Nyquist noise

At high temperatures, E(ui,T) takes its equipartition value of E(u,T) kT, (kT >> Hu) to yield the so-called Nyquist formula that describes voltage fluctuations (Nyquist noise) generated in a linear electrical system, i.e. 

Indirect evidence of nonequilibrium flucmations due to CRRs in structural glasses has been obtained in Nyquist noise experiments by Ciliberto and co-workers. In these experiments a polycarbonate glass is placed inside the plates of a condenser and quenched at temperatures below the glass transition temperature. Voltage fluctuations are then recorded as a function of time during the relaxation process and the effective temperature is measured ... 

In the absence of electrical bias, the absolute minimum internal noise exists, termed Johnson noise, Nyquist noise or thermal noise. This form of noise arises from the random motion of the current carriers within any resistive material and is always associated with a dissipative mechanism. The Johnson noise power is dependent only upon the temperature of the material and the measurement bandwidth, although the noise voltage and current depend upon the value of the resistance. 

Voltage fluctuation much greater than the thermal noise t/(h (Nyquist noise) of an ohmic resistance R with an amplitude... 

Let us first shortly consider velocity fluctuation noise. This is the only noise mechanism that exists without electric bias. It is variably denoted as Johnson noise, thermal noise, Nyquist noise, Johnson-Nyquist noise, resistance noise [59, 60]. It is a consequence of stochastic motion of charge carriers within material with finite resistance, and it represents a mechanism to maintain thermal equilibrium in semiconductor [61]. In a general case the spectral density of thermal noise voltage is 5v(co) = 4J (hv/2 + hv/(c " / - l) = 2/flivch(hv/ i,7 ), which in the case hv becomes Sy = Ak TR, i.e., in this case the squared current due to this noise mechanism is... 

Johnson noise is also known as thermal noise or Nyquist noise. It applies only to resistive elements a feedback resistor, a load resistor, or a PC detector. It does not... 

An important early paper on fluctuation processes is that of Harry Nyquist (1928), who suggested an equation linking the mean-square amplitude of thermal noise in an electrical circuit to the resistance R of the noise EMF (or current) generator ... 

The noise thermometer is based on the temperature dependence of the mean square noise voltage V2 developed in a thermistor (Nyquist theorem, 1928) ... 

The SIN defined by Equation 7.6 for a given NMR resonance is proportional to the square of the nuclear precession frequency (mo, rad/s), the magnitude of the transverse magnetic field (Bi) induced in the RE coil per unit current (/), the number of spins per unit volume (Ns), the sample volume (Vs), and a scaling constant that accounts for magnetic field inhomogeneities. The SIN is inversely proportional to the noise generated in the RE receiver and by the sample (Vnoise) as defined by the Nyquist theorem,... 

Thermal electric noise thermometry 1. Josephson junction point contact 2 Conventional amplifier 0.001-1 4-1400 Mean square voltage fluctuation Nyquist s law oc fegT Other sources of noise serious problem for T > 4 K... 

Fig. 5 Object (shaded) used in computer simulations Its diffraction image is the solid curve The data image (dashed curve) is the diffraction image plus 4% amplitude random noise All plotted points are spaced by one-half the Nyquist interval. Hence to resolve the central dip in the object would require superresolution.

The image data were formed by adding 4% (of peak image value) Gaussian noise to the signal image. Sampling was at one-half the Nyquist interval so as to permit superresolution of the central dip in the object. 

Here vmax is the maximum wavenumber present (Nyquist wavenumber). Radiation v above vmax must be removed by suitable optical filtering or additional features and noise will be folded back onto the spectrum. Aliasing, as this phenomenon is called, places constraints on the operation of real... 

It is only a small step from here to the equivalent statement, known as the Nyquist theorem, for current noise of thermal fluctuations in a circuit with resistance R.4... 

Signal-noise separation (SNS) by Froissart doublets within the FPT<+) and FPT( ) is illustrated in Figures 4.10 and 4.11 for the noise-free and noise-corrupted time signals, respectively. Only a small number of all the obtained Froissart doublets appears in the shown frequency window in Figure 4.10. The selected subinterval 0-6 ppm is important because all the MR-detectable brain metabolites lie within this chemical shift domain of the full Nyquist range. Froissart doublets as spurious resonances are detected by the confluence of poles and zeros in the list of the Pade-reconstructed spectral parameters. 

Interestingly, due to the linearity of the generalized Langevin equation (22), the same effective temperature T,eff(( ) can consistently be used in the modified Nyquist formula linking the noise spectral density C/ /- ([Pg.313]

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