability is understood as the existence of infinitely many conserved currents. In particular, a gauge invariant description of the weak and strong integrable sectors is provided. The pertinent integrability conditions are given by a U(1) generalization of the standard strong and weak constraints for models with two dimensional target space. The Bogomolny sector is discussed, as well, and we find that each Bogomolny configuration supports infinitely many conserved currents. Finally, other models with U(1) gauge symmetry are investigated.Comment: corrected typos, version accepted in J. Phys.