5,147 research outputs found
Random Networks Tossing Biased Coins
In statistical mechanical investigations on complex networks, it is useful to
employ random graphs ensembles as null models, to compare with experimental
realizations. Motivated by transcription networks, we present here a simple way
to generate an ensemble of random directed graphs with, asymptotically,
scale-free outdegree and compact indegree. Entries in each row of the adjacency
matrix are set to be zero or one according to the toss of a biased coin, with a
chosen probability distribution for the biases. This defines a quick and simple
algorithm, which yields good results already for graphs of size n ~ 100.
Perhaps more importantly, many of the relevant observables are accessible
analytically, improving upon previous estimates for similar graphs
A Model for the Self-Organization of Microtubules Driven by Molecular Motors
We propose a two-dimensional model for the organization of stabilized
microtubules driven by molecular motors in an unconfined geometry. In this
model two kinds of dynamics are competing. The first one is purely diffusive,
with an interaction between the rotational degrees of freedom, the second one
is a local drive, dependent on microtubule polarity. As a result, there is a
configuration dependent driving field. Applying a molecular field
approximation, we are able to derive continuum equations. A study on the
solutions shows nonequilibrium steady states. The presence and stability of
such self-organized states are investigated in terms of entropy production.
Numerical simulations confirm analytical results.Comment: 23 pages, 10 figures, LaTeX, ep
From Geophysics to Microgeophysics for Engineering and Cultural Heritage
The methodologies of microgeophysics have been derived from the geophysical ones, for the sake of solving specific diagnostic and/or monitoring problems regarding civil engineering and cultural heritage studies. Generally, the investigations are carried out using different 2D and 3D tomographic approaches as well as different energy sources: sonic and ultrasonic waves, electromagnetic (inductive and impulsive) sources, electric potential fields, and infrared emission. Many efforts have been made to modify instruments and procedures in order to improve the resolution of the surveys as well as to significantly reduce the time of the measurements without any loss of information. This last point has been achieved by using multichannel systems. Finally, some applications are presented, and the results seem to be very promising and promote this new branch of geophysics. Therefore, these methodologies can be used even more to diagnose, monitor, and safeguard not only engineering buildings and/or large structures, but also ancient monuments and cultural artifacts, such as pottery, statues, and so forth
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