1,721,098 research outputs found
Continuous and first-order polymer adsorption on hierarchical fractal walls
No full textPolymer 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 one and the transition changes to 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
Discontinuous interface depinning from a rough wall
No full textDepinning of an interface from a random self-affine substrate with roughness exponent zeta(S) is studied in systems with short-range interactions. In two dimensions transfer matrix results show that for zeta(S) 0. Thus critical wetting may be impossible to observe on rough substrates
Spectral Properties of Fractal Surfaces
No full textThe first investigation of the spectral dimension d double bar of a deterministic fractal surface is presented. Somewhat unexpectedly, numerical results strongly suggest d double bar = 2 for a whole class of surfaces, enclosing space regions with ordinary volume dimension. This conclusion is also supported by scaling arguments based on a connection with processes of diffusion in the presence of hierarchical waiting times. The problem of diffusion on our surface is also compared with that of random chain conformations. Within the numerical uncertainties the two problems seem to be characterized by identical end-to-end distance exponents
Reentrant Interface Depinning from Rough Walls
No full textDepinning 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(W), the roughness exponent of the wall. For all zeta(W) the Following scenario is observed. Ar a very low-temperature T, the interface is not pinned for wall attraction energies below a certain zeta(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(W). As found in related work, the two transitions are both continuous or both first-order, according to whether zeta(W)1/2, respectively. The border value zeta(0) = 1/2 coincides with the intrinsic roughness of the interface in the bulk
Compactness, aggregation, and prionlike behaviour of protein: a lattice model study
No full textThe solubility and compactness of proteins is investigated within the framework of models amenable to an exact numerical study through exhaustive enumeration. We study how the average inter-amino acid interaction potential affects the properties of both isolated and interacting proteins. In a concentrated solution, depending on the value of the average potential, individual proteins may remain stable in the isolated native structure (soluble case), may aggregate preserving their geometrical shape (nonsoluble case) or aggregate changing their geometrical shape (prionlike behavior). The number of sequences that have compact native states and are soluble is maximal at a fine-tuned average interaction potential and of the same order of the corresponding number of nonsoluble prionlike proteins. The viable protein sequences selected by such a fine-tuned potential are found to have an amino acid composition similar to naturally occurring proteins
Solid--on--Solid Model for Adsorption on Self--Affine Substrate: a Transfer Matrix Approach
No full textWe study a d = 2 discrete solid-on-solid model of complete wetting of a rough substrate with random self-affine boundary, having roughness exponent zeta(s). A suitable transfer matrix approach allows to discuss adsorption isotherms, as well as geometrical and thermal fluctuations of the interface. For zeta(s) less than or equal to 1/2 the same wetting exponent psi = 1/3 as for flat substrate is obtained for the dependence of the coverage, theta, on the chemical potential, h (theta similar to h(-psi) for h --> 0). The expected existence of a zero temperature fixed point, leading to psi = zeta(s)/(2 - zeta(s)) for zeta(s) > 1/2, is verified numerically in spite of an unexpected, very slow convergence to asymptotics
Lattice-gas model for adsorption on fractally rough surfaces
No full textA lattice-gas model for physical adsorption of a gas on a fractal surface is solved in mean-field approximation. Adsorption isotherms display a rich structure with first and second order transitions. Surface tension and temperature effects are analysed. The possibility of determining the surface fractal dimension on the basis of "monolayer" adsorption measurements is discussed. Results for the multilayer adsorption regime are also presented and compared with recent scaling conjectures
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Reentrant Wetting Transition of a Rough Wall
No full textA 2D 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, zeta(S), of the attractive wall. For all zeta(S) > 0 the following scenario is observed. In first place, in contrast to the case of a flat wall (zeta(S) = 0), for wall attraction energies between zero and a zeta(S)-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
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