13,754 research outputs found
On signalling over through-silicon via (TSV) interconnects in 3-D integrated circuits.
This paper discusses signal integrity (SI) issues and signalling techniques for Through Silicon Via (TSV) interconnects in 3-D Integrated Circuits (ICs). Field-solver extracted parasitics of TSVs have been employed in Spice simulations to investigate the effect of each parasitic component on performance metrics such as delay and crosstalk and identify a reduced-order electrical model that captures all relevant effects. We show that in dense TSV structures voltage-mode (VM) signalling does not lend itself to achieving high data-rates, and that current-mode (CM) signalling is more effective for high throughput signalling as well as jitter reduction. Data rates, energy consumption and coupled noise for the different signalling modes are extracted
Diversity and noise effects in a model of homeostatic regulation of the sleep-wake cycle
Recent advances in sleep neurobiology have allowed development of
physiologically based mathematical models of sleep regulation that account for
the neuronal dynamics responsible for the regulation of sleep-wake cycles and
allow detailed examination of the underlying mechanisms. Neuronal systems in
general, and those involved in sleep regulation in particular, are noisy and
heterogeneous by their nature. It has been shown in various systems that
certain levels of noise and diversity can significantly improve signal
encoding. However, these phenomena, especially the effects of diversity, are
rarely considered in the models of sleep regulation. The present paper is
focused on a neuron-based physiologically motivated model of sleep-wake cycles
that proposes a novel mechanism of the homeostatic regulation of sleep based on
the dynamics of a wake-promoting neuropeptide orexin. Here this model is
generalized by the introduction of intrinsic diversity and noise in the
orexin-producing neurons in order to study the effect of their presence on the
sleep-wake cycle. A quantitative measure of the quality of a sleep-wake cycle
is introduced and used to systematically study the generalized model for
different levels of noise and diversity. The model is shown to exhibit a clear
diversity-induced resonance: that is, the best wake-sleep cycle turns out to
correspond to an intermediate level of diversity at the synapses of the
orexin-producing neurons. On the other hand only a mild evidence of stochastic
resonance is found when the level of noise is varied. These results show that
disorder, especially in the form of quenched diversity, can be a key-element
for an efficient or optimal functioning of the homeostatic regulation of the
sleep-wake cycle. Furthermore, this study provides an example of constructive
role of diversity in a neuronal system that can be extended beyond the system
studied here.Comment: 18 pages, 12 figures, 1 tabl
From quasiperiodic partial synchronization to collective chaos in populations of inhibitory neurons with delay
Collective chaos is shown to emerge, via a period-doubling cascade, from
quasiperiodic partial synchronization in a population of identical inhibitory
neurons with delayed global coupling. This system is thoroughly investigated by
means of an exact model of the macroscopic dynamics, valid in the thermodynamic
limit. The collective chaotic state is reproduced numerically with a finite
population, and persists in the presence of weak heterogeneities. Finally, the
relationship of the model's dynamics with fast neuronal oscillations is
discussed.Comment: 5 page
Jamming transition in air transportation networks
In this work we present a model of an air transportation traffic system from
the complex network modelling viewpoint. In the network, every node corresponds
to a given airport, and two nodes are connected by means of flight routes. Each
node is weighted according to its load capacity, and links are weighted
according to the Euclidean distance that separates each pair of nodes. Local
rules describing the behavior of individual nodes in terms of the surrounding
flow have been also modelled, and a random network topology has been chosen in
a baseline approach. Numerical simulations describing the diffusion of a given
number of agents (aircraft) in this network show the onset of a jamming
transition that distinguishes an efficient regime with null amount of airport
queues and high diffusivity (free phase) and a regime where bottlenecks
suddenly take place, leading to a poor aircraft diffusion (congested phase).
Fluctuations are maximal around the congestion threshold, suggesting that the
transition is critical. We then proceed by exploring the robustness of our
results in neutral random topologies by embedding the model in heterogeneous
networks. Specifically, we make use of the European air transportation network
formed by 858 airports and 11170 flight routes connecting them, which we show
to be scale-free. The jamming transition is also observed in this case. These
results and methodologies may introduce relevant decision making procedures in
order to optimize the air transportation traffic
Emergent global oscillations in heterogeneous excitable media: The example of pancreatic beta cells
Using the standard van der Pol-FitzHugh-Nagumo excitable medium model I
demonstrate a novel generic mechanism, diversity, that provokes the emergence
of global oscillations from individually quiescent elements in heterogeneous
excitable media. This mechanism may be operating in the mammalian pancreas,
where excitable beta cells, quiescent when isolated, are found to oscillate
when coupled despite the absence of a pacemaker region.Comment: See home page http://lec.ugr.es/~julya
A microscopic mechanism for self-organized quasi periodicity in random networks of non linear oscillators
Self-organized quasi periodicity is one of the most puzzling dynamical phases
observed in systems of non linear coupled oscillators. The single dynamical
units are not locked to the periodic mean field they produce, but they still
feature a coherent behavior, through an unexplained complex form of
correlation. We consider a class of leaky integrate-and-fire oscillators on
random sparse and massive networks with dynamical synapses, featuring
self-organized quasi periodicity, and we show how complex collective
oscillations arise from constructive interference of microscopic dynamics. In
particular, we find a simple quantitative relationship between two relevant
microscopic dynamical time scales and the macroscopic time scale of the global
signal. We show that the proposed relation is a general property of collective
oscillations, common to all the partially synchronous dynamical phases
analyzed. We argue that an analogous mechanism could be at the origin of
similar network dynamics.Comment: to appear in Phys. Rev.
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