Measurement of cell impedance in frequency domain using discontinuous current clamp and white-noise-modulated current injection

1992 ◽  
Vol 421 (5) ◽  
pp. 469-472 ◽  
Author(s):  
M. Weckstr�m ◽  
E. Kouvalainen ◽  
M. Juusola
Keyword(s):  
White Noise ◽  
Frequency Domain ◽  
Current Injection ◽  
Current Clamp ◽  
Cell Impedance

CHARACTERIZATION OF NUCLEAR IMAGES BASED ON ANALYSIS OF FRACTIONAL SUMMATION SYSTEMS

Fractals ◽  
2004 ◽  
Vol 12 (02) ◽  
pp. 157-169 ◽  
Author(s):  
HAI-SHAN WU ◽  
ANDREW J. EINSTEIN ◽  
LIANE DELIGDISCH ◽  
TAMARA KALIR ◽  
JOAN GIL
Keyword(s):  
White Noise ◽  
Frequency Domain ◽  
Discrete System ◽  
Fractional Integral ◽  
Continuous System ◽  
Time Range ◽  
System Function ◽  
Autocovariance Function ◽  
Frequency Domain Methods

While frequency-based methods for the characterization of fractals are popular and effective in many applications, they have limitations when applied to irregularly shaped images, such as nuclear images. The irregularity renders texture characterization by frequency domain methods, based upon Fourier transform, problematic. To address this situation, this paper presents an algorithm based upon the signal analysis in the spatial domain. An autocovariance function can be estimated regardless of the shape and size of regions where the image is defined. As in the continuous fractional Brownian motion (FBM) that results from inputting white noise into a specific fractional integral system, a discrete FBM can be related to white noise by a specific fractional summation system (FSS) that is linear, causal and shift-invariant. Although the method of direct sampling is not valid for converting a continuous fractional integral to a discrete fractional summation, discrete fractional summations similar to the sampled system functions can be obtained through an iterative process. While the continuous system function of a fractional integral is linear in the frequency domain when plotted in log-log scales, unfortunately, it is not true for the comparable discrete system function. The discrete system function is actually approximately linear in the log-log scales over a very limited range. The slope of the straight line that approximates the function curve in the mean-square-error (MSE) sense in a specific time range provides a description of the autocovariance function that reveals the statistical relations among the local textures. Applications to characterization of ovary nuclear images in groups of normal, atypical and cancer cases are studied and presented.

The response of a spatially distributed neuron to white noise current injection

1979 ◽  
Vol 33 (1) ◽  
pp. 39-55 ◽  
Author(s):  
Frederic Y. M. Wan ◽  
Henry C. Tuckwell
Keyword(s):  
White Noise ◽  
Current Injection ◽  
Noise Current ◽  
Spatially Distributed

scholarly journals Mathematical model of parametrically controlled matched filters

2017 ◽  
Vol 1 (1) ◽  
pp. 27-31
Author(s):  
Borislav Georgiev Naydenov ◽  
Antim Hristov Yordanov ◽  
Lyubomir Petrov Kamburov
Keyword(s):  
Mathematical Model ◽  
White Noise ◽  
Frequency Domain ◽  
Mobile Communication ◽  
Communication Systems ◽  
Noise Resistance ◽  
Matched Filters ◽  
Variable Parameters ◽  
Radar Systems ◽  
Auto Correlation

A one model of parametrically controlled coherent filters is described and analyzed, applied also in radar systems and mobile communication systems to improve noise resistance. Application of the Nyquist-Shannon theorem in the frequency domain to obtain a set of frequency filters with variable parameters. The conversion of the signal at the output of the parameter filter using the auto correlation feature is shown when a normal white noise occurs.

A DSP-Based Design for Generating Limited White Noise Wave

2010 ◽  
Vol 34-35 ◽  
pp. 1228-1232
Author(s):  
Ming Ma ◽  
Run Jie Shen ◽  
Bing Fang ◽  
Ming Wei Sun ◽  
Wen He
Keyword(s):  
White Noise ◽  
Frequency Domain ◽  
Simulation Experiment ◽  
Amplitude Spectrum ◽  
Random Numbers ◽  
Zero Section ◽  
Signal Source ◽  
External Data ◽  
Noise Simulation ◽  
Data Memory

In this paper, based on the analysis of white noise generation, equably distributed pseudo-random numbers are generated by a method of mixed congruency. In the case that the pseudo-random numbers are taken as the phase spectrum and the amplitude spectrum is equally set, the waveform array of frequency-domain is made up. The array is transformed from frequency-domain to time-domain by the IFFT before stored into the external data memory. Based on the wave generating technology of DDS, the timer interruption of DSP2812 is installed to change the frequency for generating wave .Then the number is taken out from the external memory. The limited white noise is formed by the way of D/A and zero-section maintenance .This generator can be used as signal source in the noise simulation experiment.

Active Dendritic Membrane Properties of XenopusLarval Spinal Neurons Analyzed With a Whole Cell Soma Voltage Clamp

2000 ◽  
Vol 83 (3) ◽  
pp. 1381-1393 ◽  
Author(s):  
Benoit Saint Mleux ◽  
L. E. Moore
Keyword(s):  
Action Potential ◽  
Frequency Domain ◽  
Voltage Clamp ◽  
Membrane Potentials ◽  
Calcium Currents ◽  
Membrane Properties ◽  
Constant Current ◽  
Negative Slope ◽  
Spinal Neurons ◽  
Current Clamp

Voltage- and current-clamp measurements of inwardly directed currents were made from the somatic regions of Xenopus laevisspinal neurons. Current-voltage ( I-V) curves determined under voltage clamp, but not current clamp, were able to indicate a negative slope conductance in neurons that showed strong accommodating action potential responses to a constant current stimulation. Voltage-clamp I-V curves from repetitive firing neurons did not have a net negative slope conductance and had identical I-V plots under current clamp. Frequency domain responses indicate negative slope conductances with different properties with or without tetrodotoxin, suggesting that both sodium and calcium currents are present in these spinal neurons. The currents obtained from a voltage clamp of the somatic region were analyzed in terms of spatially controlled soma membrane currents and additional currents from dendritic potential responses. Linearized frequency domain analysis in combination with both voltage- and current-clamp responses over a range of membrane potentials was essential for an accurate determination of consistent neuronal model behavior. In essence, the data obtained at resting or hyperpolarized membrane potentials in the frequency domain were used to determine the electrotonic structure, while both the frequency and time domain data at depolarized potentials were required to characterize the voltage-dependent channels. Finally, the dendritic and somatic membrane properties were used to reconstruct the action potential behavior and quantitatively predict the dependence of neuronal firing properties on electrotonic structure. The reconstructed action potentials reproduced the behavior of two broad distributions of interneurons characterized by their degree of accommodation. These studies suggest that in addition to the ionic conductances, electrotonic structure is correlated with the action potential behavior of larval neurons.

On the Use of the White-Noise Approximation for Modelling the Slow-Drifts of a FOWT: An Example Using FAST

2018 ◽  
Author(s):  
Alexandre N. Simos ◽  
Lucas Henrique Souza do Carmo ◽  
Ewerton Carlos Camargo
Keyword(s):  
White Noise ◽  
Frequency Domain ◽  
Time Domain ◽  
Significant Loss ◽  
Second Order ◽  
Preliminary Design ◽  
Original Formulation ◽  
Slow Drift ◽  
Wave Induced

When designing the mooring system of a floating unit, performing extensive time-domain simulations in several sea conditions is common practice. For this, the second-order wave induced forces, expressed by QTF matrices, are most often precomputed in frequency domain diffraction codes. However, the computation of the full QTFs is quite demanding and it is also not uncommon for the designer to be in doubt as to the frequency limits and resolution required for their construction. Among the approximations that can be used to ease this burden, the most well-known is Newman’s approximation, which performs quite well as long as the natural periods of drift and the water depth are sufficiently large. The white noise approach, on the other hand, leads to an approximation of a different kind. Taking advantage of the fact that the slow-drift response is narrow-banded, it approximates the second-order force spectrum where it contributes the most, and in a way that is independent of the natural periods and depth. However, its original formulation, based on the force spectra, is certainly more convenient in frequency domain. This article presents an easy way to make use of the white noise approach in time domain simulations. For this, the well-known OC4 semi-submersible FOWT is taken as a case-study. Simulations in different wave conditions are performed with the software FAST using both, the original full QTFs and new ones, simplified according to the principle of the white noise approximation. It is shown that, with the latter, the simulations can be performed without significant loss of accuracy, indicating that the white-noise approach indeed is an interesting option for preliminary design stages.

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