8 research outputs found
1D-Disordered Conductor with Loops Immersed in a Magnetic Field
We investigate the conductance of a 1-D disordered conducting loop with two
contacts, immersed in a magnetic flux. We show the appearance in this model of
the Al'tshuler-Aronov-Spivak behaviour. We also investigate the case of a chain
of loops distributed with finite density: in this case we show that the
interference effects due to the presence of the loops can lead to the
delocalization of the wave function.Comment: 8 pages; LaTeX; IFUM 463/FT; to appear in Phys. Lett.
Optimality in self-organized molecular sorting
We introduce a simple physical picture to explain the process of molecular
sorting, whereby specific proteins are concentrated and distilled into
submicrometric lipid vesicles in eukaryotic cells. To this purpose, we
formulate a model based on the coupling of spontaneous molecular aggregation
with vesicle nucleation. Its implications are studied by means of a
phenomenological theory describing the diffusion of molecules towards multiple
sorting centers that grow due to molecule absorption and are extracted when
they reach a sufficiently large size. The predictions of the theory are
compared with numerical simulations of a lattice-gas realization of the model
and with experimental observations. The efficiency of the distillation process
is found to be optimal for intermediate aggregation rates, where the density of
sorted molecules is minimal and the process obeys simple scaling laws.
Quantitative measures of endocytic sorting performed in primary endothelial
cells are compatible with the hypothesis that these optimal conditions are
realized in living cells
Statistics of the One-Electron Current in a One-Dimensional Mesoscopic Ring at Arbitrary Magnetic Fields
The set of moments and the distribution function of the one-electron current
in a one-dimensional disordered ring with arbitrary magnetic flux are
calculated.Comment: 10 pages; Plain TeX; IFUM 448/FT; to appear in J. Stat. Phy
The Lyapunov Spectrum of a Continuous Product of Random Matrices
We expose a functional integration method for the averaging of continuous
products of random matrices. As an application, we
compute exactly the statistics of the Lyapunov spectrum of . This
problem is relevant to the study of the statistical properties of various
disordered physical systems, and specifically to the computation of the
multipoint correlators of a passive scalar advected by a random velocity field.
Apart from these applications, our method provides a general setting for
computing statistical properties of linear evolutionary systems subjected to a
white noise force field.Comment: Latex, 9 page
Long-time dynamics of the infinite-temperature Heisenberg magnet
Infinite-temperature long-time dynamics of Heisenberg model
is investigated. It is shown that the quantum spin pair-correlator is equal to
the correlator of classically evaluated vector field averaged over the initial
conditions with respect to the gaussian measure. In the continious limit case
the scaling estimations allow one to find one-point correlator that turns out
to be . All results are obtained
by straightforward procedure without any assumptions of the phenomenological
character.Comment: 11 pages, RevTex 3.0, to be published in PRB Feb. 199
Threshold robustness in discrete facility location problems: a bi-objective approach
The two best studied facility location problems are the p-median problem and the uncapacitated facility location problem (Daskin, Network and discrete location: models, algorithms, and applications. Wiley, New York, 1995; Mirchandani and Francis, Discrete location theory. Wiley, New York, 1990). Both seek the location of the facilities minimizing the total cost, assuming no uncertainty in costs exists, and thus all parameters are known. In most real-world location problems the demand is not certain, because it is a long-term planning decision, and thus, together with the minimization of costs, optimizing some robustness measure is sound. In this paper we address bi-objective versions of such location problems, in which the total cost, as well as the robustness associated with the demand, are optimized. A dominating set is constructed for these bi-objective nonlinear integer problems via the Δ-constraint method. Computational results on test instances are presented, showing the feasibility of our approach to approximate the Pareto-optimal set