Reentrant interface depinning from rough walls GIUGLIARELLI, G; STELLA, A. L
International journal of thermophysics,
05/1998, Letnik:
19, Številka:
3
Conference Proceeding, Journal Article
Recenzirano
Depinning of an interface from a rough self-affine wall delimiting an attractive substrate is described in terms of directed paths on a square lattice. Short range interactions are assumed and the ...phase diagram is determined by transfer matrix methods for several values of zeta sub(w), the roughness exponent of the wall. For all zeta sub(w) the following scenario is observed. At a very low temperature T, the interface is not pinned for wall attraction energies below a certain zeta sub(w)-dependent, nonzero threshold. This contrasts with the case of smooth walls, for which the threshold is zero. In a range of attraction energies just below the threshold, a pinning transition first occurs, as T increases, followed by a depinning one (reentrant depinning). This unusual reentrance phenomenon, in which, upon increasing T, dewetting is followed by wetting, is peculiar of self-affine roughness and does not occur, e.g., with a periodic substrate corrugation. The nature of both wetting and dewetting transitions is determined by the value of zeta sub(w). As found in related work, the two transitions are both continuous or both first-order, according to whether zeta sub(w)<1/2, or zeta sub(w)>1/2, respectively. The border value zeta sub(0) identical with 1/2 coincides with the intrinsic roughness of the interface in the bulk.
Wetting of rough walls STELLA, A; SARTONI, G; GIUGLIARELLI, G ...
International journal of thermophysics,
07/1998, Letnik:
19, Številka:
4
Conference Proceeding, Journal Article
Recenzirano
Quenched geometric disorder of a wall delimiting a spectator phase can have dramatic effects on the nature of critical wetting transitions. We consider self-affine walls in 2D with roughness exponent ...zeta sub(W). Transfer matrix results for directed interfacial models with short-range interactions suggest that wetting turns first-order as soon as zeta sub(W) exceeds zeta sub(0), the anisotropy index of interface fluctuations in the bulk. Discontinuous interface depinning is best identified by a peculiar two-peak structure in the statistical distributions of wall-interface contacts obtained by sampling over disorder. On the other hand, for zeta sub(W) < zeta sub(0) wetting remains continuous, most plausibly in the same universality class as with flat walls. This occurs both with ordered ( zeta sub(0) identical with one half ) and with bond-disordered ( zeta sub(0) identical with 2/3) bulk. A precise location of the thresholds at zeta sub(W) identical with zeta sub(0) can be argued on the basis of an analysis of different terms in the interfacial free energy. This analysis elucidates the peculiar role played by the intrinsic interfacial roughness and suggests extensions of the results to 3D and to long-range substrate forces.
Interface unbinding in structured wedges Giugliarelli, Gilberto
Physical review. E, Statistical, nonlinear, and soft matter physics
71, Številka:
2 Pt 1
Journal Article
Odprti dostop
The unbinding properties of an interface near structured wedges are investigated by discrete models with short range interactions. The calculations demonstrate that interface unbinding takes place in ...two stages: (i) a continuous filling-like transition in the pure wedge-like parts of the structure, and (ii) a conclusive discontinuous unbinding. In 2D an exact transfer matrix approach allows us to extract the whole interface phase diagram and the precise mechanism at the basis of the phenomenon. The Metropolis Monte Carlo simulations performed in 3D reveal an analogous behavior. The emerging scenario allows us to shed new light onto the problem of wetting of geometrically rough walls.
Electron spin relaxation rates over the temperatue range 1.41-15.6 K are presented for the copper-containing protein plastocyanin. Measurements are described for two samples, each derived from a ...different preparation of equivalent purity, for which the ionic, redox, and protein compositions varied slightly. X-band data are analyzed in terms of a phonon-limited direct process and a Raman relaxation process, where the index of the Raman transport integral is treated as a fitting parameter. Both samples yield rate data at the highest temperatures that are characterized by small deviations from a simple T(n) power law dependence, with n in the range 4.8-5.2. These deviations are most easily quantified when the T(n) power law fits are compared with similar functions that allow for a finite cutoff in the phonon density of states corresponding to Debye temperatures between 90 and 100 K with n in the range 5.0-5.5.
A 2
D model describing depinning of an interface from a rough, self-affine substrate, is studied by transfer matrix methods. The phase diagram is determined for several values of the roughness ...exponent,
ζs, of the attractive wall. For all
ζs > 0 the following scenario is observed. In first place, in contrast to the case of a flat wall (
ζs = 0), for wall attraction energies between zero and a
ζs-dependent positive value, the substrate is always wet. Furthermore, in a small range of attraction energies, a dewetting transition first occurs as
T increases, followed by a wetting one. This unusual reentrance phenomenon seems to be a peculiar feature of self-affine roughness, and does not occur, e.g., for periodically corrugated substrates.
The interaction of copper ions with tRNA has been studied by optical and EPR spectroscopies. The interaction results in two different paramagnetic complexes characterized by a tetragonal symmetry of ...the ligand electric field sensed by the ions. The complete set of the spin Hamiltonian parameters has been extracted by computer simulation with the Monte Carlo method. Hypotheses concerning the putative ligands are put forward.
Polymer adsorption on fractally rough walls of varying dimensionality is
studied by renormalization group methods on hierarchical lattices. Exact
results are obtained for deterministic walls. The ...adsorption transition is
found continuous for low dimension $d_w$ of the adsorbing wall and the
corresponding crossover exponent $\phi$ monotonically increases with $d_w$,
eventually overcoming previously conjectured bounds. For $d_w$ exceeding a
threshold value $d_w^*$, $\phi$ becomes 1 and the transition turns
first--order. $d_w^*>d_{saw}$, the fractal dimension of the polymer in the
bulk. An accurate numerical approach to the same problem with random walls
gives evidence of the same scenario.
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