scholarly journals Identification of Linear and Nonlinear Causal Relationship Among Low-Frequency Climatic Phenomena in the Last Millennium

2019 ◽  
Author(s):  
Lucas Massaroppe ◽  
Maria Gabriela Louzada Malfatti ◽  
Igor Stivanelli Custodio ◽  
Pedro Leite da Silva Dias
Keyword(s):  
Causal Relationship ◽  
Low Frequency ◽  
Last Millennium ◽  
Linear And Nonlinear

scholarly journals Systems-based analysis of dendritic nonlinearities reveals temporal feature extraction in mouse L5 cortical neurons

2017 ◽  
Vol 117 (6) ◽  
pp. 2188-2208 ◽  
Author(s):  
Brian E. Kalmbach ◽  
Richard Gray ◽  
Daniel Johnston ◽  
Erik P. Cook
Keyword(s):  
High Frequency ◽  
Cortical Neurons ◽  
Action Potentials ◽  
Nonlinear Response ◽  
Functional Model ◽  
Low Frequency ◽  
Fast Variable ◽  
Nonlinear Component ◽  
Dendritic Spikes ◽  
Linear And Nonlinear

What do dendritic nonlinearities tell a neuron about signals injected into the dendrite? Linear and nonlinear dendritic components affect how time-varying inputs are transformed into action potentials (APs), but the relative contribution of each component is unclear. We developed a novel systems-identification approach to isolate the nonlinear response of layer 5 pyramidal neuron dendrites in mouse prefrontal cortex in response to dendritic current injections. We then quantified the nonlinear component and its effect on the soma, using functional models composed of linear filters and static nonlinearities. Both noise and waveform current injections revealed linear and nonlinear components in the dendritic response. The nonlinear component consisted of fast Na+ spikes that varied in amplitude 10-fold in a single neuron. A functional model reproduced the timing and amplitude of the dendritic spikes and revealed that they were selective to a preferred input dynamic (~4.5 ms rise time). The selectivity of the dendritic spikes became wider in the presence of additive noise, which was also predicted by the functional model. A second functional model revealed that the dendritic spikes were weakly boosted before being linearly integrated at the soma. For both our noise and waveform dendritic input, somatic APs were dependent on the somatic integration of the stimulus, followed a subset of large dendritic spikes, and were selective to the same input dynamics preferred by the dendrites. Our results suggest that the amplitude of fast dendritic spikes conveys information about high-frequency features in the dendritic input, which is then combined with low-frequency somatic integration. NEW & NOTEWORTHY The nonlinear response of layer 5 mouse pyramidal dendrites was isolated with a novel systems-based approach. In response to dendritic current injections, the nonlinear component contained mostly fast, variable-amplitude, Na+ spikes. A functional model accounted for the timing and amplitude of the dendritic spikes and revealed that dendritic spikes are selective to a preferred input dynamic, which was verified experimentally. Thus, fast dendritic nonlinearities behave as high-frequency feature detectors that influence somatic action potentials.

Linear and nonlinear properties of an obliquely propagating dust magnetosonic wave

2009 ◽  
Vol 75 (2) ◽  
pp. 217-233 ◽  
Author(s):  
W. MASOOD ◽  
H. A. SHAH ◽  
A. MUSHTAQ ◽  
M. SALIMULLAH
Keyword(s):  
Small Amplitude ◽  
Low Frequency ◽  
Ion Concentration ◽  
Magnetosonic Wave ◽  
Kp Equation ◽  
Linear Dispersion ◽  
Nonlinear Properties ◽  
Pressure Term ◽  
Linear And Nonlinear ◽  
The Magnetic Field

AbstractLinear and nonlinear properties of the two-dimensional obliquely propagating dust magnetosonic wave are studied in a three-component dusty plasma. The dispersion relations in the linear and Kadomstev–Petviashvili (KP) equation in the nonlinear regime are derived for small-amplitude perturbations. It is shown that the linear dispersion properties of the low-frequency dust magnetosonic wave depend on the angle θ that the magnetic field makes with the x-axis, the ratio of ion to electron concentration, and the plasma beta. It is found that retaining the electron pressure term gives rise to novel features in the dust magnetosonic wave. The slow magnetosonic wave is found to be the damped mode and, therefore, the only propagating mode in our system is the fast magnetosonic mode. It is found that the KP equation admits compressive solitary structures. Finally, it is found that the amplitude of the soliton increases as the ratio of electron to ion concentration, p, angle θ, and the plasma beta, β, is increased.

scholarly journals Variations of the Atlantic meridional overturning circulation in control and transient simulations of the last millennium

2011 ◽  
Vol 7 (1) ◽  
pp. 133-150 ◽  
Author(s):  
D. Hofer ◽  
C. C. Raible ◽  
T. F. Stocker
Keyword(s):  
Ocean Circulation ◽  
North Atlantic ◽  
Low Frequency ◽  
Surface Air Temperature ◽  
Meridional Overturning Circulation ◽  
Last Millennium ◽  
Climate System Model ◽  
The North ◽  
Transient Simulations ◽  
Gin Seas

Abstract. The variability of the Atlantic meridional overturing circulation (AMOC) strength is investigated in control experiments and in transient simulations of up to the last millennium using the low-resolution Community Climate System Model version 3. In the transient simulations the AMOC exhibits enhanced low-frequency variability that is mainly caused by infrequent transitions between two semi-stable circulation states which amount to a 10 percent change of the maximum overturning. One transition is also found in a control experiment, but the time-varying external forcing significantly increases the probability of the occurrence of such events though not having a direct, linear impact on the AMOC. The transition from a high to a low AMOC state starts with a reduction of the convection in the Labrador and Irminger Seas and goes along with a changed barotropic circulation of both gyres in the North Atlantic and a gradual strengthening of the convection in the Greenland-Iceland-Norwegian (GIN) Seas. In contrast, the transition from a weak to a strong overturning is induced by decreased mixing in the GIN Seas. As a consequence of the transition, regional sea surface temperature (SST) anomalies are found in the midlatitude North Atlantic and in the convection regions with an amplitude of up to 3 K. The atmospheric response to the SST forcing associated with the transition indicates a significant impact on the Scandinavian surface air temperature (SAT) in the order of 1 K. Thus, the changes of the ocean circulation make a major contribution to the Scandinavian SAT variability in the last millennium.

scholarly journals Linear and nonlinear low-frequency collisional quantum Buneman Instability in electron-positron-ion Plasmas

2021 ◽  
Vol 49 (1) ◽  
Author(s):  
M. Nasir Khattak ◽  
◽  
U. Zakir ◽  
M. Yaqoob Khan ◽  
Niaz. Wali ◽  
...  
Keyword(s):  
Low Frequency ◽  
Coulomb Systems ◽  
Nonlinear Problems ◽  
Momentum Equation ◽  
Quantum Plasma ◽  
Potential Term ◽  
Quantum Hydrodynamic Model ◽  
Bohm Potential ◽  
Linear And Nonlinear ◽  
Quantum Limits

The linear and nonlinear low-frequency collisional quantum Buneman instability in electronpositron- ion plasmas have been studied. Buneman instability in low frequency three species quantum plasma has been investigated using the approach of the quantum hydrodynamic model. The one-dimensional low-frequency collisional model is revisited by introducing the Bohm potential term in the momentum equation along with the role of the positron. Low-frequency Buneman instability which arises by one stream of particles drifting over another is investigated in the presence of the positron. Different plasma configurations based on the relative velocities of streaming particles are analyzed and it is observed that positron content enhances the instability in classical limits. Further, we found that in pure quantum limits the instability growth rate is decreased by increasing the positron concentration. The present work is very useful for the nonlinear problems in Quantum Coulomb systems.

scholarly journals Linear and nonlinear linkage of conditional stochastic volatility of interbank interest rates: Empirical evidence of the BRICS countries

2021 ◽  
Vol 2 (2) ◽  
pp. 4-16
Author(s):  
Zouhaier Dhifaoui ◽  
Faicel Gasmi
Keyword(s):  
Time Series ◽  
Interest Rates ◽  
Stochastic Volatility ◽  
Causal Relationship ◽  
Granger Causality ◽  
Granger Causality Test ◽  
Causality Test ◽  
Brics Countries ◽  
Volatility Model ◽  
Linear And Nonlinear

The purpose of this article is to detect a possible linear and nonlinear causal relationship between the conditional stochastic volatility of log return of interbank interest rates for the BRICS countries in the period from January 2015 to October 2018. To extract the volatility of the analyzed time series, we use a stochastic volatility model with moving average innovations. To test a causal relationship between the estimated stochastic volatilities, two steps are applied. First, we used the Granger causality test and a vector autoregressive model (VAR). Secondly, we applied the nonlinear Granger causality test to the raw data to explore a new nonlinear causal relationship between stochastic volatility time series, and also applied it to the residual of the VAR model to confirm the causality detected in the first step. This study demonstrates the existence of some unidirectional/bidirectional linear/nonlinear causal relationships between the studied stochastic volatility time series.

scholarly journals Functional Linear and Nonlinear Brain–Heart Interplay during Emotional Video Elicitation: A Maximum Information Coefficient Study

Entropy ◽  
2019 ◽  
Vol 21 (9) ◽  
pp. 892 ◽  
Author(s):  
Vincenzo Catrambone ◽  
Alberto Greco ◽  
Enzo Pasquale Scilingo ◽  
Gaetano Valenza
Keyword(s):  
Emotional Processing ◽  
Right Hemisphere ◽  
Power Spectra ◽  
Low Frequency ◽  
Emotional Valence ◽  
Brain Regions ◽  
Time Varying ◽  
Maximum Information ◽  
Information Coefficient ◽  
Linear And Nonlinear

Brain and heart continuously interact through anatomical and biochemical connections. Although several brain regions are known to be involved in the autonomic control, the functional brain–heart interplay (BHI) during emotional processing is not fully characterized yet. To this aim, we investigate BHI during emotional elicitation in healthy subjects. The functional linear and nonlinear couplings are quantified using the maximum information coefficient calculated between time-varying electroencephalography (EEG) power spectra within the canonical bands ( δ , θ , α , β and γ ), and time-varying low-frequency and high-frequency powers from heartbeat dynamics. Experimental data were gathered from 30 healthy volunteers whose emotions were elicited through pleasant and unpleasant high-arousing videos. Results demonstrate that functional BHI increases during videos with respect to a resting state through EEG oscillations not including the γ band (>30 Hz). Functional linear coupling seems associated with a high-arousing positive elicitation, with preferred EEG oscillations in the θ band ( [ 4 , 8 ) Hz) especially over the left-temporal and parietal cortices. Differential functional nonlinear coupling between emotional valence seems to mainly occur through EEG oscillations in the δ , θ , α bands and sympathovagal dynamics, as well as through δ , α , β oscillations and parasympathetic activity mainly over the right hemisphere. Functional BHI through δ and α oscillations over the prefrontal region seems primarily nonlinear. This study provides novel insights on synchronous heartbeat and cortical dynamics during emotional video elicitation, also suggesting that a nonlinear analysis is needed to fully characterize functional BHI.

scholarly journals Using simulations of the last millennium to understand climate variability seen in palaeo-observations: similar variation of Iceland–Scotland overflow strength and Atlantic Multidecadal Oscillation

2015 ◽  
Vol 11 (2) ◽  
pp. 203-216 ◽  
Author(s):  
K. Lohmann ◽  
J. Mignot ◽  
H. R. Langehaug ◽  
J. H. Jungclaus ◽  
D. Matei ◽  
...  
Keyword(s):  
Large Scale ◽  
Climate Models ◽  
Model Simulation ◽  
Low Frequency ◽  
Atlantic Multidecadal Oscillation ◽  
Underlying Mechanism ◽  
Meridional Overturning Circulation ◽  
Last Millennium ◽  
Nordic Seas ◽  
Similar Variation

Abstract. A recent palaeo-reconstruction of the strength of the Iceland–Scotland overflow during the last 600 years suggests that its low-frequency variability exhibits strong similarity with palaeo-reconstructions of the Atlantic Multidecadal Oscillation (AMO). The underlying mechanism of the similar variation remains unclear, however, based on palaeo-reconstructions alone. In this study we use simulations of the last millennium driven by external forcing reconstructions with three coupled climate models in order to investigate possible mechanisms underlying the similar variation of Iceland–Scotland overflow strength and AMO index. Similar variation of the two time series is also largely found in the model simulations. Our analysis indicates that the basin-wide AMO index in the externally forced simulations is dominated by the low-latitude sea surface temperature (SST) variability and is not predominantly driven by variations in the strength of the Atlantic meridional overturning circulation (MOC). This result suggests that a large-scale link through the strength of the MOC is not sufficient to explain the (simulated) similar variation of Iceland–Scotland overflow strength and AMO index. Rather, a more local link through the influence of the Nordic seas surface state and density structure, which are positively correlated with the AMO index, on the pressure gradient across the Iceland–Scotland ridge is responsible for the (simulated) similar variation. In the model simulation showing a weaker correlation between the Iceland–Scotland overflow strength and the AMO index, the wind stress in the Nordic seas also influences the overflow strength. Our study demonstrates that palaeo-climate simulations provide a useful tool to understand mechanisms and large-scale connections associated with the relatively sparse palaeo-observations.

Reconstruction of the Extratropical NH Mean Temperature over the Last Millennium with a Method that Preserves Low-Frequency Variability

2011 ◽  
Vol 24 (23) ◽  
pp. 6013-6034 ◽  
Author(s):  
Bo Christiansen ◽  
Fredrik Charpentier Ljungqvist
Keyword(s):  
Low Frequency ◽  
Temperature Reconstruction ◽  
Ice Age ◽  
Last Millennium ◽  
Screening Process ◽  
Calibration Period ◽  
Mean Temperature ◽  
Reconstruction Methods ◽  
Low Frequency Variability ◽  
In The Beginning

Abstract A new multiproxy reconstruction of the Northern Hemisphere extratropical mean temperature over the last millennium is presented. The reconstruction is performed with a novel method designed to avoid the underestimation of low-frequency variability that has been a general problem for regression-based reconstruction methods. The disadvantage of this method is an exaggerated high-frequency variability. The reconstruction is based on a set of 40 proxies of annual to decadal resolution that have been shown to relate to the local temperature. The new reconstruction shows a very cold Little Ice Age centered around the 17th century with a cold extremum (for 50-yr smoothing) of about 1.1 K below the temperature of the calibration period, AD 1880–1960. This cooling is about twice as large as corresponding numbers reported by most other reconstructions. In the beginning of the millennium the new reconstruction shows small anomalies in agreement with previous studies. However, the new temperature reconstruction decreases faster than previous reconstructions in the first 600 years of the millennium and has a stronger variability. The salient features of the new reconstruction are shown to be robust to changes in the calibration period, the source of the local temperatures, the spatial averaging procedure, and the screening process applied to the proxies. An ensemble pseudoproxy approach is applied to estimate the confidence intervals of the 50-yr smoothed reconstruction showing that the period AD 1500–1850 is significantly colder than the calibration period.

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