80 research outputs found
Finite-size scaling analysis of biased diffusion on fractals
No full textDiffusion on a T fractal lattice under the influence of topological biasing fields is studied by finite size scaling methods. This allows to avoid proliferation and singularities which would arise in a renormalization group approach on infinite system as a consequence of logarithmic diffusion. Within the scheme, logarithmic diffusion is proved on the basis of an analysis of various temporal scales such as first passage time moments and survival probability characteristic time. This confirms and puts on firmer basis previous renormalization group results. A careful study of the asymptotic occupation probabilities of different kinds of lattice points allows to elucidate the mechanism of trapping into dangling ends, which is responsible of the logarithmic time dependence of average displacement
Branching interfaces with infinitely strong couplings
No full textA hierarchical froth model of the interface of a random q-state Pens ferromagnet in 2D is studied by recursive methods. A fraction p of the nearest-neighbour bonds is made inaccessible to domain walls by infinitely strong ferromagnetic couplings. Energetic and geometric scaling properties of the interface are controlled by zero-temperature fixed distributions. For p < p(c), the directed percolation threshold, the interface behaves as for p = 0, and scaling supports random Ising (q = 2) critical behaviour for all q's. At p = p(c) three regimes are obtained for different rates of ferro versus antiferromagnetic couplings. With rates above a threshold value the interface is linear (fractal dimension d(f) = 1) and its energy fluctuations, Delta E scale with length as Delta E proportional to L(omega), with omega similar or equal to 0.48. When the threshold is reached the interface branches at all scales and is fractal (d(f) similar or equal to 1.046) with omega(c) similar or equal to 0.51. Thus, at p(c), dilution modifies both low-temperature interfacial properties and critical scaling. Below threshold the interface becomes a probe of the backbone geometry (d(f) similar or equal to (d) over bar similar or equal to 1.305; (d) over bar = backbone fractal dimension), which even controls energy fluctuations (omega similar or equal to d(f) similar or equal to (d) over bar). Numerical determinations of directed percolation exponents on diamond hierarchical lattice are also presented
First order wetting of rough substrates and quantum unbinding
No full textReplica and functional renormalization group methods show that, with short-range substrate forces or in strong fluctuation regimes, wetting of a self-affine rough wall in two dimensions turns first order as soon as the wall roughness exponent exceeds the anisotropy index of hulk interface fluctuations. Different thresholds apply with long-range forces in mean held regimes. For bond-disordered bulk, fixed point stability suggests similar results, which ultimately rely on basic properties of quantum bound states with asymptotically power-law repulsive potentials
Branching transition of a directed polymer in random medium
No full textA directed polymer is allowed to branch, with configurations determined by global energy optimization and disorder. A finite-size scaling analysis in 2D shows that, if disorder makes branching more and more favorable, a critical transition occurs from the linear scaling regime first studied by Huse and Henley (Phys. Rev. Lett., 54, (1985) 2708) to a fully branched, compact one. At criticality clear evidence is obtained that the polymer branches at all scales with dimension (d) over bar(c) and roughness exponent zeta(c) satisfying ((d) over bar(c) - 1)/zeta(c) = 0.13 +/- 0.01, and energy fluctuation exponent omega(c) = 0.26 +/- 0.02, in terms of longitudinal distance
Singular Dynamical Renormalization-group and Biased Diffusion On Fractals
No full textAn exact renormalization group describes extremely slow, logarithmic diffusion in the presence of a biasing field on ramified fractal structures. Recursion equations are singular at the fixed point and the standard analysis to extract asymptotic behaviors has to be reconsidered. The model reproduces mechanisms working for biased diffusion on percolation clusters. For 1 - d structures, logarithmic diffusions generalizing that discussed by Sinai [Theory Probab. Its Appl. 27, 256 (1982)] are obtained by the same methods
Misfire and Partial Burn Detection based on Ion Current Measurement
No full textThe paper presents the implementation of a combustion
diagnosis system that integrates crankshaft speed oscillations
analysis with ion current signal processing, for V8 and V12
high performance engines.
Ion current sensing has been introduced in the last V8 and
V12 Ferrari models in order to improve combustion control
by implementing ion current based closed-loop sparkadvance
control systems, both under knocking and nonknocking
conditions (respectively based on measured
knocking level, and on ion current peak position control).
Another area where ion current sensing can improve the
engine controller performance is related to the ability of
detecting and isolating missing and partial burn combustions.
The typical approach to misfire detection (based on engine
speed oscillation measurement) is in fact particularly critical
for engines with a large number of cylinders, and ion current
sensing provides additional information not only about
presence (or absence) of combustion, but also about the
causes that generated the fault. Moreover, the paper shows
that real-time analysis of specific ion current signal features
allows isolating incomplete and inefficient combustion
events, thus providing extremely useful information to the
engine control system, which can for example be used to
activate multi-spark discharge ignition mode.
The first part of the paper shows the main critical aspects of
speed-measurement based misfire detection, and introduces
the ion current signal main features during regular engine
operation. Then, ion current signal is analyzed during
abnormal combustion events: absence of combustion (both
due to missing injections and missing ignitions) and partial
burn cycles. It is shown how it is possible to isolate missing
and incomplete combustions in a relatively straightforward
way, and also how the causes that induced the fault may be
isolated by integrating standard diagnostic functions with
specific ion current signal processing algorithms. Finally, the
performance of the diagnostic system that integrates engine
speed oscillation analysis and information extracted from the
ion signal has been evaluated during on-board tests, and the
main results are presented at the end of the paper
Effect of surface roughness on bulk disorder induced wetting
No full textTransfer-matrix results in 2D show that wetting of a rough, self-affine wall induced by bulk bond disorder turns discontinuous as soon as the wall roughness exponent zeta w exceeds zeta(0) = 2/3, the spatial anisotropy index of interface fluctuations in the bulk. For zeta(W) < 2/3 critical wetting is recovered, in the same universality class as for the flat-wall case. These and related findings suggest a free-energy structure such to imply first-order wetting also without disorder, or in 3D, whenever zeta(W) exceeds the appropriate zeta(0). The same thresholds should apply also with van der Waals forces, in cases when Co implies a strong-fluctuation regime
Figure 1 in Species composition and patterns of diversity of macroalgal coralligenous assemblages in the north-western Mediterranean Sea
No full textFigure 1. Map of the study area. Notes: L, Livorno; A, Argentario; V, Vada; Me, Meloria; Go, Gorgona; C, Capraia; E, Elba; P, Pianosa; Mo, Montecristo; F, Formiche di Grosseto; Gn, Giannutri; Gi, Giglio.Published as part of Piazzi, L., Balata, D., Cecchi, E., Cinelli, F. & Sartoni, G., 2010, Species composition and patterns of diversity of macroalgal coralligenous assemblages in the north-western Mediterranean Sea, pp. 1-22 in Journal of Natural History 44 (1-2) on page 3, DOI: 10.1080/00222930903377547, http://zenodo.org/record/466672
UNUSUAL UNIVERSALITY OF BRANCHING INTERFACES IN RANDOM-MEDIA
No full textWe study the criticality of a Potts interface by introducing a froth model which, unlike its solid-on-solid Ising counterpart, incorporates bubbles of different phases. The interface is fractal at the phase transition of a pure system. However, a position space approximation suggests that the probability of loop formation vanishes marginally at a transition dominated by strong random bond disorder. This implies a linear critical interface, and provides a mechanism for the conjectured equivalence of critical random Potts and Ising models
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