Search results for "Low frequency"
showing 10 items of 97 documents
Evidence of electrical activity on Titan drawn from the Schumann resonances sent by Huygens probe
2008
Abstract A procedure is shown for extracting weak resonances from the responses of electromagnetic systems excited by electric discharges. The procedure, based on analysis of the late-time system response, is first checked using an analytical function and later with the data for the electric field generated by the computational simulation of Titan's atmosphere using the Transmission Line Matrix (TLM) method. Finally, the low frequency spectrum of the natural electric field in Titan's atmosphere sent by the mutual impedance sensor (MIP) included in the Huygens probe is analyzed employing this technique. The MIP sensor was initially designed to measure the horizontal component of the electric…
Nonlinear Current Generation in Degenerate Semiconductors Embedded in Constant and Low-Frequency Electric Fields
2006
The explicit analytical forms of nonlinear currents in degenerate semiconductors serving as sources of coherent radiation in the wavelength millimetric and submillimetric ranges are established.
Dynamics of an elongated magnetic droplet in a rotating field
2002
A model is proposed for the dynamics of an elongated droplet under the action of a low frequency rotating magnetic field. This model determines a set of critical frequencies at which the transitions to more complex bent shapes take place. These transitions occur through propagation of jumps of the droplet's axial tangent angle described by a nonlinear singularly perturbed partial differential equation with the intrinsic viscosity of the droplet playing the regularizing role.
Neuroprotective Effects of Low Intensity and Low Frequency Electromagnetic �in vitro� Stimulation on Glial Cells
2020
Degenerative neurological diseases (senile dementia, Alzheimer`s disease, glaucoma), post-stroke sequelae are increasing as prevalence nowadays, in context of aging in general population, and there are strong evidences that astrocytes may play a significant role in neuroprotection. The study evaluates the effects of low intensity low frequency electromagnetic field (EMF) �in vitro� stimulation (195 mA, 7-8 Hz) on the glial cells, in different conditions, in order to identify the neuroprotective potential. Three cell lines were used for the study: the Clonetics (Lonza) line of normal human astrocytes, U87 glioblastoma tumor cells (ATCC) and L929 murine fibroblasts. The cell cultures were ex…
The mass load effect on the resonant acoustic frequencies of colloidal semiconductor nanoplatelets
2016
Resonant acoustic modes of ultrathin CdS and CdSe colloidal nanoplatelets (NPLs) with varying thicknesses were probed using low frequency Raman scattering. The spectra are dominated by an intense band ascribed to the thickness breathing mode of the 2D nanostructures. The measured Raman frequencies show strong deviations with respect to the values expected for simple bare plates, all the more so as the thickness is reduced. The deviation is shown to arise from the additional mass of the organic ligands that are bound to the free surfaces of the nanoplatelets. The calculated eigen frequencies of vibrating platelets weighed down by the mass of the organic ligands are in very good agreement wit…
Interpretation of capacitance spectra and transit times of single carrier space-charge limited transport in organic layers with field-dependent mobil…
2007
The ac impedance characteristics of a single carrier with space-charge limited current (SCLC) transport in organic layers with field-dependent mobility is analyzed, indicating the similarities as well as the differences to the constant mobility case. The model provides capacitance spectra and transit times from different calculation methods, in relation to the electric field distribution in the SCLC regime. It is found that the low frequency capacitance lies in the range 3Cg/4 < Cif < Cg, with respect to the geometric capacitance Cg. An approximated expression for the variation of the transit time with applied bias is derived, in good agreement with exact calculations. Experimental results …
Effects of low frequency electric fields on synaptic integration in hippocampal CA1 pyramidal neurons: implications for power line emissions
2014
The possible cognitive effects of low frequency external electric fields, such as those generated by power lines, are poorly understood. Their functional consequences for mechanisms at the single neuron level are very difficult to study and identify experimentally, especially in vivo. The major open problem is that experimental investigations on humans have given inconsistent or contradictory results, making it difficult to estimate the possible effects of external low frequency electric fields on cognitive functions. Here we investigate this issue with a realistic model of hippocampal CA1 pyramidal neurons. The model suggests how and why external electric fields, with environmentally obser…
EFFECT OF LOW-FREQUENCY NOISE ON ADIABATIC PASSAGE IN A SUPERCONDUCTING NANOCIRCUIT
2011
Recent experiments have demonstrated coherent phenomena in three-level systems based on superconducting nanocircuits. This opens the possibility to detect Stimulated Raman Adiabatic Passage (STIRAP) in artificial atoms. Low-fequency noise (often 1/f) is one of the main sources of decoherence in these systems, and we study its effect on the transfer efficiency. We propose a way to analyze low frequency fluctuations in terms of fictitious correlated fluctuations of external parameters. We discuss a specific implementation, namely the Quantronium setup of a Cooper-pair box, showing that optimizing the trade-off between efficient coupling and protection against noise may allow us to observe co…
Low-Frequency Imaginary Impedance at the Superconducting Transition of 2H - NbSe2
2020
The superconducting transition leads to a sharp resistance drop in a temperature interval that can be a small fraction of the critical temperature ${T}_{c}$. A superconductor exactly at ${T}_{c}$ is thus very sensitive to all kinds of thermal perturbation, including the heat dissipated by the measurement current. We show that the interaction between electrical and thermal currents leads to a sizable imaginary impedance at frequencies of the order of tens of hertz at the resistive transition of single crystals of the layered material $2H$-${\mathrm{Nb}\mathrm{Se}}_{2}$. We explain the result using models developed for transition-edge sensors. By measuring under magnetic fields and at high cu…
Acoustic methods for measuring the porosities of porous materials incorporating dead-end pores
2013
International audience; The acoustic properties of porous materials containing dead-end (DE) pores have been proposed by Dupont et al. [J. Appl. Phys. 110, 094903 (2011)]. In the theoretical description, two physical parameters were defined (the dead-end porosity and the average length of the dead-end pores). With the knowledge of the open porosity (measured with non-acoustic methods), and the measurement of kinematic porosity (also called the Biot porosity in this article), it is possible to deduce the dead-end porosity. Two acoustic methods for measuring the Biot porosity for a wide range of porosities are proposed. These methods are based on acoustic transmission and on the low and high …