1,985 research outputs found
The Efroimsky formalism adapted to high-frequency perturbations
The Efroimsky perturbation scheme for consistent treatment of gravitational
waves and their influence on the background is summarized and compared with
classical Isaacson's high-frequency approach. We demonstrate that the Efroimsky
method in its present form is not compatible with the Isaacson limit of
high-frequency gravitational waves, and we propose its natural generalization
to resolve this drawback.Comment: 7 pages, to appear in Class. Quantum Gra
Is High-frequency stiffness a measure for the number of attached cross-bridges?
Muscle stiffness is an important property for movement control. Stiffness is a measure for the resistance against mechanical disturbances in muscular-skeletal systems. In general muscle stiffness is assumed to depend on the number of attached cross-bridges. It is not possible to measure this number in vivo or vitro. In experiments, high frequency perturbations are used to obtain a measurement of stiffness. In this paper a simulation study is presented concerning the correlation between the number of attached cross-bridges and high-frequency stiffness. A model based on the sliding-filament theory was used for the simulation of dynamic contractions. It is concluded that these two methods of muscle stiffness determination do not yield compatible results during lengthenin
Model of theta frequency perturbations and contextual fear memory
Theta oscillations in the hippocampal local field potential (LFP) appear during translational movement and arousal, modulate the activity of principal cells, and are associated with spatial cognition and episodic memory function. All known anxiolytics slightly but consistently reduce hippocampal theta frequency. However, whether this electrophysiological effect is mechanistically related to the decreased behavioral expression of anxiety is currently unclear. Here, we propose that a reduction in theta frequency affects synaptic plasticity and mnemonic function and that this can explain the reduction in anxiety behavior. We test this hypothesis in a biophysical model of contextual fear conditioning. First, we confirm that our model reproduces previous empirical results regarding the dependence of synaptic plasticity on presynaptic firing rate. Next, we investigate how theta frequency during contextual conditioning impacts learning. These simulations demonstrate that learned associations between threat and context are attenuated when learning takes place under reduced theta frequency. Additionally, our simulations demonstrate that learned associations result in increased theta activity in the amygdala, consistent with empirical data. In summary, we propose a mechanism that can account for the behavioral effect of anxiolytics by impairing the integration of threat attributes of an environment into the cognitive map due to reduced synaptic potentiation
Modulated wave trains in generalized Kuramoto-Sivashinksi equations
This paper is concerned with the stability of periodic wave trains in a
generalized Kuramoto-Sivashinski (gKS) equation. This equation is useful to
describe the weak instability of low frequency perturbations for thin film
flows down an inclined ramp. We provide a set of equations, namely Whitham's
modulation equations, that determines the behaviour of low frequency
perturbations of periodic wave trains. As a byproduct, we relate the spectral
stability in the small wavenumber regime to properties of the modulation
equations. This stability is always critical since 0 is a 0-Floquet number
eigenvalue associated to translational invariance
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