8,083 research outputs found
The Dynamics of Internet Traffic: Self-Similarity, Self-Organization, and Complex Phenomena
The Internet is the most complex system ever created in human history.
Therefore, its dynamics and traffic unsurprisingly take on a rich variety of
complex dynamics, self-organization, and other phenomena that have been
researched for years. This paper is a review of the complex dynamics of
Internet traffic. Departing from normal treatises, we will take a view from
both the network engineering and physics perspectives showing the strengths and
weaknesses as well as insights of both. In addition, many less covered
phenomena such as traffic oscillations, large-scale effects of worm traffic,
and comparisons of the Internet and biological models will be covered.Comment: 63 pages, 7 figures, 7 tables, submitted to Advances in Complex
System
Macroscopic models of local field potentials and the apparent 1/f noise in brain activity
The power spectrum of local field potentials (LFPs) has been reported to
scale as the inverse of the frequency, but the origin of this "1/f noise" is at
present unclear. Macroscopic measurements in cortical tissue demonstrated that
electric conductivity (as well as permittivity) is frequency dependent, while
other measurements failed to evidence any dependence on frequency. In the
present paper, we propose a model of the genesis of LFPs which accounts for the
above data and contradictions. Starting from first principles (Maxwell
equations), we introduce a macroscopic formalism in which macroscopic
measurements are naturally incorporated, and also examine different physical
causes for the frequency dependence. We suggest that ionic diffusion primes
over electric field effects, and is responsible for the frequency dependence.
This explains the contradictory observations, and also reproduces the 1/f power
spectral structure of LFPs, as well as more complex frequency scaling. Finally,
we suggest a measurement method to reveal the frequency dependence of current
propagation in biological tissue, and which could be used to directly test the
predictions of the present formalism
Criticality and the Onset of Ordering in the Standard Vicsek Model
Experimental observations of animal collective behavior have shown stunning
evidence for the emergence of large-scale cooperative phenomena resembling
phase transitions in physical systems. Indeed, quantitative studies have found
scale-free correlations and critical behavior consistent with the occurrence of
continuous, second-order phase transitions. The Standard Vicsek Model (SVM), a
minimal model of self-propelled particles in which their tendency to align with
each other competes with perturbations controlled by a noise term, appears to
capture the essential ingredients of critical flocking phenomena. In this
paper, we review recent finite-size scaling and dynamical studies of the SVM,
which present a full characterization of the continuous phase transition
through dynamical and critical exponents. We also present a complex network
analysis of SVM flocks and discuss the onset of ordering in connection with
XY-like spin models.Comment: 15 pages, 4 figures. To appear in Interface Focu
Piezo-electromechanical smart materials with distributed arrays of piezoelectric transducers: Current and upcoming applications
This review paper intends to gather and organize a series of works which discuss the possibility of exploiting the mechanical properties of distributed arrays of piezoelectric transducers. The concept can be described as follows: on every structural member one can uniformly distribute an array of piezoelectric transducers whose electric terminals are to be connected to a suitably optimized electric waveguide. If the aim of such a modification is identified to be the suppression of mechanical vibrations then the optimal electric waveguide is identified to be the 'electric analog' of the considered structural member. The obtained electromechanical systems were called PEM (PiezoElectroMechanical) structures. The authors especially focus on the role played by Lagrange methods in the design of these analog circuits and in the study of PEM structures and we suggest some possible research developments in the conception of new devices, in their study and in their technological application. Other potential uses of PEMs, such as Structural Health Monitoring and Energy Harvesting, are described as well. PEM structures can be regarded as a particular kind of smart materials, i.e. materials especially designed and engineered to show a specific andwell-defined response to external excitations: for this reason, the authors try to find connection between PEM beams and plates and some micromorphic materials whose properties as carriers of waves have been studied recently. Finally, this paper aims to establish some links among some concepts which are used in different cultural groups, as smart structure, metamaterial and functional structural modifications, showing how appropriate would be to avoid the use of different names for similar concepts. © 2015 - IOS Press and the authors
Fractals in the Nervous System: conceptual Implications for Theoretical Neuroscience
This essay is presented with two principal objectives in mind: first, to
document the prevalence of fractals at all levels of the nervous system, giving
credence to the notion of their functional relevance; and second, to draw
attention to the as yet still unresolved issues of the detailed relationships
among power law scaling, self-similarity, and self-organized criticality. As
regards criticality, I will document that it has become a pivotal reference
point in Neurodynamics. Furthermore, I will emphasize the not yet fully
appreciated significance of allometric control processes. For dynamic fractals,
I will assemble reasons for attributing to them the capacity to adapt task
execution to contextual changes across a range of scales. The final Section
consists of general reflections on the implications of the reviewed data, and
identifies what appear to be issues of fundamental importance for future
research in the rapidly evolving topic of this review
Networking - A Statistical Physics Perspective
Efficient networking has a substantial economic and societal impact in a
broad range of areas including transportation systems, wired and wireless
communications and a range of Internet applications. As transportation and
communication networks become increasingly more complex, the ever increasing
demand for congestion control, higher traffic capacity, quality of service,
robustness and reduced energy consumption require new tools and methods to meet
these conflicting requirements. The new methodology should serve for gaining
better understanding of the properties of networking systems at the macroscopic
level, as well as for the development of new principled optimization and
management algorithms at the microscopic level. Methods of statistical physics
seem best placed to provide new approaches as they have been developed
specifically to deal with non-linear large scale systems. This paper aims at
presenting an overview of tools and methods that have been developed within the
statistical physics community and that can be readily applied to address the
emerging problems in networking. These include diffusion processes, methods
from disordered systems and polymer physics, probabilistic inference, which
have direct relevance to network routing, file and frequency distribution, the
exploration of network structures and vulnerability, and various other
practical networking applications.Comment: (Review article) 71 pages, 14 figure
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