Modelado numérico de las oscilaciones frontales y ocurrencia de formación de diques de hielo del Glaciar Perito Moreno, Campo de Hielo Patagónico Sur

The present study conducts the design and development of a computational numerical model to describe the behavior of the seasonal oscillatory cycle of advance and recession of the Perito Moreno glacier, named MO-ACAR. Within its oscillatory behavior, in some years the glacier advances and reaches the Magellan Peninsula forming an ice-dam that break down due to the water pressure of the lake after a certain time. Thus, the main goal of the MO-ACAR model is to simulate the daily ice-front position of the glacier and the events occurrence of the ice-dam formation during 1994-2018 period. The model is calibrated and validated from an iterative optimization process, based on the maximization of correlation values and minimization of distance errors to the Magallanes Peninsula. The simulation of the ice-dam’s formation and the oscillation of the frontal position achieved high performance, reaching optimal correlation values (0.99) and small errors in the position (9.56 ± 13.94 m), respectively. The results show that glacier dynamics and ice-dam’s formation respond to different time-scales; whilst in short-, intermediate-term (daily seasonal scales), the occurrence depends as much on the characteristics of the event as on the phase and intensity of the previous event. On the contrary, in long-term periods (scales greater than one year), low-frequency modulation of the ice flow velocity, caused by variations in air temperature, controls the periods with the formation of ice-dams and free of them.

Forecasting Bubble Bursts Assessing the Ex-ante Usability of the Log-Periodic Power Law Singularity Model

Speculative bubbles have throughout the times foiled various scholars; many have tried to accurately predict their ends, but few have succeeded. In this study, we examine the robustness and ex-ante usability of the log-periodic power-law model in predicting end dates of speculative bubbles on one mature and two emerging financial markets. We have found that the predicted end dates are somewhat dependent on at which point in time the prediction is conducted, especially in regards to at which point in the oscillatory cycle the prediction is conducted. This is mostly due to that predictions are sensitive to their most recent price movements, especially when data is limited and a clear oscillatory pattern is not yet established. We conclude that observing one particular estimation without further context can be misleading. To achieve a sound understanding of and reasonable expectations on how prices might develop it is necessary to follow a bubble as it develops. This study is, to our knowledge, first to examine to what extent the predictions of the model are dependent on at which point in time the predictions are conducted.

Brain State-dependent Gain Modulation of Corticospinal Output in the Active Motor System

The communication through coherence hypothesis suggests that only coherently oscillating neuronal groups can interact effectively and predicts an intrinsic response modulation along the oscillatory rhythm. For the motor cortex (MC) at rest, the oscillatory cycle has been shown to determine the brain’s responsiveness to external stimuli. For the active MC, however, the demonstration of such a phase-specific modulation of corticospinal excitability (CSE) along the rhythm cycle is still missing. Motor evoked potentials in response to transcranial magnetic stimulation (TMS) over the MC were used to probe the effect of cortical oscillations on CSE during several motor conditions. A brain–machine interface (BMI) with a robotic hand orthosis allowed investigating effects of cortical activity on CSE without the confounding effects of voluntary muscle activation. Only this BMI approach (and not active or passive hand opening alone) revealed a frequency- and phase-specific cortical modulation of CSE by sensorimotor beta-band activity that peaked once per oscillatory cycle and was independent of muscle activity. The active MC follows an intrinsic response modulation in accordance with the communication through coherence hypothesis. Furthermore, the BMI approach may facilitate and strengthen effective corticospinal communication in a therapeutic context, for example, when voluntary hand opening is no longer possible after stroke.

Oscillatory integration windows in neurons

Oscillatory synchrony among neurons occurs in many species and brain areas, and has been proposed to help neural circuits process information. One hypothesis states that oscillatory input creates cyclic integration windows: specific times in each oscillatory cycle when postsynaptic neurons become especially responsive to inputs. With paired local field potential (LFP) and intracellular recordings and controlled stimulus manipulations we directly tested this idea in the locust olfactory system. We found that inputs arriving in Kenyon cells (KCs) sum most effectively in a preferred window of the oscillation cycle. With a computational model, we found that the non-uniform structure of noise in the membrane potential helps mediate this process. Further experiments performed in vivo demonstrated that integration windows can form in the absence of inhibition and at a broad range of oscillation frequencies. Our results reveal how a fundamental coincidence-detection mechanism in a neural circuit functions to decode temporally organized spiking.

Resistance of a Ship Undergoing Oscillatory Motion

In this paper, we describe extensions to the research of Doctors et al. (Doctors, L. J., Day, A. H., and Clelland, D., 2008, Unsteady effects during resistance tests on a ship model in a towing tank, Journal of Ship Research, 52, 4, 263–273) and Day et al. (Day, A. H., Clelland, D., and Doctors, L. J., 2009, Unsteady finite-depth effects during resistance tests in a towing tank, Journal of Marine Science and Technology, 14, 3, 387–397) in which the oscillations in the wave resistance during the constant-velocity phase of a towing-tank resistance test on a ship model were measured and predicted, in the cases of relatively deep and relatively shallow water. In the current study, the ship model was towed with a harmonic velocity component superimposed on the usual constant forward velocity. This work constitutes a first step in the understanding of the unsteady hydrodynamics of a racing shell (rowing boat). We show here that the unsteady wave resistance varies considerably from the traditional (steady) average value. Indeed, the wave resistance is frequently negative during part of the oscillatory cycle. However, the general effect is an increase in the temporal mean value of the wave resistance; this suggests that every effort should be made to reduce the unsteadiness of the motion. We also demonstrate that the unsteady wave-resistance theory provides an excellent prediction of the measured effects summarized here. These predictions are often within a few percent of the measured values of the resistance.

Analysis of the Dynamics and Vibrations of Structures Subjected to Unsteady Aerodynamic Loads for Crack Detection

This paper is devoted to the analysis of the dynamics and vibrations of wing-like structures with bonded piezoelectric strips and subjected to unsteady aerodynamic loads for crack detection. Pairs of piezoelectric strips, acting as strain sensors, are bonded at the same locations on the opposite sides of a thin structure executing flexural oscillations. In this crack detection strategy, the measured voltage outputs of the two piezoelectric sensors forming a pair are conveniently subtracted in order to eliminate the voltage corresponding to the same level of strain on both sides. This differential voltage output is used to indicate the presence of a crack in the structure. The nonlinear mechanical behavior of the crack in the compression and extension phases of the oscillatory cycle increases substantially the sensitivity of this detection procedure. Furthermore, this crack detection method can take advantage of the aeroelastic oscillations of the wing structures, which are always present during normal flight evolutions of an aircraft. The numerical analysis of the dynamics of structure subjected to unsteady aerodynamic loads uses a finite element formulation for the structure and the piezoelectric strips and a panel method is used to compute the unsteady aerodynamic loads acting on the oscillating wing structure. Numerical simulation results are presented in the paper to explore the feasibility of this crack detection strategy by using the aeroelastic oscillations of the wing-like structures with bonded piezoelectric strips.

Oscillatory Synchronization Requires Precise and Balanced Feedback Inhibition in a Model of the Insect Antennal Lobe

In the insect olfactory system, odor-evoked transient synchronization of antennal lobe (AL) projection neurons (PNs) is phase-locked to the oscillations of the local field potential. Sensory information is contained in the spatiotemporal synchronization pattern formed by the identities of the phase-locked PNs. This article investigates the role of feedback inhibition from the local neurons (LNs) in this coding. First, experimental biological results are reproduced with a reduced computational spiking neural network model of the AL. Second, the low complexity of the model leads to a mathematical analysis from which a lower bound on the phase-locking probability is derived. Parameters involved in the bound indicate that PN phase locking depends not only on the number of LN-evoked inhibitory postsynaptic potentials (IPSPs) previously received, but also on their temporal jitter. If the inhibition received by a PN at the current oscillatory cycle is both perfectly balanced (i.e., equal to the mean inhibitory drive) and precise (without any jitter), then the PN will be phase-locked at the next oscillatory cycle with probability one.

Contributions of Intrinsic Membrane Dynamics to Fast Network Oscillations With Irregular Neuronal Discharges

During fast oscillations in the local field potential (40–100 Hz gamma, 100–200 Hz sharp-wave ripples) single cortical neurons typically fire irregularly at rates that are much lower than the oscillation frequency. Recent computational studies have provided a mathematical description of such fast oscillations, using the leaky integrate-and-fire (LIF) neuron model. Here, we extend this theoretical framework to populations of more realistic Hodgkin–Huxley-type conductance-based neurons. In a noisy network of GABAergic neurons that are connected randomly and sparsely by chemical synapses, coherent oscillations emerge with a frequency that depends sensitively on the single cell's membrane dynamics. The population frequency can be predicted analytically from the synaptic time constants and the preferred phase of discharge during the oscillatory cycle of a single cell subjected to noisy sinusoidal input. The latter depends significantly on the single cell's membrane properties and can be understood in the context of the simplified exponential integrate-and-fire (EIF) neuron. We find that 200-Hz oscillations can be generated, provided the effective input conductance of single cells is large, so that the single neuron's phase shift is sufficiently small. In a two-population network of excitatory pyramidal cells and inhibitory neurons, recurrent excitation can either decrease or increase the population rhythmic frequency, depending on whether in a neuron the excitatory synaptic current follows or precedes the inhibitory synaptic current in an oscillatory cycle. Detailed single-cell properties have a substantial impact on population oscillations, even though rhythmicity does not originate from pacemaker neurons and is an emergent network phenomenon.

Serotonin and NO Complementarily Regulate Generation of Oscillatory Activity in the Olfactory CNS of a Terrestrial Mollusk

Synchronous oscillation of membrane potentials, generated by assemblies of neurons, is a prominent feature in the olfactory systems of many vertebrate and invertebrate species. However, its generation mechanism is still controversial. Biogenic amines play important roles for mammalian olfactory learning and are also implicated in molluscan olfactory learning. Here, we investigated the role of serotonin, a biogenic amine, in the oscillatory dynamics in the procerebrum (PC), the molluscan olfactory center. Serotonin receptor blockers inhibited the spontaneous synchronous oscillatory activity of low frequency (approximately 0.5 Hz) in the PC. This was due to diminishing the periodic slow oscillation of membrane potential in bursting (B) neurons, which are essential neuronal elements for the synchronous oscillation in the PC. On the other hand, serotonin enhanced the amplitude of the slow oscillation in B neurons and subsequently increased the number of spikes in each oscillatory cycle. These results show that the extracellular serotonin level regulates the oscillation amplitude in B neurons and thus serotonin may be called an oscillation generator in the PC. Although nitric oxide (NO) is known to also be a crucial factor for generating the PC oscillatory activity and setting the PC oscillation frequency, the present study showed that NO only regulates the oscillation frequency in B neurons but could not increase the spikes in each oscillatory cycle. These results suggest complementary regulation of the PC oscillatory activity: NO determines the probability of occurrence of slow potentials in B neurons, whereas serotonin regulates the amplitude in each cycle of the oscillatory activity in B neurons.

An increase in cytosolic Ca2+ delays cAMP oscillations in Dictyostelium cells

We have shown that calmidazolium (R24571) causes a transient increase in the cytosolic free Ca2+ concentration ([Ca2+]i) in Dictyostelium discoideum [Schlatterer and Schaloske (1996) Biochem. J. 313, 661–667]. Here we have used R24571 to artificially increase [Ca2+]i during light-scattering oscillations and have found that, depending on the time of addition during the oscillatory cycle, R24571 suppressed cAMP synthesis and delayed the next spike for several minutes. Addition of Ca2+ to the medium, which also elevates [Ca2+]i, induced phase delays and resulted in a similar phase response curve as R24571. The magnitude of the phase delay was correlated with the point during the oscillatory cycle at which Ca2+ was added, indicating that an artificial increase in [Ca2+]i also resets the phase of the intrinsic oscillator.