Search results for "Nonlinear"

Inference of proto-neutron star properties from gravitational-wave data in core-collapse supernovae

2021

The eventual detection of gravitational waves from core-collapse supernovae (CCSN) will help improve our current understanding of the explosion mechanism of massive stars. The stochastic nature of the late post-bounce gravitational wave signal due to the non-linear dynamics of the matter involved and the large number of degrees of freedom of the phenomenon make the source parameter inference problem very challenging. In this paper we take a step towards that goal and present a parameter estimation approach which is based on the gravitational waves associated with oscillations of proto-neutron stars (PNS). Numerical simulations of CCSN have shown that buoyancy-driven g-modes are responsible …

Ghost stochastic resonance in FitzHugh–Nagumo circuit

2014

International audience; The response of a neural circuit submitted to a bi-chromatic stimulus and corrupted by noise is investigated. In the presence of noise, when the spike firing of the circuit is analysed, a frequency not present at the circuit input appears. For a given range of noise intensities, it is shown that this ghost frequency is almost exclusively present in the interspike interval distribution. This phenomenon is for the first time shown experimentally in a FitzHugh-Nagumo circuit.

Quantum Non-Markovian Piecewise Dynamics from Collision Models

2017

Recently, a large class of quantum non-Markovian piecewise dynamics for an open quantum system obeying closed evolution equations has been introduced [B. Vacchini, Phys. Rev. Lett. 117, 230401 (2016)]. These dynamics have been defined in terms of a waiting-time distribution between quantum jumps, along with quantum maps describing the effect of jumps and the system's evolution between them. Here, we present a quantum collision model with memory, whose reduced dynamics in the continuous-time limit reproduces the above class of non-Markovian piecewise dynamics, thus providing an explicit microscopic realization.

Non-linear analysis of plane steel prestressed truss in fire

2002

The concept of analysis of 2-D static loaded prestressed steel trusses till failure during fire using a modified method of forces is presented. Failure of steel trusses in fire is based on the criterion of stresses. Behaviour of steel is described by non-linear constitutive model (based on hypo-elastic Ramberg-Osgood formula and Dorn creep theory) and Plem proposition (for string). Both models are approximated in calculations by hyperbolic Norton-Bailey rule. Fire simulates thermal force as an action of high temperature that increases linearly up to some level. The complete formulation of this method is illustrated by the algorithm of model parameters identification. Analysis of results for…

Efficient numerical methods for simulating continuous casting processes

2014

Third order nonlinear optical properties of novel TetrathiafulvalenePhenanthroline based dyads

2011

The non-linear optical properties of π-conjugated organic molecules such as TTF and their derivatives have recently gained particular interest due to their extended π-system and the strong electron donating character. The knowledge of the nonlinear optical response, as well as the impact of the charge transfer on the nonlinearity is very important. As such systems can be used in a variety of applications. In this study we investigate the nonlinear absorption of novel tetrathiafulvalene-phenanthroline based dyads by means of the Z-scan technique.

ICA and stochastic volatility models

2016

We consider multivariate time series where each component series is an unknown linear combination of latent mutually independent stationary time series. Multivariate financial time series have often periods of low volatility followed by periods of high volatility. This kind of time series have typically non-Gaussian stationary distributions, and therefore standard independent component analysis (ICA) tools such as fastICA can be used to extract independent component series even though they do not utilize any information on temporal dependence. In this paper we review some ICA methods used in the context of stochastic volatility models. We also suggest their modifications which use nonlinear…

Nonlinear dissipation phenomena in optomechanics

2016

Yksikään kvanttisysteemi ei voi olla täysin eristetty ympäristöstään, mikä johtaa informaation välittymiseen systeemin ja ympäristön välillä. Optomekaniikassa, missä tyypillinen tutkittava systeemi on peileistä koostuva optinen kaviteetti yhdistettynä mekaaniseen värähtelijään, systeemin ja ympäristön lineaarisesta kytkennästä johtuvat dissipaatioilmiöt ovat hyvin tunnettuja. Epälineaarisia ilmiöitä ei kuitenkaan ymmärretä yhtä laajasti. Tutkin epälineaarista kytkentää kaviteetin ja lämpökylvyn välillä ja havainnollistan tästä kytkennästä johtuvia ilmiöitä kuten epälineaarista dissipaatiota. Esitän myös optisen kaviteetin epälineaarisen dissipaation oikeuttavan mallin, missä optinen kavitee…

Wiener-Granger Causality in Network Physiology with Applications to Cardiovascular Control and Neuroscience

2016

Since the operative definition given by C. W. J. Granger of an idea expressed by N. Wiener, the Wiener–Granger causality (WGC) has been one of the most relevant concepts exploited by modern time series analysis. Indeed, in networks formed by multiple components, working according to the notion of segregation and interacting with each other according to the principle of integration, inferring causality has opened a window on the effective connectivity of the network and has linked experimental evidences to functions and mechanisms. This tutorial reviews predictability improvement, information-based and frequency domain methods for inferring WGC among physiological processes from multivariate…

Theoretical and experimental study of two discrete coupled Nagumo chains

2001

We analyze front wave (kink and antikink) propagation and pattern formation in a system composed of two coupled discrete Nagumo chains using analytical and numerical methods. In the case of homogeneous interaction among the chains, we show the possibility of the effective control on wave propagation. In addition, physical experiments on electrical chains confirm all theoretical behaviors.