An optimal transient growth of small perturbations in thin gaseous discs

A thin gaseous disc with an almost keplerian angular velocity profile, bounded by a free surface and rotating around point-mass gravitating object is nearly spectrally stable. Despite that the substantial transient growth of linear perturbations measured by the evolution of their acoustic energy is possible. This fact is demonstrated for the simple model of a non-viscous polytropic thin disc of a finite radial size where the small adiabatic perturbations are considered as a linear combination of neutral modes with a corotational radius located beyond the outer boundary of the flow.Comment: 15 pages, 5 figures, accepted for publication in Ast

Synchronous chaos and broad band gamma rhythm in a minimal multi-layer model of primary visual cortex

Visually induced neuronal activity in V1 displays a marked gamma-band component which is modulated by stimulus properties. It has been argued that synchronized oscillations contribute to these gamma-band activity [... however,] even when oscillations are observed, they undergo temporal decorrelation over very few cycles. This is not easily accounted for in previous network modeling of gamma oscillations. We argue here that interactions between cortical layers can be responsible for this fast decorrelation. We study a model of a V1 hypercolumn, embedding a simplified description of the multi-layered structure of the cortex. When the stimulus contrast is low, the induced activity is only weakly synchronous and the network resonates transiently without developing collective oscillations. When the contrast is high, on the other hand, the induced activity undergoes synchronous oscillations with an irregular spatiotemporal structure expressing a synchronous chaotic state. As a consequence the population activity undergoes fast temporal decorrelation, with concomitant rapid damping of the oscillations in LFPs autocorrelograms and peak broadening in LFPs power spectra. [...] Finally, we argue that the mechanism underlying the emergence of synchronous chaos in our model is in fact very general. It stems from the fact that gamma oscillations induced by local delayed inhibition tend to develop chaos when coupled by sufficiently strong excitation.Comment: 49 pages, 11 figures, 7 table

Micro-connectomics: probing the organization of neuronal networks at the cellular scale.

Defining the organizational principles of neuronal networks at the cellular scale, or micro-connectomics, is a key challenge of modern neuroscience. In this Review, we focus on graph theoretical parameters of micro-connectome topology, often informed by economical principles that conceptually originated with Ramón y Cajal's conservation laws. First, we summarize results from studies in intact small organisms and in samples from larger nervous systems. We then evaluate the evidence for an economical trade-off between biological cost and functional value in the organization of neuronal networks. Various results suggest that many aspects of neuronal network organization are indeed the outcome of competition between these two fundamental selection pressures.This work was supported by the National Institute of Health Research (NIHR) Cambridge Biomedical Research Centre.This is the author accepted manuscript. It is currently under an indefinite embargo pending publication by the Nature Publishing Group

26th Annual Computational Neuroscience Meeting (CNS*2017): Part 3 - Meeting Abstracts - Antwerp, Belgium. 15–20 July 2017

This work was produced as part of the activities of FAPESP Research,\ud Disseminations and Innovation Center for Neuromathematics (grant\ud 2013/07699-0, S. Paulo Research Foundation). NLK is supported by a\ud FAPESP postdoctoral fellowship (grant 2016/03855-5). ACR is partially\ud supported by a CNPq fellowship (grant 306251/2014-0)

Can a submarine be perished by internal waves?

The recent tragedy of the Nanggala submarine that occurred off the coast of Bali, once again reminds of the possible role of internal waves in such tragedies. The article briefly outlines the nature of internal waves and analyzes the circumstances of the losses of three submarines - the atomic submarines Thresher (1963) and Scorpion (1968) of the US Navy and the diesel Indonesian submarine KRI Nanggala (2021). The hypothetical scenarios of the accidents are discussed. The danger of internal waves for underwater navigation is reasoned

Scalar description of three-dimensional vortex flows of incompressible fluid

An essential progress in the investigation of flows of incompressible fluid may be achieved with the help of stream-function. Flow description by means of one scalar stream-function is much simpler than the description based on the three-dimensional vector field. Many interesting and physically important problems were solved by this way. However, the traditional usage of a stream-function is restricted by the assumption of certain symmetry of the flow: the method is applicable only to two-component flows, i.e. when the corresponding velocity field is effectively two-dimensional, e.g., plane flow. This restriction essentially limits the range of applicability of such approach. In this paper we propose another approach, also based on the introduction of only one scalar function. However, we show that with this scalar function a wide class of non-stationary three-dimensional flows can be described. This class of flows includes both potential and vortex flows. In the latter case, the corresponding vorticity field may be two-component, in general. Characteristic features of such flows are described in details. Particular examples of flows are presented in the explicit form